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A gold-specularite deposit, Unuk River, B.C. Seraphim, Robert Henry 1948

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3  /-  S3  33 ~7  &C  C O p> • /  A GOLD  SPBGULARITE DEPOSIT, UNUK RIVEB, B.C.  A t h e s i s s u b m i t t e d i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r the degree o f M a s t e r o f A p p l i e d S o i e n o e i n t h e Department o f Geology and Geography, UNIVERSITY OF BRITISH  COLUMBIA  A p r i l , 1948.  ROBERT HENRY SEHAPHIM  ABSTRACT On the (Jraoey group of claims, Unuk River, B.C., mesothermal-type quartz veins;  are  (1) with speoularite-gold  mineralization, (2) with galena-pyrite-gold mineralization, and (3) with chalcopyrite^pyrite mineralization containing no precious metals.  The veins outcrop i n a "band of Late Palaeo-  zoio(?) andesite t u f f bordered  t  s i l t s t o n e , a r g i l l i t e , and  limestone  on the northeast and southwest by Triassic(?) d i o r i t e  gneiss s i l l s .  The main body of Coast Range intrusives out-  crops f i v e miles southwest of the property, but several stocks are exposed about f i v e miles east of the property. The regional-type metamorphism, and most of the f o l d i n g and f a u l t i n g of the bedded rocks on the property have been caused by orogeny associated with the Coast Range intrusives; but some r e c r y s t a l l i z a t i o n of andesite-tuff can be attributed to  thermal metamorphism produoed by the adjacent  gneiss s i l l s .  diorite-  The vein-forming f l u i d s are probably derived  from Coast Range intrusive rather than the l o c a l  sills.  In the quartz-galena-pyrite veins anhedral gold fragments are associated with three soft minerals, possibly t e l l u r i d e s , which form inclusions i n the galena.  In the quartz-specular^-  ite-gold veins the gold has been deposited i n disruptions between specularite 'cleavage' plates.  Both classes of veins  contain minor amounts of gold i n or near fractures i n the quartz.  '  '  '  No veins contain both abundant specularite and abundant sulfides.  The specularite probably has been deposited e a r l i e r  than the sulfides but i n the same period of mineralization. Specularite does not necessarily indicate hypothermal deposition, but i t i s usually one from hydrothermal solutions. i z i n g conditions, and and  of the f i r s t minerals deposited It i s formed only under oxid-  i f exposed to l a t e r sulfide-bearingi  thus reducing, solutions, i t tends to be reduced to  magnetite or an iron-bearing  sulfide.  AOXUOWLBD (xSMEN US  F i e l d work on the Sraoey group was superfcvsed "by D r . D . F , E i d d of L e i t c h Gold M i n e s , and much c r e d i t i s due him f o r sound a d v i c e on some o f the f i e l d p r o b l e m s .  The w r i t e r  his  is  i n d e b t e d to D r . H . C . Gunning and D r . K . DeP. Watson f o r a s s i s t a n c e and guidance i n the l a b o r a t o r y w o r k . Thompson gave many h e l p f u l s u g g e s t i o n s lems.  Dr. H.M.  on m i n e r a l o g i c a l p r o b -  J . A . Donnan gave a d v i c e on p r e p a r a t i o n o f t h i n and  polished  sections.  TABLE OF CONTENTS Page MTRODUC TION  ,  1  PURPOSE OF THESIS  3  METHOD OF INVESTIGATION.  4  LOCATION AND ACCESSIBILITY.......................  6  TOPOGRAPHY.  * ...............  CLIMATE...,  ,  7 8  HISTORY,  8  GENERAL GEOLOGY  9  Structural Correlation - Intrusives......  10  Structural Correlation - Sedimentary and Volcanic Rooks  ,,•>•  L i t h o l o g i c a l Correlation.,  11  Mineralization, LO.CAL GEOLOGY.  10  13  ...........................  Rook Types.  14 16  Limestone Siltstone.,  16 ,  31  Tuff  El  Gneiss of Tuff Origin....................  24  Intrusive D i o r i t e Gneiss..,.,,.  25  Dykes  ••••  26  Coast Range Intrusives (not including Triassic(?J s i l l s )  29  TABLE OF CONTENTS (CONT'D) METAMORPHISM.  Page  ,  30  STRUCTURE.......................................... Folding.  i....  31 31  Regional Fracture Pattern........  33  Relation of Veins to S i l l s  35  VEINS.  36 ' General...............  36  Wall Rook Alteration.......  36  Mineralization............................  40  Chaleopyrite-pyrite Galena-pyrite  Class..............  Class.......  40 41  Specularite Class......................  46  Significance of Specularite............  47  Mineralogical Conclusions.....• GENERAL CONCLUSIONS.  58 60  TABLE OP CONTENTS (CONT'D) A f t e r Page  PLATE NO. 1. ..............................  6  2.  7  3.  7  mm  SECTION PHOTOGRAPH NO. 1.  15  2. ..............................  15  3. .,  21  4.  21  5.  24  6.  24  7.  • ...  18  8. 9.  18  ...........  17  POLISHED SECTION PHOTOMICROGRAPH NO. 1.  42  2. ..............................  42  3.  42  4. ............  ..............  44  5.  44  6. ..............................  44  7.  44  8. ..............................  45  9  45  INTRODUCTION I n the 1946 f i e l d s e a s o n ,  Thomas M c Q u i l l a n and F a t  Onhasy, p r o s p e c t i n g f o r L e i t c h S o l d M i n e s , s t a k e d the Graoey group o f c l a i m s on the  "South F o r k ' o f the Unuk R i v e r .  Of  the e i g h t q u a r t z v e i n s sampled t h e r e by the p r o s p e c t o r s , gave a s s a y s above o n e - h a l f ounce i n g o l d .  five  F o u r o f these h i g h  a s s a y s were from samples t a k e n a c r o s s mineable w i d t h s .  The  w r i t e r was i n charge of open c u t t i n g and i n t e n s i v e p r o s p e c t i n g on the Graoey group d u r i n g the 1947 f i e l d  season.  The f i v e v e i n s , g i v i n g h i g h a s s a y s were named a f t e r prospectors  1  sample numbers.  (Map H o . 3 . )  the  Q-17 v e i n has  been t r a c e d f o r f o u r hundred f e e t , and averages f i v e f e e t wide..  A t the west end the q u a r t z p i n c h e s out but m i n e r a l i z e d  shearing continues.  T h i r t y f e e t f a r t h e r west q u a r t z has  a g a i n been d e p o s i t e d , f o r m i n g Q-17 west v e i n . averages  This v e i n  se-een f e e t w i d e , and has been t r a c e d two hundred  f e e t t o the w e s t , where i t i s c o v e r e d by deep g l a c i a l d r i f t . Q-22 v e i n i s the p r o b a b l e f a u l t e d e a s t e r n e x t e n s i o n o f Q-17 vein.  Q-22 v e i n has been t r a c e d one thousand f e e t , t o where  i t becomes o n l y e i g h t t o t e n i n c h e s wide and a s s a y s o n l y traoes i n gold.  I t i s s u s p e c t e d t h a t Q-18 sample was out  from .a l a r g e b o u l d e r of f l o a t .  F l o a t i s abundant i n the  area  where the sample was t a k e n , but no v e i n was found i n p l a c e , a l t h o u g h the p r o s p e c t o r searohed f o r i t . h i m s e l f .  Q-19 v e i n  was t r a c e d f o r seven hundred f e e t , but o n l y one s m a l l p o s s i b l e ore shoot was d e l i n e a t e d .  Q-24 v e i n i s n o t o f m i n e a b l e w i d t h ,  ^3-  and i s too i r r e g u l a r t o w a r r a n t s u r f a c e development under present c o n d i t i o n s . least  Three a d d i t i o n a l v e i n s , of w h i o h a t  one CQ-25) w a r r a n t s f u r t h e r development, were f o u n d . I n the l a t t e r p a r t o f August g e o l o g i c a l mapping of  the  major showings on a s c a l e o f two hundred f e e t t o one i n c h was oommenoed.  Inclement weather f o r c e d c e s s a t i o n o f work  i n e a r l y September,  but f u r t h e r e x p l o r a t i o n ,  inoluding  diamond d r i l l i n g and g e o l o g i c a l mapping, w i l l be c o n t i n u e d i n the 1948 f i e l d  season.  G e o l o g i c a l b r e a k s show up i n the l a t e snow.  PURPOSE OF THESIS To d e s c f i b e  the l o o a t i o n , a o o e s s i b i l i t y ,  o l i m a t e , h i s t o r y , and g e o l o g y o f the r e g i o n ; particularly 1.  topography, and more  to  determine the age o f the r o o k s by s t r u o t u r a l and  l i t h o l o g i c a l c o r r e l a t i o n o f the geology w i t h t h a t o f nearby areas* 2.  determine the host r o c k of the v e i n s , and the reasons  f o r i t s s u s c e p t i b i l i t y to m i n e r a l i z a t i o n . 3.  a n a l y s e the s t r u c t u r e  of the r e g i o n as a g u i d e t o  f u r t h e r p r o s p e c t i n g and development. 4.  determine the p r o b a b l e source of m i n e r a l i z i n g f l u i d s .  5.  determine the m i n e r a l or m i n e r a l s a s s o c i a t e d  g o l d i n the v e i n s as a guide t o f u r t h e r 6.  with  development.  determine the s i z e o f g o l d p a r t i c l e s i n the  and i t s a s s o c i a t i o n w i t h f r a c t u r i n g , t o i n d i c a t e s i z e  'ore , 1  of  g r i n d i n g necessary f o r m i l l i n g . 7.  determine the s i g n i f i c a n c e o f s p e o u l a r i t e i n the  q u a r t z v e i n s , and i t s a s s o c i a t i o n w i t h the o t h e r minerals.  metallic  GRACEY GROUP. - Graoey Creek i n background; South F o r k i n v a l l e y on the l o w e r r i g h t ; Graoey c l a i m s are r i g h t c e n t e r .  METHOD  OF  INVESTIGATION  G e o l o g i c a l mapping c o u l d n o t be done t o b e s t  advantage  u n t i l A u g u s t , when most of the ground was f r e e o f snow*  A  c l a i m map was made i n J u l y , u s i n g a B r u n t o n oompass and c h a i n * T h i s map was drawn a t 500 f e e t t o the i n o h . the s u r v e y i n g was about one i n a t h q u s a n d .  The a c c u r a c y Notes of  of  the  s u r v e y were k e p t , When g e o l o g i c a l mapping was s t a r t e d each c l a i m was drawn a t 200 f t ,  to the i n c h on a s e p a r a t e s h e e t .  The c l a i m s were  then g e o l o g i c a l l y mapped one a t a time u s i n g B r u n t o n compass and c h a i n , as no plane t a b l e was a v a i l a b l e . run n o r t h - e a s t  and s o u t h - w e s t ,  of the o u t c r o p s . ' points.  Traverses  i n o r d e r t o f o l l o w the  The c l a i m p o s t s were used f o r  The s u r v e y o r ' s h e l p e r kept n o t e s o f the  A f t e r each f i v e c h a i n s (500 f t . ) ,  and g e o l o g y were p l o t t e d on the o l a i m s h e e t . mapped i n about two d a y s .  the  trend  'tie-in' survey,  i n c l u d i n g t o p o g r a p h y , and the s u r v e y o r k e p t n o t e s o f geology.  were  the  topography  A c l a i m was  The g e o l o g i c a l maps of a l l the  c l a i m s were c o m p i l e d i n one map (Map N o . 3 i n back  pocket).  Rock specimens c o l l e c t e d d u r i n g mapping were  labelled  numerically;  and the number put on the map t o show where  each specimen was c o l l e c t e d .  A s u i t e of specimens was  c o l l e c t e d from the w a l l of Q - l ? v e i n ;  specimens b e i n g t a k e n  at 8 f t . ,  and £ f t .  4 ft. i 3 ft.,  2 ft.,  !•§• f t . ,  from the  v e i n , a n d , as c l o s e l y as c o u l d be d e t e r m i n e d , from the same  -5bed.  Laok of o u t c r o p made i t d i f f i c u l t t o o b t a i n o t h e r  s u i t e s of a l t e r e d w a l l rook.  Specimens o f  " o r e " were  collect-  ed from each i m p o r t a n t v e i n * T h i n s e c t i o n s were made o f each o f the s i x t y r o c k specimens c o l l e c t e d , and o f the important v e i n s .  'ore  1  from s e v e r a l o f  P o l i s h e d s e c t i o n s were made o f the  from each i m p o r t a n t v e i n .  The d e s c r i p t i o n s of a l l  were kept on i n d e x e d c a r d s t o f a c i l i t a t e  the 'ore'  sections  reference.  L i t e r a t u r e was s e a r c h e d f o r i n f o r m a t i o n on the g e o l o g y of the Unuk and s u r r o u n d i n g a r e a s , and f o r i n f o r m a t i o n on the s i g n i f i c a n c e o f the s p e c u l a r i t e i n the q u a r t z v e i n s . The g e o l o g i c a l s k e t c h map o f the Unuk by J . T . Mandy ( B i b l . Ho* 10)  has. been r e p r o d u c e d on a l a r g e r s c a l e (Map  No. 2 back p o c k e t ) . ( B i b l . No. 5),  T h i s map, w i t h maps o f P o r t l a n d Ganal  I s k u t ( B i b l . No* 13) and S o u t h e a s t e r n A l a s k a  ( B i b l . No* 4) have been c o m p i l e d (Map No* 1 back p o c k e t ) .  r  ^ A  S u p p l i e s d r o p p i n g a t campsite from p l a n e f l y i n g a t two hundred f e e t .  Boxes o f d y n a m i t e d r o p p e d f r o m p l a n e a t camp on South F o r k .  GRAOEY GROUP - LOCATION AND ACCESSIBILITY The Graoey group i s on the South F o r k o f the Unuk R i v e r , twenty-eight miles north-west  of P r e m i e r , B . C . (see map N o . l ) .  The n a t u r a l r o u t e to the p r o p e r t y i s "by the Unuk R i v e r , whioh d r a i n s i n t o the P a c i f i c a t Burroughs B a y i A l a s k a ,  sixty  m i l e s n o r t h of K e t c h i k a n .  from  A wagon road was c o n s t r u c t e d  Burroughs Bay t o the i n t e r n a t i o n a l boundary t w e n t y - f i v e m i l e s u p r i v e r , and s i x m i l e s beyond, i n 1903, into disrepair.  but has s i n c e f a l l e n  However, Boundary L a k e , on the  boundary, i s a c c e s s i b l e to s m a l l a i r o r a f t ,  international  A good w a l k i n g  t r a i l has been m a i n t a i n e d u p r i y e r from Boundary Lake to L a .. B r a n t Creek on the South F o r k .  A t r a i l from L a B r a n t  Creek  to the Graoey group was s t a r t e d but not completed i n  1947.  The t r i p from Boundary Lake to the Graoey group t a k e s two d a y s , but o a b i n s a t G l a c i e r Creek and the mouth o f the F o r k p r o v i d e good o v e r n i g h t  South  accommodation.  An a l t e r n a t e r o u t e i s from P r e m i e r , B . C . to B i g M i s s o u r i by r o a d , and thence t o Tide Lake by pack t r a i l .  From Tide  Lake to South F o r k no t r a i l e x i s t s , but Frankmaokie  glacier  a f f o r d s a good grade over the summit to C a b i n Creek on the South F o r k . experienced  (See  p l a t e No. 1 ) .  T h i s r o u t e i s used o n l y by  mountaineers.  F r a g i l e equipment was back-packed t o the camp frpm Boundary L a k e .  