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Petrogenetic study of the Guichon Creek Batholith, B.C. Westerman, Christopher John 1970

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A PETROGENETIC  STUDY  GF THE GUICHON C R E E K B A T H O L I T H ,  B.C.  by Christopher B.Sc.  A THESIS 1  J.  University  Westerman  of  London,  1967  S U B M I T T E D I N P A R T I A L F U L F I L M E N T OF  THE R E Q U I R E M E N T S FOR T H E DEGREE OF MASTER OF in  the  SCIENCE  Department of  GEOLOGY We a c c e p t required  this  thesis  as  conforming  to  standard  THE U N I V E R S I T Y  OF B R I T I S H  April,  1970  COLUMBIA  the  In presenting this thesis in partial fulfilment of the requirements f o r an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree tha  permission for extensive copying of this thesis  f o r scholarly purposes may be granted by the Head of my Department or by his representatives.  It is understood that copying or publication  of this thesis f o r financial gain shall not be allowed without my written permission.  Department of The University of British Columbia Vancouver 8, Canada  Date  f^tJP  lf7&  ABSTRACT The  Guichon Creek  2 0 0 miles pluton  of  consists  N . E . of  of  quartz  seven  gradual  mineral  rock  of  as  Tho  individual  is  and q u a r t z  are  the  potassic  little  of  the  change.  feldspars  structural  early  of  the  i n the  early  with  The in  phases  bulk  7 1 - 8 6 Wt% O r a n d components  phases of  equivalent  intermediate  phases)  of  batholith  however,  microperthitic  porthitic  Valley  the  revealed  discussed.  of  phases  of  variations  compositions  plagioclase  amounts  has  proportions  show v e r y  range  The  compositions  arc  to  perthites  of  orthoclase. with low  Plagioclase  (Hybrid  pure  the  oligoclases  states.  batholith  that  the  approach  from  have  to the  and H i g h l a n d  show n o r m a l z o n i n g w h e r e a s t h o s e  from  1  batholith  Tho  with lessor  compositions,  i n the  states  The  monzonite.  relative  compositions  structural  'granitic  a s s i m i l a t i o n a n d magma c o n v e c t i o n  feldspars  The  a zoned  phases.  crystallisation  b a t h o l i t h are  end members.  and i s  approximately  ( 1 9 8 - 8 m y ) .  and m i n e r a l  compositional  Alkali  exposed  granodiorite  chemical  of  B.C.  intrusive  mineral phases  roles  producing the  age  v a r i a t i o n i n the  proceeded.  of  typo  rock  phases  relative  major  diorite  Study a  Vancouver,  Lower J u r a s s i c  predominant of  batholith is  tho  later  oscillatory the  (Bethlehem  phases  zoning.  b a t h o l i t h have  with  the  to  crystallize  from the suggests  crystallisation tho  magma.  the  early  that  later  pressures  p h a s e s may h a v e  i n the  crystallisation.  This  most  to  duo  crystallisation.  order  of  the  phases  mineral  during  suggest  conditions  order  of  1  of  or 2  subjected  5 kb  but  stationary  systems  been  1+ o r  host  batholith  from a  under  i n the  the  phases.  of  experimental  of  ratios  older  early  magma c o n v e c t o d phases  of  i n the  tho  crystallised  with  total  pressures  probably  older  Fe/(Fc+Mg)  major  magma c r y s t a l l i s e d  low  the  that  phases  content  early was  show  major  lower  silica  younger  phases  Comparisons  the  total  of  younger  relatively but  increasing  b a t h o l i t h whereas quartz  Evidence  that  from tho  Plagioclase crystallized  of  that  Biotites  progressively  progressively  rocks.  and B e t h s a i d a )  kb  to  during  increase  in total  pressures  was  increasing  volatile  pressures  during  iv  LIST  OF CONTENTS PAGE  I  Introduction  II  Geologic  III  The  Alkali  a.  Mode o f  b.  Method of  c.  Compositions Feldspars  d. e.  setting  V  VI  of  the  9  of  the  Alkali  of  the  Natural  Alkali 17  of  the  homogenised  feldspars  a.  Mode o f  b,  Plagioclase  The  Biotite,s  a.  Mode o f  b.  Method of  c.  Discussion  25  Feldspars  occurrence  27  Compositions  and Zoning  Occurrence  Modal Analyses Compositions  Summary a n d  Natural  15  states  Plagioclase  VIII  9  study  The  Geological  5  occurrence  Bulk compositions  VII  batholith  feldspars  Structural Feldspars  alkali IV  1  and  27  ^-2  Study of  ....  UU  Results  ^6  Calculated  evolution  Chemical 56  of  Conclusions  the  batholith  72 83  V  PAGE  References Appendix  Cited  ...  90  1.  Petrographic  2.  Modal a n a l y s e s and c a l c u l a t e d chemical compositions  3.  descriptions  B i o t i t e electron microprobe analysis - experimental procedures  95 102  ;  110  vi  L I S T OF T A B L E S TABLE I. II. III. IV. V.  VI.  VII. VIII.  IX.  X.  XI.  PAGE Phases  and v a r i e t i e s  of  intrusive  Unit c e l l parameters a l k a l i feldspars  of  K rich  rock  phases  k in 11  Compositions of the p e r t h i t i c phases of the a l k a l i f e l d s p a r s , and d a t a p l o t t e d i n F i g . 5 Unit c e l l feldspars  parameters .  for  homogenised  .  13  alkali Ik  R e l a t i o n between e s t i m a t e d b u l k c o m p o s i t i o n and degree of anomoly f o r computer r e f i n e d a l k a l i feldspars  19  ° 2 9 v a l u e s f o r 201 r e f l e c t i o n s ( C u K ^ ) a n d estimated b u l k compositions of homogenised a l k a l i f e l d s p a r s from the Guichon Creek batholith  26  Table  28  of  plagioclase  compositions  O b s e r v e d X - r a y i n t e n s i t y r a t i o I^j^: f o r 3 b i o t i t e samples as a f u n c t i o n of sample preparation  k5  R e s u l t s of p a r t i a l electron-microprobe a n a l y s i s of b i o t i t e s from the Guichon Creek batholith  k'd  C r i t e r i a , s u g g e s t e d by B u d c d n g t o n (1959) as i n d i c a t i v e of mesozonal i n t r u s i o n which are present i n the Guichon Creek b a t h o l i t h  80  E l e c t i ' o n microprobe analyses of b i o t i t e standards. Data used i n c o n s t r u c t i o n of F i g . 17  115  vii  L I S T OF FIGURES FIGURE  PAGE  1.  Geology  2.  Sample l o c a t i o n map  3-  Orthoclase content of a l k a l i feldspars p l o t t e d as a f u n c t i o n o f the a c e l l _ d i m e n s i o n , u n i t c e l l volume a n d 2 0 2 0 1 CuKoi . S i m p l i f i e d f r o m W r i g h t a n d S t e w a r t (i960) and W r i g h t ( 1 9 6 8 )  16  R e f i n e d c e l l parameters f o r a l k a l i f e l d s p a r s from the Guichon Creek b a t h o l i t h p l o t t e d on a b - £ p l o t , s i m p l i f i e d f r o m W r i g h t and S t e w a r t (i960)  18  4.  of t h e Guichon  Creek b a t h o l i t h  ....  3 8  5.  A l k a l i f e l d s p a r s from t h e Guichon Creek b a t h o l i t h p l o t t e d on a 0 6 0 - 2 0 4 (°20 CuK «* ) p l o t , s i m p l i f i e d from W r i g h t ( 1 9 6 8 ) 18  6.  X-ray d i f f r a c t i o n p a t t e r n  7.  f o r sample  31  . i n t h e r e g i o n o f 30°29 CuK * Modal f e l d s p a r c o n s t i t u e n t s o f t h e Guichon Creek b a t h o l i t h samples r e c a l c u l a t e d t o 1 0 0 % An+Ab+Or  22 33  8.  P l a g i o c l a s e z o n i n g schemes  36  9.  Compositions of p l a g i o c l a s e s i n e q u i l i b r i u m v/ith g r a n i t i c m e l t s as a f u n c t i o n o f temperature at 2kb water p r e s s u r e (From P i w i n s k i , 1 9 6 8 , p. 5 6 0 )  40  10.  R e l a t i o n between abundance o f b i o t i t e and s i l i c a c o n t e n t o f h o s t .rock  43  11.  B i o t i t e compositions as a f u n c t i o n of the s i l i c a content of the host rock  47  12.  S t a b i l i t y o f b i o t i t e s as a f u n c t i o n of f0£ and t e m p e r a t u r e a t 2070 b a r s t o t a l p r e s s u r e (From Wones a n d E u g s t e r , 1 9 6 5 ) . . . .  50  viii  FIGURE 13a.  b.  1^1-.  PAGE P l o t o f modal q u a r t z - o r t h o c l a s e - a l b i t e a n o r t h i t e f o r t h e Guichon Creek b a t h o l i t h samples  35  Schematic phase diagram f o r t h e t e r n a r y s y s t e m Qz-Or-Ab-An a t 1 k i l o b a r w a t e r vapour p r e s s u r e  55  C a l c u l a t e d component o x i d e s p l o t t e d a s a function o f s i l i c a content f o r the Guichon Creek b a t h o l i t h samples  6^,65  15.  Chemical c o m p o s i t i o n s o f proposed Guichon C r e e k b a t h o l i t h p r i m a r y nagma, ' c o n t a n i n a t e d ' G u i c h o n r o c k s a n d N i c o l a Group e x t r u s i v e rocks 68  16.  Summary o f c o m p o s i t i o n a l v a r i a t i o n s i n the Guichon Creek b a t h o l i t h  82  17.  Microprobe analyses. T o t a l counts observed as a f u n c t i o n of c o m p o s i t i o n f o r b i o t i t e standards  11^  ix  LIST  OF P L A T E S  PLATE 1.  2.  3.  k.  5.  PAGE P a r t i a l l y resorbed plagioclase enclosed within poikilitic alkali feldspar. Sample #11. Chataway v a r i e t y . Crossed n i c o l s , x 30 *  31  P a r t i a l l y resorbed plagioclase enclosed within poikilitic alkali feldspar. Sample #10. Chataway v a r i e t y . Crossed n i c o l s , x 30  31  P a r t i a l l y r e s o r b e d , o s c i l l a t o r y zoned plagioclase enclosed i n p o i k i l i t i c , perthitic alkali feldspar. Note the a l b i t i c rim to the p l a g i o c l a s e . Sample #25, B e t h l e h e m p h a s e . Crossed n i c o l s , x 30 .  35  Oscillatory zoning i n plagioclase. Sample # 34» B e t h s a i d a p h a s e . Crossed n i c o l s , x 30  35  Sample from a c h i l l e d B e t h s a i d a dyke from east o f the Bethlehem Copper p r o p e r t y . Note presence of s u b h e d r a l - e u h e d r a l p h e n o c r y s t s of q u a r t z and e u h e d r a l poikilitic biotite. Scale i n centimetres..  62  X  ACKNOWLEDGEMENTS The Drs.  author  K.C.  McTaggart,  who a c t e d due  to  as  Dr.  Department supplied of  the  thesis  to  E.P.  of  M i n e s and the  samples  Geological  Survey  analysed  express his  thanks  Meagher  u .A.  supervisors.  K.E. Northcote  a l l  chemically of  wishes  of  chemical  supplied  by  Dr.  used, of  Gower  Thanks are British  Gower.  to  Dr.  and to Research  of  the  also  Columbia who  J.H.Y.  C a n a d a who  biotites  analyses  J.A.  r  Petroleum Resources  Cominco L t d . , G e o l o g i c a l  provided  the  and  to  M.  Rimsaite  supplied Osatenko  division  biotite  who  standards  1  I  Introduction  The Guichon Creek batholith crops out over an area of approximately if00 sq. miles near to and southeast of the town of Ashcroft i n the Interior Plateau of B r i t i s h Columbia.  The batholith i s of considerable s c i e n t i f i c  and economic interest.  The Bethlehem Copper and  Craigmont Mines, and several potential mines such as Lornex and Valley Copper occur within or adjacent to the batholith. Early geological mapping of the eastern half of the Guichon Creek batholith, at a scale of if miles to 1 inch, was completed  by W.E.  Cockfield ( 1 9 i f 7 ) , and of  the western half by S. D u f f e l l and K.C. McTaggart ( 1 9 5 2 ) . Several detailed reports of parts of the batholith have been prepared by J.M.  Carr ( 1 9 5 9 - 1 9 6 3 ) and the geology  of mineral deposits associated with the batholith has been described by W.H.  White, R.M.  K.C. McTaggart ( 1 9 5 7 ) .  Thompson and Radiometric K/Ar  age  determinations from the batholith have been published by Baadsgard et a l ( (  1  1  9  9  6  6  9  )  1  9  6  9  6  1  ) 7  , Dirom (  5  , 1  )  .  Christmas et a l (  1  9  6  , White et a l (  1  9  6  9  5  ) 1  , Wanless et a 9  6  7  ) have studied the  rubidium/strontium, sulphur and oxygen isotopic composition of samples from the batholith and the  )  ,  2  associated  Craigmont ore body.  Previous work on  batholith culminated i n a detailed geologic  the  and  geochronologic study by Northcote (1969).  Northcote  mapped seven separate intrusive phases of the batholith, described  them, and explained the differences between  them as due to the combined action of assimilation magmatic d i f f e r e n t i a t i o n .  In addition Northcote  proposed that a change from mesozonal to  epizonal  environments occurred during emplacement of the The present work was further describe  and  pluton.  undertaken as an attempt to  the mineralogy of the various phases  and the mechanisms involved i n the emplacement of the batholith.  It was  hoped that the d i f f e r e n t i a t i o n  occurring within the pluton would be reflected i n the changing compositions of feldspars and b i o t i t e s which occur throughout the batholith.  In addition i t was  hoped that study of the variation i n the structural states of the a l k a l i feldspars would help i n determining the history of c r y s t a l l i s a t i o n and changes i n the environment of emplacement of the batholith. A l l of the samples used i n the present investigation were collected by Dr.. K..E. during the preparation of his Ph.D  Northcote  thesis  of B r i t i s h Columbia) i n the summers of 1963  (University and  196^.  TABLE I Phases and V a r i e t i e s of Intrusive Rocks (from Northcote 1969) Relatively Old (1)  Hybrid phase - quartz d i o r i t e , granodiorite  (2)  Highland Valley phase (2G)  Guichon variety - quartz granodiorite  (2C)  Chataway variety - granodiorite, quartz monzonite  diorite,  ( 2 L R ) LeRoy granodiorite - granodiorite, quartz monzonite Intermediate Age (3)  Gump Lake phase - granodiorite, quartz monzonite  (4)  Bethlehem phase - granodiorite, quartz monzonite  (5)  Witches Brook phase Variety A  -  granodiorite  Variety B  -  granodiorite  Variety C  -  granodiorite, quartz monzonite, granite  Bethlehem  porphyries  Relatively Young (6)  Bethsaida phase - quartz monzonite. granodi. or? t ^  (7)  Gnawed Mountain porphyries, younger Bethlehem porphyries and associated intrusive breccias Leucocratic dykes and irregular-shaped bodies  5  1  Geological  1  The has  general  been  brief  The  in  geology  described  summary  pluton  of the Guichon Creek  be g i v e n  of  concentric  sedimentary  Triassic)  causing  local  overlain  sediments  and Lower  hornfels  rocks.  significant  metamorphic  after  emplacement  radiometric give  an average  Wanless 1969;  age  et  Christmas Northcote  major  phases  relationships batholith  is  Creek  activity  a l ,  White  Upper  Jurassic  volcanic  occurring i n the  region  Published  of rocks  et  of  and  o f any  from the  198 m y .  a l 1967;  batholith  (Dirom, Northcote  the b a t h o l i t h i n t o  F i g . 1)  and t e x t u r a l composed  albite-  1969).  has d i v i d e d I,  Group  and Upper  age o f a p p r o x i m a t e l y 1967;  rocks  The b a t h o l i t h  i s no e v i d e n c e  determinations  (Table  arranged  facies.  of the b a t h o l i t h .  et  phases  metamorphism t o  by M i d d l e  There  a l 1965,  'granitic'  Cretaceous and T e r t i a r y  sedimentary  a  zoned,  (Karnian stage:  contact  unconformably  and only  The b a t h o l i t h i c  o f t h e Cache  and N i c o l a Group  or hornblende  intrusive  pattern.  rocks  1969)  batholith  here.  several  (Permian)  is  (1968,  b a t h o l i t h i s a semiconcordant,  a roughly  epidote  of the B a t h o l i t h  by N o r t h c o t e  will  consisting  intrude  Setting  p r i m a r i l y on  variations.  granodiorite,  seven  field  Most o f with  the  lesser  1965;  6  amounts minor to  of  quartz  granite.  be. b a s i c ,  has  that  the  body  on t h e  and W i t c h e s bodies range a  Chilled for  this  hot  at  of  this  magma.  concentric  Gump L a k e eastern  may v a r y between  reason  Northcote  time  phases  of  the  texture,  include Witches  granodiorite o r i g i n a l magma  rocks  the  result  of  of  to  as  a  the  are  minor  the  LeRoy  dyke-like  between  broadly  phases  serniperipheral  irregular  time,  phases  gradational  and  along i t s  length.  extremely  rare  that  and  all., phases  i n f e r r i n g only  intrusive  and o n l y  of  major  batholith,  considers  a  the  three  as  phases  b a t h o l i t h have  Northcote  of  the  same  tend  result  i n nature  i n t e r v a l between  h y p i d i amorphic  Valley,  the  phases  the  Contacts  intrusive  with  may b e  occur  phases.  and  acidic.  the  occurs  margin of  contacts  short  older  be  pattern  phase  Brook phases  contact  to  d i s r u p t e d by  approximately  phases  rocks acidic  within older  single  the  Guichon v a r i e t y  basic  from s h a r p l y  monzonite  composition of  batholith is The  phases  more  The r o u g h l y  phases.  way  the  differentiation  the  the  the  more  contamination,  of  younger  that  may a p p r o x i m a t e and  quartz  In a general  the  suggested  diorite,  pulses.  The  were a major  coarse-grained, the  youngest,  minor  porphyritic rocks.  The  Hybrid,  Brook and p a r t s  the  Bethlehem  of  Highland phases  7  all  e x h i b i t , to v a r y i n g  plagioclase  crystals.  mafic minerals  degrees, alignment  of  In a d d i t i o n a rough f o l i a t i o n  i s present,  locally,  w i t h i n the  of  Guichon  variety. On has  the  b a s i s of t e x t u r a l evidence, Northcote  suggested t h a t the  e a r l y phases of the b a t h o l i t h  were e m p l a c e d u n d e r m e s o z o n a l c o n d i t i o n s and progressive epizonal phases.  (1969)  e r o s i o n of the  conditions during  cover rocks  that  established  emplacement o f t h e  later  1  Fig. 2 . Sample location map.  \ /  "A A  I  —c  \ )  \  / /  \  /5 V  L  \  /  I 7\  O n  \  N  \  /  / /  /  ^  /  V l S'jli/ B  J  \  \  30\\  -V-  .A  •  / / 2 2  \  V  \  H  /  23  *,y  \  j/\ \ •  \  \  \  \  24  A  \  \  \  \  \ ^  33  20  16^27 \  A  r\'  21  )W  —t  / /  w  II  II  w  35  /  / /I  \  f  K-28 ^•17  N\ \ •29  9  III a)  Mode o f  Alkali  investigated  feldspar,  poikilitic,  most  of  enclosing  and b i o t i t e .  rule  interstitial alkali  grained  rocks  is  are  in  subordinate,  Wherever  thin  the  present  the  b)  w i t h i n the of  Method of  hornblende  whereas i n  A l l the or  Ailing,  feldspar  feldspar  is  plagioclase  these  features  coarse  samples cryptoperthite  a l b i t e - r i c h phase (c.f.  rocks  occurs  1938,  i n contact  either  forms  with  embayments are  marginal regions. i n discussed  as  p.1^2).  or myrmekitic i n t e r g r o w t h s  The  in  combination Magnetite  Study  Feldspars  fraction  removed  feldspar  or  IV.  Alkali mesh  alkali  plagioclase,  significance chapter  alkali  interstitial  quartz,  microperthite  stringlets.  poikilitic  plagioclase in  either  1% a n d 2 0 %  fine-grained  poikilitic.  