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The geology and mineralogy of the Brown McDade mine 1947

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THE GEOLOGY AND MINERALOGY OP THE BROWN MCDADE MINE BY JOHN LAMB A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE IN THE DEPARTMENT OF GEOLOGY AND GEOGRAPHY THE UNIVERSITY OF BRITISH COLUMBIA APRIL 1947 ABSTRACT The Brown MeDade Mine i s a recent g o l d - s i l v e r d i s c o v e r y i n the Yukon T e r r i t o r y , halfway between Whitehorse and Dawson. I t l i e s i n the area u n g l a c i a t e d during the P l e i s t o c e n e P e r i o d . Diamond d r i l l i n g and s t r i p p i n g i n 1946 i n d i c a t e d commercial values across a width of 10 f e e t and over a l e n g t h of 1000 f t . The geologic s t r u c t u r e i s that of a Late T e r t i a r y , d y k e - l i k e body of quartz f e l d s p a r porphyry c u t t i n g quartz d i o r i t e of o J u r a s s i c or l a t e r age. This body has a Northwest s t r i k e and dips s t e e p l y west. The ore zone l i e s i n the porphyry and i s b e l i e v e d g e n e t i c a l l y r e l a t e d to i t . The m i n e r a l i z a t i o n c o n s i s t s of a c h e r t y - l i k e f i n e grained blue q u a r t z , w i t h disseminated sulphides comprising l e s s than 5% of the mass. M e t a l l i c minerals are p y r i t e , arsenopyrite, and s p h a l e r i t e , w i t h " l e s s e r amounts of galena, c h a l c o p y r i t e , t e t r a h e d r i t e , s t i b n i t e , bournonite, jamesonite and gold. The gold i s ass o c i a t e d w i t h the p y r i t e i n f i n e p a r t i c l e s , the m a j o r i t y l e s s • t h a n -150 microns i n s i z e . The g o l d - s i l v e r r a t i o , i s about one to ten. S e r i c i t i z a t i o n and c a r b o n a t i z a t i o n are the c h i e f forms of hydrothermal a l t e r a t i o n , while considerable l i m o n i t e , and around the ore zone, j a r o s i t e , have been produced by weathering. On the- b a s i s of comparisons w i t h known deposits, the Brown McDade i s considered to belong to the deeper epithermal type. I t should continue to reasonable depths although the ore shoots are l i k e l y to be e r r a t i c . The area south of the main ore zone, u n d e r l a i n by s c h i s t o s e rocks w i l l probably be unfavorable f o r the occurrence of ore. ACKNOWLEDGMENTS The w r i t e r worked as r e s i d e n t engineer at the Brown McDade property i n 1946, under the management of Dr. W.V. Smitheringale, to whom he i s indebted f o r many h e l p f u l suggestions, and f o r permission to use the maps and data contained h e r e i n . The l a b o r a t o r y i n v e s t i g a t i o n s and co m p i l a t i o n of- the report were c a r r i e d out under the personal d i r e c t i o n and guidance of Dr. H.C. Gunning of the Department of Geology and Geography, whose advice was g r e a t l y appreciated. Dr. H.V. Warren 'of the same department, though not as s o c i a t e d d i r e c t l y w i t h the work, a s s i s t e d the w r i t e r i n the deter- mination of some of the m e t a l l i c minerals, and i n t a k i n g photographs of p o l i s h e d sections of ore. Dr. K.D. Watson was consulted on s e v e r a l petrographic problems. Of gre^at assistance i n completing the study were the X-ray powder analyses of two minerals by Dr. R.M. Thompson of the U n i v e r s i t y of Toronto, and spectrographic analyses by Mr. L.O. Gouin, a s s i s t a n t i n the department of Geology. Mr. J.A. Donnan, t e c h n i c i a n , supervised the pr e p a r a t i o n of t h i n s e c t i o n s and po l i s h e d s e c t i o n s . TABLE OF CONTENTS PAGE PART 1 INTRODUCTION 1 PART 11 GENERAL INFORMATION 2 1. L o c a t i o n 2 2. Physiography and G l a c i a t i o n • 2 3. Climate and Vegetation 5 PART 111 REGIONAL. GEOLOGY 6 1. Summary 6 2. Formations . 6 PART TV LOCAL GEOLOGY 9 1. I n t r o d u c t i o n 9 2. General D e s c r i p t i o n 10 3. Rock Types - , 10 (a) Quartz D i o r i t e •••• -10 (b) Quartz Feldspar Porphyry 12 (c) .Yukon S c h i s t s 15 4. 'Weathering •. • • 15 5. Hydrothermal A l t e r a t i o n 17 6. St r u c t u r e 18 PART V MINERALOGY 20 1. General C h a r a c t e r i s t i c s of The Ore 20 2. Texture and Composition of Vein M a t e r i a l 21 3. M e t a l l i c Minerals 23 4. Paragenesis 28 5. Conclusions 29 PART VI ORIGIN OF THE ORE DEPOSIT.. 31 1. Source of The Ore So l u t i o n s 31 2. Comparisons With Other Mineral Deposits 32 (a) I n t r o d u c t i o n 32 (b) M i n e r a l o g i c a l Comparisons 32 (c) Age of Deposition ' 34 (d) S t r u c t u r a l Comparisons 34 (e) Wall Rock A l t e r a t i o n v. .. 35 3. Conclusions 35 TABLE OF CONTENTS PAGE PART V l l DEVELOPMENT OF THE MINE ... 37 1. Discovery . .• 37 2. Diamond D r i l l i n g 38 (a) Plan 1 . . . 38 (b) D r i l l i n g Problems . . 38 3. Surface S t r i p p i n g 39 4. Underground Development 40 5. Tr a n s p o r t a t i o n Problems 40 6. Power Problems 41 J LIST OF ILLUSTRATIONS FACING PAGE Figure 1. L o c a t i o n of Mine 2 2 ) 3 5,) Photographs i l l u s t r a t i n g topography 3 4 ) of the regions 4 5' ) 4 ,6 ) Photographs of the Area 5 7 ) 5 8 ))Gamera Lucida drawings of t h i n s e ctions 12 9 ) " 12 ,10 ) Camera Lucida drawings of t h i n sections 14 11 ) ^ 1 4 12 ) Cross s e c t i o n of a diamond d r i l l h o l e . . 18 13 ) B o t r y o i d a l formation i n the ore 21 14 ) 15 Photomicrograph of Vein M a t e r i a l 22 16 ) ' 23 17 ) 23 18 ) Photomicrographs of Ore Minerals 24 19 ) . 24 20 ) 26 21 ) 26 22 ) 27 23 ) . 27 24 Photograph of a b u l l d o z e r trench 39. LIST OF MAPS. 1. Hansen & V i c t o r i a Creek Areas 7 2. B i g Thing Mineral Claim ( i n s i d e back cover) INTRODUCTION' PART 1 . Although the Carrnacks d i s t r i c t , has been known to, prospectors and g e o l o g i s t s since the Klondike gold r u s h , i t d i d not r e c e i v e much a t t e n t i o n u n t i l the past few years. The e a r l y gold-seekers n o t i c e d that there was p l a c e r gold i n parts of the d i s t r i c t but they were i n t e r e s t e d i n the r i c h e r f i e l d s to the north. Between 1910 and 1920 some i n t e n s i v e p l a c e r prospecting was c a r r i e d out i n the area around Nansen and V i c t o r i a creeks, but t h i s proved to be u n p r o f i t a b l e . About 15 years ago the Freegold Mountain lode prospects r e v i v e d i n t e r e s t t e m p o r a r i l y but t h i s d i d not l a s t long. The current a c t i v i t y i n the d i s t r i c t was s t a r t e d i n 1945 w i t h the disco v e r y of gold near V i c t o r i a Creek by George McDade. From the foregoing statements one can see that the area i s v i r t u a l l y v i r g i n ground f o r p r o s p e c t i n g . At present there are no producing lode gold mines i n the Yukon. The s u c c e s s f u l development of the Brown McDade property i n t o a producing mine would therefore be of great value to the whole t e r r i t o r y . I t would st i m u l a t e the search f o r s i m i l a r occurrences i n the b e l t of country extending t o the northwest f o r 40 or 50.miles. The w r i t e r spent f i v e months i n 1946 at the Brown McDade property where a diamond d r i l l i n g program was i n progress. 9 /.ocati'oH of Property. : U»y/ac/a.fec/ Area 2 GENERAL -INFORMATION PART 11 1. L o c a t i o n ; The Brown McDade Mine i s i n the Dawson Mining D i v i s i o n near the southern boundary of the Carmacks Map Area. I t i s at an e l e v a t i o n of 4000 f e e t on Pony Greek, a t r i b u t a r y of V i c t o r i a Creek. Carmacks, on the Lewes R i v e r , l i e s 35 miles to the east. From the town of. Whitehorse, access may be obtained to the property i n three ways. The most d i r e c t route i s by a i r p l a n e 115 miles northwest. Planes land e i t h e r on V i c t o r i a Lake or on an a i r f i e l d , both w i t h i n s i x miles of the camp. The route over which supplies are brought i n , i s by motor road, 150 miles to A i s h i h i k , thence by t r a c t o r t r a i l 40 miles northward. A t h i r d r o u t e , seldom used, i s by r i v e r boat to Carmacks and by pack t r a i l the remaining d i s t a n c e . " 2. . Physiography and G l a c i a t i o n : The Nansen-Victoria Creek area i s s i t u a t e d e n t i r e l y w i t h i n the Yukon Plateau physiographic province, which corresponds i n a general way w i t h the i n t e r i o r Plateau running northwesterly through B r i t i s h Columbia.. The term plateau does not imply that~the land surface i s f l a t . , To the observer the d i s t r i c t presents the appearance of a rounded, g e n t l y r o l l i n g country w i t h a remarkably even s k y l i n e . E s p e c i a l l y i s t h i s t r u e , l o o k i n g from the mine anywhere south of an east-west l i n e . The average e l e v a t i o n of the h i l l s and ridges i s approximately 4200 f e e t . To the north and horth- FIGURE 2 Headwaters of V i c t o r i a Creek - l o o k i n g n o r t h . Mt. V i c t o r i a on s k y l i n e - e l e v a t i o n 6200 f e e t . FIGURE 3 The Dawson Range, l o o k i n g northwest. Headwaters of Nansen Creek. Headwaters of V i c t o r i a Creek. L e f t : - Right:- west the mountains of the Dawson Range r i s i n g to heights of 6400 f e e t , i n t e r r u p t the plateau surface. Smaller ranges or even i n d i v i d u a l mountains standing above the general l e v e l , are n o t i c e a b l e i n other d i r e c t i o n s . I t i s b e l i e v e d by Bostock ( l ) that the physiographic h i s t o r y i s that of a mature g e n t l y r o l l i n g upland s u r f a c e , u p l i f t e d before the close of the Miocene p e r i o d and sub- sequently d i s s e c t e d by v a l l e y s cut w e l l below i t . He does not consider that i t represented a peneplain or even a c o n d i t i o n of old-age because there i s a r e l i e f of over 500 f e e t i n the surface. The present streams have cut down about 1000 f e e t below t h i s , g i v i n g -tin thr, noun hrgg a t o t a l r e l i e f of more than 3000 f e e t . The stream v a l l e y s are broad and except i n the upper reaches of the s m a l l e r t r i b u t a r i e s , have smooth p r o