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Geology of Mount Washington, Vancouver Island British Columbia Carson, David John Temple 1960

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GEOLOGY OF MOUNT WASHINGTON VANCOUVER ISLAND, BRITISH COLUMBIA by DAVID JOHN TEMPLE CARSON B.Se., Queen s- University, 1  1958  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of GEOLOGY We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , I960  In the  presenting  requirements  f o r an  of  B r i t i s h Columbia,  it  freely  agree that for  available  o r by  copying  gain  s h a l l not  of  in partial  advanced  degree a t  or  for reference  and  study.  I  f o r extensive be  copying  g r a n t e d , by  publication  of t h i s  a l l o w e d w i t h o u t my  _  ^VMCM^  2  University s h a l l make  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 . Date  the  of  Library  his representatives.  be  fulfilment  the  p u r p o s e s may  that  Department  thesis  I agree that  permission  scholarly  Department  this  }  Columbia,  \U0  of  the  It i s  thesis  this  Head o f  thesis my  understood  for  written  further  financial  permission.  (i) ABSTRACT Mount Washington rises abruptly to the west of the Coastal plain of Vancouver Island near Courtenay, B r i t i s h Columbia.  It is € -shaped possessing two cirques which face  northeast. The basement rocks of the Mount Washington area consist of several thousand feet of massive basic to intermediate volcanics of the Triassic Vancouver group.  A layer composed  of gently dipping Upper Cretaceous shales, sandstones, and minor conglomerate and coal overlies the Triassic rocks on the Coastal plain, and outliers of this layer are present on the higher areas west of the p l a i n .  D i o r i t i c intrusions cut  the Triassic and Upper Cretaceous rocks. The higher portions of Mount Washington are composed mainly of Upper Cretaceous rocks.  These, and the Triassic  rocks underlying them have been domed by the intrusion of a centrally located quartz diorite stock.  Numerous offshoots  of this stock are present in the Upper Cretaceous rocks surrounding i t .  At i t s west border there are two breccia  pipes. Copper-bearing quartz veins are present on the west side of the mountain in the v i c i n i t y of the stock.  These were  formed at high temperatures in a near-surface environment. The distribution of the breccias and s i l l - l i k e intrusions at Mount Washington suggests that the development of the stock was highly restricted as i t moved upward through the Triassic volcanics and that on reaching the Upper Cretaceous sediments  (ii)  it  encountered  laterally  much less:; r e s i s t a n c e so t h a t i t  to f o r m d y k e s ,  s i l l s , and  spread  laccoliths(?).  The p r e s e n t i n v e s t i g a t i o n p r o v i d e s , the o n l y geological Hill  mapping done i n the Mount  a r e a , and i t s  contributions  Washington-Constitution  are as  follows:  ( 1 ) a d d i t i o n s to the knowledge o f the and s t r u c t u r e (2)  o f the  rocks  i n the  these  stratigraphy  area;  i n f o r m a t i o n on the p r o b a b l e  o f the d i o r i t i c i n t r u s i o n s ,  detailed  methods  of  and the r e l a t i o n s h i p s  emplacement among  intrusions; (3) the e x i s t e n c e ,  e x t e n t , and n a t u r e  o f the  breccias;  (4) a d d i t i o n s to the knowledge o f the c h a r a c t e r the m i n e r a l d e p o s i t s , mineral  wehrlite.  i n c l u d i n g the o c c u r r e n c e of  the  of  (iii) ACKNOWLEDGEMENTS  The w r i t e r i s indebted to M.M. Menzies of Noranda Mines; Limited and G. Murray, president of Mt. Washington Copper Company, f o r making a v a i l a b l e a l l maps and reports on Mt. Washington.  H. Veerman, Noranda g e o l o g i s t f o r Mt. Washing-  ton was e s p e c i a l l y h e l p f u l i n gathering information and o f f e r i n g suggestions  on the geology of Mt. Washington.  Discussions with A.F. Buckham of Canadian C o l l i e r i e s Limited and N.D. McKechnie of the B.C. Department of Mines were very h e l p f u l i n c l e a r i n g up c e r t a i n aspects of the geology. The w r i t e r also wishes to thank Dr. W.H. Mathews of the U n i v e r s i t y of B r i t i s h Columbia, under whose supervision the thesis? was w r i t t e n , f o r the valuable advice and a i d given during the organizing of the t h e s i s .  A d d i t i o n a l advice on  c e r t a i n aspects of the geology was obtained from Dr. White, Dr. McTaggart, and Dr. Ross. Dr. Warren aided the w r i t e r i n i n t e r p r e t i n g the r e s u l t s of the stream sediment analyses which were made by h i s assistants.  Dr. Thompson i d e n t i f i e d the mineral wehrlite i n  the v e i n m a t e r i a l , and Dr. Rouse, paleobotanist, worked on some samples of f o s s i l i f e r o u s sediment. Mrs-. L. Egan who typed the t h e s i s , and Miss P. McFeely who drafted the maps, were of great assistance during the f i n a l preparation of the t h e s i s .  (iv)  TABLE OF  CONTENTS  Chapter  Page  I  INTRODUCTION A. G e n e r a l Statement B. L o c a t i o n and A c c e s s C. H i s t o r y and P r e v i o u s Work 1. Mineral Exploration 2. G e o l o g i c a l Mapping D. Scope o f the I n v e s t i g a t i o n  II  PHYSIOGRAPHY, CLIMATE, VEGETATION A. Regional P h y s i c a l Features: B. Local P h y s i c a l Features C. L o c a l C l i m a t e and V e g e t a t i o n  7 7 9 11  III  REGIONAL GEOLOGY A. G e n e r a l Statement B. P e r m i a n - T r i a s s i c V o l c a n i c and Sedimentary Rocks C. Late J u r a s s i c - E a r l y Cretaceous I n t r u s i v e s D. Upper C r e t a c e o u s Sedimentary Rocks 1. G e n e r a l E x t e n t and G e n e r a l Description 2. Comox B a s i n at Cumberland 3« Types of S t r u c t u r e s E. L a t e C r e t a c e o u s or T e r t i a r y I n t r u s i o n s F. P l e i s t o c e n e and Recent D e p o s i t s  14 14  IV  LOCAL GEOLOGY A. G e n e r a l Statement B. T r i a s s i c V o l c a n i c Rocks 1. E x t e n t and G e n e r a l D e s c r i p t i o n 2. Microscopic Description C. Upper C r e t a c e o u s Sedimentary Rocks1. G e n e r a l E x t e n t and G e n e r a l Description 2. D e s c r i p t i o n of Rock Types 3. D e s c r i p t i o n of Some O c c u r r e n c e s 4» C o r r e l a t i o n w i t h the Comox Formation D. L a t e C r e t a c e o u s or T e r t i a r y I n t r u s i o n s 1. Rock Types and G e n e r a l E x t e n t 2. Equigranular Variety 3. Porphyritic Varieties 4. D e s c r i p t i o n of Some O c c u r r e n c e s 5. Age and C o r r e l a t i o n Among the I n t r u s i v e B o d i e s w i t h i n the A r e a E. B r e c c i a s and F r a c t u r e d and B r e c c i a t e d Rocks: 1. G e n e r a l Statement  1 1 1 3 3 5 6  16 18 19 19 19 21 24 24 26 26 26 26 29 30 30 31 35 38 38 38 40 42 46 51 52 52  (v) TABLE OF CONTENTS (CONTINUED) Chapter  Page 2. 3. 4.  F. G. H.  Murray Breccia Washington Breccia Fractured and Brecciated Rocks Along the West Contact of the Stock Metamorphism and Alteration 1. General Statement 2. Metamorphism 3. Alteration Major Structures 1. General Statement 2. Folds 3. Faults or Fractures Mineral Deposits 1. General Extent and General Description 2. West arm-Central arm Deposits 3. Deposits of Murex Creek and Vicinity and of Ice Creek  54 66 71 72 72 73 75 80 80 81 81 86 86 87 97  V  STRUCTURAL DEVELOPMENT OF MT. WASHINGTON  99  VI  ORIGIN OF THE PORPHYRY BODY AT CONSTITUTION HILL  102  VII  ORIGIN OF THE BRECCIAS AND FRACTURED AND BRECCIATED ROCKS A. Current Theories on the Origin of Breccia Pipes B. Development of the Murray Breccia C. Development of the Washington Breccia D. Development and Significance of the Fractured and Brecciated Rocks  105 105 106 109  SEQUENCE OF GEOLOGICAL EVENTS  112  VIII  BIBLIOGRAPHY  .  110 114  (vi) LIST OF Plates  ILLUSTRATIONS  (photographs or p h o t o m i c r o g r a p h s )  Page  I  Mt. Washington  II  View west  from Mt. Washington  8  III  View e a s t from Mt. Washington  8  IV  E a s t arm o f Mt. Washington  13  V  Summit of Mt. Washington  13  VI  T r i a s s i e pillow lavas  28  VII  Upper Cretaceous; sediments o v e r l a i n by p o r p h y r y s i l l at C o n s t i t u t i o n H i l l  28  VIII  P h o t o m i c r o g r a p h o f carbonaceous s i l t s t o n e  41  IX  Photomicrograph of e q u i g r a n u l a r quartz d i o r i t e  41  X  Photomicrograph o f q u a r t z d i o r i t e p o r p h y r y  44  XI  Photomicrograph of s u b - c a t a c l a s t i c d i o r i t e porphyry  44  XII  Breccia  XIII  Rubbly Murray b r e c c i a  55  XIV  Dioritic  57  XV  P e b b l y Murray b r e c c i a i n c o n t a c t w i t h a r g i l l i t e  57  XVI  S h r i n k a g e (?) j o i n t s i n the Murray b r e c c i a  61  XVII  S h r i n k a g e ( ? ) j o i n t s i n the q u a r t z d i o r i t e porphyry of C o n s t i t u t i o n H i l l  61  Photomicrograph of b r e c c i a from G l a c i e r c r e e k (plain light)  63  Photomicrograph o f b r e c c i a from G l a c i e r c r e e k (crossed n i c o l s )  63  XX  Photomicrograph o f Murray b r e c c i a  65  XXI  Photomicrograph o f Murray b r e c c i a nicols)  XXII  P i p e - l i k e o u t c r o p o f Washington  XVIII XIX  ridge  and C o n s t i t u t i o n H i l l  at Ice c r e e k  taken from C e n t r a l  quartz  arm  Murray b r e c c i a  (plain light) (crossed  breccia  (ix)  55  65 67  (vii)  LIST OF ILLUSTRATIONS (continued) Plates:. XXIII  B o u l d e r o f Washington  XXIV  Photomicrograph light)  XXV  Photomicrograph o f s i l i c i f i e d b r e c c i a ( c r o s s e d nicols-)  XXVI  Photomicrograph o f b i o t i t i z e d Murray (plain light)  XXVII  Photomicrograph (plain light)  o f c h l o r i t i z e d Murray  XXVIII  Photomicrograph quartz vein  of brecciated  XXIX  Photomicrograph sandstone  of disseminated sulphides i n  XXX  Photomicrograph sphalerite  of exsolution  Photomicrograph  of wehrlite-hessite  XXXI  breccia  o f Washington  67 breccia  (plain 70  Washington(?)  70  breccia 79 breccia 79  sulphide-bearing  92 92  chalcopyrite i n 95 veinlet  95  Page  Figures; 1.  L o c a t i o n and G e n e r a l Geology o f the B u t t l e Lake-Mt. Washington A r e a  2.  Topography H i l l Area  3.  S t r a t i g r a p h i c Column o f the Upper C r e t a c e o u s Rocks o f the Comox B a s i n a t Cumberland  22  4.  Hypothetical Fault Nanaimo S e r i e s  22  o f the Mt. W a s h i n g t o n - C o n s t i t u t i o n  i n the Lower Part  o f the  10A  15  Table of Formations 'CoJcurut 8 Map S3 ( i n po«fee±-) 1.  Geology o f Mount Washington  ( l " = 1000')  2.  Geology o f the West arm o f Mt. Washington '•(!" = 400')  (viii)  Cross  Sections  (in  •&&@leert)  1.  Cross  section  2.  Cross s e c t i o n from H i l l ( 1 " = 2640')  Cabinet  t  o f Mt. W a s h i n g t o n  (1" =  Mt. W a s h i n g t o n  to  1000') Constitution  (ix)  P l a t e I - Mt. Washington ( r e a r c e n t e r ) and C o n s t i t u t i o n H i l l ( r e a r " r i g h t ) as seen f r o m the C a m p b e l l R i v e r r o a d on the C o a s t a l p l a i n a few m i l e s west of C o u r t e n a y . Photo t a k e n i n e a r l y w i n t e r , l o o k i n g northwest.  I  A.  INTRODUCTION  G e n e r a l Statement D u r i n g the summers o f 1957 and 1958, Ndranda  L i m i t e d and Mt. Washington Copper Company diamond  Mines drilled  some c o p p e r - g o l d d e p o s i t s a t Mt. Washington n e a r C o u r t e n a y on the e a s t s i d e o f Vancouver I s l a n d .  These two companies  j o i n t l y h o l d t h e m i n e r a l r i g h t s f o r an a r e a which i n c l u d e s ; Mt. Washington and extends f i v e m i l e s e a s t o f i t t o Constitution H i l l .  T h e i r work was a f o l l o w - u p o f e x p l o r a t i o n  c a r r i e d out p r e v i o u s l y by o t h e r m i n i n g companies, and i t s r e s u l t s were e n c o u r a g i n g . Due t o the rugged t e r r a i n , no g e o l o g i c a l mapping o f large  s e c t i o n s o f the mountain was done, though maps o f  s e v e r a l copper showings were p r o d u c e d .  As a r e s u l t ,  was known o f the g e n e r a l g e o l o g y o f the mountain.  little  The f i e l d  work which l e d t o the w r i t i n g o f t h i s t h e s i s was d e s i g n e d t o r e c t i f y the d e f i c i e n c y i n g e o l o g i c a l mapping  o f the a r e a .  The t h e s i s i s concerned m a i n l y w i t h the mountain, and e s p e c i a l l y w i t h the r e g i o n o f former<igneous a c t i v i t y and c o p p e r - g o l d m i n e r a l i z a t i o n on the west s i d e o f the mountain.  B.  L o c a t i o n and A c c e s s (see f i g . l  and fig.2)  Mt. Washington i s 15 m i l e s northwest o f Courtenay on Vancouver I s l a n d , B r i t i s h Columbia.  Most o f the a r e a immed-  i a t e l y e a s t o f Mt. Washington and below  2500  feet  i n elev-  a t i o n , i s t r a v e r s e d by a network o f l o g g i n g r o a d s b u i l t by the  Comox L o g g i n g and R a i l w a y Company.  O r i g i n a t i n g at  b r a n c h e s o f t h i s network a r e two a c c e s s j e e p r o a d s which were  built  by Noranda Mines and Mt. Washington Copper Company,  first  road  terminates  gives access feet  a t the lower end o f the Murex b a s i n and  t o copper d e p o s i t s at an e l e v a t i o n o f about 2500  i n Murex c r e e k .  of 4000 f e e t  The  The second road p e n e t r a t e s  t o an e l e v a t i o n  on the West arm where i t g i v e s a c c e s s  t o an ex-  tensive area of copper-gold m i n e r a l i z a t i o n .  C.  H i s t o r y and P r e v i o u s Work  1.  