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Mineralization of the driftwood property, McConnell creek district, British Columbia Panteleyev, Andrejs 1969

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MINERALIZATION1 OF THE DRIFTWOOD PROPERTY, McCONNELL CREEK DISTRICT, BRITISH COLUMBIA by ANDREJS PANTELEYEV B S c , University of B r i t i s h Columbia, 196k-A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Geology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1 9 6 9 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 t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 a n d S t u d y . I f u r t h e r a g r e e 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 c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e Head o f my D e p a r t m e n t o r b y h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f 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 n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a D a t e tijsuJ- Jtf flfa i i A n o r t h w e s t e r l y view of the r i d g e on which the Driftwood Property i s l o c a t e d . The gossanous outcrops i n the foreground are i n t r u s i v e rooks of a Kastberg Porphyry and s t r a t a of the T a k l a - H a z e l t o n Group. i i i ABSTRACT The Driftwood Property i s l o c a t e d i n the southwest corner of the McConnell Creek map-area, about 87 miles n o r t h of Smithers, B. C. The p r o p e r t y l i e s i n a n o r t h w e s t e r l y t r e n d i n g b e l t of v o l c a n i c - s e d i m e n t a r y rocks that were mapped as T a k l a Group - Upper D i v i s i o n (Lord, 1 9 ^ 8 ) . The rocks are more c o r r e c t l y c o r r e l a t e d w i t h the Hazelton Group. They are bounded on the west and east by younger sedimentary forma-t i o n s . To the west i s the Bowser Group and to the e a s t , the Sustut Group. A Kastberg porphyry of T e r t i a r y age has i n t r u d e d the T a k l a Group r o c k s . I n t r u s i o n was i n t o the e p i z o n a l e n v i r o n -ment and produced an i r r e g u l a r d y k e - l i k e body having a r o o f zone w i t h anastamosing dykes and s m a l l r o o f pendants. The composition of the s t o c k v a r i e s from g r a n o d i o r i t e to quartz monzonite and a l a s k i t e . D i f f e r e n c e s i n the s t o c k are ob-served i n t e x t u r a l , m i n e r a l o g i c a l , and chemical v a r i a t i o n s . Automorphism of the s t o c k has r e s u l t e d i n p r o p y l i t i c a l t e r a t i o n and c o n t a c t metamorphism has r e s u l t e d i n an e n v e l -oping zone of h o r n f e l s . Temperatures at the i n t r u s i v e con-t a c t as d e r i v e d from heat flow c a l c u l a t i o n s were probably a maximum of about ^ 9 5 to 550°C and v a r i e d w i t h r e s p e c t to the type of rocks intruded.. A b i o t i t e h o r n f e l s of the a l b i t e -e p i d ote h o r n f e l s f a c i e s has formed an aureole over 1 0 0 f e e t wide. A h o r n f e l s of the hornblende h o r n f e l s f a c i e s has been i v developed i n narrow zones adjacent to p a r t s of the i n t r u s i v e c o n t a c t . The porphyry i s a metal-enriched i n t r u s i o n i n which some m e t a l l i c g r a i n s formed i n an accessory manner but most of the m i n e r a l i z a t i o n i s e p i g e n e t i c . The d e p o s i t has charac-t e r i s t i c s of both porphyry copper and quartz stockwork d e p o s i t s w i t h disseminated, f r a c t u r e f i l l i n g , v e i n , and r e -placement m i n e r a l i z a t i o n i n the i n t r u s i v e rock, h o r n f e l s , and skarn. The primary m e t a l l i c minerals i d e n t i f i e d were: molybdenite, p y r i t e , p y r r h o t i t e , c h a l c o p y r i t e , a r s e n o p y r i t e , s p h a l e r i t e , galena, t e t r a h e d r i t e , marcasite, a i k i n i t e , b o u r n o nite, and magnetite. Secondary or a l t e r a t i o n minerals are r a r e and only minor g o e t h i t e , maghemite, malachite, and f e r r i m o l y b d e * i t e were found. A f i v e stage paragenesis i s shown w i t h at l e a s t three s u c c e s s i v e stages of v e i n i n g . S u l p h i d e d e p o s i t i o n i s b e l i e v e d t o have s t a r t e d at tempera-t u r e s i n the order of 7 0 0°C and continued along w i t h r e -e q u i l i b r i a t i o n of s u l p h i d e s down to temperatures below **00°C and p o s s i b l y 3 0 0°C f o r the s u l p h o s a l t s . V . TABLE OF CONTENTS INTRODUCTION PAGE L o c a t i o n 1 H i s t o r y 3 Physiography . . 1+ G l a c i a t i o n 6 REGIONAL GEOLOGY I n t r o d u c t i o n . . i 7 T a k l a Group . . 7 Lavas 12 Sedimentary Rocks 13 ... Greywaekes 13 Conglomerates 13 Shales and a r g i l l i t e s Other rocks 1*+ Bowser Group • 1*+ Sustut Group 15 P l e i s t o c e n e and Recent Deposits . . . . . . . . . . . . 1 7 . I n t r u s i v e Rocks 17 Coast I n t r u s i o n s 17 Kastberg P o r p h y r i e s 18 B a s a l t s ^ 19 S t r u c t u r e 19 GEOLOGY OF THE DRIFTWOOD PROPERTY I n t r o d u c t i o n 2 3 v i . PAGE T a k l a - Hazelton Rocks , 23 Conglomerate and greywacke 2 6 S h a l e , a r g i l l i t e , and s i l t s t o n e 2 7 Q u a r t z i t e and s i l i c i o u s s i l t s t o n e .. 28 Tuffaceous sediments ......... . 2 9 V o l c a n i c b r e c c i a 3 0 V o l c a n i c s 3 0 I n t r u s i v e Rocks 3 2 S t r u c t u r e 36 PETROLOGY OF THE STOCK I n t r o d u c t i o n *+l Textures k-2 M i n e r a l Composition of the I n t r u s i o n . . . . . . . kh C l a s s i f i c a t i o n of Rock Type . 52 V a r i a t i o n s W i t h i n the Stock 5*+ I n t r u s i v e H i s t o r y . . . . 57 ROCK ALTERATION AND METAMORPHISM I n t r o d u c t i o n 59 A l t e r a t i o n of G r a n o d i o r i t e - Q u a r t z Monzonite . . . 59 Contact Metamorphism 6 2 ECONOMIC GEOLOGY I n t r o d u c t i o n 6 7 'Disseminated' M i n e r a l i z a t i o n . . . 6 7 Quartz V e i n i n g and Stockwork 68 Other M i n e r a l i z a t i o n 6 9 T e x t u r a l R e l a t i o n s 7 0 v i i . PAGE Paragenesis 81 Diagramatic Representations of the Paragenesis . . 88 Temperature of I n t r u s i o n and M^tamorphism . . . . 93 Ge other mo me t r y 98 Anhydrous i r o n oxides 99 Sul p h i d e s 100 SUMMARY AND CONCLUSIONS 109 REFERENCES CITED 112 v i i i . LIST OF TABLES TABLE PAGE I. TABLE OF FORMATIONS (modified a f t e r Lord, 1 9 ^ 8 ) 9 I I . Weight-Percent Compositional Average and Compositional Range f o r 18 Specimens . . . . 52 I I I . Sequence of M i n e r a l i z a t i o n 8 2 IV. Temperature Data from S i l i c a t e Systems, Heat Flow C a l c u l a t i o n s , and I n v a r i e n t P o i n t s from Condensed Phase Diagrams of Systems a p p l i c a b l e to the Driftwood M i n e r a l Assemblage . 1 0 6 i x . LIST OF FIGURES FIGURE PAGE 1 . L o c a t i o n of Driftwood P r o p e r t y , McConnell Creek Map-Area 2 2 . Geology - Driftwood Area 1 1 3 . G e n e r a l i z e d S t r a t i g r a p h i c Column, Driftwood Property 2 5 h. Geology and Cross S e c t i o n s , Driftwood Property . 37 5 . C l a s s i f i c a t i o n of the Driftwood I n t r u s i o n Based on Modal Q u a r t z - O r t h o c l a s e -P l a g i o c l a s e . 18 Specimens used. ( A f t e r Peterson, i 9 6 0 ) 53 6 . Larsen V a r i a t i o n Diagram . 55 7 . D i f f e r e n t i a t i o n Trend of a G r a n o d i o r i t e Magma using the System N^O-K^O- CaO. ( A f t e r Nockolds and A l l e n , 1 9 5 3 ) 57 8 . Vandeveer Representations of Paragenesis . . . - 9 1 9 . Paragenesis of Driftwood M i n e r a l i z a t i o n . . . . 92 1 0 . Heating of Country Rock w i t h Calcareous Shale Composition Adjacent t o a G r a n o d i o r i t e I n t r u s i o n . ( M o d i f i e d a f t e r Winkler, 1 9 6 5 ) ; Temperature at Contact C a l c u l a t e d According t o Buseck, ( 1 9 6 6 ) 9 7 X. LIST OF PLATES PLATE PAGE F r o n t i s p i e c e . A n o r t h w e s t e r l y view of the r i d g e on which the Driftwood Property i s l o c a t e d . The gossanous outcrops i n the foreground are i n t r u s i v e rocks of a Kastberg Porphyry and s t r a t a of the T a k l a - H a z e l t o n Group . . . i i 1 . Photomicrograph. Q u a r t z - f e l d s p a r mosaic w i t h r e l a t i v e l y uniform g r a i n s i z e i n a l a s k i t e . •> C r o s s e d n i c o l s . M a g n i f i c a t i o n X 53 ^8 2. Photomicrograph. Coarse grained g r a n o d i o r i t e ('crowded porphyry'). P l a g i o c l a s e , o r t h o -c l a s e , and b i o t i t e phenocrysts with i n t e r -g r a n u l a r q u a r t z - f e l d s p a r . Crossed n i c o l s . M a g n i f i c a t i o n X 58. ^8 3. Photomicrograph. M a t r i x i n quartz monzonite porphyry showing i n t e r l o c k i n g q u a r t z - f e l d s p a r , shredded b i o t i t e , c a l c i t e , and minor sphene. Crossed n i c o l s . M a g n i f i c a t i o n X 58. . . . . . ^9 k-. Photomicrograph. G r a n o d i o r i t e w i t h f i n e g r a i n e d q u a r t z - f e l d s p a r matrix, hornblende, and anhedral phenocrysts of o r t h o c l a s e . Crossed n i c o l s . M a g n i f i c a t i o n X 58 *+9 x i . PLATE PAGE 5. Photomicrograph. Phenocrysts of p l a g i o c l a s e and hornblende i n a f i n e - g r a i n e d matrix. Crossed n i c o l s . M a g n i f i c a t i o n X 58 50 6. Photomicrograph. Zoned p l a g i o c l a s e and g r a i n s o" of hornblende i n f i n e - g r a i n e d matrix of q u a r t z - f e l d s p a r s , b i o t i t e , and minor a p a t i t e . Crossed n i c o l s . M a g n i f i c a t i o n X 58 50 7. Photomicrograph. Zoned and twinned phenocryst of p l a g i o c l a s e . Crossed n i c o l s . M a g n i f i c a -t i o n X 58 51 8. Photomicrograph. P o r t i o n of composite p l a g i o c l a s e - o r t h o c l a s e phenocryst. P l a g i o -c l a s e i n core shows zoning, twinning, a p a r t l y corroded o u t l i n e w i t h p o i k i l i t i c border and i s mantled by p o i k i l i t i c r i m of o r t h o c l a s e . Crossed n i c o l s . M a g n i f i c a t i o n X 53. . 51 9 . Photomicrograph. Disseminated magnetite and a few s u l p h i d e g r a i n s w i t h an accessory or i n t e r s t i t i a l d i s t r i b u t i o n . Note a s s o c i a -t i o n of opaque g r a i n s and mafic m i n e r a l s . P l a i n l i g h t . M a g n i f i c a t l o n X $8 72 10. Photomicrograph. Subhedral accessory g r a i n s of magnetite i n q u a r t z - f e l d s p a r matrix. Crossed n i c o l s . M a g n i f i c a t i o n X 150 72 x i i . PLATE PAGE 11. Photomicrograph. Fine grained accessory magnetite and i n t e r g r a n u l a r , replacement s u l p h i d e s . P l a i n l i g h t . M a g n i f i c a t i o n X 58. . 73 12. Photomicrograph. A s s o c i a t i o n of s u l p h i d e g r a i n s w i t h f i n e - g r a i n e d , shredded (secondary) b i o t i t e and corroded hornblende and c o a r s e - g r a i n e d b i o t i t e . P l a i n l i g h t . M a g n i f i c a t i o n X 150 73 13 and 1^ -. Photomicrograph. P o i k i l i t i c p l a g i o -c l a s e phenocrysts w i t h opaque g r a i n s c o n c e n t r a t e d i n zones i n d i c a t i n g e a r l y m e t a l l i c m i n e r a l i z a t i o n d u r i n g s i l i c a t e c r y s t a l l i z a t i o n . P l a i n l i g h t . • M a g n i f i c a t i o n X 150 7^ 15. Photomicrograph. Sulphide replacement of hornblende along g r a i n boundaries and cleavage planes. P l a i n l i g h t . M a g n i f i c a t i o n X 150 75 16. Photomicrograph. Or i e n t e d s u l p h i d e g r a i n s r e p l a c i n g a l a r g e p l a t e of b i o t i t e . P l a i n l i g h t . M a g n i f i c a t i o n X 150 75 x i i i . PLATE PAGE 17 and 18. Photomicrograph. Zonation or c o n c e n t r i c banding i n marcasite g r a i n s . Grains are h i g h l y corroded due to p o l i s h i n g . R e f l e c t e d l i g h t . M a g n i f i c a t i o n X 550. . . . 78 19. Photograph. P o l i s h e d s e c t i o n of diamond d r i l l core w i t h Stage l a a p l i t e dyke and Stage 11 "blue q u a r t z " v e i n cut by Stage IV q u a r t z - c a l c i t e v e i n 86 2 0 . Photomicrograph. C h a l c o p y r i t e (cpy) t r u n c a t i n g marcasite (mcs) bands. R e f l e c t e d l i g h t . M a g n i f i c a t i o n X 550. . . . 90 21. Photomicrograph. Shattered p y r i t e (py) w i t h younger rims of p y r r h o t i t e (po). R e f l e c t e d l i g h t . M a g n i f i c a t i o n - X . . . 90 MAP Geology Driftwood Property ( 1" = 5 0 0 1 ) . Pocket i n back. MAP 1. x i v . ACKNOWLEDGEMENT Data and m a t e r i a l s were c o l l e c t e d by the author while employed by Kennco E x p l o r a t i o n s (Western), L i m i t e d . The author wishes t o thank Dr. P h i l i p T. Black, Dr. J . A. Gower, and Mr. C. S. Ney f o r help i n s e l e c t i n g the problem, a s s i s t a n c e r e c e i v e d i n the f i e l d , and i n copying the manuscript. Dr. W. D. McCartney and Dr. K. C. McTaggart read p a r t s of the t h e s i s . Dr. A. J . S i n c l a i r f a m i l i a r i z e d the author w i t h the method of approximating chemical analyses u s i n g a F o r t r a n programme and p e t r o l o g i c modal an a l y s e s . Dr. W i l l i a m H. White c r i t i c a l l y read the manuscripts and s u p e r v i s e d the p r e p a r a t i o n of t h i s t h e s i s . T h e i r comments and many h e l p f u l suggestions are a p p r e c i a t e d . MINERALIZATION OF THE DRIFTWOOD PROPERTY, McCONMELL CREEK DISTRICT, BRITISH COLUMBIA INTRODUCTION Location The McConnell Creek D i s t r i c t i s the area underlain by a north-west trending belt of Late Paleozoic to Cenozoic rocks that i s contained i n the McConnell Creek map-area and the areas immediately adjacent to the west and south. To the west and south no published maps of the region are available but the area has been mapped by the author and others. To the east, i s the southwest corner of the Aiken Lake map-area and to the southeast, the Fort Saint James map-area. The Driftwood Property i s found i n the extreme south-west corner of the McConnell Creek map-area at la t i t u d e 56° 2 ' 1 5 " and longitude 126° 5 ' 1 3 " approximately 87 miles north of Smithers. The property i s contained within the MOTASE B Claim Group which l i e s along the east flank of an isolated ridge overlooking the Driftwood River. The ridge i s near the north end of the Driftwood Range about three miles south of D r i f t Lake, f i v e miles west of Bear Lake, and three and a half miles east of Motase Lake, as shown i n Figures 1 and 2. Location of Driftwood Property , McConnell Creek M a p - A r e a 3 History The e a r l i e s t mining interest i n the area was i n 1899 when placer gold was discovered i n McConnell Creek. However, the placers were not very productive and interest i n the area lagged. Prospecting i n the area was only casual and intermit-tent p r i o r to mapping by the Geological Survey of Canada. Systematic mapping of the area by C. S. Lord during 19^1, 19^> and 19*+5 resulted i n the publication of Memoir 251: McConnell Creek Map-Area, Cassiar D i s t r i c t , B r i t i s h Columbia, i n 19^8. Varied and widespread mineral pot e n t i a l was indicated during the mapping but despite recommendations by Lord as to the most favourable rock types, exploration was only s l i g h t l y i n t e n s i -f i e d and was largely r e s t r i c t e d to the northeast and eastern portions of the map-area i n the gold-bearing regions near the Omenica intrusions. Some discoveries of placer gold together with platinum, mercury, and vanadium and a large number of lode deposits of gold, copper, s i l v e r , lead, zinc, beryllium, molybdenum, and chromium were made. In the southwest part of the map-area the Atna group of claims and located by M. S. Lang i n June, 19^5 > i n the center of what i s now the D r i f t -wood Property. One mile to the northwest on the same ridge, t h i r t y f i v e claims were staked during the same summer on behalf of Yukon Northwest Explorations, Limited. A l l these discoveries and a number of occurrences on the Tsaytut Spur to the east were of copper usually accompanied by s i l v e r or If occasionally gold values i n volcanics that were mapped as Takla Group. Exploration a c t i v i t y decreased during the late 19^0's and was carried on. mainly by independent prospectors. In the 1950's some gold deposits were located on Motase Moun-t a i n and Northwest Exploration Company and other companies examined parts of the map-area but nothing warranting a continuing inte r e s t was discovered. In i 9 6 0 the younger sedimentary formations of the Sustut Group were examined by Pan American O i l Company but again no apparent interest i n the. area was generated. Renewed interest i n the entire region was shown i n the early 1960's as a re s u l t of discoveries of economic ore-bodies and promising mineral deposits to the south. By 1965 there had been arid were a number of companies and independent prospectors working i n the McConnell Creek map-area and sur-rounding regions. Their work resulted to the discovery of more gold veins i n the Motase Peak area, a number of d i s -seminated copper - molybdenum deposits associated with i n t r u -sive stocks and some stratabound copper and associated copper-s i l v e r vein deposits i n sedimentary and volcanic rocks. Active exploration and evaluation of many of these deposits has been i n progress since 1966. Physiography The southwest corner of the McConnell Creek map-area 5 and regions to the south and west are characterized by north-westerly-trending mountain ridges separated by broad va l l e y s . The Driftwood River and drainages to the south of the D r i f t -wood Property flow southeast into the r o l l i n g h i l l country of the Takla region which i s part of the Praser River system. To the west and east of the Driftwood Property the Motase and Bear Lake Valleys drain northwesterly into the Skeena River system. Topography i s strongly influenced by underlying rock types and structures and shows decreasing ruggedness and elevations from the west towards the east. In the central area to the west of Bear Lake and around the Driftwood Valley, Takla Group rocks are exposed as northwesterly-trending r i d -ges such as the Driftwood Range and Tsaytut Spur. These ridges r a r e l y exceed 7000 feet i n elevation and are charac-t e r i z e d by asymmetrical cross-sections due to in c l i n e d strata. They show ragged, knife-edged portions, spires, well devel-oped c l i f f faces and loose crumbling slopes on one side and more gentle, uniform slopes on the other. To the west the topography i s much more rugged. The mountains such as the S i c i n t i n e Range have g r a n i t i c cores and are asymmetrical, extremely ragged i n p r o f i l e , many being over 8000 feet high. To the east of Bear Lake i n the Sustut Group rocks the topo-graphy i s d i s t i n c t l y d i f f e r e n t . In regions of f l a t - l y i n g s t r a t a there are gently undulating or f l a t , plateau-like 6 surfaces which are bounded by steep c l i f f s such as those found along the east margin of Bear Lake. Further to the east where the strata are more contorted and i n c l i n e d , are hogback and cuesta structures such as those observed i n the Connelly Range. There, the ridge crests are close to 6500 feet i n elevation and many have spectacular c l i f f s and talus slopes on one side. G l a c i a t i o n Most ridges and peaks are so rugged that l i t t l e or no g l a c i a l record has been preserved on them. G l a c i a l l y scoured outcrops were observed on the crest of a ridge near the Driftwood property at an elevation of about 6*4-00 feet. To the north g l a c i a l e r r a t i c s were found on a small plateau surface at an elevation of 5500 feet. No d i r e c t i o n of Ice movement could be determined. The main northwest-trending valleys such as the Bear Lake and Driftwood River Valleys show the best evidence for widespread g l a c i a t i o n . They are U-shaped i n p r o f i l e with truncated spurs and hanging val l e y s . Some drumlin-llke structures are v i s i b l e i n the Driftwood Valley but generally i n most parts of the valley and other valleys only a t h i n g l a c i a l cover of t i l l or outwash gravels can be seen. Alpine g l a c i e r s are common i n the western part of the region such as the S i c i n t i n e Range and parts of the Tsaytut Spur. 7 REGIONAL GEOLOGY Introduction The regional geology of the Driftwood Area as shown i n Figure 2 has been taken from the southwest corner of Lord's McConnell Creek map-area (19h8) and reconaissance work to the south and west by the author and others during 1965 and 1966. The oldest rocks i n the area are to the west of Bear Lake and underlie the Driftwood Property. Lord dated the rocks as Lower Jurassic on the basis of f o s s i l evidence and cal l e d them 'Takla Group - Upper D i v i s i o n 1 . To the west Bow-ser Group rocks of Upper Jurassic to Lower Cretaceous age unconformably overlie the Takla Group, and to the east are Upper Cretaceous to Tertiary rocks of the Sustut Group. Granitic plutons and smaller masses of at least two ages intrude the str a t a as well as minor dykes, s i l l s , and necks of basalt. Takla Group The Mesozolc volcanic-sedimentary rocks to the west of Bear Lake contain late Lower Jurassic faunal remains and were c a l l e d the Upper Divisions of the Takla Group by Lord. Further to the east i n the central and eastern parts of McConnell Creek map-area Lord found l i t h o l o g i c a l l y d i f f e r e n t , n o n - f o s s i l i f e r o u s volcanic-sedimentary assemblages which he ca l l e d the Lower D i v i s i o n of the Takla Group. In the same 8 regions the Upper D i v i s i o n was found to contain Middle and Upper Jurassic (Oxfordian) f o s s i l s . The d i v i s i o n of the Takla Group into an upper and lower unit was accepted by Armstrong who had o r i g i n a l l y defined the Takla Group further to the south. However, as a r e s u l t of work i n other map-areas i t became necessary to re-examine and re-define Meso-zoic rocks that had been assigned to the Takla and Hazelton Groups. The r e d e f i n i t i o n for the McConnell Creek area was included i n the general r e v i s i o n of the Hazelton and Takla Groups by H. W. Tipper (1959). According to Tipper: •In McConnell Creek map-area, the Takla group i s subdivided into upper and lower d i v i s i o n s , roughly cor-responding to Hazelton and Takla groups i n t h e i r type areas, and a l i t h o l o g i c change from f i n e to coarse c l a s t i c s e d i -mentary st r a t a occurs between the two d i v i s i o n s . This change, however, apparently started i n Early Jurassic time... 1 'The d e f i n i t i o n of the Hazelton and Takla groups i s most d i f f i c u l t when the Lower Jurassic strata have to be assigned. Upper T r i a s s i c sedimentary strata are almost invari a b l y shales or argillaceous limestones c l e a r l y as-signable to the Takla, and Middle Jurassic or l a t e r beds are generally conglomerates or greywackes t y p i c a l of the Hazeljton, but Lower Jurassic sedimentary beds may be either coarse or fine grained ... In McConnell Creek area, Lower Jurassic strata are c l o s e l y related to and inseparable from the upper d i v i s i o n of the Takla group (equivalent to Hazel-ton group). In Port St.James area, the type area of the Takla group, Armstrong recorded the occurrence of Lower Jurassic conglomerates, greywackes, and shales and postulated marine, near-shore, or nonmarine conditions. These beds are d i s t i n c t l y d i f f e r e n t from the Upper T r i a s s i c sedimentary s t r a t a . Thus i n both McConnell Creek and Fort St.James areas the Lower Jurassic could r i g h t l y be considered to be part of the Hazelton group (although i n the Fort St.James . 