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The Seagull Creek batholith and its metamorphic aureole Gower, John Arthur 1952

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THE  SEAGULL CREEK'BATHOLITH AND I T S METAMORPHIC  AUREOLE  by  JOHN ARTHUR GOWER  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n t h e Department of GEOLOGY AND  We a c c e p t t h i s t h e s i s standard degree  required  from  GEOGRAPHY  as conforming t o t h e candidates f o r the  o f MASTER OF APPLIED SCIENCE.  Members o f t h e D e p a r t m e n t o f GEOLOGY AND THE  GEOGRAPHY  UNIVERSITY OF BRITISH COLUMBIA April,  1952.  Abstract  The  main f e a t u r e s of the  are d e s c r i b e d .  The  S e a g u l l creek  most n o t e w o r t h y o f t h e s e  i s the  dance o f b o r o n i n t h e g r a n i t e s t h e m s e l v e s and tact  aureole.  cavities  T h i s has  containing tourmaline,  m a l i n e and  axinite  ing  and  in  l e d to the  rocks,  v e i n s and  Laboratory s i m i l a r rocks 1.  2.  of the  liquid  caused the  i n the  toursurround-  borates  on  following conclusions: final  residual  magma.  e i t h e r gaseous or l i q u i d ,  formation  of  reference to l i t e r a t u r e  a major c o n s t i t u e n t of the  Segregations,  miarolitic  o f magnesium i r o n  s t u d i e s and  S e a g u l l creek  of  con-  deposit.  have l e d t o t h e  B o r o n was  liquid  iron  abun-  i n the  formation  disseminations  to the formation  a c o n t a c t metamorphic  formation  to the  batholith  of m i a r o l i t i c  from t h i s  cavities i n  final  the  granite. 3.  Fine grained  granite 4.  and  aplitic  are younger than  The  Cornwall,  rocks  are  the  similar  Seward p e n i n s u l a ,  phases of the  coarser grained  Seagull phase.  i n many r e s p e c t s t o t h o s e Alaska,  regions.  i  and  other  creek  of  t i n bearing  Table  of Contents Page  CHAPTER 1.  INTRODUCTION  1  General Statement  1  Location  2  Physical  Features  3  Drainage  3  Climate  3  Vegetation  4  CHAPTER 2.  GENERAL GEOLOGY OF THE AREA  5  Regional Setting  5  S e d i m e n t a r y and R e g i o n a l l y Intrusive  Metamorphosed  Rocks  Rocks  Cassiar Swift  Seagull  6  Batholith  River  5  6  D i o r i t e and G r a n o d i o r i t e  Creek B a t h o l i t h  7 7  Minor Intrusives  8  C o n t a c t Metamorphic Rocks  9  Structure  9  CHAPTER 3.  THE SEAGULL CREEK BATHOLITH AND I T S METAMORPHIC AUREOLE  The S e a g u l l Origin  Creek B a t h o l i t h  of the M i a r o l i t i c  Cavities  .The M e t a m o r p h i c A u r e o l e  11 11 16 23  Description  of the Aureole  23  Description  o f t h e Rock T y p e s  24  Mineralogy of the Aureole  25  The Contact Metamorphic Deposit CHAPTER 4 .  BORON METASOMATISM  i CHAPTER 5.  SPECTROGRAPHS AND X-RAY STUDIES  Tourmaline '  Borates  CHAPTER 6.  .  CONCLUSIONS  REFERENCES CITED  L i s t of  Plate I  Illustration  X - r a y powder photographs X909 L u d w i g i t e , M o r a v i c z a , Hungary X882 L u d w i g i t e , P h i l i p s b u r g , Montana  Plate II  X - r a y powder photographs X$#5 V o n s e n i t e ( = p a i g e i t e ) , C a l i f o r n i a X887 L u d w i g i t e , S e a g u l l c r e e k , w i t h f i b r o u s magnetite  Plate III  X - r a y powder photographs X883 P i n a k i o l i t e , Langban, Sweden X881 H u l s i t e , Brooks M o u n t a i n , Seward, Alaska  P l a t e IV  X - r a y powder photographs X886 Warwickite, E d e n v i l l e , New York X879 Unknown b o r a t e , D r i l l Core No. 1  Plate V  X - r a y powder photographs X8&4 Unknown b o r a t e , France X890 Magnetite  P l a t e VI  St.  C h r i s t o p h e Mine,  The S e a g u l l creek b a t h o l i t h from the n o r t h e a s t The a m p h i b o l i t e x e n o l i t h south of.Camp IS  iii  Figure  1.  Tourmaline  Figure  2.  G n e i s s i c s t r u c t u r e bending cavities  Table 1.  i n granite  Distribution  56 into  miarolitic  of minerals, S e a g u l l creek  19  area  In  pocket  Table  2.  Spectrographs  analyses of tourmaline  39  Table  3»  Spectrographic  analyses of borates  45  Map  S e a g u l l c r e e k a r e a , g e o l o g i c a l map  In  pocket  THE SEAGULL GREEK BATHOLITH AND ITS 'METAMORPHIC AUREOLE  CHAPTER 1 INTRODUCTION  General  Statement  T h i s r e p o r t i s based on f i e l d work c a r r i e d out i n the summer of 1951  f o r the G e o l o g i c a l  under W.H. P o o l e , p a r t y c h i e f .  Survey of Canada  Mapping, on a s c a l e  of  f o u r m i l e s t o one i n c h , was commenced on the Wolf l a k e s h e e t , a 5000-square m i l e quadrangle bounded b y . t h e  60th  and 6 l s t p a r a l l e l s and the 130th and 132nd m e r i d i a n s . The a r e a d e s c r i b e d i n t h i s r e p o r t i s i n the s o u t h - c e n t r a l p a r t of the s h e e t . i s the S e a g u l l creek b a t h o l i t h , i n texture,  I t s most prominent noteworthy f o r i t s  f o r i t s abundant m i a r o l i t i c c a v i t i e s , 1  feature  variations for  the  2 h i g h content of boron w i t h i n the b a t h o l i t h and i n the metamorphic a u r e o l e , and f o r an unusual m i n e r a l assemblage r e l a t e d contact  raetamorphic  in a  deposit.  These were the subject  of c o n s i d e r a b l e laboratory-  i n v e s t i g a t i o n and the r e s u l t s form the body o f t h i s G r a t e f u l acknowledgement  report.  i s made t o W.H. Poole  of the G e o l o g i c a l Survey of Canada f o r p e r m i s s i o n t o use m a t e r i a l c o l l e c t e d d u r i n g the 1951  f i e l d season.  Thanks are  a l s o due to D r s . H . C . Gunning, W.H. White, R.M. Thompson, and K . C . McTaggart, of the Department o f Geology and Geography o f the U n i v e r s i t y o f B r i t i s h Columbia, f o r  advice  on the p r e p a r a t i o n o f the r e p o r t and a i d i n d e t e r m i n i n g the minerals,  and t o M r . J . A . Donnan, L a b o r a t o r y T e c h n i c i a n ,  who a s s i s t e d i n the p r e p a r a t i o n of t h i n - s e c t i o n s and polished  sections.  Location  The S e a g u l l and 60°15 f  creek area l i e s between l a t i t u d e s  North and l o n g i t u d e s 131° and 131°30'  West.  Alaska highway cuts a c r o s s the southeastern c o r n e r of  60° The  the  area from mileage 726.to 733.5 measured from Dawson Creek. Swift  r i v e r C o n t r o l S t a t i o n at m i l e post 733  settlement  i n the a r e a .  i s the o n l y  An emergency a i r s t r i p i s  two m i l e s n o r t h of the highway at m i l e post 722,  located just  east  of the a r e a . The highway i s served by B r i t i s h Yukon N a v i g a t i o n  buses t h a t run twice weekly between Whitehorse and Dawson Creek.  Physical  The  Features  area marks t h e n o r t h e r n e x t e n s i o n o f the  C a s s i a r mountain ranges which have a core o f g r a n i t i c r o c k s , the C a s s i a r b a t h o l i t h  (Bostock, 1948).  It i s essentially a  d i s s e c t e d p l a t e a u with an e l e v a t i o n o f over 5|000 f e e t i n which the r i v e r v a l l e y s a r e entrenched  about 3,000 f e e t below  the p l a t e a u s u r f a c e . G l a c i a l e r r a t i c s up t o 6,500 f e e t e l e v a t i o n cate t h a t the e n t i r e r e g i o n has been g l a c i a t e d .  indi-  U-shaped  v a l l e y s and h e a v i l y d r i f t - c o v e r e d v a l l e y f l o o r s a r e t h e r u l e .  Drainage  The area i s d r a i n e d by t r i b u t a r i e s o f the T e s l i n r i v e r , the main ones being the Smart, the S w i f t and t h e Morley  rivers.  The Rancheria r i v e r , a t r i b u t a r y o f t h e  L i a r d , r i s e s near the n o r t h e r n edge o f the area and flows i n p a r t through the same v a l l e y as the S w i f t r i v e r . creek, a t r i b u t a r y o f the S w i f t r i v e r ,  Seagull  r i s e s i n the c e n t r e  o f the area and flows almost due south t o j o i n the S w i f t a t m i l e post 733 on t h e A l a s k a highway.  Climate  The  c l i m a t e d u r i n g the 1951 f i e l d  season was m i l d  and d r y .  F i e l d work was c a r r i e d on from June 15  September 7,  d u r i n g which time v e r y l i t t l e  Night f r o s t s were common a f t e r August  to  rain f e l l .  15.  Vegetation  Timber l i n e i s about 4>500 f e e t ,  below which  s m a l l c o n i f e r s and dwarf b i r c h are the most abundant vegetation.  Horse f e e d i s p l e n t i f u l , and except i n burned over  c o u n t r y , t r a i l s do not have t o be  cut.  CHAPTER 2 GENERAL GEOLOGY OF THE AREA  Regional  Cassiar batholithic form  the core of the area.  Setting  rocks, t r e n d i n g  They o c c u p y a n a r r o w  s e v e r a l h u n d r e d m i l e s l o n g and a r e p r o b a b l y o f t h e Omineca b a t h o l i t h i c Paleozoic tic  from  Teslin  these  lake north.  rocks, probably  basalt  valleys.  o l d e r than  occur i n b e l t s along t h e i r  belt.  sedimentary  Tertiary  some o f t h e m a i n r i v e r  basic  a continuation  r o c k s , metamorphosed near  rocks o v e r l i e  the graniMesozoic  r o c k s on t h e west, outcrops  those sist  oldest  locally  Intrusions of ultra-  the Cassiar batholiths,  e a s t e r n and western  flanks.  S e d i m e n t a r y and R e g i o n a l l y M e t a m o r p h o s e d  The  belt  rocks to the southeast.  rocks, l i e along the f l a n k s of t h i s  volcanic  in  sedimentary  northwest,  Rocks  r o c k s i n t h e a r e a a r e b e l i e v e d t o be  i n c o n t a c t w i t h t h e m a i n C a s s i a r b a t h o l i t h and o f , from  con-  t h e c o n t a c t westwards, q u a r t z - f e l d s p a r -  biotite  gneiss, quartz-biotite  schist,  and q u a r t z - c h l o r i t e  by L o r d  (1944)  schist,  schist.  quartz-sericite  T h e s e r o c k s were mapped  as a separate group because o f t h e i r  higher  d e g r e e o f metamorphism t h a n t h e r o c k s t o t h e w e s t , and b e c a u s e  o f a p o s s i b i l i t y t h a t the c h l o r i t e s c h i s t s may have been d e r i v e d from o l d e r v o l c a n i c r o c k s . i n 1951  to support t h i s  No evidence was seen  possibility.  I n apparent s t r u c t u r a l conformity above these r o c k s l i e , i n ascending o r d e r , q u a r t z i t i e argillaceous quartzite, quartzite, youngest  encrinal limestone,  argillaceous  c o r a l l i m e s t o n e , and f i n a l l y b l a c k c h e r t ,  the  sedimentary rock o f the a r e a . It  estimates  conglomerate,  i s p o s s i b l e t o make o n l y the roughest  of the t h i c k n e s s e s  of these r o c k s .  of  At most o f  the o u t c r o p s , e s p e c i a l l y those p o o r l y exposed,  it  was  i m p o s s i b l e t o determine the bedding with c e r t a i n t y .  The  q u a r t z i t e g i v e s the most r e l i a b l e a t t i t u d e s ,  bedding  f o r the  i s u s u a l l y o b l i t e r a t e d i n the s c h i s t s and g n e i s s e s , limestone i s so complexly f o l d e d t h a t of l i t t l e  attitudes  and the  in it  are  use. Two f o s s i l i f e r o u s beds were mapped.  