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Surface geology at the Granduc Mine Davidson, Donald Alexander 1960

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SURFACE GEOLOGY AT THE GRANDUC MINE by DONALD ALEXANDER DAVIDSON B.A.Sc., U n i v e r s i t y of B r i t i s h Columbia, 1957 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of Geology We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , I960 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department The U n i v e r s i t y of B r i t i s h Columbia Vancouver Canada. ABSTRACT The Granduc Mine i s near the B r i t i s h Columbia-Alaska boundary i n rugged mountainous country about 36 m i l e s n o r t h -west of Stewart B.C. The w r i t e r p a r t i c i p a t e d i n d e t a i l e d surface mapping i n the v i c i n i t y of the mine during the f i e l d season of 1959. Rock specimens were c o l l e c t e d i n the f i e l d and examined m i c r o s c o p i c a l l y i n the l a b o r a t o r y . The r e s u l t s of the l a t t e r i n v e s t i g a t i o n form the greater part o f t h i s t h e s i s . The o l d e s t rocks i n the area are n o r t h t r e n d i n g , s t e e p l y d i p p i n g and i s o c l i n a l l y f o l d e d metavolcanic and metasedimentary rocks that are b e l i e v e d to be c o r r e l a t i v e w i t h the Hazelton group. These c o n s i s t of a basal andesite complex which i s o v e r l a i n by a l a r g e thickness of metasedi-mentary rocks. The Hazelton group rocks have been r e g i o n a l l y metamorphosed and s y n k i n e m a t i c a l l y i n t r u d e d by s m a l l subcon-cordant bodies of f o l i a t e d d i o r i t e and hornblende grano-d i o r i t e . The metasediments are b e l i e v e d to have formed from greywackes, marls and sandstones that have been p r o g r e s s i v e l y metamorphosed to form s c h i s t s that can be c l a s s i f i e d i n the q u a r t z - a l b i t e - e p i d o t e - b i o t i t e subfacies of the greenschist f a c i e s . Almost i d e n t i c a l m i n e r a l assemblages are found i n the a l t e r e d d i o r i t i c and metavolcanic rocks, and i t i s con-cluded that these i n i t i a l l y h i g h temperature assemblages have r e t r o g r e s s e d during r e g i o n a l metamorphism to a t t a i n or approach e q u i l i b r i u m i n the same metamorphic f a c i e s . At a l a t e stage i n the metamorphism strong d i f f e r e n t i a l movement was l o c a l -i z e d i n a q u a r t z - r i c h member of the metasedimentary rocks i n a zone near the contact w i t h metavolcanic rocks. A l l rocks i n t h i s zone have undergone r e t r o g r e s s i v e metamorphism, and have a t t a i n e d e q u i l i b r i u m i n the q u a r t z - a l b i t e - m u s c o v i t e -c h l o r i t e subfacies of the greenschist f a c i e s . Drag f o l d s show that t h i s d i s l o c a t i o n metamorphism was r e l a t e d to the formation of an a n t i c l i n a l s t r u c t u r e that l i e s to the east o f the map area. Some of the major s t r u c t u r a l ore c o n t r o l s appear to have formed at t h i s time. The strongly-developed i s o c l i n a l f o l d i n g was l a t e r f l e x e d during or f o l l o w i n g i n t r u s i o n of the Coast Range batho-l i t h . Ore bearing s o l u t i o n s are b e l i e v e d to have been de-r i v e d from b a t h o l i t h i c emanations and these were channeled along crumpled and b r e c c i a t e d zones that formed during the e a r l i e r p e r i o d of r e g i o n a l metamorphism. Two m i n e r a l i z e d zones are present and these are e s s e n t i a l l y conformable w i t h the metasediments and c o n s i s t c h i e f l y of c h a l c o p y r i t e , p y r r h o t i t e and s p h a l e r i t e . M i n e r a l -i z a t i o n has replaced the host rock along favourable l i t h o -l o g i c h o r i z o n s , but appears most h e a v i l y concentrated i n b r e c c i a t e d zones. The deposit i s c l a s s i f i e d as Mesothermal Replacement. TABLE OF CONTENTS Page CHAPTER I I n t r o d u c t i o n 1 Lo c a t i o n and Access 1 H i s t o r y of the Property 2 Previous Work i n the Area 2 Purpose of the Thesis 4 CHAPTER I I Physiography 5 Topography 5 Drainage . 6 Climate 6 F l o r a and Fauna 6 G l a c i a l Features 7 Physiographic H i s t o r y . . . . 9 CHAPTER I I I Regional Geology 11 CHAPTER IV Geology o f the Granduc Mine Area 14 I n t r o d u c t i o n 14 Metavolcanic Rocks 14 D i s t r i b u t i o n 14 Petrography 16 Mine Member 21 D i s t r i b u t i o n 21 Petrography 22 Q u a r t z - S e r i c i t e - ( G r a p h i t e - C h l o r i t e ) P h y l l o n i t e 23 Q u a r t z - B i o t i t e - ( C h l o r i t e ) P h y l l o n i t e . . . . 27 P l a g i o c l a s e - B i o t i t e - C h l o r i t e - ( C a l c i t e ) S c h i s t 30 Amphibolite 33 Limestone 34 S c h i s t Member 35 D i s t r i b u t i o n 35 Petrography 36 P l a g i o c l a s e - B i o t i t e - A c t i n o l i t e - E p i d o t e S c h i s t 36 P l a g i o c l a s e - B i o t i t e S c h i s t 36 P l a g i o c l a s e - A c t i n o l i t e - E p i d o t e S c h i s t . . . . 38 Amphibolite 40 Quartz-Rich S c h i s t s 43 Limestone 44 I n t r u s i v e Rocks 44 D i s t r i b u t i o n 44 Petrography 46 Page Hornblende G r a n o d i o r i t e 46 D i o r i t i c Phase of the Hornblende G r a n o d i o r i t e . 47 D i o r i t e " S i l l " 49 D i o r i t e Core 50 Greenstone-Greenschist Zone 51 Green P h y l l o n i t e Zone 54 G r a n o d i o r i t e 56 A p l i t e and Gr a n o d i o r i t e S i l l s . . 57 Quartz D i o r i t e - G r a n o d i o r i t e S i l l s and Dikes . . 58 S t r u c t u r a l Geology 59 A n a l y s i s of Fold S t r u c t u r e s , F o l i a t i o n and Li n e a t i o n s 63 Shearing and F a u l t i n g 67 Petrogenesis 69 Metavolcanic Rocks .... 69 Mine Member 7 2 Q u a r t z - S e r i c i t e - ( G r a p h i t e - C h l o r i t e ) P h y l l o n i t e . . 7 2 Q u a r t z - B i o t i t e - C h l o r i t e - ( C a l c i t e ) S c h i s t 73 P l a g i o c l a s e - B i o t i t e - C h l o r i t e - ( C a l c i t e ) S c h i s t . . 74 Amphibolite 76 Limestone 76 S c h i s t Member 77 P l a g i o c l a s e - B i o t i t e - A c t i n o l i t e - E p i d o t e S c h i s t . . 77 Amphibolite . 80 Quartz-Rich S c h i s t s 81 Limestone 81 I n t r u s i v e Rocks 81 Hornblende G r a n o d i o r i t e 81 D i o r i t e 82 Conclusions 85 C o r r e l a t i o n of the Granduc Rocks 85 Metasedimentary and Metavolcanic Rocks 85 I n t r u s i v e Rocks 89 CHAPTER V Economic Geology 91 D e s c r i p t i o n of the Ore Bodies 91 Mineralogy 91 Hydrothermal A l t e r a t i o n . 97 Ore Co n t r o l s and Genesis of the Deposit 99 C l a s s i f i c a t i o n of the Ore Deposit 102 B i b l i o g r a p h y 104 ILLUSTRATIONS Figur e Page 1 L o c a t i o n map 2 2. Steep hanging g l a c i e r w i t h i c e f a l l s 8 3. Toe of the Unuk G l a c i e r l o o k i n g to the southeast 8 4. Photomicrograph of a t y p i c a l p o r p h y r i t i c andesite 19 5. Photomicrograph of sheared andesite . . . . . . 19 6. Photomicrograph of q u a r t z - s e r i c i t e p h y l l o n i t e . 24 7. Photomicrograph of a q u a r t z - s e r i c i t e p h y l l o n i t e showing an a x i a l - p l a n e cleavage f i l l e d w i t h l a t e quartz 24 8. Photomicrograph of a q u a r t z - b i o t i t e p h y l l o n i t e . 28 9. Photomicrograph of a lense of more coarse-grained quartz i n a q u a r t z - b i o t i t e p h y l l o n i t e 28 10. Photomicrograph of a p o r p h y r o c l a s t i c p l a g i o -c l a s e - b i o t i t e - c h l o r i t e - ( c a l c i t e ) s c h i s t . . 31 11. Photomicrograph of sheared limestone 31 12. Photomicrograph of a p l a g i o c l a s e - b i o t i t e s c h i s t showing a f r a c t u r e f i l l e d w i t h more coarse-grained quartz, c h l o r i t e and " i r o n o re" . . 39 13. Photomicrograph of a crumpled p l a g i o c l a s e -a c t i n o l i t e - e p i d o t e s c h i s t 39 14. Photomicrograph of amphibolite 42 15. Photomicrograph of sheared d i o r i t e $2 16. Photomicrograph of a greenschist 52 17. Photomicrograph of a green p h y l l o n i t e 55 18. Photomicrograph of a green p h y l l o n i t e 55 19. Tight f o l d i n g i n metasediments 61 20. I s o c l i n a l f o l d i n g i n q u a r t z - b i o t i t e p h y l l o n i t e s i n the 3250 l e v e l 61 Figure 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. Map 1. 2. 3. Page F o l d i n g i n metavolcanics 62 Recumbent f o l d i n sheared andesite 62 S e c t i o n along 3250 cross-cut through the Crapper Creek F a u l t i l l u s t r a t i n g changes i n m i n e r a l -ogy i n the v o l c a n i c s w i t h i n t e n s i t y of shearing 71 Graph i l l u s t r a t i n g changes i n mineralogy w i t h i n t e n s i t y of shearing i n d i o r i t e s i l l . . . . 83 B r e c c i a t e d ore 93 Replacement ore 93 Photomicrograph showing mutual boundary r e l a t i o n s of ; p y r r h o t i t e (P) and c h a l c o p y r i t e (C) . . . 94 Photomicrograph showing quartz (Q) rimmed by p y r r h o t i t e (P) 94 Photomicrograph showing e x s o l u t i o n of chalco-p y r i t e i n s p h a l e r i t e 96a Photomicrograph of galena (G) m a r g i n a l l y r e -p l a c i n g c h a l c o p y r i t e 96a Vanderveen diagram showing the paragenesis of m i n e r a l i z a t i o n 97a Photomicrograph of replacement ore 98a Photomicrograph showing aggregates of more coarse-grained quartz and opaques c u t t i n g f o l i a t i o n i n a quartz b i o t i t e p h y l l o n i t e . . 101 Photomicrograph showing the replacement of a q u a r t z - b i o t i t e p h y l l o n i t e by sulphides . . . 101 Geology of the Granduc Area S c a l e 1 i n c h = 800 f e e t In -Peoteet Outcrop Map showing d e t a i l e d surface geology above Granduc Mine, S c a l e 1 i n c h = 100 feet In £€rek-et-S t r u c t u r a l Elements o f the Granduc Area Scale 1 i n c h = 800 feet In -Pe-ek-et-F r o n t i s p i e c e South Fork of Leduc G l a c i e r l o o k i n g to the southeast. 3250 p o r t a l of the Granduc Mine i n foreground. ACKNOWLEDGMENTS The w r i t e r i s indebted to Dr. G.W.H. Norman and Mr.K. Saunders of Newmont Mining Corporation L i m i t e d , f o r data, suggestions, and f i n a n c i a l a s s i s t a n c e . Dr. W.H. White and Dr. J.V. Ross c o n t r i b u t e d h e l p -f u l suggestions and c r i t i c i s m s i n the pre p a r a t i o n o f t h i s paper. Thanks are due Mr. J.A. Donnan and Mr. W. P l a y e r f o r the pr e p a r a t i o n of the t h i n s e c t i o n s and p o l i s h e d s e c t i o n s , and to Mr. L. Iverson f o r i n s p i r a t i o n i n the f i e l d . CHAPTER I - INTRODUCTION LOCATION AND ACCESS The Granduc Mine i s near the B r i t i s h Columbia-Alaska boundary i n rugged mountainous country about 36 m i l e s n o r t h -west o f Stewart B.C., at l a t i t u d e 56°13'N and long i t u d e 130° 22«W (Figure 1) . Stewart B.C., at the head of the P o r t l a n d Canal, i s the supply base f o r the area. Northland Navig-a t i o n steamships maintain a schedule between Vancouver and Stewart. P a c i f i c Western A i r l i n e s and Omenica Airways are a v a i l a b l e f o r charter f l i g h t s i n the area. Access to the mine from Stewart i s somewhat d i f f i c u l t because o f the rugged, mountainous t e r r a i n , and the presence of extensive snow and i c e f i e l d s over much of the route. In the w i n t e r months, "snow-cats" can negotiate the d i f f i c u l t t e r r a i n from Stewart to the mine over the snow-covered g l a c i e r s . Access by foo t t r a v e l i s p o s s i b l e i n the summer months, but the journey i s d i f f i c u l t , dangerous and time-consuming. A i r p l a n e s are used f o r t r a n s p o r t of personnel and a l l but the heaviest of equipment, which i s brought i n by "snow-cat". Granduc Mines L t d . has b u i l t a hangar and supply depot at the a i r - s t r i p at Stewart. A d i r t l a n d i n g s t r i p has been b u i l t on the west side of Granduc Mountain f o r summer use, and i n winter snow-covered g l a c i e r s form s a t i s f a c t o r y l a n d i n g - s t r i p s . 3 HISTORY OF THE PROPERTY The f i r s t o f f i c i a l reference to the Granduc showings i s found i n the 1 9 3 1 B.C.Minister of Mines Report. Wendell Dawson and the l a t e W. Fromholz are reported to have ascended the Leduc Ri v e r i n 1 9 3 1 and l o c a t e d three claims that appear to have covered at l e a s t a part of the present Granduc property. The claims lapsed, and i t was not u n t i l 1 9 4 8 that the showings were "rediscovered" by E. Kvale. E. Kvale and T.McQuillan l o c a t e d claims on these showings i n 1 9 5 1 . Add-i t i o n a l claims were lo c a t e d i n 1 9 5 2 . Granby Mining Smelting and Power Co.Ltd. examined the showings i n 1 9 5 2 , and formed a new company, Granduc Mines L t d . L a t e r , Newmont Mining Corp. L t d . , entered i n t o an agreement w i t h Granby, whereby they would a i d i n f i n a n c i n g the development of the mine. PREVIOUS WORK IN THE AREA The r e g i o n drained by the Unuk Riv e r remains one o f the major unmapped areas on the eastern f l a n k of the Coast Range Mountains. Regional mapping has been done i n the areas to the south, west, and n o r t h . Most of t h i s work has been c a r r i e d out by the G e o l o g i c a l Survey of Canada, and the United S t a t e s G e o l o g i c a l Survey. A small scale sketch map of the area appeared i n the 1935 B.C. M i n i s t e r of Mines Report, while a sketch map of the 4 area immediately surrounding the mine appeared i n the 1953 B.C. M i n i s t e r o f Mines Report. In 1955> W.R.Bacon mapped 148 square mi l e s i n the Granduc Area on a sc a l e of 1 i n c h = 1 m i l e . As yet only a p r e l i m i n a r y map of t h i s work has been rel e a s e d by the B.C.Department of Mines. PURPOSE OF THE THESIS The author p a r t i c i p a t e d i n the mapping of a 40 square m i l e area i n the v i c i n i t y of the Granduc Mine during the f i e l d season of 1959. Most of t h i s area was mapped on a s c a l e of 1 i n c h = 800 f e e t , but a smaller p o r t i o n near the mine was mapped on scales of 1 i n c h = 100 f e e t , and 1 i n c h = 200 f e e t . Because of r e l a t i v e l y h i g h grade metamorphism, com-pl e x s t r u c t u r e , and the l a c k of complete r e g i o n a l mapping, i t i s d i f f i c u l t to c o r r e l a t e the s t r a t i f i e d rocks o f the Granduc area w i t h those mapped to the n o r t h and south. I t i s hoped that the present study w i l l help i n understanding the petrogenesis of the Granduc ro c k s , t h e i r c o r r e l a t i o n s , and the genesis and ore c o n t r o l s of the mi n e r a l d e p o s i t . The l a b o r a t o r y study i s based on 461 specimens from which 128 t h i n s e c t i o n s , 3 p o l i s h e d t h i n s e c t i o n s , and 15 p o l i s h e d s e c t i o n s were prepared. CHAPTER I I - PHYSIOGRAPHY TOPOGRAPHY The topography i s that of a y o u t h f u l rugged moun-tainous r e g i o n , which has been deeply d i s s e c t e d by r i v e r e r o s i o n , and both P l e i s t o c e n e and modern a l p i n e g l a c i a t i o n . The e x i s t i n g g l a c i e r s are fed by and i n part c o n s i s t of ex-t e n s i v e i c e and snow f i e l d s that cover as much as 60% of the Granduc area. Snow-line on the r i d g e s i s at an e l e v a t i o n of 4000 to 5000 f e e t , and v a l l e y g l a c i e r s terminate at l e s s than 2000 f e e t e l e v a t i o n i n the Leduc and Unuk R i v e r s . Gradients on the main v a l l e y g l a c i e r s range from 500 to 1000 feet per m i l e , but hanging g l a c i e r s have gradients of 2000 or more f e e t per m i l e . R e l i e f w i t h i n the area i s g r e a t , w i t h peaks r i s i n g to 7000 or 8000 feet from v a l l e y s or g l a c i e r s 2000 to 4000 f e e t i n e l e v a t i o n . Mountains l e s s than 7000 f e e t e l e v a t i o n tend to have smooth rounded tops, but the higher mountains have sharp jagged peaks. Mountain slopes are steep, some averaging over 40° f o r thousands of f e e t . The main v a l l e y s of the Leduc and the Unuk R i v e r s below the g l a c i e r s are broad, f l a t - f l o o r e d and 11U" shaped as a r e s u l t of g l a c i a t i o n . As the g l a c i e r s r e t r e a t e d , the streams cut channels i n the f l a t , d e bris f i l l e d v a l l e y f l o o r s . DRAINAGE The Granduc area i s drained by the South Fork o f the Unuk R i v e r (shown as Gracey Creek on some maps) and the Leduc R i v e r . The former flows about 12 mi l e s due n o r t h to j o i n the main Unuk R i v e r , which then flows 40 mi l e s i n a southwest l y d i r e c t i o n to the head of the Behm Canal i n A l a s k a . The Leduc R i v e r flows 36 miles i n a southwesterly d i r e c t i o n , and enters the Behm Canal about 14 miles south of the mouth of the Unuk R i v e r . Both streams cut through the core of the Coast Mountain system. T r i b u t a r y streams cascade down the steep s l o p e s , and e i t h e r disappear beneath v a l l e y g l a c i e r s , or d i r e c t l y enter the main stream channels almost at r i g h t angles. Seasonal v a r i a t i o n i n the flow of these streams i s very l a r g e . CLIMATE P r e c i p i t a t i o n i s heavy and except f o r the summer months l a r g e l y i n the form of snow. During the winter snow may reach a depth i n excess of 20 f e e t i n the v a l l e y s . FLORA AND FAUNA On mountains p r o t r u d i n g from the snow and i c e f i e l d s , v e g e t a t i o n i s sparse, c o n s i s t i n g almost e x c l u s i v e l y of heather, and a l p i n e grasses and f l o w e r s . On the slopes of the main v a l l e y s below the toes of the g l a c i e r s , timber and 7 underbrush become increasingly abundant. Animal l i f e i n the immediate area i s scant. Numerous marmots, ptarmigans and an occasional ermine were seen. GLACIAL FEATURES The Leduc and the Unuk Glaciers are the p r i n c i p l e g l a c i e r s i n the Granduc area. Eaeh consists of two main forks that range i n width from ^ to 1 mile, and are as much as 4 miles long. These are fed by the extensive snow and i c e f i e l d s that cover much of thi s region. As stated previously, the gradient of the main v a l l e y g l a c i e r s ranges from 500 to 1000 feet per mile. Steeper hanging glaciers have gradients up to 3000 feet per mile. These vary up to 1/4 mile i n width, and are generally less than % mile long. Ice f a l l s are common on some of the steeper g l a c i e r s . (Figure 2). The toes of the main gl a c i e r s are 50 to 100 feet thick and d r i l l i n g has shown that the i c e i s approximately 700 feet thick i n the South Fork of the Leduc Glacier near the mine. Maps show that the toes of the main glaciers have r e -ceded at least \ mile since 1955 and at the mine, the ele-vation of the surface of the g l a c i e r has decreased 50 to 100 feet since 1953. (Figure 3). Lat e r a l , medial and terminal moraines, ... cirques and hanging valleys i n a l l stages of development occur F i g u r e 3 Toe o f the Unuk G l a c i e r l o o k i n g to the southeast. Granduc Mountain i s i n the background. R e t r e a t o f the g l a c i e r i s shown by the s h a r p l y d e f i n e d t i m b e r l i n e . 