f i l e s . Prom the a i r the impression gained i s that the p r e v a i l i n g drainage p a t t e r n trends northwest-southeast. This i s probably the p a t t e r n that was set up during e a r l y T e r t i a r y times but i t has been'complicated s i n c e , by the u p l i f t and p o s s i b l y by g l a c i a l a c t i o n . Some large streams c u t t i n g across the general trend, seem to i n t e r r u p t the e a r l y pattern." The N i s l i n g and Klaza Rivers are examples of such streams. The'Brown McDade Mine i s j u s t w i t h i n the u n g l a c i a t e d part of the Yukon. On the Carmacks map sheet Bostock (1) i n d i c a t e s the western boundary of the l a s t extensive P l e i s t o c e n e i c e sheet. According to him i t extends i r r e g u l a r l y northward, passing about 20 miles to the east of the mine. Of t h i s FIGURE 4 The v a l l e y of V i c t o r i a Creek, l o c k i n g North. F l a t area i n foreground composed of a l l u v i a l sands f i l l i n g the v a l l e y bottom. FIGURE 5 boundary he says, "The p o s i t i o n of the edge of the g l a c i a t e d area as shown on the accompanying map of the d i s t r i c t could be a c c u r a t e l y determined i n a few p l a c e s , but f o r the most part i t s p o s i t i o n i s l a r g e l y a matter of conjecture. I t approximately marks the boundary of the country' i n which g l a c i a l phenomena due to the l a s t main g l a c i a t i o n are f r e s h and widespread". B o s t o c k - ( l ) b e l i e v e s t h a t c e r t a i n phenomena such ,as a boulder c l a y found i n Nansen Creek,belong to an e a r l i e r g l a c i a t i o n . Although t h i s formation was not seen by the w r i t e r , he doesn't b e l i e v e that i t i s due to a widespread i c e sheet but r a t h e r to a l o c a l g l a c i a t i o n of l i m i t e d extent. The area f o r s e v e r a l miles around the mine'shows no v i s i b l e evidence of any g l a c i a t i o n . There i s an absence of d r i f t , or g l a c i a l e r r a t i c s . Instead, the surface i s covered by a t h i c k mantle of weathered m a t e r i a l c o n t a i n i n g loose angular fragments of r o c k , s i m i l a r i n composition to the u n d e r l y i n g or nearby formations. This mantle, exposed i n b u l l d o z e r c u t s , e x h i b i t s 'the usual c h a r a c t e r i s t i c s of r e s i d u a l weathered m a t e r i a l , being w e l l o x i d i z e d and showing a gradual c o n s o l i d - a t i o n downward-into the bed-rock. Depths of mantle up. to 10 f e e t are common. Supporting t h i s b e l i e f that g l a c i a t i o n was not widespread i n the area i s the l a c k of any g l a c i a l modif- i c a t i o n s of the mature topography of the area. The v a l l e y s of V i c t o r i a and Nansen Creeks and that of the N i s l i n g R i v e r , i n t o which they f l o w , are f i l l e d w i t h f i n e a l l u v i a l sands and minor amounts of g r a v e l . These form,- FIGURE 6 Looking southwest from Brown McDade Mine, Arrow i n d i c a t e s ore zone. Sk y l i n e of Yukon Plateau i n background. FIGURE 7 r ^ Looking southeast across the Yukon Plateau .wide f l a t t e r r a c e s i n the bottoms of the v a l l e y s , through which the present streams have cut to depths of 75 f e e t . The N i s l i n g River has eroded i t s t e r r a c e s so that only remnants are l e f t , b u t i n the t r i b u t a r y creeks they are very w e l l developed and extensive. The o r i g i n of these deposits i s not c l e a r . One suggestion i s that they o r i g i n a t e d during the P l e i s t o c e n e p e r i o d when damming of r i v e r v a l l e y s by i c e tongues, f ormed"'lakes i n which the sediments were deposited. (3) Climate and Vegetation: The. climate i s t y p i c a l of the whole i n t e r i o r p l a t e a u r e g i o n . I t i s c h a r a c t e r i z e d by a medium to low annual p r e c i p i t a t i o n and due to i t s northern l a t i t u d e , a low mean temperature. The lakes and streams freeze (over i n l a t e October or November while the Spring breakup occurs i n May or June. Snowfall i s not heavy, u s u a l l y being not over three f e e t deep at any time. During the Summer there i s a wet p e r i o d i n J u l y and e a r l y August. The c h i e f forms of v e g e t a t i o n are mosses and low brush. These cover almost the whole land surface l i k e a t h i c k carpet The trees are stunted and grow i n groves, u s u a l l y on the w e l l drained southern slopes. Spruce i s the main tree and has been seen up to 40 f e e t i n h e i g h t , w i t h an 18 i n c h b u t t . The average s i z e i s considerably l e s s than t h i s . - Sparse stands of cottonwood trees grow i n the s h e l t e r e d v a l l e y bottoms. REGIONAL GEOLOGY PART 111 (1) Summary The geology i s that of a s e r i e s of f o l d e d , h i g h l y metamorphosed sedimentary and v o l c a n i c r o c k s , the Yukon group, o v e r l a i n by sediments and v o l c a n i c s of Mesozoic age. In t r u d i n g these are numerous bodies of Upper Mesozoic and T e r t i a r y p l u t o n i c and v o l c a n i c rocks w i t h a wide v a r i e t y of compositions. T e r t i a r y v o l c a n i c flows are extensive i n the Carmacks area although not l o c a l l y present i n the v i c i n i t y of the Brown McDade Mine. A l l i e d to these are i n t r u s i v e plugs, dykes and i r r e g u l a r bodies of p o r p h y r i t i c rocks, which are presumed to be of Late T e r t i a r y age. Recent a l l u v i u m f i l l s most of the v a l l e y s and a l a y e r of v o l c a n i c ash covers the present land surface. (2) Formations; TABLE OF FORMATIONS Recent Late T e r t i a r y Miocene or Older Upper J u r a s s i c or L a t e r Upper J u r a s s i c or Lower Cretaceous pal e o z o i c or Pre-Cambrian Carmacks Volcanics Mt.Nansen Group Yukon Group A l l u v i u m , ash, etc. Quartz prophyry, g r a n i t e porphyry, granophyre, r h y o l i t e . B a s a l t , andesite, d a c i t e , b r e c c i a , t u f f s . G r a n i t e , g r a n o d i o r i t e , etc Sye n i t e , monzonite, e t c . D i o r i t e , gabbro, e t c . Andesite, b a s a l t , d a c i t e , b r e c c i a s , t u f f s , and some sediments. quarts-mica s c h i s t , horn- blende s c h i s t , q u a r t z i t e , gneiss and limestone. NANSEM & VICTORIA CREEKS CARMALKS AREA YUKON SCALE 1M = 1 Ml. LEGEND MODERN RECEA/T Cl'/v vium , ask etc * f 47' TERTIARY porphyry , r^J° IGVEOUS ROCKS jra. no diortte.5 et. Mr. NANSEN GP ct ndesite , ba&atl' Irccc/aS MESOLO/C YUKON GP. schists , <yi/<3r/zi/es, ysre/sses /ime&tone. PRE-CAM3. & LATER. ii ii n 11 The foregoing table i s derived from that .given by Bostock ( 1 ) . i t has .been shortened to i n c l u d e only the rocks shown on the accompanying maps. (a) Yukon Group This group c o n s i s t s of c r y s t a l l i n e rocks of sedimentary and v o l c a n i c o r i g i n . The m a j o r i t y are s c h i s t o s e and g n e i s s i c , although i n the V i c t o r i a Greek'area there >is some q u a r t z i t e . The t o t a l t h ickness of the formations i s very great but i s not known. 1 The s t r u c t u r e i s that of a s e r i e s of a n t i c l i n a l and s y n c l i n a l f o l d s w i t h a general trend to the northeast. The aips observed are v a r i a b l e , up to 35 degrees. These rocks are the oldest i n the d i s t r i c t being over- • l a i n unconformably or intruded by a l l other formations. The exact age i s unknown, except that i t i s P r e - T r i a s s i c . Some of the members of the group are l o c a l l y considered to be Pre- Gambrian rocks although 60 miles to the north a few Paleozoic f o s s i l s have been found. (b) Mount Nansen Group These rocks include v a r i e t i e s of'andesites and b a s a l t s which to some extent are p o r p h y r i t i c , b r e c c i a s , t u f f s and a s s o c i a t e d i n t r u s i v e s . The predominant c o l o r i s a dark greenish gray. The rocks are not r e g i o n a l l y metamorphosed l i k e the Yukon group,upon which they l i e unconformably w i t h a low angle of -dip. The age of the group has been determined by Bostock (1) as being not o l d e r than Upper J u r a s s i c . This i s based on r e l a t i o n s between the Mount Nansen group and the f o s s i l i f e r o u s sedimentary formations i n the r e g i o n of Carmacks. (c) Mesozoic I n t r u s i v e s Included i n t h i s group are many rock types, ranging from b a s i c to a c i d i c . In the Victoria-Nansen Creek area, they have the composition of g r a n i t e s , g r a n o d i o r i t e s • and quartz d i o r i t e s , are g r a y i s h white i n c o l o r , and contain f e l d s p a r s , quartz, b i o t i t e , hornblende and minor accessory minerals. The age of these i n t r u s i v e s i s known to be younger than the Mt. Nansen group. Bostock (1) c o r r e l a t e s them w i t h the i n t r u s i v e s of the main Coast Range B a t h o l i t i i , probably of J u r a s s i c or l a t e r age. (d) T e r t i a r y A c i d I n t r u s i v e s < Numerous small bodies and dykes of a c i d i c , i n t r u s i v e , - p o r p h y r i t i c rocks outcrop i n the d i s t r i c t and northwest along the Dawson Range.' They include types ranging from g r a n i t e porphyries to r y h o l i t e s and i n t r u s i v e . b r e c c i a s . L o c a l l y the rocks are cherty l o o k i n g b u f f c o l o r e d r h y o l i t e s w i t h con- spicuous phenocrysts of quartz and f e l d s p a r s . The'"quartz i s hard and g l a s s y but the f e l d s p a r s are a l t e r e d , o f t e n l e a v i n g only casts i n the rock. I t i s b e l i e v e d that these are the . i n t r u s i v e s to which the m i n e r a l i z a t i o n of the Brown McDade ore body i s g e n e t i c a l l y r e l a t e d . R e l a t i o n s between these i n t r u s i v e s and the Carmacks v o l c a n i c s , which are not found i n the immediate map area, are such that they are considered to be of Late T e r t i a r y age. (e) Recent Deposits: Unconsolidated deposits of a l l u v i a l o r i g i n are found i n the v a l l e y bottoms as the products of e r o s i o n of the older rocks. Covering the whole