e n c r i n a l limestone o f unknown age.  One i s  The o t h e r i s mainly  c o r a l limestone of Upper M i s s i s s i p p i a n age-*-.  These beds are  each about 200 f e e t t h i c k i n a sedimentary s u c c e s s i o n o f 5,000 t o 10,000 f e e t .  Intrusive  Rocks  Gassiar Batholith A l a r g e body of i n t r u s i v e r o c k s , mapped by L o r d  1.  D r . P e t e r Harker, v i a W.H. P o o l e , p e r s o n a l communication.  (1944) as a p o s s i b l e extension l i e s t o the e a s t o f the map east corner.  The  area and  c u t s a c r o s s the  p r i n c i p a l rock, a c c o r d i n g  b i o t i t e - q u a r t z monzonite. not  o f the C a s s i a r b a t h o l i t h ,  to L o r d ,  northis a  T h i n - s e c t i o n s of t h i s rock were  s t u d i e d , but hand specimens c o l l e c t e d i n 1951  contain  approximately: 30% 30% 30% 10$  Pink f e l d s p a r ( o r t h o c l a s e and/or m i c r o c l i n e ) White f e l d s p a r ( p l a g i o c l a s e ) Quartz B i o t i t e and-Muscovite Pegmatitic  phases are r i c h e r i n potash f e l d s p a r and musco-  v i t e than the quartz monzonite, and and  small red  tourmaline  garnets.  S w i f t R i v e r D i o r i t e and Two  contain black  Granodiorite  dome-shaped mountains on o p p o s i t e  sides of  S w i f t r i v e r near Camp 11 are composed c h i e f l y o f granod i o r i t e with a d i o r i t i c  envelope.  i n t r u s i v e are about a mile the two  phases, estimated  The  square.  The  exposed p a r t s of  the  compositions of ,  from hand specimens, a r e :  Diorite Feldspar, l a r g e l y a l t e r e d to s e r i c i t e Hornblende B i o t i t e and C h l o r i t e Quartz G r a n o d i o r i t e (or Quartz D i o r i t e ) Feldspar Hornblende Biotite Quartz  1+0% 50% 8% 2%  10% 10%  S e a g u l l Creek B a t h o l i t h The  S e a g u l l creek b a t h o l i t h , at l e a s t t e n  miles  l o n g and up t o seven m i l e s wide, p a r t of the a r e a .  i s exposed i n the  Small exposures  the n o r t h and n o r t h e a s t  of s i m i l a r rock l i e  of the main body.  fresh looking.  i n a few p l a c e s , Its  and t h i n - s e c t i o n s ,  is  granite,  but otherwise  hard and  average c o m p o s i t i o n , from hand specimens is  Quartz Potash f e l d s p a r Plagioclase (An e) Biotite 2  J  The t e x t u r e ,  to  The b a t h o l i t h  composed p r i n c i p a l l y o f c o a r s e - g r a i n e d massive deeply weathered  central  structure,  1+0% 35% 15% 10%  and other f e a t u r e s  w i l l be d e s c r i b e d  i n Chapter 3 .  Minor  Intrusives S e v e r a l dykes and s i l l s were mapped.  p o s i t i o n ranges from p e r i d o t i t e ,  T h e i r com-  through a n d e s i t e ,  to  Most o f them are a s s o c i a t e d w i t h the main C a s s i a r but two,  c u t t i n g a m p h i b o l i t e near Camp 18,  associated  with the S e a g u l l  are  creek b a t h o l i t h .  batholith  apparently One i s an  altered peridotite,  composed of o l i v i n e ,  t i n e and c h r y s o t i l e  a s b e s t o s , w i t h minor magnetite.  o t h e r i s r h y o l i t e with g l a s s y b o r d e r s . f e e t wide,  rhyolite  enstatite,  The dyke, A  serpenThe  about  four  i s composed o f a white p o r c e l a i n - l i k e i n t e r i o r  and green o b s i d i a n margins a few inches t h i c k . s e c t i o n of the o b s i d i a n (No. 108) e r a l s o c c u r r i n g as p h e n o c r y s t s . l a t h l i k e with i n c l i n e d e x t i n c t i o n  A thin-  shows shreds of two m i n One i s c o l o u r l e s s and (probably  plagioclase).  The other i s pale green, with low b i r e f r i n g e n c e ,  straight  extinction,  and probably b i a x i a l .  I t may be c h l o r i t e  A  placing biotite  as i t appears t o have h i g h e r r e l i e f and  birefringence  than pure c h l o r i t e .  i n t e r i o r part  (No. 109) c o n t a i n s phenocrysts  plagioclase,  biotite  fine  A t h i n - s e c t i o n of of  the  quartz,  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 a  s m a l l g r a i n of sphene. i s extremely  re-  The ground mass i n both  specimens  grained.  Contact Metamorphic Rocks  Contact metamorphic rocks outcrop i n an i r r e g u l a r aureole  surrounding the S e a g u l l  Swift r i v e r g r a n o d i o r i t e . crystalline  creek b a t h o l i t h and the  Hornfels, amphibolite,  and  limestone are the most abundant rock t y p e s .  c o n t a c t metamorphic i r o n d e p o s i t  l i e s w i t h i n the  on the south f o r k of Swift r i v e r .  A  aureole  The rocks and t h i s  d e p o s i t , w i l l be d e s c r i b e d i n Chapter 3 .  Structure  L o r d (1944i p . 15)  s t a t e s t h a t the  sedimentary  r o c k s o f t h i s a r e a probably occupy a major s y n c l i n e trends northwesterly.  n  that  T h e s t r a t a w i t h i n the c e n t r a l  part  o f t h i s major s y n c l i n e t r e n d i n many d i r e c t i o n s and probably form s e v e r a l s m a l l e r f o l d s ,  the axes of which  p o s s i b l y t r e n d about north-northwest  and l i e  several  miles  apart." On the B r i t i s h Columbia-Yukon boundary,  j u s t east  of P a r t r i d g e c r e e k ,  approximately  crops mapped by L o r d as "Group was observed.  i n the centre o f the , a major s y n c l i n a l  The rocks f o r m i l e s on both s i d e s  g e n e r a l l y g e n t l y toward t h i s a x i s , somewhat c o n t o r t e d near the  the  answer.  states,  axis.  limbs can be s a f e l y  before  and s t r a t i g r a p h i c  the  correlated.  F o s s i l h o r i z o n s are probably numerous, however, detailed collections  axis  dip  but a r e , as Lord  A g r e a t d e a l more work i s necessary rocks on the o p p o s i t e  out-  and c a r e f u l  s t u d i e s may p r o v i d e  CHAPTER 3 THE SEAGULL CREEK BATHOLITH AND ITS METAMORPHIC AUREOLE  The S e a g u l l Creek B a t h o l i t h  The g r a n i t e of the S e a g u l l creek b a t h o l i t h h i b i t s two d i s t i n c t t e x t u r a l phases, pegmatitic,  the o t h e r f i n e t o ,  ex-  one coarse t o almost  i n some c a s e s , a p l i t i c .  The  coarse g r a n i t e forms about 90% of the b a t h o l i t h o u t c r o p s . It  i s remarkably u n i f o r m ,  specimens from w i d e l y  separated  l o c a l i t i e s being p r a c t i c a l l y i d e n t i c a l i n c o l o u r , and c o m p o s i t i o n .  The f e l d s p a r c r y s t a l s ,  texture  about 5 mm. d i a m e t e r ,  -are cream c o l o u r e d , and show abundant c a r l s b a d t w i n n i n g . The quartz g r a i n s are a n h e d r a l , g e n e r a l l y feldspar crystals,  s m a l l e r than the  and have a f r o s t e d appearance.  Except  i n the i n s t a n c e s mentioned below they are c o l o u r l e s s , or l i g h t  white  grey. The f i n e - t e x t u r e d  phase o f the g r a n i t e i s composed  o f the same m i n e r a l s as the coarse but the average g r a i n s i z e i s l e s s than 1 mm., except f o r o c c a s i o n a l o f quartz and f e l d s p a r up to 5 mm. diameter.  phenocrysts Most of  the  f i n e - t e x t u r e d g r a n i t e forms l a r g e i r r e g u l a r bodies but some of i t  occurs i n dykes r a n g i n g i n width from a few i n c h e s  t e n s of f e e t .  These dykes are probably t r u e a p l i t e s .  rock has a sugary t e x t u r e , feldspar,  and i s composed of l i g h t  c o l o u r l e s s q u a r t z , and a l i t t l e  biotite.  to  The  grey The f i n e -  grained granite  i s s p o r a d i c a l l y d i s t r i b u t e d , but seems t o  be more abundant near the margins o f the b a t h o l i t h .  Large  masses o f i t outcrop i n the canyon of the south f o r k o f Swift r i v e r (Specimen 51), large xenolith Its  and j u s t t o the n o r t h o f  (see map) south of Camp 18  (Specimen  c o m p o s i t i o n , estimated from hand specimens,  s e c t i o n 119, ,.- \  the 119).  and t h i n -  is: Quartz Potash F e l d s p a r P l a g i o c l a s e (Ang) Biotite Fluorite ) Topaz (?) \ I r o n ores J  50$ 35$ 10$ 4$ 1$  A p l i t e dykes outcrop on the r i d g e near the n o r t h boundary o f the main exposure o f the b a t h o l i t h  (Specimen 61),  near the e a s t e r n boundary (Specimens 69,  70).  average c o m p o s i t i o n , from t h i n - s e c t i o n s ,  is:  Quartz Potash F e l d s p a r P l a g i o c l a s e (Ang) Biotite \ Tourmaline J Fluorite ) Sphene \ Apatite ( I r o n ores / Two i n c l u s i o n s of q u a r t z i t e  60$ 25$ 10$ 5$ <1$  (see map).  The bedding has  been preserved and the rock shows no s i g n s o f  mentioned p r e v i o u s l y ,  Their  were mapped, i n both cases near  the margin o f the main exposure  o t h e r than b l e a c h i n g .  and  The l a r g e a m p h i b o l i t e  alteration xenolith,  w i l l be d e s c r i b e d l a t e r i n t h i s  Chapter. The S e a g u l l creek b a t h o l i t h i s c h a r a c t e r i z e d by  an abundance of m i a r o l i t i c cavities. is  sporadic.  Their distribution  They are most abundant i n a c i r q u e near the  c e n t r e o f the b a t h o l i t h (Specimen 62) where f o r  several  hundred f e e t of exposure they are o n l y a few f e e t  apart  and where almost every boulder on the t a l u s slope below the outcrop c o n t a i n s one o r more c a v i t i e s  (see F i g .  1).  They are a l s o abundant near the e a s t e r n boundary o f  the  main exposure near the a p l i t e dykes mentioned p r e v i o u s l y . Very few were seen i n the canyon of the south fork of Swift  river. The average s i z e o f the m i a r o l i t i c c a v i t i e s  is  about f o u r inches i n diameter, but some were seen up to a foot across. (Fig. 1).  T h e i r shapes range from s p h e r i c a l to  elongate  G e n e r a l l y speaking the l a r g e r ones tend t o a  less-perfect  s p h e r i c a l form, p o s s i b l y due to the f u s i o n o f  two or more of them d u r i n g t h e i r f o r m a t i o n . The m i a r o l i t i c c a v i t i e s  are l i n e d with  o f quartz and t o u r m a l i n e , and l o c a l l y f l u o r i t e . crystals,  about an i n c h i n l e n g t h ,  of the surrounding g r a n i t e , or white. specimens.  are,  crystals The quartz  i n contrast to  those  smoky r a t h e r than c o l o u r l e s s  Rhombohedral t e r m i n a t i o n s were noted i n many Black t o u r m a l i n e , i n p r i s m a t i c c r y s t a l s  about  an i n c h l o n g , has grown r a d i a l l y inwards from the w a l l s o f the c a v i t i e s .  The bases of both the quartz and tourmaline  c r y s t a l s are intergrown with the q u a r t z and the surrounding g r a n i t e .  feldspar of  Each o f the c a v i t i e s  i s surrounded  14.  