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Wall-rock alteration at Zeballos, B. C. Allen, Alfred Roy 1941

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WALL—ROCK ALTERATION AT ZEBALLOS, B. G. by A l f r e d . Roy A l l e n  A T h e s i s submitted I n P a r t i a l Ed. I f i l m e n t o f The. Requirements f o r the Degree of MASTER OF APPLIED SCIElfCE in- the Department of GEOLOGY  The U n i v e r s i t y  o f B r i t i s h Columbia.  A p r i l j 1941.  f a l l - R o c k . A l t e r a t i o n a t Z e b a l l o s . B. G. coraaras  A... Introd.ucti.on.; B. General. Geo l o g y : C. Wall-Rock A l t e r a t i o n : (a) Spud. V a l l e y V e i n . "1. G e n e r a l Geology. 2.. The i'resh W a l l - r o c k . 3* The A l t e r e d W a l l — r o c k . 4. D e s c r i p t i o n o f S l i d e s . 5. Summary and C o n c l u s i o n s ;  :  (t>) P r i d e n t V e i n . 1. G e n e r a l Geology. 2 i. The ITresh W a l l - r o c k . 3. The A l t e r e d W a l l - r o c k . 4. D e s c r i p t l o t i of Slides.. 51 Summary and C o n c l u s i o n s .:• (c.) The 1. 2. 3V 4. 5.  Mount Zeballos. V e i n . G e n e r a l Geology. The i'resh W a l l - r o c k . The Altered.. Wall-rock.. Description"- of. S l i d e s . Summary and Conclusions.  (d) The li 2. 3.. 4. 5.  White S t a r V e i n . G e n e r a l Geology. The F r e s h ? / a l l - r o c k . The A l t e r e d W a l l - r o c k . D e s c r i p t i o n of Slides.. Summary and C o n c l u s i o n s .  (e) The .1.. 2... 3.. 4. 5.  Privateer Veins. General. Geology. The J?resh w a l l - r o c k . The A l t e r e d W a l l - r o c k . D e s c r i p t i o n of Slides.. Summary and C o n c l u s i o n s .  :  D. Summary and C o n c l u s i o n s ; (a) C l a s s i f i c a t i o n , o f t h e Ore D e p o s i t s . (b) The Ore S o l u t i o n - - i t s o r i g i n and composition. . (c) The E f f e c t of the W a l l - r o c k on Alteration.  G E O L O G Y OP T H E Z E B A L L O S 7  "  AREA M i n e s - J, S. Steve-nson..  A. Introduction.: Z e b a l l o s , the newest mining camp i n B r i t i s h Columbia, i s l o c a t e d on the west coast of Vancouver I s l a n d , 200 m i l e s n o r t h w e s t , of V i c t o r i a . The. f i v e mines i n c l u d e d i n t h i s r e p o r t occur c l o s e to t h e southwest c o n t a c t of t h e Z e b a l l o s b a t h o l i t h i n the area d r a i n e d by Spud and G o l d v a l l e y c r e e k s . The a r e a d r a i n e d by the Z e b a l l o s r i v e r i s v e r y rugged* and. much o f i t i s covered w i t h a l u x u r i o u s growth of t i m b e r . The annual r a i n f a l l i s about 200 inches p e r y e a r . Gold was f i r s t found i n the g r a v e l s o f the Z e b a l l o s river.  I n t e n s i v e p r o s p e c t i n g was s p u r r e d to a "rush"  s e v e r a l s m a l l high-grade l o d e - v e i n s were d i s c o v e r e d .  after The  P r i v a t e e r and Spud v a l l e y mines s t a r t e d m i l l i n g ore i n the e a r l y w i n t e r o f 1938* the Mount Z e b a l l o s in. August,. 1939,. and the C e n t r a l Z e b a l l o s i n January, 1940. Today these f o u r producing mines form t h e nucleus mining  o f an a c t i v e and p r o g r e s s i v e new  community.  B... G e n e r a l Geology; The  rocks u n d e r l y i n g the Z e b a l l o s mining area, are  l a t e T r i a s s i c t o early. J u r a s s i c sediments and v o l c a n i c s i n t r u d e d by an igneous assemblage ranging from quartz gabbro t o quartz, monzonite and f e l s i t e . The sedimentary and v o l c a n i c r o c k s , named t h e Vancouver group, a r e d i v i d e d i n t o the Karmutsen v o l c a n i c s , Q,uats i n o l i m e s t o n e , and Bonanza groups.  -2*Tiie Karmutsen v o l c a n i c s ^ c o n s i s t o f dark green to b l a c k a n d e s l t i c and b a s a l t i c f l o w s w i t h p i l l o w and amygdaloidal structure.  The f l o w rocks c o n t a i n zones of green, grey, and  r e d d i s h v o l c a n i c b r e c c i a s and t u f f s , and a few l e n t i c u l a r beds of w h i t e to dark grey limestone»  The c o n t a c t between the K a r -  mutsen v o l c a n i c s and Q,uatsi.no f o r m a t i o n i s w e l l d e f i n e d , and along i t t h e r e i s some evidence of f a u l t i n g . The Q,uatsino f o r m a t i o n c o n s i s t s , o f a t l e a s t s e v e r a l hundred f e e t of f i n e - g r a i n e d t o c o a r s e l y c r y s t a l l i n e dark grey to white limestone.. Through t h e l i m e s t o n e , p a r t i c u l a r l y near the top there, a r e green v o l c a n i c flows,, and grey, green, and brown t u f f s  -  L y i n g conformably upon the Quatsino f o r m a t i o n t h e Bonanza group c o n s i s t s -6f"^liiir-toebg- of thin-bedded l i m e s t o n e , a r g i l l i t e , and q u a r t z i t e . heterogeneous  O v e r l y i n g the sediments there i s a  assemblage o f green o r g r e y , f i n e - g r a i n e d , ande-  s l t i c a c i d f l o w s , i n t e r l a y e r e d w i t h green, p u r p l e , r e d or. grey b r e c c i a s , and f i n e - g r a i n e d t u f f s .  Some of t h e c o a r s e - g r a i n e d  f l o w s a r e p o r p h y r i t i c , and a few of. the c r y s t a l l i n e t u f f s r e semble p o r p h y r i e s i The Z e b a l l o s b a t h o l i t h c u t s the v o l c a n i c and s e d i mentary-rocks.  The igneous r o c k s range from q u a r t z gabbro and  d i o r i t e t o q u a r t z monzonite and p e g m a t i t e , the a c i d types b e i n g most abundant i n the southwest.  An i n t r i c a t e network of dykes,  s t o c k s , and i r r e g u l a r bodies occur around t h e p e r i p h e r y of the batholith. A l l of t h e p r o d u c i n g mines a r e l o c a t e d near the  MICRO-PHOTOGRAPH Crossed E i c o l s  Magnification  A T h i n - s e c t i o n o f The Z e b a l l o s B a t h o l i t h  80 Diam.  ^uartz-diorite.  Note the f e l t of s e r i c i t e r e p l a c i n g a l l but the outer zone of f e l d s p a r c r y s t a l s . Platey c h l o r i t e , i n e x t i n c t i o n , i s closely associated w i t h the s i r i c i t e .  MXCROPHOTOGRAPH  Magnification  Approximately  160  Diameters.  A T h i n - s e c t i o n of The A l t e r e d W a l l - r o c k Adjacent To The Spud V a l l e y V e i n . R A  A f e l t of t i n y r u t i l e  crystals.  Apatite crystals.  f  F e l d s p a r almost w h o l l y r e p l a c e d by s e r i c i t e and c h l o r i t e .  Q,  Uuartz.  MICROPHOTQGRAPH  Magnification  A Thin-section  Approximately  160  Diameters.  o f The A l t e r e d Vsall-rock Adjacent To The Spud V a l l e y V e i n .  Py S  R  A grain of p y r i t e . A c o l l o r l e s s , f i b r o u s aggregate of r a t h e r coarse s e r i c i t e s c a l e s , d e v e l o p e d around and p e n e t r a t i n g the p y r i t e . Innumerable v e r y s m a l l a c i c u l a r c r y s t a l s of r u t i l e i n the s e r i c i t e .  Groundmass Feldspar a l t e r e d to s e r i c i t e , carbonate, and p r o b a b l y some k a o l i n .  southwest'cbntact  o f the Z e b a l l o s b a t h o l i t h w i t h the Bonanza  group, some i n the igneous rock, and others i n the v o l c a n i c and sedimentary  rocks.  0. Wall-Rock A l t e r a t i o n s .(a) Spud V a l l e y V e i n . 1. G e n e r a l GeologyThe main v e i n l i e s i n the q u a r t z d i o r i t e of the Z e b a l l o s b a t h o l i t h , 150G f e e t t o 3000 f e e t n o r t h e a s t of- the southwest c o n t a c t .  The s t r i k e i s n o r t h 60° t o 85° northwest.  2. F r e s h Wall-rock-The f r e s h rock i s a l i g h t grey medium-grained quartz d i o r i t e .  Brown b i o t i t e and dark green hornblende  occur  i n about e q u a l amounts a l o n g w i t h g l a s s y q u a r t z and s h i n e y , well-formed f e l d s p a r s . 5. A l t e r e d W a l l - r o c k Kext to t h e v e i n the rock i s a l i g h t to greenish grey  s  medium-grained, f r i a b l e aggregate  and c h l o r i t e . chlorite,  The b i o t i t e and hornblende  of s e r i c i t e ,  albite,  have been converted to  s e r i c i t e , and p r o b a b l y some m a g n e t i t e .  The r u t i l e  and t i t an I t e have been p a r t i a l l y a l t e r e d t o leucoxene.  There  Is l i t t l e sulphide m i n e r a l i z a t i o n i n the a l t e r e d w a l l - r o c k . T h i n bands o f brown weathering  carbonate l i e p a r a l l e l to the  vein. 4. D e s c r i p t i o n o f S l i d e s i . Slide_S _V j£l. JL  JL  S l i g h t l y A l t e r e d Wall-rock'.  -4" '  Mlnea?al  Composition:  Plagioclase  fLabradoxite  feldspar  P l a g i o c laseffeIdspara..  f e Q  fM  . V-Oligoclase • • \ Quartz' BlotIte Hornblende Sericite Chlorite Accessories  • •  Ab  An  5 0  n 4 G  Ab An o 8 0  2  36^  'J 5<g 16% 14$ 1Q#: 4$ 4$ 2%~  Medium t o l a r g e c r y s t a l s of zoned  f e l d s p a r are the c h i e f c o n s t i t u e n t of the s l i d e .  The  inner  zone i s l a b r a d o r i t e w i t h maximum e x t i n c t i o n to the a l b i t e t w i n laminae, a t 28°.  The  second zone i s andesine,  and the  outer  zone o l i g o c l a s e , w i t h r e v e r s e d e x t i n c t i o n on the a l b i t e - t w i n n i n g 0  lamenae from. -10°  t o +-7.  S e r i c i t e r e p l a c e s c h i e f l y the l a b r a -  d o r i t e , but a l s o the a n d e s i n e - o l i g o c l a s e to a l e s s e r degree, p a r t i c u l a r l y along s m a l l f r a c t u r e s .  Some f e l d s p a r c r y s t a l s are  almost c o m p l e t e l y a l t e r e d to s e r i c i t e , and others are u n a l t e r e d . Q.uartz.  Quartz occurs as an i n t e r s t i t i a l f i l l i n g between the  feldspar crystals. Biotite.  E l o n g a t e d p l a t e s , of dark brown b i o t i t e occur between  f e l d s p a r c r y s t a l s and q u a r t z . the b i o t i t e .  The  C h l o r i t e and magnetite r e p l a c e  r e p l a c i n g m i n e r a l s occur t o g e t h e r , the magne-  t i t e i n s m a l l i r r e g u l a r g r a i n s , t i n y a c i c u l a r needles,  or  l a r g e r shapeless g r a i n s , and the c h l o r i t e p e n e t r a t i n g the b i o t i t e i n l o n g s h a r p l y d e f i n e d tongues. Hornblende«  Dark green hornblende, p l e o c h r o i c from straw  y e l l o w to dark o l i v e green, i s p a r t i a l l y a l t e r e d t o c h l o r i t e and.  magnetite.  Sericite.  T i n y blades and fan-shaped aggregates of s e r i c i t e  r e p l a c e tlie> f e l d s p a r .  The replacement I s most Intense i n the  l a b r a d o r i t e , but i t a l s o occurs a l o n g c r a c k s I n the andeslne and o l i g o c l a s e .  Some o f t h i s white m i c a may be p a r a g o n i t e ,  but by the s p e c t r o g r a p h i t i s i d e n t i c a l t o muscovite and i s t h e r e f o r e c h i e f l y a p o t a s s i c mica* Accessoriesi Apatite;. - Numerous c r y s t a l s o f a p a t i t e occur embedded I n the f e l d s p a r , b i o t i t e , and q u a r t z .  