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Genesis of the sulphide mineralization at the Big Ledge Property, B.C. Morris, Arthur 1948

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*-£3  cop-  £ 7  I  GENESIS OP THE SULPHIDE MINERALIZATION AT THE BIG LEDGE PROPERTY, B.C.  BY  A. Morris  A Thesis submitted i n p a r t i a l f u l f i l l m e n t of the requirements of the course leading to the degree of Master of Arts i n the Department of Geology and Geography  THE UNIVERSITY OP BRITISH COLUMBIA  MAY 1948  ABSTRACT  The  B i g Ledge p r o p e r t y i s a g r o u p o f c l a i m s i n the  U p p e r Arrow l a k e a r e a , o p p o s i t e S t . L e o n h o t about  7 m i l e s west o f the  u n d e r l a i n by r o c k s age. and  These r o c k s crystalline  rocks  are  of the  is  are  The  mineralized  feet the  Precambrian  beds s t r i k e  and  Nelson  approximately  t o be  granitic  east-west  t o the  conformable  with a decrease  t o the e a s t , t h e same e a s t - w e s t  seems t o i n d i c a t e  with  i s t o be  control  attributed  ledge and  south.  to outcrop  throughout  a structural  rocks  The  the t o the  south  i n e l e v a t i o n o f 3000  zone c o n t i n u e s  direction  these  batholith.  However, i n s t e a d o f s w i n g i n g  would e x p e c t  mineralization  paragneisses,  r o c k s a l o n g the  d i p i s a b o u t 40 d e g r e e s  enclosing rocks. one  complex of the  zone a p p e a r s  Precambrian  Intimately associated with  banded g n e i s s i c  s t r u c t u r e o f the  t h e i r average  as  and  and  property i s  of l a t e  composed o f s c h i s t s ,  limestone.  pegmatite,  regular.  The  of the H a m i l l s e r i e s  pegmatite-gneiss  The  lake I t s e l f .  springs  to  i n roughly  i t s length.  This  o f some s o r t  i f the.  hydrothermal  solutions. The  m i n e r a l i z a t i o n of  zone r e m a r k a b l e Pyrrhotite pyrite present  the B i g L e d g e  f o r i t s c o n t i n u i t y and  i s confined to a  u n i f o r m l y low  grade.,  i s the most a b u n d a n t s u l p h i d e , s p h a l e r i t e  occur  i n about equal q u a n t i t i e s ,  i n m i n o r amounts.  The  and  galena  and  is  m i n e r a l i z a t i o n does n o t  / /  /  extend  across  the  entire width  o f the. l e d g e b u t  is  c o n f i n e d /  s  to bands or lenses a few inches to several feet thick within the zone.  In these bands the sulphides occur either as  disseminations minerals  i n or as massive replacements of s i l i c a t e  that are the products of metamorphism of impure  dolomitic limestones.  Commonly massive bodies of sulphides  appear to be associated with pegmatitic  intrusives i n the  mineralized zone. Geological reconnaissance and laboratory investigations indicate at least two d i s t i n c t kinds of metamorphism.  The  f i r s t type, regional metamorphism, i s indicated by the prevalence of garnet-mica schist throughout the Upper Arrow lake area.  The second kind, thermal metamorphism, i s  apparently r e s t r i c t e d to the mineralized zone.  It i s  thought that the thermal metamorphism was the f i r s t of a sequence of events, including i n j e c t i o n of the pegmatitic material and c i r c u l a t i o n of hydrothermal solutions, that resulted i n the low-grade mineralization of the Big Ledge.  ACKNOWLEDGMENTS  The writer wishes to thank Dr. C O . Swanson f o r suggesting the subject of this research; Drs. .H.C. Gunning and K. De P. Watson, f o r t h e i r h e l p f u l advice. The technical assistance given by Mr. J.A. Donnan was invaluable.  CONTENTS  PAGE  Purpose of Thesis Abstract Introduction Location History Topography  1 1 1 2  Regional Geology Table of formations Hamill series Slocan series Intrusive rocks (a) Nelson b a t h o l i t h (1) Nelson gabbro-gneiss (2) Nelson pegmatite-gneiss complex (c) Kuskanax b a t h o l i t h Structure  4 5 6 6 7 7 7 7 8 9  Big Ledge Property S u r f i e i a l rocks (a) Precambrian rocks (c) Intrusive rocks Metamorphism Mineralization Estimation of Values Structure  9 9 9 11 11 12 12' 14  Sunshine Tunnel Geology Laboratory investigations (a) Petrology (b) Mineralography Metamorphism  15 15 17 17 26 28  Origin  30  Bibliography  ILLUSTRATIONS Plate 1.  Precipitous north slopes of ridge on which the Big Ledge i s located.  Plate 2.  Inclusions of tremolite, with common optic orientation i n sphalerite.  Plate 3.  Inclusions of carbonate with common optic orientation i n tremolite.  Plate 4.  Complex twinning of basic plagioclase, showing three kinds of multiple twinning.  Plate 5.  Spindle shaped twinning i n d i c a t i n g development due to stress.  Plate 6 .  Twin laminae bent by fracture - l a t e r twinning discontinuous, spindle shaped.  Plate 7.  S i l l i m a n i t e growing i n feldspar grain.  Plate 8.  P a r a l l e l trains of f l u i d inclusions crossing quartz grains.  Plate 9.  Pyrrhotite replacing s i l l i m a n i t e ? i n ' feldspar grain.  Plate 10.  Myrmekite  Maps  In Pocket.  L E G E N D R E C E N T AND P L E I S T O C E N E  " Pos+ T r i a s s i c granite  ("chiefly)  Melsoin Berth oli"th  Complex of coarse pcomo~t~i\1~ic gr-amite , -fine To rned- gnoiSSic gran and inclusions of Pre Com br ion roc  a.. gabbrO  Ttnassic  Slocon  -  gneiss  Senes  3<aie Jimesline, qvarTxiTb f  ,  Wmdeirnei-e  argilhte, T-uffaceOdS  •  //mes^one, sTratiaraphic of &odsho~f  approximate eo/valmnT JimesTorte  lo 8  i  j  Sen,sTs,/>oroan»/**•* Crystalline, and mtyusives probably reldTed *° ™e Nelson &*Tholi1h  Mops  232.A  and  235A  UPPER ARROW L A K E K O O T E N A Y  D I S T R I C T  BRITISH COLUMBIA Scale ag^'o  AREA  1  '"c^i To 4 m i l e s  8  SKETCH  P L A N OF BIG L E D G E MINERAL CLAIMS,ARROW LAKE DIV. B.C.  N  37QOO  PLAN OF'SUNSHINE. T U N N E L S c a l e : \ i n c W T o \ 0 -Fee-i"  36  90OA/  JV  SUNSHINE.  TUNNEL  SECTION A-A' SOUTH  WALL  Alt. h~~f, of "•**2Jg» outrr-tt.re Sfmt-  * thl'KTt*  . "** 4  JCA/j/  io/To^,  «»/  ttCflTH  -  ftp*  t>~*.nj  ,  n-tve?  WAIL  SECTION B-B' L.rrrrs  to~ e  w*5T  Oo'fy mf  :  z;?;;'„  WALL  s  B  s  i+s i th  ***** ** +  £AS7~  f  m  pro.  to /*-r***f'*o~  WALL  SECT/ON CC* SOUTH  WALL -f  NORTH  ?y'Z3  SrVAU  SECT/ON D*D *3'  T~mrt*iti.  Itrifl)  NORTH  WALL  PURPOSE OF THESIS The Big Ledge i s e s s e n t i a l l y a large, low sulphide replacement  grade,  body i n metamorphosed limestones.  It  consists of mineralized bands or lenses that contain varying amounts of sulphides, of which pyrrhotite i s the most abundant.  Sphalerite and pyrite are present i n about equal  amounts, and galena constitutes a very minor portion of the sulphides. The subject f o r this study was of Dr. C O .  chosen on the suggestion  Swanson, Chief Geologist f o r the Consolidated  Mining and Smelting Company of Canada, Limited. In the course of examining one of the old exploration tunnels on the property, i t was  thought  that a rather unusual  type of g r a n i t i c rock may have developed as a r e s u l t of the metamorphism to which the o r i g i n a l impure calcareous sediments had been subjected.  