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Geology of the Ox Lake Cu - Mo porphyry deposit Richards, Gordon Gwyn 1974

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GEOLOGY OF THE OX LAKE Cu - Mo PORPHYRY DEPOSIT by GORDON GWYN RICHARDS B . A . S c . , 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 , 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n t h e Depa r tment o f GEOLOGICAL SCIENCES We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA F e b r u a r y , 1974 In presenting t h i s t h e s i s in p a r t i a l f u l f i l m e n t of the requirements an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree th the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I f u r t h e r agree that permission for extensive copying of t h i s thesis f o r s c h o l a r l y purposes may be granted by the Head of my Department o by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Depa rtment The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada i i ABSTRACT The Ox Lake copper-molybdenum deposit i s l o c a l l i z e d i n the margin and contact zone of a Late Cretaceous granodiorite porphyry. Hazelton Group rocks, including a lower F e l s i c Tuff, a middle Andesitic Tuff and an upper Sandstone-SiItstone, are country rocks i n the area. The granodiorite porphyry i s nearly c i r c u l a r i n cross-section with a radius of 1500 feet and plunges f i f t y degrees west. Intrusive breccia occurs mainly along the southwestern contact of the porphyry. Nine vein types are grouped into four stages of vein develop-ment based on r e l a t i v e ages determined from vein intersections. They are: Stage I Potassic and B i o t i t e Veins Stage II P r o p y l i t i c and Pyrite-Chalcopyrite Veins Stage I I I Quartz-Molybdenite and Quartz Veins Stage IV C a l c i t e , Gypsum and Sphalerite Veins Potassic, a l b i t i c , p r o p y l i t i c , s e r i c i t i c and intermediate a r g i l l i c a l t e r a t i o n zones are related to host rock and position around the in t r u s i o n . In the east, an outer potassic a l t e r a t i o n zone i s separated from the intrusion by a zone of a l b i t i c - p r o p y l i t i c a l t e r a t i o n . Three p r o p y l i t i c assemblages are distr i b u t e d zonally about the intrusion. S e r i c i t i c and intermediate a r g i l l i c a l t e r a t i o n occur only i n rocks of ac i d i c composition. The intrusion i s unaltered except within 100 feet of i t s western contact. i i i B r e c c i a t e d and u n b r e c c i a t e d h o r n f e l s w e s t o f t h e i n t r u s i o n c o n t a i n s t h e h i g h e s t and most p e r s i s t e n t g r a d e s o f c o p p e r and m o l y b d e n u m - -a b o u t 0 . 5 p e r c e n t c o p p e r and 0 . 0 2 p e r c e n t molybdenum. W i t h i n t h i s z o n e , f e l d s p a r p o r p h y r y c o n t a i n s two t o f i v e t i m e s t h e molybdenum c o n t e n t and a b o u t o n e - h a l f t h e c o p p e r c o n t e n t o f a d j a c e n t a n d e s i t i c r o c k s . The Ox L a k e p o r p h y r y d e p o s i t i s one o f a g r o u p h a v i n g s i m i l a r g e o l o g i c a l f e a t u r e s , t h a t i n c l u d e s L e n , F a b , L a u r a and B e r g e t t e d e p o s i t s . A l l c o n t a i n c o p p e r and molybdenum m i n e r a l i z a t i o n and have a p p a r e n t K - A r a g e s o f 83 ± 3 my, e x c e p t f o r t h e B e r g e t t e w i t h an age o f 7 6 . 7 ± 2 . 5 my [ C a r t e r and H a r a k a l p e r s o n a l c o m m u n i c a t i o n ] . i v TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v LIST OF FIGURES v i i i ACKNOWLEDGEMENTS x i Chapter I. INTRODUCTION 1 LOCATION 3 ACCESS 4 HISTORY 4 I I . GENERAL GEOLOGY 6 REGIONAL GEOLOGY 6 LOCAL GEOLOGY 9 1. Hazel ton Group 9 (a) F e l s i c T u f f 11 (b) A n d e s i t i c T u f f 16 (c ) S a n d s t o n e - S i l t s t o n e 18 2 . I n t r u s i v e Rocks 19 (a) G r a n o d i o r i t e 20 (b) I n t r u s i v e B r e c c i a 24 (c) D i o r i t e 25 (d) Dykes 26 V C h a p t e r P a 9 e 3 . M e t a m o r p h i s m . . . . 27 ( a ) R e g i o n a l 27 (b ) C o n t a c t 27 4 . S t r u c t u r e 28 I I I . VEINS 34 VEIN TYPES 35 1. P o t a s h F e l d s p a r V e i n s - - 35 2 . B i o t i t e V e i n s . 35 3 . P r o p y l i t i c V e i n s 36 4 . P y r i t e - C h a l c o p y r i t e V e i n s 37 5 . Q u a r t z - M o l y b d e n i t e V e i n s 38 6 . Q u a r t z V e i n s 40 7 . C a l c i t e V e i n s • 40 8 . Gypsum V e i n s 40 9 . S p h a l e r i t e V e i n s 41 DISCUSSION • • • • 42 VEIN STAGES 44 1. S t a g e I 44 2 . S t a g e I I 44 3 . S t a g e I I I 46 4 . S t a g e IV 46 I V . ALTERATION 50 EAST ZONE 52 INTRUSIVE ZONE 54 v i Chapter Page 1. Intermediate A r g i l l i c A l t e r a t i o n 55 2. Potash Feldspar A l t e r a t i o n 59 ORE ZONE 59 1. Peripheral Zone 61 2. A c t i n o l i t e Zone 61 3. Epidote Zone 62 4. Chlorite Zone 63 BRECCIA ZONE 66 DISCUSSION 67 1. Potassic A l t e r a t i o n 70 2. A l b i t i c A l t e r a t i o n 72 3. P r o p y l i t i c A l t e r a t i o n 72 4. S e r i c i t i c A l t e r a t i o n 73 5. Intermediate A r g i l l i c A l t e r a t i o n 74 V. OPAQUE MINERALOGY 75 MINERALS 75 1. Pyrite 75 2. Chalcopyrite 77 3. Bornite 79 4. Hematite 79 5. Magnetite 80 6. Pyrrhotite 80 7. Molybdenite 80 8. Others 81 v i i Chapter Page ZONING OF COPPER AND MOLYBDENUM 81 SUMMARY 83 . V I . REGIONAL CHARACTERISTICS OF PORPHYRY DEPOSITS . . . . 85 SUMMARY 85 DISCUSSION . . . . . . 88 V I I . SUMMARY 92 REFERENCES 97 APPENDIX map i n pocket v i i i LIST OF FIGURES Figure Page 1. Location map of the Ox Lake copper-molybdenum deposit 2 2. Diagrammatic restored sections i l l u s t r a t i n g the accumulation and i n t e r r e l a t i o n s of the Takla-Hazelton assemblage. After Souther and Armstrong [1966], 7 3. Above: Oblique drawing of topography and general geology. Below: Detailed geology projected from d r i l l holes onto plane of projection shown i n to diagram 8 4. Schematic st r a t i g r a p h i c column of Hazel ton Group i l l u s t r a t i n g interpreted i n t e r r e l a t i o n s of units. Sandstone-SiItstone dips steeply SW 10 5. Sample pairs of unaltered feldspar porphyry. Note v a r i a b i l i t y of texture. Lower samples etched with hydrofluoric acid and stained with sodium cobalt-i n i t r i t e . Yellow indicates potash feldspar, white indicates plagioclase, clear indicates quartz and grey indicates other minerals 12 6. Thin section of feldspar porphyry showing a l b i t e phenocrysts set in matrix containing spheres of intergrown potash feldspar and quartz with small a l b i t e c r y s t a l s 12 7. Samples of f e l s i c t u f f . Dark layers and bedding are rare within this rock type 14 8. Typical dark brown mafic crystal t u f f containing few rock fragments and a l b i t e c r y s t a l fragments . . . . 14 9. Three samples of l a p i l l i t u f f and one sample of the more abundant fine-grained andesite. F e l s i c fragments are s i m i l a r to feldspar porphyry and f e l s i c t u f f 17 10. From l e f t to r i g h t ; s i l t s t o n e , sandstone, chert-pebble conglomerate 17 11. Shape of plug and occurrence of breccia. West-ward plunge of plug indicated from elevation contours of granodiorite-hornfels contact 21 i x Figure Page 12. Typical texture of granodiorite porphyry. Sample i s hornblende r i c h variety 22 13. Typical sample of medium-grained d i o r i t e with a-ty p i c a l a l t e r a t i o n along fracture 22 14. A i r photograph interpretation of lineaments . . . . . 29 15. Position of the various zones about the grano-d i o r i t e porphyry. Section l i n e i s f o r Figures 22, 25 and 26 32 16. Above: Diagrammatic intersections of some vein types showing r e l a t i v e ages. Below: Data i n -dicating r e l a t i v e ages of vein types . . 33 17. Diagrammatic map i l l u s t r a t i n g a l t e r a t i o n of plagioclase phenocrysts within feldspar por-phyry and granodiorite porphyry . 48 18. Diagrammatic map i l l u s t r a t i n g occurrence of ,alteration minerals b i o t i t e , c h l o r i t e , epidote, and a c t i n o l i t e related to the granodiorite porphyry 49 19. Sample pairs showing a l t e r a t i o n products within feldspar porphyry of the East Zone. Sample on r i g h t i s unaltered feldspar porphyry. Dark coloured matrix i n three altered samples on l e f t i s caused by hydrothermal b i o t i t e . Phenocrysts i n l e f t sample are a l b i t e . Phenocrysts in middle two samples are potash feldspar. Note a l b i t e envelope about an epidote subtype p r o p y l i t i c vein i n second sample from l e f t 51 20. Photograph of intermediate a r g i l l i c a l t e r a t i o n envel-ope and corresponding graph of mineral abundances away from vein. Note quartz vein with central c a l c i t e 56 21. Photograph of a potash feldspar envelope and corresponding graph of mineral abundances away from vein. Note p y r i t e - c a l c i t e vein 58 22. Variation of mineral abundances within the Ore Zone and adjacent Intrusive Zone. Line of section shown in Figure 15. Note control of host rock on a l t e r a t i o n assemblages X Figure Page 23. Samples of andesite and feldspar porphyry within the Epidote Zone of the Ore Zone s i x hundred feet from the intrusion. Middle feldspar porphyry sam-ple contains a pyrite vein with quartz-sericite a l t e r a t i o n . Andesite samples contain epidote subtype veins with a l b i t e and minor potash feldspar envelopes 64 24. Samples of feldspar porphyry within the Chlorite and Epidote Zones of the Ore Zone within two hundred feet of the in t r u s i o n . Potash feldspar, s e r i c i t e , k a o l i n i t e and montmorillonite are present as a l t e r a t i o n products of a l b i t e but t h e i r relationship to individual veins i s obscure. Some of the potash feldspar c l e a r l y occurs along fractures 64 25. F i r s t three stages of vein development. Line of section indicated i n Figure 15 68 26. Four stages of vein development and associated a l t e r a t i o n assemblages. Refer to Figure 25. Question mark denotes mineral may not have developed with indicated vein type. Note control of host rock on vein-alteration assemblage 69 27. Diagrammatic d i s t r i b u t i o n of the f i v e most abundant opaque minerals within the deposit 76 28. One of the larger bornite-chalcopyrite inclusions and a smaller one within a disseminated pyrite grain 78 29. Zoning of copper and molybdenum assays within the deposit. Note strong control of host rock on grades. Plane of projection i s indicated i n Figure 3 82 30. Apparent K-Ar ages of porphyry deposits within the general area of Ox Lake from Carter and Harakal (personnal communication). Geology taken from Geological Survey of Canada map 1064A 89 31. Comparison of the Ox Lake porphyry deposit with several other porphyry deposits. After White et al_. (1968), Carter and Harakal personal communication. B.C. Minis-ter of Mines and Petroleum Resources Annual Reports — 1964, 1966, 1968, 1969, 1970, 1971 90 ACKNOWLEDGEMENTS The writer thanks Mr. T. Osborne of American Smelting and Refining Company for offering the Ox Lake deposit as a thesis topic and for providing the author with ten days on the property to c o l l e c t samples. American Smelting and Refining Company and S i l v e r Standard Mines Limited who hold j o i n t ownership of the deposit provided reports of the property and assay data of d r i l l hole samples. Assistance from the personnel of these companies i s g r a t e f u l l y acknowledged. Supervision of the thesis was provided by the l a t e Dr. J. Gower, Dr. J . Chamberlain, and Dr. A.J. S i n c l a i r . Their guidance and assistance throughout the study has been of great value. Unpublished apparent K-Ar ages were generously provided by Mr. N. Carter of the B r i t i s h Columbia Department of Mines and Petroleum Resources and Mr. J . Harakal of the Geophysics Department, at the University of B r i t i s h Columbia. Frontispiece View looking northeast over Ox Lake towards Tahtsa Reach on the left and Ootsa Lake in the centre distance. 1 CHAPTER I INTRODUCTION The Ox Lake granodiorite porphyry, i n west central B r i t i s h Columbia, i s associated with low-grade copper-molybdenum mineralization. The purpose of t h i s thesis i s to describe the geology of the deposit and examine i t s genesis. Chapter II describes the geology outlined above under the headings of Regional Geology, Local Geology, Metamorphism and Structure. Hazelton Group volcanics are divided into three units and t h e i r d i s t r i -butions, l i t h o l o g i e s and certain primary structural features are discussed i n some d e t a i l . Intrusive rocks include granodiorite, d i o r i t e and basic dykes. An i n t r u s i v e breccia related to the granodior-i t e i s also described separately. The section on metamorphism outlines textures related to hornfels development around the granodiorite and d i o r i t e . Large scale structures such as major lineaments and doming are discussed i n the section on structure. Chapters I I I , IV, and V describe veining, a l t e r a t i o n and mineralization, respectively. As these features are cl o s e l y r e l a t e d , an attempt to show the significance of each i s made i n a discussion following each chapter. Nine vein types are described and grouped into four stages of vein development. Five a l t e r a t i o n types are described and related where possible to s p e c i f i c vein types. Mineral-F i g u r e 1 L o c a t i o n map o f t h e Ox Lake c o p p e r - m o l y b d e n u m d e p o s i t 3 iz a t i o n i s described and zoning of Cu and Mo i s shown to be related to rock type, veining and a l t e r a t i o n . Chapter VI compares the Ox Lake deposit with other Cu-Mo deposits on a regional scale, and summarizes the work of others on K-Ar dating of mineralized intrusions. Chapter VII synthesizes conclusions reached i n previous chapters and presents a summary conclusion on the o r i g i n of the Ox Lake Cu-Mo deposit. LOCATION: (53° 40.2'N; 127° 03'W) Ox Lake i s two miles south of Tahtsa Reach and four miles east of Huckleberry Mountain i n the northern l i m i t of Whitesail Range seventy miles southwest of Smithers, B.C. (Figure 1). The lake i s approximately one-half mile long l i e s at an elevation of 3,080 feet and i s drained by a small creek at i t s north end. Locally, h i l l s r i s e to 3,500 feet compared with the 2,800 foot elevation of Tahtsa Reach, but peaks i n Whitesail Range r i s e to elevations of over 6,500 feet. The h i l l s are t h i c k l y timbered. 4 ACCESS A three-mile-long "cat" road leads south from the south shore of Tahtsa Lake to the property at Ox Lake. This road can be reached by float-equipped a i r c r a f t from several bases such as those at Smithers and Burns Lake both seventy miles distant. The road i s also accessible by boat via the Tahtsa Lake road from Houston to Tahtsa Reach, or via several other roads further east on Ootsa Lake. HISTORY Exploration in the general area began with Alexander Mackenzie's voyage to the P a c i f i c i n 1793. In the l a t e nineteenth century, the area was v i s i t e d by several members of the Geological Survey of Canada, notably G.M. Dawson i n 1875, and James Richardson i n 1879. The beginning of the twentieth century saw the a r r i v a l of s e t t l e r s to the shores of Ootsa Lake. Even with the building of the railway and a paved highway to the east with gravel roads into the area, the s e t t l e d area has not grown west from Ootsa Lake. The building of Kenny Dam on the Nechako River i n 1951 to 1952 by the Aluminium Company of Canada Limited, as part of the Kemano power project, has flooded many of the lakes, thereby providing easy water transport through much of the area. Geological mapping has been carried out by the Geological Survey of Canada and the B.C. Department of Mines over the past 100 years. Mineral exploration began soon a f t e r the turn of the century 5 and continued intermittently to the present day. The main i n t e r e s t i n the area has been with gold, l e a d - z i n c - s i l v e r , tungsten and high grade copper deposits, but since the l a t e 1950's interest has turned to the search f o r low-grade, large-tonnage "porphyry" deposits of which the Ox Lake Cu-Mo deposit i s an example. The Ox Lake deposit was found i n 1968 as a r e s u l t of geo-chemical s i l t sampling by S i l v e r Standard Mines and American Smelting and Refining Co. Follow-up prospecting of a copper anomaly from s i l t taken from the stream draining Ox Lake led to the discovery of dissemin-ated chalcopyrite and molybdenite i n the Ox Lake intrusion and surround-ing volcanic rocks. Eleven diamond d r i l l holes, d r i l l e d i n the f a l l of 1968, outlined a mineralized zone around the western side of the Ox Lake i n t r u s i o n . An additional twenty-three holes were d r i l l e d i n 1969 to better outline t h i s zone and to test other areas near Ox Lake. A prominent gossan associated with a Pb-Zn-Ag vein occurs on a b l u f f over-looking Ox Lake. The author spent ten days on the property i n the f a l l of 1969 to c o l l e c t core and rock samples f o r material f o r t h i s thesis. 