The c r y s t a l s range  from almost s u b - m i c r o s c o p i c s t o one m i l l i m e t e r l o n g . S m a l l i n c l u s i o n s of. an unknown c o m p o s i t i o n a r e common i n the a p a t i t e  crystals.  Magnetite.  Sub-angular t o c u b i c and o c t a h e d r a l g r a i n s ,  s m a l l a c i c u l a r c r y s t a l s and s h a p e l e s s masses, o f magnetite l i e i n the c h l o r i t e , hornblende and b i o t i t e . ii.  S l i d e S. V. #2. A l t e r e d Quartz D i o r i t e . M i n e r a l Composition: ^ .. ' f L a b r a d o r i t e AbR Anfr Plagioclase j Ab^An^ » l o i l g o c l a s e Ab|gAn|g Quartz Biotite Hornblende Sericite Chlorite. Accessories Sulphides n  0  A  E  •  Feldspars•  e  l  d  s  a  r  i  d  r  e  s  i  n  e  n  36^ 6% 4 28$ 10% 3% 10% 4% "6% 2%  Much o f the s l i d e c o n s i s t s o f w e l l - f o r m e d c r y s t a l s  of f e l d s p a r up t o two'millimeters.: l o n g .  The z o n i n g , l i k e i n  S e c t i o n S. V. #1, rangesfrom l a b r a d o r i t e , AbsoAn^Q, i n the c e n t e r t o andesine, AbgQAn^Q, and oligoclase,Ab^QAn^Q, a t t h e  outer s u r f a c e .  The a l t e r a t i o n of f e l d s p a r t o s e r i c i t e has i n  s e v e r a l c r y s t a l s p r o g r e s s e d t o the o l i g o c l a s e zone and stopped. C h l o r i t e i s c l o s e l y i n t e r g r o w n w i t h s e r i c i t e and a l i t t l e c a l c i t e replaces  f e l d s p a r , b u t some b i o t i t e p e n e t r a t e s the  f e l d s p a r c r y s t a l s , and the c h l o r i t e and c a l c i t e may be an. a l t e r a t i o n o f the b i o t i t e r a t h e r than the f e l d s p a r . Quartz.  I r r e g u l a r g r a i n s o f q u a r t z l i e between the f e l d s p a r  crystals..  The q u a r t z , in. a minor way  feldspar*  The q u a r t z i s more abundant, i n s l i d e S. V. #2. than  r  appears to r e p l a c e the  i n s l i d e S. V. #1, but i t . i s s i m i l a r i n h a b i t and occurrence, and i s not a secondary Biotite.  generation.  Dark brown p l a t e s o f b i o t i t e o c c u r developed between  f e l d s p a r c r y s t a l s . The b i o t i t e . Is. c l o s e l y a s s o c i a t e d i hornblende...  with.  C h l o r i t e and m a g n e t i t e ^occur I n the b i o t i t e .  S m a l l grains^ o f m a g n e t i t e have b e e n ' p a r t i a l l y a l t e r e d , t o r u t l i e and. t i t a n i t e . and the t i t a n i t e has been a l t e r e d -to ..leucoxine (?) . . Fornblende.. Dark green hornblende, c l o s e l y a s s o c i a t e d b i o t i t e is. p a r t i a l l y c o n v e r t e d t o c h l o r i t e and a l i t t l e  with calcite.  S e r i c i t e • S e r i c i t e , i n a compact, f e l t o f v e r y s m a l l f a n - l i k e f l a k e s replaces, f e i d s p a r . Chlorite.  O l i v e green c h l o r i t e r e p l a c e s b i o t i t e and hornblende.  The l a r g e i r r e g u l a r f l a k e s show anomolous b l u e , black, and purple b i r e f r i n g e n c e , and p a r a l l e l e x t i n c t i o n .  M a g n e t i t e , r u t l i e , and  t i t a n i t e a r e c l o s e l y a s s o c i a t e d with. the. c h l o r i t e . Accessories % R u t l l e . and. T i t a n i t e .  B i o t i t e . and magnetite appear t o be  p a r t i a l l y a l t e r e d t o r u t i l e and t i t a n i t e *  One p l a t e o f  b i o t i t e i s almost completely a l t e r e d t o an: extremely f i n e f e l t of r u t i l e needles.  The t l t a n i t e occurs as. l a r g e r  stubby c r y s t a l s showing s y m e t r i c a l Apatite•  extinction.  numerous c r y s t a l s o f a p a t i t e occur through t h e  section. Sulphides.  P y r i t e appears to replace- hornblende . iii.  S l i d e S. V. #3. A l t e r e d Quartz D i o r i t e . M i n e r a l Composition: Plagioclase/ Oligoclase Ab£oAn20 Feldspar \ A l b i t e Abg5An 5 Quartz Sericite Chlorite Carbonate R u t i l e , T l t a n i t e and Leucoxene Accessories Sulphides  12% 20% 18% 18% 16% 5%  ;  Plagioclase  Feldspars.  The c l o s e l y packed f e l d s p a r  are. p a r t l y a l t e r e d t o s e r i c i t e c h l o r i t e and c a l c i t e . (  7% 1% 3%  crystals The com-  p o s i t i o n o f most of the c r y s t a l s i s albite,Abg5An5, but i t ranges to o l i g o c l a s e ,Abg An.2 . 0  0  I n t e r s t i t i a l q u a r t z appears to  have, r e p l a c e d t h e f e l d s p a r , and. a l b i t e may have r e p l a c e d o l i g o clase.  The i n d e x of. r e f r a c t i o n of the a l b i t e . i s l e s s than  balsam. Quartz. replacing  Granules o f q u a r t z l i e between, the. f e l d s p a r them t o a minor degree.  grains,  The: q u a r t z i n most of t h e  s l i d e i s as abundant as. i n S l i d e S. V. #1 •, b u t a s c a r c i t y o f q u a r t z on the one s i d e o f the s l i d e brings, t h e t o t a l content down to 18%.  S e r i c i t e . "A very f i n e f e l t o f s e r i c i t e r e p l a c e s  feldspar.  S e v e r a l large: p i a t e y g r a i n s o f s e r i c i t e are c l o s e l y a s s o c i a t e d w i t h , and most p r o b a b l y a l t e r e d t o , r u t i l e , t i t a n i t e , and chlorite* Chlorite.  The c h l o r i t e i s s i m i l a r i n occurrence t o t h e sericite.  The very f i n e c h l o r i t e I s c o l o r l e s s w i t h b i r e f r i n g e n c e t o p a l e orange, and the. green c o a r s e r v a r i e t y shows anomolous blue and dark p u r p l e b i r e f r i n g e n c e . Carbonate•  i r r e g u l a r patches of carbonate occur i n t i m a t e l y  a s s o c i a t e d , with, t h e s e r i c i t e , e v i d e n t l y r e p l a c i n g the p l a g l o clase feldspar. brown.  The m i n e r a l l i e s I n narrow bands and weathers  I t i s p r o b a b l y c a l c i t e c o n t a i n i n g a. l i t t l e  iron*  R u t i l e and T i t a n i t e . Brown a c i c u l a r c r y s t a l s , of. r u t i l e c h l o r i t e , s e r i c i t e and p r o b a b l y c a l c i t e . r a d i a t i n g groups cleavage p l a n e s .  replace  The c r y s t a l s a r e i n  i n masses, I n some p l a c e s , o r i e n t e d along Under r e f l e c t e d ! l i g h t they appear, l i g h t .. ;  yellow w i t h a resinous  luster.  The t i t a n i t e occurs as stubby  t e t r a g o n a l c r y s t a l s , but. few. a r e diamond-shaped.  The t i t a n i t e  a n d r u t i l e a r e p a r t i a l l y a l t e r e d t o w h i t e leucoxene. A c c e s s o r y Minerals..  A p a t i t e occurs i n about the same q u a n t i t y  and a s s o c i a t i o n s as i n the p r e v i o u s Sulphides.  slides.  P y r i t e I n aggregates o f s m a l l rounded and i r r e g u l a r  g r a i n s occurs w i t h t h e c h l o r i t e , c a l c i t e and t i t a n i t e . i v . S l i d e S. ¥. #4. 'Altered  Wall-rock.  Mine r a l G omp os i t i o n ; Plagiocia.se [Feldspar  COllgo clase 1Albite  1Q% 54%  —9-  '' ' ' Sericite Chlorite Carbonate R u t i l e and T l t a n i t e Accessories:  •• ' . Plagioclase  Feldspar.  There are two  g e n e r a t i o n s of  i n t h e h i g h l y a l t e r e d quartz: d i o r i t e . clase.  Small, oriented,  i n the a l b i t e . project  The  feldspar  A l b i t e replaces o l i g o -  corroded remnants of o l i g o c l a s e . occur  contacts, are uneven and  i n t o the o l i g o c l a s e .  twinning  9% 1% 11$%' 4% 1%  tongues of a l b i t e  Maximum e x t i n c t i o n in. t h e a l b i t e  i n the a l b i t e i s 18°,  and  i n the o l i g o c l a s e , 7;°*  The  Index of r e f r a c t i o n of the a l b i t e i s l e s s than t h a t of balsam, and .the o l i g o c l a s e almost e q u a l t o * or g r e a t e r than t h a t  of  balsam. Sericite.  S e r i c i t e occurs, as f a i r l y l a r g e f l a x e s , c l o s e l y  s o c i a t e d w i t h r u t i l e , c h l o r i t e and  c a l c i t e , or as s m a l l f a n -  shaped scales-, matted w i t h c h l o r i t e and r e p l a c i n g , Some of t h i s , m i n e r a l may  feldspar.  be t a l c , s i n c e a chemical t e s t on  g r a i n s which look l i k e t a l c , was  as-  small,  p o s i t i v e f o r magnesium and  n e g a t i v e f o r aluminium. Chlorite.  L i g h t green f l a k e s of c h l o r i t e are Intergrown w i t h  s e r i c i t e , c a l c i t e , r u t i l e and  t l t a n i t e , and  tiny colorless  scales are a s s o c i a t e d w i t h s e r i c i t e . Calcite.  . I r r e g u l a r masses of c a l c i t e are a s s o c i a t e d w i t h serir./  c i t e , c h l o r i t e , ' r u t i l e and p l a c e f e l d s p a r , but  tltanite.  The  c a l c i t e . appears to  t h e r e are i n d i c a t i o n s t h a t the c a l c i t e  r e p l a c e s s e r i c i t e . a n d c h l o r i t e , which had. p r e v i o u s l y the  replaced  feldspar.  R u t i l e and T l t a n i t e .  Brown a c l c u l a r c r y s t a l s of r u t i l e ,  re-  -10r e p l a c e s e r i c i t e ( ? ) I n , l o n g , r o u g h l y p a r a l l e l bands, r e s u l t i n g in. a f i b r o u s matted appearance.  The  pseudo-fibres  are bent around other c r y s t a l s : such as p y r i t e , f e l d s p a r , and c a l c i t e , i n d i c a t i n g t h a t the r u t i l e i s a l a t e p r o d u c t .  A  few  l a r g e r stubby c r y s t a l s of" t i t a n i t e occur throughout the mass of r u t i l e but none of these are l a r g e enough to g i v e an f e r e n c e f i g u r e under c r o s s e d n l c o l s .  inter-  Rhombic s e c t i o n s ,  however, show s y m e t r i c a l e x t i n c t i o n , under r e f l e c t e d l i g h t  the  m i n e r a l has a l i g h t straw y e l l o w c o l o r and a resinous, l u s t e r . The most common a s s o c i a t i o n i s w i t h s e r i c i t e , r u t i l e and p y r i t e Accessories. Sulphides«-  A p a t i t e i s abundant i n the s e c t i o n . P y r i t e , ; i n the form, o f .skeleton c r y s t a l s ,  rounded g r a i n s , i s a s s o c i a t e d w i t h the , t i t a n i t e . and v. S l i d e S. V.  and rutile.  #5.  Altered Quartz,Diorite. K i n e r a l Gomp o s i t i o n. t A l b i t e Abg5An5 Quartz Sericite Chlorite Titanite Accessories Sulphides  ^ Albite.  -1% 36% 50% 20f 5% 3% 1% o  A l l the f e l d s p a r except a few s m a l l g r a i n s i s a l t e r e d  to s e r i c i t e , c h l o r i t e and c a l c i t e .  The u n a l t e r e d f e l d s p a r i s  albite. Quartz.  Large angular quartz g r a i n s are f r e s h and  unaltered,  but some show s t r a i n shadows. S e r i c i t e and C h l o r i t e .  The  f e l d s p a r c r y s t a l s are w h o l l y r e -  p l a c e d by a f i n e f e l t of s e r i c i t e f l a k e s : t h r o u g h o u t , w h i c h are  -11i r r e g u l a r : p a t c h e s of l i g h t green to c o l o r l e s s c h l o r i t e . R u t i l e and T l t a n i t e .  