9 along the main v a l l e y s and i n the source areas of the g l a c i e r s . Roches moutonnees are f a i r l y well-developed on some sl o p e s , producing a t e r r a c e d slope marked by s u b p a r a l l e l rock benches. PHYSIOGRAPHIC HISTORY The nature of the stream gradients and the narrowness of the i n t e r s t r e a m d i v i d e s , i n d i c a t e that the area i s approach-ing a stage of e a r l y m a t u r i t y . S c h o f i e l d and Hanson (1922, p 3 D s t a t e that i n the adjacent Salmon R i v e r d i s t r i c t B.C., the Coast Range was almost peneplained during the Cretaceous, and that the present v a l l e y s were eroded during the T e r t i a r y p e r i o d . Buddington (1928, p.22) agrees that a mature topo-graphy had been developed at l e a s t l o c a l l y i n pre-Eocene times i n southeast A l a s k a . He p o s t u l a t e s a considerable up-l i f t i n post-Eocene times, p o s s i b l y i n the P l i o c e n e or e a r l y P l e i s t o c e n e . Buddington describes u p l i f t e d T e r t i a r y sand-stones, conglomerates, and v o l c a n i c rocks that have a dip of 8° southeast, suggesting t i l t i n g as w e l l as u p l i f t . The Leduc and Unuk Rivers cut through the core of the Coast Mountain system, and i t i s probable.that these are pre-Eocene, antecedent streams. The P l e i s t o c e n e g l a c i a t i o n l a t e r modified the master v a l l e y s of the Leduc and Unuk R i v e r s g i v i n g them t h e i r pro-nounced "U" shape. With a b l a t i o n of the P l e i s t o c e n e and Recent g l a c i e r s , these v a l l e y s have been p a r t i a l l y f i l l e d w i t h d e b r i s that now forms the f l a t v a l l e y f l o o r s . The P l e i s t o c e n e i c e sheet appears to have reached a maximum e l e v a t i o n of 7500 feet above present sea l e v e l . Mountain and r i d g e tops below t h i s e l e v a t i o n are scoured and have d i s t i n c t i v e l y rounded tops. A few sharp jagged peaks ranging from 8000 to 8500 feet i n e l e v a t i o n appear to be un-g l a c i a t e d . Recent g l a c i e r s have f u r t h e r modified the top-ography, and g l a c i e r features of many kinds can be observed i n a l l stages of development. The South Fork of the Unuk R i v e r may have been captured from the Leduc R i v e r . U p l i f t and p o s s i b l y the damming e f f e c t s of the i c e f i e l d s may have caused the South Fork to flow i n a n o r t h e r l y d i r e c t i o n i n p o s t - P l e i s t o c e n e times. CHAPTER I I I Regional Geology The Granduc area l i e s 1^ to 5 miles north and n o r t h -east of the eastern contact of the g r a n i t i c complex that forms the backbone of the Coast Mountains. The d i s c u s s i o n of r e -g i o n a l geology w i l l be r e s t r i c t e d to a b e l t 40 to 60 miles wide on the east f l a n k o f t h i s complex, extending from the Nass R i v e r , n o r t h to the S t i k i n e R i v e r (Figure 1) . The Granduc area i s c e n t r a l l y l o c a t e d i n t h i s b e l t . P r e - b a t h o l i t h i c rocks on the eastern f l a n k of the Coast Mountains c o n s i s t of P a l e o z o i c and Mesozoic sedimentary and v o l c a n i c rocks that have been metamorphosed to varying degrees, and are commonly c l o s e l y f o l d e d . P a l e o z o i c rocks occur i n i s o l a t e d patches i n the Lower S t i k i n e and Western Iskut R i v e r areas (Kerr 1948, p.22), apparently outcropping i n eroded a n t i c l i n a l s t r u c t u r e s that p a r a l l e l the a x i s of the Coast Mountains. Pre-Mesozoic rocks have not been reported i n areas mapped to the south (Hanson 1929, 1935). P a l e o z o i c rocks i n the S t i k i n e Area are pre-dominantly sediments, c h a r a c t e r i z e d by abundant limestone, w i t h minor amounts of a r g i l l i t e , c h e r t , q u a r t z i t e , sandstone, t u f f , and t h e i r metamorphic e q u i v a l e n t s . Although the s t r u c t u r e i s complex, and most s e c t i o n s are incomplete, Kerr (1948, p.22) p o s t u l a t e s a maximum thickness of 15,000 f e e t f o r Permian and pre-Permian r o c k s . Sedimentary and volcanic rocks of Mesozoic age and th e i r metamorphosed equivalents form the major portion of the rocks east of the Coast Range g r a n i t i c complex. The sediments consist l a r g e l y of greywacke, arkose, a r g i l l i t e , and t u f f -aceous rocks, with numerous thi n beds of limestone, sandstone, and conglomerate. Interbedded andesltic and b a s a l t i c lavas and related p y r o c l a s t i c rocks are abundant and widespread, although th e i r d i s t r i b u t i o n i s i r r e g u l a r . Measurements of a complete stratigraphic section of Mesozoic rocks i n the St i k i n e area i s lacking, however, a minimum value of 10,000 feet i s suggested by White (1959). The g r a n i t i c complex of the Coast Mountain systems includes rocks of widely variable composition that range i n age from pre-Upper Jurassic to post-Lower Cretaceous, Hanson (1935) mapped granite, granodiorite, quartz d i o r i t e , and related phases as a unit i n the Portland Canal area, whereas Buddington (1928) and Kerr (194-8) emphasize the composite nature of the bat h o l i t h . This g r a n i t i c complex intrudes pre-Lower Cretaceous sedimentary and volcanic rocks, and i s over-l a i n unconformably by T e r t i a r y volcanics and continental sediments. The structure of the Coast Mountains i s extremely complex. The Paleozoic and Mesozoic rocks occur i n north to northwesterly trending folds on the flank on the g r a n i t i c complex. In a few places remnants of pre-Mesozoic structure 13 have been recognized, but f o r the most p a r t , any o l d e r s t r u c t u r e s have been completely o b l i t e r a t e d by those r e s u l t -i n g from Mesozoic orogeny. CHAPTER IV - GEOLOGY OF THE GRANDUC MINE AREA INTRODUCTION The o l d e s t rocks i n the Granduc area are a sequence of metavolcanic and metasedimentary rocks of Lower Mesozoic (?) age. These have been c l o s e l y f o l d e d and intruded by Coast Range b a t h o l i t h i c rocks and by g r a n i t i c dikes and s i l l s that are g e n e t i c a l l y r e l a t e d to the b a t h o l i t h i c i n t r u s i o n s . The major r o c k - u n i t s are l i s t e d i n h y p o t h e t i c a l chronologic order i n a t a b l e of formations on page 15, and t h e i r general d i s t r i b u t i o n i s shown on the a r e a l map (Map 1). More de-t a i l e d l i t h o l o g i c map u n i t s are shown on Map 2. In the f o l l o w i n g d i s c u s s i o n , the Metasedimentary f o r -mation has been d i v i d e d i n t o two l i t h o l o g i c a l l y d i s t i n c t i v e members that w i l l be r e f e r r e d to as the Mine member and the S c h i s t member. The former i s c h a r a c t e r i z e d by c l o s e l y f o l d e d q u a r t z - r i c h p h y l l o n i t i c r o c k s , whereas the l a t t e r c o n s i s t s e s s e n t i a l l y of p l a g i o c l a s e - b i o t i t e - a c t i n o l i t e - e p i d o t e s c h i s t s and amphibolites. METAVOLCANIC ROCKS D i s t r i b u t i o n The metavolcanic rocks outcrop c h i e f l y along the eastern s i d e of the map area. In the southeastern corner of the map sheet (Map 1), the metasedimentary-metavolcanic con-t a c t s t r i k e s i n a n o r t h e a s t e r l y d i r e c t i o n , and disappears 15 TABLE OF FORMATIONS SEDIMENTARY AND VOLCANIC ROCKS ERA PERIOD GROUP FORMATION MEMBER MAP UNIT Mesozoic J u r a s s i c and/or T r i a s s i c Hazelton Meta-sediment-ary S c h i s t P l a g i o c l a s e -b i o t i t e a c t -i n o l i t e -epidote sch-i s t ; amphi-b o l i t e ; q u a r t z - r i c h s c h i s t s ; limestone. Mine Q u a r t z - s e r i -c i t e ( g r a -p h i t e - c h l o r - ' i t e ) phy-l l o n i t e ; q u a r t z - b i o -t i t e - ( c h l o r -i t e ) phy-l l o n i t e ; p l a g i o c l a s e b i o t i t e - c h l -o r i t e ( c a l -c i t e ) s c h i s t ; amphibolite; limestone Meta-v o l c a n i c T P o r p h y r i t i c and non-p o r p h y r i t i c andesite; l o c a l l y p i l l o w e d , fragmental, b r e c c i a t e d . Sheared equi-v a l e n t s INTRUSIVE ROCKS ERA PERIOD DESCRIPTION Mesozoic (mainly or e n t i r e l y ) Lower Cretaceous or L a t e r . G r a n o d i o r i t e ; g r a n o d i o r i t e , a p l i t e , quartz d i o r i t e s i l l s and d i k e s . J u r a s s i c (?) Hornblende g r a n o d i o r i t e . Dio-r i t e and sheared e q u i v a l e n t s . under the snow-cap on Granduc Mountain. Mapping to the east o f t h i s contact shows an apparent thickness o f v o l c a n i c rocks that d e s p i t e l o c a l c o m p l e x i t i e s o f s t r u c t u r e s , amounts to at l e a s t 1000 f e e t t h i c k . On the northwest corner of Granduc Mountain metavolcanic rocks outcrop i n the c r e s t s of erroded, n o r t h plunging a n t i c l i n e s . In t h i s area, the s t r i k e of the contact i s i n a northwesterly d i r e c t i o n . The western contact of a t h i c k band of v o l c a n i c rocks cuts across the northeast corner of Mount W i l l i b e r t . Petrography The petrographic study deals o n l y w i t h the extreme western p o r t i o n of the v o l c a n i c sequence on the south s i d e of Granduc Mountain. Two complete s e c t i o n s from unsheared por-p h y r i t i c andesite to the metasedimentary contact were studied one on the surface and the other underground. Further east, the v o l c a n i c s c o n s i s t of p o r p h y r i t i c (pyroxene and/or f e l d -spar) and n o n - p o r p h y r i t i c f l o w s , w i t h minor amounts of p i l l o w e d , b r e c c i a t e d , and fragmental types. In hand specimen, the unsheared p o r p h y r i t i c andesite c o n s i s t s of dark green phenocrysts of "pyroxene" averaging about 1.0 mm i n diameter, set i n a f i n e - g r a i n e d ( 0.15 mm diameter), medium green groundmass. Generally these rocks are s t r u c t u r e l e s s . In t h i n s e c t i o n , the phenocrysts are found to c o n s i s t of a c t i n o l i t e pseudomorphous a f t e r a u g i t e . Rarely s m a l l r e l i c t patches of augite can be observed. (The pyroxene has moderate b i r e f r i n g e n c e , ZAC = 36°, and i n one instance the t y p i c a l 90° cleavage was observed.) The a l t e r e d phenocrysts are set i n a f i n e - g r a i n e d matrix composed of p l a g i o c l a s e (An^2)J a c t i n o l i t e , c h l o r i t e and epidote. Many of the a c t i n -o l i t e pseudomorphs e x h i b i t a s l i g h t p o r p h y r o c l a s t i c t e x t u r e (Figure 4 ) . P l a g i o c l a s e tends to be h i g h l y a l t e r e d to s e r i -c i t e and epidote. R e l i c t a l b i t e twinning was observed i n the l e s s a l t e r e d areas. L o c a l l y , almost a l l o f the p l a g i o c l a s e has been a l t e r e d to epidote and s e r i c i t e . The average m i n e r a l composition of s i x p o r p h y r i t i c andesites as estimated from t h i n s e c t i o n s i s as f o l l o w s : A c t i n o l i t e 4-7% P l a g i o c l a s e ( A n ^ ) 26$ Epidote 9% B i o t i t e 6% S e r i c i t e % C h l o r i t e % Carbonate 2% Sphene, A p a t i t e 1% Quartz 1% Opaques 1% C h l o r i t e and b i o t i t e appear to be r e p l a c i n g a c t i n -o l i t e m a r g i n a l l y and along c r y s t a l l o g r a p h i c boundaries. Sphene, a p a t i t e and i r o n ore(?) are present as a c c e s s o r i e s . A r e l a t i v e l y t h i n l a y e r of brownish to brownish-green rock occurs between the unsheared p o r p h y r i t i c andesite and the q u a r t z - r i c h p h y l l o n i t e s of the Mine member. This brownish rock i s dense and f i n e - g r a i n e d w i t h a r a t h e r granular t e x t u r e and a weakly developed s c h i s t o s i t y . An e x c e l l e n t cleavage and i r r e g u l a r colour banding p a r a l l e l s t h i s s c h i s -t o s i t y . O c c a s i o n a l l y , r e l a t i v e l y l a r g e (up to 1.5 mm i n diameter) dark green grains of amphibole, and s l i g h t l y greenish anhedral grains of f e l d s p a r were observed. These are g e n e r a l l y o r i e n t e d p a r a l l e l to the s c h i s t o s i t y . P y r i t e occurs i n f i n e l y disseminated grains and a l s o i n lens-shaped concentrations that p a r a l l e l the s c h i s t o s i t y . L i t h o l o g i c a l l y s i m i l a r rock i s found underground at the contact of the v o l c a n i c s and Mine member and near the Crapper Creek f a u l t , but here, the rocks tend to be greener i n colour and somewhat more f i n e -grained. In t h i n - s e c t i o n , these rocks c o n s i s t c h i e f l y of por-ph y r o c l a s t s of a c t i n o l i t e and p l a g i o c l a s e ( A n ^ ) up to 1.0 mm i n l e n g t h , which tend to be o r i e n t e d p a r a l l e l to the s c h i s -t o s i t y . These grains are f r a c t u r e d and shreaded, and pro-g r e s s i v e l y decrease i n g r a i n s i z e as the contact w i t h the sediments of the Mine member i s approached. (Figure 5). The prophyroclasts are set i n a f i n e - g r a i n e d matrix composed e s s e n t i a l l y of b i o t i t e , c h l o r i t e , and f i n e - g r a i n e d p l a g i o c l a s e . The micaceous minerals i n the mat r i x are o r i e n t e d and produce the s c h i s t o s i t y i n the rock. The average mineral composition of seven of these sheared andesites i s tabulated on page 20. Figure 4 Photomicrograph of a t y p i c a l p o r p h y r i t i c andesite. Many of the pseudomorphs of a c t i n o l i t e are p o r p h y r o c l a s t i c (X16) Figure 5 Photomicrograph of sheared andesite. Porphyroclasts of a l t e r e d p l a g i o c l a s e and a c t i n o l i t e are set i n the f i n e - g r a i n e d s c h i s t o s e groundmass (X16). P l a g i o c l a s e (An^ 2) 38$ B i o t i t e 31% Carbonate 11% C h l o r i t e 5% Quartz. 4% A c t i n o l i t e 3% Epidote • 3% S e r i c i t e 2% Opaque ( p y r i t e ) 2% Sphene, A p a t i t e 1% Samples were taken underground across an i n t e n s e l y sheared s e c t i o n where the Crapper Creek f a u l t zone cuts the v o l c a n i c rocks. The rocks i n t h i s zone c o n s i s t of f i n e -grained green p h y l l o n i t e s and somewhat coarser grained c h l o r i t i c s c h i s t s . These rocks have a well-developed s c h i s -t o s i t y that i s p a r a l l e l l e d by lenses and l a y e r s of quartz-r i c h c h l o r i t e - r i c h and b i o t i t e r i c h m a t e r i a l . Crumpling and drag f o l d i n g i s commonly found i n the p h y l l o n i t i c rocks. F i n e l y disseminated p y r i t e i s abundant i n the less-sheared types. In t h i n - s e c t i o n , these rocks were found to c o n s i s t e s s e n t i a l l y of green b i o t i t e , c h l o r i t e , s e r i c i t e , carbonate and quartz. Compositional banding i s well-developed, w i t h micaceous bands and lenses a l t e r n a t i n g w i t h lenses r i c h i n e i t h e r quartz or carbonate. Tourmaline (var. s c h o r l i t e ) which i s common i n some of these rocks may have been i n t r o -21 duced hydrothermally during shearing. A few r e l i c t shreds of a c t i n o l i t e p e r s i s t i n some of the l e s s sheared specimens, but these are e x t e n s i v e l y a l t e r e d to b i o t i t e and c h l o r i t e . These rocks are g e n e r a l l y f i n e - g r a i n e d ( 0 . 1 5 mm d i a -meter), but some q u a r t z - r i c h and c a r b o n a t e - r i c h lenses have an average g r a i n s i z e of up to 0.40 mm diameter. The l a r g e r s i z e and the absence of any features i n d i c a t i v e of s t r a i n i n g , suggests that the m a t e r i a l i n the lenses c r y s t a l l i z e d at a l a t e stage i n the deformational h i s t o r y . The average composition of f i v e of these green p h y l l o n i t e s or c h l o r i t i c s c h i s t s i s as f o l l o w s Quartz 22% C h l o r i t e 21% Carbonate 1% B i o t i t e 1% S e r i c i t e (Muscovite) 12% A c t i n o l i t e 2% S c h o r l i t e 2% Opaques ( P y r i t e ) 2% Epidote 1% Sphene 1% MINE MEMBER D i s t r i b u t i o n The rocks of the Mine member occur at the apparent base of the Metasedimentary formation, and o v e r l i e the meta-v o l c a n i c rocks. T h e i r s t r a t i g r a p h i c r e l a t i o n s h i p s are most c l e a r l y shown on the northeast corner of Mount W i l l i b e r t (Map 1), where t h e i r apparent thickness i s 400 f e e t . On the n o r t h s i d e o f Granduc Mountain these rocks are i n t e r f o l d e d w i t h the metavolcanics, and outcrop i n s y n c l i n a l depressions. On the south s i d e of Granduc Mountain, the apparent thickness o f these beds i s probably l a r g e because of cl o s e i s o c l i n a l f o l d i n g . I n f o l d i n g o f the underlying metavolcanics and al s o of the o v e r l y i n g S c h i s t member i s suggested by the presence of bands of these rocks w i t h i n the Mine member. Petrography The Mine member rocks are c h a r a c t e r i s t i c a l l y f i n e -g r a i n e d , q u a r t z - r i c h , and t i g h t l y f o l d e d . Included i n the sequence i s a limestone marked bed, and some i r r e g u l a r i n t e r -bedded or i n t e r f o l d e d bands of rocks that resemble those i n the S c h i s t member. The Mine member i s d i v i d e d i n t o the f o l l o w i n g map u n i t s , each of which w i l l be described ( i ) Q u a r t z - S e r i c i t e - ( g r a p h l t e - c h l o r i t e ) p h y l l o n i t e ( i i ) Q u a r t z - b i o t i t e - ( c h l o r i t e ) p h y l l o n i t e ( i i i ) P l a g i o c l a s e - b i o t i t e - c h l o r i t ' e - ( c a l c i t e ) s c h i s t ( i v ) Amphibolite (v) Limestone 23 Q u a r t z - S e r i c i t e - ( G r a p h i t e - C h l o r i t e ) P h y l l o n i t e This u n i t i s most commonly found i n the lower part of the Mine S e r i e s near the contact w i t h the underlying meta-v o l c a n i c s . The rocks are extremely f i n e - g r a i n e d , the grains averaging l e s s than 0 . 