The b u l k o f s u p p l i e s was w e l l t r u s s e d  about s e v e n t y - f i v e  into  pound b u n d l e s and dumped i n t o the snow  G l a c i e r pass from South F o r k to Bowser-Salmon P L A T E  HO.  1  valley.  •7-  from a l o w - f l y i n g p l a n e based a t K e t c h i k a n . dropped s u p p l i e s was w e l l above n i n e t y  Recovery  of  percent.  TOPOGRAPHY The topography of the Unuk i s t y p i c a l of the n o r t h e r n Coast Range.  Maximum r e l i e f i s seven thousand f e e t .  w a l l s i n most p l a c e s a r e s c a l a b l e .  Above t i m b e r l i n e  Valley at  t h i r t y - f i v e hundred f e e t , h e a t h e r s l o p e s p a s s upward i n t o domed r o c k r i d g e s , o r , i n the h i g h e r m o u n t a i n s , rough s e r r a t e d peaks out by g l a c i e r s .  (See  p l a t e H o . 2).  Tongues of  glacier  extend from the main i c e f i e l d s i n t o the heads o f the v a l l e y s ; and the main v a l l e y s e x h i b i t the  ' U ' shape c h a r a c t e r i s t i c  of  glaciation. P l a t e H o . 3 shows the headwaters Map No. 2 ) .  o f the Unuk ( a l s o  Gracey Creek i n the r i g h t f o r e g r o u n d  a long straight glaciated v a l l e y trending  see  oocupies  north-easterly.  Two m i l e s below i t s j u n c t i o n w i t h the South F o r k , l a B r a n t Creek e n t e r s f r o m the n o r t h , and the v a l l e y swings n o r t h w e s t e r l y t o i t s c o n f l u e n c e w i t h the v a l l e y o f Ketohum Creek and the main Unuk R i v e r .  The main Unuk R i v e r i s  considered  to be the r i v e r below the j u n c t i o n o f Ketohum and S u l f i d e Greeks.  It flows south-westerly,  and i s j o i n d d by many  t r i b u t a r y streams b e f o r e f l o w i n g i n t o Burroughs B a y . A l l t r i b u t a r i e s a r e l a d e n w i t h g l a c i a l s i l t , much o f whioh i s d e p o s i t e d i n the l o w e r r e a c h e s o f the r i v e r . lower r i v e r consists  o f many r e t i c u l a t i n g and  The  constantly  PLATE NO.  2  McQuillan  i i d g e and t h a headwaters o f the Unak. PLATS HQ. 3  changing c h a n n e l s , narrow panyons. r i v e r boats,  e x c e p t where i t plunges t h r o u g h f o u r  I t has been n a v i g a t e d w i t h f l a t - b o t t o m e d  but o n l y a t the expense of almost c o n t i n u o u s  lining. GLLMATB The c l i m a t e I s s i m i l a r t o t h a t of P o r t l a n d Oanal a r e a . A l t h o u g h no r e c o r d s o f p r e c i p i t a t i o n are a v a i l a b l e , i t  is  e s t i m a t e d t h a t w i n t e r s n o w f a l l would r e a c h twenty f e e t  at  the p r o p e r t y .  Patohes o f snow from one season l i n g e r u n t i l  i  j o i n e d by f r e s h snow of the next s e a s o n .  Above f o u r thousand  f e e t e l e v a t i o n snow f l u r r i e s can be expected a t any time d u r i n g the summer.  The abundance o f snow p r o h i b i t s g e o l o g i c a l  mapping u n t i l l a t e i n the summer, and i n c e s s a n t  rainfall  makes i t d i f f i c u l t even t h e n . HISTORY  The f i r s t a c t i v e p r o s p e c t i n g of the Unuk was done i n the e i g h t e e n n i n e t i e s ; Oreek.  but was m a i n l y f o r p l a c e r on S u l f a r e t s  The Cumberland p r o p e r t y , on S u l f a r e t s  C r e e k , was  s t a k e d f o r l o d e g o l d and s i l v e r about 1900 but has n e v e r been developed.  The a f o r e m e n t i o n e d wagon road was b u i l t t o  this property.  The Globe p r o p e r t y , n e a r the headwaters  the South P o r k , was a l s o staked about 1900. m i l l was e r e c t e d ,  service of  Though a stamp  no g o l d was p r o d u c e d .  A f t e r the d e a t h on the t r a i l i n 1903 o f Ketohum, the owner o f the Globe, i n t e r e s t  i n the Globe and the Unuk i n  Slobe g l a c i e r i n June (above) and i n September ( b e l o w ) .  Rough v a l l e y bottom near head of South Fork,  Campsite a t t i m h e r l i n e on the Graoey C l a i m s .  P l a n * l a n d i n g on Boundary l a k e a t the B r i t i s h C o l u m b i a - A l a s k a boundary t o take the orew out i n September.  l o o k i n g d o w n r i v e r ( s o u t h ) from M c Q u i l l a n ' s c a b i n at the j u n c t i o n of the South F o r k w i t h the main Unuk.  g e n e r a l waned u n t i l the n i n e t e e n t h i r t i e s , when p r o s p e o t p r s from P o r t l a n d C a n a l e n t e r e d the r e g i o n . Premier i n t e r e s t s  I n 1933 and  1934  diamond d r i l l e d and made open o u t s on a  group of c l a i m s s t a k e d i n 1932 on P r o u t P l a t e a u .  In  1946  Canadian E x p l o r a t i o n f u r t h e r developed the showings on these claims. GENERAL GEOLOGY V e r y l i t t l e geology has been done i n the Unuk. o n l y g e o l o g i c a l map i s a s k e t c h (Map N o . . 2 i n hack  The pocket)  made i n 1935 by D r . J . T, Mandy o f the B r i t i s h Columbia Department o f M i n e s . i e s t h i s map. trip,  A b r i e f report  ( B i b l . N o . 10)  I t was c o m p i l e d a f t e r a t e n - d a y  aocompan^  reconnaissance  d u r i n g w h i c h D r . Mandy had the a d v i c e and guidance  s e v e r a l o f the  'old-time  1  prospeotprs.  of  D r . Mandy had p r e v -  i o u s l y v i s i t e d Prout P l a t e a u ( B i b l . No. 11).  He s t a t e s  'The  s e d i m e n t a r y and v o l c a n i c r o o k s composing P r o u t P l a t e a u a r e s i m i l a r i n e x t e n t and c h a r a c t e r  and may p o s s i b l y be  w i t h the Upper Bear R i v e r s e r i e s o f J u r a s s i c the exposures  age.  correlated In places  o f t h i s s e r i e s may p o s s i b l y apprpach the  younger Nass s e r i e s h o r i z o n . ' r e p o r t on the Unuk i n 1905  F . E . Wright p u b l i s h e d a short  ( B i b l . No, 8 ) .  In an endeavor to determine the age o f the f o r m a t i o n s  in  the Unuk by s t r u c t u r a l and l i t h o l o g i o a l c o r r e l a t i o n , maps from nearby a r e a s have been c o m p i l e d i n Map N o . 1 ( i n back pocket). 1).  These i n c l u d e The I s k u t R i v e r A r e a , by P.A. K e r r o f the  Geological  -10Survey o f Canada. 2) .  ( B i o l . Ho.  13.)  The P o r t l a n d C a n a l A r e a by G. Hansen o f the  c a l Survey o f Canada. 3) .  Geologi-  ( B i b l . No. 5 : )  Southeastern  A l a s k a , by A . E . B u d d i n g t o n and  Chapin o f the U n i t e d S t a t e s G e o l o g i c a l S u r v e y . Structural Correlation -  Theodore  ( B i b l . No.  4.)  Intrusives.  The Coast Range i n t r u s i v e s r u n n o r t h w e s t e r l y through the correlated  areas*  The e a s t e r n c o n t a c t o f the  intrusives  a p p r o x i m a t e l y f o l l o w s the i n t e r n a t i o n a l boundary; t a c t s a r e i r r e g u l a r i w i t h many s a t e l l i t e s i n t r u s i v e s show c o n s i d e r a b l e granodiorite, biotite  heterogenity.  on b o t h f l a n k s .  hornblende  and gabbro f r o m  s e c t i o n s a l o n g P o r t l a n d C a n a l and Chiokamin r i v e r . reports d i o r i t e , orthoolase  p o r p h y r y , and s y e n i t e ,  Kerr as w e l l  most of the f a e i e s mentioned by B u d d i n g t o n , from the onofstikine  The  Buddington reports  quartz monzonite, quartz d i o r i t e ,  d i o r i t e , monzonite, hornblendlte,  but. c o n -  as  Iskut  sections.  The age o f the i n t r u s i v e s i s g i v e n by K e r r as t o Lower C r e t a o e o u s , Lower Cretaoftous.  Triassic  and by B u d d i n g t o n as Upper J u r a s s i c  The d e s c r i p t i o n s o f the T r i a s s i c  g i v e n by K e r r ( B i b l , No. 1)  to  intrusives  i n d i c a t e they a r e v e r y s i m i l a r t o  the d i o r i t e g n e i s s ' s i l l s ' on the Graoey g r o u p . S t r u c t u r a l C o r r e l a t i o n - Sedimentary and V o l c a n i c R o c k s . The r e g i o n a l t r e n d o f the p r e - i n t r u s i v e s e d i m e n t a r y and v o l c a n i c rooks i s n o r t h to n o r t h w e s t ,  p a r a l l e l that of  the  -11intrusives. flank.  T h i s t r e n d i a p a r t i c u l a r l y marked on the  western  C o r r e l a t i o n of sediments and v o l o a n i o s of the Unuk  a r e a on the e a s t f l a n k w i t h those of S o u t h e a s t e r n  A l a s k a on  the west f l a n k i s d i f f i c u l t because of the i n t e r v e n i n g i n trusives. Of the I s k u t a r e a K e r r s t a t e s "the s t r u c t u r e l y complex;  intense unsystematic  i s extreme-  f o l d i n g and f a u l t i n g are  p r e s e n t everywhere so t h a t the b o u n d a r i e s between  formations  are not w e l l d e f i n e d and can be i n d i c a t e d o n l y i n a g e n e r a l way."  ( B i b l . H o . 1 , P» 4 8 ) .  Structural correlation with  the Unuk i s thus w e l l n i g h i m p o s s i b l e . I n P o r t l a n d C a n a l the s t r u c t u r a l t r e n d o f the H a z e l t o n group i s g e n e r a l l y n o r t h to n o r t h w e s t .  This t r e n d , i f oon- '  t i n n e d , would b r i n g H a z e l t o n group r o c k s t h r o u g h a t the e a s t e r n p a r t of the Unuk d r a i n a g e b a s i n .  least  Mandy's o b s e r -  v a t i o n s i n the Unuk i n d i c a t e a n o r t h e r l y t r e n d t o the mentary and v o l c a n i c r o c k s , and t h u s s u b s t a n t i a t e  sedi-  correlation  with Portland Canal. Lithological Correlation. Mandy has mapped t h r e e main types of p r e - i n t r u s i v e rook i n the Unuk;  limestone,  volcanics with associated The l i m e s t o n e recrystallized.  argillaceous  sediments,  bedded  and  hypabyssals.  i s w h i t e t o grey i n c o l o r , and h i g h l y  S e c t i o n s o f w e l l over one thousand f e e t  predominantly limestone,  but f o l d i n g or f l o w a g e may g i v e  are  -12-  r e p e t i t i o n o r e x a g g e r a t i o n of the t r u e t h i c k n e s s .  The l i m e -  stone i n the I s k u t ( a r e ) t h i r t y m i l e s t o the n o r t h - w e s t s i m i l a r i n e x t e n t and c h a r a c t e r , d e f i n i t e l y Permian' i n age.  is  and has been c a l l e d  'fairly  Limestone i s known i n the  H a z e l t o n group o f P o r t l a n d C a n a l , but o c c u r s o n l y i n a few lenses of several f e e t thickness.  In Southeastern Alaska  l i m e s t o n e o c c u r s i n s e c t i o n s hundreds of f e e t i n t h i c k n e s s i n P a l a e o z o i c r o o k s , but o n l y i n t h i n l e n s e s i n Mesozoio r o o k s * The l i m e s t o n e of the Unuk R i v e r a r e a i s thus p r o b a b l y P a l a e o z o i o and l i k e l y P e r m i a n . A m i l e o r two to the west of the l i m e s t o n e band the s e d i m e n t a r y and v o l c a n i c r o o k s are metamorphosed to p h y l l i t e s , slates,  and s c h i s t s .  metamorphism; massive.  To the e a s t t h e y have undergone l i t t l e  the sediments are w e l l bedded and the v o l o a n i o s  The metamorphism t o the west may be a t t r i b u t e d t o  the g r e a t e r age o f these r o o k s , o r t o p r o x i m i t y t o the main body o f Coast Range i n t r u s i v e s . not intense  However, metamorphism i s  i n 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 a t are i n  c o n t a c t w i t h Coast Range i n t r u s i v e s i n P o r t l a n d C a n a l .  The  metamorphism of the Unuk r o o k s west o f the l i m e s t o n e , i s t h e n more l i k e l y due to the f a c t t h a t t h e y are o f g r e a t e r  age,  and have undergone more d i a s t r o p h i s m than those on the e a s t of the l i m e s t o n e , On the e a s t o f the l i m e s t o n e band, and on P r o u t P l a t e a u , the s e d i m e n t a r y r o c k s a r e w e l l bedded a r g i l l i t e s ,  sandstones,  and f i n e c o n g l o m e r a t e s , and the v o l c a n i o r o c k s a r e massive  green andesites.  The assemblage, as stated by Dr. Mandy,  ( B i b l . Ho. 11) olosely resembles the Bear River and Hass formations of the Hazelton group i n Portland Canal. The struotural and l i t h o l o g i c a l c o r r e l a t i o n suggests that the Unuk limestone i s Permian, the sedimentary and volcanic rocks to the east are Hazelton group and those to the west are Pre-.Permian.  (Jurassic?)  Ho f o s s i l s were found  i n the limestone and i t i s doubtful i f determinable f o s s i l s w i l l be found i n the. limestone or the rocks to the west because of the metamorphism. Mineralization. Rook exposed on the west flank of the Coast Range i n trusives has undergone metamorphism of a higher grade than rock exposed on the east flank. by pegmatite dykes predominate  Gneisses and schists cut on the west, i n d i c a t i n g a  deeper-seated type of metamorphism than on the east where a r g i l l i t e s and slates predominate.  Erosion has cut down to  the zone of flowage on the west, and the rocks exposed now were probably at a high temperature during the period of mineralization and thus not affected markedly by mineralizing fluids.  On the other hand, the rocks on the east would f r a c -  ture rather than flow, and the mineralizing f l u i d s would encounter new conditions of temperature and pressure, and deposit much of t h e i r load.  Mineralization i s not pronounced  on the western flank of the i n t r u s i v e s , but on the eastern  -14f l a n k oontaot metamorphic d e p o s i t s and m i n e r a l i z e d v e i n s are r e l a t i v e l y abundant. LOCAL GEOLOGY The Graoey Group i s on the mountain between Graeey Greek and the South F o r k (see  P l a t e N o . 3 and map N o . 2 ) .  mountain i s composed o f l i m e s t o n e , t u f f , and d i o r i t e g n e i s s .  The s e d i m e n t s ,  siltstone,  This argillite,  including tuff,  trend  n o r t h - w e s t e r l y , and d i p 40 t o 60 degrees n o r t h e a s t .  They  grade i n t o . o n e a n o t h e r ,  and a r e i n p l a c e s i n t i m a t e l y i n t e r - -  bedded, i n d i c a t i n g p r a c t i c a l l y s i m u l t a n e o u s d e p o s i t i o n d u r i n g some p e r i o d s . $  position.  The abundance o f l i m e s t o n e shows marine d e -  The beds o f the e l a s t i c s range f r o m a f r a o t i o n o f  an i n c h t o s e v e r a l f e e t i n t h i c k n e s s .  