investigated which the  either  plagioclase,  As a g e n e r a l  it  c o n t a i n between  which i s  contain  extremely  Feldspars  Occurrence  The r o c k s alkali  The  of  of  the  were  separated  crushed  and s i e v e d  electromagnetic  and o t h e r  from the  strongly  size  r e m a i n i n g m a t e r i a l was  from the  80-120  rock using  and h e a v y - l i q u i d  magnetic  methods.  m i n e r a l s were  f r a c t i o n w i t h a hand magnet. then passed  through a  a  Franz  first The  10  electromagnetic remove m a f i c The in  remaining  separater  minerals  s e t a t maximum amperage, t o  and any h e a v i l y a l t e r e d f e l d s p a r .  f r a c t i o n v/as t h e n p r o c e s s e d  by s e p a r a t i o n  bromoform d i l u t e d w i t h a c e t o n e t o a s p e c i f i c g r a v i t y  such that a quartz crystal  crystal  s a n k a n d an o r t h o c l a s e  f l o a t e d i n the mixture.  from t h i s  final  The " f l o a t "  fraction  separation consists of a l k a l i  w i t h v e r y m i n o r amounts o f a d h e r i n g f r a c t i o n s c o n s i s t mainly  quartz.  feldspar The " s i n k "  o f d i s c r e t e q u a r t z and  p l a g i o c l a s e g r a i n s w i t h m i n o r b u t v a r i a b l e amounts o f composite g r a i n s and o c c a s i o n a l non-magnetic  mafic  minerals. Smear mounts were made o f e a c h sample a n d t h r e e X - r a y d i f f r a c t o m e t e r p a t t e r n s were r u n f o r e a c h CaF  2  ( a = 5.4631 - .0006&) a s an i n t e r n a l s t a n d a r d .  r u n s v/ere made u s i n g N i f i l t e r e d 29 a n g l e and  using The  Cu r a d i a t i o n from a  o f 58° t o 19°, a t a s c a n s p e e d o f -}°/m±n.  c h a r t s p e e d o f 2cm/min. For t w e l v e  o f t h e samples a l l peaks present  were  m e a s u r e d and i n d e x e d  u s i n g t h e t a b l e s g i v e n by W r i g h t  and  Unit c e l l parameters (Table  Stewart  (1968).  the K - r i c h phase i n these  II) for  s a m p l e s have been c a l c u l a t e d  u s i n g t h e ' v a r i a b l e - i n d e x i n g ' computer program by E v a n s , Appleman a n d H a n d w e r k e r  developed  (1963) o f t h e U.S.G.S.  i  J3a-ple ./  rp  J-TVJ  4  1  6  2G  13 17  "  Q?  n  •  91. 5  I>7 j i L K * T , I  ^"^LDS^/'^S  I Std. No. of 1 r) r> y» l i n e s used (°29) 18 .017  8.58l - .003  12.984 .003  0 c(A) 7.205 .001  +8.575 - .002  12.994 .002  7.201 .001  90° 1 1 6 ° 1 . 5 9 ' 1.02»  90°  721.06 1 p  15  . 009  3.576 12.985 - . 00/-I.003  7.203 .001  90° 116°  90°  7PO  70 '. ^ 3 1  13  .013  90°  7  qo .36  15  j.016 •  h(A)  +  H  Q  cx  _V(A)  y8  3  90° 116 ~ 2 . 5 5 ' 1.45  90°'  721.13 xo  1  P ••—  ? 7 l • '— _ /  I  2C  91. 5  .8.573 - .004  12.987 .003  7.204 .002  2C  92. o  .3.577 - .005  12.988 .004  7.203 .002  90° 116° 2.49' 1.70'  90°  721.02 .42  14  .017  2LE  38.  ,8.555 - .007  12.989 "!6o5  7.203 .002  90° 116° 3.29' 2.05'  90°  719.60 .60  13  .023  ,8.580 - .005  12.935 .004  7.206 .002  on  90°  721.13 .45  12  .013  12.938 .002  7.206 .001  90°  COO-  721.97  14  .  12.992 . 003  7.204 .001  90  721.57 .27  17  O"!  ^  . vj J_  C  12.990 .002  7.206 90° 116° 0 . 2 2 ' O H^.\ ' ."001  90°  720.46 .16  13  000  12.930 .003  7.203 .002  2 2Q '  r* 0 ^  71 0  1 0  . 013  nP.c;  7.204 .001  1  . 014  OP >  /,.  —.  n.  96.  O  Q  I  r.nO m  QQ X  0 rr  27  5  90.  PQ  5  89. o  '6  OP  f  17 0 1,  - .003  93. o  23  33  APAMETE'RS OP K P J C P I PF'-'SE  0 a(A)  Or op 0  10  1.29 ' 90° 116° 1 . 0 8 ' 1.58'  ]_0  22  CELT.  TpJIT  Phase 1  12  p  _  CT.  i  o o p  ,8.562 - .004 0  cO-i  - .003  10  . 003  0  116° 3 . 0 4 ' OR  1  -i- •  116°  X r> •-•  0  I  > w  • ' !-u •  P  O  ••"^7 i  0 7  r  —* /  1 1 6 ° 0.16' 1.45*  • O O  0  1  010 UL'^  •-•  ^0  . 40  90° 116° 1 . 3 5 ' 1.36'  0O°  noi  x o  .28  12  Input  for the c a l c u l a t i o n s  reflections showed three of  that  a total  deviation  been  peak  height.  peaks  measured  were  of less  patterns.  and Stewart  have  For  c o u l d be u n i q u e l y  diffractometer  Wright  (1968)  as close  However,  measured  a n d 201 r e f l e c t i o n s  (Table  III).  a K-rich, chance  and an N a - r i c h  as p o s s i b l e  of the samples,  greatly  subordinate  reflection  effects  are minimal.  sufficient Na-rich  height  phase,  f o r some  measured. contain  there  of the  both  i s the reflections.  p h a s e v/as  f r o m t h e (201) a n d  - and hence  None o f t h e s a m p l e s  to allow  204,  a n d t h e 201  the Na-rich  number o f c h a r a c t e r i s t i c  phase,  cases,  position.  been  and hence  - as estimated  peaks  o f t h e 060,  investigated  however,  intensities  of the  or ambiguous  phase,' have  phase  precedent  t o t h e maximum  the positions  of mutual interference  and which  0 . 0 1 5 ° 20 f r o m  the majority  A l l the samples  those  Following the  for the K-rich  I n most  (002)  that  a t t h e 2/3 p e a k  for the Na-rich  to  indexed  i n uncertain  t h e r e m a i n i n g samples  reflection  was r e s t r i c t e d  calculation  interference exhibited  reflections, o f the u n i t  a  for the cell  parameters. In alkali  order  to estimate  feldspar  silica-glass  separates,  tube  at  990°C  the bulk composition of the each  sample  for three  was h e a t e d  days.  in a  At t h e end  13  TABLE I I I Potass i c Phase Sample Phase E s t . Or Wt% # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35  1 1 . 1 1 2G 2G 2G 2G 2C 2C 2C 2C 2C 2LR 2LR 2LR 2LR 2LR 3 3 3 4 4 4 4 5 5 5 5 5 5 6 6 6 6  89.0 88.5 90.0 89.0 91.5 89.0 88.0  degrees 20 201  060  21.034 21.039 41.714 21.014 41.705 21.030 41.661 20.996 41.709 21.034 41.687 21.037 41.696 2 a l k a l i feldspars 89.0 21.029 41.676 91.0 21.009 41.686 21.026 41.701 89.0 88.0 21.038 41.701 89.5 21.019 41.674 85.5 21.064 41.679 86.5 21.052 41.684 85.0 21.071 41.681 86.0 21.058 41.683 89.0 21.026 41.693 89.0 21.035 41.687 21.046 41.681 87.5 89.5 21.021 41.684 21.004 41.686 91.0 89.5 21.024 41.676 2 a l k a l i feldspars 89.0 21.029 41.654 89.5 21.024 41.672 86.5 21.055 41.679 21.061 41.729 86.0 85-5 21.067 41.708 21.046 41.676 87.5 91.5 20.996 41.766 89.5 21.021 41.681 21.011 41.681 90.51 89.5 21.021 41.698 88.5 21.039 41.684  204  50.612 50.669 50.706 50.692 50.673 50.641 present 50.659 50.644 50.667 50.673 50.677 50.624 50.677 50.684 50.636 50.657 50.656 50.629 50.647 50.646 50.668 present 50.682 50.664 50.652 50.639 50.634 50.672 50.582 50.654 50.642 50.672 50.662  So die' Phase E s t . Ab degrees 2Q 201 Wt%  99.5 98.0 95-5 99.0 97.0  22.041 22.018 21.985 22.037 21.998  97.0 97.0 98.0  22.001 21.999 22.019  97.5  22.014  98.5  22.029  99.0  22.035  .98.5 98.0 97.5  22.029 22.020 22.015  97.5 96.0 98.5  22.014 21.976 22.027  100.0  22.059  100.0  22.051  j •  TABLE IV  UNIT CELL PARAMETERS FOR HOMOGENISED ALKALI FELDSPARS  U n i t C e l l Parameters Sample If-  Phase V/t% Or  a (A)  b(A)  c(A)  8.540  12.996  7.200  .004  .003  .001  0  P  -z  V(AK  Std. No. o f error l i n e s used (°2G)  13  Homogenised  2C  83.0 -  90°  115°  58.79'  90°  718.41  16  .017  11,  .017  . ^6  1.75'  ?-9  Homogenised  5  73.5  8.513  - .006  12.976  7.199  .004  .002  90°  116°  0.13' 1.71'  90°  71':-. 8 5 .53  h-p-  1  15  of  t h i s p e r i o d most samples showed only a s i n g l e  (201)  r e f l e c t i o n on d i f f r a c t o r c e t e r p a t t e r n s , i n d i c a t i n g that homogenisa.tion was complete *  Any samples e x h i b i t i n g more  than one (201) r e f l e c t i o n were r e t u r n e d f o r f u r t h e r h e a t i n g u n t i l no f u r t h e r change i n the p o s i t i o n of the 201 r e f l e c t i o n ( s ) was recorded. were determined f o r tv;o  Unit c e l l parameters  of the homogenised samples  u s i n g CaF2 as an i n t e r n a l standard,(Table IV) and the p o s i t i o n of the 201 r e f l e c t i o n was measured f o r the remainder (Table VI) u s i n g KBrO-^ (101 r e f l e c t i o n at  20.215°29 CuK ^ ) as an i n t e r n a l standard. c)  Compositions of the N a t u r a l F e l d s p a r s Wright and Stewart  ( I 9 6 8 ) have shown that the a  c e l l dimension, u n i t c e l l volume, and the p o s i t i o n of the 201 X-ray r e f l e c t i o n of a l k a l i  f e l d s p a r s show a d i r e c t  c o r r e l a t i o n with composition which i s independent of the s t r u c t u r a l state of the m a t e r i a l .  (Fig.  3).  Thus, f o r  those samples f o r which u n i t c e l l dimensions have been r e f i n e d , the compositions of the K - r i c h phase have been estimated from the u n i t c e l l volume  (Table I I ) .  Compositions f o r the remaining samples have been estimated from a knowledge of the p o s i t i o n of the 201 reflection.  (Table V I ) .  Table V compares compositions estimated from u n i t  T  6601  1  1  1  1  1  1  1  *  1——I  1  r  1  1  L  i  i  1  1  1  1  1  1  r  I  i  i  i  i  i  i  i  i  i  20  40 Weight  3  1  I  Ab  Fig.  1  60 %  80  i Or  Or  Orthoclase content of a l k a l i feldspars p l o t t e d as a f u n c t i o n o f t h e _ a c e l l dimension, u n i t c e l l volume and °28 201 CuK«. . S i m p l i f i e d f r o m W r i g h t and S t e w a r t (1968) and W r i g h t (1968).  17  cell  volumes, a c e l l  dimensions  diffraction reflections alkali,  feldspars.  X-ray  for the twelve  'refined'  In general the e s t i m a t e s o b t a i n e d  from t h e s e t h r e e parameters accuracy  and 201  agree  w i t h i n the  c l a i m e d f o r t h e methods by W r i g h t  -2%  and  Stewart  (1968). The  samples i n v e s t i g a t e d  comprise  whose c o m p o s i t i o n s v a r y from 87  K-rich  t o 92 Wt%  r i c h p h a s e s w i t h c o m p o s i t i o n s b e t w e e n 95 V!t% Ab.  alkali  Or, and and  - 2Wt%  t h e p l u t o n have  a p p r o x i m a t e l y t h e same s t a g e o f p e r t h i t i c  evidence  composition  Or i t c a n be s t a t e d t h a t t h e  f e l d s p a r s throughout  Although  none o f t h e s a m p l e s e x h i b i t  o f c o m p o s i t i o n a l z o n i n g t h e 201  reached  unmixing. any  optical  diffraction  peaks f o r the K - r i c h phase i n s e v e r a l samples are slightly  skewed t o w a r d s h i g h e r Or Wt%  suggesting that s l i g h t d)  z o n i n g may  values,  i n f a c t be  S t r u c t u r a l S t a t e s o f the N a t u r a l A l k a l i The  structural  Na  100  B e c a u s e t h e e r r o r i n measurement o f  i s approximately  phases  very  thus present.  Feldspars  s t a t e s of the K - r i c h phases of  the  n a t u r a l p e r t h i t e s have been e s t i m a t e d f r o m a k n o w l e d g e of the  t h e b and _c c e l l (060) and  dimensions,  (20Z+) X - r a y  F i g u r e L\. ( s i m p l i f i e d  o r from t h e p o s i t i o n  diffraction  from Wright  and  of  reflections. Stewart)  shows d a t a  18  I  12.80  i  i  12.84  i  i  1  —  12.88  i  r  12.32  ~  —  i  12.96  1 — r  13.00  b. A F i g . 4: Refined c e l l p a r a m e t e r s for alkali feldspars from the Guichon Creek batholith plotted on a b-c plot simplified from Wright a Stewart ( 1 9 6 8 ) . Dashed lines r e p r e s e n t contours for the a_ c e l l d i m e n s i o n .  Fig. 5'. Alkali feldspars from  the Guichon Creek  batholith  060-204 plot simplified from Wright ( 1 9 6 8 ) . Dashed lines represent c o n t o u r s for 2 9 201 .  plotted  on a  R e l a t i o n between e s t i m a t e d  bulk compositions  computer r e f i n e d a l k a l i  Sample  V(X)3  a(Calc)(A) a(est)(A)  and degree o f anomoly f o r feldspar  Anomoly 201 o b s .  C o m p o s i t i o n V/t% Or E s t i m a t e d f r o m V~ .a(Calc) a(est) 201 obs.  0o. 5coo  21.011  92.5  94  9/4  on  8.576  8.575  21.03.'+  91..5  93  91  721.18  o . >o±  8.58  21.014  PQ.0  92.0  94-  94  on  13  721.02  8.577  8.59  ,012  21.019  92.0  96  89.5  19  721.13  8.530  8.60  ,02  21.035  93 9/4  12  720.90  8.573  8.59  ,02  21.038  91.5  92  96  29  719.79  8.562  8.59  ,030  21.067  39.0  90  96  23  721.57  8.578  8.61  .032  21.02/f  93-0  93  99  22  721.97  8.584  8.62  .038  21.004  Or,  94  100  721.06  8.575  8.62  . 0/45  21.030  92.0  719.60  8.555  3.61  .060  21.058  PP ^  21.035  or>  33  721.32  6  720.79  '4  17 27  720./.;.6  8.56/+  8.62  .060  5  q  00  100 O O  on  95 100  q  n  89.0 88.0 Q ".5 89.5 01 n Po . • n-' o O D  or  .  J c;  20  for  the  "refined"  12  diagram.  S i m i l a r l y Figure  °20(2O4)  plot  When t h e are  plotted  estimated half  of  estimated  does not cell  have  described  the the  of  unit  Wright samples  agree  with  cell.  the  on t h e  regardless  cell  the  values.  for  a  of  for  calculated  observations values  reverse  that  in  may b e  holds  that the  atoms  that  the structural  and c a l c u l a t e d 'computer  than  (1968) h a s The  and  refined'  agrees  in a l l  true.  will  configuration  'apparent'  lower  such  estimated the  state  that  Tilling  'calculated'  suggest  study  are  (1968)  having  an  the  so  A as  they  The p r e s e n t  However,  i n which the  be  .02  of  volumes,  parameters  a calculated  value  than  premise  V lists  Stewart's  sample  approximately  i n which a  sample  Table  and  any  a value  They  Furthermore,  investigated.  For  the  by more  i n terms  a cell  for  W r i g h t and Stewart  dimensions.  volume  investigated.  d i m e n s i o n may  the  feldspars  volume,  vs.  (060)  samples  contours.  defined  estimated samples  a cell  investigated  alkali  same  a °20  the  may b e  estimated samples  cross  o n a b v s . _c  dimensions  refinement.  cell  cell  the  state.  1+ t h e  composition of  occupy  sample  a l l  from a ' e s t i m a t e d '  'anomolous'  the  for  plotted  5 is  b a n d _c c e l l  samples  the  from  data  on F i g .  from  cases  of  from the  the  differs  samples  with  anomolous the  a  reported anomalous  condition appear be  exhibited  by such  t o be r e l a t e d  due t o s t r a i n s  perthitic The Figures  alkali  to their  imposed on t h e s t r u c t u r e  Guicho  tholith alkali  orthoclase  the  maximum m i c r o c l i n e o f O r v i l l e  exception  of Wright  P50-56F  to this  i s sample  the intermediate  from a s m a l l i n t r u s i v e batholith,  to  Or.  grained  a subhedral  samples  studied.  sample  tentatively  and a b u l k  for the  potasium r i c h  reflections  i n the region  between  30.1° 20 C u K * i s m o s t  probably  with the  feldspar  which  76 Wt% Si02 a n d of the  pattern  for  131 o r 131  phase.  The  29.25° a n d 30.50° 20  . The h i g h e r  o f symrnettry at  is  margin of the  c o m p o s i t i o n o f 6^Wt?&  defined  i l l u s t r a t e d i n Fig.6. with centre  The sample  26 v o l % o f m e d i u  The X - r a y d i f f r a c t o m e t e r  reflections  reflection  on F i g . 5  differentiated  no w e l l  (1968) a n d  correlated  contains  contains  CuK*are  field.  between  The o n l y  which plots  on t h e western  highly  field  (1967).  t h e rock, c o n t a i n s  t o be t h e most  p l o t t e d on  and Stewart  microperthitic alkali  habit,  In addition,  #31  The r o c k  appears  this  during  feldspars  microcline mass  and has been  Brook phase.  coarse  has  a n d may  unmixing.  i+ a n d 5 l i e w i t h i n t h e o r t h o c l a s e  Witches  would  p e r t h i t i c nature  the  within  feldspars  intensity  approximately  a composite  reflection  22  Fig.  6  X-ray diffraction t h e r e g i o n o f 30°  pattern for 2 0 CuK<*  sample  31  in  A l s o shown a r e t h e r a n g e s o f p o t a s s i c a n d s o d i c a l k a l i f e l d s p a r r e f l e c t i o n s w h i c h may appear i n t h i s r e g i o n . (From W r i g h t and Stewart, 1968)  23  caused  by t h e i n f e r e n c e  a n d . a 131  microcline  reflection  2©  triclinic  potassium  In  p otassium  that  the  rich  theoretical  alkali  rich  range  alkali  feldspar  phase  This of the states.  from the relatively  bulk  from  from  order  so s h o u l d  compositions  the Rader  Creek  The c o m p o s i t i o n s  components  i n sample  #31 a p p r o a c h  compositions  suggested  of a  the purity  (1968) h a s  i n 't r i c l i n i c i t y ' with  Montana.  samples  a  distinct  here.  are  Tilling  Batholith,  member  i s a  as the S i - A l  increases,  increase  albitic  have  that  components.  a general  feldspars  from  of structural  sample  (1961)  considerations  increasingly  29.9°  defined.  the p e r t h i t i c  observed  potassium  i n this  to  from a m o n o c l i n i c  be r e p r e s e n t e d  i n a wide  phase  broad  29-5°  and there  reflection  Smith and Mackenzie  of  The v e r y  t h e 060 a n d 204 r e f l e c t i o n s  and w e l l  perthitic  phase  may a l s o  i s present  contrast  sharp  a 131  phase  would i n d i c a t e  rich  reflection  a 131 r e f l e c t i o n  represents  that  albite  from a p p r o x i m a t e l y  potassium  possibility  perthite  reflection.  extending  probably  CuKot  o f t h e 131  and are very  .from t h e G u i c h o n C r e e k  of  -oerthitic  Pluton,  Boulder  of the p e r t h i t i c  closely  the pure end  s i m i l a r to the  batholith.  other  Sample  #31  is  unique however,  because  ordered with respect sodic  place  degree  i n sample  degree  of  Si-Al  Thus, the  probably £.nd t h e  #31,  ordering to  of  their  vary.  The r e l a t i v e  alkali  feldspar  solid and  over The  state,  tho  is  tho  greater  the  alkali  dependent  Al into  cooling history  structural  states.  and 5  k  the  of  The  the  however,  state  on t h e  of  that  of  the not  Al/Si  tctrahcdral  by d i f f u s i o n ,  t h o more  favourable  the  alkali  a monoclinic  degree  T^ a n d  most  errors  samples.  achieved  of  higher  feldspars  experimental  mean,  nonequivalent  amount  exhibiting  structural state  structural  a  taken  original crystallisation did  ordering i s of  have  allowed a  orthoclase  many o f  necessarily  Thus  place.  part,  of  'apparent'  of  a more  d a t a p o i n t s on F i g s ,  i n large  does not  temperature  ordering  may h a v e  take  more  samples.  consequently  'apparent'  anomalous nature in  other  exception,  equivalent  reflects,  feldspars  sites.  and the  An a n d K i o n s  scatter  equivalence  and has  p e r t h i t i c u n m i x i n g must  Guichon b a t h o l i t h are  slight  considerably  A l and S i ,  v/ith a s i n g l e  approximately The  of  d i f f u s i o n of  from  is  b u l k composition than tho  greater  of  to  it  material will  T^  in  the  sites,  determine  25  the  amount  Therefore and  the  final, e  )  time  both  the  relative  of  structural  VI gives  and the  Wt% O r .  with  the  Phase  are  w h i c h have  alkali  the  b a t h o l i t h to  with  the  of  bulk  two  feldspar  another, oxide  from chemical  for  estimated  the  bulk  Feldspar homogenised  compositions  alkali  feldspar  bulk  in  range  to  the  be  71  from the of  65  no r e g u l a r  compositions nor i s contents estimates,  of  Wt% Or  (see  Wt% Brook  and  variation  any  the  86  Pitches  f r o m one  there  the  feldspar.  