by a dark grey zone up to s i x inches t h i c k c a r r y i n g abundant t o u r m a l i n e .  B i o t i t e i s l a c k i n g i n such zones and  f e l d s p a r shows replacement  by t o u r m a l i n e .  A partly  replaced plagioclase c r y s t a l i n a t h i n - s e c t i o n of t h i s material' has a composition o f Ang and minor topaz  (Specimen 6 2 ) .  Fluorite  (?) were seen i n the t h i n - s e c t i o n .  I n the a p l i t e dykes, and to a ' l e s s e r extent i n the c o a r s e r - g r a i n e d g r a n i t e , dark grey s p h e r i c a l masses w i t h no c e n t r a l c a v i t y occur (see F i g . 1),  which c o n t a i n  the same m i n e r a l assemblage as the zones around the cavities.' " 1  These masses range i n s i z e from one i n c h to  s i x i n c h e s diameter.  The dark grey c o l o u r i s here a l s o  due to tourmaline which c o n s t i t u t e s about 10$ The  :  of the mass.  l i g h t grey f i n e - g r a i n e d g r a n i t e a l s o c o n t a i n s tourmaline  but commonly o n l y one or two p e r c e n t .  Some b i o t i t e i s p r e -  sent, corroded and p a r t i a l l y r e p l a c e d by t o u r m a l i n e . granophyric i n t e r g r o w t h s are common i n a l l of the  Micro-  fine-  grained g r a n i t e . The tourmaline of the g r a n i t e i s probably c l o s e to s c h o r l i t e i n composition i n Chapter  5)«  (see s p e c t r o g r a p h s  analyses  In t h i n - s e c t i o n most of i t i s s t r o n g l y  p l e o c h r o i c , from p a l e blue to dark g r e e n i s h - b l u e , but some from p a l e y e l l o w t o g r e e n i s h - y e l l o w .  The  refractive  i n d i c e s , measured w i t h monochromatic l i g h t and an o i l o f known r e f r a c t i v e index, are e = 1.638, w - I . 6 6 5 .  1.  These  A p l i t e s c o n t a i n i n g s i m i l a r masses o f tourmaline are "puddingstone" by F l e t t (Ussher, e t a l , 1909).  called  fit  data f o r s c h o r l i t e , g i v e n by W i n c h e l l At one l o c a l i t y  (1951).  (Specimen 104a) the g r a n i t e has  a r u s t c o l o u r e d weathered s u r f a c e .  Investigation  an abundance o f t i n y i r r e g u l a r vugs c o n t a i n i n g c r y s t a l s of a r s e n o p y r i t e .  revealed  microscopic  Disseminated i n t e r s t i t i a l  maline i s a l s o abundant i n t h i s There can be l i t t l e  tour-  rock.  doubt t h a t the f i n e - t e x t u r e d  g r a n i t e i s younger than t h e coarse.  The f i e l d r e l a t i o n s h i p s ,  as i l l u s t r a t e d i n F i g . 1, show the c r o s s - c u t t i n g r e l a t i o n s h i p o f the a p l i t e s t o t h e c o a r s e - g r a i n e d  granites.  Con-  t r i b u t i n g evidence, brought out by l a b o r a t o r y study, i s t h a t the tourmaline and f l u o r i t e content i s much h i g h e r f i n e - t e x t u r e d phase than i n the coarse,  i n the  and t h a t t h e compo-  s i t i o n o f t h e p l a g i o c l a s e i s more s o d i c i n the f i n e .  Ghosh  (1934)>,discussing the r e l a t i o n s h i p s o f f i n e - and coarset e x t u r e d phases o f t h e C a r n m e n e l l i s g r a n i t e , concludes t h a t the f i n e - t e x t u r e d g r a n i t e c u t s t h e coarse.  He envisages  a s e m i s o l i d cover o f t h e e a r l i e r phase being cracked  by t h e  f o r c e o f i n t r u s i o n o f the l a t e r phase, the f i s s u r e s being immediately s e a l e d by i n j e c t i o n s o f magma. Fine-grained  g r a n i t e s t h a t occur as dykes i n t h e  Dartmoor g r a n i t e a r e d e s c r i b e d by F l e t t  (Reid, e t a l , 1912).  "They a r e l a t e r than the coarse g r a n i t e s but belong undoubtedl y t o t h e same magma.  U s u a l l y p a l e grey i n c o l o u r they range  i n t e x t u r e from c r y p t o c r y s t a l l i n e t o f a i r l y  coarse-grained.  As a r u l e they c o n t a i n l e s s b i o t i t e and more tourmaline than the  coarse g r a n i t e .  On the whole they are more a c i d i n  c h a r a c t e r than the main g r a n i t e and c o n t a i n l e s s clase  and more a l k a l i  feldspar.?  oligo-  1  O r i g i n of the M i a r o l i t i c  Cavities  The f o l l o w i n g d e f i n i t i o n i s g i v e n by Johannsen  (1939) of the word m i a r o l i t i c .  " M i a r o l i t i c (after  I t a l i a n word m i a r o l o , a l o c a l name f o r a v a r i e t y  an  of  granite)  used by Rosenbusch as a term t o d e s c r i b e the t e x t u r e c e r t a i n g r a n i t e s between whose c o n s t i t u e n t s angular c a v i t i e s constituents  i n t o which small c r y s t a l s  project."  Greek, miaros=stained, Miarolitic  of  t h e r e are s m a l l o f the  different  The word may be o r i g i n a l l y from the and l i t h o s =  cavities  stone.  are common i n some  but the s i z e and type o c c u r r i n g i n the S e a g u l l  granites  creek  granite  are r a t h e r u n u s u a l . Of the g e o l o g i c a l  r e p o r t s on areas adjacent  the Wolf lake area o n l y two mention m i a r o l i t i c Watson and Mathews  (1944> p .  to  cavities.  2 6 ) mapped a s m a l l stock  of  g r a p h i c and m i a r o l i t i c g r a n i t e i n the T u y a - T e s l i n a r e a , B.C.,  composed o f pink f e l d s p a r and quartz and c o n t a i n i n g  "miarolitic ....  cavities  which range from | to 5" i n diameter  l i n e d with w e l l formed c r y s t a l s  i n some cases  fluorite."  Fyles quartz g r a n i t e s cavities  of q u a r t z , f e l d s p a r and  (1950, p . 53) s t a t e s t h a t c e r t a i n smokyi n the Whitehorse area c o n t a i n m i a r o l i t i c  from 1 i n c h diameter to m i c r o s c o p i c f i l l e d by  17. b l a c k quartz, orange f e l d s p a r , f l u o r i t e and l o c a l l y an unknown green m i n e r a l . F u r t h e r a f i e l d Watson (1902, p. 186), d e s c r i b i n g tourmaline "bunches" i n the Stone mountain g r a n i t e o f Georgia, notes an "abundant occurrence o f s m a l l areas o f aggregated  b l a c k tourmaline c r y s t a l s .  Hardly a b l o c k o f  q u a r r i e d stone does not show a few a r e a s .  The m i n e r a l i s  not a c h a r a c t e r i z i n g a c c e s s o r y but more a f t e r the order o f s e g r e g a t i o n s i n b i o t i t e - b e a r i n g muscovite  g r a n i t e ... [ i t ]  r a r e l y occurs i n i s o l a t e d o r s i n g l e c r y s t a l s i n the g r a n i t e proper but n e a r l y always as r a d i a t i n g and roughly  parallel  groups which occupy the c e n t r e s o f p e r f e c t l y white areas o f q u a r t z and f e l d s p a r from which ... muscovite have been  and b i o t i t e  excluded." These white areas "vary i n s i z e from a f r a c t i o n  to s e v e r a l i n c h e s diameter,  i n shape from oblong,  r e c t a n g u l a r to complete s p h e r i c a l or c i r c u l a r  irregularly  outlines."  The t o u r m a l i n e occurs i n " s l e n d e r p r i s m a t i c forms v a r y i n g from a f r a c t i o n t o s e v e r a l m i l l i m e t e r s i n c r o s s s e c t i o n without t e r m i n a l f a c e s . . . [ i s ]  j e t b l a c k i n c o l o u r and i n  every case examined c o n s i d e r a b l y f r a c t u r e d . " Watson noted "no tendency  t o g r a d i n g o r merging  o f the c o l o u r o f the white mass i n t o the g r a n i t e " and saw "no  d i f f e r e n c e i n t e x t u r e and s i z e o f component g r a i n s from  that of granite."  In t h i n - s e c t i o n s he observed  that " i n  some cases tourmaline i s c o n f i n e d t o f e l d s p a r i n d i v i d u a l s , i n others i t cuts w e l l i n t o q u a r t z and f e l d s p a r g r a i n s i n  such  a way  as t o c l e a r l y  indicate  H i s c o n c l u s i o n was resulted acting  from  on  fumeroles  "the t o u r m a l i n e  h i g h l y charged  f e l d s p a r and  mica."  The  and  textural  i t s subsequent  age  has  been s t u d i e d by U s s h e r ,  the g r a n i t e s t a r t e d biotite out.  and  et a l  crystallizing  continued t i l l  c l a s e and  enclosing idiomorphic albite."  with boric  have acid,  tourmaline  St. Austell granites  (1909). at the  Tourmaline same t i m e  o r t h o c l a s e and  " I t i s n o t uncommon t o f i n d  tourmaline  areas  relationships of  t o o t h e r m i n e r a l s i n t h e Bodmin and  formation."  quartz  in  as  separated  s h a p e l e s s masses o f crystals  of quartz,  Z o n a l bands i n t o u r m a l i n e  ortho-  indicate  i  idiomorphic  crystals  a t the  a c o n s i d e r a b l e p a r t o f the  start  of c r y s t a l l i z a t i o n  r o c k was  still  liquid.  when  The  o u t e r z o n e s become p r o g r e s s i v e l y more and more  irregular.  In s c h o r l rocks tourmaline  part  1  the tourmaline  in granites i s  (1937)  Gallagher in  the magnetite  c a v i t i e s are is in,  1'  x 3'  and  but  perceptibly  i n t o the  line  distributed.  albite  cavities  York.  They are l i n e d  e n c l o s i n g w a l l rock The  cavities  size  to  crawl  with im-  s t r u c t u r e without  are  (Abc^), quartz - r a r e l y  and ^smoky w i t h f r o s t e d  The  T h e i r average  l o n g , t h e b a s e s o f w h i c h merge  of demarcation.  orthoclase, clear  d e s c r i b e s the m i a r o l i t i c  s m a l l o n e s a r e uncommon. to 1 foot  of  primary.  some a r e l a r g e enough f o r a man  c r y s t a l s up  any  but  d e p o s i t s a t L y o n m o u n t a i n , New  sporadically  x 4'  replaces biotite  s u r f a c e s -, and  composed i n good  of crystals,  hastingsite,  in  c r y s t a l s up t o 1 f o o t l o n g with t h e average a few c e n t i meters, and a s b e s t i f o r m amphibole, a white, wet, mushy mass f i l l e d  with g r a i n s o f o t h e r  minerals.  In d i s c u s s i n g the o r i g i n o f these  cavities  G a l l a g h e r mentions t h e f a c t t h a t the c a v i t i e s must have formed under h i g h pressure because when a d r i l l hole penet r a t e s a c a v i t y , water shoots 20 t o 35 f e e t out of the h o l e . He does not t h i n k they a r e s o l u t i o n c a v i t i e s because t h e r e i s no means o f e x i t o r entry o f s o l u t i o n s .  The c a v i t i e s  do not t r u n c a t e s t r u c t u r e s i n the e n c l o s i n g r o c k .  Gneissic  s t r u c t u r e s bend around the c a v i t i e s .  Figure  2  G a l l a g h e r ' s diagram ( F i g . 2) shows banding bending  inward towards a c a v i t y .  At a time when the g n e i s s  was s t i l l a mobile mass some m a t e r i a l , probably gas, moved l a t e r a l l y under the i n f l u e n c e o f d i f f e r e n t i a l f o r c e and merged with the m a t e r i a l f i l l i n g suggests  the c a v i t y .  This  case  (to Gallagher):  1. The m a t e r i a l f i l l i n g  the c a v i t y was a g a s .  2. The gas was mobile w i t h i n the magma i n masses l i k e  20. bubbles. 3. There was a tendency f o r gas t o c o l l e c t  i n major  bubbles. 