0 5 mm i n diameter, and have a d u l l cherty appearance. Colour v a r i e s from l i g h t grey or cream to dark grey, w i t h t h i n ( l e s s than £ inch) colour-banding f r e q u e n t l y well-developed. In t h i n - s e c t i o n , compositional banding i s a prom-inent f e a t u r e . Layers r i c h i n quartz a l t e r n a t e w i t h l a y e r s r i c h i n s e r i c i t e (muscovite), and l e s s commonly w i t h c h l o r i t e -or g r a p h i t e - r i c h l a y e r s . Minerals i n these l a y e r s tend to be o r i e n t e d p a r a l l e l to the colour l a y e r i n g . The q u a r t z - r i c h l a y e r s c o n s i s t of t i n y i n t e r l o c k i n g anhedral grains that have a crude p a r a l l e l o r i e n t a t i o n ; both p h y s i c a l l y and o p t i c a l l y . I n d i v i d u a l q u a r t z - r i c h l a y e r s or lenses tend to be equigranular, but adjacent q u a r t z - r i c h l a y e r s or lenses may d i f f e r markedly i n g r a i n s i z e , (Figure 6). Tiny micaceous l a t h s ( u s u a l l y s e r i c i t e ) , occur i n t e r -s t i t i a l l y to the quartz g r a i n s , and these are o r i e n t e d p a r a l l e l to e i t h e r the f o l i a t i o n or to an i n c i p i e n t a x i a l plane cleavage that i s v i s i b l e i n the more crumpled mica-r i c h l a y e r s . The micaceous l a y e r s c o n s i s t l a r g e l y of f i n e - g r a i n e d s e r i c i t e (muscovite) associated w i t h minor amounts of 24 Figure 6 Photomicrograph of q u a r t z - s e r i c i t e p h y l l o n i t e . Microcrumpling i s shown i n the s e r i c i t e - r i c h l a y e r s . Note the sharp contacts between equigranular l a y e r s of quartz. A few lenses of more coarse-grained r e c r y s t a l l i z e d quartz are shown (X16) Figure 7 Photomicrograph of a q u a r t z - s e r i c i t e p h y l l o n i t e showing an a x i a l - p l a n e cleavage f i l l e d w i t h l a t e quartz. Note that s c h i s t o s i t y i s marked by the t i n y l a t h s of s e r i c i t e ( l i g h t ) (X42). 2 5 c h l o r i t e and b i o t i t e . Microcrumpling may be well-developed i n these l a y e r s w i t h a new S- plane produced that tends to p a r a l l e l the a x i a l plane cleavage i n the l a r g e r f o l d s . L o c a l l y , g r a p h i t e - r i c h l a y e r s are present i n these p h y l l o n i t e s . Fine-grained graphite occurs i n t e r s t i t i a l l y t o , and i s included i n f i n e - g r a i n e d quartz. More coarse-grained quartz (up to 0.60 mm diameter) i s found f r e q u e n t l y i n lenses that p a r a l l e l the s c h i s t o s i t y at the c r e s t of f o l d s ; and al s o i n f r a c t u r e s that p a r a l l e l a x i a l - p l a n e cleavage, (Figure 7). With, or near some of these coarser grained aggregates are grains of s e r i c i t e , i r o n o r e , c h l o r i t e , carbonate, and tourmaline (both d r a v i t e and s c h o r l i t e ) . The quartz shows undulatory e x t i n c t i o n and the development of Boehm l a m e l l a e , and some of the other minerals are bent or s l i g h t l y f r a c t u r e d . Some of the specimens c o n t a i n a few anhedral porphyro-b l a s t s o f p l a g i o c l a s e ( A n r ? ) that are as l a r g e as 0.30 mm i n diameter. Tiny grains of a p a t i t e and sphene are present as a c c e s s o r i e s . An average composition f o r e i g h t q u a r t z - s e r i c i t e samples from the surface i s as f o l l o w s : Quartz %% S e r i c i t e (Muscovite) 23% Graphite 10$ B i o t i t e 3% A l b i t e (An.7) 2% Carbonate 2% C h l o r i t e 2% D r a v i t e & S c h o r l i t e 1% A p a t i t e , sphene, i r o n ore 1% M a c r o s c o p i c a l l y , samples of q u a r t z - s e r i c i t e p h y l l o n i t e s from underground are i d e n t i c a l to types obtained from the surface s e c t i o n . However, i n t h i n - s e c t i o n s e v e r a l notable d i f f e r e n c e s i n composition were observed. L i t t l e or no graphite i s . present, and the percentages of carbonate and c h l o r i t e are much higher. An average of f i v e q u a r t z - s e r i c i t e p h y l l o n i t e s from underground i s as f o l l o w s : Quartz 53% S e r i c i t e (Muscovite) 22% Carbonate 9% C h l o r i t e % A l b i t e (An 6) 3% Iron ore 2% B i o t i t e 1% Sphene, A p a t i t e 1% Epidote 1% S c h o r l i t e , D r a v i t e 1% Carbonate and c h l o r i t e occur i n p o r p h y r o b l a s t i c grains (up to 0.50 mm i n diameter) throughout the rock; i n anhedral grains i n f r a c t u r e s ; and ass o c i a t e d w i t h more coarse-grained lenses and l e n t i c l e s . Some of the p o r p h y r o b l a s t i c 27 g r a i n s p o i k i l o b l a s t i c a l l y i n c l u d e small grains of quartz and s e r i c i t e . Tourmaline ( d r a v i t e and s c h o r l i t e ) , i r o n ore, a and coarse-grained quartz are commonly as s o c i a t e d w i t h the carbonate and c h l o r i t e . As the ore zones are approached, there i s a grad-a t i o n a l increase i n the b i o t i t e content of these rocks, w i t h a corresponding decrease i n the s e r i c i t e and c h l o r i t e content. Q u a r t z - B i o t i t e - ( C h l o r i t e ) P h y l l o n i t e I n hand specimen these rocks are t e x t u r a l l y very s i m i l a r to the q u a r t z - s e r i c i t e p h y l l o n i t e j u s t d e scribed. However, they are much darker i n c o l o u r , ranging from medium to dark brown to dark greenish-grey. F o l i a t i o n i s marked by a l t e r n a t i n g t h i n l a y e r s o f browns and greys of va r y i n g shades. P y r i t e i s commonly present i n t r a i n s of small grains that p a r a l l e l the f o l i a t i o n . In t h i n - s e c t i o n these rocks are very f i n e - g r a i n e d , (averaging 0.01 mm.) s c h i s t o s e , and s l i g h t l y p o r p h y r o b l a s t i c . Compositional l a y e r i n g i s well-developed w i t h t h i n a l t e r n a t -i n g l a y e r s of q u a r t z - r i c h , b i o t i t e - r i c h , and b i o t i t e - c h l o r i t e -r i c h m a t e r i a l . The b i o t i t e v a r i e s i n colour from brown to o l i v e - g r e e n , w i t h a s i n g l e colour g e n e r a l l y predominating i n a p a r t i c u l a r specimen. S e r i c i t e i s present i n appreciable q u a n t i t i e s i n some of these rocks g e n e r a l l y as t i n y l a t h s i n the q u a r t z - r i c h l a y e r s . R a r e l y , s e r i c i t e i s found i n the micaceous l a y e r s , 28 Figure 8 Photomicrograph of a q u a r t z - b i o t i t e p h y l l o n i t e . Note c e n t r a l zone cont a i n i n g " r o l l e d " aggregates of more coarse-grained quartz, " i r o n ore" and carbonate. Sp planes are i n c i p i e n t l y developed i n the f i n e - g r a i n e d p h y l l o n i t e (X16). Figure 9 Photomicrograph of a lense of more coarse-grained quartz i n a q u a r t z - b i o t i t e p h y l l o n i t e . Note the t h i c k e n i n g of the lense i n the c r e s t s of the m i c r o f o l d (Xl6). 29 and i t appears that most of the b i o t i t e , and at l e a s t some of the c h l o r i t e , has formed at the expense of s e r i c i t e . E p i d o t e , s c h o r l i t e , i r o n o r e , c h l o r i t e , carbonate and lenses o f coarser grained quartz occur i n or adjacent to the micaceous l a y e r s (Figures 8 and 9). Most of these min-e r a l s occur i n subhedral to anhedral grains up to 0.20 mm i n diameter, many of which are unoriented. The quartz shows undulatory e x t i n c t i o n , and some of the other minerals are bent or s l i g h t l y f r a c t u r e d . A l b i t e occurs i n anhedral porphyroblasts up to 0.20 mm i n diameter. Only a few of these grains e x h i b i t simple a l b i t e twinning. The porphyroblasts do not show a p r e f e r r e d o r i e n t a t i o n , some have t h e i r longest a x i s perpendicular to the f o l i a t i o n of the more f i n e - g r a i n e d s c h i s t o s e groundmass. Tiny grains of a p a t i t e , epidote, and sphene are present as a c c e s s o r i e s i n the f i n e - g r a i n e d q u a r t z - r i c h bands. The average composition of s i x q u a r t z - b i o t i t e ( c h l o r i t e ) p h y l l o n i t e s i s as f o l l o w s : Quartz 47% B i o t i t e 26% S e r i c i t e 6% P l a g i o c l a s e (An^) 6% Epidote 4-% Tourmaline 3% Opaques 3% Carbonate 2% 30 C h l o r i t e 2$ A p a t i t e , Sphene 1% P l a g i o c l a s e - B i o t i t e - C h l o r i t e - ( C a l c i t e ) S c h i s t s On the south side of Granduc Mountain, these rocks occur on both sides of the limestone bed. To the west of the limestone, these rocks grade imperceptably i n t o sheared d i o r i t i c rocks that w i l l be described p r e s e n t l y . The rocks are dark brown to green i n c o l o u r , and although f i n e - g r a i n e d , t h e i r average g r a i n s i z e i s much l a r g e r than that of the b i o t i t e - r i c h p h y l l o n i t i c rocks. L o c a l l y these rocks appear markedly p o r p h y r o c l a s t i c w i t h elongate "metacrysts" of p l a g i o c l a s e up to 3 mm lo n g , set i n a f i n e - g r a i n e d s c h i s t o s e groundmass. F o l i a t i o n i s defined by the s u b p a r a l l e l o r i e n -t a t i o n of b i o t i t e , p l a g i o c l a s e porphyroclasts (when p r e s e n t ) , and by t h i n colour l a y e r i n g . M i c r o s c o p i c a l l y , these rocks are composed c h i e f l y of anhedral porphyroclasts of p l a g i o c l a s e (An42) that range i n s i z e up to 2.5 mm i n l e n g t h (Figure 10). These are set i n a f i n e - g r a i n e d b i o t i t e - r i c h groundmass. Many of the l a r g e grains of p o r p h y r o c l a s t i c p l a g i o c l a s e are w e l l twinned, and to some degree a l l are f r a c t u r e d . Smaller grains of p l a g i o c l a s e i n the b i o t i t e - r i c h groundmass appears to be p o r p h y r o b l a s t i c . Both the p o r p h y r o b l a s t i c and p o r p h y r o c l a s t i c p l a g i o c l a s e have the same composition. As the o r i g i n a l p l a g i o c l a s e was reduced i n g r a i n s i z e by shearing of i n -Figure 10 Photomicrograph of a p o r p h y r o c l a s t i c p l a g i o c l a s e -b i o t i t e - c h l o r i t e - ( c a l c i t e ) s c h i s t . P o r p h y r o c l a s t i c p l a g i o c l a s e (Pc) as w e l l as smaller grains of porphyro-b l a s t i c p l a g i o c l a s e (Pb) are shown (X16). Figure 11 Photomicrograph of sheared limestone. Some patches of f i n e - g r a i n e d granular quartz (Q) are present. Note o r i e n t a t i o n of c a l c i t e cleavage traces (X42). 32 t e n s i t y , the r e l a t i v e p r o p o r t i o n of the p o r p h y r o b l a s t i c p l a g i o c l a s e increased. The p l a g i o c l a s e has been a l t e r e d v a r i a b l y to f i n e - g r a i n e d aggregates of epidote and s e r i c i t e . A few r e l i c t g rains of a c t i n o l i t e were noted i n some specimens, the amphibole was l a r g e l y a l t e r e d to b i o t i t e . In some cases b i o t i t e appears to have a l t e r e d to c h l o r i t e , p a r t i c u l a r l y near lenses of coarse-grained c a r b o n a t e - c h l o r i t e -quartz aggregates. Carbonate, c h l o r i t e , and some quartz occur i n more coarse-grained (to 0.30 mm diameter) lens-shaped aggregates that cut across the f o l i a t i o n and i n c l u d e grains of p l a g i o c l a s e and b i o t i t e . Fine-grained carbonate also " f l o o d s " the ground-mass i n i r r e g u l a r zones that p a r a l l e l the f o l i a t i o n . Some carbonate and quartz g r a i n s show o p t i c a l s t a i n . F ine-grained epidote, quartz, a p a t i t e , and sphene are present as accessory minerals i n the f i n e - g r a i n e d b i o t i t e -r i c h groundmass. An average composition of these p o r p h y r o c l a s t i c s c h i s t s i s * P l a g i o c l a s e ( A n 4 2 ) 43$ B i o t i t e 20$ Carbonate 11$ C h l o r i t e 9$ S e r i c i t e 7$ Epidote 3$ 3 3 Quartz 2$ A p a t i t e , Sphene 1% Iron Ore 1% A c t i n o l i t e 1% Amphibolite An i r r e g u l a r narrow l a y e r o f a f i n e - g r a i n e d , dark green s c h i s t o s e rock was observed at the 2C surface showing, where the rock was c l o s e l y a s s o c i a t e d w i t h the p o r p h y r o c l a s t i c p l a g i o c l a s e - b i o t i t e s c h i s t s . Fragments of a s i m i l a r rock were found i n some o f the ore specimens from the underground workings. M i c r o s c o p i c study showed that t h i s rock i s an amphibolite. In t h i n - s e c t i o n , the rock i s f i n e - g r a i n e d , s c h i s t o s e , and p o r p h y r o c l a s t i c , and i s composed almost e n t i r e l y of a c t i n o l i t e . The a c t i n o l i t e occurs i n subhedral to anhedral po r p h y r o c l a s t s up to 0.40 mm i n l e n g t h set i n a f i n e - g r a i n e d m a t r i x of the same m a t e r i a l . Most grains are bent and shredded. A c t i n o l i t e appears to be a l t e r i n g to c h l o r i t e and b i o t i t e along g r a i n boundaries and cleavage t r a c e s . "Iron o re" and c h a l c o p y r i t e ( ? ) occur i n euhedral to anhedral grains of v a r y i n g s i z e included i n or i n t e r s t i t i a l to a c t i n o l i t e . " T r a i n s " of opaque minerals tend to p a r a l l e l the s c h i s t o s i t y . A l i t t l e quartz and s e r i c i t e form f i n e - g r a i n e d lenses that p a r a l l e l the s c h i s t o s i t y . 34 Limestone The limestone occurs as a t h i n , h i g h l y c o n t o r t e d , bed near the hanging w a l l of the Mine member sediments, on the south side of Granduc Mountain. In hand specimen, the limestone i s f i n e - g r a i n e d and v a r i e s i n colour from l i g h t to dark grey or green. Where weathered the limestone has a rough surface produced by small lenses and i n d i v i d u a l grains of more r e s i s t a n t m a t e r i a l . Weakly-developed colour l a y e r i n g and m o t t l i n g plus the o r i e n t a t i o n of lenses of other minerals produce a f o l i a t i o n that i s p a r a l l e l to the contacts of the bed. S t a i n i n g w i t h potassium f e r r i c y a n i d e and f e r r i c c h l o r i d e shows that the carbonate i s c a l c i t e . Two beds of limestone are reported underground where-as on l y one was observed on surface on the south s i d e of Granduc Mountain. On the northeast corner of Mt. W i l l i b e r t , only a s i n g l e bed of limestone i s present i n what appears to be a c o n t i n u a t i o n of the Mine member sediments. On the nor t h s i d e of Granduc Mountain limestone and Mine member rocks have been i n v o l v e d i n extremely complex f o l d i n g . Both r e p e t i t i o n and l o c a l l y great apparent thicknesses of these beds can be explained by t i g h t f o l d i n g . In t h i n - s e c t i o n , these rocks c o n s i s t almost e n t i r e l y of anhedral i n t e r l o c k i n g grains of c a l c i t e that average about 0.15 mm i n diameter. An i n c i p i e n t f o l i a t i o n i s marked by the s u b - p a r a l l e l arrangement of coarser and f i n e r - g r a i n e d lenses of c a l c i t e . Some lenses c o n t a i n carbonate that i n c l u d e s t i n y grains of opaque m i n e r a l s , f e l d s p a r q u a r t z , and epidote, whereas other lenses c o n s i s t of c l e a r , c l e a n c a l c i t e . One set of twin lamellae i n the c a l c i t e tends to p a r a l l e l the f o l i a t i o n , (Figure 11). Small grains of f e l d s p a r , epidote, a p a t i t e , opaque m i n e r a l s , quartz and c h l o r i t e occur i n t e r s t i t i a l l y to the carbonate g r a i n s . Most of the p l a g i o c l a s e (An^tj) i s a l t e r e d to s e r i c i t e and epidote. Many of the quartz grains show s t r a i n shadows, and i n many instances the grains appear to have been granulated. The f i n e r - g r a i n e d and i n c l u s i o n - f r e e c a l c i t e appears to have been r e c r y s t a l l i z e d during metamorphism w i t h sub-sequent g r a n u l a t i o n and bending of twin l a m e l l a e . The absence of any i n d i c a t i o n of r e a c t i o n of the c a l c i t e w i t h the inc l u d e d quartz during metamorphism, i n -d i c a t e s that a high pressure was maintained i n the pore f l u i d SCHIST MEMBER A. D i s t r i b u t i o n Rocks of the S c h i s t member of the Metasedimentary formation outcrop over most of the western part of the map sheet. Because of complex f o l d i n g the true thickness of these rocks could not be determined a c c u r a t e l y , but i t i s thought to be s e v e r a l thousand f e e t . B. Petrography P l a g i o c l a s e - b i o t i t e - a c t i n o l i t e - e p i d o t e s c h i s t s w i t h interbedded amphibolites are the predominant rock types i n the S c h i s t member. S e v e r a l quar.tz-rich s c h i s t s and one t h i n band of limestone are a l s o present. The S c h i s t member i s di v i d e d i n t o the f o l l o w i n g u n i t s f o r study and d e s c r i p t i o n , ( i ) P l a g i o c l a s e - b i o t i t e - a c t i n o l i t e - e p i d o t e s c h i s t ( i i ) Amphibolite ( i i i ) Q u a r t z - r i c h s c h i s t ( i v ) Limestone P l a g i o c l a s e - B i o t i t e - A c t i n o l i t e - E p i d o t e S c h i s t s These rocks are g e n e r a l l y f i n e - g r a i n e d , s c h i s t o s e , and are e i t h e r a dark reddish-brown or greenish-grey i n co l o u r . Commonly the s c h i s t s have a l t e r n a t i n g l a y e r s o f these c o l o u r s . Such l a y e r i n g i s p a r a l l e l to the s c h i s t o s i t y . From the microscopic study i t was found that the s c h i s t s can be r e l i a b l y sub-divided i n t o two major groups on the ba s i s o f co l o u r . The reddish-brown s c h i s t s c o n s i s t e s s e n t i a l l y of p l a g i o c l a s e and b i o t i t e , whereas the greenish-grey v a r i e t i e s c o n s i s t l a r g e l y of p l a g i o c l a s e , a c t i n o l i t e , and epidote. ( i ) P l a g i o c l a s e - B i o t i t e S c h i s t . Megascopically the p l a g i o c l a s e - b i o t i t e s c h i s t i s f i n e - g r a i n e d and has an o v e r a l l r e d d i s h brown colour w i t h t h i n a l t e r n a t i n g l a y e r s o f l i g h t e r shades o f brown and green. F o l i a t i o n i s expressed both by colour l a y e r i n g and by a pronounced cleavage that has a micaceous sheen. M i c r o s c o p i c a l l y the rock i s found to c o n s i s t essen-t i a l l y o f s mall ( 0.10 mm diameter), anhedral, i n t e r l o c k i n g g r a i n s o f p l a g i o c l a s e ( A n ^ ) , c l o s e l y a s s o c i a t e d w i t h i n t e r -s t i t i a l , f i n e - g r a i n e d , dark brown b i o t i t e . Both p l a g i o c l a s e and b i o t i t e tend to be o r i e n t e d p a r a l l e l to the f o l i a t i o n . Most of the p l a g i o c l a s e grains are untwinned w i t h o n l y a few e x h i b i t i n g simple a l b i t e twinning. anhedral grains that are o r i e n t e d p a r a l l e l to the s c h i s t o s i t y . This m i n e r a l i s found disseminated throughout the rock, and i t i s abundant i n the t h i n greenish l a y e r s noted above. O p t i c a l c h a r a c t e r i s t i c s of the a c t i n o l i t e are ZAC = 20°, and the m i n e r a l i s p l e o c h r o i c n x = pale y e l l o w , n y = pale y e l l o w -i s h green, n z = pale green. The average mineral composition of t h i s v a r i e t y of s c h i s t i s as f o l l o w s : A c t i n o l i t e occurs i n s l i g h t l y l a r g e r , subhedral to P l a g i o c l a s e ( A n ^ ) B i o t i t e 50$ 2% A c t i n o l i t e C h l o r i t e 6$ Epidote 2$ Quartz 2% Carbonate 2% Sphene, Opaque minerals 3% Carbonate 2% Tourmaline ( S c h o r l i t e ) 1% C h l o r i t e occurs throughout the rock as small l a t h s and aggregates associated w i t h a c t i n o l i t e and b i o t i t e , apparently an a l t e r a t i o n product. In some places b i o t i t e appears to have formed at the expense of a c t i n o l i t e . Such a c t i n o l i t e g e n e r a l l y i s not as p l e o c h r o i c as the unaltered types, p o s s i b l y because of l o s s of i r o n to b i o t i t e . More coarse-grained lenses p a r a l l e l to the f o l i a t i o n , and some c r o s s - c u t t i n g f r a c t u r e s contain aggregates of quartz and carbonate w i t h l e s s e r amounts of epidote, c h l o r i t e , s c h o r l i t e and " i r o n ore", (Figure 12). ( i i ) P l a g i o c l a s e - A c t i n o l i t e - E p i d o t e S c h i s t . This v a r i e t y of s c h i s t i s f i n e - g r a i n e d , compact and g e n e r a l l y of a medium to dark green c o l o u r . F o l i a t i o n i s marked c h i e f l y by the presence of t h i n l i g h t e r green l a y e r s . Cleavage i s not as well-developed as i n the p l a g i o c l a s e - b i o t i t e r i c h s c h i s t . M i c r o s c o p i c a l l y , these s c h i s t s are found to c o n s i s t e s s e n t i a l l y of subhedral grains of l i g h t green a c t i n o l i t e averaging 0.15 mm i n l e n g t h , set i n a matrix of f i n e -grained (0.02 mm diameter) p l a g i o c l a s e . I n t e r l a y e r e d w i t h t h i s m a t e r i a l are t h i n lenses and l a y e r s that are composed c h i e f l y of anhedral i n t e r l o c k i n g g r a i n s of quartz and Figure 12 Photomicrograph o f a p l a g i o c l a s e - b i o t i t e s c h i s t showing a f r a c t u r e f i l l e d w i t h more coarse-grained quartz, c h l o r i t e and " i r o n ore" (X16). Figure 13 Photomicrograph of a crumpled p l a g i o c l a s e - a c t i n o l i t e epidote s c h i s t . The dark m a t e r i a l i s a c t i n o l i t e (X16). 