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The geology and mineralogy of the Brown McDade mine Lamb, John 1947-12-31

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THE GEOLOGY AND MINERALOGY OP THE BROWN MCDADE MINE  BY  JOHN LAMB  A THESIS SUBMITTED I N 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 MeD de Mine i s a r e c e n t g o l d - s i l v e r d i s c o v e r y a  i n the Yukon T e r r i t o r y , h a l f w a y 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 d u r i n g 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 v a l u e s a c r o s s a w i d t h o f 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 q u a r t z f e l d s p a r porphyry c u t t i n g q u a r t z d i o r i t e o f o  J u r a s s i c o r l a t e r age. dips s t e e p l y west.  T h i s body has a Northwest s t r i k e and  The ore zone l i e s  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 .  i n the p o r p h y r y and 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 d i s s e m i n a t e d s u l p h i d e s c o m p r i s i n g l e s s than 5% o f the mass. M e t a l l i c m i n e r a l s are p y r i t e , a r s e n o p y r i t e , and s p h a l e r i t e , w i t h " l e s s e r amounts o f g a l e n a , 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 , b o u r n o n i t e , jamesonite  and g o l d .  The g o l d i s  a s s o c i a t e d w i t h t h e 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 about one t o t e n .  i n size.  The g o l d - s i l v e r r a t i o , 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 a r e t h e  c h i e f forms of h y d r o t h e r m a l  a l t e r a t i o n , while considerable  l i m o n i t e , and around t h e ore zone, j a r o s i t e , have been produced by w e a t h e r i n g .  On the- b a s i s o f comparisons w i t h  known d e p o s i t s , the Brown McDade i s c o n s i d e r e d t o b e l o n g t o the deeper e p i t h e r m a l t y p e .  I t should continue to reasonable  depths a l t h o u g h t h e ore shoots are l i k e l y t o be e r r a t i c . The  area s o u t h o f the main ore zone, u n d e r l a i n by s c h i s t o s e  r o c k s w i l l p r o b a b l y be u n f a v o r a b l e f o r the occurrence  of o r e .  ACKNOWLEDGMENTS The  w r i t e r worked as r e s i d e n t e n g i n e e r a t the Brown  McDade p r o p e r t y i n 1946,  under the management o f Dr. W.V.  S m i t h e r i n g a l e , t o whom he i s i n d e b t e d f o r many h e l p f u l s u g g e s t i o n s , and f o r p e r m i s s i o n t o use the maps and data contained herein. 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 c o m p i l a t i o n of- the  r e p o r t were c a r r i e d out under the p e r s o n a l d i r e c t i o n and guidance o f Dr. H.C. Gunning o f t h e Department o f Geology and Geography, whose a d v i c e was g r e a t l y a p p r e c i a t e d .  Dr.  H.V. Warren 'of the same department, though n o t a s s o c i a t e d d i r e c t l y w i t h t h e work, a s s i s t e d the w r i t e r i n t h e d e t e r m i n a t i o n o f some of the m e t a l l i c m i n e r a l s , and i n t a k i n g photographs o f p o l i s h e d s e c t i o n s of o r e . was  c o n s u l t e d on s e v e r a l p e t r o g r a p h i c Of gre^at a s s i s t a n c e i n c o m p l e t i n g  X - r a y powder a n a l y s e s  Dr. K.D. Watson  problems. the s t u d y were t h e  o f two m i n e r a l s b y Dr. R.M. Thompson  of the U n i v e r s i t y of T o r o n t o , and s p e c t r o g r a p h i c a n a l y s e s b y Mr. L.O. G o u i n , a s s i s t a n t i n the department o f Geology. Mr.  J.A. Donnan, t e c h n i c i a n , s u p e r v i s e d t h e p r e p a r a t i o n o f  t h i n s e c t i o n s and p o l i s h e d s e c t i o n s .  TABLE OF CONTENTS  1. 2. 3.  PART 1 INTRODUCTION  1  PART 11 GENERAL INFORMATION  2  Location P h y s i o g r a p h y and G l a c i a t i o n C l i m a t e and V e g e t a t i o n PART 111 REGIONAL. GEOLOGY  1.  Summary  2.  Formations  4. 5. 6.  1. 2. 3. 4. 5.  •  2 2 5 6 6  . PART TV  1. 2. 3.  PAGE  6 LOCAL GEOLOGY  9  Introduction General D e s c r i p t i o n Rock Types , (a) Quartz D i o r i t e •••• (b) Quartz F e l d s p a r P o r p h y r y (c) .Yukon S c h i s t s 'Weathering •. • • Hydrothermal A l t e r a t i o n Structure  9 10 10 -10 12 15 15 17 18  PART V  20  MINERALOGY  G e n e r a l C h a r a c t e r i s t i c s o f The Ore Texture and C o m p o s i t i o n o f V e i n M a t e r i a l Metallic Minerals Paragenesis Conclusions  20 21 23 28 29  PART V I ORIGIN OF THE ORE DEPOSIT.. 31 1. 2.  Source o f The Ore S o l u t i o n s Comparisons W i t h Other M i n e r a l D e p o s i t s (a) I n t r o d u c t i o n (b) M i n e r a l o g i c a l Comparisons (c) Age o f D e p o s i t i o n ' (d) S t r u c t u r a l Comparisons (e) W a l l Rock A l t e r a t i o n  3.  Conclusions  31 32 32 32 34 34 v . .. 35 35  TABLE OF CONTENTS PART V l l 1. 2.  3. 4. 5. 6.  DEVELOPMENT OF THE MINE ...  D i s c o v e r y . .• Diamond D r i l l i n g (a) P l a n 1. .. (b) D r i l l i n g Problems Surface S t r i p p i n g Underground Development T r a n s p o r t a t i o n Problems Power Problems  PAGE  ..  37 37 38 38 38 39 40 40 41  J  LIST OF ILLUSTRATIONS FACING PAGE F i g u r e 1.  L o c a t i o n o f Mine  2 ) 5,) Photographs i l l u s t r a t i n g 4 ) o f the r e g i o n s 5' )  2 3 3 4 4  topography  ,6 ) Photographs o f the A r e a 7 )  5 5  8 ))Gamera L u c i d a drawings o f t h i n s e c t i o n s 9 ) "  12 12  ,10 ) Camera L u c i d a drawings of t h i n s e c t i o n s  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 f o r m a t i o n i n the ore 14 ) 15 Photomicrograph of V e i n M a t e r i a l  21  16 17 18 19 20 21 22 23  ) ' ) ) Photomicrographs o f Ore M i n e r a l s ) . ) ) ) ) .  23 23 24 24 26 26 27 27  24  Photograph o f a b u l l d o z e r t r e n c h  39.  22  LIST OF MAPS. 1.  Hansen & V i c t o r i a Creek Areas  2.  B i g Thing Mineral Claim  7  ( i n s i d e back c o v e r )  INTRODUCTION' PART 1  .  Although  the Carrnacks d i s t r i c t , has been known to,  p r o s p e c t o r s and g e o l o g i s t s s i n c e the K l o n d i k e g o l d 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 t h e p a s t few y e a r s .  The  e a r l y g o l d - s e e k e r s n o t i c e d t h a t t h e r e was p l a c e r g o l d i n p a r t s o f the d i s t r i c t b u t 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 t o the n o r t h .  Between 1910 and 1920 some i n t e n s i v e  p l a c e r p r o s p e c t i n g was c a r r i e d out i n t h e area around Nansen and V i c t o r i a c r e e k s , b u t t h i s proved  t o be u n p r o f i t a b l e .  About 15 years ago the F r e e g o l d M o u n t a i n l o d e  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 l o n g .  The  c u r r e n t 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 t h e d i s c o v e r y of g o l d near V i c t o r i a Creek by George McDade. From the f o r e g o i n g statements  one can see t h a t t h e 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 p r e s e n t there a r e no p r o d u c i n g lode g o l d mines i n the Yukon.  The s u c c e s s f u l development o f the Brown McDade  p r o p e r t y i n t o a p r o d u c i n g mine would t h e r e f o r e be o f g r e a t v a l u e t o the whole t e r r i t o r y . f o r s i m i l a r occurrences the northwest  I t would s t i m u l a t e the s e a r c h  i n the b e l t o f c o u n t r y e x t e n d i n g t o  f o r 40 o r 5 0 . m i l e s .  The w r i t e r spent f i v e months i n 1946 a t t h e Brown McDade p r o p e r t y 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 M i n i n g  near the s o u t h e r n boundary of the Carmacks Map at  Area.  It is  an e l e v a t i o n o f 4000 f e e t on Pony Greek, a t r i b u t a r y o f  V i c t o r i a Creek. to  Division  Carmacks, on the Lewes R i v e r , l i e s 35  miles  the e a s t . From the town of. W h i t e h o r s e , a c c e s s may  the p r o p e r t y i n t h r e e ways.  The  a i r p l a n e 115 m i l e s n o r t h w e s t .  be o b t a i n e d  to  most d i r e c t r o u t e i s by  Planes l a n d 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 , b o t h w i t h i n s i x m i l e s of the camp. The  r o u t e over w h i c h s u p p l i e s are b r o u g h t i n , i s by motor  r o a d , 150 m i l e s to A i s h i h i k , thence by t r a c t o r t r a i l miles northward.  A t h i r d r o u t e , seldom u s e d , i s by  boat t o Carmacks and by pack t r a i l 2. . Physiography The  and  the r e m a i n i n g  40 river  distance."  Glaciation:  N a n s e n - V i c t o r i a Creek a r e a 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 P l a t e a u p h y s i o g r a p h i c p r o v i n c e , w h i c h corresponds  i n a g e n e r a l way  w i t h the i n t e r i o r P l a t e a u  r u n n i n g n o r t h w e s t e r l y through B r i t i s h Columbia..  The  term  p l a t e a u does not i m p l y t h a t ~ t h e l a n d s u r f a c e i s f l a t . ,  To  the o b s e r v e r the d i s t r i c t p r e s e n t s 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 o f an east-west  line.  The  average e l e v a t i o n o f the h i l l s  r i d g e s i s a p p r o x i m a t e l y 4200 f e e t .  south and  To the n o r t h and h o r t h -  FIGURE  2  Headwaters o f 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 n o r t h w e s t . Left: Right:-  Headwaters of Nansen Creek. Headwaters o f V i c t o r i a Creek.  west the mountains of the Dawson Range r i s i n g t o h e i g h t s 6400 f e e t , i n t e r r u p t the p l a t e a u s u r f a c e .  of  S m a l l e r ranges o r  even i n d i v i d u a l mountains s t a n d i n g above the g e n e r a l  level,  are n o t i c e a b l e i n o t h e r d i r e c t i o n s . I t i s b e l i e v e d by B o s t o c k ( l ) t h a t the  physiographic  h i s t o r y i s t h a t of a mature g e n t l y r o l l i n g u p l a n d s u r f a c e , u p l i f t e d before sequently  the c l o s e of the Miocene p e r i o d and  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 .  not c o n s i d e r t h a t i t r e p r e s e n t e d  a peneplain  subHe  does  o r even a  c o n d i t i o n of old-age because t h e r e i s a r e l i e f of over f e e t i n the s u r f a c e . 1000  The  present  streams have cut down about  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  of more t h a n 3000 f e e t .  