It was  also thought  that the  g r a n i t i z a t i o n may be associated with the genesis of the sulphides. In an attempt to check this association conclusively, specimens were collected along certain beds, across a fracture that appeared to'have a l o c a l control over the mineralization, and at contacts and across.massive  zones, f o r the purpose of  making a petrographic and mineralographic study.  It was  hoped that such a study would be of d i r e c t i v e value i n future exploration.  INTRODUCTION Location The Mr. by  B i g Ledge p r o p e r t y  F o w l e r of the  Nakusp, B.C.  Consolidated  i s a group of  claims,  owned  which have been r e c e n t l y  M i n i n g and  Smelting  Company o f  hy  leased Canada  Limited. The opposite lake  property  St. Leon hot  itself.  232A b y  i s on  A  map  the  west  springs  of  the  Walker, B a n c r o f t  s i d e o f U p p e r Arrow  and  area,  and  about 7 miles  lake,  west  of  the  t a k e n f r o m G.S.C. maps  Gunning,  (1929) and  235A  by  IS  Cairnes this  ( 1 9 2 8 ) , w h i c h shows the  exact  location,,included i n  report.  History I n t e r e s t has located in  the  along late  the  long  been a t t a c h e d  B i g Ledge.  n i n e t i e s by  Mr.  r u s t y weathering mineralized Subsequently other Symon's h o l d i n g s , mineralized Little until  1925,  a fairly effort  claims and  A.  initial  discovery  Symons who  learned  was  of  zone f r o m a h a l f - b r e e d  were s t a k e d  along  properties  the  on  apparent  made  the Indian.  e i t h e r side  of  continuation  Mr.  of  the  zone. e f f o r t was when an  extensive  to determine  same t i m e , f o r m u l a t e of  The  to the  made t o d e v e l o p the  a m a l g a m a t i o n was  effected.  e x p l o r a t i o n p r o g r a m was the  c o n t i n u i t y o f the  some i d e a  i t s mineralization.  The  of  the  several  holdings  Following  started in ledge  character  and, and  work i n c l u d e d numerous  this,  an at  the  extent open-cuts  2  d i s t r i b u t e d at i r r e g u l a r intervals along the Big Ledge}.about 700 feet of tunnelling; and 16 diamond d r i l l holes, aggregating 3400 feet of d r i l l i n g , distributed c h i e f l y over the central and western claims.  The findings did not  encourage development and as a result l i t t l e or no work was done on the property from 1929 u n t i l 1947.  Early i n that  year the Consolidated Mining and Smelting Company leased these claims, now  owned by Mr.  Fowler.  Last summer, the Consolidated Mining and Smelting t  Company b u i l t a road from Upper Arrow lake, near the mouth of Pingston creek, i n to the Big Ledge property. time an exploration program was  started.  At the same  Included i n this  program were geologic and topographic mapping, and a magnetometer survey. In the course of the geologic mapping, three of the old exploration tunnels were examined.  The Sunshine tunnel was  the f i r s t to be investigated. It was Swanson suggested  at this point that Dr.  that a detailed study of a suite of  specimens from this tunnel would be of interest and might supply information regarding the genesis of the sulphides. Topography The Big Ledge property extends f o r 3-g- miles along a ridge between two streams flowing east.  In that distance, the  elevation rises from 4000 feet on the east to 7000 feet on the west.'  The north slopes of the ridge' are precipitous;  t h e i r rugged nature i s indicated by plate 1.  The south slopes  3  are rounded and, although i n many places steep, can he traversed without d i f f i c u l t y .  The v a l l e y that i s i n part  formed by these slopes, has Empress lake at i t s head.  This  lake i s drained by Brownie creek which, l i k e many of the smaller streams i n the area, has developed an underground channel i n c r y s t a l l i n e limestone f o r i t s f i r s t 7000 or 8000 feet.  In that distance the creek drops 900 feet and would  provide the source of e l e c t r i c a l power f o r future development.  4  REGIONAL GEOLOGY According to Cairnes and Gunning (1928 p. 111A) host rocks at the Big Ledge are of Precambrian age.  the However,  within 8 miles to the south the bedrock geology, as shown by Cairnes (1928 p 96A)  includes an assemblage of formations  ranging from Precambrian to Tertiary, as indicated i n the following Table of Formations.  TABLE OP FORMATIONS IN THE UPPER ARROW LAKE AREA.{Quaternary  Superficial Deposits  Recent and Pleistocene  Delta and Valley Deposits,Bench lands; G l a c i a l D r i f t  GREAT UNCONFORMITY Kuskanax Batholith  Granite, quartz-syenite, syenite  -Nelson Batholith  INTRUSIVE CONTACT  Tertiary and Mesozo'ic  Intimate association of pegNelson Pegmatite- matite and banded gneissic and Gneiss Complex g r a n i t i c rocks with inclusions of Precambrian rocks. CONTACT NOT OBSERVED Nelson Gabbro Gneiss  Foliated hornblende-gabbro gneiss  INTRUSIVE CONTACT Mesozoic  Triassic  Slocan Series  Slate, a r g i l l i t e , quartzite, limestone,and tuffaceous sediments  GREAT UNCONFORMITY  Precambrian  Hamill Series  Schists, greenstones, paragneisses, and c r y s t a l l i n e limestones.  6  (1) .  Hamill Series These rocks were c l a s s i f i e d as late Frecambrian  Vifalker, Bancroft and Gunning, (1929 p. 9).  by  They are a  group of interbedded c r y s t a l l i n e schists, paragneisses, limestones, and quartzites.  The c r y s t a l l i n e schists are  medium to coarse grained with schistose structure.  Quartz,  muscovite, b i o t i t e , and feldspar are the most abundant minerals.  Such minerals as garnet, s t a u r o l i t e , and  scapolite occur as metacrysts i n these rocks.  The quartzites  are commonly l i g h t colored, massive rocks, generally containing b i o t i t e and garnet.  The limestone beds are coarsely  c r y s t a l l i n e , f o r the most part white, but occasionally buff colored.  They commonly contain impurities such as quartz,  small graphite flakes, garnet, diopside, and epidote.  The  paragneisses appear to be a gradational phase between c r y s t a l l i n e schists and the associated gneissic intrusives of the Nelson b a t h o l i t h .  They consist of quartz, orthoclase,  plagioclase, b i o t i t e , muscovite, diopside, o l i v i n e , apatite, s e r i e i t e , k a o l i n i t e , sphene, graphite, and sulphides. (2) .  Slocan Series Outcrops of rocks of this series are found about 8 miles  south of the Big Ledge.  There the series consists essent-  i a l l y of metamorphosed sedimentary rocks such as slate, a r g i l l i t e , quartzite, and limestone.  In this series the  limestones are i n general l i g h t to dark grey, fine grained to semi-crystalline rocks.  The age of these beds was  determined.  7  on the basis of f o s s i l collections obtained i n the Slocan d i s t r i c t roughly 25 miles to the south-east. (3) Intrusives There are two batholiths i n the Big Ledge country; the Nelson which i s the larger and older, and the Kuskanax. (a)  Nelson Batholith This intrusive i s subdivided into 3 members, only two  of which, however, are s u f f i c i e n t l y close to the Big Ledge to warrant discussion here. Nelson  G-abbro-gneiss  This gneiss forms a narrow dyke-like body along the contact between the Kuskanax b a t h o l i t h and the Slocan series south of Pingston creek.  I t i s a medium grained, greenish  rock consisting of hornblende, plagioclase feldspar, epidote, some b i o t i t e , and a l i t t l e quartz.  