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The geology of the Aufeas mine at Silver Creek, B.C. Wallace, James Alan 1942

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THE GEOLOGY OF THE AUFEA3 MINE AT SILVER GREEK, B.C. James Alan Wallace Thesis submitted i n P a r t i a l F u l f i l m e n t The Requirements f o r the Degree of MASTER OF APPLIED SCIENCE i n the Department of GEOLOGY The U n i v e r s i t y of B r i t i s h Columbia A p r i l , . 1942. -C 0 E T E I T S -1. INTRODUCTION ...... 2. TOPOGRAPHY 3. GENERAL GEOLOGY 4. PETROGRAPHY .... 5* S «]?!RTJ 0 Q?URE ••••••••• 6• ORE DEP03ITS *•«•«•••••*••••« 7. MIHER&LOGY '... •8. PARAGENES IS 9. GENESIS ................. 10. AGE OP QUARTZ DIORITE ... 11. ORIGIN OF SOLUTIONS 12. OTHER DEPOSITS 13. ACKNOWLEDGMENTS .. ..... 14. BIBLIOGRAPHY LIST OF ILLFSTRAT103STS P l a t e I. The Town of Hope, B.C. from~ 'the upper l e v e l of ..the Aufeas M i n e - f r o n t i s p i e c e . I I . Ohalcopyrite r e p l a c i n g Sphal-e r i t e * Specimen from West Stope. Hag. 600X. 15 I I I . Ohalcopyrite r e p l a c i n g Shaler-i t e . Specimen from East Stope. Mag. 650X. 16 IV. Ohalcopyrite r e p l a c i n g Sphaler-i t e . Specimen from East Stone. Mag. 650X. 17 IT. Sketch Map of Ooguihalla and Skagit Areas. 24 MAPS 1. Plan of Surface of Aufeas Mine. v 2. P l a n of Main Level of Aufeas Mine. 3. Block Diagram of Aufeas Mine. In pocket. In pocket. In pocket. PLATE 1. 1. THE GEOLOGY OF THE AUFEAS MINE AT SILVER CREEK, B.C. INTRODUCTION: One hundred miles east of Vancouver, the Fraser River outs through the western f l a n k of the Coquihalla River area. The region i s one of rugged topography characterized by numerous small streams whicb rush down c l e f t s i n the steep mountain sides i n t o the h e a v i l y wooded v a l l e y s . On such a creek i s the Aafeas Mine. The creek r e f e r r e d to i s Yfardle Creek, a t r i b u t a r y of S i l v e r Creek and the mine work-ings are 3000 feet west of the, j u n c t i o n of the two. A good road runs to with l / 4 mile of the workings and a good, though steep, pack t r a i l leads to the a d i t , 1000 feet above the road* The Cariboo Highway which crosses S i l v e r Greek 3/4 of a mile below the s t a r t of the pack t r a i l c a r r i e s dependable bus and good t r u c k i n g s e r v i c e s at a l l seasons of the year. In a d d i t i o n , both the Canadian P a c i f i c and Canadian Na t i o n a l Railways serve the town of Hope, 5 miles north-east of the mine. D e t a i l s of the h i s t o r y of the mine are not abundant 2. "but they do r e l a t e that i t was found i n 1909. Charles Oamsell made passing reference to i t i n h i s report on the area i n 1911 hut apparently l i t t l e work had been done. Brewer examined the mine i n 1914 f o r the B r i t i s h Columbia Department of Mines and included i n h i s report a d e t a i l e d d e s c r i p t i o n of the underground workings.. At the time of t h i s examination an a e r i a l tram l i n k e d the lower a d i t w i t h the road, but t h i s was l a t e r removed and a system of rawhiding was introduced. Cairnes made a r a p i d examination of the property i n 1923, and found i t s u b s t a n t i a l l y as Brewer had l e f t i t nine years e a r l i e r . I t i s evident from these reports that most of the work done since these examinations has been i n the form of stoping-.on the main v e i n from the lower d r i f t s . The ore i s hand-picked underground and shipped to Tacoma f o r smelting. Because of i t s high arsenic content, the ore incurs heavy p e n a l t i e s during treatment and i t r e q uires w e l l over 3/4 oz. Aper ton to make the mine a commercial success. 1* The average grade i s 1.08 oz./ton f o r gold and about 1 oz./ton f o r s i l v e r . • G' M o G i l l i s (lessee, Aufeas Mine, 1941) personal communication. TOPOGRAPHY: . , The Goquihalla Map Area c o n s i s t i n g of s t r i p s of land, on both f l a n k s of the Goquihalla River from above i t s head-waters down to Hope on the Fraser River, comprises a sheet that i s over 35 miles long and about 10 miles wide* The area l i e s e n t i r e l y w i t h i n the northward extension of the American Cascade physiographic province. This province, crossing the boundary between the 120th and 122nd degrees of longitude, extends as f a r north as the Thompson Riv e r where i t grades i n t o the I n t e r i o r Plateau. At the 49th p a r a l l e l the