The  500  relief  stream v a l l e y s are b r o a d  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 i m p r e s s i o n gained  i s t h a t the p r e v a i l i n g  drainage p a t t e r n t r e n d s n o r t h w e s t - s o u t h e a s t . the p a t t e r n t h a t was  This i s  probably  s e t up d u r i n g e a r l y T e r t i a r y times but i t  has b e e n ' c o m p l i c a t e d s i n c e , by the u p l i f t and p o s s i b l y by glacial action.  Some l a r g e streams c u t t i n g a c r o s s  t r e n d , seem to i n t e r r u p t the e a r l y pattern."  The  the  general  Nisling  and  K l a z a R i v e r s 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 of the Yukon.  On the Carmacks map  sheet B o s t o c k (1) i n d i c a t e s  the w e s t e r n boundary of the l a s t e x t e n s i v e sheet.  According  t o him  part  Pleistocene ice  i t extends i r r e g u l a r l y n o r t h w a r d ,  p a s s i n g about 20 m i l e s t o the east o f the mine.  Of  this  FIGURE 4  The v a l l e y o f V i c t o r i a Creek, l o c k i n g N o r t h . F l a t a r e a i n f o r e g r o u n d composed o f 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 s a y s , "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.  It  a p p r o x i m a t e l y marks the boundary of the c o u n t r y ' i n which g l a c i a l phenomena due t o the l a s t main g l a c i a t i o n are f r e s h and w i d e s p r e a d " . 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 s u c h ,as a b o u l d e r c l a y found i n Nansen C r e e k , b e l o n g t o an e a r l i e r glaciation.  A l t h o u g h t h i s f o r m a t i o n was n o t seen by the  w r i t e r , he doesn't b e l i e v e t h a t i t i s due t o a w i d e s p r e a d i c e sheet but r a t h e r t o 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 m i l e s 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 . or g l a c i a l e r r a t i c s .  There i s an absence of d r i f t ,  I n s t e a d , the s u r f a c e i s c o v e r e d by a  t h i c k mantle o f weathered m a t e r i a l c o n t a i n i n g l o o s e a n g u l a r fragments of r o c k , s i m i l a r i n c o m p o s i t i o n t o the u n d e r l y i n g o r nearby f o r m a t i o n s .  T h i s m a n t l e , 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 u s u a l 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 , b e i n g w e l l o x i d i z e d and showing a g r a d u a l c o n s o l i d a t i o n downward-into the bed-rock. f e e t are common.  Depths of mantle up. t o 10  Supporting t h i s b e l i e f that g l a c i a t i o n  was  not w i d e s p r e a d i n the a r e a i s the l a c k of any g l a c i a l modifi c a t i o n s of the mature topography of the a r e a . The v a l l e y s of V i c t o r i a and Nansen Creeks and t h a t of the N i s l i n g R i v e r , i n t o which t h e y 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  L o o k i n g southwest from Brown McDade Mine, i n d i c a t e s ore zone.  Arrow  S k y l i n e o f Yukon P l a t e a u i n background. FIGURE 7  r  L o o k i n g s o u t h e a s t a c r o s s the Yukon P l a t e a u  ^  .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 w h i c h the p r e s e n t The  streams have cut t o depths of 75 f e e t .  N i s l i n g R i v e r has  eroded i t s t e r r a c e s so t h a t o n l y  remnants are l e f t , b u t i n the t r i b u t a r y creeks w e l l developed and e x t e n s i v e . i s not c l e a r .  One  The  they are  o r i g i n of these  very  deposits  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 d e p o s i t e d . (3)  C l i m a t e and  Vegetation:  The. c l i m a t e i s t y p i c a l of the whole i n t e r i o r region.  I t i s c h a r a c t e r i z e d by a medium t o low  p r e c i p i t a t i o n and due temperature.  The  plateau  annual  t o i t s n o r t h e r n l a t i t u d e , a low mean  l a k e s and streams f r e e z e o v e r i n l a t e (  October or November w h i l e the S p r i n g breakup occurs June.  i n May  or  S n o w f a l l i s not heavy, u s u a l l y b e i n g not over t h r e e  f e e t deep a t any t i m e .  During  the Summer t h e r e i s a  wet  p e r i o d i n J u l y and e a r l y A u g u s t . The  c h i e f forms of v e g e t a t i o n are mosses and low  brush.  These c o v e r almost the whole l a n d s u r f a c e l i k e a t h i c k c a r p e t The  t r e e s are s t u n t e d and grow i n g r o v e s , u s u a l l y on  w e l l drained southern  slopes.  the  Spruce i s the main t r e e  and  has been seen up t o 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 c o n s i d e r a b l y l e s s t h a n t h i s . -  stands  Sparse  of cottonwood t r e e s 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 s e d i m e n t a r y and v o l c a n i c r o c k s , t h e Yukon group, o v e r l a i n by sediments and v o l c a n i c s o f Mesozoic age. I n t r u d i n g t h e s e a r e numerous b o d i e s o f 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 r o c k s w i t h a wide v a r i e t y o f compositions.  T e r t i a r y v o l c a n i c flows are extensive  i n the  Carmacks a r e a a l t h o u g h not l o c a l l y p r e s e n t i n t h e v i c i n i t y of the Brown McDade Mine.  A l l i e d t o these are i n t r u s i v e  p l u g s , dykes and i r r e g u l a r b o d i e s of p o r p h y r i t i c r o c k s , w h i c h are presumed t o be of L a t e T e r t i a r y age. fills  alluvium  most o f the v a l l e y s and a l a y e r o f v o l c a n i c a s h c o v e r s  the p r e s e n t l a n d (2)  Recent  surface.  Formations; TABLE OF FORMATIONS  Recent  Alluvium,  Late T e r t i a r y  Quartz p r o p h y r y , g r a n i t e p o r p h y r y , granophyre, rhyolite.  Miocene o r O l d e r  Carmacks Volcanics  ash, etc.  Basalt, andesite, breccia, tuffs.  dacite,  Granite, granodiorite, etc S y e n i t e , monzonite, e t c . D i o r i t e , gabbro, e t c .  Upper J u r a s s i c o r Later Upper J u r a s s i c o r Lower Cretaceous  Mt.Nansen Group  paleozoic or Pre-Cambrian  Yukon Group  Andesite, b a s a l t , dacite, b r e c c i a s , t u f f s , and some sediments. quarts-mica s c h i s t , hornblende s c h i s t , q u a r t z i t e , g n e i s s and l i m e s t o n e .  NANSEM  &  VICTORIA  CREEKS  CARMALKS  AREA  YUKON SCALE  1M  = 1 Ml.  LEGEND MODERN RECEA/T Cl'/v vium  *  f  , ask  etc  TERTIARY  4' 7  porphyry  ,  r  IGVEOUS jra.  Mr.  ^J°  ROCKS  no diortte.5  NANSEN  et.  MESOLO/C  GP  ct ndesite , ba&atl'  Irccc/aS  PRE-CAM3. YUKON  schists , <yi/<3r/zi/es, /ime&tone.  ii ii n 11  &  GP. ysre/sses  LATER.  The f o r e g o i n g t a b l e i s d e r i v e d from t h a t .given by Bostock  (1).  i t has .been s h o r t e n e d to i n c l u d e o n l y the  r o c k s shown on the accompanying maps. (a) Yukon Group T h i s group c o n s i s t s of c r y s t a l l i n e r o c k s of 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  a l t h o u g h i n the V i c t o r i a Greek'area The  sedimentary gneissic,  t h e r e >is some q u a r t z i t e .  t o t a l t h i c k n e s s of the f o r m a t i o n s i s v e r y g r e a t but i s  not known. The  1  s t r u c t u r e i s t h a t 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 g e n e r a l t r e n d to the n o r t h e a s t . a i p s observed  are v a r i a b l e , up to 35  The  degrees.  These r o c k s are the o l d e s t i n the d i s t r i c t b e i n g  over-  • l a i n unconformably or i n t r u d e d by a l l o t h e r f o r m a t i o n s . e x a c t age  i s unknown, except t h a t i t i s P r e - T r i a s s i c .  The Some  of the members of the group are l o c a l l y c o n s i d e r e d t o be  Pre-  Gambrian r o c k s a l t h o u g h 60 m i l e s to the n o r t h a few P a l e o z o i c f o s s i l s have been f o u n d . (b)  Mount Nansen Group These r o c k s i n c l u d e v a r i e t i e s o f ' a n d e s i t e s and b a s a l t s  w h i c h to some e x t e n t 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 associated intrusives. greenish gray.  The  and  predominant c o l o r i s a dark  The r o c k s are not r e g i o n a l l y metamorphosed  l i k e the Yukon group,upon which t h e y l i e u n c o n f o r m a b l y w i t h a low angle of -dip. The  age of the group has been determined  as b e i n g not o l d e r than Upper J u r a s s i c .  by B o s t o c k  T h i s i s based  on  (1)  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 (c)  f o r m a t i o n s i n the r e g i o n of Carmacks.  Mesozoic I n t r u s i v e s I n c l u d e d i n t h i s group are many r o c k t y p e s , r a n g i n g  from b a s i c t o a c i d i c .  In the V i c t o r i a - N a n s e n Creek a r e a ,  t h e y have the c o m p o s i t i o n of g r a n i t e s , g r a n o d i o r i t e s • and q u a r t z 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 f e l d s p a r s , q u a r t z , b i o t i t e , hornblende  contain  and minor a c c e s s o r y  minerals. The  age  of these i n t r u s i v e s i s known t o be younger than  the Mt. Nansen group.  Bostock  i n t r u s i v e s of the main J u r a s s i c or l a t e r (d)  (1)  c o r r e l a t e s them w i t h the  Coast Range B a t h o l i t i i , p r o b a b l y of  age.  Tertiary Acid Intrusives < Numerous s m a l l b o d i e s and dykes of a c i d i c ,  intrusive,-  p o r p h y r i t i c rocks o u t c r o p i n the d i s t r i c t and n o r t h w e s t  along  the Dawson Range.' They i n c l u d e types r a n g i n g from g r a n i t e p o r p h y r i e s t o 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  r o c k s are c h e r t y 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 conspicuous phenocrysts  of q u a r t z and f e l d s p a r s .  The'"quartz i s  h a r d 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 o n l y c a s t s i n the r o c k .  I t i s b e l i e v e d t h a t these are the .  i n t r u s i v e s t o 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 , w h i c h are not found i n the immediate map such t h a t t h e y are c o n s i d e r e d to be of L a t e T e r t i a r y  a r e a , are age.  (e)  Recent D e p o s i t s : Unconsolidated  the v a l l e y bottoms  d e p o s i t s of a l l u v i a l o r i g i n are found i n as the products  o f e r o s i o n o f the o l d e r  rocks. C o v e r i n g the whole c o u n t r y f o r many m i l e s 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 m i l e s t o the s o u t h .  