Mineral Exploration Panning f o r g o l d on the Oyster  r i v e r , which d r a i n s an a r e a  i n c l u d i n g the western s l o p e s o f Mt. Washington, was a common occupation  d u r i n g the d e p r e s s i o n .  Some i n d i v i d u a l s panned  four  d o l l a r s worth o f g o l d p e r day. In 194D the Mackay b r o t h e r s= d i s c o v e r e d and s t a k e d  several  g o l d v e i n s on the C e n t r a l and West arms o f Mt. Washington. 1941 K . J . S p r i n g e r d i d e x p l o r a t o r y work on a g o l d - q u a r t z called  In  vein  the N o . l v e i n (maps 1 and 2 ) .  In 1944 and 1945, C o n s o l i d a t e d M i n i n g  and S m e l t i n g  Company  d i d f u r t h e r e x p l o r a t o r y work which i n v o l v e d t r e n c h i n g and d r i v i n g of short tunnels i n t o No.l v e i n . During  the summer o f 1951>  t h i r t e e n X - r a y diamond  drill  Noranda Mines L i m i t e d  drilled  h o l e s i n an a r e a on the West arm  n o r t h o f N o . l v e i n and the r e s u l t s were c o n s i d e r e d  to be d i s -  couraging. Mt. Washington Copper Company, which was formed to f u r t h e r e x p l o r e and d e v e l o p e the d e p o s i t s o f Mt. Washington, b u i l t the a c c e s s road carried was  to the West arm i n 1956.  Some t r e n c h i n g was a l s o  out i n the lower Murex b a s i n where copper m i n e r a l i z a t i o n  discovered.  In 1957,  Noranda Mines j o i n e d Mt.  Washington Copper  Company i n the e x p l o r a t i o n o f the d e p o s i t s of the Murex basin.  A jeep road was  built  to the Murex showings and  program which i n c l u d e d diamond d r i l l i n g , mapping, a s e l f p o t e n t i a l was  carried The  survey,  and  drilling  One  trenching, geological  a soil  sampling  survey,  out. r e v e a l e d a zone of low  copper p o s s i b l y s e v e r a l hundred f e e t wide.  a  grade  l o n g , and  (about  0.5%  over 100  feet  s e l f p o t e n t i a l anomaly upstream from the f i r s t  indicated.  Soil  sampling  showed one  In 1958  work was  of No.l v e i n .  concentrated  was  sulphides.  on the West arm  T h i r t e e n diamond d r i l l  A l s o , much o f the West arm  covered  to the  by an  electromagnetic  and  anomalous areas were s t r i p p e d by b u l l d o z e r .  result  of t h i s work, a n e a r - s u r f a c e f l a t - l y i n g v e i n , or a  l y i n g zone c o n t a i n i n g s e v e r a l v e i n s , was ness v a r i e d from seven to f i f t e e n f e e t  Mt.  I t outcropped  Company.  i t s ; grade  Its thickaveraged  e x p l o r a t i o n work was  splits  negligible  X-ray d r i l l i n g c a r r i e d  feet.  a r e a of the  Railway  should  i n 1959. out  E&N  Railway  Canadian P a c i f i c  r e a c h agreement on p r o f i t  of C o n s t i t u t i o n H i l l  flat  by 600  owned by the Canadian P a c i f i c  e l e c t r o m a g n e t i c work and  As; a  at the s u r f a c e i n s e v e r a l  Because Noranda Mines and  mine be found,  lower  and  Washington l i e s w i t h i n the l a n d grant  Company c o u l d not  An  indicated.  o c c u r r e d over a known a r e a of about 250  r a i l r o a d which i s now  north  h o l e s were completed.  survey  about 2% Copper.  was  a r e a o f h i g h readings:, but  subsequent s t r i p p i n g r e v e a l e d o n l y s p a r s e  p l a c e s and  Cu)  a Some  j u s t west  revealed only s l i g h t m i n e r a l i z a t i o n .  e x t e n s i v e program o f e x p l o r a t i o n on the West arm  east s l o p e s o f the mountain i s planned  and  f o r the summer o f  5. 1960. 2.  Geological Mapping Very l i t t l e geological mapping has been done i n the imm-  ediate area of Mt. Washington.  A report by Gunning (1930) on  the Buttle Lake area which includes Mt. Washington,  contains;  reference to the Vancouver group rocks near Wolfe Lake (p.61A). It also includes a brief description of the Upper Cretaceous outliers (p.63A) on the Forbidden Plateau, Mt. Washington.  one of which i s at  The origin and nature of the Upper Cretaceous  coal-bearing rocks at Cumberland, which i s twenty miles east of Mt. Washington, have been described by MacKenzie (1922). These rocks are similar to the sediments on the upper parts of Mt. Washington. Included i n reports by Clapp> (1917-Sooke-Duncan area), Buckham (1947-Nanaimo coal f i e l d ) , and Fyles (1955-Cowichan Lake area) are further descriptions of Upper Cretaceous and Triassic rocks which are similar to those found at Mt. Washington. A map at the scale of 1" = 200' was made of part of the West arm by Consolidated Mining and Smelting Company i n 1945. Several detailed maps of the West arm and Murex creek showings were made by Noranda Mines geologists i n 1957 and 1958. However, no reasonably complete mapping of any sizable area of the mountain was done. In 1957 l i t t l e was known of the geology of the mountain, but, because of i t s crescent shape and radial fault pattern (map 1), H . Veerman of Noranda Mines proposed that i t repre-  6. sented the ruins of an ancient volcano. D.  Scope of the Present Investigation The writer spent a total of about 35 days (mostly on  weekends;) in the f a l l s of 1958 and 1959 gathering geological information on the Mt. Washington area. was mapped at 1" = 400'  (map 2).  Part of the West arm  Several traverses were made  to the Central and East arms and the information obtained was combined with aerial photograph interpretation to yield a map of the entire mountain at 1" = 1000'  (map 1).  In the f i e l d  outcrops were plotted directly on contour maps or recorded in a note book.  Several claim survey pegs on the West arm were  used for locating outcrops in that area.  An altimeter with a  maximum error of about 100 feet was used to help locate outcrops on the 1" = 1000' map-. Traverses: were made to points of interest in the Mt. Washington-Constitution H i l l area.  Sufficient information was  gathered for a generalized cross section from Mt. Washington to Constitution H i l l (cross section 2). Sediment samples from several streams and rivers of the area were taken for chemical analyses. Map plotting and microscopic study of rocks collected were done at the University of British Columbia during the winter of 1959-60. 1  Veerman, H . , 1957, "Report on the Mount Washington Property Courtenay, Vancouver Island B.C. (unpublished property report of Noranda Mines Limited)  7.  II  A.  Regional  PHYSIOGRAPHY, CLIMATE, VEGETATION  P h y s i c a l Features  (see f i g . l  and p l a t e s I , I I ,  & III) Along  the e a s t c o a s t o f Vancouver I s l a n d t h e r e i s a  narrow p l a i n 5 t o 25 m i l e s i n w i d t h . i s about 250 f e e t  I t s average e l e v a t i o n  above s e a l e v e l and i n p l a c e s i t r i s e s :  a b r u p t l y from the s e a .  Most o f the p l a i n has been logged o f f  so t h a t o n l y a few p a t c h e s o f f o r e s t r e m a i n .  I t i s on t h i s  c o a s t a l p l a i n t h a t the towns and farms o f Vancouver I s l a n d are s i t u a t e d . Numerous e l o n g a t e d feet long are present  r i d g e s up t o 100 f e e t h i g h and 1000  on the p l a i n .  These r i d g e s t r e n d  north-  west and a r e composed o f g l a c i a l m a t e r i a l o r o f Upper C r e t aceous s e d i m e n t a r y r o c k s .  I n t e r v e n i n g a r e a s are  3enferally  swampy. Small east  streams r u n n i n g northwest o r s o u t h e a s t  to Georgia  and t u r n i n g  S t r a i t ) or j o i n i n g small steep-walled  which have t h e i r headwaters i n the h i l l s  rivers  t o t h e west, d r a i n  the c o a s t a l p l a i n . To  the west o f the c o a s t a l p l a i n the l a n d r i s e s  a b r u p t l y t o an i r r e g u l a r - s u r f a c e d p l a t e a u a v e r a g i n g 3500 t o 5000 f e e t  i n elevation.  fairly about  Most o f the p l a t e a u i s under-  l a i n by f a i r l y massive b a s i c v o l c a n i c r o c k s o f T r i a s s i c age. Small  l a k e s d r a i n e d by s t e e p w a l l e d  area.  streams a r e common i n t h i s  S c a t t e r e d mountains r i s i n g t o maximum h e i g h t s o f about  7000 f e e t a r e p r e s e n t  on t h e p l a t e a u .  F u r t h e r i n l a n d i n the v i c i n i t y o f B u t t l e Lake, the country  isstill  more rugged than i t i s on t h e p l a t e a u .  8.  Plate  II  Plate  III  - V i e w s o u t h w e s t f r o m Mt. W a s h i n g t o n s h o w i n g Mt. A l b e r t Edward ( b a c k g r o u n d ) and e r o s i o n a l outlier of Upper C r e t a c e o u s s e d i m e n t s ( l e f t c e n t e r ) . Photo taken i n e a r l y w i n t e r .  - View Hill  e a s t f r o m Mt. W a s h i n g t o n and G e o r g i a S t r a i t .  towards  Constitution  Mountains o f over 6000 f e e t are f a i r l y vening ice  v a l l e y s are  steep-walled.  common and  S m a l l l a k e s and  the  inter-  permanent  or snow f i e l d s on n o r t h - f a c i n g s l o p e s , are a l s o  fairly  common*  B.  Local P h y s i c a l Features In the Mt.  m i l e s wide and  (see f i g . 2 and  map  1)  Washington a r e a the c o a s t a l p l a i n i s o n l y ends at C o n s t i t u t i o n H i l l .  This h i l l  of  four  quartz  d i o r i t e p o r p h y r y r i s e s a b r u p t l y from the p l a i n to more than 1900  f e e t above sea l e v e l .  southeast  d i r e c t i o n and  are  cliffs  steep  It i s elongated  along  i t s north  and  which i s 625  level.  To  and west s i d e s  s e v e r a l hundred f e e t h i g h .  length of C o n s t i t u t i o n H i l l f e e t above s e a  i n a northwest-  Parallel  there to  the  on i t s west s i d e i s Wolfe Lake  the west o f Wolfe Lake the  s u r f a c e , most o f which i s  composed of T r i a s s i c v o l c a n i c , r o c k s , r i s e s to 2500 f e e t above sea l e v e l w i t h i n two are  and  one-half  s e v e r a l hundred f e e t h i g h and  Several  miles. trend  Numerous r i d g e s here northwest-southeast.  streams d r a i n i n g to the n o r t h e a s t  from h i g h e r  areas  t r a v e r s e t h i s a r e a and most of these such as Murex and (creeks, have f a i r l y through the r i d g e s .  steep-walled  v a l l e y s where they cut  T h i s a r e a of r i d g e s i s t r a v e r s e d  numerous l o g g i n g r o a d s and  MacKay  much o f i t i s c o m p l e t e l y  by  logged  off. From 2500 f e e t above s e a l e v e l , Mt. q u i t e s t e e p l y to the west. i n n e r s l o p e s and  It i s crescent-shaped with  more g r a d u a l  t h i r d s o f the mountain t h e r e  Washington r i s e s  outer  slopes.  On  steep  the upper  are n e a r l y f l a t - l y i n g Upper  two  10.  Cretaceous of  s e d i m e n t s , whereas the lower p o r t i o n s are composed  Triassic volcanics.  distinct (i)  physiographic  East  arm  ments and It  Washington can be  units:  a sill  The  and  i s about 1^ m i l e s l o n g by f  n o r t h edge o f the arm  up to 700  which have t a l u s s l o p e s at t h e i r lower ends.  cliffs. (ii)  i s composed o f f a i r l y s t e e p  To  the n o r t h e a s t  West arm  the arm  shape than  sea the  feet  The  high,  south  side  s l o p e s but has no  large  drops o f f q u i t e s t e e p l y .  - a r i d g e whose summit i s at above the 4800  f o o t l e v e l and which t r e n d s r o u g h l y NNW. in  mile  d r o p s o f f s h a r p l y to  Murex b a s i n i n a s e r i e s o f s t e e p c l i f f s  the arm  sedi-  which o v e r l i e T r i a s s i c v o l c a n i c s ( p l a t e V ) .  I t s h i g h e s t p o i n t i s more than 4900 f e e t above  level.  of  divided into six  - a r i d g e composed of n e a r l y f l a t - l y i n g  t r e n d s r o u g h l y ENE  wide.  Mt.  the E a s t arm,  and  It i s less regular  i s composed o f Upper C r e t -  aceous sediments o v e r l y i n g T r i a s s i c v o l c a n i c s , both o f which are c u t by d i o r i t i c •f m i l e w i d e .  The  s t e p - c l i f f s with steep  I t i s about l£ m i l e s l o n g  e a s t edge o f the West arm  To  to the E a s t arm.  m i l e l o n g and  intrusionsIt  (iv)  and and  extends NNE  i s 4800 f e e t  runs  roughly  I t i s composed of Upper  sediments o v e r l y i n g T r i a s s i c v o l c a n i c s and minor  separates  few  the n o r t h  - a rounded r i d g e whose c r e s t  above s e a l e v e l and which i s f  and  by  d r o p s o f f much more g e n t l y .  C e n t r a l arm  parallel  contains a  s m a l l t a l u s s l o p e s at t h e i r lower ends,  s l o p e s l e a d i n g down to MacKay L a k e .  west t h i s arm (iii)  intrusions.  Cretaceous  dioritic  from the summit o f Mt.  Washington,  the Murex b a s i n from the MacKay b a s i n .  MacKay b a s i n - a n e a r l y f l a t - b o t t o m e d , U-shaped  valley  o >  11  which i s opened t o the n o r t h .  I t i s between  the C e n t r a l arm  and the West arm and i s about 1000 f e e t deep. which s l o p e s g e n t l y to the NNE,  a r e at l e a s t  On i t s f l o o r , two f l a t  which s l o p e v e r y g e n t l y towards the summit o f Mt. One  o f these  flat  a r e a s c o n t a i n s MacKay L a k e .  b a s i n i s d r a i n e d to the NE by the s m a l l but c r e e k , MacKay (v)  arm. but  Washington.  The MacKay  steep-walled  creek.  Murex b a s i n - a U-shaped  northeast  areas  v a l l e y which i s open to the  and i s s i t u a t e d between  I t i s over  1500 f e e t deep.  the C e n t r a l arm and E a s t Its floor  s l o p e s t o the e a s t  l o c a l f l a t - s u r f a c e d a r e a s which s l o p e g e n t l y t o the west  are p r e s e n t . cut  Murex b a s i n i s d r a i n e d by Murex c r e e k which has  a s m a l l but s t e e p - w a l l e d ,  (vi)  V-shaped v a l l e y i n i t s f l o o r .  