4. The g n e i s s i c  s t r u c t u r e was i n e x i s t e n c e  before  the  magma s o l i d i f i e d . 5. The gas p r e s s u r e was s u f f i c i e n t open a g a i n s t  to h o l d the  l o a d pressure from above and a g a i n s t  cavities forces  of i n t r u s i o n . 6.  The s t a b i l i t y  7.  Its  of gas i n the magma was low.  power t o r e a c t c h e m i c a l l y with o t h e r  constituents  o f the magma must have been low. Since g n e i s s i c  s t r u c t u r e s were not observed i n  the S e a g u l l creek b a t h o l i t h , G a l l a g h e r ' s i n f e r e n c e s be a p p l i e d h e r e .  cannot  However, c e r t a i n s i m i l a r i t i e s between  the two occurrences are seen, namely, the d i s t r i b u t i o n of the c a v i t i e s ,  t h e i r mode of occurrence and the r e l a t i o n s h i p  o f the c r y s t a l s  l i n i n g the i n t e r i o r t o those o f the  enclosing  rock. At l e a s t the c a v i t i e s . inclusions.  t h r e e modes of o r i g i n are p o s s i b l e  1. They may have been l e f t  by removal of  2. They may be the r e s u l t o f s o l u t i o n o f  g r a n i t e by f l u i d s from an o u t s i d e s o u r c e .  for  the  3 . They may be  the s i t e s o f pockets of f l u i d r e s u l t i n g from the  crystalliza-  t i o n o f the magma. The g r e a t e s t d i f f i c u l t y  i n the f i r s t  hypothesis  i s a c c o u n t i n g f o r the removal of the i n c l u s i o n s .  The xeno-  l i t h s o f the S e a g u l l c r e e k b a t h o l i t h , although i n some cases  21.  c o n s i d e r a b l y a l t e r e d by metasomatism, been d i s s o l v e d away o r otherwise d a t i o n of the  removed a f t e r  the  through f r a c t u r e s  consoli-  source would be guided  i n the rock and the d i s t r i b u t i o n of  would thus be r e l a t e d to these f r a c t u r e s .  the j o i n t s and l a r g e r f r a c t u r e s no r e l a t i o n t o the c a v i t i e s with tourmaline. crystals  have  granite.  F l u i d s from an o u t s i d e  cavities  do not appear t o  of the g r a n i t e  and a r e ,  Furthermore, i t  of quartz, feldspar,  the  However,  seem to  i n general,  not  i s u n l i k e l y that  bear  filled  certain  and t o u r m a l i n e would be  left  i n t a c t while o t h e r s immediately a d j o i n i n g them would be completely  removed. The l a s t  hypothesis  conclusion i s therefore  i s the most l i k e l y ,  and the  reached t h a t these c a v i t i e s  true m i a r o l i t i c c a v i t i e s .  The f o l l o w i n g evidence  i n support of t h i s c o n c l u s i o n . s p h e r i c a l or o v o i d , suggesting l i q u i d o r a bubble of gas.  are  is  Most o f the c a v i t i e s  The c r y s t a l s  l i n i n g the  o f the w a l l s ,  open s p a c e ) .  the c a v i t i e s suggesting  The bases of the  merge with those  of  cavities suggesting  growth i n an environment t h a t d i d not r e s t r i c t t h e i r (e.g.  are  formation from a g l o b u l e  are more n e a r l y euhedral than those  shape  offered  crystals  crystal lining  of the surrounding g r a n i t e ,  t h a t they and the m i n e r a l s o f the normal g r a n i t e  formed s i m u l t a n e o u s l y .  There are a p p a r e n t l y no  c o n n e c t i n g the c a v i t i e s  to p r o v i d e e n t r y and e x i t  channelways of  material. In order to t e s t t h i s h y p o t h e s i s  i t might be  advisable to attempt a reconstruction of the history of formation of the cavities.  One of the most acceptable  theories, supported by laboratory investigations (Smith, 1948), i s that a crystallizing granitic magma commonly yields a residual liquid rich in alkalies, s i l i c a , water, and other volatile-constituents.  To form the minerals  lining the cavities this liquid, in the case of the Seagull creek batholith, must have contained boron, fluorine, s i l i c a , and water, and probably contained alumina, and iron, although i t i s conceivable that they could be derived from the earlier formed crystals. The process starts with the crystallization of minerals from the magma. An i n t e r s t i t i a l magmatie liquid w i l l remain.  As crystallization proceeds this liquid  probably becomes more dilute.  By the process of diffusion,  aided by the surface tension of the liquid, or perhaps by the formation of an aqueous immiscible phase of the liquid constituents (Smith, 1948, p. 544), this liquid i s concentrated into spherical drops or globules either saturating the crystal mush or excluding the crystals from the interior of the drops. The size of the drops would decrease as crystallization proceeds.  A point would eventually be  reached where the surrounding crystals would no longer encroach on the drop because of the increased r i g i d i t y of the crystal framework. The f i n a l crystals to be formed would then grow under conditions of lower confining pressure and could take on their normal crystal forms.  I n the case of the  spherical clots  of t o u r m a l i n e -  r i c h f i n e - g r a i n e d g r a n i t e w i t h no c e n t r a l c a v i t y , the  pro-  cess would f o r some reason not be c a r r i e d f a r enough t o ; form c a v i t i e s .  An answer should be sought  i n the  c o n d i t i o n s of f o r m a t i o n of the a p l i t i c g r a n i t e , faster magma.  c o o l i n g , lower c o n f i n i n g p r e s s u r e ,  different  namely,  and more a c i d i c  The c o n c e n t r a t i o n o f s p h e r u l i t e s i n l a v a s at  p o i n t where the v o l a t i l e of o r b i c u l a r s t r u c t u r e s  content  i s high,  in granite,  and the  may be due to  a  formation similar  causes. It  i s not known whether i t  would be necessary  for  the r e s i d u a l l i q u i d t o b o i l t o cause the formation o f a cavity.  If  so then the s p h e r i c a l c l o t s may be  more simply by the i n f e r e n c e reached.the  explained  t h a t i n them the l i q u i d  never  boiling point.  The Metamorphic A u r e o l e  D e s c r i p t i o n of the  Aureole  The contact metamorphic a u r e o l e e n c l o s e s  the  crops o f the S e a g u l l creek b a t h o l i t h i n an i r r e g u l a r ranging i n t h i c k n e s s from a few f e e t t o s e v e r a l  out-  envelope  thousand.  The aureole was not c a r e f u l l y mapped but was c r o s s e d on r i d g e s by s e v e r a l t r a v e r s e s was obtained  and a rough i d e a o f i t s  (see accompanying map).  The best  extent  exposures  are on the r i d g e n o r t h o f the b a t h o l i t h , near Camp 18, at a x e n o l i t h on the mountain top south of Camp IS.  and  The  metamorphic e f f e c t s Hornfels,  d i f f e r a c c o r d i n g t o the type o f r o c k .  amphibolite,  formed from c a l c a r e o u s  and c r y s t a l l i n e  limestone, have been  sedimentary r o c k s .  Quartzite  has  been much l e s s a l t e r e d although t o u r m a l i n e and a x i n i t e formed i n i t by metasomatism.  A contact metamorphic  have  deposit  o f magnetite  and p y r r h o t i t e o c c u r s w i t h i n the a u r e o l e a few  hundred f e e t  south o f the g r a n i t e  the south f o r k of Swift  outcrops i n the canyon of  river.  D e s c r i p t i o n o f the Rock Types H o r n f e l s outcrops on the r i d g e n o r t h e a s t 18 and a l o n g the bank o f the  south f o r k of Swift  the contact metamorphic d e p o s i t .  t h e i r compositions to be p r a c t i c a l l y  Thin-sections identical.  composed o f d i o p s i d e and intergrown p l a g i o c l a s e hornblende and  r i v e r near  The rock at both l o c a l i -  t i e s i s g r e e n , h a r d , dense h o r n f e l s .  a little  of Camp  show  They are (An^g)  with  calcite.  Amphibolite outcrops i n a x e n o l i t h south of Camp 18.  The p r i n c i p a l rock i s a medium-grained d a r k - g r e e n amphi  bolite  composed of hornblende, f e l d s p a r ,  biotite,  diopside,  and  but t h e r e are numerous l o c a l v a r i a t i o n s i n  and c o m p o s i t i o n .  texture  C r y s t a l l i n e limestone and bands o f h o r n f e l  are a s s o c i a t e d with the a m p h i b o l i t e s but the s t r u c t u r e s complex and were not s o l v e d i n the time a v a i l a b l e outcrops.  at  the  are  Mineralogy of the Aureole A wide v a r i e t y of m i n e r a l s occurs w i t h i n the a u r e o l e but d e s c r i p t i o n w i l l be r e s t r i c t e d t o the metasomatic m i n e r a l s c o n t a i n i n g boron and f l u o r i n e .  These are  tourmaline, f l u o r i t e , a x i n i t e , c l i n o h u m i t e , l u d w i g i t e , and an unknown b o r a t e .  (See Table  Tourmaline contact aureole. i n amphibolite. stone.  1)  occurs i n a t l e a s t f o u r ways i n the  1. I n t e r s t i t i a l l y and as c a v i t y 2. In v e i n s .  3.  As replacements  4. In q u a r t z i t i c sedimentary  grains(?), (b) produced  by  rock,  (a) as  fillings i n limedetrital  replacement.  The tourmaline of the a m p h i b o l i t e occurs as c r y s t a l aggregates interstitially. (Specimen 118)  as much as two  i n c h e s a c r o s s , as w e l l as  The t o u r m a l i n e of such an  aggregate  i s seen i n t h i n - s e c t i o n t o be s t r o n g l y and  i r r e g u l a r l y zoned w i t h sharp angular boundaries.  It is  p l e o c h r o i c from p a l e blue-green t o deep green, from p a l e , o l i v e - g r e e n t o almost tan. Harker  b l a c k , and from p a l e t a n t o very  As mentioned by F l e t t  (Ussher et a l , 1909)  and  dark  by  (1950) the p l e o c h r o i c c o l o u r s are a guide t o the  composition, b l u e r e p r e s e n t i n g s o d a - r i c h v a r i e t i e s , brown, magnesium-rich t y p e s .  Since the c o l o u r s of t h i s  tourmaline  are not as b l u e as those o f the tourmaline i n the g r a n i t e , t h i s type i s probably not as r i c h i n a l k a l i e s and r i c h e r i n magnesium than the g r a n i t i c t o u r m a l i n e . spectrographic Two  (See Chapter  5 for.  analyses.) occurrences of v e i n tourmaline were mapped.  26 - One  i s a t the c r e s t o f the r i d g e west of S e a g u l l creek  south of Camp 12. south.  just  The v e i n s t r i k e s N 80° E and d i p s 80°  The main p a r t o f i t i s about a f o o t wide but t h e r e  are s e v e r a l branches over a t o t a l width o f t e n . f e e t i n which the country rock, normally a p a l e green q u a r t z i t e , i s bleached a creamy white.  The w a l l s are t i g h t and r a t h e r i r r e g u l a r  but reasonably s t r a i g h t . aggregates,  Black f i b r o u s t o u r m a l i n e  crystal  growing a t acute a n g l e s t o the w a l l s , c o n s t i t u t e  most of the v e i n f i l l i n g . o f these aggregates  Disseminated  among the  crystals  are abundant f l u o r i t e and c a l c i t e ,  minor q u a r t z , c h a l c o p y r i t e , and p y r r h o t i t e .  