6 CHAPTER II GENERAL GEOLOGY REGIONAL GEOLOGY The following summary of the regional geology i s taken from Souther and Armstrong [1966] except where otherwise noted. The Ox Lake granodiorite intrudes sedimentary and volcanic rocks of the Takla-Hazelton Assemblage which developed from submarine and subaerial volcan-ism i n the Nechako Trough. (Figure 2). Much volcanoclastic material, derived from the erosion of volcanic islan d s , i s inter!ayered with the volcanics. Takla Group rocks have an upper T r i a s s i c to Lower Jurassic age and Hazelton Group rocks a Middle Jurassic age. In Whitesail Lake map area the Hazelton group comprises interbedded volcanic and sedimentary rocks over 11,000 feet thick. [Duffel!, 1959]. The most common rock types are volcanic breccias and tu f f s with sedimentary and intermediate to basic flow rocks less common than the fragmental volcanics. Duffel! [1959] separated lower and upper volcanic units by a middle marine sedimentary unit. The main Coast Range Bat h o l i t h i c Complex borders the Takla-Hazelton assemblage to i t s east. Many small intrusions believed related to the Coast Range intrusions intrude the Takla-Hazelton rocks as far east as the Pinchi Geanticline. These intrusions were emplaced from the end of T r i a s s i c time to at least Oligocene time. 7 Figure 2 Diagrammatic restored sections i l l u s t r a t i n g the accumulation and i n t e r r e l a t i o n s of the Takla-Hazelton assemblage. After Souther and Armstrong [1966] j A [ Diorite | fl | Granodiorite Porphyry j c | Sandstone-Siltstone j o [ Andesitic Tuff [ f |fe/s/c 7u/Y S3 Granodiorite Porphyry Andesitic tuff Mafic crystal tuff Felsic tuff l+f-f) Feldspar porphyry intrusive breccia drill hole no. 18 HOUS l n r F U S I V f - H O F r * m S C O N T A C T IS PTWPTNDfCUlAt T O F A F F * H A N I O f P P O / f C T l O N A P P P C f ' W A T f I f r *»*UI tS A l l D»IU H O U S A C T U A L P O R T I O N S O P O M U - M O U C O U A R i INO'C A T F D r My J : - O D C C H T F F£*r m o w P L A N ! 'P(»>(NniCLMA»iFI • I/O ' i p r i ' p f f r A * O V F p o u t ( P f P p f . D i r u t A i i r i Figure 3 Above: Oblique drawing of topography and general geology. Below: Detailed geology projected from d r i l l holes onto plane of projection shown in top diagram 9 Metamorphism of the Hazelton group i s t y p i c a l l y lowgrade with epidote, a l b i t e and c h l o r i t e , the most common a l t e r a t i o n products. More intense a l t e r a t i o n exists near contacts with Coast Range Intrusions. Structures trend northwest. A l l rock units are folded to some degree, usually to braod open folds following the northwest trend. Faults more-or-less p a r a l l e l i n g f o l d axes accentuate the northwest trend. The possible existence of more intense f o l d i n g and major f a u l t s might be obscured by the lack of both marker beds and better exposures. LOCAL GEOLOGY Hazelton Group rocks at Ox Lake are intruded by a d i o r i t e and granodiorite stock and by basic dykes. The position of the Hazelton Group rocks within the general stratigraphic column i s unknown. Figure 3 i s an oblique drawing of the geology at Ox Lake based on f i e l d observations and diamond d r i l l hole data. Appendix I i s a more detailed geology and sample location map. 1. Hazelton Group Hazelton Group at Ox Lake i s subdivided by the w r i t e r into three units: (1) Fel s i c Tuff; (2) Andesitic Tuff; and (3) Sandstone-S i l t s t o n e unit. The contact between the lowermost F e l s i c Tuff and m Feldspar porphyry j Felsic tuff | Mafic crystal tuff 400 FT . VERTICAL EXAGERATION 5X Andesitic tuff and volcanic sediment Lapilli tuff A A /. A A Sandstone, siltstone Pebble conglomerate Volcanic sediment Sedimentary breccia Figure 4 Schematic stratigraphic column of Hazelton Group i l lus t ra t ing interpreted interrelations of units. Sandstone-Siltstone dips steeply SW 11 overlying Andesitic Tuff i s gradational over several hundred feet. The uppermost Sandstone-Si Itstone i s d i s t i n c t l y d i f f e r e n t from the lower two units and might be separated from them by an unconformity. Figure 4 i s a schematic stratigraphic column of the Hazelton Group at Ox Lake. (a) F e l s i c Tuff Outcrops of the F e l s i c Tuff extend at least three thousand feet east and northeast of Ox Lake. Of the approximately one thousand foot section, an estimated 50 per cent i s feldspar porphyry, 40 per cent a pale-grey s i l i c e o u s t u f f , and 10 per cent mafic c r y s t a l t u f f . The base i s not exposed and the top i s a gradational contact with the Andesitic Tuff. The top of the feldspar porphyry section i n the "ore-zone" seems to mark the middle of a two or three hundred foot t r a n s i t i o n zone between F e l s i c Tuff and Andesitic Tuff and i s therefore used to separate the two units. North and east of Ox Lake t h i s contact i s not as well known but appears to pass through d r i l l holes 5 and 25 north of Ox Lake and j u s t east of d r i l l hole 8, east of Ox Lake. Bedding occurs in some sections of s i l i c e o u s t u f f and mafic c r y s t a l t u f f . Six alt i t u d e s measured i n outcrop indicate gentle dips of 20 to 30 degrees south. This regional dip i s supported by consistent dips of about 20 degrees indicated from several sections of well-bedded cherts in v e r t i c a l d r i l l hole 27. Feldspar porphyry at Ox Lake has been described previously as dykes and s i l l s [Sutherland-Brown, 1968] but are considered by the writer to be largely extrusive i n o r i g i n with possibly some dyke feeders. Figure 5 Sample pairs of unaltered feldspar porphyry. Note variability of texture. Lower samples etched with hydrofluoric acid and stained with sodium cobalinitrite. Yellow indicates potash feldspar, white indicates plagioclase, clear indicates quartz and grey indicates other minerals I 5 mm Figure 6 Thin section of feldspar porphyry showing albite phenocrysts set in matrix containing spheres of intergrown potash feldspar and quartz with small a lb i te crystals 13 Evidence i n support of an extrusive o r i g i n for the feldspar porphyries l i e s i n t h e i r large area! extent northeast of Ox Lake, t h e i r i n t e r -s t r a t i f i c a t i o n with well-bedded cherts and mafic crystal t u f f s , and the grossly conformable pattern of feldspar porphyry units to known bedding. Flow structures, c r y s t a l ! i n i t y , and other textures can be interpreted as either extrusive or intru s i v e features. In hand specimen the feldspar porphyries are pale-grey dense rocks with barely discernable plagioclase phenocrysts 1 to 5 mm long and with 1 to 3 per cent f i n e l y disseminated mafic minerals. Samples etched and stained with hydrofluoric acid and sodium c o b a l t i n i t r i t e enhance the v a r i a b i l i t y of the texture (Figure 5). Mafic and f e l s i c patches 3 to 10 mm i n diameter constitute up to one per cent of tota l rock volume and are probably fragments. Phenocryst content varies from 5 or 10 per cent to 20 or 30 per cent of rock, volume from outcrop to outcrop and occasionally within a single outcrop. Mafic content i n places varies abruptly, from absent to 5 per cent of rock volume. Microscopically the feldspar porphyry i s a rhyodacite porphyry. The average modal composition based on four thin sections and about twenty stained rock samples i s as follows: Phenocryst Total Volume Volume Mineral Per cent Per cent Plagioclase 20 30 Quartz 1 35 Potash Feldspar 30 Chlorite 4 Others 1 Total 21 100 Figure 7 Samples of felsic tuff. Dark layers and bedding are rare within this rock type Figure 8 Typical dark brown mafic crystal tuff containing few rock fragments and albite crystal fragments Refer to Figure 5 for explanation of stains. 15 A c h a r a c t e r i s t i c of the porphyry i s the occurrence of spheres of 0.1 to 0.4 mm diameter. These spheres are composed of plagioclase laths set i n myrmekitic intergrowths of potash feldspar i n o p t i c a l l y contin-uous quartz (Figure 6). The spheres constitute 10 to 50 per cent of the groundmass, sometimes border on each other and sometimes occur alone i n the groundmass. Size of groundmass cry s t a l s i s generally .05 mm or l e s s . The plagioclase i s everywhere a l b i t e and both feldspars are s l i g h t l y clouded from a l t e r a t i o n . Mafic minerals are r e s t r i c t e d to clot s of c h l o r i t e , quartz phenocrysts, epidote, carbonate, s e r i c i t e and opaques and have probably been derived from an e a r l i e r mafic mineral. The second most abundant rock type of the F e l s i c Tuff i s pale-grey f e l s i c t u f f with a somewhat variable texture. Included with th i s rock unit are f i n e l y bedded cherts and rare a r g i l l i t e sections up to one or two feet thick (Figure 7). In general, the s i l i c e o u s t u f f i s characterized by a pale-grey colour and dense nature. Siliceous and a l b i t i c fragments, .01 to .04 mm diameter, and set i n a very f i n e -grained cloudy quartz-plaigioclase-potash feldspar groundmass, make up as much as twenty per cent of the rock volume. With the exception of some s i l i c e o u s t u f f s which are lacking in potash feldspar, these rocks are compositionally s i m i l a r to feldspar porphyry. In some sections they grade into one another repeatedly. Mafic cry s t a l t u f f occurs throughout the Fe l s i c Tuff and near the base of the Andesitic Tuff. Sections usually measure one to twenty feet thick but an unusually thick section occurs i n d r i l l 16 holes southwest of Ox Lake and apparently extends under the h i l l southeast of Ox Lake. This thick section occurs j u s t above the Fel s i c Tuff. In hand specimen the mafic crystal tuffs are characterized by abundant a l b i t e phenocrysts set i n a dark brown matrix (Figure 8). The l a t h - l i k e phenocrysts are .5 to 2 mm long, much narrower than phenocrysts of the felspar porphyry, and make up 5 to 15 per cent of the rock volume. Volcanic fragments, as large as l a p i l l i s i z e , constitute 1 to 10 per cent of rock volume. Bedding i s not uncommon. A l b i t e laths are somewhat aligned i n bedded samples. (b) Andesitic Tuff The middle unit occurs i n both d r i l l holes and outcrop west and north of Ox Lake. Of the approximately 1,000 feet of exposed section, an estimated 30 per cent i s l a p i l l i t u f f and the remaining 70 per cent i s undivided f i n e - t o coarse-grained t u f f s . Some and possibly much of t h i s unit could be volcanic sediments. This unit immediately overlies the F e l s i c Tuff unit and i s ove r l a i n , probably unconformably by the Sandstone-Siltstone unit. Bedding i s indicated within the unit by sections of l a p i l l i t u f f . Three such sections on the h i l l s i d e northwest of Ox Lake indicate 5 to 10 degrees dips to the north or northwest. Bedding within the "ore-zone" near the intrusion i s some-what steeper as described below under structure. The middle unit i s described as andesitic although i t s composition i s not known. Potash feldspar i s rare, a l b i t e common, and s i l i c a content undetermined within rocks of t h i s unit. In hand 1_1 -Figure 9 Three samples of lap i l l i tuff and one sample of the more abun-dant fine-grained andesite. Felsic fragments are similar to feldspar porphyry and felsic tuff I Figure 10 From left to right; siltstone, sandstone, chert-pebble conglomerate 18 specimen, rocks of t h i s unit are c h a r a c t e r i s t i c a l l y dark green to almost black with l i t t l e colour v a r i a t i o n . There i s an apparent coarsening of fragment s i z e toward the base of the unit. The bulk of the rocks forming outcrops on the ridge northwest of Ox Lake are very fine-grained t u f f s and volcanic sediments (Figure 9). L a p i l l i t u f f and mafic crystal t u f f are common at the base of the unit. Feldspar porphyry occurs at the top of the exposed section on the h i l l t o p northwest of Ox Lake and also halfway down the slope towards Ox Lake. Sections of l a p i l l i t u f f from f i v e to f i f t y feet thick and several hundred feet long contain up to 70 per cent fragments of andesitic and more a c i d i c composition. The andesitic fragments are commonly ves i c u l a r , indicating they were largely a i r f a l l t u f f s . Porphyritic fragments are not uncommon. More acid fragments look s i m i l a r to the feldspar porphyries and s i l i c e o u s t u f f s of the F e l s i c Tuff unit, and may be derived from them. The cloudy groundmass commonly contains a few per cent a l b i t e fragments. (c) Sandstone-Siltstone The most westerly outcrops examined by the writer at Ox Lake have been grouped into the Sandstone-SiItsone unit. Of the s i x hundred to eight hundred feet of section examined, approximately f i v e per cent i s chert-pebble conglomerate and the remaining 95 per cent undivided sandstone, s i l t s t o n e and minor volcanic sediment (Figure 10). This unit overlies the Andesitic Tuff apparently unconformably although the exact contact was not located and could be interpreted as a t i g h t f o l d or a f a u l t . No evidence for either of the l a s t two p o s s i b i l i t i e s was seen by the writer. The upper contact of the 19 Sandstone-Siltstone unit was not located. An a i r photograph i n t e r -pretation, (Figure 14) suggests t h i s unit extends at least 2 miles further west. Bedding i s well developed with dips of 50 degrees to 70 degrees west i n marked contrast to the underlying, nearly f l a t -l y i n g , Andesitic Tuff. Structures interpreted as current bedding were observed i n a slumped block of sandstone. A sedimentary breccia with s i l t s t o n e and sandstone cl a s t s up to one foot long forms a conspicuous outcrop at the south end of the h i l l west of Ox Lake. Chert-pebble conglomerate sections one to f i f t y feet wide and up to several hundred feet long occur throughout the unit. There i s an apparent increase in amount of coarse-grained sandstones and conglomerates towards the base of the section. The basal part of the un i t , within two hundred feet of the supposed unconformity, contains dark green and grey volcanic sediments. The bulk of the unit consists of pale-grey and brown sandstones and s i l t s t o n e s . Although the occurrence of volcanic sediment near the base of t h i s unit suggests some gradation from the middle unit, the wr i t e r f e e l s that the marked contrast i n rock types and dips indicates the li k e l i h o o d that an uncomformity exists between the upper two units. The Sandstone-Siltstone unit i s of pre-ore age as i t contains fringe a l t e r a t i o n from the Cu-Mo deposit. 2. Intrusive Rocks The Hazel ton Group at Ox Lake i s intruded by two acid intrusions and many dykes. Centered about Ox Lake i s a granodiorite 20 porphyry plug, i n t r u s i v e into the F e l s i c Tuff unit. A d i o r i t e stock intrudes the Andesitic Tuff and Sandstone-Siltstone units on the west side of the ridge that l i e s northwest of Ox Lake. Basic dykes intrude a l l Hazel ton Group rocks, the granodiorite porphyry and possibly the d i o r i t e . Hornfels surrounding the granodiorite i s described i n the section which follows on Metamorphism. (a) Granodiorite The granodiorite underlies the southern half of Ox Lake and adjacent land. I t i s oval in plan, measuring 2,400 feet long by 1,400 feet wide but plunges steeply west 45 to 60 degrees and i s thus nearly c i r c u l a r i n true cross-section. Dykes of granodiorite measuring up to twenty or t h i r t y feet thick have been recognized i n d r i l l core near the contact with hornfels. These dykes occur less than two hundred feet from the main in t r u s i v e body and are most numerous along the western side. Intrusive breccia occurs along the southwest margin and i s discussed i n d e t a i l i n the following section. Figure 11 shows elevation contours of the contact determined from d r i l l hole intersections and s u r f i c i a l geology. Also shown on the figure i s occurrence of i n t r u s i v e breccia. In hand specimen the granodiorite i s a porphyry with phenocrysts of plagioclase, b i o t i t e , hornblende and quartz comprising 54 per cent of rock volume (Figure 12). The average modal composition based on three thin sections and seven stained rock samples i s as follows: 21 Figure 11 Shape of plug and occurrence of breccia. Westward plunge of plug indicated from elevation contours of granodiorite-hornfels contact 22 Figure 12 Typical texture of granodiorite porphyry. Sample is hornblende rich variety Figure 13 Typical sample of medium-grained diorite with atypical alteration along fracture * Refer to Figure 5 for explanation of stains. 23 Phenocryst Total Volume Volume Mineral Per cent Per cent Plagioclase 45 50 Potash Feldspar 18 Quartz 1 20 B i o t i t e 4 5 Hornblende 4 5 Apatite 1 Opaque 1 Total 54 100 A pink to grey fine-grained matrix makes up the remaining 46 per cent rock volume. The mafic content varies between samples that are b i o t i t e - r i c h to those that are hornblende-rich. The most noticeable change of texture occurs along the western contact where some of the dykes exhi b i t a f i n e r grain size of phenocrysts and groundmass. In a few cases individual granodiorite dykes with a normal texture grade with decreasing width into t h i s fine-grained variety and then ultimately into a mafic-free sugary-textured quartz-feldspar dyke one-half inch wide. In thin section, complexly zoned plagioclase ranges from An20 to An40. The matrix i s a fine-grained sugary-textured mixture of quartz and potash feldspar. Accessory minerals are apatite and magnetite. 