province i s broken i n t o three mountain ranges: the Okanagan Range on the east, between the Similkameen and Okanagan Riv e r s , the Hozameen Range between the Skagit and Similkameen Rivers and the Skagit Range between the Skagit River and the edge of the c o a s t a l depression at Sumas. A l l parts of the area are characterized by extremely rugged topography with elevations varying from 160 f e e t f o r the r i v e r v a l l e y s up to heights of over 7400 feet on some of the l o f t i e r peaks. The mountains l e s s than 6000 fe e t have been rounded on t h e i r peaks by g l a c i a l a c t i o n but those of greater elevations are u s u a l l y matterhorns, often with small mountain g l a c i e r s on t h e i r northward slopes. GENERAL GEOLOGY; ' , Rocks "of pre-Carboniferous age are absent from the area; they may have existed at one time but now have been e i t h e r completely removed by erosion or covered up by sub-sequent deposition. A submersion of the land i n the Pennsylvanian, or p o s s i b l y the e a r l y Permian, accompanied by widespread s e d i -mentation and some vulcanism, provided the oldest rooks i n the area - the Cache Greek s e r i e s . These rocks, composed of andesite, greenstone, limestone and chert, are i n t e n s e l y folded and f a u l t e d , and u s u a l l y dip steeply to the south-west. They occupy a north-west trending b e l t about 5 miles wide c u t t i n g through the middle of the map area, and are a l s o exposed to a smaller extent East of the town of Hope. Following the deposition of the Cache Creek group there was a period of u p l i f t and erosion which was i n turn, followed i n the mid-Triassic by another p e r i o d of sedimen-t a t i o n and widespread vulcanism, during which the rocks of the N i c o l a S e r i e s , represented i n the area by the Tulameen Group, were l a i d down. These rocks con s i s t mainly of medium to basic volcanios, together with a number of horizons of grey to black s l a t e . They are very l i m i t e d i n extent and are found only i n the extreme north-east p o r t i o n of the d i s t r i c t . The l a t e T r i a s s i c saw a r e c e s s i o n of the seas, 5. accompanied "by c r u s t a l warping along the P a c i f i c border, which was followed i n the middle J u r a s s i c by another sub-, mergence of the land. Sedimentation brought about by t h i s inundation of the area, r e s u l t e d i n the formation of the Ladner and Dewdney Creek se r i e s of conglomerates, s l a t e s and volcanios. The l a t t e r formation l i e s conformably on the Ladner s e r i e s and the whole i s folded i n t o a t i g h t , north-west s t r i k i n g s y n c l i n e . This s y n c l i n a l b e l t i s three miles wide and l i e s along the north-east contact of the main exposure of the Cache Greek S e r i e s . As the J u r a s s i c drew to a close, the seas r e t r e a t e d from a l l but the deeper v a l l e y s and the e x i s t i n g s t r a t a were deformed along a north-west, south-east a x i s . Accompanying t h i s deformation was the i n t r u s i o n of a number of a c i d rock types. This period of i n t r u s i o n was, however, only the vanguard of i n j e c t i o n on a much grander scale extending i n t o the middle T e r t i a r y . Following the i n i t i a t i o n of t h i s igneous c y c l e , e a r l y Cretaceous sediments were l a i d down i n the v a l l e y s that s t i l l remained under water. These rocks consisted mainly of poorly s t r a t i f i e d conglomerate and sand-stone, some of the pebbles of which were derived from the Ju r a s s i c i n t r u s i v e s . The sediments outcrop i n the lower and upper parts of the sheet and i n a l l cases are folded to a considerable extent. The upper Cretaceous saw the continuation of the i n t r u s i o n begun i n the J u r a s s i c with the 6. formation of a large b a t h o l i t h of granite and a l l i e d rooks i n the extreme northern part of the d i s t r i c t . The. orogenic disturbances of the Laramide Revolution which closed the Mesozoic, u p l i f t e d the surface and fu r t h e r deformed the e x i s t i n g s t r a t a ; such deformation p r o v i d i n g a basis upon which a separation of pre and post-Laramide i n t r u s i o n can be made. The T e r t i a r y , commonly noted f o r i t s v o l c a n i c s , i s i n t h i s area equally important f o r i t s i n t r u s i v e s . The sole representative of the extrusives i s