Homogenised A l k a l i  compositions  bulk  affect  an a l k a l i  °2©(201)  place.  temperature  rock w i l l  of  samples  seems t o  component  derived  seen  host  state  the  generally  There  the  the  corresponding  exception  Wt% O r .  crystallisation  observed  A s may b e  compositions  as  initial  Bulk Compositions of  samples  65  d u r i n g w h i c h d i f f u s i o n may t a k e  cooling history  Table  in  of  of  phase  of  correlation  rock  samples  Appendix  2)  26  TABLE V I 20 v a l u e s f o r 201 r e f l e c t i o n s . (CuK«radiation) a n d e s t i m a t e d b u l k c o m p o s i t i o n o f homogenised a l k o . l i f e l d s p a r s from t h e Guichon Crook b a t h o l i t h Sample #  Phase  1 ? 3 4 5 6 7 8 9 10 11 12 13 14 15 16 . 17 13 19 20 21 22 23 24 25 26 27 28 29 • 30 31 32 33  1 1 1 1  21.113 21.124  2G 2G 2G 2G 2C 2C 2C 2C 2C 2LR 2LR 2LR 2LR 2LR  21.216  3k  35  3 3 3 4 4 4 5 5 5 5 5 5 6 6 6 6  °20(2O1)*  °20 Spread """Estimated from 3 t r a c e s Wt% Or. .005 .013 .003 .003 .003 .008 .002 .005 .005 .013 .005 .015 .010 .010 .005 .005 .008 .008 .010 .003 .013 .005 .013 .010 .003 .005 .008  21.116 21.111  21.146 21.089 21.169 21.213 21.119 21.120 21.082 21.116 21.131 21.123 21.141 21.132  21.164  21.200 21.096 21.184 21.197 21.144 21.241 21.139 21.125 21.293 21.150 21.204  21.166  21.319 21.152 21.231 21.179 21.070  .006 .003 .008 .003 • .003 .007 .008 .005  81.5 80.0 81. 82. 72 79. 84.  76.  72. • 80.5 80.5 34. 81. 79.5 80. 79. 79.5  77.  73-5 82.5 7573.5 78.5 70. 79. 80. 65.5 78. 73.0  76.5  63. 78. 71. 74.5 85.  *°29 ( 2 0 1 ) v a l u e s a r c a v e r a g e s o f 3 d i f f r a c t o m e t c r + A c c u r a c y e s t i m a t e d a t - 2 Wt% O r .  traces  27  IV a  )  Mode  of  Plagioclase  Occurrence  Plagioclase in  all  phases  variable Albite  size  but  oscillatory frequently  inclusions  zoning  phase,  albite-carlsbad  are  to  restricted commonly  core  as  Hybrid  and  b)  regions  of  Plagioclase  thin-section a of  4-axis 2Vz  universal  indicate  plagioclases  the  mica i s  all  vary  the  a  slight  the  samples  and  have  structural to  Hybrid phase,  to  be  to  a  common i n  in  the  plagioclase  studies.  Zoning been  Universal  from low  alteration  occurs  in biotite  In the  especially  perpendicular  stage.  that  and  Highland Valley  Intense  compositions  using  magnetite  and  is  fully  an i n c l u s i o n and t e n d s  Compositions  Plagioclase  Normal  more  showing  0.5mm.  is  zoning  rim regions.  some a l t e r a t i o n almost  than  scarce.  discussed  i n the  regions.  colorless  core  to  crystals  extremely  less  common a n d p a t c h y  with biotite  fine-grained phase  twinning i s  Zoning i s  appears  an  twinning  common,  be  euhedral  from 4mm t o  Hornblende,  are  also  restricted  ranging  or  and has  section.  and l e s s  pyroxene  subhedral  batholith,  present.  to  as  pericline  following  tendency  the  combined  ubiquitous  the  occurs  of  grain  or  F eMjsjDjar_s  to  measured 'a'  stage states  intermediate.  in  method  and  measurements of  the Because  28  Plagioclase  Sample #  Phase  1 1 1 1 2G 2G 2G 2G 2C 2C 2C 2C 2LR 2LR 2LR 2LR 2LR  JL  2 3 4 5 6  7 8  9 10 11 12 14 15  16 17 18 19  3 3 3 4 4 4 4 5 5 .5 5 5 5  20 21 22 23  24 25 26  27  28 29  30 31  32  I !  c o m p o s i t i o n s - see t e x t  6  6 6 6  3 3  34 35 i  for explanation  Bulk composition Wt% An Wt % An Core M a i n R i m Rim c o n t a c t w i t h O p t i c a l X-Ray A l k a l i feldspar 47 35 30 38 36 38 38 48 38 36 36  36 28 26 27 27 25 27  20 20 20  45  26 32 25  41  24  32 39 31 32 33 32 27 36 38 38 38 48 36 29 33  40 24 38  32 34 23  36  heavy a l t e r a t i o n ?12heavy a l t e r a t i o n 20 none o b s e r v e d 24 20 zero 20 zero 26 32  20 20 20 20 20  myrmekitic 24 20 20 20 zero zero zero  20 20 20 20 20 20 20 20 7 20 20 20 16  zero zero zero zero zero zero zero zero 7 or zero zero 20 zero zero  25  18  18  44.0  43 32  • , ,  30 35  31 34 32  .  30  .  33 33 33  '  32 39 33 33 28 28  23.5 30.5 35.5 25.5 35.5 28  24 • 0  36 33 33 25.0 32.0  32.0  33 27.5 31-5  29.0  50  27 29 31 28 28 30 35 28  do  . )  29.0  32.0 27.5 29.5 31.5  27  26.5 27.5 26.5  27 12  23.0 11.0  28.0  28  28 28 30  24  1  28.5 27.5 29-5 23.5  29  the p l a g i o c l a s e e x h i b i t  considerable compositional  zoning i t i s rather d i f f i c u l t  to estimate bulk  compositions.  Because o f t h i s d i f f i c u l t y X-ray d i f f r a c t o m e t e r p a t t e r n s v/ere o b t a i n e d  f o r a l l the samples, w i t h s i x o s c i l l a t i o n s  b e i n g made i n t h e r a n g e 2 9 ° t o 3 3 ° 29 u s i n g The  s e p a r a t i o n o f t h e (131)  and  the average value  a n d (131)  CuK^radiation.  p e a k s was m e a s u r e d  f o r e a c h sample compared t o t h e  ' l o w ' . p l a g i o c l a s e curve  o f Smith  (1956).  F o r 75% o f t h e  samples i n v e s t i g a t e d the average composition d i f f r a c t o m e t e r method a g r e e s  t o w i t h i n 2 Wt% An w i t h  t h e a v e r a g e v a l u e e s t i m a t e d by o p t i c a l the r e m a i n i n g lower  from t h e  examination.  For  samples t h e d i f f r a c t o m e t e r averages are  i n An c o n t e n t  and a l l t h e s e  samples' c o n t a i n  p l a g i o c l a s e s w i t h s t r o n g l y s e r i c i t i s e d core r e g i o n s . In  such  accepted Table  cases t h e average or bulk composition was t h a t o b t a i n e d by o p t i c a l  VII lists  finally  examination.  c o m p o s i t i o n a l r a n g e s a n d o p t i c a l and  X-ray d i f f r a c t o m e t e r e s t i m a t e s o f average p l a g i o c l a s e compositions. In g e n e r a l , core c o m p o s i t i o n s An3§ t o An£8  a  n  d  a r e i n t h e range  i t i s o n l y i n t h e W i t c h e s Brook phase  t h a t t h i s r a n g e i s e x c e e d e d - An 32  t o An^Q.  Plagioclases  f r o m t h e H y b r i d p h a s e and f r o m t h e G u i c h o n v a r i e t y o f t h e Highland  V a l l e y p h a s e have r i m c o m p o s i t i o n s  averaging  30  Ar^y  whilst  a l l  compositions  of  Many o f feldspar In  such  the  cases  suggests  that  the  samples.  final  of  crystal. put  albite  rims:  (i)  It  plagioclase magmatic  is  be  inner  plagioclase. occupies  l a n d 2) was  thin  r i m of  that,  the  than  been  i n granitic rocks  calcium r i c h expected. edges,  crystals  sodium,  hypotheses  presence  diffusing  is  of  out  Late  commonly  The a l b i t e  between  w o u l d be  and hence  component  these  out  of  the  the  the  of  the  stage  believed  late  greater  more r a p i d  rims appear  w h i c h may s u p p o r t  outline  during r e s o r p t i o n of  composition gradient  for  occurs  resorbed  r i m more r a p i d l y t h a n s o d i u m .  the  place  these  albite  Two a l t e r n a t i v e for  which  taking  crystallisation in  account  possible  and p l a g i o c l a s e  calcium  to  (ple.tcj  p a r a l l e l i n g the 3)  rim  alkali  e n r i c h e d i n sodium and p o t a s s i u m r e l a t i v e  liquid  the  commonly  plagioclase  c a l c i u m may h a v e  liquid  Therefore  of  feldspar  of  (Plate  forward to  plagioclase,  be  stages  plagioclase,  may b e  poikilitic  plagioclase,  have  .  with subheclral-euhedral  alkali  the  investigated  Anp  exhibit  Furthermore, a very  the  to  samples  resorption of  within the  samples  the  into  other  approximately  i n contact  embayments  during  the  to  calcium.  magmatic for  diffusion  plagioclase to  have  diffusion  is  diffuse  hypothesis.  31  Plate  1  P a r t i a l l y resorbed plagioclase enclosed within p o i k i l i t i c a l k a l i feldspar. S a m p l e #11. Chataway v a r i e t y . C r o s s e d n i c o l s , x 30.  32  However,  the  of  feature.  this (ii)  albite the  of  diffusion  margins  scorn t o  samples, the  be  a very  however,  associated  than w i t h the  Late  by  the  system  the  line  solution  component  to  of  limit  corresponding two  may t a k e  magmatic  with the  to  2  of  line  the  plagioclase  enter  been  the  #31  to  In F i g .  2  solid  DBF i s  single  a  compositions at  1 kb  1969).  which  water  plagioclase  field  7  Strongly  BEF, at  and replacement  Sample  liquid  has  feldspar  liquid  feldspars  resorption place.  scale  In a d d i t i o n ,  crystallised  may e v e n t u a l l y  present  fine  CaAl Si 0g.  and H a m i l t o n  l i q u i d s which  plagioclase  relatively  does  (1958) w i t h r e f e r e n c e  and the  (James  This  i n tho  plagioclase  in this  pressure  unmixing.  be  feldspars.  the  fractionated  albite  lamellae.  ABC r e p r e s e n t s  stage  may  KAlSi^Og -  in equilibrium with  that  feldspars  the  a n d Bowen  system  study  alkali  continuous  resorption  Tuttle  boundary  feldspar  of  a closfe  suggested  explanation  alkali  NaAlSi^Og -  fractionated  time  likely  optically  stage  explained  early  have  the  perthitic  rather  vapour  1958  of  because  rims are  are  rims prevents  during perthitic  albite  field  the  r i m s on o r t h o c l a s c - r i c h  crystal  of  of  Bowen and T u t t i e  result  not  thinness  by  represents  which i n i t i a l l y  at  an  which  alkali a  highly  crystallised  H y b r i d , Highland Leroy  phase  v a l l e y and  samples.  Bethlehem, Witches and Bethsaida c,  Gump l a k e  brook  phase  phase  samples  samples.  A n o rt h i t e  Albite  Orthoclase  Fig. 7 .  Modal  samples  recalculated  the  limit  the  boundary  alkali  of  feldspar constituents  ternary curve  fe I d s p a r .  to  100%  solid  of the  Guichon  An + A b + O r .  ABC  Creek  batholith  represents  solution in natural f e l d s p a r s .  separating  t h e f i e l d s of p l a g i o c l a s e  DEF and  is  3k  plagioclase became, o u t was  of  feldspar  equigranular with  variation zonation  Thus  consists alkali  of  an  cores  and  by  and  and  an  •  feldspar  gradational  patchy  zoned  crystals  alkali  phases i n t o  from the  only  whilst  those  phases have  normal  may h a v e  zones  zoned  Samples either these  in all  Gump L a k e p h a s e  three  followed  or  two four  both  samples  of are  the  two  and with  the  rims. cases  exhibit  a  previously very  by a  schemes, to  zoning described,  broad normally  Witches  related  The  zoning.  continuously  from N o r t h c o t e ' s or  from  zoned  progressive  the  Hybrid  the  delicately  and n o r m a l l y  between  of  normal zoning  through  oscillatory  of  the  is  cores  may e x h i b i t  and d i v i d e s  rim regions  intermediate  little  nature  zoning,  from the  very  the  plagioclases  cores  show  batholith,  to  Plagioclases  rim.  compositions  phases e x h i b i t  from core  some  the  and B e t h s a i d a  oscillatory  that  liquid  and r e p l a c e d  plagioclase  plagioclase  Valley  Bethlehem  that  #31  quartz,  significant  superimposed  in  of  throughout is  Highland  scheme  resorbed  Thus  resorbed  groups.  change  Or-^.  magmatic  rapidly  mantles.  Although  major  partially  mosaic  partially  feldspar  This plagioclase  e q u i l i b r i u m w i t h the  consequently  alkali  An22«  feldspar  Brook  phase  suggesting the  Highland  35  Plate  Plate  3  P a r t i a l l y r e s o r b e d , - o s c i l l a t o r y zoned plagioclase enclosed within p o i k i l i t i c , p e r t h i t i c a l k a l i feldsnar. N o t e t h e a l b i t i c r i m t o the p l a g i o c l a s e . S a m p l e #2$, B e t h l e h e m p h a s e . C r o s s e d n i c o l s , x 30.  if O s c i l l a t o r y z o n i n g i n p l a g i o c l a s e . Cample Bethsaida phase. Crossed n i c o l s , x 30.  #3%.  36 Fig . 8  Plagioclase  zoning  schemes.  O  0-5  I  i Millimetres  I'O 1  Valley  phase  illustrates #27  is  the  Highland  of  the the  Bethlehem phase. z o n i n g schemes. i n that  core  (An-^)  similar  Valley  phase,  which terminates  and i s  inner  nature  to  particularly interesting  homogenous  rind  and o t h e r s  followed  by a more  r i m A n ^ g g i v i n g way  to  (An^7_2Q), a c h a r a c t e r i s t i c  to  it  samples  basic  the  8  Sample  displays from  i n an  a  the absorption  oscillatory  a n o r m a l l y zoned of  Fig.  zoned  outer  Bethlehem  and  rim  later  phases. Normal believed the  to  result  solid  of  r e a c t i o n would  Hybrid  believed  to  and H i g h l a n d  have  magma f l o w .  leading  the  to  Valley  zoning i n plagioclases  to  are  of  and  falling for  under  the  delicate  imperfectly  theories  repeated partial movement  c a n be  variations volatile  known.  of  pressure  crystal  or require  a n d magma,  are of  Vance  Basically  of  pressure  plagioclases  oscillatory  those  temperature,  magma  mechanisms  d i v i d e d between  that  invoke  and/or  repeated  and those  in  temperatur  conditions  (1957) h a s d i s c u s s e d t h e v a r i o u s t h e o r i e s . the  crystals  phases which  Conversely  development  generally  between  seem l i k e l y  crystallised  convective  is  solution series  c r y s t a l l i s a t i o n i n response  Such l a c k the  crystals  fron non-reaction  anorthite-albite  during  of  zoning i n plagioclase  based  relative on  the  diffusion expanded  supersaturation by H i l l s  The l a t t e r in  (1936)  authors  theory  of Harloff  and B o t t i n g a et a l  relate  the degree  t h e magma i m m e d i a t e l y a d j a c e n t  of  to  (192?) (1966).  supersaturation  the c r y s t a l - l i q u i d  interface  t o the mechanism o f n u c l e a t i o n and t h e  geometric  configuration of that  of  a supersaturated  interface in  of o s c i l l a t o r y  the glassy  by B o t t i n g a e t The  theory  between layer  layer  interface.  zoned bytownite  that  there  growing plagioclase  presence to the  crystals  basalt  a l u s i n g an e l e c t r o n  requires  The  immediately adjacent  m a t r i x o f an oceanic  be no r e l a t i v e  crystals  set  has been  microprobe  analyser. movement  from  the Bethlehem and Bethsaida phases i s o f the  to  variations  magma c h a m b e r extremely reason is  If  of temperature i t  regular  type  that  i n both timing  plagioclases  o f z o n i n g v/ere d u e  or pressure  would r e q u i r e  within  these  and degree.  explanation  author  currently available  delicate  oscillatory  Some o f t h e B e t h l e h e m p h a s e  the  v a r i a t i o n s be  the modified d i f f u s i o n - s u p e r s a t u r a t i o n  c o n s i d e r e d by the present  regular  this  in  interface.  of the o s c i l l a t o r y  type.  zoning observed  to the  Most  delicate  proven  and the boundary  i n t h e magma i m m e d i a t e l y a d j a c e n t  regular,  as  For this theory  t o be t h e most  f o r the presence  zoning i n igneous plagioclase  crystals  viable  of plagioclase do,  39  however,  contain  have i r r e g u l a r  one  or  outlines.  z o n e s may r e p r e s e n t accompanying Vance  two  i n t r u s i o n of  succeeding  plagioclase  crystals. of  operation  of  growth  oscillatory  carried from  of  out  the  in  the  zoned  suggested  sufficient  zoned  to  feldspars  water  saturated  w i t h the  increase  system,  melt  This the  cause  composition  to  the  decrease  plagioclase  crystallisation of  of  consequent prevent  the  process  thus  causing  the  ( 1 9 6 8 ) has samples  determined  w i t h the study  melt  has  at  shown  plagioclase  change  of  that  composition initial  The  plagioclase onset  of  equilibrium compositions  slow  and  Further increases i n  markedly.  would probably any  the  changes r a p i d l y w i t h  rate  normally  in  on g r a n o d i o r i t e  i n temperature.  temperature  effectiveness  9 )  phase.  Piwinski  coexisting  (Fig.  pressures  that  plagioclase,  n o r m a l l y zoned r i m s .  of  these  cores  with  that  o r i g i n of  diffusion-supersaturation  temperatures.  changing  the  S i e r r a Nevada b a t h o l i t h and had  coexisting slight  that  Brook dyke  discussed  melting experiments  compositions various  Witches  saturation  b o i l i n g may b e  zones  in volatile  Ho h a s  resurgent  deposition  possible  oscillatory  volatile  the  is  variations  zoned r i m s  of  It  ( 1 9 5 7 ) has  attainment  s l i g h t l y wider  tend to  during  terminate  diffusion process  rapidly  the  likely  to  40  l  1  1  subsolidus —I 1 20  1  1  I  i  40  Weight  Fig.  1  1  1  i  •  60  %  r  |  80  An.  9 Compositions of p l a g i o c l a s e s i n e q u i l i b r i u m w i t h g r a n i t i c m e l t s asa f u n c t i o n of temperature at 2 kb water pressure. (After Piwinski,  1968, p.560)  41  cause of  oscillatory  normally  that  the  under  zoning,  zoned  previously therefore  of  higher  probably  evidence  phases  volatile  precipitation  applicable  i n those  on h i s  presented  to  pressures  than data  had are  plagioclase  phases and the as  suggests  crystallised  P i w i n s k i ' s experimental  crystallisation is  the  Textural  and B e t h s a i d a  existed.  study  causing  plagioclase.  Bethlehem  conditions  thus  hypothesis  an a l t e r n a t i v e  to  based  Vance's  suggestion. The u n i q u e of  the  Witches  easily zoned the  cores  of  schemes a r e  the  Brook phase  explained.  Highland  phase  plagioclase  these  Valley  major  then  the  resorbed  may b e  mantled being lack  was  typical  may be  possible  of  dykes  to  deeper  the, fact within  not  affinities  tho  outer  suggested  a dyke If  of  is  the  samples  material,  the  more  main  case #27  prior  Bethlehem  complete  chamber.  and  were  Brook type.  major  that  associated  phases which  Witches  that  phase  such  to  zoning  (1969) h a s  phase  the  is  Bethlehem  earlier  within  a n d #26)  suggest  cores  the  two  in  phase.  of  in  normally  present  may b e  Bethlehem  xenocrysts due  those  present  resorbed,  whilst  plagioclase  xenocrysts  such  (#27  Northcote  Bethlehem  i n t r u d e d as of  rocks  by  to  Brook phase  the  samples,  partially  phase,  plagioclases.  Witches  scheme  plagioclases  identical  with  #26  The  zoning  to The phase  assimilation  4 2  V a  )  Mode o f  Occurrence  Biotite from  the  present  in a l l  The amount  In rocks  with less  biotite  is  Biotite  and h o r n b l e n d e those  occur  rocks with  Wt% a n d 70 W t % , a n d b i o t i t e more  than  siliceous  alkali  present.  