24 The intrusion was probably emplaced i n approximately the same attitude as i t presently l i e s . A l t e r a t i o n and mineralization, which are shown below to be contemporaneous with i n t r u s i o n , are most intense "over" the western contact of the intrusion. S i m i l a r l y , sections of f a u l t gouge and dykes of granodiorite porphyry are also more numerous along t h i s contact. Evidence of forceful i n t r u s i o n of the granodiorite porphyry i s also shown below to occur "above" this western contact. The asymmetric nature of the above features a l l lend support to the idea that the westward rake of the intrusion i s a primary feature. (b) Intrusive Breccia An i n t r u s i v e breccia occurs along the southwestern contact of the granodiorite (Figure 11). Sections of breccia ninety to one hundred and s i x t y feet long are intersected i n d r i l l holes 14, 20, 21, 23, and 35. Sections of breccia less than t h i r t y feet wide are intersected i n d r i l l holes 12, 16, and 17. The shape of the breccias i s not c l e a r , but they appear to be sheet-like bodies associated with granodiorite dykes. Breccia occurs along the sides of the main grano-d i o r i t e , along sides of granodiorite dykes and as separate bodies containing small granodiorite dykes within hornfels near the i n t r u s i o n . Thus a zone of brecciation can be outlined p a r a l l e l and peripheral to the southwestern intrusion-hornfels contact. Fragments of hornfels and altered feldspar porphyry are cemented by two types of matrix. The most common matrix i s a mixture of rock f l o u r and g r a n i t i c material probably consisting of ground up 25 hornfels and granodiorite porphyry. About f i v e per cent of the breccia i s cemented by the second type of matrix, v i z . hydrothermal minerals f i l l i n g open spaces. Most common minerals are coarse-grained b i o t i t e , gypsum-anhydrite, and c a l c i t e with lesser amounts of quartz, epidote, chalcopyrite, p y r i t e , c h l o r i t e , magnetite, hematite, potash feldspar, and molybdenite. (c) D i o r i t e A medium-grained d i o r i t e intrusion i s exposed on the ridge northwest of Ox Lake. Its dimensions although poorly known are approxi-mately one mile long by one-half mile wide. In hand specimen the rock i s a mottled-grey, medium-grained d i o r i t e containing 30 per cent b i o t i t e plus hornblende and 70 per cent feldspars plus quartz (Figure 13). The average modal composition based on three stained rock samples and one thin section i s as follows: Mineral V o l u m e P e r c e n t Plagioclase 50 Potash Feldspar 15 Quartz 5 Hornblende 15 B i o t i t e 15 Total 100 26 The contacts are r e l a t i v e l y sharp with no dykes observed in outcrop. The d i o r i t e i s i n contact with rocks of Andesitic Tuff along i t s eastern contact and with rocks of Sandstone-Siltstone along i t s eastern contact. In thin section, plagioclase, hornblende, and b i o t i t e p o i k i l i t i c a l l y enclosed by potash feldspar, form 30 to 50 per cent of the rock. The remaining 50 to 70 per cent i s made up of euhedral medium-grained plagioclase, b i o t i t e and hornblende set i n fine-grained quartz and potash feldspar. Minor apatite occurs with mafic minerals. Plagioclase i s weakly zoned with an average composition of An^. Alter a t i o n of the d i o r i t e i s weak with some s a u s s e r i t i z a t i o n of plagioclase and minor c h l o r i t i c a l t e r a t i o n of b i o t i t e and horn-blende. (d) Dykes Basalt and andesite dykes occur i n a l l rocks of the Hazel ton Group, the granodiorite, and probably the d i o r i t e . These dykes are both pre- and post-mineralization. Most d r i l l holes intersect one or more of these dykes. The dykes are recognized by well-developed c h i l l contacts, textures and by absence of mineralization i n post-mineralization dykes occurring in the hornfels. Diabase textures are p a r t i c u l a r l y abundant. As noted above at least some of the feldspar porphyry might be dykes. 27 3. Metamorphism Metamorphism of rocks near Ox Lake i s consistent with the regional development of low-grade greenschist facies within Hazelton Rocks, and of higher grades of metamorphism occurring near intrusions. (a) Regional Rocks unaffected by the two intrusions have a well-developed a l t e r a t i o n assemblage of a l b i t e , c h l o r i t e , c a l c i t e and epidote, with lesser amounts of a c t i n o l i t e and b i o t i t e . The l i m i t of contact metamorphism i s unknown and thus some, but not a l l , of the a c t i n o l i t e and b i o t i t e might be a product of regional metamorphism. (b) Contact Near the d i o r i t e , development of hornfels, i f present, i s not pronounced. Outcrops near the d i o r i t e are occasionally s l i g h t l y crackled and minor amounts of pyrite occur along a few fractures i n these rocks. In contrast to the d i o r i t e , the granodiorite has a w e l l -developed hornfels surrounding i t . The outer l i m i t of hornfels, which i s roughly coincident with the outer l i m i t of p y r i t e , varies from about 500 feet from the east contact to about 1,500 feet from the west contact. I t i s d i f f i c u l t to distinguish overall thermal effects from hydrothermal vein a c t i v i t y . From the a l t e r a t i o n study de-28 scribed i n Chapter IV i t i s suggested that the e a r l i e s t a l t e r a t i o n events are related to intense micro-fracturing and more closely approach contact metasomatism. Subsequent a l t e r a t i o n events become more and more closely related to individual veins and thus more cl o s e l y approach hydrothermal a l t e r a t i o n . Potassic, a l b i t i c , p r o p y l i t i c , s e r i c i t i c and intermediate a r g i l l i c a l t e r a t i o n assemblages are present and discussed i n d e t a i l i n Chapter IV. 4. Structure Major structures at Ox Lake appear to be: a broad a n t i c l i n e or dome; two f a u l t s , intersecting at the north-west end of Ox Lake; and a vein stockwork related to intrusion of the granodiorite and discussed i n d e t a i l i n the following chapter. A broad a n t i c l i n e possible related to doming over the granodiorite i s indicated from dips of Hazelton Group rocks. Northwest, north and east of Ox Lake bedding has gentle dips as described previously. Within the Ore Zone immediately west of the granodiorite, bedding roughly p a r a l l e l s the granodiorite-hornfels contact at dips of 45 to 60 degrees. Figure 3 shows how the feldspar porphyry section within the Ore Zone wraps around the granodiorite. D r i l l data suggests that t h i s feldspar porphyry section i s s l i g h t l y concave upward. Variations i n bedding are interpreted to be the r e s u l t of forceful intrusion of the granodiorite causing folding of Hazelton Group rocks. The r e s u l t has been the formation of an a n t i c l i n e whose westward plunging axis l i e s over the westward plunge of the in t r u s i o n . Some of 29 Figure 14 A i r photograph interpretation of lineaments 30 the apparent folding could be the r e s u l t of structural adjustments along f a u l t s . Steep bedding within Sandstone-Siltstone could be related to the above described doming e f f e c t of the granodiorite. However, t h i s steep bedding i s more of a regional feature of t h i s unit and probably i s the eastern limb of a syncline of unknown magnitude. As the upper unit dips 50 to 70 degrees west and the granodiorite rakes about 50 degrees west, folding involving t h i s upper unit most l i k e l y occurred p r i o r to emplacement of the granodiorite. Otherwise the plug would have been emplaced at a very shallow angle. Figure 14 i s an a i r photograph interpretation of the geology near Ox Lake. The northeast trending lineaments p a r a l l e l g l a c i a l s t r i a t i o n s . The northerly trending bedding scarps i n the middle of the figure indicate the s t r i k e of the Sandstone-Siltstone. This unit apparently outcrops one to two miles west as indicated there by s i m i l a r north-south bedding scarps. Three major lineaments converge at Ox Lake and fo r two of these, there i s some evidence of f a u l t o r i g i n . The two f a u l t - c o n t r o l l e d lineaments are the north-south and east-west trending features that intersect at the west side of Ox Lake. The feldspar porphyry section within the ore zone i s apparently o f f s e t , possibly by the supposed east-west f a u l t . A diabase dyke reportedly crops out along t h i s f a u l t on the ridge west of Ox Lake. (Sutherland-Brown, 1968). A f a u l t zone, mapped by Mr. D.H. Olson of Asarco, s t r i k e s north, dips 70 degrees east and l i e s on the ridge north-31 west of Ox Lake. The presence of Pb-Zn-Ag mineralization i n the exposed f a u l t , of magnetite i n breccia near the f a u l t , and of pyrite mineralization extending out along the f a u l t i n a broad pattern from the granodiorite, indicates a premineralization age of t h i s f a u l t . D r i l l holes within hornfels contain numerous sections of f a u l t gouge indicating that f a u l t i n g i s much more prevalent than recognized i n outcrop. D r i l l holes outside the hornfels contain much fewer sections of f a u l t gouge than d r i l l holes within hornfels, which might indicate f a u l t i n g i s related to emplacement of the granodiorite. The vein stockwork described i n the following chapter i s good evidence of fracturing and f a u l t i n g near the int r u s i o n . 32 7 PERIPHERAL I / ZONE j ..- / / Figure 15 Position of the various zones about the granodiorite porphyry. Section line is for Figures 22, 25 and 26 33 EARLY VEIN LATE VEIN NUMBER OF INTERSECTIONS Biotite Propylitic Quartz-Mo Quartz Biotite _^ 7 6 Propylitic 0 ^ ^ 87 34 Quartz-Mo 0 10 ^ ^ 35 Quartz 0 1 Figure 16 Above: Diagrammatic intersections of some vein types showing r e l a t i v e ages. Below: Data indicating r e l a t i v e ages of vein types 34 CHAPTER III VEINS Veins are developed to some extent i n a l l rocks adjacent to the granodiorite porphyry but are most abundant along i t s western contact, a zone that also contains the most intense a l t e r a t i o n and highest grades of Cu and Mo. The f i r s t part of this chapter describes nine vein types. Four stages of vein development are presented at the end of the chapter. A l t e r a t i o n and mineralization, which are related to veining, are discussed i n the following two chapters. Throughout these three chapters reference i s made to several zones shown i n Figure 15. Veins are c l a s s i f i e d into nine types based on commonly occurring mineral assemblages. P r o p y l i t i c veins are subdivided into three subtypes. One vein type i s shown to occur only i n rocks of ac i d i c composition where i t i s analogous to p r o p y l i t i c veins elsewhere. Cross-cutting relationships between d i f f e r e n t vein types within the well-mineralized western hornfels and contact granodiorite are summar-ized i n Figure 16. At t h e i r most intense development veins are fracture f i l l i n g s 0.1 to 5 mm wide, spaced 3 to 10 mm apart. Wider veins are uncommon and narrower veins are not e a s i l y recognized i n hand specimen. Along the less intensely veined eastern contact of the in t r u s i o n , vein spacing i s about 10 to 50 mm. The intensity of veining decreases 35 with distance from the intrusion i n a general way, and the l i m i t of veining i s roughly coincident with the l i m i t of p y r i t e . VEIN TYPES 1. Potash Feldspar Veins Potash feldspar occurs as t h i n smears along fractures, but more commonly as an envelope up to one-quarter inch wide. B i o t i t e i s present as a thin fracture f i l l i n g with a few potash feldspar veins. Potash feldspar envelopes occur with some p r o p y l i t i c veins, p a r t i c u l a r l y those that are nearer the i n t r u s i o n , and with few quartz-molybdenum veins and quartz veins. The r e l a t i v e age of the development of potash feldspar i s discussed below. 2. B i o t i t e Veins B i o t i t e veins are composed e n t i r e l y of b i o t i t e with one or two exceptions where traces of pyrite and c h l o r i t e occur. The b i o t i t e i s fine-grained and generally dark brown and f e l t y looking. Where i t occurs less than 100 feet from the i n t r u s i o n , i t i s black. Because vein widths are very narrow, always less than one millimeter, b i o t i t e veins are d i f f i c u l t to recognize and are probably more abundant than indicated by the number i d e n t i f i e d . A number of narrow b i o t i t e veins were observed only i n thin section. 36 Of the twenty b i o t i t e veins observed, s i x were cut by quartz-molybdenite veins, seven were cut by p r o p y l i t i c veins and seven occurred by themselves, indicating an early age f o r these veins. 3. P r o p y l i t i c Veins P r o p y l i t i c veins, by f a r the most abundant type, are subdivided into three subtypes: a c h l o r i t e - c a l c i t e - p y r i t e subtype; an epidote-hematite-chlorite-calcite-pyrite subtype; and an a c t i n o l i t e - p y r i t e -magnetite subtype. They are referred to as the c h l o r i t e , epidote and a c t i n o l i t e subtypes respectively. The subtypes are mutually exclu-sive within a single sample. Di s t i n c t i o n between the three i s based on hand specimen examination. Veins are characterized by the mineralog-ies l i s t e d above. They also contain the following: c h l o r i t e subtype-trace amounts of epidote, rare hematite and no magnetite or a c t i n o l i t e ; epidote subtype -- v i s i b l e c l o t s and smears of epidote, common magnetite; a c t i n o l i t e subtype -- minor c h l o r i t e , c a l c i t e and hematite. Chalcopyrite and apatite are associated with a l l subtypes. Quartz i s rare, and plagioclase or potash feldspar i s commonly present as an envelope less than f i v e mm wide. Hornblende was noted i n three veins of epidote subtype near the intrusion. P r o p y l i t i c veins contain a s i g n i f i c a n t proportion of the t o t a l copper content of the deposit. P r o p y l i t i c veins are rarely more than three mm wide and generally occur as a stockwork of closely-spaced f r a c t u r e - f i l l i n g s less than 0.2 mm wide. P r o p y l i t i c veins are pervasive throughout the hornfels and rare within the i n t r u s i o n , i n t r u s i v e breccia and feldspar porphyry. 37 Of 97 cross-cutting relationships observed between p r o p y l i t i c veins and quartz-molybdenum veins, 87 indicate the p r o p y l i t i c veins are e a r l i e r and ten l a t e r than the quartz-molybdenite veins. A s i g n i f i c a n t feature of t h i s analysis i s that the 10 "anomalous" relationships a l l represent a single p r o p y l i t i c vein cross-cutting a quartz-molybdenite vein, whereas the other 87 relationships represent, i n the majority of cases, a single quartz-molybdenite vein cross-cutting several p r o p y l i t i c veins. Thus the 10 "anomalous" relationships probably represent much less than 5 per cent of the to t a l p r o p y l i t i c veining. A l l 34 cross-cutting relationships between p r o p y l i t i c veins and quartz veins indicate the quartz veins are l a t e r . The three subtypes are zoned about the intrusion (Figure 15). The a c t i n o l i t e zone l i e s peripheral but adjacent to the epidote zone. The c h l o r i t e zone occurs as a core adjacent to the intrusion and surrounded by the epidote zone. These zones are outlined i n more de t a i l i n the following chapters. 4. Pyrite-Chalcopyrite Veins These sulphide veins are characterized by narrow fracture-f i l l i n g s of pyrite and/or chalcopyrite. C a l c i t e i s generally present and quartz i s present i n small amounts. The veins are less than one mm wide and not as common as other vein types. They are most common in acidic rocks, p a r t i c u l a r l y feldspar porphyry, f e l s i c t u f f overlying and underlying the feldspar porphyry and granodiorite near the contact. 38 Separate sections of feldspar porphyry occur i n d r i l l holes 5, 19, and 24 and near sample 63C. In each case adjacent andesite contains only p r o p y l i t i c veins although the feldspar porphyry contains only pyrite-chalcopyrite veins. Feldspar porphyry nearer the intrusion contains pyrite-chalcopyrite veins as well as a l l other types except p r o p y l i t i c veins. Thus the pyrite-chalcopyrite veins within feldspar porphyry are considered to be related genetically to p r o p y l i t i c veins outside feldspar porphyry. The granodiorite porphyry contains many pyrite-chalcopyrite veins which may also be the equivalent of p r o p y l i t i c veins as t h i s l a t t e r type i s rare within the i n t r u s i o n . There are, however, other pyrite-chalcopyrite veins occurring outside the feldspar porphyry which occur with p r o p y l i t i c veins. Less than ten such veins have been recognized and t h e i r r e l a t i v e age i s unclear, but appears to be p o s t - p r o p y l i t i c . Some of these contain appreciable quartz and thus may be related to quartz-molybdenum or quartz veins. They are r e l a t i v e l y few compared with pyrite-chalcopyrite within feldspar porphyry and are not grouped together as a type, because of t h e i r few number and questionable association. A l l ten cross-cutting relationships between pyrite-chalcopyrite veins and quartz-molybdenite veins indicate the pyrite-chalcopyrite veins are e a r l i e r ~ a fact which further supports the contemporaneous developments of p r o p y l i t i c and pyrite-chalcopyrite veins. 