country f o r many miles i s a t h i n l a y e r of v o l c a n i c ash, l y i n g j u s t below the moss. I t has been n o t i c e d by the w r i t e r 60 miles to the south. I t i s l i g h t gray i n c o l o r and averages about s i x inches t h i c k . In some places two l a y e r s may be seen, separated by a few inches of e a r t h . A t h i n b l a c k compact l a y e r of carbonaceous matter l i e s immediately below the ash, probably the remains of organic m a t e r i a l b u r i e d by the f a l l of the ash. Bostock (1) estimates that- i t o r i g i n a t e d w i t h i n the past 2000 years from a volcano to the west or southwest. LOCAL GEOLOGY PART IV ' " / 1. I n t r o d u c t i o n : U n t i l the time the w r i t e r l e f t the Brown McDade property, the only g e o l o g i c a l i n f o r m a t i o n a v a i l a b l e was obtained from rock outcrops, b u l l d o z e r trenches and about 13 short•diamond d r i l l h o l e s . The surface of the ground i s almost t o t a l l y covered by a t h i c k mantle of overburden, w i t h very few out- crops. As a r e s u l t of these conditions,some of the opinions expressed on the following- pages are put f o r t h t e n t a t i v e l y , u n t i l more complete i n f o r m a t i o n becomes a v a i l a b l e . The f i e l d w o r k was confined to two mineral c l a i m s , the B i g Thing and part of the Glouser, hence the d i s c u s s i o n w i l l 10 centre around theserareas. The B i g Thing i s s i t u a t e d across a low s a d d l e - l i k e ridge between Pony Greek, and Dome Greek to the south, both of which are t r i b u t a r y to V i c t o r i a Creek. I t i s near the southern end of the Brown McDade group of c l a i m s , which extends two miles north, beyond Pony Creek. 2. General D e s c r i p t i o n ; In a pocket on the i n s i d e r e a r cover of the r e p o r t i s a map of the working Areas (scale 40 f e e t = 1 i n c h ) , which w i l l be of value i n c l a r i f y i n g the f o l l o w i n g d i s c u s s i o n . Outcropping on the claims and presumably u n d e r l y i n g most of the area i s quartz d i o r i t e . Near the southern boundary of the B i g Thing M.C., there i s a small area u n d e r l a i n by s c h i s t s of the Yukon Group. The contact between the quartz d i o r i t e and the s c h i s t s i s not v i s i b l e but appears to run east-west. C u t t i n g the quartz d i o r i t e and p o s s i b l y the s c h i s t s , i s an i r r e g u l a r d y k e - l i k e body of q u a r t z - f e l d s p a r porphyry, s t r i k i n g N25° W and d i p p i n g 55 to 70° westward'. A w e l l defined ore zone, 10 to 15 f e e t i n width i s a s s o c i a t e d c l o s e l y w i t h t h i s body, apparently conforming i n s t r i k e and d i p w i t n the porphyry. S u b s i d i a r y zones of m i n e r a l i z a t i o n occur p a r a l l e l to and branching from the main zone. 3. Rock Types: (a) Quartz D i o r i t e ; The t y p i c a l quartz d i o r i t e i n the hand specimen i s a gray, medium grained rock of a g r a n i t i c t e x t u r e . I t i s composed of white f e l d s p a r and dark green l a t h - l i k e c r y s t a l s of hornblende. Quartz i s v i s i b l e but not abundant. Minor amounts of epidote 11 and p y r i t e are n o t i c e a b l e , s c a t t e r e d widely through, the rock. The p y r i t e i s i n the form of small masses or t i n y cubes,seldom over two m i l l i m e t r e s i n s i z e . L o c a l v a r i a t i o n s i n t e x t u r e , c o l o r and composition are common. These are probably due, e i t h e r to i n c l u s i o n s of country rock, or segregation of c e r t a i n masses w i t h i n the magma before i t s f i n a l s o l i d i f i c a t i o n . Thin s e c t i o n study of the quartz d i o r i t e i d e n t i f i e s the f e l d s p a r s as o l i g o c l a s e - a n d e s i n e . The f e l d s p a r s as the c h i e f mineral c o n s t i t u e n t s of the rock, together w i t h the horn- blende which i s of the common green v a r i e t y , compose 90 per cent or more of the mass. Quartz i s found i n anhedral grains, u s u a l l y much sma l l e r than the two major minerals. I t i s not evenly d i s t r i b u t e d , o c c u r r i n g r a t h e r as i n t e r s t i t i a l masses of small grains between the f e l d s p a r s . A few rounded gr a i n s of e a r l y primary quartz l i e as i n c l u s i o n s i n the hornblende. Epidote i s present as a secondary mineral formed by the a l t e r a t i o n of f e l d s p a r s and hornblende, and i s o f t e n seen around the margins of or w i t h i n the l a t t e r . Epidote i s commonly i n t i m a t e l y a s s o c i a t e d w i t h c h l o r i t e . C e r t a i n i r r e g u l a r areas of c h l o r i t e around the hornblende are formed as an a l t e r a t i o n product of that m i n e r a l . Streaks of an opaque mineral probably magnetite appear i n p a r a l l e l arrangement w i t h i n the c h l o r i t e . This may be the r e s u l t of a l t e r a t i o n of a hornblende w i t h a h i g h content of i r o n . Accessory mi n e r a l s , seen i n the sect-ion i n minor amounts are z i r c o n and a p a t i t e , u s u a l l y i n the form of small euhedral grains s c a t t e r e d through the rock. FIGURE 8 Thin s e c t i o n of auartz f e l d s p a r porphyry, taken from diamond d r i l l core, near the ore zone. Camera l u c i d a drewing Magnified 20 diameters. FIGURE 9 Thin s e c t i o n of cuartz d i o r i t e , taken f r o c diamond d r i l l core. Camera l u c i d a drawing Magnified 20 diameters. 12 There i s cloudiness i n the f e l d s p a r s i n t h i n s e c t i o n , caused by the development of s e r i c i t e i n t i n y scattered'shreds or i n l a r g e r masses.' A l l the f e l d s p a r s show more or l e s s a l t e r a t i o n to s e r i c i t e . The quartz d i o r i t e s u n d e r l y i n g the B i g Thing M.C. are mapped by Bostock (1) as a part of one formation that includes s e v e r a l g r a n i t i c types. Two d i s t i n c t types other than that j u s t described have been n o t i c e d by the w r i t e r w i t h i n a mile of the property. The one i s a s l i g h t l y f i n e r grained g r a y i s h rock,probably a d i o r i t e . The other has the composition of a true g r a n i t e with f e l d s p a r , quartz, a n d ' b i o t i t e as the c h i e f c o n s t i t u e n t s . These rocks were not stud i e d i n d e t a i l . Figure $ ' ( f a c i n g page], i l l u s t r a t e s the quartz d i o r i t e . (b) Quartz Feldspar Porphyry: The composition of t h i s rock i s v a r i a b l e i n s o f a r as the numbers and the types of phenoerysts are concerned. I t contains widely s c a t t e r e d quartz as the only type of pheno- e r y s t s , or contains both quartz and f e l d s p a r s . In places i t seems to have a predominance of f e l d s p a r s and where t h i s occur the phenoerysts are abundant and c l o s e l y packed. The t y p i c a l porphyry' i s a gray to b u f f colored a p h a n i t i c rock c o n t a i n i n g s c a t t e r e d euhedral phenoerysts of quartz and white f e l d s p a r s , to an approximate s i z e of one e i g h t h of an i n c h . I t i s dense and hard w i t h a sub-conchoidal c h e r t y f r a c t u r e . ' Weathering has reduced the f e l d s p a r s to s o f t gray powdery masses or else has removed them completely, l e a v i n g only t h e i r c r y s t a l o u t l i n e s i n the matrix. The quartz i n 13 the phenoerysts i s f r e s h and g l a s s y i n appearance. Under the microscope the groundmass of the porphyry i s seen to he composed of a c r y p t o c r y s t a l l i n e mosaic of quartz and very h i g h l y s e r i c i t i z e d , cloudy f e l d s p a r . The average g r a i n s i z e i s 0.05 ram. The quartz was e a s i l y i d e n t i f i e d but the cloudiness of the f e l d s p a r grains together w i t h the small size,made t h e i r i d e n t i f i c a t i o n d i f f i c u l t . However, i n d e x - o f - r e f r a c t i o n measurements on gr a i n s at the edge of the t h i n s e c t i o n showed them to be l e s s than that of balsam. Dr. Watson obtained s e v e r a l negative i n t e r f e r e n c e f i g u r e s on a few g r a i n s . From these r e s u l t s i t was deduced th a t the f e l d s p a r i s probably o r t h o c l a s e . The quartz phenoerysts show some i n t e r e s t i n g f e a t u r e s . In most of them the o r i g i n a l euhedral o u t l i n e has been modified by the corroding e f f e c t of the magma i n which the phenoerysts formed. The c o r r o s i o n takes the form of an i r r e g u l a r o u t l i n e on the quartz g r a i n s , showing deep indentations where they are embayed by the groundmass. Figure Mo. to opposite page^ i l l u s t r a t e s t h i s p o i n t . Some of the c r y s t a l s show a p a r t i a l s o l u t i o n of quartz around the boundaries, f o l l o w e d b y , r e c r y s t a ' l l i z a t i o n under c o n d i t i o n s of l e s s pressure,or a d d i t i o n of quartz. This process has formed narrow r i n g s of f i n e grained quartz around the phenoerysts. The f e l d s p a r phenoerysts are composed l a r g e l y of ol i g o c l a s e - a n d e s i n e . They are a l l more or l e s s a l t e r e d to s e r i c i t e and some carbonate, being quite cloudy i n t h i n s e c t i o n . In places the a l t e r a t i o n has l e f t only c l u s t e r s of s e r i c i t e i n FIGURE 10 Thin s e c t i o n of ousrtz f e l d s p a r porphyry taken from "The Dome", outcropping 1 mile west of the ore zone. Camera l u c i d a drawing Magnified 20 diameters. FIGURE 11 Thin s e c t i o n of cuartz f e l d s p a r porphyry, taken from a diamond d r i l l hole near the ore zone. Camera l u c i d a drawing Magnified 20 diameters. 