and  Both purple  and p a l e green f l u o r i t e were noted, i n c r y s t a l s up t o 5 across.  mm.  A t h i n - s e c t i o n of p a r t of the v e i n and w a l l con-  t a i n s tourmaline c r y s t a l s up t o 1 mm.  l o n g and 0.5  a c r o s s , which are p l e o c h r o i c from c o l o u r l e s s t o  mm.  blue-green.  A measurement of the r e f r a c t i v e i n d i c e s gave e » 1.625, w = 1.66-. up to 0.5  A s s o c i a t e d v e i n quartz o c c u r s i n anhedral  mm.  diameter.  The w a l l r o c k c o n s i s t s of v e r y  g r a i n e d q u a r t z , t o u r m a l i n e , c a l c i t e , sphene and  crystals fine-  black  metallics. The  second occurrence o f v e i n tourmaline i s i n the  c i r q u e west o f the m a g n e t i t e - p y r r h o t i t e d e p o s i t at the head o f the south f o r k of S w i f t r i v e r .  V e i n l e t s t r e n d roughly  north-south and are l e s s than an i n c h wide. a x i n i t e occur t o g e t h e r . b l u e s or browns.  Tourmaline  and  The tourmaline i s p l e o c h r o i c i n  The w a l l r o c k s are l i g h t - c o l o u r e d  quartzites.  Bunches o f tourmaline c r y s t a l s occur i n e n c r i n a l  27.  limestone and dolomite on the east side of Seagull creek batholith just north of mile 731 on the Alaska highway.  The  crystals appear to be associated with siliceous bands in the dolomitic beds.  They are minute and perfectly euhedral.  The  brown colour and refractive indices (e = 1.631, w. = I.646) suggest a magnesian tourmaline.  The specific gravity,  3.14,  suggests a composition of 50% dravite, 50% schorlite (Winchell, 1951, p. 466). A rounded and fractured grain of tourmaline was noted in thin-section 66 from the quartzite on the south boundary of the Seagull Creek batholith.  Its texture and  relationship suggest formation before or near the beginning of metamorphism. Section 65, from a locality a few hundred feet closer to the granite contact, contains tourmaline which appears to be moulded around quartz grains suggesting formation late in the process. .Fluorite occurs most abundantly in the granite, but i s also present in veins with tourmaline.  Its colour  ranges from colourless to green and to purple. Clinohumite occurs as a gangue mineral in the magnetite-pyrrhotite d r i l l core specimens. amber-coloured  Small anhedral  crystals are disseminated through massive  pyrrhotite in some specimens.  They have a hardness of 6  and a specific gravity of 3.20 + 0.05.  In thin-section they  show high r e l i e f , pleochroism from colourless to pale lemonyellow, and lamellar twinning.  The extinction angle, measured  on the twinning in a section normal to z, i s 9°.  Another  28. thin-section  shows c l i n o h u m i t e  m a g n e t i t e and l u d w i g i t e . obtained  t o be b i a x i a l  study.  was  I t occurs with magnetite,  humite and d o l o m i t e Its  i n some o f t h e d r i l l  identified  calcite,  core  somewhat s i m i l a r t o l u d w i g i t e i n i t s  p h y s i c a l properties, but apparently d i f f e r i n g structure,  occurs  s e c t i o n No. 1.  i n the d r i l l  The m i n e r a l  core  until  i t s identity  a s a n unknown  i n i t s atomic  specimens o f i n t e r -  i s apparently a tin-bearing  magnesium i r o n b o r a t e , a n d may be a v a r i e t y  to  are described  i n the chapter. A mineral  but  of ludwigite,  i s established i t w i l l  be  referred  borate.  Investigations regarding the i d e n t i t y tion  of t h i s mineral  The  are d e s c r i b e d i n Chapter  Contact Metamorphic  and composi-  5.  Deposit  A magnetite-pyrrhotite deposit outcrops e a s t bank o f t h e s o u t h of  clino-  specimens.  o p t i c a l p r o p e r t i e s j under r e f l e c t e d l i g h t ,  later  with  near the l u d w i g i t e end-,  member o f t h e l u d w i g i t e - p a i g e i t e s e r i e s , x-ray  positive  was  angle.  A mineral, probably  by  calcite,  Here an i n t e r f e r e n c e f i g u r e  showing t h e m i n e r a l  a large optic  associated with  fork of Swift river,  two s m a l l l a k e s t h a t mark i t s s o u r c e  mineralized  rocks  are limestones  N 8 0 ° W and d i p 4 0 ° s o u t h w e s t .  on t h e  one m i l e  (Camp 1 2 ) .  and d o l o m i t e s  that  north The trend  A v e i n , e x p o s e d f o r -20 f e e t ,  29. is  about t h r e e f e e t  southeast. metallic  The  w i d e , s t r i k e s N 20°  v e i n matter  minerals.  c o n s i s t s almost  Rough b a n d i n g  c o n s i s t s of - from  3";  and  marked on thousand  p a r a l l e l t o the  pyrrhotite,  s p h a l e r i t e with minor galena,  pyrrhotite,  24".  feet  w a l l s i d e of the  of core l i e s  and  Smelting  Specimens from thick,  mineral often  i s magnetite.  The were o b s e r v e d magnetite, pyrite,  silver  and  green  stations  are  about  two  The  1947  about f i v e  by  the  The  and  along  principal  metallic  and  massive,  v a r i o u s gangue m i n e r a l s ,  s e r p e n t i n e , dark  following minerals,  feet ,  ( T a b l e 1)  disseminated  minor c h l o r i t e  and  green  diopside,  clinohumite.  i n order of  abundance,  i n polished sections of t h i s material:  pyrrhotite,  galena,  silver  rock.  I t occurs  c h i e f o f which are dark  ruby  intersections,  with p y r r h o t i t e  calcite,dolomite,  magnetite  Company.  specimens of country  intergrown  9";  and  o f m i n e r a l i z e d r o c k , were c o l l e c t e d  w i t h a few  chalco-  outcrop.  work i s b e l i e v e d t o h a v e b e e n done i n 1946 Hudson.Bay M i n i n g  walls  wall -  v e i n , and  s t a c k e d at the  of  and  S e v e r a l diamond d r i l l  the hanging  d i p s gently-  entirely  the f o o t w a l l t o the hanging  galena with minor s p h a l e r i t e , pyrite,  E, and  sphalerite,  pyrite,  marcasite,  chalcopyrite,  stannite, ludwigite,  (probably p y r a r g y r i t e ) ,  ( ? ) , and  t h e unknown  Magnetite  occurs  tetrahedrite  (?), native  borate. i n the m a j o r i t y of the s e c t i o n s ,  a s s o c i a t e d most commonly w i t h p y r r h o t i t e , amounts o f c h a l c o p y r i t e ,  arseno-  sphalerite,  and  with  smaller  and a r s e n o p y r i t e .  30 Exsolution and  blebs of chalcopyrite,  tetrahedrite  pyrite  are rare  contains  pyrrhotite, rarely  (?), occur i n the s p h a l e r i t e . i n the d r i l l  cores.  b l e b s o f ruby s i l v e r  stannite,  G a l e n a and  Some o f t h e g a l e n a  and n a t i v e  silver  (?).  Some  secondary m a r c a s i t e has formed i n t h e outcrop m a t e r i a l a t the  expense o f p y r r h o t i t e  ludwigite 3,  6 a n d 11. , The l a t h s , a b o u t 0.1  strongly  anisotropic, giving four  unknown b o r a t e  compared t o l u d w i g i t e , colours,  The  cores,  b u t a p p e a r s t o have  suggests that o r the d r i l l  of the vein.  similar  zones,  grains.  o fthe  intersected  either the deposit  changes  h o l e s m i s s e d t h e downward  However, f o r t h e p u r p o s e s o f t h i s are the deficiency o f s i l i c a  t h e p r e s e n c e o f b o r o n , f l u o r i n e a n d t i n w h i c h have l e d  to the formation of t i n - b e a r i n g The  I t takes a poor  i n mineralogy and t e x t u r e  paper the s i g n i f i c a n t features and  section appears .  and t o o c c u r i n t i n y r e c t a n g u l a r  difference  i n character  extension  Some o f t h e l a t h s  grained.  outcrop and t h e m i n e r a l i z e d  the d r i l l  rapidly  extinctions per revolution,  i n polished  homogeneous b u t i s e x t r e m e l y - f i n e  by  and v e r y  curved.  The  anisotropic  are strongly  slate-grey,  red-orange t o b l u i s h - g r e e n .  slightly  vein-like  b y 0.5, mm.,  from s i l v e r - g r e y t o b l u i s h  from f i e r y  polish,  Laths o f  i n a s s o c i a t i o n w i t h m a g n e t i t e o c c u r i n Specimens  pleochroic  are  and a r s e n o p y r i t e .  deposit  Thompson  lies  (1944)  within  a n d t h e main g e o l o g i c  be d e s c r i b e d  and o f  clinohumite.  t h e t i n b e l t o u t l i n e d b y W a r r e n and  to those of c e r t a i n regions which w i l l  borates,  containing  i n Chapter  4.  features  are s i m i l a r  important t i n  deposits,  CHAPTER 4 . BORON METASOMATISM  T u r n e r (1948), q u o t i n g Goldschmidt  (1922), de-  f i n e s metasomatism as a p r o c e s s o f a l t e r a t i o n which i n ,f  v o l v e s enrichment o f t h e r o c k by new s u b s t a n c e s brought i n f r o m t h e o u t s i d e , " such enrichment t a k i n g p l a c e " b y  definite  c h e m i c a l r e a c t i o n s between t h e o r i g i n a l m i n e r a l s . a n d t h e e n r i c h i n g substances."  T h i s d e f i n i t i o n i s more l i m i t e d i n  i t s scope t h a n a l a t e r one by L i n d g r e n (1933), v i z . " t h e p r o c e s s o f p r a c t i c a l l y s i m u l t a n e o u s c a p i l l a r y s o l u t i o n and d e p o s i t i o n by which a new m i n e r a l o f p a r t l y  or wholly  d i f f e r i n g c h e m i c a l c o m p o s i t i o n may grow i n t h e body o f an o l d m i n e r a l o r m i n e r a l aggregate." Boron metasomatism i n t h i s a r e a f a l l s w i t h i n t h e more l i m i t e d d e f i n i t i o n as t h e b u l k c o m p o s i t i o n o f t h e r o c k i s changed by t h e a d d i t i o n o f b o r o n . The agents o f metasomatism a r e c h e m i c a l l y a c t i v e l i q u i d s o r gases, f o r example aqueous s i l i c a t e  solutions  e n r i c h e d i n t h e r a r e c o n s t i t u e n t s o f t h e magma. The main t y p e s o f metasomatism have been c l a s s i f i e d by Goldschmidt  (1922) as  A. Metasomatism o f s i l i c a t e and q u a r t z r o c k s . B. Metasomatism o f c a r b o n a t e r o c k s . C. Metasomatism o f s a l t d e p o s i t s . D. Metasomatism o f s u l p h i d e d e p o s i t s .  32.  (1939)  Eskola  s u b d i v i d e s Type A  1.  Alkali  2.  Lime metasomatism.  3.  Iron-magnesium-silica  4.  Metasomatism with F,  5.  CO2  metasomatism.  Cl,  et a l . ( 1 9 0 9 )  a r o u n d Bodmin and  i n g t h a t pneumatol^ic  less  Calcareous granite,  contain larger  green  concentric Strong  went on  with  and  rock".  albite  and  till  has  w-  fluorite. of  the  Pneumatotourmaline-  r e p l a c e s mica constituent.  violet  and The  and o c c a s i o n a l l y  centre  be  of the  Tourmaline enclosed  o r t h o c l a s e and shapeless  crystals  been p a r t l y  crystal. started  in feldspar.  quartz  separated  masses o f  of quartz,  i n normal u n a l t e r e d g r a n i t e .  of tourmaline  and  a l t e r n a t e i n well-marked  may  uncommon t o f i n d  enclosing idiomorphic  crystal  blue,  stat-  produced  produces a  original  deep brown i n t h e  biotite  boric  rarely  Tourmaline  S h a d e s may  crystallizing  o u t . •• I t i s not line  and  p l e o c h r o i c h a l o s are f r e q u e n t .  