Summit - a rounded knob about 1000 f e e t  which i s composed o f Upper C r e t a c e o u s rocks  (plate V I I ) .  i t s maximum h e i g h t  i n diameter  sediments and  dioritic  I t s n o r t h and e a s t edges a r e c l i f f s and i s 5215  feet.  *  R a d i a t i n g from i t are the  t h r e e arms o f Mt. Washington, and the E a s t arm and the West arm are s e p a r a t e d  from i t by the E a s t  saddle r e s p e c t i v e l y . approximately  and the West  Both s a d d l e s d i p to e l e v a t i o n s o f  4600 f e e t .  A s u b - r a d i a l drainage d r a i n s the o u t e r to  saddle  system c o n s i s t i n g o f s m a l l streams  s l o p e s o f Mt. Washington.  To the s o u t h  the west o f the mountain t h e r e are v a l l e y s whose average  e l e v a t i o n s are about 3200 f e e t above s e a l e v e l .  C.  and  L o c a l Climate During  and  Vegetation  the summer s e a s o n , b r i g h t sunny days and  dull  12  r a i n y days u s u a l l y o c c u r i n about e q u a l numbers. the days are c o o l and average  the m a j o r i t y o f them are r a i n y .  e l e v a t i o n by November 15 but  The  snow accumulates  On  vary  the upper p o r t i o n s o f  to depths o f over twenty f e e t  t h a t v e g e t a t i o n i s s t u n t e d and from  feet i n  some y e a r s i t s coming may  t h i s date by s e v e r a l weeks.  the h i l l  melt  fall  y e a r l y p r e c i p i t a t i o n i s about f o r t y i n c h e s .  Snow sometimes c o v e r s the a r e a s above 1500  from  In the  contorted.  the upper p a r t s o f the h i l l  The  until  so  snow does not  the middle  of  June. Except  f o r the a r e a s below 3000 f e e t which have been  l o g g e d o f f , the lower p a r t s o f Mt. Washington are h e a v i l y timbered.  Above 4000 f e e t  the t r e e s are s m a l l e r and  the  c o u n t r y has a s u b - a l p i n e a s p e c t w i t h open s t r e t c h e s c o n t a i n i n g heather  and  s m a l l ponds.  Cypress, balsam, Douglas f i r ,  western  hemlock are the main t r e e s p e c i e s on Mt.  red cedar, Washington.  and  13.  Plate  IV  Plate  V -  - E a s t arm o f Mt. W a s h i n g t o n t a k e n f r o m t h e C e n t r a l arm s h o w i n g f l e x e d and f r a c t u r e d s e d i m e n t s o v e r l a i n by a q u a r t z d i o r i t e s i l l ( a b o v e t h e dotted l i n e on t h e r i g h t ) . Photo taken i n e a r l y w i n t e r after snowfall, looking southeast.  Summit o f Mt. W a s h i n g t o n i n b a c k g r o u n d . Breccia ridge along r i g h t side. Photo taken i n e a r l y w i n t e r a f t e r s n o w f a l l , l o o k i n g south from northeast side of B r e c c i a r i d g e .  14  III  A.  General The  REGIONAL GEOLOGY  Statement  c o n s o l i d a t e d and u n c o n s o l i d a t e d d e p o s i t s o f the  g e n e r a l a r e a i n c l u d i n g B u t t l e Lake, Campbell R i v e r , and Courtenay,  f a l l n a t u r a l l y i n t o f i v e major groups.  o l o g y and c h a r a c t e r i s t i c  The l i t h -  s t r u c t u r e s o f the f i v e groups a r e  d e s c r i b e d i n the f o l l o w i n g pages and the e x t e n t o f t h e i r c r i p t i o n b e a r s d i r e c t l y on t h e i r importance  des-  f o r comparison  w i t h the r o c k s o f the Mt. Washington a r e a . P e r m i a n - T r i a s s i c v o l c a n i c and sedimentary first  group and a r e the o l d e s t r o c k s o f the a r e a .  i n t r u d e d by the second of  They a r e  group o f r o c k s , the Coast I n t r u s i o n s  L a t e J u r a s s i c and E a r l y C r e t a c e o u s  first  r o c k s form the  age.  The r o c k s o f the  two groups a r e o v e r l a i n unconformably by c o a l - b e a r i n g  rocks of Late Cretaceous w i t h i n some d e t a i l  age.  These l a t t e r r o c k s a r e d e a l t  i n t h i s chapter i n order to f a c i l i t a t e  t h e i r comparison l a t e r  i n the t h e s i s w i t h the c a p p i n g o f  sediments on Mt. Washington. The  b e s t exposures  Cretaceous  o f the f o u r t h group o f r o c k s , L a t e  o r T e r t i a r y i n t r u s i o n s , are i n the t h e s i s  area.  These r o c k s a r e o n l y b r i e f l y mentioned i n t h i s c h a p t e r but a r e f u l l y d e s c r i b e d i n the c h a p t e r e n t i t l e d  " L o c a l Geology."  B r i e f mention i s made o f P l e i s t o c e n e and Recent d e p o s i t s , the f i f t h group d e a l t w i t h i n t h i s  chapter.  15  T a b l e of Era  Cenozoic  Formations;  Period or Epoch Recent and Pleistocene  Name  S a l i s h Sediments C a p i l a n o Sediments, Vashon D r i f t , Quadra Sediments, p l u s other unnamed d e p o s i t s :  Lithology  Marine and R i v e r Sediments g r a v e l , sand, s i l t c l a y , peat G l a c i a l Deposits t i l l , c l a y , sand, gravel, s i l t  unconformity Late Cretaceous;; or Tertiary  Late  Cretaceous or Tertiary Intrusions Washington B r e c c i a Murray B r e c c i a  granodiorite, quartz d i o r i t e , quartz d i o r i t e porphyry, breccias  i n t r u s i v e contact  Late Cretaceous  Trent R i v e r Formation Comox  Formation  Cenozoic or Mesozoic  sandstones, s h a l e s conglomerates s h a l e s , sands t o n e s and minor c o a l and conglomerates:  unconformity Late Jurassic and/or Cretaceous; and/or Tertiary  Quinsam granodiorite etc.  intrusive  Triassic  diorite, quartz d i o r i t e , granodiorite, granite  contact  Vancouver group  pillow lavas, breccias, andesite, a m y g d a l o i d a l and porphyritic b a s a l t s , minor d a e i t e and f e l s i t e , minor l i m e s t o n e , a r g i l l i t e , quartzite  conformity  Paleozoic  Permian  andesite, basalt, tuff, volcanic b r e c c i a , limestone, minor q u a r t z i t e and argillite  16.  B.  Permian-Triassic Volcanic  and Sedimentary Rocks  The o l d e s t r o c k s o f the g e n e r a l a r e a o u t c r o p i n the r e g i o n of B u t t l e Lake. or b a s a l t i c  They c o n s i s t  flows, t u f f s ,  of a t h i c k s e r i e s of a n d e s i t i c  and c o a r s e v o l c a n i c b r e c c i a s w i t h  two or t h r e e i n t e r b e d d e d h o r i z o n s o f l i m e s t o n e and minor amounts o f q u a r t z i t e and a r g i l l i t e . Permian i n age  They are b e l i e v e d to be  (Gunning, 1930, p.59A), and l i k e l y c o r r e s p o n d  to the S i c k e r group o f Cowichan Lake d e s c r i b e d by F y l e s  (1955»  pp.13-19). The Permian r o c k s are o v e r l a i n , a p p a r e n t l y c o n f o r m a b l y , by a g r e a t  t h i c k n e s s o f l a v a s and f r a g m e n t a l s known as the  Vancouver group o f T r i a s s i e age. near B u t t l e Lake east  These r o c k s o u t c r o p from  to the c o a s t a l p l a i n .  developed p i l l o w l a v a s and a m y g d a l o i d a l and f l o w s than do the Permian r o c k s .  They have  better  porphyritic  They a l s o i n c l u d e  a n d e s i t e s , and r a t h e r minor l i m e s t o n e , a r g i l l i t e , q u a r t z i t e , and v e r y minor d a c i t e and f e l s i t e .  breccias,  and  They are c u t  by a n d e s i t e and d i a b a s e dykes, and by a few more a c i d i c  dykes.  Rocks of the Vancouver group exposed elsewhere on Vancouver I s l a n d , have been d e s c r i b e d by C l a p p (1917, pp.93-104, SookeDuncan a r e a ) , and F y l e s  (1955, pp.l9-25»  Cowichan Lake  area).  An e x t e n s i v e d e s c r i p t i o n o f the c o m p o s i t i o n and p r i m a r y s t r u c t u r e s o f the Vancouver group r o c k s i s u n n e c e s s a r y i n this: report  since:  ( i ) - t h e r e i s no doubt t h a t  s i m i l a r r o c k s at Mt.  Washington  are o f t h i s group so t h a t o n l y a b r i e f comparison need be made • ( i i ) - i n the Mt. Washington a r e a they a r e n e a r l y a l l  massive  17. basaltic primary  or a n d e s i t i c r o c k s from which the d e t e r m i n a t i o n o f s t r u c t u r e s i s very d i f f i c u l t .  i n f o r m a t i o n was  o b t a i n e d on such  As a r e s u l t  little  structures.  S e v e r a l m i n e r a l d e p o s i t s are found  i n limestone lenses  or  sheared v o l c a n i c s of the Vancouver group.  Some of  those  in  the B u t t l e Lake a r e a have been d e s c r i b e d by Gunning  (1930,  PP.65A-78A). The  s t r u c t u r a l t r e n d of the r o c k s on Vancouver I s l a n d i s  northwest.  At B u t t l e Lake l i m e s t o n e beds i n the Permian  rocks c l e a r l y  show broad  about t h i r t y d e g r e e s .  f o l d s whose l i m b s d i p a maximum o f  West o f B u t t l e Lake t h e r e are some  v e r t i c a l l y d i p p i n g shear zones which s t r i k e n o r t h w e s t . are a l s o s e v e r a l f a u l t s w i t h s i m i l a r t r e n d s and right  l a t e r a l displacements  o f more than one  There  some p o s s e s s  mile.  Gunning (1930, p.61A) s t a t e s t h a t wherever  limestone  beds o c c u r over c o n s i d e r a b l e d i s t a n c e s f a u l t i n g i s observed, but  i f limestone  i s absent^the  are s u f f i c i e n t l y inconspicuous.  v o l c a n i c r o c k s o f the  s i m i l a r i n appearance to r e n d e r He  series  faulting  c o n c l u d e s however, t h a t the whole Permian  s e c t i o n i s broken i n t o a number of b l o c k s by numerous f a u l t s . As i s the case w i t h the Permian r o c k s , the s i m i l a r i t y i n appearance of the Vancouver group v o l c a n i c s r e n d e r s w i t h i n them i n c o n s p i c u o u s .  They, l i k e  the Permian r o c k s , are  l i k e l y broken i n t o numerous b l o c k s by northwest faults.  In the a r e a between B u t t l e Lake and Mt.  the r o c k s are not twenty degrees  s t r o n g l y f o l d e d and  trending Washington  g e n e r a l l y d i p about  to the n o r t h or n o r t h e a s t .  west o f Mt. Washington on Mt.  faulting  Eight miles  south-  A l b e r t Edward t h e y d i p to the  18 n o r t h or n o r t h e a s t  C.  at a low  angle.  L a t e J u r a s s i c - E a r l y C r e t a c e o u s Coast Dykes, s t o c k s , and  Jurassic rocks.  b a t h o l i t h s r e f e r r e d to the  or E a r l y C r e t a c e o u s ,  i n t r u d e the  They a r e b e l i e v e d to be  of the m i n e r a l diorite, The  diorite,  east l i m i t  about f i v e m i l e s at l e a s t  source  o f many  are composed  of  g r a n o d i o r i t e , or g r a n i t e .  o f the l a r g e s t o f these  southwest of B u t t l e L a k e .  intrusions i s The  intrusion i s  twenty m i l e s l o n g by t e n m i l e s wide and  o f g r a n o d i o r i t e w i t h minor d i o r i t e the Upper Quinsam and  Late  Triasslc-Permian  the o r i g i n a l  d e p o s i t s o f the a r e a and  quartz  Intrusions  and  i s composed  soda g r a n i t e .  Upper Campbell R i v e r s t h e r e  Between  i s an i n -  t r u s i v e body about e i g h t m i l e s l o n g by f i v e m i l e s wide. is called diorite  the Quinsam g r a n o d i o r i t e , but  or q u a r t z  been o b s e r v e d .  d i o r i t e - g a b b r o , and  no g r e a t  suggested that  depths by a body of g r a n o d i o r i t e .  Washington which may  that  more a c i d i c phases have  Washington may  i n t r u s i o n s i n c l u d i n g s e v e r a l a few  put  p a r t s of i t are  Gunning (1930, p.63A) has  l a r g e a r e a which i n c l u d e s Mt.  Numerous s m a l l  m i l e s southwest o f  be T e r t i a r y i n  of post  mentions  age. River-  Lake region,where the P e r m i a n - T r i a s s i c  Upper C r e t a c e o u s r o c k s o c c u r e q u a l l y deformed.  Mt.  be upward p r o j e c t i o n s o f t h i s body are  At many l o c a l i t i e s i n the e n t i r e Campbell Courtenay-Buttle  a  be u n d e r l a i n at  i n the Coast I n t r u s i o n group by Gunning, but he some of them may  It  s i d e by  and  s i d e , t h e y appear to  T h i s might i n d i c a t e t h a t the Puget  Late C r e t a c e o u s times (White, 1959,  p.96)  was  be  orogeny the  19.  major period of deformation i n the entire area and that most of the intrusive rocks, like the rocks at Mt. Washington, were emplaced during this orogeny. D.  Upper Cretaceous Sedimentary Rocks.  1.  General Statement and General Extent A report by Mackenzie (1922) contains descriptions of the  rocks of the Comox basin, and a report by Buckham (1947) contains descriptions of the Nanaimo basin rocks.  Most of the  information in this section was obtained from these two reports;. Coal-bearing Upper Cretaceous rocks of the Nanaimo series: underly the east coastal plain of Vancouver Island and outcrop on islands in the Strait of Georgia.  They occur i n five  distinct basins, one of which i s the Comox basin extending south from Campbell River to Nanoose Bay. The sediments of Cumberland and upper Mt. Washington belong to this basin. At the time of deposition of the sediments the Comox basin was co-extensive with the largest of the present day basins - the Nanaimo basin of Nanaimo.  Buckham (1947, pp.460-  472) has described the rocks of the Nanaimo basin. In the Nanaimo area the Nanaimo series has a total average thickness of 6,760 feet, and has a maximum thickness of 9,000 feet (Mackenzie, 1922, p.388).  At other places on Van-  couver Island the total thickness of the series i s nearly 10,000 feet. The six lowest formations of the Nanaimo basin, t o t a l l i n g 1900 feet i n thickness, were not formed north of Qualicum river (Buckham, 1947, p.462).  Mackenzie (1922, p.389) con-  20.  