feldspar  samples  but  euhedral size.  rim  crystals  content  Hybrid  or replace  phases b i o t i t e  Si0  is  the  is  the  the  Si0  and  hornblende.  absent. ragged,  a wide  in a l l  samples  in  coexist  to  grain  contain  large,  quartz  inclusions.  exhibit  the  subhedral  range  and h o r n b l e n d e ,  and hornblende  mineral  greater  with plagioclase,  does b i o t i t e  65  plagioclase,  entirely  biotites  equal  ferromagnesian  present  as  rock  content  2  between  arc  occurs  host  containing  only  coarse-grained  pyroxene  the  to  dominant mafic  o c c u r r i n g commonly as phase  tends  of  contents  2  In r o c k s is  studied  i n approximately  and e x h i b i t s  poikilitic  magnetite the  biotite  t h a n 65 Wt%  and m a g n e t i t e  generally  Some o f  euhedral,  in  of  samples  In a d d i t i o n , quartz,  muscovite  Biotite  and  rocks.  75 Wt% S i O p b i o t i t e  silicate  the  accompanied by b o t h pyroxene  amounts i n  in  of  with increasing s i l i c a  10).  (Fig  is  batholith.  decrease  Biotites  Only  a tendency in a l l  without  to  other replacement.  Fig.10. and  Relation  silica  content  between of  host  abundance rock.  of b i o t  44  The  type of i n c l u s i o n s present i n a l l of the b i o t i t e s  suggest that  biotite  s t a r t e d to c r y s t a l l i s e  simultaneous c r y s t a l l i s a t i o n but  p r i o r t o the  Chloritic majority  separation  during  of p l a g i o c l a s e of  alkali  and  the  quartz,  feldspar.  a l t e r a t i o n of b i o t i t e s i s i n s i g n i f i c a n t i n of the  s a m p l e s but  up  t o about 50%  the  chloritisation  o c c u r s i n a fev; s a m p l e s . b)  Method o f  Study  B i o t i t e m i c a s e x h i b i t a. l a r g e r a n g e o f  possible  chemical s u b s t i t u t i o n s w i t h i n the  crystal  3+ Thus A l ^  tetrahedral  Na,  Ba,  may  Rb  p l a c e o f K., F  .  The  replace  e t c may and  U+  i n the  OH  a n i o n s may  be  most p e t r o g e n e t i c a l l y  by  Fe  2+  layer,  s u b s t i t u t e as i n t c r l a y e r c a t i o n s  however o c c u r i n t h e replaced  Si  structure.  replaced  important  octahedral  by  v  and  Mn  2+  +  .  i n physical properties  of the  wide range of p o s s i b l e  chemical s u b s t i t u t i o n .  that  b i o t i t e s arc  or  may  c a u s e d by It i s  with  o f a s i n g l e e l e m e n t or  s i m p l e e l e m e n t r a t i o have b e e n  largely unsuccessful.  ( c . f . R i m s a i t e 1967).  p r e s e n t a u t h o r has  the not  changes  in physical properties  The  variation in  be  Differences  attempts to c o r r e l a t e the  in  substitutions  l a y e r where Mg^  3+ 3+ 3+ , Fe^ , A l , Ti^  surprising therefore  CI™  Ca,  concentration  a t t e m p t e d t o make e s t i m a t e s  45  of t h e p e r c e n t a g e o f t o t a l o c t a h e d r a l i r o n group present  i n biotites  metals  from t h e G u i c h o n B a t h o l i t h u s i n g  Gower's (1957) X - r a y d i f f r a c t o m e t e r method.  The r e s u l t s  have shown t h a t v a r i a t i o n i n t h e d e g r e e o f p r e f e r r e d o r i e n t a t i o n o f t h e sample may i n t r o d u c e a s much a s 10% v a r i a t i o n i n the estimated i r o n group m e t a l s ,  percentage of t o t a l  ( T a b l e V I I I ) when i n t e n s i t y  IQQ^/IQQ^ a r e r e l a t e d t o R i m s a i t e ' s The  s t u d y was t h u s  direct  F i g 11  discontinued i n favour  octahedral ratios  (1957  p.37).  o f more  chemical a n a l y s i s .  Sample #  Sample P r e p a r a t i o n  T x  004 005  % Fo o c t .  A.l A.2  Coar se g r i n d Fine grind  - s l u r r y mount - s l u r r y mount  .684 .570  28 22  B.l B.2 B.3 B.4  Fine Fine Fine Fine  -  s l u r r y mount s l u r r y mount centrifuged centrifuged  .661 .937 .848 .822  27 40 36 35  C.l C.2  Fine grind Fine grind  - s l u r r y mount - s l u r r y mount  .827 .741  35 31  Table  VIII  grind grind grind grind  Observed i n t e n s i t y r a t i o  IQQT| f o r 3  biotite  samples a s a f u n c t i o n o f sample p r e p a r a t i o n  Any mineral  form o f s t a n d a r d concentrates  chemical  a n a l y s i s technique  of  s u f f e r s from t h e f a c t t h a t i t i s  sometimes i m p o s s i b l e t o o b t a i n a c o m p l e t e l y In a n a l y s i s of b i o t i t e  pure  concentrates, admixtures  sample. of i r o n  46  oxide, c h l o r i t e , sphene, r u t i l e ,  amphibolc a p a t i t e and  and unknown e r r o r s . microprobc biotites  i n c l u s i o n s of  q u a r t z may  For t h i s r e a s o n ,  zircon,  introduce large the  electron-  has been used f o r p a r t i a l a n a l y s e s o f  from t h e G u i c h o n b a t h o l i t h .  i n s t r u m e n t has of the  and  The  use  the  of  this  t h e added a d v a n t a g e t h a t o n l y s m a l l amounts  sample a r c r e q u i r e d .  Biotite mineral  concentrates  f o r a p p r o x i m a t e l y h a l f o f t h e s a m p l e s s t u d i e d had been produced  by K.E.  determinations. Dr. N o r t h c o t e and these  The  Northcote  f o r use  i n K/Ar  age  present author i s g r a t e f u l  t o Dr. W.H.  already  to  White f o r p e r m i s s i o n to  c o n c e n t r a t e s i n the p r e s e n t  study.  Biotites  t h e r e m a i n i n g s a m p l e s were c o n c e n t r a t e d by s i e v i n g crushed  r o c k f o l l o w e d by h a n d p i c k i n g o f t h e +40  fraction.  D e t a i l s of the experimental  employed i n the e l e c t r o n microprobe  °)  from of  mesh  techniques  a n a l y s e s and  d i s c u s s i o n o f t h e e r r o r s i n v o l v e d i n t h e method presented i n Appendix  use  a are  3.  D i s c u s s i o n of R e s u l t s The  r e s u l t s o f the- p a r t i a l a n a l y s e s o f 14  biotite  s a m p l e s from t h e G u i c h o n b a t h o l i t h a r e g i v e n i n T a b l e R e s u l t s a r e g i v e n i n t e r m s o f Wt%  Mg  and  IX.  Fe s i n c e i t i s  not p o s s i b l e t o d i s t i n g u i s h v a r i o u s v a l e n c e s t a t e s w i t h the e l e c t r o n microprobe.  For t h i s reason the r e s u l t s f o r  hi  F i g .11: B i o t i t e c o m p o s i t i o n s as a f u n c t i o n silica  content  of  the  host  rock.  of  the  ample  31 14 19 20 6 2 23 4 29 15 9 34 34 11 35  (Dup)  Table  IX  Wt% Mg microprobo  Fe microprobe  crFe Wt%  6.0 7.8 8.1 8.6 8.6 9.1 9.2 9.3 9.4 9.4 9.4 9.5 9.7 10.0 10.0  19.5 15-5 15.1 15-3 14.8 16.0 13.0 13.3 12.6 13.3 12.9 12.4 12.2 13.0 13.3  .25 .10 .20 .25 .70 .40 .30 .10 .20 .05 .10 .20 .25 .10 .10  Results analysis Creek  of of  partial biotites  batholith.  deviation)  is  inhomogeneity, statistical  electron-microprobo  a  cr ( o n e function  surface  variation (see  from the  Guichon  standard of  sample  roughness of  Appendix  X-ray 3)  and  the  generation,  k9  iron  must  Relative  be  regarded  errors  experimental generation, -  zoning  was  magnesium  errors,  is  contents  bearing  samples  of  the  the  the  host  greater  there  rock  within  the  complex,  the  that  of this  the  are  coexisting  ferromagnesian  of  the  rock  trend  the  are  i.e. The  as  are  biotites.  of  only  rocks  of  to  those  that  complex;  i n the  exactly  Ben  as  Nevis  exhibit  analogous  Haslam has  what  forro-  biotite  to  emphasised  F e / ( F c + Mg) r a t i o s  with increasing  reverse  in  containing  ingcous  decreasing  SIO^  reversed  clinopyroxenes  that  of  the  Furthermore,  and  and  Fe/(Fo + Mg)  similar  Scotland,  compositional  content  observed  remarkably  as  hornblendethe  those  X-ray  studied.  trend i s  biotite  in  increasing  the in  ).  estimated  iron  with  for  This  silicates is  variation  with increasing  variations  in  account  samples  a decrease  (1968).  observed  host  is  hornblendes  compositional  the  Thus  Ben N e v i s ,  by Haslam  into  No r e g u l a r  biotites  Wt% S i 0 2 >  reported  those  the  mineral,  trends  + Fe^  v a r i a t i o n i n the  contain  silicate  compositional  of  ( F i g 11).  that  t h a n 73  Wt% F e .  rock.  biotites  samples  magnesian  host  taking  (Fe  statistical  i n any  of  iron  inhomogeneity:  a regular  of  exist  the  and sample  acidity  those  i n analyses;  observed  There  in  total  Wt% Mg a n d - 0 . 2 5  0.35  ratio  as  might  differentiation be  suggested  Fig.  12  S t a b i l i t y o f b i o t i t e s a s a f u n c t i o n o f fOp 2070 b a r s t o t a l p r e s s u r e . Subhorizontal li o f c o n s t a n t 100 F e / ( F e + M g ) v a l u e s . Arrows r e p r e s e n t o x i d i s i n g and r e d u c i n g t r e n d s i n D i a g r a m f r o m Wones a n d E u g s t e r , (1965)  and temperature at n e s represent contours l a b e l l e d I and I I c r y s t a l l i s i n g magmas.  51  by  the  results  systems. reversal water  The  of  factors  include  and the  assemblages  experimental  the  total  p a r t i a l pressures pressures  variable  of  Wones a n d E u g s t e r ' s  oxygen  stability  temperature  of  at  are  a total  to  I  and  II  the  fact  represent  Trend I represents  with that  environment.  and  cooling,  component,  Under  is  phase  function of  the  a  such  remain e s s e n t i a l l y  crystallised  reproduction  p.1254) of  and  f0  The  This  compositions  because  with Wones  extrapolations  two  the  and  amphibolo  a magma w h i c h ,  hydrogen  conditions biotite Trend I I  two  during  becomes s a t u r a t e d  constant.  labelled  conditions  c r y s t a l l i s a t i o n of  and l o s e s  and  from  trend lines  changing  shows  and  2  2070 b a r s .  containing biotite  magmas.  crystallisation  a  that  during hypothetical  will  and  and tho  than with o l i v i n e s .  unreliable.  o n F i g 12  (1965>  bulk  expected  reacts  oxygen  commonly a s s o c i a t e d  assemblages are  as  unusual  and p y r o x e n e s  Fig.  pyroxene  this  biotites  F i g 12  pressure  much more  emphasise  i  to  studied  synthetic  F i g 13  biotites  Eugster  have  fugacities.  diagram represents  12  of  operative,  (1965)  v a r i a t i o n of  at  amphiboles  synthetic  present.  compositional  biotites  of  w h i c h may c o n t r i b u t e  Wones a n d E u g s t e r  the  studies  in  K^O,  to  the  compositions represents  52  a magma t h a t  is  'buffered'  that  it  contains.  also  d e c r e a s e s and b i o t i t e  consecutively Evidence  be  suggests  that  occurred  under  volatile  pressures.  exists  that  increasing the  loss  explain Fe/Fe  due t o  to  the  observed  slight  occurs  also  corresponds  silicate  present.  the  to  biotite It  may h a v e  prevailing  oxygen  present  w i t h the  If  is  a  is  then the  i n the  in  tho  -  increasing  have  water  been  a n d magma a n d This would decreases  host  of  rock  tho  only that  assemblage  the  new m i n e r a l  on  the  that  existing mineral fugacity and the  F e / F e + Mg r a t i o  11  ferromagnesian  effect  temperature  trend  in Fig  mineral  an e f f e c t  oxygen  in  progressive  the  'buffering'  with decreasing  increase  the  which  possibility  The r e v e r s a l  possible  previously  the  with  becomes  fugacities  correct  become  Guichon b a t h o l i t h  progressive  magma.  a change  VI  environment.  in biotites  assemblage  rapid  the  r  where  the  may a l s o  73 Vi t% S i O ^ o f  present,  decrease  Chapter  progressively  fugacities  hydrogen  at  in  In such a case  of  that  this  presented  r e a c t i o n between  + Kg r a t i o s  fC^  rich.  c o n d i t i o n s of  of  assemblage  compositions w i l l  c r y s t a l l i s a t i o n of  oxygen  consolidation  mineral  Thus w i t h f a l l i n g t e m p e r a t u r e ,  more i r o n  will  by t h e  was  not  assemblage. would observed  in biotites  would  53  be  produced.  I t i s therefore  assemblage and t h e p a r t i a l existed during  suggested that the mineral  pressures  crystallisation  of v o l a t i l e s  of that  that  a s s e m b l a g e may  b o t h have h a d a n e f f e c t on t h e c o m p o s i t i o n o f t h e biotites Tho  crystallising  f r o m t h e magma.  discussion of biotite  Guichon b a t h o l i t h has, qualitative.  crystallisation  o f n e c e s s i t y , been  Wones and S u g s t o r  i n the  purely  (1965) have  data that allow q u a n t i t a t i v e estimates  published  t o be made o f t h e  independent i n t e n s i v e parameters, temperature, o f HpO, and. f u g a c i t y o f o x y g e n , w h i c h were during  crystallisation  sanidine the  + magnetite.  operative  o f t h e assemblage b i o t i t e  sulphides, biotite,  - clinopyroxene,  hornblende,  p y r i t e or other  sphene a p a t i t e a n d z i r c o n , i n a d d i t i o n t o  alkali  f e l d s p a r and m a g n e t i t e .  Furthermore i n  c a l c a l a t i o n of the intensive variables  during  +  The common a s s e m b l a g e s p r e s e n t i n  Guichon b a t h o l i t h samples, however, i n c l u d e  plagioclase, quartz  any  fugacity  crystallisation,  the a c t i v i t y  operative  of the  KFe^AlSi^O-^Q(OH) component i s a c r i t i c a l  factor.  The  data p r e s e n t l y a v a i l a b l e f o r the Guichon b a t h o l i t h biotites  does n o t a l l o w an e s t i m a t e  of this  parameter  b e c a u s e o f t h e l a c k o f any q u a n t i t a t i v e d a t a on t h e 3+ 2+ Fe-' /Fe ratio  i n the b i o t i t e s .  The e v a l u a t i o n  of this  ratio  by  standard  inacuracies and/or  that  chlorite  wet are  as  chemical due  to  the  analysis presence  i n c l u s i o n s i n the  suffers of  from  magnetite  biotite.  H y b r i d  AnorthUe  L e r o y  , Hlghjond phase  B e t h l e h e m , and  Wltchas  B e t h s a l d a  G u m p  valley  L o k t  p h a s e  p h a s e  Orthoclo se  A l b i t e  .Anorthite  a n d  s a m p l e s .  B r o o k , s a m p l e *  s a m p l e s .  Orthoclase  A l b i t e  Fig. 13 o: Plot of modal quartz — o r t h o c l a s e - a l b i t e - a n o r t h i t e  Fig. 1 3 b : S c h e m a t i c  for  system  the  trend  Guichon  line for the  a projection from  Creek batholith s a m p l e s . A—B is the  the  of  s a m p l e s in three  A - B onto  anorthite  d i m e n s i o n s . C—D is  the b a s e of the  corner.  tetrahedron  p h a s e d i a g r a m for  Qz^Or.-Ab.-An.  pre s s u re .  at  I kilobar  the water  quote/nary vapour  vn  56  VI  Modal  Analysesand  Calculated  Modal  analyses  approximately  investigated For  the  out  500 p o i n t s  wore  a point  Modal  13a  1mm,  spacing are  shows  pluton  expressed  albite  and a n o r t h i t e  the with all  the lie  base  of  on t h e the  describes  in  tho Fig  13b  granodiorite  samples  with  were  a  analysed counted.  2.  of  to  100  in line the  increasing  the  samples,  Gump L a k e  CD.  The  gradually  quartz  orthoclase, Within  F i g 13a  from the  tho  line  phase, Q,  Or,  Ab  AB  differentiating  and o r t h o c l a s e  components  the  Wt%.  ABCD w h i c h i n t e r s e c t s  plagioclase  Ab/An  traversing  p o i n t s v/ere  of modal q u a r t z ,  those  t r e n d 'of  magma t o w a r d s decreasing  of  tetrahedron  the  were  mineralogical variation within  recalculated  plane  samples  i n Appendix  tetrahedron  exception  section  -g-mm a n d 1000  i n terms  'granodiorite*  samples  (1969).  using a  thin  fine-grained  the  the  For c o a r s e - g r a i n e d  i n each  presented  of  modal a n a l y s e s  sections  stage.  of  half  Compositions  by N o r t h c o t e  samples thin  counted  of  analyses  Fig  the  microscope  spacing  with  of  reported  on s t a n d a r d  count  point  been  remainder  carried point  have  for  Chemical  contents,  and c o n c o m i t a n t  increase  ratio. is  a hypothetical  system  investigations  of  based  the  phase  partly  ternary  on  diagram of  the  experimental  systems  that  constitute  the  57  f a c e s o f the t e t r a h e d r o n .  Phase r e l a t i o n s i n t h e system  Ab-Or-Q have been s t u d i e d a t water vapour p r e s s u r e s from 0.5  t o 10Kb by Tut t i c and Bowen (1958) and L u t h , Jahns and  T u t t l e (1964).  Yodcr 0-967) i n v e s t i g a t e d t e r n a r y c o m p o s i t i o n s  i n t h e system Ab-An-Q a t 5 kb water vapour p r e s s u r e . Tho b i n a r y system An-Q has been s t u d i e d a t atmospheric p r e s s u r e by S c h a i r e r and Bowen ( 1 9 4 7 ) and at l k b Ph^O by Stewart  (1967).  P r e l i m i n a r y d a t a on t h e system An-Ab-Or  have been p u b l i s h e d by Franco and S c h a i r e r ( 1 9 5 1 ) > Stewart and Smith ( 1 9 5 7 ) and James and Hamilton Similarly  Yoder,  (1969).  e x p e r i m e n t a l r e s u l t s i n the system An-Ab-Or-Q-^O  have been p u b l i s h e d by Von. P l a t e n ( 1 9 6 5 ) and by James and Hamilton (1969).  The curved s u r f a c e abed w i t h i n the  tetrahedron of F i g 13b separates regions of compositions first  c r y s t a l l i s i n g f e l d s j j a r , from those f i r s t c r y s t a l l i s i n g  quartz.  Compositions l y i n g on t h i s plane w i l l be i n  e q u i l i b r i u m w i t h both o f t h o m i n e r a l s whose r e g i o n s i t separates.  Tho plane d e f g s i m i l a r l y s e p a r a t e s tho two  f e l d s p a r r e g i o n s ; above t h i s plane p l a g i o c l a s e i s t h e p r i m a r y phase, and below i t a l k a l i f e l d s p a r i s the p r i m a r y phase.  The tv/o s u r f a c e s i n t e r s e c t t o form a l i n e a l o n g  which l i q u i d s a r e i n e q u i l i b r i u m w i t h p l a g i o c l a s e + a l k a l i feldspar + s i l i c The  61  Vci.pOU.3T •  sequence o f r o c k c o m p o s i t i o n s from tho H y b r i d  58  phase,  through  granodiorite positions evidence  the  occupy  along  from t h e s e  rocks  indicates  first  followed  felsic at  by  alkali  or  poikilitic.  mineral  a much l a t e r  feldspar  which i s  This i s  crystallisation  that  trend  displaced  towards  Northcote  (1969)  be  surface  the has  related  exactly  quartz  central  corner  it  that to  suggestion.  Plagioclase  Lake  phase  tend  they  perhaps  be  is  samples  to  of  by  of  finally  felsic  Fig  13.  phase  do n o t  but  tetrahedron.  of  support  phase  tho  an o f f s h o o t the  cither plot  almost  of  east.  Northcote's  crystals  o n F i g 13b  plagioclase  -  quartz  surface  plagioclase  -  quartz  -  some  orthoclase  or  i n the  above  Gump  that whilst  poikilitic.  