Mineral composition i's  d i s t i n c t l y d i f f e r e n t from the Kuskanax b a t h o l i t h .  The  gneiss i s cut by the Kuskanax b a t h o l i t h and has a sharply defined contact with i t .  Cairnes (1928 p. 100A)•believes  that the gneiss may be an early basic phase of the Nelson batholith. Nelson pegmatite-gneiss  complex  This complex i s i n contact with the Precambrian  rocks  less than 1-g- miles to the south of the Big Ledge property. The areal extent of this complex i s greater than that of any other formation within the area covered by Cairnes i n h i s  8  reconnaissance Two First  distinctive  rock types  are found  quartz, plagioclase,  garnets.  The s e c o n d  Abundant m i n e r a l s biotite,  matitic gneissic  tongues  r e d garnet,  intergrowths  a r e common.  Criteria  ranges listed  from  a r e sphene,  and s u l p h i d e s .  of these  binary granite to quartz  by Cairnes  the banded s t r u c t u r e c h a r a c t e r i s t i c  assimilated  suggest contact  r o c k s ; and  of the gneisses  to c o n f o r m i t y w i t h laminae  of completely  older rocks.  Kuskanax  Batholith  These r o c k s sedimentary  monzonite.,  (1928 p . 103A) w o u l d  t h e p e g m a t i t i c - g n e i s s complex i s a d e e p - s e a t e d  m i g h t be a t t r i b u t e d  (c)  magnetite, .Micropeg-  The c o m p o s i t i o n  phase o f t h e N e l s o n b a t h o l i t h w i t h P r e c a m b r i a n that  grain.  of pegmatitic g r a n i t e .  accessory minerals  kaol.inite,  rocks  t e x t u r e and f i n e r  are quartz, p l a g i o c l a s e , orthoclase,  muscovite,  chlorite,  and  i s d i s t i n g u i s h e d by i t s g n e i s s i c  may be i n t r u d e d b y narrow  that  complex.  o r t h o c l a s e , muscovite  or, b a n d e d a p p e a r a n c e , more u n i f o r m It  i n this  i s a pegmatitic granite of i r r e g u l a r texture,  containing red  o f t h e U p p e r Arrow l a k e r e g i o n .  are also  rocks  i n contact with  5 or 6 miles  intrusive,  the  t o the south  Ledge.  In t h i s  the rocks  grained  and commonly a r e p o r p h y r i t i c  e a s t of the B i g  a r e medium near  Precambrian  to f i n e  the border.  Cairnes  (1928, p . 104A) r e c o g n i z e d two m a i n t y p e s ; s y e n i t e , w h i c h grades the  through  quartz  syenite into  g r a n i t e which occurs  adjacent  granite.  Of t h e s e ,  t o the Precambrian  only  rocks  9  w i l l be d i s c u s s e d .  The g r a n i t e i s l i g h t c o l o r e d , c o n t a i n i n g  v a r y i n g amounts of q u a r t z , green amphibole, o r t h o c l a s e , m i c r o c l i n e , and minor p l a g i o c l a s e as p e r t h i t i c  intergrowths.  A c c e s s o r y minerals are sphene, a p a t i t e , magnetite, an  cf  garnet, o c c a s i o n a l s u l p h i d e g r a i n s w i t h secondary }  kaolin^and  yellow calcite,  chlorite.  Structure Across Upper Arrow l a k e , In the v i c i n i t y of Pingston and S t . Leon creeks, the Precambrian rocks form an a n t i c l i n e , p l u n g i n g to the south.  F a r t h e r south, i n the area of Saddle  mountain, these beds form a broad  dome.  L y i n g unconforraably  i n the trough between these two s t r u c t u r e s i s a northwestt r e n d i n g b e l t of sedimentary Series.  rocks b e l o n g i n g t o the S l o c a n  The general s t r u c t u r e of the Slocan s e r i e s , which  i s s y n c l i n a l , i s complicated by much f o l d i n g and f a u l t i n g and on the whole by s t e e p e r dips than those  o b t a i n i n g i n the  u n d e r l y i n g Precambrian f o r m a t i o n s . BIG LEDGE PROPERTY S u r f i c i a l Rocks ' The rocks on the B i g Ledge p r o p e r t y are c h i e f l y Precambrian i n age and comprise s c h i s t s , limestones, and q u a r t z i t e s . one  paragneisses,  Included i n the s c h i s t s are  or two d i s t i n c t i v e bands of g a r n e t - m i c a - s c h i s t i n which  garnet metacrysts i n c h i n diameter.  are abundant and a t t a i n s i z e s up to l / 2 Other minerals  i n c l u d e much quartz, some  10  plagioclase,  and  biotite  with  m i n o r amounts o f m u s c o v i t e  serieite.  The  r e m a i n i n g bands o f m i c a  those  just  discussed  bands  of c o a r s e l y c r y s t a l l i n e ~ l i m e s t o n e a l s o occur  For  the  most p a r t  but  two  or  three  type a c q u i r e s  but  the  The  limestone  bands a r e  garnet  On  are  s i m i l a r to  and  Several here.  fairly  dense,  w e a t h e r i n g , the  surface  latter  somewhat s i m i l a r i n  weathered p o r t i o n s  limestones  are  crystals.  i s white  buff.  a rusty granular  c o l o r to l e s s deeply zone.  l a c k the  schist  and  of the  commonly i n t e r b e d d e d  mineralized with  gneissose  occasionally  and  schistose  pegmatitic  rocks  stream  on  B i g Ledge  types are  111A)  channels  In are  comprise  one  from  In t h e i r  the  not u n u s u a l . para-and  other.  r e p o r t note  carry a larger proportion  h a v e , as  texture  as  types  i s not  c o n t a i n much the  quartz, apatite,  are  the  and  i n the  magnetite, garnet,  proportion  muscovite,  serieite,  and  "salt  pepper" Both  that i s ; sphene,  sulphides, appeared  r u s t y w e a t h e r i n g , a p p e a r e d t o c o n t a i n more  sulphides.  dark  and  diopside,  of f e l d s p a r while  (1928 commonly  gneisses.  Some g n e i s s e s  two  Gunning  ( i n some c a s e s a  rocks  to  paragneisses  a result,  under-  The  i t is difficult  Cairnes  that  and  gneissic  same s u i t e o f m i n e r a l s ,  plagioclase, biotite,  a greater  and  noticeable  m i n o r v a r i a t i o n s were n o t e d . contain  The  to  orthogneisses.  of b i o t i t e  g r e e n a m p h i b o l e ) and which  granitic  these beds, s i n k holes  intimately associated  distinguish p.  ocnn.rcj:.Ly c o n t a i n  inclusions.  ground the  and  but to  others, iron  that  11  Intrusives The  rocks  pegmatitic (1928  and  p. 111A)  of the  of Precambrian  age  gneissic  that  rocks  intrusives cambrian  n e e d no  intersect  rocks.  The  of these  serieite  and  Gunning  further discussion.  The  the g n e i s s e s as w e l l  Quartz,  rocks.  plagioclase,  Minor  complex  g n e i s s e s have a l r e a d y b e e n  the a b u n d a n t m i n e r a l s . . M u s c o v i t e mica  C a i r n e s and  c o r r e l a t e d w i t h the p e g m a t i t e - g n e i s s  Nelson b a t h o l i t h .  m e n t i o n e d and  have been i n t r u d e d by  as  and  i s the  pegmatitic  the  Pre-  o r t h o c l a s e are characteristic  c o n s t i t u e n t s are  red  garnet,  iron sulphides.  Metamorphism The  rock types  attainment not  identified  necessary  structure  with  In B a r k e r s '  for  t h e B i g Ledge p r o p e r t y  o f metamorphism.  f o r the p u r p o s e a fairly  to develop  d i o p s i d e may  s u c h as  on  o f a h i g h grade  would appear t h a t be  found  of t h i s  h i g h grade  of f l a k y  micas,  zoisite,  t h e most p a r t ,  t o the  lower and  They are u l t i m a t e l y  m i n e r a l s h a v i n g no  force  and  and  are  and  Gneissic  or a c i c u l a r amphibole  middle  and  grades  habit  belong, of  r e p l a c e d l a r g e l y by  the  would  o f metamorphism.  