5. Quartz-Molybdenite Veins These veins are characterized by quartz and molybdenite but other minerals occur with these veins as described below. Quartz often 39 has a cockade structure with molybdenite concentrated along the vein walls and c a l c i t e f i l l i n g a central parting. The molybdenite content of a single vein i n some samples varies appreciably within a few centimeters. Chalcopyrite and pyrite are generally present i n small amounts with pyrite predominating. Chlorite i s rarely present and potash feldspar occurs as a narrow envelope less than two mm wide on some veins. These veins contain p r a c t i c a l l y a l l the molybdenite i n areas that have no brecciation. Quartz-molybdenite veins are wider than the p r o p y l i t i c veins, ranging from one to ten mm, but change t h e i r widths appreciably from one area to another. They have not formed as extensively as the p r o p y l i t i c veins, being fewer and more lo c a l i z e d near the intrusion. They are p a r t i c u l a r l y common in feldspar porphyry but do occur i n a l l rock types. Quartz-molybdenite veins have already been shown to be generally l a t e r than the p r o p y l i t i c veins. Of 36 intersections of quartz-molybdenite veins with quartz veins, 35 indicate the quartz-molybdenite veins to be older and one younger then the quartz veins. The one "anomalous" intersection occurred within the granodiorite porphyry. There were also 12 intersections noted between quartz-molybdenite veins of d i f f e r e n t molybdenite content. Eleven i n t e r -sections indicated the molybdenite-rich vein to be older than the more molybdenite-poor vein. 40 6. Quartz Veins Quartz veins are characterized by absence of molybdenite. P y r i t e and chalcopyrite are normally present, forming up to ten or twenty per cent of vein volume. Ca l c i t e often f i l l s a central parting of the vein. Narrow potash feldspar smears along vein walls and c h l o r i t e are rarely present. Quartz veins are s i m i l a r to quartz-molybdenite veins i n s i z e , number and d i s t r i b u t i o n . B i o t i t e , p r o p y l i t i c and quartz-molybdenite veins are c l e a r l y e a r l i e r than the quartz veins. 7. C a l c i t e Veins C a l c i t e veins are almost pure c a l c i t e with only a few veins containing trace amounts of p y r i t e . Some veins have a central parting. Vein widths vary from 1 to 20 mm but are generally about 3 mm. They are an abundant vein type occurring i n a l l d r i l l holes and outcrops within about s i x or seven hundred feet on the west side and two or three hundred feet on the east side of the intrusion. Intersections with other veins are numerous but were not counted as they are c l e a r l y l a t e r than a l l previously mentioned vein types. 8. Gypsum Veins Gypsum also forms a l a t e vein set. X-ray d i f f r a c t i o n patterns indicate anhydrite i s present with or without gypsum in 41 many veins but no zoning of these minerals was indicated from the few veins analyzed. Vein width i s generally less then 2 mm. These veins are most common within the contact granodiorite and adjacent hornfels, although as a vein type they are r e l a t i v e l y few. Intersections with other vein types are rare. Three intersections with quartz veins indicate a l a t e age for gypsum veins. Occurrence of gypsum-anhydrite with c a l c i t e in vugs i n the Breccia Zone also suggests a l a t e age f o r gypsum veins. 9. Sphalerite Veins Sphalerite veins t y p i c a l l y contain 70 per cent carbonate and 30 per cent sulphides. S i d e r i t e i s more abundant than c a l c i t e . Sulphides are pyrite and sphalerite with minor amounts of galena. The ten or so veins found are generally one to four cm wide, occurring i n hornfels and granodiorite more commonly on the west side than the east side of the i n t r u s i o n . A l e a d - z i n c - s i l v e r vein of larger dimensions occurs i n a f a u l t system on the ridge northwest of Ox Lake [D.H. Olsen, personal communication]. The r e l a t i v e age of t h i s vein type i s uncertain except that i t i s post-quartz veins. 42 DISCUSSION A s i g n i f i c a n t conclusion to be drawn from the veining study i s that the rocks, both volcanic and i n t r u s i v e , have been intensely fractured many times. This i s indicated by the fact that veins of one type formed i n a fracture stockwork p r i o r to refracturing and development of another vein type. Cutting of one vein by several other veins of the same type indicates that fracturing occurred many times during even the formation of a single vein type. Thus the model for vein formation i s the addition of hydrothermal solutions, chemically varying with time, into a fractured stock that i s continually being healed by formation of one vein set and refractured prior to formation of a second set. Sequence of vein formation and intrusion of granodiorite porphyry i s not simple. A l t e r a t i o n of the contact portion of the intrusion indicates that at least t h i s portion of the intrusion was b r i t t l e enough to fracture f o r vein formation. However, small dykes of unaltered granodiorite porphyry within the hornfels c l e a r l y i n t e r -sect some veins. Both replacement and open-space f i l l i n g textures occur within the deposit. Open space f i l l i n g textures are more common in l a t e than i n early formed veins. Vugs and c a v i t i e s are common i n c a l c i t e , gypsum and sphalerite veins, not uncommon i n the centre of quartz-molybdenite and quartz veins, rare in p r o p y l i t i c veins and absent i n b i o t i t e and potash feldspar veins. Comb quartz i s present i n some 43 quartz-bearing veins. Symmetrical banding is common in quartz-molybdenum, and sphalerite veins and to a lesser extent in quartz veins. Replacement is a common feature of the early formed minerals potash feldspar and biotite. Propylitic mineralogies appear to have formed by both open-space f i l l ing and replacement. S t i l l later quartz-molybdenite, quartz, calcite, gypsum and sphalerite veins display practically no replacement phenomena of vein material. Although later veins are formed by open-space f i l l i ng , much hydrothermal alteration is associated with some of these veins. This alteration is described in the following chapter. Evolution from an early process involving much replacement and some open space f i l l ing to a later replacement-free fracture f i l l ing process is also reflected by variation of vein widths. Biotite and potash feldspar occur as envelopes on fractures with fracture f i l l i ng , where present, less than 0.1 mm wide. Propylitic veins are in general 0.5 mm to 5 mm wide and quartz-molybdenite and quartz veins are 2 to 10 mm wide. St i l l later veins vary from 2 to 20 mm wide. The evolution of vein types within the Ore Zone has been described. The other zones, outlined in Figure 15, are the East Zone, Intrusive Zone and Breccia Zone. All vein types described from within the Ore Zone occur in the other zones but to a much less extent. The number of intersections of different vein types is small in these other zones, but they all indicate similar age relations to those found in the Ore Zone. 44 VEIN STAGES Four stages of vein development are proposed based on age relationships of the nine vein types. Formation of veins within each stage is presented below. The four stages were probably not discrete events. Stage I veins probably developed through Stage II and into Stage III. Similarly Stage II veins developed to some extent during the early part of Stage III. Stage IV veins, however, appear to have developed after all previous stages. Thus early stages overlap much, and late stages l i t t l e of the other stages. 1 . Stage I Development of Stage I veins is the least distinct of the four stages. Development of potash feldspar and biotite veins began early and persisted throughout development of Stage II veins. Formation of biotite and potash feldspar is more closely related to hydrothermal alteration than to open-space f i l l ing and will be described more fully in the following chapter. However this chapter has shown that these minerals formed earlier than other vein minerals and continued to develop for some time. 2. Stage II The three subtypes of propylitic veins and the pyrite-chalcopyrite veins are grouped in Stage II. Within the Ore-Zone, pyrite-chalcopyrite veins in feldspar porphyry have been shown to be the equivalent of propylitic veins in 45 more mafic rocks. The same relationship has been suggested for pyrite-chalcopyrite veins within the Intrusive Zone. Feldspar porphyry and granodiorite are in marked chemical contrast to the andesite and probably reacted to mineralizing solutions differently, thereby yielding two different mineral assemblages. These two assemblages are further differentiated by associated alteration products as discussed in the following chapter. Within the East Zone, both the epidote sub-type of propylitic veins and pyrite-chalcopyrite veins occur in feldspar porphyry. How-ever mafic rocks in the East Zone contain only the epidote subtype of propylitic veins. The three sub-types of propylitic veins have been grouped as subtypes for several reasons. Only one subtype occurs in a single hand specimen and the three zones of each subtype are adjacent to each other and roughly concentrically zoned. The epidote and chlorite subtypes have identical age relationships with other vein types. Similar age relationships can be shown indirectly. All three zones contain sections of feldspar porphyry that contains pyrite-chalcopyrite veins but not propylitic veins. Mineralogical similarities described previously also provide evidence for a genetic relationship between these subtypes. The three zones of propylitic veins may have developed simultan-eously or in some sequence. There is no evidence to indicate how these zones were developed. Development of Stage II veins clearly began after Stage I veins began. Some overlap with Stage III vein development is -indicated 46 from the ten "anomalous" intersections with quartz-molybdenum veins. No "anomalous" intersections were noted with quartz veins. 3. Stage III Stage III includes development of quartz-molybdenite and quartz veins. Although the two vein types appear to have developed as consecutive stages themselves, they are grouped as one stage on the basis of similarities in mineralogy, size and distribution. There is an apparent evolution from quartz-molybdenite veins with high molybdenite content to quartz-molybdenite veins with lower molybdenite content to quartz veins with no molybdenite content. Intersections of quartz-molybdenite veins of different molybdenite content indicate an earlier age for the vein with more molybdenite. Although the molybdenite content of a single vein can vary within a few cm, the above relationship is interpreted to indicate a general decrease with time of molybdenite content of these veins. This argument is strengthened by the fact that quartz veins, which are molybdenite free, are younger than the quartz-molybdenite veins. Occurrence of molybdenite as a coating on vein walls probably reflects its early age relative to quartz. 4. Stage IV Calcite, gypsum and sphalerite veins are grouped together under Stage IV. Further subdivision of these veins might be possible with more detailed information. Calcite veins are far more common 47 than either gypsum or sphalerite veins. Calcite forms with Stage II and III veins in appreciable amounts particularly with Stage III veins where i t occurs in the vein centre. This relationship provides further evidence of a continuous evolution of veins types. Granodiorite Porphyry Feldspar Porphyry J Plagioclase An20^n40 Montmorillonite Kaolinite Albite - Regional metamorphism Sericite Quartz bearing vein j fjtji Potash feldspar -Hydrothermal alteration Sericite-Clays Unresolved vein relations Albite- Hydrothermal alteration Py rite-Chalcopyrite Vein Quartz Sericite Envelope Sericite - C/a ys Unresolved vein relations Figure 17 Diagrammatic map illustrating alteration of plagioclase phenocrysts within feldspar porphyry and granodiorite porphyry 49 Figure 18 Diagrammatic map illustrating occurrence of alteration minerals biotite, chlorite, epidote, and actinolite related to the granodiorite porphyry 50 CHAPTER IV ALTERATION The p r e c e e d i n g c h a p t e r d e s c r i b e d n i n e v e i n t y p e s and a r r a n g e d them i n t o f o u r s t a g e s . As a l t e r a t i o n i s i n t i m i t e l y a s s o c i a t e d w i t h v e i n d e v e l o p m e n t i n s p a c e and t i m e , t h i s c h a p t e r w i l l a t t e m p t t o r e l a t e t h e two w h e r e v e r p o s s i b l e . The f i r s t s e c t i o n o f t h i s c h a p t e r d e s c r i b e s a l t e r a t i o n t y p e s w i t h i n t h e f o u r z o n e s p r e v i o u s l y d e s c r i b e d ; E a s t Z o n e , I n t r u s i v e Z o n e , Ore Zone and B r e c c i a Zone ( F i g u r e 1 5 ) . B e c a u s e a l t e r a t i o n w i t h i n t h e Ore Zone i s c o m p l i c a t e d , i t has been s u b d i v i d e d i n t o f o u r s m a l l e r z o n e s . A l t e r a t i o n i n e a c h o f t h e s e zones i s d e s c r i b e d i n d e t a i l . A l t e r a t i o n e f f e c t s a r e s t r i k i n g l y d i f f e r e n t f o r f e l s i c and m a f i c r o c k s . F i g u r e s 17 and 18 i l l u s t r a t e t h e d i s t r i b u t i o n o f s e v e r a l o f t h e more a b u n d a n t a l t e r a t i o n m i n e r a l s . The s e c o n d s e c t i o n o f t h i s c h a p t e r i s a d i s c u s s i o n o f a l t e r a t i o n a c c o r d i n g t o a l t e r a t i o n t y p e . A l t e r a t i o n d e s c r i b e d i n t h e f i r s t s e c t i o n i s s u m m a r i z e d u n d e r t h e h e a d i n g s p o t a s s i c , a l b i t i c , p r o p y l i t i c , s e r i c i t i c and i n t e r m e d i a t e a r g i l l i c a l t e r a t i o n . F i g u r e s 25 and 26 s u m m a r i z e v e i n - a l t e r a t i o n a s s e m b l a g e s f o r m e d i n t h e f o u r s t a g e s . 51 I Figure 19 Sample pairs showing alteration products within feldspar porphyry of the East Zone. Sample on right is unaltered feldspar porphyry. Dark coloured matrix in three altered samples on left is caused by hydrothermal biotite. Phenocrysts in left sample are albite. Phenocrysts in middle two samples are potash feldspar. Note albite envelope about an epidote subtype propylitic vein in second sample from left * Refer to Figure 5 for explanation of stains. 52 EAST ZONE Feldspar porphyry is abundant and mafic rocks rare within the East Zone. Alteration patterns are outlined from four cross-sections of the hornfels within dr i l l-hole sections 8, 31, 10 and 9-32. The East Zone is characterized by a wide zone of feldspar constructive alteration with both albite and potash feldspar forming zones as indicated in Figures 17 and 19. A potash feldspar zone extends outwards five hundred to one thousand feet from the granodiorite and is separated from the contact by a two to four hundred foot-wide albi te zone. Potash feldspar has replaced original a lbi te phenocrysts and some groundmass a lb i te . In some phenocrysts at the outer l imits of the zone, this replacement is not complete and a core of a lb i te remains unaltered. In thin section the potash feldspar is s l ight ly cloudy but generally freshlooking. The transit ion from the above alteration assemblage to the more central a lb i te alteration zone is transitional over several hundred feet. Going towards the intrusion from the potash feldspar zone the f i r s t noticeable change is the occurrence of propyl i t ic fractures with an albi te envelope up to two cm wide. Al l potash feldspar has been hydrothermally altered to a lb i te along these fractures . (Figure 19). Albite has corroded the secondary potash feldspar phenocrysts along their margins and has replaced groundmass potash feldspar to some degree. Nearer the intrusion, veining with associated a lb i te a l te r -ation becomes more intense, until f i na l l y only minor amounts of potash 53 f e l d s p a r r e m a i n , l e a v i n g a zone two t o f o u r h u n d r e d f e e t w i d e , o f n e a r l y c o m p l e t e a l b i t e a l t e r a t i o n . L e s s t h a n h a l f o f t h e o r i g i n a l g roundmass p o t a s h f e l d s p a r r e m a i n s i n s a m p l e s n e a r t h e i n t r u s i v e c o n t a c t . In t h i n s e c t i o n t h e a l b i t e i s c h a r a c t e r i s t i c a l l y a d a r k c l o u d y m a t e r i a l w i t h e a s i l y r e c o g n i z e d p o l y s y n t h e t i c t w i n n i n g . I n t e n s e a l b i t e a l t e r a t i o n i s a l s o a s s o c i a t e d w i t h a c r a c k l e -b r e c c i a zone i n t e r s e c t e d by d r i l l - h o l e t h i r t y - t w o . D i s s e m i n a t e d m o l y -bdenum m i n e r a l i z a t i o n o c c u r s i n t h i s zone w h i c h i s t w e n t y t o t h i r t y f e e t w i d e . L a t e p o t a s h f e l d s p a r e n v e l o p e s a r e a b s e n t . P e r v a s i v e p o t a s h f e l d s p a r a l t e r a t i o n a s d e s c r i b e d i s n o t known t o be d i r e c t l y r e l a t e d t o any p a r t i c u l a r v e i n t y p e . B i o t i t e v e i n s w i t h t r a c e p y r i t e , and e p i d o t e s u b t y p e p r o p y l i t i c v e i n s o c c u r as f r a c t u r e f i l l i n g s much l e s s t h a n one mm w i d e . H y d r o t h e r m a l a l b i t e a l t e r a t i o n e n v e l o p e s a r e commonly r e l a t e d t o e p i d o t e s u b t y p e p r o p y l i t i c v e i n s one t o t h r e e mm w i d e . R e l a t i o n s h i p o f more p e r v a s i v e a l b i t e a l t e r a t i o n t o v e i n t y p e i s amb iguous b u t p o s s i b l y i s s i m i l a r t o t h e a b o v e . D i s s e m i n a t e d m i n e r a l i z a t i o n a s s o c i a t e d w i t h t h e s e a l t e r a t i o n t y p e s i s m a i n l y b i o t i t e w i t h l e s s e r amounts o f c h l o r i t e and p y r i t e . B i o t i t e i s u s u a l l y a l t e r e d t o c h l o r i t e w h e r e v e r b i o t i t e i s i n . c o n t a c t w i t h p y r i t e . A s i g n i f i c a n t amount o f p o t a s h f e l d s p a r a l t e r a t i o n o c c u r s as e n v e l o p e s a b o u t v e i n s t h a t c r o s s - c u t v e i n s w i t h a l b i t e e n v e l o p e s . V e i n m i n e r a l o g y i s a n a l o g o u s t o e p i d o t e s u b t y p e v e i n s . T h i s l a t e p o t a s h f e l d s p a r a l t e r a t i o n i s n o t p e r v a s i v e l i k e t h e e a r l i e r e v e n t s b u t i s r e s t r i c t e d t o v e i n s and v e i n e n v e l o p e s . 