eludes with 2.  t h a t the Comox b a s i n r o c k s c o u l d l i k e l y be c o r r e l a t e d  the P r o t e c t i o n f o r m a t i o n Comox B a s i n a t Cumberland  o f the Upper Nanaimo b a s i n . (see f i g . 3 )  In the Comox b a s i n at Cumberland t h e r e a r e two formations.. The  lower f o r m a t i o n ,  Triassic  the Comox f o r m a t i o n ,  Vancouver group r o c k s .  l i e s d i r e c t l y on the  I t underlies a s t r i p of  c o u n t r y which i s from one and one h a l f to two m i l e s wide and trends  southeast  from Brown's R i v e r t o beyond T s a b l e  River.  I t s southwestern boundary where i t i s i n c o n t a c t w i t h the Vancouver group v o l c a n i c s , i s i r r e g u l a r . Upper C r e t a c e o u s r o c k s and  Embayments o f the  extend back i n t o the T r i a s s i c  o u t l i e r s o f Comox sediments a r e p r e s e n t  the main a r e a o f o u t c r o p The  Comox f o r m a t i o n  though c o a r s e  t o the west o f  o f Comox rocks;. i s 80 t o 1000 f e e t t h i c k , but i t s  average t h i c k n e s s i s 576 f e e t . medium g r a i n e d  I t i s composed o f f i n e t o  g r e y - w h i t e , remarkably homogeneous sandstone, sandstones and g r i t s a r e o c c a s i o n a l l y f o u n d .  Grey and b r o w n i s h - g r e y c l a y s h a l e s and carbonaceous occur  rocks,  t y p i c a l l y associated with  are g e n e r a l l y e n c l o s e d  the c o a l seams.  shales  These seams  i n l a y e r s o f s h a l e and the carbonaceous  m a t e r i a l o f the c o a l c o n s i s t s almost e n t i r e l y o f t r a n s p o r t e d plant remains.  In s e v e r a l p l a c e s t h e r e  i s a basal b r e c c i a of  heterogeneous t e x t u r e , formed from a n g u l a r  or rounded  ments o f the u n d e r l y i n g v o l c a n i c r o c k s .  I n most  however, the lowest  fine-grained.  stone, rocks.  s t r a t a are t y p i c a l l y  s h a l e , and even s h a l y c o a l l i e d i r e c t l y  frag-  localities Sand-  on the T r i a s s i c  An i n t r a f o r m a t i o n a l conglomerate composed o f w e l l  rounded a r g i l l i t e ,  q u a r t z i t e , q u a r t z , and g r a n i t i c  found near the t o p o f the f o r m a t i o n  i n the v i c i n i t y  pebbles- i s . of Tsable  21.  River. The u n c o n f o r m i t y between the Comox f o r m a t i o n and the T r i a s s i c v o l c a n i c s has c o n s i d e r a b l e r e l i e f , (Mackenzie, 1922, p.391).  amounting t o 440 f e e t  D e p r e s s i o n s i n t h i s : s u r f a c e were a t  p l a c e s f i l l e d w i t h a n g u l a r b r e c c i a composed o f v o l c a n i c r o c k s , and h i l l s  on the s u r f a c e caused l o c a l wedging out o f the lower  beds o f the f o r m a t i o n , i n c l u d i n g some o f the lower c o a l In  the v i c i n i t y  northeast In  seams.  o f Cumberland the u n c o n f o r m i t y d i p s t o the  a t two t o t h r e e d e g r e e s .  s e v e r a l l o c a l i t i e s the T r i a s s i c v o l c a n i c r o c k s at the  u n c o n f o r m i t y a r e decomposed t o depths o f up t o t e n f e e t , p r o b a b l y due t o p r e - L a t e C r e t a c e o u s w e a t h e r i n g . O v e r l y i n g the Comox f o r m a t i o n i s the T r e n t R i v e r formation.  I t extends from the S t r a i t  of Georgia i n l a n d  about  f o u r m i l e s where i t o v e r l i e s , a p p a r e n t l y c o n f o r m a b l y , the Comox f o r m a t i o n .  I t i s about  1000 f e e t  t h i c k and i s ; composed  d o m i n a n t l y o f s h a l e w i t h minor beds o f f i n e g r a i n e d sandstone. ;  3.  Types The  of Structures g e n e r a l s t r u c t u r e o f the Nanaimo r o c k s o f the Comox  b a s i n i s a monocline  of gently northeastward dipping  strata,  m o d i f i e d i n some p l a c e s by f o l d i n g , and a l s o by f a u l t s o f small displacement dip  i s about  (Mackenzie, 1922, p.397).  The average  f i v e d e g r e e s , but n o r t h e a s t d i p s o f up t o f i f t y  degrees o c c u r l o c a l l y ,  and i n some p l a c e s the r o c k s d i p  g e n t l y to the west. In  the v i c i n i t y  o f Cumberland, broad s h a l l o w f o l d s  o c c u r , but these a r e n o t as s i g n i f i c a n t w i t h r e s p e c t a r e a s o f workable  c o a l as i s the i r r e g u l a r  Triassic-  t o the  a c o  Satic< and  23'  ^  —  Sr«y Ony Sha'e  .-  *Z.  364' S O O TrtW E S T  N ORT H E A S T  Fi^3 - S t r a t i <jfQp^i'c C o l u m n  Clay Shale  of t h e U p p e r  Cretaceous  85 Sediments  Coo/  7'  Sandf ^one  59'  Coo/  «'  iandllomo  Coal  at  (after  Cunr>t> Mackenzie,  «' n a * , p. 39*)  3'  Wh.fe Sandstone  Coal  CooJ Wk.k  Ktnd-  6 « v Shale  Coo/ 5hale - ^ i  A^flom trottt  FIGURE  4  -  Fault  Nanaimo S e r i e s FIGURE:  3.  by  Buckham  in  Lower  as envisaged  (1^4-7, p. 4<bT ) .  23.  Cretaceous  unconformity.  S e v e r a l s m a l l normal f a u l t s w i t h d i s p l a c e m e n t s i n c h e s t o twenty f e e t a r e found They do not appear to extend are b e l i e v e d by MacKenzie  o f a few  i n the Cumberland mines*.  i n t o the T r i a s s i c basement and  (1927, p.398) t o be caused  by l o c a l  a n t i c l i n a l b u l g i n g o f the basement r o c k s c a u s i n g the o v e r l y i n g l a y e r e d sediments t o be s t r e t c h e d and c r a c k e d , and t h e a r c h e s so formed to c o l l a p s e .  Few j o i n t s i n t e r s e c t  the Comox  rocks. Some s t r u c t u r e s i n the Nanaimo b a s i n r o c k s 1947,  (Buckham,  pp.463-466) which a r e more deformed than the Comox  rocks, are p e r t i n e n t to t h i s t h e s i s .  The dominant  f e a t u r e o f the Nanaimo c o a l f i e l d  i s the presence  strong f a u l t s t r e n d i n g northwest.  Most o f these  appear to be r o t a t i o n a l t h r u s t s i d e to the n o r t h e a s t .  structural o f numerous  faults  f a u l t s w i t h t h e i r downthrow  Buckham (1947, p.464) r e c o r d s s e v e r a l  such f a u l t s whose downthrow i s zero t o p o s s i b l y 1000 f e e t . Buckham (1947» p.466) c o n s i d e r s the f a u l t s i n the Upper Cretaceous  r o c k s o f Nanaimo a r e a t o be due to p o s t - L a t e  C r e t a c e o u s movements o f l a r g e b l o c k s o f the T r i a s s i c basement rocks along p r e - e x i s t i n g breaks. south f a u l t  He s t a t e s t h a t a n o r t h -  i n the basement r o c k s , i n which the west s i d e  has moved upward r e l a t i v e o v e r l y i n g sediments.  to the e a s t , would r u p t u r e the  T h i s r u p t u r e would occur a l o n g a plane  which d i p s west, the west s i d e moving over the e a s t i n a •thrust which d i e s out upward i n a sharp r o l l  (fig.4).  he b e l i e v e s , o c c u r r e d i n t h e lower p a r t o f the Nanaimo s e c t i o n , and caused  the s h e a r i n g and smearing  a l o n g the  This,  24..  fault  E.  surface,  o f c o a l from the  L a t e C r e t a c e o u s or T e r t i a r y  faulted  seams.  Intrusives;  MacKenzie (1922, p.397) mentions two Comox b a s i n where s i l l s c l a s e p o r p h y r y and At  one  and  locations in  c r o s s - c u t t i n g bodies of  d a c i t e porphyry intrude  l o c a t i o n some of the  c o a l was  a semibituminous n a t u r e , but  i n the  the  Many o f the I s l a n d may  as  plagio-  coal  seams.  improved i n q u a l i t y other l o c a t i o n i t  changed "to a mass of impure carbonaceous and quite valueless  the  sandy  was  material  coal."  s o - c a l l e d Coast I n t r u s i o n s  b e l o n g to t h i s group, the  on  l a c k of  Vancouver  cross-cutting  r e l a t i o n s h i p s w i t h the Upper C r e t a c e o u s sediments b e i n g to the  F.  and  Recent  Deposits  D e p o s i t s o f marine and t h i c k c o v e r most o f the  a r e a west of Campbell R i v e r they extend i n l a n d o f up  to 500  deposits of 1000 features  are  feet.  glacio-marine materials coastal p l a i n . where the  about s i x m i l e s . 1  Except i n  They o c c u r at  feet.  to  300  the  elevations  ground moraine  found west o f the marine d e p o s i t s  to 1500  up  c o a s t a l p l a i n widens,  G l a c i o - f l u v i a l and  F u r t h e r west g l a c i a l  to  elevations  eroslonal  predominate.  D e p o s i t s a l o n g the  1  due  absence o f such sediments.  Pleistocene  feet  to  s h o r e s of the  F y l e s , J.G., S u r f i c i a l Can. Map 49 1959.  Strait  of  Geology, O y s t e r R i v e r ,  Georgia  Geol. Surv.  25.  i n c l u d e the Recent S a l i s h s e d i m e n t s w h i c h c o n s i s t o f s h o r e , d e l t a i c , and f l u v i a l m a t e r i a l .  These d e p o s i t s ,  terraced  f l u v i a l d e p o s i t s , and v a l l e y a l l u v i u m and c o l l u v i u m l o c a l l y f u r t h e r i n l a n d on the c o a s t a l  plain.  occur  26.  IV  A.  General  LOCAL GEOLOGY  Statement  This:; c h a p t e r c o n t a i n s d e s c r i p t i o n s o f the r o c k s , s t r u c t u r e s , metamorphism and  alteration,  o f the Mt. W a s h i n g t o n - C o n s t i t u t i o n H i l l  and m i n e r a l d e p o s i t s area.  a t t e n t i o n i s g i v e n to the Upper C r e t a c e o u s the i n t r u s i o n s , and  the b r e c c i a s at Mt.  ions of s t r u c t u r e s c h a r a c t e r i s t i c are i n c l u d e d w i t h the l i t h o l o g i c  Special  sedimentary  Washington.  rocks,  Descript-  of each of the r o c k u n i t s d e s c r i p t i o n s o f such  units.  L a r g e r s c a l e s t r u c t u r e s than those c h a r a c t e r i s t i c  o f the  i n d i v i d u a l r o c k u n i t s , and which g e n e r a l l y extend  from  unit  into  the o t h e r , are d e s c r i b e d under the h e a d i n g  one  "Major  Structures."  B.  T r i a s s i c V o l c a n i c Rocks  1.  E x t e n t and The  General  Description  basement r o c k s o f the e n t i r e Mt. Washington a r e a are  a l t e r e d v o l c a n i c r o c k s of b a s a l t i c They are p o r p h y r i t i c b r e c c i a s , and Triassic  age.  or a n d e s i t i c  and a m y g d a l o i d a l  composition.  flows, pillow  lavas,  t u f f s b e l o n g i n g to the Vancouver group of The w r i t e r d i d not observe  l a y e r e d w i t h these  any sediments  volcanics.  At Mt. Washington the Vancouver group v o l c a n i c s p r a c t i c a l l y a l l the o u t c r o p s below 3800 f e e t on the C e n t r a l arm feet.  inter-  form  i n elevation,  but  they are found at e l e v a t i o n s o f up to 4500  Except where s m a l l p a t c h e s of Upper C r e t a c e o u s  ments o v e r l i e them, they o u t c r o p c o n t i n u o u s l y from  Mt.  sedi-  27.  Washington to the west s i d e of C o n s t i t u t i o n The  rocks  are  t y p i c a l l y greenish  p u r p l i s h i n colour, f i n e grained to a brownish c o l o u r . the  Hill.  g r e y , dark g r e y ,  to a p h a n i t i c , and  Their s i m i l a r i t y  A c c u r a t e measurement o f a t t i t u d e s i s d i f f i c u l t ,  r e v e a l t h e i r approximate a t t i t u d e s .  weather  i n appearance makes  d i s t i n c t i o n of s e p a r a t e f l o w s or beds almost  l o c a l i t i e s , w e l l developed p i l l o w s up  impossible. but  i n some  to f o u r f e e t i n  length  Immediately west o f  Washington they appear to d i p about twenty degrees to north.  or west.  the  Mt.  the  In the c e n t r a l p o r t i o n of MacKay c r e e k they have been  observed d i p p i n g at a n g l e s of up  rocks  or  to f i f t y  degrees to the  In s e v e r a l l o c a l i t i e s n e a r C o n s t i t u t i o n H i l l  d i p at f a i r l y low  east.  these  a n g l e s of ten to f i f t e e n degrees to  I t appears t r u e t h a t u n l e s s  d i s t u r b e d by  east  they have been  l o c a l f a u l t i n g the v o l c a n i c s o f the e n t i r e  3€nerally d i p f a i r l y g e n t l y and  g e n e r a l l y to the n o r t h  area  or  northeast. Randomly s c a t t e r e d white or dark green amygdules from one  to s i x mm.  l o n g are common i n many f l o w s .  White-  w e a t h e r i n g p l a g i o c l a s e p h e n o c r y s t s a v e r a g i n g about two d i a m e t e r and  occuring  i n c l u s t e r s are common i n o t h e r s ,  many f l o w s are both p o r p h y r i t i c and are  amygdaloidal.  in  and  Many f l o w s  composed of w e l l formed p i l l o w s w i t h or w i t h o u t pheno-  c r y s t s and one  mm.  amygdules.  of medium g r a i n e d  Several  beds of v o l c a n i c b r e c c i a  and  t u f f i n MacKay c r e e k , have been  observed. Scattered from Mt.  o u t l i e r s of Upper C r e t a c e o u s sediments  Washington to C o n s t i t u t i o n H i l l  r e v e a l that  occuring the  28.  Plate  V I I - Upper C r e t a c e o u s s h a l e s and s a n d s t o n e s o v e r l a i n by v e r t i c a l l y j o i n t e d q u a r t z d i o r i t e p o r p h y r y on the west s i d e o f C o n s t i t u t i o n H i l l .  29.  T r i a s s i e - U p p e r Cretaceous' u n c o n f o r m i t y dips: g e n t l y to the e a s t and c o i n c i d e s a p p r o x i m a t e l y w i t h the p r e s e n t surface.  land  At a l o c a t i o n south of the Summit where the  Triassic  and Upper C r e t a c e o u s r o c k s are i n c o n t a c t , the  Triassic  s u r f a c e of u n c o n f o r m i t y i s decomposed to a white sheared,  c l a y e y m a t e r i a l to a depth of more than f i f t e e n f e e t . lee  c r e e k j u s t west o f C o n s t i t u t i o n H i l l  o c c u r r e n c e o f decomposed v o l c a n i c r o c k .  