It is  l i g h t g r a y i n c o l o r and averages about s i x inches t h i c k . some p l a c e s two l a y e r s may of e a r t h .  be seen, s e p a r a t e d by a few  A t h i n b l a c k compact l a y e r o f carbonaceous  In  inches matter  l i e s i m m e d i a t e l y below the a s h , p r o b a b l y the remains of o r g a n i c m a t e r i a l b u r i e d by the f a l l  of the ash.  Bostock  e s t i m a t e s that- i t o r i g i n a t e d w i t h i n the p a s t 2000 years  (1) from  a v o l c a n o t o the west or southwest. LOCAL GEOLOGY PART IV ' 1.  "  /  Introduction: U n t i l the time the w r i t e r l e f t the Brown McDade p r o p e r t y ,  the o n l y 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  o b t a i n e d from  r o c k o u t c r o p s , b u l l d o z e r t r e n c h e s and about 13 short•diamond d r i l l holes.  The  s u r f a c e o f the ground i s almost  totally  c o v e r e d by a t h i c k mantle of o v e r b u r d e n , w i t h v e r y few crops.  As a r e s u l t o f these c o n d i t i o n s , s o m e  expressed  of the  on the f o l l o w i n g - pages are put f o r t h  out-  opinions  tentatively,  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 Big  c o n f i n e d t o two m i n e r a l c l a i m s , the  Thing and p a r t of the G l o u s e r , hence the d i s c u s s i o n w i l l  10 c e n t r e around t h e s e r a r e a s . The B i g Thing i s s i t u a t e d a c r o s s a low s a d d l e - l i k e r i d g e between Pony Greek, and Dome Greek to the s o u t h , b o t h of w h i c h are t r i b u t a r y t o V i c t o r i a Creek.  It  i s near the s o u t h e r n end of the Brown McDade group of c l a i m s , w h i c h extends 2.  two m i l e s n o r t h , beyond Pony Creek.  General D e s c r i p t i o n ; I n a pocket on the i n s i d e r e a r cover o f the r e p o r t i s a  map  of the w o r k i n g Areas  ( s c a l e 40 f e e t = 1 i n c h ) , which  be of v a l u e i n c l a r i f y i n g the f o l l o w i n g Outcropping  will  discussion.  on the c l a i m s and presumably u n d e r l y i n g most  of the area i s q u a r t z d i o r i t e . the B i g T h i n g M.C., of the Yukon Group.  Near the s o u t h e r n boundary of  t h e r e i s a s m a l l area u n d e r l a i n by The  schists  c o n t a c t between the q u a r t z 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 t o r u n  east-west.  C u t t i n g the q u a r t z 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 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 p o r p h y r y , N25° W and d i p p i n g 55 to 70° westward'.  an striking  A w e l l d e f i n e d ore  zone, 10 t o 15 f e e t i n w i d t h 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, a p p a r e n t l y conforming porphyry.  i n s t r i k e and d i p w i t n the  S u b s i d i a r y zones o f m i n e r a l i z a t i o n o c c u r  parallel  t o and b r a n c h i n g from the main zone. 3.  Rock Types: (a)  Quartz  Diorite;  The t y p i c a l q u a r t z d i o r i t e i n the hand specimen i s a g r a y , medium g r a i n e d r o c k o f a g r a n i t i c t e x t u r e .  I t i s composed of  w h i t e 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 Quartz  i s v i s i b l e but not abundant.  hornblende.  Minor amounts of e p i d o t e  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 w i d e l y through, the r o c k . The p y r i t e i s i n the form o f s m a l l masses o r 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 . c o l o r and c o m p o s i t i o n  Local variations i n texture,  are common.  These a r e p r o b a b l y  due,  e i t h e r to i n c l u s i o n s o f country rock, or segregation of c e r t a i n masses w i t h i n the magma b e f o r e  its final  solidification.  T h i n s e c t i o n study of the q u a r t z 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  m i n e r a l c o n s t i t u e n t s of the r o c k , t o g e t h e r w i t h the h o r n blende which i s of the common green v a r i e t y , compose 90 p e r cent o r more of the mass.  Q u a r t z i s found i n a n h e d r a l  u s u a l l y much s m a l l e r than the two major m i n e r a l s .  grains,  I t i s not  e v e n l y 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 s m a l l g r a i n s between the f e l d s p a r s .  A few rounded g r a i n s  of e a r l y p r i m a r y q u a r t z l i e as i n c l u s i o n s i n the h o r n b l e n d e . Epidote  i s present  as a secondary m i n e r a l formed by the  a l t e r a t i o n of f e l d s p a r s and h o r n b l e n d e , and i s o f t e n seen around the margins o f 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 .  Certain  i r r e g u l a r areas of c h l o r i t e around t h e hornblende a r e formed as an a l t e r a t i o n p r o d u c t of t h a t m i n e r a l . opaque m i n e r a l p r o b a b l y  Streaks  o f an  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 .  T h i s may be the r e s u l t o f  a l t e r a t i o n o f a hornblende w i t h a h i g h content  of i r o n .  A c c e s s o r y m i n e r a l s , seen i n the sect-ion i n minor amounts a r e 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 o f s m a l l g r a i n s s c a t t e r e d t h r o u g h the r o c k .  euhedral  FIGURE  8  T h i n s e c t i o n o f a u a r t z f e l d s p a r p o r p h y r y , taken diamond d r i l l c o r e , near the ore zone. Camera l u c i d a drewing M a g n i f i e d 20 d i a m e t e r s .  FIGURE  from  9  T h i n s e c t i o n o f c u a r t z d i o r i t e , t a k e n f r o c diamond d r i l l core. Camera l u c i d a drawing M a g n i f i e d 20 d i a m e t e r s .  12 There i s c l o u d i n e s s i n the f e l d s p a r s i n t h i n  section,  caused by the development o f s e r i c i t e i n t i n y s c a t t e r e d ' s h r e d s o r i n l a r g e r masses.' A l l the f e l d s p a r s show more o r l e s s a l t e r a t i o n to s e r i c i t e . The q u a r t z d i o r i t e s u n d e r l y i n g t h e B i g Thing M.C. mapped by B o s t o c k  are  (1) as a p a r t o f one f o r m a t i o n t h a t i n c l u d e s  several g r a n i t i c types.  Two d i s t i n c t types o t h e r t h a n t h a t  j u s t d e s c r i b e d have been n o t i c e d by the w r i t e r w i t h i n a m i l e of the p r o p e r t y .  The one i s a s l i g h t l y f i n e r g r a i n e d g r a y i s h  rock,probably a d i o r i t e .  The o t h e r has the c o m p o s i t i o n of a  t r u e g r a n i t e w i t h f e l d s p a r , q u a r t z , a n d ' b i o t i t e as the c h i e f constituents. Figure $ ' (b)  These r o c k s were n o t s t u d i e d i n d e t a i l . ( f a c i n g page], i l l u s t r a t e s the q u a r t z  Quartz F e l d s p a r  diorite.  Porphyry:  The c o m p o s i t i o n of t h i s r o c k 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.  It  c o n t a i n s w i d e l y s c a t t e r e d q u a r t z as the o n l y type of phenoe r y s t s , o r c o n t a i n s b o t h q u a r t z 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 the phenoerysts  occur  are abundant and c l o s e l y packed.  The t y p i c a l porphyry' i s a g r a y t o b u f f c o l o r e d a p h a n i t i c r o c k c o n t a i n i n g s c a t t e r e d e u h e d r a l phenoerysts  of q u a r t z and  w h i t e f e l d s p a r s , t o an approximate s i z e o f one e i g h t h o f an inch.  I t i s dense and h a r d w i t h a s u b - c o n c h o i d a l  fracture.'  Weathering has reduced  cherty  the f e l d s p a r s t o s o f t  gray  powdery masses or e l s e has removed them c o m p l e t e l y , l e a v i n g o n l y t h e i r c r y s t a l o u t l i n e s i n the m a t r i x .  The q u a r t z 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 o f the porphyry i s  seen to he composed o f a c r y p t o c r y s t a l l i n e mosaic of q u a r t z and v e r y h i g h l y s e r i c i t i z e d , c l o u d y f e l d s p a r . g r a i n s i z e i s 0.05 ram. The q u a r t z was e a s i l y  The average identified  but the c l o u d i n e s s of the f e l d s p a r g r a i n s t o g e t h e r w i t h t h e s m a l l 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 g r a i n s a t the edge of the t h i n s e c t i o n showed them t o be l e s s than t h a t o f balsam. Dr. Watson o b t a i n e d s e v e r a l n e g a t i v e 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 t h 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 q u a r t z phenoerysts In  show some i n t e r e s t i n g f e a t u r e s .  most of them the o r i g i n a l e u h e d r a l o u t l i n e has been  m o d i f i e d by the c o r r o d i n g e f f e c t of the magma i n w h i c h 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 q u a r t z g r a i n s , showing deep i n d e n t a t i o n s where they are embayed by the groundmass. Mo. to  opposite page^ i l l u s t r a t e s t h i s p o i n t .  Figure  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 q u a r t z around the b o u n d a r i e s , 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 p r e s s u r e , o r a d d i t i o n of q u a r t z .  T h i s process has formed  narrow r i n g s of f i n e g r a i n e d q u a r t z around the p h e n o e r y s t s . The f e l d s p a r phenoerysts oligoclase-andesine.  a r e composed l a r g e l y of  They are a l l more o r l e s s a l t e r e d t o  s e r i c i t e and some c a r b o n a t e , b e i n g q u i t e c l o u d y i n t h i n s e c t i o n . I n p l a c e s the a l t e r a t i o n has l e f t o n l y c l u s t e r s of s e r i c i t e i n  FIGURE 10 T h i n s e c t i o n o f o u s r t z f e l d s p a r porphyry taken from "The Dome", o u t c r o p p i n g 1 m i l e west of the ore zone. Camera l u c i d a drawing M a g n i f i e d 20 d i a m e t e r s .  FIGURE 11 T h i n s e c t i o n of c u a r t z f e l d s p a r p o r p h y r y , taken a diamond d r i l l h o l e near the ore zone. Camera l u c i d a drawing M a g n i f i e d 20 d i a m e t e r s .  from  14 trie m a t r i x , some w i t h vague o u t l i n e s s u g g e s t i v e of o r i g i n a l feldspar crystals.  