54 Mafic rocks in the East Zone form about ten per cent of rock volume. They exhibit intense development of hydrothermal biotite and epidote subtype propylitic veins. Some actinolite subtype veins occur. Alteration effects associated with these veins are similar to those described below within the Ore Zone. Later quartz-molybdenite, quartz, calcite, gypsum and sphalerite veins exhibit only minor alteration effects. Some quartz-bearing veins have alteration envelopes less than one cm wide. Feldspar phenocrysts have been slightly altered to sericite and clays within these envelopes. INTRUSIVE ZONE Alteration within the intrusion is restricted to its contact with hornfels and is extensively developed only where the intrusion is in contact with the Ore Zone. Destruction of plagioclase has resulted in the recognition by the writer of two different types --potash feldspar alteration which is rare, and intermediate argi l l ic alteration which is extremely common. Detailed descriptions of each type are presented following a general description of alteration intensity. Development of alteration is classed as intense, moderate or weak depending on the degree of destruction of plagioclase: Intense alteration is characterized by complete destruction of plagioclase 55 to sericite-clay minerals in sections of drill-core several feet long. Weak alteration is characterized by destruction of plagioclase occurring only near individual fractures, leaving over half the sample unaltered. Moderate alteration is intermediate between weak and intense alteration. The intrusion is characterized by absence of alteration effects except near its contact. Alteration of granodiorite in contact with the East Zone is absent or extremely weak over a width up to ten feet. Granodiorite in contact with the Breccia Zone is weakly to moderately altered over widths of twenty or thirty feet. Granodiorite in contact with the Ore Zone is intensely altered over widths of thirty to seventy feet. In drill-hole 15 the section-of intense alteration is separated from the hornfels by twenty feet of unaltered granodiorite. Intense alteration is believed to have resulted from overlap of many alteration envelopes of the intermediate argi l l ic type, and here identification of individual envelopes is di f f icult . The following descriptions are based on isolated envelopes from moderately or weakly altered granodiorite. 1. Intermediate Argil l ic Alteration Intermediate argi l l ic alteration was outlined by examination of seven alteration envelopes found in dr i l l core samples. Altered feldspar phenocrysts were selected every cm or so outwards from the vein. The material collected from each of these areas was analyzed by use of X-ray diffraction techniques to determine the mineralogy. All seven samples showed alteration patterns similar to the one presented here. 56 I 0 5 10 Distance from vein Cm. Figure 20 Photograph of intermediate argi l l ic alteration envelope and corresponding graph of mineral abundances away from vein. Note quartz vein with central calcite 57 However the sharp boundaries between different zones as described below'are developed in only three samples. The other four samples have somewhat gradational boundaries between adjacent zones. Potash feldspar content was determined by etching the sample with hydro-fluoric acid and staining with sodium cobaltinitrite. Veins are quartz and quartz-molybdenite types. Quartz is always abundant, pyrite is always present and calcite is usually present. Chalcopyrite, molybdenite, and hematite were present in three different samples. Vein width is one to three mm. The alteration envelopes vary from one cm to one meter wide. The best developed envelopes are about ten cm wide. Figure 20 shows a photograph of intermediate argil l ie alteration envelope and a graph of mineral abundances away from the veins. The abundances are based on visual estimation and probably contain serious errors. Since all plagioclase is completely destroyed, i t is assumed the sericite-clay abundances equal the plagioclase content of unaltered granodiorite. The amount of potash feldspar does not seem to vary much. Variation of quartz content could be appreciable. Calcite occurs throughout the altered zones but not in fresh granodiorite. Epidote is present but its variation unknown. Alteration of hornblende has not been determined. Biotite is stable up to the middle of the kaolinite zone. Veinward from here, the biotite has been altered to a golden brown mica. Magnetite has been altered to hematite at the outer limits of the alteration .envelopes. Nearer the vein neither iron oxide is present. Pyrite and chalcopyrite occur disseminated in altered rock but not the unaltered rock. 58 0 5 10 Distance from Vein Cm. Figure 21 Photograph of a potash feldspar envelope and corresponding graph of mineral abundances away from vein. Note pyrite-calcite vein 59 2. Potash Feldspar Alteration Potash feldspar alteration was outlined by use of thin sections and X-ray diffraction. Only two of these envelopes were found, one in drill-hole twelve, and the other in drill-hole seventeen, both near the north end of the well-altered zone of the intrusion. Pyrite and calcite form veins one mm and five mm wide. Envelopes are four cm wide about the narrower vein and ten cm wide about the wider vein. Figure 21 shows a photograph of the narrower envelope vein assemblage, and a graph of mineral abundances away from the wider vein. The narrower vein has a similar mineral assemblage although the minerals are not as well zoned. Near the vein, plagioclase phenocrysts have been albitized and about f i fty percent replaced by potash feldspar. Coarse-grained sericite, epidote, and carbonate also occur within the plagio-clase phenocrysts. Replacement is patchy but all minerals are easily recognized in thin section. Further out from the vein, plagioclase is altered to kaolinite and then montmorillonite. Near the vein, biotite and hornblende have been destroyed and chlorite, epidote and calcite are abundant in the groundmass. Magnetite is only partly destroyed as i t occurs right up to within one cm of the vein. ORE ZONE Both feldspar constructive and feldspar destructive alteration assemblages are common within the Ore Zone. The occurrence of one or the other type is dependent on host rock. Alteration is described within 60 ORE Peripheral Zone 2 5 - , 2CM Actinolite Zone ZONE Epidote Zone Chlorite Zone n INTRUSIVE\ ZONE Primary Plagioclase 50% Bio .4* II i « II * » « t I t II i | I I Primary i Quartz Primary \ Kspar ? + (Mont 0-10-1 t i l l c E 5 -to I 0 i l l ! i , itol r-J i I • »* . Cp /Wo P'i;i;iw ' Primary \ ^ Magnetite Feldspar .Porphyry Andesite Granodiorite Porphyry Figure 22 Variation of mineral abundances within the Ore Zone and adjacent Intrusive Zone. Line of section shown in Figure 15. Note control of host rock on alteration assemblages 61 mafic and then felsic rocks within four different zones of the Ore Zone. These four zones are shown on Figures 15 and 22 and are: the Peripheral Zone; the Actinolite Zone; the Epidote Zone; and the Chlorite Zone. The latter three zones are defined by the distri-. bution of actinolite, epidote, and chlorite subtypes of propylitic veins as described in the previous chapter. 1. Peripheral Zone Alteration most remote to the intrusion is the occurrence of actinolite along fractures and as disseminations in andesite one mile from the intrusion on the ridge northwest of Ox Lake. Magnetite commonly occurs with the actinolite and both are particularly abundant within brecciated andesite. There is an apparent zone of brecciation near the fault on the ridge. Within the breccia, actinolite and magnetite f i l l voids and replace wall-rock, forming up to twenty per cent of total rock volume in hand specimen. 2. Actinolite Zone • A zone of actinolite, biotite, magnetite and pyrite extends outwards five hundred feet from the Epidote Zone, and at least one-quarter of the way around the intrusion on its northwest side. Green acicular actinolite occurs associated with olive-brown and occasionally green biotite within veins and throughout the rock. Over half the magnetite occurs in desseminated form. Pyrite occurs in veins with magnetite and to a limited extent is disseminated within the rock. 62 M i n o r q u a r t z i s p r e s e n t i n t h e n a r r o w v e i n s . C h l o r i t e i s a r a r e a l t e r a t i o n p r o d u c t o f b i o t i t e . O t h e r a l t e r a t i o n m i n e r a l s , w h i c h o c c u r n e a r e r t h e i n t r u s i o n a r e s c a r c e o r a b s e n t . One known s e c t i o n o f f e l d s p a r p o r p h y r y o c c u r s w i t h i n t h e A c t i n o l i t e Z o n e . T h e r e i s a s t r i k i n g c o n t r a s t o f v e i n and a l t e r a t i o n m i n e r a l s f r o m w i t h i n t h i s f e l d s p a r p o r p h y r y and a d j a c e n t a n d e s i t e . W i t h i n a n d e s i t e , v e i n - a l t e r a t i o n m i n e r a l s a r e as d e s c r i b e d a b o v e . W i t h i n f e l d s p a r p o r p h y r y , , p y r i t e - c h a l c o p y r i t e v e i n s have w e l l - d e v e l o p e d q u a r t z - s e r i c i t e a l t e r a t i o n e n v e l o p e s up t o one cm w i d e . Away f r o m t h e a l t e r a t i o n e n v e l o p e s t h e f e l d s p a r p o r p h y r y a p p e a r s u n a f f e c t e d by a l t e r a t i o n r e l a t e d t o t h e g r a n o d i o r i t e p o r p h y r y . No o t h e r v e i n t y p e s o r a l t e r a t i o n a s s e m b l a g e s h a v e . b e e n o b s e r v e d i n t h i s z o n e . 3. E p i d o t e Zone T h i s zone c o n t a i n s a b u n d a n t e p i d o t e , b i o t i t e , c h l o r i t e , c a l c i t e , h e m a t i t e , p y r i t e and m a g n e t i t e b u t i s c h a r a c t e r i z e d by e p i d o t e and h e m a t i t e . E p i d o t e o c c u r s a l o n g v e i n s and t o a l e s s e r e x t e n t a s b l e b s and d i s s e m i n a t i o n s i n a n d e s i t e . B i o t i t e i s commonly brown and more e u h e d r a l , a b u n d a n t and r e s t r i c t e d t o w a l 1 - r o c k t h a n b i o t i t e i n t h e A c t i n o l i t e Z o n e . C h l o r i t e i s common i n most v e i n s and o c c u r s as d i s s e m i n a t i o n s n e a r s u l p h i d e g r a i n s . C a l c i t e i s commonly r e s t r i c t e d t o v e i n s . H e m a t i t e , p y r i t e and m a g n e t i t e a r e p r e s e n t i n v e i n s and as d i s s e m i n a t i o n s . H e m a t i t e and m a g n e t i t e a r e more r e s t r i c t e d t o v e i n s w i t h i n a b o u t f i v e h u n d r e d f e e t o f t h e i n t r u s i o n . P y r i t e i s more r e s t r i c t e d t o v e i n s f u r t h e r o u t t h a n t h i s d i s t a n c e . A p a t i t e and c h a l -63 copyr i te are general ly present in varying amounts in veins and as disseminations. P r o p y l i t i c veins commonly have e i ther an a l b i t e or potash fe ldspar envelope which i s general ly noticeable in hand specimen. Some specimens contain both types of envelopes on d i f f e r en t ve ins. Potash fe ldspar envelopes are much more abundant than a l b i t e envelopes and appear to have developed nearer the in t rus ion — wi th in about seven hundred fee t . The number of a l b i t e envelopes observed i s low and as some do ex i s t near the in t rus ion th i s zoning of fe ldspar envelopes i s not ce r t a in . A l te ra t ion in mafic rocks near quartz-bearing veins is weak. Potash fe ldspar envelopes occur on many of these ve ins. Minor amounts of se r i c i t e-c l ay minerals occur along some vein wa l l s . Feldspar porphyry wi th in d r i l l - h o l e s 5 and 24 contain pyr i te-chalcopyr i te veins with quar tz-ser i c i t e envelopes as described above with in the A c t i n o l i t e Zone (Figure 23). A few samples from d r i l l -hole 5 contain secondary b i o t i t e . Other samples from d r i l l - h o l e 5 contain fractures with potash fe ldspar occurring along them and pa r t l y replac ing adjacent p lagioclase phenocrysts. These potash fe ldspar envelopes are cut by the pyr i te-chalcopyr i te veins. Other a l t e r a t i on assemblages in feldspar porphyry occur near quartz-bearing veins l i k e those described below wi th in the Ch lor i te Zone-. 4. Ch lo r i t e Zone The Ch lor i te Zone contains abundant c h l o r i t e , b i o t i t e , c a l c i t e , and py r i t e . Epidote, apat i te and chalcopyr i te are present Figure 23 Samples of andesite and feldspar porphyry within the Epidote Zone of the Ore Zone six hundred feet from the intrusion. Middle feldspar porphyry sample contains a pyrite vein with quartz-sericite alteration. Andesite samples contain epidote subtype veins with albite and minor potash feldspar envelopes I Figure 24 Samples of feldspar porphyry within the Chlorite and Epidote Zones of the Ore Zone within two hundred feet of the intrusion. Potash feldspar, sericite, kaolinite and montmorillonite are present as alteration products of albite but their relationship to the individual veins is obscure. Some of the potash feldspar clearly occurs along fractures Refer to Figure 5 for explanation of stains. 65 in small amounts. Hematite and magnetite are scarce to absent. Biotite is pervasive except near sulphides where i t is chloritized and near most veins where i t is absent. Biotite is commonly brown and euhedral as in the Epidote Zone. Chlorite, calcite, apatite, epidote, pyrite and chalcopyrite occur in veins and disseminations in wall-rock. The zone occurs in contact with the intrusion. The zones' surface area is about 800 feet by 1,500 feet and it extends downwards parallel to the intrusive contact to at least as deep as dri l l ing — over eight hundred feet. As in the Epidote Zone, feldspar envelopes occur on propylitic veins. Potash feldspar envelopes are particularly abundant and albite envelopes scarce. Alteration in mafic rocks near quartz-bearing veins is weak. As in the Epidote Zone, potash feldspar envelopes occur on many veins and minor amounts of sericite-clay minerals along some vein walls. Sections of feldspar porphyry lying within the Chlorite Zone have complex alteration assemblages (Figure 24). Plagioclase has been almost completely altered to potash feldspar and sericite-clay minerals in all samples. Much primary potash feldspar has been destroyed. Secondary potash feldspar occurs as envelopes up to one cm wide on hairline fractures containing minor amounts of pyrite and on pyrite-chalcopyrite, quartz-molybdenite and quartz veins. Albitiz-ation within feldspar porphyry of the Ore Zone has not been recognized by the writer. 