9 Table 1 : TABLE OF FORMATIONS (modified a f t e r Lord, 1 9 * f 8 ) . E r a P e r i o d or epoch Formation and thickness i n f eet Character Cenozoic Recent Stream a l l u v i u m and d e l t a d e p o s i t s , t a l u s , and s o i l . P l e i s t o c e n e G l a c i o f l u v i a l and g l a c i o -l a c u s t r i n e d e p o s i t s , other g l a c i a l d r i f t . T e r t i a r y t o Recent B a s a l t necks, dykes and l a v a . I n t r u s i v e contact T e r t i a r y Kastberg I n t r u s i o n s F e l d s p a r and f e l d s p a r -q u a r t z p o r p h y r i e s w i t h dense, chalky weathering groundmass; medium g r a i n -ed p o r p h y r i t i c grano-d i o r i t e and quartz d i o r i t e . Dykes, s i l l s and s t o c k s . I n t r u s i v e c o n t a c t Mesozoic and Cenozoic Upper c r e t a -ceous and Paleocene Sustut Group 3,000 + f e e t i u i f f to grey impure sand-stone, conglomerate, and s h a l e s ; minor d a c i t i c t u f f and c o a l . Well bed-ded c o n t i n e n t a l d e p o s i t s c h a r a c t e r i z e d by c r o s s -bedding and f o s s i l p l a n t remains. Unconformity Mesozoic Cretaceous and l a t e r Coast I n t r u s i o n s B i o t i t e g r a n o d i o r i t e , q u a r t z d i o r i t e , i n plutons and s a t e l l i t i c b odies to the Coast Range B a t h o l i t h . Intrus] Lve contact Upper J u r a s s i c Lower Cretaceous Bowser Group 20,000 + f e e t ? F o s s i l i f e r o u s marine and t e r r e s t r i a l conglomerate, greywacke, and s h a l e . Unconformity J u r a s s i c T a k l a -H a z e l t o n Group P o r p h y r i t i c a n d e s i t e f l o w s , b r e c c i a ; minor d a c i t e and r h y o l i t e ; t u f f s w i t h interbedded conglomerate, greywacke s h a l e , and a r e i l l i t e . 1 0 area Armstrong considered i t part of the Takla group)'... 'With which group should the Lower J u r a s s i c s t r a t a be c o r r e l a t e d ? They never have been included i n the Hazeljton group, but i n places there now seems to be some j u s t i f i c a t i o n f o r so doing. Armstrong placed both Upper T r i a s s i c and Lower J u r a s s i c i n the same group but probably more f o r convenience than because there was no v a l i d reason f o r separating them. 'Earl y J u r a s s i c time was apparently a t r a n s i t i o n a l period i n which environmental c o n d i t i o n s changed from moder-a t e l y s t a b l e to c h a o t i c . . . The e f f e c t of these c o n d i t i o n s was not f e l t everywhere at the same time, so that d i f f i c u l t y p e r s i s t s i n mapping and c o r r e l a t i n g Lower J u r a s s i c s t r a t a . I t seems probable that i n time the Takla group w i l l be r e s -t r i c t e d t o Upper T r i a s s i c s t r a t a , l i k e the N i c o l a group of southern B r i t i s h Columbia, and the Lower J u r a s s i c s t r a t a w i l l be mapped as a new group. U n t i l that i s f e a s i b l e there i s no a l t e r n a t i v e but to map Lower J u r a s s i c rocks w i t h the Takla , group where p o s s i b l e , as i n Nechako River area, but as Hazel-t o n group where they are l i t h o l o g i c a l l y inseparable from Mid-d l e J u r a s s i c s t r a t a , as may be the case i n McConnell Creek area.* In view of t h i s statement, the Lower J u r a s s i c v o l c a n i c -sedimentary rocks i n the Driftwood area are r e f e r r e d to here-i n as *Takla-Hazelton Group 1. The v o l c a n i c and sedimentary rocks of t h i s u n i t occupy a north-westerly trending b e l t to the west and south of Bear Lake V a l l e y . At the north end of Tsaytut Spur by the north end of Bear Lake the b e l t i s only about four miles wide but broadens southward to form the Driftwood and B a i t Ranges and northern part of the Babine Lowlands where i t i s at l e a s t 2 0 miles wide. The p r i n c i p a l rock types are l a v a s , b r e c c i a t e d f l o w s , and p y r o c l a s t i c s , w i t h conglomerates, greywackes, shales and a r g i l l i t e s . They form dark green and grey s t r o n g l y j o i n t e d but otherwise seemingly s t r u c t u r e l e s s outcrops. II 12 L i t h o l o g i c units are extremely d i f f i c u l t to recognize from a distance and even on close examination i n d i v i d u a l flows and volcanic members are inseparable. According to Lord (page 1 9 ) : "The precise sequence i s not known. A v a i l -able evidence indicates that volcanic members greatly pre-dominate among the lower strata and sedimentary members i n the upper parts of the d i v i s i o n , where, however, they are interlayered with volcanic rocks. Approximately 18,000 feet of volcanic rocks outcrop between Bear Lake v i l l a g e and Driftwood River, where neither t h e i r upper nor t h e i r lower l i m i t s were recognized. Because of r e l a t i v e l y complex structure few data are available on the aggregate thickness of the Jurassic sedimentary rocks. ...(Thus) the complete assemblage assigned to the upper d i v i s i o n i s probably considerably more than 23,000 feet t h i c k . 1 Lavas These are mainly massive, dark green porphyritic rocks with lesser purplish red and grey v a r i e t i e s . Two types of porphyritic volcanics were observed. The more common type i n the Driftwood region has small dark phenocrysts of c h l o r i -t i z e d pyroxene and amphibole. The phenocrysts appear as small, equant spots less than 1/16 inch across the face with dif f u s e boundaries and a shredded outline due to c h l o r i t e a l t e r a t i o n . The other porphycy^ifc&'e type has white or buff plagioclgse laths which may be only s l i g h t l y larger than the f i n e f e l t e d goundmass and almost indistinguishable from i t but commonly grade to small phenocrysts up to 1/16 inch long that form at least 15% of the rock. Fragmental flows and portions of flows contain angular and rounded fragments of 13 varying s i z e s . The composition of the fragments i s almost i d e n t i c a l to the matrix and they can usually be distinguished only on weathered surfaces. The matrix has a green c h l o r i t i c appearance and fractures contain epidote, c h l o r i t e , c a l c i t e , and quartz which denote greenchist f a c i e s regional a l t e r a t i o n . Sedimentary rocks The sedimentary rocks i n the Driftwood area are mainly coarse c l a s t i c types. The description by Lord (page 2 1 - 2 2 ) i s complete and l i t t l e needs to be added to i t . 1 Greywackes. These are f i n e - t o medium-grained, dark green to grey, sandy-textured rocks that weather green, grey-brown, or yellowish-brown. They are well bedded, and are i n t e r l a y e r -ed with conglomerates, sl a t e s , and a r g i l l i t e s . The beds range from a few inches to several feet i n thickness; a few payers are i n d i s t i n c t l y crossbedded. ... Occasional well-sorted beds grade from coarse at the bottom to fi n e at the top. The greywackes comprise mainly subangular to partly rounded grains of chert and microcrystalline volcanic rocks. ... Occasional grains of plagioclase feldspars and of quartz were also noted....' Conglomerates. Most of the conglomerates have about the same composition as the greywackes and d i f f e r from them main-l y i n grain s i z e . These are thoroughly consolidated grey, greenish grey, or limonite-stained rocks, and f r e s h fractures commonly pass through rather than around the pebbles. The conglomerates form layers ranging from a foot or so to many feet i n thickness, but the thicker layers commonly contain lenses and beds of greywacke. The pebbles are subangular to rounded and are generally less than 2 inches i n diameter. Most of them are black, grey, and green, cherty rocks Pebbles of white quartz and red and green volcanic rocks, with 1/16 - to 1/8 inch feldspar phenocrysts, are l o c a l l y abundant. The matrix i s apparently i d e n t i c a l with the grey-wackes previously described. These conglomerates were prob-ably derived from the same source as the greywackes, and are not known to mark s i g n i f i c a n t breaks i n deposition.' 1>+ Shales and a r g i l l i t e s . These commonly occur as grey and black beds one to two feet thick interbedded as well defined beds and lenses with the finer-grained greywacke beds and occa-s i o n a l l y as lenses i n conglomerate-greywacke sections. Most beds are hard and s l l i c i o u s . A very few are calcareous and many probably contain f i n e tuffaceous material. According to Lord (page 22): . . . . ' A r g i l l i t e s predominate, and are compact, banded rocks that break without p a r t i c u l a r reference to the banding into small, sharply angular blocks. Shaly beds, on the other hand, break along the bedding to form t h i n plates and slabs' . Other rocks. Minor strata found i n the Driftwood section intercalated with brecciated volcanic flows are t h i n beds of dense, purple t u f f with a concoidal fracture and beds of f i n e -grained tuffaceous sandstone and quartzite. Bowser Group The Bowser Group i s a marine and continental series of c l a s t i c sedimentary rocks containing Upper Jurassic and Lower Cretaceoaas; f o s s i l s . The minimum t o t a l thickness i s i n the order of 20,000 feet but i n the Driftwood area only 2,000 to 3>000 foot sections of the basal portions were ob-served where they unconformahly overlie Takla-Hazelton rocks. Conspicuous bedding can be seen i n a l l the Bowser Group out-crops and t h i s , along with the grey colour, e a s i l y d i f f e r e n -t i a t e s them from the Takla-Hazelton volcanic-sedimentary rocks. aJ'5 Rocks of the Bowser Group form the S i c i n t i n e Range. Their eastern boundary i s Takla-Hazelton rocks along the Squingula and Nilkitkwa Rivers and Motase Lake. Greywackes are the most common rock type. They vary i n grain size and grade into g r i t s , pebble conglomerates, and coarse boulder conglomerates on one hand and to a r g i l l i t e s and slates on the other. A l l the rocks seem to have a similar composition and vary mainly i n grain s i z e . Bedding i s well developed and d i s t i n c t . Fine c l a s t i c beds are two to three feet thick; greywacke and conglomerate beds are commonly 5 to 10 feet i n thickness but have been reported to be hundreds of feet thick i n other areas. Bedding i s emphasized by differences i n dark-ness and resistance to weathering of the beds. Limestones and volcanic rocks are v i r t u a l l y absent. Coal forms t h i n seams i n the basal sections of the group. Sustut Group The Sustut Group i s a well bedded succession greater than 3 ,000 feet thick of Upper Cretaceous to Paleocene c l a s -t i c rocks. They occur i n a northwesterly trending belt 10 to 15 miles wide along the east shore and to the northwest and southeast of Bear Lake. The succession unconformably overlies Takla-Hazelton rocks. The outcrops are bedded, grey to buff i n colour, and composed mainly of pebble conglomerate, coarse sandstone and sandstone containing pebbles. The conglomerates most f r e -16 quently have pebbles one to two Inches i n diameter but a few are up to eight inches. The fragments are rounded and composed of white vein quartz, chert, volcanic porphyries,, green massive lav&s and some equigranular g r a n i t i c rocks, t u f f s and shale fragments. The sandstones are f i n e r grained equivalents of the conglomerates and crossbedding i n them i s not uncommon. The conglomerates form the thickest beds and may be as much as 100 feet i n thickness. The sandstone beds rar e l y exceed 20 feet. , Together, conglomerates and sand-stones may be interbedded to form spectacular c l i f f s hun-dreds of feet high. The finer-grained sandstones are asso-ciated with dark grey, soft weathering, f r i a b l e shale beds. In such sections small lenses of coal and many f l o r a l im-pri n t s and pieces of f o s s i l wood are found. In sections examined by Lord, white-weathering d a c i t i c t u f f bands were noted. These showed thicknesses from 2 to 50 feet and were believed to occur only i n the upper parts of the Sustut succession. The o v e r a l l appearance of the Sustut Group i s quite s i m i l a r to parts of the Bowser Group but can be distinguished i n the Driftwood region by the v i r t u a l l y f l a t - l y i n g or gently r o l l i n g structures; smaller average thicknesses of beds; greater abundance and composition of the conglomerates; l e s -ser abundance of shales and a r g i l l i t e s ; and the presence of t u f f beds. Examination of f o s s i l remains, of course, c l e a r l y indicates t h e i r age difference despite some general l i t h o -l o g i c similarities. The Sustut rocks are fr e s h looking and 17 v i r t u a l l y u naltered. Where they are intruded by dykes and s i l l s of g r a n i t i c porphyries and b a s a l t , n e g l l g a b l e contact metaraorphic a f f e c t s a r e . v i s a b l e . P l e i s t o c e n e and Recent deposits G l a c i a l and a l l u v i a l deposits cover the v a l l e y f l o o r s i n a l l the main v a l l e y s but u n l i k e the regions to the south where such deposits reach great t h i c k n e s s e s , bedrock i n the Driftwood r e g i o n i s u s u a l l y w i t h i n 10 f e e t of the surface and i s exposed i n most areas that have been i n c i s e d by streams. I n t r u s i v e Rocks Coast I n t r u s i o n s . These form s m a l l s a t e l l i t i c plutons along the e a s t e r n margin of the Bowser B a s i n i n the S i c i n t i n e Range and the n o r t h end of the B a i t Range i n Takla-Hazelton rocks. The i n t r u s i o n s are so named to i n d i c a t e a s i m i l a r age w i t h the Coast Range B a t h o l i t h . The i n t r u s i o n s l i e along an east-west 'arch' between the Omenica and Coast Ranges and should not be g e n e t i c a l l y a s s ociated w i t h e i t h e r except i n a time sense. I n t r u s i o n occurred over an extended time period from p o s s i b l y as e a r l y as Upper J u r a s s i c t o as l a t e as T e r t i a r y time. The i n t r u s i o n s form i r r e g u l a r , l i g h t grey, w e l l j o i n t e d stocks having very l i t t l e thermal a f f e c t on the surrounding rock s . The compositions are most commonly of medium t o coarse g r a i n e d , e q u i g r a n u l a r , quartz d i o r i t e and g r a n o d i o r i t e . An 18 e x c e p t i o n i s a s m a l l h i g h l y i r r e g u l a r d y k e - l i k e mass over-l o o k i n g the Squiingula R i v e r i n the northwest corner of the Driftwood area. The rock there i s a p o r p h y r i t i c grey to pink g r a n o d i o r i t e and quartz monzonite. A l t e r a t i o n of t h i s s t o c k i s s t r o n g and has produced a l a r g e goassanous zone i n and around the stock. K a s t b e r g P o r h h y r i e s . The Kastberg i n t r u s i o n s o c c u r - i n T a k l a -H a z e l t o n and Sustut S t r a t a and are b e l i e v e d to be e a r l y T e r -t i a r y i n age (Lord, 1 9 ^ 8 ) . They are l o c a l i z e d i n the south-west corner of the McConnell Creek map-area i n the Driftwood r e g i o n and f u r t h e r to the south i n the v i c i n i t y of Babine Lake (N. C. C a r t e r , p e r s o n a l communication). The i n t r u s i o n s occur as s i l l s and dykes and h i g h l y i r r e g u l a r plugs of por-p h y r i t i c g r a n o d i o r i t e , quartz d i o r i t e , and f e l d s p a r and quartz porphyry. They are grey and b u f f i n c o l o u r and weather deeply w i t h a s o f t , chalky s u r f a c e . The g r a i n s i z e of the p o r p h y r i e s v a r i e s widely. The f i n e s t - g r a i n e d f a c i e s may show only s m a l l quartz eyes as phenocrysts. Most commonly v i s i b l e are phenocrysts of p l a g i o -c l a s e and needles of amphibole and b i o t i t e . The c o a r s e s t -g r a i n e d rocks such as those found at the Driftwood Property c o n t a i n p l a g i o c l a s e phenocrysts w i t h hornblende and b i o t i t e and c h a r a c t e r i s t i c p o i k i l i t i c o r t h o c l a s e phenocrysts up to one i n c h i n l e n g t h . Most sma l l i n t r u s i v e bodies show a t h i n marginal c h i l l zone but otherwise very l i t t l e c o ntact 19 a l t e r a t i o n a f f e c t s . Basalts. Minor dykes, s i l l s and one prominent bas a l t i c neck intrude Sustut Group rocks to the east of Bear Lake. The c i r c u l a r neck remains as a resistant mass, with well devel-oped columnar j o i n t s and stands above the f l a t - l y i n g Sustut st r a t a as a prominant landmark c a l l e d fThe Thumb'. Structure Most major f a u l t s and f o l d axes i n the McConnell Creek map-area and regions to the west and south r e f l e c t the northwest C o r d i l l e r a n trend. A few major and many minor f a u l t s s t r i k e north, northeast, and east. The Driftwood area l i e s to the west of a major f a u l t zone which i s bounded on the east by the Omenica River. This f a u l t zone contains the Omenica, Carruthers, and Ominicelta f a u l t s and i s ten to twelve miles wide. It i s the northern extension of the Pinchi f a u l t zone (Roots, 195*+-) mapped by Armstrong i n the Ft. St.James area to the southeast. Faults are 25 to 1000 feet or more wide and are marked by fractured, sheared and otherwise altered rocks. Lord postulated that dips are steep and displacements along the major f a u l t s may be as much as ten thousand feet. He suggested that the southwest side of the Omenica f a u l t moved upward but i n the other northwest trending f a u l t s the northeast side moved upward r e l a t i v e to the southwest. Major displacements are believed to have taken place i n pqst-Paleocene time. 20 In the Driftwood V a l l e y Lord suggests t h a t there may be an unmapped f a u l t as suggested by the abrupt v a r i a t i o n s i n a l t i t u d e s and steep i n c i n a t i o n s d i s p l a y e d there by the Sustut s t r a t a . The author concurs and noted t h a t mapping along the Driftwood V a l l e y l i n e a r t rend across the drainage d i v i d e i n t o the Squingula V a l l e y i n d i c a t e d t h a t t h i s v a l l e y system marked the abrupt e a s t e r n l i m i t of Bowser Group Rocks. F u r t h e r , the very presence of i n c l i n e d s t r a t a of the Sustut Group on the f l o o r of the Driftwood V a l l e y would suggest t h a t the v a l l e y may be a s m a l l graben s t r u c t u r e r e l a t i v e t o the T a k l a - H a z e l t o n rocks on the Driftwood Property and Tsaytut Spur. F o l d i n g , has taken p l a c e about n o r t h w e s t e r l y t r e n d i n g axes and a c c o r d i n g to Lord has occurred during two p e r i o d s . The f i r s t was d u r i n g i n t r u s i o n , of the Omenica (and Coast I n t r u s i o n s ) f o l l o w i n g the d e p o s i t i o n of the T a k l a - H a z e l t o n r o c k s . The second i n t e r v a l was post-Paleocene, a f t e r d e p o s i -t i o n of the Sustut Group. During t h i s time the r e g i o n was s u b j e c t e d to some compression and t h r u s t i n g from the south-west. The v a r i o u s age-rock u n i t s i n the area r e f l e c t the i n t e n s i t y and manner of deformation. The T a k l a - H a z e l t o n rocks are r e l a t i v e l y t i g h t l y f o l d e d . Dips from 10 to 65 degrees were r e p o r t e d w i t h dips of 30 to 50 degrees most common but no overturned s t r u c t u r e s were noted. The Bowser Group rocks are moderately f o l d e d i n t o w e l l - d e f i n e d , l a r g e 2 1 open f o l d s w i t h dips r a r e l y exceeding 3 0 to 3 5 degrees. In some areas around i n t r u s i v e masses the beds are contorted and show complicated s t r u c t u r e s and beds w i t h h i g h l y v a r i a b l e d i p s . Most of the Sustut Group s t r a t a are warped i n t o l a r g e open f o l d s w i t h dips of 10 to 20 degrees or l e s s . However, along the east f l a n k of the Sustut b e l t i n such regions as the Sustut and Omenica River V a l l e y s the beds are crumpled i n t o s e r i e s of s m a l l , t i g h t f o l d s w i t h some overturning i n places towards the northeast. I t appears that the beds have been pushed against a r i g i d b a r r i e r formed by the older T a k l a -Hazelton rocks to the east. The i n t r u s i v e rocks d i s p l a y very l i t t l e i n t e r n a l s t r u c -t u r e . The Coast I n t r u s i o n s are massive rocks which have sharp, c h i l l e d contacts w i t h the Bowser Group sediments. Most of the plugs are i r r e g u l a r i n o u t l i n e but the contacts are steep and e a s i l y t r a c e a b l e w i t h the exception of the one a l t e r e d gossanous i n t r u s i o n overlooking the Squingula R i v e r . There the plug i s h i g h l y i r r e g u l a r , has many i n t e r f i n g e r i n g dykes and i r r e g u l a r apophyses- a d j o i n i n g the c e n t r a l i n t r u -s i v e core. The small plugs and p r o j e c t i o n s from the l a r g e plugs i n the B a i t and S i c i n t i n e Ranges seem to cut the Bowser and Takla-Hazelton rocks without d i s t u r b i n g them. However, i n the Motase Peak re g i o n of the S i c i n t i n e Range and the Atna Range to the west, the s t r a t a around the l a r g e r i n t r u s i v e stocks are contorted w i t h i r r e g u l a r overturned f o l d s . Such 22 d e f o r m a t i o n could be caused both by the f o r c e f u l i n j e c t i o n of the i n t r u s i o n s and g r a v i t y c o l l a p s e of the beds from domed areas. The Kastberg i n t r u s i o n s form t h i n s i l l s and dykes or h i g h l y i r r e g u l a r stocks and plugs. Some s i l l s show colum-nar j o i n t i n g which serves to d i s t i n g u i s h them at a d i s t a n c e from the e n c l o s i n g Sustut s t r a t a . The i n t r u s i o n s may show a t h i n c h i l l margin composed of m i c r o c r y s t a l l i n e matrix i n which there i s v i s i b l e some p l a