40 epidote up to 0.10 mm i n diameter. These produce the l i g h t e r coloured l a y e r s noted i n the hand specimens. Sphene and i r o n ore are present as a c c e s s o r i e s . B i o t i t e i s c l o s e l y a s s o c i a t e d w i t h a c t i n o l i t e and appears to be an a l t e r a t i o n product of that m i n e r a l . In t h i s v a r i e t y of s c h i s t , as i n that described p r e v i o u s l y , a l t e r e d a c t i n o l i t e i s not as s t r o n g l y p l e o c h r o i c . Most g r a i n s , and i n p a r t i c u l a r those of a c t i n o l i t e , tend to be o r i e n t e d producing a w e l l - d e f i n e d microscopic s c h i s t o s i t y that p a r a l l e l s the compositional banding (Figure 13). An average p l a g i o c l a s e - a c t i n o l i t e - e p i d o t e s c h i s t has the f o l l o w i n g mineral composition. A c t i n o l i t e 40% P l a g i o c l a s e ( A n ^ ) 30$ Epidote 10$ Quartz 15$ B i o t i t e 3$ C h l o r i t e 1$ Sphene and Opaques 1$ Amphibolite Zones of amphibolite as much as 400 f e e t wide occur i n the S c h i s t member conformable to the f o l i a t i o n o f the enclosing s c h i s t s . In hand specimen the amphibolite i s dark green and medium- to f i n e - g r a i n e d . Small ( 1.0 mm diameter) dark green grains of hornblende are conspicuous i n the f i n e -grained green matrix. F o l i a t i o n i s well-developed, expressed mainly by the p a r a l l e l o r i e n t a t i o n of hornblende. A good cleavage p a r a l l e l s the f o l i a t i o n . Near contacts w i t h the b a t h o l i t h i c r o c k s, the amphibolite i s commonly more coarse-grained. In t h i n - s e c t i o n , the amphibolite i s found to c o n s i s t e s s e n t i a l l y of almost equal amounts of o l i v e - g r e e n hornblende, and p l a g i o c l a s e ( A n ^ ) . The hornblende occurs as subhedral to anhedral grains up to 1.0 mm l o n g , a few of which are twinned on (100). F o l i a t i o n i s marked by the s u b p a r a l l e l o r i e n t a t i o n of hornblende grains which are set i n a grano-b l a s t i c matrix,of i n t e r l o c k i n g , anhedral grains of p l a g i o -clase up to 0.30 mm i n diameter, (Figure 14). P l a g i o c l a s e e x h i b i t s both a l b i t e and p e r i c l i n e twinning. "Iron o re", a p a t i t e , sphene and epidote are a c c e s s o r i e s . P l a g i o c l a s e i s s l i g h t l y s e r i c i t i z e d , and some of the hornblende appears to be p a r t l y a l t e r e d to b i o t i t e . The average m i n e r a l composition of f i v e amphibolites i s as f o l l o w s : P l a g i o c l a s e ( A n ^ ) 46$ Hornblende 39$ B i o t i t e 3$ Quartz 3$ S e r i c i t e 2$ Figure 14 Photomicrograph of amphibolite. Subhedral grains of hornblende (Hb) are set i n a more fi n e - g r a i n e d g r a n o b l a s t i c groundmass of p l a g i o c l a s e ( P I ) . Some of the hornblende i s s l i g h t l y p o r p h y r o c l a s t i c (X42). Sphene 2% Epidote 2% A p a t i t e 1% Opaques 1% These rocks are h o l o e r y s t a l i n e , medium- to f i n e -g rained, w i t h a pronounced nematoblastic t e x t u r e . In some specimens i n c i p i e n t c a t a c l a s t i c e f f e c t s were noted. Some of the p l a g i o c l a s e grains are granulated and e x h i b i t sutured c o n t a c t s , and some hornblende l a t h s are bent and shredded. A l t e r a t i o n e f f e c t s are s l i g h t . Compositional l a y e r i n g i s present i n some amphibol i t e s , w i t h p l a g i o c l a s e - r i c h lenses a l t e r n a t i n g w i t h hornblende-rich l e n s e s . Quartz-Rich S c h i s t Numerous l a y e r s o f q u a r t z - r i c h s c h i s t occur through-out the S c h i s t member. Most o f these are l e s s than 30 f e e t wide, but s e v e r a l i n the southwest p o r t i o n of the map-area (Map 1) may have a t r u e thickness o f s e v e r a l hundred f e e t . M a c r o s c o p i c a l l y these rocks are medium-grained, reddish-brown to pale grey or green i n c o l o u r , and c o n s i s t e s s e n t i a l l y of l a y e r s of g r a n o b l a s t i c quartz. Colour l a y e r -i n g i s g e n e r a l l y well-developed and l o c a l l y t h i n ( 2.0 mm) lenses o f more coarse-grained quartz accentuate the f o l -i a t i o n . An e x c e l l e n t cleavage p a r a l l e l s the f o l i a t i o n , and on cleavage surfaces a micaceous sheen i s prominent. F i n e l y disseminated p y r i t e and a few small grains of f e l d s p a r and amphibole were noted i n some specimens. 44 Although these rocks were not studied m i c r o s c o p i c a l l y i t i s suspected that most have a considerable content of f i n e - g r a i n e d micaceous mi n e r a l s . Limestone A s i n g l e band of limestone that ranges i n width from 15 to 30 f e e t was traced along the southeast s i d e of Mount W i l l l b e r t and i t s probable c o n t i n u a t i o n outcrops on the south side of the Leduc g l a c i e r . This map-unit i s i n t e r -bedded w i t h p l a g i o c l a s e - b i o t i t e - a c t i n o l i t e - e p i d o t e s c h i s t s . In hand specimen, the limestone i s medium-grained, pale grey to green i n c o l o u r , and c o n s i s t s e s s e n t i a l l y of i n t e r l o c k i n g anhedral grains of carbonate. Ready e f f e r -vescence w i t h c o l d d i l u t e HC1 i n d i c a t e s that the carbonate i s c a l c i t e . Weathered surfaces are g e n e r a l l y rough due to the presence of t h i n lenses and i n d i v i d u a l grains of mater-i a l that i s more r e s i s t a n t to weathering. Colour banding and the s u b p a r a l l e l o r i e n t a t i o n of lenses of l e s s s o l u b l e m a t e r i a l produce a f o l i a t i o n i n the limestone. This l i m e -stone i s very s i m i l a r i n appearance to that which occurs i n the Mine member. INTRUSIVE ROCKS D i s t r i b u t i o n The eastern contact of the main b a t h o l i t h i c complex i s approximately two m i l e s due south o f the Granduc mine, 45 where i t i s r e l a t i v e l y r e g u l a r and trends approximately n o r t h 80° west. A few miles both east and west of the map-area, the contact resumes i t s normal northwesterly trend. Two miles northwest of the mine, i r r e g u l a r migmatite zones are present near the contact of the Metasedimentary formation and the b a t h o l i t h i c rocks. In t h i s v i c i n i t y , an i r r e g u l a r apophysis of g r a n o d i o r i t e p r o j e c t s eastward from the main body of the i n t r u s i v e mass. This p r o t r u s i o n i s shown on the western edge of Map 1. . Here, as w e l l as at the contact to the south, the b a t h o l i t h i c rocks cut across the n o r t h -trending s c h i s t o s i t y of the metamorphic rocks. S e v e r a l smaller s a t e l l i t i c i n t r u s i o n s outcrop on and n o r t h of Granduc Mountain. The l a r g e s t of these i s a subconcordant, elongated mass of f o l i a t e d hornblende grano-d i o r i t e , the soutfr end of which i s shown on the top o f Map 1. To the east of the body of hornblende g r a n o d i o r i t e there i s a thinner (1000 f e e t ) subconcordant body of f o l i a t e d d i o r i t e . I t i s probable that t h i s i s r e l a t e d to the i r r e g u l a r , h i g h l y sheared and c l o s e l y f o l d e d d i o r i t i c zone on Granduc Mountain that extends from west of the mine northward i n t o the "limestone basin". Small i r r e g u l a r outcrops of d i o r i t e are found both east and n o r t h of the mine i n t r u d i n g v o l c a n i c rocks. A p l i t e and g r a n o d i o r i t e s i l l s occur i n swarms as much as 800 f e e t wide on the mountains to the south and west of the mine. Quartz d i o r i t e s i l l s and dikes that range i n width 4 6 from one foot to s e v e r a l tens of f e e t are found on Granduc Mountain. Petrography The i n t r u s i v e rocks are d i v i d e d i n t o the f o l l o w i n g u n i t s f o r study and d e s c r i p t i o n : ( i ) Hornblende g r a n o d i o r i t e ( i i ) D i o r i t i c phase of the hornblende g r a n o d i o r i t e ( i i i ) D i o r i t e " S i l l " ( i v ) G r a n o d i o r i t e (v) A p l i t e and g r a n o d i o r i t e s i l l s ( v i ) Quartz d i o r i t e - g r a n o d i o r i t e s i l l s and dikes Hornblende G r a n o d i o r i t e The hornblende g r a n o d i o r i t e i s a medium-grained, l e u c o c r a t i c , p o r p h y r i t i c rock, c o n s i s t i n g e s s e n t i a l l y of phenocrysts of dark green hornblende and pale grey p l a g i o -c l a s e up to 1 . 0 mm i n diameter, set i n a f i n e r - g r a i n e d groundmass of anhedral quartz and f e l d s p a r . A w e l l develop-ed f o l i a t i o n i s produced by the common o r i e n t a t i o n of the hornblende. In t h i n - s e c t i o n t h i s rock was found to c o n s i s t e s s e n t i a l l y of subhedral to anhedral phenocrysts of p l a g i o -c l a s e ( A n ^ ) and hornblende that average 1 . 0 mm i n s i z e , set i n a f i n e r grained ( 0 . 3 0 mm) m a t r i x of potash f e l d s p a r , q u a r t z , and p l a g i o c l a s e . The f e l d s p a r s are p a r t l y s e r i c i t i z e d . 47 A strongly-developed p r e f e r r e d o r i e n t a t i o n of the pheno-c r y s t s , and to a l e s s e r extent of the m a t e r i a l i n the ground-mass, produces the f o l i a t i o n and l i n e a t i o n that can be ob-served i n the hand specimens. Sphene, a p a t i t e and t i t a n i t e ( ? ) occur as a c c e s s o r i e s . Epidote, c h l o r i t e and s e r i c i t e are probably d e u t e r i c . A t y p i c a l hornblende g r a n o d i o r i t e sample has the f o l l o w i n g m i n e r a l composition: P l a g i o c l a s e ( A n ^ ) *3% Quartz 18% Hornblende 12% K - f e l d s p a r 10% Epidote 7% Sphene, A p a t i t e % S e r i c i t e 3% C h l o r i t e 2% Opaques ( T i t a n i t e ?) 1% E i o r i t i e Phase of the Hornblende G r a n o d i o r i t e I r r e g u l a r l y shaped d i o r i t i c phases occur throughout the hornblende g r a n o d i o r i t e mass, but are most abundant near the western contact of t h i s body where i t has intruded p o r p h y r i t i c andesite. The d i o r i t e i s a medium-grained, mesocratic por-p h y r i t i c rock w i t h a hypidiomorphic granular t e x t u r e . Phenocrysts of dark green hornblende and l i g h t greenish 48 p l a g i o c l a s e are set i n a f i n e - g r a i n e d green groundmass. Commonly the phenocrysts have a p r e f e r r e d o r i e n t a t i o n pro-ducing a well-developed f o l i a t i o n . The d i o r i t i c phases appear to be the r e s u l t of a s s i m i l a t i o n of and/or r e a c t i o n w i t h the country rock. In t h i n - s e c t i o n , the d i o r i t e c o n s i s t s e s s e n t i a l l y of phenocrysts of p l a g i o c l a s e (An^g) and hornblende that average 1 mm i n s i z e . These are set i n a f i n e r - g r a i n e d (0.10 mm) groundmass of s e r i c i t e , epidote, c h l o r i t e , p l a g i o c l a s e , and hornblende. The te x t u r e of the rock i s h o l o c r y s t a l l i n e , medium-grained, p o r p h y r i t i c , and hypidiomorphic granular. An i n c i p i e n t p o r p h y r o c l a s t i c t e x t u r e i s expressed l o c a l l y by f r a c t u r e d grains and bent cleavage and twin l a m e l l a e . Much of the p l a g i o c l a s e i s a l t e r e d to s e r i c i t e and epidote, and c h l o r i t e appears to have formed at the expense of horn-blende. Sphene, a p a t i t e and t i t a n i t e are a c c e s s o r i e s . An average mineral composition of t h i s d i o r i t i c phase i s as f o l l o w s : P l a g i o c l a s e (An 4g) 46$ Hornblende 35$ S e r i c i t e 10$ C i l o r i t e 3$ Epidote 3$ Sphene, A p a t i t e 2$ Opaques ( t i t a n i t e ? ) 1$ Carbonate 1$ Smaller bodies of d i o r i t e that i n t r u d e the v o l c a n i c rocks to the n o r t h and east of the mine are t e x t u r a l l y and c o m p o s i t i o n a l l y s i m i l a r to t h i s hybid phase of the horn-blende g r a n o d i o r i t e . D i o r i t e " S i l l " T his i s a zone of e s s e n t i a l l y d i o r i t i c composition roughly conformable w i t h the metasedimentary rocks, that i s i t s e l f m a r g i n a l l y sheared and l o c a l l y c l o s e l y f o l d e d . The zone extends from a point immediately west of the mine northward to the "limestone b a s i n " , and i t s probable n o r t h -ern c o n t i n u a t i o n occurs east of the hornblende g r a n o d i o r i t e mass. Gn the n o r t h s i d e o f Granduc Mountain d i o r i t e has been c l o s e l y folded along w i t h the limestone u n i t of the Mine member. At t h i s place t r a n s i t i o n s can be traced from normal d i o r i t e through carbonatized greenstones and green-s c h i s t s to mixed c a l c - s i l i c a t e rocks. On the south side of Granduc Mountain, the d i o r i t e occurs i n a zone 500 to 600 f e e t wide immediately west of the mine. This concordant body c o n s i s t s of a t h i n i r r e g u l a r l y - s h a p e d core of d i o r i t e that grades through greenstone and g r e e n s c h i s t , to very f i n e - g r a i n e d green p h y l l o n i t i c rock. The gradation represent p r o g r e s s i v e stages' i n the c a t a c l a s t i c d e s t r u c t i o n of the o r i g i n a l d i o r i t i c mass by d i s l o c a t i o n metamorphism. The petrographic study i s r e s t r i c t e d to that part of the d i o r i t e zone on the south side of Granduc Mountain where the zone can be d i v i d e d i n t o three map u n i t s : ( i ) the d i o r i t i c core, 50 ( i i ) the adjacent greenstone-greenschist zone, and ( i i i ) the marginal green p h y l l o n i t e zone. D i o r i t i c Core. Megascopically, t h i s rock i s a green medium-grained, s l i g h t l y p o r p h y r i t i c d i o r i t e . Dark green phenocrysts of hornblende(?) and cloudy greenish-grey grains of p l a g i o c l a s e are set i n an a l t e r e d f i n e - g r a i n e d green m a t r i x . A f a i r l y well-developed f o l i a -t i o n i s produced by the s u b p a r a l l e l o r i e n t a t i o n of some of the phenocrysts. M i c r o s c o p i c a l l y , the rock i s f o l i a t e d and h o l o -c r y s t a l l i n e , and c o n s i s t s e s s e n t i a l l y of h i g h l y a l t e r e d porphyroclasts of a c t i n o l i t e - h o r n b l e n d e and p l a g i o c l a s e set i n a f i n e - g r a i n e d m a t r i x of epidote, s e r i c i t e , c h l o r i t e , p l a g i o c l a s e , and amphibole, (Figure 15). The o r i g i n a l t e x -ture appears to have been hypidiomorphic granular, but t h i s has been masked by the extensive a l t e r a t i o n and g r a n u l a t i o n of the primary s i l i c a t e s . P l a g i o c l a s e (An^g) occurs i n anhedral grains up to 1.5 mm i n diameter, now almost completely a l t e r e d to s e r i -c i t e and epidote. A l b i t e twinning can be seen i n the l e s s a l t e r e d areas. Most of the amphibole present i n the s e c t i o n appears to be i r o n - r i c h , a c t i n o l i t e (ZAC<20°). The a c t i n o l i t e i s p l e o c h r o i c . (n x= y e l l o w i s h to c o l o u r l e s s , n y = y e l l o w i s h -green, nz= pale green to dark b l u i s h green). Some green hornblende (ZAC = 28°) i s a l s o present, but the r e l a t i v e p roportions of the two minerals could not be accurately-determined because of t h e i r s i m i l a r c o l o u r . The amphibole appears to be a l t e r e d to c h l o r i t e along g r a i n boundaries. Some of the amphibole i s pseudomorphic a f t e r pyroxene, p o s s i b l y a u g i t e , a few small i s o l a t e d r e l i c t s of which per-s i s t i n some amphibole g r a i n s . This pyroxene has moderate b i r e f r i n g e n c e and a maximum ZAC = 48°, and i n one i n s t a n c e , pyroxene cleavage was observed. The mineral composition and r e l a t i v e m i n e r a l per-centages are as f o l l o w s : P l a g i o c l a s e (An^g) 23$ A c t i n o l i t e 20$t ) ••; ) 25$ Hornblende 5$t ) C h l o r i t e 10$ Epidote S e r i c i t e 10$ Sphene 5$ A p a t i t e 1$ Augite 1$ Greenstone-Greenschist Zone. These rocks border the d i o r i t e core and r e -present an intermediate stage i n the c a t a c l a s t i c d e s t r u c t i o n of the d i o r i t e . M egascopically, these rocks are g e n e r a l l y f i n e -grained, dark to medium green i n c o l o u r , and may, or may not Figure 15 Photomicrograph of sheared d i o r i t e . Porphyroclasts of p l a g i o c l a s e (PI) and a c t i n o l i t e (Ac) set i n a f i n e -grained matrix o f p l a g i o c l a s e , amphibole, epidote, c h l o r i t e and s e r i c i t e ( X l 6 ) . Photomicrograph of a gr e e n s c h i s t . Note porphyro-c l a s t s of p l a g i o c l a s e (PI) set i n the f i n e - g r a i n e d gro undmas s (X42). be f o l i a t e d or schistose. An occasional small porphyroclast of amphibole and feldspar may be observed. Thin bands of l i g h t e r coloured material that p a r a l l e l the f o l i a t i o n are present i n the more schistose types. In thin-section, the rock has a well-developed por-phyroclastic texture. S e r i c i t i z e d plagioclase (An^) and amphibole grains are extensively fractured, shredded and oriented p a r a l l e l to the f o l i a t i o n . The porphyroclasts of plagioclase and amphibole (up to 1.0 mm i n the