UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Pasco Creek breccia, Horseshoe Bay, B.C. Von Rosen, G. E.A. 1966

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1966_A6_7 V6.pdf [ 11.75MB ]
Metadata
JSON: 831-1.0053013.json
JSON-LD: 831-1.0053013-ld.json
RDF/XML (Pretty): 831-1.0053013-rdf.xml
RDF/JSON: 831-1.0053013-rdf.json
Turtle: 831-1.0053013-turtle.txt
N-Triples: 831-1.0053013-rdf-ntriples.txt
Original Record: 831-1.0053013-source.json
Full Text
831-1.0053013-fulltext.txt
Citation
831-1.0053013.ris

Full Text

PASCO CREEK BRECCIA Horseshoe Bay, B. C. by G. E. A. von Rosen B.So., U n i v e r s i t y of B r i t i s h Columbia, 1962  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF ' THE REQUIREMENTS FOR THE DEGREE OF . Master o f Science i n the Department of GEOLOGY  -We accept t h i s t h e s i s as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1966  In p r e s e n t i n g r e q u i r e m e n t s f o r an Columbia, for  extensive granted It  the  gain  this  Head o f my  i s understood  financial  the  study.  copying of by  that  shall  thesis  in p a r t i a l  advanced degree at  I agree that  r e f e r e n c e and  this  Library  the  shall  University  Department or  by  his  be  a l l o w e d w i t h o u t my  Department The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a  of  Columbia  the  British available  permission  for  f o r s c h o l a r l y p u r p o s e s may  copying or p u b l i c a t i o n not  of  make i t f r e e l y  I f u r t h e r agree that thesis  f u l f i l m e n t of  be  representatives. this  thesis  written  for  permission  ABSTRACT  An  800  f o o t - s q u a r e o u t c r o p o f a g n e i s s - b r e c c i a body a t P a s c o  c r e e k , 3 m i l e s n o r t h a l o n g t h e h i g h w a y f r o m H o r s e s h o e Bay, was  mapped, and  A survey  i t s relationship  of the l i t e r a t u r e  t h e s i s was  B.C.  to the g n e i s s c o u n t r y r o c k s t u d i e d ,  o f b r e c c i a s i n c l u d e d i n the  u s e d as a b a s i s , t o g e t h e r w i t h t h e f i e l d  present  data, f o r  a method o f b r e c c i a f o r m a t i o n p r o p o s e d as a r e s u l t o f t h i s The  b o d y was  found  t o be p i p e - l i k e i n s h a p e ,  d i r e c t i o n s of s t r u c t u r a l weakness i n the r o c k .  The  work.  following size  of  b r e c c i a f r a g m e n t s and  v a r y i n g amounts o f m a t r i x , a s w e l l a s  border  r o c k s were t h o u g h t  phase d i o r i t i c  several processes these  t o have r e s u l t e d  a c t i v e i n t h e f o r m a t i o n o f the b r e c c i a ,  e x p l o s i v e a c t i o n o f g a s e s ahead o f a n  gether w i t h f l u i d i z a t i o n of a mixture country rock are thought of the b r e c c i a .  t o be  the  from Amorig  i n t r u s i v e body, t o -  of these  g a s e s and  of prime importance  i n the  shattered formation  ii.  iv.  TABLE OF CONTENTS  I.  II.  III.  INTRODUCTION  1•  Location and. Access  2  Physiography and Topography  2  Aknowledgements  3  GENERAL GEOLOGY OF THE AREA  .  GNEISS-BRECCIA PIPE Fragments  5 6  1. 2.  Schistose fragments Gneissic fragments  6 7  3. 4.  Gneiss blocks Granitic pebbles & Pegm. inter-clast material .  7 8  Matrix  10  Structures  11  1.  Orientation of clasts  11  2. 3. 4. 5. 6. 7*  Deformation of clasts Shear zones Gouge-filled faults Joints Foliation in border phases Secondary foliation  11 12 12 12 12 13  Relation of Pipe to Country Rocks 1. 2.  Gneiss Hornblendite  13 13 14  V  TABLE OP CONTENTS  R e l a t i o n o f Pipe to Country Rocks (cont'd) 3.  Border phases o f b r e c c i a  14  a.  Porphyritic diorite  15  b.  Foliated granite  16  c.  Dikes  19  Summary o f C h a r a c t e r i s t i c s o f t h i s B r e c c i a IV. V.  13  EXISTING THEORIES OF BRECCIA FORMATION  ,  •„ ' 23  INTERPRETATION OF BRECCIA FORMATION Pre-breccia  ,28  Geology  O r i g i n o f Pasco G n e i s s - B r e c c i a  28 Pipe  29  A p p l i c a t i o n o f Data to Theory Conclusion  20  31 ;  35  vi.  LIST OF PLATES AND FIGURES  Figures 1  Index Map:  Vancouver North, B r i t i s h Columbia  .opp. p. 2  2a  Outcrop Distribution Flap, Pasco Creek, Horseshoe Bay, B r i t i s h Columbia  appendix  2b  Map of Breccia Body, Pasco Creek, Horseshoe Bay, B.C. appendix  3  Diagrammatic Cross-sections, Pasco Creek  appendix  Mottled plagioclase i n typical groundmass  opp. p. 7  Plates la. b.  Contact of amphibolite clast with groundmass  c.  Pyrite-epidote associations  opp. p. 7  Pegmatitic space-fillings and rimmed clasts  opp. p. 8  b.  Pegmatitic plagioclase against matrix  opp. p. 8  c.  Recrystallized intruded matrix  opp. p. 8  Breccia near contact with d i o r i t e  opp. p. 10  Breccia at contact with diorite  opp. p. 10  Granitic pebbles i n breccia  opp. p. 11  Sub-horizontal orientation of fragments  opp. p. 11  Va.  Gneiss fragment with e l l i p s o i d a l shape  opp. p. 12  ' b.  Deformed elongate breccia c l a s t ;  opp. p. 12  Ila.  Ilia. b. TVa. b.  .  opp. p. 7  vii.  Va. b.  Vila. b.  Villa. b.  IXa. b.  Xa. b.  XIa. b.  Gneiss country rock  .opp. p. 13  Augen g n e i s s i n country rock  Contact o f p o r p h y r i t i c d i o r i t e w i t h b r e c c i a  ©PP. P« 13  ....... opp. p. 15  Contact o f d i o r i t e d i k e w i t h b r e c c i a  opp. p. 15  P l a g i o c l a s e phenocryst  opp. p. 16  A l t e r e d p l a g i o c l a s e phenocryst and groundmass  .....  opp. p. 16  P i n k , f o l i a t e d b o r d e r phase rock  opp. p. 17  S e r i o i t i z e d , f o l i a t e d b o r d e r phase rock  opp. p. 17  Zoned p l a g i o c l a s e phenocryst- c r o s s e d n i c o l s  opp. p. 18  Zoned p l a g i o c l a s e phenocryst- p l a i n p o l a r i z e d l i g h t  opp. p. 18  South c o n t a c t o f b r e c c i a on road  opp. p. 20  R e l a t i o n s near n o r t h c o n t a c t o f b r e c c i a p i p e  opp. p. 20  INTRODUCTION  B r e c c i a occurrences by  geologists.  have l o n g r e c e i v e d s p o r a d i c a t t e n t i o n  This i n t e r e s t has i n c r e a s e d  since the r e a l i z a -  t i o n o f t h e a s s o c i a t i o n between o r e d e p o s i t s and b r e c c i a p i p e s . Thus t h e r e h a v e b e e n many a t t e m p t s a t d e t a i l e d d e s c r i p t i o n a n d c l a s s i f i c a t i o n of a l l types Breccias, like always m i n e r a l i z e d .  other  of breccia.  o r e - l o c a l i z i n g structures, are not  According  a r e m i n e r a l i z e d , and e v e n t h e n , ore-bearing.  t o W a l k e r ( 1 9 2 8 ) o n l y one p e r c e n t only small p a r t s o f these a r e  They g e n e r a l l y have no g e n e t i c  r e l a t i o n s h i p with  o r e d e p o s i t s , b u t a r e m e r e l y phenomena o f t e c t o n i c and v o l c a n i c activity. The to*...  term " B r e c c i a p i p e ' , a c c o r d i n g a crudely c y l i n d r i c a l ,  t u r a l u n i t composed w h o l l y  country  purpose of t h i s rock  formation  highly inclined  matrix."  (l96l),  or vertical  or p a r t l y of angular,  rock fragments with o r without The  t o Bryner  refers struC'  o r rounded,  ( p . 490)  t h e s i s i s t o d e s c r i b e a b r e c c i a mass i n  o f g n e i s s , a n d t o c l a s s i f y a»d a s c r i b e a mode o f  f o r t h e same.  A review  o f t h e l i t e r a t u r e on b r e c c i a s  i n f o r m o f a summary s h a l l be i n c l u d e d i n t h i s  work  v  2  L o c a t i o n and Access The  location  crops  out  which  here  feet,  the Two  of  the  on  the  the  steep  rises  breccia  western  rapidly  summit of excellent  from  Black  (fig,  highway  and  Three  miles  exposures  .line  railroad,  a tangle  of  along  line the  brambles  in  Figure  the of  Coast  It  1.  Mountains,  Howe  Sound  to  3,992  are  found  in  the  breccia  and  the  rock  the of  Pacific  covers  obscuring  is  Vancouver. Bay,  and f e l l e d  Great slope  the  The  of  uphill  of  Bay,  for  .B.C.  easily  can  B.C.  the  Eastern  outcrop.  area  the  cuts  between  Horseshoe  a necessity  right-of-way  map a r e a ,  the  some o f  highway  from Horseshoe  across  of  shore  the  the  A power  cuts  of  Much b l a s t e d  boat  mapping.  Authority ing  by  the  highway  located s o m e 20 m i l e s n o r t h be r e a c h e d  shown  aspect  2)  south  is  Mountain.  Vancouver-Squamish  Railway, the  of  shore-  Hydro  Power  highway,  leav-  logs.  Physiography and Tonography The slopes feet  rising  altitude,  pecially high  area  well  area,,  typical  from  the  of  h i d d e n by are  Glacial  and b e d s o f  the  shores  make t r a v e l  because of  Outcrops lichens.  is  the  of  Coast  fjords,  on t h e  in  forested  sudden p r e c i p i c e s ,  coniferous  scarce,  forests  steep  and f l u v i a l highly  rugged  and  competent  Steep  many p l a c e s slopes 10's  to  5,000  hazardous,  to  100's  of  esfeet  undergrowth.  and u s u a l l y  gravel  Mountains  covered  by  covers  many p a r t s  'freshet'  streams  moss of  and  the  incise  s l o p e s and w i d e n i n t o  s m a l l g r a v e l beaches, t h a t dot the b l u f f y  shore.  Acknowledgements I am i n d e b t e d thesis topic,  t o D r , J.V. R o s s who  and h e l p e d  organize  g r a t i t u d e i s due t o Dr.. R.M,  made me aware o f t h i s  the manuscript.  Thompson who  helped  i d e n t i f i c a t i o n o f some m i n e r a l s , and t o D r . K.C. aided w i t h helpful." d i s c u s s i o n s  Further with  th© X - r a y  McTaggart  wh©  GENERAL GEOLOGY OF THE AREA Howe S o u n d , w i t h i t s s e v e r a l i s l a n d s , and t h e V a n c o u v e r A  N o r t h map a r e a were mapped b y A r m s t r o n g ( 1 9 5 4 ) and l a t e r b y Roddick  (1965).  