the Coquihalla Series of r h y o l i t e and basalt flows which outcrop i n the north-eastern p o r t i o n of the sheet. They have been but s l i g h t l y deformed and generally dip at angles l e s s than 25 degrees. They are Miocene i n age. The i n t r u s i v e s of t h i s age are mainly quart z-d i o r i t e and outcrop i n the southern part of the d i s t r i c t only. As implied e a r l i e r , the p l a c i n g of these rocks i n the T e r t i a r y r e s t s almost e n t i r e l y on the f a c t that they present a r e l a t i v e l y unsheared appearance which i s i n marked contrast to the sheared i n t r u s i v e s of p r e - T e r t i a r y age. The Pleistocene brought g l a c i a t i o n . The i c e sheet swept across the area i n a south-westerly d i r e c t i o n and rounded the summits of most of the mountains. I t di d , how-ever, leave a number of arretes as e x h i b i t e d by the higher peaks i n the Skagit Range. 7. PETROGRAPHY: Si x specimens from the w a l l rock adjacent to the main ve i n were taken from the upper a d i t and examined i n t h i n - s e c t i o n . In both the hanging w a l l and the f o o t w a l l the procedure was i d e n t i c a l ! one specimen was taken at the vein, another 1§- feet from the vein, and a t h i r d 6 feet from the vei n . The w a l l rock of the mine i s a medium to f i n e -grained quartz d i o r i t e . In the hand specimen i t i s l i g h t i n co l o r , containing 60 per cent feldspar, 15 per cent horn-blende, 15 per cent b i o t i t e , and 10 per cent quartz. I t i s remarkably sheared and i n some places e x h i b i t s an almost g n e i s s i c banding of the darker constituents. M i c r o s c o p i c a l l y , the predominating mineral i s an albite-twinned feldspar with a maximum e x t i n c t i o n angle of 19 degrees and an index of r e f r a c t i o n of 1,55. These c h a r a c t e r i s t i c s determine the composition of the feldspar a t about A336 A n 4 , thus p l a c i n g i t w e l l w i t h i n the andesine range. The g r a i n s i z e of the andesine i s extremely v a r i a b l e but the majority of the c r y s t a l s are over .5 m.m. i n s i z e . The f e l d s p a r i s nearly always f r e s h , but i n places where the rock i s f r a c t u r e d i t i s a l t e r e d to s e r i c i t e , c a l c i t e and some c h l o r i t e . In some instances i t was noted that the feld s p a r was c l o s e l y intergrown w i t h the b i o t i t e and hornblende and frequently appeared i n the l a t t e r mineral producing a 8. p o i k i l i t i c texture. The amphibole i s common hornblende and i s present as rather l a r g e , i r r e g u l a r f l a k e s and masses showing l i g h t brown to dark green pleochroism and a l t e r e d i n some parts to c h l o r i t e . . A few of the f l a k e s show a twinned e x t i n c t i o n and at the same time are vernacularly intergrown w i t h quartz. I t i s p o s s i b l e that these grains are the r e s u l t of deuteric a l t e r a t i o n of a pyroxene since e n s t a t i t e has been reported as a constituent of a quartz d i o r i t e occurring about one-half mile north of the mine. Brown b i o t i t e , occurring as large sheets and small remnants, accounts f o r 10 per cent of the s l i d e s . In the specimens taken f a r t h e s t from the vein, the mica i s not a l t e r e d to any great extent, but where a l t e r a t i o n has proceeded, C h l o r i t e i s developed. Quartz, forming about 8 per cent of the s l i d e s , appears as small to medium-sized grains r e p l a c i n g the f e l d s p a r and as f i n e -grained p a r t i c l e s intergrown with b i o t i t e and hornblende. The accessory.minerals, magnetite, i l m e n i t e , a p a t i t e , p y r i t e and z i r c o n , make up about 2 per cent of the rock. Of these, magnetite i s the most abundant and together w i t h the other m e t a l l i c s i s found i n small i r r e g u l a r patches associated with the b i o t i t e and hornblende. Apatite occurs as small rounded grains and lath-shaped c r y s t a l s second only i n number to those of magnetite. P y r i t e and z i r c o n are very minor accessories, one or two grains of each being found i n the s l i d e s . In some places patches of i l m e n i t e are surrounded by an opaque mineral 9. which i s white i n r e f l e c t e d l i g h t ; i t may he leueoxene. Hearer the v e i n the w a l l rock a l t e r a t i o n becomes more intense. The