g i o c l a s e phenocrysts and sometimes f i n e s u l p h i d e s and magnetite. T h e i r emplacement appears to have been l a r g e l y i n f l u e n c e d by p r e - e x i s t i n g s t r u c t u r e s and zones of weakness such as bedding planes and f a u l t s . In most cases i n t r u s i o n of the p o r p h y r i e s seems to have caused very l i t t l e d eformation and metamorphism of the i n t r u d e d s t r a t a . An e x c e p t i o n i s at the Driftwood Property where some p a r t s of the i n t r u s i v e rock are enveloped i n a t h i n zone of s c h i s t and the e n t i r e i n t r u s i v e body i s su r -rounded by an aureole of h o r n f e l s . GEOLOGY OF THE DRIFTWOOD PROPERTY I n t r o d u c t i o n The Driftwood Property i s u n d e r l a i n by a s e c t i o n of w e s t e r l y - d i p p i n g sedimentary and v o l c a n i c rocks of the T a k l a -H a z e l t o n Group which has been i n t r u d e d by a s m a l l , i r r e g u l a r s t o c k of g r a n o d i o r i t e - q u a r t z monzonite porphyry. The i n t r u -s i o n has been mapped by Lord (19^8) as belonging t o the Kastberg I n t r u s i o n s of T e r t i a r y age. Chalcopyritei,- p y r i t e , p y r r h o t i t e , and some molybdenite are contained i n the i n t r u -s i v e r o c k as disseminated g r a i n s . Most molybdenite and p y r r h o t i t e and some c h a l c o p y r i t e and p y r i t e are found i n a quar t z stockwork and f r a c t u r e s i n the h o r n f e l s i c p e r i p h e r y along the southern i n t r u s i v e c o n t a c t . T a k l a - H a z e l t o n Rocks S t r a t i g r a p h i c S e c t i o n . I r o n s t a i n e d and dark grey-green outcrops of i n c l i n e d s t r a t a r e p r e s e n t i n g a s t r a t i g r a p h i c t h i c k n e s s of over 2000 f e e t are exposed along the r i d g e form-i n g the Driftwood P r o p e r t y . The base of the f o r m a t i o n was not seen. The lowermost 1500 f e e t of the s e c t i o n i s composed of sedimentary rocks and the upper 500 f e e t i s a v o l c a n i c assemblage. The b a s a l p o r t i o n of the sedimentary s e c t i o n i s composed of coarse c l a s t i c beds. These grade upwards i n t o beds of f i n e - g r a i n e d sediments and are o v e r l a i n by massive v o l c a n i c flows w i t h some i n t e r c a l a t e d b r e c c i a and t u f f beds and an uppermost t h i n capping of t u f f and t u f f a c e o u s sedimen-2h tary beds. A generalized stratigraphic column based on v i s u a l estimates of bed thicknesses and a few points of known elevation i s shown i n Figure 3« The basal portion of the sections i s composed of grey-wacke and conglomerate beds and lenses a few inches to tens of feet i n thickness. Commonly the beds are graded and bed-ding planes or sharp d i s t i n c t i o n s between i n d i v i d u a l beds are not apparent. Thus, the beds represent a continuous depositional sequence without any major change i n environ-ment of deposition or supply. The middle portion o f the section shows a t r a n s i t i o n from coarse to fine c l a s t i c sedi-mentation. The lower boundary was a r b i t r a r i l y placed where greywacke became the dominant rock type r e l a t i v e to conglome-rate. Conglomerate i s present i n minor quantities probably, as lenses and greywacke, s i l t s t o n e , shale, and a r g i l l i t e become the dominant rock types. The top of the sedimentary unit i s marked by the presence of s i l i c l o u s and calcereous beds. The s i l i c i o u s beds are not cherty chemical p r e c i p i t a t e s but rather fine-grained c l a s t i c debris. They indicate a decrease i n rate of sedimentation and an i n f l u x of a more mature sediment. The volcanic section forms the top of the s t r a t i -graphic column. The bottom i s marked by a basal bed of t u f -faceous sediments that marks the advent of volcanism. Vol-canic flows and brecciated flows are interrupted by the i n t e r c a l a t i o n of at least two t h i n units of pyr o c l a s t l c Figure 3 > GENERALIZED STRATI GRAPHIC COLUMN,. DRIFTWOOD PROPERTY 25 2000' to o < o > 1500' CO o o cr v or < r-O CO 1000 50 0 • -V- Tuff, tuffaceous and volcanic greywacke, siltstone ; minor quartzite Volcanic flows, intercalated breccia and tuff ; basal tuffaceous greywacke Shale, arg i l l i te , siltstone, greywacke; minor quartzite, calcareous shale Greywacke , siltstone , conglomerate, shale Conglomerate, greywacke; minor siltstone and shale LEGEN D A ' - . - " A Tuff, breccia mixed tuffaceous and volcanic sediments Massive volcanics Mixed fine grained clastic and calcareous beds Shale, argillite, siltstone Conglomerate , greywacke material. The lower one i s composed of t u f f and tuffaceous sediments and the upper one of glassy welded t u f f s or flow breccia. The uppermost part of the section i s a complex succession of tuffaceous and sedimentary beds. The sedi-mentary beds are composed of tuffaceous greywacke, greywacke derived from volcanics and minor quartz-rich c l a s t i c detritus and may indicate the return to a predominately sedimentary environment. Conglomerate and Greywacke The two rock types can be described together because they have the same composition and d i f f e r only i n grain s i z e . The rocks are dark grey i n colour with a f a i n t deeplblue or brown cast and weather medium grey or brown with a t h i n chalky or l i m o n i t i c surface layer. The conglomerates have a matrix of greywacke containing rounded and subangular pebbles. Angular fragments are not common but were observed to form a few lenses or beds of *sharpstone' conglomerate. The pebbles are both l i g h t e r and darker than the matrix but frequently blend i n and are discernable only due to subtle differences on the weathered surfaces. In a l l cases fresh fractures pass through and not around the pebbles. Pebbles form up to 60% of the conglomerate beds. In many of the greywacke beds pebbles and gravel form lenses or are uneven-l y dispersed throughout them so that i t i s an arbi t r a r y d i s t i n c t i o n between pebbly greywacke and conglomerate. Thin sections of greywacke showed 80% of the rock to be composed of coarse sand-sized g r a i n s w i t h the remainder a f e r r u g i n -ous matrix of s a l t s i z e d p a r t i c l e s and opaque 'dusty' s u l p h -i d e s or carbonaceous m a t e r i a l . In zones near igneous con-t a c t s f i n e - g r a i n e d brown b i o t i t e may be r e c r y s t a l l i z e d from the matrix. S e v e n t y f i v e percent of the fragments are der-i v e d from v o l c a n i c r o c k s . Most are from p o r p h y r i t i c v o l c a n i c composed of a f e l t e d matte of p l a g i o c l a s e m i c r o l i t e s and f i n e l y disseminated opaque m a t e r i a l and a s m a l l number of fragments are from a microporphyry i n which i r r e g u l a r r a d i a -t i n g groups of f e l d s p a r m i c r o l i t e s i n the i n d i s t i n c t grey groundmass form a cumulophyric t e x t u r e . The remaining 2%y of the fragments i s comprised of c h e r t , a few g r a i n s of c r y s t a l l i n e q u a r t z and a very s m a l l amount of f e l d s p a r , shale c h i p s , and very f i n e l y d i v i d e d white micas and c l a y s . S h a l e , A r g i l l i t e , and S i l t s t o n e The t h r e e rock types were d i s t i n g u i s h e d from each other i n the f i e l d on the b a s i s of t h e i r f f a c t u r i n g . The sh a l e s s p l i t along bedding planes and p a r a l l e l t o them i n t o t h i n p l a t y fragments w h i l e a r g i l l i t e and s i l t s t o n e broke i n t o fragments without r e f e r e n c e to bedding planes. Beds were c a l l e d s i l t s t o n e when the f i r s t t r a c e of a c l a s t i c t e x t u r e c o u l d be d e t e c t e d w i t h an unaided eye. S i l i c i o u s beds were d i s t i n g u i s h e d by t h e i r hardness, toughness, and l i g h t grey c o l o u r . The rock made a r i n g i n g sound when s t r u c k and broke i n t o spoon shaped fragments w i t h c o n c o i d a l 28' f r a c t u r e planes. Calcareous beds were i n d i s t i n g u i s h a b l e i n outcrop from o r d i n a r y shale and a r g i l l i t e beds. However, near the igneous c o n t a c t s they contained c a l c - s i l i c a t e a l t e r a t i o n minerals and durin g g e o l o g i c a l mapping could be e a s i l y t r a c e d w i t h h y d r o c h l o r i c a c i d b o t t l e . M i c r o s c o p i c a l -l y about 15% of the s i l t s t o n e - a r g i l l i t e i s composed of i d e n t i f i a b l e g r a i n s of q u a r t z , f e l d s p a r , and fragments of v o l c a n i c rock and shale while the r e s t i s an indeterminable matrix of s i l t and c l a y s i z e d p a r t i c l e s . A weak banded t e x t u r e i s emphasized by alignment of some of the mineral g r a i n s and f i n e g r a i n s of p y r i t e and carbonaceous m a t e r i a l . Q u a r t z i t e and S i l i c i o u s S i l t s t o n e The beds form t h i n u n i t s i n the s t r a t i g r a p h i c column. The rocks are formed from f i n e g rained c l a s t i c sediments whose maximum g r a i n s i z e i s i n the v e r y - f i n e sand t o f i n e sand s i z e range. On the b a s i s of the s i z e c l a s s i f i c a t i o n the beds range from s i l t s t o n e to very f i n e sandstone. The l a r g e s t g r a i n s observed were 0.2 mm. Most g r a i n s are quartz or perhaps very f i n e g rained c h e r t fragments and minor amounts of p l a g i o c l a s e f e l d s p a r . The matrix appears to be an i r o n - r i c h c l a y and c o n t a i n s a s m a l l percentage of f i n e s e r i c i t e and opaque mi n e r a l s . I t v a r i e s i n volume from i n t e r s t i t i a l amounts i n q u a r t z i t e beds to dominant q u a n t i t i e s i n s i l i c i o u s s i l t s t o n e . No mafic minerals were seen and only minor amounts of mica and opaque minerals could be i d e n t i f i e d i n the matrix. The g r a i n s are surrounded and t i g h t l y packed and held together w i t h the matrix to produce a dense, tough rock w i t h an i n d u r a t e d appearance. Tuffaceous Sediments The outcrops are dark brown i n c o l o u r w i t h a weak t o d i s t i n c t purple c a s t . They are s t r o n g l y j o i n t e d but there i s no s u g g e s t i o n of bedding or p a r t i n g planes or other f o l i a t i o n . Hand specimens show c l a s t i c t e x t u r e w i t h g r a i n s from s i l t t o medium-sand s i z e i n a dark, g l a s s y matrix.. Some specimens show weakly developed bands of c o a r s e r g r a i n s or p r e f e r r e d o r i e n t a t i o n of the g r a i n s . Under the microscope the composition i s seen to be l a r g e l y g r a i n s of v o l c a n i c r o c k s and m i c r o l i t e s or s m a l l l a t h s of p l a g i o c l a s e w i t h some opaque minerals and f i n e , ronimded quartz g r a i n s . A number of g r a i n s of a p a t i t e were observed. These and the f e l d s p a r l a t h s are somewhat corroded but s t i l l m a intain roughly e u h e d r a l o u t l i n e s . The matrix i s l i g h t brown to grey and l o o k s to be composed of g l a s s y m a t e r i a l . I t c o n t a i n s f i n e , r e c r y s t a l l i z e d c h l o r i t e and i n a number of specimens, a l i t t l e c a l c i t e . The abundance of v o l c a n i c fragments and p l a g i o c l a s e g r a i n s over quartz and c h e r t and the g e n e r a l appearance of the matrix can be used to d i f f e r e n t i a t e t u f -faceous rocks from those i n the sedimentary s e c t i o n . 30 V o l c a n i c B r e c c i a T h i s u n i t forms a t h i n bed or group of beds not more than 20 f e e t t h i c k , and l i e s between two v o l c a n i c flow u n i t s . The outcrops are d i s t i n c t l y purple or red-brown i n c o l o u r . Hand specimens show a fragmental t e x t u r e w i t h purple and green fragments up t o £ i n c h across i n a dense, g l a s s y , purple groundmass. Under a microscope the rock appears t o be almost e n t i r e l y composed of g l a s s fragments i n a g l a s s matrix of very s i m i l a r composition. The boundaries of f r a g -ments are almost i n d i s t i n g u i s h a b l e from the matrix. In p o l a r i z e d l i g h t the fragments are s l i g h t l y cloudy or grey i n appearance compared to the matrix but under cro s s e d n i c o l s the matrix shows many minute p o l a r i z a t i o n t i n t s . Fragments are present but form l e s s than 10% of the b r e c c i a by volume. Some fragments are greywacke composed of f i n e v o l c a n i c rock g r a i n s and others are v o l c a n i c r o ck fragments w i t h abundant f i n e opaque minerals. C r y s t a l fragments,are almost a l l p l a g i o c l a s e but one g r a i n of what appeared t o be m i c r o c l i n e was seen. V o l c a n i c s The v o l c a n i c s probably formed flows and flow b r e c c i a s which now occur as j o i n t e d outcrops i n which i n d i v i d u a l beds cannot be r e c o g n i z e d . Two types of v o l c a n i c s were d i f f e r e n t i -ated on the b a s i s of c o l o u r . The more common type i s dark green and shows s m a l l spots of dark mafic minerals. 31 The other type i s a darker green to b l a c k v a r i e t y which may show a few amygdules f i l l e d w i t h c a l c i t e . A l l the v o l c a n i c r o c k s are s t r o n g l y a l t e r e d and c o n t a i n much c h l o r i t e and have c r o s s c u t t i n g f r a c t u r e s c o n t a i n i n g c a l c i t e , e p i d o t e , and sometimes hematite. In the f i e l d the v o l c a n i c s were simply c l a s s i f i e d as 'greenstone 1. M i c r o s c o p i c examination showed the rocks to be completely and thoroughly a l t e r e d . Whether the a l t e r a t i o n i s r e p r e s e n t a t i v e of the r e g i o n a l a l t e r a t i o n i n t e n s i t y or whether i t i s p a r t l y due t o the a f f e c t s of the i n t r u s i v e mass i s u n c e r t a i n . In some t h i n s e c t i o n s from specimens near igneous c o n t a c t s higher grade a l t e r a t i o n a f -f e c t s are obvious and thus the lowest grade a l t e r a t i o n was assumed t o be r e p r e s e n t a t i v e of the r e g i o n a l i n t e n s i t y . The v o l c a n i c s were probably a n d e s i t i c and b a s a l t i c i n composition. They now show only a r e l i c t t e x t u r e w i t h a l t e r e d p l a g i o c l a s e l a t h s i n a matrix of c h l o r i t e and a c t i n o -l i t e - t r e m o l i t e . No t r a c e of the o r i g i n a l mafic c o n s t i t u e n t s remains. The p l a g i o c l a s e l a t h s are s a u s s u r i t i z e d and have corroded o u t l i n e s . There i s a s i z e v a r i a t i o n shown i n almost a l l the specimens between l a r g e p l a g i o c l a s e l a t h s i n the order of 0 . 2 to 0 . 3 mm. and f i n e p l a g i o c l a s e m i c r o l i t e s i n i n t e r s i t i a l p o s i t i o n s . In the c o a r s e s t grained specimens, p l a g i o c l a s e phenocrysts up t o 1 .0 mm. long were seen. The l a t h s commonly show no twinning or at best have poorly de-f i n e d , broad t w i n l a m e l l a e from which a maximum a n o t h i t e content of An ho could be determined. C h l o r i t e and t r e m o l i t e -a e t i n o l i t e are i n t i m a t e l y a s s o c i a t e d and enclose the p l a g i o -c l a s e t o produce an o p h i t i c t o s u b o p h i t i c t e x t u r e . The c h l o r i t e i s p l e o c h r o i c green, has almost p a r a l l e l e x t i n c -t i o n and i s probably of the p e n n i n i t e type. The t r e m o l i t e -a c t i n o l i t e i s weakly p l e o c h r o i c green t o blue-green and may be a t r e m o l i t i c hornblende i n some cases. A l l specimens c o n t a i n v a r y i n g amounts of c a l c i t e and opaque mi n e r a l s . Most of the opaques are magnetite and the g r a i n s were ob-served t o form from l e s s than one percent to as much as 10% of the rock. The g r a i n s most f r e q u e n t l y occur as f i n e - g r a i n e d , rounded t o euhedral c r y s t a l s but i n one specimen, l a r g e s k e l e t a l g r a i n s were o b s e r v e d . i n which only p a r t s of the o r i g i n a l cube remained. E p i d o t e forms up t o 5% of some specimens but i n most i t i s minor and forms only a few i n -d i v i d u a l or aggregated g r a i n s . Some specimens c o n t a i n minor amounts of c l i n o z o i s i t e and very f i n e - g r a i n e d , micaceous, aggregated masses of what appear t o be b i o t i t e or s t i l p n o -melane. The i n d i v i d u a l p l a t e s are very f i n e g r a i n e d , have str o n g p l e o c h r o i s m from y e l l o w to brown to r e d d i s h brown, and show moderate a n i s o t r o p i s m . C h l o r i t e and the s t i l p h o -melane or b i o t i t e forms the spots i n the 'spotted v o l c a n i c s 1 and r e p r e s e n t a t o t a l replacement of the o r i g i n a l mafic g r a i n s . I n t r u s i v e Rocks The i n t r u s i v e body i s a s m a l l s t o c k along the east f l a n k of a low r i d g e w i t h i r r e g u l a r s p l a y i n g dykes across the c r e s t of the r i d g e . The outcrops forming the main part of the r i d g e are gossanous reddish-brown i n c o l o u r and form steep to moderately steep s l o p e s . The goasanous appearance i s due to a t h i n s u r f a c e s t a i n of i r o n oxides and does not c o n s t i t u t e an e x t e n s i v e gossanous capping. F r e s h to weakly a l t e r e d r o c k l i e s immediately beneath the s t a i n . Wear the bottom of the gossanous outcrops i s a broad b e n c h - l i k e area that forms a break i n the slope p r o f i l e . Below t h i s the i n t r u s i v e rocks formna grey p r e c i p i t o u s c l i f f w i t h a r e l i e f of over 300 f e e t . The i n t r u s i o n has an i r r e g u -l a r p l a n due t o the anastamosing dyke p a t t e r n near the top of the i n t r u s i v e mass along the r i d g e c r e s t . Despite the i r r e g u l a r appearance and abundance of dykes, the i n t r u s i v e rocks c o n s t i t u t e a s i n g l e i n t r u s i v e body w i t h a massive core from which the dykes have i s s u e d . No c r o s s - c u t t i n g r e l a t i o n s between igneous rocks were seen nor was there any evidence f o r more than one p e r i o d or s p e c i e s of magmatic i n t r u s i o n . In the f i e l d the rock was mapped as a g r a n o d i o r i t e porphyry but zones of d i f f e r e n t a t i o n r e f l e c t i n g v a r i a b l e c o o l i n g h i s t o r i e s were obvious. The m a j o r i t y of hand specimens were co a r s e , g r e y - c o l o u r e d p o r p h y r i e s c o n t a i n i n g t i g h t l y - p a c k e d p l a g i o c l a s e phenocrysts to 0 .3 inches i n l e n g t h w i t h i n t e r -mingled s m a l l e r needles of hornblende, s m a l l p l a t e s of b i o -t i t e , and i n some cases s u l p h i d e m i n e r a l s . S c a t t e r e d i n -f r e q u e n t l y throughout are l a r g e p o i k i l i t i c potash f e l d s p a r phenocrysts up t o 1.6 inches i n l e n g t h and 0 .5 inches i n width. The i n t e r s t i t i a l m a t e r i a l i s extremely f i n e - g r a i n e d and was judged to be an assemblage of q u a r t z , f e l d s p a r , and mafic and a c c e s s o r y m i n e r a l s . Weak f o l i a t i o n i s developed i n many hand specimens by p r e f e r r e d o r i e n t a t i o n of the p o i k i l i t i c f e l d s p a r phenocrysts and mafic m i n e r a l s . There i s no apparent r e l a t i o n betx^een the v a r i o u s p a r t s of the i n t r u s i v e body and i n each outcrop or p a r t of an outcrop the f o l i a t i o n seems t o have a l o c a l o r i e n t a t i o n . T e x t u r a l and c o m p o s i t i o n a l v a r i a t i o n s are most obvious i n border and con-t a c t zones where the i n t r u s i o n i s f i n e r - g r a i n e d and l a c k s the l a r g e potash f e l d s p a r phenocrysts. In other zones pot-ash f e l d s p a r i s abundant as l a r g e phenocrysts and s m a l l e r g r a i n s throughout the matrix and the rock was mapped as a q u a r t z monzonite porphyry. Igneous c o n t a c t s w i t h bedded rocks are r e a d i l y d l s -c e r n a b l e . A l l the dykes show sharp, d i s t r i c t boundaries w i t h a t h i n c h i l l e d zone. The width of the c h i l l zone i s governed by the t h i c k n e s s of the dyke and the s t r a t i g r a p h i c p o s i t i o n or l e v e l of emplacement of the dyke i n the s t r a t i g r a p h i c column. The t h i n dykes and those i n t r u d i n g the upper u n i t s of the s t r a t i g r a p h i c column i n t o the v o l c a n i c rocks along the top of the r i d g e , have a t h i n c h i l l e d selvage and a border zone up to 1 i n c h t h i c k i n which the g r a i n s i z e i s f i n e r than the r e s t of the rock and more uniform. In the t h i c k e r dykes i n the lower p o r t i o n of the s t r a t i g r a p h i c column the c h i l l e d margin was observed t o be 2 inches i n width and the border e f f e c t w i t h diminished g r a i n s i z e and u n i f o r m l y - s i z e d g r a i n s extended to a width of 6 to 8 inches. The c h i l l zone i s a dark, g l a s s y band which c o n t a i n s a few s c a t t e r e d phenocrysts of p l a g i o c l a s e and f i n e p l a t e s of b i o t i t e which show a f o l i a t i o n p a r a l l e l to the c o n t a c t . The con t a c t along the main p o r t i o n s 6f the i n t r u s i v e mass i s not as s h a r p l y d e f i n e d as i n the dykes. As the i n t r u s i v e c o n t a c t i s approached, the porphyry becomes l e s s coarse and the phenocrysts d i m i n i s h i n s i z e so t h a t the s i z e d i f f e r e n c e between the phenocrysts and the r e s t of the g r a i n s d i m i n i s h e s . The e f f e c t i s v i s i b l e over tens of f e e t and f i n a l l y r e s o l v e s i n a border zone that i s e q u i g r a n u l a r . Along the border zone the i n t r u s i o n i s composed of p l a g i o c l a s e and o r i e n t e d needles of hornblende, f i n e mica and a extremely f i n e g r a i n e d matrix. The a c t u a l c o n t a c t i s a zone from 2 inches to a f o o t wide that i s shear-ed, b r e c c i a t e d and s i l i c i f i e d . Quartz forms i r r e g u l a r patche and f r a c t u r e f i l i n g s of coarse, c r y s t a l l i n e , white, vein-type q u a r t z i n a g r a n u l a r rock w i t h an a p l i t i c t e x t u r e t h a t i s composed of f i n e quartz and some f e l d s p a r and su l p h i d e g r a i n s To country rock a d j o i n i n g the c o n t a c t zone i s f o l i a t e d but does not appear t o be s i l i c i f i e d or otherwise s t r o n g l y