largest dimension) are set i n a finer-grained matrix consisting of epidote, s e r i c i t e , c h l o r i t e , plagioclase, and amphibole, (Figure 16). Two v a r i e t i e s of amphibole are present, i r o n - r i c h a c t i n o l i t e and hornblende. Some values of ZAC approach 28°, while others are less than 20°. Both minerals are similar i n colour, so that an accurate estimate of th e i r r e l a t i v e proportions could not be made. The composition of a t y p i c a l greenstone i s as follows Plagioclase (An^) 35$ A c t i n o l i t e 12$t ) ^ ) 22$ Hornblende 10$I Epidote 27$ C h l o r i t e 8$ S e r i c i t e (Muscovite) 5$ Carbonate 3$ B i o t i t e 2$ 54 I n c i p i e n t metamorphic d i f f e r e n t i a t i o n appears to have taken place producing compositional l a y e r i n g on an almost microscopic s c a l e . A l t e r n a t i n g t h i n l a y e r s and lenses of m a t e r i a l r i c h i n epidote, p l a g i o c l a s e or amphibole are common. Most of the c h l o r i t e , e pidote, b i o t i t e , and s e r i c i t e present i n . t h e rock i s probably an a l t e r a t i o n product of the primary s i l i c a t e s . Green P h y l l o n i t e Zone. The rocks of t h i s zone, marginal to the d i o r i t e " s i l l " , have undergone the greatest e f f e c t s of d i s l o c a t i o n metamorphism. In hand specimen, these rocks are very f i n e - g r a i n e d , and g e n e r a l l y medium to l i g h t , green i n co l o u r . F o l i a t i o n i s marked by t h i n , a l t e r n a t i n g bands of l i g h t and dark green m a t e r i a l . An e x c e l l e n t cleavage p a r a l l e l s -this f o l i a t i o n . Such rocks effervesce r e a d i l y i n c o l d d i l u t e HC1 i n d i c a t i n g a h i g h c a l c i t e content. In t h i n - s e c t i o n , these rocks c o n s i s t e s s e n t i a l l y of porphyroclasts of p l a g i o c l a s e ( A n ^ ) set i n a f i n e - g r a i n e d (0.10 mm i n diameter) m a t r i x of c h l o r i t e , carbonate, and p l a g i o c l a s e (Figure 17 and 1 8 ) . Grain s i z e of the s e r i c i t i z e d porphyroclasts of p l a g i o c l a s e has been reduced to an average of 0.45 mm diameter. A t y p i c a l green p h y l l o n i t e had the f o l l o w i n g composition.. Figure 17 Photomicrograph of a green p h y l l o n i t e . Note the p l a g i o c l a s e porphyroclasts set i n the f i n e - g r a i n e d s c h i s t o s e m a t r i x (X42). \ v act * / * v .,.4 Figure 18 Photomicrograph of a green p h y l l o n i t e . Note zone "flooded" w i t h carbonate ( l i g h t ) ( X 4 2 ) . Plagioclase (An^ 2) 40$ Chlor i t e 30$ Carbonate 2% S e r i c i t e 1% Opaques 2% C h l o r i t e and carbonate appear to have formed at the expense of the amphiboles and epidote. Granodiorite No samples of rock from the main body of batho-l i t h i c rocks were studied. Buddington (1928, p. 180) found that 16 analysed specimens of b a t h o l i t h i c rock from an area about 10 miles south of the mine had the average composition of quartz monzonite. Bacon (1955) mapped the igneous rocks 2*js- miles south of the mine, and c a l l e d them medium-grained granodiorite of the following composition: Plagioclase (Oligoclase-Andesine) 4-5% Quartz 26% Potash Feldspar 18% B i o t i t e + Hornblende 9% Accessories 2$ The rock i n the apophysis that cuts the Schist member on the west side of the map-area i s a medium-grained, l o c a l l y p orphyritic, leucocratic b i o t i t e granodiorite that consists e s s e n t i a l l y of plates of dark green b i o t i t e set i n a groundmass of interlocking anhedral grains.of feldspar and quartz. B i o t i t e and f e l d s p a r commonly show a p r e f e r r e d o r i e n t a t i o n that produces an i n c i p i e n t f o l i a t i o n . A p l i t e and G r a n o d i o r i t e S i l l s A p l i t i c s i l l s predominate i n the s i l l swarms on the mountains to west and south of Granduc Mountain, but a few granophiyric g r a n o d i o r i t e s i l l s are present a l s o i n these swarms. The s i l l s range from a few f e e t to $0 fe e t i n t h i c k -ness. L o c a l l y they cut the S c h i s t member w i t h s l i g h t d i s -cordancy. M a c r o s c o p i c a l l y the a p l i t e i s l e u c o c r a t i c , medium-grained, and c o n s i s t s almost e n t i r e l y of anhedral i n t e r l o c k -ing grains of white f e l d s p a r and quartz which are set i n a f i n e - g r a i n e d s i l i c e o u s matrix. In places these rocks are markedly p o r p h y r i t i c , and some have a graphophyric t e x t u r e . In t h i n - s e c t i o n the a p l i t e c o n s i s t s of anhedral grains of quartz, a l b i t i c p l a g i o c l a s e , and some potash f e l d -spar up to 2.0 mm i n diameter. These are set i n a f i n e -grained matrix of quartz, m i c r o p e r t h i t e , m i c r o c l i n e , and potash f e l d s p a r . B i o t i t e , muscovite, a p a t i t e and epidote are present i n small amounts. The rock i s h o l o c r y s t a l l i n e , hypidiomorphic gr a n u l a r , medium- to coarse-grained and por-p h y r i t i c . A t y p i c a l specimen has the f o l l o w i n g composition: 58 P l a g i o c l a s e (AnoJ 45$ Quartz 30$ Potash Feldspar 20$ Muscovite 2$ Epidote 1$ B i o t i t e 1$ A p a t i t e 1$ The l e s s numerous g r a n o d i o r i t e s i l l s are s i m i l a r to those found on Granduc Mountain, except that many have a more pronounced granophyric t e x t u r e i n the groundmass. Quartz D i o r i t e - G r a n o d i o r i t e S i l l s and Dikes Numerous s i l l s and dikes are found on Granduc Mountain. These range i n width from one foot to s e v e r a l tens of f e e t . In handspecimen, the rocks are medium-grained, p o r p h y r i t i c , l e u c o c r a t i c and c o n s i s t e s s e n t i a l l y of a l t e r e d , subhedral to anhedral phenocrysts of p l a g i o c l a s e (An^Q - A n ^ ) up to 1.5 mm i n le n g t h set i n a f i n e r - g r a i n e d groundmass. Some phenocrysts are normally zoned, having more a l b i t i e rims. The groundmass c o n s i s t s of p l a g i o c l a s e ( g e n e r a l l y more a l b i t i e than An-^o)» quartz, hornblende, and c h l o r i t e . Potash f e l d -spar may or may not be present. Quartz and f e l d s p a r may form granophyric intergrowths i n the groundmass, p a r t i c u l a r l y i n dikes to the south of the mine near the contact w i t h the b a t h o l i t h i c rocks. Much of the f e l d s p a r i s a l t e r e d to s e r i c i t e and 59 epidote, and some c h l o r i t e appears to have formed at the ex-pense of hornblende. Sphene, a p a t i t e and t i t a n i t e ( ? ) occur as a c c e s s o r i e s . The compositions of these dikes vary from g r a n o d i o r i t e to quartz d i o r i t e . R e l a t i v e proportions of p l a g i o c l a s e to potash f e l d s p a r could not be a c c u r a t e l y determined because of the i n t e n s i v e a l t e r a t i o n of much of the f e l d s p a r , but p l a g i o c l a s e appears to predominate. The average composition of four specimens from Granduc Mountain i s : P l a g i o c l a s e ( A n ^ - A n ^ 39$^) J J b •:) 49$ K - f e l d s p a r 10$I) Quartz 15$ S e r i c i t e 10$ C h l o r i t e 10$ Epidote 6$ Hornblende 3$ B i o t i t e 2$ A p a t i t e , Sphene 2$ Carbonate 1$ Opaques ( t i t a n i t e ? ) 1$ STRUCTURAL GEOLOGY The "tops" of the ste e p l y d i p p i n g s t r a t i f i e d rocks could not be asc e r t a i n e d w i t h the a v a i l a b l e evidence. Loc-a l l y , p i l l o w s t r u c t u r e was seen i n the p o r p h y r i t i c andesite east of the mine, and s t r u c t u r e s that might be graded bedding \ were observed i n the S c h i s t member i n the southwest corner of the map sheet, but because of complex f o l d i n g these "top" determinations could not be r e l a t e d to the o v e r a l l s t r u c t u r e . However, the o r i e n t a t i o n of d r a g - f o l d s , both s m a l l and l a r g e , on Granduc Mountain i s compatable w i t h the presence of a major a n t i c l i n a l a x i s to the east. F u r t h e r , the v o l c a n i c rocks s t r u c t u r a l l y u n d e r l i e the metasedimentary rocks w i t h apparent conformity, so that unless the s t r a t i f i e d rocks are completely overturned, the v o l c a n i c rocks must be o l d e r . Overturning on a l a r g e s c a l e would be required because the we s t e r l y dips i n the v o l c a n i c rocks f l a t t e n markedly to the east of the mine. I f the v o l c a n i c rocks are o l d e r , t h e i r map d i s t r i b u t i o n a l s o i n d i c a t e s a major a n t i c l i n a l a x i s to the east. Therefore, although the evidence i s not c o n c l u s i v e , i t i s b e l i e v e d that the Granduc mine i s on the west limb of a major a n t i c l i n e . The metasedimentary formation i s c h a r a c t e r i z e d by t i g h t i s o c l i n a l f o l d i n g w i t h sharp c r e s t s , (Figures 19 and 20). Folds i n the metavolcanic rocks tend to be more open and have more rounded c r e s t s , (Figures 21 and 22). Ampli-tudes of the f o l d s range from a few m i l l i m e t e r s to hundreds of f e e t . Much of the apparent interbedding of map u n i t s seen both on surface and underground i s a t t r i b u t e d to r e p e t i t i o n by close f o l d i n g . Ptygmatic f o l d i n g i s found i n the igneous-metasedimentary complex of the dike swarms and migmatite zones on Mount W i l l i b e r t . Figure 19 T i g h t f o l d i n g i n metasedi-ments di s p l a y e d on a faceted spur. Figure 20 I s o c l i n a l f o l d i n g i n a q u a r t z - b i o t i t e p h y l l o n i t e i n the 3250 l e v e l . Face i s approximately 6 f e e t high. Figure 21 F o l d i n g i n metavolcanics to the east of the mine on Granduc Mountain. View lo o k i n g northeast. Recumbent f o l d i n sheared a n d e s i t e on top o f Granduc Mountain 1^ - m i l e s east o f the mine. Note t h i c k e n i n g at the c r e s t . T h i s outcrop i s approximately 20 f e e t wide. Most of the rocks i n the area are f o l i a t e d , and l o c a l l y sheared and f a u l t e d . The s t r u c t u r a l elements are considered i n d e t a i l i n the f o l l o w i n g s e c t i o n s . ANALYSIS OF FOLD STRUCTURES, FOLIATIONS AND LIN EAT IONS The Granduc Area i s d i v i d e d i n t o f i v e zones (Map 3 ) , f o r the f o l d a n a l y s i s . W i t h i n each of these zones the o r i e n t a t i o n of f o l i a t i o n s were measured and the poles to planes p l o t t e d and contoured on a stereographic net (lower hemisphere p r o j e c t i o n ) . L i n e a t i o n s were p l o t t e d on the same diagram but were not contoured. Poles to a x i a l - p l a n e s of drag f o l d s were p l o t t e d on separate diagrams. In a l l zones, there i s a s t r i k i n g c oncentration of poles to f o l i a t i o n and a correspondence of poles to a x i a l planes that i s i n d i c a t i v e of i s o c l i n a l f o l d i n g . On the south side of Granduc Mountain the average © s t r i k e of both f o l i a t i o n s and a x i a l - p l a n e s i s no r t h 31 west w i t h a dip of 62° west i n Zone I , and n o r t h 29° west w i t h a dip of 83° west i n Zone I I . In each zone, there i s a;con-c e n t r a t i o n of l i n e a t i o n s ( f o l d axes) near the pole to the great c i r c l e that can be drawn through the contoured poles o f f o l i a t i o n . This i n d i c a t e s that the l i n e a t i o n s are r e l a t e d to i s o c l i n a l f o l d i n g . In Zones I and I I the average l i n -e a t i o n trends south 52° west w i t h a plunge of 60° to the southwest, and south 30° west w i t h a plunge of 50° to the south r e s p e c t i v e l y . A few sc a t t e r e d l i n e a t i o n s are present, 6 4 and these probably represent the i n c i p i e n t m o d i f i c a t i o n o f the i s o c l i n a l f o l d s by a second p e r i o d of f o l d i n g . A marked f l a t t e n i n g of f o l d axes to the n o r t h was found i n a study made along the 3750 d r i f t at the mine. The plunges of f o l d axes were measured and the r e s u l t s averaged f o r each 400-foot i n t e r v a l of the 1600 f o o t t u n n e l . From south to n o r t h the averages were 5 1 ° , 3 9 ° , 38° and 23° r e s p e c t i v e l y . On the northwest corner of Granduc Mountain and on the east side of Mount W i l l i b e r t (zones IV and V r e s p e c t i v e l y ) there i s a pronounced change i n the s t r u c t u r a l trend as com-pared w i t h the area p r e v i o u s l y mentioned. In zones IV and V, the average trend of f o l i a t i o n s and a x i a l planes i s n o r t h 44° west w i t h a dip of 80° to the west, and n o r t h 34° west w i t h a dip of 50° to the west r e s p e c t i v e l y . In both zones, l i n e a t i o n s tend to p l o t along a l i n e that b i s e c t s a great c i r c l e drawn through the concentration of poles to f o l i a t i o n s . A weakly developed c o n c e n t r a t i o n of l i n e a t i o n s about the pole (B) of t h i s great c i r c l e shown i n Zone IV, i n d i c a t e s that a f o l d a x i s trending S38°E and plunging moderately south i s r e l a t e d to i s o c l i n a l f o l d i n g . A second period of f o l d i n g i s suggested by the s c a t t e r i n g of the remaining l i n e a t i o n s . L i n e a t i o n s i n zone V trend both northwesterly and southeaster-l y w i t h no apparent concentration. These l i n e a t i o n s represent f o l d a x i s of i s o c l i n a l f o l d s , hence the absence of a con-c e n t r a t i o n i s i n d i c a t i v e of a second pe r i o d of f o l d i n g . Zone I I I i s an area of i n f l e c t i o n i n which the n o r t h -east s t r u c t u r a l trend of zones I and I I swings to the n o r t h -west trend that i s e s t a b l i s h e d i n zones IV and V. I s o c l i n a l f o l d i n g i s i n d i c a t e d by the c o n c e n t r a t i o n of poles to f o l i a -t i o n s and a x i a l - p l a n e s on the stereographic p r o j e c t i o n . Two "high" p o i n t s of poles to f o l i a t i o n s are apparent, one i n d i -c a t i n g an average a t t i t u d e of n o r t h 8° east w i t h a v e r t i c a l dip and the other n o r t h 19° west w i t h a v e r t i c a l d i p . The former i s thought to r e f l e c t the s t r u c t u r a l trend of zones I and I I , whereas the l a t t e r r e f l e c t s the northwesterly trend of zone IV and V. L i n e a t i o n s ( f o l d axes of i s o c l i n a l f o l d s ) trend roughly n o r t h and south, w i t h plunges to the south tending to be steeper than those to the north. The absence of a concentration of l i n e a t i o n s i s i n d i c a t i v e of a second per i o d of f o l d i n g . Drag f o l d i n g i n the metasedimentary and metavolcanic rocks i n d i c a t e s that the i s o c l i n a l f o l d i n g i s r e l a t e d to the formation of the l a r g e a n t i c l i n e that i s believed to l i e to the east of the mine. The a n t i c l i n e s and s y n c l i n e s i n Zones I I I and IV and on the northwest corner of Granduc Mountain are i n t e r p r e t e d as l a r g e drag f o l d s which have the same sense as the minor f o l d s . The o r i g i n a l "b" l i n e a t i o n s ( i . e . f o l d axes of i s o c l i n a l f o l d s ) produced by r e g i o n a l metamorphism probably p a r a l l e l e d the kinematic "b" a x i s , w i t h compressional forces a c t i n g along east or northeast axes. Both f i e l d observations and graphic a n a l y s i s suggest 66 that a l a t e r period of f o l d i n g i s i n v o l v e d i n the defor-mational h i s t o r y of the area, and t h i s i s represented by warping of the s t r u c t u r a l elements r e l a t e d to the i s o c l i n a l f o l d i n g . The a x i a l t r a c e of these broad, younger f o l d s trend westerly (see Zone I I I and I V ) . A cyelographic r e p r e -s e n t a t i o n of the average f o l i a t i o n i n zones I I and IV shows that the f o l d a x i s of the younger f o l d trends approximately due west, and plunges s t e e p l y . However, the d i s t r i b u t i o n and o r i e n t a t i o n of l i n e a t i o n s ( i s o c l i n a l f o l d axes) i n zones I I I , IV and V r e q u i r e s a more h o r i z o n t a l a x i s f o r the younger f o l d s , as regardless of plunge the trends of l i n e a -t i o n s have not been swung appreciably to the east or west. This c r i n k l i n g of the o l d "b" a x i s does not appear to have taken place i n zones I and I I , as here the p l o t t e d l i n e a t i o n s have a pronounced con c e n t r a t i o n . The strongly-developed s t r u c t u r a l trend ( n o r t h e r l y ) of the i s o c l i n a l l y f o l d e d s t r a t i f i e d rocks continues south of the map-area and e v e n t u a l l y i s sharply terminated by the con-t a c t of the Coast Range b a t h o l i t h . The c r o s s - c u t t i n g r e -l a t i o n s h i p of the b a t h o l i t h i c rocks w i t h respect to the i s o -c l i n a l l y f o l d e d s t r a t i f i e d rocks i s shown also by the grano-d i o r i t e apophysis on the east side of Mount W i l l i b e r t . Hence, i s o c l i n a l f o l d i n g preceded the i n t r u s i o n of the b a t h o l i t h i c rocks. The second pe r i o d of f o l d i n g i s b e l i e v e d to have taken place d u r i n g , or a f t e r i n t r u s i o n o f the Coast Range b a t h o l i t h i c rocks. Post-folding i n t r u s i o n of quartz d i o r i t e s i l l s and dikes (considered cl o s e l y related to the b a t h o l i t h i c rocks) i s suggested by a s i l l - l i k e body that cuts across a warped band of amphibolite on the west side of Granduc Mountain. On the other hand, a f a i r l y large continuous quartz d i o r i t e s i l l that i s present near the snow l i n e i n Zone III appears to have been flexed by the second period of fo l d i n g . Buddington (1928, p. 288) and Mackenzie (1916, p. I l l ) have recognized Eocene folding i n Alaska and northeastern B r i t i s h Columbia with compressional forces acting almost at right angles to those that acted during Mesozoic orogeny. The sense and time relationship of such a compression i s com-patible with the flexuring produced by the younger folds i n the Granduc area. SHEARING AND FAULTING A 1000-foot zone to the west of, and including the Mine member-metavoleanic contact on the south side of Granduc Mountain appears to have been a zone of s t r u c t u r a l weakness over a considerable period of geologic time. The rocks i n this zone were dynamically metamorphosed to phyllonites i n the late stages of regional metamorphism. Drag folding and the development of a x i a l plane cleavage indicate that this i n i t i a l d i f f e r e n t i a l movement was related to the formation of the postulated a n t i c l i n e that l i e s to the east of the mine. 68 Evidence of p a r t i c u l a r l y i ntense deformation at a l a t e metamorphic stage i s evidenced by b r e c c i a t e d ore specimens that contain fragments of both r e g i o n a l l y meta-morphosed s c h i s t s and p h y l l o n i t i c r o c k s . The b r e c c i a t e d zone appears to