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The gossan of a lead deposit in limestone : Yukon territory MacDonald, Ralph Crawford 1947

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^  THE  GOSSAN  OF  A  LEAD  YUKON  DEPOSIT  IN  LIMESTONE  TERRITORY  fey R.C.  MAGDONALD  A t h e s i s submitted i n p a r t i a l  fulfillment  o f t h e r e q u i r e m e n t s f o r t h e degree o f MASTER  OF  APPLIED SCIENCE  I n t h e Department of GEOLOGY  AND  GEOGRAPHY  The U n i v e r s i t y o f B r i t i s h A p r i l , 1947.  Columbia  <- 6 (0 J  P R E F A C E T h i s t h e s i s i s b a s e d on t h e f i e l d o c c u r r e n c e  and  l a b o r a t o r y i n v e s t i g a t i o n s o f numerous m i n e r a l , r o c k , and l i m o n i t e specimens f r o m the S t a r Group o f c l a i m s i n s o u t h c e n t r a l Yukon.  The w r i t e r s u p e r v i s e d t h e  p r o s p e c t i n g , s t a k i n g , and e x p l o r a t i o n o f t h e c l a i m s , and a s s i s t e d Dr. D.R. map.  D e r r y i n c o m p i l i n g the g e o l o g i c a l  The w r i t e r w i s h e s t o t h a n k t h e management o f  Western Ranges P r o s p e c t i n g S y n d i c a t e f o r p e r m i s s i o n t o make f u l l use o f t h e i n f o r m a t i o n and m a t e r i a l o b t a i n e d d u r i n g t h i s t i m e , and i n p a r t i c u l a r t o thank Dr. D e r r y f o r making a v a i l a b l e c o p i e s o f h i s g e o l o g i c a l map. Thanks and a p p r e c i a t i o n are a l s o extended t o Dr. H.C.  Gunning, under whose d i r e c t i o n t h i s s t u d y  was  c a r r i e d o u t , f o r h i s s u g g e s t i o n s and a s s i s t a n c e .  Dr.  V . J . O k u l i t c h a d v i s e d i n t h e m a t t e r o f t a k i n g photographs and Dr. K. deP. Watson a s s i s t e d i n Acknowledgement i s due t o J.A.  petrography.  Donan, l a b o r a t o r y  t e c h n i c i a n i n the Dept. o f G e o l o g y , U.B.G., f o r h i s i n t e r e s t and e x p e r i m e n t a t i o n i n d e v i s i n g a s a t i s f a c t o r y method o f p r e p a r i n g t h i n and p o l i s h e d - s e c t i o n s o f weathered specimens, and f o r h i s a s s i s t a n c e i n making them. The r e s u l t s o b t a i n e d i n t h i s s t u d y c o u l d n o t have been a c h i e v e d w i t h o u t t h e c o - o p e r a t i o n o f t h e s e  people.  TABLE  OF  CONTENTS  ABSTRACT INTRODUCTION ' Statement o f t h e P r o b l e m Location Prospecting  1 l 2 2  GENERAL GEOLOGY  5  GEOLOGY OF THE STAR GROUP Table o f Formations Description of formations Banded A r g i l l a c e o u s Sandstone • Gray L i m e s t o n e F a i t h Limestone C a l Gray L i m e s t o n e C h a r i t y H i l l Limestone C a s s i a r Omineca B a t h o l i t h . . . Quartz Feldspar Porphyry.... MINERAL DEPOSITS V e i n No. 1 V e i n No. 2 V e i n No. 3 Area o f Disseminated I'lineralization L i m o n i t i c Areas  7 9 10 10 12 12 ;...15 16 16 17  ...  19 19 21 21 -2? 24  HIH^RaLOGY  24  DESCRIPTION OF LIMONITE Type No. 1- B l u e - b l a c k . B o t r y o i d a l L i m o n i t e Type No. 2- Reddish-brov/n H a r d L i m o n i t e Type No. 3- Y e l l o w - b r o w n S o f t L i m o n i t e Type No. 4- Porous brown Crumbly L i m o n i t e Type No. 5- Porous O r a n g e - y e l l o w L i m o n i t e Type No. 6- L l i x e d Caverno'us L i m o n i t e Limonite Table  27 28 32 34 36 39 44 47  CONCLUSIONS D e r i v a t i o n o f S p e c i f i c L i m o n i t e Types " M a t e r i a l f o r m i n g t h e Boxworks. Source o f I r o n Secondary Lead M i n e r a l s S o l u b i l i t y o f L i m o n i t e i n HC1  48 48 50 52 53 54  TABLE OF CONTENTS  (Cont.'d.)  ILLUSTRATIONS" 56 t o 72 Fhotographs o f Hand Specimens P l a t e s 1-4; 7,10,11,13B,21,22,25,26. • Photomicrographs o f P o l i s h e d S e c t i o n s P l a t e s 5*, 6,8,9,12,13A ,14 14A, 17-19,23,9.7. Photomicrographs o f Thin S e c t i o n s P l a t e s 15,16,20,24,24A,28. ?  BIBLIOGRAPHY . APPENDIX • P r e p a r a t i o n o f T h i n and P o l i s h e d S e c t i o n s  73 74 74  A B S T R A C T  The  i n t e r p r e t a t i o n o f l e a c h e d o u t c r o p s as g u i d e s  t o t h e s p e c i f i c m i n e r a l s f r o m w h i c h t h e y were formed has "been d e v e l o p e d  t o a r a t h e r h i g h degree b y e a r l i e r  among whom B o s w e l l and B l a n c h a r d deserve mention.  workers,  particular  In' t h e p r e s e n t work, a gossan t h a t l e d t o t h e  discovery of a lead deposit i s described.  S i n c e many  hand specimens o r t h e l i m o n i t e f r o m t h i s gossan l a c k t h e c h a r a c t e r i s t i c boxwork s t r u c t u r e s d e s c r i b e d b y t h e a u t h o r s above, m i c r o s c o p i c i n v e s t i g a t i o n s o f t h i n and p o l i s h e d s e c t i o n s were c a r r i e d o u t .  However, t h e gossan  i s c l a s s i f i e d i n t o s i x t y p e s m a i n l y on t h e b a s i s o f i t s p h y s i c a l p r o p e r t i e s . A t l e a s t three o f these are c o r r e l a t e d w i t h t y p e s d e s c r i b e d b y B o s w e l l and B l a n c h a r d , one o f p y r i t e d e r i v a t i o n and t h e others f r o m g a l e n a . The r e l a t i v e s o l u b i l i t y o f d i f f e r e n t l i m o n i t e t y p e s i n d i l u t e HC1 was n o t found t o be o f as much v a l u e as some w r i t e r s have i n d i c a t e d . The m i n e r a l d e p o s i t s t o w h i c h t h e l i m o n i t e p o i n t e d the way have n o t been s u f f i c i e n t l y exposed t o a l l o w d e t a i l e d s t u d y , b u t t h e presence  o f t r e m o l i t e and  p h l o g o p i t e i n an a r e a o f d i s s e m i n a t e d m i n e r a l i z a t i o n i n d i c a t e s t h a t t h i s p o r t i o n a t l e a s t may be o f c o n t a c t metamorphic o r i g i n .  THE  GOSSAN  OF  A  LEAD  YUKON  /  DEPOSIT  IN  LIMESTONE  TERRITORY  I N T R O D U C T I O N STATEMENT OF THE PROBLEM During the 1945-46 term at the U n i v e r s i t y of B r i t i s h Columbia, the writer was introduced to the subject of "Leached Outcrops" i n a course i n Economic Geology.  While prospecting i n the summer of 1946, a  p r a c t i c a l f i e l d example was encountered, which i l l u s t r a t e s some of the problems of t h i s subject, as well as the benefit which might be derived from i t s further study. A t y p i c a l piece of "limonite f l o a t " from the surface of a leached outcrop of a mineral deposit i s shown i n plate 1.  A t y p i c a l specimen of the p a r t i a l l y oxidized or  leached mineral deposit, which was found about 4 feet below, i s shown i n Plate 2.  The. former appears to give  no indications as to i t s o r i g i n , while the l a t t e r contains abundant fresh galena as well as a boxwork structure reminiscent of the cubic cleavage of galena. I t was therefore decided to carry out a laboratory investigation of numerous mineral specimens from t h i s deposit i n an attempt to a r r i v e at some d e f i n i t e conclusions as to t h e i r o r i g i n , and the possible significance of the various limonite types.  To do so, i t was  deemed a d v i s a b l e t o d e s c r i b e  first  t h e environment o f t h e l i m o n i t e , and t h e known m i n e r a l d e p o s i t s t o w h i c h some o f t h e l i m o n i t e p o i n t e d t h e A c c o r d i n g l y , the f i r s t p a r t o f t h i s r e p o r t c o v e r s geology  and m i n e r a l o g y  of the area, w h i l e the  way. the  latter  p o r t i o n d e a l s w i t h the study of the v a r i o u s types  of  limonite. LOCATION The S t a r Group o f c l a i m s i s s i t u a t e d i n t h e Dawson m i n i n g d i s t r i c t o f Yukon T e r r i t o r y , about f i v e m i l e s n o r t h o f t h e B.C.  - Yukon boundary, and about 2Jjj- m i l e s  south o f M i l e P o s t 702 on t h e A l a s k a highway. Map  No.- 1, The  (See  i n pocket.) c l a i m s c o v e r a group o f l o w = l y i n g h i l l s on  eastern contact of the C a s s i a r b a t h o l i t h .  the  These h i l l s  r e a c h e l e v a t i o n s o f about 4400 f e e t , w h i l e the  immediately  a d j a c e n t v a l l e y f l o o r has>.an e l e v a t i o n o f about 3600 f e e t . The  e l e v a t i o n o f t h e R a n c h e r i a R i v e r , which f l o w s  e a s t e r l y t h r o u g h t h e C a s s i a r M o u n t a i n s , i s about 2900 f e e t at m i l e  702. PROSPECTING  These c l a i m s were s t a k e d i n t h e summer o f 1946  by  p r o s p e c t o r s w o r k i n g f o r t h e Western Ranges P r o s p e c t i n g Syndicate.  -3The  f i r s t i n d i c a t i o n s o f m i n e r a l i z a t i o n found by  prospectors  the  c o n s i s t e d o f numerous p a t c h e s o f " l i m o n i t e  f l o a t " s c a t t e r e d over a number o f t h e h a r e h i l l s i n a r e s t r i c t e d a r e a o f about 6,000 f e e t long' and 600 f e e t wide c l o s e t o the i n t r u s i v e c o n t a c t . some o f t h i s was f r e s h galena.  On c l o s e r  examination,  found t o c o n t a i n o c c a s i o n a l g r a i n s of  A f t e r e x a m i n a t i o n by t h e a u t h o r , i t was  d e c i d e d t o e x p l o r e t h e ground more t h o r o u g h l y t o f i n d t h e source o f t h e l i m o n i t e .  The  t o attempt  following points  favored t h i s d e c i s i o n : (1)  Occasional  specks o f f r e s h r e s i d u a l g a l e n a were  founuL i n some p i e c e s ' o f l i m o n i t e . (2) d e b r i s was  A s m a l l amount o f n e a r s u r f a c e , l o o s e ,  found t o c o n t a i n a s m a l l percentage of galena  i n t i n y v e i n l e t s or as d i s s e m i n a t e d (3)  rock  The  grains.  s o u r c e o f t h e l i m o n i t e appeared t o be  None o f t h i s f l o a t was  local.  found on the s u r f a c e o f t h e b a r e  i n t r u s i v e mass Immediately t o t h e w e s t , and i t was considered  t h a t i f t h e l i m o n i t e had been t r a n s p o r t e d  and  d e p o s i t e d by i c e , some o f t h e l i m o n i t e s h o u l d a l s o have been f o u n d on t h e s u r r o u n d i n g source was (4)  area.  Further, a l o c a l  p o s t u l a t e d by L o r d ( 9 ) . Some o f the l i m o n i t e " l o o k e d "  t y p e s d e s c r i b e d by Bateman (2) from m e t a l l i c s u l p h i d e s .  The  s i m i l a r to c e r t a i n  as h a v i n g been d e r i v e d a u t h o r was  not  sufficiently  -  4  -  f a m i l i a r w i t h t h e s e l i m o n i t e boxworks t o s t a t e definitely their derivation. (5)  The d i s t r i c t was a p p a r e n t l y f a v o r a b l e f o r t h e  location of lead-zinc deposits.  M i n e r a l i z a t i o n along the  e a s t e r n edge o f t h e C a s s i a r - O m i n e c a  b a t h o l i t h has been  known f o r some y e a r s n e a r such l o c a l i t i e s as Manson C r e e k , I n g e n i k a R i v e r , and McDame Creek.  I n the v i c i n i t y of  t h e A l a s k a highway, L o r d ( 9 , p . 16-18) r e p o r t s g a l e n a and s p h a l e r i t e a t t h r e e l o c a l i t i e s , one about t w e l v e m i l e s n o r t h o f t h e highway and two o t h e r s a t f i v e and seven m i l e s south o f t h e highway,' a l l c l o s e t o t h e i n t r u s i v e . (6)  L i m e s t o n e and d o l o m i t e , which underlie t h e  l i m o n i t e f l o a t , f o r m f a v o r a b l e h o s t r o c k s f o r numerous i m p o r t a n t l e a d - z i n c d e p o s i t s i n many p a r t s o f t h e w o r l d .  -5GENERAL The  GEOLOGY  f o l l o w i n g i s a summary f r o m L o r d ' s r e p o r t (9)  of the r e g i o n a l geology c o v e r i n g a narrow s t r i p along the e a s t e r n edge o f the C a s s i a r - o m l n e c a b a t h o l i t h  extending  s e v e r a l m i l e s n o r t h and south o f the A l a s k a Highway. The  sedimentary r o c k s c o n s i s t m a i n l y o f l i g h t g r a y  l i m e s t o n e ana b u f f - w e a t h e r i n g d o l o m i t e , b u t i n c l u d e some a r g i l l i t e , s l a t e , p h y l l i t e , q u a r t z i t e , and s c h i s t .  Fossil  c o r a l s i n d i c a t e t h a t some o f t h i s group i s p r o b a b l y o f Carboniferous  age.  S c h i s t o s e l i m e s t o n e and d o l o m i t e a r e p r o m i n e n t n o r t h o f t h e highway, b u t were n o t n o t e d south o f the highway. L o c a l l y , a l o n g t h e g r a n i t i c c o n t a c t , some o f the r o c k s o f t h i s group- have been c o n s p i c u o u s l y a l t e r e d by c o n t a c t metamorphism a c r o s s a zone which i s g e n e r a l l y l e s s t h a n 200 f e e t wide. Most o f t h e s e f o r m a t i o n s have a -strike n e a r l y p a r a l l e l t o t h e edge o f t h e b a t h o l i t h and d i p about 45 degrees away f r o m i t .  However, n e a r the highway the beds  s t r i k e i n many d i r e c t i o n s and some a r e n e a r l y f l a t - l y i n g . The Cassiar-Omineca  b a t h o l i t h i s about 14 m i l e s wide  i n t h i s r e g i o n , and has a n o r t h - n o r t h w e s t  trend.  