P l u t o n i c rock  u n d e r l i e most o f t h e a r e a . morphic rocks  P r e p l u t o n i c and p o s t - p l u t o n i c  comprise t h e remainder of t h e area,  some s e d i m e n t a r y r o c k s P l u t o n i c rocks be  of the Coast Mountain i n t r u s i v e s  a r e mainly  dioritic;  than a q u a r t z - f e l d s p a r r a t i o . v i e w i s s u p p o r t e d by R o d d i c k  mafics  together  of t h i s region can best  they a r e thought t o percentage basis  ( A r m s t r o n g , 1954) ( 1 9 6 5 ) who m a i n t a i n s be c l a s s i f i e d  that the p l u t o n i  according  Such a c l a s s i f i c a t i o n i s b a s e d upon t h e o b s e r v a t i o n p r e v a i l i n g genetic  order  i n the minerals,  plagioclase-hornblende-biotite-quartz-potash  pendants a r e brought t o present i s brought to contact  are created  that there i s as f o l l o w s :  faults  He a l s o roof rock  w i t h p r e - e x i s t i n g metamorphic rock i n  from metamorphic r o c k s  f o l l o w i n g sequence:  manner.  l e v e l s , whereby p l u t o n i c  which connate water has been r e t a i n e d . rocks  t o the  feldspar.  concludes that through the a c t i o n of s y n p l u t o n i c  rather ,  This point of  r a t h e r than q u a r t z - f e l d s p a r i n the c o n v e n t i o n a l  a definite  with  o f l o w m e t a m o r p h i c g r a d e and v o l c a n i c s .  c o r r e l a t a b l e on a h o r n b l e n d e - b i o t i t e  rocks  meta-  The r e s u l t t h a t p l u t o n i c i si n f e r r e d i n the  hornblende d i o r i t e - b i o t i t e g r a n i t e - a l a s k i t e -  pegmatite, during retrograde  metamorphism.  f i n d s that the country  o f the Pasco b r e c c i a b e l o n g t o a  slice  rocks  o f metamorphic rock  Horseshoe Bay Pendant.  R o d d i c k (1965'p. 29)  ( T w i n I s l a n d s G r o u p ) w h i c h he c a l l s t h e  5.  A r m s t r o n g (1954) r e p o r t s  t h a t the metamorphic rocks a r e  m a i n l y , o r e n t i r e l y M e s o z o i c i n age.  The Bowen I s l a n d  group  c o n s i s t i n g o f s l i g h t l y m e t a m o r p h o s e d , f o l d e d b a s a l t i c and a n d e sitic  l a v a s , with interbedded  T r i a s s i c ? and/or e a r l i e r . later,  t u f f s and s e d i m e n t a r y r o c k s , i s  The G a m b i e r g r o u p , T r i a s s i c ? a n d / o r  c o n s i s t s m a i n l y o f p y r o c l a s t i c ^ r o c k s and l a v a s , w i t h  interbedded  sedimentary m a t e r i a l .  On Mt. B r u n s w i c k a 6,000 f o o t  s e c t i o n c o n t a i n i n g a t l e a s t 2,000 f e e t o f s l a t e , q u a r t z i t e , and a r k o s e , b e l o n g s t o t h e l a t t e r , to which g n e i s s i c . c o u n t r y  rocks  minor  argillite,  Pre-granitic  rocks,  of the t h e s i s area are thought to  b e l o n g , had been t e n t a t i v e l y c o r r e l a t e d w i t h  t h e Bowen I s l a n d  g r o u p m a i n l y on l i t h o l o g i c  (1965) a s s e r t s  that  around the t h e s i s area belong to the P r e - J u r a s s i c  Twin  the  rocks  Islands  age.  He s t a t e s  Several  Little  that  many t o be  c a n be s a i d a b o u t t h e s t r u c t u r e o f t h e a r e a t o A r m s t r o n g (1954) mentions  "... i s t h e n e a r - v e r t i c a l a v e r a g e d i p o f t h e p l a n e  of u n c o n f o r m i t y s e p a r a t i n g i n d i c a t i n g that  t h e Gambier group from the o l d e r  the l a t t e r , i n c l u d i n g the o l d e r p l u t o n i c  s e v e r e l y deformed."  TIT. The  occur i n the area, of  synplutonic.  what was m e n t i o n e d a b o v e .  that there  were;all  the Gambier group i s Upper J u r a s s i c  v a r i e t i e s of young d i k e s  w h i c h he b e l i e v e s  supplant  Roddick  g r o u p p o s s i b l y t h e same a s t h e Bowen I s l a n d g r o u p o f  s i m i l a r age. in  grounds.  breccia pipe,  rocks,  rocks,  ( A r m s t r o n g , 1 9 5 4 , p. l )  GNEISS-BRECCIA P I P E a s i t i s c u t b y t o p o g r a p h y , i s a b o u t 800  -  6.  feet^square, with  plunges s t e e p l y , and has  the g n e i s s i c country  cross c u t t i n g r e l a t i o n s  rock.  Fragments i n the dark b r e c c i a , mainly of a m p h i b o l i t i c composition  s i m i l a r to mafic  bands i n the g n e i s s , are surrounded  by scant matrix, mostly of n e a r l y microscopic  g r a i n s i z e , between  c l o s e l y packed fragments. The  b r e c c i a face looks uniformly dark from a d i s t a n c e of  s e v e r a l f e e t because of the predominance of- mafic  fragments.  This u n i f o r m i t y changes to v a r i e t y on c l o s e r i n s p e c t i o n when smaller compositional  and  t e x t u r a l changes, as w e l l as the e x i s t e n c e  of  minor s t r u c t u r e s , become e v i d e n t . Fragments - Fragment s i z e v a r i e s from m i c r o s c o p i c , thick; and and  to 30 f e e t  35 f e e t long; a common s i z e i s about 1 to 2 inches wide  2 to ? inches l o n g . . Small fragments are u s u a l l y bounded by  planar s i d e s p a r a l l e l  to s c h i s t o s i t y , but fragments have been  noted where the f o l i a t i o n i s oblique to the l e n g t h .  Only  one  f o l i a t i o n i s evident i n the fragments. Texture  and  composition  s c h i s t o s e , to f e l s i c are moat common.  The  and  of fragments vary from g r a n i t i c  mafic, r e s p e c t i v e l y , although  g r a n i t i c and f e l s i c  and  mafic s c h i s t s  fragments are r a r e  enough to arouse a t t e n t i o n e s p e c i a l l y f o r t h e i r rounded shapes. The  term g r a n i t i c pebbles has been a p p l i e d to 1.  these.  S c h i s t o s e fragments--Most common are amphibolite  They are normally  dark, t a b u l a r i n shape, 1 to 4 inches  v a r i o u s l y textured from spotted p o r p h y r o b l a s t i o , to  fragments.  long,  fine«g?ained  Plate  f a c i n g page'; 7  I  xlO  c..Association of p y r i t e with vein  of f r e s h  quartz.  epidote  near  schistose. In t h i n s e c t i o n s c h i s t o s i t y i s d e f i n e d f r e s h grains clase  by o r i e n t a t i o n of  of green hornblende, between s l i g h t l y cloudy  (oligoclase-andesine),  and quartz i n a g r a n o b l a s t i c  plagiotexture,  ( p l a t e l b ) Fragment boundaries are sharp and there i s no v a r i a t i o n i n texture  or composition near the margins.  Where s l i v e r s have  separated from s c h i s t - f r a g m e n t s brown b i o t i t e i s found to replace 'green hornblende.  E p i d o t e , s e r i c i t e , c h l o r i t e , p y r i t e and mag-  n e t i t e occur i n minor amounts. 2.  Gneissic  fragments—Somewhat l a r g e r fragments e x h i b i t  gneissose banding comprising amphibollte s i m i l a r to the ones just described,  and f o l i a t e d  f e l s i c bands composed of p l a g i o c l a s e ,  with some quartz i n v a r i a b l e p r o p o r t i o n s .  These l a r g e r s i z e s  are not common, and one such fragment ( P l a t e V) i s w e l l I t has s e v e r a l ellipsoidal 3.  form.  Two have been observed.  One occurs at the north  a l o n g the r a i l r o a d and the other i s w i t h i n  along the highway. contact  to the a x i s of i t s sub-  Gneiss b l o c k s — T h e r e are l a r g e r i n c l u s i o n s of gneiss i n  the b r e c c i a . contact  g n e i s s i c bands o b l i q u e l y  rounded.  the s e c t i o n  The l a t t e r i s about 25 f e e t wide, has a " f a u l t  with the b r e c c i a on the south side and a p o r p h y r i t i c septum  on the north contact.  ( f i g . 3)  normal country rock trend, i n c l u s i o n within  I t s a t t i t u d e d i f f e r s from the  i n d i c a t i n g r e l a t i v e r o t a t i o n of the  the b r e c c i a .  Another block i s about the same s i z e as the f i r s t  and i s  Plate I I  f a c i n g page 8  a. P e g m a t i t i c s p a c e - f i l l i n g and  xlO  rimmed c l a s t s .  8. wedged apart from the "breccia wallrock by tightly-packed breccia and some porphyry.  Rotation relative to the country rock again i s indicated  by the change i n strike, as well as the change i n dip. . 4.  Granitic pebbles and pegmatitic inter-clast m a t e r i a l —  Pebbles  of f o l i a t e d granitic material and white plagioclase inter-clast f i l l i n g s are infrequent but contrast noticeably with the dark, angular fragments of the rest of the breccia,  (plates I l a , IVa&b)  Granitic pebbles with e l l i p t i c a l cross-sections appear to by c y l i n d r i c a l i n shape.  Their sides are p a r a l l e l to t h e i r f o l i a t i o n s which  generally impart to the rock structural weakness i n at least two direc-' . ... tions.  Various shapes and sizes, of this rock type occur i n several places  in the breccia.  In thin section i t i s seen to contain quartz, plagio-  clase, and brown and green b i o t i t e , s e r i c i t e , chlorite, and epidote with pyrite. .Most of the plagioclase i s cloudy with s e r i c i t e and kaolin. Quartz i s clear.  The fabric i s medium-grained, or f i n e r .  The texture i n  part i s granophyric, especially i n plagioclase crystals, but f o r the most part i t tends to be granoblastic.  Cracks i n crystals, as well as i n t e r -  granular boundaries are f i l l e d with sodic plagioclase and quartz. latory extinction i s common, and the shadowy and indistinct  Undu-  contacts  between many grains are due to joined rims of sodic plagioclase. These textures are interpreted as indications o f • r e c r y s t a l l i z a t i o n of a f o l i a t e d , but i n i t i a l l y granitic textured rock.  The h e a l e d c r a c k s , are t h o u g h t  to he s i g n s  replacement during  overgrown  the  of  these  of  boundaries,  and g r a n o p h y r i c .  e i t h e r magmatic  areas  l a t e r .magmatic  by more s o d i c stages  processes.-'or plagioclase,  texture  possibly active  when c r y s t a l l i z a t i o n had  already  ensued. On w e a t h e r e d s u r f a c e with  the n o r m a l l y  distance  white  aspect  fragments  with  a variety  In  they  seem r a t h e r  other 'fragments. in  some c a s e s ,  foliated with  with  layers  in  grey In  ones  thin  of  (plate  the w h i t e  contrast Ii)  areas  to be s p a c e  is  fillings  with b a s i c  others.  that  material  space-fillings.  In  such f r a g m e n t s  s e c t i o n • these  of  white  around gradational  fragments  in d i r e c t connection,  f o l i a t i o n , and p l a i n  c o n t a i n i n g wisps  are  angular.  