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The economic geology of the Polaris-Taku mine, Tulsequah, B.C. 1942

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2!HE EGOMOMIG GEOLOGY OF THE POLARIS ̂TAEU MIHE,:TULSEQUAH, B.G. •by W i l l i a m R u s s e l l Bacon - 0 - A Thesis submitted i n P a r t i a l F u l f i l l m e n t of the Requirements f o r the Degree of MASTER OF APPLIED SO M C E i n the Department of GEOLO&Y - 0 - 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 CONTESTS Page INTRODUCTION. 1 ACKNOWLEDGMENTS 1 HISTORY. .. . . . . ., 2 PHYSICAL FEATURES . 3 GENERAL GEOLOGY . 5 STRUCTURE 6 ECONOMIC GEOLOGY. . . 9 General Statement 9 Mater i a l s of the Al t e r e d Zones 10 Descr i p t i o n of the Ore Zones 22 CONCLUSION. 27 BIBLIOGRAPHY. 28 THE. SCO!;OLIO GEOLOGY .Off THE, POLARIS-TAKU MIKE,TULSEQUAH,B.O. • ' • INTRODUCTION The Polaris-Taku Mine i s a gold property s i t u a t e d i n the f a r northwestern corner of B r i t i s h Columbia* In a s t r a i g h t l i n e i t i s approximately t h i r t y - e i g h t miles north- east of Juneau, Alaska and s i x miles northwest of Tulsequah, B. C. The I n t e r n a t i o n a l Boundary separating B r i t i s h Columbia from Alaska i s f i v e miles to the west. The mine camp and townsite l i e at an e l e v a t i o n of seventy-five feet above sea- l e v e l i n the v a l l e y of the Tulsequah River, s i x miles north of i t s confluence with the Taku Ri v e r . The mine workings, c o n s i s t i n g of eight l e v e l s , are opened from four a d i t s at elevations between 135 feet and 575 feet on the steep, east slope of the northwesterly trending mountain range forming the west side of Tulsequah v a l l e y . AOCTOWLEDGMEHTS . .. , The w r i t e r i s g r e a t l y indebted to Dr. Alex Smith, mine geologist at Polaris-Taku, f o r making a v a i l a b l e two representative s u i t e s of a l t e r e d m a t e r i a l . S p e c i a l thanks are due Dr. H. 0. Gunning of the U n i v e r s i t y of B r i t i s h Columbia f o r advice and guidance given throughout the work. HISTORY The f i r s t important i n t e r e s t i n the Taku River d i s t r i c t r e s u l t e d from the discovery of two promising z i n c , copper, lead, gold, s i l v e r prospects from 1923 to 1925. One of these, the B i g B u l l , located about two miles from Tulsequah, was extensively prospected and developed by the Alaska Juneau Gold Mining Company, while the other, the Tulsequah Chief, located along the east bank of the Tulsequah River,' approximately nine miles above i t s confluence with the Taku River, was f i r s t prospected by the Alaska Juneau Gold Mining .Company, and l a t e r extensively developed by the United Eastern Mining Company. Both these operations ceased i n 1929. In 1929, three men, f r e i g h t i n g up the Tulsequah River to the United Eastern Mine, discovered the Whitewater property, now known as the Polaris-Taku. In 1931, the I . A. Timmins Corporation examined the' showings and secured an option on the claims. From subsequent d r i l l i n g and trenching they reached the conclusion that the veins were extremely e r r a t i c , l e n t i c u l a r , and r e s t r i c t e d replacements. Consequently, the option was dropped i n the f a l l of 1932. Immediately upon Timmins dropping t h e i r option the property was taken over by the Alaska Juneau Gold Mining Company. In the f a l l of 1934 they r e l i n q u i s h e d t h e i r option f o r the twofold reason t h a t : 1. Vein structures seemed too complicated and 2„ Tests i n d i c a t e d a complex m e t a l l u r g i c a l problem and poor gold recovery<> ' Late i n 1934 an option on the property was obtained by Edward 0. Oongdon and associates, of Duluth, Minnesota. Work was started i n May, 1935 and, by February, 1937, s u f f i c i e n t ore had been developed to warrant construction of a 150 ton m i l l . Production o f f i c i a l l y s t a r t e d November 1st., 1937 and was increased i n the summer of 1940 to 225 tons d a i l y . In A p r i l , 1942, because of increased t r a n s p o r t a t i o n d i f f i c u l t i e s , labour shortage, and i n a b i l i t y to obtain necessary equipment, the Company decided to discontinue operation f o r the duration of the war. PHYSICAL FEATURES The Taku River area, l y i n g on the steep, rugged, Coast Range mountains, i s one of extreme r e l i e f , with elevations ranging from s e a - l e v e l to 8500 f e e t . Extensive g l a c i a t i o n has been the dominant f a c t o r i n the development of the physiographic features. The Taku and Tulsequah Ri v e r s , which d i s s e c t the area, provide i t s most s t r i k i n g