It is  l i g h t g r a y , m a s s i v e , medium t o c o a r s e - g r a i n e d . g r a n i t e t o g r a n o d i o r i t e , b u t t h e common v a r i e t y i s p r o b a b l y b i o t i t e - q u a r t z monzonite.  Numerous a p l i t e dykes, and  a  -6-  few p e g m a t i t e  and lamprophyre dykes c u t t h e  G n e i s s i c phases w i t h f o l i a t i o n and h a n d i n g  intrusive. striking  p a r a l l e l t o the b o r d e r were n o t e d a l o n g t h e w e s t e r n o f the i n t r u s i v e .  edge  L o c a l l y a l o n g the ea^ern edge, t h e  r o c k w i t h i n s e v e r a l f e e t o f the c o n t a c t i s f i n e - g r a i n e d , and c o n t a i n s v e r y l i t t l e dark m i n e r a l s . Under t h e h e a d i n g o f " M e t a l l i c M i n e r a l D e p o s i t s " , L o r d ( 9 , p.17)  reports:  " B o t r y o i d a l l i m o n i t e f l o a t i s abundant about 2 m i l e s s o u t h o f t h e highway a t m i l e 702. I t occurs i n d r i f t o v e r l y i n g dense, w h i t e , b u f f - w e a t h e r i n g d o l o m i t e o r l i m e s t o n e , o r b o t h , w i t h i n a few hundred f e e t o f the edge o f t h e g r a n i t i c b a t h o l i t h and has p r o b a b l y n o t been t r a n s p o r t e d more t h a n a few f e e t . The a r e a o f l i m o n i t e f l o a t p a r a l l e l s the g r a n i t e c o n t a c t f o r more t h a n 1,000 fe,et. One specimen o f n e a r l y s o l i d , dark brown l i m o n i t e assayed; g o l d , 0.005 ounce a t o n ; s i l v e r , 0.79 ounce a t o n ; tungsten, n i l . " No mention was made o f t h e presence  of galena here, .  b u t on p. 19 L o r d (9) f u r t h e r s t a t e s : "Most known m i n e r a l d e p o s i t s i n the map a r e a l i e w i t h i n t h e l i m e s t o n e s , d o l o m i t e s , and a s s o c i a t e d r o c k s o f Group C c l o s e t o t h e e a s t e r n edge o f the C a s s i a r b a t h o l i t h , t h a t i s n o r t h and s o u t h o f the highway a t about m i l e 701. T h i s s e c t i o n c o n t a i n s ^ g o l d , s i l v e r , copper, l e a d , z i n c , t u n g s t e n , and t i n , and c l e a r l y w a r r a n t s f u r t h e r p r o s p e c t i n g . "  -7-  GEOLOGY  OF  THE  STAR  GROUP  I n t h e area covered by t h e S t a r c l a i m s , P a l e o z o i c sediments o f c l a s t i c and c h e m i c a l d e p o s i t i o n a r e f o l d e d o r domed t o f o r m a s o u t h e r l y - p l u n g i n g a n t i c l i n a l structure^Map  No. 1)  These.are I n t r u d e d b y t h e C a s s i a r -  Omineca b a t h o l i t h w h i c h i s c o n s i d e r e d b y L o r d ( 9 ) t o be o f J u r a s s i c o r l a t e r age.  An i r r e g u l a r mass o f q u a r t z -  f e l d s p a r p o r p h y r y a l s o i n t r u d e s some o f t h e s e d i m e n t s , b u t t h e r e l a t i o n o f t h i s t o t h e main b a t h o l i t h i c i n t r u s i o n i s n o t known.  I t i s assumed b y t h e w r i t e r ,  however, t h a t t h i s may be a l a t e r o f f - s h o o t g e n e t i c a l l y r e l a t e d t o t h e main i n t r u s i v e . The  c o n t a c t o f t h e b a t h o l i t h w i t h t h e sedimentary  s t r a t a , c o i n c ^ e s f a i r l y c l o s e l y w i t h , and i s l o c a l l y d e f i n e d by a c o n t i n u o u s  depression or v a l l e y .  Several  summits i n t h i s t r e n c h d i r e c t t h e l o c a l d r a i n a g e two  opposite d i r e c t i o n s .  i n the  S i n c e t h e sediments d i p towards  t h e b a t h o l i t h , and c o n t a c t metamorphic m i n e r a l s were n o t noted i n t h i s v i c i n i t y , Dr. Derry considered t h a t t h e c o n t a c t t r e n c h might be t h e s u r f a c e e x p r e s s i o n o f a f a u l t between t h e b a t h o l i t h and t h e s e d i m e n t s , a l o n g w h i c h m i n e r a l i z i n g s o l u t i o n s may have p e n e t r a t e d o r d e p o s i t e d . The  c o l o r and t a s t e o f t h e w a t e r , and t h e brown r u s t on  p l a n t s i n t h e upper r e a c h e s o f I r o n C r e e k , a r e f u r t h e r evidence  t h a t a m i n e r a l d e p o s i t may be l o c a t e d i n a  p o s s i b l e f a u l t zone b e l o w t h e pond from which t h e c r e e k i s fed. Outcrops a r e numerous above t h e t r e e l i n e ,  which  i s a t an e l e v a t i o n o f about 3900-4000 f e e t i n t h i s a r e a . •The overburden  c o n s i s t s o f s o i l ana g r a s s i n p l a c e s ,  •but m a i n l y o r r e s i a u a l r o c k fragments  and p a r t i c l e s  b r o k e n ana weatherea from t h e u n d e r l y i n g s t r a t a .  Glacial  e r r a t i c s consisting p r i n c i p a l l y of g r a n i t i c boulders, which were p r o b a b l y x r a n s p o r t e a from t h e C a s s i a r b a t h o l i t h , are p r e s e n t t o t h e t o p s o f t h e h i l l s .  However, t h e r e i s no  g e n e r a l mantle o f g l a c i a l d e b r i s , and most o f t h e s e e r r a t i c b o u l d e r s a r e above t h e s i z e o r p e b b l e s . ' Apparently,  the smaller p a r t i c l e s or g l a c i a l d r i f t ,  which  may have been spread over t h e area'.at one t i m e , have been washed o f f t h e s e h i l l s i n t o t h e v a l l e y . Short v e i n s o f pure, white t o transparent c a l c i t e a r e exbosea i n some o f t h e l i m e s t o n e o u t c r o p s .  I n two  l o c a l i t i e s near t h e t r e e l i n e , n a r r o w b a r r e n q u a r t z v e i n s cut  a lower sandstone  member.  -9-  TABLE  Jurassic  or  later  OF  FORMATIONS  Quartz  Feldspar  Cassiar  (1)  Porphyry  Batholith  /"Charity H i l l C a l Gray  Carboniferous  or  \  Faith  D e v o n i a n.  Shale Gray  Limestone  Limestone  Limestone  Limestone  Banded A r g i l l a c e o u s  mica  In the  valley  schist  are  underlie  (1)  the  of  the  Rancheria River,  widespread,  series  listed  and these  Sandstone.  outcrops  strata  of  presumably  above.  Mapped ana c o m p i l e d by D . R . D e r r y , Ventures Limited..  Geologist  for  -10DESCRIPTION  OF  FORMATIONS  BANDED ARGILLACEOUS SANDSTONE These s t r a t a were o r i g i n a l l y mapped as l i m e s t o n e , h u t f u r t h e r examination o f the s i n g l e representative  sample  a v a i l a b l e , c o l l e c t e d from C l a i m 4, p o i n t Y, p r o v e s i t t o be an impure sandstone.  The r o c k i s d a r k g r a y i n c o l o r  and exposed s u r f a c e s show bands o r laminae t h a t  weather  d i f f e r e n t i a l l y t o produce r i d g e s up t o \ i n . t h i c k . The f i n e l y laminated nature of t h i s rock i s quite d i s t i n c t i v e even m  f r e s h l y broken  specimens.  I n some p l a c e s where t h e c o n t a c t between t h i s and t h e Gray l i m e s t o n e above i s . , exposed, t h e sandstone member i s seen t o be l o c a l l y f o l d e d and t w i s t e d whereas t h e g r a y limestone I s not. nonconformity. generally  Such a r e l a t i o n s h i p s u g g e s t s a l o c a l  However, s i n c e t h e i r a t t i t u d e s a r e  s i m i l a r t h r o u g h o u t t h e mapped a r e a , i t may be  t h a t no u n c o n f o r m i t y e x i s t s h e r e .  P o s s i b l y t h e Gray  l i m e s t o n e was l e s s competent a t t h e t i m e o f f o l d i n g , and was deformed by f l o w a g e . In t h i n s e c t i o n , the laminated structure  i s seen t o  be due t o t h e v a r i a t i o n I n c o m p o s i t i o n o f t h e d i f f e r e n t l a m i n a e , as w e l l as g r a i n s i z e v a r i a t i o n s .  Anhedral  q u a r t z g r a i n s about .1 mm. d i a m e t e r predominate, b u t some are as l a r g e as .5 mm.  These have been h i g h l y r e -  c r y s t a l l i z e d , as p r o v e n b y t h e i r compaction and  -11interpenetratmg contacts. An unknown mineral (Cordierite? or Anorthoclase?) which appears very similar to quartz and also forms t i g h t interpenetrating contacts with i t , forms possibly 10% of t h i s specimen.  It- has a pale pinkish tinge, i s s l i g h t l y  s e r i c i t i z e d , and apparently lacks good cleavage. o p t i c a l properties are: B-.006;  Other  n=1.53; 2V=40°; negative;  Occasional grains resemble Carlsbad twins, and  i n these the optic plane i s normal to the twinning.plane. Most grains are s l i g h t l y larger than the quartz grains, some are rimmed with quartz, and some contain t i n y inclusions of a c t i n o l i t e ? Brown b i o t i t e and green a c t i n o l i t e make up about 20% of the rock, and diopside i s present i n smaller amounts. Since these minerals would not normally be found to such an extent i n a fine-grained sandstone or quartzite, i t i s l i k e l y that l o c a l l y , at l e a s t , t h i s member has been highly altered during the intrusion of either the Cassiar batholith, or the quartz feldspar porphyry stock, or both, ana that the introauction of most of these minerals due to metasomatic replacement  at f a i r l y high  was  temperatures.  P y r i t e and magnetite form more than 3% of the t h i n section, and a s l i g h t amount of brown iron stain may attributed to them.  be  I r r e g u l a r grains of p y r i t e are more  or less concentrated along c e r t a i n bands or v e i n l e t s , and  T h i s a l s o c o n t r i b u t e s t o the l a m i n a t i o n .  Apatite,  t i t a n i t e and c h l o r i t e are p r e s e n t i n minor amounts, the l a t t e r n e a r areas o f p y r i t e . GRAY  u H 5 5 3 T O N E  T h i s i s a l i g h t - g r a y r o c k which weathers t o a d a r k e r gray.  VThen f r e s h l y b r o k e n i t has  Occasional  a m o t t l e d appearance.  c o a r s e c a l c i t e g r a i n s , sometimes r e s e m b l i n g  p h e n o e r y s t s i n an.igneous r o c k , may  be  seen i n the  fine-  g r a i n e d dense "groundmass" which shows vague b e d d i n g o r foliation. In t h i n s e c t i o n , f i n e - g r a i n e d ( l e s s than  .1mm)  compact c a l c i t e gra.ins f o r m a m a t r i x f o r l a r g e r c r y s t a l g r a i n s or o o l i t i c - a p p e a r i n g a r e a s -of c o a r s e r ' g r a i n e d calcite.  A Planar  s t r u c t u r e i s apparent i n the  "groundmass" as w e l l as i n the e l l i p t i c a l shapes l i n e a l arrangements o f the l a r g e r g r a i n s . due  t o f o l i a t i o n , or i t may  and  T h i s may  represent bedding since  be the  l i n e a t i o n t e n d s t o f l o w around some o f the l a r g e r g r a i n s . A minor amount o f c l a s t i c q u a r t z i s p r e s e n t as  small  irregular grains. FAITH LIMESTONE T h i s i s a dense, f i n e - g r a i n e d g r a y i s h - w h i t e  rock  t h a t weathers on a l l exposed s u r f a c e s t o a b u f f or r u s t y color.  The  r o c k appears m a s s i v e , w i t h a l a c k o f b e d d i n g  -13f o l i a t i o n i n t h e hand, specimen. outcrops,  Even i n w e l l exposed  i t i s o f t e n d i f f i c u l t t o d i s t i n g u i s h between  b e d d i n g and f r a c t u r e systems. A t h i n s e c t i o n showed f i n e - g r a i n e d ( l e s s t h a n .1 mm. compact c a r b o n a t e g r a i n s , w i t h an o c c a s i o n a l v e i n l e t o f l a t e r (?) c o a r s e r ( . 5 mm.)  calcite.  These s t r a t a u n d e r l i e most o f t h e h i l l s c o v e r e d b y t h e c l a i m s , and f o r m t h e h o s t r o c k f.or a l l t h e known mineralization.  While outcrops  a r e numerous, most o f  t h i s a r e a i s c o v e r e d w i t h a f o o t o r two o f l o o s e fragments and p a r t i c l e s c o n s i s t i n g m a i n l y lying Faith  o f t h e under-  limestone.  In view o f the p o s s i b i l i t y t h a t the composition o f t h i s member-may have been more f a v o r a b l e t h a n t h e u n d e r l y i n g Gray l i m e s t o n e  f o r the p r e c i p i t a t i o n of the  ore m i n e r a l s , c o m p a r a t i v e t e s t s were made t o d e t e r m i n e what d i f f e r e n c e s d i d e x i s t . Gray l i m e s t o n e  I n HC1, and HN0 , t h e 3  e f f e r v e s c e d f r e e l y and d i s s o l v e d r e a d i l y ,  while the F a i t h limestone dissolved with d i f f i c u l t y .  e f f e r v e s c e d s l o w l y and An e q u a l amount o f each was  dissolved i n a c i d , and.after f i l t e r i n g o f f the p r e c i p i t a t e s caused b y t h e a d d i t i o n o f ammonia, t h e f i l t r a t e s were t e s t e d under s i m i l a r c o n d i t i o n s f o r t h e presence o f c a l c i u m and magnesium.  Ammonium o x a l a t e  gave two s u c c e s s i v e p r e c i p i t a t e s " i n t h e Gray  limestone,  -14and o n l y one i n t h e F a i t h l i m e s t o n e , p r o v i n g t h e p r e s e n c e o f more c a l c i u m i n t h e f o r m e r .  Sodium ammonium phosphate  gave no p r e c i p i t a t e i n t h e f o r m e r , b u t d i d i n t h e l a t t e r , which p r o v e s t h e absence o f magnesium i n t h e Gray l i m e s t o n e and i t s p r e s e n c e i n t h e F a i t h l i m e s t o n e .  