Some f e l d s p a r s have t h i n bands of i n t e n s e  a l t e r a t i o n around t h e i r rims w h i l e the i n t e r i o r s of the c r y s t a l s are c o m p a r a t i v e l y f r e s h . Specimens of q u a r t z f e l d s p a r porphyry  taken near the ore  zone c o n t a i n c o n s i d e r a b l e e p i d o t e i n the groundmass and to a l e s s e r e x t e n t i n the f e l d s p a r p h e n o e r y s t s .  I t has  formed  p r o b a b l y as the metamorphic p r o d u c t 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 f e r r o m a g n e s i a n  minerals.  There i s o f t e n an  a s s o c i a t i o n o f c h l o r i t e and e p i d o t e i n such a way as to suggest  an o r i g i n a l f e r r o m a g n e s i a n  pletely altered.  m i n e r a l which has been com-  I n some p l a c e s the c h l o r i t e i s q u i t e  n o t i c e a b l e i n the r o c k .  S c a t t e r e d s p a r s e l y through  the  porphyry are t i n y e u h e d r a l c r y s t a l s of p y r i t e , most of w h i c h 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  e u h e d r a l c r y s t a l s d i s s e m i n a t e d through the m a t r i x . t h e r e i s an abundance o f carbonate  Locally  i n the form o f s m a l l 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 q u a r t z f e l d s p a r porphyry,  out-  c r o p p i n g '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 m i l e west of the mine.  Both i n the hand specimens and i n t h i n s e c t i o n s 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 r o c k l o c a t e d i n the holes.  The  suggest  they o r i g i n a t e d from the same s o u r c e .  and No. H  drill  s i m i l a r i t y between these r o c k s i s such as t o  f a c i n g Page  F i g u r e No. 'O  show t h i n s e c t i o n s of both r o c k s .  The f i e l d r e l a t i o n s between the two w i l l be d i s c u s s e d 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 o n l y to' those  of the Yukon.group which a r e exposed i n t r e n c h "No.  rocks  8 near the  s o u t h e r n boundary o f the B i g Thing c l a i m . . No t h i n s e c t i o n s of t h i s r o c k were s t u 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 o f muscovite t h r o u g h o u t .  I t feels slightly  g r e a s y and has w e l l developed s c h i s t o s i t y a l o n g planes.  several  T h i s s c h i s t o s i t y c a u s e s i t t o break i n t o s p l i n t e r y  fragments.  I n the f i e l d t h i s r o c k 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  r o c k s a d j a c e n t to the ore zone and a t l e a s t s e v e r a l  hundred f e e t of the q u a r t z 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 t o 200 f e e t deep.  On the  f o o t w a l l s i d e .of the zone, the q u a r t z  diorite i s fresh i n  appearance and n o t h i g h l y f r a c t u r e d .  The l a c k o f g l a c i a l  s c o u r i n g has a l l o w e d remain u n d i s t u r b e d ,  the r e s i d u a l weathered m a t e r i a l s t o probably since T e r t i a r y time,for i t i s  l i k e l y t h a t the g r e a t e s t p a r t of the w e a t h e r i n g t o o k p l a c e p r i o r t o the P l e i s t o c e n e P e r i o d , b e f o r e f r o s t l a y e r i n the ground. breaking  t h e r e was a permanent  The w e a t h e r i n g has r e s u l t e d i n a  down of the e s s e n t i a l rock f o r m i n g m i n e r a l s  q u a r t z w h i c h remains u n a l t e r e d .  except  The p r o d u c t s formed are  l i m o n i t e , k a o l i n i t e , some c a r b o n a t e , and j a r o s i t e , a l l o f which have changed the c o l o r s of the rocks  t o a r u s t y brown  16 or b u f f shade.. While the o r i g i n a l t e x t u r e s of b o t h the p o r p h y r y and the q u a r t z d i o r i t e are o f t e n v i s i b l e ,  the  f e r r o m a g n e s i a n 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 o n l y 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  with limonite.  On the s u r f a c e of the b e d r o c k a b l a c k  i s o f t e n p r e s e n t as a t h i n f i l m . d e n d r i t i c p a t t e r n suggestive accumulation. has  stain  I n t i n y f r a c t u r e s i t has  a  of secondary manganese  Immediately above the ore zone the overburden  a p e c u l i a r lemon-yellow to brown c o l o r q u i t e 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 s u r r o u n d i n g m a t e r i a l . I t i s formed as a t h i n c o a t i n g over the fragments of ore 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 .  and  Chemical a n a l y s i s  r e v e a l e d the presence of a c o n s i d e r a b l e amount of  sulphate,  w h i l e a s p e c t r o g r a p h i c a n a l y s i s showed l e a d and a r s e n i c .  It  i s b e l i e v e d t h a t t h i s i s a secondary m i n e r a l formed by weathering  of the ore m i n e r a l s , w i t h the p o s s i b l e c o m p o s i t i o n  a r to a j a r o s i t e .  simil-  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  means used t o i d e n t i f y the m i n e r a l w i l l be found i n P a r t  and 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 t o the same e x t e n t as the w a l l r o c k s . ore appears q u i t e f r e s h a t the s u r f a c e .  In f a c t  the  I n p l a c e s , however,  the p y r i t e has been l e a c h e d away l e a v i n g o n l y a honeycomb mass of q u a r t z .  The  i t s disseminated  nature may  weathering  comparative s c a r c i t y of s u l p h i d e  i n much of the  and  account f o r the apparent l a c k of ore.  17 5.  Hydrothermal  Alteration;  S e r i c i t i z a t i o n i s the main form of w a l l r o c k a l t e r a t i o n . I t i s p r e s e n t b o t h i n the q u a r t z 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 q u a r t z d i o r i t e t h e r e i s a s t r o n g development o f 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  d i s p e r s e d s h r e d s , g i v i n g t o the f e l d s p a r s a v e r y c l o u d e d appearance.  I t i s a l s o i n confused masses of minute f l a k e s ,  c o m p l e t e l y r e p l a c i n g the o r i g i n a l m i n e r a l s .  In the porphy-  r i t i c r o c k s the s e r i c i t i z a t i o n i s s t r o n g i n the groundmass and the p h e n o c r y s t s . A more d e t a i l e d d i s c u s s i o n o f the f i e l d  o c c u r r e n c e of a  p o r p h y r i t i c r o c k o u t c r o p p i n g a m i l e west of the m i n e , i s i n P a r t VI , 1.  found  I t i s w o r t h n o t i n g a t t h i s p o i n t , however,  the a l t e r a t i o n i n the r o c k .  L i k e the porphyry found on the  p r o p e r t y , 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 c o n s i d e r e d t o 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 ter  t h a t 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 o f 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 t i o n s t h a t t h e r e 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 u n d e r s t o o d . There i s some development o f carbonate i n the r o c k s , 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 G e n e r a l i z e d Cross S e c t i o n o f a Diamond D r i l l H o l e , i l l u s t r a t i n g the S t r u c t u r e o f the Brown McDade Ore Zone. S c a l e 1 i n c h = 40 f e e t .  18 f l a k e s , shreds or s m a l l 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 t o be a major a l t e r a t i o n except i n c o n t a c t w i t h the ore zone, where w a l l rocks'some-" times show replacement by f i n e g r a i n e d  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 c t i o n s of the ore zone. P y r i t e and e p i d o t e are common i n many of the  igneous  r o c k s i n the Carmacks A r e a , as d e s c r i b e d by B o s t o c k ( 1 ) . w r i t e r confirms  t h i s statement from p e r s o n a l  The  observations.  There i s a l s o no e v i d e n c e to show t h a t they i n c r e a s e i n abundance near the ore zone.  Therefore  i t i s believed that  these m i n e r a l s are the r e s u l t of r e g i o n a l metamorphism  and  are not connected w i t h the h y d r o t h e r m a l s o l u t i o n s t h a t d e p o s i t e d the Brown McDade ore body. 6.  S t r u c t u r e of the Ore F i g u r e No.  A?  f a c i n g t h i s page r e p r e s e n t s 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 12a  inclusive.  Body;  of the diamond d r i l l h o l e s , 2a t o  I t i s g i v e n t o show the r e a d e r how  knowledge of the s t r u c t u r e was ion  obtained.  the  Knowing the  of the ore on the s u r f a c e , the p o s i t i o n  posit-  of the h o l e ,  and  the p o i n t s at which the h o l e i n t e r s e c t s the p o r p h y r i t i c r o c k and the ore zone, i t was ore i n t h a t h o l e , and porphyry and  p o s s i b l e t o c a l c u l a t e the d i p of the  the r e l a t i o n s h i p s between o r e ,  quartz d i o r i t e .  a l l the h o l e s .  The  This procedure was  repeated  in  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 w i d t h of 10 to 15 f e e t  and  19  d i p s 55 to 70° 'westward. (b)  S m a l l e r v e i n s e x i s t , p a r a l l e l to and b r a n c h i n g from the  main ore zone. (c)  The  ore zone l i e s w i t h i n a q u a r t z f e l d s p a r porphyry  rock  i n every h o l e t h a t i n t e r s e c t s i t . (d)  The  f i n e g r a i n e d a l t e r e d gray r o c k i n the b u l l d o z e r  t r e n c h e s , t h a t l i e s on e i t h e r s i d e o f the ore zone, i s p r o b a b l y a s u r f a c e phase o f the q u a r t z 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 p o r p h y r y , v a r y 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 q u a r t z (f)  The presence  t r e n c h e s No.  diorite.  of s t i c k y c l a y gouge near the ore zone i n  5 and 2,  of the, o r e , suggest  and the b r e c c i a t e d appearance of much c o n s i d e r a b l e movement and s h e a r i n g .  Summing up the above f a c t s g i v e s 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 o f q u a r t z f e l d s p a r porphyry  which  s t r i k e s N. 25 degrees W and d i p s about 60° westward.  The'  p o r p h y r i t i c r o c k i s younger than, and c u t s the c o u n t r y r o c k , a quartz d i o r i t e . a l o n g the ore zone.  Movement and s h e a r i n g have t a k e n p l a c e Post m i n e r a l 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 t r e n c h No. 2 and d r i l l h o l e s 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 S m i t h e r i n g a l e , were l o c a t e d l a t e r by d r i l l i n g . porphyry was  No t r a c e o f the o r e , or of the  found i n h o l e No. l a .  