features with t h e i r broad v a l l e y s bounded by steep, sheer mountains. Numerous t r i b u t a r y streams emanate from U-shaped and sometimes hanging v a l l e y s , many of which are f i l l e d with g l a c i e r s . The majority of the g l a c i e r s are f i n g e r s branching from the extensive Muir Ice Cap l y i n g to the northwest of the Taku River, but some are of alpine type, occurring as _  4  - i n d i v i d u a l u n i t s . Heavy overburden, c o n s i s t i n g of g l a c i a l boulders and clay,,covers the surface of the claims to a depth of from two to f i f t e e n f e e t . .GENERAL GEOLOGY The oldest rocks on the west side of Tulsequah V a l l e y are of Paleozoic age. They d i f f e r g r e a t l y i n character and include c r y s t a l l i n e limestone, q u a r t z i t e s , s c h i s t s , s l a t e s , a r g i l l i t e s , and some v o l c a n i c s . The c r y s t a l l i n e limestone, u s u a l l y l i g h t grey i n colour, occurs almost e n t i r e l y i n one group at the top of the s e r i e s . These Paleozoic sediments are the most abundant rocks i n the area and, as yet, have not been found favourable f o r m i n e r a l - i z a t i o n . Unconformably o v e r l y i n g the Paleozoic rocks i s a ser i e s of metamorphosed vol c a n i c s and associated rocks, c o n s i s t i n g mainly of p y r o c l a s t i c s which were probably o r i g i n a l l y of a n d e s i t i c composition. Included as p y r o c l a s t i c s are coarse fragmentals and i n t i m a t e l y associated, f i n e - grained, w e l l banded t u f f s • Soft p h y l l i t e , i n t r u s i v e serpentine bodies, and minor interbeds of limestone a l s o occur. Of Mesozoic age, probably T r i a s s i c , t h i s s e r i e s i s the host rock f o r the Polaris-Taku ore-bodies. The main g e o l o g i c a l feature of the area, as i n the S t i k i n e and other better known areas to the south, i s the Coast Range b a t h o l i t h which, here as elsewhere, occupies the core of the Coast Range. The most common rock types vary from granite to g r a n o d i o r i t e . D i o r i t e , gabbro, syenite, and rocks, of intermediate composition occur l o c a l l y i n r e l a t i v e l y small amounts. The eastern contact of the b a t h o l i t h s t r i k e s i n a north-westerly d i r e c t i o n across the Taku River and appears to f o l l o w t h i s course about f i v e miles to the west of the mine. STRUCTURE The structure of the rocks i s complex as i s f a i r l y w e l l shown by t h e i r d i s t r i b u t i o n as indi c a t e d i n F i g . l . In the main the west side of Tulsequah V a l l e y conforms to the same side of a synclinorium which has a general plunge to the south. The v o l c a n i c s present, though f a i r l y extensive, are more or l e s s i n the form of a s h e l l on the v a l l e y w a l l . Owing to the innumerable small 'and complex f o l d s the s h e l l shows a wide range i n thickness; i n s ynclines i t may be c a r r i e d to a considerable depth, whereas over the c r e s t s of a n t i c l i n e s i t may be e n t i r e l y absent, as i s the case at the base of Whitewater Mountain on the east si d e , not f a r south of Whitewater Creek. Wilms Creek (See F i g . 1) has cut completely through the s h e l l ; i t i s not believed that there i s any connecting band between the v o l c a n i c s on e i t h e r side of t h i s creek. There i s thus indic a t e d a maximum possible thickness f o r the Mesozoic v o l c a n i c s of about twenty-seven thousand f e e t . Over most of the area i t i s probably much l e s s than t h i s .  Because of the i n t e n s i t y of the f o l d i n g , the volca n i c s are sheared i n many places along minor s t r u c t u r e s . Owing to the complexity of the structure and the v a r i a b i l i t y of the rocks, the shearing i s very i r r e g u l a r . A wide, w e l l - sheared zone may s p l i t i n t o many t h i n zones or may vary i n almost any way. In the main, the zones are narrow, i r r e g u l a r , and discontinuous. The beds i n the v i c i n i t y of the mine s t r i k e from east-west to north f o r t y - f i v e degrees west and dip from ninety degrees to s i x t y degrees to the south. In these rocks a complex system of fr a c t u r e zones occurs. Roughly these zones can be divided i n t o two groups: 1. Those occurring along contacts between p y r o c l a s t i c s and l e s s competent p h y l l i t e and serpentine. 