T i n y a c i c u l a r r u t i l e needles matted  f i b r o u s brown masses occur a s s o c i a t e d w i t h s e r i c i t e .  into  Stubby,  brown t o c o l o r l e s s , t i t a n i t e c r y s t a l s are d i s s e m i n a t e d throughout the s e r i c i t e and e h l o x i t e *  The . f e l d s p a r c r y s t a l s which a r e  not c o m p l e t e l y a l t e r e d t o s e r i c i t e a r e clouded by acicular rutile crystals.  innumerable  The r u t i l e and t i t a n i t e i s p a r t i a l l y  a l t e r e d t o leucoxene* A c c e s s o r i e s and S u l p h i d e s .  A p a t i t e occurs through the s e c t i o n ,  p y r i t e occurs c l o s e l y a s s o c i a t e d w i t h r u t i l e and t i t a n i t e . S e v e r a l s m a l l g r a i n s of magnetite occur c l o s e to the r u t i l e and titanite. v i S l i d e S. V. #6:. .  Altered  Quartz" D i o r i t e .  M i n e r a l Composition.:: Albite Ab An Quartz Sericite Chlorite Titanite Accessories Sulphides 9 5  Albite.  5  Large c r y s t a l s o f a l b i t e I n c l u d e a few  60% 8.8% 14% 3% 10% 2% 2% f l a k e s and •  needles of s e r i c i t e , c h l o r i t e and r u t i l e . Quartz.  G r a i n s o f quartz showing s t r a i n shadows l i e between the  feldspar crystals.  Aggregates  of s m a l l unoriented quartz  g r a i n s appear t o be secondary. S e r i c i t e and C h l o r i t e .  S e r i c i t e , and a l i t t l e c h l o r i t e , i n a  fine felt,replace feldspar^ l i k e s e r i c i t e may be t a l c .  Much, of the m i n e r a l which  appears  -12-  Sulphides Accessories Titanium Minerals  •o a N EH H CQ O  I o o  EH  o  h  e  crystals i s associated with s e r i c i t e . of t r a n s p a r e n t section.  Many w e l l - f o r m e d c r y s t a l s  to brown t i t a n i t e occur i n swarms through the  These a r e p a r t i a l l y a l t e r e d t o leucoxene.  Accessory M i n e r a l s .  A p a t i t e is. abundant i n the s e c t i o n i n  large c r y s t a l s . Sulphides.  P y r i t e i s abundant. Y;»- Summary and C o n c l u s i o n s C r y s t a l l o b l a s t i c a l b i t e , titanium minerals i n  f e l t e d masses, and s e r i c i t e pseudomorphic a f t e r f e l d s p a r c h a r a c t e r i z e the a l t e r a t i o n , o f w a l l rock i n the Spud v a l l e y vein.  S l i d e s . S. Y. #5 and. S.V. #6 a r e each composed o f h i g h l y  a l t e r e d w a l l - r o c k , one a l b i t i z e d and the other suggesting  silicified,  t h a t t h e two p r o c e s s e s were a l t e r n a t e l y i n f o r c e .  The presence o f t i t a n i u m m i n e r a l s g r a p h ! c analysis..  was checked by a s p e c t r o -  Because they occur as n e e d l e - l i k e c r y s t a l s ,  g e n i c u l a t e d t w i n s , and appear q u i t e d i f f e r e n t from the c r y s t a l s known t o be t i t a n i t e , t h e v e r y s m a l l c r y s t a l s a r e c a l l e d r u t i l e . The  absence o f c a l c i t e and abundance of s e r i c i t e i n the h i g h l y  a l t e r e d w a l l - r a c k i s noteworthy.  Away from t h e v e i n i n the  outer zone o f a l t e r a t i o n c h l o r i t e i s s c a r c e , i t i s abundant i n the c e n t r a l zone of a l t e r a t i o n , and a g a i n scarce in. the h i g h l y altered wall-rock.  A l b i t e , q u a r t z , c a l c i t e and c h l o r i t e occur  i n zones or bands i n the w a l l - r o c k p a r a l l e l to t h e v e i n .  This  suggests t h r e e a l t e r n a t i v e s ; 1., t h a t t h e aqueous s o l u t i o n was flowing along the vein-channels i n a " p u l s a t i n g " fashion, 2.., t h a t the. s o l u t i o n r e a c t e d on  the w a l l - r o c k u n t i l chemical e q u i l i b r i u m was reached, and r e a c t i o n ' s u b s i d e d u n t i l the w a l l - r o c k was redharged w i t h f r e s h s o l u t i o n ; or •• .  3., t h a t t h e c o m p o s i t i o n o f t h e  s o l u t i o n was changing w i t h r e s p e c t t o some c o n s t i t u e n t s and not others*  (b) P r i d e n t V e i n . I* General D e s c r l p t l o n The P r i d e n t v e i n s l i e . i n t h e q u a r t z d i o r i t e o f the Z e b a l l o s b a t h o l i t h about 1000 f e e t east o f t h e west contact, and about 1200 f e e t n o r t h o f t h e White S t a r mine. Two v e i n s , one s t r i k i n g n o r t h e a s t and t h e other e a s t , i n t e r s e c t i n t h e mine workings.  The v e i n s l i k e l y belong  to t h e same age o f m i n e r a l i z a t i o n . The mine i s operated by the P r i v a t e e r mining company, and t h e ore i s c o n c e n t r a t e d i n t h e p r i v a t e e r m i l l . 2. F r e s h W a l l - r o c k The f r e s h w a l l - r o c k i s a l i g h t grey, mediumgrained quartz d i o r i t e .  I t i s b r i t t l e , w i t h a conchoidal  fracture. 3. A l t e r e d \ f a l I - r o c k The a l t e r e d w a l l - r o c k is. d u l l grey t o l i g h t , buff, f i n e - g r a i n e d and carbonaceous.  I t i s s o f t e r than t h e fresh,  r o c k and has a n i r r e g u l a r f r a c t u r e .  The q u a r t z content i s  s l i g h t l y h i g h e r than t h a t o f the f r e s h r o c k , and t h e f e l d s p a r , b i o t i t e and hornblende  a r e converted t o s e r i c i t e , c a l c i t e and  -15chc$>i$e«' Hear the. v e i n c h l o r i t e i a abundant, but i n t h e v e i n i t . i s absent.  Tiny, roughly p a r a l l e l , I n t e r l a c i n g v e i n l e t s ,  weathering brown, c u t t h e a l t e r e d rock, p a r a l l e l t o t h e v e i n . 4. D e s c r i p t i o n o f S l i d e s The. f i v e t h i n - s e c t i o n s i n c l u d e rocks adjacent t o , and i n , t h e P r i d e n t v e i n . i.  Slide Pr. ^1. Fresh quartz d i o r i t e . M i n e r a l composition; l a b r a d o r i t e AbsoAngQ^ Average, Andesine A b A n A Andes i n e O l i g o c l a s e Ab An-, ( • ^ Biotite Hornblende Sericite Calcite Chlorite Accessories Sulphides. ? 0  qn u  Quartz.  56  3  ^"  n  5% 2% 5% 3% 2% 1.5% 0*5%  The q u a r t z i s i n l a r g e i r r e g u l a r g r a i n s d i s s e m i n a t e d  r e g u l a r l y through the s e c t i o n .  No s t r a i n shadows a r e e v i d e n t  and i n c l u s i o n s a r e n o t abundant. Feldspar.  Large, zoned c r y s t a l s o f f e l d s p a r c o n s t i t u t e more  than, h a l f t h e s l i d e . s i t i o n , Ab An Q. g0  labradorite. Ab An Q. ?0  3  5  The i n n e r zone i s l a b r a d o r i t e w i t h compo-  S e r i c i t e i s developed  throughout t h e  The c e n t r a l zone i s andesine, w i t h c o m p o s i t i o n  This, zone i s almost v o i d of s e r i c i t e .  zone i s . o l i g o c l a s e , c o m p o s i t i o n AbgoAn^Q-  The outer  Most of t h e c r y s t a l  boundaries are. w e l l - d e f i n e d , but a. few a r e i r r e g u l a r .  Sericite,  c h l o r i t e , b i o t i t e , and hornblende p e n e t r a t e t h e outer zone. I n t e r p e n e t r a t i o n twins a r e common. sory  Apatite,  t h e c h i e f acces-  m i n e r a l occurs i n many f e l d s p a r c r y s t a l s .  The abrupt  change i n * c o m p o s i t i o n "between t h e zones i s apparent w i t h o u t c r o s s e d n i c o l s - - t h e d i f f e r e n c e i n I n d i c e s o f r e f r a c t i o n clearlyshowing t h e zone boundaries . The a l b i t e-twinning on the outer zone v a r i e s from a n e g a t i v e t o a zero, and p o s i t i v e angle of extinction. Biotite.  Large 5 f l a k e s o f d a r k brown b i o t i t e , p a r t i a l l y  chlori-  t i z e d , occur throughout the s l i d e . . Hornblende.  The dark green hornblende i s p a r t i a l l y  chlori-  t i z e d , and. p l e o c h r o i c from green t o brown. Sericite..  B l a d e s and f l a k e s occur abundantly throughout the  l a b r a d o r i t e zone o f the f e l d s p a r s , and s p a r i n g l y throughout the outer zones.  Some o f t h i s white, m i c a may be p a r a g o n i t e , but a  s p e c t r o g r a p h i c a n a l y s i s , proves i t i d e n t i c a l t o a known sample of m u s c o v i t e , hence i t i s a l l r e f e r r e d t o as s e r i c i t e . Caielte.  S m a l l i r r e g u l a r patches o f c a l c i t e occur i n the  section.  There a r e o f t e n c l o s e l y a s s o c i a t e d w i t h the c h l o r i t e .  Chlorite.  L i g h t a p p l e green and c o l o r l e s s f l a k e s of c h l o r i t e  occur throughout t h e s l i d e .  They show, anomalous blue t o grey  maximum i n t e r f e r e n c e c o l o r s , and e x t i n c t i o n i s p a r a l l e l t o t h e cleavage.  The v a r i e t y i s b e l i e v e d t o be p e n n l n i t e .  I t i s as-  s o c i a t e d w i t h the b i o t i t e , hornblende and c a l c i t e . Accessories.  C o l o r l e s s a p a t i t e i n elongated c r y s t a l s w i t h  s m a l l , rounded i n c l u s i o n s i s common, a l o n g w i t h brown, t i n y a c i c u l a r c r y s t a l s and b l a c k S k e l e t a l c r y s t a l s of. magnetite imbedded i n t h e c h l o r i t e and c a l c i t e . Sulphides:.  A s m a l l amount o f p y r i t e occurs, i n t h e s e c t i o n .  -17'  i i S l i d e Br." #2. S l i g h t l y A l t e r e d Quartz. D i o r i t e . M i n e r a l Composition: Labradorite A b A n 25$) Andesine A W n ^ f\ Andesine Oligoclase Ab9 An 5%) Quartz Sericite Chlorite Calcite Biotite • Magnetite Accessories 5 0  5 0  0  Quartz.  A v  1 0  32$ ' 20$ 18$ 12$" 12$; 3$ 2$~ 2$  Quartz i n f i n e r grains, than i n the u n a l t e r e d rock i s  e v e n l y d i s s e m i n a t e d throughout t h e s e c t i o n . Feldspar.  Most o f t h e f e l d s p a r  c r y s t a l s are a l t e r e d t o f i n e -  g r a i n e d masses of s e r i c i t e , c h l o r i t e and. c a l c i t e .  The a l t e r a -  t i o n , appears t o have s t a r t e d i n the c e n t e r of t h e c r y s t a l s and m i g r a t e d outwards.  The remaining f r e s h f e l d s p a r  comprises  about 32$ o f t h e s e c t i o n , and t h e zones from the c e n t e r to the edges o f the s e c t i o n s a r e l a b r a d o r i t e , andesine and o l i g o c l a s e , respectivley.  The p r o p o r t i o n and c o m p o s i t i o n o f each i s e s t i -  mated as f o l l o w s : Labradorite Ande s i n e Oligoclase Biotite.  A small quantity  occurs i n the s e c t i o n .  80$ 10$" 10$  AbgQAn^ Ab QAn Q AbgQAnio 7  3  o f b i o t i t e , but no hornblende,  The b i o t i t e f l a k e s a r e p a r t i a l l y r e -  p l a c e d by c h l o r i t e and c a l c i t e . Calcite.  The c a l c i t e occurs i n i r r e g u l a r patches through the.  section.  C a l c i t e i s present i n s m a l l q u a n t i t i e s i n the r e -  placed feldspar  c r y s t a l s and b i o t i t e f l a k e s .  cut p a r a l l e l ? a c r o s s the s e c t i o n .  