metasomatised. The i n t r u s i o n appears to be only weakly a l t e r e d . Only i n the v i c i n i t y of diamond d r i l l hole Number 1 does the f e l d s p a r show any s u g g e s t i o n of a l t e r a t i o n and e l s e -where the only obvious a l t e r a t i o n i s c h l o r i t i z a t i o n of the mafic m i n e r a l s . The composition of the i n t r u s i v e mass a l s o appears to be r e l a t i v e l y homogeneous. Only a few s m a l l x e n o l i t h s were seen and the l a r g e s t of these was not more than one i n c h i n diameter. S t r u c t u r e The Driftwood Property i s u n d e r l a i n by west-dipping beds t h a t have been i n t r u d e d by an i r r e g u l a r l y - s h a p e d mass and numerous dykes of g r a n o d i o r i t e - q u a r t z monzonite porphyry The beds s t r i k e i n a n o r t h w e s t e r l y d i r e c t i o n and have v a r i -a b l e d i p s from twenty f i v e to seventy f i v e degrees towards the southwest. The beds l i e along a r i d g e t h a t forms on the western limb of a major a n t i c l i n e , the e a s t e r n limb of which forms the T s a y t u t Spur. Dips that are steeper than the aver age of f o r t y degrees are seen only i n the p r o x i m i t y of the i n t r u s i v e body. The s t r u c t u r e of the i n t r u s i o n i s h i g h l y i r r e g u l a r w i t h many anastamosing dykes and may be d e s c r i b e d as a chono l i t h . However, the s t r u c t u r e i s easy t o v i s u a l i z e i f the e f f e c t s of topography are c o n s i d e r e d and a number of c r o s s -s e c t i o n s are drawn at v a r i o u s e l e v a t i o n s as shown i n F i g u r e h. The s e c t i o n s cut the cupola and core of a t h i c k , FIGURE 4 ' G E O L O G Y and CROSS S E C T I O N S , 37 DRIFTWOOD PROPERTY D 4000 LEGEND 5500 5000 4500 4000 3500 3 4 ^ Granodiorite- Quartz Monzonite Volcanic Rocks Sedimentary Rocks Bedding Attitude Fault - observed - inferred SCALE 1000 Feet 2000 38 n o r t h w e s t e r l y t r e n d i n g dyke. The western and southwestern r e g i o n of the map i s the area of highest e l e v a t i o n . There the i n t r u s i o n i s exposed as the r o o f zone of the .cupola. The u n d e r l y i n g i n t r u s i v e body has g i v e n r i s e t o many steep, i n t e r f i n g e r i n g dykes t h a t c o n t a i n between s l i c e s of the country rock t h a t a r e , i n e f f e c t , r o o f pendants. Towards the n o r t h e a s t the i n t r u s i o n as exposed at lower e l e v a t i o n s and forms a s i n g l e body at l e a s t 800 f e e t t h i c k that has v e r t i c a l or s t e e p l y northwest-dipping w a l l s . The most n o r t h -e a s t e r n outcrops of the dyke are exposed below *+000 f e e t e l e v a t i o n . At such low e l e v a t i o n s both the n o r t h and south dyke w a l l s are v e r t i c a l or d i p s t e e p l y toward the southeast. Thus, i t appears that at depth the d i p of the dyke changes from a steep northwest or v e r t i c a l d i p to a s o u t h e a s t e r l y d i p . Numerous s m a l l dykes are found along the border of the main dyke. Most can be fo l l o w e d f o r only s h o r t d i s t a n c e s . A few, such as the dyke i n the southern part of the map-area and two p a r a l l e l dykes i n the n o r t h - c e n t r a l p a r t of the map are continuous f o r s e v e r a l hundred f e e t . The most prominent trend of the dykes i s n o r t h e a s t e r l y roughly p a r a l l e l to the tre n d of the main i n t r u s i o n . A n o r t h to northwest trend i s a l s o common. The dykes i n most cases have steep d i p s . In two cases, s i l l - l i k e bodies have formed. One i s at the ex-treme n o r t h e r n l i m i t of mapping where a body of medium-g r a i n e d , p o r p h y r i t i c g r a n o d i o r i t e has a l o p o l i t h i c s t r u c t u r e . 39 The other i s i n the southeast corner of the map where a t h i n g r a n o d i o r i t e body i s conformable w i t h the west-dip-ping beds f o r a d i s t a n c e of about 200 f e e t and then at the n o r t h e r n end s w e l l s i n t o a wide, s t e e p l y d i p p i n g dyke w i t h a n o r t h e a s t e r l y s t r i k e . The i n t r u d e d beds have been deformed by the i n t r u s i o n . The n o r t h to northwest s t r i k e i s preserved but the dips are g e n e r a l l y s t e e p e r than the average f o r the r e g i o n . The main mass of the i n t r u s i o n appears to have f o r c e f u l l y i n t r u d e d the beds and f o l d e d them about n o r t h to northwest-trending axes. At higher e l e v a t i o n s i n the r o o f zone of the c u p o l a , the beds have been u p l i f t e d and domed. At the c r e s t of the r i d g e the beds are not deformed but have been u p l i f t e d i n b l o c k s t h a t r e t a i n t h e i r moderate w e s t e r l y d i p s and form v o l c a n i c d i p s l o p e s along the west f l a n k of the r i d g e . A f a u l t i s b e l i e v e d to be marked by a prominent n o r t h - s t r i k i n g g u l l e y i n the southeast of the mapped area. Outcrops on both s i d e s of the g u l l e y are sheared and coarse b r e c c i a specimens w i t h vuggy q u a r t z - l i n e d c a v i t i e s and a c h a l c e d o n i c matrix are found i n the g u l l e y . From the l i n -ear trend of the g u l l e y , the f a u l t a t t i t u d e i s i n f e r r e d t o be n o r t h w i t h a d i p about 65 degrees e a s t . Three v e r t i c a l or s t e e p l y d i p p i n g f a u l t s were observed. A n o r t h - s o u t h f a u l t cuts the r i d g e near the southern l i m i t of mapping. No sense of movement could be determined. Two other ko f a u l t s are i n the n o r t h - c e n t r a l p o r t i o n of the map c l o s e to the i n t r u s i v e c o n t a c t . Both trend e a s t e r l y and i n the case of at l e a s t the more western f a u l t have the south si d e up-thrown. Three normal f a u l t s were mapped. One l i e s to the east of the g u l l e y , has a n o r t h e a s t e r l y s t r i k e and a d i p towards the southeast of 65 degrees. The other two f a u l t s cut the r i d g e c r e s t . The most southern of these s t r i k e s n o r t h e a s t and has a r e l a t i v e l y f l a t d i p or 3 2 degrees to the southeast. The t r a c e i s exposed on the c l i f f f a c e and shows a downthrown t h i n wedge of v o l c a n i c r o c k s . The s t r a t i g r a p h i c throw i s i n the order of two hundred f e e t . The n o r t h e r n f a u l t i s a l s o r e l a t i v e l y f l a t - l y i n g and cuts sedimentary p o r t i o n s of two r o o f pendants. Shearing adjacent to the main i n t r u s i v e contact has formed a b i o t i t e s c h i s t or p h y l l o n i t e from the horn-f e l s i n c e r t a i n areas. I t i s best developed around the northernmost part of the main i n t r u s i o n and to the east of diamond d r i l l hole Number 3« In these l o c a l i t i e s the w i d t h of the s c h i s t o s e zone i s about t e n f e e t . The s c h i s t o -s i t y i s g r a d a t i o n a l from a w e l l developed b i o t i t e s c h i s t at the contact to a n o n f o l i a t e d h o r n f e l s that i s c h a r a c t e r i s -t i c of the thermal a u r e o l e . hi PETROLOGY OF THE STOCK I n t r o d u c t i o n Twenty three t h i n s e c t i o n s from outcrops r e p r e s e n t -i n g the c o n t a c t , border, c o r e , and dyke environments were examined. E i g h t e e n s e c t i o n s were s e l e c t i v e l y s t a i n e d w i t h sodium c o b a l t i n i t r a t e to d i s t i n g u i s h p l a g i o c l a s e , o r t h o c l a s e and quartz g r a i n s . The t h i n s e c t i o n s were then p r o j e c t e d w i t h a 35 m i l l i m e t e r s l i d e p r o j e c t o r equipped w i t h a wide angle lens from a d i s t a n c e of 15 to 25 f e e t onto a l a r g e g r i d w i t h 6 i n c h squares. Areas were determined and volume-percent modal compositions determined. The r e s u l t s are e q u i v a l e n t to 750 to 1150 counts using standard m i c r o s c o p i c p o i n t counting techniques. The method was found t o be good f o r r a p i d a n a l y ses of the c o a r s e r - g r a i n e d r o c k s . The use of s t a i n e d s e c t i o n s i s e s s e n t i a l and a p r o j e c t o r w i t h a long f o c a l plane r e s u l t i n g i n high m a g n i f i c a t i o n i s a d v i s a b l e . The modes of the c o a r s e s t grained rocks were c o n s i s t e n t l y r e -producable by t h i s method but the p o r p h y r i t i c rocks w i t h a f i n e - g r a i n e d matrix y i e l d e d r e s u l t s which v a r i e d by about 25 p e r c e n t . In a number of cases where the matrix was extremely f i n e - g r a i n e d , only the phenocrysts were counted from the p r o j e c -t i o n s and standard microscopic p o i n t counting had to be used t o determine the matrix compositions. The modes d e r i v e d from the volume-percent d e t e r m i n a t i o n s were converted t o weight-percent and the i d e a l chemical composition of the rock was c a l c u l a t e d i n terms of oxides using a f o r t r a n programme ac c o r d i n g to the h2 method of D i e t r i c h and Sheehan, (196l+). Textures Textures i n a l l the rocks are p o r p h y r i t i c . The pheno-c r y s t s are of v a r i o u s s i z e s but do not develop a s e r i a t e tex-t u r e . Rather, there i s a number of s i z e groups such as the l a r g e , p o i k i l i t i c o r t h o c l a s e s , somewhat s m a l l e r p l a g i o c l a s e phenocrysts, and the much s m a l l e r needles of hornblende and p l a t e s of b i o t i t e . The matrix i n a l l cases i s a r e l a t i v e l y u n i f o r m l y - s i z e d g r a n u l a r to e x t r e m e l y - f i n e g r a n u l a r mosaic of q u a r t z , o r t h o c l a s e , p l a g i o c l a s e , accessory m i n e r a l s , a l t e r a t i o n m i n e r a l s , and s u l p h i d e s . D i f f e r e n c e s i n f a b r i c and t e x t u r e w i t h i n the s t o c k enable f o u r environments to be d i s t i n g u i s h e d : border zone, dyke, core zone, and contact zone. These have three corresponding t e x t u r a l types. The main t e x t u r a l type i s a p o i k i l i t i c porphyry. I t forms the cores of the l a r g e r dykes and the core zone of the main i n t r u s i v e body and r e p r e s e n t s almost n i n e t y - e i g h t per-cent of the volume of the i n t r u s i v e mass. The rock may be d e s c r i b e d more f u l l y as a 'crowded porphyry' w i t h an i n t e r -s t i t i a l , g r a n u l a r t e x t u r e . The term 'crowded porphyry' i s used because from *+5 to 35 percent of the rock i s composed of phenocrysts. The crowded appearance and l a r g e , p o i k i l i t i c o r t h o c l a s e phenocrysts are the d i a g n o s t i c c h a r a c t e r i s t i c s . The border zone comprises about two percent of the t o t a l volume of the i n t r u s i o n and forms the c h i l l e d margins ^3 of the stock and dykes. Two v a r i e t i e s of porphyry are d e v e l -oped i n the border zone. The more s t r i k i n g i s a g l a s s y , c h i l l e d margin t h a t i s developed along some of the dyke w a l l s . I t v a r i e s i n t h i c k n e s s from a t h i n selvage to about two inches wide and i s a porphyry i n which p l a g i o c l a s e and a few mafic phenocrysts are contained i n a dark, g l a s s y matrix. The other v a r i e t y i s by f a r the more abundant and widespread. I t i s a porphyry i n which there i s only s l i g h t d i f f e r e n c e i n s i z e between the phenocrysts and matrix. I t grades from an almost e q u i g r a n u l a r f i n e - g r a i n e d rock at the i n t r u s i v e contact t o a w e l l developed porphyry over a d i s t a n c e of s i x to e i g h t i n -ches i n the s m a l l e r dykes and up to twenty f e e t i n the main i n t r u s i o n . The l e a s t common t e x t u r a l type r e p r e s e n t s a f r a c t i o n of a percent of the t o t a l volume of the i n t r u s i o n . I t i s a l e u c o c r a t i c rock w i t h an a p l i t i c appearance t h a t i s found i n a s m a l l r e s t r i c t e d zone near the southern c o n t a c t of the st o c k c a l l e d the contact zone. The rock has a r e l a t i v e l y s m a l l p r o p o r t i o n of p l a g i o c l a s e phenocrysts set i n an a p l i t i c groundmass. I t appears t o grade i n t o a r e g u l a r p o i k i l i t i c porphyry t o the n o r t h and no t r a c e of i t could be seen on the c l i f f f a c e some two hundred f e e t to the west. A some-what s i m i l a r a p l i t i c rock can be found along p a r t s of the e a s t e r n i n t r u s i v e c o n t a c t w a l l adjacent to the i n t r u d e d sedimentary r o c k s . In these l o c a t i o n s a contact zone a few in c h e s t h i c k can be seen between the h o r n f e l s and border zone. The rock has an a p l i t i c matrix that c o n t a i n s abundant, i r -r e g u l a r white quartz s e g r e g a t i o n s . M i n e r a l Composition of the I n t r u s i o n F e l d s p a r s are the most abundant minerals i n the stock and form the l a r g e s t g r a i n s . The l a r g e p l a g i o c l a s e pheno-c r y s t s are s t r o n g l y twinned and zoned i n an o s c i l l a t o r y -normal manner. I n d i v i d u a l growth zones are of d i f f e r i n g t h i c k n e s s e s but are u s u a l l y t h i n so that a l a r g e number of zones or groups of zones are observed i n each c r y s t a l . The maximum a n o r t h i t e content i s found i n the cores of the c r y s -t a l s and ranges from An kh to An 3 9 w i t h An ko most common. From the ce n t r e outward complex o s c i l l a t o r y - n o r m a l zoning i s observed and there i s a decrease to a minimum a n o r t h i t e con-t e n t of An 2 8 . The most f r e q u e n t l y observed a n o r t h i t e content i n the outermost zones i s from An 3 0 to An 3 2 . Small p l a g i o -c l a s e l a t h s and m i c r o l i t e s form up to 25 percent of the matrix. Twinning i s d i f f i c u l t t o d i s t i n g u i s h but where i t could be r e s o l v e d and the a n o r t h i t e content measured, i t was found t o vary from An 27 to An 3 2 . Thus, i t appears t h a t the a n o r t h i t e content of the p l a g i o c l a s e i n the matrix i s the same or s l i g h t l y l e s s than the outermost zones of the l a r g e p l a g i o c l a s e phenocrysts. The p l a g i o c l a s e v a r i e s from b a s i c to a c i d i c andesine and the average a n o r t h i t e content i s about An 3!+. h5 Potash f e l d s p a r i s o r t h o c l a s e and forms l a r g e , p o i k i l i -t i c phenocrysts and f i n e - g r a i n e d anhedral granules i n the matrix. The g r a i n s i n the matrix are intergrown w i t h quartz and p l a g i o c l a s e . The phenocrysts are euhedral and u s u a l l y show c a r l s b a d twinning. Abundant i n c l u s i o n s are s m a l l , o r i -ented c r y s t a l s and g r a i n s of hornblende, p l a g i o c l a s e , and o c c a s i o n a l l y b i o t i t e and qu a r t z . In a number of i n s t a n c e s an unusual mantling e f f e c t or corona of o r t h o c l a s e around a l a r g e g r a i n of p l a g i o c l a s e are observed. The r e s u l t i s a combined phenocryst which c o n t a i n s a l a r g e g r a i n of p l a g i o -c l a s e rimmed by o r t h o c l a s e . The p l a g i o c l a s e core shows weakly developed twinning and zoning and has a ragged, s t r o n g l y corroded or resorbed o u t l i n e . Quartz i s found i n specimens of the i n t r u s i v e rock as very s m a l l i n t e r s t i t i a l g r a i n s i n the matrix along w i t h pot-ash f e l d s p a r and sometimes p l a g i o c l a s e . The quartz g r a i n s are intergrown w i t h each other and w i t h the f e l d s p a r s i n an anhedral i n t e r l o c k i n g mosaic. The mafic minerals are hornblende and b i o t i t e . Horn-blende i s the more abundant of the two. I t forms p r i s m a t i c c r y s t a l s and i s green i n c o l o u r w i t h yellow-green to dark green pleochroism. Two v a r i e t i e s of b i o t i t e are found. One type forms l a r g e , s c a t t e r e d p l a t e s and t h i n hexagonal "books" and appears t o be a r e l a t i v e l y e a r l y mafic c o n s t i t u e n t i n the porphyry. The other type forms f i n e , shredded-looking i n t e r -growths i n the q u a r t z - f e l d s p a r matrix and can be regarded as it6 a younger or 'secondary' b i o t i t e . T h i s f i n e g r a i n e d , or secondary, b i o t i t e appears to be commonly a s s o c i a t e d w i t h the s u l p h i d e s and was observed i n some cases to weakly r e -p l a c e or at l e a s t r i m the hornblende. Both the coarse b i o -t i t e and hornblende are at l e a s t p a r t l y r e p l a c e d by c h l o r i t e . Accessory minerals are contained i n .the matrix of the r o c k and a l s o sometimes i n the outer zones of p o i k i l i t i c f e l d s p a r phenocrysts. They c o n s i s t of magnetite, s u l p h i d e s , sphene, and a p a t i t e . Magnetite i s the most abundant and forms s m a l l , equant c r y s t a l s t h a t are d i s t r i b u t e d throughout a l l p a r t s of the matrix. A p a t i t e occurs as s m a l l p r i s m a t i c c r y s t a l s t h a t are randomly s c a t t e r e d . Sphene shows a s i z e v a r i a t i o n from f i n e g r a i n e d to r e l a t i v e l y l a r g e g r a i n s and i s very i r r e g u l a r l y d i s t r i b u t e d . Most sphene g r a i n s have the c h a r a c t e r i s t i c rhombic cross s e c t i o n s and some show twinning. Minerals formed as a l t e r a t i o n products are c h l o r i t e , c a l c i t e , e p i d o t e , s e r i c i t e , c l a y minerals ( m o n t m o r i l l o n i t e ? ) , and hydrous i r o n oxides. The f e l d s p a r s are not s t r o n g l y a l t e r e d but d i f f e r e n c e s i n a l t e r a t i o n i n t e n s i t y can be seen i n them throughout the v a r i o u s p a r t s of the i n t r u s i o n . Most f r e q u e n t l y the f e l d s p a r s have a clouded or corroded appear-ance, e s p e c i a l l y i n zones near the edges of zoned p l a g i o -c l a s e s; , S a u s s u r i t i z a t i o n has r e s u l t e d in'.the breakdown and r e c o n s t i t u t i o n of the f e l d s p a r s i n t o very f i n e - g r a i n e d i n t e r -growths of z o i s i t e or e p i d o t e , a l b i t e , s e r i c i t e , c a l c i t e , and h7-other c o n s t i t u e n t s . In the more a l t e r e d zones s e r i c i t e can be recognized along cleavage planes and f r a c t u r e s . In the most h i g h l y a l t e r e d zones a s s o c i a t e d w i t h m i n e r a l i z a t i o n , a l t e r a t i o n has produced s e r i c i t e , c l a y minerals and c a l c i t e . The c l a y and s e r i c i t e form c r y s t a l l i t e s t h a t are p e r v a s i v e throughout the f e l d s p a r s but are more s t r o n g l y developed along g r a i n boundaries. Because of the extremely s m a l l g r a i n s i z e and e r r a t i c d i s t r i b u t i o n of c l a y c o n c e n t r a t i o n s , micro-s c o p i c examination cannot c o n f i r m the type of c l a y minerals p r e s e n t . I t i s most l i k e l y t h a t the c l a y i s a mixture of m o n t m o r i l l o n i t e and hydromica. C h l o r i t e has formed as an a l t e r a t i o n product of horn-blende and b i o t i t e . I t i s developed i n s c a l y masses and f i n e g r a i n e d aggregates. The s p e c i e s i s probably p r o c h l o r i t e and p o s s i b l y p e n n i n i t e . C a l c i t e i s found as i n t e r s t i t i a l g r a i n s i n the m i n e r a l i z e d p a r t s of the i n t r u s i o n e s p e c i a l l y i n zones where th e r e i s c l a y , s e r i c i t e , or strong s a u s s u r i t i c a l t e r a t i o n . E p i d o t e i s a r a r e c o n s t i t u a n t that occurs as s m a l l g r a i n s throughout a l l p a r t s of the i n t r u s i o n . Hydrous i r o n oxides form minor e n c r u s t a t i o n s along f r a c t u r e s . The substance appears to be a l a t e a l t e r a t i o n product formed by o x i d a t i o n and p e r c o l a t i o n of groundwaters. P l a t e 1: Q u a r t z - f e l d s p a r mosaic w i t h r e l a t i v e l y u n i form g r a i n s i z e i n a l a s k i t e . Cros-sed n i c o l s . M a g n i f i c a t i o n X 58. P l a t e 2 : Coarse grained g r a n o d i o r i t e ('crowded porphyry'). P l a g i o c l a s e , o r t h o c l a s e , and b i o t i t e phenocrysts w i t h i n t e r g r a n u l a r q u a r t z - f e l d s p a r . Crossed n i c o l s . M a g n i f i c a t i o n X 58. P l a t e 3* Matrix i n quartz monzonite porphyry showing i n t e r l o c k i n g q u a r t z - f e l d s p a r , shredded b i o t i t e , c a l c i t e , and minor sphene. Crossed n i c o l s . M a g n i f i c a -t i o n X 53. P l a t e h: G r a n o d i o r i t e w i t h f i n e - g r a i n e d quartz f e l d s p a r matrix, hornblende, and an-h e d r a l phenocrysts of o r t h o c l a s e . Crossed n i c o l s . M a g n i f i c a t i o n X 58. 50 P l a t e 5 : Phenocrysts of p l a g i o c l a s e and hornblende i n a f i n e - g r a i n e d matrix. Grossed n i c o l s . M a g n i f i c a t i o n X 5 3 . P l a t e 6 : Zoned phenocrysts of p l a g i o c l a s e and g r a i n s of hornblende i n f i n e grained matrix of q u a r t z - f e l d s p a r s , b i o t i t e , and minor a p a t i t e . Grossed n i c o l s . M a g n i f i c a t i o n X 5 8 . 51 P l a t e 7 : Zoned and twinned phenocryst of p l a g i o c l a s e . Crossed n i c o l s . M a g n i f i c a t i o n X 5 3 . P l a t e 3 : P o r t i o n of composite p l a g i o c l a s e -o r t h o c l a s e phenocryst. P l a g i o c l a s e i n core shows zoning, twinning, a p a r t l y corroded o u t l i n e w i t h p o i l i l i -t i c border and i s mantled by p o i k i l i -t i c r i m of o r t h o c l a s e . Crossed n i c o l s . M a g n i f i c a t i o n X 5 8 . 52 C l a s s i f i c a t i o n of Rock Type The sto c k seems to have been i n t r u d e d as a s i n g l e mass of magma. No i n t e r n a l c r o s s c u t t i n g r e l a t i o n s , i n t e r n a l c o n t a c t s , nor b r e c c i a zones were observed. The modal average and m i n e r a l o g i c a l v a r i a t i o n f o r the e i g h t e e n t h i n s e c t i o n s examined i s g i v e n i n Table 11. The modal average i s prob-a b l y a c l o s e approximation of the bulk composition of the s t o c k . Table 11: ¥eight-Percent Compositional Average and C o m p o s i t i o n a l Range f o r 18 Specimens. Average Standard C o m p o s i t i o n a l ( %) D e v i a t i o n • Range ( %) potash f e l d s p a r 23.0 5.7 1^.3 - 39.8 p l a g i o c l a s e . ^ 7 .0 6.8 29.1+ - 51+. 