approximately way  the  The  simultaneously,  institial  lie  are  Gump L a k e  rest  to  it  interstitial  the  the  the  and q u a r t z  and  cquidimonsional suggesting  crystallised  feldspar  Gump L a k e  to  quartz,  F i g 13  may be  tend  and t h a t  sequence  ABCD i n  genetically  s h o w n i n F i g 13  plagioclase  Gump L a k e  N i c o l a b a t h o l i t h which l i e s  relations  alkali  by  predicted  suggested  Guichon b a t h o l i t h and t h a t  that  the  LeRoy  Textural  conspicuously  from tho  the  crystallise  stage  w o u l d be  compositions  general  to  to  differentiated  A - B i n F i g 13.  was  may n o t  more  trend  the  on t h e  successively  phase  the  was  Rock  Highland Valley  on  the  equilibrium line,  The the  59  which  supports  The plot  the proposed  samples  crystallisation  from the Bethlehem and B c t h s a i d a  o n F i g 13 i n a p o s i t i o n t h a t  trend  and i s not r a d i c a l l y  Highland  Valley  enrichment  phase,  i n albite.  lies  different  differentiated  from t h a t  but which i n d i c a t e s  Bcthsaida  phase  samples.  slight  samples  that  . This  tends  to confirm  i n response  whilst  the b u l k o f the Bethlehem and Bcthsaida  t h e LeRoy g r a n o d i o r i t e  to l o c a l  Brook phase  w i t h t h e Bethlehem phase  -  the widest  range  A d i s t i n c t i o n has already those and this  samples  those  feature  made  containing oscillatory  of the Bethlehem  arc  essentially  The  three  t h e same  samples  (Chap.  zoned  IV)  - have  as those  between  plagioclase  plagioclase,  plagioclases  phase  with only  (1969)  o f c o m p o s i t i o n on F i g 13.  been  zoned  phases  tentatively  c o n t a i n i n g o n l y n o r m a l l y zoned  oscillatory  cupolas,  by N o r t h c o t e  d i s t i n c t i o n i s c o n f i r m e d by F i g 13.  containing  phase  chamber.  - which has been  correlated  Northcote's  dyke  differentiation i n  c r y s t a l l i s e d w i t h i n t h e m a i n magma  exhibits  are  the b u l k o f the Bethlehem and  formed  Witches  plot  they  suggestion  The  general  of the  (1969)  later  that  a  LeRoy g r a n o d i o r i t e  than  phases  w i t h i n the  o n F i g 13 i n a p o s i t i o n w h i c h i n d i c a t e s more  sequence.  The two - a  samples  distinctive  compositions  of the Bethlehem  n o r m a l l y zoned  and  that phase.  plagioclases  60  have  compositions  highly  differentiated  suggested phase  corresponding  of  therefore  that  separate  phases.  the  differentiated  phases  of  with  the  Both  of  later  the  these  The  less  Witches  first  of  late  these  exhibit  quartz  and  is  second  Spatsum  quartz  of  the  is  with  early  associated phase.  plagioclase;  sample  which  monzonite equated  phase,  the  most  differentiated  is  The r o c k quartz,  contains  highly roughly  plagioclase  m i n e r a l s was  this  sample  and a l k a l i  to  the  During  Early  euhedral  of  feldspar  that  that  univariant tho  sample  subhedral  i n the  The it  proportions  crystals,  those  position  lies  very  curve.  the  felsic  Bethlehem phase  plagioclase  Brook  studied.  Bethlehem phase  formation of  (outer)  Witches  c r y s t a l l i s a t i o n of  indicates  c r y s t a l l i s a t i o n of order  w i t h the  simultaneous.  hypothetical  i n the  occurred.  almost  o n F i g 13  #31>  equidimensional  41:30:26 v o l %, s u g g e s t i n g  large  associated  interstitial  tentatively  change  two  anhedral,  has  close  dyke-like  euhedral  Northcote  of  most  is  Bethlehem  early  final  It  Brook  components  and tho  the  feldspar.  The  three  of  represents  differentiated  groups  anhcdral  alkali  the  batholith,  later,  those  LeRoy g r a n o d i o r i t e .  (1969) i n f a c t  Northcote  more  to  some  minerals  samples of  a  contain  which  exhibit  61  a preforod of  orientation,  plagioclase,  indicates (inner) largo, to  be  by  the  quartz  early  set  phase  subhcdral,  fractured  Bethlehem  that  Copper  cuts  quartz  (White  large  euhedral  set  finer  grained matrix of  (see  Photo  portions began  of  the  the  The  progressive be  silica  i n the  (1958) a n d o t h e r s progressive increases  enrichment  c a l l e d upon to  phenocrysts  increases  i n the  Ab-Or-Qz-H n  later have  it  size is  the  duo t o  e x p l a i n the phases.  the  quartz  suggested  phase of  similarity  been  and  the of  the  noted.  Thus  differentiation presence and  shown e x p e r i m e n t a l l y  of  dyke  later  field  phase  Tuttle  i n PIL,0 w i l l  This  feldspar  the  essential  the  phenocrysts  quartz  already  of  Bethsaida  Highland Valley  Bethlchem/Bcthsaida phases has  cannot  and the  Bethsaida  oast  and  that  appear  confirmed  1956).  quartz  contain  of  quartz  would appear  tetrahedron'. of  al  subhedral  Bethlehem phase  compositions  rocks  later  v/hich  by a dyko  et  c r y s t a l l i s a t i o n from w i t h i n  'granodiorite the  Thus i t  5).  The  This i s  Guichon phase  to  This  crystals  exhibited  property  mosaic  B e t h s a i d a pha.se  contains in a  feldspar.  phenocrysts.  evidence  grained  crystallisation.  and the  s l i g h t l y resorbed textural  finer  and a l k a l i  plagioclase  Bethlehem  granodiorite  in a  cause field  therefore  of  quartz  Bowen that  progressive i n the that  the  system  62  Plate  5  Sample from a c h i l l e d B e t h s a i d a dyke from e a s t o f the Bethlehem Copper p r o p e r t y . Note presence of s u b h e d r a l - e u h e d r a l p h e n o c r y s t s of q u a r t z and euhedral p o i k i l i t i c b i o t i t e . Scale i n centimetres.  63  Bethlehem  and B e t h s a i d a  phenocrysts  may h a v e  considerably existed. other  higher  of quartz  may r e q u i r e  5 k b ( I t must best  an  suggested  total  be e m p h a s i s e d  'inspired' estimate). that  which would produce  o f 1.5  follows  to  order  evidence  that  a  of the Bethsaida  conditions  this  of k or represents  (1969)  phase  pressure  i n an  i n the arc  existing must  of high v o l a t i l e  correct,  during  have  Furthermore there  i s  been  pressures  d u r i n g t h e f o r m a t i o n o f many o f t h e s m a l l ,  igneous  bodies  or/and explain  Bethsaida  phases.  tho presence  Bethlehem explosions  Copper  ore believed White  o f numerous  property  estimates  et  al  volatile  f o r the samples  to the  (1956),  breccia  on t h e b a s i s  due t o i n c r e a s i n g  Chemical  related  of  in  considerable  existed  that  has  6 t o 8 km  estimates  pressures  by  the  crystallised  'load'  I f the above  o f 2. t o 3 - 5 k b .  that  done  'granodiorite'  i m p l y i n g , at most,  the v o l a t i l e  crystallisation the  thus  2 kb.  that  that  Northcote  t h e B e t h s a i d a phase  of  cover  systems  i n the order  however  of  than had p r e v i o u s l y  to indicate  pressures  quartz  conditions  on t h e l i q u i d u s i n t h e  environment,  it  pressures  w o u l d seem  epizonal  order  under  E x p e r i m e n t a l work i n s y n t h e t i c  presence  at  containing early  crystallised volatile  investigators  system  samples  pipes  late  Bethlehem  for  instance,  on t h e  subvolcanic  pressures. have  been  calculated  64 4  Wt  r  %  K 0 2  6 r  Wt  %  Na 0 2  5 -O-  o  4 3 2  J  I  I  I  8 7 h  wt  %  CaO  80 Wt %  Fig.  14  SiO-  C a l c u l a t e d component o x i d e s as a f u n c t i o n s i l i c a content for the Guichon Creek batholith samples. Hybrid  and H i g h l a n d V a l l e y  Gump L a k e Bethlehem,  of  phases  phase Witches  Brook and B e t h s a i d a  phases  66  u s i n g t h e c o m p u t e r p r o g r a m o f D i e t r i c h and m o d i f i e d f o r use  Shoohan  on t h e U n i v e r s i t y o f B r i t i s h The  Columbia,  I.B.M. 360  computer.  parameters  t o t h e m i n e r a l s p r e s e n t i n t h e mode and  program a s s i g n s average  chemical  these t o c h e m i c a l e s t i m a t e s f o r the r o c k sample. i s i n the  form o f m i n e r a l volume p e r c e n t a g e s  i s p r e s e n t e d as m i n e r a l weight oxide weight  percentages.  percentages  (1964)  Input  and  and  converts  output  component  O r t h o c l e . s e , a l b i t e and  anorthitc  a r e t r e a t e d a s s e p a r a t e m i n e r a l c o n s t i t u e n t s , and t h e r e f o r e t h e d a t a o f T a b l e s V I and input. those  V I I was  B i o t i t e , hornblende from  'average  recent l i t e r a t u r e ,  5  and  utilised  f o r program  a u g i t e a n a l y s e s u s e d were  g r a n o d i o r i t i c r o c k s as r e p o r t e d i n  and a l l opaque m i n e r a l s v/ere t r e a t e d  as magnetite.  Chemical  A p p e n d i x 2 and  s i l i c a v a r i a t i o n diagrams f o r the  oxides are presented The  estimates are presented i n  as F i g  component  14.  diagrams emphasise the r e s t r i c t e d range  of  c o m p o s i t i o n a l v a r i a t i o n w i t h i n t h e b a t h o l i t h , and  also  the o v e r l a p p i n g nature of the c o m p o s i t i o n a l ranges  of  v a r i o u s phases.  The  r a t h e r wide v e r t i c a l  scattering  d a t a p o i n t s on t h e v a r i a t i o n d i a g r a m s i s t o be and i s p a r t l y due F i g 14  to the  of  expected  e r r o r s i n h e r e n t i n modal a n a l y s e s .  shows t h a t t h e s e q u e n c e  Chataway-Leltoy  the  Hybrid-Guichon-  phases d i s p l a y s a p r o g r e s s i v e  displacement  67  towards  more  largely  the  later  tho  result  phases  belong very  silica  to  basis  sample  called  the  phase  has  result The  comes  been  the  of  several  hundred  Hybrid  An  attempt  diagram  of  phase  Witches  parameter adjacent  the  by  by  The the  to to  predominantly  of  scries  between  and  them  The most  Northcote  of  country  certainly made  average  the  on  acidic  body  at  the  has he  the  Guichon  o r i g i n a l magma  p l u t o n may b e  tho  rock during intrusion. extending  to  outer  this  of  suggestion.  'addition'  test  the  assimilation  composition of  the  rocks  The  to  an  for  margins  support  construct  p.76)  batholith is  present  that the  from the  tends to  The  phase.  members  inwards  estimate. the  made  a x c n o l i t h - r i c h zone feet  the  composition of  B o w e n 1928,  hypothesis. intruded  Brook  suggested  ha.s b e e n  (c.f.  of  M o n z o n i t e , and which  a s s i m i l a t i o n of  the  members  b a t h o l i t h which Northcote  more b a s i c  presence  probably  Bethsaida  from a s m a l l i s o l a t e d  the  approximates  and t h a t  Brook and  estimates.  S p a t sum Q u a r t z  equates with the It  Witches  chemical  margin of  which i s  continuing differentiation.  d i s c r i m i n a t i o n c a n be  of  the  compositions,  intermediate  analysed  western  of  Bethlehem,  the  little  rich  a particularly P e r m i a n Cache  b a t h o l i t h contact  andesitic  greenstones  difficult  Creek is  with  Group  composed subordinate  68  Fig.  15  Chemical compositions of p r i m a r y magma ( ' a v e r a g e ' Guichon r o c k s and N i c o l a N i c o l a a n a l y s e s are from to h i s proposed ' A ' and  proposed Guichon b a t h o l i t h Guichon), 'contaminated' Group e x t r u s i v e r o c k s . S c h a u (1968) a n d r e l a t e ' P ' type e x t r u s i v e cycles.  69  a r g i l l i t c and c h e r t .  The Upper T r i a s s i c N i c o l a group i s  predominantly a n d e s i t i c or b a s a l t i c v o l c a n i c rocks with minor l i m e s t o n e , a r g i l l i t c , q u a r t z i t e , groywacko and arkoso.  ( C o c k f i c l d , 1947, D u f f e l and McTaggart, 1951).  Schau (1969) has presented chemical a n a l y s e s o f v o l c a n i c r o c k s from t h o N i c o l a group.  An average c o m p o s i t i o n f o r  tho N i c o l a v o l c a n i c group taken from Schau's d a t a , has been p l o t t e d on F i g 15 a l o n g w i t h t h o e s t a b l i s h e d t r e n d s of c h e m i c a l v a r i a t i o n f o r t h e Guichon b a t h o l i t h  samples.  I t i s obvious t h a t t h e 'average' N i c o l a v o l c a n i c , supposedly  contaminated  Guichon samples and tho proposed  Guichon magma, c o m p o s i t i o n s do not l i e on s t r a i g h t l i n e trends.  The absence of such t r e n d s would tend t o i n d i c a t e  t h a t a s s i m i l a t i o n has not been a major f a c t o r i n p r o d u c i n g c h e m i c a l v a r i a t i o n through t h e b a t h o l i t h . I t must be emphasised however t h a t t h e v a r i a b l e amounts o f sedimentary r o c k present i n both t h e N i c o l a and Cache Creek groups may p o s s i b l y have a s i g n i f i c a n t e f f e c t on the c o m p o s i t i o n o f t h o assumed c o n t a m i n a t i n g m a t e r i a l . Bowen (1928) has emphasised t h a t i n order t o melt  basic  m a t e r i a l added t o a more a c i d i c magma c o n s i d e r a b l e amounts o f superheat would be necessary t o prevent r a p i d c r y s t a l l i s a t i o n o f t h o magma.  The presence o f  p r e f e r e n t i a l l y oriented plagioclase  crystals i n  70  most o f t h e H y b r i d  rocks  s u g g e s t s t h a t t h e magma h a d  r e a c h e d l i q u i d u s c o n d i t i o n s p r i o r t o i n t r u s t i o n and hence d i d n o t h a v e a n y a p p r e c i a b l e Thus m e l t i n g  amount o f s u p e r h e a t .  o f any a s s i m i l a t e d m a t e r i a l i s u n l i k e l y t o  have o c c u r r e d .  Bowen ( 1 9 2 8 ) h a s s u g g e s t e d , h o w e v e r ,  that  o f more b a s i c m a t e r i a l i n t o  conversion  constituents  t h a t a r c i n e q u i l i b r i u m w i t h t h e a c i d magma may t a k e place  without molting.  Northcote  x c n o l i t h s w i t h i n the Hybrid  (1969) has r e p o r t e d  p h a s e w h i c h d i s p l a y a marked  v a r i a t i o n i n degree o f a s s i m i l a t i o n .  Some x c n o l i t h s  have s h a r p a n g u l a r o u t l i n e s w h i l s t o t h e r s indistinct that  c l u s t e r s of mafic minerals.  a r e reduced t o  This  suggests  t h e more a c i d i c components o f t h e x c n o l i t h s may  have b e e n more e a s i l y c o n v e r t e d i n t o c o n s t i t u e n t s i n equilibrium with  t h e magma t h a n t h e more b a s i c  components.  I f such i s t h e case i t would e x p l a i n t h e l a c k o f agreement between t h e e v i d e n c e from t h e f i e l d  and t h a t  from t h e  ' a d d i t i o n ' diagram o f F i g 15. An a l t e r n a t i v e h y p o t h e s i s basic rocks  f o r t h e o r i g i n o f t h e more  i s t h a t t h e y a r c t h e d i r e c t r e s u l t o f magmatic  differentiation.  The f o l i a t e d n a t u r e o f t h e o a r l y p h a s e s  of t h e b a t h o l i t h suggests that  t i c flow has occurred,  p o s s i b l y as a r e s u l t of n a t u r a l convection magma chamber.  I f convoctivc  flow  within the  d i d take place  during  71 intrusion  there  exists  formed, c r y s t a l s may b e c o m e chamber, acidic  -  the  to  earlier  when  series  and  renewed  i n t r u s i o n of  discussed  the  under  therefore,  exhibited  by t h e s e  heterogenics compositional the  of  suggests  crystallised likely,  caused  Bethlehem  that  the  magma  magma i n more-  action  have  exhibited  plagioclase -  suggests  from w h i c h  of  largely  be  phases  zonation  that  prior  of  a  to  Textural  bulk of  incomplete  members  and B e t h s a i d a  phase.  range  phases i s by  of  quiescent  the  -  magmatic  magma o c c u r r e d  fairly  the  intermediate  o n p a g e 3k  that  of  compositions  Bethlehem  evidence  the  and pyroxene  batholith.  r a n g e s may a l s o  modal a n a l y s e s  calculated.  by t h e  the  -  the  of  chemically  schemes  information  range  early  assimilative  to  the  the  probability  of  combined w i t h  consolidation  enriching  phases  exhibited  as  or w a l l s  subordinate the  that  oligoclase  roof  In a l l  produce  Tho r e t u r n the  the  successively  differentiation  by  to  components.  combined  possibility  predominantly  attached  thus  the  this  magma  conditions. chemical the  chemical  due  of  magma. to  seems  compositions  result  m i x i n g of partly  It  local The  errors  estimates  were  in  72  VII  Geological Evolution of tho Batholith  Tho h i s t o r y o f emplacement o f t h e G u i c h o n b a t h o l i t h h a s p r e v i o u s l y been d i s c u s s e d (1969)  Creek  by N o r t h c o t e  and t h e f o l l o w i n g i n t e r p r e t a t i o n i s l a r g e l y an  extension  of Northcote's ideas.  The o n l y  significant  d i f f e r e n c e b e t w e e n t h e two schemes i s t h a t t h e p r e s e n t work s u g g e s t s t h a t responsible  (1964),  magma f l o w h a s b e e n l a r g e l y  f o r t h e t e x t u r a l and c o m p o s i t i o n a l  between s u c c e s s i v e convection  convectivo  phases.  difference  The p o s s i b i l i t i e s o f magma  have been d i s c u s s e d  (1918),  by G r o u t  Shaw ( 1 9 6 5 ) a n d B a r t l e t t  (1969),  a u t h o r s have c o n c l u d e d t h a t c o n v e c t i o n  Knopoff  and t h e s e  may c o n s t i t u t e a  s i g n i f i c a n t physical factor during the c r y s t a l l i s a t i o n o f g r a n i t i c magmas.  Shaw ( 1 9 6 5 ) a l s o s u g g e s t s  that  p o c k e t s o f s t r o n g l y d i f f e r e n t i a t e d l i q u i d may d e v e l o p c l o s e t o t h e t o p o f a magma chamber due t o t h e a c t i o n o f l o c a l high l e v e l Very l i t t l e  convective v o r t i c e s . i s known c o n c e r n i n g  o f t h e ma.gma t h a t c r y s t a l l i s e d batholith. strontium and  from t h e Craigmont mine.  Sr V S r  ratio  origin  t o form t h e Guichon  Christmas et a l (1969) i s o t o p i c composition  the ultimate  Creek  have i n v e s t i g a t e d t h e  of rocks  from t h e b a t h o l i t h  They r e p o r t  an i n i t i a l  f o r t h e Craigmont i s o c h r o n  which f a l l s w i t h i n t h e range o f values  from  of 0.7037 recent  75  basalts "... not  that  the  ore  originate  Cache  They  (0.703-0.706).  by  conclude  m i n e r a l s and K - f c l d s p a r fusion of  Creek or N i c o l a  ancient  rocks,  but  recent  w i t h low  basalt.  oceanic  crust  layer  i n the  imply  that  developed  the  part  less  tho  place  of  of  the  accomplished xenoliths  time  of  of  heat  into  within  the  or a  They  basic  further  Guichon b a t h o l i t h Initial  rise  the  the  rocks  of  early  the  present  early  a n d may h a v e b e e n  phases the  have  between  been  chamber  a  by  the  batholith.  