there i s a  In  similar  However, i n another  l o c a t i o n lower i n the same c r e e k the C r e t a c e o u s r o c k s o v e r l y unweathered p i l l o w l a v a s ( p l a t e V I ) .  These are the o n l y  l o c a t i o n s where the exact Upper C r e t a c e o u s - T r i a s s i c c o n t a c t was  observed.  At Mt. Washington the e l e v a t i o n o f the uncon-  f o r m i t y v a r i e s from about E a s t arm, arm  to about  south of No.2  3500 f e e t a t the east end of the  4500 f e e t fault  on the C e n t r a l arm.  (maps 1 and  u n d u l a t i n g s u r f a c e broken  2) i t appears  i n s e v e r a l p l a c e s by  J o i n t i n g i s v e r y common i n the T r i a s s i c  On the West to be  an  faults.  rocks.  In many  l o c a l i t i e s c o n s p i c u o u s j o i n t s d i p p i n g g e n t l y to the n o r t h e a s t were o b s e r v e d .  In one  l o c a l i t y northwest  of C o n s t i t u t i o n  H i l l where a s e r i e s of p i l l o w l a v a f l o w s o u t c r o p ,  similar  f r a c t u r e s were found to be b e d d i n g p l a n e j o i n t s .  Crude  columnar j o i n t i n g was In  the v i c i n i t y  a l s o observed i n these f l o w s . of f a u l t s the T r i a s s i c v o l c a n i c  are  highly  2.  Microscopic Description The  rocks  fractured.  t e x t u r e of the l e s s a l t e r e d f l o w r o c k s i s - v . , .  o p h i t i c , p o r p h y r i t i c , or f e l t e d ,  the main m i n e r a l s b e i n g  unzoned or weakly zoned l a b r a d o r i t e  (An^  fic  -)  or, l e s s  30.  commonly, andesine, and augite or hornblende.  Magnetite is:  everywhere present and in some instances makes up 15% of the rock.  Amygdules, when present, may be composed of penninite  or may contain c a l c i t e ,  epidote, and quartz.  In many of these  rocks, composite phenocrysts of plagioclase occur as radiating clusters up to four mm. in diameter. In most of the rocks plagioclase has been partly saussuritized and the ferromagnesian minerals are altered to c h l o r i t e , magnetite, a c t i n o l i t e , and epidote. C.  Upper Cretaceous Sedimentary Rocks;  1.  General Extent and General Description (see maps 1 and 2; cross sections 1 and 2) Sandstone, siltstone,  shale, impure coal, minor conglom-  erate, quartzite, and a r g i l l i t e of Late Cretaceous age l i e unconformably upon the Triassic volcanics and form the capping of Mt. Washington (map 1 ) .  Their maximum thickness on the;  mountain i s at the central part of the East arm where they are approximately 900 feet thick. Around the outer edge of the capping the sediments are nearly f l a t - l y i n g .  However, in the inner Central arm-West  arm area they invariably dip away from MacKay Lake at angles of 5 ° to 3 0 ° .  In the v i c i n i t i e s of some faults they are  disturbed so that erratic dips of up to 5 5 ° may be encountered. A l l of these rocks excepting the a r g i l l i t e s and quartzites, are similar to the Upper Cretaceous sediments exposed in the Comox basin at Cumberland and described by  31.  MacKenzie  (1922, pp.390-396).  the most p a r t C e n t r a l arm  over a f a i r l y  and  The  two  exceptions occur f o r  s m a l l a r e a which i n c l u d e s the  the i n n e r h a l f of the West arm.  r o c k s i n t h i s a r e a are c l o s e to d i o r i t i c  Most of the  i n t r u s i o n s and  are  highly indurated. Outcrops  of the Upper C r e t a c e o u s r o c k s on a l l p a r t s of  Mt. Washington, except at the c l i f f s limited.  o f the E a s t arm,  Most o f them o c c u r as s m a l l moss-covered  as d i s c o n t i n u o u s p a t c h e s i n stream  l e d g e s or  beds.  P a t c h e s of Upper C r e t a c e o u s r o c k s o c c u r between Washington and C o n s t i t u t i o n H i l l .  are v e r y  Mt.  The w e s t e r n edge o f the  c o n t i n u o u s l a y e r o f Upper C r e t a c e o u s sediments  u n d e r l y i n g the  C o a s t a l p l a i n i s exposed  on the west s l o p e s o f C o n s t i t u t i o n  Hill  are cut by a s i l l  where the sediments  porphyry 2.  of quartz d i o r i t e  (plate V I I ) .  D e s c r i p t i o n o f Rock Types Sandstones.  Upper C r e t a c e o u s sandstones o f v a r i o u s t y p e s  form the m a j o r i t y o f o u t c r o p s on the upper ington.  p a r t s o f Mt. Wash-  Most of them are not t r u e s a n d s t o n e s .  f e l d s p a t h i c , a r g i l l a c e o u s , or l i t h i c  s a n d s t o n e s , and many of  the more h i g h l y i n d u r a t e d t y p e s are greywackes. in are  the d i f f e r e n t light  absent. posed  They are  t y p e s v a r y from v e r y f i n e  g r e y or b l u i s h g r e y and bedding  Grain sizes  to c o a r s e .  Most  i s very f a i n t  or  T h e i r compositions vary c o n s i d e r a b l y .  Some are com-  c h i e f l y o f q u a r t z w i t h minor a r g i l l a c e o u s m a t r i x  whereas i n o t h e r s the a r g i l l a c e o u s m a t r i x dominates.  Most,  however, are composed o f a homogeneous m i x t u r e c o n s i s t i n g of g r a i n s of q u a r t z , f e l d s p a r , and r o c k fragments  set i n a matrix  32.  of r e c r y s t a l l i z e d a r g i l l a c e o u s , s l i g h t l y material.  Primary  Rocks t y p i c a l  calcite  i s extremely  quartz  or a n d e s i n e ,  to c o n t a i n angular  (45% a v e r a g e ) ,  ( 1 0 $ average),  at s e v e r a l p l a c e s  medium grey,  m a s s i v e , and medium t o f i n e g r a i n e d .  strained  rare.  o f the sandstones found  i n c l u d i n g the Summit, a r e w h i t e ,  they a r e observed  carbonaceous  or b l u i s h - g r e y ,  Under the m i c r o s c o p e elongated  clouded  grains of  orthoclase, oligoclase,  and fragments o f c h e r t , s h a l e ,  b a s i c v o l c a n i c r o c k s , and g r a n i t e (15% a v e r a g e ) .  These a r e  i n a m a t r i x which i n c l u d e s s e r i c i t e , c h l o r i t e , b i o t i t e , oxides, p y r i t e ,  iron  o r g a n i c m a t e r i a l , and minor amounts o f  a p a t i t e , z i r c o n , and sphene. Several outcrops coarse  of grey  or t a n c o l o u r e d , medium t o  g r a i n e d , massive a r g i l l a c e o u s sandstone occur on t h e  o u t e r p o r t i o n s o f the West arm and on the west s i d e o f Constitution H i l l .  T h e i r c o n s t i t u e n t s a r e s i m i l a r t o those o f  the f i n e r g r a i n e d v a r i e t i e s d e s c r i b e d above, but the m a t r i x i n some i s g r e a t e r than 50% o f the r o c k and does n o t c o n t a i n organic m a t e r i a l .  F l a k e s and e l o n g a t e d  fragments o f s h a l e  d e r i v e d from the u n d e r l y i n g r o c k s by w e a t h e r i n g a r e common i n the c o a r s e  sandstones.  Carbonaceous S h a l e s  and S i l t s t o n e s .  grey t o b l a c k s h a l e , generally i n t e r b e d d e d brown s i l t s t o n e ,  with l i g h t e r  grey-  a r e common i n areas u n d e r l a i n by unmeta-  morphosed Upper C r e t a c e o u s fissile  Outcrops o f dark  rocks.  Some o f the s h a l e s a r e v e r y  and a few c o n t a i n p y r i t e n o d u l e s .  Both the s h a l e s and  the s i l t s t o n e s c o n t a i n o r g a n i c m a t e r i a l , and c a r b o n i z e d remains ( p l a t e V I I I ) l y i n g p a r a l l e l  plant  to b e d d i n g p l a n e s a r e  33.  r e a d i l y seen. two  Beds o f low grade c o a l a r e known t o o u t c r o p i n  l o c a l i t i e s on Mt. Washington. Under the microscope  these r o c k s a r e observed  l a y e r s and l e n s e s o f s i l t y m a t e r i a l . to  to contain  This c o n s i s t s o f angular  sub-rounded q u a r t z , rock fragments,  and f e l d s p a r ,  ina  m a t r i x o f c h l o r i t e - c l a y m i n e r a l - s e r i c i t e p l u s carbonaceous m a t e r i a l and i r o n o x i d e . extremely  These a r e e n c l o s e d w i t h i n dark,  fine grained o r g a n i c - r i c h a r g i l l a c e o u s m a t e r i a l  c o n t a i n i n g s c a t t e r e d , small angular g r a i n s of quartz.  In some  p l a c e s the s i l t y l a y e r s c o n t a i n minor amounts o f c a l c i t e . P y r i t e nodules, of  euhedral  i f p r e s e n t , a r e composed o f composite  crystals.  Conglomerates and B r e c c i a s . e r a t e s were noted  I n t r a f o r m a t i o n a l conglom-  at o n l y two l o c a l i t i e s .  Summit, and one i s on the East arm.  One i s south o f the  At the f i r s t  l o c a t i o n the t h i c k n e s s o f the conglomerate feet  and i t o c c u r s a p p r o x i m a t e l y  Cretaceous-Triassic  100 f e e t  mentioned  i s at l e a s t  twenty  above the Upper  unconformity.  These conglomerates  a r e g r e e n i s h - g r e y and a r e composed o f  w e l l rounded c h e r t , g r a n i t e , g r e e n s t o n e , pebbles  masses  averaging f i n c h i n diameter.  composed o f c o a r s e g r a i n e d sand  q u a r t z and s h a l e  T h e i r matrixes are  and a r g i l l a c e o u s m a t e r i a l .  B a s a l b r e c c i a composed o f a n g u l a r t o rounded fragments o f the u n d e r l y i n g T r i a s s i c v o l c a n i c s was observed j u n c t i o n o f Murex and MacKay c r e e k s . p u r p l i s h i n c o l o u r and s i m i l a r Triassic volcanic breccias. c o a r s e sandstone  near the  I t i s dark green o r  i n appearance to some o f the  However, i t c o n t a i n s l e n s e s o f  and i s v e r y l o c a l  i n occurrence,  having  34.  formed i n a d e p r e s s i o n on the Upper C r e t a c e o u s - T r i a s s i e unconformity. A r g i l l i t e s and Q u a r t z i t e s .  Many o f the sedimentary  r o c k s a t Mt. Washington have been h i g h l y i n d u r a t e d and r e crystallized.  T h i s i s e s p e c i a l l y t r u e o f r o c k s i n the i n n e r  West arm - C e n t r a l arm a r e a . so common i n the v i c i n i t y will  be d e s c r i b e d h e r e .  A r g i l l i t e s and q u a r t z i t e s a r e  o f the m i n e r a l d e p o s i t s t h a t Other  they  l e s s common a l t e r e d and  metamorphosed r o c k s a r e d e s c r i b e d l a t e r under the h e a d i n g Metamorphism and A l t e r a t i o n . The  t y p i c a l a r g i l l i t e s a r e dark g r e y o r b l a c k ,  a p h a n i t i c , tough and massive,  and break c o n c h o i d a l l y .  of them a r e l a m i n a t e d but these laminae  Many  have a melted  appearance. Under the microscope i n t e r l o c k w i t h one another Bedding  t h e m i n e r a l s a r e observed t o i n an e x t r e m e l y  f i n e g r a i n e d mat.  i s v i s i b l e , but i t i s not as d i s t i n c t  the s h a l e s .  Quartz  as i t i s i n  g r a i n s ( a p p r o x i m a t e l y 25$),  ( a p p r o x i m a t e l y 20$), s e r i c i t e  ( a p p r o x i m a t e l y 20%),  ( a p p r o x i m a t e l y 25$), and opaques ( a p p r o x i m a t e l y p y r i t e ) , are present. biotite  chlorite biotite  10$-mainly  V e i n l e t s o f q u a r t z , p y r i t e , and  c u t a c r o s s the b e d d i n g .  Quartzitic  r o c k s a r e found  only w i t h i n the general  a r e a o f the Upper C r e t a c e o u s - T r i a s s i e u n c o n f o r m i t y o b v i o u s l y the r e s u l t s o f s i l i c i f i c a t i o n  and a r e  and r e c r y s t a l l i z -  a t i o n o f sandstones. These r o c k s a r e f i n e textured, greyish-fawn  to coarse grained,  sugary  c o l o u r e d , and c o n t a i n g l a s s y q u a r t z  35.  g r a i n s s e t i n a dense m a t r i x . observed  In t h i n s e c t i o n they  are  to c o n t a i n i n t e r l o c k i n g fragments of q u a r t z  some g r a i n s o f s i l i c i f i e d  and  f e l d s p a r , and v a r i o u s r o c k  types.  V e i n l e t s of f i n e g r a i n e d q u a r t z i n v a r i a b l y c r o s s c u t rock.  The  m a t r i x i s m a i n l y q u a r t z but minor amounts o f  biotite, chlorite, generally present. been b a s a l q u a r t z 3.  s e r i c i t e , p y r i t e , and  i r o n oxides  Some o f these r o c k s may  have  originally  Occurrences  (see maps 1  2)  G e n e r a l Statement.  In o r d e r to i l l u s t r a t e  the  c h a r a c t e r i s t i c s o f the o u t c r o p s o f Upper C r e t a c e o u s found  at the Mt. W a s h i n g t o n - C o n s t i t u t i o n  specific  are  sandstones.  D e s c r i p t i o n of Some S p e c i f i c and  the  Hill  rocks  area several  o c c u r r e n c e s are d e s c r i b e d i n t h i s s e c t i o n .  b a s i s of the n a t u r e o f the o c c u r r e n c e s  On  the  some i n f e r e n c e s are  made r e g a r d i n g t h e i r s t r a t i g r a p h y . On West Arm. and  Nearly f l a t - l y i n g interlayered  s i l t s t o n e s are found  saddle along No.l f a u l t In  both l o c a l i t i e s  i n P y r i t e c r e e k and west o f No.l at e l e v a t i o n s of about 3750 f e e t .  the u n d e r l y i n g rock i s a b l u i s h - g r e y ,  medium to c o a r s e - g r a i n e d w e l l i n d u r a t e d and  rusty  S i n c e T r i a s s i c v o l c a n i c r o c k s occur about f i f t y the sandstone Triassic  and  shales  s i n c e t h i s type of sandstone  sandstone.  feet  below  overlies  the  r o c k s south o f the Summit, i t i s b e l i e v e d to be  t h e lowest  r o c k of the Upper C r e t a c e o u s  p a r t s of Mt. Washington. occurrence  This belief  of s e v e r a l o u t c r o p s of  recrystallized  s e c t i o n at most  i s supported  by  the  quartzite—silicified  s a n d s t o n e — d i r e c t l y above the T r i a s s i c  rocks  36.  