products of t h i s a l t e r a t i o n now amount to almost 40 per cent of the s l i d e with s e r i c i t e accounting f o r almost l / 2 t h i s f i g u r e . The feldspar i s present i n about the -same proportion as i n the f r e s h rock, but i t has become h e a v i l y s t i p p l e d with c a l c i t e , s e r i c i t e and c h l o r i t e . Horn-blende i s e n t i r e l y absent,.while b i o t i t e , now reduced to about 5 per cent of the rock, appears only as bleached fragments surrounded by a mass of s e r i c i t e , c a l c i t e , magnetite and c h l o r i t e . A number of the s l i d e s showed an opaque mineral which was white i n r e f l e c t e d l i g h t . The author h e s i t a t e s to determine a l l these aggregates as leueoxene since concentra-tions of titanium on such a scale would undoubtedly be determined by chemical means. ' Microchemical t e s t s , however, made on s e v e r a l specimens showed no titanium present. With these r e s u l t s i n mind., i t i s probable that a great deal of the m a t e r i a l resembling leueoxene i s a c t u a l l y k a o l i n r e s u l t i n g from the weathering of the f e l d s p a r . The w a l l rock has been subjected to two periods or types of a l t e r a t i o n ; f i r s t c h l o r i t i z a t i o n followed by s e r i -c i t i z a t i o n and carbonatization. The ascending s o l u t i o n s , s l i g h t l y a l k a l i n e and containing some carbon dioxide reacted f i r s t w i t h the feromagnesium minerals, converting the amphibole to c h l o r i t e , ?/hich was i n t u r n a l t e r e d to s e r i c i t e . The 10. b i o t i t e , under the a c t i o n of the s o l u t i o n s , was reduced to a fine-grained mass of s e r i c i t e while the fel d s p a r , being attacked along f r a c t u r e s and g r a i n boundaries, was converted to s e r i c i t e and c a l c i t e . The quartz, i n general, remained unaltered although i n places i t too showed development of s e r i c i t e along f r a c t u r e s i n the grains. K a o l i n which i s present i n the a l t e r e d wall, rock, i s regarded as being super-gene (as i s p o s s i b l y leucoxene) and forming through the a c t i o n of downward moving meteoric s o l u t i o n s leaching the already s e r i c i t i z e d rock. During these processes of a l t e r a t i o n , there was some change i n the concentrations of the mineral groups w i t h i n the rock. S i l i c a and magnesia, f o r example, were reduced, but alumina remained f a i r l y constant. Potash was increased to some extent due to the widespread formation of s e r i c i t e , Water, carbon dioxide and some lime were also added. / STRUCTURE; The s t r u c t u r e of the deposit i s simple. The l o c a t i o n of the ore has been c o n t r o l l e d e x c l u s i v e l y by a major shear zone trending U85°E and dipping south at 50 degrees. A l l the ore mined has been taken from t h i s one zone. A second, l e s s important shear s t r i k i n g U20°E and dipping south-east at 65 degrees i s cut by the main a d i t 120 fee t from the p o r t a l and i s exposed i n the caved d r i f t 190 f e e t from the entrance of the mine. As may be seen from the accompanying map, t h i s 11. minor shear i s s t r i k i n g so that i t w i l l i n t e r s e c t the main shear i n the west d r i f t . Such an i n t e r s e c t i o n could be responsible f o r the large, amount of gouge present i n t h i s d r i f t . I t w i l l also be noted that large q u a n t i t i e s of ore have been removed from the stope above the west d r i f t . As f a r as the author has been able to determine, t h i s extensive mining i s not due to an increase i n the grade of the ore i n t h i s part of the mine but rather to the f a c t that the large q u a n t i t i e s of compact gouge make the removal of rock i n stoping a r e l a t i v e l y easy operation. ORE DEPOSITS: The property c o n s i s t s of the Jumbo group of f i v e claims s t r a d d l i n g Wardie Greek. The development work has, however, been confined to two veins outcropping on No. 2 claim above the south bank of the creek about 3000 feet west of i t s j u n c t i o n with S i l v e r Greek. Of the two, the upper or main v e i n has received the majority of the work, having been followed on the surface f o r over 150 feet and underground f o r more than 350 f e e t . I t s t r i k e s p a r a l l e l w i t h the main shear zone at N85°E and dips south at about 50 