crystallizing It  g r a n i t e has  granite i t s e l f  i s brown, y e l l o w ,  zones,  by  Series, north  i s o c c a s i o n a l l y an  or c o l o u r l e s s .  Cornwall,  amounts o f a x i n i t e .  of the  or "schorl  and  tourmaline  the  beds o f t h e Meadfoot  rock  feldspar  St. Austell,  commonly t o u r m a l i n e ,  alteration  quartz  B, L i ,  d e s c r i b e metasomatism i n  a c t i o n on g r e e n s t o n e s  v a p o u r s g i v e n o f f by  axinite,  litic  i n t r o d u c t i o n o f S i , Sn,  metasomatism.  country  fluoric  metasomatism.  S.  . Ussher the  as  tourma-  orthoclase  Sometimes an  surrounded  early  by f e l d s p a r  and  p r o t e c t e d from subsequent  i n d i c a t e t h a t the at  the  start.  Fluorite, less,  tourmaline  violet,  or dark b l u e .  z o n a l and  hour-glass  It  i n grains  origin,  c r y s t a l s were  bands  idiomorphic irregular.  stage,  Dark c o l o u r e d  i s colour-  crystals  show  weak b i r e f r i n g e n c e .  s c a t t e r e d through the f e l d s p a r , principally  i n c a v i t i e s w h i c h may o r f o r m e d by  zonal  more  pheumatolitic  s t r u c t u r e s and  e s p e c i a l l y p l a g i o c l a s e , but deposits  The  L a t e r z o n e s a r e more and  formed d u r i n g the  occurs  deposit.  as  interstitial  have b e e n o f  miarolitic  removal of other minerals  (e.g.  feldspar). Three passing 1.  T o u r m a l i n i z a t i o n - no shown.  remains of the  F e l d s p a r has  always i n t e n s e l y z o n a l , the  zones b l u e . variety  e f f e c t e d by  The  z o n e s may  be  original  disappeared.  and  The  an  t h e more a l k a l i n e  formed from f e l d s p a r .  Tinstone, lies  in  blue  the  in a  matrix.  Greisening - this  aggregate of quartz  secondary topaz. a little  Tourmaline  brown m a g n e s i a n  f o r m o f s m a l l d a r k brown t e t r a g o n a l p r i s m s , secondary  granite  c e n t r e s brown, the' o u t e r  alternate.  i s formed from b i o t i t e  v a r i e t y may  2.  vapours  through g r a n i t e : -  s t r u c t u r e are is  s o r t s o f changes are  i s the and  mica, with  Fluorite,  tourmaline,  conversion the  of granite  into  development  of  some l i t h i u m - b e a r i n g m i c a ,  magnetite,  zircon  and  and  cassiterite  appear. 3.  K a o l i n i z a t i o n - not  important  f o r the  purposes of  this  paper. Barrow and Thomas (1908), d e s c r i b i n g the t i o n s between contact  rela-  metamorphic m i n e r a l s and metasomatic  m i n e r a l s i n the Bodmin and Camelford a r e a , C o r n w a l l ,  state  t h a t thermal metamorphism, produced by the i n t r u s i o n of granite,  caused the formation of v e s u v i a n i t e ,  and b r i g h t green pyroxene,  garnet,  epidote and a c t i n o l i t e .  Later  a l t e r a t i o n by the a c t i o n of heated gases p e n e t r a t i n g cracks and f i s s u r e s  pale  along  of the t h e r m a l l y metamorphosed r o c k s  profoundly a l t e r e d them, c o n v e r t i n g s h a l e s a x i n i t e and green p r i s m a t i c pyroxene. m i n e r a l s are f l u o r i t e ,  sphalerite,  to aggregates o f  Other  metasomatic  and b r i g h t y e l l o w  garnet  The geology of the Seward P e n i n s u l a , A l a s k a , d e s c r i b e d by Knopf slates,  (1908), who s t a t e s t h a t e a r i y  Paleozoic  and O r d o v i c i a n and C a r b o n i f e r o u s limestones  i n t r u d e d by c o a r s e - g r a i n e d g r a n i t e o f f e l d s p a r and smoky q u a r t z . r i c h i n boron, f l u o r i n e , teristically  containing  The g r a n i t e  are.  phenocrysts  i s unusually  c h l o r i n e , and i r o n ,  surrounded by a p n e u m a t o l i t i c  is  and i s  contact  characaureole.  Large amounts of the magmatic emanations were r e t a i n e d by the l i m e s t o n e s ludwigite,  i n such m i n e r a l s as t o u r m a l i n e ,  hulsite,  hedenbergite,  paigeite,  fluorite,  boron^vesuvianite,  scapolite  creek area are s t r i k i n g l y  o f the Seward P e n i n s u l a , and to a l e s s e r Cornish areas.  magnetite  and c h o n d r o d i t e .  The m i n e r a l assemblages, t e x t u r e s and o f the S e a g u l l  axinite,  paragenesis  s i m i l a r to extent t o  those the  C o n c l u s i o n s drawn from f i e l d and p e t r o -  g r a p h i c evidence by the authors quoted may be a p p l i e d with reservations  t o the S e a g u l l  has not been as i n t e n s e other l o c a l i t i e s  creek a r e a .  i n the S e a g u l l  The metamorphism creek as i n the  nor have the. metasomatic  changes  been as  complete.The r e l a t i v e effecting  metasomatic  is closely  importance of l i q u i d s and gases i n changes  l i n k e d to t h a t  i s not known.  The problem  o f the emplacement  metallic mineral deposits.  of ores i n  Considerable difference  o p i n i o n e x i s t s among v a r i o u s a u t h o r s .  of  The proponents  o f a gaseous agency are Fenner, L a c r o i x , and many o f earlier writers  such as F l e t t ,  (1933)  Fenner  Barrow, and Thomas.  believes  that  the gases l i b e r a t e d  at the time of the peak of the thermal and chemical of the magma are the m i n e r a l i z i n g a g e n t s . m i t s an e x p l a n a t i o n f o r ore d e p o s i t s Summarizing L a c r o i x ' w r i t i n g s volatile  emanations  i n and near  (Fenner, 1926)  (gases) at Vesuvius have  important.  Bowen  gas phase i s l e s s carry less  (1933)  cupolas.  he s t a t e s  that  transformed containing  that  l i q u i d s are more  reaches the c o n c l u s i o n t h a t  effective  the  as a s o l v e n t and thus can  s o l u t e than the l i q u i d phase of the same compo-  He b e l i e v e s  t h a t a c i d s o l u t i o n s are the p r i n c i p a l  agents o f t r a n s f e r of m a t e r i a l .  (1933)  per-  cavities. Later writers believe  sition.  energy  H i s concept  limestone to c r y s t a l l i n e aggregates of s i l i c a t e s drusy  the  hold that  Ross  (1933)  and S c h a l l e r  the dominant agent o f t r a n s p o r t and d e p o s i -  t i o n i s an a l k a l i - r i c h l i q u i d of l a t e magmatic d e r i v a t i o n . Graton*s c o n c l u s i o n s ( G r a t o n , 1940,  p p . 340-350) are too  l e n g t h y f o r more than a b r i e f mention of the most p e r t i nent t o t h i s d i s c u s s i o n .  Regarding the r e l a t i v e times o f  the p n e u m a t o l i t i c and o r e - f o r m i n g stages he concludes ore d e p o s i t s are p o s t - p e g m a t i t i c o f the main magma.  but are d i r e c t  S e p a r a t i o n o f the ore f l u i d  main body may be accomplished e i t h e r "by  that  descendants from the  crystallization  o f the o t h e r magmatic components l e a v i n g the s p e c i a l ore f l u i d as the f i n a l and o n l y l i q u i d then e x i s t i n g i n the magma chamber, or by breakdown o f the r e s i d u a l l i q u i d about the pegraatitic  stage,  at  i n t o two i m m i s c i b l e l i q u i d s ,  o f these the l e s s abundant, l e s s dense and l e s s would be the s p e c i a l ore f l u i d . "  viscous  Such i m m i s c i b l e l i q u i d s  were produced e x p e r i m e n t a l l y by Smith (1948,  p.  53&).  Regarding l i q u i d s v e r s u s s o l i d s as t r a n s p o r t i n g agents Graton concludes the " c a p a c i t y o f the gas phase, above o r below c r i t i c a l (temperature") necessary g r e a t pletely  whether  to accomplish the  task o f m i n e r a l t r a n s p o r t i s found com-  inadequate under those c o n d i t i o n s of u n d e r - c o v e r  i n t r u s i o n which alone are s u i t a b l e f o r the degree o f metal c o n c e n t r a t i o n r e q u i r e d to form o r e s . " The f i e l d and p e t r o g r a p h i c evidence from the metamorphic aureole o f the S e a g u l l creek b a t h o l i t h and from the m a g n e t i t e - p y r r h o t i t e have made any s i g n i f i c a n t  d e p o s i t does not appear t o  c o n t r i b u t i o n t o the  knowledge  o f the processes o f metasomatism and ore d e p o s i t i o n ,  other  37 than to concur with evidence o f t h i s type from s i m i l a r localities, processes  on which the t h e o r i e s  are,  in part,  of the nature o f  such  based.  From the f o r e g o i n g d i s c u s s i o n i t t h a t , although gases were probably e f f e c t i v e t i o n of e a r l y boron m i n e r a l s , aqueous  i s concluded , i n the forma-  s o l u t i o n s were most  l i k e l y the dominant agents i n the formation of t o u r m a l i n e v e i n s and the m a g n e t i t e - p y r r h o t i t e  deposit.  Unfortunately  no c r i t e r i a are known f o r d i s t i n g u i s h i n g products o f t r a n s p o r t from those a gas phase g e n e r a l l y  of l i q u i d t r a n s p o r t .  gas  Furthermore,  since--  e x i s t s i n e q u i l i b r i u m with a l i q u i d  phase the two may w e l l act  together.  CHAPTER 5 SPECTROGRAPHIC AND X-RAY STUDIES  Tourmaline  The formula g i v e n by W i n c h e l l (1951) f o r tourmal i n e i s (Na,Ca) (Al,Fe,Mg,Mn,Ti) (Si,B) Og (OH) (?). 5  27  27  6  4  Although t o u r m a l i n e v a r i e s w i d e l y i n composition, c e r t a i n end members and continuous s e r i e s between p a i r s o f them are r e c o g n i z e d .  Of these t h e most common a r e : Dravite Schorlite Elbaite  H^NaMg-jAl^Si^! H NaFe3Al6B3Si503 i!f  1  HgNagLi^Al-^B^Si-^O^  There i s a continuous s e r i e s from d r a v i t e t o s c h o r l i t e and from s c h o r l i t e t o e l b a i t e but not from d r a v i t e t o e l b a i t e . In an e f f o r t t o determine t h e d i f f e r e n c e s i n composition from the f o u r types o f occurrence i n the a r e a , samples c o n s i s t i n g o f about 20 mg. o f powdered m i n e r a l were s u b j e c t e d t o s p e c t r o g r a p h i c a n a l y s i s . used was as f o l l o w s .  The procedure  The powdered samples were p l a c e d i n  a small d r i l l e d h o l e i n the lower carbon e l e c t r o d e o f a H i l g e r medium q u a r t z s p e c t r o g r a p h .  Each was f u s e d  separately  and the a r c s p e c t r a exposed f o r a t e n - and twenty-second p e r i o d on Eastman type I I F ( T r o p i c a l ) p l a t e s which have a u s e f u l range from 2200 t o 6800 Angstrom  u n i t s on t h i s  39. instrument.  Standards used were - 1. the i r o n arc from  H i l g e r ' s "Specpure" i r o n r o d s ; 2. R . U . ("Raies U l t i m e s " ) powder which g i v e s l i n e s f o r 30 of the common elements; and 3. a wave l e n g t h  scale.  The a n a l y s e s are only s e m i - q u a n t i t a t i v e , c o n s i s t of comparisons of elements.  