on the i n n e r West arm supported  by  l y i n g on  and  on the C e n t r a l arm.  the o c c u r r e n c e  the T r i a s s i c  It i s also  o f s m a l l p a t c h e s of sandstone  rocks  on the n o r t h  s l o p e s of  Mt.  Washington. A bed enclosed 4180  o f low  grade c o a l d i p p i n g g e n t l y to the west  i n beds of sandstone i s exposed at an e l e v a t i o n of  f e e t on the o u t e r p a r t of the West arm,  o f No.l  1000  feet north  fault.  Summit and  C e n t r a l Arm.  Grey-white f i n e  to medium  g r a i n e d m a s s i v e , homogeneous sandstone at l e a s t 300 t h i c k occurs  at the Summit.  twenty d e g r e e s .  v a r i e t i e s of s i l i c i f i e d o f the  E a s t Arm. was  and  the C e n t r a l arm,  extension  slightly  argillites, s h a l e and  south  quartz  Due  feet  at about  diorite  foliated. q u a r t z i t e s , and  sandstone u n d e r l y  sandstone beds exposed at the to i t s i n a c c e s s i b i l i t y ,  not mapped i n d e t a i l .  feet  I t d i p s to the  Near i t s c o n t a c t w i t h  p o r p h y r y i t i s dark g r e y On  other a north  Summit.  the E a s t  arm  It contains approximately  900  of Upper C r e t a c e o u s sediments which g e n e r a l l y d i p  g e n t l y to the  south.  summit of the arm  and  The  topmost bed  i s exposed at  of b l u i s h s h a l e occur  S i m i l a r s h a l e and  argillites e a s t end  and  of the  to the east  quartzitic  Its  out-  at t h a t d i s t a n c e below i t .  some sandstone o u t c r o p  top s u r f a c e of the arm  the  i s composed of w h i t e s a n d s t o n e .  maximum p o s s i b l e t h i c k n e s s i s about twenty f e e t f o r crops  and  along  the e n t i r e  of i t s summit,  sandstones o u t c r o p  and  at the  lower  arm.  Samples from the  t a l u s s l o p e s on  the n o r t h edge of  the  37  E a s t arm  consist  of w e l l i n d u r a t e d s i l t y  and  carbonaceous  s h a l e s and g r e y - b l u e s a n d s t o n e s , and c o a l y m a t e r i a l . three rocks c o n t a i n plant remains. was  also obtained.  Outcrops  A sample o f  at the upper  s l o p e , p r o b a b l y a p p r o x i m a t e l y 300  feet  s h a l e and carbonaceous  Vicinity  of C o n s t i t u t i o n H i l l .  f o o t t h i c k remnant of a d i o r i t i c  The  sill  sediments  twenty-five degrees.  sediments  o v e r l a i n by a  of  twenty  o c c u r s at about  and d i o r i t e  overly T r i a s s i c volcanics. of q u a r t z d i o r i t e  VII).  These sediments  feet  i n t u r n , by a  ( c r o s s s e c t i o n 2 and  However, about  shales  i n thickness  d i p to the east at about  where they u n d e r l y the s i l l .  outlier.  sandstone,  They are o v e r l a i n ,  porphyry  d i r e c t l y below the s i l l  fifteen  S i m i l a r but l a r g e r o u t c r o p s of  occur to the s o u t h of t h i s  sill  1500 of  d i p to the e a s t at  and c o a l y beds t o t a l l i n g a p p r o x i m a t e l y 150  ten  fifty  plate degrees  feet  they d i p 35° e a s t and lower s t i l l  they  65° to the e a s t . About 1000  Cretaceous  f e e t n o r t h e a s t of C o n s t i t u t i o n H i l l  sandstones  and  f o r m a b l y by the s i l l , In  Conglomerate  the sediments  the Upper  s h a l e s d i p 60° to the e a s t but at  the n o r t h e a s t edge of the h i l l  Hill  of beds o f c a r b o n -  A small o u t l i e r  On the west s i d e of C o n s t i t u t i o n H i l l  dip  talus  i n e l e v a t i o n i n Ice c r e e k west o f the n o r t h end  Constitution H i l l . to  of the  sandstone.  Upper C r e t a c e o u s s h a l e and sandstone  feet  conglomerate  above the Upper  C r e t a c e o u s - T r i a s s i c unconformity, c o n s i s t aceous  end  All  where t h e y are o v e r l a i n  con-  they d i p g e n t l y to the e a s t . c r e e k about  one m i l e n o r t h of C o n s t i t u t i o n  d i p twelve degrees  eastward.  38.  4.  C o r r e l a t i o n With the Comox F o r m a t i o n Gunning  (1930, p.65A) c o n c l u d e d t h a t  the Mt. Washing-  ton sediments r e p r e s e n t an o u t l i e r o f the Comox b a s i n sediments because  of t h e i r l i t h o l o g i c  s i m i l a r i t y and prox-  i m i t y t o the c o a s t a l p l a i n sediments o f the Comox b a s i n . At b o t h Cumberland  ( f i g . 3 ) and Mt. V/ashington, the  lower beds a r e s a n d s t o n e s , carbonaceous s a n d s t o n e s , c a r b o n aceous s h a l e s , and c o a l beds. hundred  t o f i v e hundred  i s the main r o c k .  feet  From a p p r o x i m a t e l y two above t h e i r base,  sandstone  The c o a l seams o c c u r r i n g i n t h i s  o f the s e c t i o n at Cumberland,  part  ( t o which the r o c k s o f the  Summit s h o u l d c o r r e s p o n d ) were not seen a t Mt. Washington, p o s s i b l y because  o f t h e i r absence.  be due t o the f a c t  I t c o u l d , however, a l s o  t h a t t r a v e r s e s by t h e w r i t e r from the  Summit to the West arm a l o n g the t o p o f the E a s t s a d d l e were n e a r l y i n t h e p l a n e o f bedding o f t h e sediments so t h a t c l o s e o b s e r v a t i o n o f the c r o s s s e c t i o n c o u l d not be made. S i n c e the maximum r e c o r d e d t h i c k n e s s o f t h e Comox f o r m a t i o n a t Cumberland  i s 1000 f e e t but i t s average  thick-  ness i s o n l y 576 f e e t , and s i n c e the E a s t arm sediments a r e a maximum o f a p p r o x i m a t e l y 900 f e e t t h a t the s i l t y  thick, i t i s l i k e l y  s h a l e s and sandstones on the upper p a r t s o f  the East arm a r e w i t h i n the T r e n t R i v e r f o r m a t i o n .  D.  Late Cretaceous or T e r t i a r y  1.  Rock Types and G e n e r a l E x t e n t (see maps 1 and 2 ; . c r o s s s e c t i o n s 1 and 2)  Intrusions  39  Sills, porphyry  dykes and i r r e g u l a r b o d i e s o f q u a r t z  and q u a r t z d i o r i t e  Cretaceous  i n t r u d e the T r i a s s i c  diorite and Upper  r o c k s o f the a r e a .  At Mt. Washington t h e r e i s a c e n t r a l l y l o c a t e d subj a c e n t body o f q u a r t z d i o r i t e  and q u a r t z d i o r i t e  It  be r e f e r r e d  i s l i k e l y a s t o c k and w i l l  this thesis.  o f q u a r t z d i o r i t e porphyry,  ing  the c e n t r a l  occur i n the r o c k s  outliers, Hill. of  of s i m i l a r composition a r e found  quartz d i o r i t e  i n the T r i a s s i c  i n the Upper  rocks,  Cretaceous  between Mt. Washington and C o n s t i t u t i o n  The upper f i v e  The  surround-  intrusion.  Dykes o f q u a r t z d i o r i t e porphyry sills  to as such i n  Apophyses o f t h i s body, dykes, and s i l l s ,  all  and  porphyry.  sixths of Constitution H i l l  i s composed  porphyry.  dominant t e x t u r e o f the d i o r i t i c  intrusions i s  p o r p h y r i t i c but the i n t e r i o r o f the Mt. Washington s t o c k i s composed o f e q u i g r a n u l a r q u a r t z A detailed  diorite.  study o f v a r i a t i o n s i n the c o m p o s i t i o n s o f  the i n t r u s i v e r o c k s was n o t made by the w r i t e r .  However,  d e t e r m i n a t i o n s made on p l a g i o c l a s e c r y s t a l s from the i n t r u s i o n s suggest in  that s l i g h t  d i f f e r e n t i a t i o n has o c c u r r e d  the s t o c k as i t was i n t r u d e d .  Some zones c o n t a i n e d i n  c r y s t a l s from t h e i n t e r i o r o f the s t o c k a r e more a l b i t i c any  o f t h e zones i n those  (pages 42., 43 , G 4 , 6 5 believed  to be i n d i c a t i v e  those o f temperature, existed  ) .  o f the dykes, s i l l s  or breccias  Complex z o n i n g i n the c r y s t a l s i s o f u n s t a b l e c o n d i t i o n s , such as  pressure,and  i n the magmas.  than  volatile  c o n t e n t , which  40.  Some of the i n t r u s i o n s which c o n t a i n q u a r t z o n l y i n t h e i r groundmasses may i n t r u s i o n o f the  have formed at an e a r l y stage  Washington, these  and  e s p e c i a l l y on the West arm  i n t r u s i o n s are a l t e r e d  2.  the  "Alteration".  Equigranular Variety Equigranular  quartz d i o r i t e  i s found  c e n t r a l p o r t i o n s of the s t o c k and seated  o n l y w i t h i n the  i n some of the more deep  dykes.  In the hand specimen i t i s g r e e n i s h - g r e y medium g r a i n e d , and and  of  to some d e g r e e .  These a l t e r e d v a r i e t i e s w i l l be d e s c r i b e d l a t e r under section entitled  the  stock.  In many l o c a l i t i e s , Mt.  of  or l i g h t  contains p l a g i o c l a s e , quartz,  b i o t i t e c r y s t a l s which average two  Some hornblende c r y s t a l s are t e n mm.  hornblende,  to f i v e mm.  i n length.  i n length.  In t h i n s e c t i o n ( p l a t e I X ) , the rock i s observed c o n t a i n about 65$ (An-j^c^)  a  euhedral  s  poikilitic  h i g h l y zoned and or incomplete  hornblende  grey,  to  twinned p l a g i o c l a s e subhedral  crystals,  ( Z A C = 17°; p l e o e h r o i s m - X =  8%  yellow  brown, Y = medium brown-green, Z = medium brown; a b s o r p t i o n Z>Y>X) as ragged e u h e d r a l biotite  (pleochroism-X  brown), 20$  Minor s e r i c i t e  and  slightly  euhedral  Z = mahogany  strained quartz,  m a g n e t i t e , i l m e n i t e , a p a t i t e and occurs  i n some o f i t s i n n e r and f r a c t u r e s and  c r y s t a l s , 4%  = p a l e y e l l o w , Y and  interstitial  accessory hematite,  to s u b h e d r a l  cleavage  and  sphene.  as a replacement o f p l a g i o c l a s e  intermediate  zones and  planes w i t h i n i t .  c h l o r i t e r e p l a c e s some of the  biotite.  along  A minor amount of  P l a t e IX - Photomicrograph o f e q u i g r a n u l a r q u a r t z d i o r i t e from the c e n t r a l p o r t i o n o f the Mt. Washington s t o c k near MacKay Lake, ( c r o s s e d n i c o l s , x l 6 )  42.  S m a l l i n c l u s i o n s of q u a r t z and scattered  throughout  hornblende  zoned.  The  shape due  distinct  t w i n n i n g and  seven z o n e s .  The  l g  t h i n n e r than the f i r s t T h e i r ranges  to A n ^ * and  are from about  The  An^  Q  l a r g e r than the p r e v i o u s f o u r .  s i x t h zone.  next  to A n ^ . G  The  crystal  zone c o n s i s t s i t s range i s  f o u r zones are  are a l s o o f the normal  has an i n v a r i a b l e c o m p o s i t i o n of about  zone of the c r y s t a l  One  outermost  f o u r minor normal type zones and  a p p r o x i m a t e l y from A n  3.  concentrically  to r e s o r p t i o n or r e c r y s t a l l i z a t i o n .  at l e a s t  range  are  a l b i t e and com-  o u t e r edges o f most c r y s t a l s are i r r e g u l a r i n  studied possesses of  are  crystals.  Plagioclase crystals exhibit bination carlsbad-albite  plagioclase  The  An^  and  type.  s i x t h zone i s slightly  r a d i u s o f the  innermost  i s s i m i l a r i n l e n g t h to t h a t o f the  However, t h i s c o r e i s zoned r e v e r s e l y , and i t s  i s approximately A n ^  Porphyritic  to  An^ . Q  Varieties  Quartz d i o r i t e p o r p h y r i e s form the b u l k of the i n t r u s i o n s i n the Mt. W a s h i n g t o n - C o n s t i t u t i o n H i l l The  upper and  area.  o u t e r p o r t i o n s of the s t o c k , i t s apophyses,  p r a c t i c a l l y a l l the dykes and  s i l l s are p o r p h y r i t i c .  On  l a t e r pages these r o c k s , which are d e s c r i b e d below, w i l l referred  and  be  to as the p o r p h y r i e s .  Unaltered porphyry  i s light  g r e y or l i g h t  greenish-grey.  T h i r t y t o s i x t y p e r c e n t of the r o c k c o n s i s t s to a l a r g e e x t e n t of n e a r l y equant p h e n o c r y s t s o f white C l e a r p h e n o c r y s t s of q u a r t z two  to f i v e mm.  e l o n g a t e , dark green hornblende  c r y s t a l s two  plagioclase. i n diameter  and  to t e n mm.  long  43. a r e commonly s c a t t e r e d  t h r o u g h o u t the r o c k .  o f the i n t r u s i o n s , q u a r t z i s p r e s e n t Alignment of phenocrysts,  However, i n some  o n l y i n the  groundmass.  e s p e c i a l l y hornblende, i s v i s i b l e  i n many o u t c r o p s . Microscopic observations  reveal that  these rocks  are  n e a r l y i d e n t i c a l i n m i n e r a l c o m p o s i t i o n t o the  equigranular  variety.  (An£2 52^'  H i g h l y zoned and t w i n n e d p l a g i o c l a s e  poikilitic  h o r n b l e n d e , a n d , i n most c a s e s , q u a r t z , o c c u r  phenocrysts  (plate  X).  The m a t r i x c o n s t i t u t e s  most o f the r o c k s and i s v e r y f i n e g r a i n e d to  as  about 50% o f aphanitic  h y p a u t o m o r p h i c g r a n u l a r , and c o n t a i n s q u a r t z and p l a g i o c l a s e w i t h shreds of hornblende. present  A p a t i t e , sphene,  and opaques  are  t h r o u g h o u t the groundmass and as m i n u t e i n c l u s i o n s i n  the p h e n o c r y s t s .  M i n o r b i o t i t e may be p r i m a r y but m i n o r  amounts o f c h l o r i t e and e p i d o t e o c c u r as a l t e r a t i o n o f h o r n b l e n d e and p l a g i o c l a s e . zones, f r a c t u r e s ,  and c l e a v a g e  Sericite  replaces  planes w i t h i n  products  certain  plagioclase  phenocrysts. Many q u a r t z p h e n o c r y s t s  are rounded ( p l a t e X) and some  p o s s e s s embayments c a u s e d by r e s o r p t i o n . quartz replace edges,  Smaller grains  some p l a g i o c l a s e c r y s t a l s a r o u n d t h e i r  of  outer  o r t h e y may even f o r m v e i n l e t s w h i c h c u t a c r o s s  the  crystals. Some p l a g i o c l a s e  i s present  as b r o k e n c r y s t a l  fragments.  