such pronounced h a b i t ,  diopside, forsterite,  crystallizing  o f metamorphism  t h e h i g h e s t ,grade  opinion, minerals  was  t h e s i s , however i t  a garnet-biotite-schist.  chloritea,  kyanite,  garnet  the development of g a r n e t , p l a g i o c l a s e ,  indicate  metamorphism.  The  indicate  s u c h as  like  characteristic  other  garnet,  w h i c h have a s t r o n g minerals  of the  •  12  highest  grades  o f metamorphism.  F o r these reasons  h i g h l y metamorphosed r o c k s , o f a l m o s t commonly show l i t t l e and  their  t h e most  any composition,  o r n o t h i n g o f the s c h i s t o s e c h a r a c t e r ,  structure  i s o f t e n d e s c r i b e d as g n e i s s o s e .  Mineralization The mainly of  s u l p h i d e m i n e r a l i z a t i o n i n . these  t o a zone, r e m a r k a b l e  this  the o r i g i n a l  zone.  beds. of  A l t e r a t i o n has  c h a r a c t e r of the rocks  Inclusions of limestone  that at least  to several f e e t  past would  persistent  outcropping i n suggest  p a r t of the ledge i n c l u d e d a l i m e s t o n e bed o r across the e n t i r e  t h e l e d g e b u t i s c o n f i n e d t o bands  the  largely  i n the s u l p h i d e s  M i n e r a l i z a t i o n does n o t e x t e n d  inches  i s confined  f o r i t s c o n t i n u i t y and u n i f o r m i t y  character of mineralization.  obscured  rocks  indicate  o r l e n s e s , a few  t h i c k w i t h i n the zone. that  width  Work done i n  i n a g e n e r a l way t h e most  mineralization follows along or close  h a n g i n g - w a l l , where i t h a s an a v e r a g e  width  t o the  o f about  10 f e e t .  E s t i m a t i o n of Values An within of  estimate the ledge  of the average  as a whole a n d a l s o  i t i s given by Cairnes  compiled  from  assays  assay  foot  and h a n g i n g - w a l l s  average  logs of o n l y those  holes.  drill  holes  across this  tables  Table l i s compiled  of the B i g Ledge.  of z i n c  contained  across selected portions  t h i c k n e s s o f the B i g Ledge  percentage  of zinc  (1928 p . 117A) i n 3  o f 16 d r i l l  from  the a v e r a g e  percentage  that  cross  From t h i s  both table  i s 137 f e e t  and t h e  w i d t h 0.64.  Table  2  13  is of selected widths including from one to several mineralized bands situated so close to each other as to suggest that they might be mined together as a u n i t , i f values were s u f f i c i e n t l y encouraging.  The average width of "selected widths" over the  area d r i l l e d i s 29 feet and the average percentage of zinc i s 2.45 across this width.  Table 3 includes the highest grade  zinc encountered i n each d r i l l hole.  In this case the average  width i s 4.23 feet and the average percentage of zinc i s 8.35. The figures f o r the average percentage of zinc do not mean that a single body of zinc ore of the character indicated by these averages persists along Big Ledge over the area d r i l l e d . In connection with the d r i l l i n g Cairnes states "The  drill  holes are f o r investigation of the Big Ledge close to the surface only.  There are no deep holes.  Consequently  little  is known of the character of the mineralization at any considerable distance below the surface.  To some extent this  information appears to be supplied by nature i n that a longitudinal section with a v e r t i c a l range of 3000 feet i s exposed between Skyline claim (towards the east end) and Adventurer claim (towards the west end). to  This might seem  imply that 3000 feet v e r t i c a l l y below the Skyline  exposures we might expect to f i n d mineralization of a type similar to that on Adventurer claim. is not necessarily the case. Big  Ledge may,  Such however,  The mineralized bodies within  f o r example, rake more or less c l o s e l y  with the surface, a feature c h a r a c t e r i s t i c of many ore deposits i n Kootenay d i s t r i c t .  Mineralization i n such a case,  14  might he confined to a depth, at most, of a few hundred feet. ' Although such a p o s s i b i l i t y represents a rather extreme case, the chance of a more or less pronounced be kept i n mind.  easterly rake should  On the other hand the rake may be  approximately with, or to the west of, the dips of the ledge, in which cases the natural section exposed along the slope of  the h i l l might be expected to represent, more or less  c l o s e l y , the character of mineralization anywhere within the Big Ledge down to the lowest l e v e l of the section. One point noted i n recent surface work that i s supported by the d r i l l core assays i s that sphalerite i s more abundant towards the east end"of the ledge than i t i s towards the west end.  This suggests that i f the rake i s  with, or to the west of, the dip of the ledge an increase in the grade of zinc could be expected at depth towards the west end of the zone. Structure The structure of the Precambrian rocks along the ledge is regular.  The beds strike approximately east-west and  t h e i r average dip i s about 40 degrees to the south.  A section  along the Anna S. Gulch indicated on the sketched plan of the mineral claims included i n this report, showed that many of  the footwall beds had been increased to at least twice  t h e i r normal thickness by drag f o l d i n g , but no folds were found in the hanging wall beds.  Throughout i t s length, the mineralized zone of the Big Ledge appears to he conformable with the bedding.  It i s to  be noted however, that i n general the outcrop of the beds i s approximately p a r a l l e l with the trend of the ridge.  Thus i f  the mineralized zone were conformable with the bedding the delineation of i t s outcrop should swing to the  south,  especially towards the east end of the property where the slope of the ridge i s much steeper and where the dip of the beds decreases to about 20 degrees south.  This would  indicate that there must have been a s t r u c t u r a l control other than bedding i f the mineralization is to be a t t r i b u t e d to hydrothermal solutions. SUNSHINE TUNNEL Geology The a d i t , as shown by the accompanying plan, is 220 feet long.  It i s composed of a d r i f t and cross-cut.  Prom  the portal the d r i f t has been driven f o r 78' on the bearing S 63 degrees W.  At this point there i s a change of bearing  to S 35 degrees W, and the d r i f t continues bearing to i t s end.  on this  new  At 78 f e e t , where the d r i f t changes  d i r e c t i o n , a cross-cut has been driven on the bearing S 35 degrees E f o r 76 f e e t .  Forty-six feet along the cross-cut  there i s a short d r i f t 16 feet i n length whose bearing i s S 57 degrees west. S t r a t i g r a p h i c a l l y , the lowest beds i n the tunnel are thin-bedded micaceous quartzite and mica s c h i s t .  These are  16  d i r e c t l y beneath, the mineralized zone and are believed to be the top of the footwall beds.  The mineralized zone i s comp-  osed of banded lime/ s i l i c a t e beds that are more or less gneissose and contain a wide assemblage of minerals including both disseminated and massive pyrrhotite, and disseminated sphalerite, p y r i t e , and galena. of these beds i s approximately 14 f e e t .  