and  s t r e n g t h s o f l i n e s of the v a r i o i  The r e s u l t s are shown i n Table 2. Table 2 Spectrographs  Analyses of Tourmaline  I n t e n s i t i e s of Lines Locality  Amphibolite  Limestone  Vein  Granite  Iron  moderate  low  high  very h i g h  Magnesium  very h i g h  very h i g h  high  low  Boron  very h i g h  very h i g h  very h i g h  very h i g h  Sodium  moderate  low  low  very h i g h  Aluminum  moderate  moderate  moderate  high  Manganese  very low  very low  very low  very low  Silicon  very h i g h  very h i g h  very h i g h  very h i g h  Calcium  high  nil  nil  Lithium  nil  nil  nil  nil  Tin  low  low  low  low  r  .moderate  O p t i c a l and p h y s i c a l p r o p e r t i e s i n d i c a t e t h a t  the  tourmaline of the a m p h i b o l i t e s i s p r o b a b l y i n the d r a v i t e - . schorlite series. that i t to  The s p e c t r o g r a p h i c a n a l y s i s  suggests  i s probably c l o s e r t o d r a v i t e i n composition than  schorlite.  40. The t o u r m a l i n e o f t h e spectrographic that  it  is  analysis  close  to  in  The v e i n t o u r m a l i n e  amphibolite  as  colour i n thin-section.  optical  colours the  as  probably  of  That  evidenced  the  in thin-section,  series  also  granite  is  pale  than  the the  blue-green  above a n a l y s i s ,  yellow  the  to  analysis.  probably  to  compared w i t h p a l e  primary tourmaline of  The  evidence  shown by t h e  replacing biotite  by t h e  cited  closer  s u g g e s t e d by t h e  i n d i c a t e d by t h e  properties.  however,  of  as  is  This is  The t o u r m a l i n e  brown.  composition.  dravite-schorlite  tourmaline,  pure s c h o r l i t e  is  confirms previously  dravite  s c h o r l i t e . end o f t h e  limestone  may be  almost and  the  magnesian,  greenish-yellow and deep  blue  cavities.  Borates  Of t h e following mine t h e  were borate  anhydrous b o r a t e s  studied  1.  deposit  on. t h e  the  contact  south f o r k  the  deter-  metamorphic  of Swift  river.  Ludwigite-Paigeite  2.  Pinakiolite  3.  Hulsite  4.  Warwickite  The end members o f t h e  "Ludwigite1  by Dana (1951)  i n connection with attempts to  minerals o c c u r r i n g at  magnetite-pyrrhotite  ludwigite,  listed  ftMgjFe^FeW'BO^] o c c u r s as  ludwigite  and p a i g e i t e ,  series  are:  JJFejMgJgFe'WBO^].  f i b r o u s masses w i t h a f a i n t  silky  lustre,  as  embedded  like  s h e a f - l i k e aggregates,  crystals,  or granular.  t o u g h upon f r a c t u r e . gravity The  o f 3.6  (pure  inclining black  r o s e t t e s of  I t l a c k s cleavage,  I t has  t o 4.7  to greenish  black  The  I t i s opaque e x c e p t i n  Mg  i s called  and  Ca may  stitutes  with  Fe"  s u b s t i t u t e s f o r Fe"'  Sn  n  f o r Fe'"  contact  i n some m a t e r i a l  s e r i e s are  metamorphic  high  apparently  associated with  L o c a l i t i e s a r e M o r a v i c z a , Hungary; H o i  ada;  i n the  Cottonwood d i s t r i c t s ,  Lemhi C o u n t y , I d a h o ; and  M o n t a n a , a s w e l l as  other  f r o m B r o o k s M o u n t a i n on •Vonsenite  The found  ( a h y d r o u s magnesium  United  States  Kol  mine,  the  Big  U t a h ; L i n c o l n C o u n t y , Nev-  Philipsburg, Granite  districts. the  sub-  magnetite,  borate).  Little  Mn  1910).  forsterite  and  with  amounts.  diopside,  K o r e a ; N o r b e r g , Norway; and  P a i g e i t e was  Seward P e n i n s u l a ,  County, originally  Alaska.  ( = p a i g e i t e ) i s from R i v e r s i d e , R i v e r s i d e  California.  X-ray photographs are  M o r a v i c z a , Hungary, t h e M o n t a n a , and  from Crestmore, R i v e r s i d e differences  i n the  shown o f  type l o c a l i t y ,  from S e a g u l l  creek,  and  ludwigite  County, from  from P h i l i p s b u r g ,  of p a i g e i t e  County, C a l i f o r n i a .  patterns  is  paigeite.  (Schaller,  szaibelyite  and  small  temperature minerals  deposits  and  Mg,  i n small  substitute f o r (Mg,Fe ).  members o f t h e in  ludwigite,  specific  streak  of h i g h l y magnesian l u d w i g i t e . . M a t e r i a l  Al  a  in paigeite  grains Fe"  is  (pure p a i g e i t e ) .  toward dark green i n l u d w i g i t e .  to b l a c k i s h green.  needle-  and  5 and  a hardness of  ludwigite)  colour i s coal black  as  indicate that  the  (vonsenite)  Slight compositions  are s l i g h t l y d i f f e r e n t  but the s t r u c t u r e s are s i m i l a r . '  The p h y s i c a l p r o p e r t i e s of the S e a g u l l  creek  l u d w i g i t e are almost i d e n t i c a l t o those g i v e n i n Dana (1951).  The only d i f f e r e n c e s  i n the x - r a y p a t t e r n s  the l i n e s of admixed magnetite  (see P l a t e  are  II).  , P i n a k i o l i t e i s a magnesium manganese  borate,  o c c u r r i n g g e n e r a l l y as t h i n t a b l e t s with a r e c t a n g u l a r o u t l i n e and showing good (010) hardness o f 6,  a specific  metallic lustre,  cleavage.  gravity  I t has a  o f 3.88, a b r i l l i a n t  and i s b l a c k with a brownish grey  streak.  I n t r a n s m i t t e d l i g h t p i n a k i o l i t e i s deep r e d d i s h - b r o w n . It  i s found at Langban, Sweden,  i n bands i n g r a n u l a r  dolomite with hausmannite (MnlVh^O^), and other r a r e manganese m i n e r a l s .  tephroite  (M^SiO/J ,  The x - r a y p a t t e r n of  p i n a k i o l i t e i s s i m p l e r than t h a t of l u d w i g i t e and i n t h i s respect  i s more l i k e t h a t of the unknown b o r a t e ,  but  although the grouping o f c e r t a i n l i n e s i s the same i n b o t h , the d i s t a n c e s between them suggest t h a t perhaps pinakiolite structure,  the  i f s i m i l a r , i s more c o n t r a c t e d than  t h a t of the unknown borate  (Hate III)"'".  Warwickite i s a magnesium i r o n t i t a n i u m b o r a t e . I t has p e r f e c t  c l e a v a g e , a hardness of 3 2 t o 4,  specific gravity subvitreous,  of 3 . 3 5  The l u s t r e i s d u l l  to  the c o l o u r dark h a i r - b r o w n t o d u l l b l a c k , and  the s t r e a k b l u i s h - b l a c k .  1.  ±. 0 . 0 1 .  and a  In t r a n s m i t t e d l i g h t  An expanded p a t t e r n i n d i c a t e s a s m a l l e r u n i t  it  i s reddish-  cell  brown i n c o l o u r .  It  occurs i n c r y s t a l l i n e  limestone  a s s o c i a t e d with c h o n d r o d i t e , blue and b l a c k s p i n e l , magnetite,  i l m e n i t e , d i o p s i d e , and pseudomorphous g r a i n s  and masses of s e r p e n t i n e . ( P l a t e IV) shows l i t t l e borates  graphite,  The x - r a y p a t t e r n of  warwickite  resemblance t o any of the  other  studied. H u l s i t e i s p o s s i b l y an i r o n c a l c i u m magnesium  t i n borate.  The formula d e r i v e d from an average o f  p a r t i a l analyses by S c h a l l e r (1910) i s .[(Fe,.Ca,Mg)^(Fe , S n " ) 2 B 2 0 i o ] • ,w  w  rectangular c r y s t a l s , t a b u l a r masses. and a s p e c i f i c  It  gravity  possibly  H u l s i t e occurs as s m a l l ,  with uneven and d u l l f a c e s ;  has good 110 of 4 . 2 8 .  The l u s t r e i s black.  submetallic It  i n marmorized l i m e s t o n e , about 1 0 . f e e t from the  fluorite  a l s o as  c l e a v a g e , a hardness of 3,  t o v i t r e o u s and the c o l o u r and s t r e a k ,  with vesuvianite,  several  d i o p s i d e , magnetite,  i s found  granite,  brown g a r n e t ,  and  at Brooks mountain, Seward p e n i n s u l a , A l a s k a .  The x - r a y powder photograph of h u l s i t e  ( P l a t e HI)  indi-  c a t e s about the same complexity o f s t r u c t u r e , as the b o r a t e s but i s d i s s i m i l a r i n o t h e r  other  respects.  An unknown magnesium i r o n borate from the S t .  '.  C h r i s t o p h e Mine, F r a n c e , i s at p r e s e n t b e i n g s t u d i e d by D r . R.M. Thompson of the U n i v e r s i t y o f B r i t i s h Columbia. The m i n e r a l i s b l a c k , tough.  Its  ludwigite,  has a hardness of 5,  and i s  rather  o p t i c a l p r o p e r t i e s are s i m i l a r to those but the x - r a y powder p a t t e r n i s q u i t e  of  different,  and i s i n f a c t almost i d e n t i c a l t o t h a t of the unknown  borate from Swift  river.  The p h y s i c a l p r o p e r t i e s of the unknown borate are as f o l l o w s : - c o l o u r and s t r e a k b l a c k , p o s s i b l y r e d d i s h brown i n t h i n n e s t s p l i n t e r s , hardness 5, 3.45  ± 0.02, l u s t r e f a i n t l y  silky,  specific  gravity  cleavage absent.  The  m i n e r a l occurs i n t i m a t e l y intergrown with magnetite, o f which i s f i b r o u s and may be pseudomorphous a f t e r ludwigite,  or c h r y s o t i l e .  It  i s a l s o i n contact  some it,  with  s e r p e n t i n e which, normally a pale green, i s very dark green f o r about an e i g h t h o f an i n c h from the boundary between it  and the unknown b o r a t e .  magnetite  In some specimens the f i b r o u s  i s a s s o c i a t e d with an unknown soft white powdery  m i n e r a l which has been i n l a r g e p a r t removed l e a v i n g the f i b r e s as open space f i l l i n g .  Attempts to x - r a y t h i s m i n e r a l  have so f a r been u n s u c c e s s f u l .  A spectrographic  o f the unknown borate  shows the presence o f  (Table 3)  analysis  magnesium, i r o n , t i n , boron, and a l i t t l e manganese,  and i t  i s concluded that the m i n e r a l i s a t i n - b e a r i n g magnesium i r o n borate i n which manganese s u b s t i t u t e s p a r t of the i r o n .  f o r a small  Ludwigite from P h i l i p s b u r g , Montana,  and from S e a g u l l creek area were a l s o spectrographed f o r comparison with the unknown b o r a t e . The t i n content of the Swift be 5 o r 10 p e r c e n t . c o n t a i n s probably 15$  Paigeite, Sn02»  r i v e r borates may  d e s c r i b e d by Knopf  (1908),  H u l s i t e , analysed by S c h a l l e r  (1910), c o n t a i n s 7.07$ S n 0 . 2  Table Spectre-graphic  3  Analyses  of  Intensities Mineral Locality  Unknown B o r a t e Swift River  Magnesium  very  Iron  Borates of Lines  Ludwigite Swift River  Ludwigite Philipsburg  very  high  very  high  very  high  high  Boron  high  high  high  Titanium  nil  nil  moderate  Tin  high  high.  nil  Silicon  low  low  low  Manganese  moderate  moderate  very  '..  F u r t h e r work w i l l  1  the  high  near f u t u r e .  borate  be done on t h e s e  s p e c i e s , but, a l t h o u g h  p r o p e r t i e s a r e most l i k e  those  minerals i n  the p h y s i c a l  o f the ludwigite  t h e powder p a t t e r n i s a s d i f f e r e n t  siderable  low  I t i s p r e m a t u r e t o c l a i m t h e unknown  a new m i n e r a l  other borates  high  series,  from i t as a r e the  d e s c r i b e d , and t h e r e must t h e r e f o r e be c o n  d i f f e r e n c e i n s t r u c t u r e between l u d w i g i t e and  t h e unknown  borate.  