Small veinlets  -18-  C h l o r i t e . ' L i g h t green or c o l o r l e s s c h l o r i t e occurs i n the r e p l a c e d f e l d s p a r and b i o t i t e , as w e l l as throughout stitial filling.  the i n t e r -  Mast of the f l a k e s are very.-small and the  c o l o r l e s s . I s more abundant than the green v a r i e t y . f l a k e s c a r r y numerous brown, r u t i l e  The  crystals..  Accessory M i n e r a l s . A p a t i t e , r u t i l e and t i t a n i t e  occur  throughout t h e q u a r t z , f e l d s p a r , s e r i c i t e , c a l c i t e and Magnetite.  green  M a g n e t i t e , i n v e r y f i n e g r a i n s , occurs  chlorite.  throughout  the s e c t i o n . ill.  Slide  #3.  A l t e r e d Quartz D i o r i t e . ' M i n e r a l Composition; Quartz; .. ' 23%~ • Andesine Abgo-^40 ~) Average, O l i g o c l a s e Ab^QAn-jA O l i g o c l a s e 11% ^ Bio'tite 0.5%' Sericite 38% Calcite 20%: Chlorite 4% Accessories 3% Sulphides•. 0.5% Q.uartz.  Quartz occurs i n an aggregate  of f i n e g r a i n s cut by a  second g e n e r a t i o n in. s m a l l veInlets.. Feldspar.  Most of the f e l d s p a r c r y s t a l s are c o m p l e t e l y r e -  p l a c e d by s e r i c i t e , c h l o r i t e and c a l c i t e , but the c r y s t a l shapes are p r e s e r v e d .  Other f e l d s p a r c r y s t a l s are r e p l a c e d ex-  cept f o r a narrow zone aound the outer edge.  The  albite  t w i n n i n g and i n d e x of r e f r a c t i o n on the u n r e p l a c e d zone i n d i cate t h a t i t i s o l i g o c l a s e .  The remaining f e l d s p a r c r y s t a l s  are p a r t i a l l y r e p l a c e d a l o n g c r a c k s and cleavage p l a n e s . Enough of the c r y s t a l i s p r e s e r v e d to measure the e x t i n c t i o n on  -19the a l b i t e t w i n n i n g , and these c r y s t a l s , l i k e those i n the f r e s h rock show an. increase, i n the s o d i c c o n s t i t u e n t toward the outer zone. B i o t i t e .. A. few I r r e g u l a r flakes^o'f. b i o t i t e , l a r g e l y r e p l a c e d by c h l o r i t e and c a l c i t e occur as a v e r y minor c o n s t i t u e n t of the rock. Sericite.  The r e p l a c e d f e l d s p a r c r y s t a l s are m o s t l y s e r i c i t e ,  w i t h minor amounts of c h l o r i t e and c a l c i t e .  Much of the i n t e r -  s t i t i a l m a t e r i a l i s a v e r y f i n e f e l t of s e r i c i t e and c a l c i t e w i t h a minor amount of. c h l o r i t e .  S e r i c i t e f l a k e s and plume-  shaped c r y s t a l s p e n e t r a t e every m i n e r a l i n the s e c t i o n except the s u l p h i d e s * Calcite«  S m a l l v e i n s of c a l c i t e t r a v e r s e the s e c t i o n .  I r r e g u l a r patches of c a l c i t e occur h a p h a z a r d l y arranged through the r o c k .  Very f i n e g r a i n s of c a l c i t e occur a s s o c i a t e d  w i t h the s e r i c i t e and Chlorite.  chlorite.  Light..apple-green c o l o r e d f l a k e s of c h l o r i t e occur  i n the s e c t i o n .  S e v e r a l of these are l a r g e enough t o produce  an i n t e r f e r e n c e f i g u r e .  The m i n e r a l i s p l e o c h r o i c from straw-  y e l l o w to l i g h t a p p l e - g r e e n .  A . f i n e r , c o l o r l e s s v a r i e t y of  c h l o r i t e i s s p a r s e l y d i s s e m i n a t e d throughout the s e r i c i t e and calcite. A c c e s s o r y Minerals..  A c i c u l a r c r y s t a l s of a p a t i t e are abundant  throughout the q u a r t z , f e l d s p a r , and s e r i c i t e - c a l c i t e aggregate. I r r e g u l a r g r a i n s , a c i c u l a r needles i n r a d i a t i n g masses of r u t i l e , and. s h o r t , w e l l - f o r m e d c r y s t a l s , of t i t a n i t e occur c l o s e l y a s s o c i a t e d w i t h the c h l o r i t e and c a l c i t e .  I r r e g u l a r g r a i n s of  -20magnetite* aire s p a r s e l y s c a t t e r e d through.' the section.. Sulphide M i n e r a l s .  S e v e r a l s m a l l grains, of p y r i t e occur- i n  the section:. i v . S l i d e #4.: A l t e r e d w a l l - r o c k adjacent  to v e i n .  M i n e r a l 0Qmpo.sltl.oji: quartz. Andes i n e Sericite Calcite Chlorite Accessories Sulphides Quartz.  30$ 25$ 23$ 8$' 3$ 8$  Quartz occurs i n medium s i z e d i r r e g u l a r g r a i n s  evenly  d i s t r i b u t e d throughout the rock.. Feldspar..  S e v e r a l s m a l l , i r r e g u l a r zones o f f e l d s p a r remain  unreplaced  by s e r i c i t e , c a l c i t e and c h l o r i t e . .  Many weJL-  d e f i n e d areas of f i n e --grained m i c a and carbonate a r e able a s completely  r e p l a c e d f e l d s p a r crystals..,.  S e r i c i t e , C a l c i t e and C h l o r i t e . s t i t u t e over h a l f the r©ck.  These three m i n e r a l s  C a l c i t e occurs i n .-several  small veins, probably a l a t e r generation. f i n e f l a k e s and b u n d l e s , occurs  may  con-  The: s e r i c i t e i s the most abundant  m i n e r a l I n the a l t e r e d f e l d s p a r s .  and c a l c i t e .  recognize—  C h l o r i t e , i n very  c l o s e l y intergrown w i t h s e r i c i t e  Some of the m i n e r a l which appears to be  sericite  be t a l c , s i n c e a chemical t e s t on s e v e r a l g r a i n s r e s u l t e d  i n a p o s i t i v e r e a c t i o n f o r magnesium. Accessories.  Apatite i n small a c i c u l a r c r y s t a l s , r u t i l e  In  a c i c u l a r aggregates, t i t a n i t e i n s t u b b y c r y s t a l s , and magnetite, or i l m e n i t e , i n s k e l e t o n c r y s t a l s c o n s t i t u t e the  accessory  -21minerals. S u l p h i d e s . P y r i t e i n cubes, and g r a i n s occurs along w i t h a few grains  of s p h a l e r i t e . v. S l i d e #5. V e i n m a t e r i a l , w i t h i n c l u s i o n s of w a l l - r o c k M l ne r a l C omp o s i t i o n : Quartz Sericite Calcite Accessories Sulphides  Quartz.  Calcite.  3% Oof  Quartz, i n i r r e g u l a r , medium-sized g r a i n s , ,:vs,-evenly  d i s t r i b u t e d throughout Sericite.  28% 25% 42%  the s e c t i o n .  S e r i c i t e occurs i n f i n e - g r a i n e d c l o s e l y packed  Many p a r a l l e l bands o f c a l c i t e t r a v e r s e t h e s e c t i o n .  A minor amount of c a l c i t e i s i n t e r g r o w n w i t h the s e r i c i t e . The t i n y v e i n s a r e p a r a l l e l t o t h e main v e i n , and appear t o be a l a t e r g e n e r a t i o n t h a n the d i s s e m i n a t e d type o f c a l c i t e . Accessory M i n e r a l s .  A p a t i t e , r u t i l e and t i t a n i t e c r y s t a l s a r e  d i s s e m i n a t e d throughout Sulphide M i n e r a l s .  the section.  S e v e r a l c u b i c p y r i t e c r y s t a l s and shapeless  g r a i n s occur i n the s e c t i o n . 5 • Summary and Con.cluslo.nsA l t e r a t i o n of the w a l l rock i s i n t e n s e , but i t does n o t p e n e t r a t e f a r from the v e i n . The amounts of q u a r t z , a c c e s s o r y m i n e r a l s , and sulphides, do not change a p p r e c i a b l y from f r e s h t o a l t e r e d w a l l rock.  - 2 2 -  A' uniform- I n c r e a s e i n the. carbonate c o n s t i t u e n t of the rock, occurs, w i t h i n t e n s i f i c a t i o n of a l t e r a t i o n . The p l a g i o c l a s e feldspar, i s r e p l a c e d c h i e f l y by s e r i c i t e , and t o a minor degree by c a l c i t e and c h l o r i t e . The ferromagnesian m i n e r a l s , b i o t i t e and horneblende, are a l t e r e d t o c h l o r i t e , c a l c i t e and m a g n e t i t e . The development of c h l o r i t e has been r e s t r i c t e d to the outer zone of a l t e r a t i o n , or the c h l o r i t e next to the v e i n has been a l t e r e d to s e r i c i t e . SUMMARY OE THE. PRIDENT SLIDES CQ  <D 43  tsi -p  CO  CS  a)  •H •P O •H  d l <D  P r . 2.  20  f 56" \ 5 ! i f l "t * 32 ? 3  P r .-  23  :  30  i •  3.  Pr. !  •  1 2  1  <  P r . 5.  11  i  0.5  18 12 i J.; .. . | 0 ! 28 20  12  2.  2  , • C"O  1  '  5  id o  0  0 0  1 25 I 25  "'  CO  •  3  2  2.5  ;.8  3  8  0  3  4  ™  23  ; 0  P( H  1.5  !: 0  02  fH o  •rl XI  2  '1'  1 0  CQ  3  3  r  k  28  0.5  •H O H O  H  W 24  •RL  •p  CQ CD  d3 o o  O  >  P r . 1.  U o  -P  0)  -H O 0  0) •H  s i  40  |  -23(c) t h e Mount Z e b a l l o s V e i n , -k • General GeologyThe  f i s s u r e — v e i n l i e s i n metamorphosed v o l -  . c a n i c rocks of the Bonanza f o r m a t i o n .  The northeast end of the  v e i n i s about 600 f e e t southwest of the c o n t a c t between t h e Bonanza f o r m a t i o n and the Z e b a l l o s b a t h o l i t h . 2. F r e s h The  Wall-rockr o c k i s a dark green to b l a c k compact f i n e -  g r a i n e d a n d e s i t e , c o n t a i n i n g s m a l l phenocrysts  of g l a s s y  f e l d s p a r , and s p a r s e l y d i s s e m i n a t e d g r a i n s of i r o n s u l p h i d e . I t i s h a r d and b r e a k s . w i t h a. c o n c h o l d a l f r a c t u r e . 3  * Altered lall-rockThe a l t e r e d w a l l - r o c k is. b u f f - g r e y and fine-  g r a i n e d , w i t h an e a r t h y t e x t u r e .  When breathed upon i t g i v e s  a s t r o n g aluminous, or c l a y e y odor. The f e l d s p a r has. been a l t e r e d to s e r i c i t e , c h l o r i t e and c a l c i t e .  The hornblende and b i o t i t e have been con-  v e r t e d to c h l o r i t e , r u t i l e and magnetite. abundant i n the v e i n s .  S i l i c a i s only  C a l c i t e i s abundant i n the  1  altered zone  and a l a t e r g e n e r a t i o n i s a minor c o n s t i t u e n t of the s i l i c e o u s vein material.  The presence of a small, amount of v e s u v i a n i t e  i n d i c a t e s , high-temperature a l t e r a t i o n , p r o b a b l y p r e - v e i n cont a c t metamo.rphism by the u n d e r l y i n g q u a r t z — d i o r i t e b a t h o l i t h . 4• D e s c r i p t i o n of T h i n S e c t i o n s F i v e t h i n s e c t i o n s r e p r e s e n t f r e s h rock, a l t e r e d rock and v e i n m a t e r i a l .  -24i*-. S l i d e M. Z.  #1.  P a r t i a l l y a l t e r e d a n d e s i t e 3" from the v e i n . M i n e r a l Composition; A n d e s i n e - o l i g o c l a s e Abr^An, Hornblende L i g h t brown b i o t i t e R u t i l e and t i t a n i t e Calcite Sericite Accessories Feldspar.  2% 1% 1%  Large phenocrysts of untwinned and weakly-zoned  f e l d s p a r occur embedded i n a groundmass of s m a l l lath-shaped feldspars.  The l a r g e f e l d s p a r s are p a r t i a l l y r e p l a c e d by horn-  blende... b i o t i t e and s e r i c i t e , p r i n c i p a l l y a l o n g f r a c t u r e s and the outer edges.  Tfeie c o m p o s i t i o n i s about Ah^. An Q *. The. f i n e 0  g r a i n e d v a r i e t y shows a s u g g e s t i o n of p a r a l l e l  S  orientation.  I t s c o m p o s i t i o n i s s i m i l a r t o t h a t ...of the p h e n o c r y s t s . Hornblende.  