2. Those c u t t i n g the p y r o c l a s t i c s t r a n s v e r s e l y , i . e . i n a north-south d i r e c t i o n . These zones are of s i m i l a r age and contain s i m i l a r minerals. In the mine' a s e r i e s of reverse f a u l t s occur which s t r i k e generally about north ten degrees west, and dip s i x t y to t h i r t y - f i v e degrees east. F a u l t i n g i s both pre- and post-mineral and may in d i c a t e a continuous period of adjustments which began before m i n e r a l i z a t i o n and continued a f t e r m i n e r a l i z a t i o n had ceased. ECONOMIC GEOLOGY General Statement « _The Polaris-Taku ore bodies are probably, best described as metasomatic replacement zones. This term i s applied to properly emphasize the r o l e played by metasomatism i n the formation of these deposits. In many cases the f i s s u r e s were not opened to any noteworthy extent, but only so much as to admit the passage of the mineral-bearing f l u i d . The l a t t e r attacked the rock on e i t h e r side of the f i s s u r e s , depositing ores i n the place of the simultaneously dissolved rock-constituents. The t y p i c a l metasomatic replacement zone c o n s i s t s of a network of quartz-carbonate v e i n s , s t r i n g e r s , and v e i n l e t s with intervening p a r t i a l or complete a l t e r a t i o n of the rock formation. The main sulphides are arsenopyrite, p y r i t e , and, with l o c a l l y important exceptions, minor amounts of s t i b n i t e . The arsenopyrite and p y r i t e occur so f i n e l y disseminated that i t i s often very d i f f i c u l t underground to d i s t i n g u i s h between good ore and country rock. A l l of the deposits are marked by an a l t e r a t i o n of the green v o l c a n i c s to dark grey, l i g h t grey, and, where the a l t e r a t i o n has been most intense, to cream-coloured m a t e r i a l , These a l t e r e d zones may grade into the normal v o l c a n i c s or may end abruptly against them. The zones are i r r e g u l a r i n shape and t h e i r s i z e does not u s u a l l y give any i n d i c a t i o n as to whether an economically important - 10 - concentration of sulphides may he present. Often a large a l t e r e d zone may contain p y r i t e as the only sulphide. A good example of t h i s occurs on 6 D r i f t - G Level where the greyish zone extends over a width of one hundred feet yet, •pyrite, with very small amounts of gold, i s the only m i n e r a l i z a t i o n . Many zones, however, carry s u f f i c i e n t concentrations of sulphides and associated gold to make mining quite p r o f i t a b l e . M a t e r i a l s of the A l t e r e d Zones With a view towards determining more exactly the nature of the m a t e r i a l s comprising the metasomatic replacement zones, a number of t h i n sections and correspond- ing hand specimens were studied i n d e t a i l . The r e s u l t s of t h i s study, as w e l l as some methods used i n obtaining these r e s u l t s , w i l l now be discussed. Specimens PI - PI5 Suite taken from foot w a l l to hanging w a l l (6" i n t e r v a l s ) across 224 D r i f t zone - 300 L e v e l . I t i s a north-south zone. Megasoopically Specimen P i i s a s o f t , d i r t y green, f i n e grained c h l o r i t i c rock showing considerable f o l i a t i o n . There occurs throughout the rock a general alignment of l e n t i c u l a r patches of darker green m a t e r i a l . Late o a l c i t e s t r i n g e r s traverse the rock i n a winding manner. Under the microscope t h i s rock i s seen to be h i g h l y carbonatized. In f a c t , at l e a s t seventy-five per cent of the t h i n s e c t i o n c o n s i s t s of very f i n e anhedral grains of - 11 - carbonate. The remaining twenty-five per cent i s mainly c h l o r i t i c m a t e r i a l . In order to determine the carbonate, a small sample of t h i s rock was taken and ground very f i n e . The rock f l o u r was given a c o l d , d i l u t e hydrochloric a c i d leach f o r only one minute. A short, weak leach was insurance against decomposing any c h l o r i t e . On f i l t e r i n g and t e s t i n g the f i l t r a t e , l arge amounts of calcium and magnesium and a s l i g h t amount of i r o n were obtained. Thus the carbonate i s a f e r r i f e r o u s dolomite. The c h l o r i t i c m a t e r i a l occurs as l e n t i c u l a r masses of f i n e , slender shreds. I t s mode of o r i g i n i s a question.' The constituents necessary f o r i t s formation may haVe been derived from the o r i g i n a l rock which, i t i s believed, was a r i d e s i t i c i n composition. Dynamic metamorphism could have a l t e r e d t h i s andesite to a c h l o r i t e s c h i s t . G e r t a i n l y the p a r a l l e l arrangement of l e n t i c u l a r patches of c h l o r i t e suggests t h i s o r i g i n . I t i s also p o s s i b l e , however, that