are  schistose  short  they  and r i m s  fragments  There are  sharply  From a  shapes between rounded and  of . s i a l i c  to be masked by c o a r s e r into  of  The c o n t a c t s  sharp  the w h i t e  fillings  dark-green breccia.  the o v e r a l l  detail  space  oriented  schistqsity  white  areas  tends  grade  mafics.  space-fillings  are  notably  j  pegmat.i t i c , composed o f . p l a g i o c l a s e intergrown,  b u t a l w a y s more c o a r s e l y  remainder  of  overgrown  and shadowed.  blastic  is  the r o c k .  intergrowths  and d i s p l a y caused  by  plagioclase  (An^g)  (plate  of  a fish-net  which  are  these  represent material  light.  around  textures in  are  it  lightly,  grano-  fine-grained  between c l o u d e d g r a i n s rims  the  include cloudy  t e x t u r e under p l a i n  plagioclase  seldomly  than  Crystal''margins  areas  plagioclase  An an i n t e r p r e t a t i o n of the w h i t e a r e a s  crystallized  b)  The w h i t e  the c o n t r a s t and s o d i c  II  or q u a r t z ,  Such.a  texture  of  altered  these  grains.  is  the p r o c e s s  thought of  that  solidifying  Plate I I I  Breccia near contact with d i o r i t e . Note p o r p h y r i t i c m a t r i x and l o o s e p a c k i n g . (Numbers indicate origin  of  thinsections)  b. B r e c c i a near contact with d i o r i t e . Note p o r p h y r i t i c m a t r i x , f l o a t i n g f r a g m e n t s , and s t a r t o f t i g h t e r p a c k i n g . (Numbers  indicate origin of thinsections)  facing  page 10  10.  from the  liquid solid  form;  form  some w h i t e  while  others  have  shapes  fragments  if  not l i q u i d i t y of the q u a r t z - f e l d s p a r - The m a t r i x  differs  fragments  diorite,  whereas  cemented  thus  dependent  indicating  material  are widely  within  together  within  spaced  the b r e c c i a pipe  by t h i n  seams  restricted, section  textures  belonging  to the border  scribed.  The m a t r i x  in  i s present  direct  only  birefringence over  short  differ with  biotite,  each  as most  other.  These  chlorite,  because  in fabric.  later  textured  epidote,  parts  Quartz  Green  lost  matrix be d e -  the whole  small  mafic  and a p a t i t e a r e  i s often  riddled  i s clear. with  Some  with gra.no-  anomalous  Texture  fragments  varies  themselves  granoblas tic Grain  of  Generally -plagio-  biotite.  the l i t h i c  i s common.  their  pyrite,  chlorite  brown  consist  areas.  PIagioclase  with  On  a earns  partly  and p y r i t e .  i s associated  slightly  have  i s present.  distances  granitic  that  proportions.  of epidote  intergrpwth  breccia  o f t h e .fragments a r e  seams  o r i e n t a t i o n ' , and q u a r t z - f e l d s p a r  phyric  A t the  as t h i n  mineral  intergrcwths  surrounding  packed  b r e c c i a w i t h i n the  fragments,  in varied  material.  of the b r e c c i a , w i l l  lithic  Present  by p o r p h y r i t i c  of the p o r p h y r i t i c d i o r i t e  phases  A t the  of the t i g h t l y - p a c k e d  contact, with  quartz,  diorite  (plateIII)  altered  clase.  with  the b r e c c i a .  of s i a l i c  to the contact.  plasticity,  they, a r e t i g h t l y  fragments,  pipe  at least  and s u r r o u n d e d  a p s e u d o - a g m a t i t'e o f p o r p h y r y ,  thin  on t h e o u t l i n e s  melt.  periphery,  In  t o he f r a g m e n t s o f  of the b r e c c i a a t the contact  from, t h e i n t e r c l a s t  contact,  and  them,  appear  of  Matrix  surrounding  areas  texture  boundaries  are  P l a t e IV  a. G r a n i t i c pebbles i n b r e c c i a with some o r i e n t a t i o n of fragments.  b. D e f i n i t e s u b - h o r i z o n t a l of a l l types of fragments.  orientation  11.  overgrown.  .'  The i n t e r p r e t a t i o n g i v e n .that of  the m a t r i x  fine  well  as  of the t i g h t l y  grained  lithic  textural  relations is  packed b r e c c i a c o n s i s t s  small  some p l a c e s ,  nearly  all  on g r a i n  c o in m i nu t j. o n . fragments'  texture', granophyric  and o v e r g r o w t h s  as  of  whole ~ and dismembered  i n d i c a t e d by t h e i r g r a n o b l a s t i c in  mainly  The p r e s e n c e of f r e s h ,  disrnembere d f r a gm e n t s , s u gge's t s so r« e p r o c e s s  growth  inter-  boundaries  in  instances, '  Struotures  -  orientation  otruptures of  gouge-rich  e n c o u n t e r e d d u r i n g mapping are  clasts. within  shearing across  -  these  fragments.'  Re c r y s t a l 1 i'/.a t i on of both is  for  .'small  folds,  the. b r e c c i a , larger  structures  f a u l to , '. j o i n t s , f o l i a t i o n  o f t e n a c c o m p a n i e d by j o i n t i n g ,  b e n d i n g of  of  and s e c o n d a r y  following:  fragments  such as  granitic  the  shear  rocks,  with  zones,  gn e i ss o s i ty  foliation  in  the  gneiss. 1. axes  O r i e n t a t i o n of  of a l l  types  o v e r a 150 f o o t "ear was  vertical vaguely  the highway s e c t i o n .  alignment  of  long  at  alignment  that factor  Plastic  in  axes  orientations, is  the f o r m a t i o n  deformation.—Most  shown i n p l a t e Vb.  whereas  very l i k e l y  p 1 a n a r , ' 'many a r e bent, • some of s h e a r e d as  within  the  of  long  Bent  a,  b)  section  t h e s e may be  expression' of  some'  breccia.  fragments  them are  but  IV  occurs  the r . u b - h o r i z o n . t a l  the  the  (plate  the' p l a n e . o f  two l o c a l i z e d p o i n t s ,  section  of  i n a. s u b - h o r i z o n t a l d i r e c t i o n  of  similar  2..  alignment  stretch  fortuitously  controlling  fragments  of  visible  in  clasts.--Definite  in  not. o n l y  fragments  the b r e c c i a , a r e ben t bu t have  are u b i q u i t o u s  in  Plate V  facing page 12  the  breccia.  impingement 3. south  Flexure o f two  Shear  contact  the  zone  The  central  which  grained  no'ticeahle  35  foot-wide- shear  of t h e b r e c c i a i n t h e r o a d green,  through  a 1ight  shot  green,  through  friable  r a t h e r impermeable,  boundary  b e t w e e n b r e c c i a and c o u n t r y  11  not. h e f o l i o w o d a l o n g  attitude  of the fracture  would  the l a t e s t  4. to  Gouge f i l l e d  a lesser  extent  slickensided,'and of  strike  5. rock and  of f a u l t s  faults  :i.n. t h e c o u n t r y i n - some c a s e s  one s e t w h i c h  been  part  of fused  section,  direc tion.  The  o f the zone, whi ch  those  a- w e a t h e r e d  found  rocks.  constitute  i n the b r e c c i a ,  Scarps  are vaguely  the f a c e  of the d e t a i l  of the section  of the rock.  i n c r a c k l e and fragmented j o i n t s . are found  parallel dike  and  breccia.  i n . ho t h c.oun t r y  t o ' g n e i s s o s i t y (l35°/70°NE)  parallels  ( l 5 0 / 7 0 ° N W; o  have  measured. f\.  border ments  often results  only  fine-  r e p r e s e n t s the  i n the road  i n e i 1;her  are mainly  J o i n t s .--A1 though, many  and b r e c c i a ,  v e i n of very  creek,  o f m o v e m e n t , i s 06*0°/85° S S .  t r i e r a i l r o a d ' c u t , o b s c u r i n g much  Juncture  rock  a t the c e n t r a l  locus  by. P a s c o  m y l o n i t i c zone  at the  grained.  with anastomosing v e i n l e t s  This  he  of  The r o c k i n  and i s f i n e  zone i s i n c i s e d  quartz.  couId  the l i n e  zone o c c u r s  section.  w i t h brown a r e a s ,  por.tion of the shear  epidote  near  fragments.  zones.-—One  i s - dark  cuts  i s especially  Foliation  i n border  phases, --Grani t i c  of the b r e c c i a are f o l i a t e d . . of f o l i a t i o n  possibility  exists  were  taken  Prom  rocks  three  outcrops,  and a r e shown i n f i g u r e  that i f further  outcrops- were  at the south  2b.  measureThe  t o he f o u n d ,  they  Plate VI  b. •Typical band with augen from g n e i s s .  f a c i n g page 13  would pipe  suggest outline  that  the f o l i a t i o n h e a r s  rather  Secondary  7.  than  in  could  he m e a s u r e d .  structure finding  country Only  scarcity  P:iye to  of  scale  mafic  is  (plate  VI  grained zones  a)  evident  Minute  migrnatized  the m a f i c m i n e r a l s no r e l a t i o n  migmatization Infinite within  very  to  of  this  variations  short  crops  in  distances  The r o c k - f o r m i n g m i n e r a l s  are  and  out  the  rock.  i n some  area.  chlorite, biotite,  of  grain  sizes,  grained  to p o r p h y r o b l a s t i c  Incipient  changes  outcrops.  and  epidote,  from f i n e  which  (oliogoclase-  as  vary  these  plagioclase  of  Textures  In  swirls  the  small  veinlets.  •'• ,  i n medium  and c o m p o s i t i o n a l  includes  quantities  parallel,  coarser  boundaries.  seen i n many o f  mainly  follows  weathered o u t c r o p s .  assemblage  in  of  foliated,  i n the  and b i o t i t e ,  mainly  this  chance  jointed  green hornblende, q u a r t s ,  calcite,  dip  country  minutely  andesine),  pyrite,  of  and f o l l o w  t r e n d of  textural are  the  frequently disappear  occur in c l o t s  type  types  foliation  indistinct  the g e n e r a l  is  banded,  some s m o o t h l y  zones w i t h  reduces  show  they can be d e s c r i b e d as  in d e t a i l ,  foliations  secondary  Th.e f o l i a t i o n  the g n e i s s  Various  A secondary in  the  foliation.  conspicuously  foliation.  in  to  rock..  shows d e f i n i t e  good o u t c r o p  secondary  gneiss,  to the m a j o r layers  the c o u n t r y  few hands  of  relationship  (175°/?)  C o u n t r y Rocks -  Gneiss.--The  on o l a r g e r  have  rock.  s u r r o u n d / ' the b r e c c i a p i p e ; 1.  and  the  more examples  R e l a t i o n , of rock  gneissic  and  t r e n d of  f Q 1 i a t i o n . - - P l a t e VI  foliation not  the  some  present  a l t e r a t i o n minerals apatite,  schistose,  with  the  such  sericite,  and  through  range  xen.oblastic  a  augen  of  14.  f e l d s p a r between a l i g n e d m a f i c s .  These e l o n g a t e m a f i c m i n e r a l s .  