The main band of l i m e -  stone has an apparent t h i c k n e s s of w e l l over one thousand feet.  The sediments are i n t r u d e d by d i o r i t e g n e i s s  stocks  and s i l l ; l i k e b o d i e s , and a p l i t e , l a m p r o p h y r e , and s y e n i t e dykes. The mountain as a whole has not been mapped g e o l o g i c a l l y , but an o u t o r o p map was made c o v e r i n g the most i m p o r t a n t m i n e r a l showings (Map No. 3 ) .  The most i m p o r t a n t v e i n s l i e  i n a thousand-foot-wide sedimentary b e l t t r e n d i n g n o r t h w e s t e r l y . The b e l t i s bounded on the n o r t h - e a s t l i k e b o d i e s of d i o r i t e g n e i s s . northeast,  and s o u t h - w e s t by  The ' l o w e r s i l l ' ,  sill  on the  i s about t h r e e hundred f e e t wide and has been  t r a c e d f o r t h r e e thousand f e e t .  The ' u p p e r s i l l ' ,  on the  -15southwest, i s more i r r e g u l a r and not as well delineated, but is estimated to be several hundred to one thousand feet wide. Veins occur i n the sediments outside the s i l l s , but, though similar i n mineralization and attitude, have shown neither the widths nor the gold content-of the veins i n the central band of sediments. In some parts of the mapped area the sediments show olose folding and crenulation. The t u f f s have i n places been r e c r y s t a l l i z e d to a fine-grained gneiss.  The gneissic struc-  ture strikes northwest, p a r a l l e l to the s t r i k e of the beds and the axes of the f o l d s .  To the west high angle shearing  with a westerly s t r i k e i s widespread.  Discontinuous shears  are abundant throughout most of the mapped area.  No major  f a u l t s were proven, but one of about one thousand  feet h o r i -  zontal offset, s t r i k i n g northerly, may occur west of Ptarmigan H i l l .  x 80 THIN SECTION PHOTOGRAPH NO. 1  Quartz and oalcite have r e c r y s t a l l i z e d side by side, without formation of s i l i c a t e s . Serioite i s also present.  THIN SECTION PHOTOGRAPH NO. 2 Near the c o n t a c t with i n t r u s i v e g n e i s s the f i n e l a m i n a e i n t h e sediments a r e c r e n u l a t e d . liinerala are q u a r t z , c h l o r i t e and s e r i o i t e .  -16BOCK TYPES Limestone. fhe main band of limestone l i e s northeast of the lower sill,  outside the mapped area, but a few beds l i e i n the  central band of sediments. orystallized.  Thin sections show an interlocking mosaic of  grains up to three mm. twin-gliding.  A l l the limestone i s highly r e -  i n diameter.  Many grains show strong  Chemical tests prove a traoe of magnesium i n  the limestone. Knobby protrusions up to one foot i n diameter have formed from d i f f e r e n t i a l erosion where the limestone contains quartz. The alignment  of these protrusions i s p a r a l l e l to the con-  tacts of the bed and t h i s alignment age of the limestone, or may bedding, or both. .05 to .15 mm,  could be caused by flow-  be i n d i c a t i v e of the o r i g i n a l  The quartz grains i n the knobs range from  i n diameter.  The l a r g e r grains are strongly  fractured, s t r a i n shadowed, sutured, and intergrown.  Isolated  quartz grains i n the limestone are of smaller average s i z e , about .05 mm.  and are strongly s t r a i n shadowed.  The quartz i n the limestone could have originated as wind blown s i l t , water transported s i l t , or oherJb_nodules.  I f wind  or water transported, the quartz would possibly be accompanied by feldspars and/or s e r i o i t e .  A little  s e r i o i t e does occur  with quartz i n the limestone.  Chert nodules, on r e e r y s t a l l i z a -  t i o n would have quartz grains of considerable size v a r i a t i o n .  17 The grains here show a markedly small v a r i a t i o n i n size (.05 to  . i 5 mm.) i n spite of the r e c r y s t a l l i z a t i o n they have under-  gone. of  Ho beds of ohert have been found i n the area, but beds  s i l t s t o n e , i n places composed almost e n t i r e l y of quartz,  and i n other places grading into a r g i l l i t e and t u f f , are abundant.  The quartz i n the limestone i s of the same average  grain size as that i n the s i l t s t o n e , a r g i l l i t e , and t u f f .  The  quartz i s thus probably wind or water transported, or both. According to Tweahofel ( B i b l . Ho. 14) more grains tend to be rounded, and rounding occurs down to a smaller grain size (.03 mm.) silt  i n wind transported s i l t , than i n water transported  (.1 to .05 mm.).  R e c r y s t a l l i z a t i o n , however, has changed  the size and shape of the grains so much that these c r i t e r i a are no longer applicable.  Aeolian s i l t , however, tends to be  better sorted than water-transported s i l t , and as t h i s  silt  shows l i t t l e v a r i a t i o n i n grain size and i s predominantly quartz i t i s l i k e l y aeolian.  The i r r e g u l a r knotty aggregates  have formed from a ' r o l l i n g up' of the grains during the limestone  flowage. Other impurities i n the limestone are s e r i o i t e , tremolite,  c h l o r i t e , and opaque metallios.  These minerals are i n minute  amounts i n some beds, but are abundant i n others where the limestone grades into a r g i l l i t e s and t u f f s .  The tremolite  occurs as a few f i b e r s replacing quartz and carbonate i n a bed of s i l i c i o u s limestone close to the lower d i o r i t e gneiss sill.  x 25  THIN SECTION PHOTOGRAPH NO.9. Irregular contact of twin-glided carbonate with fine-grained t u f f .  Aotinolite  3hreds  have developed i n the carbonate.  .18Several beds of limestone about f i v e feet thick which outcrop twelve hundred feet north of Ptarmigan H i l l are intercalated with beds of t u f f , and contain inequidimensional fragments of green andesite t u f f up to several inches i n diameter.  These fragments are probably thin lenses of t u f f  which have 'rolled up' i n the limestone during i t s flowage. The e s s e n t i a l minerals i n the t u f f fragments are hornblende and plagioclase (oligoolase to andesine) i n about equal proportions. meter.  Grains of these average .15 mm. i n d i a -  Sphene, p y r i t e , and apatite are minor, forming about  one percent of the t o t a l . In the i n t e r i o r s of the t u f f fragments the hornblende grains are ragged, s l i g h t l y p o i k i l o b l a s t i c , and altered i n part (about one-third) to c h l o r i t e .  The plagioclase i s  kaolinized, p a r t i c u l a r l y i n the centers of the grains, and shows very l i t t l e twinning. ene.  Titanite i s clouded with leucox-  One or two small epidote grains are present. The carbonate f i v e or ten millimeters away from the t u f f  fragments has r e c r y s t a l l i z e d to grains several millimeters i n diameter, and these grains are strongly twin-?glided. Highly s t r a i n shadowed, fractured, sutured, and intergrown quartz grains up to .7.5 mm. i n diameter are present i n one or two knots i n the limestone.  They have probably originated i n  the same way as the knotty aggregates of quartz previously discussed. At the contacts of the t u f f fragments with the limestone  x 80 THIN SECTION PHOTOGRAPH NO. 7. P y r i t e oube w i t h i n c l u s i o n o f d i o p s i d e and a n o t h e r r e p l a c e d by a c t i n o l i t e a t oontact  o f t u f f fragment w i t h  limestone.  x 80 THIN SECTION PHOTOGRAPH NO. 8. P l a g i o c l a s e ( l i g h t grey) w i t h o r i e n t e d i n c l u s i o n s of f i b r o u s a c t i n o l i t e  (white).  -19r e a c t i o n a between the minerala  o f the t u f f and the carbonate  have produced d i o p s i d e , - t r e m o l i t e , and a c t i n o l i t e . r a d i a l aggregates o f a f i b r o u s c h l o r i t e after  are pseudomorphous  a pyroxene, p o s s i b l y d i o p s i d e , and others, w i t h  i a t e d magnetite, r e p l a c e a c t i n o l i t e . Shi;.owing much a l t e r a t i o n carbonate. and  Some  One p y r i t e  A few t i t a n i t e  to leucoxene are i s o l a t e d  g r a i n has an i n c l u s i o n  others a r e r e p l a c e d by a c t i n o l i t e  graph No. 7 ) .  No p y r i t e  the t u f f fragments.  assocgrains  i n the  of diopside,  ( T h i n s e o t i o n photo-  i s found i n the carbonate away from  The p y r i t e  has thus formed before  of the metamorphic s i l i c a t e s , and i s probably  some  not from  later  hydrothermal a c t i v i t y . The  d i o p s i d e , t r e m o l i t e , and a c t i n o l i t e  g r a i n s are most  abundant i n a band seven o r e i g h t m i l l i m e t e r s wide a t the contacts  o f the t u f f fragments and l i m e s t o n e .  They are not  found i n the c e n t r a l p o r t i o n s o f the t u f f fragments. rough z o n i n g has taken p l a c e .  Actinolite  has formed f o r  s e v e r a l m i l l i m e t e r s on both s i d e s of the c o n t a c t s . showing no green pleochroism,  A  Tremolite,  and d i o p s i d e have formed  only  i n the carbonate s e v e r a l m i l l i m e t e r s away from the c o n t a c t s . P l a g i o c l a s e has r e c r y s t a l l i z e d  a t the c o n t a c t .  The  g r a i n s are f o u r or f i v e times the diameter of those i n the t u f f , and i n one p l a c e c o n t a i n o r i e n t e d i n c l u s i o n s o f a c t i n o lite  (Thin s e c t i o n photograph No. 8 ) , thus must have r e p l a c e d  the a c t i n o l i t e .  Some o f the f e l d s p a r was probably  coarse as i t occurs  originally  i n bands a n g l i n g away from the c o n t a c t .  -20The coarse plagioclase has the same composition as that i n the t u f f (oligoclase to andesine), and thus has undergone no chemical change. No metasomatism was necessary to produce the a l t e r a t i o n at the contacts.  The iron i s provided by the hornblende and  pyrite of the t u f f , the s i l i c a by the hornblende of the t u f f , and/or the quartz inclusions i n the carbonate.  The magnesium  comes from the hornblende or i t s c h l o r i t e a l t e r a t i o n i n the t u f f , and from the s l i g h t l y magnesian carbonate.  The oalcium  comes from the carbonate and from the hornblende i n the t u f f . The t i t a n i t e may be a primary constituent of the t u f f , or may have i t s titanium derived from t i t a n i f e r o u s magnetite or ilmenite i n the t u f f , The rough zoning of the silicates.supports the hypothesis that a l t e r a t i o n i s purely metamorphic.  Calcium and magnesium  and s i l i c a need not migrate f a r as they are present i n both limestone and t u f f .  Iron, which i s present only i n the tuff»  has not migrated f a r from the contacts. Ferriferous a c t i n o l i t e at the contact gives way to the non-ferriferous tremolite and diopside several millimeters away from the contacts. Tuff near Q-25  vein contains disseminated carbonate  grains, and no reaction has taken place here between t u f f minerals and carbonate.  However, the carbonate i s less  abundant, the rock has undergone shearing rather than flowage. The shearing may have prevented the formation of the new metamorphic minerals, p a r t i c u l a r l y diopside,  Siltstone. . The s i l t s t o n e i s very t h i n l y bedded, white to grey and green i n color, and composed predominantly of quartz.  Some  beds contain abundant feldspar and c h l o r i t e , and grade into tuff. The quartz grains i n the s i l t s t o n e have diameters up to •3 mm., but i n most t h i n sections the maximum i s .1 mm. are  Grains  s t r a i n shadowed, sutured, and intergrown to form a f i n e -  grained quartzite. noted.  No evidence of aocretionary growth was  Serioite,. c h l o r i t e , and c a l o i t e f i l l i n t e r s t i c e s , and  andesine forms minute laminae i n the s i l t s t o n e . The feldspar i s probably both volcanic and d e t r i t a l . The s i l t s t o n e s grade into andesite t u f f s , containing andesine but some bands i n the s i l t s t o n e that are high i n feldspar contain no mafic minerals, and are thus l i k e l y d e t r i t a l rather than volcanic i n o r i g i n .  The feldspar i n these bands i s of  the same grain size as the associated quartz. zation  The r e c r y s t a l l i -  prevents determining whether the s i l t i s water transport-  ed or aeolian. Tuff  Thin bedded, green to grey, water-lain andesite-tuff forms the bulk of the central band of 'sediments\ ant  minerals are andesine and hornblende.  constituent.  Predomin-  B i o t i t e i s a minor  The grains average .15 mm. i n diameter, and  show markedly l i t t l e v a r i a t i o n i s size i n any one bed, and even i n different beds.  The o r i g i n a l fragments have been well  compacted and r e c r y s t a l l i z e d ;  no fragmental outlines were  x 80 THIN SECTION PHOTOGRAPH NO. 3 H o r n b l e n d e forme ' f e a t h e r - a m p h i b o l e ' i n the r e g i o n a l l y metamorphosed t u f f a . The o t h e r m i n e r a l i a a n d e a i n e p l a g i o c l a s e .  x 25 THIN SECTION PHOTOGRAPH NO. 4 The  d a r k band c r o a a - c u t t i n g t h e h o r n b l e n d e l i n e a t i o n i s c a u s e d by a l t e r a t i o n o f f e l d s p a r t o o l a y -  minerala.  I t may r e p r e s e n t t h e o r i g i n a l bedding.  -22seen i n the f i e l d or i n thin section. interstitial  Fine o h l o r i t i c material  to the plagioolase and hornblende  d e v i t r i f i e d ash or glass.  i s probably  Aooessory magnetite, p y r i t e , hema-  t i t e and sphene are associated with the mafio minerals. Although quartz i s present i n many of the specimens, i t i s considered to be d e t r i t a l rather than v o l c a n i c  The r e l a -  tive amount of quartz varies greatly i n d i f f e r e n t beds. t u f f s grade into s i l t s t o n e .  The  The quartz grains are i n many  places i n bands and lenses rather than disseminated.  The  d i o r i t e s i l l s are the intrusives nearest i n age and i n d i s tance to the. t u f f .  The s i l l s and the t u f f may represent  early igneous a c t i v i t y associated with the Ooast Range intrusives.  