One o s c i l l a t o r y - z o n e d p l a g i o c l a s e c r y s t a l s t u d i e d c o n s i s t s s i x m a j o r s i m i l a r - s i z e d z o n e s , many o f w h i c h c o n t a i n smaller zones.  The o u t e r m o s t  o f the m a j o r zones  several  exhibits  n o r m a l z o n i n g and i t s range i s f r o m a p p r o x i m a t e l y A n  of  0 0  to  Plate  X - Photomicrograph of quartz d i o r i t e porphyry from a d y k e on t h e West arm, ( c r o s s e d n i c o l s , x l 6 )  Plate  XI - P h o t o m i c r o g r a p h o f s u b - c a t a c l a s t i c q u a r t z d i o r porphyry from near No.l f a u l t , ( c r o s s e d n i c o l s  xl6)  45.  AII^Q.  The  next two major zones have ranges of from  An^,-to An^Q.  The  f o u r t h zone i s o f the normal  contains a small unconformity w i t h i n i t . approximately An^ zones  to An^Q.  Q  i s a distinct  and  to  c o r e shows normal  a p p r o x i m a t e l y An^Q A distinct dykes and  sills  fifth  of approximately  An^Q  from  v a r i e t y of p o r p h y r y i s found i n some of the on the upper p a r t s of Mt. Washington.  It i s  i n apophyses o f the s t o c k , and  i n net v e i n s c u t t i n g the b r e c c i a t e d r o c k s around the s t o c k .  fifth  The  z o n i n g and ranges  of  to An^g»  found l e s s p e r f e c t l y developed  of  and  I t has a range  i r r e g u l a r unconformity.  r e v e r s e l y w i t h a range  The  type  Between the f o u r t h and  zone i s zoned An^.  about  It i s mineralogically i d e n t i c a l  the  fringes  to the common  p o r p h y r y but most o f i t s p h e n o c r y s t s are broken and many are p a r t i a l l y r e s o r b e d , and  i n some i n s t a n c e s they are crowded  together i n a scanty matrix (plate X I ) . that  t h i s v a r i e t y of porphyry was  intruded along active  faults.  believes  f o r c e f u l l y i n t r u d e d or  It w i l l  l a t e r pages as " s u b - c a t a c l a s t i c "  The w r i t e r  be r e f e r r e d  was  to on  porphyry.  Another v a r i e t y of porphyry which i s d a r k e r c o l o u r e d than the normal b o r d e r and in  v a r i e t y i s found at some l o c a t i o n s near  i n apophyses of the s t o c k , and near the c o n t a c t s  some o t h e r i n t r u s i o n s .  the presence  I t s brownish-grey  c o l o u r i s due  of numerous f o r e i g n i n c l u s i o n s i n the m a t r i x .  On l a t e r pages p o r p h y r i e s o f t h i s type w i l l as "contaminated" West arm  the  porphyries.  be r e f e r r e d  to  B i o t i t i z e d p o r p h y r i e s on the  have a somewhat s i m i l a r  appearance.  to  46.  4.  D e s c r i p t i o n s of Some S p e c i f i c Mt.  Washington " s t o c k " .  Occurrences  The  Mt.  Washington s t o c k may-  be an upward p r o j e c t i o n of the l a r g e b u r i e d body o f d i o r i t e whose p r e s e n c e  was  proposed  by  grano-  Gunning (p-. 18 ).  c e n t r a l l y - l o c a t e d body of q u a r t z d i o r i t e  i s exposed over  a r e a of about 2000 by at l e a s t  (map  5000 f e e t  p o r t i o n s are p o r p h y r i t i c whereas i t s i n t e r i o r ular.  1).  I t s outer  At p l a c e s a l o n g i t s west s i d e where i t i s i n c o n t a c t  b r e c c i a t e d , and  q u a r t z d i o r i t e which has  the s u b - c a t a c l a s t i c p o r p h y r i e s — s o m e  crystals.  are  the network of f r a c t u r e s so formed i s f i l l e d  with p o r p h y r i t i c  of  an  i s equigran-  w i t h the T r i a s s i c v o l c a n i c r o c k s the h o s t r o c k s  of  This  In many p l a c e s near  some c h a r a c t e r i s t i c s  rounded and  broken  i t s o u t e r c o n t a c t s the  diorite  the s t o c k i s b r e c c i a t e d and network o f f r a c t u r e s formed i s  f i l l e d with p o i k i l i t i c pleochroism-Y Z = brownish  actinolitic  hornblende  (ZAC = 1 6 ° ;  = g r e e n i s h yellow-brown, X = p a l e yellow-brown, green;  absorption-Y = Z>X).  and network v e i n q u a r t z d i o r i t e s e x h i b i t  These c o n t a c t zones seriate texture,  t h e i r l a r g e s t c r y s t a l s b e i n g o f s i m i l a r s i z e to the phenoc r y s t s o f the normal p o r p h y r i t i c The  exact n o r t h e r n l i m i t  definitely established.  variety.  of the s t o c k has not  At an e l e v a t i o n o f 2700 f e e t i n  MacKay c r e e k q u a r t z d i o r i t e  i s i n v e r t i c a l contact with  T r i a s s i c v o l c a n i c r o c k s i n an o u t c r o p a p p r o x i m a t e l y feet  i n diameter.  stock. and of  This i s l i k e l y  o u t c r o p upstream from  equigranular quartz d i o r i t e .  twenty  the n o r t h c o n t a c t of the  Lower i n the creek o n l y T r i a s s i c  the c l o s e s t  been  The  r o c k s are  found,  t h i s c o n t a c t i s composed quartz d i o r i t e  at the  47 contact  is chilled  and  i s medium f i n e g r a i n e d .  o n l y l o c a t i o n found where the d i o r i t i c c r y s t a l s of at l e a s t The  rock  r o c k s do not  and  i n at l e a s t  i s nearly horizontal.  On  one  place  the West arm  the network v e i n s mentioned p r e v i o u s l y .  e a s t and  holes c o l l a r e d  i n the  areas  stock contact  S e v e r a l apophyses o f the  i n these  on  the  country The  a few  s e v e r a l hundred f e e t n o r t h of No.l  suggest t h a t the  contain  size.  zone i s i n p l a c e s composed of x e n o l i t h s of  of s e v e r a l d r i l l feet  millimeters  T r i a s s i c - p o r p h y r y contact  the C e n t r a l arm contact  two  T h i s i s the  results  hundred saddle  vicinities  i s steep.  s t o c k composed o f contaminated  p o r p h y r y i n t r u d e the Upper C r e t a c e o u s r o c k s on the  Central  arm. D e d u c t i o n of the t h i c k n e s s of the Upper C r e t a c e o u s sediments at Mt.  Washington d u r i n g the  c o u l d r e v e a l the  approximate minimum depth of overburden  e x i s t i n g above the and  Trent  River formations  in thickness feet  (p.21).  miles  sediments r e a c h c o u l d be  No.5  No.3  The  (1872,  p.5l)  formations  o f Courtenay and  b l o c k on the east f a u l t s may  fault  intruded.  s i d e of No.5  have o c c u r r e d  Comox feet  reports  4912  near Denman  the Nanaimo b a s i n These f a c t s  i n t e r p r e t e d as i n d i c a t i n g t h a t the c o v e r s t o c k was  stock  1600  10,000 f e e t i n t h i c k n e s s • ( p . 1 9 ) .  t h i c k when the  of the and  Richardson  south  intruded.  average a p p r o x i m a t e l y  of sediments o v e r l y i n g these  I s l a n d a few  was  s t o c k when i t was  i n t r u s i o n o f the  However, fault  and  of sediments foundering  between  No.l  s i n c e the main movement  at t h i s l o c a t i o n c o u l d be  i n t e r p r e t e d as  having  on  48.  been dilational (p.109).  Foundering of the roofs over  intrusions is suggested by Noble (1952, p.55)  as indicating  that the intrusions reached near to the surface so that the present position of the upper part of the Mt. Washington stock may have been very near to the surface when the stock was emplaced.  If this is true then i t follows that the Upper  Cretaceous sediments must have been thin during the intrusion of the stock. In the outer portions of the stock especially, i t is: traversed by numerous joints, but no definite pattern was observed. West Arm Intrusions.  Dykes, s i l l s , and irregular bodies  of quartz diorite porphyry intrude the Upper Cretaceous sediments of the West arm.  Along Pyrrhotite creek there are  several bodies of porphyry which appear to be faulted s i l l s and/or parts of a sheared dyke (map 1).  Many of these, and  other intrusions on the inner West arm exhibit some rounded, resorbed, and broken crystals.  However, an intrusion in Pyrr-  hotite creek and many porphyry bodies along No.l fault exhibit sub-cataclastic structure.  To the north and to the east of  No.2 fault the Triassic volcanic rocks contain some porphyry dykes. At most l o c a l i t i e s on the outer slopes of the West arm where the Upper Cretaceous-porphyry contacts have been observed, they are concordant. observed.  However, vertical contacts have been  The porphyry intrusions,in this area appear to be  fingers of the thicker and more continuous Main s i l l described in the following pages.  49  Main S i l l ,  The Main s i l l  i s the largest i n t r u s i o n , other  than the stock, at Mt. Washington.  I t s shape i s not  fully  known,partly because the present e r o s i o n a l surface i s below its  o r i g i n a l upper contacts, and i t may  not be a s i l l .  How-  ever, i t appears to be mainly f l a t - l y i n g and extends from the top of the East arm  through the East saddle, across the  Summit, and p o s s i b l y to the north end of the West arm where i t may sill It  wedge out i n several f i n g e r s .  Because much of the  has been eroded away, i t s o r i g i n a l extent i s unknown.  i s composed of porphyry, and at some places near i t s  contacts with older rocks, of contaminated or b i o t i t i z e d porphyry. A sample taken from the East arm contains quartz only i n its: matrix. at  Otherwise i t i s a t y p i c a l porphyry.  Also  found  the East arm are small round masses of porphyry about  two  inches i n diameter which stand about 3/8" above the porphyry enclosing i t but appeared to be i d e n t i c a l to i t .  Two  hundred  feet southwest of the Summit the s i l l contains what appear to be widely scattered amygdules of c h l o r i t e 3/8" i n diameter. On the lower west side of the Summit v e r t i c a l prismatic j o i n t i n g i s very conspicuous  and the rock contains some small  i n c l u s i o n s of shale. At the East saddle the Main s i l l unusual  features.  side of No.4  fault  Upper Cretaceous (map  possesses several  sediments on the east  1) which crosses the saddle have been  displaced downward several hundred feet with respect to those on the west s i d e .  However, the Main s i l l  west to the east sides of the saddle.  steps up from the  On the inner west side  50.  of  the s a d d l e where the Upper C r e t a c e o u s  downward, the Main s i l l planes  ( p l a t e IV) and  cuts steeply across t h e i r  s e v e r a l hundred f e e t  east at the summit o f the E a s t arm sill  is foliated.  sediments are  bedding  f u r t h e r to the  the lower  c o n t a c t of the  W i t h i n the s a d d l e the p o r p h y r y  p o s s e s s e s w e l l developed Murex Creek Dyke. f e e t wide by at l e a s t  flexed  o f the  sill  prismatic j o i n t s . A dyke of q u a r t z d i o r i t e p o r p h y r y  2000 f e e t l o n g and  t r e n d i n g ENE,  40  cuts  the T r i a s s i c v o l c a n i c r o c k s at about the 2500 f o o t l e v e l i n Murex c r e e k  (map  1).  I t i s of s i m i l a r c o m p o s i t i o n  common q u a r t z d i o r i t e p o r p h y r i e s but altered calcite,  to c h l o r i t e , e p i d o t e and  to the  i t s hornblende  i s highly  i t s p l a g i o c l a s e i s somewhat a l t e r e d sericite,  euhedral p y r i t e c r y s t a l s .  and  i t contains  to  poikilitic  Many of i t s q u a r t z p h e n o c r y s t s  are  rounded. Ice porphyry level  Creek Dyke and  Sills.  o v e r l i e s Upper C r e t a c e o u s  of q u a r t z  sandstone  diorite  at the 1500  i n Ice c r e e k i m i l e west of C o n s t i t u t i o n H i l l .  l a r g e r outcrops of porphyry present  s i l l s o v e r l y i n g sandstones  twenty f e e t wide c u t s T r i a s s i c  Constitution H i l l  are  one  and  one  rocks.  about e i g h t m i l e s  h a l f m i l e s wide o c c u r s i n the Upper  Cretaceous  r o c k s at C o n s t i t u t i o n H i l l .  least  feet  1000  dyke  (see p l a t e I I I , c r o s s s e c t i o n 2 ) .  e l o n g a t e body of q u a r t z d i o r i t e p o r p h y r y  In  Other  i n e l e v a t i o n i n Ice c r e e k a v e r t i c a l  s i m i l a r porphyry  l o n g and  foot  i n the g e n e r a l a r e a from $ to f i v e m i l e s south of i t .  At 2000 f e e t of  A sill  In p l a c e s i t i s at  thick.  mineral composition  and g e n e r a l appearance, the  An  51.  i n t e r i o r p o r t i o n s o f the i n t r u s i o n are i d e n t i c a l the normal p o r p h y r i e s .  At i t s northwest  groundmass i s a p h a n i t i c and  almost  At an e l e v a t i o n of about 850 of  Constitution H i l l  Cretaceous  the p o r p h y r y  sediments ( p l a t e V I I ) .  south i t extends  b o r d e r however, i t s  glassy. feet  on the northwest  side  c o n c o r d a n t l y o v e r l i e s Upper One  thousand  feet  further  below Wolfe Lake which i s at an e l e v a t i o n of  o n l y 624  feet.  locality  s t r i k e approximately  150  thick.  feet  to most of  The  Upper C r e t a c e o u s  The  r o c k s at the  n o r t h - s o u t h and  first  are o n l y about  i n t r u s i o n must e i t h e r extend  downward  i n t o the T r i a s s i c v o l c a n i c s , or e l s e t h e r e must be a f a u l t between the two exists  locations.  Such a f a u l t  almost  (p.85).  V e r t i c a l p r i s m a t i c j o i n t s a few  t o s e v e r a l hundred  l o n g are the main s t r u c t u r a l f e a t u r e s o f the Hill  porphyry.  On  the summit of C o n s t i t u t i o n  equant l o a v e s of bread well-developed  slightly 5.  Age  arched, and  Clapp porphyry  (plate XVII).  