some of i t I s of hydrothermal o r i g i n . ? Under the microscope two d i s t i n c t types of c h l o r i t e can be seen. They are very i n t i m a t e l y associated. In attempting to-name these c h l o r i t e s the w r i t e r encountered two d i f f i c u l t i e s . The f i r s t was how to i s o l a t e the two types i n order to do q u a l i t a t i v e chemical analyses of them. The second was, a f t e r e s t a b l i s h i n g c e r t a i n c r i t e r i a d i s t i n g u i s h i n g each type, what to c a l l them. There i s a - 12 - decided l a c k of unanimity among recognized petrographers p e r t a i n i n g to the naming of the c h l o r i t e minerals and also to the number of d i f f e r e n t minerals included i n the c h l o r i t e group. The w r i t e r found that i n grinding the rock s u f f i c i e n t l y f i n e to unlock the two c h l o r i t e s , i t became almost impossible under the microscope to separate enough of each to run worth while q u a l i t a t i v e analyses. A t e s t run on the combined minerals showed s u b s t a n t i a l l y more magnesium and aluminum than. i r o n . F i n a l l y , use was made of three o p t i c a l properties to c l a s s i f y these c h l o r i t e s . Interference O r i e n t a t i o n of Index of Name Colour Cleavage Traces R e f r a c t i o n F i r s t - o r d e r white Length Slow 1.55 A n t i g o r i t e F i r s t - o r d e r grey Length Fast 1.59- Clinochlore (?) The i n d i c e s of r e f r a c t i o n were obtained by removing the cover glass from the t h i n slice» removing a l l the balsam with xylene, and applying d i r e c t l y to the s l i c e o i l s whose ind i c e s of r e f r a c t i o n were known. The various o i l s were l i k e w i s e thoroughly removed by applying xylene to the s l i c e with a p a i n t brush. In Specimen PI there also are very small amounts of chromite and a few grains of p y r i t e and magnetite. The chromite occurs both as anhedral grains and as minute octahedra. I • fl - 13 - This whole s l i d e i s dusted with a white, opaque, amorphous-looking substance which may be leuooxene. The common associates of t h i s a l t e r a t i o n product, ilmenite and j sphene, however, are not i n evidence* I j Specimens PS and P3 are very s i m i l a r m i c r o s c o p i c a l l y I to P I . A l a t e quartz-carbonate s t r i n g e r i s present i n the j t h i n s e c t i o n P3. The hand Specimen P3 has a l i g h t e r green i appearance caused p a r t l y by bleaching of the c h l o r i t i c m a t e r i a l . I t i s the c h l o r i t e i n these rocks that i s l a r g e l y responsible f o r t h e i r colour and, by i i s masking e f f e c t , makes a l l the rocks, despite considerable differences i n composition, appear very s i m i l a r megascopically. Specimen P4 represents a decided change i n the m i n e r a l i z a t i o n of the a l t e r e d zone. The o r i g i n a l l y dark green c h l o r i t e has been bleached to a nondescript grey colour. Mica, c o l o u r l e s s i n t h i n s e c t i o n , i s developed as f i n e , wavy shreds. Very often i t surrounds corroded c r y s t a l s of chromite which are r e l a t i v e l y abundant i n t h i s specimen. In many places the mica seems to be rep l a c i n g the chromite. This idea i s substantiated i n the hand specimen where the mica has a br i g h t green colour, suggesting i t i s a chrome- mica which obtained i t s chrome from the chromite. On c l o s e r examination of the t h i n s e c t i o n , however, some complications a r i s e to t h i s simple theory. Some chromite occurs surrounded by carbonate and some mica occurs without any i d e n t i f i a b l e chromite. Thus, what seems to be an obvious r e l a t i o n s h i p - 14 - between the chromite and the mica, cannot be proved d e f i n i t e l y . From Specimen P4. 245 X. Chromite surrounded and invaded by mica. In s p i t e of the bright green colour of the mica i n the hand Specimen, i t w e l l might be asked i f there i s proof that any of the mica i s chromiferous. In order to prove that some of the mica does contain chromium, the w r i t e r ground some very f i n e , screened i t , and superpanned the minus 200 mesh m a t e r i a l to remove the chromite present. The product was examined under the Ultrapak microscope and found to be very pure, iviany borax and phosphorous bead t e s t s were run on t h i s mica but no r e a l l y conclusive r e s u l t s were obtained. Spectrographic t e s t s , however, revealed that a small but d e f i n i t e amount of chromium i s present i n some of the mica. Whether the mica i s chromiferous where i t i s not - 15 - d i r e c t l y associated with the chromite remains a question. I t would he impossible to scrape some mica from the hand Specimejn .