66 The m i n e r a l o g y o f a l t e r e d p l a g i o c l a s e p h e n o c r y s t s was e x a m i n e d i n f i f t e e n s a m p l e s u s i n g X - r a y d i f f r a c t i o n t e c h n i q u e s . E i g h t s a m p l e s c o n t a i n e d p y r i t e v e i n s and a l s o c o n t a i n e d s e r i c i t e i n t h e a l t e r e d p h e n o c r y s t s . S i x s a m p l e s c o n t a i n e d no p y r i t e v e i n s and no s e r i c i t e . One s a m p l e c o n t a i n e d no p y r i t e b u t d i d c o n t a i n a p p r e c i a b l e s e r i c i t e . K a o l i n i t e a n d / o r m o n t m o r i l l o n i t e w e r e a l s o p r e s e n t i n mos t s a m p l e s . Q u a r t z v e i n s o c c u r r e d i n a l l s a m p l e s . R e l a t i n g a l t e r a t i o n a s s e m b l a g e t o v e i n s w i t h i n f e l d s p a r p o r p h y r y i s i m p o s s i b l e w i t h o u t more d e t a i l e d i n f o r m a t i o n . H o w e v e r , i t a p p e a r s t h a t c o n d i t i o n s f l u c t u a t e d between f e l d s p a r c o n s t r u c t i v e and f e l d s p a r d e s t r u c t i v e a l t e r a t i o n s i n c e b o t h t y p e s o c c u r on s i m i l a r v e i n t y p e s . P o t a s h f e l d s p a r e n v e l o p e s m i g h t have z o n e s o f s e r i c i t e - c l a y m i n e r a l s f u r t h e r removed f r o m t h e v e i n . Q u a r t z - b e a r i n g v e i n s m i g h t be zoned s e r i c i t e - k a o l i n i t e - m o n t m o r i l l o n i t e as t h e y a r e w i t h i n t h e I n t r u s i v e Z o n e . Q u a r t z - s e r i c i t e a l t e r a t i o n a b o u t p y r i t e - c h a l c o p y r i t e v e i n s i s a l s o p o s s i b l e as s u g g e s t e d by X - r a y d i f f r a c t i o n a n a l y s i s and by t h e o c c u r r e n c e o f s i m i l a r a l t e r a t i o n w i t h i n t h e E p i d o t e and A c t i n o l i t e Z o n e s . BRECCIA ZONE I n t e n s e a l b i t i z a t i o n and some p o t a s h f e l d s p a r a l t e r a t i o n o c c u r s i n t h e few s a m p l e s o f b r e c c i a t h a t a r e cemented by h y d r o t h e r m a l m i n e r a l s d e s c r i b e d p r e v i o u s l y . I n t e n s e p o t a s h f e l d s p a r a l t e r a t i o n i s much more common, o c c u r r i n g i n t h e many s a m p l e s where f r a g m e n t s a r e 67 cemented w i t h i n t r u s i v e m a t e r i a l . S e q u e n c e o f d e v e l o p m e n t o f t h e s e a l t e r a t i o n t y p e s i s o b s c u r e d b e c a u s e t h e a l t e r a t i o n m i n e r a l s c a n no t be r e l a t e d t o v e i n s o f known r e l a t i v e ages as i n o t h e r p a r t s o f t h e d e p o s i t . M a f i c r o c k s o c c u r r i n g a d j a c e n t t o b r e c c i a c o n t a i n v e i n s o f t h e e p i d o t e s u b t y p e o f P r o p y l i t i c V e i n s and q u a r t z - b e a r i n g v e i n s . They e x h i b i t a l l t h e c h a r a c t e r i s t i c a l t e r a t i o n e f f e c t s d e s c r i b e d f o r s i m i l a r r o c k s i n t h e O re Z o n e . A l t e r a t i o n o f f e l d s p a r p o r p h y r y i s s i m i l a r t o a l t e r a t i o n o f t h i s same r o c k t y p e w i t h i n t h e C h l o r i t e Zone o f t h e Ore Z o n e . DISCUSSION Hemley and Meyer [ 1 9 6 7 ] r e v i e w t h e p r o b l e m o f i n t e r p r e t i n g s e q u e n c e s o f a l t e r a t i o n and c o n c l u d e t h a t : The p r o b l e m o f i n t e r p r e t i n g t h e age r e l a t i o n s h i p s between d i f f e r e n t a s s e m b l a g e s o f w a l l r o c k a l t e r a t i o n m i n e r a l s i s p r o b a b l y t h e most d i f f i c u l t and c o n f u s i n g o f any i n t h e e n t i r e s t u d y o f t h e s u b j e c t . As has been p o i n t e d o u t , unambiguous c r i t e r i a a r e f e w . In t h i s s t u d y , a l t e r a t i o n a s s e m b l a g e s have been r e l a t e d t o v e i n s o f p r e - d e t e r m i n e d r e l a t i v e a g e s t h a t were b a s e d on v e i n i n t e r s e c t i o n s . Even t h i s c r i t e r i a f o r d e t e r m i n i n g r e l a t i v e ages o f a l t e r a t i o n a s s e m b l a g e s i s n o t d e c i s i v e i n a l l c a s e s . The r e l a t i v e age o f p o t a s s i c a l t e r a t i o n i s ambiguous s i n c e a l t e r a t i o n o f t h i s t y p e o c c u r s as e n v e l o p e s on s e v e r a l d i f f e r e n t v e i n 68 STAGE I STAGE II STAGE III Figure 25 First three stages of vein development. Line of section indicated in Figure 15 69 ZONE HOST ROCK VEIN TYPE ALTERATION m CD ORE Andesite Feldspar Porphyry Potash feldspar B iot i te Potash feldspar? B iot i te? pervasive b iot i te pervasive biot i te? pervasive potash feldspar? INTRUSIVE Granodiorite Porphyry n i l ? n i l ? 5 " CO EAST Andesite Feldspar Porphyry Potash feldspar B iot i te Potash feldspar B iot i te pervasive b iot i te pervasive b iot i te pervasive potash feldspar STAGE II ORE Andesite Feldspar Porphyry Chlori te Epidote Act ino l i te Pyrite-Chalcopyrite chlor i te-calc i te-pyr i te-apat i te tchalcopyrite ±epidote tquartz often with potash feldspar (occasionally a lb i te ) and b iot i te envelope 3pi dote-hemati te-chlori te-cal c i te-pyri te-rnagneti te-apati te tchalcopyrite ±quartz often with potash feldspar (occasionally albite) and b io t i t e envelope ac t i noli te-magneti te-pyri te-apati te-ca 1 ci te-chl ori te tchalcopyrite tepidote tquartz with narrow albite? or potash feldspar? and b io t i te envelope pyr i te tchalcopyrite tca lc i te tquartz with quartz-se r i c i t e envelope; near intrusion potash feldspar? and a r g i l l i c ? envelope STAGE II INTRUSIVE Granodiorite Porphyry Pyrite-Chalcopyrite pyr i te tchalcopyrite t ca l c i te tquartz with potash feldspar and s e r i c i t i c and a r g i l l i c envelope STAGE II EAST Andesite and Feldspar Porphyry mainly Epidote, minor Chlorite and Ac t ino l i t e as above within Ore Zone STAGE III ORE Andesite Feldspar Porphyry Quartz-Molybdeni te Quartz Quartz-Molybdeni te Quartz quartz-molybdenite t ca l c i t e tpyr i te tchalcooyrite with potash feldspar (some ser ic i te? ) envelope as above except no molybdenite quartz-molybdenite t ca l c i t e tpyr i te tchalcopyrite with a r g i l l i c ? and/or s e r i c i t i c ? and/or potash feldspar? envelope as above except no molybdenite STAGE III INTRUSIVE Granodiorite Porphyry Quartz-Molybdenite Quartz quartz-molybdenite t ca l c i t e tpyr i te tchalcopyrite . with sericite-kaolinite-montmoril lqnite envelope as above except no molybdenite STAGE III EAST Andesite and Feldspar Porphyry Quartz-Molybdenite Quartz quartz-molybdenite t ca l c i t e tpyr i te tchalcopyrite with some potash feldspar (trace ser ic i te? ) as a narrow envelope as above except no molybdenite STAGE IV ALL A l l Calc i te Gypsum Sphalerite l i t t l e or no a l terat ion Figure 26 Four stages of vein development and associated alteration assemblages. Refer to Figure 25. Question mark denotes • mineral may not have developed with indicated vein type. Note control of host rock on vein-alteration assemblage 70 types and as pervasive alteration in some areas. Albit ic, propylitic, ser ic i t ic , and intermediate argi l l ic alteration assemblages are restricted to one vein type everywhere in the deposit except within feldspar porphyry of the Chlorite Zone. Here alteration-vein relation-ships are poorly understood. Supergene alteration effects are considered to be minimal. Oxides occur in out crop and dr i l l core to a maximum depth of ten feet. Gypsum and anhydrite occur together to a depth of at least one hundred feet. The following is a discussion of the different alteration assemblages observed within the deposit arranged in the approximate order in which they began to develop. Names used for the various alteration types are taken from Hemley and Meyers [1967]. Figures 25 and 26 are helpful in reading the text. 1. Potassic Alteration Potassic alteration occurs in all four zones and is indicated by development of potash feldspar and biotite. In the East Zone, pervasive potash feldspar alteration is associated with micro-fracturing containing trace amounts of propylitic minerals. Biotite occurs in veins but more commonly as disseminations out to the limit of potash feldspar alteration. Later albitization and potash feldspar alteration are associated with individual epidote subtype propylitic veins. Within feldspar porphyry of the Ore Zone-Breccia Zone, biotite and potash feldspar might have developed more extensively 71 t h a n i s now i n d i c a t e d . M i n o r b i o t i t e o c c u r s i n d r i l l - h o l e 5 n e a r t h e f r i n g e o f i n t e n s e a l t e r a t i o n w i t h i n f e l d s p a r p o r p h y r y . I f b i o t i t e d e v e l o p e d more p e r v a s i v e l y w i t h i n now i n t e n s e l y a l t e r e d f e l d s p a r p o r p h y r y , i t has been s u b s e q u e n t l y d e s t r o y e d . The w e a k l y a l t e r e d f e l d s p a r p o r p h y r y w i t h i n d r i l l - h o l e 5 i n d i c a t e s t h a t i f p e r v a s i v e p o t a s h f e l d s p a r a l t e r a t i o n d i d e x t e n d a r o u n d t h e d e p o s i t w i t h i n t h e Ore Z o n e , i t d e v e l o p e d n e a r e r t h e i n t r u s i o n t h a n i n t h e E a s t Zone and was s u b s e q u e n t l y d e s t r o y e d . W i t h i n t h e Ore Z o n e , b u t o u t s i d e f e l d s p a r p o r p h y r y , b i o t i t e i s commonly p e r v a s i v e b u t p o t a s h f e l d s p a r i s r e s t r i c t e d t o e n v e l o p e s . B o t h m i n e r a l s began t o f o r m e a r l y as documented by i n t e r s e c t i o n s o f v e i n s o f t h e s e m i n e r a l s w i t h l a t e r v e i n s . However b o t h m i n e r a l s o c c u r as e n v e l o p e s on p r o p y l i t i c v e i n s and p o t a s h f e l d s p a r o c c u r s a s e n v e l o p e s on some q u a r t z - b e a r i n g v e i n s . I s o l a t e d p r o p y l i t i c v e i n s have a f e l d s p a r e n v e l o p e a d j a c e n t t o t h e v e i n , a b i o t i t e e n v e l o p e f u r t h e r f r o m t h e v e i n and d i s s e m i n a t e d p r o p y l i t i c m i n e r a l s w i t h i n a l t e r e d w a l l r o c k . The number o f t h e a b o v e d e s c r i b e d v e i n s i s f e w , p r o b a b l y b e c a u s e o v e r l a p o f a d j a c e n t v e i n s has made v e i n - a l t e r a t i o n r e l a t i o n s h i p s a m b i g u o u s . Thus i t a p p e a r s t h a t p o t a s s i c a l t e r a t i o n began e a r l y and c o n t i n u e d t h r o u g h S t a g e I I and p r o b a b l y i n t o S t a g e I I I . P o t a s h f e l d s p a r a l t e r a t i o n i s r a r e i n t h e I n t r u s i v e Zone b u t m i g h t have f o r m e d p r i o r t o t h e e x t e n s i v e d e v e l o p m e n t o f f e l d s p a r d e s t r u c t i v e a l t e r a t i o n . B i o t i t e does n o t o c c u r as an a l t e r a t i o n p r o d u c t w i t h i n t h e I n t r u s i v e Zone . 72 2 . A l b i t i c A l t e r a t i o n A l b i t i z a t i o n o c c u r s i n t h e B r e c c i a Zone where i t s age i s u n c e r t a i n , and i n t h e E a s t and Ore Zones where i t s age i s b e t t e r known. W i t h i n t h e e a s t Z o n e , a s s o c i a t i o n o f a l b i t e e n v e l o p e s w i t h p r o p y l i t i c v e i n s e s t a b l i s h e s a l b i t i z a t i o n a s a S t a g e I I e v e n t . The z o n e o f o v e r l a p between p e r v a s i v e p o t a s h f e l d s p a r a l t e r a t i o n and p e r v a s i v e a l b i t i z a t i o n i n d i c a t e s a l b i t i z a t i o n i s l a t e r t h a n p e r v a s i v e p o t a s h f e l d s p a r a l t e r a t i o n . B i o t i t e o c c u r s as d i s s e m i n a t i o n s w i t h i n t h e zone o f p e r v a s i v e a l b i t i z a t i o n . The c r a c k l e b r e c c i a z o n e has c o m p l e t e a l b i t i z a t i o n o f a l l p r e v i o u s l y e x i s t i n g f e l d s p a r . W i t h i n m a f i c r o c k s o f t h e Ore Z o n e , a l b i t i z a t i o n o c c u r s as e n v e l o p e s on p r o p y l i t i c v e i n s b u t i s much l e s s common t h a n p o t a s h f e l d s p a r e n v e l o p e s on s i m i l a r v e i n s . T h e r e i s some s u g g e s t i o n t h a t a l b i t e e n v e l o p e s a r e g e n e r a l l y f u r t h e r f r o m t h e i n t r u s i o n t h a n p o t a s h f e l d s p a r e n v e l o p e s . T h e r e i s no e v i d e n c e f o r a l b i t i z a t i o n w i t h i n f e l d s p a r p o r p h y r y o f t h e Ore Z o n e . 3 . P r o p y l i t i c A l t e r a t i o n T h r e e p r o p y l i t i c z o n e s o c c u r a b o u t t h e i n t r u s i o n . The C h l o r i t e Zone o c c u r s o n l y i n t h e Ore Zone and c o n t a i n s c h l o r i t e -c a l c i t e - p y r i t e w i t h l e s s e r amounts o f c h a l c o p y r i t e , a p a t i t e , e p i d o t e , and q u a r t z . H e m a t i t e i s r a r e l y p r e s e n t . The E p i d o t e Zone i s t h e most w i d e s p r e a d , o c c u r r i n g p e r i p h e r a l t o t h e I n t r u s i v e and C h l o r i t e Z o n e s . The E p i d o t e Zone c o n t a i n s e p i d o t e - c h l o r i t e - c a l c i t e - p y r i t e - h e m a t i t e w i t h 73 l e s s e r amounts o f m a g n e t i t e , c h a l c o p y r i t e , a p a t i t e and q u a r t z . The A c t i n o l i t e Zone o c c u r s o u t s i d e t h e E p i d o t e Zone and i s w e l l -d e v e l o p e d o n l y w i t h i n t h e Ore Z o n e . The A c t i n o l i t e Zone c o n t a i n s a c t i n o l i t e -m a g n e t i t e - p y r i t e w i t h l e s s e r amounts o f c h a l c o p y r i t e , a p a t i t e , c h l o r i t e and c a l c i t e . The a b o v e m i n e r a l s o c c u r i n v e i n s and as d i s s e m i n a t i o n s i n w a l l r o c k . P r o p y l i t i c a l t e r a t i o n as d e s c r i b e d a b o v e i s r a r e i n t h e I n t r u s i v e Zone and a b s e n t i n f e l d s p a r p o r p h y r y o f t h e O re Zone a n d B r e c c i a Z o n e . I n t h e s e a r e a s , i t s age e q u i v a l e n t i s r e p r e s e n t e d by s e r i c i t i c a l t e r a t i o n a b o u t p y r i t e - c h a l c o p y r i t e v e i n s . 4. S e r i c i t i c A l t e r a t i o n S e r i c i t i c a l t e r a t i o n i s w e l l d e v e l o p e d o n l y w i t h i n f e l d s p a r p o r p h y r y o f t h e Ore and B r e c c i a Zones and p o s s i b l y w i t h i n t h e I n t r u s i v e Z o n e . S e r i c i t e and q u a r t z o c c u r as e n v e l o p e s on p y r i t e -c a l c o p y r i t e v e i n s w i t h i n f e l d s p a r p o r p h y r y t h a t i s w e l l removed f r o m t h e i n t r u s i o n . H e r e no o t h e r v e i n o r a l t e r a t i o n t y p e s o c c u r . I n more i n t e n s e l y a l t e r e d f e l d s p a r p o r p h y r y n e a r t h e i n t r u s i o n , t h e r e i s i n d i r e c t e v i d e n c e f o r t h e o c c u r r e n c e o f t h e same v e i n - a l t e r a t i o n a s s e m b l a g e . S e r i c i t i c a l t e r a t i o n i s no t known i n t h e I n t r u s i v e Z o n e , b u t m i g h t o c c u r t h e r e . S e r i c i t e does o c c u r w i t h i n i n t e r m e d i a t e a r g i l l i c a l t e r a t i o n e n v e l o p e s as d e s c r i b e d b e l o w . 74 5 . Intermediate Argil l ic Alteration Intermediate argil l ie alteration occurs in the Intrusive Zone and within feldspar porphyry of the Ore and Breccia Zones. Within the intrusion sericite-clay minerals are zoned sericite-kaolinite-montmorillonite outwards from a quartz-bearing vein. Within feldspar porphyry, the relation of clay minerals to veins is not known. In general, intermediate argil Tic alteration appears to be late because of its association with Stage III veins. However, some of this alteration within feldspar porphyry may have a different origin and relative age. Stage III veins in mafic rocks of the Ore Zone and all rocks of the East Zone contain one or more of the sericite-clay minerals within narrow envelopes. The minerals were observed in thin section but their amounts were insufficient to determine using X-ray diffraction techniques. 75 CHAPTER V OPAQUE MINERALOGY This chapter describes the distribution of the opaque minerals, particularly within the well-mineralized Ore Zone. Zoning of the more abundant minerals is shown in Figures 22 and 27. Distribution of these and other less abundant minerals is described below. Zoning of copper and molybdenum is well known from assay data and is presented near the end of this chapter. MINERALS 1 . Pyrite Probably more than 95 per cent of the pyrite is contained in Stage II veins and as disseminations in adjacent wall rock. Stage III veins contain most of the remaining five per cent of pyrite. Sphalerite and calcite veins contain only minor amounts of the total pyrite. Disseminated pyrite grains are 0.02 to 0.5 mm in diameter. Pyrite within veins occurs as blebs and smears 0.1 to 3 mm wide. Occurrence of pyrite is zoned in several v/ays. In mafic rocks near the intrusion, pyrite occurs in near equal amounts as vein material and as disseminations. Within similar rocks in the Actinolite Zone, . V • Pyrite FeS2 Chalcopyrite C u F e S ^ 1 0 0 0 FT Magnetite Fe^Oj^ 1 0 0 0 FT Hematite Fe2^3 Molybdenite M0S2 Granodiorite Porphyry •Feldspar Porphyry Felsic Tuff Andesite Disseminated Mineralizatio Vein Mineralization Figure 27 Diagrammatic distribution of the five most abundant opaque minerals within the deposit 77 o v e r e i g h t y p e r c e n t o f t h e p y r i t e i s r e s t r i c t e d t o v e i n s . The c h a n g e between t h e s e e x t r e m e s i s g r a d a t i o n a l . I n f e l d s p a r p o r p h y r y n e a r t h e i n t r u s i o n o v e r s e v e n t y p e r c e n t o f t h e p y r i t e o c c u r s i n v e i n s . W i t h i n s i m i l a r r o c k s i n t h e A c t i n o l i t e Zone a l m o s t a l l t h e p y r i t e o c c u r s i n v e i n s . W i t h i n t h e i n t r u s i o n a b o u t 70 p e r c e n t o f t h e p y r i t e o c c u r s i n S t a g e I I and I I I v e i n s . The r e m a i n i n g 30 p e r c e n t o c c u r s i n a l t e r e d w a l l r o c k . 2 . C h a l c o p y r i t e P r o b a b l y more t h a n 90 p e r c e n t o f t h e c h a l c o p y r i t e i s c o n t a i n e d i n S t a g e I I v e i n s and as d i s s e m i n a t i o n s w i t h i n a d j a c e n t w a l l - r o c k . A l l o t h e r c h a l c o p y r i t e o c c u r s i n S t a g e I I I v e i n s . C h a l c o p y r i t e o c c u r s as d i s s e m i n a t e d g r a i n s 0 . 0 5 t o 0 . 