I t i s b e l i e v e d that a  f a u l t c u t t i n g , a c r o s s between t h i s h o l e and h o l e 2a  may  20 explain 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 t h e ore zone between trenches  No. 4  and No. 5. I n t r e n c h No. 8 n e a r the s o u t h e r n boundary o f t h e B i g T h i n g c l a i m the p o r p h y r y may be seen c u t t i n g the s c h i s t s , b u t 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 . yet known whether the ore zone w i l l  continue  d i o r i t e i n t o the s c h i s t s o r whether i t w i l l  I t i s not  from the q u a r t z d i e out near the  contact. PART V 1.  '. MINERALOGY  Introduction: The  vein material i s a bluish-gray cryptocrystalline  quartz c o n t a i n i n g f i n e l y disseminated sulphide content  L o c a l l y the  i s r e l a t i v e l y h i g h , b u t on the average i t i s  l e s s than 5 p e r cent o f the t o t a l is  sulphides.  (mass o f the o r e ' .  Pyrite  the p r i n c i p a l s u l p h i d e w i t h a r s e n o p y r i t e i n l e s s e r q u a n t i t i e s  and o n l y minor amounts o f o t h e r m e t a l l i c m i n e r a l s . Tfte ore commonly has a b r e c c i a t e d appearance, w i t h s m a l l a n g u l a r w h i t e fragments cemented i n a groundmass of s i l i c e o u s material.  These fragments resemble some o f the b l e a c h e d  gray  r o c k i n c l o s e p r o x i m i t y t o t h e ore zone and a r e thought t o have been o r i g i n a l l y o f the c o m p o s i t i o n porphyry.  o f the q u a r t z f e l d s p a r  S t u d i e s o f t h i n and p o l i s h e d s e c t i o n s o f v e 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 o f p y r i t e , a r s e n o p y r i t e and sphalerite.  Many o f the s m a l l vugs and d r u s y c a v i t i e s i n the  ore are f i l l e d w i t h i n w a r d p o i n t i n g q u a r t z c r y s t a l s and some a r e f i l l e d w i t h y e l l o w masses o f a j a r o s i t e m i n e r a l .  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 is noticeable occasionally  i n hand s p e c i m e n s , w i t h  interlocking  c r y s t a l s o f q u a r t z up t o one q u a r t e r i n c h i n l e n g t h .  On a  m i c r o s c o p i c s c a l e , comb s t r u c t u r e  veinlets  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  i s common, i n t i n y  groundmass.  Some banding i n  the v e i n has been seen, p a r a l l e l t o c o n t a c t s , b u t t h i s f e a t u r e i s not o f t e n observed.  Where £he ore zone was c u t by one of  the d r i l l h o l e s a t 125 f e e t v e r t i c a l d e p t h , structure of s e v e r a l section  botryoidal  was p r e s e n t i n the q u a r t z .  I t assumed the form  rounded masses c l u s t e r e d  t o g e t h e r , which i n c r o s s  showed a c o n c 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 t o the  surfaces. 2.  Texture and C o m p o s i t i o n o f V e i n  Material:  The q u a r t z i n t h e m a t r i x o f the ore i s e x c e e d i n g l y f i n e grained.  Under the h i g h e s t 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 , about 12 microns i n s i z e .  averaging  The m a t r i x i s c u t by v e i n l e t s and  masses o f c r y s t a l l i n e f i n e g r a i n e d q u a r t z .  I n comparison t o  the groundmass i t i s much c o a r s e r i n t e x t u r e . of t h i s l a t e r q u a r t z i s v a r i a b l e  The g r a i n  size  depending oh t h e w i d t h o f t h e  v e i n l e t b u t i t may be s a i d t o average 10 o r 15 times the s i z e of t h a t i n the groundmass. Large masses o f minute lemon y e l l o w c r y s t a l s a r e 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 q u a r t z i n the v e i n l e t s . characteristics.  They have the f o l l o w i n g  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 c h a r a c t e r of the ore and the g r a i n s i z e o f the groundmass (12 microns) M a g n i f i e d 31 d i a m e t e r s .  22 (a)  i n d e x of r e f r a c t i o n .....  (b)  b i r e f r i n g e n c e (^f?^A .^ . . fpA'".). . f o u r t h o r d e r or h i g h e r  .(c)  r  very high  c e  pleochroism  s l i g h t , yellow to l i g h t yellow  (d)  extinction  parallel  (e)  optical sign  uniaxial  negative.  Some of the e a r t h y y e l l o w c o a t i n g over s u r f a c e s e c t i o n s of the ore zone (see under "Weathering" i n P a r t IV) 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.  was 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)  color  lemon y e l l o w  crystals  (b)  form  h e x a g o n a l prisms  and  rhorabohedrons (c)  pleochroism  yellow to pale  (d)  i n d e x of r e f r a c t i o n ....  1.76  yellow  --1.78 +  I t i s b e l i e v e d t h a t the y e l l o w 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 i n d e x of r e f r a c t i o n i s found t o be about 1.75  the upper one  i s w e l l above  while  1.7S.  A l l the above p r o p e r t i e s suggest t h a t the m i n e r a l b e l o n g s t o the f a m i l y o f j a r o s i t e s .  The  j a r o s i t e s ' are complex  secondary hydrops s u l p h a t e s formed by the w e a t h e r i n g sulphide ores.  of  They are common i n the d e e p l y o x i d i z e d d e p o s i t s  of the southwestern  U n i t e d S t a t e s and many o t h e r 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 e u h e d r a l a p a t i t e . are p r o b a b l y o f hypogene o r i g i n .  These  FIGURE 16  P h o t o m i c r o g r a p h , showing j a m e s o n i t e ( j a ) and a r s e n o p y r i t e (as) i n o u a r t a . X  200  FIGURE  17  Photomicrograph showing jamesonite ( j a ) i n b r e c c i a t e d p y r i t e (py) X 200  23 3.  M e t a l l i c Minerals': " A- s t u d y of hand specimens and p o l i s h e d s e c t i o n s o f 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 , j a m e s o n i t e , b o u r n o n i t e and g o l d . (a) P y r i t e ; F e S  g  P y r i t e i s the main m e t a l l i c m i n e r a l i n the o r e .  It is  f i n e l y disseminated i n subhedral to anhedral grains ranging from s u b - m i c r o s c o p i c fragments to c r y s t a l s and masses a few millimetres across. the c r y s t a l s .  Cubes aid p y r i t o h e d r a are common forms of  F r a c t u r i n g and b r e c c i a t i o n of the  masses of p y r i t e has reduced  larger  them to f i n e r f r a g m e n t s ,  are cemented t o g e t h e r by l a t e r q u a r t z .  which  Much,of-the p y r i t e  i n the s u r f a c e showing has been p a r t i a l l y o r w h o l l y removed  • .  by w e a t h e r i n g , l e a v i n g o n l y r e s i d u a l l i m o n i t e o r a mass of honeycombed q u a r t z w i t h o n l y the c a s t s o f the o r i g i n a l to indicate t h e i r (b)  Arsenopyrite:  crystals  composition. FeAsS  T h i s m i n e r a l seems to be the second most abundant s u l p h i d e i n the o r e .  L i k e the p y r i t e i t occurs f i n e l y  disseminated,  rhombs and prisms b e i n g the commonest ' c r y s t a l forms.  I n hand  specimens i t i s r e c o g n i z e d as elongated' s i l v e r y w h i t e  crystals  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, observed  and where  i n s u r f a c e ore i t has been p a r t l y a l t e r e d t o l i m o n i t e .  I t seems t h a t a r s e n o p y r i t e i s not as e v e n l y d i s t r i b u t e d out the ore as. i s the, p y r i t e .  through-  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 o f d i s s e m i n a t e d a r s e n o p y r i t e i n a u a r t z X 65  24 (c)  Sphalerite:  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 v e r y d a r k brown w i t h a h i g h l y r e s i n o u s  luster.  I t appears to  l o c a l l y c o n c e n t r a t e d r a t h e r than e v e n l y d i s p e r s e d S m a l l v e i n l e t s of s p h a l e r i t e one have been o b s e r v e d . As  studied  quarter  i n the  '  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  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 , w h i l e as a replacement m i n e r a l . of s p h a l e r i t e has  It  contains  c o v e l l i t e i s common  A c e r t a i n amount of b r e c c i a t i o n  taken place  i n a s i m i l a r manner to t h a t  CuFeS  T h i s m i n e r a l has  2  been observed o n l y as minute b l e b s i n  s p h a l e r i t e , v i s i b l e under medium or h i g h m a g n i f i c a t i o n . determination  low/ r e l i e f which b e i n g about the same as the  Covellite:  surrounding  of s i m i l a r h a r d n e s s .  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 r e p l a c e d c o v e l l i t e w h i c h has  by  the appearance of a deep b l u e i r r e g u l a r  t a r n i s h on i t s s u r f a c e .  Under p o l a r i z e d l i g h t the  covellite  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 r e v o l u t i o n , w i t h b r i g h t r e d and (f.)  Galena:  purple  seen a few  per  colours,  PbS  None of the p o l i s h e d s e c t i o n s was  Its  i s based on i t s b r a s s y c o l o r , smooth p o l i s h ,  s p h a l e r i t e , indicates a mineral (e)  of  arsenopyrite.  (d) ' Chalcopyrite.;,  and  vein.  of an i n c h wide .  a n h e d r a l masses w i t h rounded i r r e g u l a r o u t l i n e s .  p y r i t e and  be  times i n the d r i l l  showed any  g a l e n a , but i t  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 . T h i s m i n e r a l was  i d e n t i f i e d i n hand specimens as  s i l v e r y p r i s m a t i c aggregates.  slender  In p o l i s h e d s e c t i o n i t i s  r e c o g n i z a b l e by i t s n e e d l e - l i k e f o r m , i t s v e r y s t r o n g a n i s o t r o p i s r n i n p o l a r i z e d l i g h t and the y e l l o w t a r n i s h produced/ on i t s s u r f a c e by e t c h i n g w i t h p o t a s s i u m  hydroxide.  I n 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 s u l p h o - s a l t s , t e t r a h e d r i t e and j a m e s o n i t e . common o c c u r r e n c e (h)  3Cu„S. Sb  —  jamesonite  of  S  2 2 3  Only i n one p o l i s h e d s e c t i o n was where i t was  I t i s not  i n the Brown McDade o r e .  Tetrahedrite: .  