are o f t e n bent around the l a r g e r c r y s t a l s . schists  commonly c o n t a i n p a r a l l e l  ( p l a t e VI b)  elongate  c l o t s of  hornblende  c r y s t a l s a s s o c i a t e d w i t h p l a g i o c l a s e augen s e t i n a f i n e schistose 2.  Hornblendite.—Dark  o f the s m a l l b a y s . a vague p a r a l l e l  green h o r n b l e n d i t e c r o p s out  on  a c a v e - l i k e i n d e n t a t i o n of  one  The  r o c k has  no d i r e c t i v e  around  texture other  e l o n g a t i o n of- t h e p i t s w h i c h  out c l o t s o f m a i n l y brown b i o t i t e t h e p i t s a r e due  hornblende-rich areas. and  grained  matrix.  a p o i n t of the s h o r e l i n e near  Ridges  Spotted  brown b i o t i t e  r e p r e s e n t weathered by  green  Small areas  of s e r i c i t i z e d  The  similar  and  plagioclase  brown b i o t i t e  i s similar  r e p l a c i n g some of t h e h o r n b l e n d e .  of f r e s h p l a g i o c l a s e ,  hornblende.  t o more r e s i s t a n t p l a g i o c l a s e  c u t the r o c k .  to t h a t i n c i p i e n t l y  surrounded  than  A  selvage  t o t h a t i n t h e rock., b o r d e r s  the  veins. Contact n o t known.  relations The  of t h i s h o r n b l e n d i t e w i t h the g n e i s s  l a c k of b a n d i n g  and  t h e o t h e r w i s e homogeneous c  c h a r a c t e r of the r o c k , t o g e t h e r w i t h the h i g h c o n t e n t crystallized plagioclase  hornblende crystals,  are  of  well-  surrounding i n t e r g r a n u l a r patches  i n d i c a t e an i g n e o u s  origin,  rather  of than  metamorphic. 3. border  Border  p h a s e s o f the b r e c c i a , a p p e a r to be  occur near colour, dark  phases of the b r e c c i a . — R o c k s , here  igneous.in origin  t h e p e r i p h e r y of the b r e c c i a , b u t  t e x t u r e , and  green d i o r i t e ,  composition. through  c l a s s e d under and  they d i f f e r i n  Composition  v a r i e s from  l i g h t e r c o l o u r e d igneous  rocks  very to  Plate VII  facing page 15  15.  l e u c o c r a t i c pink a. and  within  granites.  Porphyritic diorite.  Both a t the b r e c c i a  the b r e c c i a mass a r e o c c u r r e n c e s o f p o r p h y r i t i c  Those w e l l w i t h i n t h e b r e c c i a a r e l e s s p l e n t i f u l those a t the p e r i p h e r y .  A l t h o u g h ;the  mafic mineral  r e l a t i o n s d i f f e r f r o m one o c c u r r e n c e o f d i o r i t e t e x t u r a l and c o m p o s i t i o n s i m i l a r i t y  c o n t e n t , as  contact  rock type.  to the n e x t ,  F i g u r e .3 shows the c o n t a c t s and b r e c c i a  of d i o r i t e with t o the s o u t h .  slightly  c r o s s c u t s , the g n e i s s i c f o l i a t i o n ,  distance  o f few t e n s o f f e e t  to the g n e i s s o s i t y .  the c o n t a c t  i s sensibly  The d i o r i t e - b r e c c i a c o n t a c t  two v a r i a t i o n s i n b r e c c i a d i o r i t e  periphery  contact  at the  and one a t t h e d i k e  within.the  at the dike w i t h i n the b r e c c i a  Diorite  parallel  i s sharp  when  in detail.  Plate  contacts,  one a t  breccia i t s e l f .  The p e r i p h e r a l  the o t h e r hand, grades o v e r a w i d t h of 2 t o 3 i n c h e s on one s i d e  gneissic  i s s h a r p ; the d i k e  a p o p h y s i s b e i n g younger than the b r e c c i a .  t i g h t l y packed b r e c c i a  of t h i s  y e t seen from the  s e e n f r o m t e n f e e t , b u t somewhat g r a d a t i o n a l VII depicts  occurring  of the b r e c c i a , d i s p l a y s r e l a t i o n s t y p i c a l  country rocks to the north  on  contact  o f them.  north  on  than  s u g g e s t s common o r i g i n f o r  The b e s t e x p o s u r e o f p o r p h y r i t i c d i o r i t e ,  the  diorite.  and s m a l l e r  w e l l as t h e d e g r e e o f p h e n o c r y s t d e v e l o p m e n t and t h e  all  contacts  The  or contact,  from  to d i o r i t e devoid of b r e c c i a  the o t h e r . Plate  contact,  I I I shows t h a t  described  the p o r p h y r i t i c m a t r i x  a b o v e , o c c u r s b o t h as m a t e r i a l  of t h e g r a d a t i o n a l with  few  scattered  f a c i n g page 16  Plate V I I I  x 10 b.  Myrmekite i n zoned p l a g i o c l a s e phenocryst. T y p c i a l groundmass. Note zoned c r y s t a l at arrow, ( c f . p l a t e X f a c i n g p. 17)  16.  fragmental  i n c l u s i o n s , and as s m a l l p o c k e t s  more t i g h t l y content  packed b r e c c i a .  and p h e n o c r y s t  the o u t c r o p  Furthermore,  and a r e shown i n t h e p h o t o g r a p h s .  breccia contact. occurrences  to f r e q u e n t  changes i n mafic  mineral  size w i t h i n short distances, are evident i n  the l a r g e p l a g i o c l a s e p h e n o e r y s t s  few  between fragments i n  decreases  The f r e q u e n c y  of  away f r o m t h e d i o r i t e -  I t s h o u l d be p o i n t e d o u t t h a t t h e r e a r e o n l y of d i o r i t e w i t h i n the b r e c c i a body, i n c o n t r a s t  occurrence  near the periphery.  Dark green d i o r i t i c  r o c k , found  a t the n o r t h b r e c c i a margin  i n t h e h i g h w a y s e c t i o n ( e s p e c i a l l y on t h e w e s t s i d e o f t h e r o a d ) , e x h i b i t s c o n t a c t r e l a t i o n s which grade from g r e e n i s h through  foliated  diorite,  t h i s gradation occurs  t o dark  gneissic  o v e r a few i n c h e s  country rock.  Of i n t e r e s t , h o w e v e r , i s t h e f a c t  diorite  occurs  t h a t green  i n close proximity to p o r p h y r i t i c  hornblendic  light  d i o r i t e ' , a l o n g t h e c o n t a c t w i t h t h e same g n e i s s i c granite.  Because  the c o n t a c t i s s e n s i b l y  sharp.  b. F o l i a t e d  diorite,  coloured  country  P i n k and o t h e r l i g h t  rock.  coloured  granitic  r o c k s near the south margin of t h e b r e c c i a a r e w e l l  foliated  with respect to b i o t i t e  not  Contacts are  e x p o s e d b u t by t h e i r p r o x i m i t y t o t h e b r e c c i a m a r g i n  foliates  a r e here grouped under b o r d e r  In t h i n s e c t i o n combination phyric  these  phase r o c k s .  t w i n n i n g (Ross, 1957),  grano-  t e x t u r e , and s e r r a t e d edges on q u a r t z g r a i n s w o u l d i n -  d i c a t e igneous and  and f e l d s p a r s .  o r i g i n f o r t h i s rock type.  Alteration,  zoning,  r e c r y s t a l l i z a t i o n o f p l a g i o c l a s e c a n be s e e n i n some s e c t i o n s . The  pink f o l i a t e d  granitic  r o c k s c o n s i s t o f medium  i  grained  Plate IX  f a c i n g page 17  17.  o r t h o c l a s e , q u a r t z , and s o d i c p l a g i o c l a s e m i x e d i n v a r i o u s proportions with chlorite,  e p i d o t e and p y r i t e .  A l t e r a t i o n of  t h e f e l d s p a r s i s s t r o n g , m a s k i n g t w i n n i n g and i n t e r n a l s t r u c t u r e of the c y r s t a l s . by  ( p l a t e I X a) i s produced  the s e g r e g a t i o n of f e l d s p a r s i n elongate  with similar of c h l o r i t e and  F o l i a t i o n of the fock  zones o f q u a r t z . and p y r i t e .  C r y s t a l boundaries  the c o n t a c t s o f p h e n o c r y s t s  light.  are i r r e g u l a r ,  quartz occurs  and  o r t h o c l a s e have u n d u l a t o r y  small  fragments of m a t e r i a l s i m i l a r  Orthoclase  and  sutured  Shadowy m a t e r i a l a t  w i t h the m a t r i x surround  of o p t i c a l l y disconnected  to the l a r g e r c r y s t a l s .  sub-parallel  These a r e d i v i d e d by l o n g smears  shadowy a s s e e n w i t h p o l a r i z e d  patches  zones  a l o n g some a l b i t e  replaces cloudy f e l d s p a r , cleavage  extinction.  planes.  Quartz  Other f o l i a t e d  border  phase r o c k s a r e s i m i l a r . I n t e r p r e t a t i o n of the t e x t u r e s , such suggests  an i g n e o u s  comitant  s t r e s s alignment  o r i g i n f o r the f o l i a t e d  c r y s t a l boundaries,  twinning,  granite, with  during c r y s t a l l i z a t i o n  R e c r y s t a l l i z a t i o n a t some l a t e r brecciated  as c o m b i n a t i o n  con-  of the m a t e r i a l .  t i m e , i n d i c a t e d by t h e h e a l e d may have o c c u r r e d a f t e r q u a r t z and  o r t h o c l a s e were f r a g m e n t e d a l o n g t h e i r c r y s t a l b o u n d a r i e s . alteration  of b i o t i t e  Porphyritic  occurred during  Chlorite  recrystallization.  t e x t u r e and l a c k o f f o l i a t i o n d i s t i n g u i s h  rocks near the n o r t h margin of the b r e c c i a .  Texture  of t h i s rock vary e s p e c i a l l y near the b r e c c i a c o n t a c t  dioritic  and c o m p o s i t i o n (plate I I I )  as d e s c r i b e d b e f o r e on page 14. In t h i n s e c t i o n the rock i s seen to c o n s i s t o f q u a r t z ,  oligo-  f a c i n g page 18  Andesine grain a l t e r e d from the center. Crossed n i c o l s .  (note t h a t the v e r y c e n t e r o f the c r y s t a l i s more c a l c i c than the zone s u r r o u n d i n g i t , - t h i s point i s seen i n Xb where t h e c e n t e r i s o f h i g h e r r e l i e f than the area s u r r o u n d i n g i t )  Andesine grain a l t e r e d from the center. Inclined plain polarized light.  18.  clase, with b i o t i t e , pyrite  sericite,  i n a granoblastic matrix surrounding  phenoerysts. typically  Zoning  o f t h e n o r m a l t y p e w i t h a v a r i a t i o n f r o m more two o r t h r e e c o m p o s i t i o n a l z o n e s ,  sodic a t the periphery. i n many c a s e s  matrix.  zoned p l a g i o c l a s e  of s o d i c p l a g i o c l a s e i s complex, b u t i t i s  at the c e n t e r through  is  c h l o r i t e , a p a t i t e , e p i d o t e and  t o more  The p e r i p h e r a l z o n e , u s u a l l y v e r y s o d i c ,  enlarged  t o j o i n w i t h p l a g i o c l a s e g r a i n s i n the:  I n some g r a i n s ( p l a t e X ) , h o w e v e r , c o m p o s i t i o n  from c a l c i c  (andesine)  calcic  a t the v e r y c e n t e r through  sodic  changes (oligo-  c l a s e ) a r o u n d t h e c e n t e r , t o more c a l c i c n e a r t h e p e r i p h e r y , w i t h a s o d i c r i m w i t h t h e same c o m p o s i t i o n sodic rims normally are f r e e of a l t e r a t i o n , part i s very cloudy.  