̂ and be sure that i t came from a place i n which not even microscopic grains of chromite were present. Therefore i t i s probably wise to consider the mica as a l i g h t green s e r i c i t e where a d e f i n i t e r e l a t i o n s h i p with the chromite i s not v i s i b l e , P y r i t e i n i r r e g u l a r disseminated grains i s r e l a t i v e l y abundant. Specimen P5 i s very s i m i l a r to P4 but contains l e s s green mica. I t i s approximately e i g h t y - f i v e per cent carbonate, ten per cent c h l o r i t e , and f i v e per cent green mica. P6 i s taken w i t h i n s i x inches of the foot w a l l of the ore zone. I t i s approximately ninety per cent carbonate, seven per cent green mica, and three per cent c h l o r i t e . The i n e t a l l i c s , which occupy l e s s than one per cent of the s e c t i o n , are, i n order of t h e i r abundance, p y r i t e , chromite, arsenopyrite, and magnetite. Specimen P7 i s i n the foot w a l l of the ore zone. There are remnants of w a l l rock that have been completely a l t e r e d to green mica, carbonate, and f i n e granular quartz (.05mm.). The green mica and, to a l e s s e r extent, the carbonate are w e l l mineralized with arsenopyrite and p y r i t e . The character of the l a t e r s o l u t i o n s v a r i e d considerably as quartz and dolomite are found v e i n i n g each other as w e l l as e a r l i e r quartz and dolomite, 'The l a t e carbonate was i d e n t i f i e d as dolomite by s p e c i f i c g r a v i t y t e s t s . The l a t e r gangue minerals are much more coarsely c r y s t a l l i n e , (quartz = .6 mm., dolomite = .8 mm.) suggesting deposition i n more or l e s s open spaces. A r e l a t i v e l y small amount of arsenopyrite and p y r i t e are found associated with the l a t e r gangue minerals, mostly along f r a c t u r e s i n the dolomite. Specimen 3?8 i s v e i n m a t e r i a l from the foot w a l l of the ore zone. In the hand Specimen there i s hard, dark grey a l t e r e d rock separated sharply i n most places from the l a t e r , d u l l greyish-white quartz-carbonate m a t e r i a l by a very t h i n l i n e of sulphides. There are also small patches of mineralized w a l l rock i n the l i g h t e r material.The sulphides are i n s u f f i c i e n t concentration along the boundary of the two types of m a t e r i a l to give the aspect i n the hand Specimen of a massive, t i n y s t r i n g e r or cement. Close examination of these sulphides under the microscope, however, reveals that they are i n t i m a t e l y associated with the small amount of mica present. C l e a r l y the a l t e r e d w a l l rock was f i r s t m ineralized with arsenopyrite and p y r i t e , l a t e r quartz-carbonate s o l u t i o n s r e p l a c i n g p r a c t i c a l l y a l l the a l t e r e d w a l l rock except that which was c l o s e l y associated with and protected by the m e t a l l i c s . Following the same l i n e of reasoning, the w r i t e r believes that where the m e t a l l i c s are not v i s i b l y associated with any a l t e r e d w a l l rock, the l a t t e r may have been completely replaced as i t - 17 - quite evidently has been i n sections free of sulphides. From Specimen P8. 162 X. Sulphides associated with mica. Replacement quartz on the l e f t . Vein quartz on the r i g h t . Under the microscope the dark grey m a t e r i a l i s seen to be almost completely s i l i c i f i e d . This replacement quartz i s much f i n e r grained (.02 mm.) than the l i g h t e r m a t e r i a l (.7 mm.) which obviously was deposited i n more open spaces. The l a t t e r i s barren of sulphides. Here, as i n the previous Specimen, quartz and carbonate v e i n eaoli other as w e l l as e a r l i e r quartz and carbonate. Evidently s h a t t e r - ing must have recurred a number of times during m i n e r a l i z a t i o n or alternated with i t to give such a s e r i e s of v e i n l e t s , - 18 - one crossing the other. The large c r y s t a l s of quartz e x h i b i t wavy e x t i n c t i o n and even the l a t e r carbonates are not altogether free from the e f f e c t s of deformation. Specimen P9 i s f a i r l y t y p i c a l of the ore found i n the l e s s s i l i c i f i e d zones. The rock has been completely a l t e r e d to a dark grey aggregate c o n s i s t i n g of e i g h t y - f i v e per cent dolomitie carbonate, ten per cent s e r i c i t e , and very small q u a n t i t i e s of quartz and leucoxene. I t i s mineralized w i t h arsenopyrite and p y r i t e . The m e t a l l