The thickness  Above these are 20  feet or more of impure, t h i n bedded to massive limestone. In the lime s i l i c a t e and limestone beds are found i r r e g u l a r patches of pegmatitic rocks that cut across the bedding. The sulphides are unevenly distributed throughout mineralized zone.  the  They occur either as disseminations i n  or as massive replacements  of the s i l i c a t e s .  It i s not  uncommon f o r the sulphides, c h i e f l y pyrrhotite, to occur i n massive zones adjacent to the pegmatitic areas. Sphalerite appears to be associated with the disseminated pyrrhotite rather than the massive pyrrhotite. The d r i f t cuts across four fractures which are. /s approximately para l i e lj^an^ave rage strike wi»uld -bd^ about N 25 degrees W.  They a l l dip steeply east.  On none of ~the  fractures was there any noticeable displacementi^ane fracture 47 feet from the portal was  h^^^k  f i l l e d with a greater  amount of gouge than any of the others. cut  N  Where this fracture  the mineralized zone there was a marked increase i n the  amount of sulphides both i n and following along the fracture zone.  This concentration decreased rapidly along the bedding  a'way from the f r a c t u r e .  17  Laboratory Investigations Specimens were collected i n the Sunshine tunnel across and along mineralized beds, from limestone, pegmatite, and massive sulphides at the places indicated on the accompanying plans.  It was hoped that a petrographic and  mineraiographic  study of these specimens would give some information regarding the genesis of the sulphides. Petrography Thin section 1 represents a specimen from the mica-schist, containing augen-like q u a r t z i t i c bands, immediately below the mineralized zone.  Quartz and orthoclase i n about equal  amounts make up most of the section, with minor amounts of phlogopite, c h l o r i t e , pyrrhotite, p y r i t e , and sphalerite. About half of the section i s fine grained and exhibits schistosity.  Nearly a l l of the pyrrhotite and much of the  phlogopite are confined to this part of the section.  The  pyrrhotite occurs as roughly p a r a l l e l , l e n t i c u l a r blebs, with ragged edges.  I t i s c l o s e l y associated with the  phlogopite and i n t e r s t i t i a l to the quartz and orthoclase. The q u a r t z i t i c part of the section i s of medium to coarse grained quartz and orthoclase.  Some of the quartz grains  show s t r a i n shadows., Micropegmatitic present i n the feldspar.  intergrowths  are  The orthoclase has also suffered  minor s e r i c i t i z a t i o n . Thin sections 2 and 3 were made from specimens that were collected across a band containing disseminated  to  18  massive sulphides,  29 feet i n from the p o r t a l .  The  minerals  i d e n t i f i e d are plagioclase, (labradorite-bytownite), phlogopite,  muscovite, diopside,  (since no attempt was  quartz,  sphene, apatite, carbonate,  made to i d e n t i f y this mineral more  accurately "carbonate" w i l l mean c a l c i t e and/or  dolomite),  tremolite, c h l o r i t e , pyrrhotite, and sphalerite.  In these  sections there i s a vague l i n e a t i o n which appears to be gneissic.  In places  the sulphides  completely replaced the s i l i c a t e s .  were found to have almost This is i l l u s t r a t e d i n  plate #2 i n which sphalerite completely encloses fragments of tremolite that have the same optic orientation.  The  common optic orientation of the tremolite fragments would indicate that they o r i g i n a l l y belonged to a large grain that has been almost completely replaced by the sphalerite. Elsewhere the sulphides cleavage planes of. the  occur as disseminations along silicates.  Evidence of ""replacement of carbonate by tremolite found i n these sections.  was  This i s shown i n plate #3 i n which  areas of carbonate having the same o p t i c a l orientation are enclosed i n a large grain of tremolite.  In turn the  tremolite has been i n part altered to a c h l o r i t i c product. Apatite was  also present i n these sections i n amounts  approaching 10 percent.  It is thought that this amount is  greater than would be expected i n sedimentary beds of this type. A high grade of metamorphism i s indicated by  the  vaguely gneissic structure possessed by the specimens and  by  19  the development of minerals such as basic plagioclase, diopside, and sphene. Thin sections 4, 5 and 6 were made from specimens collected obliquely across a band containing disseminated sulphides, d i r e c t l y above 1, 2, and 3.  These sections  d i f f e r from 2 and 3 i n the absence of muscovite, and i n the presence of untwinned a l b i t e found i n section 4.  Section 5  is composed almost e n t i r e l y of plagioclase which possesses various kinds of multiple twinning.  Twinning according  the a l b i t e and p e r i c l i n e laws is very common.  to  A t h i r d kind  of multiple twinning, t e n t a t i v e l y i d e n t i f i e d as Ala B shown i n plate 4 i s also f a i r l y common.  The  twinning possesses  various features that suggest a development due to stress a f t e r the growth of the feldspar.  Much of the twinning can  be attributed to mutual interference of growing c r y s t a l s . R.C.  Emmons and R.M.  Gates (1943  p. 302 f i g . 2 ) )  This  would be indicated by the broad, simple twin laminae shown in some of the grains i n plates 4 and 5.  Plate 5 also  shows multiple twin laminae cutting across a simple twin thus indicating a later growth f o r the multiple twinning. The spindle shaped twins i n the adjacent grains also indicate a late development of the twinning.  Although not  well displayed, a feldspar grain i n plate 6 shows 2 or 3 twin laminae at one end that extend e n t i r e l y across  the  grain? these laminae have been bent by a f r a c t u r e .  Other  twin laminae in the grain are short and discontinuous not cross the fracture thus i n d i c a t i n g t h e i r late  and  > do  development.  Because of the complexity of the twinning the  plagioclase was  determined by means of immersion o i l s .  index, n, (001), was found to be 1.570  t(.005).  The  Using  Tsuboi's curves, i l l u s t r a t e d i n Rogers and Kerr (1942 p.  244)  this would indicate a plagioclase of composition near that of labradorite-bytownite (Ah^ A n ) . ?  With l a t e r work maximum  extinction angles of a l b i t e twin laminae were found to be 42 degrees; this indicates a plagioclase s l i g h t l y more c a l c i c than Ah^ An^. The presence oflabradorite-bytownite would indicate attainment of a high grade of metamorphism.  If any d e t r i t a l  or authigenic a l b i t e had been present i t would have been incorporated i n the plagioclase to develop a more sodic plagioclase.  Since much of the twinning of the plagioclase  appears to be a secondary development produced by stress, Emmons and Gates state (1943)^) (  the deformation of the  c r y s t a l i s apparently casually related to the twinning.  Not  only i n the "tapering o f f " of the lamellae related to the deformation, but the continuity of the lamellae i s s i m i l a r l y related, hence the deformation and the twinning are v  l o g i c a l l y cause and e f f e c t ) ; i t would suggest that the a l b i t e which i s untwinned was formed at a lat«'r date, probably by metasomatism. Nothing new was found concerning the occurrence of the sulphides in these sections. Thin sections 8, 9, 10 and 11 represent specimens collected along a moderately mineralized lime s i l i c a t e bed  21  cut by the most conspicuous fracture i n the tunnel.  