degrees. At the surface, the v e i n consists of an i r r e g u l a r band of massive arsenopyrite with smaller amounts of chalcopyrite and quartz, accompanied on the foot-w a l l by about 6 inches of red gouge. The sulphide band i extremely i r r e g u l a r and v a r i e s i n width up to 6 inches; LS i n 12. some places i t disappears completely, only to reappear f u r t h e r along the s t r i k e , again i n l e n t i c u l a r form. A second l e s s important vein, s t r i k i n g p a r a l l e l with the f i r s t hut dipping south at only 20 degrees, outcrops 50 feet below the main vein. I t i s made up l a r g e l y of quartz with some arsenopyrite and very l i t t l e ohalcopyrite. I t reaches a maximum width of only a l i t t l e over 3 inches and e x i s t s as a ve i n f o r l e s s than 100 f e e t along the s t r i k e . A f t e r t h i s distance i t becomes a t h i n shear f i l l e d with grey gouge. Because of the low angle of dip and the absence of a s i m i l a r v e i n i n the lower a d i t i t i s probable that t h i s second vein j o i n s the main vein at some point between the upper and lower crosscuts. The main v e i n has been exposed on two l e v e l s by underground work. The upper, and shorter of the two a d i t s , has been driven 40 feet below the outcrop of the upper vein and i n t e r s e c t s the vein 47 feet from the p o r t a l . The lower tunnel cuts i n t o the h i l l s i d e about 200 fee t below the upper crosscut and i n t e r s e c t s the main v e i n 387 fee t from the entrance. D r i f t s approximately 190 fee t i n length have been run to the north-east and south-west along the s t r i k e of the ve i n and three stopes have been opened up above these d r i f t s . The main ore body as exposed on the lower l e v e l c o n s i s t s of an i r r e g u l a r v e i n of massive suplhides occupying a shear zone, w i t h i n the quartz--diorite, s t r i k i n g s l i g h t l y 13. north of east and dipping to the south at 50 degrees. For the greater part of the exposed distance the zone maintains a constant width of two and one-half f e e t . Occasionally, however, i t pinches or swells. Shearing has been extensive along the zone and as a r e s u l t of the movement a great deal of gouge has been formed; t h i s i s e s p e c i a l l y noticeable i n the west d r i f t and west stope. The vein, composed of arsenopyrite and quartz t o -gether with some smaller amounts of ohalcopyrite and p y r i t e , i s located near the f o o t w a l l of the shear. I t averages four inches wide but contains s e v e r a l lenses exceeding one foot i n width. I t i s not uncommon f o r the ve i n to f i n g e r out i n t o two or three smaller s t r i n g e r s which may or may not unite to reform the v e i n . Frequently, however, a l l but one of the branches die out, the remaining one inc r e a s i n g to the s i z e of the o r i g i n a l v e i n . , A poorly defined dyke a l s o occupies the shear. I t i s confined^ f o r the most par t , to the f o o t w a l l of the vein but i s , i n places, cut by the ore so that i t appears i n the hanging w a l l of the ve i n . The i n t e n s i v e shearing i n the zone has, however, reduced the dyke to a s o f t , grey gouge, thus making i t very d i f f i c u l t to obtain a f r e s h specimen. One or two narrow v e i n l e t s of c a l c i t e , w i t h some arsenopyrite and quartz are commonly found p a r a l l e l i n g the vei n and close to the hanging w a l l of the shear. These s t r i n g e r s r a r e l y exceed one inch i n width and ge n e r a l l y s t r i k e 14. and dip with the sulphide vein. They appear to have been formed at about the same time as the main m i n e r a l i z a t i o n . M i n e r a l i z a t i o n has proceeded i n t o the w a l l rock f o r a short distance. Arsenopyrite and chalcopyrite are found i n f r a c t u r e s i n the a l t e r e d q u a r t z - d i o r i t e on the f o o t w a l l and also to some extent on the hanging w a l l . A l l traces of m e t a l l i c s , however, u s u a l l y disappear w i t h i n four inches of the shear. I t does not appear that replacement played a very large part i n the m i n e r a l i z a t i o n of the w a l l rock f o r the sides of the v e i n l e t s i n the quartz- d i o r i t e n e a r l y always match p e r f e c t l y . MINERALOGY: The mineralogy of the deposit i s not complex. Arsenopyrite i s the most abundant m e t a l l i c mineral. I t