3 mm i n d i a m e t e r and w i t h b o r n i t e a s i n c l u s i o n s l e s s t h a n 0 . 0 3 mm i n d i a m e t e r w i t h i n some d i s s e m i n a t e d p y r i t e g r a i n s . V e r y l i t t l e o f t h e p y r i t e w i t h i n v e i n s c o n t a i n s i n c l u s i o n s o f c h a l c o p y r i t e . T h e r e i s a c o n t r a s t o f mode o f o c c u r r e n c e o f c h a l c o p y r i t e f r o m w i t h i n m a f i c r o c k s and f e l d s p a r p o r p h y r y o f t h e Ore Zone n e a r t h e i n t r u s i o n . W i t h i n m a f i c r o c k s c h a l c o p y r i t e o c c u r s i n n e a r e q u a l amounts i n v e i n s and as d i s s e m i n a t i o n s i n w a l l - r o c k , b u t w i t h i n f e l d s p a r p o r p h y r y , more t h a n a b o u t e i g h t y p e r c e n t o f t h e c h a l c o p y r i t e o c c u r s i n v e i n s . 78 Figure 28 .05 mm One of the larger bornite-chalcopyrite inclusions and a smaller one within a disseminated pyrite grain 7 9 3 . Bornite Bornite occurs only as inclusions within disseminated pyrite grains within hornfels but not within the intrusion. Chalcopyrite is associated with bornite in some grains. Grain size varies from sub-microscopic to 0.03 mm in diameter. Near the intrusion where the copper grade is high, one-half to two per cent of the total copper is accounted for by chalcopyrite and bornite inclusions within pyrite. More than three hundred feet perpendicular to the granodiorite contact, the amount of copper occurring within pyrite is as high as f i f ty per cent of the total copper in a single sample but probably averages about fifteen per cent. This value seems to increase to twenty or thirty per cent at the outer limits of propylitic veining. This zoning is probably due to the decrease in copper content outwards from the intrusion as the amount of included copper minerals is about the same throughout the Ore Zone. Thus copper minerals occurring as inclusions contribute more to the total copper content where the total content is low. 4. Hematite More than 80 per cent of the hematite occurs within epidote subtype propylitic veins. A significant proportion of the remaining 20 per cent occurs as an alteration product of magnetite within the Actinolite Zone and the altered portion of the Intrusive Zone. Only trace amounts occur in a few Stage III veins. Hematite occurs as blades 0.5 to 1 mm long and as rims on magnetite. 80 A t t h e o u t e r l i m i t s o f t h e E p i d o t e Zone h e m a t i t e o c c u r s w i t h i n v e i n s as d e s c r i b e d and t o a l e s s e x t e n t as d i s s e m i n a t i o n s w i t h i n w a l l - r o c k . W i t h i n a b o u t f i v e h u n d r e d f e e t o f t h e i n t r u s i o n , h e m a t i t e i s a l m o s t e n t i r e l y r e s t r i c t e d t o v e i n s . 5 . M a g n e t i t e P r i m a r y m a g n e t i t e o c c u r s w i t h i n u n a l t e r e d g r a n o d i o r i t e f o r m -i n g a b o u t one p e r c e n t o f r o c k v o l u m e . M a g n e t i t e i s a l s o a s s o c i a t e d w i t h e p i d o t e s u b t y p e p r o p y l i t i c v e i n s . H o w e v e r , most o f t h e m a g n e t i t e o c c u r s w i t h a c t i n o l i t e s u b t y p e p r o p y l i t i c v e i n s . W i t h i n t h e E p i d o t e Z o n e , m a g n e t i t e o c c u r s a s b l a d e s 0 . 5 t o 1 mm w i d e and as e q u a n t g r a i n s 0 . 0 5 t o 0 . 5 mm i n d i a m e t e r i n v e i n s and as d i s s e m i n a t i o n s i n w a l l - r o c k . M a g n e t i t e i s a l m o s t e n t i r e l y r e s t r i c t e d t o v e i n s w i t h i n a b o u t f i v e h u n d r e d f e e t o f t h e i n t r u s i o n . W i t h i n t h e A c t i n o l i t e Zone m a g n e t i t e o c c u r s as v e i n m a t e r i a l and more commonly as d i s s e m i n a t e d g r a i n s 0.01 t o 0 . 4 mm d i a m e t e r . 6 . P y r r h o t i t e A b o u t t e n s a m p l e s c o n t a i n m i n o r amounts o f p y r r h o t i t e o c c u r r i n g as s m a l l d i s s e m i n a t e d g r a i n s and t h i n smears on f r a c t u r e s . A l l o f t h e s e s a m p l e s o c c u r a t t h e o u t e r l i m i t s o f v e i n i n g e x c e p t one w h i c h o c c u r s w i t h i n t h e E a s t Z o n e . 7 . M o l y b d e n i t e M o l y b d e n i t e o c c u r s w i t h q u a r t z - m o l y b d e n i t e v e i n s as f l a k e s 0 .1 t o 0 . 5 mm i n d i a m e t e r a l o n g v e i n w a l l s . T h e s e v e i n s a r e p a r t i c u l a r l y 81 a b u n d a n t w i t h i n f e l d s p a r p o r p h y r y o f t h e Ore Zone . M o l y b d e n i t e a l s o o c c u r s i n d i s s e m i n a t e d f o r m w i t h i n i n t r u s i v e b r e c c i a and w i t h i n t h e c r a c k l e b r e c c i a o f t h e E a s t Z o n e . 8 . O t h e r s M i n e r a l o g y o f s p h a l e r i t e v e i n s has n o t been s t u d i e d i n t e n s i v e l y . The known s u l p h i d e s p r e s e n t , i n o r d e r o f d e c r e a s i n g abundance a r e p y r i t e , s p h a l e r i t e and g a l e n a . P o s s i b l y some s i l v e r m i n e r a l s a r e p r e s e n t as i n d i c a t e d f r o m s i l v e r a s s a y s o f t h e l e a d - z i n c - s i l v e r v e i n - s y s t e m on t h e r i d g e n o r t h o f Ox L a k e . A r s e n o p y r i t e was o b s e r v e d i n one q u a r t z v e i n f r o m w i t h i n t h e Ore Z o n e . ZONING OF COPPER AND MOLYBDENUM Z o n i n g o f c o p p e r and molybdenum m i n e r a l s i s i n d i c a t e d f r o m d r i l l c o r e a s s a y s ( F i g u r e 2 9 ) . S e c t i o n s o f d r i l l c o r e a v e r a g i n g more t h a n 0.1 p e r c e n t Cu and 0 . 0 5 p e r c e n t Mo o c c u r up t o a d i s t a n c e o f f o u r h u n d r e d f e e t f r o m t h e g r a n o d i o r i t e c o n t a c t a l o n g i t s w e s t s i d e . Beyond t h i s d i s t a n c e , a s s a y g r a d e s d e c l i n e g r a d u a l l y . W i t h i n t h e i n t r u s i o n Cu and Mo o c c u r i n b a c k g r o u n d amounts ( e . g . 100 ppm) . Cu and Mo g r a d e s a l o n g t h e e a s t e r n c o n t a c t o f t h e g r a n o d i o r i t e r i s e a b r u p t l y f r o m b a c k g r o u n d v a l u e s w i t h i n t h e g r a n o d i o r i t e t o a b o u t . 0 5 p e r c e n t Cu and . 0 0 5 p e r c e n t Mo i n h o r n f e l s a d j a c e n t t o t h e 82 Figure 29 Zoning of copper and molybdenum assays within the deposit. Note strong control of host rock on grades. Plane of projection is indicated in Figure 3 83 granodiorite. Grades decline gradually away from the contact. Although veining is rare within the Breccia Zone, disseminated mineralization is abundant enough to result in Cu-Mo grades comparable to the Ore Zone. No paragenetic sequence of mineralization can easily be determined in this zone. Mineralization might have followed the sequence outlined from vein relationships in the Ore Zone. Control of host rock on assay grades is clearly indicated in Figure 29. Molybdenum grades within feldspar porphyry of the Ore Zone-Breccia Zone average two to five times the value for adjacent hornfels. This is in strong contrast to the granodiorite which is similar in bulk composition to the feldspar porphyry, yet contains a molybdenum content less than a f ifth the value of the feldspar porphyry. Feldspar porphyry also has somewhat lower copper grades than adjacent hornfels although the contrast is not as striking as with molybdenum. In general, feldspar porphyry contains average copper grades of one-half the average grade for surrounding more mafic hornfels. Granodiorite also has low copper grades but the average is much less than the average for feldspar porphyry. SUMMARY Distribution of opaque minerals outlines the propylitic, quartz-molybdenite and sphalerite vein types. The three propylitic subtypes are particularly distinguished by opaque minerals. 84 Z o n i n g s t u d i e s o f molybdenum and c o p p e r a s s a y s f r o m d r i l l d a t a i n d i c a t e a g e n e r a l d e c r e a s e i n g r a d e s o u t w a r d f r o m t h e i n t r u s i v e c o n t a c t . T h e r e i s a l s o a c o r r e l a t i o n between g r a d e s and h o s t r o c k w i t h l o w Cu and Mo g r a d e s w i t h i n m i n e r a l i z e d i n t r u s i o n and r e l a t i v e l y h i g h Mo and l o w Cu g r a d e s w i t h i n f e l d s p a r p o r p h y r y . T h u s , d i s t r i b u t i o n s o f opaque m i n e r a l s , l i k e d i s t r i b u t i o n s o f n o n - o p a q u e m i n e r a l s , c a n be c o r r e l a t e d w i t h (1) v e i n t y p e , ( 2 ) p o s i t i o n a r o u n d and w i t h i n t h e i n t r u s i o n , and (3) h o s t - r o c k t y p e . 85 CHAPTER VI REGIONAL CHARACTERISTICS OF PORPHYRY DEPOSITS SUMMARY S t u d i e s o f r e g i o n a l d i s t r i b u t i o n s o f p o r p h y r y d e p o s i t s i n B r i t i s h C o l u m b i a have shown t h e y a r e most p r e v a l e n t i n t h e I n t e r -m o n t a i n e B e l t where t h e y . . . p r e f e r e n t i a l l y o c c u r i n c e r t a i n b r o a d t e c t o n i c r e g i o n s s u c h as t h e S k e e n a A r c h , t h e s o u t h e r n I n t e r m o n t a n e a r e a and t h e S t i k i n e A r c h . F u r t h e r m o r e , t h e y o c c u r w i t h i n t h e s e r e g i o n s i n l o c a l c l u s t e r s s u c h as t h o s e a t B a b i n e L a k e , M o r i c e t o E u t u s k L a k e , A l i c e Arm and H i g h l a n d V a l l e y . I n g e n e r a l , t h e l o c a l c l u s t e r s have s i m i l a r p e t r o l o g y and m e t a l r a t i o s , b u t o v e r t h e b r o a d t e c t o n i c r e g i o n s t h e r e a r e commonly m a j o r d i f f e r e n c e s i n t h e s e f a c t o r s . F o r e x a m p l e , i n t h e Skeena A r c h , mo lybdenum-b e a r i n g p o r p h y r i e s o c c u r i n t h e s o u t h w e s t e r n h a l f and c o p p e r w i t h o u t molybdenum i n t h e n o r t h e a s t e r n h a l f . [ S u t h e r l a n d B r o w n , e_t a ] _ . , 1 9 7 1 ] . The Ox L a k e d e p o s i t b e l o n g s t o t h e l o c a l c l u s t e r o f m o l y b d e n u m - b e a r i n g p o r p h y r y d e p o s i t s t h a t o c c u r between M o r i c e and E u t s u k L a k e s i n t h e s o u t h w e s t e r n h a l f o f t h e S k e e n a A r c h . M i n e r a l i z e d p o r p h y r y i n t r u s i o n s i n t h e C a n a d i a n C o r d i l l e r a a r e r e l a t e d t o two magma s e r i e s ; t h e ma in c a l c - a l k a l i n e s u i t e : and t h e b a r e l y s a t u r a t e d s y e n i t e s u i t e . M i n e r a l i z e d i n t r u s i o n s o f t h e ma in c a l c - a l k a l i n e s u i t e a r e g e n e r a l l y q u a r t z m o n z o n i t e , and l e s s commonly 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 o r g r a n i t e . Molybdenum i s 86 a l m o s t a l w a y s p r e s e n t i n t h e c o p p e r d e p o s i t s o f t h e c a l c - a l k a l i n e s u i t e , w h e r e a s m i n e r a l i z e d i n t r u s i o n s o f t h e s y e n i t e s u i t e c o n t a i n c o p p e r w i t h o u t s i g n i f i c a n t molybdenum o r t u n g s t e n . [ S u t h e r l a n d B r o w n , e t a j _ . , 1 9 7 1 ] . The m i n e r a l i z e d Ox L a k e g r a n o d i o r i t e i s a t y p i c a l member o f t h e c a l c - a l k a l i n e s u i t e o f i n t r u s i o n s . M i n e r a l i z e d p o r p h y r y d e p o s i t s o f B r i t i s h C o l u m b i a have been d i v i d e d i n t o : S i m p l e , E l a b o r a t e , Complex and P l u t o n i c t y p e s on t h e b a s i s o f s t r u c t u r a l c o m p l e x i t y [ S u t h e r l a n d B r o w n , 1 9 6 9 ] . S u t h e r l a n d Brown c o r r e l a t e s more s t r u c t u r a l l y c o m p l e x d e p o s i t s w i t h g r e a t e r d e p t h o f f o r m a t i o n . The Ox L a k e d e p o s i t i s a Cu-Mo p o r p h y r y o f t h e s i m p l e t y p e . S i m p l e p o r p h y r y d e p o s i t s , as d e f i n e d , . . . a r e t h o s e a s s o c i a t e d w i t h s m a l l c y l i n d r i c a l p o r p h y r y p l u g s . (Ox L a k e , Red B i r d ) T h e s e show t h e m i n e r a l o g i c a l z o n i n g o f o r e , a l t e r a t i o n and m e t a m o r p h i c m i n e r a l s mos t c l e a r l y . The w a l l r o c k s a r e t h e r m a l l y metamorphosed i n an a n n u l a r zone o f v a r i a b l e r a d i u s i n w h i c h g r o w t h o f v e r y f i n e brown f e l t e d b i o t i t e i s c h a r a c t e r i s t i c . R o u g h l y c o i n c i d e n t w i t h t h i s h o r n f e l s i c a u r e o l e i s a p y r i t i c a n n u l u s w h i c h commonly g r a d e s i n w a r d t h r o u g h a c h a l c o p y r i t e - r i c h zone t h a t i s n o r m a l l y e x t e r n a l t o t h e p l u g t o a m o l y b d e n i t e zone e i t h e r s t r a d d l i n g o r i m m e d i a t e l y i n t e r n a l t o t h e c o n t a c t . The c o r e i s commonly b a r r e n o r v e r y s p a r s e l y m i n e r a l i z e d . A l t e r a t i o n i s zoned i n a p a r a l l e l manner w i t h i n t e n s e p o t a s h f e l d s p a r a l t e r a t i o n , i f d e v e l o p e d , c o i n c i d e n t w i t h t h e b a r r e n c o r e . A l t e r a t i o n v a r i e s g r e a t l y i n i n t e n s i t y , and i n some d e p o s i t s may o n l y r i s e a b o v e a r g i l l i c i n e n v e l o p e s t o v e i n s o r i n t e n s e s t o c k w o r k a r e a s . [ S u t h e r l a n d B r o w n , e t a l . , 1 9 7 1 ] . E x c e p t i o n s t o t h e above d e s c r i p t i o n f o r t h e Ox L a k e d e p o s i t a r e : t h e o c c u r r e n c e o f i n t r u s i v e b r e c c i a w h i c h c o m p l i c a t e s t h e s t r u c t u r e ; t h e molybdenum z o n e o c c u r r i n g i m m e d i a t e l y e x t e r n a l t o t h e i n t r u s i v e and n o t s t r a d d l i n g o r i n t e r n a l t o t h e i n t r u s i v e c o n t a c t ; and t h e p o t a s h 87 feldspar alteration occurring in hornfels and not the barren core. Otherwise, the definition above very aptly describes the deposit. Mineralized porphyry deposits of British Columbia have been further subdivided into Phallic, Volcanic and Plutonic porphyry deposits on the basis of: shape and size of the intrusion; age of intrusion relative to an orogenic cycle; and genetic relationship of the intrusion to host rocks. Under this classification the Ox Lake deposit is a typical Phallic type. Phallic porphyry deposits are ones centred on cylindrical plutons or related pluton groups intruded into an unrelated host rock at a high crustal level during late orogenic or platform tectonics. Metamorphic (1) alteration, (2) and ore (3) zones are characteristically annular and normally consist of (1) biotite hornfels, (2) an internal potassic zone, variably developed, a contact phyllic zone, and an external propylitic zone, (3) variably developed outward grading sequence, molybdenum, copper, iron, which at maximum development consists of barren core, molybdenum contact zone, copper external zone, and iron outermost zone. Examples within the group range from simple to elaborate, and are: Ajax, Red Bird, Berg, Alice (British Columbia Molybdenum), Lucky Ship. [Sutherland Brown, 1972]. More recently mineralized porphyries in the general area of the Skeena Arch have been classified on the basis of apparent K-Ar ages, into three separate belts transverse to the trend of the Arch. K-Ar dating of copper and molybdenum-bearing porphyries in the central part of the Intermontane tectonic belt indicates two major periods of intrusion and associated mineralization. Results of the K-Ar dating indicate three north to northwest trending belts of porphyry intrusions, each being distinctive in rock composition and contained metallic mineralization. These are, from east to west: (1) Babine Lake area--50 my copper bearing dykes, plugs and dykes swarms of quartz diorite composition; (2) Hazelton to Whitesail Lake area—70-80 my., granodiorite and quartz 88 monzonite porphyries, containing copper-molybdenum mineralization; (3) an area marginal to the Coast Plutonic Complex--50 my molybdenum bearing stocks of quartz monzonite composition. [Carter, 19 ]. DISCUSSION Figure 30 shows the distribution of known mineralized porphyries and prospects in the vicinity of Ox Lake. Figure 31 lists several features of these deposits and the Laura deposit near Hazelton. The f i rst five deposits, which include the Ox Lake deposit, belong to the second group of porphyry deposits described by Carter that l ie between Hazelton and Whitesail Lake. The other two deposits belong within the third group of porphyries that l ie marginal to the Coast Plutonic Complex. The Ox, Len, and Fab porphyries show remarkable similarity in age, petrology, size, and associated mineralization. These similarities and their proximity to each other probably indicate a similar genesis for these plugs and possibly the same source at depth. The Bergette porphyry is slightly younger than the other deposits. The Laura porphyry is of similar age, but has a higher molybdenum and lower copper content than the other deposits and is one hundred thirty miles distant. These discrepancies probably indicate that intrusion of this group of mineralized porphyries was not local and possibly extended through several millions of years. 