Three  s p e c i f i c g r a v i t y t e s t s on each gave c o n s i s t e n t v a l u e s o f 2.70 f o r t h e f o r m e r and S.82 f o r t h e l a t t e r .  These  r e s u l t s , combined w i t h t h e t y p i c a l b u f f w e a t h e r i n g  color  o f t h e F a i t h l i m e s t o n e , would seem t o i n d i c a t e t h a t i t i s f a i r l y p u r e d o l o m i t e , w h i l e t h e Gray l i m e s t o n e i s f a i r l y pure c a l c i t e . A s s o c i a t e d w i t h some o f t h e s u r f a c e p a t c h e s o f l i m o n i t e f l o a t , and i n some c a s e s w i t h o u t any l i m o n i t e , are p a t c h e s o f l i g h t brown p i e c e s o f F a i t h debris.  This material  limestone  i s h i g h l y f r a c t u r e d , and c r i s s -  c r o s s e d w i t h t i n y d a r k brown v e i n l e t s . (See P l a t e 3 ) . T h i s r o c k has been d e s i g n a t e d " F r a c t u r e d F a i t h  limestone."  T h i n and p o l i s h e d s e c x i o n s p r o v e t h a t t h e v e i n l e ' t s a r e due t o e u h e d r a l g r a i n s o f p y r i t e d i s s e m i n a t e d a l o n g t i n y fractures.  The p y r i t e has been a l m o s t w h o l l y  altered  t o m e t a l l i c l i m o n i t e , and a brown i r o n s t a i n permeates the carbonate  along the f r a c t u r e s .  V e r y s l i g h t movement  a l o n g some o f t h e f r a c t u r e s i s i n d i c a t e d by o f f s e t s of cross v e i n l e t s .  No q u a r t z was found i n t h e t h i n  section of t h i s material.  -15Another "Erecciated fragments about  -|  of  matrix  differential  This was of  so  of  large  brown  stain  C A L GRAY This numerous  4).  has  loose  or  of  Faith  was  seen  to  seen m  just  this  out  as  calcite  packed  of  the  of  in  with  veins.  seen  on the  but  of  to  grains, average  fragments  In consist which than are  of  light  outside  boundaries.  rock.  LIMESTONE is  a dark  calcite  further  gray  rock  veinlets.  study.  No  which  is  specimen  cut was  by  and  areas  concentration their  a  the  relief.  in place,  associated  closely  fine-  erosion  stand  are  a  to  surfaces,  well  fragments  smaller  in  up  areas  greater  as  angular  yellowish  circular  fragments  slight  of  embedded  caused  termed  limestone  On e x p o s e d  The b o r d e r s  and a  may b e  less  adjacent  tiny,  been  consists  closely  breccia  has  slightly  debris  generally  groundmass.  quartz  Plate  considerably  definite,  for  in  the  quite  No  or  breccia  number  actually the  the  float,  section,  in  (See  be  thin  are  It  stained  more  weathering  to  limonite  is  small,  occurs  found  a  which  that  rock  limestone".  i n maximum d i m e n s i o n ,  calcite.  matrix  included here  normal grayish-white  contains  white  type  Faith  inch  grained also  rock  fairly available  those  -16CHARITY H I L L LIMESTONE This i s a gray c r y s t a l l i n e limestone  or dolomite  I t contains at l e a s t t w o  t h a t weathers p i n k i s h b u f f .  f o s s i l i f e r o u s bands t h a t weather t o a r u s t y red-brown color.  Thin sections of the f o s s i l i f e r o u s material  c o n t a i n f i n e - t o medium-grained c a r b o n a t e mixed w i t h q u a r t z , b l a c k carbonaceous and k a o l i n i c m a t e r i a l , and s m a l l e r amounts o f t i n y m i c a f l a k e s .  The q u a r t z  forms  about 5%' o f t h e r o c k and c o n s i s t s o f a n g u l a r t o rounded c l a s t i c g r a i n s between rusty weathering'is  ,1mm.  and .3mm.  diameter.  confined t o a f a i r l y sharply  The defined  s u r f a c e l a y e r l e s s t h a n 2 mm. t h i c k . A f t e r examination of the t h i n s e c t i o n , Dr. O k u l i t c h o f t h i s U n i v e r s i t y s t a t e d t h a t t h e s t r u c t u r e was t o o g r e a t l y a l t e r e d by r e c r y s t a l l i z a t i o n t o d e t e r m i n e t h e genus.  D r . M.A. F r i t z o f the. R o y a l O n t a r i o  Museum  t e n t a t i v e l y c l a s s i f i e d o t h e r specimens f r o m t h i s band as Ordovician c o r a l s . CASSIAR/OMINECA BATHOLITH I n t h e v i c i n i t y o f t h e S t a r Group, t h e b a t h o l i t h i s a medium- t o c o a r s e - g r a i n e d  g r a y i s h r o c k , and i s c u t  by numerous s m a l l , w h i t e t o p i n k i s h a p l i t e d y k e s .  No  specimen o f t h i s m a t e r i a l was a v a i l a b l e f o r t h i n s e c t i o n e x a m i n a t i o n , b u t L o r d ( 9 , p.13) s t a t e s t h a t i t v a r i e s from a g r a n i t e t o g r a n o d i o r i t e , and i s p r e d o m i n a n t l y a  -17b i o t i t e - q u a r t z monzonite. Trench 3-13 (See Map 1) was dug i n an attempt t o expose t h e c o n t a c t o f t h e b a x h o l i t h and t h e F a i t h  limestone,  b u t t h e d r i f t - f i l l e d d e p r e s s i o n p r o v e d t o o deep. However, a s m a l l specimen o f l o o s e r o c k , which showed a c o n t a c t between two r o c k t y p e s , was c o l l e c t e d here and studied i n t h i n section.  I t appears t o be t h e c o n t a c t  between a f i n e - g r a i n e d a p l i t e dyke, and a b o r d e r phase o f t h e b a t h o l i t h which c o n t a i n s v e r y l i t t l e d a r k m i n e r a l s . The dyke c o n t a i n s e x t r e m e l y f i n e - g r a i n e d q u a r t z , a l b i t e , and m i c r o c l i n e , w i t h o c c a s i o n a l a l b i t e and m i c r o c l i n e phenocrysts  l e s s t h a n 1 mm. a c r o s s .  A t the contact there  i s a sudden change i n t e x t u r e t o medium- t o c o a r s e g r a i n e d a l b i t e , o r t h o c l a s e , m i c r o c l i n e , and q u a r t z . Much o f t h e f e l d s p a r i s c l o u d e d w i t h k a o l i n , and a s m a l l amount o f s e r i c i t e i s p r e s e n t .  Muscovite  forms about 2%  o f t h i s p o r t i o n , and a v e r y minor q u a n t i t y o f m a g n e t i t e was n o t e d .  I t i slikely  t h a t t h i s l o o s e specimen had  been t r a n s p o r t e d o n l y a few f e e t f r o m t h e b a t h o l i t h . QUARTZ FELDSPAR PORPHYRY T h i s i s a g r a y i s h - w h i t e r o c k c o n t a i n i n g prominent quartz phenocrysts  f r o m about l - ^ t o 3 mm. d i a m e t e r  f i n e - g r a i n e d groundmass.  i na  Numerous s m a l l e r f e l d s p a r  p h e n o c r y s t s , up t o about 1-| mm, l o n g , show up r e a d i l y i n t h i n section, but are rather d i f f i c u l t specimens.  t o d i s c e r n i n hand  -18Th i n s e c t i o n s show two m a i n " s i z e s o f q u a r t z p h e n o e r y s t s , t h e l a r g e s t group v a r y i n g between about 1-^ t o 3 mms.,  w h i l e a n o t h e r group seems t o be about .3 mms.  diameter.  There appears t o be v e r y l i t t l e g r a d a t i o n  between t h e s e two main s i z e s , and i t i s p o s s i b l e t h e r e f o r e t h a t f o l l o w i n g t h e f i r s t q u i e s c e n t p e r i o d d u r i n g which t h e l a r g e r p h e n o e r y s t s formed, t h e r e was a f u r t h e r upward i n t r u s i o n o f t h i s m a t e r i a l , f o l l o w e d b y a n o t h e r p o s s i b l y s h o r t e r p e r i o d o f quiescence" d u r i n g which t h e smaller quartz phenoerysts  formed.  The f e l d s p a r p h e n o e r y s t s a r e p r e d o m i n a n t l y a l b i t e b u t a s m a l l number a r e o r t h o c l a s e . q u i t e pronounced  Kaolinization i s  i n these f e l d s p a r phenoerysts, e s p e c i a l l y  near t h e i r borders, w h i l e the f e l d s p a r i n the f i n e - g r a i n e d groundmass i s r e l a t i v e l y c l e a r .  However, t h e r e v e r s e i s  t r u e o f s e r i c i t e , which i s much more f u l l y d e v e l o p e d i n t h e groundmass. A c o l o r l e s s m i n e r a l t h a t may he h y d r o m u s c o v i t e ( d a m o u r i t e ) forms about 3% o f t h e s l i d e .  I t occurs i n  t a b u l a r t o l a t h - s h a p e d c r y s t a l s f r o m about .1mm. long.  Other o p t i c a l p r o p e r t i e s are:  n=1.58; B=.033; one c l e a v a g e ; p a r a l l e l length-slow.  t o 1^-mm.  u n i a x i a l ; negative; extinction;  E u h e d r a l p y r i t e c r y s t a l s make up l e s s t h a n  1% o f t h e r o c k , and a r e always c o n t a i n e d i n s i d e t h e damourite?  The p y r i t e i s p a r t i a l l y o x i d i z e d t o a r e d  -19semi-transparent limonite, and a l i g h t yellow stain invariably extends outwards to color part of the otherwise colorless damourite?  These l i g h t yellow areas are then  s l i g h t l y pleochroic, and the addition of iron has apparently changed, the composition to another unknown mineral with a s l i g h t l y higher index and a more twisted mat appearance.  MINERAL  DEPOSITS  Surface trenching exposed three widely separated veins or mineralized shears containing massive, coarsely c r y s t a l l i n e galena. VEIN NO. 1  (See Map No. 1)  The largest vein was exposed by trench 6-3 on the N.S. side of F a i t h H i l l .  Here, fresh massive galena was found  i n places within 3 feet of the surface.  The vein zone was  traced f o r a length of 160 feet along i t s strike of N 25°W that more or less p a r a l l e l s the b a t h o l i t h contact.  The  average dip i s about 70° easterly, i . e . away from the contact.  The vein zone i t s e l f pinches and swells, and the  galena occurs i n l e n s - l i k e bodies,' up to about 12 inches thick.  Where the galena lenses out, the vein zone  continues and i s r e a d i l y traced by a soft sooty, brownish, or bluish-black material that crumbles l i k e a soft s o i l i n the central portion of the zone.  In some cases t h i s  s o i l - l i k e material contains a few t i n y specks and grains of  -20-  fresh galena.  The w a l l s on e i t h e r s i d e o f t h e n a r r o w  zones a r e r e l a t i v e l y s o l i d h u t a r e more o r l e s s c o m p l e t e l y permeated w i t h t h e b l a c k m i n e r a l . Blowpipe  and c h e m i c a l a n a l y s e s c o n f i r m e d t h e p r e s e n c e  of manganese, i r o n , C 0 , and water i n t h i s b l a c k m a t e r i a l . o  I t I s p r o b a b l y a m i x t u r e o f h y d r a t e d manganese and i r o n oxides r e p l a c i n g the o r i g i n a l F a i t h limestone. C o n t i n u i n g outwards from t h e v e i n , t h e c o u n t r y r o c k p a s s e s from t h i s b l a c k r o c k t o a b r o w n i s h r o c k and grades i n t o normal F a i t h l i m e s t o n e .  The manganiferous m a t e r i a l  i s considerably l e s s evident i n the w a l l s adjacent t o the galena lenses. T h i n s e c t i o n s were s u c c e s s f u l l y made t h a t show t h e b l a c k opaque m a t e r i a l r e p l a c i n g t h e c a r b o n a t e . T r e n c h i n g a t t h i s l o c a l i t y was suggested because o f t h e presence o f s u r f a c e l i m o n i t e f l o a t .  No r e s i d u a l g a l e n a  was seen i n any o f t h i s f l o a t , n o r was t h e r e a v e r y l a r g e q u a n t i t y or patch of i t i n evidence.  However, when t h e  f i r s t t e s t p i t showed t h e b l a c k s o i l - l i k e m a t e r i a l , t h i s was f o l l o w e d and t h e whole m i n e r a l i z e d v e i n zone exposed. The overburden h e r e , as over most o f t h e t r e e l e s s  hills  c o n s i s t s p r i n c i p a l l y of r e s i d u a l products of weathering of t h e i m m e d i a t e l y u n d e r l y i n g s t r a t a , which produces a c e r t a i n amount o f s o i l mixed w i t h l o o s e c o u n t r y r o c k fragments.  Occasional g r a n i t i c boulders greater than  -21s i x ' inches i n diameter  seem t o be a l l t h a t remains o f any-  earlier glacial debris. VEIN NO.  2  T h i s v e i n , s t r i k i n g N 13°W  and d i p p i n g 68°W, was  exposed i n t r e n c h 1-1 n e a r t h e t o p o f Guy H i l l about 2,000 f e e t n o r t h - w e s t o f V e i n No,  1.  The v e i n zone i s t r a c e a b l e  over a l e n g t h o f 65 f e e t by the same b l a c k menganiferous m a t e r i a l as exposed i n V e i n No.  1.  T h i s t r e n c h was  again  prompted by t h e p r e s e n c e o f s u r f a c e l i m o n i t e f l o a t , which i n t h i s case showed an o c c a s i o n a l speck o f r e s i d u a l f r e s h galena.  When t h e t o p 12s- f e e t had been removed, t h e b l a c k  manganiferous m a t e r i a l showed up, and f u r t h e r d i g g i n g exposed g a l e n a i n p l a c e about 3 f e e t b e l o w t h e s u r f a c e . The t r a n s i t i o n  from surface l i m o n i t e through  p l a c e t o g a l e n a i n p l a c e was VEIN NO.  quite evident  limonite i n  here.  3  I n t r e n c h 1-6 n e a r t h e b o t t o m o f Guy H i l l on i t s N.VJ. c o r n e r , a s h o r t v e i n , c o n t a i n i n g a 2-4  inch width of f r e s h  t o o x i d i z e d g a l e n a a l o n g .a 4-6  i n c h band o f l i m o n i t e , d i p s  f l a t l y t o t h e south-west.  s u r f a c e l i m o n i t e h e r e showed  The  o n l y a v e r y o c c a s i o n a l speck o f g a l e n a , and t h e g a l e n a i n p l a c e was  found about 3 f e e t b e l o w t h e s u r f a c e .  -22AR3A OF DISSEMINATED MINERALIZATION L i m o n i t e f l o a t c o n t a i n i n g a few g r a i n s o f f r e s h g a l e n a , d i r e c t e d a t t e n t i o n t o t h e a r e a between t r e n c h e s 3-6 t o 3-8 n e a r t h e bottom o f F a i t h K i l l on i t s n o r t h - w e s t c o r n e r . Trenching  exposed p o o r l y - d e f i n e d a r e a s c o n t a i n i n g  disseminated galena i n f a i r l y f r e s h country rocks.  I n some  cases a s m a l l amount o f s p h a l e r i t e accompanies t h e g a l e n a , as w e l l a s minor amounts o f p y r i t e .  Some o f t h i s  galena  o c c u r s as s m a l l g r a i n s i n . f r a c t u r e c l e a v a g e j o i n t s i n t h e F a i t h l i m e s t o n e , and i t i s a l s o common i n t i n y . v e i n l e t s . I n t r e n c h 3-6, f r e s h , d i s s e m i n a t e d p y r i t e w i t h no o t h e r m e t a l l i c s forms up t o about 10% o f t h e r o c k i n a small area.  Specimens were o b t a i n e d about 7 f e e t b e l o w  t h e o r i g i n a l s u r f a c e where t h e h o s t r o c k was a l s o q u i t e fresh.  I n hand specimens, t h i s r o c k i s more c o a r s e l y  c r y s t a l l i n e and l i g h t e r c o l o r e d t h a n t h e n o r m a l b u f f — weathering F a i t h limestone. c o n s i s t predominantly  Thin sections of t h i s material  o f medium-grained (about .3mm.)  c a r b o n a t e , b u t a l s o c o n t a i n a p p r e c i a b l e amounts ( p o s s i b l y 10%)  o f v e r y p a l e p h l o g o p i t e and a l m o s t c o l o r l e s s t r e m o l i t e ,  and s m a l l e r amounts o f a l m o s t c o l o r l e s s c h l o r i t e .  Quartz  i s a minor c o n s t i t u e n t , b u t s i n c e some g r a i n s a r e l o n g (about  .2mm.) and narrow and have i r r e g u l a r o u t l i n e s , i t i s  p r o b a b l y hypogene. The p y r i t e i s e u h e d r a l t o a n h e d r a l , and i s u n i f o r m l y disseminated throughout.  P h l o g o p i t e c o n t a i n s numerous  -23carbonate  inclusions, i n d i c a t i n g replacement.  Kaolinic  material i s sometimes associated with phlogopite and c h l o r i t e , indicating that the o r i g i n a l rock was somewhat argillaceous.  The apparent lack of t y p i c a l contact  metamorphic s i l i c a t e s along the b a t h o l i t h contact (See page 7) i s not surprising, since the tremolite and phlogopite are about the same color as the carbonate  and  are not recognized i n an ordinary hand specimen.  They do  show, however, on a flattened or ground surface.  These  minerals were probably formed by contact metasomatism when heated solutions or vapors reacted with the host dolomite during or following the intrusion of the Cassiar b a t h o l i t h . Possibly the p y r i t e and quartz were also introduced at t h i s time. Probably t h i s whole area of disseminated mineralization represents an i l l - d e f i n e d contact metamorphic deposit.  It  i s about 500 feet from the closest exposure of the batholith. No d e f i n i t e mineralized zone could be outlined i n t h i s area, and no gradation from the limonite to mineralization i n place could be noted.  Within a foot or two of the  surface, i n the loose weathered mantle, fresh country rock fragments.were found to contain small percentages disseminated fresh galena.  of  -24-  LlMONITIC AREAS Numerous trenches and p i t s were dug on or near other areas of limonite f l o a t , but no further mineralization i n place was found.  In some of these, such as trenches 3-10  and 3-11, a small amount of the black manganese oxide material was found i n place with limonite i n vein zones with r e l a t i v e l y s o l i d walls.  About 50 feet east of trench  3-10 an occasional piece of country rock f l o a t contains a minor amount of disseminated fresh galena. MINERALOGY Assays of the massive galena, from the three veins indicated values i n s i l v e r averaging about one-third of an ounce per unit of lead.  Polished sections were prepared  i n an attempt to determine the source of t h i s s i l v e r , since i t i s u n l i k e l y that t h i s amount of s i l v e r could be held i n the galena i n s o l i d solution.  A mineral that may be a  s i l v e r sulpho-salt was found i n very minor amounts and i n such small areas that i t could not be dug out f o r microchemical t e s t s . (Plate 5.)  I t i s l i g h t gray m  color, i s  s l i g h t l y harder (about C-) than galena, and i s Isotropic or very weakly anisotropic.  Oblique illumination d i d not show  any i n t e r n a l r e f l e c t i o n , but the small size of the mineral renders such tests u n r e l i a b l e .  The following etch tests  were obtained: HN0  3  Pos.  HCL  KCN  FeCL  Neg.  Pos.  Neg.  3  KOH  HgCL  Neg.  Pos.  g  -25No other sulphides or primary minerals were found with the fresh massive galena from No. 1 Vein.  There was not a  great deal of limonite here, but a polished section containing a small amount of weathered material i n contact with fresh galena shows the a l t e r a t i o n i n t h i s case to have been f i r s t anglesite, and then a brown, powdery limonitic material (Plate 6.)  The band of anglesite i s about -4- inch  wide end was proven by blowpipe tests f o r lead and sulphur. The limonitic material gave p o s i t i v e i r o n and sulphate t e s t s , but no lead.  I t may be that t h i s i s J a r o s i t e .  In the p a r t i a l l y weathered galena from Vein No. 2 a small amount of p y r i t e was found i n polished section.  The  galena here i s also surrounded by anglesite. Sphalerite has been found i n small amounts i n fresh rock only, from the area of disseminated mineralization. I t i s associated with galena i n t i n y v e i n l e t s or fractures. (Plate  7.)  P y r i t e could also be detected i n hand specimens.in the fresh F a i t h limesxone only, where i t occurs as disseminated grains and euhedral c r y s t a l s up to about ^ inch across. Some or these c r y s t a l s have been almost completely altered to metallic limonlxe, while the rock i s only very s l i g h t l y iron stained, '(plates § & 9 ) .  Polished sections of  numerous specimens or limonite revealed occasional small r e s i d u a l areas of p y r i t e , but these could not be seen with a hand.lens.  -26Quartz mineral thin  was  deposits  sections  the  of  the  revealed  a white  veinlets  i n the  It  to  be  tests  were  absence  in a l l field.  i n the  specimens  from the  area  the of  presence the  black  manganiferous  metallic soft,  also  obtained  for  widely  powdery  quartz.  one m i n e r a l ,  iron,  manganese,  However,  of  of  gossans  of  Polished f r o m V e i n ITo,  narrow, i r r e g u l a r wad.  (Flate  disseminated  Under the  the  disseminated  material  mixture  oi'  s m a l l amount  non-metallic  grains.  more t h a n  a  mineral forming  black,  a coherent,  of  of  l i m o n i t e from the  c o n t a i n hypogene  mineral is  may r e p r e s e n t  its  explored  wad i n m i c r o s c o p i c  seen  by  as  Some  also  sections  The m e t a l l i c  far  proved  quartz.  deposits  the  as  of  mineralization hypogene  conspicuous  throughout  binoculars, metallic  since and  10).  i t  is  grains.  positive sulphur.  1,  -27-  D5GCRIPTI0N  O F LIMONITE  The discovery of mineralization i n place beneath or very close, to four separate areas of surface limonite f l o a t indicates that the majority of the other widely scattered areas of limonite were also formed very close to t h e i r present p o s i t i o n from pre-existing metallic sulphides. I t i s not the purpose of t h i s work to hazard an opinion as to whether t h i s limonite indicates a commercial orebody, but i t i s f e l t that further mineralization could be reasonably expected beneath some of the other areas. In examining the limonite, both i n the f i e l d and i n the laboratory, i t became evident that the limonite was not a l l of one kind.  Therefore  i t was f e l t that laboratory  investigations of the various types, coupled with t h e i r occurrences i n the f i e l d , might form a v/orthwhile  study.  The remainder of t h i s report i s directed to that end.  -28TYPE NO. .1,  BLUE-BLACK 30TRY0IDAL LIMONITE  T h i s i s a d u l l , " b l u i s h - b l a c k m a t e r i a l , which has a burned or c l i n k e r y appearance.  (See P l a t e 11 A, & P l a t e 1 ) .  Smooth, s h i n y , b l a c k b o t r y o i d a l s u r f a c e s are g e n e r a l l y s m a l l i n e x t e n t and o f t e n r e s t r i c t e d t o h o l e s o r p o c k e t s i n t h e s u r f a c e , so t h a t t h e y may n o t be seen r e a d i l y without c l o s e examination.  The p r o t r u b e r a n c e s a r e i n most  cases q u i t e s m a l l , and are formed on t h i n e n c r u s t i n g bands, b u t one specimen c o n t a i n s p r o t r u b e r a n c e s almost -g i n c h a c r o s s on an e n c r u s t i n g band about £ i n c h t h i c k .  When  l a r g e r p i e c e s are broken, b o t r y o i d a l l a y e r s e n c r u s t i n g c a v i t i e s are o f t e n p r e s e n t , b u t t h e s e are u s u a l l y d u l l u n l e s s connected t h r o u g h an opening t o t h e s u r f a c e .  This  m a t e r i a l , when pure,-does n o t s t a i n t h e hands, b u t i t i s o f t e n p a r t i a l l y contaminated w i t h other types of s o f t e r limonite. A l l o c c u r r e n c e s o f t h i s t y p e were r e s t r i c t e d t o s t r i c t l y surface exposures, although t h i s i s not the only t y p e t o be found on t h e s u r f a c e .  R e s i d u a l specks o f g a l e n a  seem t o be e n t i r e l y l a c k i n g when t h i s t y p e i s r e l a t i v e l y pure. The bands have a f i b r o u s r a d i a t i n g s t r u c t u r e w i t h t h e f i b r e s p e r p e n d i c u l a r t o the s u r f a c e .  I t has a y e l l o w i s h -  brown s t r e a k , a hardness o f about 4-^-5, and a u n i f o r m s p e c i f i c g r a v i t y o f 3.93.  I t g i v e s o f f water i n t h e  -29closed tube, becomes magnetic on heating, and gives blowpipe and chemical t e s t s f o r i r o n . Since no r e l i c t sulphides or boxwork structure were evident i n the hand specimens, polished and t h i n sections were prepared.  Plate 12 i s a photomicrograph of a  polished section,• which shows the t y p i c a l limonite v e i n l e t s forming an i r r e g u l a r and i n d e f i n i t e pattern. amount of p y r i t e was  A small  detected i n the polished sections,  and some of t h i s i s shown i n the photo.  I t i s quite evident  that t h i s p y r i t e i s being replaced or altered to limonite. Another small 'area of r e s i d u a l p y r i t e was quite s i m i l a r to that seen i n Plate 8.  seen that appears  Therefore,  i t is  thought that t h i s type of. limonite has been derived l a r g e l y from p y r i t e . In polished sections, the encrusting layers of limonite are seen to form colloform bands on the outside edges of other l i m o n i t i c areas.  This material appears white, has a  very smooth surface, and shows a fibrous r a d i a t i n g structure perpendicular to the banding. hardness of about S.  I t i s i s o t r o p i c and has a  Aqua regia stains i t l i g h t brown,  but a l l the other reagents, as used by- Short (11), give a negative  etch t e s t .  On the inside of the smooth surfaced banded limonite, the limonite has a p i t t e d white surface, i s s l i g h t l y softer, and i s negative to a l l etch reagents.  Under  -30c r o s s e d N i c o l s i t shows r e d i n t e r n a l r e f l e c t i o n s , a n l s o t r o p i s m from l i g h t blue-gray  t o b l a c k , and appears as  i r r e g u l a r .jagged p l a t e s w i t h one  cleavage.  T h i n s e c t i o n s o f t h i s m a t e r i a l a r e l a r g e l y opaque when p u r e , b u t most specimens c o n t a i n o t h e r Authigenic  minerals.  a l b i t e was n o t e d i n one o f t h e s e i n v e r y  amounts and i n g r a i n s about .1mm. q u a r t z g r a i n s up t o about .1mm. i n some s e c t i o n s .  long.  small  A n g u l a r t o rounded  diameter are also  present  T h i s q u a r t z appears t o be o f  h y d r o t h e r m a l o r i g i n s i n c e some g r a i n s show e u h e d r a l Carbonate i s p r e s e n t  i n g r e a t e r q u a n t i t y and t h i s  represents m a t e r i a l from the o r i g i n a l host rock.  shapes. probably  A minor  amount o f p h l o g o p i t e was a l s o n o t e d i n one t h i n s e c t i o n . The non-opaque l i m o n i t e v a r i e s f r o m brown t o orange t o orange-red t o b r i g h t - r e d , and forms i r r e g u l a r i n t h e opaque l i m o n i t e .  