5 quartz 2.9 11.9 - 23.5 hornblende 12.0 5.6 1.2 - 22.5 b i o t i t e 1.9 1.9 0 - 7 .0 c h l o r i t e 0.8 0 - 3 . 5 The t e r n a r y diagram ( F i g u r e ^ based on the e s s e n t i a l m inerals q u a r t z - o r t h o c l a s e - p l a g i o c l a s e r e p r e s e n t s at l e a s t s e v e n t y - e i g h t percent by weight of the rock. The remainder i s composed of mainly mafic minerals and these are r e l a t i v e l y c o n s i s t e n t i n abundance throughout the i n t r u s i o n . Using the nomenclature of P e t e r s o n ( i960) f o r g r a n i t i c r o c k s , i t can be seen from F i g u r e 5 that the composition of the Driftwood s t o c k v a r i e s from g r a n o d i o r i t e to quartz monzonite and the average composition of the e i g h t e e n specimens l i e s d i r e c t l y on the g r a n o d i o r i t e - q u a r t z monzonite boundary l i n e . 53 F i g u r e 5: C l a s s i f i c a t i o n of the Driftwood i n t r u s i o n based on modal Q u a r t z - O r t h o c l a s e - P l a g i o c l a s e . 18 specimens used. ( A f t e r Peterson, i 9 6 0 ) QUARTZ • Border Zone o Core Zone + Dyke x Contact Zone • Compositional Average The average c o l o u r index f o r both the g r a n o d i o r i t e and q u a r t z monzonite i s i d e n t i c a l at 1 5 . 6 . The s o l i t a r y specimen i n the quartz monzonite f i e l d nearest the g r a n i t e boundary has a c o l o u r index of 7 . 6 and i s t h e r e f o r e , more c o r r e c t l y c l a s s e d a l e u c o c r a t i c quartz monzonite or a l a s k i t e . 5h V a r i a t i o n s W i t h i n the Stock V a r i a t i o n i n the s t o c k i s evident i n t e x t u r a l , minera-l o g i c , and chemical d i f f e r e n c e s . The m i n e r a l o g i c a l and modal data suggest that three rock types w i t h three corresponding t e x t u r a l types can be r e c o g n i z e d i n the i n t r u s i v e mass. The porphyry w i t h f i n e - g r a i n e d matrix found along some of the dyke w a l l s and the p o r p h y r i t i c rock of the border zone as w e l l as the porphyry forming the dykes i s , i n a l l cases ex-amined, g r a n o d i o r i t e . The p o i k i l i t i c porphyry i n the core of the i n t r u s i v e mass and the l a r g e s t dykes i s g r a n o d i o r i t e or quartz monzonite. The a p l i t i c , l e u c o c r a t i c , most h i g h l y d i f f e r e n t i a t e d r o c k i n what i s termed the c o n t a c t zone, i s a l a s k i t e . Chemical v a r i a t i o n w i t h i n the i n t r u s i o n was deduced from modal compositions. A F o r t r a n programme was used to c a l c u l a t e the chemical compositions of the specimens from the volume-percent modal a n a l y s i s using i d e a l chemical com-p o s i t i o n s f o r the minerals. Representations of the r e s u l t s are shown i n a Larsen v a r i a t i o n diagram (Larsen, 1 9 3 8 ) and a t e r n a r y Ca0-Na 20-K 20 p l o t of Nockolds and A l l e n ( 1 9 5 3 ) . The Larsen v a r i a t i o n diagram ( F i g u r e 6 ) shows the amounts of i n d i v i d u a l oxides and the sum of FeO plus F e 2 0 3 plus MgO r e l a t i v e t o a base of 1/3 S i 0 2 + K 20 - (MgO +- FeO 4- CaO). T h i s r e p r e s e n t a t i o n was used r a t h e r than the more common repre-s e n t a t i o n s using S i 0 2 or some other oxide as a base value be-cause i t p r o v i d e s a much l a r g e r range along the a b s i s s c a . 70 % 0X1DES . S i0 2 , A l 2 0 3 A Mg0-Fe0-Fe 2 0 3 o CaO o Na 2 0 • K 2 0 Specimen Type • border zone 4* dyke O core zone contact zone FIGURE 6 LARSEN VARIATION DIAGRAM OQ_ 10 t j - ^ + Q 14 OOP 16 18 1/3 S i 0 2 4 K 2 0 - (Mg0+FeOf CaO) i 20 22 \-8 L 6 k 4 24 FeO calculated as (FeO t Fe 2 03) 56 The v a r i a t i o n diagrams show the t r a n s i t i o n from g r a n o d i o r i t e to quartz monzonite and a l a s k i t e . . Si02 and show s i m i l a r behaviour by i n c r e a s i n g i n the quartz monzonite and a l a s k i t e . K2O has by f a r the g r e a t e r r e l a -t i v e v a r i a t i o n . Si02 i n 15 out of 18 samples ranges from 6 2 to 66 percent and the maximum v a r i a t i o n i s only about 13$. The maximum v a r i a t i o n f o r the ICpO i s almost 250 percent between the a l a s k i t e and the l e a s t p o t a s h - r i c h g r a n o d i o r i t e . The CaO and sum of Mgo and i r o n oxides be-have i n a s i m i l a r manner and have an o v e r a l l decrease towards the quartz m o n z o n i t e - a l a s k i t e f i e l d . The CaO has a r e l a t i v e v a r i a t i o n up to 100 percent and the mafic oxides up t o 36O percent. However, there i s a g r e a t e r s c a t t e r of p o i n t s along the curve f o r the t o t a l mafic oxides than f o r any other oxide. AI2O3 and Na20 are s i m i -l a r and both remain at r e l a t i v e l y constant amounts and show very l i t t l e v a r i a t i o n . The Nockolds and A l l e n t e r n a r y r e p r e s e n t a t i o n , F i g u r e 7> shows the d i f f e r e n t i a t i o n t r e n d from a parent g r a n o d i o r i t e magma to quartz monzonite and a l a s k i t e . The K2O i s seen to i n c r e a s e r e l a t i v e to CaO while the Na20 remains r e l a t i v e l y constant. 57 F i g u r e 7'> D i f f e r e n t i a t i o n trend of a g r a n o d i o r i t e magma using the system Na20-K20-CaO a f t e r Nockolds and A l l e n , 1953' I n t r u s i v e H i s t o r y The s t o c k i s b e l i e v e d to be a h i g h - l e v e l i n t r u s i o n of probable T e r t i a r y age. A s i n g l e magma has been i n t r u d e d as an i r r e g u l a r stock and r e l a t e d dykes. D i f f e r e n c e s i n c o o l i n g r a t e have r e s u l t e d i n t e x t u r a l v a r i a t i o n throughout the stock. Dykes and the border zone have c h i l l e d margins and l o c a l l y weak f o l i a t i o n p a r a l l e l t o the co n t a c t . This suggests i n t r u s i o n i n t o r e l a t i v e l y c o l d country r o c k s . C o o l i n g was r a p i d and c o n d i t i o n s of n o n e q u i l i b r i u m c r y s t a l -l i z a t i o n are shown by the p o r p h y r i t i c t e x t u r e , a p l i t i c or f i n e g r a i n e d q u a r t z - o r t h o c l a s e - p l a g i o c l a s e matrix, s t r o n g l y zoned p l a g i o c l a s e , p o i k i l i t i c o r t h o c l a s e phenocrysts, and mantles of o r t h o c l a s e about p l a g i o c l a s e . Emplacement of the i n t r u s i o n may have been by f o r c e -f u l i n j e c t i o n . The stock has a d i s c o r d a n t r e l a t i o n s h i p w i t h the i n t r u d e d r o c k s . A l l c o n t a c t s are sharp and there i s no evidence of any s i g n i f i c a n t a s s i m i l a t i o n . The r o o f zone appears to be domed and b o d i l y u p l i f t e d . The s h e l l of s c h i s t about some p a r t s of the i n t r u s i o n may have been formed by the i n t r u s i o n of a v i s c o u s magma. The outward pressure and p o s s i b l y the drag of a v i s c o u s magma r e s u l t e d i n p l a s t i c flowage of the country rock next t o the igneous c o n t a c t (Buddington, 1959). 59 ROCK ALTERATION AND METSMORPHTSM I n t r o d u c t i o n Metamorphic a f f e c t s are evident i n p a r t s of the i n t r u -s i v e body and i n a zone surrounding i t . W i t h i n the i n t r u s i o n , automorphism i s b e l i e v e d to have caused the changes. Outside the s t o c k c o n t a c t metaraorphism has caused an aureole of horn-f e l s t o develop. Dynamic metamorphism probably due to the i n t r u s i o n of the magma has formed a t h i n l a y e r of s c h i s t next t o p a r t s of the i n t r u s i v e w a l l - r o c k . The s c h i s t grades out-ward through a t r a n s i t i o n zone of p h y l l i t e i n t o the h o r n f e l s . The o v e r a l l i n t e n s i t y of a l t e r a t i o n i s low to lower-middle grade. A l t e r a t i o n of G r a n o d i o r i t e - Q u a r t z Monzonite A l t e r a t i o n of the i n t r u s i o n i s regarded to be automor-ph i c mainly because the a l t e r a t i o n i n t e n s i t y d i f f e r s through-out the v a r i o u s p a r t s of the stock. A l s o , no younger igneous rocks are apparent i n the v i c i n i t y . The main mass of the sto c k i s v i r t u a l l y u n a l t e r e d or co n t a i n s only minor c h l o r i t e . The most s i g n i f i c a n t a l t e r a t i o n observed i s i n a r e l a t i v e l y s m a l l zone along the n o r t h - c e n t r a l part of the stock i n the v i c i n i t y of d r i l l hole Number 1. Most of the s u l p h i d e - b e a r i n g f r a c t u r e s and qua r t z v e i n s have t h i n a l t e r a t i o n envelopes. In a l l cases observed, the s t r o n g e s t a l t e r a t i o n i s c o i n c i d e n t w i t h zones of s u l p h i d e m i n e r a l i z a t i o n . The a l t e r a t i o n i s t h e r e f o r e , probably g e n e t i c a l l y a s s o c i a t e d w i t h hydrothermal processes t h a t r e s u l t e d i n s u l p h i d e d e p o s i t i o n . 60 The type of a l t e r a t i o n ean be c l a s s e d as p r o p y l i t i c , a l though the term i s not r i g i d l y d e f i n e d and i s used w i t h d i f f e r e n t i m p l i c a t i o n s by a number of authors. According t o Meyer and Hemley (1967), the p r o p y l i t i c assemblage i n -c l u d e s epidote ( z o i s i t e , c l i n o z o i s i t e ) , a l b i t e , c h l o r i t e , carbonate, commonly w i t h s e r i c i t e , p y r i t e , or i r o n exides and l e s s commonly w i t h z e o l i t e s or m o n t m o r i l l o n i t e s . Creasey (1966) l i s t s a s i m i l a r assemblage but a l s o i n c l u d e s t a l c and k a o l i n i t e as p o s s i b l e members. Sphene or leucoxene ( r u t i l e ) , and a p a t i t e accompany the a l t e r a t i o n and quartz and muscovite are almost always present. In the s e c t i o n s examined c h l o r i t e , c a l c i t e , e p i d o t e , s e r i c i t e , and s a u s s u r i t i z e d f e l d s p a r s were i d e n t i f i e d and the presence of m o n t m o r i l l o n i t e i s suspected. Both sphene and a p a t i t e are present throughout the s e c t i o n s along w i t h magne-t i t e and i r o n s u l p h i d e s . The f i n e - g r a i n e d or secondary b i o -t i t e commonly found i n s u l p h i d e r i c h p o r t i o n s of the s t o c k may p o s s i b l y be p a r t of the a l t e r a t i o n assemblage. However, almost a l l p a r t s of the s t o c k c o n t a i n some f i n e - g r a i n e d b i o -t i t e as component of the matrix. I t , thus, appears t h a t the b i o t i t e i s a l a t e # a f i c mineral that formed w i t h quartz and f e l d s p a r i n a f i n e grained i n t e r g r o w t h d u r i n g the l a s t stages of magmatic c r y s t a l l i z a t i o n . The magma remaining at such a l a t e stage of c r y s t a l l i z a t i o n may w e l l have been e n r i c h e d s u f f i c i e n t l y i n v o l a t i l e s i n some p a r t s of the stock to e f f e c t hydrothermal a l t e r a t i o n and s u l p h i d e d e p o s i t i o n f o l l o w i n g the 61 f o r m a t i o n of b i o t i t e . The observed a l t e r a t i o n assemblage i s compatible w i t h ACF-AKF diagrams of the p r o p y l i t i c a l t e r a t i o n type, as used by Meyer and Hemley and Creasey. The a l t e r a t i o n s p e c i e s observed would be c l a s s e d as the c h l o r i t e - e p i d o t e -c a l c i t e v a r i e t y using Creasey's nomenclature. From Meyer and Hemley's ACF-AKF diagrams, the mineral c o n s t i t u e n t s and r e l a t i o n s observed i n the specimens s t u d i e d can be shown to be compatible w i t h the p r o p y l i t i c a l t e r a t i o n type. The g r a n o d i o r i t e - q u a r t z monzonite co n t a i n s f e l d s p a r phenocrysts and c o a r s e - g r a i n e d hornblende and b i o t i t e i n a M a t r i x of f i n e - g r a i n e d q u a r t z , f e l d s p a r s , and shredded-looking b i o t i t e t h a t was termed 'secondary 1 b i o t i t e . Of these m i n e r a l s , potash f e l d s p a r and quartz are u n a l t e r e d , the p l a g i o c l a s e i s s a u s s u r i t i z e d , and perhaps even weakly a l t e r e d to c l a y minerals w h i l e amongst the mafics, hornblende i s the most s e v e r e l y c h l o r i t i z e d . The coarse b i o t i t e i s only weakly c h l o r i t i z e d and the secondary b i o t i t e i s v i r t u a l l y u n a l t e r e d . According to Meyer and Hemley, potash f e l d s p a r and b i o t i t e can remain as s t a b l e phases i n the p r o p y l i t i c assemblage while p l a g i o -c l a s e and hornblende are unstable i n the presence of c h l o r i t e , s e r i c i t e and c l a y m i n e r als. The only observed occurrences where the mafics i n c l u d -i n g the secondary b i o t i t e were unstable are i n a few specimens t h a t c o n t a i n s i l i c i f i e d f r a c t u r e s or quartz v e i n s w i t h s u l -phide m i n e r a l i z a t i o n . One such f r a c t u r e c o n t a i n i n g p y r i t e , p y r r h o t i t e , and c h a l c o p y r i t e had quartz-potash f e l d s p a r r e -62 placement and was bounded on both w a l l s by a ^ i n c h wide, bleached a l t e r a t i o n envelope. Nearest the f r a c t u r e a l l the mafics were destroyed and the rock was a mass of very f i n e -g r a i n e d s e r i c i t e , clouded p l a g i o c l a s e and p o s s i b l y c l a y . Be-cause of the extremely f i n e - g r a i n e d a l t e r a t i o n products the exact composition could not be determined. The s t a b i l i t y of the potash f e l d s p a r and i n s t a b i l i t y of p l a g i o c l a s e and b i o t i t e allows the p o s s i b i l i t y t h a t the a l t e r a t i o n envelopes represent i n c i p i e n t or weakly developed a r g i l l i c a l t e r a t i o n . Contact Metamorphism Contact metamorphism has r e s u l t e d i n the f o r m a t i o n of a h o r n f e l s zone t h a t envelopes the i n t r u s i v e body. A number of s p e c i e s of h o r n f e l s have developed w i t h a v a r i e t y of com-p o s i t i o n s and t e x t u r e s . T h i s v a r i a t i o n R e f l e c t s the composi-t i o n a l d i f f e r e n c e s of the parent rocks from which the horn-f e l s e s were d e r i v e d and a l s o i n d i c a t e s a d e c r e a s i n g thermal g r a d i e n t away from the i n t r u s i v e c o n t a c t s . Small zones of t a c t i t e have formed from c a l c a r e o u s beds next to both the n o r t h and south i n t r u s i v e c o n t a c t s . The rock formed i s a c a l c - s i l i c a t e h o r n f e l s t h a t c o n t a i n s s m a l l amounts of s u l p h i d e s and i r o n oxides. The a c t u a l con-t a c t r e l a t i o n s could not be observed i n s i t u due t o the p r e c i p i t o u s nature of the r e g i o n . However, a number of hand specimens were c o l l e c t e d at i n c r e a s i n g d i s t a n c e s from the c o n t a c t . Two s i m i l a r specimens were taken about 7 0 f e e t 6 3 from the c o n t a c t . Both are only p a r t l y r e c r y s t a l l l z e d and r e t a i n a r e l i c t t h i n bedding or l a m i n a t i o n . R e c r y s t a l l i z e d bands l i e p a r a l l e l to the l a m i n a t i o n and a l s o c r o s s c u t the beds. About 6 5 percent of the rock i s a f i n e - g r a i n e d horn-f e l s which a c t s as a matrix f o r the g r a n o b l a s t i c bands. The matrix i s composed of s m a l l g r a i n s of q u a r t z , p l a g i o c l a s e , c a l c i t e , b i o t i t e , c h l o r i t e , s i l t or c l a y - s i z e d p a r t i c l e s , and r e l i c t c l a s t i c g r a i n s . The r e c r y s t a l l i z e d bands have g r a n o b l a s t i c t e x t u r e and are composed of mainly a n d r a d i t e garnet, hornblende, d i o p s i d e , c a l c i t e , q u a r t z , and l e s s e r p l a g i o c l a s e , e p i d o t e , and opaque minerals. C h l o r i t e i s a minor a l t e r a t i o n product of hornblende i n one specimen. A t h i r d sample taken from very near the contact i s t o t a l l y g r a n o b l a s t i c to p o r p h y r o b l a s t i c i n t e x t u r e and i s probably r e p r e s e n t a t i v e of the most i n t e n s e thermal and metasomatic a l t e r a t i o n a f f e c t s . I t i s composed e n t i r e l y of o r t h o c l a s e , a n d r a d i t e , q u a r t z , d i o p s i d e , c a l c i t e , and a few opaque g r a i n s . The grade of c o n t a c t metamorphism i s i n the t r a n s i t i o n zone from a l b i t e - e p i d o t e h o r n f e l s t o hornblende h o r n f e l s f a c i e s f o r the two p a r t i a l l y r e c r y s t a l l i z e d specimens. Winkler ( 1 9 6 5 ) s t a t e s t h a t the appearance of d i o p s i d e , hornblende, and g r o s s u l a r i t e - a n d r a d i t e and the disappearance of tremo-l i t e , c h l o r i t e , and epidote mark the beginning of the horn-b l e n d e - h o r n f e l s f a c i e s . The two specimens c o n t a i n the pre-s c r i b e d minerals and l a c k t r e m o l i t e but they both a l s o con-t a i n epidote and one c o n t a i n s some c h l o r i t e . Thus, unless 6*f the epidote and c h l o r i t e are r e t r o g r e s s i v e a l t e r a t i o n miner-a l s , the two samples r e p r e s e n t an unstable assemblage ap-proaching c o n d i t i o n s of the hornblende h o r n f e l s f a c i e s . The g r a n o b l a s t i c specimen from near the c o n t a c t i s a w e l l -developed specimen i n the hornblende h o r n f e l s f a c i e s . The abundance of o r t h o c l a s e and the presence of d i o p s i d e without hornblende suggest that the rock may have approached the upper l i m i t s of the f a c i e s but has not reached c o n d i t i o n s of the pyroxene h o r n f e l s f a c i e s because w o l l a s t o n i t e has not formed and c a l c i t e p e r s i s t s i n the mineral assemblage. V o l c a n i c rocks have an i n t e n s i t y of a l t e r a t i o n of the g r e e n s c h i s t f a c i e s . Thus, contact metamorphism of the a l b i t e -e p i d o t e h o r n f e l s f a c i e s that r e s u l t e d from the i n t r u s i o n i s i n d i s t i n g u i s h a b l e from the r e g i o n a l a f f e c t s . The only p l a c e s where a l t e r a t i o n or metamorphism can be d e f i n i t e l y a s c r i b e d to the i n t r u s i o n are at the bases of s m a l l roof pendants and i n narrow zones along the i n t r u s i v e c o n t a c t s . A specimen from very near the c o n t a c t contained a l t e r e d , r e l i c t p l a g i o -c l a s e l a t h s i n a r e c r y s t a l l i z e d matrix of p l a g i o c l a s e , q u a r t z , b i o t i t e , and hornblende. A r e c r y s t a l l i z e d rock w i t h a g r a n o b l a s t i c t e x t u r e c o l l e c t e d from the base of a r o o f pen-dant was composed of c o a r s e - g r a i n e d hornblende, b i o t i t e , and garnet w i t h f i n e r intergrown q u a r t z , p l a g i o c l a s e and minor d i o p s i d e . These were the most i n t e n s e l y a l t e r e d v o l c a n i c rocks observed and i n d i c a t e t h a t metamorphism has produced a mafic h o r n f e l s of the hornblende h o r n f e l s f a c i e s but that 65 metamorphic a f f e c t s of t h i s grade are very l i m i t e d i n ex-t e n t and r e s t r i c t e d i n environment. Metamorphism of the i n t r u d e d non-calcareous sedimen-t a r y rocks i s shown by the f o r m a t i o n of a b i o t i t e h o r n f e l s and a t h i n zone of s c h i s t next to the c o n t a c t . The s c h i s t presumably formed as a r e s u l t of p l a s t i c flowage of the rocks due to the drag of the i n t r u d i n g , v i s c o u s magma. It grades outward i n t o a p h y l l i t e and f i n a l l y a h o r n f e l s over a d i s t a n c e of about 10 to 15 f e e t . The b i o t i t e h o r n f e l s i s developed f o r a d i s t a n c e of at l e a s t one hundred f e e t along the nor-t h e r n c o n t a c t and over a g r e a t e r width i n the southeast c o r -ner of the map-area. T h i s r e l a t i o n p l u s the abundance of dykes along the south contact i s i n keeping w i t h the sug-g e s t i o n that the area i s u n d e r l a i n by the i n t r u s i o n which has a r e l a t i v e l y f l a t d i p towards the southeast. The enveloping s c h i s t and h o r n f e l s have s i m i l a r com-p o s i t i o n s and vary only i n f a b r i c . The s c h i s t i s a f o l i a t e d , g r a n u l a r i n t e r g r o w t h of q u a r t z , f e l d s p a r , b i o t i t e , minor muscovite, and opaques. The g r a i n s are approximately u n i -form i n s i z e , and the quartz g r a i n s show c o n s i d e r a b l e s t r a i n . The h o r n f e l s maintains a r e l i c t c l a s t i c t e x t u r e i n which p o r p h y r i t i c v o l c a n i c fragments, sedimentary rock fragments, c h e r t , and c r y s t a l l i n e quartz can be r e c o g n i z e d . The matrix c o n s i s t s l a r g e l y of f i n e - g r a i n e d brown b i o t i t e but may con-t a i n minor c h l o r i t e , e p i d o t e , t r e m o l i t e , and c a l c i t e . 66 C l a s t i c q uartz g r a i n s appear t o be u n a f f e c t e d and show no s t r a i n a f f e c t s , but most ch e r t fragments d i s p l a y f i n e l y g r a n u l a r r e c r y s t a l l i z e d rims. The i n t e n s i t y of a l t e r a t i o n i s , thus, low grade. The s c h i s t can be r e l e g a t e d t o 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 s u b f a c i e s of the g r e e n s c h i s t f a c i e s of r e g i o n a l metamorphism and i s e q u i v a l e n t to a b i o t i t e horn-f e l s of the a l b i t e - e p i d o t e f a c i e s of con t a c t metamorphism th a t r e p r e s e n t s the a l t e r a t i o n i n t e n s i t y of most of the con-t a c t zone. Sedimentary rocks o u t s i d e the zone of b i o t i t e horn-f e l s m a i n t a i n t h e i r c l a s t i c f a b r i c s and show very l i t t l e evidence of r e c r y s t a l l i z a t i o n . Metamorphic minerals are minor c h l o r i t e , e p i d o t e , s e r i c i t e , and c a l c i t e . 67 ECONOMIC GEOLOGY I n t r o d u c t i o n M i n e r a l i z a t i o n at the Driftwood Property i s s i m i l a r t o that i n both 'porphyry copper' and quartz-molybdenite stockwork d e p o s i t s . Sulphides occur w i t h i n the i n t r u s i v e r o c k and i t s c o n t a c t aureole as d i s s e m i n a t i o n s , f r a c t u r e f i l l i n g s , and i n quartz v e i n s . At l e a s t 11 s u l p h i d e minerals have been d e p o s i t e d . 