i c s , which occupy about two per cent of the s e c t i o n are f i n e l y disseminated throughout the rock. The arsenopyrite i s the more abundant, occurring as f i n e needle-shaped and diamond- shaped c r y s t a l s . The p y r i t e occurs as i r r e g u l a r , rounded grains, as skeleton c r y s t a l s , and as massive i r r e g u l a r patches. In the Polaris-Taku ore the average s i z e of the p y r i t e grains i s .15 mm. to :2 mm. while the s i z e of the arsenopyrite c r y s t a l s v a r i e s from .03 to .07 mm. In same cases the sulphides are i n t i m a t e l y associated with a l i t t l e f i n e granular quartz as w e l l as with the carbonate and s e r i c i t e . A p e c u l i a r feature of P9 i s noticed on examining the t h i n s e c t i o n under crossed n i c o l s . Many d e f i n i t e l y lath-shaped forms occur suggestive of f e l d s p a r . In most cases, whatever was the o r i g i n a l mineral has been more or l e s s completely a l t e r e d to s e r i c i t e . Specimen P10, on the hanging w a l l of the ore zone, i s w e l l m i n e r a l i z e d with arsenopyrite and, to a l e s s e r - 19 - extent, with p y r i t e . The sulphides occupy at l e a s t f i v e per cent of the se c t i o n . The o r i g i n a l m a t e r i a l has been hig h l y carbonatized. S e r i c i t e i s present, sometimes occurring i n forms suggestive of the a l t e r a t i o n of l a r g e r i n d i v i d u a l s of f e l d s p a r . Late c a l c i t e s t r i n g e r s occur i n which there are very few grains of m e t a l l i c s . Specimens P l l , PIS, PI3 are t y p i c a l l y greyish a l t e r e d m a t e r i a l showing s l i g h t m i n e r a l i z a t i o n , mainly p y r i t e . A l l contain over ninety per cent dolomite and emphasize the f a c t that a s l i g h t change i n the amount of carbonatization suffered by the rock r e s u l t s i n a very considerable change i n i t s colour, A s t r i n g e r i n PIS i l l u s t r a t e s the changing character of the l a t e s o l u t i o n s . A t y p i c a l comb structure i s developed with c a l c i t e , quartz, and c a l c i t e having been deposited i n that order. Only a very l i t t l e p y r i t e i s associated- with the l a t e s t r i n g e r s . Specimens P14 - P17 Suite taken from "unaltered rocks" to ore (4" i n t e r v a l s ) across 17 D r i f t - B L e v e l . I t i s a north- south v e r t i c a l zone. Specimen P14 i s f a r l e s s carbonatized than any rock p r e v i o u s l y described. Eighty per cent of the rock i s an intergrowth of a n t i g o r i t e and c l i n o c h l o r e ( ? ) . In two places, c l i n o c h l o r e (?) also occurs v e i n i n g the groundmass. Carbonate occurs a l l along the middle of one of these c l i n o c h l o r e ( ? ) v e i n l e t s . The r e s t of the rock i s made up of - 20 - b i o t i t e which i s more or l e s s a l t e r e d to negative penninite. The l a t t e r was determined mainly on the basis of i t s " u l t r a blue" interference colours. The t h i n s e c t i o n shows sharp contacts between these b i o t i t e - p e n n i n i t e areas and the r e s t of the groundmass, suggesting i n places a b r e c c i a . Again, a few sharply defined, rounded areas of s e r i c i t e give the impression that they might have resulted from the complete a l t e r a t i o n of feldspar phenocrysts. I r r e g u l a r grains (.02 mm.) of quartz and possible f e l d s p a r are scattered throughout the groundmass. A few scattered grains of p y r i t e and magnetite and the ubiquitous leucoxene are also present, A number of l a t e c a l c i t e s t r i n g e r s cut the rock. Specimen P15, only 4inches nearer the ore than P14, is an e n t i r e l y d i f f e r e n t rock. I t i s l i g h t coloured due to i t s high carbonate content (10jo). The c h l o r i t i c m a t e r i a l , patches of which are s t i l l v i s i b l e i n the hand Specimen, i s now a l i g h t grey colour. Wavy shreds of l i g h t green s e r i c i t e occur throughout the Specimen. Small, disseminated grains of p y r i t e are r e l a t i v e l y abundant. P16 and P17 are s i m i l a r specimens from the ore zone. The rock i s much l i k e P15 but i s w e l l mineralized with arsenopyrite and p y r i t e . Fine-grained quartz (.02 mm.) i s associated with these sulphides. I t i s p l a i n l y evident, from the concentration of sulphides around the small quartz- carbonate f i l l e d f i s s u r e s , that these f i s s u r e s , before the - 21 - quartz and carbonate were deposited, served as the channels f o r the e a r l y m i n e r a l i z i n g s o l u t i o n s , and, from these channels, the arsenopyrite, p y r i t e , and fine-grained quartz invaded the a l t e r e d w a l l rock. From Specimen P17. 