patterns  Some o f t h e s e c o l o r s a r e a f u n c t i o n  o f t h e t h i c k n e s s , v a r y i n g f r o m orange n e a r t h e t h i n edges t o orange-red i n t h e t h i c k e r p o r t i o n s .  A s m a l l amount o f  r e s i d u a l p y r i t e was seen i n c e r t a i n s e c t i o n s , and one a r e a showed d e f i n i t e a l t e r a t i o n f r o m f r e s h p y r i t e t o r e d semitransparent  limonite.  O t h e r a r e a s o f s i m i l a r l i m o n i t e had  square o u t l i n e s and were p r o b a b l y p y r i t e cubes.  d e r i v e d from  euhedral  A v e r y minor amount o f t i n y g r a i n s o f f r e s h  g a l e n a was seen i n one t h i n s e c t i o n .  TYPE 1 A A s l i g h t l y m o d i f i e d form o f t h i s b o t r y o i d a l t y p e was found i n s m a l l q u a n t i t y o n l y , n e a r t h e s u r f a c e i n Trench 1-1 where V e i n No. 2 was exposed.  I t i s hard,  heavy, and t o u g h , and appears t o be a l m o s t pure m e t a l l i c i r o n oxide.  F l a t , t h i c k bands i n t e r s e c t each o t h e r a t  a n g l e s o f about 75°, l e a v i n g spaces o r c a v i t i e s which a r e rounded or f i l l e t e d a t t h e i r c o r n e r s .  Colloform  •banding and b o t r y o i d a l s t r u c t u r e i s q u i t e a p p a r e n t . (See P l a t e s 13 A, and 13 3.)  The b o t r y o i d a l s u r f a c e s a r e n o t  smooth and s h i n y as i n t h e main t y p e , b u t a r e r o u g h , and d u l l b r o w n i s h - b l a c k . No r e s i d u a l s u l p h i d e s were found i n t h i s m a t e r i a l , and as i t appears t o be o f minor i m p o r t a n c e , l i t t l e s t u d y was g i v e n t o i t .  -32TYPE NO.  2  REDDISH-BROITN HARD LIMONITE  This i s a. d u l l , dark reddish-brown, hard and heavymassive material, which contains numerous i r r e g u l a r c a v i t i e s , some of which are f i l l e d or p a r t l y coated with soft powdery material. (See plate 11 C.)  Most of the  c a v i t i e s are smaller than those shown i n the photograph. The powdery material i s p r i n c i p a l l y yellow, but some i s a very d e f i n i t e b r i c k red.  This l a t t e r powdery material  forms a t h i n d u l l coating on parts of the  surface.  Many of the c a v i t i e s that are f i l l e d with the  yellow  material show a f r a g i l e boxwork structure formed of very f i n e narrow walled p a r t i t i o n s .  Some of the smaller u n f i l l e d  c a v i t i e s have a few thick walled p a r t i t i o n s formed of the main hard material, and these appear to be pseudo or r e l i c t boxworks.  The b r i c k red powder i s generally lacking  i n boxworks. This material Is also r e s t r i c t e d to surface occurrences and was  found mainly on Hope H i l l . (See Map #1). •  I t has a dark brown streak and. a hardness of about 4^- to 5. The average of four s p e c i f i c gravity t e s t s was 3.71, these varied from 3.65  to 3.77  hut  probably as a r e s u l t of  impurities of the yellow.powdery limonite. In polished sections, white, smooth surfaced, metallic limonite may  form most of the f i e l d , or may  occur  as i r r e g u l a r areas or t i n y v e i n l e t s i n a background of  -33-  • l i g h t gray limonite. (See Plate 14, & 14 A). material appears non-metallic,  This l a t t e r  and gives orange to red  i n t e r n a l r e f l e c t i o n s under crossed ITicols.  This i s the  yellow powdery material mentioned above as f i l l i n g some of the c a v i t i e s .  The f r a g i l e boxwork structures were found to  be formed by very narrow v e i n l e t s of the white metallic limonite, but do not seem to have any d e f i n i t e pattern. small amount of p y r i t e was  A  also detected, none of which  could be noted i n hand specimens. Thin sections contain only a very minor amount of carbonate, and no quartz.  Semi-transparent orange-colored  v e i n l e t s form i n d e f i n i t e boxwork patterns i n the black opaque to reddish semi-opaque metallic limonite. (See Plates 15, and 16.)  The red limonite appears similar to that  noted as forming a f t e r p y r i t e In a t h i n section of Type 1 limonite, and many of these red areas again show square outlines.  One  fresh p y r i t e cube was  and a minor amount i n other sections.  seen i n one section, I t appears that  Type 2 limonite has also been l a r g e l y of p y r i t e derivation.  -34-  TYPE NO.  3  YELLOW BROWN SOFT LIMONITE  This i s a soft, rusty or l i g h t yellowish-brown material, with a smooth or velvety f e e l .  Usually i t does  not form large masses alone, but i s often associated with one of the previous types.  When scratched with a knife  t h i s f i n e powdery material i s r e a d i l y grooved. In two l o c a l i t i e s , hard limonite containing t h i s powdery material also has a small amount of malachite an encrusting coating, and also disseminated areas throughout the limonite.  as  i n tiny  Malachite was proven by  i t s green color, adamantine l u s t e r , hardness of about 3.5, encrusting form with b o t r y o i d a l surface and  divergent  fibrous rosettes, and also by chemical and blowpipe t e s t s that proved the presence of copper, carbon*dioxide  and  water. This limonite type, when pure, seems to occur i n small •oieces only and boxwork structure appears to be lacking i n these hand specimens.  However, when associated with  Type No. 2 hard limonite, a very f i n e - w a l l e d c e l l u l a r boxwork of t h i s powdery material may be  preserved.  In polished sections t h i s material does not present a smooth f l a t surface under the microscope, but shows a c e l l u l a r boxwork of grayish-white v e i n l e t s surrounding  metallic-appearing'  small i r r e g u l a r polygonal c e l l s that  may'he empty or f i l l e d with a non-metallic powdery  -35limonite. (See Plates 17 and 18.)  Some of these  polygonal  c e l l s have double wails.(See Plate 19.) The metallic v e i n l e t s are not the same hard limonite previously described, but have a hardness of about C . The whole f i e l d as seen i n the microscope has an orange to dark red i n t e r n a l r e f l e c t i o n under crossed H i c o l s . A considerable quantity of malachite i s present i n one polished section, and i t s f i b r o u s re.diating structure i s r e a d i l y seen. (See Plate 18.) The xhin section of the limonite containing malachite shows the t y p i c a l c e l l u l a r pattern (Plate 20) of t h i s type. Most or the c e l l s are empty, but some contain powdery limonite and others contain malachite.  -36TYP5 TO. 4  POROUS iSROW CRUMBLY L I l Q N I T E "  T h i s i s a d u l l , d a r k brov/n, p o r o u s , l i g h t - w e i g h t l i m o n i t e t h a t has a f r o t h y appearance due t o i t s l i n e c e l l u l a r boxwork s t r u c t u r e . (See P l a t e 11B.) exposed t o w e a t h e r i n g  On  surfaces  t h e d e t a i l o f t h e boxworks i s n o t  u s u a l l y w e l l p r e s e r v e d , b u t i t may r e a d i l y be o b s e r v e d by b r e a k i n g t h e specimen.  The f u l l d e t a i l o f t h i s boxwork  however, i s b e s t o b t a i n e d by sawing o r rough g r i n d i n g t o a f l a t s u r f a c e , and examining w i t h a hand l e n s o r 20 power b i n o c u l a r s . (See P l a t e s 21, end  22.)  Small areas of shiny b l a c k b o t r y o i d a l surfaces to  (similar  those d e s c r i b e d i n Type No. 1) may be seen o c c a s i o n a l l y  i n more o r l e s s p r o t e c t e d h o l l o w s o r c a v i t i e s . l e a t h e r e d s u r f a c e s a r e somewhat d a r k e r brown, w h i l e f r e s h s u r f a c e s show numerous b r o w n i s h y e l l o w and o c c a s i o n a l b r i c k r e d a r e a s o f s o f t powdery l i m o n i t e ( s i m i l a r t o t h a t d e s c r i b e d i n Type No. 3) w h i c h f i l l  some o f t h e boxwork c e l l s .  I n t h i s c a s e , however, n e i t h e r o f t h e s e powdery l i m o n i t e s f o r m c e l l w a l l s o r show any boxwork s t r u c t u r e i n t h e m s e l v e s . This m a t e r i a l contains appreciable percentages of q u a r t z , some as i r r e g u l a r g r a i n s , b u t most o f i t i n s l e n d e r , well-formed,  euhedral, doubly-terminated  c r y s t a l s up t o  \ i n . long. O c c u r r e n c e s o f t h i s t y p e were n o t r e s t r i c t e d to  entirely  t h e s u r f a c e , b u t were f o u n d down t o depths o f about one  -37f o o t , on t h e n o r t h w e s t s i d e o f Hope H i l l . ' Polished sections reveal a f a i r l y d e f i n i t e c e l l u l a r p a t t e r n formed by w h i t e , m e t a l l i c l i m o n i t e v e i n l e t s .  The  p a t t e r n c o n s i s t s o f one s t r o n g s e t o f f a i r l y l o n g , s t r a i g h t , p a r a l l e l c e l l w a l l s , w i t h one o r more o t h e r minor s e t s a t 90° o r about 45° t o t h e f i r s t .  Many o f t h e i n d i v i d u a l  v e i n l e t s a r e seen t o c o n s i s t o f two narrow l i m o n i t i c w a l l s s e p a r a t e d b y a space about t w i c e t h e i r t h i c k n e s s  which  r e s u l t s i n a "double-walled" c e l l p a r t i t i o n . ( P l a t e  23.)  ITo p y r i t e was f o u n d i n t h i s t y p e , a l t h o u g h a l l t h e l i m o n i t e i s the hard, white, m e t a l l i c v a r i e t y . I n t h i n s e c t i o n s , the l i m o n i t e v a r i e s from l i g h t t o d a r k brown opaque and orange r e d .  A s m a l l amount o f  c a r b o n a t e was n o t e d , and one t h i n s e c t i o n c o n t a i n s a s m a l l amount o f a l b i t e w h i c h i s s l i g h t l y s e r i c i t i z e d . s e c t i o n contained  This  same  o n l y v e r y minor q u a r t z i n t i n y g r a i n s ,  b u t a n o t h e r t h i n s e c t i o n , t h a t was c u t f r o m t h e specimen a. shown i n P l a t e 2 1 , c o n t a i n s c o n s i d e r a b l e A  quantity of coarse-  g r a i n e d v e i n q u a r t z w i t h some e u h e d r a l c r y s t a l s up t o 2 mm. 0  f  long.  The boxwork i n t h i s s e c t i o n c o n s i s t s p r e d o m i n a t e l y  limonite v e i n l e t s forming f a i r l y s t r a i g h t w a l l s  i n c l o s i n g square, r e c t a n g u l a r ,  and p o l y g o n a l  cells.  This  boxwork r e s e m b l e s somewhat t h e g a l e n a " c l e a v a g e boxwork" d e s c r i b e d by B l a n c h a r d and B o s w e l l ,  ( 8 , p.675.)  i n t h i s t h i n section, there i s considerable  However,  evidence o f  the l i m o n i t e g r o w i n g and e a t i n g i t s way a l o n g t h e q u a r t z  -38grain boundaries.  (See Plates 2 4 and 2 4 A . ) Some  hexagonal quartz grains ere more or less rimmed with narrow limonite v e i n l e t s .  The straight walls of some euhedral  quartz c r y s t a l s show a f a i r l y uniform depth of penetration (or replacement) by limonite, but i t i s more l i k e l y that the limonite has replaced galena that had previously p a r t i a l l y replaced and veined the quartz.  - 3 9 -  TYPS NO, 5  POROUS ORANGE-YELLOW LIMONITE  This i s a l i g h t orange-yellow to l i g h t brown colored 'limonite with a f i n e porous structure and a somewhat sandy appearing surface when examined with a hand lens or binoculars.  Residual galena i s present but most has been  oxidized. The boxwork structure i s somewhat masked by numerous •tiny -grains of limonite and carbonate coating the c e l l walls, and i t i s t h i s that gives the sandy appearance. (Plate 25).  As i n type No. 4, the structure of the boxwork  i s best demonstrated by cutting or grinding to a f l a t surface, though i t may be detected on a f r e s h l y broken surface i n small i s o l a t e d areas. small ( l e s s than 1mm.) triangular i n shape.  Individual c e l l s are quite  and are c u b i c a l , rectangular, and C e l l walls are invariably straight,  and show p r a c t i c a l l y no f i l l e t i n g or enlarging at t h e i r l i n e s of i n t e r s e c t i o n , thereby forming sharply defined corners.  Most of these p a r t i t i o n s are quite t h i n , and  appear f r a g i l e ; but large, stronger,'and more continuous p a r t i t i o n s take the place of f r a g i l e p a r t i t i o n s about every t h i r d or fourth c e l l . 2mm.)  F l a t surfaces show thick (.5mm. to  i n t e r s e c t i n g v e i n l e t s , quite widely spaced (5mm. or  more), forming a more or l e s s rectangular to triangular major pattern.  These v e i n l e t s proved to be cerussite.  The f i n e c e l l u l a r pattern could r e a d i l y be formed by the i n c i p i e n t a l t e r a t i o n of galena proceeding along i t s  -40cleavage planes.  The  commencement o f such an  alteration  vras n o t e d i n a p o l i s h e d s e c t i o n o f f r e s h g a l e n a from V e i n I7o. 1, i n w h i c h a n g l e s i t e . v e i n l e t s f o l l o w the b o u n d a r i e s and c l e a v a g e p l a n e s o f g a l e n a .  