L i g h t green, l a t h — s h a p e d c r y s t a l s - of hornblende  are e v e n l y d i s s e m i n a t e d throughout the s l i d e .  The p l e o c h r o i s m  colors, are s t r a w - y e l l o w t o blue-green and t h i s along w i t h other s i m i l a r c h a r a c t e r i s t i c s suggests t h a t i t i s i d e n t i c a l w i t h the 1  amphibole i n the p u r e e l s i l l s d e s c r i b e d by R i e e . * M a g n e t i t e i s c l o s e l y a s s o c i a t e d w i t h the Biotite.  L i g h t brown t o c o l o r l e s s b i o t i t e occurs i n bunchy  aggregates. Calcite.  hornblende.  I t i s a s s o c i a t e d w i t h no " p a r t i c u l a r m i n e r a l .  A s m a l l v e i n l e t of. c a l c i t e t r a v e r s e s the s e c t i o n .  L i t t l e or no c a l c i t e i s d i s s e m i n a t e d through the f e l d s p a r or ferromagn.esian minerals.. Sericite.  The Large f e l d s p a r s a r e hosts, f o r a s m a l l q u a n t i t y  1* R i c e ,;H.. M. A.., American M i n e r a l o g i s t , Ybl» 20,. Ho.. 4.  -25of s e r i c i t e . Acce:ssory M i n e r a l s . crystals.  V e s u v i a n i t e occurs i n one group of elongate!  I l m e n i t e or m a g n e t i t e , p y r r h o t l t e a n d p y r i t e i n very }  f i n e g r a i n s occur i n l o n g v e i n l e t s and d i s s e m i n a t e d  grains  c l o s e l y a s s o c i a t e d w i t h the hornblende. ii.  S l i d e M. Z. #2. A l t e r e d a n d e s i t e l-g-"- from t h e main v e i n , and  cut by a s m a l l q u a r t z v e i n . M i n e r a l Composition; Andesine-oligoclase Quartz i n v e i n l e t Sericite C a l c i t e .. . Chlorite R u t i l e and T i t a n i t e Pyrite. Feldspar.  One l a r g e f e l d s p a r phenocrysts,  2$ 10$ 30$ 30$ 24$ ' 4$ 2$  and many s m a l l i r -  r e g u l a r species remain o n l y p a r t i a l l y a l t e r e d t o s e r i c i t e , c h l o r i t e and c a l c i t e . quartz.  A. c l e a r - c u t v e i n l e t o f q u a r t z t r a v e r s e s t h e s e c t i o n . the -fiVs-V  A s m a l l e r one, p a r a l l e l s :1A:., and contains, some c a l c i t e . S e r i c i t e , C a l c i t e and C h l o r i t e .  Most o f the s e c t i o n I s a  f e l t e d mass o f v e r y f i n e s c a l e y aggregates of. s e r i c i t e , and c h l o r i t e .  calcite  The r e l a t i v e amounts p r e s e n t a r e a rough e s t i -  mation. Titanite..  M i n u t e , e l o n g a t e d c r y s t a l s of t i t a n i t e a r e s c a t t e r e d  throughout t h e s e c t i o n .  S e v e r a l s m a l l c l u s t e r s of c r y s t a l s  appear t o be an a l t e r a t i o n from, hornblende or b i o t i t e s i n c e , they form a s o l i d , network around, b u t not p e n e t r a t i n g f e l d s p a r drystals.  -26pyrlte.  P y r i t e , In i r r e g u l a r g r a i n s and i s o m e t r i c c r y s t a l s  occurs i n the q u a r t z and q u a r t z - c a l c i t e v e i n l e t s , and i n the w a l l - r o c k , c l o s e t o the m i n e r a l v e i n . iii.  S l i d e M. Z.  #5.  H i g h l y a l t e r e d a n d e s i t e -g-" from the v e i n . Mineral  Composition; quartz 4$" A n d e s i n e - o l i g o c l a s e AboQAn,,, 7$ Calcite 37% Chlorite 23$" Sericite 20% Vesuvianite 4$ Titanite 5%  Q.uartz.  One i r r e g u l a r v e i n l e t of quartz; c u t s the section.-  Ee I d spar > S m a l l remnants, of h i g h l y a l t e r e d , f e l d s p a r c r y s t a l s are evenly d i s t r i b u t e d throughout C a l c i t e , C h l o r i t e and S e r i c i t e . a f i n e f e l t e d mass. aggregates  The  the s e c t i o n . These t h r e e m i n e r a l s irake up  c h l o r i t e and s e r i c i t e a r e i n s e a l e y  and the c a l c i t e i n i r r e g u l a r masses.  Vesuvianite.  V e s u v i a n i t e i n patches of c l o s e l y i n t e r g r o w n  elongated c o l o r l e s s c r y s t a l s w i t h h i g h r e l i e f and low gence occur i n the r o c k .  The v e s u v i a n i t e shows no  a s s o c i a t i o n w i t h o t h e r minerals... from the high-temperature,  birefrin-  apparent  I t i s a p r e - v e i n . product  c o n t a c t metamorphic e f f e c t of the  Zeballos batholith-. Titanite.  Minute-, rounded i r r e g u l a r and e l o n g a t e d , dark brown  g r a i n s occur e v e n l y d i s t r i b u t e d through the s e c t i o n .  I n ad-  d i t i o n , t h e r e are s e v e r a l c l u s t e r s of e l o n g a t e d , p o o r l y developed c r y s t a l s .  The m i n e r a l .is. dark, brown to b l a c k under  t r a n s m i t t e d l i g h t , but w i t h r e f l e c t e d l i g h t i t i s y e l l o w i s h -  -27brown: with* a r e s i n o u s  luster.  iv.. Slide. M. : Z> #4 • Yein. m a t e r i a l , w i t h s m a l l i n c l u s i o n s of the wall-rock. M i n e r a l C omp as i t i o n ; Quartz Sulphides: Calcite Sericite Chlorite Quartz.  Elongated  c r y s t a l s of quartz a r e s e t p e r p e n d i c u l a r t o  the vein: w a l l s . Calcite.  Small q u a n t i t i e s of c a l c i t e are present  Sulphides.  The s u l p h i d e s - m i n e r a l s  i n the v e i n .  i n the v e i n a r e p y r i t e ,  s p h a l e r i t e , a r s e n o p y r i t e , p y r r h o t i t e and g a l e n a . S e r i c i t e and C h l o r i t e .  The w a l l - r o c k adjacent t o , and i n c l u d e d  i n the v e i n , i s composed of s e r i c i t e , c h l o r i t e and c a l c i t e ,  with  l i t t l e or no: s u l p h i d e m i n e r a l i z a t i o n . v. S l i d e M. Z. #5.  ,  V e i n m a t e r i a l w i t h included, wall-rack.; M i n e r a l Composition; . Quartz Sulphides Calcite Sericite Chlorite Quartz.  Most of the s l i d e i s composed of elongated c r y s t a l s  and i r r e g u l a r quartz: g r a i n s w i t h some c l o s e l y a s s o c i a t e d calcite. Sulphides.  P y r i t e , a r s e n o p y r i t e , and s p h a l e r i t e .  C a l c i t e , S e r i c i t e and C h l o r i t e .  The i n c l u d e d fragments of w a l l  -28rock. are composed of an aggregate o f minute f l a k e s and g r a i n s of c a l c i t e , s e r i c i t e and c h l o r i t e . 6  • Summary and G o n c l u s i o n s The w a l l - r o c k a l t e r a t i o n i s much t h e same as i n  the q u a r t z die-rite.-  i t does not extend f a r from the m i n e r a l  v e i n , and the f e l d s p a r , hornblende and b i o t i t e have been conv e r t e d to s e r i c i t e  calcite-. chlorite-  :  magnetite and t i t a n i t e .  One n o t a b l e d i f f e r e n c e , however, i s t h e absence o f e i t h e r s i l i c i f i c a t i o n or a l b i t i z a t i o n . The presence o f v e s u v i a n i t e i s i n d i c a t i v e of p r e - v e i n c o n t a c t me tamo r p h i sm by t h e Z e b a l l o s b a t h o l i t h .  The  m i n e r a l i s not a l t e r e d by the a c t i o n of the v e i n - f o r m i n g s o l u t i o n , hence t h e temperature i n the w a l l - r o c k d u r i n g v e i n dep o s i t i o n was lower than during, igneous i n t r u s i o n . SUMMARY OW THE MOUHT ZEBALLOS SLIDES  0) i  cd a)  o5  a a •H o ta so  0 -rl  • r-i  -P  H  | ° M. Z. 1. M. Z. 2 .  37  .a O  0  K 34'  10  M. Z. • 3» Z. 4. Z.  O «  p r e - " , "* * sent s i p r e s . I --— J . 1  -p •r-i •P O 'r-i  •P •H O H cd 0  18 1  CD P •H O •H W <D CO  p •H  Jh O  H  o  1 30  I 30  24  CD <P •H  fl  cd -P •H H  •r-t  u 0 tn as a)  0  q  7~~"  1  4  2  -29(&) The White S t a r Vein.. 1* General GeologyThe White S t a r -workings are. about 2500 f e e t southeast of the P r i v a t e e r mine, and. i n the q u a r t z d i o r i t e  of  the Z e b a l l o s b a t h o l i t h about 600 f e e t east of the west c o n t a c t . The m i n e r a l i z a t i o n i s i n two f i s s u r e v e i n s i n the q u a r t z d i o r i t e *  The v e i n s c u t p a l e g r e y , f e l s i t i c  dykes.  2. The F r e s h Dyke-rockThe r o c k i s a v e r y f i n e - g r a i n e d , g r e e n i s h ~ g r e y d a c i t e , w i t h g l a s s y f e l d s p a r phenocrysts  up to f i v e m i l i m e t e r s  l o n g , s c a t t e r e d specks of a b l a c k m e t a l l i c , m i n e r a l , and a. few g r a i n s of b l a c k t o brown hornblende.:  I t Is. hard and breaks  w i t h a clean conchoidal fracture* 3 * The A l t e r e d Dyke-rockThe a l t e r e d , rock i s w h i t e r and s o f t e r than the fresh variety  s  but b r i t t l e , with, an angular f r a c t u r e .  The  f e l d s p a r phenocrysts. and groundmass have been, completely r e p l a c e d by s e r i c i t e . c a l c i t e and c h l o r i t e * been converted to t i t a n i t e and  rutile.  4. D e s c r i p t i o n of S e c t i o n s i * S e c t i o n W*  S .. 3 *  Fresh f e l s i t i c  dyke-rock.  M i n e r a l . Composition;  The hornblende has  -30Large^ zoned f e l d s p a r c r y s t a l s are s e t i n a ground-  Feldspar.  mass l a r g e l y composed o f t i n y , i f ^ M s ^ p a r l a t h - s h a p e d ^ . c r y s t a l s . /  Some of the phenocrysts are p a r t i a l l y r e p l a c e d and others a r e w h o l l y r e p l a c e d by s e r i c i t e , c a l c i t e and  chlorite.  The c e n t e r zone i s andesine w i t h e x t i n c t i o n angles on the a l b i t e twins up to 30°, and on the outer zones, w i t h e x t i n c t i o n , at a maximum of  oligoclase,  10°.  The- t i n y , l a t h - s h a p e d f e l d s p a r s i n the m a t r i x are zoned and twinned.  The c o m p o s i t i o n i s o l i g o c l a s e w i t h maximum  e x t i n c t i o n o f 10°.  The f i n e n e s s of g r a i n , a n d the i n t i m a t e  a s s o c i a t i o n , of the f e l d s p a r w i t h the s e r i c i t e  j f  c a l c i t e and  c h l o r i t e ^ m a k e an estimate o f the c o m p o s i t i o n i m p r a c t i c a l . Quartz.  Minute, quartz, g r a i n s i n l e n t i c u l a r aggregates  about  two m i l i m e t e r s l o n g occur s p a r s e l y d i s s e m i n a t e d through t h e section. than  The t o t a l amount of q u a r t z p r e s e n t i s b e l i e v e d l e s s  5%.  Hornblende..  Several, v e r y s m a l l patches of brown  hornblende  occur c l o s e l y a s s o c i a t e d w i t h c h l o r i t e * Biotite.  One e l o n g a t e d f i b r o u s mass of brown b i o t i t e occurs i n  the s e c t i o n . S e r i c i t e , C h l o r i t e and C a l c i t e .  The t h r e e m i n e r a l s s e r i c i t e ,  c h l o r i t e and calcite«,form f e l t e d masses approximating the shape o f f e l d s p a r p h e n o c r y s t s — a p p a r e n t l y h a v i n g a l l r e s u l t e d from the a l t e r a t i o n s of the f e l d s p a r * Some r e c o g n i z a b l e f e l d s p a r c r y s t a l s are p a r t i a l l y a l t e r e d to s e r i c i t e a l o n e , others to c a l c i t e and c h l o r i t e , and some to s e r i c i t e and T i t a n i t e and R u t i l e *  calcite.  