high,  magma a n d c o u n t r y  to  part  magma a t  very  In such  w a l l r o c k s at led  the  early  considerable. the  granitic  in  of  of  at  d o m i n a n t l y NW-SE  outer  i n t r u s i o n may w e l l h a v e  differential  mantle  evidenced  need not  have been  to  reabsorbed  stopping, as  temperature  difference  probably  conduction tho  tho  emplacement  temperature would  c o n t r o l l e d by  i n the  in  g r a v i t a t i o n a l i n s t a b i l i t y of  country rocks  present  Although  formed the  Intrusion of  by magmatic  similar  crust....".  magma i n r e l a t i o n t o  formation.  or  developed  cither  upper  environment.  duo t o  magma w a s p r o b a b l y strike  ratios  tho  tho  magma w h i c h  in a similar  dense  of  have  c o u l d bo  ( W i l s o n 1968), lower  did  s i a l i c basement  must  /Sr°  Such a source  magma v/as p o s s i b l y the  Sr  gangue  or  On  an environment  therefore  tho  the the  rock cases  margin  temperature  which c o u l d not  be  of  74  satisfied magma.  by  conduction of  This i n  turn would p r e c i p i t a t e  A combination of would  account  i n the  movement  of  be  expected  to  occur  from  Hybrid  a  of  gradual  early  In t h i s  observed  minerals  -  at  to  its  intrusive  to  Northcote  that  of  e x h i b i t e d by phases.  the  manner  nature  of  - primarily of  the  magma  country  observed  into  gradual  the  must  Hybrid  pulse  must  to  Hybrid  accomplished. and  phase, have  Highland Valley have  led  change  the  Guichon V a r i e t y ,  the  rock  acidic  both plagioclase  the  a magmatic  movement  would  plagioclases  r e m a i n i n g magma i n the  might  Possible  periphery  p h a s e s may h a v e b e e n  part  as  s o l i d i f i c a t i o n , probably  the  c r y s t a l l i s a t i o n of  intrusive  Relative  convection,  a s s i m i l a t i o n of  f o l i a t i o n of  i n a large  crystals  batholith.  composition during c r y s t a l l i s a t i o n of  The  This  convection  formed m i n e r a l phases  inwards  and H i g h l a n d V a l l e y  during  the  the  convection.  plagioclase  d u r i n g magmatic  normal zoning  enrichment  magma  c r y s t a l l i s i n g plagiocla.se,  and pyroxene  a progressive  rock  of  combined w i t h l o c a l  components. in  phases  through  and magmatic  and H i g h l a n d V a l l e y  concentration  and  flow  f o l i a t i o n of  magma a n d  e x p l a i n tho  chamber,  the  outer  also  plagioclase  intrusive  for  observed  t h e r m a l energy  mafic  in  addition  suggested occurred phase.  occurred when  75 c r y s t a l l i s a t i o n of the Guichon v a r i e t y was f a i r l y  well  advanced, and movement would have taken the form o f flowage of a l a r g e l y c r y s t a l l i n e mush.  The c o n d i t i o n s  of c r y s t a l l i s a t i o n of the Chataway v a r i e t y must have been very  s i m i l a r to those e x i s t i n g during  of the Hybrid  phase.  crystallisation  The only observable d i f f e r e n c e s  between these two u n i t s are that the Chatav/ay v a r i e t y crystallised  from a more a c i d i c magma and that a s s i m i l a t i o n  was l a r g e l y i n o p e r a t i v e .  The c o n t i n u i n g  trend o f  d i f f e r e n t i a t i o n i s e x h i b i t e d by tho LeRoy g r a n o d i o r i t e phase.  The dyke l i k e nature o f t h i s phase has been  a s c r i b e d by Northcote t o l o c a l i n c r e a s e s i n v o l a t i l e pressures  p o s s i b l y w i t h i n cupolas at the r o o f o f the  magma chamber, which exceeded c o n f i n i n g pressure and strength  of o v e r l y i n g rock,  causing  f r a c t u r i n g i n cooler  c r y s t a l l i n e phases. The  Gump Lake phase does not appear to be d i r e c t l y  r e l a t e d to the other phases o f the Guichon b a t h o l i t h . As explained  i n Chapter VI, i t i s suggested that tho  Gump Lake phase may bo an o f f s h o o t o f the N i c o l a B a t h o l i t h which outcrops to tho east.  Because o f tho  r e l a t i v e l y small s i z e o f the Gump Lake phase, and i t s i n t r u s i o n i n t o rocks it  already heated by previous  phases,  i s probable that conductive heat t r a n s f e r through the  76 magma was able t o keep pace with r e l a t i v e l y slow heat l o s s t o the surrounding rocks and hence magma convection never developed.  Such c o n d i t i o n s would e x p l a i n the l a c k  of f o l i a t i o n and the coarse-grained, oquigranular nature of t h i s phase.  T e x t u r a l evidence suggests that  p l a g i o c l a s e and quartz c r y s t a l l i s e d  essentially  s i m u l t a n e o u s l y from the Gump Lake magma. The r e t u r n t o more i n t e r m e d i a t e bulk and the complete  compositions  change i n the nature o f p l a g i o c l a s e  zoning schemes e x h i b i t e d by the Bethlehem and Bethsaida phases i n d i c a t e , a renewed i n f l u x o f magma i n t o the area. Tho  composition o f t h i s magma was more b a s i c than that  which c r y s t a l l i s e d the LeRoy g r a n o d i o r i t e and yet more a c i d i c than the bulk composition o f the e a r l i e r magma. The emplacement o f the l a t e r magma was probably  governed  l a r g e l y by zones o f weakness o r i g i n a l l y created by the e a r l i e r magma, and the processes i n v o l v e d are b e l i e v e d to have i n c l u d e d at l e a s t minor r e m e l t i n g o f Highland V a l l e y phase rocks.  Remelting i s suggested by p l a g i o c l a s e  zoning schemes ( d i s c u s s e d e a r l i e r ,  p. 41) i n Witches  Brook  phase r o c k s , "which Northcote b e l i e v e s to be an a s s o c i a t e d dyke phase o f the Bethlehem phase.  In view o f the c l o s e  compositional s i m i l a r i t y between Highland V a l l e y and  77  Bethlehem  phase  not  insurmountable.  to  be  The rocks  i n t r u s i o n of  that  may h a v e  were  due  to  theory  the  oscillatory  the of  process Harloff  have  taken  apparent  place  parts  of  tho  of  magma c h a m b e r  occurred is  and  consolidation pressures  that  tho  of  feldspars  workers,  then  is  the  phases  must  conditions.  however,  is  the  An presence  orientation in Local  occurred  at  If  the  such  plagioclase viscosity  periphery  flow  the  layer  zoning continued uninterrupted.  of  the  Bethlehem phase  within  the  magma c h a m b e r  the  must  causing  crystallisation  of  c r y s t a l - l i q u i d boundary  the  convection  crystallisation  crystals. of  presence  in  diffusion-suporsaturation  preferred  stages  convection,  and l a t e r  during early  conceivable  oscillatory  the  quiescent  this,  plagioclase  relative  tho  temperatures  significant  plagioclase  by  f l o w may h a v e  during early  just  prevented  of  any  seem  batholithic  elevated  Bethlehem phase.  intrusive  orientation  If  Bethlehem very  assimilation  raagmatic  and l a t e r  plagioclase  and/or the  occur.  expounded  under  at  and hence  zoning i n  the  of  magma i n t o  already  c o n t r a d i c t i o n to  an i m p e r f e c t  outer  later  (1927)  of  problems  formation of  gradient,  crystallisation  it  the  p r o b a b i l i t y , d i d not  delicate  of  the  probably  precluded  temperature all  rocks  magma movement During  volatile have  risen  no .'°  considerably of  quartz  rather  On t h e  of  (1969) h a s  the  later  interval  separated  phases of  from  sharply  present  has  the  by  years.  The  of  the  at  elevated  hence  quiescent pressures. early  however,  present  to  variation  author  phases  conditions Thus late  tho  that  relatively early  and  contacts  suggests to  and  crystallisation  tho  presence  of  change  in textural  million intrusion  probably  and  essentially  high  volatile-  features  than  already  flow  explained  other  the  Northcote  that  under  vary  were  four  i n the  be  of  the  convoctivc  crystallised  parameters  of  only  were  prevented  of  a  interval.  arguod  p h a s e s may p o s s i b l y  i n physical  that  phases  occupied  rocks  temperatures  -  emplacement  has  rocks  phases ~ which  two  time  of  conditions,  emplacement  tho  phases  emplacement  exists  Valley  short  the  magma i n t o  later  before  The n a t u r e  that  that  early  cover  gradational  p h a s e s may h a v e  later  the  to  evidence,  the  the  the  and H i g h l a n d  a relatively  early  of  batholith.  suggested  crystallisation  mcsozonal  possibility  intrusive  author,  separated also  tho  Bethlehem  that  conditions  The  late  between  erosion  phases.  time  field  displaced under  epizonal  long  and  suggested  progressive  established  initial  plagioclase.  textural  b a t h o l i t h were  and. t h a t  of  p e r m i t t i n g the than  basis  Northcote tho  thus  by  those  from  '79  controlled  by  variations  presented  evidence during The  to  of  support  batholith, igneous Is  of  it  any  certainly  opizonal  the  older  magma c h a m b e r ,  thus  rapid  transfer  of  could  account  relationships  for to  the  plagioclase batholith  may b e  their  apparent  to  under  very  epizonal  the  of  has  the  The  late  conditions.  crystallised  listed  rock,  of  and p a r t i a l of  w i t h i n the that  crystallisation.  all  these  be  active  within  the  relatively  margins.  This  emplacement  motamorphism assimilation  preferentially older  phases  of of  oriented of  the  convection  was  occurring  If  the  case  from mesozonal  such i s to  -  mcsozonal  of  could  complex  contact  criteria  b a t h o l i t h which  a continuing, chamber  stage  type  presence  was  batholith.  Guichon  batholith  environment  the  presence  evidence  change  the  entire  presence  grade  crystals  that  convection  country  The  of  p i p e s , within t h e  X).  causing  epidote-amphibolitc rock.  i f  heat  main phases  no  occurring  (1959) - w o u l d s u g g e s t  Table  explained  contain  changes i n depth  phases  Buddington (sec  mineralogical  thesis  Northcote  w i t h i n an e p i z o n a l  adaqua.tely  country  place  conditions?  crystallisation features  the  suggests  that  w i t h i n tho to  great of  The  present  breccia  took  possible  according  the  i n the  local  activity  present  during  intrusion.  crystallisation  presence  under  depth  opizonal  then  conditions  80  TABLE X  C r i t e r i a , s u g g e s t e d by B u d d i n g t o n (1959) i n d i c a t i v e of mesozonal i n t r u s i o n , which present i n the Guichon Creek b a t h o l i t h (From N o r t h c o t e j 1968)  as are  a)  Degree o f metamorphisra o f intense than green-schist facies (400-500°).  b)  Complex emplacement i n part discordant, replacement.  c)  Planar f o l i a t i o n i s often well developed, especially i n o u t e r p o r t i o n s o f t h e p l u t o n , but i s commonly l o c a l , e l u s i v e or m i s s i n g i n the c o r e .  d)  Y o u n g e r u n i t s may c r o s s c u t f o l i a t i o n o f o l d e r u n i t s , o r t h e s t r u c t u r e may l o c a l l y b e i n d e p e n d e n t of boundary u n i t s w i t h i n a composite p l u t o n .  e)  A s s i m i l a t i o n may b e  f)  Emplacement by r e c o n s t i t u t i o n and r e p l a c e m e n t commonly a b s e n t o r s u b o r d i n a t e .  g)  C h i l l border f a c i e s , i n the sense of a p h a n i t i c texture, are absent. (Present i n the youngest of the Guichon b a t h o l i t h ) . are  c o u n t r y r o c k s n o t more and e p i d o t e - a m p h i b o l i t e  r e l a t i o n s h i p s to country rock; i n part concordant. Local  significant  absent  h)  Migmatites  i)  P e g m a t i t e s a n d a p l i t e s common e s p e c i a l l y zones. T h e y may h a v e a r a d i a l f a b r i c .  j)  Miarolitic  k)  Contact  structure  metamorphic  or  i n border  is  or  roof  zones,  is  phases  subordinate. i n the  border  absent.  aureoles  may b e  well  developed.  suggested of  by N o r t h c o t e  several  sediments not  be  thousands  therefore  that  tho  of  level  depth  of  bo r e a l  and the  feet  Lower  Jurassic  of  d u r i n g the  necessary.  may n o t of  emplacement  The  present  of  the  author  emplacement  cover,  of  may h a v e  the  batholith  would  during c r y s t a l l i s a t i o n  of  by  as  may  suggest  the  batholith,  changed  erosion  batholith  i.e.  little  the  as  two  kilometres. It the  has  already  bulk  of  the  believed  to  have  conditions.  The  conditions coarse  under  slow  naturally even  suggests  conditions  consequent  increases  eventually  resulted  magma c h a m b e r .  emplacement possibly  of  the  emplacement  the  of  the  Local  porphyry  pressures  fracturing  swarms,  of  was  of  occurred  such  as  Bethsaida. phase at  this  Bethlehem, this  time.  Trojan,  final  dykes  Tcxtural  The and  probably walls  of  accompanied  by  pipe  into  tho  breccias'and Local older  phases  Copper-rich mineral Krain,  igneous  O.K.  and  activity.  the  crystallised  pressures.  fracturing  dyke  phase.  phase  such of  magma i n v o l a t i l o s  in volatile in local  quiescent  magma u n d e r  Bethsaida  of  is  crystallisation  Bethsaida  the  phases  Gnawed M o u n t a i n P o r p h y r i e s .  also  accompanied  to  the  high .volatile  enrichment  crystallisation  essentially  of  textured  that of  under  cooling led  that  and B e t h s a i d a  occurred  continuing  the  stated  Bethlehem  grained,  evidence  been  Lornex  deposits  SAMPLE 2  .80  1  4  1  6  1. 1  1  1  1  1 .  1  Fe/Fe+Mg Biotite  •  •  .  .  •  Plagioclase  0  2  Q  10  • •  •  *  •  1  * •  1  2  Rock  7  0  6  Q  • •  1  i i  .  .1  1  1  1 1  •i •  1  i  i •  r  •  -  •  •  •  1  •  •  i  l  l  HYBRID  1  1  1  Guichon  1 i  1  1  1  1  Chataway  1  r> f  • .  • i  *  •  1  • •  .  •  1 *  • •  i  !  —  •  •  i I  1 | j Normal + ~ i Normal 1 ' I Oscillatory 1  Normal -+• Oscillatory  J  1 ••  •1 1 1  *  •  * 1  1  1*  •  .  1 1  • •  •  •  '  1.  !  1  HIGHLAND  Rnmmnru  •  i  1  j  °  •  1  i  1 1  •  «•  *  1  i  «  34 1 1  i  •  !  1  i  i i  !  i  •  i  1  1  -  •  \  1  Normal  32 1 | 1  i  •  i  1  30 1  •  1 i  •  1  i  •  1 1•  1 *•  28 1  1  !  i  -  phase.  I fi *  26 1 | 1  i  t  Fin  24 1  ©  1  •  Intrusive  1  ]  1 •  Si 0 - W t . %  2 2 1  1  1 1  [  • • * •  20  l| I  1  •  1  |  Zoning 80  *  1  -  18 1  j  I *  60  1  •  1  •  1  *  1  1  '  •  70  3  1 | 1  1 *  *  '  Feldsppr  4 0  1  1  |  80  1  NUMBER.  16  1  1 *  Or. W t . %  An.Wt.%  1  14  1 •  90  Alkali  1  12  |  1  —  .60  10  8  romnneitionol  1  ' 1  i  1 1  1  Leroy  ' VALLEY  unrintinns  1 1 1 1 1 l' 1 1 1 I |BETHLEHEM] 1 GUMP | LAKE  1 in  the  Guichon Creek  J  1  l  1  WITCHES BROOK  batholith  1  i'  i  i  i  i  1 BETHSAIDA '  !  1  i  83  VIIi The  Summary a n d  present  study  has  changing mineralogical during The  has  progressive various  change  m i n e r a l phases  compositions  the  the  very host  of  little rock.  Alkali  The  structural  orthoclase  compositions from is  tho  of  structural various  phases  Plagioclase or  (Fig  intermediate  Hybrid  i n general, relative  there  v/as a  rocks  with decreasing  throughout  states  the  slow  of  as Tho  chemical  however,  relative  batholith  potassium  rich  equivalent  to  of  and pure  the  alkali  albite  phases that  age  of  range  of the  the  alkali  of  of  to  86  bulk  these  orthoclase. are  respectively.  f r o m 71  random v a r i a t i o n  of  arc  feldspar  a r t i f i c i a l l y homogenised  of  batholith.  proportions  i n the  produced  16).  and the  states  rocks  b a t h o l i t h proceeded.  change  batholith  a seemingly  the  the  i n d i v i d u a l mineral phases,  two u n m i x e d p h a s e s  pure  with  Guichon Creek  present  the  feldspars  micropcrthitic have  the  i n the  of  concerned  composition of  shown t h a t ,  crystallisation  show  been  c r y s t a l l i s a t i o n of  study  Conclusions  The  alkali Wt%  almost bulk  feldspars  Or.  There  compositions  feldspars  from  and  the  batholith.  feldspars structural  and H i g h l a n d V a l l e y  from the  b a t h o l i t h are  of  states.  Plagioclase  from  phases  show n o r m a l z o n i n g  low the v/ith  34  An^3_32  cores  carries  a  n  ^  oscillatory  a n d r i m s An2Q. Bethsaida A n ^ g 23  samples  exhibit  rims An Q.  or  studied  silica biotite  that  batholith Fc/Fe  Fo/Fc  it  there  of  the  is  biotite  is  and tho  Fe/Fe  rapidly  with  host  samples  tho  a  only  slight  biotite  other  further  Gump L a k e to  the  between  major  is  phase rest  the of  phases  found.  than  to  bo  of in  affected  silicates. 2  present,  biotites  increases  silica  content  only  - w h i c h may n o t the  tho  Tho  73 Wt% S i 0  found  tho  silica  silicate  arc  of  occurs  decrease  appears  i n the  conditions  tho  boundaries.  with increasing  these  tho  I n many o f  ferromagnesian  increases  Such  related  in  may  cither  regular  ferromagnesian  cores  plagioclase  the  also  A n ^  and  concentration  c o n t a i n i n g more  + Mg r a t i o s  from tho  of  rock i n which i t  any  of  grain  Within  cores  Brook phase  phase.  and tho  phase  zoning with  correlation  in biotites of  rocks.  genetically  of  rocks  the  rock  also  host  presence  i n those  any  contains.  + Mg r a t i o  the  Thus  of  + Mg r a t i o  content  feldspar  Lake  Bethlehem  those  Bethlehem  an a p p r o x i m a t e  content  to  partial resorption  plagioclase-alkali is  Witches  P  with  from the  oscillatory  similar  the  u m  plagioclases  The  2  Valley  There  the  zoned  plagioclases  Highland  by  *  ^  ^^Q-ZO'  Plagioclases  phases  a n c  contain  at  rirns  Guichon  in  of. the  be Creek  •OP  batholith is  -  and  believed  to  batholith. biotites oxygon or  variations  may be  produced  of  other  variable  crystallisation  rocks,  tho  and oxygen  i n the  minor l a t e  stage  two  genetic  relationship  doubt.  It  bo  the  appears  of  genetically  the  second  porphyrys  of  Two history 'The  was  rest  of  tho  from a n a l y s i s  of  modal  is  not  directly  the  and  associated  above  some but  batholith is salic related  Guichon b a t h o l i t h and i t  l i n k e d to  major  produced  phases  i n t r u d e d at  outlined  bo  LeRoy  event  Bethsaida  events  the  major  can  first  and  and b r e c c i a s  phase  major  Gump L a k e p h a s e  phases  in  differentiation  study.  Brook, a n d  to  and  Highland Valley  the  Gump L a k e  tho  products  crystallisation  Hybrid,  the  between  present  pressures.  minoralogical  Witches  time  tho  convection  batholith,  The  compositions  phases.  with  Bethlehem,  them.  silicate  presence  reaction  the  with  the  included assimilative  from the  the  by  of  conditions.  