14 trie m atrix, some w i t h vague o u t l i n e s suggestive of o r i g i n a l f e l d s p a r c r y s t a l s . Some f e l d s p a r s have t h i n bands of intense a l t e r a t i o n around t h e i r rims while the i n t e r i o r s of the cry- s t a l s are comparatively f r e s h . Specimens of quartz f e l d s p a r porphyry taken near the ore zone c o n t a i n considerable epidote i n the groundmass and to a l e s s e r extent i n the f e l d s p a r phenoerysts. I t has formed probably as the metamorphic product of a l t e r a t i o n of f e l d s p a r s and p o s s i b l y ferromagnesian minerals. There i s o f t e n an a s s o c i a t i o n of c h l o r i t e and epidote i n such a way as to sugg- est an o r i g i n a l ferromagnesian mineral which has been com- p l e t e l y a l t e r e d . In some places the c h l o r i t e i s quite n o t i c e a b l e i n the rock. Scattered s p a r s e l y through the porphyry are t i n y euhedral c r y s t a l s of p y r i t e , most of which have been a l t e r e d to l i m o n i t e . A p a t i t e i s present i n small euhedral c r y s t a l s disseminated through the matrix. L o c a l l y there i s an abundance of carbonate i n the form of small shreds and f l a k e s and sometimes i n v e i n l e t s . A study was made of the quartz f e l d s p a r porphyry, out- cropping 'as a dome-shaped body on the mountain top midway between Nansen and V i c t o r i a v a l l e y s and a mile west of the mine. Both i n the hand specimens and i n t h i n sections i t i s almost i d e n t i c a l to the p o r p h y r y t i c rock l o c a t e d i n the d r i l l h o l e s . The s i m i l a r i t y between these rocks i s such as to suggest they o r i g i n a t e d from the same source. Figure No. 'O and No. H f a c i n g Page show t h i n sections of both rocks. The f i e l d r e l a t i o n s between the two w i l l be discussed i n 15 d e t a i l i n Part V I . (c) Yukon S c h i s t s : The f o l l o w i n g d e s c r i p t i o n a p p l i e s only to' those rocks of the Yukon.group which are exposed i n trench "No. 8 near the southern boundary of the Big Thing c l a i m . . No t h i n sections of t h i s rock were stu d i e d . The t y p i c a l s c h i s t i s a s o f t , f i n e - g r a i n e d gray rock w i t h an abundance of muscovite throughout. I t f e e l s s l i g h t l y greasy and has w e l l developed s c h i s t o s i t y along s e v e r a l planes. This s c h i s t o s i t y c a u s e s i t to break i n t o s p l i n t e r y fragments. In the f i e l d t h i s rock might be c l a s s i f i e d as a s o f t mica s c h i s t . 4. Weathering: The rocks adjacent to the ore zone and at l e a s t s e v e r a l hundred f e e t of the quartz d i o r i t e on the hanging w a l l s i d e , are p a r t i a l l y weathered from 100 to 200 f e e t deep. On the f o o t w a l l side .of the zone, the quartz d i o r i t e i s f r e s h i n appearance and not h i g h l y f r a c t u r e d . The l a c k of g l a c i a l scouring has allowed the r e s i d u a l weathered m a t e r i a l s to remain undisturbed, probably since T e r t i a r y time,for i t i s l i k e l y that the greatest part of the weathering took place p r i o r to the Ple i s t o c e n e P e r i o d , before there was a permanent f r o s t l a y e r i n the ground. The weathering has r e s u l t e d i n a breaking down of the e s s e n t i a l rock forming minerals except quartz which remains u n a l t e r e d . The products formed are l i m o n i t e , k a o l i n i t e , some carbonate, and j a r o s i t e , a l l of which have changed the c o l o r s of the rocks to a r u s t y brown 16 or b u f f shade.. While the o r i g i n a l textures of both the porphyry and the quartz d i o r i t e are o f t e n v i s i b l e , the ferromagnesian m i n e r a l s , f e l d s p a r s , and p y r i t e have only i r r e g u l a r brown o u t l i n e s . The overburden i s o x i d i z e d to an orange-brown c o l o r w i t h l i m o n i t e . On the surface of the bedrock a b l a c k s t a i n i s o ften present as a t h i n f i l m . In t i n y f r a c t u r e s i t has a d e n d r i t i c p a t t e r n suggestive of secondary manganese accumulation. Immediately above the ore zone the overburden has a p e c u l i a r lemon-yellow to brown c o l o r quite d i s t i n c t from the brown l i m o n i t i c s t a i n i n the surrounding m a t e r i a l . I t i s formed as a t h i n c oating over the fragments of ore and a l s o as i r r e g u l a r areas w i t h i n f r a c t u r e s . Chemical a n a l y s i s revealed the presence of a considerable amount of sulphate, while a spectrographic a n a l y s i s showed l e a d and a r s e n i c . I t i s b e l i e v e d that t h i s i s a secondary mineral formed by weather- ing of the ore minerals, w i t h the p o s s i b l e composition s i m i l - ar to a j a r o s i t e . A f u r t h e r d i s c u s s i o n of the p r o p e r t i e s and means used to i d e n t i f y the mineral w i l l be found i n Part V, 2 of t h i s paper. The ore zone,composed o£ so much r e s i s t a n t s i l i c a i s not weathered to the same extent as the w a l l rocks. In f a c t the ore appears quite f r e s h at the surface. In p l a c e s , however, the p y r i t e has been leached away l e a v i n g only a honeycomb mass of quartz. The comparative s c a r c i t y of sulphide and i t s disseminated nature may account f o r the apparent l a c k of weathering i n much of the ore. 17 5. Hydrothermal A l t e r a t i o n ; S e r i c i t i z a t i o n i s the main form of w a l l rock a l t e r a t i o n . I t i s present both i n the quartz f e l d s p a r porphyry and the a quartz d i o r i t e . Even i n the few samples of f r e s h - l o o k i n g f o o t w a l l quartz d i o r i t e there i s a strong development of s e r i c i t e i n the f e l d s p a r s . The s e r i c i t e i s i n small dispersed shreds, g i v i n g to the f e l d s p a r s a very clouded appearance. I t i s a l s o i n confused masses of minute f l a k e s , completely r e p l a c i n g the o r i g i n a l minerals. In the porphy- r i t i c rocks the s e r i c i t i z a t i o n i s strong i n the groundmass and the phenocrysts. A more d e t a i l e d d i s c u s s i o n of the f i e l d occurrence of a p o r p h y r i t i c rock outcropping a mile west of the mine,is found i n Part VI , 1. I t i s worth noting at t h i s p o i n t , however, the a l t e r a t i o n i n the rock. L i k e the porphyry found on the property, i t i s i n t e n s e l y s e r i c i t i z e d throughout i t s mass, As the p o r p h y r i t i c rocks of t h i s type are considered to be the youngest i n t r u s i v e s i n the r e g i o n , i t i s b e l i e v e d by the w r i - t e r that the a l t e r a t i o n was caused by l a t e hydrothermal s o l u t i o n s a s s o c i a t e d w i t h the p e r i o d of i n t r u s i o n . I t i s thought, a f t e r a study of s e v e r a l t h i n s e c tions that there i s a decrease i n the i n t e n s i t y of s e r i c i t i z a t i o n away from the ore zone. When a more complete p i c t u r e of the s t r u c t u r e becomes a v a i l a b l e , the e f f e c t s of the a l t e r a t i o n w i l l be b e t t e r understood. There i s some development of carbonate i n the rocks, but i t i s not as wide-spread as the s e r i c i t e . I t i s found i n w FIGURE 12 Generalized Cross S e c t i o n of a Diamond D r i l l Hole, i l l u s t r a t i n g the Str u c t u r e of the Brown McDade Ore Zone. Scale 1 inch = 40 f e e t . 18 f l a k e s , shreds or small v e i n l e t s through the rock. S i l i c i f i c a t i o n • doesn't seem to be a major a l t e r a t i o n except i n contact w i t h the ore zone, where w a l l rocks'some-" times show replacement by f i n e grained quartz. No a d u l a r i a c o u l d be found i n any t h i n s e ctions of the ore zone. P y r i t e and epidote are common i n many of the igneous rocks i n the Carmacks Area, as described by Bostock (1). The w r i t e r confirms t h i s statement from personal observations. There i s a l s o no evidence to show that they increase i n abundance near the ore zone. Therefore i t i s b e l i e v e d that these minerals are the r e s u l t of r e g i o n a l metamorphism and are not connected with the hydrothermal s o l u t i o n s that deposited the Brown McDade ore body. 6. Structure of the Ore Body; Figure No. A? f a c i n g t h i s page represents a g e n e r a l i z e d c r o s s - s e c t i o n of any one of the diamond d r i l l h o l e s , 2a to 12a i n c l u s i v e . I t i s given to show the reader how the knowledge of the s t r u c t u r e was obtained. Knowing the p o s i t - i o n of the ore on the surface, the p o s i t i o n of the h o l e , and the points at which the hole i n t e r s e c t s the p o r p h y r i t i c rock and the ore zone, i t was p o s s i b l e to c a l c u l a t e the dip of the ore i n that h o l e , and the r e l a t i o n s h i p s between ore, porphyry and quartz d i o r i t e . This procedure was repeated i n a l l the h o l e s . The f a c t s enumerated below are r e s u l t s of the work; (a) The ore zone has an average width of 10 to 15 f e e t and 19 dips 55 to 70° 'westward. (b) Smaller veins e x i s t , p a r a l l e l to and branching from the main ore zone. (c) The ore zone l i e s w i t h i n a quartz f e l d s p a r porphyry rock i n every hole that i n t e r s e c t s i t . (d) The f i n e grained a l t e r e d gray rock i n the b u l l d o z e r trenches, that l i e s on e i t h e r side of the ore zone, i s pro- bably a surface phase of the quartz f e l d s p a r porphyry. (e) The i n t e r s e c t i o n s , by a number of h o l e s , of the quartz f e l d s p a r porphyry, vary from 30 to 100 f e e t wide and seem to i n d i c a t e a t a b u l a r body c u t t i n g the quartz d i o r i t e . ( f ) The presence of s t i c k y c l a y gouge near the ore zone i n trenches No. 5 and 2, and the b r e c c i a t e d appearance of much of the, ore, suggest considerable movement and shearing. Summing up the above f a c t s gives an approximate p i c t u r e of the s t r u c t u r e as f o l l o w s : The Brown McDade ore body i s a m i n e r a l i z e d zone, l y i n g w i t h i n a d y k e - l i k e body of quartz f e l d s p a r porphyry which s t r i k e s N. 25 degrees W and dips about 60° westward. The' p o r p h y r i t i c rock i s younger than, and cuts the country rock, a quartz d i o r i t e . Movement and shearing have taken place along the ore zone. Post mineral f a u l t i n g i s known to e x i s t i n the v i c i n i t y of trench No. 2 and d