other  any t e t r a h e d r i t e  found,,  associated with arsenopyrite, s t i b n i t e ,  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 s t a n d a r d e t c h r e a c t i o n s d e s c r i b e d by Short') s a t i s f a c t o r y microchemical The  and  t e s t s f o r copper and antimony. .  t e t r a h e d r i t e s t u d i e d , comes from a s m a l l v e i n of  heavy s u l p h i d e ore a few d r i l l h o l e No.  inches i n wid^th, l o c a t e d i n diamond  1 c l o s e t o the main zone.  showed much h i g h e r - t h a n - a v e r a g e  Samples o f t h i s  values i n s i l v e r .  Since  ore no  o t h e r i m p o r t a n t s i l v e r - b e a r i n g m i n e r a l s have be.en found i t i s p o s s i b l e t h a t the s i l v e r v a l u e s 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 g a l e n a .  Samples of ore  from a p r o p e r t y i n the same a r e a , optioned- by the Conwest E x p l o r a t i o n Co., seem t o show a h i g h e r s i l v e r - g o l d r a t i o those of the Brown McDade-. o r e .  than  A short polished section  s t u d y of these samples' shows' c o m p a r a t i v e l y g r e a t e r amounts of  FIGURE 20  Photomicrograph of g o l d (Au) a s s 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 o f g o l d (Au) a s s o c i a t e d w i t h 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 (i)  the o t h e r s u l p h o - s a l t s .  Jamesonite: Although  2 PbS.  i t has  Sb S 2  3  not been seen i n the f i e l d , Jamesonite  was  d i s c o v e r e d 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 holes.  I t was  i d e n t i f i e d by Dr. R.M.  Thompson  who  a n a l y z e d ..the m i n e r a l .by X - r a y powder methods.  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  b a s i s of e t c h r e a c t i o n s o n l y . the amount was tests.  The  by S h o r t  The  writer  At the time of i t s d i s c o v e r y  too s m a l l to give any r e l i a b l e  microchemical  e t c h r e a c t i o n s do, however, check w i t h those  (13) f o r J e m e s o n i t e .  the  He  given  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 and  jamesonite  i s closely associated with tetrahedrite  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 .  Its  c h a r a c t e r i s t i c form i s I n l o n g f i b r o u s c r y s t a l s , sometimes s l i g h t l y b e n t , w i t h c r o s s 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; Bournonite  CUgS. 2PbS. S b g S  3  i s found i n ore from a s m a l l zone i n t r e n c h  No.  3 about 40 f e e t west of the main zone and p a r a l l e l t o i t . '>  The  sample from w h i c h the p o l i s h e d s e c t i o n i s c u t ,  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 . the b o u r n o n i t e  contains  Associated with  In the s e c t i o n a l t h o u g h not i n c o n t a c t 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 m i n e r a l i s s o f t , and almost w h i t e compared w i t h  FIGURE 22  Photomicrograph of a p a r t i c l e of g o l d (12.5 microns) i n quartz. X 1634 FIGURE 23  Photomicrograph o f p y r i t e ( p y ) , a r s e n o p y r i t e s p h a l e r i t e (sp) i n a u a r t z .  X 200  ( a s ) end  ' sphalerite.  27 I t s c o l o r as r e c o r d e d b y S h o r t  l i k e that of t e t r a h e d r i t e .  (13) i s g r a y ,  It i sdistinctly  anistropic,  showing l i g h t brown and dark brown c o l o r s when rotated, i n polarized  light.  The i d e n t i f i c a t i o n o f b o u r n o n i t e  was made by Dr.  Thompson i n an X-ray- powder a n a l y s i s . r e a c t i o n s , microchemical  On the b a s i s of e t c h  t e s t s f o r t e l l u r i u m , a n d the  a n i s o t r o p i s m , t h e w r i t e r thought i t might be' the t e l l u r i d e mineral, nagyagite.  The e t c h r e a c t i o n s , given by Short' f q r 3  b o t h m i n e r a l s , a r e 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' m i c r o c h e m i c a l w h i c h were r e p e a t e d results.  tests for tellurium,  twice, with apparently  satisfactory  I t i s now b e l i e v e d t h a t 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 o f i r o n , (k)  Gold: Au No v i s i b l e g o l d has been f o u n d i n any hand specimens,  a l t h o u g h f i n e c o l o r s may be o b t a i n e d b y panning the overburden above the ore zone.  I n p o l i s h e d s e c t i o n s from diamond d r i l l  h o l e s No. 8a and 11a and from b u l l d o z e r t r e n c h No.3 a few s m a l l p i e c e s o f g o l d were seen. The g o l d i s a b r i g h t y e l l o w 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 t o i t ,  i n polished section.  s i z e of the g o l d ranges from 3 t o 150 m i c r o n s .  The  It is  a s s o c i a t e d c l o s e l y w i t h t h e s u l p h i d e i n the o r e , 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 c o n t a c t w i t h them. A few t i n y p a r t i c l e s o f g o l d a r e found i n q u a r t z i s o l a t e d from any s u l p h i d e s .  28 4.  P a r a g e n e s i s o f The Ores; I t i s r e a l i z e d t h a t more l a b o r a t o r y work w i l l be r e -  q u i r e d t o determine ore.  the e x a c t p a r a g e n e s i s o f the Brown McDade  T h i s w i l l be f a c i l i t a t e d when underground  progresses f u r t h e r .  development  The d i s s e m i n a t e d n a t u r e o f the s u l p h i d e s  makes i t d i f f i c u l t t o s o l v e t h e i r o r d e r o f d e p o s i t i o n .  Some  c o n t a c t s between m i n e r a l s have been observed and used t o determine age r e l a t i o n s h i p s . '  The degree o f b r e c c i a t i o n o f  some o f the s u l p h i d e s makes i t p o s s i b l e t o s e p a r a t e the e a r l i e r formed ones from those w h i c h were d e p o s i t e d l a t e r . The  e x p e r i e n c e of o t h e r s who have s o l v e d such problems i n  w e l l known d e p o s i t s o f a s i m i l a r c h a r a c t e r , has been used as a g u i d e . The t a b l e below, i l l u s t r a t e s t h e p a r a g e n e s i s as determined by the w r i t e r : quartz pyrite arsenopyrite sphalerite chalcopyrite galena tetrahedrite stibnite jamesonite bournonite gold covellite oxidation  29 Q u a r t z , p y r i t e , a r s e n o p y r i t e 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 q u a r t z .  Any o f the o t h e r  m e t a l l i c m i n e r a l s may appear i n these f r a c t u r e s , b u t a r e not f r a c t u r e d themselves.  I t i s concluded  from these f a c t s  t h a t t h e r e were a t l e a s t two p e r i o d s o f m e t a l l i c m i n e r a l i z a t i o n , s e p a r a t e d by movement a l o n g 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 o f the e a r l y m i n e r a l s .  D u r i n g 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 i n t r o d u c e d w i t h q u a r t z . iod  I n the second p e r -  s t i b n i t e and the s u l p h o - s a l t s and g o l d were  with l a t e r quartz.  deposited  F o l l o w i n g the c l o 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 t h a t the two p e r i o d s o f 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 p a r a g r a p h , do not represent widely separated  p e r i o d s o f time.  They may be  i n c l u d e d i n one l o n g p e r i o d o f hydrothermal. a c t i v i t y w h i c h a s h o r t p e r i o d of d e f o r m a t i o n  during  took p l a c e , f o l l o w e d by  the d e p o s i t i o n o f s u l p h o - s a l t s and g o l d . 5.  Conclusions: The commercial v a l u e s o f the Brown McDade ores come f r o m  f r e e g o l d , and s i l v e r - b e a r i n g m i n e r a l s 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 o f s u l p h i d e 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 o f t h e s u l p h i d e s a r e u s u a l l y i n d i c a t i v e of g o l d v a l u e s .  As a r u l e the h e a v i e r the m i n e r a l i z a t i o n and  the f i n e r t h e g r a i n s i z e o f the p y r i t e , the h i g h e r w i l l be t h e amount o f g o l d i n t h e sample.  The g o l d i s c l o s e l y a s s o c i a t e d  30 w i t h the p y r i t e , l y i n g a l o n g b o u n d a r i e s of the g r a i n s o r i n f r a c t u r e s between them.  The  v e r y wide v a r i a t i o n s i n the  s i l v e r r a t i o as seen from the a s s a y r e s u l t s , may e x p l a i n e d by the e r r a t i c d i s t r i b u t i o n of g o l d and b e a r i n g s u l p h o - s a l t s i n the  ore.  gold-  p o s s i b l y be the  silver-  31 ORIGIN OF THE ORE' DEPOSIT PART V I 1.  Source o f 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 m i l e west of the mine.  The c o m p o s i t i o n o f the rounded t o p o f the  mountain i s q u a r t z f e l d s p a r p o r p h y r y .  Field  relations  between t h i s mass and the s u r r o u n d i n g area suggest t h a t i t i s an i n t r u s i v e neck c u t t i n g t h r o u g h the o l d e r s u r r o u n d i n g rocks.  Other b o d i e s o f s i m i l a r r o c k a r e common i n t h e r e g i o n  f o r 40 m i l e s northwestward.  They are c o n s i d e r e d t o be o f  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 a t the Brown McDade Mine i s b e l i e v e d  t o be g e n e t i c a l l y r e l a t e d t o these i n t r u s i o n s o f q u a r t z f e l d s p a r porphyry. (a)  The f o l l o w i n g p o i n t s support t h i s  The c o m p o s i t i o n of "the Dome" i s almost  belief.  identical  to t h a t o f t h e d y 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 a t the mine d i p s towards the Dome,  i n d i c a t i n g t h a t i t may be an o f f s h o o t ' o f t h e l a r g e r mass. (c)  Dykes o f q u a r t z f e l d s p a r ' p o r p h y r y o u t c r o p about a  m i l e west o f the Dome and a r e p r o b a b l y r e l a t e d t o i t . The w r i t e r b e l i e v e s t h a t an i n t r u s i o n o f q u a r t z f e l d s p a r porphyry  (now r e p r e s e n t e d by "The Dome") f r a c t u r e d the  s u r r o u n d i n g rocks and sent out dykes t o f i l l  the f r a c t u r e s .  These became zones o f weakness a l o n g which movement took p l a c e , a l l o w i n g t h e entrance o f 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 S i n c e the p e r i o d o f p r i m a r y m i n e r a l i z a t i o n , supergene p r o cesses have been i n a c t i o n t o a l i m i t e d e x t e n t . these processes  As evidence of  t h e r e 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 f o r m a t i o n of l i m o n i t e and  j a r o s i t e i n the o r e .  