events  of  and  in  physical  distinctive  phases  the  fugacitics  controlled  which  varying  volatile  other  variable  magma u n d e r  magmatic  produced  of  F c / F c + Mg r a t i o s  ferromagnesian  and v a r y i n g  discerned  differentiate  b a t h o l i t h are  of  conditions  country  that  in  by  textures  Guichon Creek  event  stage  w h i c h i n t u r n may b o  The  Those  S p a t sum q u a r t z - m o n z o n i t e  bo a l a t e  The  absence  the  from the  may  its in  constituents to  the  possibly  N i c o l a b a t h o l i t h which  outcrops  86  to  the  oast.  There in  the  is  a definite  nature  of  relative  ago  probably  accompanied  and  of  the  convective  produced  the  preferred  basic  phase  The more  i n the  at  sequence  highly  the  alkali  feldspar;  crystallised hornblende,  phases  and p r o g r e s s i v e l y  devoid  of  of  as  a result cupolas  magmatic and the  cores  mafic  after  The  at  Hybrid  event mafic  that  first  the  as  a  volatile margin.  LcRoy The  mineral  phases quartz,  phases (not  common),  pyroxene  pyroxene  i n pyroxene  i n plagioclase that  high  plagioclase,  pyroxene of  cmplacod  an o r i g i n .  mineral  separate  suggests  of  less  and H i g h l a n d  batholith  salic  was:  presence  inclusions  the  such the  was  locally  the  the  plagioclase  nature  of  suggests to  of  with  sequence:  biotite.  pyroxene  crystallised  tho  action  batholith,  early  in  m i n e r a l phase  lack  the  was  conditions  zoned  i n the  plagioclase  event  normal  compatible  early  decreasing  magmatic  These  margin to  through  change  minor a s s i m i l a t i v e  magma.  crystallisation  the  major  least  differentiated  is  during  early  with  Tho L c R o y g r a n o d i o r i t e  existing  of  rocks  of  possibly  granodiorite  Tho  of  The  xcnolith rich  phases.  pressures  in  by  bulk, c o m p o s i t i o n s  Valley dyke  intrusion.  flow  and m i n e r a l o g i c a l  batholith!c  orientation  phenocrysts  chemical  hornblende  separation  of  was  inclusions tho  bearing cores and  first rocks.  in  rocks  biotite  plagioclase  in  87  these-  rocks.  The l a t e r genetically records  related  a slight  crystallised little  to  the  renewed  under  flow  emplacement and  for  of  emplacement  to  those  -event.  of  hot,  this to  of  Northcote  that  (1969)  took  zoning  some as  of  the  Thus i n i t i a l  i n the due  results  to  the  directly  later  magma  of  the  to  tho  later  the  in  to  tho  its  earlier  The  conditions  were v e r y early  similar  magmatic  composition  Witches  Brook  salic  the  of  mineral  by i n i t i a l  present  in  the  in  the  separation  change  volatile  phase  phases  plagioclase  This  by'  phase.  magma a c h a n g e  experimental tho  very  o r i g i n a l l y described  phase.  an i n c r e a s e  applied to  of  Brook phase  replaced  Bethsaida  from s y n t h e t i c  due  size.  magma  of  rocks  grain  separation  was  and t h u s  probably  and  This  LeRoy granodiorite-  c r y s t a l l i s a t i o n of  quartz  c a n be  to  event  schemes and b u l k  belonging  Bethlehem phase  probably If  belong  directly,  The l a c k  the  samples  c r y s t a l l i s a t i o n of  outer  also  Witches  During  occurred.  place.  consolidated  fact  of  conditions  magma w a s  may i n  order  magmatic  LeRoy g r a n o d i o r i t e  Plagioclase  probably  i n t r u s i v e movement.  reason  tho  most  earlier  a much c o a r s e r  the  suggest  is  quiescent  in this  into  crystallised  data  event  differentiation  convoctivc  event  magmatic  was  most  pressures.  investigations case  it  suggests  that  total  during  pressures  c r y s t a l l i s a t i o n of  observed  gradual  biotites  i n rocks  events  suggests  increasing phases  i n the  of  volatile  that  the  k kilobars  Bethsaida  the  of  The  oxygen  magmatic  was  magma c h a m b e r  also  tho  continued build  w i t h i n the  in  and l a t e r  during c o n s o l i d a t i o n of The  existed  phase.  + Mg r a t i o s  earlier  fugacity  batholith.  pressures  of  i n Fe/Fe  both  gradually the  the  decrease of  order  up  major of  eventually  i  led  to  local  formation economic  fracturing  of  prophyry  mineral  mesozonal  to  dykes,  has  epizonal  c o n s o l i d a t i o n of  of  evidence  penetrated tho  crust  15000 the  to  the  Northcote  has  Lower J u r a s s i c  roof  of  tho  depth phases  that  that  data  therefore  that  the  local  to  from  wore  batholith. the  occurred the  5000 f t  the  present  support  any  great  to  The  thesis  changes the  author  of  from  emplacement.  The p r e s e n t  lack  regions  eroded  in  physical  from  phases  higher  that  sediments  collected  Due t o  successive  batholith during i t s  evidence  the  and  a change  o c c u r r i n g during c r y s t a l l i s a t i o n of of  and  environments  batholith.  suggested  of  no  margins  breccias  successively  ft  contains  pipe  suggested  suggest  c n masse' i n t o  mineralogical  chamber  emplacement  during any  tho  deposits.  (1969)  Northcote  of  in  main would  characteristics of  the  suggo  batholith  that  suggest  mesozonal  emplacement  perhaps  be  due  to  a  and the  action  of  convection within  If  such i s  changed  by  the as  case little  crystallisation  combination of  tho as  history  depth of  epizonal the  of  the  emplaccmon  magma  emplacement  2 km d u r i n g t h e  may  chamber. may  entire  batholith.  have  90  REFERENCES Ailing,  CITED  H . L ; 1938: P l u t o n i c p e r t h i t e s : G e o l . , v. 46, p. 142.  Jour.  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C . : E a r t h S c i . , v . 4 , p p . 677-690.  Wilson, Wones,  Wright,  K.C.; 1957: the H i g h l a n d Trans.,  K . E . , Dirom, Isotopic dating Can. J o u r .  J . T . ; 1968: A revolution i n earth science: C . I . M . B u l l . , v . 6 l , N o . 6 7 0 , p p . 185-192. D . R . , and E u g s t e r , H . P . ; 1965: S t a b i l i t y of biotite: experiment, t h e o r y and a p p l i c a t i o n : Am. M i n e r , v . 5 0 , p p . 1228-1272. T . L . ; 1968: X - r a y and o p t i c a l study o f a l k a l i feldspar II. An X - r a y method f o r d e t e r m i n i n g the c o m p o s i t i o n and s t r u c t u r a l s t a t e from measurement of 20 v a l u e s f o r t h r e e reflections: Am. M i n e r . , v . 5 3 , p p . 8 8 - 1 0 4 . . j Stewart, D.B. ; 1968: X - r a y and o p t i c a l study of a l k a l i feldspar. I. Determination of c o m p o s i t i o n and s t r u c t u r a l s t a t e from r e f i n e d u n i t c e l l parameters and 2v: I b i d . , v. 53 pp. 38-87. a n c  5  Yoder,  H . S . , J r . , Stewart, Ternary feldspars: v . 5 6 , pp. 206-214.  Yoder,  H . S . J r . ; 1967: I b i d , v . 6 6 , pp.  D . B . , and S m i t h , J . R . ; 1957: Y b . C a r n e g i e I n s t n . Wash:  System A b - A n - 0 - H 0 at 477-478. 2  5  kb:  95  Appendix 1 Petrographic  Descriptions  Tho f o l l o w i n g p e t r o g r a p h i c d e s c r i p t i o n s a r e concerned p r i m a r i l y with t e x t u r a l features present i n the samples. F o r modal a n a l y s e s see A p p e n d i x 2. Sample numbers g i v e n i n bra.ck.ets r e l a t e t o t h e o r i g i n a l f i e l d s a m p l e n u m b e r u s e d b y K.E. N o r t h c o t e who c o l l e c t e d a l l the samples used i n t h i s study. Grain s i z e s a r c given i n terms o f the g r e a t e s t dimension. HYBRID PHASE 1.  (K64-59A)  Quartz  Dioritc  Medium g r a i n e d , e q u i g r a n u l a r , marked p r e f e r r e d orientation of plagioclase. Plagioclase subhcdrale u h e d r a l , w i d e r a n g e i n g r a i n s i z e f r o m 2.5mm - 0 . 5 m m . , v e r y weak n o r m a l z o n i n g , s t r o n g s e r i c i t i c a l t e r a t i o n . Orthoclase p e r t h i t i c , i n t e r s t i t i a l or p o i k i l i t i c a l l y enclosing a l l other minerals. Quartz anhedral, interstitial. Ma.fics are ragged, a n h e d r a l and relatively fresh. Clinopyroxene i s subhcdral and of a p p r o x . 1 mm g r a i n s i z e . .Hornblendes have c o r e s o f s t r o n g l y a l t e r e d clinopyroxene and c o n t a i n i n c l u s i o n s o f p l a g i o c l a s e , magnetite and q u a r t z . Biotite i s partly p o i k i l i t i c , enclosing hornblende, quartz, plagioclase and opaques. M y r m c k i t c p r e s e n t a t some p l a g i o c l a s e •-• o r t h o c l a s e g r a i n boundaries, i f absent p l a g i o c l a s e has a l b i t i c r i m and i s p a r t i a l l y resorbed. 2.  (K64-49A)  Quartz  Dioritc  V e r y s i m i l a r t o s a m p l e #1 e x c e p t f o r p r e s e n c e o f traces of microcline twinning i n tho a l k a l i feldspar. Clinopyroxene occurs only as cores to hornblende. 3-  (K64-13)  Quartz  Diorite  V e r y s i m i l a r t o s a m p l e #1 e x c e p t occurs only as cores to hornblende. 4.  (k64-156A)  that  clinopyroxene  Granodiorite  Fine-medium g r a i n e d , e q u i g r a n u l a r , marked p r e f e r r e d orientation of plagioclase. Plagioclase subhcdral, grain s i z e 2mm, f r e s h , n o r m a l z o n i n g . Quartz anhedral, interstitial. O r t h o c l a s e i n t e r s t i t i a l , v e r y few p l a g i o c l a s e i n c l u s i o n s ( s t r o n g l y r e s o r b e d ) , some m y r m e k i t i c  96  intergrowths. Clinopyroxene ragged, subhedral with plagioclase inclusions.B i o t i t e markedly i n t e r s t i t i a l p o i k i l i t i c f o r m i n g g r a i n s w i t h m a x . s i z e 3mm. HIGHLAND V A L L E Y  PHASE  Gui_c h_on_ _ V a r i _cty_ 5.  (K63-196-I)  Contaminated  ? Quartz  Diorite  Medium-coarse g r a i n e d g r a n u l a r t e x t u r e , marked plagioclase preferred o r i e n t a t i o n , mafic minerals tend to form c l u s t e r s . Plagioclase subhedral-euhedral, normal z o n i n g , marked a l t e r a t i o n . Quartz and orthoclaso interstitial. A l lmafics extremely ragged. Clinopyroxene rimmed by hornblende a n d v a r i a b l y r e p l a c e d by s i e v e texture hornblende. Biotite poikilitic enclosing p l a g i o c l a s e , q u a r t z , mafics and sphene, extensive alteration to chloride. 6.  (K63-71A)  Quartz  Diorite  Medium g r a i n e d , c q u i g r a n u l a r , p r e f e r r e d o r i e n t a t i o n of larger plagioclase crystals. Plagioclase i s subhedrale u h e d r a l , e x h i b i t s weak n o r m a l z o n i n g , considerable s e r i c i t i c a l t e r a t i o n a n d p a r t i a l r e s o r p t i o n where i t i s i n contact with a l k a l i feldspar. Plagioclase grain size r a n g e s f r o m 3mm t o ,5mm. Q u a r t z i s i n t e r s t i t i a l t o pla.gioclase, anhedral and exhibits strong e x t i n c t i o n mosaics. Orthoclase i s anhedral, p o i k i l i t i c or i n t e r s t i t i a l enclosing plagioclase and hornblende. Hornblende i s ragged but subhcdra.l, often has cores o f c l i n o p y r o x e n e a n d tends t o form c l u s t e r s o f g r a i n s . B i o t i t e i s ragged and generally anhedral with strong c h l o r i t i c a l t e r a t i o n and quartz s t r i n g e r s are present a,long t h o c l e a v a g e . B i o t i t e g e n e r a l l y a b o u t 1mm b u t may b e p o i k i l i t i c u p t o 3mm. O p a q u e m i n e r a l s show a strong association with b i o t i t e and hornblende. 7.  (K63-104-I)  Granodiorite  Medium-coarse grained c q u i g r a n u l a r . Plagioclase c u h o d r a l - s u b h o d r a l , 4mm-0.4mm, s l i g h t a l t e r a t i o n a n d n o r m a l z o n i n g , p a r t i a l r e s o r p t i o n when i n c o n t a c t w i t h orthoclaso. Q u a r t z a n h e d r a l e q u a n t g r a i n s , 0.3mm. Orthoclase p e r t h i t i c , fresh, i n t e r s t i t i a l or p o i k i l i t i c u p t o 5mm. H o r n b l e n d e s u b h e d r a l , p o i k i l i t i c enclosing q u a r t z , p l a g i o c l a s e a n d o p a q u e s , u p t o 3mm. Biotite  97  ragged, p o i k i l i t i c enclosing quartz plagioclase o p a q u e s , a p p r o x . 15% c h l o r i t i c a l t e r a t i o n . 8.  (K64-207)  and  Granodiorite  V e r y s i m i l a r t o s a m p l e #6. Orthoclase i s markedly i n t e r s t i t i a l , pyroxene i s absent and micrographic i n t e r g r o w t h s o f q u a r t z a n d o r t h o c l a s e a r c common.  Chataway V a r i e t y 9.  Quartz  (K.64-H6a-I)  Dioritc  Medium-coarse g r a i n e d e q u i g r a n u l a r . Plagioclase e x h i b i t s a rough preferred o r i e n t a t i o n , i s euhedrals u b h o d r a l , 4mm - 0 . 5 m m , s l i g h t a l t e r a t i o n , n o r m a l z o n i n g , p a r t i a l r e s o r p t i o n where i n c o n t a c t w i t h o r t h o c l a s e . Quartz i s a n h e d r a l , i n t e r s t i t i a l to p l a g i o c l a s e and has strong e x t i n c t i o n mosaics. O r t h o c l a s e i s p o i k i l i t i c up t o 3mm, a n h e d r a l a n d e n c l o s e s p l a g i o c l a s e , quartz and hornblende. M y r m o k i t e i s p r e s e n t a t some o r t h o c l a s c plagioclase junctions. Hornblende i s s u b h c d r a l up t o 2.5mm, f r e s h a n d h a s q u a r t z , p l a g i o c l a s e a n d opaque inclusions. B i o t i t e i s ragged, subhcdral, with quartz a n d o p a q u e i n c l u s i o n s a n d i s a p p r o x . 5% c h l o r i t i s e d . Sphene i s s u b h c d r a l . 10.  Granodiorite  (K.64-48-I)  V e r y s i m i l a r t o s a m p l e #9 e x c e p t f o r s l i g h t l y coarser grain size. O r t h o c l a s e p o i k i l i t i c u p t o 5mm. Hornblende strongly p o i k i l i t i c . Biotite fresh. Myrmokite absent. 11.  (K64-144)  Granodiorite  Very s i m i l a r chloritised. 12.  (K64-145)  t o sample  Quartz  #9-  Biotite  approx.  2%  Dioritc *  V e r y s i m i l a r t o sample #9. Myrmokite B i o t i t e a p p r o x . 30% c h l o r i t i s e d . LeRoy 14.  absent.  Variety  (K63~209a-I) Medium-fine  Granodiorite grained,  equigranular,  average  grain  s i z e a p p r o x . 1.5mm, r o u g h p r e f e r r e d o r i e n t a t i o n o f plagioclase. P l a g i o c l a s e s u b h e d r a l - e u h e d r a l , wide r a n g e i n g r a i n s i z e 5mm - 0 . 5 m m , n o r m a l z o n i n g , m o d e r a t e l y f r e s h , p a r t i a l r e s o r p t i o n when i n c o n t a c t w i t h o r t h o c l o . s e , i n c l u s i o n s of opaques and spheno. Q u a r t z may o c c u r a s 1 ) l a r g e r ( . 7 m m ) , poikilitic a n h e d r a l g r a i n s w i t h p l a g i o c l a s e i n c l u s i o n s and mosaic e x t i n c t i o n , o r 2 ) a s s m a l l e r (.2mm) r o u n d e d o q u a n t g r a i n s w h i c h a r e p a r t i c u l a r l y common a s i n c l u s i o n s i n orthoclase. O r t h o c l a s e i s a n h e d r a l i n t e r s t i t i a l and p o i k i l i t i c e n c l o s i n g p l a g i o c l a s e , q u a r t z , h o r n b l e n d e and opaques. H o r n b l e n d e i s r a g g e d , s u b h e d r a l , u p t o 3mm, p o i k i l i t i c , e n c l o s i n g q u a r t z , spheno and opaques. B i o t i t e i s r a g g e d , a n h e d r a l , u p t o 1mm, s e m i - p o i k i l i t i c e n c l o s i n g q u a r t z and opaques. 15-  (K63~210a-I) Very  16.  17.  Very GUMP L A K E 19.  #14.  sample  •  #14.  Granodiorite  s i m i l a r to  (K63-37)  sample  Granodiorite  s i m i l a r to  (.K64-101) Very  18.  s i m i l a r to  (K63-I85a-I) Very  Granodiorite  sample  #14.  Granodiorite  s i m i l a r to  sample  #14.  PHASE  (K64-98-I)  Granodiorite  Coarse-grained weakly p o r p h y r i t i c . Quartz i s c o a r s e g r a i n e d , a n h e d r a l and e i t h e r i n t e r s t i t i a l o r forming composite? f r a c t u r e d c r y s t a l s , mosaic e x t i n c t i o n and o c c a s s i o n a l p l a g i o c l a s e i n c l u s i o n s . Plagioclase is e u h e d r a l o r s u b h e d r a l w i t h g r a i n s i z e 5mm t o Irnm, s l i g h t a l t e r a t i o n , weak o s c i l l a t o r y and n o r m a l z o n i n g w i t h a l b i t i c r i m s common. Severe r e s o r p t i o n of p l a g i o c l a s e w h e n i n c o n t a c t w i t h o r t h o c l a s e , a l s o some m y r m o k i t o present. Orthoclase i s p e r t h i t i c , anhedral, i n t e r s t i t i a l o r coarse p o i k i l i t i c , e n c l o s i n g p l a g i o c l a s e and q u a r t z . B i o t i t e i s fresh, ragged, anhedral, weakly p o i k i l i t i c  99  e n c l o s i n g p l a g i o c l a s e and q u a r t z , and tends c l u s t e r s a s s o c i a t e d w i t h accessory opaques. 20.  (K64-88)  (K64-98) Very  form  Granodiorite  Very s i m i l a r c h l o r i t i s a t i o n of 21.  to  to sample biotite.  Quartz  similar  to  #19  except  for  approx.  10%  Monzonite sample  #19.  BETHLEHEM PHASE 22.  (K63-H5)  Granodiorite  Coarse g r a i n e d , weakly p o r p h y r i t i c . Plagioclase s u b h c d r a l , l a r g e r c r y s t a l s e x h i b i t rough p r e f e r r e d o r i e n t a t i o n , weak o s c i l l a t o r y z o n i n g w i t h v a r i a b l e a l t e r a t i o n of zones. Quartz anhedral, i n t e r s t i t i a l to plagioclase, m o s a i c e x t i n c t i o n common. H o r n b l e n d e and b i o t i t e both r.ggcd, subhcdral, p o i k i l i t i c enclosing p l a g i o c l a s e and q u a r t z . Orthoclase p e r t h i t i c , anhedral i n t e r s t i t i a l or p o i k i l i t i c , s l i g h t alteration. 23.  (K64-186A) Very  Zh.  Granodiorite  similar  (K63-182)  to  sample  #22.  Granodiorite  Coarse-grained weakly p o r p h y r i t i c . Q u a r t z may be 1) s u b h c d r a l , c o a r s e f r a c t u r e d c r y s t a l s , o f t e n composite, or 2) i n t e r s t i t i a l a n h e d r a l g r a i n s . Plagioclase is e u h e d r a l , 5mm - 0 . 5 m m , e x h i b i t s oscillatory/normal z o n i n g and i s v a r i a b l y a l t e r e d . Inclusions of hornblende a n d q u a r t z . a r e common a n d p a r t i a l r e s o r p t i o n h a s o c c u r r e d when i n c o n t a c t w i t h o r t h o c l a s e . Orthoclase is p e r t h i t i c anhedral, i n t e r s t i t i a l or weakly poikilitic, i n c l u s i o n s of p l a g i o c l a s e , h o r n b l e n d e , sphene and opaques. Some s m a l l e r i n t e r s t i t i a l g r a i n s exhibit m i c r o c l i n e t y p e g r i d t w i n n i n g and t h i s a l s o o c c u r s at e d g e s o f some p o i k i l i t i c g r a i n s . B i o t i t e and hornblende ragged, subhcdral with s l i g h t c h l o r i t i c a l t e r a t i o n at edges. 25.  (K63-39) Very  Granodiorite  similar  to  sample  #2.1+ e x c e p t  for  lack  of  100  m i c r o c l i n e typo and p r e s e n c e of constituents.  g r i d twinning i n t h e a l k a l i feldspar hornblende o n l y as i n c l u s i o n s i n s a l i c  W I T C H E S BROOK P H A S E 26.  (K63-17D  Granodiorite  Medium-grained, weakly p o r p h y r i t i c . Plagioclase v a r i a b l e g r a i n s i z e 5mm - 0 . 5 m m , p o o r preferred o r i e n t a t i o n , c u h e d r a l - s u b h o d r a l , homogenous cores, o s c i l l a t o r y zoned r i m s , a l t e r a t i o n patchy, variable r e s o r p t i o n when i n c o n t a c t v / i t h o r t h o c l a s e , inclusions o f h o r n b l e n d e a n d m a g n e t i t e common. Q u a r t z a n h e d r a l , a p p r o x . 1mm, c q u a n t g r a i n s o r i n t e r s t i t i a l , m o s a i c extinction. Orthoclase p e r t h i t i c , i n t e r s t i t i a l or p o i k i l i t i c , a n h e d r a l up t o 3.5mm, e n c l o s e s a l l o t h e r mineral phases. B i o t i t e and h o r n b l e n d e r a g g e d , anhedral 0.5mm, t e n d e n c y t o form c l u s t e r s w i t h a c c e s s o r y sphene and opaques. 27.  (K64-203) Very  28.  Granodiorite  s i m i l a r to  (K64-102)  sample  #26.  Granodiorite  Medium t o f i n e g r a i n e d . Plagioclase subhcdraleuhedral, weakly p o r p h y r i t i c , l a r g e r c r y s t a l s (3mm) e x h i b i t rough preferred o r i e n t a t i o n , normal zoning. Quartz i n t e r s t i t i a l , w e a k l y p o i k i l i t i c o r a n h e d r a l cquant grains. Orthoclase i n t e r s t i t i a l or p o i k i l i t i c , patchy alteration. B i o t i t e and hornblende f r e s h , anhedral, fine grained ( O.p'-'-m) a n d r a g g e d , o f t e n f o r m i n g clusters, q u a r t z i n c l u s i o n s common. Sphene i n t e r s t i t i a l , a n h e d r a l subhcdral, associated with mafics. 29.  30.  (K63-105-D  Quarts  Very  to  similar  (K63-84)  Monzonite  sample  Granodiorite  Very s i m i l a r to sample a p p r o x . 30% c h l o r i t i s e d . 31.  (K64-17)  #28  Quartz  Medium g r a i n e d ,  #28  except  that  biotite  is  Monzonite equigranular.  Plagioclase  subhcdral  101  c o n s i d e r a b l e a l t e r a t i o n , s e v e r e r e s o r p t i o n -and a l b i t i c r i m s common, t r a c e s o f o s c i l l a t o r y z o n i n g . Quartz forms a n h e d r a l , cquant g r a i n s w i t h mosaic e x t i n c t i o n , also interstitial. Orthoclase p e r t h i t i c , anhedral-subhedral, considerable alteration, partly i n t e r s t i t i a l , partly s u b h c d r a l p r i s m a t i c , found a l s o as r i m s o f v a r i a b l e width to p l a g i o c l a s e . B i o t i t e fine grained, ragged, . a n h e d r a l , a s s o c i a t e d w i t h opaque m i n e r a l s . BETHSAIDA 32.  PHASE  K(63-192A)  Granodiorite  Coarse-grained, e q u i g r a n u l a r or weakly p o r p h y r i t i c . P l a g i o c l a s e e u h e d r a l , a v e r a g e g r a i n s i z e 3mm, c o m p o s i t e c r y s t a l s common, o s c i l l a t o r y z o n i n g , p a r t i a l r e s o r p t i o n w h e n i n c o n t a c t w i t h o r t h o c l a s e , a l b i t i c r i m s common. Q u a r t z o c c u r s as l a r g o , s u b h c d r a l , f r a c t u r e d g r a i n s of v a r i a b l e g r a i n s i z e , 6mm - 2mm. Some g r a p h i c intorgrowths o f o r t h o c l a s e and q u a r t z . Orthoclase p e r t h i t i c , coarse, i n t e r s t i t i a l anhedral or p o i k i l i t i c subhcdral, occassionally p a r t i a l l y mantling plagioclase. Hornblendeoccurs as a s i n g l e l a r g o , p o i k i l i t i c c r y s t a l approx. 1.2 cm, e n c l o s i n g p l a g i o c l a s e , quartz, magnetite and biotite. B i o t i t e c o a r s e , m a x . 3mm, r a g g e d , s u b h c d r a l , i n c l u s i o n s of q u a r t z and p l a g i o c l a s e i n o u t e r p a r t s of g r a i n s , a p p r o x 5% c h l o r i t i s a t i o n . Accessory sphene, opaques, and a p a t i t e occur as clusters. 33.  (K63-238A) Very  34-  Granodiorite  similar  (K63-231)  to  sample  #32.  Hornblende  absent.  Granodiorite  V e r y s i m i l a r t o sample #32, h a s more p o r p h y r i t i c t e x t u r e w i t h q u a r t z and p l a g i o c l a s e phenocrysts. Hornblende absent. Biotite fresh, euhedral, coarseg r a i n e d and weakly p o r p h y r i t i c . 35-  (K64--64) Very  Granodiorite  similar  to  sample  #32.  Hornblende  absent.  102  Appendix Modal  analyses  Intrusive Sample  and  2  calculatod  chc m i c a 1 _ c o m p o s i t i o n s  Phase #  Hybrid  1  3  2 .V.  Mode Plagioclase A l k a l i Feldspar Quartz Biotite Hornblende Pyroxene Opaque Spheno Apatite Zircon Chemical  60. 0 3. 2 17. 2 6. 0 0. 4 11. 2 1. 8 0. 4  55. 5. 17. 8. 7. 5.  60. 32 1 7 . 12 3 . 02  62. 2 8 16. 5 3 1. 67 3 . 7k p 66 .6* 16  7 3 3  2 0. 6  55. 0 5. 0  20. 0 8. 0 10. 0 1. 0 0. 7 7 Tr Tr Tr  0. 5  5 1 . 79  10. 8 5 20. 9 9 6. 18  8 . 80  1. 3 4  0. 0 6  Estimate  Si02 AI2O3 Fc20x  FcO MgO CaO  3- 62  2. 3 8 7 . 66 4. 04 0. 9 3 0. 14  Na20 K20 HpO  ...  P2O5  0. 5 5  Ti02 CaF2  Modal  k 0  -:(•  -  analysis  4 . 45 1. 4 3 0. 3 3 0. 2 4 0. 4 6 0. 0 4  from N o r t h c o t e  6 3 . 63 1 6 . 51 1. 8 9 3 . 69 2. 3 5 5 . 16 4 . 65 1. 2 9 0. 3 9  0. 4 4  -  (1969)  6 4 . 04  16. 11 2. 36 3 . 11 2. 01 5. 93 3 . 98 1. 9 4 0. 1 4 0. 0 3 0. 3 3  0. 01  103  Appendix 2  Intrusive  phase  Sample #  (continued)  Highland Valley  - Guichon  Variety  6  7  8  60..3 1. .1 12, .9 11. .4 1. ,8 7. ,0 4.,2 1. • 3  60.,8 5. ,0 13. • 9 7. ,1 11. ,1 0.,6 1. • 5  52. 2 11. 6 22. k 6. 0 6. 3 0. 3 1. 0 0. 2  49. 9 9. 9 27. 3 3. 8 6. 2 0. 2 I. 0 1. 1  56.23 16.40 6.05 5.69 2.41 6.06 4.60 1.12 0.29  59.94 18.16 2.75 4.01 2.33 6.01 4.66 1.34 0.38  65-79 16.38 1.87 2.82 1.55 4.36 4.41 2.14 0.26  67.02 14.91 2.79 2.78 1.23 4.34 4.29 1.57 0.21  1.15  0.42  O.42  0.80  5  Mode Plagioclase A l k a l i Feldspar Quartz Biotite Hornblende Pyroxene Opo.que Spheno Apatite Zircon Chcmical SI0  2  AI2O3  Fo oi z  FeO MgO CaO Na 0 K 0 H 0 P 0 Ti0 CaF? 2  2  2  2  Estimate  5  2  Appendix 2  I n t r u s i v e Phase Sample #  (continued)  H i g h l a n d V a l l e y - Chataway Varlot  9  10  11  12  55.15 7.50  53.2 6.8 25.2 6.8 6.6  Mode Plagioclase A l k a l i Feldspar Quar t z Biotite Hornblende PyroxeneOpaque Sphcne Apatite Zircon Chemical Si0 Al 6 ? c 0z 2  2  3  2  FeO MgO CaO NapO K 0 p  H 0 P 0 Ti0 2  2  CaF  61.6 A. 8 21.4 4.2 6.2  24.08  51.8 14.8 21.4 6.8 4.8  0.6 1.2  0.94 0.22  0.4  1.0 0.4  Tr  Estimate  65.26 17.51 1.25 2.15 1.30 5.60 4.87 0.98 0.22  66.13 16.67 1.75 2.73 1.38 4.52 4.48 1.64 0.26  66.21 17.16 1.04 2.39 1.38 4.24 4.41  0^26  66.34 15.89 1.89 2.99 1.62 4.46 4.40 1.58 0.29  0.87  0.44  0.32  0.55  5 2  2  6.99 4.65  Appendix  Intrusive Sample  Phase #  2  (continued)  Highland Valley 14  15  -  16  LeRoy  -if-  Plagioclase Alkali Feldspar Quartz Biotite Hornblende Pyroxene Opaque Sphene Apatite Zircon CJieraical S i Op AI2O3 FepOv J  MgO  CaO  NapO  K6 2  HpO P  2°5  T1O2 CaF  2  18  17  Mode  FeO  Variety  62.8 8.8 15-8 4.4 7.2  53.2 16.4 21.4 4.2 3.8  50.6 11.8 24.8 6.2 5.4  0.6 0.4  1.0 Tr  1.2  -  -  -  -  -  47.  16. 26. 6. 5.  -  42.23 20.46 28.22 3.90 3.21  -  0.89 0.39  0.63 0.19 0.15 0.02  11 32 64 51 I . 31 3 . 47 4. 31 2 . 60 0. 24  70.48 14.99 1.17 1.71 0.87 3.12 4.15  -  Estimate  4.67 1.56 0.24  0.93 4.88 4.33 2.41 0.-17  66. 48 16. 16 2. 08 2 . 81 1. 39 4 . 20 4. 25 2 . 07 0 . 25  0.47  0.20  0 . .31  62.57 19.22 1.30 2.34  1.46 6.16  -  -  .65.40 18.11 1.60  1.96  -  -  68. 15. 1. 2.  0 . 49  2.96 0.16 0.08 0.30 0.01  106  Appendix 2 Intrusive Sample  Phase  SiO;  FopOx  FoO MgO CaO Na 0 K 0 H 0 2  2  2  p o 2  Ti0 CaF  5 2 2  19  20  21  30.6 22.4 39.8 4.8  36.6 23.4 38.2 1.6  *  Plagioclase A l k a l i Feldspar Quart z Biotite Hornblende Pyroxene Opaqu o Sphene Apatite Zircon  AI2D3  Gump L a k e  #  Mode  Chemical  (continued)  37.25  16.77  39.16 5.24 0.75 0.66 —  0.09 0.09  —  -  -  0.6  0.2  —  —  -  -  76.04 12.22 1.06 1.47 P.53 1.86 2..83 3.66 0.12  76.35  0.19  0.06  Estimate 74.50 13.09 1.14  1.63 0.66 2.47 3-59 2.50 O.14  0.04  0.21 0.01  -  13-56  0.34 0.47 0..17 2.25  3.73 3-02 0.04 -  —  107  Appendix 2  Intrusive Sample Mode  Phase #  Chemical  3  FelOx FeO  MgO  CaO  Na 0 2  K0 HpO p o TiOo 2  2  CaF  5  2  Bethlehem 22  23  24  25 •  •  Plagioclase A l k a l i Feldspar Quartz Biotite Hornblende Pyroxene Opaque Spheno Apatite Zircon  SiO Al?b  (continued)  59.48 13.38 18.59 4.95  55.45 8.35 25.87 4.35 4.48  1.06  1.26  0.52 0.12 0.06  Tr Tr  1.76  -  -  -'  53.3 15.0 26.2 3.2 1.3  -  0.5 0.4  -  50.8 12.4 33.4 2.8 0.6  --  -  Estimate 65.35 17.92 1.71 1.74 0.88 4.93 5.03 1.32. 0.14 0.06 0.41 0.01  67.91 15.88 2.07 2.43 1.13 3-77 4.35 1.53 0.20  69.97 16.46 0.87 1.19 0.52 3.63 4.90 2.01 0.10  73.37 15.51 0.15 0.70 0.38 3.46 4-39  0.24  0.35  0.12  -  -  -  1.84  0.08  -  -  103  Appendix 2 ( c o n t i n u e d ) I n t r u s i v e Phase Samplc  #  Witches Brook 26  2£  27  Phase 30  29  31  if-  .ode Plagioclase A l k a l i Feldspar Quartz Biotite Hornblende Pyroxene Opaque Sphcne Apatite Zircon  53. 37  1 1 . 07  2 6 . 36 4 . 87 3 . 22  Tr 1. 06 0. 2 6 Tr  51. 33 12. 66 2 8 . 06 5 . 54  1.  87  0. 34 0. 14  0 17. 0 28. 0 5- 0 3. 0 0. 96 0. 60 —  -  Tr  J.X  45.  40. 40 2 1 . 09  41. 0 20. 0  0. 73 1. 75 Tr  0. 3 0. 3 _  2 8 . 38 3. 11 4 . 50  28. 0 5. 0 5. 0  Tr  30. 1 5  2 6 . 23 4 1 . 38 1. 84 0.  39  Chemical Estimate  67. 54  S i Op  A1 0 2  3  FcpOx FeO MgO CaO Na 0 K 0 HpO 2  2  p o 2  Ti0  5 2  16. 52 1. 75  70. 4 1 15-  80  4 . on •— i 1. 8 8 0. 17  0. 78 1. 67 0. 85 3 . 29 4. 8 8 1. 84 0. 17  0. 36  0. 3 1  o!  13 95  40  69.  62  69.  80  4. 3 3 2. 59 0. 1 8  14. 42 1. 3 1 1. 77 0. 96 3 . 62 4. 0 3 2. 82 0. 1 6  0. 55  1. 10  1 4 . 91  l . 63 2. 09 0. 95 3 . 15  70. 18 14. 0.  75 86  77. 73 12. 17  1. 2 8 2.1 4 . 09 2 . 95 0 . 22  0. 0. 0. 0. 3. 4. 0.  0 . 42  0 . 06  2. 0 3  55  58  18  65 96  07 04  Appendix  Intrusive  Phase  (continued)  B c t h s a i d a Phase32  Sample #  2  33  34  35  Mode Plagioclase A l k a l i Feldspar Quartz Biotite Hornblende Pyroxene Opaque Sphene Apatite Zircon Chemical SiO FC2O3  FeO MgO CaO Na 0 K 0 H 0 2  2  2  2°5 Ti0 CaFo P  2  58. 10. 19. 0. 7.  21 88 22 88 42  92 82 70 51 05  57. 97 Ik. 55 2 2 . 08 X 62 0 . Ik  53. 11. 30. k. 0.23  2 . 9k  0.66 0.26 0.26 Tr  0 . 44  0 . 02  1. 24 0 . 23 0 . 18  64.25 16.59 4.16 2.85 1.02 4.34 5.09 1.42 0.15 0.01 0.12 Tr  67.79 17.13 1.82 1.54 0.40 3.52 5.35 2.00 0.09 0.09 0.26 0.02  70.90 15.74 1.07 1.30 0.45 3.59 4.67 1.74 0.10 0.13 0.29 0.02  72.34 13.84 0.79 2 . 54 1.20 2.43 4.28 1.88 0.27 0.01 0.42 Tr  -  46. 5. 35. 11. 0.  0 . 02  Estimate  110  Appendix 3 Sample  1)  Biotite  Selection  Electron Microprobe  and  Preparation  Biotite  samples  than  as  sections  more  representative  sample  half  of  used  K.E.  Northcote  thin  the  samples  batholith. crushed hand  The  hand  of  use  prepared rocks  were  sample  irregular within  extremely the  glass  present  plate  expose  the  scale  mount.  Secondary  powder  on a r o t a r y  nature  the  p o l i s h i n g was  stage  often  were  deemed  to  sufficiently  was  done  necessary  produced  this  and  a  mounts  perfectly  minimise generated surface  is  perfect  because basal  hand p o l i s h i n g on was  employed of  tho  with t i n with  sample  well  was  tho  surface  p o l i s h i n g machine  second  polishing  a  each  analysis  sample  of  Initial  at  from  cylindrical  to  by the  w i t h b i o t i t e .samples  This  be  flat  much  of  sieving  X-rays  carborundum g r i t  grains  studies  from  i n order  on t h e  attain  i n micas.  w i t h 950  grains  microprobe  a  Approximately  separated  resin  rather  concentrated  combined  i n cpoxy  mounts  allowed  dating were  Several  effects  fine  biotite  by  required  to  this  originally  A perfectly  difficult  extremely  cleavage  is  grain  examined.  samples  For e l e c t r o n  sample.  since be  sample  c o l d mounted  surface  as  i n K / A r age  rock  absorption  the  to  were  remaining  size  and p o l i s h e d .  of  were  picking techniques.  sample  flat  for  Analysis  to  epoxy  oxide  cloth  laps.  surfaces  polished.  achieved  a  using  If  which further 1^  Ill  a n d i yu d i a m o n d p a s t e  on a  machine.  A l l mounts  thickness  corresponding  polished 2)  brass.  order  flourescence  to  that  Geological  a purplo-bluc  coat  colour  on  1965)  between  a number  grateful  Survey  standards  of  Dr.  author  tho  Geology  for  p r o v i d i n g the  carried  out  Department  by of  analyses  Cominco L t d . and  The i n s t r u m e n t  used  electron  /  equipped  a  at  was  flow  is The  providing  Chemical  analyses  have  been  #149  Dr.  Gower  of  J.A.  British  B i n Table  the  Trail,  (1967). of  Columbia  B standards  a  XI.  were  Geological  Research  B.C.  Japoncse  which has  spectrometer  with, gas  by  natural  Technique  JxA-3A(31 40)  beam,  the  in  of  it  Bulletin  prefixed  ' r a p i d ' , methods  Instrumontation  Laboratories  thank  for  author  standards  University  standards  The  XI.  G.S.C.  to  analysed  help  and  standards  Rimsaite  her  these  in  like  Department,  chemical  J.K.Y. for  for  Rimsaite  would also  Partial  Dr.  R i n Table  published The  chemically  Canada  prefixed  absorption  and  standards.  to  properties  by  samples  of  as  and p h y s i c a l  is  to  polishing  with a  minimise d i f f e r e n t i a l  w o u l d be u s e d  particularly  3)  rotary  carbon-coated  (Smith,  effects  decided  biotites  the  lap  Standards In  was  were  silk  Electron  a normally  take-off  proportional  angle  of  counters.  Optics  incident 20°, All  and  112  a n a l y s e s were c a r r i e d potential  of 25kv.  o u t a t an e l e c t r o n  excitation  a n d sample c u r r e n t s a p p r o x i m a t e l y .  . 0 8 y u A , u s i n g a s p o t s i z e o f a p p r o x i m a t e l y 5/tt. e l e c t r o n beam c u r r e n t was m o n i t o r e d  The  between each  analysis  by r e t u r n i n g t o a Cadmium s t a n d a r d and c h e c k i n g t h a t t h e s a m p l e c u r r e n t on t h i s s t a n d a r d v/as s t e a d y . fluctuations  o f t h e Cadium s t a n d a r d c u r r e n t were a d j u s t e d  by means o f t h o c o n d e n s e r Simultaneous u s i n g a mica FoKoi  Slight  lens bias  control.  a n a l y s e s v/ere made f o r  and FoK <* ,  MgKoc  c r y s t a l f o r M g K o c , and a q u a r t z c r y s t a l f o r  , i n t h e two s p e c t r o m e t e r s .  Counting response f o r  FoK oc , was g o o d , a v e r a g i n g 1 , 5 0 0 c o u n t s / s e c . f o r a sample c o n t a i n i n g 15  Wt% Fo.  Counting response  h o w e v e r , was e x t r e m e l y p o o r , a v e r a g e s a m p l e c o n t a i n i n g 8 Wt% Mg. f o r an a v e r a g e and  8:1  for  MgKoc?  30 counts/sec  Peak t o background  at  ratios  sample were a p p r o x i m a t e l y 2 0 0 : 1 f o r FeK  f o r MgK* .  B a c k g r o u n d c o u n t s v/ere f o u n d  t h o same a t 1°29 above and 1°29 b e l o w t h o p e a k and  for a  thus background  c o u n t s wore t a k e n  1°29 b e l o w t h e p e a k  t o be  position,  f o r a l l analyses  position.  I n v i e w o f t h e l o w c o u n t i n g r a t e s f o r KgK <* , i t was n e c e s s a r y t o count any  single  spot.  f o r r e l a t i v e l y long p e r i o d s o f t i m e a t Repeated t o n second  analyses of the  same s p o t showed t h a t a f t e r a p p r o x i m a t e l y 5 0 s e e s was a n o t a b l e d e c r e a s e  there  i n tho counting r a t e s f o r both  ,  113  and  MgKec  build out  up.  for  spots  analyses time  to  chock  cores  to  observed  samples  17  the  lie  on a v e r y  single  contamination  spot' were  for  per  sample  carried  inhomogencity  g r a i n and 5 g r a i n s of  the  i n any  of  the  3-5  analysed  samples  z o n i n g by m a k i n g l i n e a r  is  a plot per  standards  increase biotite  total  surface  grain boundaries.  collected  for  -  a  to  wore  per  checked  traverses  from  No c o m p o s i t i o n a l  standards  nor i n any  zoning  of  the  investigated.  Fig.  R.24  of  In a d d i t i o n several  compositional  counts  due  intervals.  were a n a l y s e d  grain was  sec  order  sample. for  Thus  kO  In  , presumably  FoKec  used  at  samples  a l l  straight The  the  curved  during a  single  present  study.  w i t h i n the  this  range to  running period The  l i n e which has  counting rates.  the  range  total  standards  a tendency  Tho G u i c h o n of  •'  standards  c o r r e l a t i o n curve  composition i s  to  of  effectively  a  line. relative  inspection  of  for  estimated  -  at  errors  Fig.17.  compositions  estimate  in  lie  collected  composition against  sees  higher  R . l l and i n counts  40  slightly  slope  of  takes  the  0.35  in analysis  Relative  may b e  errors  in  guaged  the  estimate  Guichon b a t h o l i t h samples Wt% Mg a n d -  i n t o account  the  0.25  Wt% F c .  'fitting'  of  by of  arc This  correlation  Ilk  70000-  Fig.  17  Microprobe analyses. T o t a l counts observed as a f u n c t i o n of c o m p o s i t i o n f o r b i o t i t e standards. C i r c l e s a p p r o x i m a t e one s t a n d a r d d e v i a t i o n of t o t a l counts observed.  115  Tabic XI Standard  #  R.31 R.24 R.26 B.12 R 11 R.13 B.16 B. 8 R. 7 B.18  Standard #  D a t a u s e d i n c o n s t r u c t i o n o f F i g 17  Wt% Mg chemical 3.49 5.53 6.21  6.99 8.63 8.80  11.46 12.84 13.15  13.69  Wt% Fo che mi c a l  B.18  2.1  B.16 B.12  6.8 8.83  B. 8 R. 7  2.4 4.71  R.ll  12.57 14.49 16.81 17.88 22.42  R.13 R.26 R.24 R.31  zr c o u n t s  c-Mg%  and  Average T o t a l counts MgKoi ( 4 0 s e e s ) 352 1500  1468 1834 2380 2488 3944 4712 4514 5228  Average Total counts FeKot ( 4 0 s e e s ) ^420  7612  14368 19408 25432 35576 43588 52192 50248 70560  c  1%  counts  counts  18 80 70 50  5.15 6.1 4.7 2.7 6.7 4.5 4.4 2.6 3.3 0.8  160  112 174 124 148 46  cr  counts 164 164 184 440 344 1200 564 2432 1348 956  counts 3.0 2.1 1.3 2.3 1.4 3.4 1.3 4.6 2.7 1.4  cr Mg% •  ->  . JL  .2 .15 • 125 .4 .25 .25 .15 .20  .1  0Yc% .1 .1 .1 .2 .2 .4 .25 .6 .4 .25  1 s t a n d a r d d e v i a t i o n f r o m t h e a v e r a g e valueo b t a i n e d from s e v e r a l s p o t a n a l y s e s on s e v e r a l g r a i n s from each sample c - F c % have b e e n e s t i m a t e d from a k n o w l e d g e o f c o u n t s and t h e c o r r e l a t i o n c u r v e s o f F i g . 14  116  curves,  sample  variation was  checked  after be  of  each  less  counts  X-ray  sot  of  one  a l l  of  and the  generation.  by a n a l y s e s  than for  inhomogoneity  of  Total  standards  unknown s a m p l e s . standard the  statistical instrumental before, Drift  d e v i a t i o n i n the  standards  employed.  during  was  found  drift and to  accumulated  

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