Some p h e n o e r y s t s  of q u a r t z , r e s u l t i n g i n a g r a n o p h y r i c or c r y s t a l ones.  as the m a t r i x .  w h i l e the c e n t r a l  are riddled with texture.  by  In general c r y s t a l s  cases  enveloped  and j o i n e d t o g e t h e r t o f o r m  P l a t e I I c shows a g r a i n i n t h e t o p r i g h t  corner which i s a combination rim surrounds  p l a g i o c l a s e pheno-  i n the matrix are o f t e n  the o u t e r zones o f p h e n o e r y s t s  l a r g e r ones.  larger  f r a g m e n t s may h a v e o v e r g r o w t h s o f  u n t w i n n e d m a t e r i a l , e n l a r g i n g them t o e u h e d r a l erysts.  both.  blebs  Some c r y s t a l s  f r a g m e n t s i n the m a t r i x a r e j o i n e d t o , f o r m  Twinned p h e n o c r y s t  The  hand  of two s m a l l e r g r a i n s ; a r e a c t i o n  P l a t e V I I I a,b d e p i c t s two more p o s s i b l e  o f t h i s phenomenon. I n t e r p r e t a t i o n of the z o n i n g i n these  plagioclase crystals,  d e p e n d i n g on w h e t h e r i t o c c u r r e d d u r i n g o r a f t e r c o u l d be t w o - f o l d .  During  crystallization,  c r y s t a l l i z a t i o n a change i n e n v i r o n m e n t  19.  of  the m e l t w o u l d  crystals;  r e s u l t i n c o r r o s i o n and  i t i s believed  subsequent  rimming  of  t h a t t h i s manner o f z o n i n g a c c o u n t s f o r  a g r e a t p r o p o r t i o n of such t e x t u r e s i n t h e s e b o r d e r phase r o c k s . The  second  manner, t h a t o f p o s t - c r y s t a l l i z a t i o n  replacement;Of  p a r t s o f c r y s t a l s by more s o d i c p l a g i o c l a s e , i s p o s s i b l e in  a c a s e as shown i n p l a t e X a & b.  The  andesine  especially  grain i n  q u e s t i o n r e p r e s e n t s a v e r y s m a l l p r o p o r t i o n of t h e r o c k , is  e v i d e n t f r o m p l a t e I I I b when i t i s r e a l i z e d  t h a t o n l y one  c r y s t a l was  o b s e r v e d , out of f i v e  the c r y s t a l  i s c a l c i c , w h e r e a s t h e zone n e x t t o t h e c e n t e r i s  sodic having a composition s i m i l a r  sections.  this  The  to the ground  c e n t r a l p a r t of  mass.  No  ways f o r s o l u t i o n e x c h a n g e a r e e v i d e n t i n the s e c t i o n , b u t s t r u c t u r e s may  pass through o t h e r p a r t s of the c r y s t a l .  a l t e r a t i o n of t h i s of  t o be r e l a t e d  matrix.  crystals  F r a g m e n t s and  are b e l i e v e d  shadows a r o u n d  recrystallized  growth  on  fragments igneous,  phenocrysts  r e s u l t i n g i n t h e p r e s e n t t e x t u r e and  One  dark brown, h i g h l y weathered  d i k e c u t s b r e c c i a i n b o t h the r a i l r o a d seems t o f o l l o w a j o i n t  over-  and  andesite  the highway  s e t a t 050°/70°N.  Cavity  sections fillings,  r e s e m b l i n g a m y g d u l e s , o c c u r n e a r t h e n o r t h s i d e o f t h i s 4-6 wide d i k e .  I n p o l i s h e d hand s p e c i m e n  it'is  seen  t o have a  t e x t u r e of t h i n p l a g i o c l a s e l a t h s , except near c l u s t e r s of taxitic  grano-  crystals. a. D i k e s .  and  such  rimming  to i n d i c a t e a p r o c e s s whereby an  somewhat m e c h a n i c a l l y g r a n u l a t e d m a t r i x e n c l o s i n g was  to the  healed  path-  Sodic  p l a g i o c l a s e p h e n o c r y s t s a t t e n d a n t w i t h f o r m a t i o n of the  blastic of  type i s thought  such  cavities filled  with white m a t e r i a l .  Areas around  foot felty diktythese  P l a t e XI  a.. South contact a t road of b r e c c i a and g n e i s s . Note the 'pink' d i k e i n the shear zone, and the f a u l t to the r i g h t of i t . (dotted line  approximates boundary of breccia; dashed line outlines pink dike; wavy symbol indicates gouge-rich fault zone and Pasco creek)  b.. Contact near n o r t h end of road s e c t i o n o f p o r p h y r i t i c d i o r i t e over b r e c c i a . Note small d i o r i t e 'dike'.  f a c i n g page 20  20.  c a v i t i e s a r e s o l i d l y c e m e n t e d by a s e c o n d a r y I n t h i n s e c t i o n t h e r o c k i s composed orthopyroxene, c h l o r i t e , ties are f i l l e d  mineral.  of fresh  andesine,  and p y r i t e , a n d t h e d i k t y t a x i t i c  by q u a r t z , c a l c i t e ,  chlorite,  cavi-  c h a b a z i t e , and  thomsonite. A dark green, f i n e - g r a i n e d , f r e s h andesite on t h e map) c u t s The c o n t a c t ing  ( n o t shown  t h e b r e c c i a i n b o t h h i g h w a y and r a i l r o a d  i s very  a t the margin.  s h a r p and t h e d i k e i s f l i n t - l i k e Pyrite,  A d i o r i t e dike cuts tact.  dike  chlorite,  and e p i d o t e  sections.  due t o c h i l l -  occur  i n cracks.  the b r e c c i a near the n o r t h highway con-  I t i s an a p o p h y s i s o f t h e p o r p h y r i t i c d i o r i t e mass o f t h e ,  b r e c c i a border phases. Small  white  locations.  (plate X i )  d i k e s c u t the g n e i s s i c c o u n t r y  Their a t t i t u d e s are mainly  gneissosity.  One s u c h d i k e was f o u n d  rocks  s u b - p a r a l l e l to the t o be e x t r e m e l y  somewhat p o r p h y r i t i c w i t h m e d i u m - g r a i n e d c r y s t a l s f e l d s p a r , and a m a t r i x  c  a r e rimmed by s l i g h t l y  is  and s e r i c i t e  C l o t s of c h l o r i t e  possibly limonite.  Fractures  groundmass.  c l e a n e r m a t e r i a l which a l s o  groundmass. '; U n d u l a t o r y  from the w a l l r o c k s .  grained ,  o f p l a g i o c l a s e ( a b o u t A n . ) and q u a r t z  e n v e l o p s g r a i n s of the c l o u d y common.  fine  o f q u a r t z and  crystals with l o n g i t u d i n a l o r i e n t a t i o n set i n a p l i t i c The p h e n o c r y s t s  i n several  are f i l l e d  extinction  c o u l d have b e e n  derived  w i t h s e r i c i t e and  '  Summary o f C h a r a c t e r i s t i c s o f t h i s B r e c c i a - The f o l l o w i n g . p o i n t s c h a r a c t e r i z e t h e b r e c c i a and must be e x p l a i n e d by a t h e o r y mode o f f o r m a t i o n  of the b r e c c i a a t Pasco  creek.  o f the  21.  1. diorite 2. and  of the b r e c c i a  i n t r u s i v e into country  dipping  Subparallelism  Existence  quantities 5.  6.  nearly  square  o u t l i n e on two s i d e s  plan  matter.  Uniform s i z e ,  tabular  with  rock.  of fragments of c o u n t r y rock w i t h  s h a p e , and e l o n g a t i o n  only  small  p a r a l l e l to  of the fragments.  Relative  r o t a t i o n o f l a r g e and s m a l l  spect to country 7.  rock.  of the b r e c c i a  of f o r e i g n  schistosity,  o f a mass o f  sides. .  g n e i s s o s i t y of the country 4.  to the contact  G e n e r a l shape o f t h e b r e c c i a body w i t h  steeply 3.  the  Proximity  fragments w i t h r e -  rocks.  Horizontal  a l i g n m e n t o f t a b u l a r f r a g m e n t s i n some  small  areas. 8.  Loose p a c k i n g of the b r e c c i a fragments near the contact  of the b r e c c i a w i t h  porphyritic diorite,  i n contrast  t o the t i g h t l y -  packed fragments w i t h i n the b r e c c i a . 9.  Presence of scant r e c r y s t a l l i z e d  packed p o r t i o n  matrix  o f t h e b r e c c i a , and p l e n t i f u l  near the l o o s e l y - p a c k e d  w i t h i n the t i g h t l y -  porphyritic  matrix  b o r d e r of the b r e c c i a .  10.  Matrix  c o n s i s t i n g of f i n e l i t h i c  11.  Small white pegmatitic  12.  G r a n i t i c pebbles i n the b r e c c i a .  13.  B e n d i n g and d e f o r m a t i o n o f f r a g m e n t s .  14.  O c c u r r e n c e o f p o r p h y r i t i c d i o r i t e as a s k i n between c o u n t r y  r o c k and b r e c c i a ^ contact.  fragments.  areas w i t h i n  partly engulfing  loose  the b r e c c i a .  fragments a t the b r e c c i a  22.  15.  Small bodies of. f o l i a t e d  granitic  rock at the p e r i p h e r y  of the b r e c c i a . .16. 17.  i .  Presence  of d i o r i t e w i t h i n  the b r e c c i a .  Signs of metamorphism i n both fragments and matrix.  •• .  •  •  23.  IV.  EXISTING THEORIES OF BRECCIA FORMATION  Much h a s been w r i t t e n a b o u t b r e c c i a erature  and a c c o u n t s i n t h e  lit-  h a v e , up t o a few y e a r s a g o , O f t e n b e e n b a s e d on b r e c c i a -  ore  body r e l a t i o n s h i p s .  However, a l t h o u g h i n d i v i d u a l d e s c r i p t i o n s  are  c l e a r , t h e mode o f f o r m a t i o n ,  and t h e r e l a t i o n s p a r t i c u l a r t o  the mapped l o c a l i t y u n d e r s t o o d , t h e . g e n e r a l o f c o r r e l a t i n g and c l a s s i f y i n g b r e c c i a  a s p e c t of the problem  types of widely  different  c h a r a c t e r i s t i c s and o c c u r r e n c e s h a s o n l y b e e n d e a l t w i t h i n the  l a s t few  years.  An a t t e m p t a t " C l a s s i f i c a t i o n by F i s h e r  of V o l c a n i c  Breccias"  ( i 9 6 0 ) , w h e r e i n he g r o u p s v o l c a n i c b r e c c i a s i n t o  major c a t e g o r i e s  b a a e d ...on t h e p r o c e s s o f f r a g m e n t a t i o n .  uses the term v o l c a n i c b r e c c i a to a l l c o a r s e - g r a i n e d ( i 9 6 0 , p.  "...  r o c k s composed  as a g e n e r a l  term  three also  applying fragments."  973) classification,  p o i n t i n g o u t s i x i n a d e q u a c i e s and i n c o n s i s t e n c i e s , and "...neither  discussion and  He  of a n g u l a r v o l c a n i c  W r i g h t and Bowes ( 1 9 6 3 ) c o u n t e r t h e p r o p o s e d  it  was made  consistent  n o r w o r k a b l e and s u b m i t t h e f o l l o w i n g  of n o n - p y r o c l a s t i c  classification. They f i n d  classification  consider  volcanic breccias,  t h e i r nomenclature,  ( 1 9 6 3 , p. 7 9 ) .  that four  criteria  of v o l c a n i c  l o c a t i o n , and r o c k - t y p e .  