r i l l holes 6a and 7a, where s l i g h t o f f s e t s , i n the v e i n , p r e d i c t e d by Smitheringale, were l o c a t e d l a t e r by d r i l l i n g . No trace of the ore, or of the porphyry was found i n hole No. l a . I t i s b e l i e v e d that a f a u l t cutting, across between t h i s hole and hole 2a may 20 e x p l a i n t h i s discrepancy. Such a f a u l t might a l s o e x p l a i n the apparent o f f s e t i n the ore zone between trenches No. 4 and No. 5. In t r e n c h No. 8 near the southern boundary of the Big Thing claim the porphyry may be seen c u t t i n g the s c h i s t s , but i t does not c o n t a i n any v i s i b l e m i n e r a l i z a t i o n . I t i s not yet known whether the ore zone w i l l continue from the quartz d i o r i t e i n t o the s c h i s t s or whether i t w i l l die out near the contact. PART V '. MINERALOGY 1. I n t r o d u c t i o n : The v e i n m a t e r i a l i s a b l u i s h - g r a y c r y p t o c r y s t a l l i n e quartz c o n t a i n i n g f i n e l y disseminated sulphides. L o c a l l y the sulphide content i s r e l a t i v e l y h i g h , but on the average i t i s l e s s than 5 per cent of the t o t a l (mass of the ore'. P y r i t e i s the p r i n c i p a l sulphide w i t h arsenopyrite i n l e s s e r q u a n t i t i e s and only minor amounts of other m e t a l l i c minerals. Tfte ore commonly has a b r e c c i a t e d appearance, w i t h small angular white fragments cemented i n a groundmass of s i l i c e o u s m a t e r i a l . These fragments resemble some of the bleached gray rock i n close p r o x i m i t y to the ore zone and are thought to have been o r i g i n a l l y of the composition of the quartz f e l d s p a r porphyry. Studies of t h i n and po l i s h e d sections of ve i n m a t e r i a l r e v e a l much b r e c c i a t i o n of p y r i t e , arsenopyrite and s p h a l e r i t e . Many of the small vugs and drusy c a v i t i e s i n the ore are f i l l e d with inwardpointing quartz c r y s t a l s and some are f i l l e d w i t h yellow masses of a j a r o s i t e mineral. Comb s t r u c t u r e FIGURE 13 B o t r y o i d a l s i l i c a taken from d r i l l core i n the ore zone. Magnified.*2. FIGURE 14 B o t r y o i d a l s i l i c a taken from d r i l l core i n the ore zone. Magnified.x2^. 21 i s n o t i c e a b l e o c c a s i o n a l l y i n hand specimens,with i n t e r l o c k i n g c r y s t a l s of quartz up to one quarter i n c h i n length. On a microscopic s c a l e , comb s t r u c t u r e i s common, i n t i n y v e i n l e t s c u t t i n g the c r y p t o c r y s t a l l i n e groundmass. Some banding i n the v e i n has been seen, p a r a l l e l to contact s , but t h i s feature i s not o f t e n observed. Where £he ore zone was cut by one of the d r i l l holes at 125 fee t v e r t i c a l depth, b o t r y o i d a l s t r u c t u r e was present i n the q u a r t z . I t assumed the form of s e v e r a l rounded masses c l u s t e r e d together, which i n cross s e c t i o n showed a conc e n t r i c l a y e r i n g . e f f e c t p a r a l l e l to the surfaces. 2. Texture and Composition of Vein M a t e r i a l : The quartz i n the matrix of the ore i s exceedingly f i n e grained. Under the highest m a g n i f i c a t i o n a v a i l a b l e , i t appears as a mosaic of t i n y i n t e r l o c k i n g g r a i n s , averaging about 12 microns i n s i z e . The matrix i s cut by v e i n l e t s and masses of c r y s t a l l i n e f i n e grained quartz. In comparison to the groundmass i t i s much coarser i n t e x t u r e . The g r a i n s i z e of t h i s l a t e r quartz i s v a r i a b l e depending oh the width of the v e i n l e t but i t may be s a i d to average 10 or 15 times the s i z e of that i n the groundmass. Large masses of minute lemon yellow c r y s t a l s are commonly seen i n t h i n s e c t i o n f i l l i n g vugs,and i n t e r s t i c e s between comb quartz i n the v e i n l e t s . They have 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 . FIGURE 15 Photomicrograph of a t h i n s e c t i o n of v e i n m a t e r i a l I l l u s t r a t e s tne b r e c c i a t e d character of the ore and the g r a i n s i z e of the groundmass (12 microns) Magnified 31 diameters. 22 (a) index of r e f r a c t i o n ..... very h i g h (b) b i r e f r i n g e n c e (^f?^A r.^c.e. fpA'".). . f o u r t h order or higher .(c) pleochroism s l i g h t , yellow to l i g h t yellow (d) e x t i n c t i o n p a r a l l e l (e) o p t i c a l s i g n u n i a x i a l negative. Some of the earthy yellow coating over surface s e c t i o n s of the ore zone (see under "Weathering" i n Part IV) was s t u d i e d m i c r o s c o p i c a l l y by o i l immersion methods. The p r o p e r t i e s of t h i s m a t e r i a l are (a) c o l o r lemon yellow c r y s t a l s (b) form hexagonal prisms and rhorabohedrons (c) pleochroism yellow to pale yellow (d) index of r e f r a c t i o n .... 1.76 --1.78 + I t i s b e l i e v e d that the yellow c r y s t a l s seen i n t h i n s e c t i o n are the same as those s t u d i e d under o i l immersion. The lower index of r e f r a c t i o n i s found to be about 1.75 while the upper one i s w e l l above 1.7S. A l l the above p r o p e r t i e s suggest t h a t the mineral belongs to the f a m i l y of j a r o s i t e s . The j a r o s i t e s ' are complex secondary hydrops sulphates formed by the weathering of sulphide ores. They are common i n the deeply o x i d i z e d deposits of the southwestern United States and many other p l a c e s . A c r y s t a l of z i r c o n was seen i n the ore under the microscope as w e l l as much, minute euhedral a p a t i t e . These are probably of hypogene o r i g i n . FIGURE 16 Photomicrograph, showing jamesonite ( j a ) and arsenopyrite (as) i n ouarta. X 2 0 0 FIGURE 17 Photomicrograph showing jamesonite (ja) i n b r e c c i a t e d p y r i t e (py) X 2 0 0 23 3. M e t a l l i c Minerals': " A- study of hand specimens and p o l i s h e d sections of ore from the Brown McDade mine shows the presence of p y r i t e , a r s e n o p y r i t e , s p h a l e r i t e , chalcopyri>t ;e, c o v e l l i t e , galena, s t i b n i t e , t e t r a h e d r i t e , jamesonite, bournonite and g o l d . (a) P y r i t e ; FeS g P y r i t e i s the main m e t a l l i c mineral i n the ore. I t i s f i n e l y disseminated i n subhedral to anhedral grains ranging from sub-microscopic fragments to c r y s t a l s and masses a few m i l l i m e t r e s across. Cubes aid p y r i t o h e d r a are common forms of the c r y s t a l s . F r a c t u r i n g and b r e c c i a t i o n of the l a r g e r masses of p y r i t e has reduced them to f i n e r fragments, which are cemented together by l a t e r quartz. Much,of-the p y r i t e i n the surface showing has been p a r t i a l l y or wholly removed • . by weathering, l e a v i n g only r e s i d u a l l i m o n i t e or a mass of honeycombed quartz w i t h only the casts of the o r i g i n a l c r y s t a l s to i n d i c a t e t h e i r composition. (b) A r s e n o p y r i t e : FeAsS This mineral seems to be the second most abundant sulphide i n the ore. L i k e the p y r i t e i t occurs f i n e l y disseminated, rhombs and prisms being the commonest ' c r y s t a l forms. In hand specimens i t i s recognized as elongated' s i l v e r y white c r y s t a l s up to a few m i l l i m e t e r s i n l e n g t h . I t has' undergone much b r e c c i a t i o n i n t o very f i n e s p l i n t e r y fragments, and where observed i n surface ore i t has been p a r t l y a l t e r e d to l i m o n i t e . I t seems that arsenopyrite i s not as evenly d i s t r i b u t e d through- out the ore as. i s the, p y r i t e . FIGURE 18 Photomicrograph of b r e c c i a t e d p y r i t e cemented by quartz X 65 FIGURE 19 Photomicrograph of disseminated arsenopyrite i n auartz X 65 24 (c) S p h a l e r i t e : ZnS Seen r a r e l y i n the f i e l d , t h e s p h a l e r i t e i s very dark brown w i t h a h i g h l y resinous l u s t e r . I t appears to be l o c a l l y concentrated r a t h e r than evenly dispersed i n the v e i n . Small v e i n l e t s of s p h a l e r i t e one quarter of an i n c h wide . have been observed. ' As s t u d i e d i n p o l i s h e d s e c t i o n the s p h a l e r i t e i s i n anhedral masses w i t h rounded i r r e g u l a r o u t l i n e s . I t contains t i n y i n c l u s i o n s of c h a l c o p y r i t e , while c o v e l l i t e i s common as a replacement mi n e r a l . A c e r t a i n amount of b r e c c i a t i o n of s p h a l e r i t e has taken place i n a s i m i l a r manner to that of p y r i t e and a r s e n o p y r i t e . (d) ' Chalcopyrite.;, CuFeS 2 This mineral has been observed only as minute blebs i n s p h a l e r i t e , v i s i b l e under medium or high m a g n i f i c a t i o n . I t s determination i s based on i t s brassy c o l o r , smooth p o l i s h , and low/ r e l i e f which being about the same as the surrounding s p h a l e r i t e , i n d i c a t e s a mineral of s i m i l a r hardness. (e) C o v e l l i t e : CuS Much of the s p h a l e r i t e i s p a r t i a l l y replaced by c o v e l l i t e which has the appearance of a deep blue i r r e g u l a r t a r n i s h on i t s surface. Under p o l a r i z e d l i g h t the c o v e l l i t e i s s t r o n g l y a n i s o t r o p i c showing s e v e r a l good e x t i n c t i o n s per r e v o l u t i o n , w i t h b r i g h t red and purple c o l o u r s , (f.) Galena: PbS None of the p o l i s h e d sections showed any galena, but i t was seen a few times i n the d r i l l cores, u s u a l l y i n small 25 v e i n l e t s near the ore zone. (g) S t i b n i t e : ShgSg . This mineral was i d e n t i f i e d i n hand specimens as slender s i l v e r y p r i s m a t i c aggregates. In p o l i s h e d s e c t i o n i t i s recognizable by i t s n e e d l e - l i k e form, i t s very strong a n i s o - tropisrn i n p o l a r i z e d l i g h t and the yellow t a r n i s h produced/ on i t s surface by e t c h i n g with potassium hydroxide. In the ore i t i s . u s u a l l y a s s o c i a t e d w i t h the other s u l p h o - s a l t s , t e