Minor amounts, of t i t a n i t e and  rutile  occur associated, w i t h the c h l o r i t e and Pyrite.:  calcite.  S e v e r a l c u b i c c r y s t a l s and g r a i n s of p y r i t e are  em-  bedded. I n the rock. •  ii.  S l i d e s W. S. 2 &  1.  A l t e r e d Dyke-rock. M i n e r a l Compositions Feldspar Quartz. Sericite Chlorite Calcite  (Andeslne-oligocILase)  R u t i l e and Feldspar.;  The p l a g i o c l a s e phenocrysts  to s e r i c i t e , c a l c i t e and c h l o r i t e .  Titanite are c o m p l e t e l y a l t e r e d  The f i n e - g r a i n e d groundmass  has been p a r t i a l l y , r e p l a c e d , but some p l a g i o c l a s e g r a i n s r e m a i n unaltered..:. Q.uartz,  The  f i n e . l e n t i c u l a r aggregates .of t i n y quartz g r a i n s 5  are not a l t e r e d . S e r i c i t e , C h l o r i t e and C a l c i t e . -  The  f e l d s p a r phenocrysts  are  c o m p l e t e l y a l t e r e d , b u t t h e i r shape i s r e t a i n e d by the f e l t e d mass of s e r i c i t e and c h l o r i t e w i t h a minor amount of c a l c i t e . These minerals, also; developed i n i r r e g u l a r areas throughout the groundmass..  S m a l l c a l c i t e . s e r i c i t e and c h l o r i t e v e i n s cut  the s e c t i o n , and one c a l c i t e v e i n l e t i s l a t e r than t h e c u b i c pyrite.  S e v e r a l e l o n g a t e d aggregates of s e r i c i t e f l a k e s  appear about, the s i z e and shape of the hornblende and p l a t e s , i n the f r e s h r o c k , and. may  biotite  be. pseudomorphic a f t e r  these  minerals* Rutile. crystals..  R u t i l e i s developed i n patches of v e r y s m a l l ac i c u l a r One  a n g u l a r a r e a appears to be. the shape and; s i z e  -32of a f e l d s p a r p h e n o c r y s t , but I t i s . c a l c i t e w i t h numerous brown, a c i c u l a r c r y s t a l s of" r u t i l e , developed a l o n g the c l e a v age p l a n e s .  The sequence of a l t e r a t i o n has been, t h e r e f o r e ,  p l a g i o c l a s e a l t e r e d to. c a l c i t e , and c a l c i t e to r u t i l e . i 1 i . g l i d e W. S.  #1.  H i g h l y a l t e r e d dyke-rock. M i n e r a l . Composition;; Feldspar Quartz Sericite Calcite Chlorite H u t i l e and T i t a n i t e This s e c t i o n , i s p r a c t i c a l l y i d e n t i c a l w i t h S l i d e W.. S. 5 c Summary and: The composition.  #2.  Conclusions-  f i n e - g r a i n e d rock i s c l o s e to a d a c i t e i n  U e a r l y 90$ of the f r e s h r o c k i s f e l d s p a r  quartz w i t h f e l d s p a r the most abundant.  The  and  small l e n t i c u l a r  zones of u n a l t e r e d quartz g r a i n s I n d i c a t e a sedimentary o r i g i n but no. o t h e r s u p p o r t i n g  c r i t e r i a are e v i d e n t .  The  feldspar  p h e n o c r y s t s are r e c o g n i z a b l e a f t e r complete a l t e r a t i o n .  Seri-  c i t e i s the maj or a l t e r a t i o n , w i t h c h l o r i t e , c a l c i t e and r u t i l e as minor p r o d u c t s . t h a t of the s i m i l a r  The i ;  a l t e r a t i o n s f o l l o w a course p a r a l l e l , to  but c o a r s e r - g r a i n e d  dio.ri.te from the Spud v a l l e y and P r i d e n t  r o c k s , the veins.  quartz  (®) The P r i v a t e e r  Veins.  1... G e n e r a l GeologyThe P r i v a t e e r , mine Is l o c a t e d i n the 'Bonanza. formation, a f:ew hundred, f e e t west of the west contact  of the  Z e b a l l o s batholith... V e i n s s t r i k i n g east-west cut sediments, v o l c a n i c b r e c c i a s , t u f f s and l a v a s , and I n t r u s i v e sheets of q u a r t z diorite.  The  veins, t e r m i n a t e before r e a c h i n g  a pronounced  f a u l t zone s t r i k i n g , east o f n o r t h and d i p p i n g •65° west'. 2  *  Fresh Wall-rocka  .  The  f r e s h •rack, i s * l i g h t g r e y , fi.ne.-grained,. h a r d  and b r i t t l e , a s i l i c i f i e d B » ^ U . S m a l l i r r e g u l a r patches: of t i n y p y r i t e g r a i n s , i n c r e a s i n g i n abundance c l o s e t o the c o n s t i t u t e the o n l y s t r u c t u r e in. t h e rock.  veins,  Microscopically  the r o c k i s . composed, of" an extremely f i n e - g r a i n e d aggregate, of l a t h - s h a p e d l a b r a d o r i t e , diopslde.., :  apatite,and  wo.llastonitevesuvianite,  g a r n e t c r y s t a l s d i s s e m i n a t e d through a groundmass  of. a l b i t e and  quartz..  3. A l t e r e d Wa.ll-rockQ l o s e to the v e i n the rock i s bleached l i g h t g r e y to w h i t e , but i t i s as hard, and b r i t t l e as the fresh, rock. P y r i t e , i n I r r e g u l a r patches,and. v e r y f i n e - g r a i n e d ,  increases  i n abundance c l o s e to the v e i n . Small, w h i t e and grey s i l i c e o u s . v e i n l e t s t r a v e r s e the a l t e r e d rock. M i c r o s . c o p i c a l l y , the c h i e f c h a r a c t e r i s t i c s of the a l t e r e d rock a r e : (1) The  abundance, of r e l a t i v e l y coarse clihozoisite.  .-34-  (2) A tendency toward p o r p h y r i n i c s t r u c t u r e w i t h c o m p a r i t i v e l y l a r g e phenocrysts of a l b i t e and quartz  developed  i n the f i n e groundmass. (3) P r a c t i c a l l y complete removal of the s m a l l , lath-shaped  labradorite crystals. (4) The presence of l a r g e b l a d e d w o l l a s t o n i t e crystals.  4. D e s c r i p t i o n of S l i d e s i.  S l i d e p r . 37  #1.  Contact Metamorphic rock. M i n e r a l Composition.: Albite ..Labradorite Ab5QAn5Q Quartz. Diopside Wollastonite. Vesuvianite Garnet (?) , Apatite pyrite Albite.  E q u l - s i z e d g r a i n s of untwinned a l b i t e c o n s t i t u t e a  l a r g e p r o p o r t i o n of the groundmass.. amount, i s 50$  of the s e c t i o n .  Labradorite.  Small, lath-shaped  of the  c r y s t a l s of. twinned f e l d s p a r  occur r a t h e r s p a r s e l y disseminated Quartz.  A rough estimate  through the section...  A ffe» g r a i n s of quartz, occur c l o s e l y intergrown  with  the f e l d s p a r . Diopside.  I r r e g u l a r bunches of g r a i n s and c r y s t a l s of  occur through the s e c t i o n .  The  i n d e x of the g r a i n s was  mined by o i l immersion to be c l o s e to Wollastonite.  diopside deter-  1.70.  B l a d e d c r y s t a l s of w o l l a s t o n i t e w i t h t i n y i n -  c l u s i o n s of. an unknown, m i n e r a l occur s p a r i n g l y through the  section. Vesuvianitev  E l o n g a t e d c r y s t a l s o f v e s u v i a n i t e occur s p a r i n g l y  i n the s e c t i o n .  The i n d e x of r e f r a c t i o n , t e s t e d w i t h  immersion  o i l s , I s 1 ..7+ . Apatite.  Abundant, w e l l - f o r m e d a p a t i t e c r y s t a l s occur l o c a l l y  through the s e c t i o n . Garnet  ( ? ) . Swarms, of t i n y , dark r e d garnet (?) i s the most  conspicuous gangue m i n e r a l . Pyrite..  S m a l l g r a i n s of p y r i t e occur s p a r s e l y d i s t r i b u t e d  through the r o c k . 11. S l i d e p, 5.7 #&. Contact metamorphic rock near the v e i n . M i n e r a l C omp o s i t i o n ; Albite Quartz Diopside YCollastonlte Vesuvianite Clin.oz.oi s i t e Calcite Apatite Garnet Pyrite Albite.  The fine--grained groundmass of a n g u l a r , c l o s e l y packed  and untwinned a l b i t e g r a i n s i s unchanged i n the altered.rock. Secondary  a l b i t e g r a i n s i n c o m p a r a t i v e l y large,, untwinned  pheno-  c r y s t s have been developed, and the s m a l l l a t h - s h a p e d l a b r a d o r i t e c r y s t a l s have been almost w h o l l y removed. Quartz..  C o m p a r a t i v e l y l a r g e g r a i n s of q u a r t z have been I n t r o -  duced, a p p a r e n t l y a l o n g w i t h the a l b i t e . Diopside.  T a b u l a r c r y s t a l s o f d i o p s i d e a r e abundant i n the  a l t e r e d rock.  -36Wallastohite. inclusions The  Large bladed c r y s t a l s c o n t a i n i n g s m a l l. dark t  o f an unknown m i n e r a l a r e abundant i n , the s e c t i o n .  Index o f r e f r a c t i o n , by o i l immersion, i s 1.62+-.  bladed c r y s t a l s do not appear t o be o r i e n t e d  The l o n g  i n any one d i r e c -  tion-.Vesuviahlte.  E l o n g a t e d c r y s t a l s i n bunches occur  sparingly  through the section.. Clinozoisite-..  .One o f t h e s t r i k i n g , d i f f e r e n c e s , between t h e  a l t e r e d and. the u n a l t e r e d r o c k under the microscope i s t h e presence o f c l i n o z o i s i t e .  Abundant sub-angular c r y s t a l s and  i r r e g u l a r g r a i n s of c l i n o z o i s i t e showing low and v a r i a b l e b i r e f r i n g e n c e , p a r a l l e l e x t i n c t i o n . , and h i g h index of. r e t f r a c t i o n ^ l i e u n i f o r m l y d i s t r i b u t e d throughout the f i n e groundmass of. quartz., feldspar,, d i o p s i d e and w . o l l a s t o n i t e . not  This mineral is:  an a l t e r a t i o n from the v e i n s o l u t i o n but a c o n t a c t —  metamorphic product formed d u r i n g the. I n t r u s i o n  o f the  Zeballos b a t h o l i t h . Apatite.  Well-formed c r y s t a l s , o f a p a t i t e a r e d i s t r i b u t e d  through, t h e a l t e r e d rock., along w i t h some, l a r g e r , p a r t i a l l y eorroded crystals,., Calcite.  C a l c i t e , i n s m a l l i r r e g u l a r patches, c o n s t i t u t e s : a  minor p a r t of the s l i g h t l y a l t e r e d Garnet ( ? ) .  wall-rock.  Small, dark r e d l s h - b l a c k g r a i n s a r e s p a r s e l y d i s -  seminated through, t h e r o c k and appear to. be g a r n e t s . pyrite.  S m a l l c u b i c c r y s t a l s and l a r g e i r r e g u l a r g r a i n s o f  p y r i t e a r e a, minor c o n s t i t u e n t o f the a l t e r e d w a l l r o c k . ..  -37' 5. Summary and C o n c l u s i o n s A l b i t e , , e l l n o z o i s i t e and quartz a r e developed I n the a l t e r e d rock, and u n l i k e t h e a l t e r a t i o n , of t h e q u a r t z diorite  c  d a c i t e or a n d e s i t e , s e r i c i t e , c h l o r i t e and t i t a n i t e  are absent.  The secondary a l b i t e and quartz, a r e c o a r s e r -  g r a i n e d t h a n the p r i m a r y m i n e r a l s . The f r e s h e s t specimen of w a l l - r o c k . r e p r e s e n t e d by S l i d e #1? contains, metamorphie m i n e r a l s and has a p p a r e n t l y been a l t e r e d by the i n t r u s i o n of the quartz: d i o r i t e p r i o r to the f o r m a t i o n  of the mineral vein.  The development o f l a r g e  • c r y s t a l s . o f a l b i t e and quartz i n d i c a t e s t h a t the v e i n s o l u t i o n -  was r i c h i n s o d i u m and s i l i c a ; The  f a c t t h a t the e l l n o z o i s i t e i s not pcesent i n  both s e c t i o n s , and t h a t s e r i c i t e and c h l o r i t e a r e absent from b o t h s u g g e s t s t h a t t h e a l t e r a t i o n o f the o r i g i n a l r o c k was 5  "^spotty" , and p r o b a b l y governed by n o w - o b l i t e r a t e d  l o c a l con-  ditions .  