These  specimens were collected primarily to determine what influence the fracture had. on the mineralization.  The  minerals  i d e n t i f i e d i n these sections are, plagioclase,  (labradorite-  bytownite) a l b i t e , carbonate, b i o t i t e , phlogopite,  diopside,  tremolite, sphene, apatite, quartz, c h l o r i t e , epidote, s e r i e i t e , pyrrhotite, sphalerite, and galena. which was  Section  collected about 3 feet east of the fracture i s  noteable i n that about 50 percent of i t is carbonate. sphalerite is present and with associated replaced  8,  only minor amounts of pyrrhotite  galena are present.  the carbonate.  The  pyrrhotite  has  In section 9, sphalerite i s s t i l l  absent and pyrrhotite showed only a minor increase than 10 percent).  No  There i s a noticeable  increase  (less i n the  amount of apatite, 5 to 10 percent, compared to number 8. Section 10, which comes from the fracture zone, contains about 40 percent sulphides. usual, about 10 percent. west of the fracture.  Sphene i s more abundant than  Section 11 was  collected 2 feet  It contains roughly the same  proportions of sulphide minerals as section  10.  These sections, indicate that the sulphide concentration was  greatest  side.  along and adjacent to the fracture on i t s west  Although there was  a s l i g h t increase  of jyDhalerite,_a__minor constituent, was  i n pyrrhotite.  The  the largest  An increase  increase  above sulphide estimates suggest  that the fracture;, provided a channel for solutions.  i n thejamqunt  mineralizing  i n the amount of sphene, and  7  ^ ^ 0 4  22  especially he  of apatite  interpreted  on t h e e a s t  side  of the f r a c t u r e  could  as a n i n d i c a t i o n o f m e t a s o m a t i c a d d i t i o n o f  some o f t h e c o n s t i t u e n t s  of these m i n e r a l s .  The d e v e l o p m e n t  of  suggests retrograde  metamorphism.  c h l o r i t e and s e r i e i t e Thin sections  13, 14, 15, 16 and 17 r e p r e s e n t  specimens  collected  a l o n g a micaceous  t o q u a r t z i t i c band, a t t h e  beginning  of the c r o s s - c u t ,  that  The  minerals  basic  plagioclase,  quartz,  pyrite.  and  sphalerite  as  interstitial replace  Apatite  alteration  blebs  feldspar,  carbonate,  product  pyrrhotite, amounts.  grain  i s also  from  BB . 1  grains.  occur They  from a dust  to almost The most  a m i n o r amount o f s e r i e i t e ,  pyrite,  They  i s c h l o r i t e , developed from  complete abundant tremolite  formed from the  present. 18, 19, a n d 28 r e p r e s e n t  impure  were c o l l e c t e d 14 f e e t cross-cut  feldspar  by i t s  i n amounts  i n amounts v a r y i n g  o f some o f t h e s i l i c a t e s .  Thin sections, collected  i n varying  albite,  s p h a l e r i t e , and  between t h e s i l i c a t e  the s i l i c a t e s  diopside;  within  untwinned  i s again present  The s u l p h i d e s  are present  the o c c a s i o n a l  replacement  and  were,'orthoclase,  diopside,  pyrrhotite,  sulphides.  A g a i n a l a t e growth of a l b i t e i s i n d i c a t e d  of twinning.  across  apatite,  sphene, s e r i e i t e ,  a p p r o a c h i n g 10 p e r c e n t .  also  sections  (labradorite-bytownite),  muscovite, b i o t i t e ,  tremolite,  lack  i d e n t i f i e d i n these  c o n t a i n e d bunched  limestone beds. and 17 f e e t  Sections  18 a n d 19  r e s p e c t i v e l y along the  Number 19 r e p r e s e n t s  the limestone.  specimens  a q u a r t z i t i c band  Number 28 was c o l l e c t e d i n t h e DD*  s e c t i o n o f the d r i f t 24 f e e t beyong t h e c r o s s - c u t . limestone  The  beds c o n t a i n i d i o b l a s t i c g r a i n s o f d i o p s i d e and  forsterite.  P y r r h o t i t e i s p r e s e n t i n minor amounts r e p l a c i n g  the c a r b o n a t e , and t o a s m a l l e r e x t e n t  the d i o p s i d e .  P o s i t i v e evidence i n support of replacement i s f o u n d i n s e c t i o n 28 where p y r r h o t i t e c o n t a i n s  i n c l u s i o n s of carbonate  most of w h i c h have the same o p t i c o r i e n t a t i o n .  Widespread  s e r p e n t i n i z a t i o n of the f o r s t e r i t e  and d i o p s i d e  grains  i n d i c a t e retrograde  S e c t i o n 19 i s composed  metamorphism.  c h i e f l y of q u a r t z , o r t h o c l a s e , untwinned a l b i t e  and twinned  oli<jo c/asc — ana/irsine  p l a g i o c l a s e of o l i g o o l a o o c n d o a i n o  composition.  amount o f m i c r o p e g m a t i t e was f o u n d . g r a i n s there a r e o p t i c a l l y suggesting  I n a few f e l d s p a r  c o n t i n u o u s embayments o f q u a r t z  r e p l a c e m e n t by the l a t t e r .  constituent also replaces  A minor  P y r r h o t i t e , a minor  the p l a g i o c l a s e .  Retrograde,  metamorphism i s i n d i c a t e d by s e r i c i t i z a t i o n of the f e l d s p a r . T h i n s e c t i o n s 2Cy and 21 were made from specimens c o l l e c t e d across cross-cut BB . 1  a quartzitic  a r e a , about 46 f e e t a l o n g the  These s e c t i o n s a r e composed l a r g e l y o f  d i o p s i d e , minor amounts o f o r t h o c l a s e , p l a g i o c l a s e , q u a r t z , t r e m o l i t e , a p a t i t e , sphene, p y r r h o t i t e and t r a c e s of s p h a l e r i t e . . No-mica o t h e r than s e r i e i t e ^ / was found i n these sections.  The s u l p h i d e s  r e p l a c e d i o p s i d e , f e l d s p a r s and  sphene. T h i n s e c t i o n s 23, 24 and 25 were made from specimens taken across  a pegmatitic  a r e a 10 f e e t wide a t the h e i g h t o f  24  5 f e e t , i n the c r o s s - c u t contact  BB .  Number 23 i s adjacent to a  1  of pegmatite w i t h massive s u l p h i d e s ,  from the  center  a contact  of the pegmatite, and  s e c t i o n 25 comes from  of pegmatite w i t h q u a r t z i t i c r o c k s .  contains, much o r t h o c l a s e , quartz and  albite  Number 23  (untwinned), andesine,  minor amounts of muscovite, p y r r h o t i t e ,  sphalerite.  The  the f e l d s p a r . feldspars  number 24 i s  sulphides  are a s s o c i a t e d  C h l o r i t i z a t i o n and  i s common.  S e c t i o n 24  w i t h and  under s t r e s s .  the It  quartz which commonly have Other minerals  i d e n t i f i e d are a p a t i t e , s i l l i m a n i t e , epidote,  shadows c o u l d be  replace  s e r i c i t i z a t i o n of  developed a m i c r o p e g m a t i t i c t e x t u r e .  Much of the  and  i s more complex than 23.  c o n s i s t s l a r g e l y of f e l d s p a r s and  pyrrhotite.  and  sphene  and  quartz shows s t r a i n shadows.  These  caused by s t r e s s a f t e r growth, or by  growth  Of p a r t i c u l a r i n t e r e s t i n t h i s s e c t i o n i s the  growth of s i l l i m a n i t e w i t h i n f a i r l y a c i d p l a g i o c l a s e , shown i n P l a t e 7.  This c o u l d be what Harker c a l l s  sillimanite".  "new  In h i s chapter on repeated metamorphism Harker  suggests t h a t s i l l i m a n i t e can be  expected i n the  highest  grade of thermal metamorphism f o l l o w i n g r e g i o n a l metamorphism. He  a l s o suggests that these extreme r e s u l t s are  i n rocks c l o s e to the "Winchell's  (1946  contact  p 201)  found  of a p l u t o n i c i n t r u s i v e .  explanation  s a t i s f a c t o r y i n t h i s case, he by  to be  i s thought to be  suggests a b s o r p t i o n  more  of AlgOg  i n t r u s i v e s from a d j a c e n t a r g i l l a c e o u s sediments.  The  abundant growth of f e l d s p a r s  i n these rocks i n d i c a t e a  p l e n t i f u l source of A 1 0  t  2  reaction '. 1  3  f  o  r  h  i  a  Apatite  25  o c c u p i e s from 5 to 10 p e r c e n t of the  section.  i s s i m i l a r to 24 i n m i n e r a l c o m p o s i t i o n . the q u a r t z c o n t a i n s  Section  In t h i s  25  section  r o u g h l y p a r a l l e l t r a i n s of i n c l u s i o n s ,  shown i n p l a t e 8, t h a t are c o n t i n u o u s a c r o s s two  o r more  q u a r t z g r a i n s w h i c h possess d i f f e r e n t o p t i c o r i e n t a t i o n s . H a r k e r (1939) suggests t h a t these f l u i d i n c l u s i o n s evidence of s t r e s s a f t e r growth of the  quartz.  shadows i n the q u a r t z of these s e c t i o n s  are  The  strain  must a l s o be  the  r e s u l t of s t r e s s a f t e r growth. In s e c t i o n 25 l e n t i c u l a r shreds of p y r r h o t i t e cut a c r o s s a f e l d s p a r g r a i n i n an en e c h e l o n f a s h i o n , as shown i n p l a t e 9. appears t o have r e p l a c e d  T h i s i s i n d i c a t e d by  been  an  s h r e d of an u n i d e n t i f i e d m i n e r a l a l o n g the edges  of the p y r r h o t i t e and the end  pyrrhotite  an e a r l i e r m i n e r a l w h i c h had  c u t t i n g a c r o s s the f e l d s p a r . occasional  The  a t one  end.  The  m i n e r a l fragment a t  of the p y r r h o t i t e i s thought t o be s i l l i m a n i t e  a l t h o u g h i t was  not  identified conclusively.  of s i l l i m a n i t e i n a d j o i n i n g f e l d s p a r g r a i n s t o the s u g g e s t i o n .  The  presence  lends  strength  I f the i d e n t i f i c a t i o n i s c o r r e c t , t h e n  i t would suggest a l a t e i n t r o d u c t i o n of p y r r h o t i t e s i n c e  in  t h i s case the s i l l i m a n i t e i s thought to have formed i n the i n t r u s i v e as the r e s u l t of a b s o r p t i o n argillaceous  from a d j a c e n t  sediments.  T h i n s e c t i o n s 30 and  31 come from specimens c o l l e c t e d  i n a l i m e s i l i c a t e band o v e r l y i n g the s e c t i o n of the d r i f t . diopside,  of Al^O^  The  l i m e s t o n e s i n the  mineral constituents  tremolite, basic plagioclase, a l b i t e ,  were apatite,  DD  1  26  sphene, p y r r h o t i t e ,  and s p h a l e r i t e .  These s e c t i o n s  offered  n o t h i n g new a n d s o need no f u r t h e r d i s c u s s i o n . T h i n s e c t i o n s 32 and 34 come f r o m adjacent Quartz  t o massive  a granitic  zone  s u l p h i d e s c l o s e t o t h e f a c e o f DD*.  and f e l d s p a r a r e t h e a b u n d a n t m i n e r a l s ^ m u c h  l a t t e r b e i n g untwinned Mi o r o g r a p h i c  o l i g o c l a s e - a n d e s i n e , and o r t h o c l a s e .  i n t e r g r o w t h s are. common, a n d i n s e c t i o n 34 b o t h  micropegmatite  a n d myrraekite  photomicrograph  occur, plate  10 i s a  o f m y r m e k i t e . As p o i n t e d o u t b y T y r r e l l (1929  p 94) myrmekite may i n d i c a t e pressure,  of the  such  development under  as m i g h t be e x p e c t e d  uniform  i n thermal  metamorphism.  Mineraiography A study the  o f r e p r e s e n t a t i v e p o l i s h e d s e c t i o n s made  specimens  sphalerite, amounts. grains,  appears  not found  and g a l e n a  pyrrhotite, i n decreasing  i n euhedral  to subhedral  t o have been i n t r o d u c e d f i r s t  Pyrrhotite  and g a l e n a .  encloses  s i n c e the individual  i n t u r n was i n t r o d u c e d b e f o r e t h e  Since the sphalerite  together "their r e l a t i v e  and galena  blebs  along cleavage  o r as r e p l a c e m e n t s  planes  and f r a c t u r e s .  along a bedding  occur  o f the I n some  as I n d i c a t e d i n s e c t i o n 16, t h e p y r r h o t i t e  have r e p l a c e d t h e s i l i c a t e s  were  ages a r e n o t known.  a l l of the p o l i s h e d s e c t i o n s the s u l p h i d e s  silicates  to  are present  which occurs  e i t h e r as i n t e r s t i t i a l  places,  that the s u l p h i d e s  r e p l a c e s and completely  grains.  sphalerite  In  pyrite  Pyrite,  pyrrhotite pyrite  indicated  from  appears  plane;  27  one boundary is very regular while the other i s i r r e g u l a r and poorly defined.  Polished sections 7 and 2,2 were made from  specimens of massive sulphide.  Number 7 represents a  sulphide lense i n a lime s i l i c a t e band, i t was  collected  about 5 feet east of the fracture mentioned above,,  lumber  22 comes from a massive sulphide zone l y i n g between the impure quartzite and pegmatite i n the cross-cut BB'.  These  sections show that pyrrhotite has taken the place of the silicates  to the almost complete exclusion of other sulphides.  In other sections where the pyrrhotite content is less than 30 percent, sphalerite is more abundant. In the petrographic discussion specimens 8, 9, 10 and 11 were described as having been collected along a moderately mineralized lime s i l i c a t e band that had been cut-by the most conspicuous fracture i n the tunnel. 3 feet east of the fracture, 9 was  Number 8 was  collected  taken lg- feet east of the  fracture, 10 i n the fracture zone, 11 was  collected 2 feet  west of the f r a c t u r e , end a f i f t h specimen number 12 collected 4 feet west of the fracture.  was  These specimens were  collected f o r the purpose of determining whether the fracture had any influence on the mineralization.  The  findings here support those of the petrographic a n a l y s i s . There i s an abrupt increase i n the amount of pyrrhotite, from about 10 percent i n number 8 to about 55 percent i n number 10 followed by just as rapid a decrease to section 12.  Sphalerite  did not increase noticeably^ at no time does i t exceed 5 percent of the section.  28  Metamorphism The geological reconnaissance i n the Slocan and Upper Arrow lakes area by Cairnes i n 1928,  together with the  present writer's laboratory investigations indicate at least two d i s t i n c t kinds of metamorphism.  This i s suggested by  the following evidence. (1)  In his discussion of the Precambrian rocks,  (1928  Cairnes  p 97A) includes the c r y s t a l l i n e schists that compose  a large part of the rocks found on the Big Ledge property. Further, the regional geology indicates that the Precambrian rocks of this area are on the outer edge of the Shuswap complex, a highly metamorphosed group of rocks. Metamorphism on such a broad scale i s classed as regional. (2)  On the Big Ledge property schistose and gneissic rocks,  containing abundant mica, are common.  In the mineralized  of  zone this schistose^gneissic structure Is not e s p e c i a l l y noticeable although a banding of the micas i s generally apparent.  