t r a h e d r i t e and jamesonite. I t i s not of common occurrence i n the Brown McDade ore. (h) T e t r a h e d r i t e : 3Cu„S. Sb S . — 2 2 3 Only i n one p o l i s h e d s e c t i o n was any t e t r a h e d r i t e found,, where i t was associated w i t h a r s e n o p y r i t e , s t i b n i t e , jamesonite and s p h a l e r i t e . I d e n t i f i c a t i o n was made on the b a s i s of the standard etch r e a c t i o n s described by Short') and s a t i s f a c t o r y microchemical t e s t s f o r copper and antimony. . The t e t r a h e d r i t e s t u d i e d , comes from a small v e i n of heavy sulphide ore a few inches i n wid^th, l o c a t e d i n diamond d r i l l hole No. 1 close to the main zone. Samples of t h i s ore showed much higher-than-average values i n s i l v e r . Since no other important s i l v e r - b e a r i n g minerals have be.en found i t i s p o s s i b l e that the s i l v e r values i n the ore come from t e t r a h e d r i t e and p o s s i b l y a l s o from galena. Samples of ore from a property i n the same area, optioned- by the Conwest E x p l o r a t i o n Co., seem to show a higher s i l v e r - g o l d r a t i o than those of the Brown McDade-. ore. A short p o l i s h e d s e c t i o n study of these samples' shows' comparatively greater amounts of FIGURE 20 Photomicrograph of gold (Au) ass o c i a t e d w i t h p y r i t e (py) i n quartz. X 200 FIGURE 21 Photomicrograph of gold (Au) ass o c i a t e d with p y r i t e (py) i n quartz. X 700 t e t r a h e d r i t e and the other s u l p h o - s a l t s . ( i ) Jamesonite: 2 PbS. S b 2 S 3 Although i t has not been seen i n the f i e l d , Jamesonite was discovered i n minor amounts i n p o l i s h e d s e c t i o n s of ore from three d r i l l h o les. I t was i d e n t i f i e d by Dr. R.M. Thompson who analyzed ..the mineral .by X-ray powder methods. The w r i t e r had i d e n t i f i e d i t t e n t a t i v e l y as a complex s u l p h o - s a l t on the b a s i s of etch r e a c t i o n s only. At the time of i t s d i s c o v e r y the amount was too small to give any r e l i a b l e microchemical t e s t s . The etch r e a c t i o n s do, however, check w i t h those given by Short (13) f o r Jemesonite. He observes a s l i g h t e f f e r v e - scence i n the r e a c t i o n w i t h n i t r i c a c i d , but t h i s was not seen b y the w r i t e r . The jamesonite i s c l o s e l y a s s o c i a t e d w i t h t e t r a h e d r i t e and s p h a l e r i t e but has a l s o been n o t i c e d l y i n g i n f r a c t u r e s i n b r e c c i a t e d masses of p y r i t e and a r s e n o p y r i t e . I t s c h a r a c t e r i s t i c form i s In long f i b r o u s c r y s t a l s , sometimes s l i g h t l y bent, w i t h cross f r a c t u r e s r e p r e s e n t i n g the b a s a l cleavage. ( j ) Bournonite; CUgS. 2PbS. SbgS 3 Bournonite i s found i n ore from a small zone i n trench No. 3 about 40 f e e t west of the main zone and p a r a l l e l to i t . '> The sample from which the p o l i s h e d s e c t i o n i s cut, contains s t i b n i t e , i d e n t i f i e d as such i n the f i e l d . A s s o c i a t e d w i t h the bournonite In the s e c t i o n although not i n contact w i t h i t , are p y r i t e and s p h a l e r i t e . •The mineral i s s o f t , and almost white compared w i t h FIGURE 22 Photomicrograph of a p a r t i c l e of gold (12.5 microns) i n quartz. X 1634 FIGURE 23 Photomicrograph of p y r i t e (py), arsenopyrite (as) end s p h a l e r i t e (sp) i n auartz. X 200 ' 27 s p h a l e r i t e . I t s c o l o r as recorded by Short (13) i s gray, l i k e that of t e t r a h e d r i t e . I t i s d i s t i n c t l y a n i s t r o p i c , showing l i g h t brown and dark brown c o l o r s when rotated, i n p o l a r i z e d l i g h t . The i d e n t i f i c a t i o n of bournonite was made by Dr. Thompson i n an X-ray- powder a n a l y s i s . On the b a s i s of etch r e a c t i o n s , microchemical t e s t s f o r t e l l u r i u m , a n d the anisotropism, the w r i t e r thought i t might be' the t e l l u r i d e m i n e r a l , nagyagite. The etch r e a c t i o n s , given by Short' 3 f q r both minerals, are p r a c t i c a l l y i d e n t i c a l . . There must have been an e r r o r i n the' microchemical t e s t s f o r t e l l u r i u m , which were repeated twice, w i t h apparently s a t i s f a c t o r y r e s u l t s . I t i s now b e l i e v e d that the t e s t , r e l i a b l e as i t may be, i s i n t e r f e r e d w i t h by the presence of i r o n , (k) Gold: Au No v i s i b l e g o l d has been found i n any hand specimens, although f i n e c o l o r s may be obtained by panning the overburden above the ore zone. In p o l i s h e d s e c t i o n s from diamond d r i l l holes No. 8a and 11a and from b u l l d o z e r trench No.3 a few small pieces of gold were seen. The gold i s a b r i g h t yellow i n c o l o r and has the c h a r a c t e r i s t i c r e l i e f common to i t , i n p o l i s h e d s e c t i o n . The s i z e of the gold ranges from 3 to 150 microns. I t i s ass o c i a t e d c l o s e l y w i t h the sulphide i n the ore, u s u a l l y l y i n g i n f r a c t u r e s between g r a i n s ' o f p y r i t e and i n contact w i t h them. A few t i n y p a r t i c l e s of gold are found i n quartz i s o l a t e d from any s u l p h i d e s . 28 4. Paragenesis of The Ores; I t i s r e a l i z e d that more l a b o r a t o r y work w i l l be r e - quired to determine the exact paragenesis of the Brown McDade ore. This w i l l be f a c i l i t a t e d when underground development progresses f u r t h e r . The disseminated nature of the sulphides makes i t d i f f i c u l t to solve t h e i r order of d e p o s i t i o n . Some contacts between minerals have been observed and used to determine age r e l a t i o n s h i p s . ' The degree of b r e c c i a t i o n of some of the sulphides makes i t p o s s i b l e to separate the e a r l i e r formed ones from those which were deposited l a t e r . The experience of others who have solved such problems i n w e l l known deposits of a s i m i l a r c h a r a c t e r , has been used as a guide. The t a b l e below, i l l u s t r a t e s the paragenesis as determined by the w r i t e r : quartz p y r i t e a r s e n o p y r i t e s p h a l e r i t e c h a l c o p y r i t e galena t e t r a h e d r i t e s t i b n i t e jamesonite bournonite g o l d c o v e l l i t e o x i d a t i o n 29 Quartz, p y r i t e , arsenopyrite and s p h a l e r i t e are a l l f r a c t u r e d and cemented by l a t e r quartz. Any of the other m e t a l l i c minerals may appear i n these f r a c t u r e s , but are not f r a c t u r e d themselves. I t i s concluded from these f a c t s that there were at l e a s t two periods of m e t a l l i c mineral- i z a t i o n , separated by movement along the vein',with consequent f r a c t u r i n g and b r e c c i a t i o n of the e a r l y minerals. During the f i r s t p e r i o d , p y r i t e , a r s e n o p y r i t e , s p h a l e r i t e and p o s s i b l y some galena were introduced w i t h quartz. In the second per- i o d s t i b n i t e and the s u l p h o - s a l t s and gold were deposited w i t h l a t e r quartz. F o l l o w i n g the clo s e of- th'e hypogene m i n e r a l i z a t i o n , supergene c o v e l l i t e began to form by the o x i d a t i o n of the s p h a l e r i t e and c h a l c o p y r i t e . I t i s the w r i t e r ' s o p i n i o n that the two periods of m i n e r a l i z a t i o n r e f e r r e d t o , i n the l a s t paragraph, do not represent widely separated periods of time. They may be included i n one long period of hydrothermal. a c t i v i t y during which a short p e r i o d of deformation took p l a c e , followed by the d e p o s i t i o n of s u l p h o - s a l t s and gold. 5. Conclusions: The commercial values of the Brown McDade ores come from f r e e g o l d , and s i l v e r - b e a r i n g minerals l i k e t e t r a h e d r i t e and' p o s s i b l y jamesonite. The i n t e n s i t y of sulphide m i n e r a l i z a t i o n and the g r a i n s i z e of the sulphides are u s u a l l y i n d i c a t i v e of gold values. As a r u l e the heavier the m i n e r a l i z a t i o n and the f i n e r the g r a i n s i z e of the p y r i t e , the higher w i l l be the amount of gold i n the sample. The gold i s c l o s e l y a s s o c i a t e d 30 with the p y r i t e , l y i n g along boundaries of the grains or i n f r a c t u r e s between them. The very wide v a r i a t i o n s i n the gold- s i l v e r r a t i o as seen from the assay r e s u l t s , may p o s s i b l y be explained by the e r r a t i c d i s t r i b u t i o n of gold and the s i l v e r - b earing s u l p h o - s a l t s i n the ore. 31 ORIGIN OF THE ORE' DEPOSIT PART VI 1. Source of The Ore S o l u t i o n s : The mountain known l o c a l l y as "The Dome", on the. summit between V i c t o r i a and Nansen Creeks i s about one mile west of the mine. The composition of the rounded top of the mountain i s quartz f e l d s p a r porphyry. F i e l d r e l a t i o n s between t h i s mass and the surrounding area suggest that i t i s an i n t r u s i v e neck c u t t i n g through the o l d e r surrounding rocks. Other bodies of s i m i l a r rock are common i n the re g i o n f o r 40 miles northwestward. They are considered to be of l a t e T e r t i a r y age. The m i n e r a l i z a t i o n at the Brown McDade Mine i s b e l i e v e d to be g e n e t i c a l l y r e l a t e d to these i n t r u s i o n s of quartz f e l d s p a r porphyry. The f o l l o w i n g points support t h i s b e l i e f . (a) The composition of "the Dome" i s almost i d e n t i c a l to that of the dy k e - l i k e p o r p h y r i t i c body around the ore zone. (b) The s t r u c t u r e at the mine dips towards the Dome, i n d i c a t i n g that i t may be an of f s h o o t ' o f the l a r g e r mass. (c) Dykes of quartz feldspar'porphyry outcrop about a mile west of the Dome and are probably r e l a t e d to i t . The w r i t e r b e l i e v e s that an i n t r u s i o n of quartz f e l d s p a r porphyry (now represented by "The Dome") f r a c t u r e d the surrounding rocks and sent out dykes to f i l l the f r a c t u r e s . These became zones of weakness along which movement took place, a l l o w i n g the entrance of l a t e m i n e r a l i z i n g s o l u t i o n s . 