D. Summary and C o n c l u s i o n s i (a) C i a s s i . f i cat i o n of t h e Z e b a l l o s ore d e p o s i t s . The  d e p o s i t s a r e m i n e r a l i z e d f i s s u r e - v e i n s of.the  mesothermal c l a s s . Data h e r e w i t h  compiled: p e r t a i n i n g t o t h e w a l l - r o c k  a l t e r a t i o n ^ a l o n g w i t h evidence r e g a r d i n g v e i n - s t r u c t u r e and m i n e r a l i z a t i o n , make p o s s i b l e t h i s d e f i n i t e c l a s s i f i c a t i o n of the Z e b a l l o s ore d e p o s i t s .  The f o l l o w i n g comparison i s con-  c l u s i v e evidence that the deposits are p r a c t i c a l l y i d e n t i c a l w i t h L i n d g r e n ' s type megothermal deposit.. 2. 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The and  fissure-veinsi  ( i n d i v i d u a l ) f i s s u r e s are f a i r l y r e g u l a r i n s t r i k e  dip. 2. They have n e i t h e r the n e a r - s u r f a c e ,  extremely b r e c c i a t e d  s t r u c t u r e nor the l e n t i c u l a r , massive form of the deep-seated deposits. 3* "Smooth w a l l s and  s l i c k e n s i d e s are abundant."  4.- "A c o a r s e l y c r y s t a l l i n e massive t e x t u r e i s most common; combs, and rough banding by d e p o s i t i o n are by no means unknown, e s p e c i a l l y where the d e p o s i t s  c o n t a i n c a l c i t e or b a r i t e . "  5. "As the f i s s u r e s were opened i n zones of f r a c t u r e , open spaces a r e p r e s e n t i n many d e p o s i t s , though, the w a l l s u s u a l l y come t o g e t h e r w i t h i n , s h o r t i n t e r v a l s * ' 6. "The  sulphides  1  are c o a r s e l y c r y s t a l l i n e and  roughly  banded,, p a r a l l e l to the walls.** Regarding drusy openings, L i n d g r e n s t a t e s ;  "If  replacement I s promoted by r a p i d moving s o l u t i o n s , s o l u t i o n may  be more a c t i v e than, d e p o s i t i o n , and d r u s y s t r u c t u r e may  re-  s u l t by l o c a l , d e f i c i e n c y of p r e c i p i t a t i n g substances i n the s o l u t i o n . " ^'  This explains  the p o s s i b i l i t y of drusy s t r u c t u r e  at moderate p r e s s u r e and depth, since, the c o n t r o l l i n g f a c t o r s are the speed, of. movement and c h e m i s t r y of the s o l u t i o n . , The one f a c t t h a t does not f i t w i t h t h e evidence 3. L i n d g r e n W., M i n e r a l D e p o s i t s ^ 1928, pp. 191-193 & p. 599. 4., L i n d g r e n F. «, The n a t u r e of Replacement, Economic Geology,  -42p o i n t i n g ' to. me so t h e r m a l o r i g i n i s t h e c r u s t i f i c a t i o n I n t h e veins p a r a l l e l t o the w a l l s *  The c r u s t i f I c a t i o n  produces a  f r i a b l e type of ore common t o e p i t h e r m a l d e p o s i t i o n * w r i t e r suggest t h a t Lindgren's  The  explanation, of drusy s t r u c t u r e  may be a p p l i e d w i t h e q u a l success t o c r u s t i f i c a t i o n .  I f local  c o n d i t i o n s were such that, a rapid-moving s o l u t i o n a l t e r n a t e d between s o l u t i o n and d e p o s i t i o n s I . can see no reason why c r u s t i f i c a t i o n may not occur a t mesothermal p r e s s u r e .  The f a c t  cannot b e denied, however, t h a t c r u s t i f i c a t i o n i s c h a r a c t e r i s t i c of low p r e s s u r e d e p o s i t i o n , and t h a t t h e f i s s u r e - v e i n s , m a y been formed a t a p r e s s u r e  have  lower than t h a t common i n mesothermal  d e p o s i t i o n , i n o t h e r words, a t mesothermal temperature and epithermal  pressure*  The. M i n e r a l i z a t i o n :  ,  In a comprehensive study of p o l i s h e d sections. from the P r i v a t e e r v e i n Mr* E. J . W. I r i s h l i s t e d the m e t a l l i c 5. m i n e r a l s i n order o f abundance as i o l l o w s : 1. p y r i t e 2. A r s e n o p y r i t e 3* Galena. 4. S p h a l e r i t e 5. C h a l c o p y r i t e 6. P y r r h o t i t e 7. G o l d 8* Unknown pyrite,  a r s e n o p y r i t e , s p h a l e r i t e and p y r r h o t i t e  were observed in. the t h i n , s e c t i o n s *  A l l o f these m i n e r a l s ex-  cept p y r r h o t i t e arer-found i n mesothermal m i n e r a l  deposits.  P y r r h o t i t e i s commonly found i n d e p o s i t s formed a t h i g h e r temperature, ahd may suggest t h a t t h e Z e b a l l o s v e i n s were 5. I r i s h . E. J. T h e J ^ e r a ^ g v _ o f _spiae of t h e G o l d Mines of B r i t i s h , Columbia, M.'A* T h e s i s , U.B.C., 1940. .  -43-" formed under high-temperature mesGthermalL c o n d i t i o n s , (h) The Ore . S o l u t l o n ~ - i t s O r i g i n and Composition. S i n c e the f i s s u r e v e i n s cut the upper s h e l l of t h e Z e b a l l o s b a t h o l i t h and p e n e t r a t e t i n t o the o v e r l y i n g r o o f - r o c k s the n a t u r a l c o n e l u s i o n i s t h a t the o r e - b e a r i n g s o l u t i o n was d e r i v e d from within-.the b a t h o l i t h , and was e m i t t e d sometime a f t e r t h e outer zone of igneous rock was s o l i d enough t o f r a c t u r e i n a smooth break.  The o r e s o l u t i o n presumably bears a.  g e h e t i e r e l a t i o n s h i p t o the. b a t h o l i t h , and was p r o b a b l y by d i f f e r e n t i a t i o n , w i t h i n t h a t igneous magma.  derived  How t h e ore-  bearing; f l u i d was f r e e d from, the magma, chamber, t r a n s p o r t e d u p T ^ a r d a n d d e p o s i t e d i n the present, f i s s u r e - v e i n s I s a m a t t e r of conjecture., s i n c e the nature o f the f l u i d and the one'—., m a t e r i a l b e f o r e t a k i n g t h e i r p r e s e n t form i s unknown and cannot be reproduced i n the l a b o r a t o r y V  Any one, o r a combination of. 9  the t h r e e f o l l o w i n g : t h e o r i e s might e x p l a i n , the 6. BoweJXf  process.  and h i s s u p p o r t e r s , suppose that, thei m i n e r a l  constituents concentrate  i n the magma chamber (as a r e s i d u e  from: f r a c t i o n a l c r y s t a l l i z a t i o n ) i n t h e form o f an a l k a l i n e aqueous s o l u t i o n w h i c h may b o i l i f i t reaches a zone o f moderatei.  The escaping gas p e n e t r a t e s  be d i s t i l l e d .  cracks and f i s s u r e s and may  The d i s t i l l a t e - f r o m the b o i l i n g s o l u t i o n s i s an  acid.; aqueous s o l u t i o n s , which c a r r i e s , t h e ore-forming m a t e r i a l oh-its^ upward ascent, t h r o u g h i n t e r s t i c e s i n the r o c k .  The  s o l u t i o n r e a c t s with, the w a l l - r o c k d e p o s i t i n g much of i t s l o a d , i n c l u d i n g ore m i n e r a l s , and r e p l a c i n g w a l l - r o c k - m l n e r a l s : , t o become c h e m i c a l l y n e u t r a l and f i n a l l y a l k a l i n e . ; The ascending  -44s o l u t i a n 1'inall.y reaches the s u r f a c e where i t is. t r a n s p o r t e d to the sea.. Secondly> Penner, " and h i s s u p p o r t e r s ,  advocate  boiling.--In the magma chamber, and the gas condensing near.the source as an acid,aqueous s o l u t i o n .  The  s o l u t i o n , forced  ward through i n t e r s t i c e s i n the roof-rock,, by gas  up-  pressure  from below, deposits.,, i t s load, r e a c t s w i t h the wall-rocks,, i n t e r c h a n g i n g c o n s t i t u e n t s , becoming n e u t r a l s or b a s i c , and " f i n a l l y passe.s;| to the s u r f a c e and the a.  sea.  L a s t l y , Sraton,  and. h i s a s s o c i a t e s p o i n t out t h a t  t h e o r i g i n a l m a t e r i a l may  be i n the form o f an. a l k a l i n e s o l u -  t i o n , w h i c h passes: upward" through the c r a c k s and J o i n t s i n the r o c k s , d e p o s i t s i t s l o a d , r e a c t s on the w a l l - r o c k , i n t e r changing m a t e r i a l , and f i n a l l y reaches, the s u r f a c e of t h e e a r t h and f l o w s t o the > .  sea.  Whether the s o l u t i o n was  a c i d or a l k a l i n e , and b o i l e d  e a r l y or l a t e , i s not known, but the. m i n e r a l changes i n the ....... a l t e r e d w a l l - r o c k , i n d i c a t e t h a t the s o l u t i o n was c a r r i e d K, Ga, Ma,  aqueous and  S i . Mg,,. 3?e, pb, Zn, As., Cu, Au, S, GGg, .'and"]S%  That the s o l u t i o n was  aqueous i s evidenced by the a d d i t i o n of  water to the w a l l - r o c k , i n the form of the f o l i o w i n g hydrous m i n e r a l s - - s e r i c i t e , c h l o r i t e , and P o t a s s i u m may  talc.  have been s u p p l i e d by the b i o t i t e p r e -  sent i n the o r i g i n a l rock, but potassium must have been i n t r o duced w i t h the m i n e r a l i z i n g s o l u t i o n t o account f o r the amount o i s e r i c i t e formed..  The presence of s e r i c i t e i s an i n d i c a t i o n  -45$hat the: hydrous s o l u t i o n may 9.  have been a l k a l i n e , but  0. C. Schmedeman says; * " S e r i c i t e as a m i n e r a l i s not I n d i c a t i v e of e i t h e r a l k a l i n e or a c i d a t t a c k , but i t p r o b a b l y forms (-where potash i s added) o n l y from, a l k a l i n e o r weak a c i d s o l u - . tions." Calcium was p r o b a b l y . a c o n s t i t u e n t of the s o l u t i o n s i n c e most of the secondary m i n e r a l s formed a r e c a l c i c , i n cluding calcite,.  Calcium would be d e r i v e d from the a l t e r a t i o n  of the f e l d s p a r s and much would p r o b a b l y be d i s s o l v e d from l i m e s t o n e beds i n the sedimentary f o r m a t i o n s cut by the sures.  any  fis-  The r e l a t i v e q u a n t i t i e s of c a l c i u m added and l e a c h e d  from the w a l l - r o c k i s not a c c u r a t e l y known, but t h e r e I s s u s pected to have been an. a d d i t i o n , from t h s , hydrous s o l u t i o n . Sodium was most l i k e l y an. important c o n s t i t u e n t of the hydrous s o l u t i o n , because a l t h o u g h some was  s u p p l i e d by  the primary feldspars:, a l a r g e amount was added In the form of albite. The term " a l b i t i z a t i o n " I s commonly a s s o c i a t e d w i t h g o l d deposits.. A f t e r a study of numerous mines where  albiti-  10  z a t i o n is. an e s t a b l i s h e d f a c t , G a l l a h e r s u g g e s t s ; * 1. "Where g o l d i s the o n l y v a l u a b l e m i n e r a l , and o t h e r m e t a l l i c m i n e r a l s are not abundant, the g e n e t i c a l l y r e l a t e d igneous, r o c k s are commonly h i g h in. a l b i t e . " 2-* "where s i l v e r is, more abundant the l i m e content of the f e l d s p a r o f t h e a s s o c i a t e d r o c k s is. higher."9~T Schmedeman, G. C., Botes, on the Chemistry of Ore S o l u t i o n s . Economic Geology, V o l . 