Under the microscope i t was noted that i n these  micaceous bands there i s no p a r a l l e l i s m i n the orientation of the mica plates,  further, these bands are separated by  equidimensional minerals The  such as diopside and feldspars.  occurrence of rocks almost lacking f o l i a t i o n i n a region  i n which schists and gneisses  p r e v a i l , the predominance of "  equidimensional minerals, and the common occurrence of untwinned a l b i t e indicates a l a t e r period of thermal metamorphism that i s apparently  r e s t r i c t e d to the mineralized  29  zone.  A t h i r d kind of metamorphism ^'retrograde i s w  ?  suggested by the development of serpentine, c h l o r i t e , and s e r i e i t e from f o r s t e r i t e , diopside, tremolite, and feldspars.  30  ORIGIN On t h e  basis  investigation, m i g h t be  1.  The  of  an  what has  igneous  indicated for shape  of  defined borders  the  origin  the  observed  for  the  following  larger  indicate  been  in  this  sulphide  minerals  reasons.  pegmatitic  emplacement  bodies  later  with  than  their  the  well  regional  metamorphism.  2.  The  thermal  c o u l d be  best  pegmatitic 3. in  The the  e x p l a i n e d on the  occurrence lime  suggests  relatively  the  material.  to  the  poor i n  of  pyrite  the  sulphides  massive  to  The  of  rocks with  the  adjacent  rocks  that  the  intrusives.  If these  disseminated  to  associated solutions  m i n o r amounts of  apatite  lime  pegmatite,  l e a v i n g the  had a d i f f e r e n t  adjacent  solutions  the  the  with  pegmatite  minerals. .  and galena  hydrothermal  sulphides  finding  than  pyrrhotite  pegmatitic  these  sulphides, host  massive  the  the  of  01.,  and sphene,  with  origin  the  PO4,  amounts  than  They  favorable  carried, F.,  pyrrhotite,  pegmatite.  explained by penetration,along  sulphides,  silicate  association  bodies  adjacent  favorable  these  sphalerite,  abundance  basis  an i n t r o d u c t i o n of  seems u n l i k e l y  c o u l d be  lime  larger  rocks  r o c k a more  would migrate  It  of  silicate  pegmatitic  silicate  the  intrusives.  intrusives the  metamorphism of  beds^of  pegmatitic  besides Ti,  the  etc.,  approaching  the 10  31  percent, is  i n  supported  pegmatitic  along,  and  i n  of the  the  paper.  more  or  i n  i n  pegmatitic The  beds  i n  could  the  adjacent are  the  by,  of  the  would the  be  is  In  present  the  explain  the  Big  the  greater  equal  mentioned the  of  earlier  l e n t i c u l a r  bodies.  v i c i n i t y  a  i n  This  mineralization  fracture  sulphide  are  explained.  approximately  for  immediate  there  basis have  factors  of of  been  sediments  a  They  the  number  Ledge  sedimentary  concentrated  during  that  should  intrusives  of  these  would  regional be  more  might  also  origin. i n  be  The  these  beds  from  .metamorphism.  d i f f i c u l t  to  However  explain,  as:  (1)  The  association  with  the  pegmatitic  (2)  The  sulphide  fracture  is  the  which  have  had  no  (3)  The  high  larger  control  massive  sulphide  bodies  rock.  above.  associated  fracture,  containing  of  concentrations  mentioned  sulphides the  rocks  this  nature  apatite  account  cut  mineralization  sulphides  such  also  also  intrusives.  on  there  silicate  which  explained  the  could  that  F i n a l l y  abundant  areas  beds  fact  would  discontinuous  be  the  lime  This  and  this  by  and  amounts.  in  some  is  with later  over  apatite  If  the  content  disseminated  along  the the  and  adjacent  d i s t r i b u t i o n of regional  than  the  to  the  the  metamorphism^  metamorphism,  would  mineralization.  of  the  sulphides.  s i l i c a t e In  his  beds  report  Cairnes  32  states  that  apatite  occurs  elsewhere  w i t h i n the  o f t h e B i g L e d g e where no s u l p h i d e s a r e seem t o d i s c o u n t e n a n c e However t h e a b u n d a n c e almost rocks  t h i s m i n e r a l and i t s  e q u i v a l e n t amounts  for  This the  rock would  apatite.  presence  in  i n the p e g m a t i t i c and l i m e - s i l i c a t e  c e r t a i n l y suggests i n t r o d u c t i o n by hydrothermal s o l u t i o n s . No s a t i s f a c t o r y  explanation for  s u l p h i d e s was f o u n d . is  present.  a hydrothermal source of  country  associated  w i t h the  w o u l d be r e l a t e d the v i c i n i t y ,  It  is  thought  pegmatitic  t o one o f  p r o b a b l y the  the that  source  of  the  the m i n e r a l i z a t i o n  i n t r u s i v e s which i n turn  the b a t h o l i t h i c complexes Nelson pegmatite-gneiss  in  complex.  33  P l a t e 1,  Photograph showing p r e c i p i t o u s n o r t h slopes of the ridge on which the B i g Ledge i s l o c a t e d ,  P l a t e 2. Photomicrograph showing fragments of t r e m o l i t e ( with common o p t i c a r i e n t a t i o n i n s p h a l e r i t e . N i c o l s uncrossed M« X80  34  P l a t e 3.  White areas are i n c l u s i o n s of c a r b o n a t e , p o s s e s s i n g comrron o p t i c o r i e n t a t i o n i n t r e m o l i t e dark f i b r o u s areas are c i i l o r i t i c a l t e r a t i o n . N i c o l s uncrossed Mag xgo  P l a t e 4.  Complex t w i n n i n g of f e l d s p a r Nicols crossed Mag. x&O  35  P l a t e 5.  Broad t w i n laminae produced by mutual i n t e r f e r e n c e of growing f e l d s p a r g r a i n s . T a p e r i n g t w i n laminae produced by s t r e s s a f t e r growth. Nicols crossed Mag. X80  Plate 6.  Twin laminae bent by f r a c t u r e , d i s c o n t i n u o u s s p i n d l e shaped t w i n laminae produced by s t r e s s a f t e r fracturing. Nicols crossed Mag. X34  36  Plate 7 .  S i l l i m a n i t e c r y s t a l s growing i n a f e l d s p a r Nicols uncrossed Mag. X 80  P l a t e 8.  P a r a l l e l t r a i n s of f l u i d i n c l u s i o n s c r o s s i n g q u a r t z g r a i n s of d i f f e r e n t o r i e n t a t i o n , produced by s t r e s s a f t e r growth of the q u a r t z . Nicols uncrossed Me . X 80  grain.  37  Plate 9.  P l a t e 10.  L e n t i c u l a r g r a i n s of p y r r h o t i t e r e p l a c i n g an e a r l i e r mineral i n a feldspar grain. N i c o l s uncrossed Mag, X80  Myrmekite, p r o b a b l y f o r m e d as a r e s u l t o f  t h e r m a l metamorphism under u n i f o r m Nicols crossed X80  pressure  38  BIBLIOGRAPHY Cairnes, C E . (1928)  Geological Reconnaissance i n Slocan and Upper Arrow Lakes Area, Kootenay D i s t r i c t B.C. Geol. Surv. Canada, Sum. Rept.pt A  Cairnes, C E . and Gunning, H.C (1928)  Big Ledge (Consolidated) Property, Upper Arrow Lake, Kootenay D i s t r i c t , B . C . Geol. Surv. Canada, Sum. Rept. pt. A  Emmons, R.C Gates, R.M.  Plagioclase Twinning, B u l l e t i n of the Geological Society of America, Vol. 54, pp. 287-304.  and (1943)  Harker, A. (1939)  Metamorphism, Methusn & Co. London.  Rogers, A.P. and Kerr, P.F. (1942)  Optical Mineralogy, McGraw-Hill, New York.  T y r r e l l , G.W.  The.Principles of Petrology, Button & Co. New. York.  (1929)  Walker, J.P. Bancroft, M.P.(1929) Gunning H.C.  Lardeau Map-area, B.C. Geol. Surv. Canada, Mem. 161  

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