have been a major channel f o r m i n e r a l i z i n g s o l u t i o n s . Some question a r i s e s as to the time r e l a t i o n s h i p of t h i s economically important period of d i f f e r e n t i a l move-ment and the second period of f o l d i n g . S e v e r a l p o s s i b i l -i t i e s are discussed under the heading "Ore C o n t r o l s " . A set of l a t e l o n g i t u d i n a l f a u l t s .iss found i n the area. These are p o s t - i n t r u s i v e , and l a t e r than the second-ary p e r i o d of f o l d i n g . On the south side of Granduc Mountain these f a u l t s trend approximately n o r t h 20° east and are e s s e n t i a l l y p a r a l l e l to the f o l i a t i o n i n the p h y l l o n i t i c rocks. To the n o r t h however, these f a u l t s appear to cut across the f o l i a t i o n where the i s o c l i n a l l y f o l d e d rocks have been f l e x e d by second-period f o l d i n g . Right-handed movements are i n d i c a t e d by f a u l t e d quartz d i o r i t e dikes and s t e e p l y plunging drag f o l d s near the f a u l t planes. Three such f a u l t s have been recognized i n surface mapping above the mine and the t o t a l apparent h o r i z o n t a l displacement of a quartz d i o r i t e dike i s i n the order of 1000 f e e t . The v e r t i c a l component of t h i s movement i s not known. The underground workings are e s s e n t i a l l y bounded by two major f a u l t s , both of which are represented by g u l l i e s on the s u r f a c e . The eastern most of these i s the Crapper Creek F a u l t which i s w e l l displayed underground j u s t west of the shaft on the 3250 l e v e l , where p o r p h y r i t i c andesites have been i n t e n s e l y sheared to green p h y l l o n i t e and c h l o r i t i c s c h i s t s over a wide zone. M i n e r a l i z e d shear zones of a minor nature are found to the east of the map-area i n the v o l c a n i c rocks, but these are not of economic s i g n i f i c a n c e . I t i s not known to which period of shearing these are r e l a t e d . PETROGENESIS Metavolcanic Rocks The a n d e s i t i c v o l c a n i c rocks are e x t e n s i v e l y a l t e r e d , even where d i s l o c a t i o n metamorphism has not been a c t i v e . O r i g i n a l ferromagnesian minerals have been a l t e r e d to a c t i n -o l i t e , c h l o r i t e and epidote, and the primary f e l d s p a r s have been a l t e r e d to s e r i c i t e and epidote. The a c t i n o l i t e and epidote present i n the unsheared metavolcanics appears to have been unstable under the con-d i t i o n s that e x i s t e d i n zones of d i f f e r e n t i a l movement, and these minerals p r o g r e s s i v e l y disappeared as the i n t e n s i t y of shearing increased. Much of the b i o t i t e , c h l o r i t e and c a r -bonate found i n the sheared metavolcanics appears to have formed at the expense of a c t i n o l i t e and epidote. Except i n 70 the more i n t e n s e l y sheared zones, p l a g i o c l a s e . h a s been only granulated. In the 3250 l e v e l , specimens were taken at 25 foot i n t e r v a l s across the Crapper Creek f a u l t zone, from a l t e r e d p o r p h y r i t i c andesite on the ea s t , w e s t e r l y through green-stones and g r e e n s c h i s t s , to c h l o r i t i c s c h i s t s and green p h y l l o n i t e s . The marked changes i n mineralogy w i t h the i n -t e n s i t y of shearing are g r a p h i c a l l y i l l u s t r a t e d i n Figure 23. A c t i n o l i t e i s the f i r s t m i n e r a l to be a f f e c t e d i n the high s t r e s s environment, a l t e r i n g to b i o t i t e , c h l o r i t e and c a r -bonate. Much of the quartz, and some of the carbonate and c h l o r i t e present i n the c h l o r i t i c s c h i s t and green p h y l l o n i t e zone appears to have been derived from p l a g i o c l a s e and epidote i n t h i s zone of intense shearing. Concordant, more coarse-grained, q u a r t z - r i c h and carbona t e - r i c h lenses are commonly found i n the s c h i s t o s e and p h y l l o n i t i c rocks. The mi n e r a l c o n s t i t u e n t s i n these lenses show l i t t l e evidence of s t r a i n i n g ( i n c i p i e n t undulatory ex-t i n c t i o n i n quartz, and bent cleavage traces i n the carbonate). I t i s thought that t h i s m a t e r i a l was "mo b i l i z e d " during shearing w i t h subsequent r e c r y s t a l l i z a t i o n at a l a t e stage o f the d i s l o c a t i o n metamorphism. S c h o r l i t e and some of the " i r o n ore" i n the more h i g h l y sheared rocks i s thought to have been introduced at a l a t e stage. ' 71 FIGURE 2 3 SECTION ALONG 3250 CROSS-CUT THROUGH THE CRAPPER CREEK FAULT ILLUSTRATING CHANGES IN MINERALOGY IN THE VOLCANICS WITH INTENSITY OF SHEARING 40n r FOOTAGE FROM SHAFT TO WEST ALONG 3250 X-CUT PORPHYRITIC ANDESITE SHEARED I I oncMr\c.L/ 1 j ANDESITE j INCREASED SHEARING CHLORITIC SCHISTS AND GREEN SHEARED PHYLLONITE ANDESITE INCREASED SHEARING 72 Ignoring the r e l i c t p o r p h y r o c l a s t i c p l a g i o c l a s e and a c t i n o l i t e , the mineral assemblage i n the sheared andesites can be c l a s s i f i e d i n the b i o t i t e - e h l o r i t e subfacies of the greenschist f a c i e s (Turner and Verhoogen (195D). L o c a l l y , i n more h i g h l y sheared zones, the rocks contain appreciable muscovite. These rocks could be c l a s s i f i e d i n the muscovite-c h l o r i t e subfacies of the greenschist f a c i e s . The extensive a l t e r a t i o n of primary s i l i c a t e s to c h l o r i t e , b i o t i t e , epidote and s e r i c i t e , and the more marked changes i n mineralogy i n zones of d i f f e r e n t i a l movement, are a r e s u l t of r e t r o g r e s s i v e metamorphism of an i n i t i a l h i g h temperature mineral assemblage. MINE MEMBER Q u a r t z - S e r i c i t e - ( G r a p h i t e - C h l o r i t e ) P h y l l o n i t e The m i n e r a l assemblage i n these rocks appears to be i n e q u i l i b r i u m (with the exception of the i n c i p i e n t a l t e r a t i o n of s e r i c i t e and c h l o r i t e to b i o t i t e ) and the rocks can be c l a s s i f i e d i n the m u s c o v i t e - c h l o r i t e subfacies of the green-s c h i s t f a c i e s (Turner and Verhoogen 195D. The o r i g i n a l rock was probably an impure sandstone, composed l a r g e l y of quartz and a r g i l l a c e o u s m a t e r i a l , w i t h l o c a l concentrations of c a r -bonaceous m a t e r i a l . The more coarse-grained quartz lenses that are found p a r a l l e l to the s c h i s t o s i t y , at the c r e s t of f o l d s , and i n f r a c t u r e s that p a r a l l e l a x i a l plane cleavage, represent m o b i l i z a t i o n and r e c r y s t a l l i z a t i o n at a l a t e stage i n the h i s t o r y of the rock. Associated w i t h these coarser-grained aggregates are grains of s e r i c i t e , i r o n ore, c h l o r i t e , c a r -bonate; d r a v i t e and s c h o r l i t e . Abundant tourmaline i s found associated w i t h sulphides i n the ore zone, and i t i s postulate d that the tourmaline m i n e r a l s , and p o s s i b l y some of the c h l o r i t e , carbonate and i r o n o r e , have been hydro-thermally introduced i n t o the p h y l l o n i t i c rocks. S t r a i n e f f e c t s are e x h i b i t e d by the quartz and some of the other m i n e r a l s , i n d i c a t i n g that c r y s t a l l i z a t i o n took place before d i f f e r e n t i a l movement had ceased. Q u a r t z - B i o t i t e - ( C h l o r i t e ) P h y l l o n i t e The mineral assemblages i n these rocks do not permit c l a s s i f i c a t i o n of the whole group i n t o a s i n g l e subfacies of the greenschist f a c i e s . B i o t i t e predominates i n the micac-eous bands of a l l rocks i n t h i s group, but most of t h i s mater-i a l appears to have formed as a r e s u l t of hydrothermal a l t e r a t i o n . The micaceous bands appear to have o f f e r e d a more permiable channel f o r hydrothermal s o l u t i o n s than d i d the dense, f i n e - g r a i n e d , q u a r t z - r i c h bands. This i s supported by the more common occurrence of introduced and/or r e -mo b i l i z e d minerals such as epidote, s c h o r l i t e , i r o n o r e , c h l o r i t e , carbonate and coarser-grained quartz, i n , or a d j a -cent to the micaceous bands. In many b i o t i t e - r i c h rocks s e r i c i t e p e r s i s t s as t i n y l a t h s i n the dense f i n e - g r a i n e d 74 q u a r t z - r i c h bands, and i n o t h e r s , some or a l l of the s e r i c i t e appears to have formed b i o t i t e . Apparently the rocks c l o s e r to the ore zones have been subjected to s u f f i c i e n t l y h i g h temperatures during m i n e r a l i z a t i o n to a t t a i n e q u i l i b r i u m i n the b i o t i t e - e h l o r i t e subfacies of the greenschists f a c i e s , whereas rocks f u r t h e r away are g r a d a t i o n a l i n t o the muscovite-c h l o r i t e subfacies of the greenschists f a c i e s . The o r i g i n a l sediment from which those rocks were formed was probably p e l i t i c , p o s s i b l y a sandy shale. Small s c a l e ( i . e . i n the order of mm's). Compositional banding and l e n s i n g i n these rocks i s a t t r i b u t e d to metamorphic d i f f e r e n t i a t i o n during the m i l l i n g down of an assemblage that was o r i g i n a l l y of higher metamorphic grade. P l a g i o c l a s e - B i o t i t e - C h l o r i t e - ( C a l c i t e ) S c h i s t s The mineral assemblage i n these rocks does not permit c l a s s i f i c a t i o n i n a metamorphic f a c i e s . The r e l i c t p l a g i o -c l a s e i s i n d i c a t i v e of a moderate to high-grade m i n e r a l assemblage, but the extensive a l t e r a t i o n of a c t i n o l i t e to b i o t i t e i s suggestive of a much lower metamorphic rank. These s c h i s t s are assumed to have formed from medium-grained rocks that consisted l a r g e l y of p l a g i o c l a s e and a c t i n o l i t e . D i o r i t i c and a n d e s i t i c rocks that c o n s i s t c h i e f l y of these m i n e r a l s , have produced s i m i l a r p o r p h y r o c l a s t i c p l a g i o e l a s e - b i o t i t e s c h i s t s i n shear zones. A d i o r i t i c parentage f o r these rocks seems u n l i k e l y s ince the p o r p h y r o c l a s t i c s c h i s t s are found immediately on e i t h e r side of the limestone band on surface. No c r o s s -c u t t i n g r e l a t i o n s h i p s were observed, and i t i s d i f f i c u l t to see how an i n t r u s i v e could have been so n e a t l y placed along both contacts of the limestone band without d i s r u p t i n g i t on surface or at depth. The p o s s i b i l i t y of a v o l c a n i c o r i g i n f o r these s c h i s t s i s r u l e d out because none o f the known v o l c a n i c rocks contain p l a g i o c l a s e grains as l a r g e as the f e l d s p a r porphyroclasts found i n the s c h i s t s . The cl o s e a s s o c i a t i o n of these s c h i s t s w i t h sedimen-t a r y rocks seems to favour a sedimentary o r i g i n . Amphibolit of an appropriate composition are found i n the S c h i s t member to the west. These c o n s i s t almost e n t i r e l y of a c t i n o l i t e , and a p l a g i o c l a s e ( A n ^ ) that i s somewhat more c a l c i c than that found i n e i t h e r the d i o r i t i c or v o l c a n i c rocks. The existence of these coarser-grained s c h i s t s i n a zone that i s c h a r a c t e r i z e d by f i n e - g r a i n e d p h y l l o n i t i c rocks can be a t t r i b u t e d to at l e a s t one of two f a c t o r s . Shearing i n t e n s i t y may have been l e s s near the hanging w a l l of the Mine member, or most of the e f f e c t s of d i s l o c a t i o n metamorphism may have been taken up i n the quartz r i c h sediments which would be much more unstable i n a h i g h s t r e s s environment. In any event, the shearing e f f e c t s were not strong enough to i n i t i a t e the chemical breakdown of the p l a g i o c l a s e i n the p o r p h y r o c l a s t i c s c h i s t s . A c t i n o l i t e , however, has a l t e r e d r e a d i l y to b i o t i t e and c h l o r i t e . The co-existence of these two minerals may permit c l a s s i f y i n g these rocks i n the b i o t i t e - c h l o r i t e subfaeies of the greenschist f a c i e s . Amphibolite The i n c i p i e n t a l t e r a t i o n of a c t i n o l i t e to b i o t i t e and c h l o r i t e i n d i c a t e s that the mineral assemblage i s not i n e q u i l i b r i u m . However, d i s l o c a t i o n metamorphism at t h i s point must have been of a minimum i n t e n s i t y . In a l l other amphibole-rich rocks i n the area, the a c t i n o l i t e i s one of the f i r s t minerals to chemically break down i n a s t r e s s en-vironment. As the adjacent p l a g i o c l a s e - b i o t i t e - c h l o r i t e -( c a l c i t e ) s c h i s t s appear to be approaching e q u i l i b r i u m i n the b i o t i t e - c h l o r i t e subfaeies of the greenschist f a c i e s , the amphibolite i s a l s o assigned to t h i s metamorphic grade. The p l o t of the composition of t h i s rock on an appropriate ACF diagram (Turner and Verhoogen 1951» p. 466) i n d i c a t e s that the amphibolite was derived from a calcareous assemblage, p o s s i b l y a marl. A sedimentary o r i g i n i s favoured because of the close a s s o c i a t i o n of the amphibolite w i t h limestone and other metasedimentary rocks. Limestone The f i n e r - g r a i n e d and i n c l u s i o n - f r e e c a l c i t e appears to have r e c r y s t a l l i z e d during metamorphism, w i t h g r a n u l a t i o n and bending of twin lamellae t a k i n g place at a l a t e r time. The i n t e r s t i t i a l f i n e - g r a i n e d f e l d s p a r , quartz, epidote, 77 and c h l o r i t e probably represent s i l i c e o u s and a r g i l l a c e o u s i m p u r i t i e s i n the parent limestone. SCHIST MEMBER P l a g i o c l a s e - B i o t i t e - A e t i n o l i t e - E p i d o t e S c h i s t The mineral assemblage present i n these rocks does not permit ready c l a s s i f i c a t i o n i n a conventional metamorphic f a c i e s . The presence of moderately c a l c i c p l a g i o c l a s e (An^4)j epidote and amphibole i s suggestive of an assemblage of moderate metamorphic grade. Ignoring the i n c i p i e n t a l t e r -a t i o n of b i o t i t e to c h l o r i t e , a n d a c t i n o l i t e to b i o t i t e and c h l o r i t e , the rocks could be c l a s s i f i e d i n the almandine amphibolite f a c i e s ( F y f e , Turner and Verhoogen 1958, p. 230). The coexistence of medium p l a g i o c l a s e and epidote i s consid-ered to be c h a r a c t e r i s t i c of the s t a u r o l i t e - q u a r t z sub-f a c i e s of t h i s f a c i e s ; which i n t u r n i s i n d i c a t i v e of h i g h grade r e g i o n a l metamorphism. However, on the northeast corner of Mount W i l l i b e r t , these s c h i s t s are separated by approximately 300 f e e t of Mine member rocks, from massive, s l i g h t l y a l t e r e d , p o r p h y r i t i c a n desites. Neither the v o l -canics nor the p h y l l o n i t i c rocks have been involved i n high grade r e g i o n a l metamorphism. T i l l e y (1924) showed that the greenschist f a c i e s of E s k o l a embraced two d i s t i n c t f a c i e s , one c h a r a c t e r i z e d by c h l o r i t e - e p i d o t e - a l b i t e , and the other by hornblende-oligo-78 c l a s e - e p i d o t e . Turner's (1933) work i n Gtago, New Zealand, showed that s c h i s t s c o n s i s t i n g of pale h o r n b l e n d e - o l i g o c l a s e -epidote appear to be the product of progressive r e g i o n a l metamorphism of rocks which had already formed as c h l o r i t e -e p i d o t e - a l b i t e - c a l c i t e s c h i s t s at lower grades of r e g i o n a l metamorphism. Turner modified T i l l e y ' s s u b d i v i s i o n by making c a l c i t e an a d d i t i o n c o n s t i t u e n t of the lower grade assemblage, thus g i v i n g the two f a c i e s c h a r a c t e r i z e d by c h l o r i t e - e p i d o t e - a l b i t e - c a l c i t e , and horn b l e n d e - o l i g o c l a s e -epidote. A c t i n o l i t e could be present i n grades of meta-morphism that were t r a n s i t i o n a l to these two f a c i e s . The e s s e n t i a l f a c t o r s r e l a t i n g the two f a c i e s i s the i n s t a b i l i t y of c h l o r i t e i n the presence of c a l c i t e , and the n e c e s s i t y of maintaining a high enough pressure of CO2 to keep the car-bonate from breaking down. The presence of hydrous s i l i c a t e s (micas and amphiboles) i n the Metasedimentary formation, i n d i c a t e s that a high pore pressure d i d e x i s t . Turner (1935) proposed subfaeies of the tgreenschist f a c i e s based on CO2 pressure, but t h i s has since been abandoned. However, he d i d show that an assemblage equivalent to that found i n the S c h i s t member can form under pressure and temperature c o n d i t i o n s that e x i s t i n the upper part of the greenschist f a c i e s . Ignoring the a n o r t h i t e content of the p l a g i o c l a s e , the m i n e r a l assemblage of these s c h i s t s can now be c l a s s i f i e d i n the q u a r t z - a l b i t e - e p i d o t e - b i o t i t e subfaeies of the green-s c h i s t f a c i e s . (Fyfe, Turner, and Verhoogen 1958). This sub f a c i e s i s c h a r a c t e r i s t i c of low to moderate r e g i o n a l meta-morphism, and more r e a d i l y explains the close a s s o c i a t i o n of these s c h i s t s w i t h the r e l a t i v e l y unaltered p o r p h y r i t i c andesites. Near the b a t h o l i t h i c contacts .there i s an increase both i n g r a i n s i z e and metamorphic grade of the s c h i s t s . This i s c h i e f l y due to thermal metamorphism. Some of these rocks undoubtedly reach the amphibolite f a c i e s , since they grade i n t o migmatites i n some places at the contact w i t h the b a t h o l i t h . A p l o t of the composition of these s c h i s t s on the appropriate ACF diagram (Fyfe , Turner and Verhoogen 1958, p. 222) i n d i c a t e s that the rock i s a "basic assemblage". The o r i g i n a l sediment th e r e f o r e i s probably the d e r i v a t i v e of a bas i c or semibasic rock, p o s s i b l y from a t e r r a i n that consisted of the ol d e r a n d e s i t i c assemblage. The great thickness and r e l a t i v e l y uniform composition of these rocks suggest r a p i d e r o s i o n and d e p o s i t i o n and the close assoc-i a t i o n w i t h semibasic v o l c a n i c rocks i s c h a r a c t e r i s t i c of a eugeosynclinal environment. A t y p i c a l sediment of t h i s environment i s greywacke. S c h i s t s derived from greywackes i n Otago New Zealand have been described by Turner that are almost i d e n t i c a l to those of the S c h i s t member. I t i s there-f o r e concluded that the p l a g i o c l a s e - a c t i n o l i t e - e p i d o t e -b i o t i t e s c h i s t s of the S c h i s t member al s o were