33, D e c , 1918, p.. 803. 10. D a v i d G a l l a h e r , A l b i t e and Gold, Economic Geology, Sept.-Oct., 1940, V o l . 35.  :3- "Where the s i l v e r i s i n c o n s i d e r a b l e excess over g o l d , as: g o l d is: s u b o r d i n a t e  to the other m e t a l s , or where the  m e t a l l i c m i n e r a l s are v e r y abundant, soda f e l d s p a r s a r e g e n e r a l l y , l a c k i n g , and not. uncommonly the g e n e t i c a l l y r e l a t e d igneous r o c k s a r e n o t a b l y potassic.:" A h apparent g e n e t i c a s s o c i a t i o n between a l b i t e and g o l d d e p o s i t s i s w e l l known throughout Canada and B r i t i s h Columbia,  i n the Skeena E i v e r D i s t r i c t , K e r r  1 1  * noted t h a t "-the  i n t r u s i v e s t h a t are v a r i a b l e i n c h a r a c t e r due t o d i f f e r e n t i a t i o n , e s p e c i a l l y those h i g h I n a c i d p l a g i o c l a s e , are by f a r the most Important p r o d u c e r s of m i n e r a l d e p o s i t s .  Those h i g h i n a l b i t e  p l a g i o c l a s e commonly have a s s o c i a t e d m i n e r a l d e p o s i t s , and these g e n e r a l l y have a h i g h g o l d c o n t e n t .  The u n i f o r m  e s p e c i a l l y some f a i r l y h i g h I n o r t h o c l a s e and  intrusives,  Intermediate  p l a g i o e l a s e , have not producedmuch important m i n e r a l i z a t i o n . " i n t h e M a l a r t i c a r e a , Gunning  :  ^* observed a probable  g e n e t i c r e l a t i o n , between a l b i t e - r i c h I n t r u s i v e rocks and g o l d d e p o s i t s , the a l b i t e b e i n g an important  component of the p r e -  m i n e r a l - v e i n i n t r u s i v e s , and a c o n s t i t u e n t of the ore s o l u t i o n s . The w r i t e r suggests t h a t , r a t h e r than the s o d a - r i c h f e l d s p a r having some a f f i n i t y f o r g o l d or some chemical c o n t r o l over i t s c o n c e n t r a t i o n or p r e c i p i t a t i o n , the g o l d and a l b i t e are cen.  simply products  r e s u l t i n g firom continued  contration  i n a, l a r g e ,  n e c e s s a r i l y h i g h l y - d i f f e r e n t i a t e d body o f magma, and s i n c e b o t h u s u a l l y a r e f r e e d n e a r the end-point i n the d i f f e r e n t i a t i o n p r o c e s s , they commonly occur t o g e t h e r ^ __ • I T T K e r r ]?. A., BeonomIc"Geology, J u n e - J u l y , .1938, p.- 432. 12.. Gunning E. C., Canadian G e o l o g i c a l Survey, Mem. 206, pp. 42-44 ;  i'lfi-e argument t h a t g o l d and other metals: may be .-carried"'-In ..solution w i t h double sodium-potassium s u l p h i d e s , as suggested by Eoxace Freeman,  * and J . E. Spurr.M.; has a  d i r e c t b e a r i n g upon the problem, of. the: c l o s e a s s o c i a t i o n o f gold:. w i t h a l b i t e , , since, the s o l u t i o n s ; forming a l b i t e and s e r i c i t e .were, n e c e s s a r i l y r i c h i n §-I^4.ti«a5,Whether the a l k a l i e s were i n t h e s u l p h i d e form o r n o t i s unknown, b u t i f they were, t h e r e seems t o be no doubt t h a t the heavy metals could be t a k e n i n t o aqueous, s o l u t i o n a s double s u l p h i d e s and t r a n s p o r t e d as such. S i l i c a h a s been an i m p o r t a n t c o n s t i t u e n t of the s o l u t i o n s i n c e most of the v e i n m a t e r i a l i s q u a r t z .  Considerable  s i l i c a i s released, by t h e f e l d s p a r when i t i s a l t e r e d t o s e r i c i t e . and t h i s may be removed t o the v e i n i n s o l u t i o n and t h e r e p r e c i p i t a t e d , but s i n c e t h e v e i n i s o f t e n s e v e r a l times g r e a t e r i n volume; than t h e volume of a l t e r e d w a l l - r o c k , s i l i c a must have been added by v e i n - f i l l i n g s o l u t i o n .  The secondary quartz i s  a l l c r y s t a l l i n e s u g g e s t i n g a c o n f i n i n g p r e s s u r e h i g h e r than t h a t o f the e p i t h e r m a l o r xenothermal. zones. Magnesium may have been a r a t h e r important of the. s o l u t i o n ,  constituent  f & e r e t h e v e i n cut t h e sedimentary and v o l -  c a n i c r o c k s , o$ course. magnesium c o u l d have been taken s o l u t i o n from, magnesium carbonate m i n e r a l s .  Into  The b i o t i t e and  hornblende i n the o r i g i n a l , unaltered,;, igneous w a l l - r o c k may s s u p p l y a s m a l l q u a n t i t y o f magnesium.:, b u t h a r d l y enough f o r 13:i. Horace, Freeman, E n g i n e e r i n g and f i n i n g J o u r n a l - P r e s s , Vol... 120, l o . . 2.5.,, pp.. 97.3-975: V o l . 121, Ho. 1.4, pp. 571, 5 Vol.. 122, Eo.... 9, pp. 340-341. 1.4.. Spurr J . E., E n g i n e e r i n g and M i n i n g J o u r n a l - P r e s s , V o l . 120, No. 25, pp.. 975-977.  •-48-  the format lean of so much c h l o r i t e ,  i:t..:was noted, however, t h a t  the c h l o r i t e seldom occurs i n the v e i n *>r a c t u a l l y adjacent  to  i t , hut u s u a l l y along a- zone i n the •wall-rock ao s h o r t d i s t a n c e from the f i s s u r e . and adjacent  Apparently  the c h l o r i t e , i f ever formed i n  to the v e i n , was  l a t e r r e p l a c e d by non-magnesium  m a t e r i a l , whi.ch suggests t h a t i f not d u r i n g the e n t i r e p e r i o d of v e i n - f o r m a t i o n , a t l e a s t d u r i n g the l a s t s t a g e s , the s o l u t i o n was. magnesium-poor..  '  The presence of the elements. J e , Pb, Zn, As, Cu, and, S i n the hydrous, s o l u t i o n i s evidenced  by the g o l d and  Au the  m e t a l l i c m i n e r a l s i n the v e i n s . The presence of COg s i n c e the abundant c a l c i t e may GOg  i n the s o l u t i o n is. q u i t e p o s s i b l e have been, formed by the a c t i o n of  on c a l c i u m — b e a r i n g m i n e r a l s , or c a l c i u m i n the hydrous s o l u -  tion..  T i t a n i u m was p r o b a b l y i n the s o l u t i o n i n the form of TiC^.  Other elements, such as H£ as HgS, probably present  and 01 as HC1, were q u i t e  i n the solution., but d e f i n i t e evidence i s  lacking. (c) The E f f e c t of the Wall-Rock on the A l t e r a t i o n . . The v e i n s cut f o u r types of w a l l - r o c k , namely, quartz d i o r i t e , a n d e s l t e , dyke-rock resembling d a c i t e , and a  silicified  c o n t a c t metamorphlc r o c k . The  quartz d i o r i t e , a n d e s i t e and d a c i t e are q u i t e  s i m i l a r I n m l n e r a l o g i c a l c o m p o s i t i o n and the a l t e r a t i o n i n each is practically identical.  The  s i l i c i f i e d r o c k , however, i s  p r a c t i c a l l y unaltered. The  a l t e r a t i o n of the p l a g i o c l a s e f e l d s p a r s to s e r i -  -49cite- c o u l d "be accompli shed by a s o l u t i o n r i c h i n H 0, K2O and 2  COrj r e a c t i n g a t moderate temperature as f o l l o w s : iNa20 • GaO . 3 / 2 A l 0 . 5Si 0 -hH 0f C © ^ K 0 s s H 0 - i l ^ O . 3 / 2 A l 0 . 3 S i 0  1.  2  3  2  2  2  11 L a b r a d o r i t e  2  2  2  S Sericite tCaC0 +3/2Si0 ff¥a Si0 . 3  2.  3  2  2  3  3 (3Ma 0. 4CaO . 7 A l 0 . 2 6 S i 0 ) -M4H 0-l-12G0 -f7K 0-2  2  3  2  2  2  2  30 Andesine 14(H 0-iK 0.3/2Al 0 .3Si0 }+12CaC0 *27Si0 4-9Na Si0 . 2  2  2  3  2  3  2  2  3  14 S e r i c i t e  3.  3 (9/2]\Fa 0 - GaO . , l l / 2 A l 0 . 2 9 S i 0 J + l l H 2 0 t 3 G 0 2 ^ H / 2 K 0 = 2  2  3  2  2  30 O l i g o c l a s e 11 (H G »iK20 - 3 / 2 A l 2 0 • 3Si 0 ) f 3CaG0 +-27/2H"a£Si.0 -+8l/2Si0 , 2  3  2  3  3  2  11 S e r i c i t e The  s o l u t i o n would be charged w i t h GaC0 , S i 0 and 3  2  N a S i 0 , which c o u l d be c a r r i e d along t h e f i s s u r e , r e a c t w i t h 2  3  other c o n s t i t u e n t s i n the s o l u t i o n or w a l l - r o c k , o r be deposit e d i n t h e w a l l - r o c k or f i s s u r e .  P r o b a b l y a combination  o f the  above t h r e e a l t e r n a t i v e s occurred i n the Z e b a l l o s d e p o s i t s , the. CaC0  3  and S i 0  2  d e p o s i t i n g i n open f i s s u r e s , and the M'a Si0 2  r e a c t i n g , under f a v o r a b l e c o n d i t i o n s , p r o d u c i n g  3  albite.  The same r e a c t i o n s , without the K 0 , would g i v e 2  p a r a g o n i t e as an a l t e r a t i o n product 1.  i n p l a c e of s e r i c i t e .  iHa 0.-Ca0.3/2Al203.5Sl02fH20-4.G0 = 2  2  -Labradorite H 0.tNa20.3/2Al 0 .3Si0 *CaC0 *2Si0 2  2  •Para^nite'  3  2  3  2  2  . 2...  3 (3^20'.4Caav.7Al 63:-26-SiQ $+14H2©+l£GQg':= 2  2  30 Andesine :  t  14 (H 0 .#Ha G .3/2Al 0 •..3Si0 .i"1 .l2Ca;ae f3:4Si02+-2¥a Si0 . 2  2  2  3  2  3  14 P a r a g o n i t e 3.  3(9/2Ma20.Ca0.1l/2Al203.29Si0 )4-llH20+3G02= 2  30 O l i g o c l a s e : •llOlgOj^  • 11 p a r a g o n i t e , Since i t i s impossible  t o t e l l p a r a g o n i t e from s e r i -  c i t e i n t h i n , s e c t i o n some o f t h e s o - c a l l e d s e r i c i t e , may be paragonite,  although spectrographic  a n a l y s i s has e s t a b l i s h e d  the mica t o be c h i e f l y p o t a s s i c r a t h e r than s o d i c . The b i o t i t e a l t e r i n g t o c h l o r i t e f r e e s some potassium carbonate, and a l t h o u g h there, i s an a d d i t i o n , of potassium t o the s o l u t i o n , i t . i s u n l i k e l y t h a t t h i s i s s u f f i c e n t t o account f o r t h e volume o f s e r i c i t e formed.  Biotite  Chlorite  The presence of. d i o p s i d e , " w o l l a s t o n i t e , v e s u v i a n i t e and c l i n o - e n s t a t i t e i n t h e w a l l - r o c k of the p r i v a t e e r mine suggests t h a t t h e rock, i s a. product from the high-temperature a l t e r a t i o n o f a calcareous, t u f f or sediment..  These m i n e r a l s  are not a f f e c t e d by n e u t r a l , weak a c i d or a l k a l i n e hydrous s o l u t i o n , at. mesothermal temperature.  I t i s . d i f f i c u l a t , however, t o  e x p l a i n why t h e f e l d s p a r was not converted t o s e r i c i t e by the  2  3  -51s o l u t i o n , u n l e s s the i n s o l u b l e m i n e r a l s made the w a l l - r o c k i m p e r v i o u s , and the s o l u t i o n could not accumulate i n s u f f i c i e n t c o n c e n t r a t i o n to a t t a c k  E.  the f e l d s p a r s .  Acknowledgements. The. w r i t e r i s . deeply g r a t e f u l to Dr. H. C. Gunning  f o r h i s u n t i r i n g guidance i n the l a b o r a t o r y ,  and h i s c a r e f u l  c r i t i c i s m of the i n t e r p r e t a t i o n of r e s u l t s , as w e l l as f o r s u p p l y i n g the hand-specimens and t h i n s e c t i o n s  upon which t h i s  study i s based. Mr. W i l l i a m H• Mathews a s s i s t e d the w r i t e r  greatly  by making, s p e c t r o g r a p h i c a n a l y s e s of s e v e r a l m i n e r a l s .  

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