have commonly been u s e d i n the  b r e c c i a s , namely, cause, These c r i t e r i a  environment,  s h o u l d be u s e d i n com-  bination. A c c o r d i n g t o them, o f t h e s e f o u r c r i t e r i a , can  only  be s t a t e d  definitely  cause of f r a g m e n t a t i o n  i n t h e c a s e where t h e r e - h a g b e e n  little  24.  t r a n s p o r t o f b r e c c i a t e d m a t e r i a l ; when a mass o f b r e c c i a t e d  material  has b e e n c a r r i e d  the  initial  somewhere e l s e , i t i s d i f f i c u l t  b r e c c i a t i o n , and  type of"environment has b e e n u s e d  thus c l a s s i f i c a t i o n a c c o r d i n g to the  i s more s i g n i f i c a n t .  L o c a t i o n of the  o n l y i n c e r t a i n i n s t a n c e s , i t s use  A c l a s s i f i c a t i o n based  to e x p l a i n  breccia  c o u l d be  avoided.  on r o c k t y p e i s l e a s t open t o c o n t r o -  v e r s y f o r i t s g e n e r a l n a t u r e , s i n c e t h e same t y p e o f r o c k c a n brecciated Bryner  i n many d i f f e r e n t (l96l) divides  ways.  .mineralized rock fragment  two m a i n g r o u p s , p r e - h y d r o t h e r m a l structures; geology. would  s t r u c t u r e s and  columns  "From t h e s t a n d p o i n t o f o r i g i n ,  cohydrothermal  the b r o a d e s t  classification  d i s t i n - g u i s h b r e c c i a s on t h e b a s i s o f the main t r a n s p o r t are.either  o r (b) c o l l a p s e , and  c o u l d be  ( a ) and  the f o l l o w i n g e x p l a n a t i o n s .  (b).  He  has  (c) o s c i l l a t o r y ,  . Intruded fragments,^writes Bryner  (l96l),  a combination  "generally  the magma o r a r e m o b i l i z e d by magmatic h e a t . " C o l l a p s e c a n be e f f e c t e d by numerous means.  intrusive activity, reduce  cause  are that  arise  (p. 505).  S l a c k e n i n g of  o f the r o o f r o c k s by l o w e r i n g t h e  M e l t i n g o f r o c k by g a s e s  c o m p r e s s e d by  a d v a n c i n g magma c o l u m n o r s t r e t c h i n g o f t h e c r u s t c a u s e d i n g may  of  t h r o u g h w i t h d r a w a l o f magma f o r e x a m p l e ,  the' s t a b i l i t y  p r e s s u r e from below.  of  (a) i n t r u s i v e " ,  i m p e l l e d by magma, o r ...el se by g a s e o u s o r a q u e o u s f l u i d s  would  into  t h i s s t a n d p o i n t i s . b a s e d on. m i n e r a l o g y and. e c o n o m i c  f r a g m e n t s . ..Such movement o f f r a g m e n t s  from  be  collapse.  F u r t h e r causes  c a n be  an  by dom-  s o l u t i o n of  s t o n e o r gypsum by w a t e r , s h r i n k a g e b e c a u s e o f c o r r o s i o n by  limegase-  25.  ous  or hydrothermal  fluids,  o r s h r i n k a g e due t o c o o l i n g  of intruded  rock, or c r y s t a l l i z a t i o n . Crackle llapse,,  b r e c c i a s would, be- the . r e s u l t o f e i t h e r  or o s c i l l a t i o n ,  Johnston the p r o b l e m fractured like  i f any o f t h e s e methods were  and L o w e l l  (l96l),  of the o r i g i n  rock,, c o n c l u d e d  having  and c l a s s i f i c a t i o n that  (6)  (4) f l u i d  explosion  intrusion;  (5) solution  s t o p i n g ; and ( 7 )  mineralization  geological  o f them..."  ( p . 931 )•» and  and  processes.  There  above,  (3)  igneous  replacement;  shrinkage.  (1954) has i n t r o d u c e d f l u i d i z a t i o n  mentioned  theories or  ( l ) explosion; (2) tectonic;  the f o l l o w i n g :  Reynolds of  of these bodies of  "The o r i g i n o f most 'of t h e p i p e -  by m o d i f i c a t i o n a n d / o r c o m b i n a t i o n  intrusion;  incipient.  s t u d i e d t h e l i t e r a t u r e on  d e p o s i t s has been e x p l a i n e d by t h e f o l l o w i n g  they l i s t  intrusion, col-  are s i m i l a r i t i e s  (8) f l u i d i z a t i o n ,  into  the l i s t  between ( l )  and (4) f l u i d  intru-  sion. (1) e x p l o s i o n due to b l o w - o u t s o f gas a s s o c i a t e d w i t h activity  produce  stratification. volcanic (2) section are  breccia  These h o l e s a r e s u b s e q u e n t l y  i n many c a s e s filled  with  bodies  of r o c k may form  of f a u l t s  zones,  o r a t bends i n f a u l t s ,  and s h e a r  across  broken  rock.  elongate brecciated  a t the i n t e r -these  breccias.  physical  force  of i n t r u s i o n  results  i n f o r m a t i o n of  columns or d i k e s .  (4) f l u i d conduit  which a r e openings  m a t e r i a l or country  tectonic (3)  diatremes  volcanic  intrusion  of fragments  broken  somewhere below b y magmatic gases  o f f the s i d e s of t h e  would  cause  them t o be  26.  "...forced  upward i n t o r o c k s  above by a r e l a t i v e l y  t h i c k mud."  ( F a r m i n , 1 9 3 4 , p. 3 7 0 ) . (5) c o r r o s i o n o f s h a t t e r e d  rock  by a s c e n d i n g s o l u t i o n s  .._ts,tes. . r o u n d i n g o f f r a g m e n t s and i n c r e a s e sequently  may be r e f i l l e d  o f open s p a c e , w h i c h s u b -  t h r o u g h :the p r e c i p i t a t i o n o f m i n e r a l s .  (6) L o c k e ' s ( 1 9 2 6 ) m i n e r a l i z a t i o n s t o p i n g to the b l o c k - c a v i n g along  theory  o f ore: and gangue m i n e r a l s  mass." ( p . 43l)» was. t h e  i n certain- stocks : increase  i s responsible  (8) f l u i d i z a t i o n  thus i n the  an e s t i m a t e d  to Hulin  a t t e n d a n t open s p a c e s w o u l d  10 p e r c e n t  (1948). VAn result.  i s a term t h a t o r i g i n a t e d - i n i n d u s t r y f o r  a p r o c e s s by w h i c h g r a i n - s i z e d p a r t i c l e s c o u l d  be s e t i n t o  turbu-  l e n t m o t i o n b y gas s t r e a m i n g t h r o u g h a bed of them c a u s i n g to f l o a t the  i n and w i t h  left  f o r much f r a c t u r i n g and b r e c c i a t i o n  and c h o n o l i t h s , a c c o r d i n g  i n volume w i t h  stage  process.  (7) c o n t r a c t i o n on c r y s t a l l i z a t i o n ^ w i t h volume s h r i n k a g e  an e a r l y  c o l l a p s e and b r e c c i a t i o n o f t h e r o c k  u n s u p p o r t e d , and d e p o s i t i o n brecciated  i ssimilar  method o f m i n i n g , -whereby " . . . r e m o v a l o f r o c k  t r u c k c h a n n e l s by r i s i n g s o l u t i o n s d u r i n g  of t h e i r a c t i v i t y ,  facili-  the gas, thus p e r m i t t i n g  movement o f t h e g a s .  As a g e o l o g i c  them  t h e i r t r a n s p o r t by  process i t i sv i s u a l i z e d  as a c t i v a t i n g and m o v i n g b r e c c i a f r a g m e n t s , and may w e l l f u r n i s h the  churning  dikes.  and c o r r o s i v e a c t i o n i n d i c a t e d by f o r example  To i n i t i a t e  the p r o c e s s ,  pass t h r o u g h . p r e - f r a c t u r e d  rock  upward s t r e a m i n g g a s e o u s until  ;and-, gas: a c h i e v e a s t a t e o f f l u i d i t y , then mobile. turbulent  flow  Reynolds  the mixture of rock  fluids fragments  the a c t i v a t e d fragments are  (1954) s t a t e s t h a t  structure with  pebble  "...The a s s o c i a t i o n o f  a b r a d e d and w e l l - r o u n d e d r o c k  frag-  27.  ments w h i c h have n o t a p p a r e n t l y - b e e n source  rocks, together  t r a n s p o r t e d away f r o m  with l a c k of grading  of the fragments  c o n c e r n e d , and t h e p o s s i b l e p r e s e n c e o f d r u s e s . . . " criteria  their  ( p . 579) a r e  f o r gas t r a n s p o r t .  F l u i d i z a t i o n of a b r e c c i a undoubtedly could a l s o produce selective  transportation, according  to fragment s i z e ,  allowing  l a r g e r f r a g m e n t s t o d e s c e n d and s m a l l e r ones t o r i s e w i t h i n t h e stream, r e l a t i v e Bryner  to the other  fragments.  ( l 9 6 l ) asserts that the lack of fused  i s normally  matrix,  found i n i n t r u s i o n b r e c c i a s , i n pebble d i k e s  which "...in-  d i c a t e s a n a q u e o u s o r g a s e o u s medium o f t r a n s p o r t a t i o n f o r t h e pebbles, and  and t h e rounding-.of  p o s s i b l y chemical In connection  pressure being  show t h a t  c o r r o s i o n took p l a c e . "  with gases, Williams  attrition  (p. 499).  (193&) e x p l a i n s  f r o m a n a d v a n c i n g magma c o l u m n , e x p l o s i v e  that  volcanism  t h e d r i v i n g f o r c e , may f o r m d i a t r e m e s i n t h e f o l l o w i n g  manner, "... R i s i n g g a s e s  'lubricate'  magma b r e c c i a t e s t h e c o v e r ; cap. r o c k s and,  the.pebbles  repeated  the roof rocks; p u l s a t i n g explosions  comminute t h e  so t h a t f r o t h i n g magma i s i n t i m a t e l y m i n g l e d w i t h  them  n e a r s u r f a c e , steam e r u p t i o n s caused by h e a t i n g o f ground  water f a c i l i t a t e the c o n d u i t Despite  the d r i l l i n g process  w a l l s enlarges the frequent  while slumping of slabs  the conduit."  reference  (p. 316).  i n the l i t e r a t u r e  o r i g i n and e x p l o s i v e a c t i v i t y , M c K i h s t r y  an u n c r i t i c a l  to volcanic  ( 1 9 5 5 ) f i n d s t h a t "...  the r o l e o f v o l c a n i c e x p l o s i o n i n c r e a t i n g o r e b e a r i n g much l e s s i m p o r t a n t - t h a n  from  reading  pipes  seems  of the l i t e r a t u r e  28.  might  suggest., (p. 214).  Sedimentary the sake t a l u s and  .r  b r e c c i a s must be added t o t h i s d i s c u s s i o n f o r  of completeness.  T h i s r o c k type can.be d e r i v e d from  o t h e r s u b - a r e a l o r sub-aqueous c l a s t i c  T h e s e , on b e i n g c o v e r e d by more m a t e r i a l , and the sedimentary  s e c t i o n , which  i n turn w i l l  accumulations.  incorporated i n  e v e n t u a l l y be  meta-  m o r p h o s e d , d i f f e r , g r e a t l y f r o m b r e c c i a s . d e r i v e d i n t h e ways mentioned  a b o v e . ' I f t h e m e t a m o r p h i s m were s t a t i c  d i s l o c a t i o n , such a t a l u s b r e c c i a would fragments The  havingjtheir original  its- history.  