o r i g i n a l l y greywackes, or tuffaceous greywackes. The greater percentage of lime s i l i c a t e s i n the p l a g i o c l a s e - a c t i n o l i t e - e p i d o t e s u b d i v i s i o n of these s c h i s t s , suggests that the greywackes l o c a l l y were more calcareous. Lenses of coarser-grained quartz and epidote are commonly found i n the c r e s t s of both macrofolds and micro-f o l d s . Apparently these minerals "flowed" from areas of high s t r e s s , and r e c r y s t a l l i z e d i n the c r e s t s of f o l d s where the c o n f i n i n g pressures would be lower. Carbonate, s c h o r l i t e and i r o n ore are commonly found a s s o c i a t e d w i t h the more coarse-grained q u a r t z - r i c h aggregates. A l l of these coarse-grained minerals appear to have c r y s t a l l i z e d near the c l o s e of d i f f e r e n t i a l movement. Quartz and carbonate show only s l i g h t s t r a i n e f f e c t s . Amphibolite The mineral assemblage of these rocks permits c l a s s i f i c a t i o n i n the s t a u r o l i t e - q u a r t z subfacies of the almandine amphibolite f a c i e s (Fyfe, Turner and Verhoogen 1958). However, they are i n t i m a t e l y a s s o c i a t e d w i t h the p l a g i o c l a s e -a c t i n o l i t e - b i o t i t e - e p i d o t e s c h i s t s which have been estab-l i s h e d as being i n the q u a r t z - a l b i t e - e p i d o t e - b i o t i t e sub-f a c i e s of the greenschist f a c i e s , and therefore must have been subjected to the same pressure and temperature c o n d i t i o n s during r e g i o n a l metamorphism. The l a c k of r e l i c t igneous t e x t u r e s , the l a c k of thermal e f f e c t s on the adjacent meta-81 sedimentary r o c k s , t h e i r uniform t e x t u r e regardless of width, and the complete absence of retrograde metamorphism seems s u f f i c i e n t evidence to e l i m i n a t e the p o s s i b i l i t y of these being b a s i c s i l l s . I t i s th e r e f o r e p o s t u l a t e d that the amphibolites were o r i g i n a l l y lime r i c h sedimentary beds, p o s s i b l y interbedded limy marls. T h e i r c o a r s e r - g r a i n s i z e and anomolous composition ( i . e . an apparent higher grade metamorphic assemblage) may be the r e s u l t of the o r i g i n a l assemblage being more s e n s i t i v e to metamorphism. Quartz-Rich S c h i s t s These rocks are be l i e v e d to represent a r g i l l a c e o u s sandstones that have been r e g i o n a l l y metamorphosed to q u a r t z - r i c h s c h i s t s or impure q u a r t z i t e s . Grain s i z e i s much l a r g e r than that found i n the q u a r t z - r i c h p h y l l o n i t e s i n the Mine member. Apparently d i s l o c a t i o n metamorphism was not as intense i n rocks of the S c h i s t member. Limestone The t h i n limestone band present i n the S c h i s t member was not studied m i c r o s c o p i c a l l y . Handspecimens of t h i s rock c l o s e l y resemble the limestone u n i t of the Mine member, and i t i s assumed that the petrogeneses are s i m i l a r . INTRUSIVE ROCKS Hornblende G r a n o d i o r i t e I r r e g u l a r d i o r i t i c phases occur throughout the hornblende g r a n o d i o r i t e mass, p a r t i c u l a r l y at the western contact n o r t h of the map-area, where i t has intruded por-p h y r i t i c andesite. The more bas i c phases appear to be the r e s u l t of r e a c t i o n w i t h and/or a s s i m i l a t i o n of b a s i c v o l c a n i c and sedimentary rocks. A l l rocks i n t h i s subconcordant i n -t r u s i v e complex are w e l l f o l i a t e d . A thinner ( 1000 f e e t ) subconcordant body of f o l i a t e d d i o r i t e occurs 1/4 m i l e east of the hornblende g r a n o d i o r i t e , and t h i s d i o r i t e i s s i m i l a r i n composition and t e x t u r e to the d i o r i t i c phases found i n the hornblende g r a n o d i o r i t e i n t r u s i o n . This t h i n d i o r i t e body appears to be the northern c o n t i n u a t i o n of the d i o r i t i c zone that i s found on Granduc Mountain. Gn the n o r t h side of Granduc Mountain, the f o l i a t e d d i o r i t e has been i n v o l v e d i n the complex i s o c l i n a l f o l d i n g , and i s considered to have been intruded s y n k i n e m a t i c a l l y during r e g i o n a l metamorphism. D i o r i t e The unsheared and r e l a t i v e l y unaltered d i o r i t e on Granduc Mountain i s s i m i l a r i n composition and t e x t u r e to the d i o r i t i c phases that are associated w i t h the hornblende g r a n o d i o r i t e . A d e t a i l e d study was made on the south side of Granduc Mountain west of the mine i n the zone where a l t e r e d d i o r i t e has been transformed through greenstones and green-s c h i s t s to green p h y l l o n i t e s by d i s l o c a t i o n metamorphism. Figure 24 i l l u s t r a t e s the changes i n mineralogy w i t h i n -creased i n t e n s i t y of d i f f e r e n t i a l movement. F I G U R E 2 4 G R A P H I L L U S T R A T I N G C H A N G E S IN M I N E R A L O G Y W I T H I N T E N S I T Y O F S H E A R I N G IN D I O R I T E S I L L SHEARING- »• DIORITE GREENSTONE GREEN CORE GREENSCHIST PHYLLONITE 84 The a l t e r e d nature of the unsheared d i o r i t e core i n t h i s zone i n d i c a t e s that the i n i t i a l h i g h temperature m i n e r a l assemblage of the i n t r u s i o n has undergone r e t r o g r e s s i v e meta-morphism. O r i g i n a l ferromagnesian minerals have a l t e r e d to a c t i n o l i t e , and the p l a g i o c l a s e to epidote and s e r i c i t e . The a l t e r e d d i o r i t e grades i n t o a greenstone-greenschist zone w i t h only s l i g h t changes i n mineralogy. However, the rocks i n t h i s zone are markedly p o r p h y r o c l a s t i c . With a f u r t h e r increase i n the i n t e n s i t y of shearing, the green-stones and greenschists are t r a n s i t i o n a l i n t o a zone of green p h y l l o n i t e s . This transformation i s c h a r a c t e r i z e d by the chemical breakdown of the lime s i l i c a t e minerals ( a c t i n o l i t e and epidote) to produce c a l c i t e and c h l o r i t e . The por-p h y r o c l a s t i c p l a g i o c l a s e has only undergone f u r t h e r mechan-i c a l breakdown i n the t r a n s i t i o n from the greenstone-green-s c h i s t rocks to green p h y l l o n i t e . Excluding the r e l i c t p l a g i o c l a s e , the m i n e r a l assemblage can be c l a s s i f i e d i n the m u s c o v i t e - c h l o r i t e subfaeies of the greenschist f a c i e s (Turner and Verhoogen, 195*1) j which i s c h a r a c t e r i s t i c of the lowest grade of r e g i o n a l metamorphism. The t r a n s i t i o n of a l t e r e d d i o r i t e to green phy-l l o n i t e i s c l e a r l y due to r e t r o g r e s s i v e metamorphism. Conclusions Both the s t r a t i f i e d rocks and the e a r l i e r i n t r u s i v e rocks have been involved i n r e g i o n a l metamorphism, and a l l appear to have tended towards e q u i l i b r i u m i n the higher grades of the greenschist f a c i e s . The greywackes and marls have been p r o g r e s s i v e l y metamorphosed to form s c h i s t s that can be c l a s s i f i e d i n the q u a r t z - a l b i t e - e p i d o t e b i o t i t e subfacies of the greenschist f a c i e s . Almost i d e n t i c a l m i n e r a l assemblages are found i n the a l t e r e d d i o r i t e and meta v o l c a n i c s , and i t i s concluded that these i n i t i a l h igh temperature assemblages have undergone r e t r o g r e s s i v e meta-morphism to a t t a i n or approach e q u i l i b r i u m i n the same meta-morphic f a c i e s . With subsequent d i s l o c a t i o n metamorphism, the q u a r t z - r i c h sediments and some of the igneous rocks have undergone r e t r o g r e s s i v e metamorphism, and have a t t a i n e d equi-l i b r i u m i n lower grade s u b d i v i s i o n s of the greenschist f a c i e s CORRELATION OF THE GRANDUC ROCKS Metasedimentary and Metavolcanic Rocks Due to the l a c k of f o s s i l s , and the complex s t r u c t u r e i n the area, the metasedimentary and v o l c a n i c rocks i n the Granduc Area can not be r e a d i l y c o r r e l a t e d w i t h e s t a b l i s h e d formations to the n o r t h or south. A t e n t a t i v e c o r r e l a t i o n w i l l be attempted on the ba s i s of l i t h o l o g i e s i m i l a r i t y . The presence of a t h i c k s e r i e s of greywackes and the abundance of semibasic v o l c a n i c s i n the area, i s suggestive of a euogeosynclinal environment. Such c o n d i t i o n s e x i s t e d i n both Upper P a l e o z o i c and Mesozoic times. These periods of sedimentation were separated by the Ca s s i a r Orogeny which terminated P a l e o z o i c d e p o s i t i o n . Kerr (1948), has mapped Permian and pre-Permian rocks i n the S t i k i n e R i v e r Area, 25 miles northwest of the Granduc Area. He di v i d e d thepxe-Permian rocks i n t o two p a r t s , a lower part which c o n s i s t e d c h i e f l y of f i n e - g r a i n e d quartz-r i c h c l a s t i c rocks, and an upper part which was made up e s s e n t i a l l y of impure limestone. V o l c a n i c rocks are of minor occurrence, and are reported only i n the lower part of the pre-Permian group. Thick limestone beds are reported n o r t h of the Granduc Area, but t h e i r r e l a t i o n s h i p to the Granduc rocks i s not known. T r i a s s i c rocks i n the S t i k i n e Area, c o n s i s t c h i e f l y of b a s a l andesites, o v e r l a i n by a t h i c k sequence of grey-wackes. Some of the basa l v o l c a n i c s are p i l l o w e d , and f r a g -mental and p o r p h y r i t i c types are a l s o reported. The v o l -canic rocks are o v e r l a i n by greywackes and tuffaceous grey-wackes, which Kerr b e l i e v e s have been derived l a r g e l y from the underlying v o l c a n i c rocks. Bands of black and dark grey a r g i l l i t e , some of them l i m y , and beds of brown sandstone are reported to be widely d i s t r i b u t e d throughout the greywacke 87 sequence. Limestone i s present i n many p l a c e s , u s u a l l y i n l o c a l l e n s e s , but i n a few instances i n f a i r l y continuous beds up to 100 feet t h i c k . F o s s i l evidence i n d i c a t e s that these sediments are Upper T r i a s s i c i n age. The J u r a s s i c rocks described by Kerr.- c o n s i s t l a r g e l y of interbedded shales and conglomerates, w i t h some t u f f s , greywackes and a r g i l l i t e s i n the upper part of the s e r i e s . L o c a l l y t h i n andesite and da e i t e flows are reported. J u r -assic-Cretaceous rocks c o n s i s t of a ba s a l andesite that i s o v e r l a i n by a sequence of t h i c k , massive, a n d e s i t i e flows a l t e r n a t i n g w i t h sediments. These sediments i n c l u d e banded jasper and c h e r t , s h a l e s , greywackes and a r g i l l i t e s . Upper Cretaceous and younger sediments appear to have been de-pos i t e d i n an i n c r e a s i n g l y c o n t i n e n t a l environment. F i n e r -grained sandstones, arkoses, and shales interbanded w i t h conglomerates predominate. Admitting the p o s s i b i l i t y of l o c a l v a r i a t i o n s i n the d e p o s i t i o n a l environment i n a euogeosyncline, i t i s thought reasonable to assume that the general g e o l o g i c a l c o n d i t i o n s e x i s t i n g i n the S t i k i n e Area, some 25 miles to the n o r t h , would c l o s e l y approximate those i n the Granduc Area at the time of d e p o s i t i o n . On studying the S t i k i n e l i t h o l & g y , Kerr's b a s a l T r i a s s i c andesite and Upper T r i a s s i c sediments seems to c l o s e l y match the l i t h o l o g y found i n the Granduc Area. The por-88 p h y r i t i c andesites are s i m i l a r , and the t h i c k greywacke se-quence w i t h t h i n l y interbedded limey a r g i l l i t e s would r e a d i l y c o r r e l a t e w i t h the Metasedimentary S e r i e s . Further Kerr's Upper T r i a s s i c rocks i n c l u d e r e l a t i v e l y t h i n limestone beds and "brown sandstones", which could be equivalent to Mine S e r i e s rocks. Hanson (1935) mapped the P o r t l a n d Canal Area j u s t to the southwest of the Granduc Area. A l l of h i s sedimentary and v o l c a n i c rocks (and t h e i r metamorphic e q u i v a l e n t s ) , w i t h the exception of very minor amounts of T e r t i a r y v o l c a n i c s , have been assigned to the Hazelton group. This group includes rocks that are b e l i e v e d to range from T r i a s s i c to Lower Cretaceous i n age. Sedimentary and v o l c a n i c rocks s i m i l a r to those found i n the Granduc Area, are found i n the Hazelton group. Sediments that Hanson b e l i e v e s to be of t h i s Group, outcrop on Mount White-Fraser, 6 miles due east of Granduc Mountain. Bacon ( 1 9 5 5 ) mapped the Granduc Area, and assigned the metasedimentary and metavolcanic rocks to the Hazelton group. In southeastern A l a s k a , Buddington ( 1 9 2 8 ) mapped a se r i e s of sedimentary and v o l c a n i c rocks of Upper T r i a s s i c to Lower J u r a s s i c age, that seem c o r r e l a t i v e w i t h the Hazelton group. The composite evidence suggests that the Granduc metasedimentary and metavolcanic rocks are of Lower Mesozoic 8 9 age, possibly Triassic or Lower Jurassic. Age, and the lithology of these rocks indicates that they are best corre-lated with the Hazelton group. Additional detailed regional work may prove corre-lation of some of Kerr's Mesozoic groups with Leech's (1901) Hazelton group. Intrusive Rocks The foliated dioritic intrusions were intruded into the rocks of the Hazelton group before or during regional metamorphism, and were involved in complex isoclinal folding with the stratified rocks. The well-developed foliation in the diorite favours synkinematic intrusion. Although the relationship of the subconcordant gneissic hornblende grano-diorite with other intrusive rocks in the area is not known, i t is considered to be closely related in time to the i n -trusion of the diorite. Kerr (194-8 p. 32) sites an example of hornblende granodiorite boulders in Jurassic conglomerates in the Stikine area. Buddington (1928 p. 2 1 9 , 239) describes hornblende andesine granodiorite intrusions of possible Jurassic age south of the mine, near Hyder Alaska. Both writers consider that the more basic phases of the Coast Range granitic complex are older than the more acid types. Granodiorite of the main Coast Range batholith cuts the well-developed, northerly trending structures in the Hazelton group rocks. Granodiorite, quartz-j' diorite and 90 a p l i t e s i l l s and dikes i n the area are be l i e v e d to be closely-r e l a t e d to the i n t r u s i o n of the major g r a n i t i c complex. Quartz d i o r i t e dikes cut across the sheared d i o r i t e zone on the south side of Granduc Mountain. The major part of the Coast Range b a t h o l i t h i n t h i s area appears to be l a t e r than both r e g i o n a l metamorphism, and the i n t r u s i o n of the d i o r i t e , and i s presumed to be Lower Cretaceous or l a t e r i n age. CHAPTER V - ECONOMIC GEOLOGY DESCRIPTION OF THE ORE BODIES The ore occurs c h i e f l y i n b i o t i t e - r i c h p h y l l o n i t i c and s c h i s t o s e rocks i n the Mine member. M i n e r a l i z e d zones are tabular and e s s e n t i a l l y conformable w i t h the metasediments on the south s i d e of Granduc Mountain. Two ore zones have been recognized, the A (west) and B ( e a s t ) , which range i n width from 25 to 50 f e e t , and 50 to 150 feet r e s p e c t i v e l y . At the 3250 p o r t a l , the two zones are approximately 400 f e e t a p a r t , but they appear to merge 1700 f e e t to the n o r t h . The ore bodies p e r s i s t at l e a s t 1500 f e e t below the 3250 l e v e l (B.C.Minister of Mines Rept. 1955, p. 16), and there appears to be a convergence of the two zones w i t h depth. 25,600,000 tons of ore averaging 1.62$ copper are reported to have been proved by diamond d r i l l i n g (Bacon 1955). MINERALOGY M i n e r a l i z a t i o n c o n s i s t s e s s e n t i a l l y of p y r r h o t i t e , c h a l c o p y r i t e , p y r i t e and s p h a l e r i t e . A narrow band of magnetite i s l o c a l l y present i n the f o o t w a l l of the 2B surface showing. Coarse-grained introduced quartz i s present i n lenses and blebs that commonly p a r a l l e l the f o l i a t i o n and produce a "knotted" t e x t u r e i n the host rock. This l a t e r quartz i s also found i n f r a c t u r e s and a x i a l plane cleavages that cut the f o l i a t i o n . 