'Disseminated' M i n e r a l i z a t i o n P y r r h o t i t e and p y r i t e are by f a r the most abundant and widespread s u l p h i d e s . Along w i t h small amounts of c h a l c o p y r i t e and molybdenite they are disseminated i n the manner of accessory minerals i n the groundmass of the por-phyry or occur as s m a l l g r a i n s along f r a c t u r e s . In the a d j o i n i n g h o r n f e l s , p y r r h o t i t e and a l i t t l e c h a l c o p y r i t e , p y r i t e , and molybdenite form i n f r a c t u r e s , s m a l l r e p l a c e -ment zones and as d i s s e m i n a t i o n s . S u l p h i d e s are found i n s m a l l amounts through the e n t i r e s t o c k and i n many of the dykes. There i s some con-c e n t r a t i o n i n the n o r t h - c e n t r a l p o r t i o n of the i n t r u s i v e body near the main co n t a c t i n the most h i g h l y a l t e r e d zones. In the h o r n f e l s , p y r r h o t i t e i s by f a r the most abundant s u l p h i d e . Sulphide c o n c e n t r a t i o n i s observed i n the sheared rock next t o the con t a c t and i n the southeast part of the map-area i n the e x t e n s i v e h o r n f e l s zone wi t h the many dykes. 68 The s u l p h i d e s appear to r e p l a c e the rocks along bedding planes and where they are sheared or f r a c t u r e d . In a num-ber of beds, c l a s t i c fragments could be d i s c e r n e d i n a r e c r y s t a l l i z e d and m i n e r a l i z e d matrix. A number of sec-t i o n s of core showed s u l p h i d e i n bands or veins up to one i n c h i n t h i c k n e s s but most commonly the s u l p h i d e s form as i r r e g u l a r , s c a t t e r e d g r a i n s . Other minerals that are disseminated or d i s p e r s e d throughout the stock and h o r n f e l s are magnetite and marca-s i t e . Magnetite forms as accessory g r a i n s i n the groundmass of the porphyry and as s m a l l g r a i n s i n f r a c t u r e s , v e i n s , and r e p l a c e d beds i n the h o r n f e l s . Marcasite i s a s s o c i a t e d w i t h p y r r h o t i t e and p y r i t e i n a s u l p h i d e - r i c h bed of coarse, h o r n f e l s i c greywacke In the s o u t h e a s t e r n h o r n f e l s zone. Quartz V e i n i n g and Stockwork Quartz v e i n s and s t r i n g e r s c o n t a i n i n g molybdenite and other s u l p h i d e s are found i n both the i n t r u s i v e rocks and h o r n f e l s . The main i n t e r e s t was i n the h o r n f e l s zone where the i n t e n s i t y of v e i n i n g was much g r e a t e r than i n the main body of the stock. Veins g r e a t e r than one i n c h i n t h i c k n e s s were not seen. Most are from 1/8 to l A i n c h wide and nowhere are they numerous or w e l l developed. D e t a i l e d examination showed the veins to have 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 w i t h a complex paragenesis based on s e q u e n t i a l f r a c t u r i n g and s u l p h i d e d e p o s i t i o n . M i n e r a l s found i n the 69 v e i n s i n order of d e c r e a s i n g abundance are: p y r i t e , c h a l c o -p y r i t e , p y r r h o t i t e , s p h a l e r i t e , molybdenite, a r s e n o p y r i t e , galena, t e t r a h e d r i t e , bournonite (PbGuSbS^), a i k i n i t e (PbCuBiS-^), and marcasite. Other M i n e r a l i z a t i o n The g a r n e t - b e a r i n g skarn developed at the contact of the i n t r u s i v e body and the c a l c a r e o u s beds c o n t a i n pods and t h i n v e i n s of magnetite. In a number of magnetite-bearing samples some p y r i t e and c h a l c o p y r i t e g r a i n s are intergrown w i t h magnetite. A number of b r e c c i a fragments from the assumed f a u l t zone i n the prominent g u l l e y i n the southeast corner of the map-area were m i n e r a l i z e d . The b r e c c i a i s composed of f r a g -ments of porphyry and sedimentary or h o r n f e l s i c rock up t o 2 inches across i n a matrix of c h a l c e d o n i c and vuggy qua r t z , i n which were found s m a l l c r y s t a l s of p y r i t e and i r r e g u l a r g r a i n s of bournonite. The bournonite was i d e n t i f i e d by i t s o p t i c a l p r o p e r t i e s and X-ray powder p a t t e r n . Weathering of the d e p o s i t has been s u p e r f i c i a l and very few a l t e r a t i o n products have formed from the s u l p h i d e m i n e r a l s . A t h i n g o e t h i t i c c o a t i n g covers most of the out-crops. M a l a c h i t e and f e r r i m o l y b d i t e were seen i n only one l o c a t i o n . The magnetite i n the skarn shows weak v e i n i n g by maghemite (^Fe 2 0o) . 70 T e x t u r a l R e l a t i o n s Most of the m e t a l l i c minerals i n the d e p o s i t are e p i g e n e t i c . The only minerals t h a t may be syngenetic are f i n e - g r a i n e d p y r i t e and magnetite which are disseminated i n the sedimentary beds. P y r r h o t i t e , p y r i t e , c h a l c o p y r i t e , and molybdenite occur i n t e r s t i t i a l l y i n the porphyry matrix as i n d i v i d u a l g r a i n s or c l u s t e r s , i n the manner of accessory m i n e r a l s . Indeed, some of the s u l p h i d e s that form as i n t e r -s t i t i a l g r anules i n the s i l i c a t e matrix are l i n k e d to each other by i n t e r g r a n u l a r selvages that c r e a t e a net or mesh t e x t u r e . These g r a i n s , perhaps, rep r e s e n t s m a l l , r e -e q u l l l b r i a t e d s u l p h i d e segregations i n the s i l i c a t e melt t h a t s o l i d i f i e d e a r l y i n the c r y s t a l l i z a t i o n h i s t o r y w i t h -out much c o m p e t i t i o n f o r space w i t h the c r y s t a l l i z i n g s i l i -c a t e s . Replacement of hornblende, b i o t i t e , and magnetite by s u l p h i d e s i s apparent a l t h o u g h i t i s g e n e r a l l y only weakly developed. Replacement i s seen along g r a i n boun-d a r i e s and cleavage planes where p y r r h o t i t e , p y r i t e , and c h a l c o p y r i t e r e p l a c e the mafic s i l i c a t e s and magnetite. Hornblende i s the most commonly and -thoroughly r e p l a c e d m i n e r a l . B i o t i t e i s only r a r e l y r e p l a c e d and when i t does show replacement i t i s u s u a l l y i n the l a r g e 'books' of b i o t i t e r a t h e r than i n the f i n e - g r a i n e d , shredded b i o t i t e of the matrix. 71 The s t r o n g e s t s u l p h i d e replacement takes plac e i n the most a l t e r e d rocks where c h l o r i t e , c a l c i t e , s e r i c i t e , and p o s s i b l y c l a y minerals have formed. The g r a i n s of hornblende t h a t had the most replacement by s u l p h i d e s were a l s o the most s t r o n g l y a l t e r e d to c h l o r i t e . I t i s , however, d i f f i c u l t t o a s c e r t a i n whether the s u l p h i d e s p r e f e r e n t i a l l y r e p l a c e d the rock because i t was the most a l t e r e d , or whether s u l p h i d e replacement and rock a l t e r a t i o n are r e l a t e d proces-ses and are interdependent. From the s u l p h i d e - s i l i c a t e r e l a t i o n s i t appears that most mafic g r a i n s c r y s t a l l i z e d before the s u l p h i d e s and were p a r t l y r e p l a c e d by them. On the other hand, the p l a g i o c l a s e and p o i k i l i t i c o r t h o c l a s e phenocrysts as w e l l as the q u a r t z -f e l d s p a r groundmass probably formed simultaneously or, per-haps, i n p a r t l a t e r , than some of the s u l p h i d e s to form s u l p h i d e - s i l l i c a t e intergrowths w i t h mesh t e x t u r e s . The d i s -seminated s u l p h i d e s are, t h e r e f o r e , c l a s s e d as e p i g e n e t i c and i n p a r t p o s s i b l y paramagraatic (White et a l , 1968) r a t h e r than acc e s s o r y because they appear to be i n part contempora-neous w i t h , and i n p a r t younger than the v a r i o u s s i l i c a t e m i n e r a l s . In the h o r n f e l s very l i t t l e replacement of the c l a s t i c c o n s t i t u e n t s can be seen. Most commonly i t appears t h a t the s u l p h i d e s and r e c r y s t a l l i z e d c o n s t i t u e n t s of the h o r n f e l s (main-l y b i o t i t e , q u a r t z , and f e l d s p a r ) a l l c o e x i s t i n e q u i l i b r i u m . 7 2 ———————————————————————-————————-.__________———— ________ P l a t e 9 : Disseminated magnetite and a few s u l p h i d e g r a i n s w i t h an ac c e s s o r y or i n t e r s t i t i a l d i s t r i b u t i o n . Note a s s o c i a t i o n of opaque g r a i n s and mafic minerals. P l a i n l i g h t . M a g n i f i c a t i o n X 58. P l a t e 10 : Subhedral accessory g r a i n s of magnetite i n q u a r t z - f e l d s p a r matrix. Crossed n i c o l s . M a g n i f i c a t i o n X 1 5 0 . 73 P l a t e 11 : F i n e grained accessory magnetite and i n t e r g r a n u l a r , replacement s u l p h i d e s . P l a i n l i g h t . M a g n i f i c a t i o n X 58. P l a t e 12 : A s s o c i a t i o n of s u l p h i d e g r a i n s w i t h f i n e g r a i n e d , shredded (secondary) b i o t i t e and corroded hornblende and coarse grained b i o t i t e . P l a i n l i g h t . M a g n i f i c a t i o n X 150. 7k P l a t e s 13 and Ih : P o i k i l i t i c p l a g i o c l a s e phenocrysts w i t h opaque g r a i n s concentrated i n zones i n d i c a t i n g e a r l y m e t a l l i c m i n e r a l i z a t i o n d u r i n g s i l i c a t e c r y s t a l l i z a t i o n . P l a i n l i g h t . M a g n i f i c a t i o n X 150. 75 P l a t e 15 : Sulphide replacement of hornblende along g r a i n boundaries and cleavage planes. P l a i n l i g h t . M a g n i f i c a t i o n X 150. P l a t e 16 : Oriented s u l p h i d e g r a i n s r e p l a c i n g a l a r g e p l a t e of b i o t i t e . P l a i n l i g h t . M a g n i f i c a -t i o n X 150. 76 In the v e i n s , quartz i s the most abundant v e i n m a t e r i a l w i t h c a l c i t e , s u l p h i d e s , and magnetite. The s u l p h i d e s i n the v e i n s , w i t h the e x c e p t i o n of molybdenite, form g r a i n s t h a t are intergrown w i t h the quartz or q u a r t z - c a l c i t e v e i n matrix. The molybdenite most f r e q u e n t l y forms along v e i n w a l l s as g r a n u l a r selvages or as f l a k e s and d u s t i n g p a r a l -l e l to v e i n w a l l s i n weakly developed 'ribbon v e i n ' s t r u c -t u r e s . The s u l p h i d e minerals form i n d i v i d u a l g r a i n s , granu-l a r aggregates, and composite g r a i n s i n which mutual boun-dary, replacement, and e x s o l u t i o n t e x t u r e s can be seen. A r s e n o - p y r i t e and some of the p y r i t e form the only euhedral s p e c i e s . E u h e d r a l g r a i n s form mainly i n the quartz v e i n s a l t h o u g h a few of the disseminated p y r i t e g r a i n s are a l s o e u h e d r a l . Most commonly the disseminated p y r i t e g r a i n s have corroded o u t l i n e s , e s p e c i a l l y i f a s s o c i a t e d w i t h p y r -r h o t i t e and c h a l c o p y r i t e . Thus, i t seems that the e a r l y g e n e r a t i o n s of p y r i t e formed r e l a t i v e l y l a r g e , euhedral g r a i n s t h a t were l a t e r corroded or resorbed and l a t e r genera-t i o n s of p y r i t e formed f i n e - g r a n u l a r intergrowths t h a t surround and r e p l a c e the o l d e r g r a i n s . Replacement t e x t u r e s are almost e n t i r e l y of the c a r i e s type. No p r e f e r e n t i a l z o n a l nor core replacement i s obvious i n the s u l p h i d e s although core replacement of magnetite by s u l p h i d e s was observed. V e i n replacement i s only weakly 77 developed and i s most commonly seen as c h a l c o p y r i t e r e -p l a c i n g f r a c t u r e d p y r i t e g r a i n s . Marcasite forms rims about p y r r h o t i t e and p y r i t e and l e s s commonly s p h a l e r i t e rims c h a l c o p y r i t e . The marcasite forms curved, l a m e l l a r , somewhat c o n c e n t r i c rims about a l t e r e d or t o t a l l y r e p l a c e d p y r i t e or p y r r h o t i t e c o r e s . The replacement i s more c o r -r e c t l y c o n s i d e r e d an a l t e r a t i o n or c o n v e r s i o n of the p y r i t e or p y r r h o t i t e t o marcasite p o s s i b l y due to changes i n a c i d -i t y and temperature (Edwards, i 9 6 0 ) . M a r c a s i t e was observed i n only two specimens. In one p y r r h o t i t e was abundant w i t h p y r i t e and c h a l c o p y r i t e i n b i o t i t e h o r n f e l s near the south-e r n c o n t a c t of the i n t r u s i o n . The other occurrence was a q u a r t z - c a l c i t e v e i n from the main body of the i n t r u s i o n i n which marcasite r e p l a c e d p y r i t e . 7 3 P l a t e s 17 and 13: Zonation or c o n c e n t r i c banding i n marcasite g r a i n s . Grains are h i g h l y corroded due to p o l i s h i n g . R e f l e c t e d l i g h t . M a g n i f i c a t i o n X 550. 79 Mutual boundary t e x t u r e s are developed i n many of the mineral p a i r s . Simultaneous d e p o s i t i o n may have occurred i n the p a i r s : c h a l c o p y r i t e - s p h a l e r i t e , s p h a l e r i t e - t e t r a h e d -r i t e , b o u r n o n i t e - a i k i n i t e , g a l e n a - s p h a l e r i t e , and g a l e n a -c h a l c o p y r i t e . E x s o l u t i o n t e x t u r e s are developed i n the m i n e r a l p a i r s : s p h a l e r i t e - c h a l c o p y r i t e , t e t r a h e d r i t e -c h a l c o p y r i t e , c h a l c o p y r i t e - p y r r h o t i t e , and perhaps bournon-i t e - a i k i n i t e . E x s o l u t i o n i s most f r e q u e n t l y observed be-tween s p h a l e r i t e and c h a l c o p y r i t e . T h i s mineral p a i r as w e l l as t e t r a h e d r i t e - c h a l c o p y r i t e and b o u r n o n i t e - a i k i n i t e i s found i n the q u a r t z - c a l c i t e v e i n s . P y r r h o t i t e - c h a l c o p y r i t e e x s o l u t i o n i s found i n only a very few specimens from the h o r n f e l s zone immediately a d j o i n i n g the i n t r u s i v e c o n t a c t . No e x s o l u t i o n t e x t u r e s were seen i n the s u l p h i d e s i n the porphyry. The s i z e and d i s t r i b u t i o n of exsolved g r a i n s depends on the degree to which unmixing has occurred. Commonly ex-s o l u t i o n has produced the c h a r a c t e r i s t i c d i s p e r s i o n of many f i n e - g r a i n e d g l o b u l e s of one s u l p h i d e w i t h i n the other. In some samples where, presumably, c o o l i n g was slower or other c o n d i t i o n s e x i s t e d that were more f a v o u r a b l e f o r d i f f u s i o n and unmixing, e x s o l u t i o n has been more advanced and formed fewer but l a r g e r exsolved g r a i n s . The most h i g h l y developed stages of unmixing have an a s s o c i a t e d phenomenon of e x p u l -s i o n . In such cases s e p a r a t i o n and m i g r a t i o n of the two substances can be seen t o occur and the exsolved s u l p h i d e 80 i s e x p e l l e d towards the g r a i n boundary. The u l t i m a t e s t a t e of e x p u l s i o n i s to have both s u l p h i d e s separated w i t h the e x p e l l e d substance at the g r a i n boundary of the host as b o r d e r i n g g r a i n s or an e n c l o s i n g rim. Both e x s o l u t i o n and e x p u l s i o n t e x t u r e s are developed i n the v e i n s u l p h i d e s and have a l l manner of i n t e r m e d i a t e stages between them. E x p u l s i o n i s best observed i n s p h a l e r -i t e - c h a l c o p y r i t e and t e t r a h e d r i t e - c h a l c o p y r i t e . E x s o l u t i o n g r a i n s of c h a l c o p y r i t e or s p h a l e r i t e can be seen as d i s p e r -s i o n s i n the cores of many of the s p h a l e r i t e or c h a l c o p y r i t e g r a i n s . The exsolved s u l p h i d e g r a i n s decrease i n number but i n c r e a s e i n s i z e near the g r a i n boundary of the host, e s p e c i a l l y i f rims or a d j o i n i n g g r a i n s of the same composi-t i o n as the exsolved s u l p h i d e are present. From these r e l a -t i o n s , i t seems most probably that at l e a s t some of the rims of s p h a l e r i t e about c h a l c o p y r i t e and boundary g r a i n s or rims of c h a l c o p y r i t e about s p h a l e r i t e have not formed by r e p l a c e -ment but r a t h e r by g r a i n boundary c o n c e n t r a t i o n through ex-p u l s i o n . The same r e l a t i o n s are probably true f o r t e t r a -h e d r i t e - c h a l c o p y r i t e p a i r s . A i k i n i t e i n bournonite forms a number of s m a l l , i r -r e g u l a r , rounded g r a i n s that are c l u s t e r e d together i n groups t h a t u s u a l l y c o n t a i n three to f i v e g r a i n s . The ex-solved granules vary i n s i z e as w e l l as shape and show no tendency t o segregate along g r a i n boundaries. For t h i s s u l p h i d e p a i r where f i n e granules appear to be e x p e l l e d 81 from the host s u l p h i d e and yet remain i n t i m a t e l y a s s o c i a t e d i n a c l u s t e r w i t h i n the host, the term e x s o l u t i o n i s prob-a b l y a p p l i c a b l e . I f the exsolved s u l p h i d e appeared to have been e j e c t e d from the host and concentrated around the host g r a i n s ' border, the term e x p u l s i o n would seem more f i t t i n g . P a r a g e n e s i s i The paragenesis of the m i n e r a l s u i t e i s complex but has been deciphered from the f a b r i c and t e x t u r e s of the min-e r a l g r a i n s and 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 of v e i n s and f r a c t u r e s . The mineral s u i t e was subdivided i n t o f o u r p a r t s based on the f o u r environments of f o r m a t i o n of m e t a l l i c m i n e r a l i z a t i o n . The d i v i s i o n s a r e : 1. disseminated s u l -phides i n T a k l a - H a z e l t o n beds ( l a r g e l y or t o t a l l y composed of p y r i t e ) ; 2. g r a n u l a r magnetite, p y r i t e , c h a l c o p y r i t e i n the s k a r n zone; 3« disseminated and f r a c t u r e f i l l i n g s u l p h i d e s and magnetite i n the quartz monzonite and h o r n f e l s : and if. v e i n s u l p h i d e s w i t h quartz and q u a r t z - c a l c i t e gangue. The disseminated s u l p h i d e s i n the hydrothermally un-a l t e r e d sedimentary beds are presumably s y n g e n e t i c . The skarn, disseminated, f r a c t u r e f i l l i n g , replacement, and v e i n m i n e r a l i z a t i o n are r e l a t e d both s p a t i a l l y and i n time to the i n t r u s i o n of the g r a n d i o r i t e - q u a r t z monzonite por-phyry. Only a very s m a l l p o r t i o n o f the t o t a l volume of s u l p h i d e s at the Driftwood Property i s found i n the un-a l t e r e d sedimentary rocks and skarn zone, and t h e r e f o r e , 82 these types of m i n e r a l i z a t i o n are of only minor importance. By f a r the g r e a t e s t volume of s u l p h i d e s and magnetite has formed as d i s s e m i n a t i o n s and f r a c t u r e f i l l i n g s i n the i n t r u -s i o n and as f r a c t u r e f i l l i n g or replacements i n the h o r n f e l s . The v e i n s are n e i t h e r l a r g e nor abundant and g e n e r a l l y con-t a i n s m a l l amounts of s u l p h i d e s . The v e i n s do, however, con-t a i n the g r e a t e s t number of s u l p h i d e s p e c i e s . The stages of m i n e r a l i z a t i o n r e l a t e d to i n t r u s i o n of the porphyry are l i s t e d i n Table I I I . Table I I I . Sequence of M i n e r a l i z a t i o n . Stage 1. Rock forming s i l i c a t e s , accessory m i n e r a l s , magnetite l a . A p l i t e dykes Stage 11. Quartz v e i n i n g ("blue quartz") - c o n t a i n i n g molybdenite, p y r i t e Stage 111. Disseminated, f r a c t u r e f i l l i n g , and r e p l a c e -ment s u l p h i d e s and magnetite i n porphyry, h o r n f e l s , (and skarn?) 111a. Quartz v e i n i n g ("white quartz") - barren or c o n t a i n i n g p y r i t e , 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 Stage IV. Q u a r t z - c a l c l t e v e i n i n g - p o l y m e t a l l i c Stage V. S u r f i c i a l weathering and a l t e r a t i o n The r e l a t i o n s between i n d i v i d u a l s i l i c a t e s and s i l i c a t e s w i t h s u l p h i d e s and magnetite have been d i s c u s -sed i n the s e c t i o n d e a l i n g w i t h t e x t u r a l r e l a t i o n s h i p s . 