to., t h e d a t a s u m m a r i z e d on t h e g e o l o g y o f  - Steeply dipping gneiss, possibly derived  s t r o n g l y f o l d e d , m e t a m o r p h o s e d , and sediments  the g e o l o g i c a l granitic the cause  reports, i n order  any i n t e r p r e t a t i o n o f b r e c c i a f o r m a t i o n .  P r e - B r e c c i a Geology  t u f f s and  ( A r m s t r o n g , 1954)  s e t t i n g of the a r e a .  granitized  i s thought  interbedded  to have  comprised  Emplacement of the v a r i o u s  Coast i n t r u s i o n s of the Coast Mountains o f f o l d i n g and m e t a m o r p h i s m o b s e r v e d  matic a c t i v i t y  this  n e c e s s a r y t o have an u n d e r s t a n d i n g o f t h e g e n e r a l  p r e - b r e c c i a g e o l o g y , a s - d e r i v e d -from g e o l o g i c a l to understand  depending  INTERPRETATION OF BRECCIA FORMATION  In a d d i t i o n breccia, i t . i s  the  a n g u l a r s h a p e s and a s s o r t e d s i z e s .  m a t r i x " w o u l d t e n d t o be h o r n f e l s i c a n d p l e n t i f u l ,  V.  than  remain undeformed,  on t h e n a t u r e o f t h e s e d i m e n t a r y b r e c c i a and  from  rather  a t t e n d a n t w i t h t h e emplacement o f  may  have b e e n  i n the r o c k s .  Mag-  diorite-granodiorite  29.  of the Coast I n t r u s i v e s and  i s thought to have supplied  magma that were a c t i v e i n b r e c c i a  O r i g i n of Pasco G n e i s s - B r e c c i a b r e c c i a summarized p r e v i o u s l y  heat, gases,  formation.  Pipe - The c h a r a c t e r i s t i c s of the should be e x p l i c a b l e by a theory  of b r e c c i a emplacement.- R e a l i z i n g t h i s , one may f i r s t l y  propose  the mechanism of emplacement and then a s c e r t a i n how each of the c h a r a c t e r i s t i c s may be r e l a t e d to the theory. The  emplacement of\the  taken place  during  b r e c c i a must be envisaged as having  the lat_p.r.-S_tages of one of the; p e r i o d s of  a c t i v i t y of the Coast i n t r u s i o n s . due  The s c h i s t s , s t e e p l y  to previous f o l d i n g , have already  dipping  been metamorphosed to  gneiss-migmatites and jointed.. With these b a s i c assumptions in. mind one must then imagine the a c t i o n of gases r i s i n g from a heat source at depth ahead of'' advancing magma.  Explosive  a c t i o n and p u l s a t i n g pressures due  to the p l u t o n i c a c t i v i t y s h a t t e r s along pronounced g n e i s s o s i t y  parts  of the roof rock e s p e c i a l l y  and j o i n t i n g .  Intersections  of major  f r a c t u r e s provide channel ways f o r the advancing gas ahead of the magma.  This  s h a t t e r i n g o f the country rock, followed by  i n - s t r e a m i n g of the gas i n t o the f r a c t u r e s u l t i m a t e l y i n a s t a t e of f l u i d i z a t i o n . l a r g e and s m a l l ,  During f l u i d i z a t i o n the fragments,  g r a i n s i z e d to block s i z e d , are envisaged as  being i n a s t a t e of suspension i n the a g i t a t e d ments and gas.  results  mixture of f r a g -  I f t h i s process continues, abrasion  by sand b l a s t -  i n g of the l a r g e r fragments occurs; i n t h i s case the s c h i s t o s i t y and  the c l o s e j o i n t i n g allow the fragments to break along those  30.  lines  of weakness, t y p i c a l l y  the case no  o f homophanous r o c k s s u c h as m i g m a t i t e  structure left,  and  r e s u l t i n g i n r e c t a n g u l a r shapes.  fragments that o r i g i n a l l y  i n which there i s  shattered along  f r a c t u r e s i n l a r g e r p i e c e s would abrade a l o n g g r a i n  joints  boundaries  i n s m a l l e r ones, r e s u l t i n g e v e n t u a l l y i n rounded shapes.  The  abraded p a r t i c l e s , mostly  the  most p a r t f l u s h e d out by i n g to theory.  g r a i n s i z e d and  s m a l l e r , are to  the gases i n t o apophyses or d i k e s , a c c o r d -  S i z e - s o r t i n g by r e l a t i v e  s i n k i n g d e p e n d i n g on  b u o y a n c y o f t h e f r a g m e n t s c o u l d be e n v i s a g e d . sank f a r e n o u g h , t h e y w o u l d p r e s u m a b l y be thus  g r a d u a l l y changing If  on  In  I f the heavy  the  pieces  i n c o r p o r a t e d i n the  melt,  i t s composition.  t h e o t h e r h a n d , f l u i d i z a t i o n had  f o r a b r a s i o n to produce f i n e p a r t i c l e s , f r a g m e n t s o f t h e s i z e p r o d u c e d by  one  not o c c u r r e d  l o n g enough  must i m a g i n e  s h a t t e r i n g w o u l d be  that  i n dominant  numbers. Extreme p r e s s u r e s d u r i n g or a f t e r  the o c c u r r e n c e  of  fluidization  w o u l d c o m p r e s s t h e m i x t u r e , r e s u l t i n g on c o o l i n g i n a v e r y  compact  r o c k i n w h i c h t h e f r a g m e n t s w o u l d i m p i n g e u p o n one  another  on a l l  sides.  zone, fragments  On  the  o u t s i d e of t h i s s h a t t e r e d - f l u i d i z e d  w o u l d i m p i n g e upon t h e w a l l dimensional  rocks.  p a c k i n g i s thought  The  gas  along f r a c t u r e s v e r t i c a l l y  t i g h t l y packed t h r e e - d i m e n s i o n a l t h e r o o f and so  rock.  r e l a x a t i o n o f the p r e s s u r e , p o s s i b l y due  most o f t h e  'mosaic' t h r e e -  o f as b e i n g much more c o m p e t e n t  t h a n t h e p h y s i c a l c o n t a c t w i t h the w a l l On  interior  and  to the escape laterally,  of  this  mosaic, not b e i n g f o r c e d a g a i n s t  t h e S i d e s of the r o o f w o u l d slump downward somewhat  t h a t a zone o f low p r e s s u r e , i f not  e v e n a gap  would occur  be-  31.  tween w a l l  and r o o f r o c k s .  Should  magma be p r e s e n t b e l o w , i t  w o u l d be f o r c e d upward a r o u n d t h i s p l u g , and c r y s t a l l i z e i  s k i n around i t . pressure  As t h e r e c o n c e i v a b l y was a f i e l d  i n t h i s magma s u r r o u n d i n g  l i z a t i o n would a l i g n should the  as a  -  i n a l l cases  themselves  of s t a t i c  t h e p l u g , t h e g r a i n s on c r y s t a l -  according to the stress.  be i n s i m i l a r r e l a t i o n  This  to the o u t l i n e of  plug. Concerning  n a t u r a l processes  past, i t i s conceivable of f i e l d  w h i c h have o c c u r r e d d u r i n g  that there w i l l  times  be s e v e r a l i n t e r p r e t a t i o n s  d a t a , d e p e n d i n g t o a g r e a t e x t e n t on t h e e x p e r i e n c e o f  the observer.  The p r i m a r y  o b j e c t i v e o f a t h e o r y o f a mode o f  f o r m a t i o n h o w e v e r , i s n o t t o be c o r r e c t t o t h e e x c l u s i o n o f a l l other proposed  t h e o r i e s i but t o i n c l u d e and s a t i s f a c t o r i l y e x p l a i n  the g e o l o g i c a l c h a r a c t e r i s t i c s  Of t h e f o r m a t i o n i n q u e s t i o n .  A p p l i c a t i o n of Data to Theory - I t i s i n defence proffered here, thesis, will  that the a v a i l a b l e data l i s t e d  earlier  be e x p l a i n e d a s r e s u l t i n g f r o m p r o c e s s e s  d u r i n g the formation of the b r e c c i a . possible  of the theory  to relate f i e l d  data  i n this active  I n t h i s manner i t w i l l be  t o t h e p r o p o s e d manner o f f o r m a t i o n ,  thus p r o v i d i n g a t e s t of the theory. The p r o x i m i t y o f t h e b r e c c i a t o a g r a n i t i c i n t o country rock leads to the b e l i e f was t h e s o u r c e  Gases and h e a t  f r o m t h e i n t r u d i n g body a r e f a c t o r s i m p o r t a n t  directly  connected  the c o u n t r y  intrusive  that the g r a n i t i c  of the b r e c c i a t i n g f o r c e .  The shape o f b o t h  body,  i n this  intrusion derived  theory.  t h e b r e c c i a p l u g and t h e f r a g m e n t s c a n be  t o t h e g n e i s s o s i t y and f a u l t  r o c k as f o l l o w s .  Contacts  structuresi n  i n t h e exposed p l a c e s to  t h e n o r t h and s o u t h a r e p a r a l l e l a very gouge-rich  shear  t o g n e i s s o s i t y , and t o t h e e a s t  zone f o r m s t h e c o n t a c t .  Here i t i s n o t  known w h e t h e r t h e f a u l t f o l l o w e d a l o n g t h e i n i t i a l l y t a c t of the b r e c c i a or whether the f a u l t v i d e d a l a y e r impermeable f o r gases, by e x p l o s i v e f o r c e s o f them.  i s p r e - b r e c c i a and p r o -  thus not p e r m i t t i n g b r e c c i a t i o  Geneissosity greatly  f r a c t u r i n g of the rock a l o n g t h i s  •.weak con-^  facilitated  structure.  The e x i s t e n c e o f c o u n t r y r o c k f r a g m e n t s  to the e x c l u s i o n of  n o t i c e a b l e q u a n t i t i e s of other rock types i s noteworthy. tends  to c o n f i r m the p o s s i b i l i t y  at depth, of  of a s c a r c i t y of other rock  as w e l l a s t h e i m p r o b a b i l i t y  material.  the b r e c c i a body i s b e l i e v e d t o r e f l e c t  attrition it  types  of s i g n i f i c a n t t r a n s p o r t  The c l o s e p a c k i n g and l a c k o f m a t r i x n e a r of  This  caused  i s thought  part  the s m a l l e f f e c t of  by t h e c h u r n i n g a c t i o n o f f l u i d i z a t i o n .  Thus,  t h a t fluidization„did n o t o c c u r l o n g enough t o  produce the f i n e r , p a r t i c l e s but merely Subsequent p r e s s u r e from  a good d e a l o f m i x i n g .  above and b e l o w and l a c k o f t h e a d v a n c i n g  gas, c a u s i n g a decrease, of f l u i d i z a t i o n , packed  the c e n t r a l  would r e s u l t i n a  t h r e e - d i m e n s i o n a l mosaic of fragments,  with very  tightly  little  matrix. Loose p a c k i n g a t the p e r i p h e r y i s a p r o d u c t of d i o r i t e  l a t e r i n the sequence.  At t h i s  of insurgence  time l o o s e  fragments  a t t h e p e r i p h e r y o f t h e t i g h t b r e c c i a body were e n g u l f e d by t h e diorite,  thus producing  gradational  the d i f f e r e n t  t y p e o f b r e c c i a , and t h e  contact.  D i o r i t e d i k e s w i t h i n t h e b r e c c i a a r e s i m p l y e x p l a i n e d by r e -  33.  calling As  t h a t d i o r i t e was  i t was  under pressure  H o r i z o n t a l alignment of i n t e r n a l  factors.  