crystal  I n t h i s Type 5  m a t e r i a l , nowever, t h e v e i n l e t s are c e r u s s i t e , and a n g l e s i t e was  found.  no  T h i s m a t e r i a l o c c u r r e d as one  p i e c e ana numerous s m a l l e r p i e c e s i n one  locality  a t p o i n t X on t h e west s i d e o f Guy H i l l .  I t was  a s s o c l a t e a w i t h any o t h e r t y p e , and t h e r e was Fractured F a i t h limestone  large  only, not  no  (the " i n d i c a t o r " ) nearby.  A  s m a l l amount o f d i g g i n g p r o v e d t h a t t h i s m a t e r i a l had been t r a n s p o r t e d , and had p r o b a b l y been r o l l e d o r moved down t h e s l o p e f r o m i t s o r i g i n a l p l a c e o f f o r m a t i o n , and  then  s u b j e c t e d t o f u r t h e r w e a t h e r i n g under d i f f e r e n t e n v i r o n mental c o n d i t i o n s . P o l i s h e d s e c t i o n s o f 'this t y p e show v e r y  little  m e t a l l i c l i m o n i t e , and hence no boxwork p a t t e r n .  The  l i m o n i t e i s p r e d o m i n a n t l y t h e n o n - m e t a l l i c powdery m a t e r i a l t h a t g i v e s a r e d d i s h - b r o w n i n t e r n a l r e f l e c t i o n under crossed N i c o l s . A s m a l l amount o f f r e s h g a l e n a i s surrounded by a l t e r a t i o n product,  an  which e f f e r v e s c e s w i t h n i t r i c a c i d ,  and was p r o v e n i n t h i n s e c t i o n t o be c e r u s s i t e .  A  small  amount o f f r e s h , p y r i t e remains i n c e n t e r s o f s m a l l areas of m e t a l l i c l i m o n i t e . I n t h i n s e c t i o n s , t h e boxwork i n t h i s case i s seen  -41to be formed by semirtransparent, non-metallic, orsnge to brownish-stained carbonate which i s probably mainly c a l c i t e or dolomite.  There i s a d e f i n i t e lack of metallic limonite-  i n the c e l l walls. Pine grained euhedral to anhedral p y r i t e i s disseminated throughout the sections, and i t s p a r t i a l oxidation accounts f o r the staining of the carbonate.  Large  areas of galena have been more or less altered to, and are contained i n , a transparent mineral determined to be cerussite.  The cerussite i s mainly white to gray, but some  i s lavender colored.  I t has an extremely high birefringence  and index of r e f r a c t i o n , and under high power the surface has a very crinkled appearance and shows considerable change of r e l i e f as the stage i s rotated.  I t i s u n i a x i a l negative  •to b i a x i a l negative with 2 V less than 10°.  The ortho-  rhombic c r y s t a l form was detected by crushing some of the material and observing i t under the binoculars. These c r y s t a l s effervesced with n i t r i c acid, but they are ©o small that a p o s i t i v e blowpipe t e s t f o r lead could not be r e l i e d upon as i t was d i f f i c u l t to ensure that a pure sample had been used. The f a c t that most of the o r i g i n a l carbonate of the limestone has been stained by the oxidation of the p y r i t e , while the cerussite i s c l e a r , may he due to the e a r l i e r and easier oxidation of p y r i t e preceding the a l t e r a t i o n of galena to cerussite.  This agrees with the well known  -42comparative rates of oxidation of various metallic minerals. An argument against t h i s explanation becomes obvious when one considers the e l e c t r o - p o t e n t i a l series of sulphides determined by Gottschalk and Buehler (12). when two  as  They found that  sulphides such as p y r i t e and galena were i n .  mutual contact, a small e l e c t r i c current was  set up that  flowed from the high p o t e n t i a l p y r i t e to the lower p o t e n t i a l galena.  This accelerates oxidation of galena and  retards oxidation of p y r i t e .  Under perfect conditions,  galena sould be completely oxidized before p y r i t e . What usually happens, of course, i s that the early oxidation forms a layer of anglesite or cerussite around the galena, thus n u l l i f y i n g the action of the e l e c t r i c c e l l ,  and  oxidation of each mineral then proceeds more or less individually.  In t h i s case i t may be that cerussite was  less susceptible to replacement or staining by i r o n oxides than was the o r i g i n a l carbonate of the  limestone.  A l b i t e was not detected i n these t h i n sections.  Only  an occasional t i n y grain of quartz i s present, but whether t h i s i s c l a s i c or hypogene i s not known. A c o l o r l e s s mineral, that occurs i n very  small  tabular plates, and r a d i a t i n g rosettes or s t e l l a t e d masses has been determined as b a r i t e .  I t s most d i s t i n g u i s h i n g  feature as seen under crossed ITico-ls i n the aggregated c r y s t a l s i s the dark cross caused by t h e i r r a d i a l uniformity of o r i e n t a t i o n . IT has perfect cleavage i n one  d i r e c t i o n , and appears to have two other cleavages intersecting at about 78°. n -1.63;  Other o p t i c a l properties are:  2Vs40°; p o s i t i v e ; length-slow; a x i a l plane  perpendicular to the length of the c r y s t a l s ( i . e . perpendicular to the best cleavage.)  An Estimation of  the birefringence i s rendered inaccurate by the d i f f i c u l t y i n determining the correct thickness of these t h i n sections. A p o s i t i v e barium flame test could not be obtained from the crushed limonite, possibly because the b a r i t e i s present i n such small amounts and i s too small to be recognized i n the hand specimen.  Barite has not been found  i n any of the ho.st dolomite, and i t i s considered that the b a r i t e i n t h i s limonite was introduced by the hydrothermal solutions along with the metallic sulphides. I t i s not 1  closely a l l i e d with the large areas of galena and cerussite,. but occurs i n small scattered areas i n the iron-stained carbonate.  -44TYPE 170, 6  MIXED CAVERNOUS LEJOIflTE  This material has a very d u l l bluish-black surface with large areas of yellow brown soft limonite (Type No. 3 ) . The l a t t e r , combined with r e l a t i v e l y large depressions or surface c a v i t i e s , gives t h i s type a rather coarse appearance. L o c a l l y , botryoidal surfaces are developed i n the c a v i t i e s . The a u l l bluish-black surface i s merely a soft, weathered coating above a hard metallic limonite.  In some  of the softer material, cubical to rectangular c e l l s form a coarse boxwork pattern. (Plate 26.) Fresh galena i s present i n some of the specimens i n f a i r l y large areas rather than as scattered grains.. This limonite was found about 2 feet to 3 feet below the surface i n Trench 1-1, where Vein No. 2 of massive galena was exposed.  The surface limonite f l o a t here was  mainly Type No. 1, blue-black b o t r y o i d a l limonite, i n which only an occasional grain of fresh galena could be found. Type No. 6 appears to be a gradation between Type No. 1, ana f a i r l y fresh, but p a r t i a l l y oxidized galena. The.cubical to rectangular boxwork (Plate 26) was not seen i n the hand specimens to grade into galena, but i t s form and proximity to galena strongly suggest such an origin*  I t appears to be quite s i m i l a r to the "cleavage  boxwork" of galena derivation aescribed by Blanchard and Boswell (S, p. 675.) However, the c e l l s are larger, with  -45the distance between p a r a l l e l plates up to Q  mm.  In polished sections, the c e l l walls were found to be formed of metallic limonite.  They ?.re straight and p a r a l l e l  over small areas, end are crossed obliquely or at r i g h t angles by other p a r t i t i o n s . (Plate 27.) are not uncommon.  Double c e l l walls  The boxwork pattern occurs i n a back-  ground of non-metallic  powdery limonite, that gives a d u l l  reddish-brown i n t e r n a l r e f l e c t i o n under crossed N i c o l s . In the large areas of massive metallic limonite, no boxworkstructure i s present. The r e s i d u a l galena i s surrounded with anglesite that grades outward to non-metallic limonite.  and then to metallic  The t y p i c a l boxwork (Plate 27) was not seen to  grade into the anglesite or galena, although possibly t h i s could be found by further polished section study. pattern formed i n p a r t i a l l y weathered galena by  The  the  replacing anglesite appears quite s i m i l a r to the l i m o n i t i c boxwork seen i n Plate 27.  The  l i m o n i t i c c e l l walls are  obviously occupying the former p o s i t i o n of anglesite noted previously as having formed along the cubic cleavage planes of galena during the l a t t e r ' s i n c i p i e n t a l t e r a t i o n . (See p.  40.)  Thin sections show the four d i s t i n c t colors of limonite; orange, brown, red, and opaque black. three are semi-transparent, and the f i r s t two are  The  first  non-  -46metallic as seen under oblique i l l u m i n a t i o n . Each of the f i r s t three colors may  occupy large separate areas or  may  form a network of t i n y v e i n l e t s through the black opaque ' metallic limonite.  This network also suggests the "cleavage  boxwork" pattern of galena, (Plate 28.)  However, i n the  polished section, the boxwork pattern i s formed by a metallic limonite network (Plate 27), whereas, i n t h i n section the network i s due to semi-transparent, non-metallic orange colored v e i n l e t s i n the black metallic opaque limonite. proving:  This apparent discrepancy  could be explained  by  (1) that the portions showing the boxwork i n t h i n  sections were equivalent to the massive metallic limonite areas i n the polished sections where no boxwork pattern i s evident, and (2) that the portions showing the metallic limonite boxwork i n polished sections were too d e l i c a t e to preserye  i n t h i n sections since t h e i r background consists  of non-metallic powdery limonite.  Accordingly, an attempt  was made to prepare thinned polished sections but  the  technique was not successfully mastered i n time f o r t h i s work. One  area of fresh r e s i d u a l p y r i t e i s p a r t i a l l y  altered to red metallic limonite i n the same manner as shown i n Plate 9 and numerous rectangular areas of s i m i l a r red limonite suggest the former presence of p y r i t e . The f i e l d relations, and the abundance of r e s i d u a l galena l e f t l i t t l e doubt as to the o r i g i n of t h i s type of limonite, but i t was microscopic  studied as a guide to the meaning of  and physical features of other  types.  -47LIMONITE  TABLE  T h i s t a b l e summarizes t h e i m p o r t a n t f e a t u r e s o f the six Typs No.  types of l i m o n i t e .  Name & Description  O c c u r r e n c e Structure ,'Iaicjrfl^c.Qpic)  1. B l u e - B l a c k  Botryoidal  Dull,  clinkery.  2JReddish-Brown  3. Yellow-brown S o f t  4. Porous Brown Crumbly C e l l u l a r Boxwork; light-weight; frothy. 5. Porous OrangeYellow. Boxwork masked by sandy appearance.  6. Mixed  Cavernous.  Dull, black & brown; c o a r s e boxwork.  Probable Source  Surface  Indefinite Pyrite. Pyrite Carbonate & Widespread C o l l o f o r m A u t h i g e n i c Galena banding. albite. Hypogene quartz. Minor galena  Hard Surface.  D u l l , massive; small c a v i t i e s .  Associated Minerals  Massive. Circular to polygonal cells.  Pyrite. Carbonate.  Pyrite.  Widespread P o l y g o n a l i n other cells. Double types. w a l l s are c ommon.  Malachite  Pyrite  Down t o 1. 'Cleavage f o o t on Boxwork" Hope H i l l  Coarse V e i n quartz crystals. Carbonate. Authigenic albite.  West s i d e N i l , Guy H i l l because o f on s u r f a c e l a c k o f metallic limonite.  Galena. Galena Cerussite. & Carbonate. Pyrite Barite. Minor p y r i t e & Hypogene? quartz.  Hope H i l l  2-3 f e e t below surfac e in vein.  "Cleavage^ boxwork." Double walls.  &  Chalcopyrite?  Galena. Angelsite, Tyrite.  V  Galena with auartz.  Galena & Pyrite.  -48CONCLUSIONS Before s t a r t i n g these i n v e s t i g a t i o n s , the w r i t e r perused the l i t e r a t u r e , i n c l u d i n g the r e f e r e n c e s l i s t e d i n t h e b i b l i o g r a p h y , and e s p e c i a l l y t h o s e papers by B o s w e l l and B l a n c h a r d (3 t o 8) who have emphasized t h e p h y s i c a l c h a r a c t e r i s t i c s t h a t d i s t i n g u i s h limonite types d e r i v e d f r o m s p e c i f i c s u l p h i d e s . A f t e r s t u d y i n g each l i m o n i t e t y p e and f o r m i n g an o p i n i o n as t o i t s s o u r c e , t h e a u t h o r r e f e r r e d back t o t h e works l i s t e d i n t h e b i b l i o g r a p h y t o p i c k out t h e most i m p o r t a n t f e a t u r e s o f corroboration or  disagreement.  DERIVATION OF SPECIFIC LIMONITE TYPES Type No 1, b l u e - b l a c k b o t r y o i d a l l i m o n i t e , which t h e a u t h o r has a t t r i b u t e d t o p y r i t e and g a l e n a ,  appears  t© be q u i t e s i m i l a r t o t h e " B o t r y o i d a l l i m o n i t e c r u s t s d e r i v e d f r o m massive p y r i t e i n l i m e s t o n e gangue" i l l u s t r a t e d and d e s c r i b e d by B o s w e l l and B l a n c h a r d ( 5 , p. 3 7 3 ) .  