i s present both as large i r r e g u l a r masses and as w e l l formed c r y s t a l s , although the l a t t e r are generally r e s t r i c t e d to the smaller veins and s t r i n g e r s . Chalcopyrite i s next i n abund-ance and occurs as anhedfcal masses i n the arsenopyrite and al s o c l o s e l y associated with p y r i t e . The l a t t e r mineral i s present i n amounts almost equal to the .chalcopyrite and i s characterized by good c r y s t a l form. S p h a l e r i t e , a l i g h t v a r i e t y probably low i n i r o n , i s present i n very minor q u a n t i t i e s as dendrites and small i r r e g u l a r masses i n the cha l c o p y r i t e . The non-metallic gangue minerals, quartz and c a l e i t e , 15. PLATE I I . Chalcopyrite r e p l a c i n g S p h a l e r i t e . Specimen from West Stope. Mag. 600X. t 16 PLATE I I I . Ohalcopyrite r e p l a c i n g S h a l e r i t e . Specimen from East Stope. Mag. 650X. PLATF. .17. Chalcopyrite r e p l a c i n g S p h a l e r i t e . Specimen from East Stope. l a g . 650Z. 18. are not p a r t i c u l a r l y abundant. Quartz i s present i n the main vein as a minor constituent but i n the smaller subsid-i a r y v e i n i t i s one of the predominating minerals. C a l c i t e , though present i n the main vein, i s of small account. I t i s , however.,: abundant i n the c a l c i t e s t r i n g e r s mentioned e a r l i e r . PARAGEfflESIS: Examination i n pol i s h e d s e c t i o n shows the f o l l o w i n g general r e l a t i o n s h i p s : Quartz was the f i r s t mineral to form and was probably long-continued i n i t s c r y s t a l l i z a t i o n , over-lapping some of the sulphides. P y r i t e was the next mineral to form, followed successively by arsenopyrite, c a l c i t e , s p h a l e r i t e and ohai'copyrite. The f a c t that quartz i s the f i r s t mineral to c r y s t a l -l i z e i s shown i n one or two of the specimens where arseno-p y r i t e d e f i n i t e l y veins the quartz. The long-continued deposition i s suggested by the apparent v e i n i n g of masses of arsenopyrite by quartz. I t i s , however, probable that the greatest period of quartz d e p o s i t i o n was post-arsenopyrite because examples of t h i s mineral invaded by quartz are much more common than examples of the reverse. The a r s e n o p y r i t e - p y r i t e r e l a t i o n s are d i f f i c u l t to determine since t h e i r ages of formation are close; i n part , they are contemporaneous. In general the p y r i t e i s e a r l i e r than the arsenopyrite as shown by the f a c t that some of the f r a c t u r e s passing through the p y r i t e terminate abruptly on 19. reaching the arsenopyrite. Che suggestion of contemporaneity i s derived from the presence of several "mutual boundaries" i n which the pyrite-arsenopyrite contact i s i l l - d e f i n e d . The c a l c i t e i s assigned the next place i n the para-genetic scheme, mainly on the basis of i t s c u t t i n g r e l a t i o n s CHftLtoPYe I T S , • with respect to the l a t e r mteesais. I t i s found around the edges of the arsenopyrite and p y r i t e and i s d e f i n i t e l y replaced by ohalcopyrite. This replacement i s frequently so extensive that the mineral takes on the appearance of a ground-mass of c a l c i t e dotted with ohalcopyrite. The s p h a l e r i t e - o h a l c o p y r i t e a s s o c i a t i o n s are p a r t i c u -l a r l y i n t e r e s t i n g . The ^sphalerite appears i n the ohalcopyrite groundmass as minute dendrites or star-shaped p a r t i c l e s -(Plate I I , I I I , IT.) without any apparent o r i e n t a t i o n c o n t r o l -l e d by the c r y s t a l structure of the groundmass. They can hardly be r e l a t e d to unmixing because of the abundant evidence f o r replacement shown by nearly a l l the examples* t h e i r boundaries are seldom smooth and where two or more grains j o i n there i s enlargement, which i s i n d i s t i n c t contrast t o the features observed i n most unmixing s t r u c t u r e s . I t appears, rat h e r , that the ohalcopyrite has replaced the s p h a l e r i t e i n very much the same manner as described by F a i r b a n k s 1 who mentions " r e s i d u a l v e i n l e t s " of s p h a l e r i t e i n ohalcopyrite. These specimens, taken from Harcuvar Mountain i n Arizona, are apparently s i m i l a r to those from the Aufeas Mine except that 1. Fairbanks, E. Laboratory I n v e s t i g a t i o n of Ores. p. 210. 