Most, of the v e i n m a t e r i a l i s f r e s h ,  even a t the s u r f a c e where g o l d i s "found i n h a r d  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 bournonite  show no s i g n s of a l t e r a t i o n .  such supergene processes  I t i s thought that  t h a t have been I n o p e r a t i o n are  v e r y minor and have not a f f e c t e d .the g o l d and s i l v e r of the 2.  and  values  ore.  Comparisons With Other D e p o s i t s : (a)  Introduction:  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 o r d e r to assess i t s p o s s i b i l i t i e s . based on m i n e r a l o g y , rock  age  The  comparisons are  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  alteration. The  w r i t e r was  unable t o f i n d any r e f e r e n c e  to d e p o s i t s ,  where a l l the above f e a t u r e s c o r r e s p o n d e d t o 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  from the r e f e r e n c e s , to draw a few  o b t a i n e d , however,  conclusions regarding i t s  possibilities. (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  b l u e c o l o r , f i n e t e x t u r e of q u a r t z , 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 s u l p h i d e m i n e r a l i z a t i o n , vugs and d r u s y  cavities  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 banding.  occasional  On the b a s i s o i t h i s i n f o r m a t i o n i t appears t o  b e l o n g t o the e p i t h e r m a l  group of m i n e r a l d e p o s i t s .  f e a t u r e s of the famous, t y p i c a l e p i t h e r m a l been seen i n the Brown McDade.  Certain  d e p o s i t s have not  Of t h e s e , the most prominent  and w i d e s p r e a d i s the presence o f 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 . i n the o r e , o n l y the a r s e n o p y r i t e •epithermal  deposits.  ,  Of the m e t a l l i c m i n e r a l s i s u s u a l l y rare i n  .  Ferguson's (19) c l a s s i f i c a t i o n of the p r e c i o u s epithermal  metal  o r e s , i s determined on the r a t i o of g o l d t o s i l v e r .  He r e c o g n i z e s ' r a t i o o f one  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 t o one  or l e s s , ,and the g o l d - s i l v e r c l a s s where  g o l d exceeds s i l v e r by w e i g h t .  These c l a s s e s v a r y  consid-  e r a b l y i n m i n e r a l o g y 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  between 1 t o 5 and 1 t o 15, which would make i t , the f i g u r e s a l o n e , a s i l v e r g o l d d e p o s i t . r  The  lies  considering  mineralogy,  however, i s such, t h a t the g o l d - s i l v e r group seems the b e t t e r c h o i c e 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 p r e s e n t  McDade."  These m i n e r a l s  are a r g e n t i t e and  i n the Brown  the s i l v e r  sulpho-  s a l t s , w h i c h are s a i d by Nolan (12) to be l a c k i n g i n g o l d s i l v e r deposits.  I t I s thought t h a t i n t h i s case the  gold-  s i l v e r r a t i o i s too c l o s e to the b o r d e r l i n e between the groups t o be a d i a g n o s t i c f e a t u r e .  two  34 (c)  Age  of D e p o s i t i o n : .  The Brown McDade ore"body, formed d u r i n g L a t e T e r t i a r y t i m e , b e l o n g s g e o l o g i c a l l y t o r e g i o n of the P a c i f i c  Rim.  T h i s r e g i o n , has the shape of a g r e a t a r c , r u n n i n g from Zealand  New  through the P h i l l i p i n e s , Japan and Western N o r t h  A m e r i c a , t o the South American C o n t i n e n t .  I t was  the scene of  i n t e n s e 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 , d u r i n g w h i c h time the g r e a t e p i t h e r t n a l d e p o s i t s , f o r which i t i s w e l l known, were formed.  C o n s i d e r i n g t h i s f a c t i n the l i g h t of the  c h a r a c t e r i s t i c s o f the Brown McDade, i t seems l o g i c a l a s s o c i a t e i t w i t h the e p i t h e r m a l (d ) 1  to  group.  S t r u c t u r a l Comparisons:  S p e a k i n g of the g o l d - s i l v e r c l a s s of e p i t h e r m a l T.B.  other  N o l a n (12) s a y s , "The  deposits,  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 w h i c h i n many p l a c e s 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 w i t h w h i c h they are a s s o c i a t e d . d i s c o n t i n u o u s and  These f r a c t u r e s are g e n e r a l l y  r a r e l y have measureable d i s p l a c e m e n t s .  a r e s u l t ore shoots  are i n many p l a c e s of r a t h e r s m a l l  and the d i s c o v e r y of new  extent  ones i s d i f f i c u l t . "  Of the s i l v e r - g o l d d e p o s i t s he s t a t e s , "The of t h i s c l a s s are commonly found i n w e l l d e f i n e d f i s s u r e s t h a t may  As-  ore  deposits  fault  be f o l l o w e d f o r c o n s i d e r a b l e d i s t a n c e s b o t h  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  faults  appear 'to be o f t e c t o n i c o r i g i n and t o have no d i r e c t conne 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 o f the B own McDade p r o p e r t y i s t h a t of r  an  35 i n t r u s i v e body of q u a r t z f e l d s p a r p o r p h y r y 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 t o which i t i s b e l i e v e d t o be gentically related.  Prom the evidence shown i n b u l l d o z e r  t r e n c h e s Nos. 4 and 8, which are 200- f e e t a p a r t , i t i s thought t h a t t h e r e i s no l a r g e h o r i z o n t a l d i s p l a c e m e n t a l o n g t h i s zone of  porphyry.  I f t h i s had happened, the c o n t a c t between the  q u a r t z d i o r i t e and the Yukon s c h i s t s would be expected t o show s i g n s of t h i s d i s p l a c e m e n t  on e i t h e r s i d e of the zone.  There  i s no s i g n of such a d i s p l a c e m e n t . C o n s i d e r i n g t h e n , the s t r u c t u r a l evidence a t the Brown McDade Mine and Nolan's  (12) s t r u c t u r a l comparisons  two groups o f e p i t h e r m a l groups,the  between the  g o l d - s i l v e r group i s the  one t o w h i c h i t i s . most s i m i l a r . () e  W a l l 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  silicification.  I t i s not c o n f i n e d t o the r o c k s a d j a c e n t t o 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 o f the e p i t h e r m a l c l a s s of ore d e p o s i t than i t i s of those formed at g r e a t e r depths. 3.  Conclus i o n s ; (a)  The Brown McDade ore d e p o s i t i s p r o b a b l y o f 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  indicate  t h a t i t , i s not one o f those formed a,t v e r y shallow- depths. (b)  A study of the s t r u c t u r a l 'features suggests  that  the ore s h o u l d c o n t i n u e t o moderate d e p t h s , but t h a t 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 w i d t h of the  (  ore zone w i l l be v a r i a b l e . (c)  The  a r e a to the s o u t h 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 Yukon Group, w i l l p r o b a b l y not N  c o n t a i n much o r e .  The  f a c t s t h a t p l a c e r g o l d 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 a r e a s , and i n the immediate v i c i n i t y of the p r o p e r t y competent to m a i n t a i n  t h a t the s c h i s t s  do not  appear  open f r a c t u r e s , tend to s u p p o r t t h i s  statement. (d) ore has  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 been found i n the streams d r a i n i n g the  extension  of the Brown McDade Group..  the  Northward  I n a d d i t i o n , some  p l a c e r g o l d has been t a k e n from the.streams and overburden y i e l d s g o l d c o l o r s i n the pan.  much of  the  These f a c t s  i n d i c a t e t h a t t h i s ground s h o u l d be f a v o r a b l e 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 o f 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 e x t e n d i n g outward i n t o the q u a r t z (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 c h a r a c t e r and  i n t e n s i t y of w a l l r o c k a l t e r a t i o n w i l l  p r o b a b l y have some b e a r i n g .(g)  diorite.  The  on the c o n t r o l of ore  deposition.  o c c u r r e n c e of the g o l d 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 t h a t the problems of e x t r a c t i o n s h o u l d not be too d i f f i c u l t . m e t a l l i c and point.  gangue m i n e r a l s  A more d e t a i l e d s t u d y of  the  w i l l be n e c e s s a r y t o prove t h i s  However,the s m a l l s i z e of the g o l d i n d i c a t e s t h a t  ore w i l l have t o be f i n e l y ground.  the  PART V l l 1.  DEVELOPMENT OF THE MINE  Discovery: The  p r o p e r t y was d i s c o v e r e d by George McDade o f Carmacks,  i n 1943. A f t e r many years o f p r o s p e c t i n g i n the a r e a , d u r i n g w h i c h time he was working  s m a l l p l a c e r h o l d i n g s 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 l o d e from w h i c h the p l a c e r g o l d had- come.  H  e  n o t i c e d t h a t the  g o l d appeared rough, o f t e n c o n t a i n i n g p i e c e s o f q u a r t z a t t a c h e d t o i t , and deduced from t h i s t h a t . i t had not travelled far.  The next s t e p he took, was t o pan  i c a l l y , upstream from t h e w o r k i n g s , but a l s o up the h i l l s i d e s .  not o n l y a l o n g the creeks  The work p r o g r e s s e d  owing to the heavy overburden.  systemat-  slowly,  He f o u n d , however, t h a t 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 l e a d s was a b l e t o t r a c e the g o l d t o 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 p a r t n e r . Brown dug a s e r i e s of t r e n c h e s a c r o s s t h e ore zone on the B i g Thing c l a i m .  The l o o s e n e s s  and depth o f overburden  them from r e a c h i n g bedrock. i n the trenches  prevented  Panning o f the l o o s e m a t e r i a l  produced good c o l o r s i n g o l d and samples o f  s o l i d fragments when assayed,  gave s a t i s f a c t o r y  results.  The c l a i m s were o p t i o n e d t o 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 e x a m i n a t i o n by S m i t h e r i n g a l e i n Sept. 1945. . Subsequent work has proved t h e a c c u r a c y o f McDade's calculations.  38  2.  