They s t a t e : "The a c i d s o l u t i o n s from t h e o x i d i z i n g p y r i t e were so s t r o n g t h a t t h e y o v e r 'whelmed t h e n e u t r a l i z i n g power o f t h e limestone."  I n Trench 1-1, t h i s l i m o n i t e was found on t h e s u r f a c e and c o n t a i n e d o n l y v e r y o c c a s i o n a l specks o f r e s i d u a l galena.  Type No. 6 l i m o n i t e c o n t a i n i n g abundant  g a l e n a was found 2-3 f e e t b e l o w t h e s u r f a c e , i m m e d i a t e l y  -49above o x i d i z i n g massive g a l e n a .  I n t h i s case a t l e a s t ,  i t appears t h a t as o x i d a t i o n proceeds t h e c h a r a c t e r i s t i c c l e a v a g e boxwork o f g a l e n a ( a s seen' i n Type 6, P l a t e 26) i s l o s t , and Type ITo.'l l i m o n i t e i s formed.  Therefore, i t  i s q u i t e l i k e l y t h a t t h i s l i m o n i t e developed i t s f i n a l c h a r a c t e r i s t i c s from t h e minor r e s i d u a l p y r i t e n o t e d , b u t t h a t g a l e n a may a l s o have been p r e s e n t o r i g i n a l l y . The s i m i l a r i t y between Type No.s 4,5,6, and t h e " c l e a v a g e boxwork" o f g a l e n a d e r i v a t i o n has been previously.  mentioned  Type ITo. 5 may be a c o m b i n a t i o n o f " c l e a v a g e  boxwork" l a r g e l y masked b y " p a r t i a l l y s i n t e r e d  limonite  c r u s t s " o f c e r u s s i t e d e r i v a t i o n . ( 8 , p. 678.) The r o l e o f f e r r i c s u l p h a t e i n t h e o x i d a t i o n o f metallic sulphides,  and t h e r a p i d n e u t r a l i z i n g a c t i o n o f  l i m e s t o n e o r d o l o m i t e on s u l p h a t e s o l u t i o n s , a r e t o o w e l l known t o be d e a l t w i t h h e r e .  B o s w e l l and B l a n c h a r d ( 4 ,  p. 424, 438-9) found t h a t t h e s i g n i f i c a n t t y p e s o f o x i d a t i o n p r o d u c t s o f s p h a l e r i t e and g a l e n a were b e s t developed i n environments such as f e l d s p a t h i c r o c k .  o f m o d e r a t e l y slow n e u t r a l i z e r s , I n environments  of rapid  n e u t r a l i z e r s , the d i s t i n g u i s h i n g c h a r a c t e r i s t i c s are often p a r t i a l l y masked by a f i n e , f l u f f y t y p e o f limonite.  pulverulent  They c o n s i d e r t h a t t h e o n l y r e a s o n f o r any  preservation  whatsoever  of s i g n i f i c a n t types i n limestone  l i e s i n t h e f a c t t h a t g a l e n a and s p h a l e r i t e u s u a l l y i n massive form, and t h a t t h e e f f e c t s o f t h e C a C 0  3  occur do n o t  -50r e a d i l y penetrate sulphides.  t o the c e n t e r s  o f l a r g e nodules o f the  On the S t a r Group, the occurrence o f massive  g a l e n a i n d o l o m i t e , and Type no. 3 s o f t , powdery l i m o n i t e p a r t i a l l y obscuring  the c h a r a c t e r i s t i c cleavage boxwork,  agrees with the f i n d i n g s s t a t e d above. MATERIAL FORiu'llJG THE BOXWORKS The  i l l u s t r a t i o n s by B o s w e l l and B l a n c h a r d a r e hand  specimen photographs, o r s l i g h t l y m a g n i f i e d sketches o f boxwork p a t t e r n s  as seen w i t h a hand l e n s o r b i n o c u l a r s .  L i t t l e mention i s made o f m i c r o s c o p i c  investigations of  p o l i s h e d or t h i n s e c t i o n s , except when e x p l a i n i n g boxwork s t r u c t u r e and i t s r i g i d i t y ,  suchas t h e i r d e s c r i p t i o n o f  the "Coarse C e l l u l a r Boxwork" o f s p h a l e r i t e d e r i v a t i o n 1  (4, p. 434.)  Here they s t a t e t h a t m i c r o s c o p i c  observations  prove t h a t p a r a l l e l quartz v e i n l e t s forming the boxwork i n the o x i d i z e d p r o d u c t s are s i m i l a r t o quartz- v e i n l e t s i n the f r e s h s u l p h i d e , and t h a t t h i s quartz  i s c l e a r l y hypogene.  " I t was f u r t h e r observed t h a t as o x i d a t i o n o f the s u l p h i d e mass proceeds, the v e i n l e t s g r a d u a l l y advance t h e i r f r o n t and  "eat" t h e i r way i n t o the l e s s c o a r s e l y f r a c t u r e d  p o r t i o n s o f the s u l p h i d e mass.... These extensions  o f the  white t o g l a s s y v e i n l e t s c o n s i s t , n o t o f pure s i l i c a , b u t of l i m o n i t i c jasper,  -  and are c l e a r l y supergene."  In a  l a t e r paper ( 6 , p . 793-4) i t i s s t a t e d t h a t the SiOg content o f some o f the supergene l i m o n i t e boxworks i s as h i g h as 55%, b u t t h a t those d e r i v e d from g a l e n a and b o r n i t e  -51are generally low i n s i l i c a .  They found that the s i l i c a  content of the boxwork varies also with-the type of gangue (the most s i l i c e o u s was derived from oxidation of p y r i t e i n limestone), the d i s t r i c t chemical laws.  concerned, and physico-  They consider that c i r c u l a t i n g ground  waters, containing s i l i c a i n solution or i n c o l l o i d a l form, may i n f i l t r a t e  along fractures i n the fresh sulphide,  and thus provide a source of limonitic jasper even when no vein quartz or s i l i c a t e  minerals were o r i g i n a l l y present.  The c e l l walls of the limonite boxworks from the Star Group contain ho quartz or limonitic jasper, but consist of undetermined metallic iron oxides.  The difference between  these findings and those of Boswell and Blanchard may be explained by: (a) the general lack of quartz i n the veins and the limonite (except i n Type No.. 4), (b) the improbability of c i r c u l a t i n g ground waters containing s i l i c a , reaching the present r e l a t i v e l y high elevations at which the veins and limonite are found.  I t i s conceivable that  during some e a r l i e r geological period the topographic and other conditions may have existed that allowed  silica-  bearing ground waters to i n f i l t r a t e  the sulphides and-  produce limonitic jasper boxworks.  However, these would  have been destroyed by erosion long before now. I f The boxwork i n Type 6 limonite contained l i m o n i t i c jasper i n the c e l l walls, i t i s not l i k e l y  that t h i s  structure would be destroyed i n i t s a l t e r a t i o n to Type 1  -52-  l i m o n i t e . (See p. 4??.) Type No.- 4 l i m o n i t e c o n t a i n s c o n s i d e r a b l e hypogene q u a r t z . N e v e r t h e l e s s , t h e c e l l w a l l s o i ' t h e boxwork s t r u c t u r e (which appears q u i t e s i m i l a r t o t h e " c l e a v a g e boxwork" o f g a l e n a d e r i v a t i o n ) c o n s i s t o f m e t a l l i c i r o n o x i d e , and n o t s i l i c a . A t l e a s t some o f t h e s t r u c t u r e was found i n t h i n s e c t i o n s -  to be p a t t e r n e d a f t e r t h e shapes o f t h e e u h e d r a l q u a r t z crystals.  However, i t i s c o n s i d e r e d t h a t most o f t h e  boxwork i n t h i s t y p e i s p a t t e r n e d a f t e r t h e c u b i c  cleavage  planes of galena. SOURCE OF IRON During the e a r l y p a r t o f the e x p l o r a t i o n of the S t a r Group, t h e a u t h o r was n o t sure o f t h e o r i g i n o f t h e i r o n i n the l i m o n i t e f l o a t .  I t became apparent t h a t t h e l i m o n i t e  had formed v e r y c l o s e t o where i t ' was found (See p . 3 ) , and t h i s was c o r r o b o r a t e d b y t h e d i s c o v e r y o f t h e m i n e r a l deposits.  However, t h e p o s s i b i l i t y s t i l l e x i s t e d t h a t t h e  i r o n had been i n t r o d u c e d i n s o l u t i o n i n c i r c u l a t i n g ground w a t e r s and had been p r e c i p i t a t e d as l i m o n i t e b y t h e n e u t r a l i z i n g a c t i o n of the limestone.  The o n l y p y r i t e  f o u n d i n t h e f i e l d was i n t h e a r e a o f d i s s e m i n a t e d m i n e r a l i z a t i o n , and t h e r e was l i t t l e evidence o f i t s alteration to limonite. l o c a l i t y suggested  The-minor s p h a l e r i t e i n t h e same  another p o s s i b l e source o f i r o n , b u t i t  a g a i n was q u i t e f r e s h .  M i c r o s c o p i c s t u d y o f p o l i s h e d and  -53t h i n sections has revealed residual- p y r i t e i n many of the limonites, and the author now considers that a l l the i r o n i n the numerous areas of limonite f l o a t was derived l o c a l l y from p y r i t e or other primary iron-bearing  sulphides.  SECONDARY LEAD MINERALS Most authors seem to agree that galena, when subjected to weathering processes,  usually a l t e r s to anglesite or  cerussite, both of which are quite insoluble i n aqueous solutions.  Anderson (1, p. 531) states that anglesite  always forms f i r s t and that sny cerussite that may be present i s due to replacement of the sulphate and not the sulphide. Boswell end Blanchard, while favoring the formation of limonite by the reaction of f e r r i c sulphate on cerussite, suggest (4, p. 445) that cerussite i s formed from anglesite, although they also state (4, p. 443) that ".... sphalerite or galena.... may oxidize to the sulphate or carbonate state by ordinary air-water oxidation processes,"  The author  considers that t h i n sections of Type No, 5 limonite prove that cerussite may form d i r e c t l y from galena (See p.41), and suggests the following as a possible reaction: PbS  E 0 + C0 2  2  ->  PbC0 +H23 3  I t was noted (See p. 40) that t h i s limonite had been weathered i n an environment remote from i t s place of formation.  The oxidizing solutions here probably c a r r i e d  more COp and less sulphate than those i n the mineral  deposits.  -54SOLUBILITY OF  LIEIONITS I N  HC1  Bateman(2, p. 251) states that limonite derived from iron-hearing sulphides i s r e a d i l y soluble i n d i l u t e HCl, while that derived from iron-bearing gangue or rock s i l i c a t e s i s not.  He makes no attempt to substantiate t h i s  statement, but i t probably originated with Morse & Locke (10, p. 25°), who state: "the sulphide i r o n , having gone to limonite, may be approximated as that e a s i l y soluble i n d i l u t e HCl", and further (p. 258): "that the capping iron soluble i n f i v e minutes i n 3 or 4% HCl was i n f a c t approximately the same as the sulphide i r o n content of what we regarded as t y p i c a l ore v e r t i c a l l y below the capping." Boswell and Blanchard (3, p. 617) state: "as the chalcopyrite approaches p u r i t y , the i r o n of the indigenous limonite, though variable, approaches one-quarter to one-third that of the sulphide, the rest being removed." A discrepancy  i s apparent i n the above findings.  S o l u b i l i t y t e s t s were made on some of the limonites from the Star Group, i n an attempt to substantiate' the former authors.  In a l l cases i t was found that the acid required  heating to dissolve even the powdered material. following shows some of the r e s u l t s .  The table  -55Type ¥.0. Q u a l i t y  Condition  Solution  Solubility  1.  50 50 50 50 30  mg. mg. mg. mg. mg.  Solid Solid Powdered Powdered Solid  Cold Hot Cold Hot 6cc.  Slight D i f f i c u l t 15 mins. Slight D i f f i c u l t 10 mins. D i f f i c u l t . Xot  2.  20 mg. 20 mg.  Powdered powdered  2 c.c Cold 1:1 HClVery l i t t l e . 2 c.c Hot 1:1 HClMost i n 5 mins.  3.  20 mg. 20 mg. 30 mg.  Powdered Powdered Powdered  Cold 1:1 HCl Some s o l u t i o n . Hot 1:1 HCl Rapid s o l u t i o n . 6 c.c Hot 1:5 HCl Most i n 5 mins.  1:1 HCl 1:1 HCl 1:1 HCl 1:1 HCl • Hot 1:5HC1  A l l these limonites -were probably derived from sulphides, and i t i s considered that t h e i r differences i n s o l u b i l i t y are r e l a t e d to the type and r e l a t i v e amounts of metallic limonite i n each. In,any event, i t i s inconceivable that a gossan containing up to 55% SiOg in-the boxworks (See p. 50) would be r e a d i l y soluble i n d i l u t e HCl.  PLATE  1•  A t y p i c a l specimen o f s u r f a c e l i m o n i t e f l o a t from the S t a r Group. X 1. C o l o r v a r i e s from r e d d i s h - b r o w n t o h l a c k .  FLATE 2 . p a r t i a l l y weathered g a l e n a a s s o c i a t e d w i t h a l i m o n i t e boxworks s t r u c t u r e . X 84. The "boxwork grades i n t o g a l e n a (g) a t t h e bottom o f t h i s p h o t o .  -57-  PLATE 4. P o l i s h e d s u r f a c e of " B r e c c i a t e d F a i t h L i m e s t o n e " t h a t o c c u r s near a r e a s o f s u r f a c e l i m o n i t e f l o a t and near pure c a l c i t e v e i n s . X 2.  -58-  PLATS 5. Photomicrograph o f p o l i s h e d s e c t i o n showing unknown m i n e r a l ( s i l v e r sulpho-sa.lt? 3) i n g a l e n a ( g ) . T h i s i s the maximum '-rain s i z e i n which t h i s m i n e r a l was found. X 570.  -59-  -60-  Photomicrograph o f o o l i s h e d s e c t i o n showing almost comp a l t e r a t i o n o f d i s s e m i n a t e d p y r i t e (P) t o g r a y m e t a l l i c l i m o n i t e ( L ) , i n f r e s h r o c k . X 200.  FLATS 9. Photomicrograph o f p o l i s h e d s e c t i o n showing i n c i p i e n t a l t e r a t i o n o f * p y r i t e (F) t o l i m o n i t e (L) . X 570.  -61-  PLATS 10. P o l i s h e d s u r f a c e o f wad f r o m V e i n No. 1, showing i r r e g u l a r masses and v e i n l e t s o f a f i n e powdery m e t a l l i c m i x t u r e o f iron-manganese m i n e r a l s . Ilote: d o u b l e - w a l l e d tendency. X 3  FLATS 11. ( n a t u r a l S i z e ) A - Type 1. B l u e - b l a c k b o t r y o i d a l l i m o n i t e . B - Type 4. Porous brown crumbly l i m o n i t e . C - T ^ e 2. Reddish-brown h a r d l i m o n i t e .  -62-  PLATE 12. photomicrograph o f p o l i s h e d s e c t i o n showing i n d e f i n i t e p a t t e r n formed by m e t a l l i c l i m o n i t e v e i n l e t s ( L ) i n Type 1 l i m o n i t e , o f p y r i t e (P) d e r i v a t i o n . X 65.  200/<  PLAT^ 13 A. Photomicrograph o f p o l i s h e d s e c t i o n showing t y p i c a l c o l l o f o r m h a n d i n g i n Type 1 and 1 A l i m o n i t e . X S5. Gray i n lower l e f t i s i m p r e g n a t i n g f l u i d .  -63-  -64-  PLAT3 14. p h o t o m i c r o g r a p h o f p o l i s h e d s e c t i o n o f Type 2 l i m o n i t e showing i r r e g u l a r a r e a s and v e i n l e t s o f m e t a l l i c l i m o n i t e ( L ) i n a background o f n o n - m e t a l l i c powdery l i m o n i t e . X 200  PLATS 14 A  P h o t o m i c r o g r a p h o f p o l i s h e d s e c t i o n showing t h e t y p i c a l c i r c u l a r t o p o l y g o n a l c e l l u l a r s t r u c t u r e formed by m e t a l l i c v e i n l e t s i n Type 2 l i m o n i t e . X 65.  -65-  FLL;  lTi_i  15  •  Photomicrograph o f t h i n s e c t i o n o f Type 2 l i m o n i t e , w i t h s e m i - t r a n s p a r e n t , n o n - m e t a l l i c , orange c o l o r e d v e i n l e t s f o r m i n g a boxwork p a t t e r n i n opaque m e t a l l i c l i m o n i t e . Note t h e double w a l l s . X 50.  T3T A TV 1 il'll J  1 IP. Ca  S i m i l a r t o above. X 60. A l t h o u g h t y p e 2 i s c o n s i d e r e d t o have been d e r i v e d m a i n l y f r o m p y r i t e , l o c a l areas i n some of t h e t h i n s e c t i o n s e x h i b i t a p a t t e r n as above t h a t resembles t h e " c l e a v a g e boxwork" n o t e d i n Types 4,5, 8c 6. (See P l a t e 23.) White areas a r e h o l e s , and c a r b o n a t e . ( C ) .  -66-  PLATS I S . S i m i l a r t o above. "Tote t h e m a l a c h i t e , (lt}g t h e l a r g e a r e a shows i t s f i b r o u s r a d i a t i n g s t r u c t u r e . X 65.  -67-  F h o t o m i c r o g r a p h o f p o l i s h e d s e c t i o n showing t h e double w a l l s o f some o f t h e t y p i c a l p o l y g o n a l boxwork i n Type 3 l i m o n i t e . X 200.  Photomicrograph o f t h i n s e c t i o n o f Type 3 l i m o n i t e showing the t y p i c a l o o l y s o n a l boxwork, and areas o f m a l a c h i t e , (LI). X 60."  -68-  F l a t s u r f a c e o f Type 4 l i m o n i t e , showing t h e w e l l developed " c l e a v a g e boxwork", p o s s i b l y o f g a l e n a d e r i v a t i o n . X 4.  S i m i l a r t o above, b u t w i t h t h e boxwork p a r t i a l l y masked by powdery l i m o n i t e . X 4.  P h o t o m i c r o g r a p h o f p o l i s h e d s e c t i o n o f Type 4 l i m o n i t e . Note t h e r e g u l a r boxwork p a t t e r n formed by d o u b l e - w a l l e d m e t a l l i c l i m o n i t e v e i n l e t s . Gray i s i m p r e g n a t i n g f l u i d . X S 5 .  PLATS 24. p h o t o m i c r o g r a p h o f t h i n s e c t i o n o f Type 4 l i m o n i t e . Y e l l o w t i n t e d a r e a s a r e q u a r t z , and w h i t e a r e a s are h o l e s . This a p p a r e n t l y shows t h e g a l e n a d e r i v e d " c l e a v a g e boxwork" p a t t e r n , b u t a l s o shows t h a t many o f t h e l i m o n i t e v e i n l e t s ( b l a c k ) a r e formed around e u h e d r a l q u a r t z c r y s t a l s , and a l o n g i r r e g u l a r f r a c t u r e s and g r a i n b o u n d a r i e s i n t h e q u a r t z . X 12.  FL^TS 24 A. Photomicrograph  o i thin section o i a relatively  f r e s h r o c k showing v e i n q u a r t z ( w h i t e ) surrounded D y sub-opaque l i m o n i t e . X 65. T h i s specimen came from b e l o w t r e n c h 6-9, ana i s u n u s u a l i n t h a t i t c o n s i s t s m a i n l y o f q u a r t z , w i t h a. s m a l l amount o f g a l e n a .  L i m o n i t e has a p p a r e n t l y formed  around t h e q u a r t z by t h e o x i a a t i o n o f p y r i t e , a minor amount o f which was n o t e d i n t h e t h i n s e c t i o n .  The dark  a r e a i n t o p c e n t e r i s t h e t y p i c a l sub-opaque r e d l i m o n i t e t h a t has r e p l a c e d a e u h e d r a l p y r i t e  crystal.  -71-  PLATS 25.  F l a t s u r f a c e o f Type 5 l i m o n i t e , showing t h e " c l e a v a g e boxwork" almost c o m p l e t e l y masked by powdery l i m o n i t e c e r u s s i t e g r a i n s , g i v i n g i t a sandy appearance. X 4 . (Note: two t y p i c a l photos r.re i n c l u d e d . )  PLATS  26.  Type 6 l i m o n i t e , showing t h e " c l e a v a g e boxwork" o f g a l e n a d e r i v a t i o n . The o t h e r s i u e o f t h i s specimen c o n t a i n s weathered g a l e n a . X 1-2,.  -72-  PLATE 27. Photomicrograph o r p o l i s h e d s e c t i o n o f Type 6 l i m o n i t e , showing t h e " c l e a v a g e boxwork" o f g a l e n a d e r i v a t i o n . The c e l l w a l l s ere m e t a l l i c l i m o n i t e . Note t h e tendency toward double w a l l s . X 65.  TE 23. Photomicrograph or ohin s e c t i o n o f Type 6 l i m o n i t e , w i t h s e m i - t r a n s p a r e n t , n o n - m e t a l l i c , orange c o l o r e d v e i n l e t s f o r m i n g a " c l e a v a g e boxwork" p a t t e r n i n opaque m e t a l l i c limonite.  -73BIBLIOGRAPHY 1. A n d e r s o n , A.L.  "The I n c i p i e n t A l t e r a t i o n o f Galena." -Scon. G e o l . , V o l . 25, Aug., 1930.  2. Bateman, A.M.  "Economic M i n e r a l D e p o s i t s . " J o h n W i l e y & Sons, I n c . , New Y o r k , 1942.  3. R o l a n d B l a n c h a r d & P . P . B o s w e l l . "Notes on t h e O x i d a t i o n P r o d u c t s D e r i v e d f r o m C h a l c o p y r i t e . " Econ. G e o l . V o l . 20, Nov., 1925. 4. P.F. B o s w e l l & R o l a n d B l a n c h a r d . " O x i d a t i o n Products Derived from S p h a l e r i t e and Galena." Econ. Geol.,. V o l . a s , Aug., 1927. 5. R o l a n d B l a n c h a r d & P.F. B o s w e l l . " S t a t u s o f Leached Outcrops I n v e s t i g a t i o n . " Eng. & M i n . J o u r . , Feb 18 & Mar. 3, 1928.. 6. P.F. B o s w e l l & R o l a n d B l a n c h a r d . " C e l l u l a r Structure i n Limonite." Econ. G e o l . , V o l . 24, D e c , 1929.. 7. Rolend B l a n c h a r d & P.F. B o s w e l l . " L i m o n i t e Types D e r i v e d from B o r n i t e and T e t f i a h e d r i t e . " E c o n . G e o l . , V o l . 25, S e p t . - O c t . , 1930. J  8. R. B l a n c h a r d & P.F. B o s w e l l . " A d d i t i o n a l L i m o n i t e Types o f G a l e n a end Sphalerite Derivation." Econ. G e o l . , V o l . 2 9 , Nov., 1934. 9. L o r d , C.S.  " G e o l o g i c a l Reconnaissance Along t h e A l a s k a Highway Between Watson Lake and T e s l i n R i v e r , Yukon & B r i t i s h Columbia. G.S.C. Paper 44-25. 1944.  10. H.W. Morse & Augustus L o c k e . "Recent P r o g r e s s w i t h Leached Ore Capping" Econ. G e o l . , V o l . 19. A p r . May, 1924. 11. S h o r t , M.N.  " M i c r o s c o p i c D e t e r m i n a t i o n o f Ore M i n e r a l s . " U.S.G.S. B u l l . 825, 1931.  12. G o t t s c h a c k , V.H. and B u e l h e r H.A. "Oxidation of Sulphides." V o l . 7, 1912. 13. Augustus L o c k e .  Econ. G e o l . ,  "Leached O u t c r o p s as G u i d e s t o Copper Ore" W i l l i a m s & W i l k i n a , . B a l t i m o r e , M..D, 1926.  -74APPSNDIX PREPARATION OF THIN AND POLISHED  SECTIONS  Due t o t h e porous sua f r a g i l e n a t u r e o f some o f t h e specimens, d i f f i c u l t y  was encountered i n a t t e m p t i n g t o make  s a t i s f a c t o r y p e l i s h e a s e c t i o n s , and i t was found almost i m p o s s i b l e t o make t h i n s e c t i o n s i n t h e normal manner, a t t e m p t s were made t o impregnate t h e specimens w i t h Canada balsam bei'ore g r i n a i n g ana p o l i s h i n g , b u t t h e s e were n o t very successful. J.A. Donari suggested end t r i e d a method t h a t p r o v e d s a t i s f a c t o r y , and t h i s method was used f o r most o f t h e t h i n and p o l i s h e d s e c t i o n s d e s c r i b e d h e r e i n .  The  specimen  s h o u l d be h e a t e d t o about 100° C f o r a few hours t o d r i v e o f f most o f t h e o i l t a k e n up d u r i n g t h e sawing o p e r a t i o n . I t i s t h e n c o m p l e t e l y immersed i n an " i m p r e g n a t i n g f l u i d " b a t h and t h e whole s u b j e c t e d t o a f a i r l y s t r o n g vacuum f o r 24 h o u r s .  Upon r e m o v a l , t h e specimen s h o u l d be found t o be  w e l l c o a t e d and impregnated w i t h t h e now s t i c k y end v i s c o u s impregnating f l u i d .  I t i s t h e n h e a t e d i n an oven a t a  c o n t r o l l e d temperature o f 70° C f o r !?4 h o u r s , f o l l o w e d by a f u r t h e r 24 h o u r s a t 100° C.  (Note- Donan has s i n c e found  t h a t one 24 hour p e r i o d o f h e a t i n g a t 100° C i s s a t i s f a c t o r y . ) A t xhe ena o f t h i s Lime t h e i m p r e g n a t i n g f l u i d has become "baked" t o a f a i r l y h a r d and b r i t t l e mass.  The p o l i s h e d  or t h i n s e c t i o n may t h e n be f i n i s h e d i n t h e normal manner.  - 75Th e i m p r e g n a t i n g f l u i d used was manufactured  "Bakelite Plastics",  by C . I . L . , and commonly r e f e r r e d t o as  Bakelite Varnish.  I t was t h i n n e d by a d d i n g m e t h y l  or a 50-50 m i x t u r e o f m e t h y l a l c o h o l and e t h e r .  alcohol,  This  reduces t h e v i s c o s i t y and a l l o w s t h e i m p r e g n a t i n g f l u i d t o more e a s i l y p e n e t r a t e t h e c a v i t i e s , p o r e s and openings.  capillary  Under t h e vacuum t h e v o l a t i l e substances a r e  " b o i l e d o f f , l e a v i n g the remaining very v i s c o u s " P l a s t i c " 1 1  f i l l i n g the  spaces.  I n t h e s e f i r s t few a t t e m p t s , w h i l e s u c c e s s  was  a c h i e v e d , i t was found t h a t some l a r g e c a v i t i e s were n o t w h o l l y f i l l e d , and some s m a l l e r ones h a r d l y a t a l l . N e v e r t h e l e s s t h e porous s t r u c t u r e was  s t i l l p r e s e r v e d even  i n t h i n s e c t i o n s , though o f c o u r s e h o l e s were l e f t .  It  seems t h a t t h e baked p l a s t i c t h a t forms an e n c l o s i n g s h e l l around the whole b o r d e r as t h e s e c t i o n i s b e i n g ground,, h o l d s i t so r i g i d l y t h a t t h e s t r u c t u r e i s saved i n s p i t e of the imperfect impregnation. improved  I t may be found t h a t  i m p r e g n a t i o n would r e s u l t by u s i n g a low vacuum  d u r i n g t h e e a r l y p a r t o f t h e immersion p e r i o d .  U n  WESTERN  SYMBOLS  i  1  GALENA  VEINS  TRENCH  OR PIT.  AREAS  WITH  IN  RAN3ES  STAR  PLACE,  PROSPECTING  D.R. DERRY R.C. MACDONALD  V \  LIMIT  OF  TREE  a  I" = 5 0 0  OCT. 19 4 6.  FLOAT.  V  GR  SCALE  GOSSAN  SYNDICATE  ^ « « y of British ColumMi ~ , Canada  GROWTH. CAMP •"'  \  L I T T L E  V"  V  /  j  • ' A  U-\--/ ^  E L E V .  3 6 0 0 '  ... %  \  \  6 4  A'  \ y>  c  \V.) r  V *  > V".'  'ii^  .^37° 'GUY HILL  '/-0  " > < ^ .  yf  3-14  a  3-;/3  3  \ \  \  /  \4\  \  .  IS  .:••<• . i  - / 5  s  ;\  \  •'  v  \ /  .. / • • •-jy•  /  s • • •• 8  — ^ .  >^ /  . r  « o»3-3,4,5 V 3-2 / V  f N/''.\/!Hk"" •  \  N  < - . . .  »o-  \ \  PORPHYRY.  T\  -\  m  > | \  v• U  - -  .' I  \  /XV  J  3  QUARTZ  \ 0 0 -  \ c L^±^V.vl"  14  LEGEND  A  * 3-7 ' \  ' "  6..,  r  ^  •• Gild  I  C H A R I T Y  HILL  •A  %'e-r, \  •  * . "  -  ^  6  8  FAITH  °  7  \ HILL\  GRANITE. DEVONIAN  OR  CARBONIFEROUS.  CHARITY HILL (with f o s s i l i f erous CAL  GREY  LIMESTONE, shale b a n d s . )  e  LIMESTONE.  SHALE  (rusty  FAITH  LIMESTONE.  • • •  • 4 2 0 0  16  X  2 0 '  weathering.)  V  SH A L E . GREY  LIMESTONE.  BANDED  ARGILLACEOUS  LIMESTONE.  GUY  s.w.  s  HILL  N.E.  r 40'  A  \  35C r  \J VV y  FAITH  S.W.  v  v vv  Vj  y  HILL  N.E.  6-3 TRENCH W  V 400C'  B  350C  0  \  v  I  \  v  \sT*0<  '  HOPE FAITH  HILL  HILL  CASSIAR BATHOLITH  \  y  ,\\\-'\  CHARITY HILL  y •4CP0  /  y  KEY SCALE  MAP f = I MILE.  y  VERTICAL  SECTIONS.  YUKON BRITISH  SCALE  = 500  V  TERRI TORY COLUMBIA  w /'  

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