8 3 The c o n c l u s i o n s drawn are that mafic minerals, magnetite, and other a c c e s s o r y g r a i n s c r y s t a l l i z e d e a r l y w i t h zoned p l a g i o c l a s e phenocrysts and these were f o l l o w e d by q u a r t z , potash f e l d s p a r , and more p l a g i o c l a s e i n a f i n e , g r a n u l a r matrix. T h i s assemblage i s c a l l e d Stage 1 and, i n e f f e c t , d e s c r i b e s the f o r m a t i o n of the g r a n o d i o r i t e - q u a r t z monzonite porphyry. During the l a t e stages of d i f f e r e n t i a t i o n potash f e l d s p a r and quartz s e g r e g a t i o n s formed sma l l a p l i t i c dykes and p r o j e c t i o n s which re p r e s e n t the l a s t stage of i n t r u s i o n and are c a l l e d Stage l a . P y r r h o t i t e probably s t a r t e d c r y s t a l l i z i n g from the magma or between the s i l i c a t e s at h i g h temperatures and formed accessory g r a i n s . However, the main d e p o s i t i o n of s u l p h i d e s began a f t e r c r y s t a l l i z a t i o n of the host rock. The e a r l i e s t m e t a l l i c minerals to form were magnetite, molybdenite, p y r r h o t i t e , and p y r i t e . The molybdenite ap-pears to have f i r s t been d e p o s i t e d along w a l l s of f r a c t u r e s . Presumably as temperature decreased, p y r i t e and more molyb-d e n i t e was d e p o s i t e d w i t h quartz to form v e i n s . F i n a l l y the v e i n s were f i l l e d w i t h c l e a r quartz to end Stage 11. d e p o s i t i o n . Formation of the Stage 11 veins c o i n c i d e d w i t h r e - e q u i l i b r i a t i o n of the accessory p y r r h o t i t e i n the por-phyry. The main d e p o s i t i o n of p y r r h o t i t e , p y r i t e , and c h a l c o p y r i t e i n the porphyry and p y r r h o t i t e , p y r i t e , c h a l c o -p y r i t e , and magnetite i n the h o r n f e l s marks the advent of 8h Stage 111 and the t r a n s i t i o n from Stage 11. The maximum age of the "blue q u a r t z " v e i n s of Stage 11 i s w e l l d e f i n e d as they can be shown to c r o s s c u t a p l i t e dykes of Stage l a . The younger age of the main s u l p h i d e m i n e r a l i z a t i o n of Stage 111 i s documented by the presence of abundant p y r r h o t i t e , p y r i t e , and c h a l c o p y r i t e as rims and b o r d e r i n g g r a i n s along "blue q u a r t z " v e i n s . The m a g n e t i t e - p y r i t e - c h a l c o p y r i t e m i n e r a l i z a t i o n i n the skarn zone i s b e l i e v e d to have formed d u r i n g Stage 111, a l t h o u g h t h i s age r e l a t i o n i s d i f f i c u l t to s u b s t a n t i a t e . The assumption i s based on the mineralogy and the c o n c l u -s i o n t h a t the skarn r e f l e c t s a c o n t a c t phenomenon s i m i l a r to t h a t which formed the h o r n f e l s and d i f f e r s only i n that i t occurred i n c h e m i c a l l y more r e a c t i v e r o c k s . The second age of quartz v e i n i n g (Stage 111a) has formed white qu a r t z v e i n s which are the most abundant type of v e i n observed, e s p e c i a l l y i n the h o r n f e l s . These v e i n s are e a s i l y r e cognised by t h e i r milky white c o l o u r , simple mineralogy, g r e a t e r than average widths, and v a r i e d shapes that r e s u l t i n h i g h l y i r r e g u l a r , l e n t i c u l a r and p o d - l i k e -c r o s s s e c t i o n s . The v e i n s have been c a l l e d Stage 111a be-cause they can be shown t o c r o s s c u t stage 11 "blue q u a r t z " v e i n s and Stage l a a p l i t e dykes. The term Stage 111a i s used r a t h e r than Stage IV t o emphasize t h e i r c l o s e time a s s o c i a t i o n t o the main p e r i o d of p y r i t e , p y r r h o t i t e , and c h a l c o p y r i t e d e p o s i t i o n i n Stage 111. I t i s assumed that 85 s u l p h i d e s forming disseminated or re p l a c e d g r a i n s and lenses d u r i n g Stage 111 were i n t r o d u c e d at the same time w i t h quartz i n t o open spaces and r e s u l t e d i n the i r r e g u l a r white quartz v e i n s of Stage 111a. The veins are not a l l m i n e r a l i z e d . More than one h a l f of the white quartz v e i n s observed were b a r r e n and those that are m i n e r a l i z e d c o n t a i n only s p a r s e l y d i s t r i b u t e d g r a i n s of p y r i t e , p y r r h o t i t e , c h a l c o p y r i t e , minor s p h a l e r i t e , and r a r e t r a c e s of galena. The youngest v e i n s are p o l y m e t a l l i c q u a r t z - c a l c i t e v e i n s t h a t have been observed to c r o s s c u t Stage 11 "blue q u a r t z " v e i n s , Stage 111 s u l p h i d e s , and Stage 111a "white q u a r t z " v e i n s . They are termed Stage IV and are e a s i l y r e c o g n i z e d both by t h e i r s u l p h i d e and gangue mineralogy. The d i a g n o s t i c minerals are a r s e n o p y r i t e , t e t r a h e d r i t e , b o u r n o n i t e , and a i k i n i t e as w e l l as c l e a r , c r y s t a l l i n e quartz set i n white t o cream-coloured c a l c i t e and white q u a r t z . The v e i n s a l s o c o n t a i n p y r i t e , p y r r h o t i t e , c h a l c o p y r i t e , s p h a l e r i t e , galena, and marcasite. The f i r s t gangue t o have formed appears t o have been c r y s t a l l i n e quartz that l e f t much vuggy space that was l a t e r f i l l e d w i t h s u l p h i d e s , milky-white q u a r t z , and c a l c i t e . The d e p o s i t i o n i n the ve i n s be-gan w i t h euhedral p y r i t e , a r s e n o p y r i t e , and qua r t z c r y s t a l s and was f o l l o w e d by a second g e n e r a t i o n of g r a n u l a r , anhed-r a l p y r i t e , white q u a r t z , p y r r h o t i t e , c h a l c o p y r i t e , and some s p h a l e r i t e and galena. C a l c i t e with s p h a l e r i t e , galena,• t e t r a h e d r i t e , s u l p h o s a l t s , and marcasite were the f i n a l , 86 P l a t e 19= P o l i s h e d s e c t i o n of diamond d r i l l core w i t h Stage l a a p l i t e dyke and Stage 11 "blue q u a r t z " v e i n cut by Stage IV q u a r t z - c a l c i t e v e i n . 8 7 minerals d e p o s i t e d . Two p o l y m e t a l l i c c a l c i t e - b e a r i n g v eins i n the por-phyry and one i n the h o r n f e l s were observed that contained molybdenite. The molybdenite was found i n i t s common habit as f i n e l y disseminated p l a t e s along the v e i n w a l l s . These r e l a t i o n s suggest at l e a s t two hypotheses r e g a r d i n g the age of the molybdenite. The f i r s t i s that molybdenite was de-p o s i t e d c o n t i n u o u s l y over a long p e r i o d of time spanning Stage 11 through to at l e a s t the s t a r t of Stage IV. A s l i g h t v a r i a t i o n of t h i s hypothesis i s t h a t molybdenite was de p o s i t e d at the beginning of Stage IV as a second p e r i o d or g e n e r a t i o n of molybdenum m i n e r a l i z a t i o n . The second and a l t e r n a t i v e hypothesis i s that the veins are composite and c o n t a i n Stage IV m i n e r a l i z a t i o n t h a t has been superimposed on Stage 11 v e i n s . The l a t t e r p r o p o s a l i s considered t o be the more l i k e l y . Molybdenite probably formed f i r s t d uring Stage 11 m i n e r a l i z a t i o n and the same f r a c t u r e s were r e f r a c -tured'and m i n e r a l i z e d at a l a t e r time d u r i n g Stage IV (and probably Stage 111a, although composite veins of t h i s age have not been r e c o g n i z e d ) . The f i n a l events i n the h i s t o r y of m i n e r a l i z a t i o n are termed Stage V and r e p r e s e n t the weathering and a l t e r a -t i o n products of the s u l p h i d e s , magnetite, and rock-forming m i n e r a l s . 88 Diagraraatic R e p r e s e n t a t i o n of the Paragenesis Both the l i n e , diagram and the Vandeveer diagrams used i n t h i s study have been s l i g h t l y modified to s u i t the p a r t i c -u l a r requirements of the Driftwood m i n e r a l i z a t i o n . The r e p r e s e n t a t i o n s have to be i n t e r p r e t e d w i t h the f o l l o w i n g r e s t r i c t i o n s and c o n d i t i o n s i n mind. The l i n e diagram shows the stages of m i n e r a l i z a t i o n as d e r i v e d from c r o s s c u t t i n g r e l a t i o n s and t e x t u r a l evidence. The boundaries between the stages have purposely been l e f t vague as t h e r e probably has been some ove r l a p of c e r t a i n minerals and c o n t i n u i t y of d e p o s i t i o n from one Stage to ano-t h e r . The s o l e e x c e p t i o n i s Stage IV which has a r b i t r a r i l y had the presence of c a l c i t e i n the v e i n s placed as i t s d i a g n o s t i c c r i t e r i o n . The use of the term ' p y r i t e 1 and 11' and 'magnetite 1 and 11' r e f e r s p r i m a r i l y to the f a b r i c and c a r r i e s only a secondary g e n e t i c i m p l i c a t i o n . In the case of p y r i t e , the s i g n i f i c a n c e i s t h a t at l e a s t two types of p y r i t e were r e c o g n i z e d . P y r i t e 1 i s the f i r s t - f o r m e d , euhed-r a l c o a r s e - g r a i n e d v a r i e t y t h a t forms i n a stage of m i n e r a l i z a -t i o n , and p y r i t e 11 i s the f i n e r - g r a i n e d , g r a n u l a r type that surrounds p y r i t e 1. The d i f f e r e n t appearance of p y r i t e s i n any stage of m i n e r a l i z a t i o n may be the r e s u l t of being formed d u r i n g at l e a s t two d i s c r e t e p e r i o d s , or may j u s t represent two or more steps i n a s i n g l e d e p o s i t i o n a l process. In the case of magnetite, the terms magnetite 1 and 11 can be used 8 9 to d i s t i n g u i s h the mineral on a t e x t u r a l and time b a s i s . Magnetite 1 r e f e r s t o the f i n e - g r a i n e d a c c e s s o r y magnetite i n the porphyry, and magnetite 11 i s formed as replacements and f r a c t u r e f i l l i n g s i n the h o r n f e l s , porphyry, and skarn d u r i n g Stage 111. The Vandeveer r e p r e s e n t a t i o n has been broken down i n t o two components i n order to present the data i n a more e a s i l y understandable manner and to emphasize the d u a l nature of the m i n e r a l assemblage. The simple mineralogy of the d i s s e m i n a t i o n , replacement, and f r a c t u r e f i l l i n g type of Stages 1 and 111 has been shown as one component and the complex mineralogy of the v e i n s i n Stages 11, 111a, and IV has been used i n the other. For a f u l l understanding of the p a r a g e n e s i s , both components must be regarded as occur-r i n g c o n c u r r e n t l y but under d i f f e r e n t p h y s i c a l c o n d i t i o n s . The Vanderveer and l i n e diagrams are shown i n F i g u r e s 8 and 9. P l a t e 2 0 : C h a l c o p y r i t e (cpy) t r u n c a t i n g marcasite (mcs) bands. R e f l e c t e d l i g h t . M a g n i f i c a t i o n X 5 5 0 . P l a t e 2 1 : Shattered p y r i t e (py) w i t h younger rims of p y r r h o t i t e (po). R e f l e c t e d l i g h t . M a g n i f i c a t i o n X iQh. FIGURE 9 PARAGENESIS OF DRIFTWOOD MINERALIZATION STAGE 1 STAGE II STAGE III - Ilia STAGE IV. STAGE V rock forming silicates "blue quartz" veins mineralization in porphyry, polymetallic quartz - alteration and accessory hornfels, (and skarn ?) calcite veins products minerals "white quartz" veins MAGNETITE 1 MOLYBDENITE QUARTZ — — _ _ . PYRITE 1 7 MAGNETITE II PYRITE II ________ ARSENOPYRITE PYHRRHOTITE — - — CHALCOPYRITE SPHALERITE — CALCITE — MARCASITE _ GALENA TETRAHEDRITE BOURNONITE AIKINITE -MAGHEMITE ? FERRIMOLYBDITE — MALACHITE 'LIMONITE'(GOETHITE) 93 Temperatures of I n t r u s i o n and Metamorphism I n t r u s i o n has been i n t o the e p i z o n a l environment which i s the zone from s u r f a c e to k k i l o m e t e r s . The Driftwood i n -t r u s i o n i s b e l i e v e d t o be i n the deeper part of the epizone and, thus, a depth of f o u r k i l o m e t e r s w i l l be assumed t o be the depth of i n t r u s i o n . At such a depth the temperature and pres s u r e i n the country rock would be about one hundred f o r t y degrees c e n t i g r a d e and pressure about 1000 bars i f the thermal and pressure g r a d i e n t s of 30 degrees and 250 bars per k i l o -meter were used (Winkler, 1965). The temperature of the s i l i c a t e melt can be estimated from the data provided by numerous authors. Temperatures of g r a n i t i c melts range from 700 to 800°C; s y e n i t i c magmas about 900°C (Winkler, 1965); and g r a n o d i o r i t e 820°G (Buseck, 1966). In the system a l b i t e - o r t h o c l a s e - q u a r t z the s o l i d u s at 1000 kg/Cm^ water p r e s s u r e f o r a melt having the composition of the average of the Driftwood g r a n o d i o r i t e - q u a r t z monzonite i s about 817°G (Annual Report Geophysics Lab., 1951-52). Thus, 8l5°0 - 25° can be regarded as a reasonable a p p r o x i m a t i o n f f o r the temperature of i n t r u s i o n o f the g r a n o d i o r i t e - q u a r t z monzonite s t o c k . The heat flow from an i n t r u s i v e body has been c a l c u l a t e d by L o vering (1936), and Jaeger (1957> 1959) and a p p l i e d by Buseck (1966), Winkler (1965)> and others to f i e l d occurrences. T h e i r c a l c u l a t i o n s determine the temperatures at the cont a c t and at v a r y i n g d i s t a n c e s from the cont a c t as f u n c t i o n s of the 9^ magma temperature, temperature of the in t r u d e d rocks and t h i c k n e s s of the i n t r u s i v e body. Loverings c a l c u l a t i o n s were based on g e n e r a l d i f f e r e n -t i a l equations t h a t r e l a t e the heat c o n d u c t i v i t i e s of two homogeneous bodies of d i f f e r e n t compositions and temperatures. Using h i s method, a magma wit h a temperature of 8 l 5°C i n -truded i n t o limestone and shale would i n c r e a s e the tempera-t u r e at the cont a c t by about hkO°C and h25°C r e s p e c t i v e l y . However, f o r the sake of convenience, Lovering assumed the temperature of the i n t r u d e d rocks to be zero. Thus, i f a c o r r e c t i o n was made f o r the temperature of the in t r u d e d r o c k s , the c o n t a c t temperature would be c o n s i d e r a b l y g r e a t e r than c a l c u l a t e d . An e x p r e s s i o n c o n t a i n i n g a c o r r e c t i o n f o r geothermal g r a d i e n t was used by Buseck (1966). The e x p r e s s i o n i s modi-f i e d from Jaeger (1959) and s t a t e s that the cont a c t temperature T c , i s : \ K 0 k l " 2 (T r a - T 0 ) T c = + Tr 1 W 1 * 1 where k Q and k-^  are the d i f f u s i v i t e s , K 0 and K-j_ are the thermal c o n d u c t i v i t e s of the i n t r u d e d rock and g r a n o d i o r i t e -q uartz monzonite, T m i s the s o l i d i f y i n g temperature of magma,. 95 and T 0 i s the. i n i t i a l temperature of the i n t r u d e d r o c k s . Assuming a depth of i n t r u s i o n of h km, a 30°C per km geo-thermal g r a d i e n t , and a s u r f a c e temperature of 20°C, and a p p l y i n g the a p p r o p r i a t e constants as l i s t e d by Lovering (1936), the temperature of i n t r u s i o n Tm of 8 l 5°C, the con-t a c t temperature f o r the Driftwood i n t r u s i o n i s found to be h7k°C i n limestone; 557°C i n shale; 1+9500 i n sandstone, and 517°C i n a n d e s i t e - b a s a l t . These temperatures would be g r e a t -er i f the magma were h o t t e r than 3 l 5°C or the thermal grad-i e n t was g r e a t e r than 30°C/Km, or the depth of i n t r u s i o n was g r e a t e r than k Km. A l s o the temperatures, as c a l c u l a t e d , apply t o the c o n t a c t s of an i n t r u s i v e body wi t h v e r t i c a l w a l l s , and any l o c a l bends or warps i n the contact would gi v e r i s e to higher temperatures. The r e s t r i c t i n g c o n d i t i o n s f o r heat flow c a l c u l a t i o n s are that heating of the i n t r u d e d rock i s due e n t i r e l y t o c o n d u c t i o n and no heat t r a n s f e r by v o l a t i l e components takes p l a c e . Since some metasomatism i s e v i d e n t , there must have been f l u i d movement. The assumption made i s that the l a t e n t heat of c r y s t a l l i z a t i o n opposes and c a n c e l s the heat l o s s through f l u i d a c t i o n and the body can be assumed to have cooled by only con-d u c t i o n . Winkler's treatment of Jaeger's method of c a l c u l a t i n g heat flow can be used to demonstrate the causes of z o n a t i o n of the c o n t a c t metamorphic f a c i e s . The temperature g r a d i e n t 96 i s s t eepest at the i n t r u s i v e c o n t a c t but decreases r a p i d l y and l e v e l s away from i t . Winkler (1965) proposed that at the c o n t a c t the temperature of the country rock i n c r e a s e s by over 60 percent of the temperature of the i n t r u s i v e magma. At d i s t a n c e s corresponding t o 1/10 the t h i c k n e s s of the i n t r u -s i v e (1/10 D), the temperature i n c r e a s e i n the country rock i s about 50 percent of the temperature of the magma, and at a d i s t a n c e of 1/2 the t h i c k n e s s (1/2 D), the temperature i n c r e a s e i s about 1/3 t h a t of the magma. Using the assumed v a l u e s of 8 l 5°C as the temperature of the i n t r u s i o n , a depth of h km, a 30°C/Km geothermal g r a d i e n t , an average t h i c k n e s s (D) of the Driftwood G r a n o d i o r i t e - q u a r t z monzonite of 1000 f e e t , and contact temperatures ( T c ) f o r the rock types ob-served as c a l c u l a t e d by Buseck's e x p r e s s i o n , the values are about 550°C f o r c a l c e r o u s s h a l e , lf95°G f o r sandstone, and 517°C f o r a n d e s i t e - b a s a l t s e c t i o n s . At a d i s t a n c e of 100 f e e t from the cont a c t (1/10 D), the temperatures are U l 5°C f o r c a l c e r e o u s s h a l e , 3*+8°C f o r sandstone, and 397°C f o r the v o l c a n i c s . At an i n c r e a s e d d i s t a n c e of 500 f e e t (1/2 D), the expected temperatures would be about 323°C, 305°C, and 311°C, r e s p e c t i v e l y . The r e l a t i o n f o r c a l c a r e o u s shale i s shown i n F i g u r e 10. The temperature l i m i t s f o r the hornblende h o r n f e l s and a l b i t e - e p i d o t e h o r n f e l s f a c i e s at a c o n f i n i n g pressure of 1000 bars and i n t r u s i o n depth of fou r k i l o m e t e r s , as d e f i n e d by Winkler (1965)> have been superimposed on the heat flow 97 F i g u r e 10: Heating of country rock w i t h c a l c a r e o u s shale c o m p o s i t i o n adjacent t o a g r a n o d i o r i t e i n t r u s i o n . ( M o d i f i e d a f t e r Winkler, 1965); temperature at co n t a c t c a l c u l a t e d a c c o r d i n g to Buseck, (1966). 700 1 600 500-400-300 200-Pyroxene hornfels facies Contact j_ Q 10 To" IO -§-D IO IO IO Depth 4 Km I40 °C Pressure 1000 bars Thickness of intrusion . D = 1000' diagram ( F i g u r e 1 0 ) . C l e a r l y , under the c o n d i t i o n s s t a t e d , i t can be seen t h a t a c a l c a r e o u s shale could have contact metamorphism of the hornblende-hornfels f a c i e s f o r a d i s t a n c e of up to .02 = twenty f e e t , and could develop a h o r n f e l s 10 u w i t h b i o t i t e i n the a l b i t e - e p i d o t e h o r n f e l s f a c i e s over a d i s t a n c e of about 135 f e e t . Intruded v o l c a n i c s w i t h ande-s l t e - b a s a l t composition would have a contact temperature of about 517°C and, thus, only a very t h i n zone of hornblende-h o r n f e l s f a c i e s c o n t a c t rock c o u l d be formed. However, a h o r n f e l s of the a l b i t e - e p i d o t e f a c i e s would be expected to 98 form f o r a d i s t a n c e of at l e a s t 100 f e e t . Sandstone w i t h a c o n t a c t temperature of ^95°C would not be metamorphosed be-yond the upper range of the a l b i t e - e p i d o t e h o r n f e l s f a c i e s . A h o r n f e l s zone c l o s e to 100 f e e t i n t h i c k n e s s would be expected. These t h e o r e t i c a l c o n s i d e r a t i o n s very c l o s e l y resem-b l e the a c t u a l observed a l t e r a t i o n p a t t e r n . In some out-crops the t h i c k n e s s of the h o r n f e l s f a c i e s was g r e a t e r than the t h e o r e t i c a l c o n s i d e r a t i o n s would p r e d i c t . Such d i s c r e -pancies would, i n f a c t , be expected i n a n a t u r a l occurrence where the i n t r u s i v e contact would be i r r e g u l a r and not the i d e a l d y k e - l i k e body on which the c a l c u l a t i o n s are based. In g e n e r a l , however, the assumed temperature of i n t r u s i o n of 815 - 25°C, and a depth of i n t r u s i o n of h Km w i t h c o n t a c t temperatures around 500°C but probably not exceeding 550°C can be regarded as reasonable and c o n s i s t e n t w i t h the f i e l d r e l a t i o n s observed at the Driftwood Property. Geothermometry Temperature-pressure c o n d i t i o n s f o r ore f o r m a t i o n can be p o s t u l a t e d using a number of c r i t e r i a . In t h i s study no attempts were made to apply or i n v e s t i g a t e the a p p l i c a b i l i t y of the popular geothermometers due to the u n c e r t a i n s t a t u s of the v a r i o u s methods. Instead, thermal s t a b i l i t y l i m i t s and s t a b i l i t y ranges of c o e x i s t i n g mineral assemblages were used to reduce the l i m i t s of c o n d i t i o n s f a v o u r a b l e f o r 99 m i n e r a l d e p o s i t i o n . In a few oases e q u i l i b r i a r e l a t i o n s could be used to d e f i n e very c l o s e l y the c o n d i t i o n s of d e p o s i t i o n . Anhydrous i r o n o x i d e s : Magnetite and maghemite are the only two minerals observed. Magnetite occurs i n at l e a s t two ages - the e a r l y - f o r m e d , disseminated, magmatic v a r i e t y i n the i n t r u s i o n , and the secondary replacement type i n the h o r n f e l s , porphyry, and s k a r n that was seen to be p a r t l y contemporaneous w i t h and p a r t l y younger than some of the p y r i t e and p y r r h o t i t e . No hematite was seen but s m a l l amounts of maghemite ( t f F e ^ - ^ ) were reco g n i z e d as an a l t e r a t i o n product of the magnetite i n the skarn ( t a c t i t e ) zone. Formation of two types of magnetite r e f l e c t s the i n t e r -p l a y of p 0 2 and p S 2 d u r i n g the c o o l i n g c y c l e of the i n t r u s i o n ( H o l l a n d , 1 9 5 9 ) . The disseminated magnetite probably formed as a primary magmatic phase i n what can be regarded as a c l o s e d system. L a t e r as a r e s u l t of c o o l i n g and p o s s i b l y as a r e s u l t of decrease i n p 0 2 and p S 2 , secondary magnetite formed i n the i n t r u s i o n , h o r n f e l s , and t a c t i t e i n the presence of v o l a t i l e s i n an e s s e n t i a l l y open system. According to S a l o t t i ' s (196*+) diagram f o r the Fe-S - 0 system, at temperatures below 6 7 5°C the p r o g r e s s i o n from p y r i t e p y r i t e + m a g n e t i t e — > p y r i t e + p y r r h o t i t e + m a g n e t i t e — * - p y r r h o t i t e + magnetite i s p o s s i b l e . Thus!, magnetite a s s o c i a t e d w i t h s u l p h i d e s i s capable of form-i n g at both h i g h and low temperatures i n accord w i t h the i n f e r r e d t e x t u r a l evidence. 