s t r e s s e s s e t up The  The  p u s h e d a r o u n d the b r e c c i a p l u g as a i t filled and  plastic  cracks.  f l o w are  deformation  i n f r a g m e n t s due  three dimensional  any  t h o u g h t t o be  of f r a g m e n t s i s due  to  f r a m e w o r k i s n o t m e r e l y c a u s e d by a shape b u t by f o r c i b l e  w h i c h i s d e m o n s t r a t e d by  fragments.  granitic  the bent  'pebbles'  results  t o i m p i n g e m e n t a g a i n s t one  o f f r a g m e n t s a c c o r d i n g t o s i z e and  The  skin.  have a r o u s e d  curiosity  another. fitting  packing  at t h i s  locality  b e c a u s e they^whow g r e a t c o l o u r c o n t r a s t w i t h t h e d r a b b a c k g r o u n d of the o u t c r o p .  The  fragments are u s u a l l y elongate  i n shape, n e a r l y c y l i n d r i c a l . general  orientation  Parallel  and  to t h e i r l o n g a x i s i s the  of m a f i c s , hence t h e s c h i s t o s i t y .  parts e a s i l y i n this d i r e c t i o n ,  and  elliptical  The  rock  because t h i s alignment  is  a c t u a l l y a l i n e a t i o n the f r a g m e n t s a c q u i r e rounded c r o s s s e c t i o n s . Yet  the shapes i n a r o c k f a c e l o o k rounded l i k e  t h o u g h t t o be lower  d i s l o d g e d p i e c e s from border  pebbles.  They  are  phase d i o r i t e  along  the  p e r i p h e r i e s of t h e b r e c c i a b o d y , p r e s u m a b l y c a r r i e d up  below, although  t h e r e i s no  i n d i c a t i o n of  port.  The  white  pegmatitic areas  probably  quartz  and  f e l d s p a r d u r i n g the l a s t  stages  the d i r e c t i o n  from  of t r a n s -  are space f i l l i n g s of c o m p a c t i o n of  by  the  breccia. V a r i a t i o n of fragment s i z e i s l i m i t e d . o f one  s i z e , although  s m a l l most p l e n t i f u l close p a r t i t i o n b r o k e n up  Of  Most f r a g m e n t s  are  t h e r e a r e some t h a t a r e b l o c k s i z e d .  The  s i z e d e r i v e d i t s d o m i n a n c e through, t h e  very  the r o c k  through  shattering.  as a c o n s e q u e n c e o f j o i n t i n g and  Thin s l i v e r s  the i n s t a b i l i t y  of  were  <>  34.  thin slivers  i n an a g i t a t e d  environment.  r o c k was b r o k e n up t o s u c h s m a l l s i z e . shredded  into small s l i v e r s  t h i s c h u r n i n g environment now  found It  T h u s , i t i s s e e n how t h e I n a l l p r o b a b i l i t y i t was  t o o b u t t h e y were t o o f r a g i l e f o r  and were r e d u c e d  to g r a i n s i z e d  b e t w e e n t h e l a r g e r f r a g m e n t s , and l a r g e l y  h a s t h u s been i n d i c a t e d  that the proposed  particle  recrystallized  method o f b r e c c i a  f o r m a t i o n i s i n agreement w i t h the f a c t s o b s e r v e d ; t h a t i t thus is  a t h e o r y o f emplacement o f t h i s The  aforementioned  also a l i s t  list  breccia.  o f modes o f f o r m a t i o n o f b r e c c i a s i s  of types of b r e c c i a occurrences.  then t h a t i n normal  c a s e s one w o u l d  find,  I t i s understandable  r a t h e r than a t y p i c a l  r o c k f o r m a t i o n , one t h a t i n c o r p o r a t e s s e v e r a l m e t h o d s - - a m i x t u r e of  processes.  T h i s i s the case i n t h i s  Theories, mentioned.before, ty  situation.  t h a t c a n be e x c l u d e d w i t h  certain  a r e s e d i m e n t a r y b r e c c i a t i o n and b r e c c i a t i o n due t o s h r i n k a g e ,  w h e r e a s t h e o t h e r t h e o r i e s may a p p l y t o some e x t e n t , as f o l l o w s . Gases s t r e a m i n g upward ahead o f an i n t r u d i n g magma mass cause  e x p l o s i v e a c t i o n ; f l u i d i z a t i o n would  would  o c c u r as e x p l a i n e d  b e f o r e ; t e c t o n i c b r e e c c i a t i o n may have been t h e c a u s e  for better  c o n d u i t s f o r t h e r i s i n g ' m a t e r i a l s ; i g n e o u s i n t r u s i o n may f o r c i b l y fracture  zones  o f r o c k above t h e p a r t i a l l y  c o n g e a l e d magma;  fluid  i n t r u s i o n , a p r o c e s s s i m i l a r i n many ways t o t h e e x p l o s i o n t h e o r y , would  consist  fragments  o f gases  or liquids  of conduit rock which  r i s i n g f r o m d e p t h s b r i n g i n g up  t h e n a r e f o r c e d upward i n t o t h e  r o c k s by a t h i c k mud, t h i s i s p o s s i b l y how g r a n i t i c were i n t r o d u c e d ; s o l u t i o n and r e p l a c e m e n t  'pebbles'  may have o c c u r r e d on a  s m a l l s c a l e ; m i n e r a l i z a t i o n s t o p i n g as such i s n o t i n d i c a t e d ,  ' 3 5,  although with  s i g n s of b l o c k c a v i n g have been n o t e d  the b l o c k s o f c o u n t r y  breccia  i n connection  rock p a r t i a l l y r o t a t e d w i t h i n  the  mass.  CONCLUSION  The  P a s c o b r e c c i a has b e e n s t u d i e d and  i n d i c a t e a combination mation  of the b r e c c i a .  of s e v e r a l p r o c e s s e s  the d a t a found a c t i v e i n the  Among t h e s e e x p l o s i v e a c t i o n o f  ahead o f an i n t r u s i v e b o d y , t o g e t h e r w i t h f l u i d i z a t i o n mixture of  o f t h e s e g a s e s and  prime importance  s h a t t e r e d rock are thought  i n the f o r m a t i o n of the  breccia..  to for-  gases of a  to  be  EXTENDED BIBLIOGRAPHY A r m s t r o n g , J.E. , 1954  B r y n e r , L., 1961  B u t l e r , B.S., 1913  P r e l i m i n a r y Map, V a n c o u v e r N o r t h , B.C. G e o l o g i c a l S u r v e y o f Canada, Paper 53-28. B r e c c i a and p e b b l e c o l u m n s a s s o c i a t e d with epigenetic ore deposits: Econ.. G e o l o g y , v . 5 6 , p. 4 8 8 - 5 0 8 . G e o l o g y and o r e d e p o s i t s Francisco r e g i o n , Utah: Survey P r o f . Paper 80  o f t h e San U.S. G e o l .  i  Emmons,  W.H.,  1938  F a i r b a i r n , W.H. a n d R o b s o n , G.M.,  D i a t r e m e s and c e r t a i n o r e - b e a r i n g A.I.M.E. T e c h , P u b l . 8 9 1 , M i n i n g T e c h n o l o g y , volume 2, no. 3. B r e c c i a a t Sudbury, O n t a r i o : G e o l . , v o l . 5 0 , p. 1 - 3 3 .  pipes:  Jour.  1942  Farmin,  Rollin,  1934  F i s h e r , R.V., I960  G a t e s , 0., 1959  G o o d s p e e d , G.E.  " P e b b l e d i k e s " and a s s o c i a t e d m i n e r a l i z a t i o n a t T i n t i c , Utah: Econ. Geol., v. 2 9 , pp. 3 5 6 . C l a s s i f i c a t i o n of v o l c a n i c b r e c c i a s : B u l l . G.S.A., v . 7 1 , p. 9 7 3 - 9 8 1 . B r e c c i a p i p e s i n t h e Shoshone Range, N e v a d a , E c o n . G e o l . , v . 54* p. 7 9 0 - 8 1 5 . Rheomorphic b r e c c i a s : 251,  Grout, F.F., 1937  PP.  453-464.  Am, J . S c . , v . '  C r i t e r i a of o r i g i n of I n c l u s i o n s i n P l u t o n i c r o c k s , B u l l . G.S.A., v . 4.8, pp. 1 5 2 1 .  H o w e l l , P.H. and Molloy, J.S., I960  Geology of t h e Braden Orebody, C h i l e , S. Am.: E c o n . G e o l . , V. 5 5 , pp.. 863-905.  H u l i n , C.D., 1948  F a c t o r s i n the l o c a l i z a t i o n of m i n e r a l ized d i s t r i c t s : A.I.M.E. T r a n s . , v . 178 pp. 36.  J o h n s t o n , ¥.P., L o w e l l , J.D. , 1961  G e o l o g y and O r i g i n o f M i n e r a l i z e d B r e c c i a P i p e s i n Copper B a s i n , A r i z o n a : Econ. G e o l . , v. 56, pp. 916-940.  Kuhn,  T.H., 1941  P i p e d e p o s i t s o f the Copper Creek a r e a , Ariz.: E c o n . G e o l . , v . 3 6 , pp. 512-538,  Locke, Augustus, 1928  The f o r m a t i o n o f c e r t a i n o r e b o d i e s by m i n e r a l i z a t i o n s t o p i n g : Econ. Geology, v . 2 1 , pp. 4 3 1 .  Lovering, 1942  P h y s i c a l f a c t o r s , i n the l o c a l i z a t i o n of ore: Ore d e p o s i t s as r e l a t e d t o s t r u c t u r a l features: Princeton University press,  T.S.,  PP.  McKinstry, 1955  5-9.  H.E.,  S t r u c t u r e of the h y d r o t h e r m a l o r e d e p o s i t s F i f t i e t h A n n i v . V o l u m e , P t . 1, E c o n o m i c P u b l i s h i n g Company, pp. 207-214.  Reynolds, D o r i s , 1954  F l u i d i z a t i o n a s a g e o l o g i c a l p r o c e s s and i t s b e a r i n g on t h e p r o b l e m o f I n t r u s i v e Granites: Am. J o u r n a l o f S c i e n c e , v . 2 5 1 , no. 1, pp. 577-613.  R i c h a r d , K., and C o u r t w r i g h t , J.H., 1958  Geology of Toquepala, Peru: Mining E n g i n e e r i n g J o u r n a l , F e b r u a r y 1 9 5 8 , pp. 262-266.  R o d d i c k , J.A., 1965  V a n c o u v e r N o r t h , C o q u i t l a m , and P i t t L a k e Map A r e a s , B r i t . C o l u m b i a : Men, 335» G e o l o g i c a l S u r v e y o f C a n a d a .  R o s s , J.V., 1957  Combination twinning i n P l a g i o c l a s e Feldspars: Am. J . S c . , V. 2 5 5 , pp. 650-655.  W a l k e r , R.T., 1928  Mineralized volcanic explosion pipes: Eng. and M i n i n g J o u r . , v. 126, pp. 895.  W a t e r s , A.C. and K r a u s k o p f , K. 1941.  P r o t o c l a s t i c border of the C o l v i l l e Batholith: B u l l , G.S.A.,:' v . 5 2 , np. 1355-1418.  Williams, 1936  P l i o c e n e volcanoes of the Navajo-Hopi Country: B u l l . G.S.A:, v . 4 7 , pp. 111-172.  Howel,  W r i g h t , A.E. and Bowes, D.R., 1963  C l a s s i f i c a t i o n of v o l c a n i c b r e c c i a s : a discussion: B u l l . G.S.A., v . 7 4 , pp. 79-86.  Legend  :  mlgmotltlo hornbltnd* gn«l»«, hornbl»ndl1« g amphibollt*  E3  gntltt brcoel a ft border  phata*  dike  gn«lt toil t y inferred  breccia  contact  bedding  HIGHWAY  SECTION  RAILROAD  SECTION  Legend 0  20  40  mam  SHEAR  BRECCIA  of BORDER  Scale'  Pasco  Creek,  DISTRIBUTION Horseshoe  MAP  Bay  y  B.C.  .  OF  BRECCIA  BODY  Pasco Creek, Horseshoe Bay, RC1  DIORITE  PHASES  tt  P L A G  P O R P H Y R T  EE''"133  /"--250 apf  ao no 'So Qg.A.*.Rol«ri  OUTCROP  amzmt  AMPMiBOL I TE  H O R N B L E N C E  o  80ft  ZONE  GNEISS G NEISS,  60  §M  '6P  Fig.3  DIAGRAMMATIC  Pasco C r e e k ,  CROSS-SECTIONS  Horseshoe  Bay,  B.C  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0053013/manifest

Comment

Related Items