20. i n the ore from Arizona the s p h a l e r i t e was commonly bordered "by f r i n g e s of e h a l c o c i t e , a feature which i s absent i n the l o c a l m a t e r i a l . The only gold recognized i n the sections was seen under the high power of 480 magnifications, as small p a r t i c l e s , about one-eighth the s i z e of r i c e grains, i n massive arsenopyrite. Unfortunately they were etched before being photographed and could not be located subsequent to r e p o l i s h i n g . An i n t e n s i v e search of the other sections f a i l e d to r e v e a l f u r t h e r examples of the metal. Gold does not, i n these sections, appear to be a l a t e mineral. From i t s - f o r m i t i s e v i d e n t l y i n t i m a t e l y associated with the arsenopyrite and may occur i n part at l e a s t i n a c o l l o i d a l state with the sulphide. GENESIS: The ore body at the mine represents a mesothermal type of deposit and i s g e n e t i c a l l y r e l a t e d to the i n t r u s i o n s of l a t e J u r a s s i c or e a r l y Cretaceous age. At the time of the formation of the ore, the present land surface was probably deeply buried and l o c a l l y o v e r l a i n by Cretaceous conglomerates. The m i n e r a l i z i n g s o l u t i o n ascended through the p l u t o n i c s and spread out along shears and j o i n t s i n the o v e r l y i n g sediments which were l a t e r u p l i f t e d and removed by erosion. A second period of u p l i f t i n the Miocene followed by g l a c i a t i o n and continued erosion reduced the land to i t s 21. present l e v e l . From t h i s hypotheses i t may be^concluded that the present vein i s only the lower part of a once more-extensive lode, reaching i n t o the overl y i n g sediments and represents merely part of the channelway along which the m e t a l l i f e r o u s s o l u t i o n s ascended. AGE OF THE QUARTZ DIORITE: The problem of the age of the quartz d i o r i t e from the Aufeas mine i s complicated by the f a c t that contacts between the i n t r u s i v e and both the older and younger rocks, are poorly exposed. I t i s , however, d e f i n i t e l y established that the i n t r u s i o n cuts the palaeozoic Cache Creek s e r i e s . West of Hope the i n t r u s i v e i s i n contact with sediments of Cretaceous age which appear to be younger than the quartz d i o r i t e . Pebbles of the l a t t e r , or at l e a s t of a rock of s i m i l a r composition, are found i n the conglomerates which o v e r l i e the i n t r u s i v e with some si&gh-t unconformity. The evidence f o r such a break i s noted by Cairnes who studied the contact i n t h i n - s e c t i o n and found that " the g n e i s s i c banding i n the quartz d i o r i t e ran at an angle to, and was truncated by the l i n e of c o n t a c t . " 2 (between the two forma-t i o n s . ) On the basis of these c r i t e r i a the quartz d i o r i t e may be assigned the age of upper J u r a s s i c or even lower Cretaceous. 2. Cairnes, C.E. G.S.C. Mem. 139. p.87. 22. In d i f f e r e n t i a t i n g between the older and younger i n t r u s i v e s , i t has been found convenient to use the amount of shearing as a y a r d s t i c k . The e a r l i e r i n t r u s i v e s having taken part i n the orogeny of the Laramide are u s u a l l y sheared to a considerable degree, whereas those of Miocene or l a t e r foV*iS> - . age having escaped the e a r l y T e r t i a r y movements^present a r e l a t i v e l y unsheared appearance. I t should be remembered, however, that t h i s comparison can be made only between rocks outcropping i n the same l o c a l i t y , since the degree of shearing may w e l l have v a r i e d considerably from one part of the area t< another. : ORIGIN OF SOLUTIONS; • I t i s notable that a l l the i n t r u s i v e s i n the area were i n j e c t e d w i t h i n the r e l a t i v e l y short period between the upper J u r a s s i c and the mid-Tertiary. I t i s not then hard, to v i s u a l i z e f o r these rocks a common source which, once being established, obviates the necessity of r e l a t i n g the ore so l u t i o n s to any p a r t i c u l a r phase of the i n t r u s i o n . I t may be suggested, then, that the m i n e r a l i z i n g f l u i d s had t h e i r ultimate o r i g i n i n the abyssal depths from whence sprung the igneous rocks of the region, and that t h e i r ascent and deposition depended e n t i r e l y on the fortunate existence of su i t a b l e channels and horizons. 