9 X. Sulphides on e i t h e r side of l a t e quartz-carbonate s t r i n g e r which i s barren except f o r a l i t t l e s t i b n i t e ( i n c i r c l e ) . These l a t e s t r i n g e r s , sometimes e x h i b i t i n g comb st r u c t u r e , are p r a c t i c a l l y barren of sulphide m i n e r a l i z a t i o n . In P17, however, a l i t t l e s t i b n i t e veins the l a t e carbonate. Associated with t h i s s t i b n i t e i s a very small amount of br i g h t red mineral which may be cinnabar. The type of a l t e r a t i o n represented by these two s u i t e s of rock i s quite t y p i c a l of Lindgren's mesothermal - 22 - deposits. He says, " S e r i c i t i z a t i o n , w ith or without carbonates but always with p y r i t e , i s the p r i n c i p a l process of a l t e r a t i o n i n igneous rocks.... .The a l t e r a t i o n of the country rock i s u s u a l l y very intense next to the ore but seldom y i e l d s coarsely c r y s t a l l i n e products as i n some high-temperature deposits. In f e l d s p a t h i c and ferromagnesian rocks the p r i n c i p a l product i s s e r i c i t e , the fine-grained f o l i a t e d form of muscovite; i n many deposits carbonates, such as c a l c i t e , dolomite, and ankeri t e , develop i n large amounts. The dark minerals are f i r s t a l t e r e d , t h e i r i r o n being u s u a l l y recombined as p y r i t e . The feldspars are also rather e a s i l y a l t e r e d ; even quartz grains are attacked and p a r t l y , at l e a s t , converted to an aggregate of s e r i c i t e and carbonates." Warm aqueous so l u t i o n s containing a r s e n i c , lime, potassium, carbon dioxide, and hydrogen sulphide would be quite competent to e f f e c t the changes noted i n these rocks. I t would seem probable that, i n most cases, the added m a t e r i a l has more than balanced l o s s e s . D e s c r i p t i o n of the Ore Zones As w i l l be remembered from the d e s c r i p t i o n of the s t r u c t u r e , there are two types of mineralized f r a c t u r e zones, contact and transverse. The l a r g e s t and most p e r s i s t e n t zone developed i s of the contact type. I t i s known as "A" zone and generally follows the contact between p y r o c l a s t i c s on the foot w a l l - 23 - and p h y l l i t e on the hanging w a l l . In places, however, i t diverges e i t h e r i n t o the p h y l l i t e or in t o the pyroclastics„ The s t r i k e of "A" zone i s north 55 degrees west and the dip i s from 55 degrees south to nearly v e r t i c a l . The zone v a r i e s from two to t h i r t y - f i v e f e e t i n width and averages about ten f e e t . Five ore shoots have been stoped along t h i s zone. The h o r i z o n t a l distance from the 1A orebody to the 5A orebody i s approximately one thousand f e e t . The a c t u a l zone p e r s i s t s past the 5A orebody but has not been found productive. This zone has been extensively worked from the surface (Elev. = 500 feet) down to the 150 l e v e l (Elev. = - 13 f e e t ) . I t has also been cut on the 450 l e v e l (Elev. - - 313 feet) but has not been explored at t h i s depth. The shape of "A" zone i s roughly tabular except i n one place. T h i r t y feet above B l e v e l the p y r o c l a s t i c s on the foot w a l l of the 5A orebody have been extensively replaced, r e s u l t i n g i n a large i r r e g u l a r body of ore extending v e r t i c a l l y to t h i r t y feet above C l e v e l . This one orebody y i e l d e d f i f t y thousand tons of ore. The ore minerals are p r a c t i c a l l y the same throughout the h o r i z o n t a l and v e r t i c a l range of "A" zone. Arsenopyrite i s the most abundant and i s the main gold c a r r i e r . P y r i t e i s next i n abundance but i s not important economically. S t i b n i t e , i n very minor q u a n t i t i e s occurs i n the l a t e quartz-carbonate s t r i n g e r s . Small q u a n t i t i e s of a grey mineral occur as i n c l u s i o n s i n and v e i n i n g the p y r i t e . - 84 - This mineral was only v i s i b l e under o i l immersion and hence could not be determined by etch r e a c t i o n s . Disseminated Arsenopyrite and P y r i t e . 