32 Since the p e r i o d of primary m i n e r a l i z a t i o n , supergene pro- cesses have been i n a c t i o n to a l i m i t e d extent. As evidence of these processes there i s the p a r t i a l replacement of s p h a l e r i t e by secondary c o v e l l i t e , as w e l l as the formation of l i m o n i t e and j a r o s i t e i n the ore. Most, of the v e i n m a t e r i a l i s f r e s h , even at the surface where gold i s "found i n hard quartz a s s o c i a t e d w i t h u n a l t e r e d p y r i t e , and where s t i b n i t e and bournonite show no signs of a l t e r a t i o n . I t i s thought that such supergene processes that have been In o p e r a t i o n are very minor and have not a f f e c t e d .the gold and s i l v e r values of the ore. 2 . Comparisons With Other Deposits: (a) I n t r o d u c t i o n : I t i s the purpose of the f o l l o w i n g d i s c u s s i o n , to compare the Brown McDade Mine w i t h ' w e l l known s i m i l a r d e p o s i t s , : i n order to assess i t s p o s s i b i l i t i e s . The comparisons are based on mineralogy, age of d e p o s i t i o n , s t r u c t u r e and w a l l rock a l t e r a t i o n . The w r i t e r was unable to f i n d any reference to d e p o s i t s , where a l l the above features corresponded to those of the Brown McDade. S u f f i c i e n t i n f o r m a t i o n was obtained, however, from the references, to draw a few conclusions regarding i t s p o s s i b i l i t i e s . (b $ M i n e r a l o g i c a l Comparisons: The main c h a r a c t e r i s t i c s of the Brown McDade ore are the blue c o l o r , f i n e texture of quartz, b r e c c i a t i o n , d i s s e m i n a t i o n of the sparse sulphide m i n e r a l i z a t i o n , vugs and drusy c a v i t i e s 33 some b o t r y o i d a l s t r u c t u r e , comb s t r u c t u r e and o c c a s i o n a l banding. On the basis o i t h i s i n f o r m a t i o n i t appears to belong to the epithermal group of mineral d e p o s i t s . C e r t a i n features of the famous, t y p i c a l epithermal deposits have not been seen i n the Brown McDade. Of these, the most prominent and widespread i s the presence of a d u l a r i a , which i s a d i a g n o s t i c mineral, i n t h i s c l a s s . Of the m e t a l l i c minerals i n the ore, only the a r s e n o p y r i t e i s u s u a l l y rare i n •epithermal d e p o s i t s . , . Ferguson's (19) c l a s s i f i c a t i o n of the precious metal epithermal ores, i s determined on the r a t i o of gold to s i l v e r . He recognizes two d i v i s i o n s , the s i l v e r - g o l d c l a s s w i t h a 'ratio of one to one or l e s s , ,and the g o l d - s i l v e r c l a s s where gold exceeds s i l v e r by weight. These cl a s s e s vary consid- e r a b l y i n mineralogy and s t r u c t u r e . The g o l d - s i l v e r r a t i o of the Brown McDade ore l i e s between 1 to 5 and 1 to 15, which would make i t , c o n s i d e r i n g the f i g u r e s alone, a s i l v e r r g o l d deposit. The mineralogy, however, i s such, that the g o l d - s i l v e r group seems the b e t t e r choice of the two. None of the c h a r a c t e r i s t i c - m e t a l l i c minerals of the s i l v e r - g o l d c l a s s are present i n the Brown McDade." These minerals are a r g e n t i t e and the s i l v e r sulpho- s a l t s , which are s a i d by Nolan (12) to be l a c k i n g i n gold- s i l v e r d e p o s i t s . I t Is thought that i n t h i s case the gold- s i l v e r r a t i o i s too close to the b o r d e r l i n e between the two groups to be a d i a g n o s t i c f e a t u r e . 34 (c) Age of D e p o s i t i o n : . The Brown McDade ore"body, formed during Late T e r t i a r y time, belongs g e o l o g i c a l l y to r e g i o n of the P a c i f i c Rim. This region, has the shape of a great a r c , running from New Zealand through the P h i l l i p i n e s , Japan and Western North America, to the South American Continent. I t was the scene of intense v o l c a n i c a c t i v i t y i n the T e r t i a r y P e r i o d , during which time the great epithertnal d e p o s i t s , f o r which i t i s w e l l known, were formed. Considering t h i s f a c t i n the l i g h t of the other c h a r a c t e r i s t i c s of the Brown McDade, i t seems l o g i c a l to a s s o c i a t e i t with the epithermal group. (d1) S t r u c t u r a l Comparisons: Speaking of the g o l d - s i l v e r c l a s s of epithermal d e p o s i t s , T.B. Nolan (12) says, "The ores of t h i s group are commonly l o c a l i z e d by f r a c t u r e s which i n many places appear to be g e n e t i c a l l y connected w i t h the emplacement of the igneous rocks with which they are a s s o c i a t e d . These f r a c t u r e s are g e n e r a l l y discontinuous and r a r e l y have measureable displacements. As- a r e s u l t ore shoots are i n many places of r a t h e r small extent and the discovery of new ones i s d i f f i c u l t . " Of the s i l v e r - g o l d deposits he s t a t e s , "The ore deposits of t h i s c l a s s are commonly found i n w e l l defined f a u l t f i s s u r e s that may be f o l l o w e d f o r considerable distances both h o r i z o n t a l l y : and v e r t i c a l l y . In most l o c a l i t i e s the f a u l t s appear 'to be of t e c t o n i c o r i g i n and to have no d i r e c t conn- e c t i o n w i t h the e x t r u s i o n of the a s s o c i a t e d v o l c a n i c s . " The s t r u c t u r e of the B rown McDade property i s that of an 35 i n t r u s i v e body of quartz f e l d s p a r porphyry w i t h which the ore zone i s c l o s e l y a s s o c i a t e d and to which i t i s b e l i e v e d to be g e n t i c a l l y r e l a t e d . Prom the evidence shown i n b u l l d o z e r trenches Nos. 4 and 8, which are 200- f e e t apart, i t i s thought that there i s no large h o r i z o n t a l displacement along t h i s zone of porphyry. I f t h i s had happened, the contact between the quartz d i o r i t e and the Yukon s c h i s t s would be expected to show signs of t h i s displacement on e i t h e r side of the zone. There i s no s i g n of such a displacement. Considering then, the s t r u c t u r a l evidence at the Brown McDade Mine and Nolan's (12) s t r u c t u r a l comparisons between the two groups of epithermal groups,the g o l d - s i l v e r group i s the one to which i t is. most s i m i l a r . ( e) Wall Rock A l t e r a t i o n : The main a l t e r a t i o n at the Brown McDade Mine i s s e r i c i t i z a t i o n and c a r b o n a t i z a t i o n , w i t h minor s i l i c i f i c a t i o n . I t i s not confined to the rocks adjacent to the ore zone but i s of r a t h e r widespread occurrence. Such a l t e r a t i o n i s more c h a r a c t e r i s t i c of the epithermal c l a s s of ore deposit than i t i s of those formed at greater depths. 3. Conclus ions; (a) The Brown McDade ore deposit i s probably of the ( epithermal c l a s s , although c e r t a i n c h a r a c t e r i s t i c s i n d i c a t e that i t , i s not one of those formed a,t very shallow- depths. (b) A study of the s t r u c t u r a l 'features suggests that the ore should continue to moderate depths, but that ore shoots w i l l be e r r a t i c i n d i s t r i b u t i o n and the width of the ore zone w i l l be v a r i a b l e . (c) The area to the south of the ore zone, which'is u n d e r l a i n by s c h i s t s of the N Yukon Group, w i l l probably not c o n t a i n much ore. The f a c t s that p l a c e r gold i s absent i n those streams l o c a t e d i n the s c h i s t o s e areas, and that the s c h i s t s i n the immediate v i c i n i t y of the property do not appear competent to maintain open f r a c t u r e s , tend to support t h i s statement. (d) Blue s i l i c e o u s f l o a t , i d e n t i c a l i n appearance w i t h the ore has been found i n the streams d r a i n i n g the Northward extension of the Brown McDade Group.. In a d d i t i o n , some pla c e r gold has been taken from the.streams and much of the overburden y i e l d s gold c o l o r s i n the pan. These f a c t s i n d i c a t e that t h i s ground should be favorable f o r e x p l o r a t i o n . * (e) Numerous s u b s i d i a r y zones of m i n e r a l i z a t i o n w i l l be found i n the v i c i n i t y of the main ore zone, some of them p o s s i b l y extending outward i n t o the quartz d i o r i t e . ( f ) Prom the i n f o r m a t i o n . a v a i l a b l e about known d e p o s i t s , the character and i n t e n s i t y of w a l l rock a l t e r a t i o n w i l l probably have some bearing on the c o n t r o l of ore d e p o s i t i o n . .(g) The occurrence of the gold i n the f r e e s t a t e i n a s s o c i a t i o n w i t h p y r i t e suggest that the problems of e x t r a c t i o n should not be too d i f f i c u l t . A more d e t a i l e d study of the m e t a l l i c and gangue minerals w i l l be necessary to prove t h i s p o i n t . However,the small s i z e of the gold i n d i c a t e s that the ore w i l l have to be f i n e l y ground. PART V l l DEVELOPMENT OF THE MINE 1. Discovery: The property was discovered by George McDade of Carmacks, i n 1943. A f t e r many years of prospecting i n the area, during which time he was working s m a l l p l a c e r holdings on Back Creek and Pony Creek, McDade became i n t e r e s t e d i n f i n d i n g the lode from which the p l a c e r gold had- come. H e n o t i c e d t h a t the gold appeared rough, often c o n t a i n i n g pieces of quartz attached to i t , and deduced from t h i s t h a t . i t had not t r a v e l l e d f a r . The next step he took, was to pan systemat- i c a l l y , upstream from the workings, not only along the creeks but a l s o up the h i l l s i d e s . The work progressed s l o w l y , owing to the heavy overburden. He found, however, that most of the ground y i e l d e d c o l o r s i n the pan, and by f o l l o w i n g these leads was able to trace the gold to i t s approximate source. A f t e r s t a k i n g c l a i m s , McDade and h i s partner. Brown dug a s e r i e s of trenches across the ore zone on the B i g Thing c l a i m . The looseness and depth of overburden prevented them from reaching bedrock. Panning of the loose m a t e r i a l i n the trenches produced good c o l o r s i n gold and samples of s o l i d fragments when assayed, gave s a t i s f a c t o r y r e s u l t s . The claims were optioned to Yukon Northwest E x p l o r a t i o n s L i m i t e d , a f t e r an examination by Smitheringale i n Sept. 1945. . Subsequent work has proved the accuracy of McDade's c a l c u l a t i o n s . 