I f so, the s i l l s , though younger than the t u f f ,  are probably derived from the same magma as the t u f f .  The  l a t e r s i l l s contain no quartz, and, as late d i f f e r e n t i a t e s of the same magmatic facies are usually more s i l i c i o u s than e a r l i e r d i f f e r e n t i a t e s i t i s doubtful that the e a r l i e r  tuff  would contain quartz. In places the t u f f grades into limestone, and here carbonate i s l o c a l l y abundant i n the t u f f .  Where oarbonate  grains are disseminated i n the t u f f no reaction between t u f f and carbonate has occurred, although, as described under limestone, i n some places fragments of t u f f i n limestone were altered on the borders to diopside, tremolite, and a c t i n o l i t e . In one or two areas, and i n p a r t i c u l a r i n the outcrop on the north side of Ptarmigan H i l l ,  the feldspar i n the t u f f has  -23"been saussuritized.  Here epidote i s very abundant, forming  over f i f t y percent of the rook.  It i s mostly i n patches  associated with plagioclase, but also occurs i n i r r e g u l a r microscopic v e i n l e t s and lenses cutting a l l other minerals. A l b i t e , untwinned and with abundant inclusions, has formed i n i r r e g u l a r masses probably replacing andesine, although andesine could not be. proven. out  Calcite grains are disseminated through-  the s l i d e s , "kaolins' cloud the feldspars, and small  z o i s i t e grains form inclusions i n the feldspars.  Chloriti-  zation of the hornblende acoompanies the s a u s s u r i t i z a t i o n of the  feldspar, but some of the c h l o r i t e has been replaced by  the  abundant epidote. A l t e r a t i o n i s not confined to the t u f f near the c h l o r i t e  gneiss s i l l s .  Areas several hundred feet from intrusive  outcrops have abundant epidote. the  Some of the t u f f beds near  s i l l s show crenulation, p a r t i c u l a r l y where the s i l l s cut  across the bedding, but thin sections show no reoonstitution of  the minerals. In some areas the t u f f shows no bedding, and i s i n d i s -  tinguishable from fine-grained intrusive d i o r i t e gneiss. These areas have been mapped as massive greenstone. the  Since  outcrops l i e on strike of t u f f beds rather than on strike  of d i o r i t e gneiss s i l l s , and since most thin sections contain quartz, which does not occur i n the intrusives, the rock i s undoubtedly 'sedimentary' i n o r i g i n . hornblende  'feather amphibole  1  Marked l i n e a t i o n of  (Thin Section photograph No. 3)  -24indieates dynamic metamorphism was stronger here than i n Surrounding areas.  In one t h i n section (see Thin Section  photograph No. 4) a band of k a o l i n i o a l t e r a t i o n orosses the amphibole l i n e a t i o n , and may Why  represent the o r i g i n a l bedding.  dynamic metamorphism has been more intense i n these areas  has not been determined.  The areas are not p a r t i c u l a r l y  close to exposed intrusives, the bedded rooks on t h e i r margins are not severely folded, and they are too i r r e g u l a r to be associated with concealed f a u l t i n g .  The gneissic structure  in them i s p a r a l l e l to the regional f o l d i n g and f o l i a t i o n . Gneiss of Tuff Origin. Where the sedimentary rocks are s i l i o i o u s the contact with the d i o r i t e g n e i s 3 s i l l s are sharp, but where andesite t u f f i s the main sediment the t u f f has r e c r y s t a l l i z e d , bedding i s obscured, and the contact with the s i l l i s i n d i s t i n g u i s h able.  Some of the rock mapped as d i o r i t e gneiss has undoubt-  edly formed by r e c r y s t a l l i z a t i o n of t u f f under dynamic metamorphism.  The gneiss i n several outcrops shows bands of  coarser and f i n e r grain size and l i g h t e r and darker grey-green colors.  These bands may be from multiple intrusion, but are  more l i k e l y o r i g i n a l bedding i n t u f f .  The gneissio structure  In these bands i s p a r a l l e l to that i n the s i l l s and to the regional l i n e a t i o n .  This paragneiss contains the same minerals  as the orthogneiss.  Andesine and hornblende  predominate;  b i o t i t e , p y r i t e , magnetite, sphene, and specularite are minor  x  85  THIH SECTION PHOTOGRAPH I O . 5  G n e i s a i c s t r u c t u r e from l e n s e y a g g r e g a t i o n s of hornblende c r y s t a l s . Andesine comprises mo3t o f t h e r e s t o f t h e s l i d e but c h l o r i t e e p i d o t e , 3 e r i c i t e and carbonate a r e a l s o p r e s e n t .  x 80 THIN SECTION PHOTOGRAPH i*0. 6 Fresh andesine i n r e c r y s t a l l i z e d t u f f . Hornblende, q u a r t z , c h l o r i t e , a e t i n o l i t o , and e p i d o t e a r e p r e s e n t .  -25  forming about one percent of the rock. size i s .2 mm.  The average grain  A few of the,specimens contain quartz, and  thus are probably sedimentary rather than i n t r u s i v e .  The  gneissic structure i s produced by aggregation of hornblende grains to p a r a l l e l lenses.  Andesine has been kaolinized and  s e r i c i t i z e d , and hornblende c h l o r i t i z e d . epidote (.05 mm.  Minute grains of  i n diameter) are associated with the kao-  l i n i o a l t e r a t i o n of plagioclase. Gneiss has been formed by r e c r y s t a l l i z a t i o n of the andesi t e t u f f f o r twenty or t h i r t y feet on each wall of the acid dykes.  The gneiss shows no addition of material, but i s  coarser i n grain size than the t u f f .  The gneissic structure  has been produoed by segregation of hornblende into p a r a l l e l lenses.  The structure i s not p a r a l l e l to the walls of the  dykes, but i s p a r a l l e l to the regional f o l i a t i o n .  The dykes  must thus have been intruded before or during the orogenio period. Intrusive D i o r i t e Gneiss. 'The intrusive gneiss, l i k e that formed from t u f f , i s composed predominantly of andesine and hornblende, but i t contains no quartz.  Apatite, t i t a n i t e , and ilmenite or  titaniferous magnetite are accessory minerals.  Euhedral  crystals of hornblende up to a millimeter i n diameter occur in p a r a l l e l lenses i n a groundmass of subhedral andesine grains of about .5 millimeters diameter.  (Thin Section photo-  -26-  graph No.  5)  At sharp contacts with the sediments the gneiss i s fine grained from c h i l l i n g , and i n places cuts the sediments at a small angle,  At one exposure the sediments have been  crenulated and shattered at the contact (Thin Section photograph No. 2.)* Angular fragments found i n boulders of gneiss may  be xenoliths of t u f f or a u t p l i t h s . The gneiss has undergone s i m i l a r a l t e r a t i o n to the t u f f .  Feldspars have been saussuritized with the production of a l b i t e , epidote, c l i n o z o i s i t e , and olay minerals, and have been s e r i o i t i z e d . epidote.  Hornblende has altered to c h l o r i t e s and to  Ilmenite or titaniferous magnetite i s rimmed by  t i t a n i t e , and the two are altered i n part to  leucoxene.  Four c r i t e r i a have been found to distinguish the orthogneiss from paragneiss.  Quartz, probably d e t r i t a l i n o r i g i n ,  i s i n places disseminated and i n minute lenses and bands i n the paragneiss, but has not been found i n orthogneiss.  In  places vague banding, probably bedding, can be traced into paragneiss.  The orthogneiss contains xenoliths of t u f f or  autoliths.  The orthogneiss, although s i l l - l i k e , i n places  crosscuts the bedding of the sediments. Dykes. Sediments and gneiss are cut by a p l i t e , lamprophyre and syenite dykes. The a p l i t e dykes are composed of about equal proportions  J  -27-, of aubhedral orthoclase, quartz and a l b i t e i n grains up to f i v e millimeters i n diameter. anorthoolase  Muscovite, c h l o r i t e , and  are minor constituents, forming less than one  percent of the dykes. One or two grains of garnet and pyrite were noted. Parts of some orthoclase grains have r e c r y s t a l l i z e d , probably because of s t r e s s .  P a r a l l e l laths, arranged en  echelon and i n places joined, are a l l of the same optic orientation, but of a d i f f e r e n t orientation than the host crystal.  The laths are clearer than the rest of the c r y s t a l .  In places orthoclase grains are replaced on the borders by anorthoolase.  Pine flamboyant quartz grains, .1 mm. i n  diameter, f i l l i r r e g u l a r fractures i n orthoolase and a l b i t e . The a p l i t e dykes have undergone l i t t l e  alteration.  Serioite flakes replace the orthoclase, and clay minerals cloud the plagioclase.  Ghlorite has completely replaced the  few grains of mafic o r i g i n a l l y present. The a p l i t e dykes have i r r e g u l a r walls, s t r i n g e r s of a p l i t e forming r e t i o u l a t i n g v e i n l e t s i n the wall-rock.  The  andesite t u f f wall-rock has r e c r y s t a l l i z e d to d i o r i t e gneiss, as discussed under 'Gneiss of Tuff Origin'. Several lamprophyre dykes also cut both sedimentary rocks and d i o r i t e gneiss.  Thin sections were made of two of these  dykes. One,, a kersantite, contains twenty percent b i o t i t e i n flakes averaging .2 mm. i n diameter.  The b i o t i t e forms  -28inolusions i n labradorite laths and p a r t i a l l y f i l l s s t i c e s between laths.  inter-  Augite, i n phenocrysts .5 mm, i n  diameter, makes up two or three percent of the rock.  Labra-  dorite laths, up to 1 mm, long and forming seventy peroent of the rock, have a sub-parallel disposition, giving the rock a trachytoid texture. grains .15 mm.  Two or three percent of quartz i n  i n diameter i s present with b i o t i t e i n the  i n t e r s t i c e s between the labradorite and augite c r y s t a l a . Minute graina of opaque, probably magnetite, are present. The other, a spesaartite, has s i x t y - f i v e percent euhedral hornblende phenocrysts up to 2 mm, long.  One percent of  b i o t i t e i s scattered through the s l i d e both i n hornblende phenocrysts and t h e i r i n t e r s t i c e a . ,5 mm.,  forms the groundmass.  Andesine i n grains up to  Minor apatite i s scattered  throughout the groundmasa and i n one place forms an aggregate of a dozen or more c r y s t a l s . Both rooks are quite fresh, augite and hornblende showing only s l i g h t a l t e r a t i o n to c h l o r i t e , and feldspar a l i t t l e clouding by clay minerals. One outcrop of a syenite dyke was found.  This dyke  contains s i x t y to seventy percent a l b i t e laths of random orientation ranging i n size from several microns to several millimeters;  and thus giving the rook a seriate texture.  Hornblende grains, mostly twinned and very a c i c u l a r , up to •5 mm. long, form inclusions i n some of the large a l b i t e grains, and are scattered through the rock with the fine  -29-*  a l b i t e laths.  Chlorite and magnetite pseudomorph pyroxene,  apatite and magnetite are aooessory minerals. Coast Range Intrusives (not inoluding Trlassio? s i l l s ) . The eastern contact of the main bodfc of Coast Range intrusives i s about five miles southwest of the property, but several stocks outcrop i n the sedimentary and volcanic rocks east of the property.  Specimens were taken from one  of these stocks, about four miles east. The rock i s a medium-grained granite.  Zoned o l i g o o l a s e -  a l b i t e forms f i f t y percent of the rock, orthoclase t h i r t y percent, quartz ten percent, and b i o t i t e and hornblende ten percent.  Some of the orthoclase enveloped  the plagioclase  and quartz, giving the rock a p o i k i l i t i o texture.  Sphene and  ilmenite or t i t a n i f e r o u s magnetite are accessory minerals. Alteration i s slight;  plagioclase i s somewhat clouded by  clay minerals, orthoclase contains a few flakes of s e r i e i t e , and hornblende shows o h l o r i t i z a t i o n . mineral are bordered by leuooxene.  Sphene and the opaque  -30MB TAMORPHISM  Sedimentary rocks have undergone minor contact metamorphism where they are intruded by d i o r i t e s i l l s , but both s e d i ments and s i l l s have undergone regional metamorphism. Where the contacts of d i o r i t e s i l l s are close to s i l i c i o u s limestone minor tremolite has formed, and where s i l l s intrude andesite t u f f the t u f f has r e c r y s t a l l i z e d  to d i o r i t e gneiss.  Where calcareous t u f f i s intruded a few garnets have formed, but these are l o c a l i z e d within a few feet of the contact. large skarn zones are found.  Uo  The d i o r i t e must have been low  in v o l a t i l e s , and transmitted l i t t l e heat to the country rock. Dynamic metamorphism has produoed a regional f o l i a t i o n . The gneissic structure i n both the s i l l s and the r e c r y s t a l l i z ed t u f f trends northwesterly.  Hornblende has the feathery  p o i k i l o b l a s t i c form t y p i c a l of dynamic metamorphism. is r e c r y s t a l l i z e d ;  Limestone  the carbonate grains show twinrgliding  from flowage, but have not reacted with inclusions of quartz. Quartz grains i n a l l rocks except the acid dykes show s t r a i n shadowing. from  Quartz inclusions i n the limestone are aligned  flowage. Most of the metamorphism i s regional, from orogenic  movements associated with the coast range intrusives;  but  some l o c a l contact metamorphism has been produoed by the diorite  sills.  -31STHUGTUBE Folding. The c e n t r a l band o f sediments has been f o l d e d i n t o n o r t h westerly-trending discontinuous a n t i o l i n e s , m o n o c l i n e s p l u n g i n g to the n o r t h w e s t .  s y n c l i n e s and  Some of t h i s f o l d i n g  may be due t o the i n t r u s i o n o f the s i l l s , f o r i t becomes l e s s i n t e n s e away from the  sills.  