92 Sulphides occur as disseminated g r a i n s , s t r i n g e r s , and massive bands or blebs that are commonly conformable w i t h the f o l i a t i o n i n the host rock. Concentrations are a l s o found adjacent to lenses of introduced quartz i n f r a c t -ures i n the quartz, and i n or near micaceous r i c h bands i n the country rock. In hand specimen, the h e a v i l y m i n e r a l i z e d samples appear to c o n s i s t of f i n e - g r a i n e d b i o t i t e - r i c h host rock, that i s impregnated w i t h concentrations of sulphides and introduced quartz. However, on c u t t i n g these specimens f o r p o l i s h i n g , i t became apparent that some of these rocks are b r e c c i a t e d , w i t h sulphides and introduced quartz f i l l i n g the i n t e r s t i c e s and r e p l a c i n g fragments of the host rock, (Figure 25"). Unbrecciated ore c o n s i s t s e s s e n t i a l l y of massive and disseminated replacements of sulphides and coarser-grained quartz along planes that g e n e r a l l y p a r a l l e l the f o l i a t i o n i n b i o t i t e - r i c h p h y l l o n i t e s (Figure 26). The con-tent of both sulphides and introduced quartz drops o f f r a p i d l y away from the b r e c c i a t e d high-grade zones. L o c a l concentrations are present near blebs of introduced quartz and i n f r a c t u r e s i n both p h y l l o n i t i c and s c h i s t o s e rocks. The ore specimens studied m i c r o s c o p i c a l l y were obtained from the underground workings, as the surface out-croppings were g e n e r a l l y too h i g h l y f r a c t u r e d and o x i d i z e d |t 93 Figure 25 B r e c c i a t e d ore. Fragments of q u a r t z - b i o t i t e p h y l l o n -i t e (B.P.) and amphibolite (A) are conspicuous on the p o l i s h e d surface. Note i n t e r s t i c e s f i l l e d w i t h s u l -phides and blebs of introduced quartz (Q) and carbonate (C). Specimen i s approximately 4 inches across. Figure 26 Replacement ore. Sulphides and introduced quartz (Q) r e p l a c i n g q u a r t z - b i o t i t e p h y l l o n i t e along favourable l i t h o l o g i c zones. Specimen i s approx-imately 3 inches across. Figure 27 Photomicrograph showing mutual boundary-r e l a t i o n s of p y r r h o t i t e (P) and chalco-p y r i t e (C). (X20). Figure 28 Photomicrograph showing quartz (Q) rimmed by p y r r -h o t i t e (P) which i s i n t u r n rimmed by an i n t e r -growth of c h a l c o p y r i t e (C) and s p h a l e r i t e (S) ( X 9 0 ) . f o r p o l i s h e d s e c t i o n p r e p a r a t i o n . Limonite, a z u r i t e , malachite, c h r y s o c o l l a and broehantite were i d e n t i f i e d i n the o x i d a t i o n products on surface. In the p o l i s h e d sections s t u d i e d , the mineral assemblage c o n s i s t e d e s s e n t i a l l y of p y r r h o t i t e , c h a l c o p y r i t e and s p h a l e r i t e , w i t h minor amounts of p y r i t e and galena. T e n t a t i v e l y i d e n t i f i e d were a few t i n y grains of t e t r a h e d r i t e and l o e l l i n g i t e . P y r i t e , t e t r a h e d r i t e and l o e l l i n g i t e occur i n an-h e d r a l to subhedral grains that average l e s s than 10 microns i n diameter. These minerals are included i n the coarser-grained quartz and i n aggregates of c h a l c o p y r i t e and p y r r -h o t i t e . The strong subhedral h a b i t of some g r a i n s , suggests that these minerals c r y s t a l l i z e d before or during the c r y s t a l l i z a t i o n of the quartz, and before any of the other su l p h i d e s . These minerals were found i n i s o l a t e d g r a i n s , and t h e i r r e l a t i v e paragenetic sequence could not be de-termined. P y r r h o t i t e , c h a l c o p y r i t e and s p h a l e r i t e occur as f i n e disseminations i n the coarser-grained quartz, but more commonly as replacements along f r a c t u r e s and g r a i n boundaries i n the quartz aggregates. For the most p a r t , these minerals appear to be l a t e r than the quartz. P y r r h o t i t e occurs i n l a r g e i r r e g u l a r aggregates g e n e r a l l y c l o s e l y associated w i t h c h a l c o p y r i t e and s p h a l e r i t e In many instances these minerals show mutural boundary r e -l a t i o n s and i n t e r p e n e t r a t i o n s that are suggestive of 96 simultaneous c r y s t a l l i z a t i o n (Figure 2 7 ) . However, i n some high grade specimens p y r r h o t i t e i s d e f i n i t e l y e a r l i e r than c h a l c o p y r i t e and s p h a l e r i t e . In these, p y r r h o t i t e i s seen rimming introduced quartz and i n t u r n i s rimmed and l o c a l l y m a r g i n a l l y replaced by a mutual intergrowth of c h a l c o p y r i t e and s p h a l e r i t e (Figure 2 8 ) . I t would appear that p y r r h o t i t e began to c r y s t a l l i z e before c h a l c o p y r i t e and s p h a l e r i t e , but that its p e r i o d of d e p o s i t i o n was prolonged so that some c r y s t a l l i z e d s i m u l t a n -eously w i t h c h a l c o p y r i t e and s p h a l e r i t e . C h a l c o p y r i t e occurs i n i r r e g u l a r aggregates of v a r y i n g s i z e c l o s e l y associated w i t h smaller grains of s p h a l e r i t e . These minerals show mutual boundary r e l a t i o n s and i n t e r p e n e t r a t i o n s that i n d i c a t e simultaneous d e p o s i t i o n . Tiny blebs of c h a l c o p y r i t e are commonly found i n s p h a l e r i t e and i n a high grade, b r e c c i a t e d specimen, these are o r i e n t e d producing an e x s o l u t i o n t e x t u r e (Figure 2 9 ) . Small anhedral grains of s p h a l e r i t e are found i r r e g u l a r l y included i n chalco-p y r i t e . Galena occurs i n anhedral grains up to 36 microns i n diameter. I t i s found as a replacement along the margins of s p h a l e r i t e and c h a l c o p y r i t e , and at contacts of these s u l -phides (Figure 3 0 ) . Smaller grains of galena are a l s o found included i n the other sulphides. C o v e l l i t e i s present i n f r a c t u r e s and along g r a i n boundaries i n t e t r a h e d r i t e , apparently an a l t e r a t i o n product. 9 6 a Figure 29 Photomicrograph showing e x s o l u t i o n of c h a l c o p y r i t e (C) i n s p h a l e r i t e (S) (X90). Figure 30 Photomicrograph of galena (G) m a r g i n a l l y r e -p l a c i n g c h a l c o p y r i t e (C) along a c h a l c o p y r i t e -quartz (Q) contact (X90). The paragenetic sequence i s i l l u s t r a t e d i n Figure 31. P y r i t e , l o e l l i n g i t e , t e t r a h e d r i t e appear to have been the f i r s t minerals to c r y s t a l l i z e . P y r r h o t i t e next began to c r y s t a l l i z e , followed by simultaneous c r y s t a l l i z a t i o n of p y r r h o t i t e , c h a l c o p y r i t e and s p h a l e r i t e . Galena appears to have been the l a s t primary sulphide to c r y s t a l l i z e . The evidence of e a r l y c r y s t a l l i z a t i o n of p y r r h o t i t e ( i . e . before the simultaneous c r y s t a l l i z a t i o n of p y r r h o t i t e , c h a l c o p y r i t e and s p h a l e r i t e ) and the e x s o l u t i o n of chalco-p y r i t e i n s p h a l e r i t e i s found only i n the high grade brecc-i a t e d specimens. This suggests a higher temperature of the m i n e r a l i z i n g s o l u t i o n s i n the b r e c c i a t e d zone. The brecc-i a t e d zone i s considered to be a main conduit f o r the m i n e r a l i z i n g s o l u t i o n s , and lowering of the temperature of these s o l u t i o n s away from the b r e c c i a t e d zone i s compatible w i t h a hydrothermal o r i g i n . HYDROTHERMAL ALTERATION B i o t i t e - r i c h s c h i s t o s e and p h y l l o n i t i c rocks predomin-ate i n the ore zones. Much of the b i o t i t e appears to have formed as a r e s u l t of hydrothermal a l t e r a t i o n . Quartz-s e r i c i t e p h y l l o n i t e s grade t r a n s i t i o n a l l y i n t o q u a r t z - b i o t i t e p h y l l o n i t e s as the ore zones are approached. B i o t i t e f i r s t appears i n the micaceous r i c h bands, where i t i s commonly asso c i a t e d w i t h tourmaline and other hydrothermally introduced m i n e r a l s . S e r i c i t e p e r s i s t s i n the dense, f i n e - g r a i n e d FIGURE 31 VANDERVEEN DIAGRAM SHOWING THE PARAGENESIS OF MINERALIZATION q u a r t z - r i c h bands of these rocks w e l l i n t o the ore zone. The i n t r o d u c t i o n of s i l i c a and s c h o r l i t e , epidote, carbonate and c h l o r i t e appear to have been c l o s e l y assoc-i a t e d w i t h m i n e r a l i z a t i o n . Blebs and lenses of coarser-grained quartz f l o o d and replace the host rock producing a "knotted" t e x t u r e i n the ore zones. S i l i f i c a t i o n of rocks immediately removed from the ore zones i s s l i g h t . Tourmaline (commonly s c h o r l i t e ) , carbonate, epidote and c h l o r i t e are a s s o c i a t e d w i t h the sulphides i n the ore zone (Figure 3 2 ) . These minerals are present a l s o i n smaller amounts as s o c i a t e d w i t h f i n e l y disseminated sulphide and more coarse-grained quartz i n the adjacent p h y l l o n i t i c and s c h i s t o s e rocks where they f i l l f r a c t u r e s , cut the f o l i a t i o n , and occur i n discontinuous lenses p a r a l l e l to the f o l i a t i o n . Commonly, these introduced minerals are found i n or c l o s e t o , micaceous-rich bands i n the p h y l l o n i t i c rocks. P o s s i b l y the micaceous bands were more permeable than the dense, f i n e - g r a i n e d g r a n o b l a s t i c quartz r i c h bands, and afforded channels f o r the ore bearing s o l u t i o n s . Further study may show that s i l i c i f i c a t i o n and the zone of b i o t i t e a l t e r a t i o n near the ore zones may be used as a guide i n the search f o r ore. However, the intense s i l i -c i f i c a t i o n seems to be too l o c a l i z e d , and the a v a i l a b l e evidence shows that b i o t i t e p h y l l o n i t e s and s c h i s t s that Figure 32 Photomicrograph of replacement ore. Note opaques r e p l a c i n g the q u a r t z - b i o t i t e p h y l l o n i t e . Tourmaline (T) i s associated w i t h the sulphides (X42). 99 are not r e l a t e d to m i n e r a l i z a t i o n are common throughout the area. ORE CONTROLS AND GENESIS OF THE DEPOSIT I t i s concluded that the pre-dike zone of brecc-i a t i o n served as the main conduit f o r m i n e r a l i z i n g s o l u t i o n s , and t h e r e f o r e , the major ore c o n t r o l i s of a s t r u c t u r a l nature. Replacement of the host rock away from the brecc-i a t e d zones appears to have been c o n t r o l l e d by favourable l i t h o l o g i c and minor s t r u c t u r a l f e a t u r e s . Micaceous bands i n the p h y l l o n i t i c rocks seem to have been more favourable f o r the tra n s m i s s i o n of sulphide bearing s o l u t i o n s than the dense, f i n e - g r a i n e d q u a r t z - r i c h bands. Higher concentrations of sulphides are commonly found i n the c r e s t s of drag f o l d s , i n f r a c t u r e s , and i n a x i a l plane cleavage. Further work w i l l be required to a s c e r t a i n the form and the extent of the b r e c c i a t e d zone. The b r e c c i a can be dated between syn-or p o s t - r e g i o n a l metamorphism and pre-quartz d i o r i t e d i k e . I f the b r e c c i a t e d zone formed during r e g i o n a l metamorphism, i t may have been involved i n the i s o -c l i n a l f o l d i n g . F o l d i n g could e x p l a i n the convergence of two ore zones at depth and to the north. However, i f the b r e c c i a formed a f t e r r e g i o n a l metamorphism, a branching b r e c c i a t e d zone would be required to e x p l a i n the convergence of the ore zones. 100 The concentration of sulphides and of s l i g h t l y -f r a c t u r e d and s t r a i n e d grains of hydrothermally introduced s i l i c a t e s and carbonates i n the c r e s t s of drag f o l d s and i n f r a c t u r e s that p a r a l l e l a x i a l plane cleavage suggest that hydrothermal a c t i v i t y took place at a l a t e stage i n the defof.mational h i s t o r y (Figure 3 3 , 3 4 ) . The e a r l y synkinematic i n t r u s i o n s are ther e f o r e e l i m i n a t e d as a p o s s i b l e source of hydrothermal s o l u t i o n s . The a l t e r n a t i v e source i s emanations r e l a t e d to the i n t r u s i o n of the g r a n o d i o r i t i c b a t h o l i t h . The ore-bearing emanations from the b a t h o l i t h may have been channelled i n t o the Granduc s t r u c t u r e along the south plung-ing drag f o l d s on the south side of Granduc Mountain. I f the crumpling of the o l d "b" a x i s of the i s o c l i n a l f o l d s occurred during i n t r u s i o n , but before m i n e r a l i z a t i o n , the f l a t t e n i n g and r e v e r s a l of plunge of many of the drag f o l d s to the n o r t h would not be a favourable s t r u c t u r a l f e a t u r e . The success of f u t u r e development w i l l depend on the p e r s i s t e n c e of the br e c c i a t e d zone to the n o r t h , and the existence of appropriate temperature and pressure c o n d i t i o n s to the south and at depth. Mineralographic studies i n d i c a t e that the mineral assemblage formed under moderate temperature co n d i t i o n s and i t i s conceivable that as the b a t h o l i t h i c contact i s approached, temperature c o n d i t i o n s may not have been favourable f o r m i n e r a l i z a t i o n . * • The dating of m i n e r a l i z a t i o n w i t h respect to the i n t r u s i o n of the quartz d i o r i t e dikes cannot be made w i t h Figure 33 Photomicrograph showing aggregates of more coarse-grained quartz and opaques c u t t i n g f o l i a t i o n i n a quartz b i o t i t e p h y l l o n i t e (X16). Figure 34 Photomicrograph showing the replacement of a q u a r t z - b i o t i t e p h y l l o n i t e by sulphides (X42). the a v a i l a b l e evidence. Although these dikes do cut the ore, i t i s p o s s i b l e that m i n e r a l i z a t i o n occurred i n post-dike times, and that the dense dike rock was not s u s c e p t i b l e to replacement. However, the b r e c c i a t e d zone which served as a conduit f o r the m i n e r a l i z i n g s o l u t i o n s was formed before the dikes were int r u d e d . The r e l a t i v e ages of the dikes and the second p e r i o d of f o l d i n g i s of economic s i g n i f i c a n c e . Some of the quartz d i o r i t e s i l l s appear to be folded w i t h the metasedimentary assemblage, but i t i s p o s s i b l e that curved tension f r a c t u r e s opened a f t e r the f o l d i n g had taken p l a c e . I f the second p e r i o d of f o l d i n g occurred a f t e r the i n t r u s i o n of the dikes and s i l l s , then the m i n e r a l i z e d shear zone would be expected to swing to the northwest. A s i m i l a r f l e x u r e of the m i n e r a l -i z e d zone would r e s u l t i f the second pe r i o d of f o l d i n g took place a f t e r p h y l l o n i t i z a t i o n and b r e c c i a t i o n , but before i n t r u s i o n of the quartz d i o r i t e s i l l s and d i k e s . However, i f the f o l d i n g took place during p h y l l o n i t i z a t i o n but before b r e c c i a t i o n , the b r e c c i a t e d zone would not be bent, and the ore bodies should continue t h e i r n o r t h e r l y trend. In the former cases, the l a t e post-dike f a u l t i n g would o f f s e t the ore bodies w i t h the west side moving to the north. CLASSIFICATION OF THE ORE DEPOSIT v The Granduc ore bodies are thought to have formed 103 during a s i n g l e generation of m i n e r a l i z a t i o n . Estimates of pressure and temperature c o n d i t i o n s that e x i s t e d during d e p o s i t i o n of the ore minerals must be obtained from s t r u c t -u r a l and m i n e r a l o g i c a l features of the ore body. The close a s s o c i a t i o n i n both time and space of m i n e r a l i z a t i o n and the b a t h o l i t h i c rocks suggests a hydrothermal o r i g i n . The m i n e r a l assemblage found i n the b r e c c i a t e d zones i s i n d i c a t i v e of an intermediate temperature of formation (Edwards 1954). E x s o l u t i o n of c h a l c o p y r i t e i n d i c a t e s that the m i n e r a l i z i n g s o l u t i o n s had a minimum temperature of 350°C. A more absolute g e o l o g i c a l thermometer t h a t might be a p p l i e d to the Granduc ore i s the i r o n content of s p h a l e r i t e that has formed i n e q u i l i b r i u m w i t h p y r r h o t i t e (Campbell, 1959). R e l a t i v e l y h i g h pressures appear to have e x i s t e d during the formation of the ore d e p o s i t s . The presence of hydrous s i l i c a t e s and the co-existence of carbonate and quartz i s i n d i c a t i v e of moderately h i g h pressures. Consider-ing the postulated Eocene peneplanation and subsequent up-l i f t , i t i s suggested that the present ore bodies were buried to a depth of at l e a s t 4000 feet during m i n e r a l i z a t i o n . How-ever, the existence of the b r e c c i a and the hydrothermal e f f e c t s of only moderate i n t e n s i t y do not imply a p a r t i c u l a r l y deep-seated environment. The deposit i s c l a s s i f i e d as a Meso-d e r m a l Replacement. BIBLIOGRAPHY 104 Bacon, W.R., (1955): P r e l i m i n a r y Map of the Granduc A r e a , B . C . Department of M i n e s . Bateman, A . M . (1955): Economic M i n e r a l D e p o s i t s . B r o c k , R . W . , and S c h o f i e l d , S . J . , (1926) : G e o l o g i c a l H i s t o r y and M e t a l l o g e n i c Epochs i n the Western C o r d i l l e r a o f Canada. P r o c . T h i r d P a n - P a c i f i c Sc ience Congress . B u d d i n g t o n , A . F . (1927): Coast Range I n t r u s i v e s of S o u t h -east A l a s k a , J o u r n a l o f Geology, V o l . 35, p p . 224-246. B u d d i n g t o n , A . F . and C h a p i n , T . , (1928): Geology and M i n e r a l Depos i t s of Southeast A l a s k a , U . S . G . S . B u l l . 800. B u d d i n g t o n , A . F . (1929): Geology o f Hyder and V i c i n i t y , U . S . G . S . B u l l . 807. B u e r g e r , N.W. (1934): The Unmixing of C h a l c o p y r i t e from S p h a l e r i t e , Am. M i n e r a l o g i s t , V o l . 19, p p . 525-530. C a m p b e l l , F . A . (1959): The Geology o f the T o r b r i t S i l v e r M i n e , Economic Geology, V o l . 54, No. 8 , pp . 1461-1495. Edwards, A . B . (1954): Textures o f the Ore M i n e r a l s . Hanson, G. (1929): Bear R i v e r and Stewart Map A r e a s , C a s s i a r D i s t r i c t , B . C . G . S . C . Mem. 159. (1935): P o r t l a n d Canal A r e a , B . C . G.S.C.Mem. 175. H s u , J . K . (1955): G r a n u l i t e s and M y l o n i t e s of the Region about Cucamonga and San Antonio Canyons, San G a b r i e l Mounta ins , C a l i f . K e r r , F . A . (1948): Lower S t i k i n e and Western I skut R i v e r A r e a s , B . C . G.S.C.Mem. 246. (1948): Taku R i v e r Map A r e a , B . C . G . S . C . Mem. 248. (1928): E a s t e r n Contact Zone o f the Coast Range B a t h o l i t h o f the S t i k i n e R i v e r , B u l l . C . I . M . M . J a n . 1928. Knopf , E . B . (1931): R e t r o g r e s s i v e Metamorphism and P h y l l o n -i t i z a t i o n , Am. J o u r . S c i . V o l . 21-22, 5 th s e r i e s , p p . 1-26. 105 Krunibein, W.C. and S l o s s , L.L. (1953): S t r a t i g r a p h y and Sedimentation. K u l l e r u d , G. (1953): The FeS-ZnS System, a G e o l o g i c a l Thermometer Norsk. Geol. T i d s . V .32, pp. 61-74. Mead, W.J. (1925): The Geologic Role of D i l a t a n c y . Jour, of Geology, V o l . 33, pp. 685-698., M c C a l l i e n , W.J. (1934): Metamorphic D i f f u s i o n . B u l l . Com. Geol. F i n . No. 104, pp. 11-27. McConnell, R.G. (1913): P o r t i o n s of the P o r t l a n d Canal and Skeena Mining D i v i s i o n s , Skeena D i s t r i c t , B.C. G.S.C. Mem. 32. MacKenzie J.D. (1916): Geology of Graham I s l a n d , B.C., G.S.C. Memoir 88. McKinstry, H.E. (1959): M i n e r a l Assemblage i n Sulphide Ores i n the System Cu-Fe-0-S. Econ. Geology, V o l . 54, No. 6. Remberg, H. (1952): The O r i g i n of Metamorphic and Meta-somatic Rocks. Short, M.N. (1940): Microscopic Determination of Ore Mi n e r a l s . U.S.G.S. B u l l . 914. T i l l e y , C.E. (1924): Facies C l a s s i f i c a t i o n of Metamorphic Rocks, Geol. Mag. V o l . 61, 1924, pp. 167-171. Turner, F.J. (1940): S t r u c t u r a l P e t r o l o g y of the S c h i s t s of Eastern Otago, New Zealand, Am. Journal of Science, V o l . 238. Turner, F.J. (1938): P r o g r e s s i v e Regional Metamorphism i n Southern New Zealand, Geol. Mag. V o l . 75, No. 886, pp. 160-174. Turner, F.J. (1933): The Genesis of O l i g o c l a s e i n C e r t a i n S c h i s t s . Geol. Mag. Vol..7 0 , pp. 529-541. Turner, F.J. F y f e , W.S., Verhoogen, J . , (1958): Metamorphic Reaction and Metamorphic F a c i e s , G.S.A. Mem. 73. 106 Turner, F.J. and Verhoogen, J . , (1951): Igneous and Meta-morphic P e t r o l o g y . White, W.H. (1959): C o r d i l l e r a n Tectonics i n B r i t i s h Columbia, B u l l . A.A.P.G. V o l . 43, No. 1, pp. 60-100. Wright, F.E. (1905): Unuk River Mining Region, G.S.C. Sum. Report, 1905. Wright, F.E. and Wright, C.W. (1908): The Ketchikan and Wrangell Mining D i s t r i c t s , A l a s k a , U.S.G.S. B u l l . 347. S.C. Report of M i n i s t e r of Mines, 1931, 1935, 1953, 1954. Ore Deposits o f the Western S t a t e s , Lindgren Volume 1933. 

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