38 2. Diamond D r i l l i n g : (a) P l a n : O r i g i n a l l y there was no evidence to i n d i c a t e the d i p of the ore zone but f o r diamond d r i l l i n g purposes i t was assumed to be v e r t i c a l . The f i r s t two holes proved that the zone was dipping westward about 70 degrees, consequently a new plan was s t a r t e d . This c o n s i s t e d of d r i l l i n g a s e r i e s of short holes i n c l i n e d at 40 degrees, 100 f e e t apart, to i n t e r s e c t the zone approximately at r i g h t angles, (b) D r i l l i n g Problems: The northern l a t i t u d e of the mine w i t h i t s consequent l a t e Spring and.early Winter, l i m i t s the time a v a i l a b l e f o r surface d r i l l i n g . The f o u r months from May to September c o n s t i t u t e the average' d r i l l i n g season. The problem of permanently f r o z e n ground i s . d i f f i c u l t . The degree of f r e e z i n g depends on slope of ground, amount of overburden and nature of vegetative cover. U s u a l l y the northern sides of the h i l l s are completely frozen below the moss roots whereas the southern exposures are often f r e e of f r o s t f o r a considerable depth. Steeply s l o p i n g ground, w i t h l i t t l e overburden and p l a n t cover i s not f r o z e n to the same extent as the more gentle slopes with a heavy blanket of moss and brush. The problem of d r i l l i n g i n such ground i s best solved by keeping the d r i l l i n operation continuously, while a hole i s being d r i l l e d . Even the two, ten-hour s h i f t s per day that were used, d i d not prevent the formation of i c e , during the e a r l y part of the season. D r i l l i n g 50 or 100 f e e t B u l l d o z e r trench No. 3 on the "Big Thing" c l a i m , l o o k i n g west. Depth of overburden approximately 8 f e e t . "Tne Dome" i n the background i s an i n t r u s i v e body of quartz f e l d s p a r porphyry. 39 of i c e wastes sev e r a l hours time. A program using three, eight-hour s h i f t s would have been more e f f i c i e n t . D r i l l rods . standing i n the hole, f o r over an hour would freeze s o l i d l y i n p o s i t i o n , preventing t h e i r f u r t h e r use. The source, of water f o r d r i l l i n g -was Pony Greek. The supply was s u f f i c i e n t during the Spring r u n o f f but a few weeks dry weather reduced the flow to a t r i c k l e . On s e v e r a l occasions work was h a l t e d f o r l a c k of water. This problem was s o l v e d by the c o n s t r u c t i o n of a large sump i n the creek to conserve the supply f o r dry weather. • . The rocks on the hanging w a l l of the ore zone through which most of the d r i l l i n g was done are badly shattered and o x i d i z e d to a depth of at l e a s t 200 f e e t . This c o n d i t i o n gives r i s e to many problems such as, low core recovery, caving h o l e s , undue abrasion of d r i l l rods, r a p i d gauge l o s s i n b i t s , and l o s s of r e t u r n water and sludge from, the h o l e s . Because these conditions were unforseen, some time was l o s t and some d r i l l i n g equipment became worn out sooner than was a n t i c i p a t e d . The s o l u t i o n of these d i f f i c u l t i e s would in v o l v e the use .of two s i z e s of d r i l l equipment, a l a r g e s i z e casing i n s i d e of which' standard s i z e d r i l l rods would be used. The casing would be d r i l l e d , f i r s t , to s e a l the h o l e . 3.' Surface S t r i p p i n g : A b u l l d o z e r was used to d i g eight l a r g e cuts across the ore zone over a l e n g t h of approximately 1500 f e e t . This method i s quick and l e s s expensive than trenching by hand. As i n d r i l l i n g , the problem of frozen ground presented d i f f i c u l t i e s . In some trenches s e v e r a l days had to elapse between successive c u t t i n g s to allo w the ground to thaw. By keeping s e v e r a l cuts i n operation at once, the maximum use was made of the bulldoze 4. Present Development: An underground program of development i s now underway. I t c o n s i s t s of a crosscut .700 f e e t l o n g , running from Pony Creek i n t o the ore zone, which i t v / i l l i n t e r s e c t under diamond d r i l l hole No. 8a, about 100 feet* below the su r f a c e . L a t e r a l development of the ore .zone v / i l l f o l l o w upon com- p l e t i o n of the cro s s c u t . 5. T r a n s p o r t a t i o n Problems: 'The f a c t o r s to be considered i n t r a n s p o r t a t i o n are, di s t a n c e , type of t r a n s p o r t a t i o n and year-round a v a i l a b i l i t y of such t r a n s p o r t a t i o n . Production costs w i l l depend l a r g e l y on these f a c t o r s . There are f o u r p o s s i b l e t r a n s p o r t a t i o n routes. The f i r s t route i s v i a the A i s h i h i k c u t - o f f road, the Alaska Highway and the Haines c u t - o f f road to the town of Haines on the coast of Alaska,near Skagw'ay. I t would r e q u i r e the c o n s t r u c t i o n of 40 miles of new road from the mine to A i s h i h i k , making i n a l l , 300 miles of haulage by motor v e h i c l e s . This route has the advantage of being independent of other forms of t r a n s p o r t a t i o n from the mine to tidewater. In the Winter months there i s a p o s s i b i l i t y that the Haines c u t - o f f , which runs through the rugged Coast Range mountains, could not be kept open continuously. The second route runs over the A i s h i h i k c u t - o f f road and 4/ the Alaska Highway to Whitehorse, where i t goes by the White Pass and Yukon Railway to Skagway. -The length of t h i s route i s about 300 m i l e s . I t too, would re q u i r e the c o n s t r u c t i o n of the new road mentioned i n the l a s t paragraph. The t h i r d and f o u r t h routes go through Whitehorse v i a Carmacks. They both r e q u i r e c o n s t r u c t i o n of 35 or 40 miles of new road from the mine to Carmacks, the cost of which would be s i m i l a r to the new A i s h i h i k road. At Carmacks the two routes separate, one using the Dawson-Whitehorse road, and the other being the steamer route up the Lewes R i v e r . The former i s not i n c o n d i t i o n f o r wheeled v e h i c l e s . y e t , but the • Government may open i t up soon. The disadvantages of the r i v e r route are, e x t r a f r e i g h t h a n d l i n g , the p o s s i b i l i t y of high f r e i g h t r a t e s , and a pe r i o d of seven months from October to May'when the r i v e r i s f r o z e n . 6. Power Problems: There i s no immediate source of water power i n the d i s t r i c t , while the timber i s too sparse to be considered as a source of power. Two p o s s i b i l i t i e s remain. . The f i r s t would require the use of d i e s e l o i l , hauled i n from Whitehorse and the second would be to use c o a l from the deposits on the Lewes River near Carmacks. The p o s s i b i l i t i e s of the l a t t e r are worth i n v e s t i g a t i n g . BIBLIOGRAPHY. 1. Bostock, H.S. "Carmacks D i s t r i c t , Yukon" Mem. 189 G e o l o g i c a l Survey of Canada, Ottawa 1936. 2. Brush, G.J. and P e n f i e l d , S.L. • "Determinative Mineralogy and Blowpipe A n a l y s i s " John Wiley and Sons Inc. New York 1926 3. Cairnes, D.D. "Nansen and V i c t o r i a Creeks, N i s l i n g R i v e r Yukon T e r r i t o r y " . Map 15l a . G e o l o g i c a l Survey of Can. Sumrn. Rept.1915. 4. Dana, E(.S. and Ford, W.E..' "A Textbook of Mineralogy" John Wiley and Sons, New York, 1932. 5. Farnham, CM. "Determination of the Opaque Mi n e r a l s " McGraw H i l l Book Co. Inc.,.New York 1931 6. . Harker, A. "Petrology f o r Students" 7. Larsen, E.S. and'Berman, H. "The Microscopic Determination of the Non-opaque Mi n e r a l s " . U.S.G.S. B u l l . 848, Washington, 1934. 8. Llndgren, W. "Mineral Deposits" McGraw H i l l Book Co., New York, 1933. 9. Lindgren, W. ) uThe Ore Deposits, of New Mexico" .Granton, L.C ) U.S.G.S. Prof. Paper 68, Washington 1910. Gordon, C.H. ) 10. Lovering, T.S. "The O r i g i n of the Tungsten Ores of Boulder County, Colorado". Ec. Geol. V o l . 36, No. 3, May 1941 11. Purington, C.W. i " P r e l i m i n a r y Report on the Mining I n d u s t r i e s of the T e l l u r i d e Quadrangle, Colorado", U.S.G.S. Ann.' Rept. Part 111 Washington, 1896-1897. 12. Rocky Mountain Fund. "Ore Deposits of the. Western S t a t e s " . American. I n s t , of Min. and Met. Engineers New York, 1933. BIBLIOGRAPHY 13. Short, M.N. "Microscopic Determination of the Ore Minerals". U.S.G.S. B u l l . 914, Washington 1940. 14. Ross, C P . • * "Some Lode Deposits i n the Northwestern Part of the Boise B a s i n , Idaho". U.'S.G.S. B u l l . 846-D, Washington, 1934. r 15. Moehlman, R.S. "Ore D e p o s i t i o n South of Ouray, Colorado, Ec. Geol. Vo l . 31, Nos. 4 and 5, 1936. 16-. Tweto, 0. • "S c h e e l i t e i n the Boulder D i s t r i c t , Colorado" Ec. Geol. V o l . 42, No. 1, Jan.1947. 17. T y r r e l l , G.W. ' "The P r i n c i p l e s of Petrology", E.P. Dutton and Co., Inc. New York. 18. Worcester, P.G. "Geology of the Ward Region, Boulder County, Colorado.". Colo. Geol I Surv. B u l l . 21, Boulder 1921 19. Ferguson, H.G. "The Mining D i s t r i c t s of Nevada" Econ. Geol." V o l . 24, 1929. + O o \ Y 1 o o •5? V B/G GEOL OG Y 'I IN &K.ANODIQR I Tt [QJZ. DZOR/TE) PORP/i VP Y VEh\] PAUL T LEGEND CONTOUR DIAMOND D HOLE TRENCH CLAIM B.WDY. ASSUMED TRACE OF PORPH/RY IN DR.ILL H0L£6 / r . . MAP OF BROWN MCDADE GROUP WORKINGS & GEOLOGY CARMACKS YUKON TV. SCALE 1 IN. -40 FT. 1946

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