100 The c o n d i t i o n s of f o r m a t i o n of maghemite (1^6203) are not w e l l known. I t i s b e l i e v e d t o be an i n t e r m e d i a t e p o l y -morph between magnetite and hematite (°<Fe203). According to Kuno (1965) maghemite may form as an a l t e r a t i o n process de-pendant on oxygen f u g a c i t y and temperature a f t e r magmatic c r y s t a l l i z a t i o n i s e s s e n t i a l l y complete. Experimental data shows t h a t maghemite can be formed by o x i d a t i o n of magnetite from 200 t o 700°C i n both n a t u r a l and s y n t h e t i c systems. Thermal s t u d i e s by G h e i t h (1952) on magnetites showed exo-thermic peaks corresponding to the f o r m a t i o n of X Fe20^ to vary from 280 to 375°C. However, more r e c e n t o p i n i o n s o f f e r e d by A b d u l l a h and A t h e r t o n (19&+) and Gross (1965) s t a t e that maghemite i s most commonly formed a f t e r prolonged s u r f a c e o x i d a t i o n or by r a p i d o x i d a t i o n at low temperatures under aqueous c o n d i t i o n s such as i n the case of low grade thermal metamorphism. S u l p h i d e s : The e a r l i e s t s u l p h i d e s to form were molybdenite along w i t h p y r i t e and some p y r r h o t i t e . Molybdenite i s a hi g h temperature m i n e r a l whose maximum temperature of s t a b i l i t y i s w e l l above the temperature of the g r a n o d i o r i t e i n t r u s i o n . S u l p h i d e d e p o s i t i o n that r e s u l t e d i n the f o r m a t i o n of molyb-d e n i t e - p y r i t e - p y r r h o t i t e i n quartz v e i n s can be assigned an upper temperature l i m i t of 7*+2 1 i ° c a c c o r d i n g to Barton and Skinner (1967) or 726°C a c c o r d i n g to K u l l e r u d and Buseck (1962) as based on s t u d i e s of system Mo-Fe-S. The temperatures of 101 f o r m a t i o n of molybdenite may, indeed, be w e l l below these maxima as Arutuyan (1966) has s y n t h e s i z e d molybdenite at r e l a t i v e l y low temperatures. Using sulphomolybdate s o l u t i o n f o l l o w e d by a n n e a l i n g , Arutuyan formed c o l l o f o r m molybdenite at 200 to 300°C and from t h i s a t r i g o n a l polymorph (3R) w i t h s h o r t runs at temperatures from 350 to 900°C. A t r a n s f o r m a t i o n i n t o the normal hexagonal molybdenite was accomplished at 600°C over a time of 22 days. The abundance of p y r i t e and p y r r h o t i t e and use „of phase r e l a t i o n s i n the system Fe-S are of very l i t t l e use i n the present study f o r purposes of geothermometry. Besides the u n c e r t a i n s t a t u s of the p y r r h o t i t e geothermometer, the s t r u c -t u r a l s t a t e of the p y r r h o t i t e i s not known and there i s a p e r s i s t a n t a s s o c i a t i o n o f c h a l c o p y r i t e . As s t a t e d by Rao and Rao (1968) a f t e r the s u g g e s t i o n by Yund and K u l l e r u d (1966), 1 ( t h e u s e f u l n e s s of p y r r h o t i t e as a geothermometer) when i t i s a s s o c i a t e d w i t h c h a l c o p y r i t e i s d o u b t f u l . ' The only use-f u l i n f o r m a t i o n d e r i v e d from the F e - S system i s that a maximum temperature of f o r m a t i o n f o r the p y r i t e can be set at 7*+2 or 7*+3 ± 1°C + lk°C per k i l o b a r , ( K u l l e r u d and Yoder, 1959; A r n o l d , 1962; K u l l e r u d , 1967). Above t h i s temperature the s u l p h i d e s would have been h i g h temperature p y r r h o t i t e i n c o e x i s t e n c e w i t h a s u l p h u r - r i c h melt. The f o r m a t i o n of marcasite, as d e f i n e d i n system Fe-S-O-H ( K u l l e r u d , 1957» 1967) > occurs at temperatures l e s s than ^32°C and i s pressure dependent. The observed a s s o c i a -t i o n of p y r i t e and marcasite at the assumed pressure of 1 0 2 1 0 0 0 bars, would have a maximum temperature of f o r m a t i o n of >+28 ± 2°C. The most important system i n t h i s study i s Cu-Fe-S because of the abundance and c o n s i s t e n t a s s o c i a t i o n of p y r i t e -p y r r h o t i t e and c h a l c o p y r i t e . However, use of phase r e l a t i o n s t o d e f i n e c o n d i t i o n s of f o r m a t i o n i s l i m i t e d due to the com-p l e x r e l a t i o n s and c o n f u s i o n at low temperatures. The phase r e l a t i o n s , as developed by Yund and K u l l e r u d ( 1 9 6 6 ) show a wide range of p y r i t e - c h a l c o p y r i t e s t a b i l i t y , s t a r t i n g at 7 3 9°C. At high temperatures ( 6 0 0 t o 7 0 0°C or more) e x t e n s i v e s o l i d s o l u t i o n f i e l d s are developed. C h a l c o p y r i t e c o e x i s t s w i t h p y r i t e and p y r r h o t i t e and both c h a l c o p y r i t e and p y r r h o t i t e have e x t e n s i v e s o l i d s o l u t i o n . As temperature decreases, s t r u c t u r a l i n v e r s i o n s i n the c h a l c o p y r i t e take p l a c e and at a temperature of about 550°C the c h a l c o p y r i t e s o l i d s o l u t i o n i s s p l i t i n t o two s m a l l e r f i e l d s of cubanite and c h a l c o p y r i t e w i t h the l i n e s forming between the cubanite and p y r i t e . Because of the abundance of i r o n over copper i n n a t u r a l s y s -tems, cubanite would be expected to be commonly formed r e l a -t i v e t o c h a l c o p y r i t e ( K u l l e r u d , 1 9 6 7 ) . However, the cubanite i s not a r e a d i l y quenchable phase and at a temperature of 3 3^°C i t cannot e x i s t w i t h p y r i t e and w i l l r e a c t to form c h a l c o p y r i t e and p y r r h o t i t e . Cubanite, furthermore, cannot, e x i s t w i t h m o n o c l i n i c p y r r h o t i t e and thus moooclinic p y r r h o t i t e , p y r i t e , and c h a l c o p y r i t e would be the expected assemblage at a tempera-t u r e l e s s than 3 1 0°C, which i s the upper temperature boundary 103 f o r m o n o c l i n i c p y r r h o t i t e ( K u l l e r u d , 1967; A r n o l d , 1968). Based on these c o n s i d e r a t i o n s , the absence of cubanite and the i n t i m a t e a s s o c i a t i o n of c h a l c o p y r i t e - p y r r h o t i t e i n the presence of p y r i t e i n the i n t r u s i v e , suggest t h a t r e - e q u i l i b r i a -t i o n of s u l p h i d e s probably s t a r t e d at hig h temperatures and continued throughout the c o o l i n g h i s t o r y . D e p o s i t i o n i n the i n t r u s i o n could have s t a r t e d at the maximum temperatures of f o r m a t i o n of p y r i t e at 757 ± 1°C (at 1000 bars) and c h a l c o -p y r i t e at 739°C, but f i n a l temperatures of f o r m a t i o n were con-s i d e r a b l y lower and may even have been below 331+0C, the s t a -b i l i t y l i m i t of cu b a n i t e . Such r e l a t i o n s are c o n s i s t e n t w i t h the occurrence of c h a l c o p y r i t e - p y r i t e - p y r r h o t i t e i n the r e l a t i v e l y low temperature h o r n f e l s environment and the para-genesis which shows some of the c h a l c o p y r i t e and p y r r h o t i t e to be younger than marcasite which has an upper temperature 6 f f o r m a t i o n at 1000 bars of ^-28°C. The system Fe-As-S o f f e r s u s e f u l and exact i n f o r m a t i o n r e g a r d i n g c o n d i t i o n s of fo r m a t i o n . C l a r k (i960) determined the phase r e l a t i o n s and found that *+91 - 12°C i s an i n v a r i e n t p o i n t that defines" the maximum temperature of s t a b i l i t y of p y r i t e w i t h a r s e n o p y r i t e . Above t h i s temperature p y r r h o t i t e and l i q u i d form w i t h a r s e n o p y r i t e . The system i s pressure s e n s i t i v e and the i n v a r i e n t p o i n t v a r i e s 18°C per k i l o b a r p r e s s u r e . The mineral assemblage observed c o n t a i n s p y r i t e and a r s e n o p y r i t e which appear to be mutually deposited i n the pre-sence of excess i r o n that formed a younger replacement ICAf p y r r h o t i t e and p y r i t e . The temperature of form a t i o n , w i t h a pressure c o r r e c t i o n f o r the assumed depth of i n t r u s i o n , can be determined t o have been a maximum of 509 - 12°C. The other minerals i n the assemblage provide very l i t t l e d e t a i l e d i n f o r m a t i o n beyond upper temperature s t a b i l -i t y l i m i t s . Galena and s p h a l e r i t e both have very high congru-ent melting p o i n t s . T e t r a h e d r i t e and t e n n a n t i t e have upper temperature l i m i t s of 555°C and 6i+0°C, r e s p e c t i v e l y (Wernick and Benson, 1957). V i r t u a l l y no phase data i s a v a i l a b l e f o r bournonite and a i k i n i t e as they are d i f f i c u l t t o s y n t h e s i z e and have complex multicomponent compositions. An upper temperature l i m i t f o r a i k i n i t e has been determined to be from ^65 to i+-75°C (Schaber, 1965). T e x t u r a l r e l a t i o n s and p a r t i c u l a r l y e x s o l u t i o n and unmixing t e x t u r e s have long been considered to provide data r e g a r d i n g temperatures of f o r m a t i o n or c o o l i n g r a t e s . Edwards ( I 9 6 0 ) provides temperatures of unmixing f o r the f o l l o w i n g m i n e r a l p a i r s : C h a l c o p y r i t e - p y r r h o t i t e 600°C c h a l c o p y r i t e exsolves 300°C p y r r h o t i t e exsolves C h a l c o p y r i t e - t e t r a h e d r i t e ?5tD°C S p h a l e r i t e - C h a l c o p y r i t e 550°C c h a l c o p y r i t e exsolves 350°C- I+00 oC s p h a l e r i t e e x s o l v e s However, the work of B r e t t (196Lra,b) and others has cast much doubt as to the v a l i d i t y of q u a n t i t a t i v e data based on tex-t u r a l s t u d i e s as g e n e t i c c r i t e r i a . 105 The c o n d i t i o n s of f o r m a t i o n of the m e t a l l i c minerals have, thus, had maximum temperature l i m i t s or temperature ranges d e f i n e d . The maximum temperature of f o r m a t i o n pos-s i b l e would have been the temperature of c r y s t a l l i z a t i o n which was assumed to be about 815 1 25°C at a c o n f i n i n g p r e s -sure of 1000 bars. W i t h i n the i n t r u d e d rocks m i n e r a l i z a t i o n was developed i n the h o r n f e l s zone, u s u a l l y w i t h i n one hundred f e e t of the c o n t a c t , where the temperatures were c a l c u l a t e d t o range from about J+OO t o a maximum of about 550°C at the c o n t a c t . The s u l p h i d e s t u d i e s i n d i c a t e t h a t f o r m a t i o n of the observed m i n e r a l assemblages occurred at h i g h tempera-t u r e s . R e - e q u i l i b r i a t i o n throughout the c o o l i n g h i s t o r y i s c o n s i d e r e d l i k e l y and the paragenesis d e f i n e s a long h i s t o r y of m i n e r a l i z a t i o n w i t h s u c c e s s i v e stages. Thus, the stages of m i n e r a l i z a t i o n c a l l e d Stages 1, 11, 111, and probably much of Stage IV were formed at e l e v a t e d temperatures under r e l a t i v e l y , s i m i l a r c o n d i t i o n s . The only minerals that may have been d e p o s i t e d under lower temperature c o n d i t i o n s are the l a t e forming s u l p h o s a l t s , and some s u l p h i d e s of Stage IV. Based on s t u d i e s of other s u l p h o s a l t assemblages, the tempera-t u r e of d e p o s i t i o n may have been i n the order of 300°C. The r e s u l t s are summarized i n Table IV. Table IV: Temperature data from s i l i c a t e systems, heat flow c a l c u l a t i o n , and i n v a r i e n t p o i n t s from condensed phase diagrams of systems a p p l i c a b l e to the Driftwood mineral assemblage. M i n e r a l or a s s o c i a t i o n System Maximum temperature High temperature Remarks and Documentation G r a n o d i o r i t e - q u a r t z monzonite H o r n f e l s contact zone Magnetite Fe - 0 Ma ghemite ( t f F e ^ - ^ ) Fe - 0 of s t a b i l i t y or (temperature range) 815 £ 25°C 550°C 1 » 675°C 11< 675°C ?28o - 375°c ? 20°C products s i l i c a t e melt hornblende h o r n f e l s f a c i e s and a l b i t e -e p i d ote -horn-f e l s f a c i e s . Fe 2 0 3 + ^  melt magnetite plus Fe s u l p h i d e s . Temperature at s o l i d u s f o r c o m p o s i t i o n a l average of 18 Driftwood specimens f o r system a l b i t e - o r t h o c l a s e -q u a r tz; (Annual Rept. Geophys. Lab., (1951-52). Contact temperatures. Contact metamorphic zone. Heat flow c a l c u l a t i o n s by L o v e r i n g , 1936; Jaeger, 1957, 1959; Buseck, 1966; and Winkler, 19&5. Primary phase. Sulphide breakdown and S -0 exchange due to decrease i n p 0 2 and pS 2. ( H o l l a n d , 1959); ( S a l o t t i , 196k),. (Buseck, I 9 6 6 ) . Hematite («Fe20o) Intermediate phase between magnetite-hematite. (Gheith, Magnetite?? Hematite ei 1952). Surface o x i d a t i o n . ( A b d u l l a h and Atherton, 196*+); (Gross, 1965). o ON Table IV: (continued) M i n e r a l or a s s o c i a t i o n System Maximum temperature of s t a b i l i t y or (temperature range) M o l y b d e n i t e - p y r i t e Fe-Mo-S 7^2 + 1 G or 726°C P y r i t e - p y r r h o t i t e Fe-S 7*+2 or 7 1 +3 ± 1°C plus lt+°C/Kbar = 7 5 7 * 1°C M a r c a s i t e - p y r i t e Fe-S-O-H < l f32°C = 1+28 ± 2°C ( w i t h pressure c o r r e c t i o n ) C h a l c o p y r i t e - p y r i t e - Cu-Fe-S 7 3 9°C ( p y r r h o t i t e ) C h a l c o p y r i t e - 6 0 0°C 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 r h o t i t e 3 3^°C High temperature Remarks and Documentation  products  P y r r h o t i t e + Low temperature s y n t h e s i s molybdenite + of molybdenite p o s s i b l e , melt. (Aratuyan, 1 9 6 6 ) ; (Barton and Skinner, 1 9 6 7 ) ; K u l l e r u d - • and Buseck, 1 9 6 2 ) . P y r r h o t i t e + K u l l e r u d and Yoder, 1 9 5 9 ; m e l t , A r n o l d , 1 9 6 2 ; K u l l e r u d , 1 9 6 7 . P y r i t e Pressure s e n s i t i v e . (Kullerud, 1 9 5 7 , 1 9 6 7 ) . p y r r h o t i t e +• melt Yund and K u l l e r u d , 1 9 6 6 . p y r r h o t i t e w i t h E x s o l u t i o n of c h a l c o -Cu s o l i d s o l u - p y r i t e . Edwards, I960, t i o n Cubanite Low temperature i n v e r -s i o n of c u b a n i t e , Yund and K u l l e r u d , 1966; o Table IV: (continued) M i n e r a l or a s s o c i a t i o n System. Maximum temperature of " s t a b i l i t y or (temperature range) C h a l c o p y r i t e -P y r r h o t i t e ( M o n o c l i n i c ) Cu-Fe-S 310°C C h a l c o p y r i t e -p y r r h o t i t e 300°C Arsenopyrite-p y r i t e Fe-As-S L f 9 1 - 1 2°C+ l 8°CAbar = 509±12°C T e t r a h e d r i t e Cu-Sb-S (Te n n a n t i t e ) T e t r a h e d r i t e -c h a l c o p y r i t e S p h a l e r i t e -c h a l c o p y r i t e Cu-As-S Cu-Fe-S Zn-Fe-S (6U0°C) ?5oo°c 55o°c 35o-IfOO°c A i k i n i t e Pb-Cu-Bi-S l+65-1+75°G High temperature products  Remarks and Documentation Cubanite (May be a s s o c i a t e d w i t h p y r r h o t i t e (hexagonal) ?Cubanite or C h a l c o p y r i t e w i t h Fe s o l i d s o l u t i o n P y r r h o t i t e + melt melt (melt) T e t r a h e d r i t e w i t h Cu s o l i d s o l u t i o n S p h a l e r i t e w i t h s o l i d s o l u t i o n C h a l c o p y r i t e w i t h Zn s o l i d s o l u t i o n Cubanite unstable i n p r e s -sence of monoclinic pyrrhot-i t e , K u l l e r u d , 1967; A r n o l d , 1968. Edwards, i 9 6 0 . P y r r h o t i t e e x s o l u t i o n . (May be r e -s u l t of cubanite i n v e r -s i o n ) . Pressure s e n s i t i v e system. (Corrected f o r k km . depth). C l a r k , i 9 6 0 . Driftwood mineral may be As - r i c h . Wernick and Benson, 1957. Edwards, i 9 6 0 . Edwards, i 9 6 0 melt Schaber, 1965. |-> o 0 0 109 SUMMARY AND CONCLUSIONS The Driftwood Property i s u n d e r l a i n by v o l c a n i c -sedimentary rocks that were dated as Lower J u r a s s i c and c a l l e d T a k l a Group - Upper D i v i s i o n by Lord, 19*+8. The rocks are more c o r r e c t l y c o r r e l a t e d w i t h the Haz e l t o n Group. To the west are Upper J u r a s s i c - Lower Cretaceous sedimen-t a r y rocks of the Bowser Group and to the east are Upper Cretaceous and Paleocene s t r a t a of the Sustut Group. A p o r p h y r i t i c Kastberg I n t r u s i o n of probable E a r l y T e r t i a r y age has in t r u d e d a sedimentary and v o l c a n i c s e c t i o n of the Ta k l a Group. The i n t r u s i v e mass has a h i g h l y i r r e g u -l a r r o o f zone w i t h many anastamosing dykes and ro o f pendants t h a t are exposed along the c r e s t of a r i d g e . At depth the i n t r u s i o n i s a t h i c k , s t e e p l y d i p p i n g d y k e - l i k e body. The main i n t r u s i o n i s surrounded by many small dykes. The composition of the stock v a r i e s from g r a n o d i o r i t e to quartz monzonite and a l a s k i t e . D i f f e r e n c e s i n the stock are shown, by v a r i a t i o n s i n texture,, mineralogy, and chemical composition. Metamorphism of the in t r u d e d rocks has produced an enveloping zone of h o r n f e l s about the i n t r u s i o n . The h o r n f e l s i s mainly a b i o t i t e h o r n f e l s of the a l b i t e - e p i d o t e h o r n f e l s f a c i e s but sm a l l zones of higher grade h o r n f e l s i n the horn-blende h o r n f e l s f a c i e s can be seen i n c a l c - s i l i c a t e and mafic h o r n f e l s zones. Automorphic a l t e r a t i o n w i t h i n the stock i s 110 a s s o c i a t e d w i t h hydrothermal m i n e r a l i z i n g processes and has formed p r o p y l i t i c a l t e r a t i o n zones. The stock i s a metal enriched i n t r u s i o n with m i n e r a l i z a t i o n c h a r a c t e r i s t i c of porphyry copper and quartz-molybdenum stockwork d e p o s i t s . M e t a l l i c minerals have been deposited as disseminated, f r a c t u r e f i l l i n g , and replacement g r a i n s and v e i n c o n s t i t u e n t s i n the s t o c k and h o r n f e l s . Minor m i n e r a l i z a t i o n i s found i n skarn and b r e c c i a zones. Weather-i n g a f f e c t s are s u p e r f i c i a l and very few a l t e r a t i o n minerals were r e c o g n i z e d . Genesis of the m e t a l l i c minerals as deduced from main-l y s i l i c a t e - s u l p h i d e and s u l p h i d e t e x t u r e s and f a b r i c s i s e p i g e n e t i c . The s u l p h i d e s may be c l a s s e d , i n p a r t , as p a r a -magmatic alth o u g h a small p r o p o r t i o n of the s u l p h i d e s and magnetite have formed as accessory g r a i n s . A f i v e stage paragenesis i s e v i d e n t . Stage 1 i s c r y s t a l l i z a t i o n of the host rock and f o r m a t i o n of accessory magnetite and some p y r i t e , p y r r h o t i t e , and p o s s i b l y molyb-d e n i t e . Stage 11 i s v e i n i n g by molybdenite-bearing quartz v e i n s c a l l e d "blue q u a r t z " v e i n s . State 111 i s the main p e r i o d of p y r i t e , p y r r h o t i t e , c h a l c o p y r i t e d e p o s i t i o n i n the s t o c k and h o r n f e l s and Stage 111a i s the c l o s e l y a s s o c i a -ted v e i n i n g w i t h p y r i t e , 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 i n "white q u a r t z " v e i n s . Stage IV i s f o r m a t i o n of p b l y m e t a l l i c a r s e n o p y r i t e and s u l p h o s a l t bearing q u a r t z -c a l c i t e v e i n s . Stage V i s a l t e r a t i o n of the m i n e r a l i z a t i o n I l l and i s r e l a t i v e l y unimportant. I n t r u s i o n i s b e l i e v e d to have been i n the epizone at a depth of about four k i l o m e t e r s . Temperature of i n t r u -s i o n i s estimated to have been about 815 - 25°-C. Temperatures at the i n t r u s i v e contact have been estimated by heat flow c a l c u l a t i o n s and are b e l i e v e d to have been about 1+95° to 550°G. Temperatures of t h i s magnitude are c o n s i s t e n t w i t h the grades and widths of the c o n t a c t metamorphic zones observed. Temperatures of m e t a l l i c m i neral d e p o s i t i o n are d i f -f i c u l t to e s t a b l i s h but maximum temperatures of f o r m a t i o n of some s u l p h i d e s p e c i e s and c o e x i s t i n g m i n e r a l p a i r s can be d e f i n e d using s y n t h e t i c phase e q u i l i b r i a s t u d i e s . Maximum temperatures of f o r m a t i o n higher than 700°C can be postu-l a t e d f o r p y r i t e , p y r r h o t i t e , molybdenite, c h a l c o p y r i t e , and magnetite using systems Pe-Mo-S, Fe-S, Fe-S-O, and Cu-Fe-S. Maximum temperatures i n the i n t e r m e d i a t e range from kOO to 600°C can be d e f i n e d f o r a r s e n o p y r i t e - p y r i t e , p y r i t e - m a r c a s i t e , t e t r a h e d r i t e , and a i k i n i t e from systems Fe-As-S, Fe-S-O-H, Cu-(Sb, As,)-S, and Pb-Cu-Bi-S. Low temperature d e p o s i t i o n i n the order of 300°C i s i n d i c a t e d by t e x t u r a l o b s e r v a t i o n s coupled w i t h temperatures of ex-s o l u t i o n and i n v e r s i o n i n r e - e q u i l i b r i a t i n g s u l p h i d e s such as p y r r h o t i t e and p y r r h o t i t e - c h a l c o p y r i t e ( o r i g i n a l l y c u b a n i t e ? ) . 112 REFERENCES CITED Ab d u l l a h , M. I., and A t h e r t o n , M. P., 196*+, The thermoraetric s i g n i f i c a n c e of magnetite i n low grade metamor-ph i c r o c k s : Am. Jour. S c i . , v. 262, p. 90*+. Armstrong, J . E., 1 9 ^ 6 , T a k l a , C a s s i a r D i c t r i c t , B r i t i s h Columbia: Geol. Surv., Canada, Map 8M+ A. , 19*+95 F o r t St. James Map - Area, C a s s i a r and Coast D i s t r i c t s , B r i t i s h Columbia: Geol. Surv., Canada, Memoir 2 5 2 . A r n o l d , R. G., 1 9 6 2 , E q u i l i b r i u m r e l a t i o n between p y r r h o t i t e and p y r i t e from 3 2 5°C: Econ. 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A d e s c r i p t i v e p e t r o l o g y of the igneous r o c k s : The Univ. of Chicago P r e s s , Chicago, 111. K e r r , P. F., 1959? O p t i c a l mineralogy: McGraw-Hill P u b l i -shing Company. K u l l e r u d , G., 1957 > Phase r e l a t i o n s i n the Fe-S - 0 system: Carnegie I n s t . Washington Year Book, v. 56, p. 195-196. , 1967? Sulphide s t u d i e s : i n -Researches i n geochemistry, v. 2: P. H. Abel'son, e d i t o r . 115 , and Yoder, H. S., 1959, P y r i t e s t a b i l i t y r e l a t i o n s i n the Fe - 3 system: Econ. Geol., v. 5^, P.535-572. , and Buseck, P. R., 1962, The Fe-Mo-S system: Carnegie I n s t . Washington Year Book, v. 61 , p. 150-151. Kuno, H., 1965, F r a c t i o n a t i o n trends i n b a s a l t magmas i n l a v a f l o w s : Jour. Pet., v. 6, p. 302. Larsen, E. S., 1938, Some new v a r i a t i o n diagrams f o r groups of igneous r o c k s : Jour. GeoL, v. ^ 6 , p. 505. Lord 19^3, McConnell Creek Map-Area, C a s s i a r D i s -t r i c t , B r i t i s h Columbia: Geol. Surv., Canada, Memoir 251. L o v e r i n g , T. S., 1936, Heat c o n d u c t i o n i n d i s s i m i l a r rocks and the use of thermal models: Geol. Soc. America B u l l . , v. 47-, p. 87-100. , 1955, Temperatures i n and near i n t r u s i o n s : Econ. Geol. F i f t i e t h A nniversary V o l . , p. 2^9-281. MacLean, W. H., and C l a r k , L. A., 1968, L i q u i d u s phase r e l a -t i o n s i n the system FeS-Fe0-Fe30q-Si0>: ( A b s t r a c t ) paper presented at symposium - Exp e r i m e n t a l methods i n P e t r o l o g y and Ore Genesis, London, Ont. Meyer, C , and Hemley, J . J . , 1967, Wall rock a l t e r a t i o n : i n Geochemistry of Hydrothermal ore d e p o s i t s , H. L. Barnes, e d i t o r . N i e l s e n , R. L., 1968, Hypogene t e x t u r e and m i n e r a l zoning i n a copper-bearing g r a n o d i o r i t e porphyry stock, Santa R i t a , New Mexico: Econ. 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America Memoir 7*+. Uytenbogaardt, W., 1951? Tables f o r m i c r o s c o p i c i d e n t i f i c a -t i o n of ore m i n e r a l s : Hafner P u b l i s h i n g Company, New York. Yund, R. A., and K u l l e r u d , G., 1966, Thermal s t a b i l i t y of assemblages i n the Cu-Fe-S system: Jour. Pet. , v. 7, P. I+57-l+88. Winkler, H. G. F., 1965> P e t r o g e n e s i s of metamorphic r o c k s : S p r i n g e r - V e r l a g , New York Inc. Wernick, J . H., and Benson, K. E., 1957? New semiconducting t e r n a r y compounds: Jour. Phys. Chem. S o l i d s , v. 3 , P. 157-159. White, W. H., Harakal, J . E., and C a r t e r , N. C. , 1968. Potassium-argon ages of some ore d e p o s i t s i n B r i t i s h Columbia: T r a n s a c t i o n s CIM, v. 6 l , No. 680. W i l l i a m s , H., Turner, F. J . , and G i l b e r t , C. M., 195*+. Petrography: V/. H. Freeman and Company. MAP h GEOLOGY - DRIFTWOOD PROPERTY *oo0 L E G E N D GRANODIORITE - QUARTZ MONZONITE PORPHYRY VOLCANICS SEDIMENTARY ROCKS Bedding attitude Fault attitude Schistosity Location of diamond drill hole - observed Fault - inferred Attitude of dyke Contact " observed - inferred Geology and topography A. Panteleyev, 1966 Base Map- Air Photograph BC 2225 97 

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