Diamond  Drilling:  (a) P l a n : O r i g i n a l l y t h e r e was  no evidence t o 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 to be v e r t i c a l .  The  assumed  f i r s t two h o l e s proved t h a t the zone  was  d i p p i n g westward about 70 degrees, c o n s e q u e n t l y  was  started.  a new  plan  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 s h o r t  h o l e s i n c l i n e d at 40 degrees, 100 f e e t a p a r t , t o i n t e r s e c t the zone a p p r o x i m a t e l y (b) D r i l l i n g  at r i g h t  angles,  Problems:  The n o r t h e r n 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, surface d r i l l i n g .  The  limits  f o u r months from May  c o n s t i t u t e the average' d r i l l i n g The The  the time a v a i l a b l e f o r to September  season.  problem of permanently f r o z e n ground i s . d i f f i c u l t .  degree of f r e e z i n g depends on s l o p e of ground, amount of  overburden and nature  of v e g e t a t i v e c o v e r .  n o r t h e r n s i d e s of the h i l l s are c o m p l e t e l y moss r o o t s whereas the southern f r o s t f o r a c o n s i d e r a b l e depth. with l i t t l e  U s u a l l y the f r o z e n below the  exposures are o f t e n f r e e of S t e e p l y s l o p i n g ground,  overburden and p l a n t c o v e r i s not f r o z e n t o the  same e x t e n t as the more g e n t l e s l o p e s w i t h a heavy b l a n k e t moss and b r u s h .  The  of  problem of d r i l l i n g i n such ground i s  b e s t s o l v e d by keeping  the d r i l l  while a hole i s being d r i l l e d .  i n operation Even the two,  per day t h a t were u s e d , d i d not prevent d u r i n g the e a r l y p a r t of the season.  continuously, ten-hour s h i f t s  the f o r m a t i o n o f i c e ,  Drilling  50 or 100  feet  Bulldozer  t r e n c h No. 3 on the " B i g Thing" l o o k i n g west.  claim,  Depth of overburden a p p r o x i m a t e l y 8 f e e t . "Tne Dome" i n the background i s an i n t r u s i v e body o f quartz f e l d s p a r porphyry.  39  of i c e wastes s e v e r a l hours t i m e . eight-hour  A program u s i n g  three,  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 .  s t a n d i n g i n the hole, f o r over an hour would f r e e z e s o l i d l y i n p o s i t i o n , p r e v e n t i n g 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  s u p p l y was  Pony Greek.  The  s u f f i c i e n t d u r i n g the S p r i n g r u n o f f but a few weeks  d r y weather reduced the f l o w t o a t r i c k l e . o c c a s i o n s work was  On s e v e r a l  h a l t e d f o r l a c k of w a t e r .  This problem  s o l v e d by the c o n s t r u c t i o n of a l a r g e sump i n the c r e e k conserve the s u p p l y f o r d r y weather. The  was  to  • .  r o c k s 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 b a d l y s h a t t e r e d  o x i d i z e d to a depth of at l e a s t 200 f e e t .  and  This c o n d i t i o n g i v e s  r i s e t o many problems such a s , low core r e c o v e r y , c a v i n g h o l e s , undue a b r a s i o n of d r i l l  r o d s , r a p i d gauge l o s s i n b i t s ,  l o s s of r e t u r n water and sludge from, the h o l e s . c o n d i t i o n s were u n f o r s e e n ,  some time was  these  l o s t and some d r i l l i n g  equipment became worn out sooner than was s o l u t i o n of these d i f f i c u l t i e s  Because  and  anticipated.  would i n v o l v e the use .of  The two  s i z e s of d r i l l equipment, a l a r g e s i z e c a s i n g i n s i d e of which' standard  size d r i l l  drilled,  f i r s t , to s e a l the h o l e .  3.'  rods would be used.  The  c a s i n g would be  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 e i g h t l a r g e cuts a c r o s s  ore zone over a l e n g t h of a p p r o x i m a t e l y i s q u i c k and l e s s expensive  1500  feet.  t h a n t r e n c h i n g by hand.  d r i l l i n g , the problem of f r o z e n ground p r e s e n t e d  the  This method As i n  difficulties.  In some t r e n c h e s s e v e r a l days had t o e l a p s e between s u c c e s s i v e c u t t i n g s to a l l o w the ground t o thaw.  By k e e p i n g s e v e r a l c u t s  i n o p e r a t i o n a t once, the maximum use was made o f the b u l l d o z e 4.  Present  Development:  An underground program of development  i s now underway.  I t c o n s i s t s o f a c r o s s c u t .700 f e e t l o n g , r u n n i n g from Pony Creek i n t o the ore zone, which i t v / i l l  intersect  under  diamond d r i l l h o l e No. 8 a , about 100 feet* below the s u r f a c e . L a t e r a l development  o f the ore .zone v / i l l f o l l o w upon com-  p l e t i o n o f the c r o 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 t o be c o n s i d e r e d i n t r a n s p o r t a t i o n a r e ,  d i s t a n c e , type of t r a n s p o r t a t i o n and y e a r - r o u n d of such t r a n s p o r t a t i o n .  Production costs w i l l  availability depend l a r g e l y  on these f a c t o r s . There a r e 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 r o u t e s .  The  f i r s t r o u t e i s v i a the A i s h i h i k c u t - o f f r o a d , the A l a s k a Highway and the Haines c u t - o f f r o a d t o the town o f Haines on the  c o a s t o f A l a s k a , n e a r 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 o f 40 m i l e s o f new r o a d from the mine t o A i s h i h i k , making i n a l l , 300 m i l e s o f haulage by motor vehicles.  T h i s r o u t e has t h e advantage of b e i n g independent  of o t h e r forms o f t r a n s p o r t a t i o n from the mine t o t i d e w a t e r . In the W i n t e r months t h e r e i s a p o s s i b i l i t y  t h a t the Haines  c u t - o f f , which runs t h r o u g h the rugged Coast Range mountains, c o u l d n o t be kept open c o n t i n u o u s l y . The second r o u t e runs over the A i s h i h i k c u t - o f f r o a d and  4/ the A l a s k a Highway t o W h i t e h o r s e , where i t goes by the White Pass and Yukon R a i l w a y t o Skagway. i s about 300 m i l e s .  -The l e n g t h of t h i s r o u t e  I t t o o , would r e q u i r e the c o n s t r u c t i o n  of the new r o a d mentioned i n the l a s t p a r a g r a p h . The t h i r d and f o u r t h r o u t e s go t h r o u g h Whitehorse v i a Carmacks. o f new  They b o t h r e q u i r e c o n s t r u c t i o n of 35 or 40 m i l e s  r o a d from the mine t o Carmacks,  be s i m i l a r t o the new A i s h i h i k r o a d .  the cost of which would A t Carmacks the two  r o u t e s s e p a r a t e , one u s i n g the Dawson-Whitehorse r o a d , and the o t h e r b e i n g the steamer r o u t e 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 d i s a d v a n t a g e s of the  r i v e r r o u t e a r e , 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 o f h i g h f r e i g h t r a t e s , and a p e r i o d of seven months from October t o 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 , w h i l e the t i m b e r i s too s p a r s e t o be c o n s i d e r e d as a source of power.  Two  p o s s i b i l i t i e s remain. . The  first  would r e q u i r e the use of d i e s e l o i l , h a u l e d i n from Whitehorse and the second would be t o use c o a l from the d e p o s i t s on the Lewes R i v e r near Carmacks. are w o r t h i n v e s t i g a t i n g .  The p o s s i b i l i t i e s of the l a t t e r  BIBLIOGRAPHY. 1.  B o s t o c k , 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 o f Canada, Ottawa 1936.  2.  B r u s h , G.J. and P e n f i e l d , S.L. • " D e t e r m i n a t i v e M i n e r a l o g y and Blowpipe A n a l y s i s " John W i l e y and Sons I n c . New York 1926  3.  C a i r n e s , D.D. "Nansen and V i c t o r i a C r e e k s , N i s l i n g R i v e r Yukon T e r r i t o r y " . Map 1 5 l a . G e o l o g i c a l Survey o f Can. Sumrn. Rept.1915.  4.  Dana, E .S. and F o r d , W.E..' "A Textbook o f M i n e r a l o g y " John W i l e y and Sons, New Y o r k , 1932.  5.  Farnham, C M . " D e t e r m i n a t i o n o f t h e Opaque M i n e r a l s " Book Co. Inc.,.New York 1931  (  McGraw H i l l  6. . H a r k e r , A. "Petrology f o r Students" 7.  L a r s e n , E.S. and'Berman, H. "The M i c r o s c o p i c D e t e r m i n a t i o n o f t h e Non-opaque M i n e r a l s " . U.S.G.S. B u l l . 848, Washington, 1934.  8.  L l n d g r e n , W. "Mineral Deposits" York, 1933.  9.  McGraw H i l l Book Co., New  L i n d g r e n , W. ) The Ore D e p o s i t s , o f New Mexico" .Granton, L . C ) U.S.G.S. P r o f . Paper 68, Washington 1910. Gordon, C.H. ) u  10. L o v e r i n g , T.S. "The O r i g i n o f the Tungsten Ores o f B o u l d e r County, C o l o r a d o " . E c . G e o l . V o l . 36, No. 3, May 1941 11. P u r i n g t o n , C.W. " P r e l i m i n a r y Report on the M i n i n g I n d u s t r i e s o f t h e T e l l u r i d e Quadrangle, C o l o r a d o " , U.S.G.S. Ann.' Rept. P a r t 111 Washington, 1896-1897. i  12.  Rocky Mountain Fund. "Ore D e p o s i t s o f the. Western S t a t e s " . American. I n s t , o f Min. and Met. E n g i n e e r s York, 1933.  New  BIBLIOGRAPHY 13. S h o r t , M.N. " M i c r o s c o p i c D e t e r m i n a t i o n o f the Ore M i n e r a l s " . U.S.G.S. B u l l . 914, Washington 1940. 14. Ross, C P . •* "Some Lode D e p o s i t s i n the N o r t h w e s t e r n P a r t o f t h e B o i s e 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 o f Ouray, C o l o r a d o , E c . G e o l . V o l . 3 1 , Nos. 4 and 5, 1936. 16-. Tweto, 0. • " S c h e e l i t e i n the B o u l d e r D i s t r i c t , C o l o r a d o " Ec. G e o l . 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 o f P e t r o l o g y " , E.P. D u t t o n and Co., Inc. New York. 18. W o r c e s t e r , P.G. "Geology o f the Ward R e g i o n , B o u l d e r County, C o l o r a d o . " . C o l o . Geol I Surv. B u l l . 2 1 , B o u l d e r 1921 19. Ferguson, H.G. "The M i n i n g D i s t r i c t s o f Nevada" Econ. Geol." V o l . 24, 1929.  +  \  o Y  O  1  o  o  •5? V  GEOL OG Y  LEGEND  &K.ANODIQR I Tt [QJZ. 'I IN  DZOR/TE)  /  CONTOUR DIAMOND D HOLE  PORP/i VP Y  TRENCH CLAIM B.WDY.  r..  VEh\] PAUL T  B/G  ASSUMED TRACE IN DR.ILL  MAP OF OF PORPH/RY  BROWN M DADE GROUP C  H0L£6  WORKINGS  &  CARMACKS  GEOLOGY YUKON TV.  SCALE 1 IN. -40 FT. 1946  

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