23. OTHER DEPOSITS: . In r e f e r r i n g to the sketch map of the Goquihalla and Skagit Areas (Plate V), i t w i l l be noted that there i s a succession of ore deposits towards the east away from the Eraser River and the main i n t r u s i o n of the Coast Range batho-l i t h . The deposits f a l l i n t o three main groups passing from west to east -( i ) Those i n which the dominant values are gold. ( i i ) Those i n which the values are s i l v e r w i t h small amounts of gold. ( i i i ) Those i n which the dominant values are z i n c . In examining these properties there are, however, revealed somei'striking; s i m i l a r i t i e s . For example, f u l l y 80 r per cent of the occ„urAen_ae;S~. contain arsenopyrite i n close a s s o c i a t i o n with gold values ranging from 1.8 to .05 ounces per ton, while over 70 per cent of the deposits have pyrrho-t i t e as an important accessory mineral. Most of the deposits contain small amounts of s i l v e r and, with the exception of the Eureka - V i c t o r i a mine which i s r e l a t e d to a. T e r t i a r y i n t r u s i v e , the s i l v e r values r i s e toward the east reaching a maximum of ; over 30 ounces per ton i n the eastern part of the Skagit Area. The zinc content of the ores also increases as the distance from the Eraser River, a t t a i n i n g a peak of 23 per cent i n some deposits on the lower Skagit River. In the author Ts opinion, these c h a r a c t e r i s t i c s • L t 6 t N D , P l a t e V. Sketch Map of Goquihalla & Skagit Areas. i n d i c a t e some sort of zonal d i s t r i b u t i o n of the ore deposits with respect to the eastern edge of the Coast Eange, hut the degree' to which such an arrangement can he applied to the discovery of new deposits i s not apparent. Further study i n the areas, with s p e c i a l a t t e n t i o n to the age r e l a t i o n s "between the various i n t r u s i v e s would, perhaps, b r i n g about a better understanding of the r e l a t i o n of these deposits to the Ju r a s s i c i n t r u s i o n . ACiQJOWLEDGMEHT; The w r i t e r wishes to- thank Dr. H.C. Gunning of the Department of Geology, under whose d i r e c t i o n t h i s work was c a r r i e d on, f o r h i s suggestions and very h e l p f u l c r i t i c i s m of the p a r t i a l l y prepared manuscript. The author i s also indebted to Mr. W.H. Matthews and Mr. Fraser Shepherd f o r t h e i r assistance during the two b r i e f t r i p s made to the mine. The U n i v e r s i t y of B r i t i s h Columbia Vancouver, B.G. A p r i l , 1942. 26. BIBLIOGRAPHY Bastin, G.S. Bowen, N.L. Brewer, W. Gairnes, C.E. Cairnes, C.E. Gamsell, Chas. Camsell, Chas. Griekmayy G.H. Dawson, G.M. Fairbanks, E.E. Fenneman, E.M. Sargent, H. Smith, G.O. " C r i t e r i a f o r age r e l a t i o n s of Minerals". A. Geo. Vol . 26, 1931. pp. 561. . "A Geological Reconnaissance of the Fraser River from Lyttoh t o Vancouver, B.C." G.S.C. Summ. Rpt. 1912, part A, p.108. B.C. M i n i s t e r of Mines, Annual Report. 1915, p. K.255. "A Reconnaissance of S i l v e r Greek, Skagit"and Similkameen Rivers, Yale D i s t r i c t , B.C.1' G.S.C. Summ. Rpt. 1923, part A, p. 81. ' "The Coquihalla Area, B r i t i s h Columbia". G.S.C. Mem. 139. 1924. "The Geology of the Skagit V a l l e y , Yale D i s t r i c t " . G.S.C. Summ. Rpt. 1911. part A, p. 115. "The Fraser Canyon and V i c i n i t y . " G.S;G. Summ. Rpt. 1911. part A. p.111. , " S t r u c t u r a l Relations between the Coast Range of B.C. and the Cascade Range of Washington." Geo. Mag. Vol. 67, 1930. p. 483. G.S.C. Annual Report, 1894. V o l . 7, part B. "Lab or at ory I n v e s t i g a t i o n of Ores. 1 1 McGraw-Hill Book Co. 1928. "Physiography of the Western States." McGraw-Hill Book Co. 1931. B.C. M i n i s t e r of Mines, Annual Report, 1938, part F. "A General Reconnaissance Across the Cascade Range near the Forty-ninth P a r a l l e l of Latitude." .U.S.G.S. B u l l 235. 1904. L E G E N D . I 1 QTZ D I O R I T E C Z I VE IN . I 1 SHEAR Z O N E . (4) P L A N OF M A I N L E V E L . A U F E A S MINE. S I L V E R C R E E K , B . C . S C A L E , I I N = 3 0 FT. J A W A L L A C E . O C T . 1 6 , 1 9 4 1 J S r n . G . L E G E N D . ] Q T Z . D IOR ITE V S U R F A C E P L A N . A U F E A S M I N E . S I L V E R C R E E K B . C . S C A L E , 1 I N . - 3 0 FT. J A W A L L A C E . O C T 1 8 , 1 9 4 1 

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