CHAPTER 6 CONCLUSIONS  I t has and  by  d e s c r i p t i o n s of the  r e f e r e n c e to the l i t e r a t u r e t h a t the  batholith, in  b e e n shown by  while perhaps unusual,  composition,  described  t e x t u r e , and  are remarkably It  the S e a g u l l creek  paragenesis.  similar  i s concluded  contributary  evidence  probably  means The  has  by  field  other  The understood limited  no  study  m e t a s o m a t i s m on Seagull  o r f o r m e d an  of  definite attempted  immiscible  c o n c l u s i o n s c a n be in this  the rocks o f the  creek b a t h o l i t h  the l o c a l i t i e s  paper.  areas, The  p o s t u l a t e d by  but  watery liquid. completely reached  The  from  effects  are, i n general s i m i l a r to  referred  been  which  contact aureole of  of  the those  t o i n t h e body o f t h e r e p o r t ,  n a m e l y , Seward p e n i n s u l a , A l a s k a , and Austell  The  certainly  mechanism o f m e t a s o m a t i s m i s n o t  and  of  b e e n p r o v i d e d by l a b o r a t o r y s t u d y .  c o n c e n t r a t i o n s o f l a t e magmatic l i q u i d , boiled  areas  coarse.  f r a c t i o n w i t h t h e more v i s c o u s s i l i c a t e - b e a r i n g  the  unique  evidence,  m i a r o l i t i c c a v i t i e s have a l m o s t  either  creek  i n these respects.  g r a n i t e i s younger than the  i s best i l l u s t r a t e d  f o r m e d by  Seagull  t h a t t h e f i n e - t e x t u r e d phase  relationship  The  i s by no  rocks  t h e Bodmin and  St.  Cornwall. S e a g u l l creek W a r r e n and  area l i e s  Thompson  w i t h i n the t i n b e l t  (1944),  and  the  occurrence  of t i n - b e a r i n g b o r a t e s  as w e l l as t h e , s i m i l a r i t y of the  to t i n - p r o d u c i n g l o c a l i t i e s of c a s s i t e r i t e  deposits.  suggests the p o s s i b l e  area  occurrence  48. REFERENCES CITED  B a r r o w , G.  Bostock,  and Thomas, H.H. (1908), "On t h e o c c u r r e n c e o f metamorphic m i n e r a l s i n c a l c a r e o u s r o c k s i n t h e Bodmin and C a m e l f o r d a r e a s , C o r n w a l l " , M i n e r a l o g i c a l M a g a z i n e , v o l . 15, 1908-1910.  H.S. (1948), P h y s i o g r a p h y o f t h e C a n a d i a n c o r d i l l e r a with s p e c i a l r e f e r e n c e t o the area n o r t h of the f i f t y - f i f t h p a r a l l e l , G e o l o g i c a l Survey, Canada, Memoir 247. ~  Bowen, N.L. (1933), "The b r o a d e r s t o r y o f magmatic d i f f e r e n t i a t i o n b r i e f l y t o l d " , Ore D e p o s i t s o f t h e W e s t e r n S t a t e s . L i n d g r e n Volume, R o c k y M o u n t a i n F u n d S e r i e s , A.I.M.E. Dana, E . S .  Eskola,  P.  (1951), S y s t e m of m i n e r a l o g y , 7th E d i t i o n , Volume 2, by C. P a l a c h e , t h e l a t e r H . Berman, C. F r o n d e l , W i l e y and S o n s , New Y o r k . (.939),  Correns, Fenner,  D i e E n t s t e h u n g d e r G e s t e i n e ( B a r t h , T.F.W., C.W., and E s k o l a , P . ) , S p r i n g e r , B e r l i n .  C.N. (1926), "The K a t m a i magmatic p r o v i n c e " , J o u r n a l o f G e o l o g y , v o l . 34, No. 7, P t . 2.  (1933), " P n e u m a t o l i t i c p r o c e s s e s i n t h e f o r m a t i o n o f m i n e r a l s and o r e s " , Ore D e p o s i t s o f t h e W e s t e r n S t a t e s , L i n d g r e n Volume, R o c k y M o u n t a i n F u n d S e r i e s , A.I.M.E. Fyles,  J.G. (1950), G e o l o g y and W e a t h e r i n g , W h i t e h o r s e , Yukon, U n p u b l i s h e d M.A.Sc. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia.  G a l l a g h e r , D. (1937), " O r i g i n o f t h e m a g n e t i t e d e p o s i t s a t L y o n m o u n t a i n , New Y o r k " , N.Y. S t a t e Museum Bulletin. Ghosh, P.K. (1934), "The C a r n m e n e l l i s g r a n i t e , i t s p e t r o l o g y , metamorphism and t e c t o n i c s " , Q u a r t e r l y J o u r n a l o f t h e G e o l o g y S o c i e t y , V o l . 90. G o l d s c h m i d t , V.M. silicate  (1922),  "On t h e m e t a s o m a t i c p r o c e s s e s i n r o c k s " , E c o n o m i c G e o l o g y , v o l . 17.  G r a t o n , L.C. (1940), " N a t u r e o f t h e o r e - f o r m i n g E c o n o m i c G e o l o g y , v o l . 35. H a r k e r , A. Johannsen,  (1950),  M e t a m o r p h i s m,  3rd  A. (1939), A d e s c r i p t i v e r o c k s , v o l . 1, U n i v e r s i t y  Edition,  fluid",  London, Methuen.  petrography of the of Chicago P r e s s .  igneous  K n o p f , A.  ( 1 9 0 8 ) , T i n d e p o s i t s o f Seward p e n i n s u l a , U.S.G.S. B u l l e t i n 356.  Alaska,  and S c h a l l e r , W.T. (190$), "Two new b o r o n m i n e r a l s o f c o n t a c t metamorphic o r i g i n " , American J o u r n a l o f S c i e n c e , 4th s e r i e s , v o l . 25. Lindgren, Lord,  C.S.  Reid,  C,  W.  (1933),  Mineral Deposits,  McGraw H i l l ,  New  York.  (1944), G e o l o g i c a l r e c o n n a i s s a n c e a l o n g t h e A l a s k a h i g h w a y between Watson L a k e and T e s l i n . r i v e r , Yukon and B r i t i s h C o l u m b i a , G e o l o g i c a l S u r v e y , Canada, P a p e r 44-25. Barrow, G., S h e r l o c k , R.L., M a c A l i s t e r , D.A., Dewey, H. and Bromehead, C.N., with c o n t r i b u t i o n s by J . S . F l e t t (1912), The G e o l o g y o f D a r t m o o r , G e o l o g i c a l S u r v e y , E n g l a n d and Wales, E x p l a n a t i o n o f sheet 338.  R o s s , C.S.  (1933),  "Differentiation  as a  source  of v e i n  and  o r e - f o r m i n g m a t e r i a l s " , Ore D e p o s i t s o f t h e W e s t e r n S t a t e s , L i n d g r e n Volume, R o c k y M o u n t a i n F u n d S e r i e s , A.I.M.E. Schaller,  W.T. (1910), " C h e m i c a l c o m p o s i t i o n o f h u l s i t e and p a i g e i t e " , A m e r i c a n J o u r n a l o f S c i e n c e , v o l . 29. (1933), " P e g m a t i t e s " , Ore D e p o s i t s o f t h e W e s t e r n S t a t e s , L i n d g r e n Volume, R o c k y M o u n t a i n Fund S e r i e s , A.I.M.E.  S m i t h , F.G. (1948), " T r a n s p o r t and d e p o s i t i o n o f t h e nonsulphide vein minerals. Ill.phase, r e l a t i o n s at . t h e p e g m a t i t i c s t a g e " , E c o n o m i c G e o l o g y , v o l . 43. Turner,  F . J . , (1948), E v o l u t i o n o f t h e m e t a m o r p h i c r o c k s , G e o l o g i c a l S o c i e t y o f A m e r i c a , Memoir 30.  U s s h e r , W.A.E., B a r r o w , G., M a c A l i s t e r , D.A. (1909), The g e o l o g y o f t h e c o u n t r y a r o u n d Bodmin and S t . A u s t e l l , w i t h n o t e s on t h e p e t r o l o g y o f t h e i g n e o u s r o c k s , by J . S . F l e t t . G e o l o g i c a l Survey, E n g l a n d and W a l e s , E x p l a n a t i o n o f s h e e t 347. W a r r e n , H.V. and Thompson, R.M. (1944), " T i n i n w e s t e r n Canada", The W e s t e r n M i n e r , A u g u s t 1944. Watson, K.  deP. Area,  and Mathews, W.H. (1944), The T u y a - T e s l i n B.C. D e p a r t m e n t o f M i n e s B u l l e t i n 19.  Watson, T . L . (1902), "On t h e o c c u r r e n c e o f a p l i t e p e g m a t i t e and t o u r m a l i n e b u n c h e s i n t h e S t o n e m o u n t a i n g r a n i t e o f G e o r g i a " , J o u r n a l o f G e o l o g y , v o l . 10. W i n c h e l l , A.N. (195D, E l e m e n t s o f O p t i c a l M i n e r a l o g y , D e s c r i p t i o n s o f m i n e r a l s , 4th E d i t i o n , W i l e y S o n s , New Y o r k .  Part I I , and  Plate I  50  X 909  L u d w i g i t e , Moravicza, Hungary I  d(meas.)  1 1  7.42 6.12 5.58 5.12 2.97 2.89  8*  2.81  10  X  I  d(meas.)  7^  2.16 2.13  6, 3  1.998  h  3,  1  2.74  3 ,2  2.32  4  2.56  1  2  2.04  1.952 1.908  I  d(meas,)  \1 2  4 4 5,1 2 1 2  1.870  1  1.769  I  1.687 1.580  2  1.536 1.523 1.501 1.473 1.377 1.310 1.295  I  1 2  d(meas.) 1  2  l  12 2  1  2  1.281  1.158  1.142 1.088  1.051 1.045 1.022 1.004  1.253 1.205  882  Ludwigite, P h i l i p s b u r g , Montana I  10  d(meas.) 7.32 6.12 5.63 5.10 3.00 2.92 2.80 2.73 2.55 2.34  I  d(meas.) 1  2  1  L  2  1  2  "I  2.30 2.17 2.12 2.03 1.995 1.955 1.911 1.867 1.762 1.710  I  d(meas.)  I  1 2 1 6  4  1.706 1.668 1.577 1.539 1.529 1.516 1.504 1.473 1.379 1.316  I  d(meas.)  1.303 1.291 1.281 1.253 1.205 1.178 I.I64 1.087 1.044 1.023  Plate I I  51  X 885  Vonsenite = ( P a i g e i t e ) C a l i f o r n i a I 2 1 1 8  d(meas.) 7.42  6.16 5.61 5.17 4.70 3.73 3.05 2.92 2.82  1  £  2z 5 2  X  I  d(meas.)  10  2.56 2.36  5 1 6 2 6 1  2.33 2.17 2.14 2.0$  i  2.75  2  1.995 1.964 1.923 1.875  I  d(meas.)  3  4.  1  52 5  2 5 1  1  2  I  d(meas.)  1.216 1.086 1.028  1.778 1.580 1.529 1.504  1.432  I.468  1.387 1.314 1.281 1.250  88  Ludwigite, S e a g u l l creek, with Fibrous Magnetite I 1 1  8  9  d(meas.) 7.37 6.16 6.06 5.22 5.10 4.64 3.83 3.72 3.33 3.01  I  1 1 10  d(meas.)  1 £ ?  1 1  2  2.95 2.90 2.82 2.76 2.56 2.54 2.48 2.36 2.32 2.27  I  d(meas.) 1 2  21 4 3  2.17 2.14 2.09 2.05 2.00 1.958 1.923 1.897 1.870 1.783  I  d(meas.) 1.621 1.595  2  I.584  5 5 5.  1.536 1.504 1.482 1.434 1.415 1.384 1.363  I  d(meas, 1.320 1.281 1.163 1.089 1.043 1.028 1.003  •Plate I I I X 883  P i n a k i o l i t e , Langban, Sweden I 6  d(meas.) 1 2  5.75 5.42 3.60 2.99 2.69  i  32  9 10  8 2 1 2 2 1  2.50  i 2 1 1 2  2.39 2.30 2.23 2.16  1  I  d(meas.)  i  h  I  ?2I  2.07 1.989 1.828 1.621 1.542 1.513 1.491 1.305 1.281 1.148  I 1  d(meas.)  i  1.080 1.032  X 881  H u l s i t e , Brooks Mountain, Seward, A l a s k a I  d(meas.)  5 1 4 4 -4  k  7 5 10  2  5.34 4.99 4.49 3.88 2.98 2.74 2.67 2.59 2.52 2.49  I  1  d(meas.)  i I |  I  6 ? I  2.35 2.25 2.19 2.13 2.09 2.04  1.979 1.937  I  d(meas.)  i  |  1  I I I  2  i  1.732 1.644 1.613 1.580 1.563 1.546 1.479 1.439  52  Plate I V  X 886  Warwickite, E d e n v i l l e , New York I  d(meas.)  2 2 1 3, i  85 10 1 I  g  i  I  6.55 4.21 3.73 2.96 2.83 2.74 2.58 2.47  1 1 3 1  2.20  I  2.24  d(meas.)  i i i z  2 3, 4  2.13 2.09 1.976 1.865 1.833 1.788 1.719 1.628 1.591 1.546  2  4  I  h  1.501 1.468 1.182 1.105  5  Unknown borate D r i l l Gore No. 1 I 5 1 8 2 2 10 1 1 1  d(meas.) 7.32 5.87 5.31 4.90 3.60 2.95 2.67 2.60 2.49 2.43  I  d(meas.)  f 5 7 2 2 2  2.35 2.27 2.24  2.18  2.13 2.04 1.774 1.563 1.540 1.507  I  2 2  d(meas.)  I  I  2  1.485 1.439 1.358 1.333 1.181 1.064  53.  Plate V X 884  Unknown b o r a t e S t . C h r i s t o p h e Mine, France I  d(meas.)  1 9 1 2 2 2 2 10 3 4  I  d(meas.)  5.90 5.34 4.88 4.18 3.55 3.09 2.94 2.66 2.60 2.13  2.03 1.778 1.755 1.559 1.546 1.529 1.358 1.335 I.252 1.229  I  d(meas.)  4  1.181  §  1.069 1.C19 1.010  I I  x 890  Magnetite d(meas.)  I 3 8 1 10 1  4  4  5, 2  4  4.86 3.31 2.98 2.79 2.54 2.43 2.32 2.10 i.788 1.719  I  d(meas  8 9,  1.621 1.491 1.333 1.283 1.270 1.216 1.124 1.096 1.051  1 1 2 4 3  4 4  54.  The  The  S e a g u l l creek b a t h o l i t h from the n o r t h e a s t  amphibolite x e n o l i t h south of Camp 18  •4(5 - /  Ajrcrro/tf'c  Cof/f/cj  <?<5--S *7raro/i'f'c. Canry  FIGURE  I  /f,  Co<*'s<r~  t*"% Co*rs<?-  '  TOURMALINE  IN  GRANITE  

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