However* the s i l l s a r e c o n s i d e r e d t o have undergone d e f o r m a t i o n w i t h the sediments because: s i m i l a r metamorphism t o the s e d i m e n t s ,  t h e y have  some  suffered  the g n e i s s i c  structure  i n them i s p a r a l l e l t o the r e g i o n a l f o l i a t i o n ( a l t h o u g h a p r i m a r y flowage s t r u c t u r e would have the same t r e n d s i n c e s t r i k e o f the s i l l s i 3 p a r a l l e l the r e g i o n a l f o l i a t i o n , would not be as marked a s t r u c t u r e ,  it  and would more l i k e l y be  caused by o r i e n t a t i o n o f i s o l a t e d g r a i n s , r a t h e r  than  a g g r e g a t i o n o f g r a i n s i n t o l e n s e s sueh as has o c c u r r e d fractures,  the  here),  i n c l u d i n g those m i n e r a l i z e d a r e c o n t i n u o u s from  sedimentary r o c k s i n t o s i l l s , no dykes of d i o r i t e from the s i l l s out i n t o the  sediments.  The time of i n t r u s i o n o f the s i l l s i s i m p o r t a n t . s i l l s were i n t r u d e d w h i l e the sediments were s t i l l flat-lying,  they would r a i s e  the  relatively  the o v e r l y i n g s e d i m e n t s ,  would p r o b a b l y n o t cause f o l d i n g i n them.  If  but  On the o t h e r hand,  i f they were i n t r u d e d a f t e r the sediments had been f o l d e d or t i l t e d so t h a t they dipped a t moderate or h i g h a n g l e s ,  32 f o l d i n g (or further folding) i n the sediments between s i l l s would more l i k e l y take place.  I f , on the basis of the  correlation discussed previously, the sediments are considered to be Palaeozoic, and the s i l l s T r i a s s i c , the problem of the conformity of Palaeozoic rocks to T r i a s s i c rocks i s s t i l l to be solved, to determine the amount of f o l d i n g before intrusion of the s i l l s .  In the Iskut area the contact be-  tween Permian and T r i a s s i c i s unconformable; eastern Alaska i t i s suspected  and i n South-  of being perhaps angularly  unconformable, but not markedly so (a v a r i a t i o n of twenty degrees i n dip but no change i n strike i s reported i n one place).  On the whole, there does not seem to be much orogeny  before T r i a s s i c time, which would indicate that the T r i a s s i c ? s i l l s were intruded into r e l a t i v e l y undisturbed  s t r a t a , and  thus would produce l i t t l e further disruption i n them. On the basis of the available f i e l d information, the upper and lower are not considered to be parts of the  one  trough-like body which contains a shallow basin of sediments, for the following reasons: dip  at the contacts the s i l l s do not  under the sediments consistently, the regional dip i s  f a i r l y steep, about s i x t y degrees northeast, the sediments between the s i l l s , though folded and fractured, contain no dykes of d i o r i t e . The r e l a t i o n of the s i l l s to the sedimentary rocks i s important  because, although veins continue from sedimentary  rocks into d i o r i t e , they diminish from about f i v e feet to one  -33foot i n width.  Samples taken on surface indioate a decrease  in gold content where d i o r i t e i s the host rook.  Apparently  the d i o r i t e i s unfavourable to mineralization. Regional Fracture  Pattern.  A l l the dykes strike from f o r t y to s i x t y degrees east of north and dip v e r t i c a l l y .  The  i r r e g u l a r i t y of the dykes»  especially the aplite» indicate the fractures they occupy are tensional. The quartz veins, including those outside the central band of sedimentary rooks, are c l o s e l y p a r a l l e l , s t r i k i n g south s i x t y - f i v e degrees east, and dipping eighty degrees north. A zone of abundant shearing with specularite mineralization i s exposed i n the outcrop north of Ptarmigan H i l l .  The  shears vary f o r t y degrees i n s t r i k e , but those of most abundant go#ge strike northerly.  Dips are v e r t i c a l .  Bands of  limestone several hundred feet wide on the east of t h i s broken zone are not found on strike*on the west of the zone. A band of limestone to the north, outside the mapped area, may  be the continuation.  A right-hand  f a u l t of over one  thousand feet horizontal offset i s suspected.  The presence  of specularite i n stringers several inches wide i n the zone *  indicates the f a u l t i n g was Q-17  and Q-E3  In part pre--mineralization.  vein are each offset several feet by l e f t -  hand f a u l t s , and a f a u l t c u t t i n g o f f the west end of  Q-22  vein has the same s t r i k e , north f i f t e e n degrees east, indicate ing Q-17 and Q-22 are the same vein, offset by a left-hand fault. If the structures, excluding the post-vein  left-hand  f a u l t s , are assumed to have resulted from one set of forces, they may be f i t t e d into the s t r a i n e l l i p s o i d diagram as follows: y<-^ reborn?/ /o/ci/nf c?nd /o/'af/o/t -/T7/f>erc7//zccS  /ace// of /c?r-ye cS'J/s/'&cr/z'esz/  fe/n  f/'//e</  jS?c<»-  r  aortas  The veins are known to have formed on shear zones, because the wall-rock, p a r t i c u l a r l y the hang-wall, has abundant gouge, and where the quartz pinches out between Q-17 and Q-17 west veins sheared rock p e r s i s t s . The folding, with regional f o l i a t i o n p a r a l l e l the axes of the folds, indicates the stress oausing the deformation was pressure.  From the s t r a i n e l l i p s o i d diagram above, this  pressure was from the southwest or northeast. The two evident  sources of pressure are the l o c a l  sills,  trending northwest, and the main body of Coast Range i n trusives, also trending northwest.  The metamorphism i s  -35* regional, thus l i k e l y produced by the orogeny associated with* the Coast Range intrusives.  I f the fractures are_ produced  by the same stress, they must be regional also, but a larger area w i l l have to be mapped to v e r i f y t h i s . Relation of Veins to S i l l s . The veins show no direct s p a t i a l r e l a t i o n to the s i l l s . Q-19 vein, Q-25 vein, and several veins outside the mapped area, are well over one thousand feet from s i l l outcrops. Ho marked ohange i s noted i n the mineralogy i n tracing the veins away from the s i l l s .  Vein fraotures occur well into  the s i l l s rather than just on the borders.  Many other  mineral deposits, including one reported to contain specul a r i t e , have been found i n the Unuk.  Thus the mineralizing  f l u i d s probably were not derived from the d i o r i t e  sills,  but probably were derived from the main Coast Range intrusive or  i t s satellites.  36VEINS.  general. The quartz veins have formed i n shear zones, as indicated "by gouge on the walls, but no movement along the zones has been proven.  The veins continue from sediments into d i o r i t e  but diminish i n width and gold content i n the d i o r i t e . veins contain about ten percent of metallios.  The  In order of  abundance these are galena, p y r i t e , specularite, chalcopyrite, sphalerite, magnetite, three soft minerals^ possibly t e l l u r i d e s , and gold.  Q-17  vein Is by f a r the most interesting, both  economically and mineralogically. opment has been done on i t .  Most of the surface devel-  In one place i t outcrops con-  tinuously f o r over one hundred  feet.  Wall Rook A l t e r a t i o n . F a i r l y fresh samples were obtained from Q-17 vein to determine the nature of the wall rock a l t e r a t i o n .  Specimens  were taken, as-closely as could be determined, from the same bed, and at 8 f t . , 4 f t . , 3 f t . , 2 f t . , 1^- f t . , and & f t . from the vein. between Q-17  A specimen was taken from the shear zone  and Q-17  west veins.  At eight feet from the vein the wall rock shows no a l t e r a tion that can be attributed to hydrothermal a c t i v i t y .  It i s  metamorphosed, but the metamorphism i s similar to that i n most t u f f specimens taken from the mapped area.  The andesine  is i n part well twinned, and although altered to clay minerals, i s not more so than i n t u f f outcrops away from the veins.  -37* E p i d o t e and c h l o r i t e have developed as a l t e r a t i o n o f p l a g i o c l a s e and h o r n b l e n d e , but these m i n e r a l s are a l s o p r e s e n t t u f f and g n e i s s  i n most o t h e r p a r t s o f the  in  area.  F o u r f e e t from the v e i n the w a l l r o c k s t i l l shows no change;  andesine  i s w e l l t w i n n e d , hornblende s t i l l  •feather-amphibole'  the  type o f the m a j o r i t y o f the t u f f  e p i d o t e , c h l o r i t e , and k a o l i n s are m i n o r .  However q u a r t z ,  w h i c h i s u s u a l l y d i s s e m i n a t e d o r i n t h i n bands i n the o c c u r s as t h i n i n t r o d u c e d v e i n l e t s i n the t h i n The n e x t s e o t i o n ,  (.03  vein,  Many o f the p l a g i o c l a s e  have been c o m p l e t e l y r e p l a c e d by s e r i o i t e . serioite  tuff,  section.  t a k e n a t t h r e e f e e t from the  shows c o n s i d e r a b l e a l t e r a t i o n .  specimens,  Only the  grains  larger  f l a k e s show the maximum b i r e f r i n g e n c e o f n o r m a l  mm. t h i c k ) s e c t i o n s ;  most f l a k e s are about . 0 1 mm.  t h i o k , and thus low i n b i r e f r i n g e n c e .  The c l a y m i n e r a l s  here abundant, but not as abundant as the s e r i o i t e .  Quartz  v e i n l e t s are more numerous, f o r m i n g t h r e e o r f o u r p e r c e n t the s e o t i o n .  are  of  The few f e l d s p a r s t h a t are f r e s h enough t o show  t w i n n i n g have t w i n l a m e l l a e o f g r e a t e r e x t i n c t i o n ( l a b r a d o r i t e instead of andesine);  angles  and one o r two g r a i n s have  two s e t s o f t w i n l a m e l l a e a t r i g h t a n g l e s .  It  is doubtful,  however, t h a t t h i s more c a l c i c f e l d s p a r has been i n t r o d u c e d , f o r i t shows the same h a z i n e s s as the andesine f u r t h e r away from the v e i n , and shows no v e i n i n g r e l a t i o n s to  indicate  replacement. A t two f e e t from the v e i n the f e l d s p a r has almost  completer  -38l y disappeared; chlorite.  and hornblende has a l t e r e d i n e n t i r e t y to,  The w a l l r o c k i s here composed o f q u a r t z and one o r  two vague p l a g i o c l a s e r e s i d u a l s i n a f i n e g r a i n e d groundmass of s e r i e i t e , c h l o r i t e , and c l a y m i n e r a l s .  A few f r a c t u r e s  a c r o s s t h e t h i n s e c t i o n a r e b o r d e r e d by f a i r l y c o a r s e (.1  mm.)  flakes of serieite. The n e x t s e c t i o n was t a k e n one and o n e - h a l f f e e t from t h e v e i n , i n an a r e a where t h e r e a r e few f r a c t u r e s o r v e i n l e t s . I t showed s u r p r i s i n g l y l i t t l e a l t e r a t i o n when compared t o t h e s e c t i o n t a k e n two f e e t from the v e i n . s p a r has been s e r i c i t i z e d ;  About h a l f t h e f e l d -  t h e remainder i s f a i r l y f r e s h and  i s w e l l t w i n n e d , andesine i n c o m p o s i t i o n . i n p a r t (about h a l f ) r e p l a c e d by c h l o r i t e .  Hornblende i s o n l y Disseminated  q u a r t z , p r o b a b l y r e s i d u a l , i s s t r a i n shadowed and r e c r y s t a l l ized* but t h i s deformation occurs i n a l l the sedimentary quartz. A t one h a l f a f o o t from t h e v e i n a l l m i n e r a l s except t h e q u a r t z a r e r e c o n s t i t u t e d t o a f i n e p u l v u r u l e n t mass o f s e r i e i t e , c h l o r i t e , and k a o l i n s .  Some Of t h e 3 e r i c i t e has  grown t o p o i k i l o b l a s t i c m u s c o v i t e , p a r t i c u l a r l y n e a r tures.  frac-  Several r e g u l a r v e i n l e t s of a l b i t e , c l e a r but w i t h  p o o r l y developed t w i n n i n g , t r a n s e c t t h e s e c t i o n . The n e x t s e c t i o n was t a k e n from t h e shear zone between Q-17 and Q-17 west v e i n s , and i s n o t from the same bed as t h e s e c t i o n s d e s c r i b e d above.  The o r i g i n a l r o c k , however, was  s i m i l a r andesite or dacite t u f f .  An assay o f t h i s  sheared  -39-  rook gave several tenths of an ounce of gold per ton.  Serio-  i t e shreds, constituting about t h i r t y peroent of the s l i d e , and c h l o r i t e (five peroent) show a marked p a r a l l e l i s m to lenses of carbonate and to the d i r e c t i o n of elongation of the a l b i t e grains.  Carbonate lenses form about t h i r t y percent  of the s l i d e , and a l b i t e , poorly twinned and p a r t l y s e r i o i t ized, forms about t h i r t y - f i v e peroent.  Highly strained  quartz i s present i n disseminated grains and lenses.  Eu- •  hedral pyrite crystals are present i n the carbonate lenses, and i n polished seotion the pyrite i s seen to be rimmed and replaced by marmatitio sphalerite.  A few subhedral grains,  possibly apatite, are too small to i d e n t i f y . Ghost-like inclusions of wall rock were found i n the vein i n many places.  The fragments are completely altered  to a soft pale green s e r i c i t i o material too f r i a b l e to permit making t h i n sections. Wall rock a l t e r a t i o n i s thus confined to narrow l i m i t s , having progressed only three or four feet into the walls. S e r i o i t e , clay minerals, and c h l o r i t e have formed by altera-? tion of the plagioclase and hornblende.  Quartz and a l b i t e  have been introduced i n v e i n l e t s a f r a c t i o n of a millimeter i n width;  and i n the shear zone i t s e l f , carbonate, p y r i t e  and sphalerite have been introduced.  The  hydrothermal  additions needed to produce this a l t e r a t i o n are potash, soda* (probably introduced as a l b i t e molecule as the a l b i t e occurs in d e f i n i t e v e i n l e t s ) , zinc, and sulphur.  The quartz, c a l -  40  c i t e , and  p y r i t e i n the  shear zone are probably hydrothermal  as they occur i n v e i n l e t s and  lenses.  The w a l l rook a l t e r a -  t i o n i s t y p i c a l of t h a t accompanying mesothermal v e i n s . Mineralization. The  quartz v e i n s may  w i t h o h a l c o p y r i t e and (2)  The  first  (1)  those  p y r i t e w i t h or without magnetite,  those w i t h galena and  larite.  