89 Figure 30 Apparent K-Ar ages of porphyry deposits within the general area of Ox Lake from Carter and Harakal (personnal communication). Geology taken from Geological Survey of Canada map 1064A 90 DEPOSIT INTRUSION K-Ar AGE SIZE METALS HOST ROCK OX Granodiorite Porphyry 83.4 ±3.2 2400 X 1400 Cu (Mo) Hornfels & Breccia Hornfels Et Breccia LEN Granodiorite Porphyry 82 ±3 2200 X 1400 Cu (Mo) Hornfels Hornfels FAB Granodiorite Porphyry 83.8 ±28 2500X 2000 Cu (Mo) Contact of Intrusion Contact of Intrusion LAURA Granodiorite Porphyry 82.4 ±31 2000X 2000 Mo (Cu) Intrusion Intrusion BERGETTE Quartz Monzonite Porphyry 76.7 ±2.5 3500 X 3000 Cu (Mo) Breccia (& Hornfels) Breccia (Et Hornfels) BERG Quartz Monzonite Porphyry 48 ±2 2400 X 2400 Cu (Mo) Hornfels Hornfels and Contact of Intrusion CAFB Quartz Monzonite Porphyry 50 3500 X 2500 Mo Contact of Intrusion Figure 31 Comparison of the Ox Lake porphyry deposit with several other porphyry deposits. After White et a]_. (1968), Carter and Harakal personal communication. B.C. Minister of Mines and Petroleum Resources Annual Reports — 1964, 1966, 1968, 1969, 1970, 1971 91 S i m i l a r i n t e r p r e t a t i o n s have been p r e s e n t e d f o r s e v e r a l g r o u p s o f p o r p h y r y d e p o s i t s i n B r i t i s h C o l u m b i a i n c l u d i n g t h i s g r o u p . [ W h i t e e t a j _ . , 1 9 6 8 ] , [ C h r i s t o p e r , 1 9 7 3 ] . R e l a t i v e ages o f m i n e r a l i z a t i o n and i n t r u s i o n o f p o r p h y r y d e p o s i t s have been s u g g e s t e d f r o m p o t a s s i u m - a r g o n age d a t i n g d e p o s i t s i n t h e B a b i n e L a k e a r e a . Age d e t e r m i n a t i o n s o f p e t r o l o g i c a l l y s i m i l a r p o s t -m i n e r a l p o r p h y r i t i c p h a s e s have y i e l d e d ages 2 t o 3 m i l l i o n y e a r s y o u n g e r t h a n t h e m i n e r a l i z e d phase and w h i l e s u c h a d i f f e r e n c e i s w i t h i n t h e l i m i t s o f e r r o r , t h e s e r e s u l t s do i n d i c a t e t h a t t h e age o f m i n e r a l i z a t i o n i s a p p r o x i m a t e l y c o n t e m p o r a n e o u s w i t h t h e age o f i n t r u s i o n . [ C a r t e r , 1970 ] A s i m i l a r age r e l a t i o n s h i p f o r t h e Ox L a k e d e p o s i t has been s u g g e s t e d a b o v e f r o m i n t e r s e c t i o n s o f v e i n s w i t h p o r p h y r y d y k e s . 92 CHAPTER V I I SUMMARY V o l c a n i c - s e d i m e n t a r y r o c k s o f unknown s t r a t i g r a p h i c p o s i t i o n a r e a s s i g n e d t o t h e H a z e l t o n Group on t h e b a s i s o f t h e v/ork o f o t h e r s , m a i n l y D u f f e l l [ 1 9 5 9 ] . T h e y a r e s u b d i v i d e d i n t o t h r e e u n i t s ; a l o w e r F e l s i c T u f f , a m i d d l e A n d e s i t i c T u f f and an u p p e r S a n d s t o n e -S i l t s t o n e . F e l s i c T u f f o v e r one t h o u s a n d f e e t t h i c k i s c h a r a c t e r i z e d by a b u n d a n t f e l d s p a r p o r p h y r y and f e l s i c t u f f . B o t h a r e r h y o d a c i t i c i n c o m p o s i t i o n and b o t h a r e c o n s i d e r e d t o be m a i n l y e x t r u s i v e i n o r i g i n . The tv/o g r a d e i n t o e a c h o t h e r t h r o u g h a zone s e v e r a l h u n d r e d f e e t t h i c k i n w h i c h t h e y a r e i n t e r c a l a t e d . A n d e s i t i c T u f f i s a b o u t one t h o u s a n d f e e t t h i c k and c o n t a i n s numerous l a y e r s o f l a p i l l i t u f f and a f e w l a y e r s o r d y k e s o f f e l d s p a r p o r p h y r y . Much o f t h i s u n i t c o u l d be o f s e d i m e n t a r y o r i g i n . The u p p e r S a n d s t o n e - S i l t s t o n e u n i t i s p o s s i b l y s e p a r a t e d f r o m t h e m i d d l e u n i t by an u n c o n f o r m i t y . C h e r t - p e b b l e c o n g l o m e r a t e o c c u r s as l e n s e s w i t h i n t h e u n i t as does some v o l c a n i c s e d i m e n t a r y m a t e r i a l . The l o w e r two u n i t s have f l a t t o g e n t l e d i p s where t h e y a r e n o t n e a r m i n e r a l i z e d g r a n o d i o r i t e p o r p h y r y . The u p p e r u n i t has d i p s o f f i f t y t o s e v e n t y d e g r e e s w e s t e r l y w h i c h p r o b a b l y r e p r e s e n t s t h e e a s t e r n l i m b o f a s y n c l i n e . A l l u n i t s have u n d e r g o n e r e g i o n a l g r e e n s c h i s t metamorph ism p r i o r t o emp lacement o f a g r a n o d i o r i t e p o r p h y r y p l u g , a d i o r i t e s t o c k 93 and many basic dykes. Emplacement of the dior i te appears to be con-t ro l led loca l ly by an unconformity between the upper two units. The granodiorite porphyry intruded the lower two units and was emplaced after regional metamorphism and probably after the . folding indicated by the steep attitude of the upper unit. The plug is 1,400 by 2,400 feet in plan, but rakes west about f i f t y degrees and is thus nearly c i rcular in true cross-section. It was intruded forcefu l ly , approximately in i ts present attitude so that Hazelton Group rocks in contact with the west side of the intrusion form an ant ic l ine whose fold axis overlies and is approximately parallel with the westward rake of the intrusion. Intrusive breccia occurs in contact with the plug, mainly along i ts southwest contact. Many dykes of granodiorite porphyry occur along the western contact within hornfels and intrusive breccia. Some but not a l l of these dykes are unaltered and intersect ear l ier formed veins. The plug is unaltered except within one hundred feet of i ts western contact. Two main lineaments intersect at the northwest edge of the . intrusion and probably represent faults . Much fault gouge occurs in d r i l l holes within the western margin of the intrusion and adjacent hornfels, less so within the eastern hornfels and even less within d r i l l holes in unaltered Hazelton Group rocks. Nine vein types and f ive alteration types have developed within four recognized stages of vein development. The stages are based on relat ive ages of veins determined from crosscutting re lat ion-ships. Alteration is largely primary; surface oxidation occurs to a maximum recognized depth of ten feet. 94 Stage I is primarily an early potassic alteration event involving development of biotite and potash feldspar within veins and as alteration products of previously existing minerals. Potassic alteration began early but continued throughout Stage II and into Stage III. Stage II is characterized by propylitic assemblages everywhere except within the intrusion and within feldspar porphyry on the west side of the deposit. Propylitic minerals show a zonal pattern as follows: a core zone of chlorite-calcite-pyrite lies adjacent to the west side of the intrusion; a zone of epidote-hematite-chlorite-calcite-pyrite surrounds the intrusion and the above zone; and an actinolite-magnetite-pyrite zone lies peripheral to the second zone. In the west half of the deposit, weakly altered feldspar porphyry contains Stage II pyrite-chalcopyrite veins with quartz-sericite envelopes. In more intensely altered feldspar porphyry the same alteration assemblage possibly exists but alteration patterns are obscured by intense overlapping of several alteration types. Granodiorite porphyry contains only minor amounts of Stage II alteration. Potash feldspar, sericite, kaolinite and montmorillonite occur outwards from Stage II veins replacing plagioclase phenocrysts. West of the intrusion, potash feldspar is common and albite rare as an alteration envelope on propylitic veins with some indication that the albite envelopes occur further from the intrusion than potash feldspar envelopes. East of the intrusion, Stage II veins have much albite and minor potash feldspar occurring as envelopes. 95 Q u a r t z and q u a r t z - m o l y b d e n i t e v e i n s r e p r e s e n t S t a g e I I I , w i t h t h o s e c o n t a i n i n g o n l y q u a r t z b e i n g l a t e p a r a g e n e t i c a l l y . A l t e r a t i o n o c c u r r i n g w i t h t h e s e v e i n s w i t h i n t h e i n t r u s i o n i s s e r i c i t e -k a o l i n i t e - m o n t m o r i l l o n i t e as a r e p l a c e m e n t o f p l a g i o c l a s e o u t w a r d s f r o m v e i n w a l l s . B i o t i t e i s s t a b l e t o t h e c e n t r e o f t h e k a o l i n i t e z o n e . V e i n w a r d f r o m h e r e , t h e b i o t i t e i s r e p l a c e d by a g o l d e n brown m i c a . M a g n e t i t e i s d e s t r o y e d a t t h e o u t e r edge o f a l t e r a t i o n where i t i s f i r s t r e p l a c e d by h e m a t i t e . W i t h i n w e l l - a l t e r e d f e l d s p a r p o r p h y r y w e s t o f t h e i n t r u s i o n q u a r t z v e i n s m i g h t have a s i m i l a r a l t e r a t i o n e n v e l o p e . W i t h i n o t h e r r o c k s , some S t a g e I I I v e i n s have p o t a s h f e l d s p a r e n v e l o p e s and o t h e r s have m i n o r amounts o f what i s p r o b a b l y s e r i c i t i c a l t e r a t i o n . S t a g e IV v e i n s a r e c a l c i t e , gypsum and s p h a l e r i t e t y p e and have no n o t i c e a b l e a l t e r a t i o n e n v e l o p e s . E c o n o m i c m i n e r a l s i n o r d e r o f d e c r e a s i n g i m p o r t a n c e a r e c h a l c o p y r i t e , m o l y b d e n i t e and b o r n i t e . S t a g e I I v e i n s and a s s o c i a t e d d i s s e m i n a t e d m i n e r a l i z a t i o n r e p r e s e n t s t h e b u l k o f t h e i n t r o d u c e d c o p p e r . B o r n i t e o c c u r s o n l y as i n c l u s i o n s , commonly w i t h c h a l c o p y r i t e , w i t h i n d i s s e m i n a t e d p y r i t e g r a i n s . S t a g e I I I v e i n s c o n t a i n a l l m o l y b d e n i t e e x c e p t a s m a l l p o r t i o n o c c u r r i n g as d i s s e m i n a t i o n s i n b r e c c i a . B r e c c i a , a l t h o u g h c o n t a i n i n g v e r y few v e i n s , does c o n t a i n Cu and Mo g r a d e s c o m p a r a b l e t o a d j a c e n t u n b r e c c i a t e d h o r n f e l s . U n a l t e r e d g r a n o d i o r i t e p o r p h y r y c o n t a i n s no v i s i b l e s u l p h i d e s . A l t e r e d g r a n o d i o r i t e p o r p h y r y c o n t a i n s l e s s t h a n 0 . 0 5 p e r c e n t Cu and l e s s t h a n 0 . 0 0 5 p e r c e n t Mo. G rades o f b o t h e l e m e n t s 96 a r e h i g h e s t i n h o r n f e l s a l o n g t h e w e s t e r n c o n t a c t o f t h e i n t r u s i o n and d e c l i n e g r a d u a l l y o u t w a r d s f r o m t h e c o n t a c t where g r a d e s a v e r a g e a b o u t 0 . 5 p e r c e n t Cu and 0 . 0 2 p e r c e n t Mo. The zone o f Mo m i n e r a l i z -a t i o n does n o t e x t e n d a s f a r f r o m t h e i n t r u s i o n a s does t h e z o n e o f Cu m i n e r a l i z a t i o n . F e l d s p a r p o r p h y r y seems t o e x e r t a s t r o n g c o n t r o l on Cu and Mo. Mo i s 2 t o 5 t i m e s h i g h e r and Cu a b o u t o n e - h a l f as h i g h i n f e l d s p a r p o r p h y r y r e l a t i v e t o a d j a c e n t a n d e s i t i c h o r n f e l s . The Ox L a k e d e p o s i t i s one o f a g r o u p o f d e p o s i t s a l l a s s o c i a t e d w i t h s i m i l a r i n t r u s i o n s and h a v i n g c o m p a r a b l e m i n e r a l i z a t i o n p r o d u c t s . T h i s g r o u p i n c l u d e s Ox L a k e , L e n , F a b , L a u r a and B e r g e t t e d e p o s i t s i n t h e s o u t h w e s t e r n h a l f o f t h e Skeena A r c h f r o m H a z e l t o n t o W h i t e s a i l L a k e . The i n t r u s i o n (and p r o b a b l y t h e m i n e r a l i z a t i o n ) have a p p a r e n t K - A r a g e s o f 7 0 - 8 0 my [ C a r t e r , 1 9 7 3 ] . They have been d e s c r i b e d by o t h e r s and c l a s s i f i e d as S i m p l e t y p e b a s e d on s t r u c t u r a l c o m p l e x i t y [ S u t h e r l a n d B r o w n , 1 9 6 9 ] , and as P h a l l i c t y p e b a s e d o n ; s h a p e and s i z e o f t h e i n t r u s i o n , age o f i n t r u s i o n r e l a t i v e t o o r o g e n i c c y c l e , and g e n e t i c r e l a t i o n s h i p o f t h e h o s t r o c k s [ S u t h e r l a n d B r o w n , 1 9 7 2 ] . 97 REFERENCES C a r r , J . M . [ 1 9 6 4 ] . L e n . I n M i n i s t e r o f M i n e s and P e t r o l e u m R e s o u r c e s , P r o v i n c e o f B r i t i s h C o l u m b i a , A n n u a l R e p o r t 1 9 6 4 , pp . 5 3 - 5 5 . C a r t e r , N . C . [ 1 9 7 0 ] . L e n . I n M i n i s t e r o f M i n e s and P e t r o l e u m R e s o u r c e s , P r o v i n c e o f B r i t i s h C o l u m b i a , A n n u a l R e p o r t 1 9 7 0 , p p . 1 0 4 - 1 0 7 . . [ 1 9 7 0 ] . C o p p e r and Molybdenum P o r p h y r y D e p o s i t s i n C e n t r a l B r i t i s h C o l u m b i a . In C a n a d i a n M i n i n g J o u r n a l , A p r i l 1 9 7 0 , p p . 7 4 - 7 6 . . [ 1 9 7 3 ] . G e o c h r o n o l o g y o f P o r p h y r y C o p p e r and Molybdenum D e p o s i t s i n W e s t - C e n t r a l B r i t i s h C o l u m b i a ( A b s t r a c t ) . In The C a n a d i a n M i n i n g and M e t a l l u r g i c a l B u l l i t i n , V o l . 6 6 , No. 7 3 1 , M a r c h 1 9 7 3 , p. 6 1 . C h r i s t o p h e r , P . A . [ 1 9 7 3 ] . A p p l i c a t i o n o f K - A r and F i s s i o n - T r a c k D a t i n g t o t h e M e t a l l o g e n y o f P o r p h y r y and R e l a t e d M i n e r a l D e p o s i t s i n t h e C a n a d i a n C o r d i l l e r a . U n p u b l i s h e d P h . D . T h e s i s , 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 , 1 6 1 p . C h u r c h , B . N . [ 1 9 7 1 ] . B e r g e t t e . I n M i n i s t e r o f M i n e s and P e t r o l e u m R e s o u r c e s , P r o v i n c e o f B r i t i s h C o l u m b i a , A n n u a l R e p o r t 1 9 7 1 , p p . 1 4 7 - 1 5 7 . D u f f e l l , S . [ 1 9 5 9 ] . W h i t e s a i l L a k e M a p - A r e a , B r i t i s h C o l u m b i a . G e o l . S u r v . C a n . Memoir 2 9 9 , 109p . L o w e l l , J . D . , and G u i l b e r t , J . M . [ 1 9 7 0 ] . L a t e r a l and V e r t i c a l A l t e r a t i o n -M i n e r a l i z a t i o n Z o n i n g i n P o r p h y r y Ore D e p o s i t s . I n Economic G e o l o g y , V o l . 6 5 , No. 4 , J u n e - J u l y 1 9 7 0 , p p . 3 7 3 - 4 0 8 . M c l n t y r e , D. [ 1 9 7 3 ] . Z o n a t i o n o f A l t e r a t i o n and S u l p h i d e A s s e m b l a g e s a t t h e C o l e s C r e e k C o p p e r P r o s p e c t , C e n t r a l B . C . U n p u b l i s h e d M . S c . T h e s i s , U n i v e r s i t y o f W e s t e r n O n t a r i o , L o n d o n , O n t a r i o . M e y e r , C. and H e m l e y , J . J . [ 1 9 6 7 ] . W a l l Rock A l t e r a t i o n . In G e o c h e m i s t r y o f H y d r o t h e r m a l Ore D e p o s i t s ( e d i t o r , B a r n e s , H . L . ) , pp . 1 6 6 - 2 3 5 . 98 S o u t h e r , J . G . and A r m s t r o n g , J . E . [ 1 9 6 6 ] . N o r t h C e n t r a l B e l t o f t h e C o r d i l l e r a o f B r i t i s h C o l u m b i a . I n A Symposium on t h e T e c t o n i c H i s t o r y and M i n e r a l D e p o s i t s o f t h e W e s t e r n C o r d i l l e r a i n B r i t i s h C o l u m b i a and N e i g h b o u r i n g P a r t s o f t h e U n i t e d S t a t e s ( s e n i o r e d i t o r , H . C . G u n n i n g ) , p p . 1 7 1 - 1 8 4 . The C a n a d i a n I n s t i t u t e o f M i n i n g and M e t a l l u r g y , S p e c i a l Vo lume No . 8 , 3 5 3 p . S u t h e r l a n d B r o w n , A . [ 1 9 6 6 ] . B e r g . I n M i n i s t e r o f M i n e s and P e t r o l e u m R e s o u r c e s , P r o v i n c e o f B r i t i s h C o l u m b i a , A n n u a l R e p o r t 1 9 6 6 , p p . 1 0 5 - 1 1 2 . . [ 1 9 6 6 ] . Red B i r d ( C A F B ) . I n M i n i s t e r o f M i n e s and P e t r o l e u m R e s o u r c e s , P r o v i n c e o t B r i t i s h C o l u m b i a , A n n u a l R e p o r t 1966,.. p p . 1 1 2 - 1 1 6 . • . [ 1 9 6 8 ] . B e a r . I n M i n i s t e r o f M i n e s and P e t r o l e u m R e s o u r c e s , P r o v i n c e o f B r i t i s h C o l u m b i a , A n n u a l R e p o r t 1 9 6 8 , p p . 1 1 3 - 1 1 6 . . [ 1 9 6 9 ] . Ox. I n M i n i s t e r o f M i n e s and P e t r o l e u m R e s o u r c e s , P r o v i n c e o f B r i t i s h C o l u m b i a , A n n u a l R e p o r t 1 9 6 9 , p p . 9 3 - 9 7 . . [ 1 9 6 9 ] . M i n e r a l i z a t i o n i n B r i t i s h C o l u m b i a and t h e C o p p e r and Molybdenum D e p o s i t s . In The C a n a d i a n M i n i n g and M e t a l l u r -g i c a l B u l l e t i n , V o l . 6 2 , No. 6 8 1 , J a n u a r y 1 9 6 9 , p p . 2 6 - 4 0 . , C a t h r o , R . J . , P a n t e l e y e v , A . , and N e y , C . S . [ 1 9 7 1 ] . M e t a l l o g e n y o f t h e C a n a d i a n C o r d i l l e r a . In The C a n a d i a n M i n i n g and M e t a l l u r g i c a l B u l l e t i n , V o l . 6 4 , No. 7 0 9 , J u n e 1 9 7 1 , p p . 3 7 -6 1 . . [ 1 9 7 2 ] . M o r p h o l o g y and C l a s s i f i c a t i o n o f P o r p h y r y D e p o s i t s o f t h e C a n a d i a n C o r d i l l e r a . I n P r o c e e d i n g s o f t h e 9 t h A n n u a l W e s t e r n I n t e r - U n i v e r s i t y G e o l o g i c a l C o n f e r e n c e , 1 8 p . W h i t e , W . H . , H a r a k a l , J . E . and C a r t e r , N . C . [ 1 9 6 8 ] . P o t a s s i u m - A r g o n Ages o f Some Ore D e p o s i t s i n B r i t i s h C o l u m b i a . I n The C a n a d i a n M i n i n g and M e t a l l u r g i c a l B u l l e t i n , V o l . 6 1 , p p . 1 3 2 6 - 1 3 3 4 . \ 

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