675 X. Mote grey mineral v e i n i n g p y r i t e . (In c i r c l e ) There has been greater movement and more continuous movement along "A" zone than along any of the transverse zones. Consequently the f u l l mineral sequence i s best developed i n "A" zone. In places the l a t e r quartz and carbonate have completely replaced the w a l l rock, g i v i n g the zone somewhat the appearance of an i r r e g u l a r f i s s u r e v e i n . The transverse zones s t r i k e from north 10 degrees west to north 20 degrees east and dip very steeply. Zones of t h i s type are abundant, but are smaller than the contact type. They a l l l i e i n the foot w a l l and - 25 - to the north of "A" zone. The zones occur s o l e l y i n the competent p y r o c l a s t i c s , dying out where they i n t e r s e c t a p h y l l i t e band. However, not i n f r e q u e n t l y , what appears to be a continuation of the zone i s found on the other side of a p h y l l i t e band. Several of the zones have been found to branch from "A" zone but none cross i t and continue beyond on the:hanging w a l l s i d e . The longest transverse zone developed i s approximately f i v e hundred feet long. These zones are u s u a l l y much, narrower than the "A" zone. "Y" zone on the 300 l e v e l , however, reached a width of over twenty f e e t . 18 Zone and 23 Zone are two of the r i c h e r transverse zones which have been mined r i g h t to the over- burden. They vary from s i x f e e t to s i x inches i n width. Within the upper one hundred feet of these zones s t i b n i t e i s by f a r the most abundant ore mineral. In places arsenopyrite and p y r i t e are p r a c t i c a l l y absent. This s t i b n i t e has run from s i x to f i f t e e n times as much i n gold as the average ore from "A" zone. In s p i t e of t h i s no gold was seen i n even the r i c h e s t polished sections of s t i b n i t e from t h i s zone. In s i x sections examined only two small pieces of gold were found and they were i n quartz, not s t i b n i t e . Extremely small q u a n t i t i e s of a grey mineral were seen i n two of the polished s t i b n i t e sections. Upon tes.ting t h i s mineral the f o l l o w i n g c h a r a c t e r i s t i c s were noted. - 26 - Colour - Grey Hardness - C to D Crossed n i o o l s - I s o t r o p i c Etch t e s t s HNOg - Fumes t a r n i s h HC1, KCIT, F e C l 3 , KQH, BgClg - Negative Spectrographic a n a l y s i s of the s t i b n i t e showed medium to weak copper and s i l v e r l i n e s , 'i'he evidence thus suggests that t h i s mineral might be t e t r a h e d r i t e . Arsenopyrite and S t i b n i t e , 1-23 Stope. 165 X. The v e r t i c a l range of t h i s type of ore zone i s not known. However, as a t y p i c a l transverse zone i s smaller i n length and width than "A" zone, i t seems reasonable to expect that i t w i l l be smaller than "A" zone i n the t h i r d dimension, depth. CONCLUSION The Polaris-Taku mine l i e s w i t h i n the eastern contact-belt of the Coast Range b a t h o l i t h . The sol u t i o n s responsible f o r t h i s deposit may have been g e n e t i c a l l y connected e i t h e r with the b a t h o l i t h i c i n t r u s i o n or with some l a t e r , deeper-seated, igneous source* The Paleozoic sediments were apparently unfavourable f o r replacement by the m i n e r a l i z i n g s o l u t i o n s which deposited ores i n the Mesozoic v o l c a n i c s . These s o l u t i o n s showed a considerable range of composition over a period of time. The f o l l o w i n g sequence of events i s suggested f o r the emplacement of the orebodies: 1. Dynamic metamorphism, r e s u l t i n g i n shearing and a l t e r a t i o n of the o r i g i n a l rock to one high i n c h l o r i t e . 2. Penetration along narrow f i s s u r e s of the rock by warm aqueous s o l u t i o n s , r e s u l t i n g i n a l t e r a t i o n of the w a l l rock to an aggregate of c h l o r i t e and dolomite. 3. Further carbonatization; bleaching of the c h l o r i t e ; development of greenish s e r i c i t e (chromiferous i n places) p y r i t e , and some fine-grained quartz. 4. Replacement of the a l t e r e d w a l l rock by abundant arsenopyrite, p y r i t e , and some fine-grained quartz. Most of the gold was introduced with t h i s arsenopyrite. 5. F r a c t u r i n g , a l t e r n a t i n g with v e i n introductions of quartz and carbonate, and a very l i t t l e arsenopyrite and p y r i t e . 6. Continued f r a c t u r i n g ; i n t r o d u c t i o n of s t i b n i t e , o f t e n w i t h important amounts of gold. — 28 — BIBLIOGRAPHY Kerr, 'F. A. Geol. Survey of Canada, Summary Report, 1930, Pp. 17A-55A. Geol. Survey of Canada, Summary Report, 1932, Part A I I . Lindgren, W. Mineral Deposits, P. 532. Rogers, A. F. and Kerr, P. F. Thin-Section Mineralogy, 1933. Sharpstone, D. C. The Development and Geology of the Polaris-Taku Mine, The Miner, Hovember, 1938. Winchell, i<. H. and Winchell, A. N. Elements of O p t i c a l Mineralogy, 1927.

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