be c l a s s i f i e d as f o l l o w s :  p y r i t e , and  c l a s s was  (3)  those w i t h speeu-  found to c o n t a i n only t r a c e s  of  p r e c i o u s metals, i r r e s p e c t i v e of the amount of m e t a l l i e s , the l a s t  two  c l a s s e s give good assays i n g o l d ,  but  particularly  where m e t a l l i e s are abundant. In a l l v e i n s found the quartz up  has  crystallized  to s e v e r a l m i l l i m e t e r s i n diameter.  were noted, and quartz.  One  these are bordered by the c o a r s e s t  s m a l l vugs grains  of  Exoept f o r the r a r e vugs, v e i n f i l l i n g shows none of  the f e a t u r e s of open space d e p o s i t i o n , and deposited  or two  i n grains  thus was  probably  a t moderate depth.  Chalcopyrite  - p y r i t e Class.  Pour v e i n s c o n t a i n i n g o h a l o p p y r l t e - p y r i t e m i n e r a l i z a t i o n were found on the c l a i m s , but none gave an assay above a hundredths of an ounoe i n g o l d .  In these v e i n s the p y r i t e  occurs i n cubes up to s e v e r a l m i l l i m e t e r s a c r o s s , and, magnetite i s present,  where  forms i n c l u s i o n s i n the magnetite.  C h a l c o p y r i t e , where abundant, v e i n s and where sparse,  few  replaces quartz,  i s found only as i n c l u s i o n s i n p y r i t e .  Ho  and,  -41d e f i n i t e paragenetic  r e l a t i o n s , other than that the s u l f i d e s  were l a t e r than the quartz, could he established. Q-23 vein.  vein i s rather a zone of quartz stringers than a true  Associated with the quartz i s a dark green c h l o r i t e ,  which i n t h i n seotion shows the anomalous blue birefringence of penninite. and  The quartz contains aggregations of s e r i o i t e ,  i s clouded by clay minerals.  to ten percent  Magnetite constitutes f i v e  of the polished sections.  The footwall side of Q-25  vein contains  quartz-chalcopyrite  mineralization, and the hangwall quartz-galena-pyrite ization.  mineral-  Gold assays i n the footwall side were very low,  in the hangwall side were very encouraging.  but  No fracture or  selvage separates the two classes of mineralization. Galena P y r i t e Glass. The galena pyrite veins usually carry good values i n gold. The gold i s generally proportional to the amount of s u l f i d e s , but may  continue into sulfide-poor quartz.  However, two  found outside the central band of sedimentary rocks  veins  contain  f i f t e e n or twenty percent galena with minor p y r i t e , but gave assays as low as one or two tenths of an ounce per The small possible ore shoot i n Q-19  ton.  vein contained  l i t t l e galena but did contain a few disseminations of coarse (up to a centimeter i n diameter) p y r i t e .  and  very lenses  The pyrite  grains are oxidized oh the rims' so that they f a l l out o f quartz,  •  .Some were collected and mounted i n a polished  the  -48-  section.  Although inclusions of chalcopyrite and sphalerite  are abundant, no gold was found i n the p y r i t e .  One small free  p a r t i c l e of gold was found i n the section, l i k e l y a remnant after oxidation of the p y r i t e , or a p a r t i c l e that was deposited i n quartz near p y r i t e . Q-17 and Q-17 west veins are on the same shear zone, separated by t h i r t y feet that i s barren of quartz.  As afore-?  mentioned, the sheared rock between these two quartz veins i s mineralized with p y r i t e and sphalerite, and gave gold assays of several tenths of an ounce per ton. mineralized with f i v e to ten percent  Q-17 west vein i s  of galena and pyrite but  contains no specularite. Q-17 vein i s mineralized with about f i v e percent specularite but contains no s u l f i d e s .  The s i g n i -  ficance of t h i s marked change i n mineralization i s discussed later. The mineralization of Q-17 west vein was studied i n det a i l as i t afforded some i n t e r e s t i n g specimens.  In t h i n  section the quartz grains are found to be strongly s t r a i n shadowed and fractured, and the coarser grains (5 mm.) are cut by many v e i n l e t s of small (.1 mm.)  flamboyant grains.  Pyrite and galena occur i n these v e i n l e t s , and replace the coarser quartz i n t h e i r  walls.  Coarse quartz i s clouded by  clay minerals. Polished sections show the pyrite to be markedly free of fractures and inclusions.  The galena, however, has inclusions  of gold and three other soft metallio minerals.  The soft  x 700  Intergrowth i n galena of gold w i t h i s o t r o p i c w h i t e m i n e r a l (No. 1) and i s o t r o p i c grey m i n e r a l (No. 2 ) .  POLISHED SECTION PHOTOMICROGRAPH NO. 1 (see Appendix f o r p h o t o g r a p h i c  data.)  x 700 POLISHED SECTION PHOTOMICROGRAPH NO. 2  x 700  POLISHED SECTION PHOTOMICROGRAPH NO. 3 Lensey fractures i n galena, with no r e l a t i o n to galena cleavage, contain intergrowths of gold, isotropic white, (No. 1) and i s o t r o p i c grey (No. minerals.  -43minerals are i n places found singly, but i n most places are in aggregations of two or more (see Polished Section photomicrographs Nos. 1,2,3,4 and 5 ) . The three soft metallios other than gold have not been i d e n t i f i e d owing to t h e i r small size.  They can be seen under medium power (8 ocular, 3b  objective), only when sections have been well polished.  Their  reaotions to tests are as follows: No.l Color  Hardness  Ho.2  No. 3  l i g h t e r white  a very l i t t l e  moderately  than galena  darker grey  than galena with  than galena  a t i n t of brown  no r e l i e f  no r e l i e f  softer than  from galena  from galena  Anisotropism  nil  nil  darker  galena moderate with a brownish b i r e f r i n g ence  M0  negative  negative  HCl  negative  negative  KCN  negative  negative  quick blaok etch  dark brown,  negative  darker brown than  3  PeClg  stronger than galena  s l i g h t etoh to neg. negative  galena  -44. No.l HgClp  No. 2  negative  No, 3  negative  moderate brown stain  KOH  some remain c l e a r and o t h e r s  negative  negative  turn  brown, even i n same reagent drop  A s p e o t r o g r a p h i o a n a l y s i s on minute amounts i n c l u d i n g some g a l e n a i n d i c a t e d the presence  of:  No.l  No,2  N.o.g  Ag  medium  medium  medium  Cu  weak  weak  weak  Pb  p r e s e n t but known i n g a l e n a i n o l u d e d  Te  traoe  As  strong  traoe  trace  negative  negative  These r e a c t i o n s d i d n o t conform t o those o f any o f the minerals l i s t e d i n 'Short'  ( B i b l . N o . 15)..  The f r a g m e n t s  are so s m a l l t h a t on e t c h i n g the reagent drop o v e r l a p s onto the g a l e n a , and r e a c t i o n s cannot be t a k e n as d i a g n o s t i c . S p e o t r o g r a p h i o a n a l y s e s were t a k e n on minute amounts, and thus may n o t be e n t i r e l y r e l i a b l e .  The m i n e r a l s a r e  r e f e r r e d t o by t h e i r number i n t h e above  hereafter  table.  The l o n g s t r i n g e r - l i k e form o f some o f the  aggregations  (see P o l i s h e d S e c t i o n P h o t o m i c r o g r a p h s N o s . 2 and 3) suggests  w \7  i  y  /  L  I  m  i  i/  / i—> i I  x 700 POLISHED SECTION PHOTOMICROGRAPH NO. 4  Gold f i l l i n g a minute  x 570 POLISHED SECTION PHOTOMICROGRAPH NO. 5 Gold i n a n i s o t r o p i c grey m i n e r a l (No. 3) i n g a l e n a .  x 204 POLISHED SECTION PHOTOMICROGRAPH NO. 6  x 204 POLISHED SECTION PHOTOMICROGRAPH NO. 7 The g o l d remains i n p i t s formed hy the o x i d a t i o n o f p y r i t e and g a l e n a .  -46they are of l a t e r age than the galena.  They do not show any  r e l a t i o n to cleavage directions i n the galena. Besides occurring as blebs and minute v e i n l e t s both alone and with the other soft minerals i n the galena, gold was  found  i n p i t s where galena has oxidized (see Polished Section photomicrographs Nos.  6 and 7), and i n or near fractures i n the  quartz. Q-22 Q-17  vein, the probable faulted eastern extension  of  vein, i s mineralized with galena and p y r i t e , but not  abundantly as Q-17  west vein.  as  Polished sections show i r r e g u -  l a r l y walled v e i n l e t s of galena cutting into pyrite grains. Chalcopyrite and sphalerite form l e n s - l i k e inclusions, l i k e l y replacements, i n the p y r i t e , and rounded grains with no apparent paragenetic relations i n the galena. gold was  One  small fragment of  found i n the oxidized material at the edge of galena.  A v e i n l e t of specularite a f r a c t i o n of an inch wide was  noted  in one trench across the vein, but the trench contained  no  other m e t a l l i c s . The galena-pyrite mineralization i n Q-25  vein i s , as found  i n polished section examination, accompanied by minor sphale r i t e , chalcopyrite, the soft mineral No.  1 and gold.  i n i r r e g u l a r l y walled v e i n l e t s , replaces p y r i t e , and rounded inclusions of sphalerite and chalcopyrite. was  Galena, contains  The  gold  found as a small stringer i n fresh galena, Paragenetic r e l a t i o n s i n the galena-pyrite  e r a l i z a t i o n are (1) p y r i t e , (2). sphalerite and  type of minchalcopyrite,  x 204 POLISHED SECTION PHOTOMICROGRAPH NO. 8  x 204 POLISHED SECTION PHOTOMICROGRAPH NO. 9  The gold i n the quartz specularite shoot occurs mostly i n disruptions between specularite'cleavage*plates, but i n a few places forms lenses between plates.  -46-  (3) galena, (4) soft minerals Including Specularite  gold.  Glass.  Only one vein, Q-17, mineralization was  containing abundant specularite  found on the property,  although one  small  veinlet of specularite was noted i n one of the p i t s on vein.  Q-22  However, the presence of other quartz specularite veins  i s suspected because of abundant f l o a t i n one  or two  drift  covered areas. Thin section shows the specularite to be associated with fractures i n the quartz, but replacing quartz on the edges of the fractures. grains, and  Plates of the specularite cut well into quartz  even traverse several grains.  clouded by fine clay minerals,  and  The quartz i s  i n places includes masses  of s e r i e i t e which are l i k e l y altered fragments of wall rock. Polished sections show the specularite 'cleavage' flakes to be markedly twisted and folded.  In the open spaces or weak-  nesses produced by the deformation gold has been In no place was  deposited.  gold observed to cut across the 'cleavage'  plates, and replace the speoularite.  It has been deposited  as  lenses between p a r a l l e l plates, but most i s found where the cleavage'is disrupted, leaving angular openings. ed Section photomicrographs Nos.  8 and  9).  (See P o l i s h -  A few small f r a g -  ments of gold were noted i n or near fractures i n the  quartz.  Significance of Speoularite. Although speoularite i n places comprises as much as ten percent  of the vein f i l l i n g , and s u l f i d e s i n places comprise  f i f t e e n percent,  i n no place was 3 p e c u l a r i t e found i n contact  with the s u l f i d e s .  Speoularite i s the only m e t a l l i c , except  for gold, i n Q-17 vein, and yet none i s found i n Q-17 west vein, which i s i n the same 'hreai: with only a t h i r t y - f o o t 1  length that i s barren of quartz intervening.  Both speoularite  and s u l f i d e s are found i n the eastern part of Q-32 vein, but they are neither abundant nor i n contact.  -48Speoularite, though f a i r l y common i n the 'contaot metamorphic' type of deposits, i s not a common vein mineral.  This  discussion w i l l .be primarily on the significance of'hydrothermal hematite i n veins,  Most, but not a l l , hematite of  hydrothermal o r i g i n occurs as speoularite rather than "as earthy-lustered hematite. iindgren (Bibliography No. 25) presents c h a r a c t e r i s t i c mineral gin*.  speoularite as a  i n 'ore deposits of deap-seated o r i r  Aooording to Lindgren,  i n these deposits i t i s found  i n the o a s s i t e r i t e veins, where i t i s commonly associated with c a s s i t e r i t e , arsenopyrite, p y r i t e , tourmaline,  etc., and i n  the gold and s i l v e r - b e a r i n g veins, where i t i s commonly associated with gold, pyrrhotite, ilmenite, magnetite, galena, zincklende, eto. The structure and the wall rock a l t e r a t i o n of the specularite-bearing veins i n the Unuk suggested the veins were formed under mesothermal conditions, rather than hypothermal. l i t e r a t u r e was searched for examples of deposits  The  containing  speoularite (or hydrothermal hematite) to see i f they are consistently hypothermal, and at the same time to see what the relations are between the hematite and s u l f i d e s . Before examples of deposits are considered, concerning  some discussion  the chemical r e l a t i o n s of hematite to s u l f i d e s w i l l  give more significance to the mineralogical associations i n _ the deposits.  In the f i r s t place, s u l f i d e s are deposited  only  under reducing conditions, and hematite, including the weather-  -49ing product, only under oxidizing conditions.  In the second  place, i f hematite, FeO , containing t r i v a l e n t ( f e r r i c ) iron, 2, 3 i s subjected to reducing conditions, i t should be reduced to magnetite, Fe 0 .FeO, containing t r i v a l e n t ( f e r r i c ) iron and o  divalent (ferrous) iron or, of sulphur i s abundant, to p y r i t e . Pyrite, according to Partington (Bibliography l o , 34) i s supposed to contain divalent i r o n .  Hematite thus should not  be deposited from the same solutions as sulfides., and i f a f t e r deposition i t i s exposed to l a t e r sulfide-bearing solutions, i t should be reduced to magnetite or p y r i t e .  Gilbert  (Bibliog-  raphy) No. 27) mentions several deposits i n whioh hematite has been replaced by magnetite, and magnetite by hematite, and mentions that both replacements are found i n the same mineral deposit.  He attributes the replacements to changes from oxid-  i z i n g to reducing conditions and vice versa.  In another paper .  (Bibliography No. 32) he mentions that the replacement of magnetite by hematite i s most vigorous i n ores that are s u l phur poor.  Reducing conditions connected with s u l f i d e s would  i n h i b i t the oxidation of the magnetite. According to Van Hise (Bibliography No. 33) hematite i s reduced by hydrogen s u l f i d e as follows: F e  2°3 *  2  H  to form p y r i t e .  2  S  * 2 G 0  F e S  2  F e 0 0  3  * 2° 2  H  Hematite can form, however, by the action of  alkaline carbonates on pyrite as follows: 8 FeSg  15 Na 00g — 2  4 FegOg *• 14 NagS * H a S 0 g + 15 GOg g  2  The l a t t e r reaction has been carried out i n the laboratory.  -50  Hydrogen sulfide and alkaline carbonates are both possible constituents of hydrothermal solutions. There seems to be l i t t l e p o s s i b i l i t y of a s o l i d solution of magnetite and hematite.  Broderick (Bibliography No. 19)  shows that specimens of an iron oxide that were described as s o l i d solutions of magnetite are i n r e a l i t y mechanical mixtures.  The components of the mixture are v i s i b l e i n polished  sections studied under the microscope. The r e l a t i v e temperatures of c r y s t a l l i z a t i o n of f e r r i c oxide, ferrous oxide, and s u l f i d e s of iron may also have a bearing on the apparent antipathy of hydrothermal hematite to sulfides.  Butler (Bibliography No. 23) has, on empirical e v i -  dence, constructed a chart showing the r e l a t i v e temperatures of formation of oxides and sulfides of the common ore metals. The temperature zones shown on t h i s chart are f a i r l y well i n harmony with Emmons* zonal theory and with the zoning implied 1  by Lindgren's o l a s s i f i e a t i o n of ore deposits.  F e r r i c oxides  and s i l i c a t e s are very l a r g e l y confined to the. high temperature zone.  Ferrous minerals are formed at high temperatures,  and continue to form, though i n less abundance, to the low temperature zone.  Sulfides do not form above the intermediate  temperature zone, but. continue to form i n the low temperature zone.  Thus.unless a low temperature type of mineralization i s  superimposed upon a high temperature  typf,  or vice versa,  hematite v^ould not be l i k e l y to occur with s u l f i d e s .  The  zoning suggests a gradual change i n the nature of the deposit-  51ing f l u i d , from oxidizing during i t s early,  higher-temperature  stages to reducing during i t s l a t e , lower-temperature stages. The influence of pressure may also be important cases.  In the Ouray d i s t r i c t of Colorado  i n some  (Bibliography No.  35) l a c c o l i t h s and s i l l s ^ h a v e associated veins containing hematite, magnetite, chalcopyrite, and p y r i t e . magnetite was deposited before hematite.  Most of the  A decrease i n pres-  sure on the depositing l i q u i d s a f t e r they deposited magnetite i s evident from the forma'tion of f i l l e d f i s s u r e s cutting magnetite-bearing lodes.  The l i q u i d i s presumed to have v o l a t i l -  ized to some extent, owing to this decrease  In pressure.  FeClg, being quite v o l a t i l e , probably formed.  This f e r r i c  iron has been deposited i n f i s s u r e s as hematite.  The oxida-  tion of ferrous to f e r r i c iron provides considerable heat, and so the hematite was not necessarily deposited at a lower temperature than the magnetite,•though i t was deposited l a t e r in the period of mineralization. Examples that are relavant to the above discussion are now given, tabulated according to t h e i r probable  temperature of :  formation. Epithermal deposits. Some copper deposits i n Tertiary sediments and voloanfca i n Japan are 'often i n t r i c a t e l y cut by veins and v e i n l e t s of quartz and micaceous speoularite', edly primary i n o r i g i n * .  'The speoularite i s decid-  Its formation i n Tertiary rocks,  thus at shallow depth, was considered by Takeo Koto ( B i b l l o g -  -52raphy No. 26) t o "be worthy o f comment as i t r e f u t e s the general  o p i n i o n t h a t s p e c u l a r i t e i s a hypothermal  mineral.  On I r o n M o u n t a i n , a t the j u n c t i o n o f the C o l d w a t e r and N i c o l a R i v e r s , v e i n s o f s p e c u l a r i t e a r e found i n T e r t i a r y ( ? ) volcanics  ( B i b l i o g r a p h y No. 2 6 ) . I f the d e p o s i t s  a r e Ter-  t i a r y they must have been d e p o s i t e d a t s h a l l o w d e p t h s . At K a t l m a i ,  Alaska,  s p e c u l a r i t e was observed as an i n r  o r u s t a t i o n formed by f u m a r o l e s ;  thus here i t formed under  atmospheric pressure. At H i c k e y ' s Pond, f i v e m i l e s west o f t h e head o f P l a c e n t i a Bay,  i n S o u t h e a s t e r n Newfoundland, a r e d e p o s i t s  associated deposits ite  w i t h abundant a l u n i t e .  are i n a s i l i c i f i e d  and v o l c a n i c s c h i s t .  of s p e o u l a r i t e  ( B i b l i o g r a p h y No. 2L)  zone a t the c o n t a c t o f g r a n o d i o r -  S p e c u l a r i t e , a l u n i t e , and q u a r t z  i n the zone a r e i n p a r a l l e l bands g i v i n g a g n e i s s i c to the d e p o s i t .  The  structure  The s p e c u l a r i t e occurs i n ragged masses o r  i n d i v i d u a l g r a i n s and b l a d e s , l i n e a t e d p a r a l l e l t o the gneissic structure.  S m a l l amounts o f p y r i t e o c c u r o n l y i n  the s p e c u l a r i t e - p o o r  silicified  a l u n i t e s u g g e s t s the d e p o s i t  grains of a l u n i t e .  quartz, two  The presence o f  i s epithermal.  l o c a l i t y are specularite-bearing few  schist.  I n the same  quartz veins containing  The sequence o f d e p o s i t i o n  (2) s p e c u l a r i t e , (3) p y r i t e and a l u n i t e ,  places  p y r i t e cubes r e p l a c e  No r e d u c t i o n  a  i s (1) I n one o r  specularite.  of s p e c u l a r i t e to magnetite i s reported.  However, t h e abundance o f a l u n i t e (KgO.3Al2Og.6H2O.4SO3),  -53indicates s u l f u r r l o h solutions i n the l a t e r stages of deposition, and the p y r i t e may have formed from the reduction of speeularite rather than from introduction of p y r i t e as such.  The reactions may he as follows: F e  2°3  2 H  2° ^  2fe(-0H)  3  27eS  23  ^  +  2Pe(0H)  3HgS  3  2FeS f S t 6H 0 g  Fe 3 s  4  (pyrite)  Only HgS and S need he added i n aqueous solution to cease the replacement, but they would be reducing, and a l a t e r change back to oxidizing conditions i s necessary for the formation of a l u n i t e .  The deposit may then be an example of reduction  of hematite to pyrite by s u l f u r r i c h solutions introduced at a late stage.  The a l u n i t e , introduced at a s t i l l l a t e r stage,  may have formed at much lower temperature than the speeularite. Mesothermal deposits. An example of replacement of hematite by magnetite during the introduction of s u l f i d e s i s found i n the George Copper deposit of Portland Canal, B.^. (Bibliography No. 28). In this deposit the paragenetic  sequence i s given as (1) wall  rock a l t e r a t i o n (2) pyrite (3) arsenopyrite (4) quartz (5) speoularite (6) magnetite (replacing speoularite§(7) fithalcopyrite. The deposition of quartz midway i n the deposition of the metallic minerals suggests a change i n conditions, sinoe i t Is usually the f i r s t mineral deposited i n a vein, and the  -54speoularite indicates this change was to oxidizing conditions. The replacement of hematite hy magnetite before the deposition of chalcopyrite indicates a renewal of the reducing  conditions  necessary f o r the deposition of s u l f i d e s . The deposit was considered  to have formed under i n t e r -  mediate temperatures at a depth approximating eight thousand feet. In the large quartz veins of Great Bear Lake, N.W.T. Bibliography No. 29) specularite has been deposited than other .metallics.  It i s not stated whether or not  hematite and l a t e r . s u l f i d e s are i n contact. considered  earlier  formed at 'not very elevated  the  The veins are  temperatures'.  At the Eldorado mine, Great Bear Lake, N.W.T., hematite i s associated with deposits of pitchblende 22 and No.  30).  The hematite i n the  (Bibliography No.  'veins' was deposited  after pitchblende, and before the s u l f i d e s . Sulfides that are i n contact with hematite include pyrite and chalcopyrite, and these i r o n bearing s u l f i d e s have formed by reduction of hematite. The temperature of formation  of t h i s deposit i s d i f f i c u l t  to e s t a b l i s h as the deposit shows several f a i r l y  distinct  periods of mineralization. Hypothermal deposits. At Kalgoorlie, Western A u s t r a l i a , specularite i s found i n the "deep vein zone' with quartz, magnetite, and ilmenite (Bibliography No. 36).  These are cut by the l a t e r t e l l u r i d e  -55bearing quartz veins. In the V i r g i l i n a D i s t r i c t , North Carolina and V i r g i n i a , primary bornite and chalcocite i n quartz veins have minor associated speoularite. No r e l a t i o n i s given between the sulfides and the oxide.  The veins are considered to belong  to the 'deeper vein zone . 1  On T i p e l l a Mountain, near Harrison Lake, B.C. micaceous hematite oocurs i n a zone of l e n s - l i k e bodies.  Highly altered  rocks on the contact of granite, and i n places the granite i t s e l f i s the host rock.  (Bibliography No. 16.)  If the speoularite i s derived from the granite, i t s dep o s i t i o n i n the granite indicates formation under high temperature. Lindgren (Bibliography No. 25) states 'at many contacts of intrusive rocks not characterized by pegmatites,  quartz vein-  l e t s abound and often carry c r y s t a l l i z e d s p e o u l a r i t e . 1  Other Deposits. It i s perhaps noteworthy that speoularite occurs without other associated m e t a l l i c s i n many veins, and these hematite veins are probably more abundant than the l i t e r a t u r e indicates, for,  since they are seldom economic, they receive l i t t l e pub-  licity.  The veins at T i p e l l a Mountain are apparently barren  of s u l f i d e s .  Others i n which no indication of temperature of  formation i s given occur at Finger Lake, near Vanderhoof, B.C., and. on Iron Range Mountain, near Kitchener,  B.G.(Bibliography  No. 16). The Kitchener deposits have been c a l l e d sedimentary  -56in o r i g i n (Bibliography Io. 17), but l a t e r work shows the zone of mioaoeous and earthy hematite crosscuts the bedding.  A  small amount of magnetite occurs but as a rule l i t t l e or no pyrite or other s u l f i d e i s v i s i b l e . Hydrothermal hematite i s much more common i n the 'contact metamorphic' deposits, but i s seldom associated with s u l f i d e s in these deposits.  The hematite i s always i n parts of the  deposit that contain l i t t l e s u l f i d e , and the -sulfides i n parts that contain l i t t l e hematite. The almost complete lack of hematite i n pyrrhotite bearing deposits has been attributed to the fact that pyrrhotite i s a stronger reducing agent than most other s u l f i d e s .  Since  both pyrrhotite and hematite are commonly deposited i n the 'deep vein zone' they would normally be associated.  I f an  iron oxide i s found with pyrrhotite i t i s invariably magnetite rather than hematite (Bibliography Io. 27). Further evidence of the tendency of hematite to be reduced to magnetite and/or pyrite i s found i n some deposits i n which the  hematite was probably o r i g i n a l l y sedimentary or a product  of weathering.  Reduction of hematite to magnetite and pyrite  is considered to have occurred i n the iron deposits of Michigan* Veins of pyrite indicate the presence of a reducing agent which could be organic acids (Bibliography Io. 20).  At Mesabi,  'graphite i n considerable amounts associated with the magne- • * t i t e , and s i d e r i t e , indicate the former presence of reduoing material which would convert the higher oxides of iron into  -57magnetite' (Bibliography No. 31). Oxidation by hematite solutions carrying copper and s u l f u r i s presumed to have caused deposition of native copper rather than copper s u l f i d e s i n parts of the Michigan Copper Deposits (Bibliography No. 38). Bleaching of hematite from the wall rock o f ore zones attests the the p a r t i c i p a t i o n of hematite i n the reactions producing deposition. In summary, though hydrothermal hematite i s commonly deposited under hyp.othermal conditions,- i t has formed in. veins which appear to be mesothermal and epithermal, and i n fumarole incrustations.  The hematite i s usually one of the f i r s t min-  erals to be deposited from vein-forming solutions.  Where  hydrothermal hematite was formed a f t e r hydrothermal (or magmatic) magnetite, an accompanying inorease i n temperature has l i k e l y occurred. ditions.  Hematite i s deposited under oxidizing con-  I f sulfur bearing, and thus reducing, solutions i n  contact-with hematite, the hematite tends to be replaced by magnetite, or i f the solutions are very r i c h i n s u l f u r , pyrite or perhaps some other iron bearing s u l f i d e .  Abundant hematite  thus should not occur with abundant s u l f i d e s becasue  of.their  chemioal incompatibility, and geologic evidence substantiates this theory. Thus the sulfides of Q-17 west vein, and the speoularite of Q-17 vein, could not be deposited from the same solution at the same time.  Bo marked shearing of the quartz has taken  place i n either lens, thus reopening of the main 'break' by  -58continued movement a f t e r the formation of vein i s improbable. The mineralization of the two veins more l i k e l y occurred  at  different times i n the same general period of mineralization, that of Q-17  vein occurring f i r s t under oxidizing conditions  and that of Q-17  west vein occurring l a t e r under  reducing  conditions. According to Schwartz (Bibliography No. 39, p. 371)  the  association of gold with specularite has no p a r t i c u l a r s i g n i ficance.  He states 'A few examples of association of gold with  specularite have been described.  This occurrence does not  seem s i g n i f i c a n t except as an indication of f a i r l y high temperature of formation at an early stage i n formation of the veins'. Mineralogical  Conclusions.  In the galena-jayrite type of mineralization most of the gold is associated with three soft minerals which may  be  tellurites.  These minerals ocour as i n d i v i d u a l grains and aggregations i n the galena.  Minor amounts of gold are present i n and near  fractures i n the quartz.  The gold p a r t i c l e s are up to 50  microns long, but are mostly i r r e g u l a r and much narrower than this. In the specularite type of mineralization the gold occurs in disruptions between specularite 'cleavage' plates, and i n minor amounts i n and near fractures i n the quartz.  The  gold  p a r t i c l e s are f a i r l y equidimensional, and up to f i f t y microns  -59 in  diameter. The granularity of the quartz, and the mineralogic assem-  blage point to deposition under moderate temperature and pressure.  Under Lindgfen's c l a s s i f i c a t i o n the veins would be  mesothermal. The difference i n mineralogy  between Q-17 west vein and  Q-17 vein i s probably the result of deposition at d i f f e r e n t times during one general period of mineralization.  The hema-  t i t e of Q-17 vein was probably deposited f i r s t under o x i d i z ing conditions, and the s u l f i d e s of Q-17 west vein deposited l a t e r under reducing conditions.  -60-  GENERAL CONCLUSIONS The limestone of the Unuk Area i s probably Permian, the sedimentary and volcanic rocks to the west of the  limestone  Pre-Permian, and those to the east T r i a s s i c and Jurassic (Hazelton). The host rock of the veins i s a dynamo-thermal metamorphosed water-lain dacite t u f f , or andesite t u f f containing d e t r i t a l quartz.  The veins do cut intrusive d i o r i t e gneiss,  but diminish i n both size and grade i n the i n t r u s i v e . The intrusive d i o r i t e has caused r e c r y s t a l l i z a t i o n of t u f f on i t s contacts, forming paragneiss which i s d i f f i c u l t to d i s t i n g u i s h from the intrusive orthogneiss.  L i t t l e or no  skarn has developed i n s i l i c e o u s limestone beds near the intrusive d i o r i t e .  A c t i n o l i t e , tremolite, and dippside have  formed, l i k e l y by metamorphism rather than metasomatism, i n bands of a few millimeters' width rimming t u f f fragments i n limestone.  Epidote i s abundant i n most andesitic and  rocks, both intrusive and extrusive.  dioritic  The area has undergone  regional metamorphism of medium grade. The quartz veins show a marked p a r a l l e l i s m i n a t t i t u d e , s t r i k i n g 115 degrees, and dipping 80 degrees northeast, with the exception of Q-19 degrees north-east.  vein, which dips only twenty to f o r t y They have been intruded along  caused by shearing forces.  'breaks'  Mineralized f a u l t s , d y k e - f i l l e d  tension fractures, the vein 'breaks', folding, and regional  -61foliation  can  be  indicates  the  deforming pressure  or n o r t h e a s t . associated gneiss  but  The  with  sills,  ising veins the  fitted  from  coast  a strain-ellipsoid came f r o m t h e  of this  pressure  i n a band  the  p a t t e r n which southwest  c o u l d be  range i n t r u s i v e s ,  i s more l i k e l y  occur  evidence  derived  source  the  but  into  or the  former.  The  orogeny local  fluids  Ooast Range I n t r u s i v e s r a t h e r t h a n  diorite  most, prom-* .  o f s e d i m e n t s b e t w e e n two  i n d i c a t e s the v e i n - f o r m i n g  and/  the  sills,  were Triassic(.?)  sills. The fluids oite, by  w a l l - r o c k a l t e r a t i o n produced has  penetrated  kaolin,  chlorite,  r e p l a c e m e n t and  typical  of veins  devoid  be  tellurides,  l e t s and the  divided into (1)  and  three  (2)  gold.  as  The  gold  veins,  containing l i t t l e  o r no  quartz.  formed  is  the  basis  magnetite  soft minerals  occurs  quartz.  sulfides.  one  Classes  (2)  with  which  in irregular  may  vein-  o r more  of  and  as  (3)  Speoularite  The  gold  between s p e o u l a r i t e 'cleavage' f l a k e s ,  n e a r f r a c t u r e s i n the i n gold.  have  Galena p y r i t e v e i n s  i n c l u s i o n s i n galena;  i n o r n e a r f r a c t u r e s i n the  assays  c l a s s e s on  usually associated with  grains  irregularities  quartz  Seri-  class.  c h a l c o p y r i t e , three  segregations,  soft minerals  and  Chalcopyrite, pyrite,  of precious metals  minor s p h a l e r i t e ,  vein-forming  into vein walls.  albite,  of the mesothermal  t h e i r mineralogy.  veins  pyrite,  feet  the  f r a c t u r e - f i l l i n g . . This a l t e r a t i o n  Quartz v e i n s are of  o n l y a few  by  and  (3)  individual  occurs and give  in  i n or good  -62 The gold grains i n olass (2) are quite irregular, up to 50 microns long and about ten microns wide. (3) are more equidimensional, meter.  Those i n class  and up to 50 microns i n d i a -  Extraction of gold should not be d i f f i c u l t .  Speoularite i s deposited under oxidizing conditions, and thus cannot be deposited from the same f l u i d at the same time as s u l f i d e s , which require reducing conditions f o r deposition. No geologic evidence f o r two periods of mineralization was found, so the speoularite and s u l f i d e s are considered  to be  deposited at s l i g h t l y d i f f e r e n t times, the speoularite f i r s t , i n the one general period of mineralization. The metallic minerals  i n the veins are members of the mod-  erate to high temperature type of mineralization. grains are f a i r l y coarse  The quartz  (several millimeters i n diameter) thus  not of the epithermal type.  The lack of banding and other  structures diagnostic of open^space deposition, except for a few vugs, indicate deposition at moderate pressure.  Vein  f i l l i n g , wall rock a l t e r a t i o n , and the r e g u l a r i t y and continuity  of the 'breaks' a l l indicate a mesothermal deposit.  The  veins show good promise of continuing to depth. Theoretical sequence of events i n the region i s (1) Dep o s i t i o n of sediments - limestone, quartz s i l t s t o n e ,  argillite,  and t u f f , i n marine environment, at times p r a c t i c a l l y simultaneously, during late Palaeozoic time.  (2) U p l i f t , erosion,  and probably some t i l t i n g or s l i g h t f o l d i n g during the Appalachian Revolution.  (3) Depression of the area, and continued  -63sedimentation ion  o f t u f f and  of d i o r i t e  causing time.  some f o l d i n g (4)  Slight  sediments as assic ments.  'sills',  time, (5)  p r o b a b l y as  i n the  uplift  argillite, giving  probably minor limestone.  and and  fairly  time,  d e p o s i t i o n of shallow v o l c a n i c s (Hazelton)  Coast  f o l l o w e d and  Range c o m p o s i t e  and  i n p a r t by g l a o i a t i o n ,  again  exposed.  till  Triassic  water  during Jur-  further  uplift  today  sedi-  batholith  folding,  o f the  accompanied by m i n e r a l i z a t i o n .  sion,  perhaps  o f the P a l a e o z o i c  producing  r e g i o n a l metamorphism, f a u l t i n g , rocks,  bodies,  i n t r u d e d sediments d u r i n g  deep b u r i a l  I n t r u s i o n o f the  during Jura-Cretaceous  separate  Intrus-  bedded (6)  Palaeozoic rocks  Eroare  BIBLIOGRAPHY  No. 1.  P.A.Kerr ...... " P r e l i m i n a r y Report on Iskut R i v e r Area» B.O,'  2.  P.A. K e r r  G.S.C. Summ. Rept. 1929, P a r t A.  ' P r e l i m i n a r y Report on S t i k i n e Area,*.  B.O.-'  River  G.S.G. Summ. Rept. 1926,  P a r t A. 3.  P.A. K e r r . . . . . . .  'Second P r e l i m i n a r y Report on S t i k i n e R i v e r Area, B.C.' 1928,  4.  G.S.C, Summ. Rept.  P a r t A.  A.P. Buddington and 0?. Chapin ...'Geology and M i n e r a l Deposits  o f Southeastern  Alaska'  Bulle-  t i n 800, U.S.G.S. /929 5.  G. Hanson....... 'Portland Canal Area, B r i t i s h G.S.C. Mem. 175.  6.  P.A. K e r r . . . . . . .  /93S  ' D e f i n i n g the M i n e r a l Zones o f Northern B r i t i s h Columbia' 34,  7.  P.A. K e r r .  Columbia'  C.I.M.M. TRANS. V o l .  pp. 68 - 72. '93/  'The R e l a t i o n s h i p s o f M i n e r a l  Deposits  i n the Skeena R i v e r D i s t r i c t ,  British  Columbia*  Be. Geol.  V o l . 33, No.4,  pp. 428 - 439. '9*8 8.  P.B. Wright.....  'The Unuk R i v e r M i n i n g Region o f B r i t i s h Columbia'  G.S.C, Summ. Rept. 1905,  pp. 46 - 53.  BIBLIOGRAPHY (CONT'D) NO.  9.  A.F. Buddington... 'Types of Mineralization and of Coast Range Intrusives', Eo. Geol. Vol. 22,  •a.  No. 2, pp. 158-179. / « 7 10.  J i T . Mandy  'Unuk River Area', Annual Rept. of Minister of Mines, 1935. Pp. B 7B 12.  11.  J.T, Mandy........ 'Unuk River Seotion - Northwestern D i s t r i c t No. 1',Annual Rept. of Mini s t e r of Mines, 1934.  12.  L.V. Pirrson  'Microscopical Character of Volcanio Tuffs', American Journal of Science, 4th series, Vol. 40, 1915. pp. 191. 211,  13.  P.A. Kerr...  'Map 311A South Sheet, Stikine River Area, Cassiar D i s t r i c t * , G.S.C., 1935.  14.  Twenhofel........, 'Principles of Sedimentation*.  15.  M.N. Short......,, 'Microscopic Determination of the Ore Minerals', U.S.G.S,  16,  B u l l . 914. s*40  G.A. Ypung and W.L. Uglow...'The Iron Ores of Canada, Vol. 1, B r i t i s h Columbia and Yukon*, G,S,C.  17.  Ec. Geol. Series No. 3. /&6  S.J. Schofield.... 'The Ore Deposits of B r i t i s h Columbia*, Trans, Can. Inst. Min. and Met. V o l . 24, 1922. p. 86.  BIBLIOGRAPHY (CONT'D) NO. 18.  G.M. Dawson  'Preliminary Report on the Physical and  Geological Features of the South-  ern Portion of the I n t e r i o r of B r i t i s h Columbia,' G.S.C, Rept. of Prog. 1877-78, p. 122B. 19.  T.M, Broderiok  'Some of the Relations of Magnetite and Hematite', Be. Geol. V o l . 14, August, 1919.  20.  Van Hise and L e i t h . 'The Geology of the Lake Superior  Re-  gion', U.S.G.S. Monograph No. 52./?// 21.  A.L. Howland........ 'iSpecularite-alunite Mineralization at Hickey's Pond, Newfoundland', American Mineralogist, V o l . 25, 1940. P. 34.  22.  Eldorado Mine Staff...'The  Eldorado Enterprise', C.I,M.M,  B u l l . 413, Sept., 1946, 23.  p. 423.  B.S. Butler........ 'Some Relations between Oxygen Minerals and Sulfur Minerals  i n Ore Depos-  i t s ' , Ec. Geol. Vol. 22, No. 3, p.233. 24.  H.A. Tableman and J.A. Potter... A.I.M.E. B u l l . 146, p. 485.  25.  W. Lindgren,  'Ore Deposition  and Physical Condit-  ions', Ec. Geol. Vol. 2, p. 105. /907 26.  Editor, Ec. Geol... E d i t o r i a l , Ec. Geol. V o l . 18, 1923, p. 695."  BIBLIOGRAPHY (CONT'D) No. 27.  G. Gilbert  'Significance of Hematite i n Certain Ore Deposits', Ec.Geol. Vol. 22, No.6, p. 560.  28.  /927  W.V. Smitheringale.. 'Mineral Associations of the George Gold Copper Mine, Stewart, B.C.', Ec. Geol. Vol. 23, pp. 193.  29.  /s*8  G.M. Furnival...... 'The Large Quartz Veins of Great Bear Lake, Canada', Ec, Geol. Vol. 30, p.  30.  843,  SS3S-  D.P. Kidd and M.H. Haycook... 'Mineragraphy of the Ores of Great Bear Lake', G.S.A. B u l l . Vol.  31.  46, pp. 879-960.  J.W. Gruner,,.,... 'Paragenesis of Martite Ore Bodies and. Magnetite  of the Mesabi Range*, Eo.  Geol. Vol, 17, No. 1, p. 1. /92z 32.  G, G i l b e r t . . . . . . . . 'Some Magnetite-Hematite Relations', Ec. Geol. Vol. 20, 1925, pp. 587-596.  33.  Van Hise  *A Treatise on Metamorphism', U,S,G.S. Monograph 47. /so*  34.  Partington........ 'Textbook of Inorganic  35.  W.S. Burbank  Chemistry*.  'A Source of Heat Energy i n the Crysta l l i z a t i o n of Granodiorite Magma, and Some Related Problems of Vulcanismf, Am. Geophys, anion. 'Trans. 17th, 1936, p. 236.  BIBLIOGRAPHY (CONT'D) No. 36.  W. lindgren....,.. 'Metasomatic Processes i n the Gold Deposits of Western A u s t r a l i a ' , Ec. Geol. Vol. 1, p. 530.  37.  F . B . Laney  /s?&s  'The Relation of Bprnite and Chalooc i t e i n the Copper Ores of the V i r g i l i n a D i s t r i c t of North Carolina and Virginia',  38.  Ec. Geol. Vol. 6, p. 399.  G.M. Schwartz,.... 'The' Host Minerals of Native Gold', Ec. Geol. Vol. 39, 1944.  POLISHED.SECTION PHOTOGRAPHS MicroNO. scope Oo. Obj. Mag. Time l/7a 700  Filter  Niool not 8 sec. dark blue(#2) crossed  Section No.  1.  H.V.W. x8  2.  it  n  ii  300 sec.  none  #10  3.  it  it  it  10 sec.  none  #2  4,  it  1!  ii  15 sec.  none  #2  5.  ii  6a  570  8 sec. dark blue(#2)  6.  n  3b  204  13 sec.  none  #15  7.  ii  6a  570  10 sec.  none  #19  8,  ii  3b  204  15 sec. l i g h t blue  "  #11  9.  ti  3b  204  15 See. l i g h t blue  "  #6  "  #1  #1  THIN SECTION PHOTOGRAPHS MicroNo. scope Oo.  Obj . Mag. Time  Leitz 1. 331223  x8  3B  80  tt  rt  32  25  15 sec*  it  not crossed  Q-25  ti  n  3B  80  840 sec.  ii  not crossed  Q-40  ii  ii  32  25  17 sec.  n  not crossed  Q-40  "  rt  32  25  15 sec,  n  not crossed  Q-22  6,  n  n  3B  80  840 sec.  ti  crossed  Q-53  7.  n  ii  3B  80  600 see.  n  crossed  Q-26  8.  it  ii  3B  80  600 sec.  ti  crossed  Q-26  9.  tt  ti  32  25  60 sec.  ii  orossed  Q-26  2. 3  «  4. 5.  Light  Lamp600 sec. box  Niool  Sectioi No.  crossed  Q-51  SURVEYS AND  NATIONAL TOPOGRAPHIC  SERIES  ENGINEERING BRANCH  HYDROGRAPHIC AND  MAP  SERVICE  S H E E T 104 S.E W  Aerial photography  j ^ ^ j  Contours (approximate)  ^~ 0o 3  0  Contours are shown at, 500, 1000,2000, 3000 4000 6000 and 8000feet above mean sea level '  132°  Price 25 cents  128°  Index to adjacent sheets  SHEET 104 S.E.  /  ) Miles  L E G E N D Recent lava flows • Unconsolidated deposits (Sand a n d gravel) Coast Range Intrusives. granite, granodiorite,quartz I—-I ggg] vv-/i Y'/t/A  \~~\ \yy\  Mainly  sediments,  diorite,etc  a r g i 111te, s a n d s t o n e , q u a r t z i t e , s o m e  t u f f  L i m e s t o n e Mainly igneous r o c k s : sediments v o l c a n i c t u f f s a n d f l o w s , some : Geological b o u n d a r y ( d e f inneedd ) ( a p p r o xx i ir m a t e ) B e d d i n g (inclined, vertical) Trail Glacier  C o n t o u r s (500 feet)  D C  Geological Sketch-map of Unuk River Area.  Department  o f M ines.1935  CRACEVSWANSEA CROUP UA/UK R/VER ttn  200  ft.  L eyencl Ou/c~op /> e d d tne/ g/?e/65/c contour  hound'city a/ft/tide  as <//////e j tp //  hand/no-  cl/Or-/ he  //ncs  g-n e/ss greens/one  mossrise  :.-'-V"  dyke  'cimprophyrc jjgjjj  ^Z7\*  C/Uo.rf'z l/c/r/d AlP con-facts  cfm  dyke  Op/the QNo\  /oc<jf/on  of  ^pectmcn  "r i  0-0 ••  0-33 —  .40*  '  ' (c-  Q-53 v — •-  \  )  s \ i—£L ,^0«'i  \  \ \  

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