Hill  o c c u r w i t h i n the  resembling  At the n o r t h end  nearly f l a t - l y i n g  feet  Constitution  s h r i n k a g e (?) j o i n t s d i v i d e the rock i n t o b l o c k s  hill,  certainly  of the  j o i n t s which are  porphyry.  C o r r e l a t i o n Among the I n t r u s i o n s W i t h i n the (1917, p.304) has c o r r e l a t e d  which c u t s the Comox sandstone  Area  a body of d a e i t e near Cumberland  and  which i s s i m i l a r to the i n t r u s i o n s of the Mt. Washington a r e a , w i t h the E a r l y O l i g o c e n e  i n t r u s i v e s of the Sooke a r e a o f  s o u t h e a s t Vancouver I s l a n d .  Gunning (1930, p.64A) c o n s i d e r s :  t h a t i n a l l p r o b a b i l i t y a l l o f the i n t r u s i v e r o c k s of the Washington and  Mt.  Goss Lake a r e a s s h o u l d be p l a c e d i n the same  period. The  s i m i l a r i t y i n mineral composition  i n t r u s i o n s i n the Mt. suggests  o f a l l the  Washington-Constitution  a common s o u r c e .  Their textural  d i f f e r e n c e s appear to be due  or  Hill  area  structural  to t h e i r d i f f e r e n t  physical  forms and methods o f emplacement.  E.  B r e c c i a s and F r a c t u r e d and and  1.  2; c r o s s s e c t i o n s 1 and  General  2)  Statement.  B r e c c i a s and related  B r e c c i a t e d Rocks (see maps 1  f r a c t u r e d and b r e c c i a t e d r o c k s  i n o r i g i n and  age  to the d i o r i t i c  i n l a r g e q u a n t i t i e s at Mt. which averages  1000  feet  Washington.  i n w i d t h and  i n t r u s i o n s are  found  They occur i n a zone extends  more than 4000  f e e t n o r t h o f G l a c i e r Lake a l o n g the West arm. c o i n c i d e s approximately  closely  T h i s zone  w i t h the p o s i t i o n of the Upper  Cretaceous-Triassic unconformity.  The  r o c k s are  d i v i d e d i n t o t h r e e t y p e s on the b a s i s o f t h e i r  readily  physical  characteristics. Both of the f i r s t  two  t y p e s are composed of r o c k  fragments s e t i n a comminuted m a t r i x . first  t y p e , which w i l l  However, v/hereas  be named the Murray b r e c c i a ,  g r e a t l y i n appearance from p l a c e to p l a c e and g e n e r a l l y b i o t i t e - r i c h , most o f the second be named the Washington b r e c c i a , contains a magnetite-rich matrix. Murray b r e c c i a may  the  varies  i t s matrix is;  t y p e , which  will  i s s i m i l a r i n appearance A l s o , fragments of the  be w e l l rounded or a n g u l a r and  very  few  are s l a b - s h a p e d whereas many fragments o f the Washington  and  53.  b r e c c i a are  s l a b - s h a p e d and  not  many are  N e a r l y c o n t i n u o u s o u t c r o p s of the found a l o n g the of g r e a t e r  entire length  than 4600 f e e t .  c e r t a i n l y parts  rounded.  Murray b r e c c i a  of B r e c c i a  ridge  at  These o u t c r o p s are  o f a p i p e - s h a p e d mass.  b r e c c i a s i m i l a r to the  well  are  elevations  almost  A small  body  of  Murray b r e c c i a i s p r e s e n t i n G l a c i e r  creek. The  Washington b r e c c i a o u t c r o p s as  a l o n g much of the  east  n e a r - v e r t i c a l contact The  edge o f B r e c c i a w i t h the  Murray  Murray b r e c c i a i s o l d e r  Washington s t o c k .  than the  Rock b u r s t i n g  within  a dilational  by  i n t r u s i o n of the  the  i b l e f o r the  s t o c k may  Fractured  and  brecciated  ?  collapse  formed or  and  n o r t h of the  S m a l l a r e a s of b r e c c i a t e d  zone, but r o c k s and  v e i n l e t s of p o r p h y r y or of s e v e r a l constitute The  to  stock.  third  the  i n a zone  The  outer  Rocks of a l l  p o r p h y r y i s most common. rocks cross  cut  by  net  t y p e s of m i n e r a l s  zone.  o r i g i n s of the three t y p e s of r o c k s d e s c r i b e d  s e c t i o n are the  most of the  found  the  Washington b r e c c i a s  a r b i t r a r i l y chosen.  p r e s e n t i n the  reactivated  Washington b r e c c i a .  which extends a l o n g the west s i d e of the  t y p e s are  the  rock  r o c k s which c o n s t i t u t e  Murray and  l i m i t s of t h i s zone are  of  and  have been l a r g e l y r e s p o n s -  type o f rocks: c o n s i d e r e d i n t h i s s e c t i o n are east  breccia  Wash.ri /on  i n t r u s i o n above  and  f r a c t u r e which was  development of the  r i d g e where i t i s i n breccia.  appears to have been formed l a r g e l y by Mt.  a p i p e - s h a p e d mass  in this  dealt with i n a l a t e r chapter e n t i t l e d "Origin  Breccias".  of  54. 2.  Murray B r e c c i a Field  crops  Occurrence and D e s c r i p t i o n .  almost c o n t i n u o u s l y  on B r e c c i a r i d g e  Murray b r e c c i a out-  f o r a l e n g t h o f more than 2000 f e e t  (plate XII).  The o u t l i n e o f the o u t e r  of the exposures i s t h a t o f an e l o n g a t e d parallel  t o the l e n g t h o f the r i d g e .  the east  contact with b i o t i t i z e d  On i t s n o r t h porphyry.  contact with  i t i s i n vertical  limit  o f the b r e c c i a i t  i n c o n t a c t w i t h metamorphosed a r g i l l i t e .  possibility ever,  that t h i s a r g i l l i t e  the c o n t a c t  likely  Washing-  At a l o c a t i o n on the west  s i d e o f the r i d g e near the n o r t h e r n is  600 f e e t .  i t i s i n near v e r t i c a l  ton b r e c c i a (see p . g o ) .  NNW  The maximum known w i d t h  of the b r e c c i a zone i s a p p r o x i m a t e l y To  oval trending  limit  There i s a  c o u l d be an i n c l u s i o n .  represents  the w e s t e r n l i m i t  Howo f the  zone i n t h i s p a r t i c u l a r l o c a t i o n s i n c e the o n l y i n d i c a t i o n s of bedrock on the upper p o r t i o n s o f the s l o p e s t o t h e west o f the e n t i r e zone a r e l i t t l e  disturbed boulders  On  s i d e s the zone i s almost  i t s south  i n contact  and s o u t h e a s t  with b i o t i t i z e d  of porphyry. certainly  porphyry.  At an e l e v a t i o n o f about 4400 f e e t i n G l a c i e r c r e e k ,  a  l a y e r o f b r e c c i a s i m i l a r i n appearance to the Murray b r e c c i a and  possibly thirty  At one p l a c e  f e e t t h i c k , o v e r l i e s green-grey porphyry.  the c o n t a c t  appears t o d i p about 3 5 °  Other s m a l l e r zones o f s i m i l a r b r e c c i a o c c u r  southeast.  about two  hundred f e e t upstream. The  g e n e r a l appearance o f the Murray b r e c c i a v a r i e s from  p l a c e to p l a c e  on B r e c c i a r i d g e .  Some o u t c r o p s  contain  fragments o f p o r p h y r y o n l y , whereas o t h e r s a r e composed o f a  55.  P l a t e X I I - B r e c c i a r i d g e taken from the C e n t r a l looking northwest.  arm,  P l a t e X I I I - R u b b l y Murray b r e c c i a . Sandstone fragment above k n i f e , p o r p h y r y fragment above and t o r i g h t o f k n i f e . Dark-rimmed s e d i m e n t s throughout.  56. heterogeneous mixture of shale, sandstone, and porphyryfragments. colour.  The matrixes of the breccias vary in amount and  These colour differences are due to the different  proportions of the various constituents and to the varying degrees of alteration.  Despite their wide variations in  appearance, there appear to be gradations among the different types. A rubbly Murray breccia is well exposed about 200 feet south of the small pond on the ridge.  It is grey and contains  angular and rounded fragments of white porphyry, grey sandstone, dark grey shale, and broken crystals of quartz and feldspar (plate XIII).  The rock fragments vary in size from  microscopic to about six inches in diameter.  Most of the  fragments less than five mm. in size are plagioclase and quartz.  The shale and sandstone fragments possess dark  altered rims up to f of an inch thick, whereas the porphyry fragments appear to be unaltered.  No layering was observed  in this type of breccia. The breccia described above appears to grade to the south into another type of breccia which possesses a more d i o r i t i c appearance (plate XIV).  It contains fragments of porphyry  almost exclusively and most of these are rounded to some degree.  It also contains d i o r i t i c material which occurs in  streaks,  some of which are arranged in a swirling manner.  Some hornblende crystals are found in the matrix.  In some  places this breccia contains a very crude but discontinuous layering which i s partly expressed by the regular arrangement of d i o r i t i c streaks, and partly by the different  57.  P l a t e XV - C o n t a c t o f p e b b l y Murray b r e c c i a w i t h b l o c k at s o u t h end o f B r e c c i a r i d g e .  argillite  58  p r o p o r t i o n s o f p o r p h y r y fragments w i t h i n a d j a c e n t l a y e r s . However, even w i t h i n the i n d i v i d u a l i n d i s t i n c t fragment c o n t e n t v a r i e s c o n s i d e r a b l y .  The l a y e r i n g  i n d i p from 45° SSW t o 75° SSW w i t h i n 100 f e e t outcrop.  l a y e r s the varies  i n a single  I n the a d j a c e n t o u t c r o p s i m i l a r l a y e r i n g  varies  i n d i p from 40° SSW t o 80° -NNE, and i n an o u t c r o p immedi a t e l y t o the south o f the l a s t  the l a y e r i n g i s bent and  c o n t o r t e d and v a r i e s i n d i p from h o r i z o n t a l t o v e r t i c a l w i t h i n a few f e e t .  One l a y e r d i p p i n g about 40° SSW c o n t a i n s  a c o n c e n t r a t i o n o f round fragments o f p o r p h y r y i n the vicinity  o f i t s lower but i n d i s t i n c t  but f i n e r g r a i n e d b r e c c i a . fold  i s about  contact with  The c o n t a c t  similar  i s drag f o l d e d .  This  s i x i n c h e s wide and the p e b b l e s appear to be  s w i r l e d about i n i t s v i c i n i t y . Host o f the Murray b r e c c i a o f the n o r t h , v/est and south p o r t i o n s o f the r i d g e i s somewhat s i m i l a r i n appearance to conglomerate and c o n s i s t s of e v e n l y d i s t r i b u t e d and w e l l rounded r o c k fragments up t o e i g h t  i n c h e s i n d i a m e t e r but  a v e r a g i n g about one t o one h a l f i n c h e s , s e t i n a b r o w n i s h g r e y m a t r i x which has the appearance  o f a h i g h l y contaminated  and b i o t i t i z e d  P o r p h y r y fragments  porphyry (plate XV).  predominate. At tv/o l o c a t i o n s near the n o r t h end o f B r e c c i a r i d g e the b r e c c i a i s c u t by v e r t i c a l map 2 ) .  One o f these i s about 25 f e e t wide and f o l l o w s a l o n g  p a r t o f the c o n t a c t breccia.  q u a r t z d i o r i t e p o r p h y r y dykes (see  o f the Washington b r e c c i a w i t h the Murray  Near the c e n t e r o f the r i d g e t h e r e i s a cream  c o l o u r e d p o r p h y r y mass c o n t a i n i n g round masses o f p o r p h y r y  59. which a r e a p p r o x i m a t e l y one i n c o m p o s i t i o n to the r e s t structure. it  The  foot  o f the mass but p o s s e s s b r e a d c r u s t  a t t i t u d e o f t h i s p o r p h y r y mass i s unknown but  appears to be f l a t - l y i n g .  breccia also traverse northwest  i n d i a m e t e r and a r e s i m i l a r  peripheral  Small v e i n s o f m a g n e t i t e - r i c h  the Murray  b r e c c i a i n i t s n o r t h e a s t and  regions.  Large i n c l u s i o n s o f Upper C r e t a c e o u s sediments i n the o u t e r p o r t i o n s o f the b r e c c i a have been o b s e r v e d .  One i s  twenty  pebble  f e e t . i n diameter and  conglomerate.  i s composed o f rounded  I t i s near the n o r t h end  west s i d e .  Near to i t are what appear  argillite.  At the n o r t h end  i n c l u s i o n s of a r g i l l i t e  a v e r a g i n g about  b r e c c i a from the s o u t h e a s t w a l l .  argillite  three feet  and a r g i l l i t e  diameter which d i p s 55° west, appears  which  to be l e n s e s o f  o f the r i d g e t h e r e a r e  A foundered b l o c k o f sandstone  breccia s i l l  of the r i d g e on the  200  several i n diameter.  feet i n  to p r o j e c t  into  the  I t i s c u t by a p e b b l y  i s a p p r o x i m a t e l y one  f o o t wide.  The  o f t h i s b l o c k i s s l i g h t l y f o l i a t e d where i t i s i n  c o n t a c t w i t h the b r e c c i a . At  the n o r t h end o f the r i d g e where the b r e c c i a i s i n  sharp v e r t i c a l closely  contact with b i o t i t i z e d  jointed parallel  p o r p h y r y the l a t t e r i s ;  to the c o n t a c t .  W i t h i n the  f i f t e e n f e e t a d j a c e n t t o the c o n t a c t , the b r e c c i a  first  itself  changes g r a d a t i o n a l l y from a r o c k w i t h i r r e g u l a r  shaped  i n c l u s i o n s of a r g i l l i t e  fragments  set  and  sub-rounded  i n a m a t r i x which has the appearance  porphyry  of b i o t i t i z e d  contaminated p o r p h y r y , to a s i m i l a r r o c k c o n t a i n i n g a l a r g e r p r o p o r t i o n o f i n c l u s i o n s and more f u l l y  rounded  fragments.  60.  T h i s change i n the c h a r a c t e r that  i t cross-cuts The  the  east  o f the b r e c c i a c l e a r l y  the p o r p h y r y .  o u t e r east  s i d e o f a ledge about t h i r t y f e e t wide on  edge o f B r e c c i a  ridge  b e a r i n g Washington b r e c c i a .  i s composed o f m a g n e t i t e -  The west s i d e o f the same l e d g e  i s composed o f Murray b r e c c i a c o n t a i n i n g magnetite-bearing b r e c c i a . jointed p a r a l l e l to the west.  indicates  only  a few v e i n s o f  Both r o c k s a r e sheared or c l o s e l y  to t h e i r mutual c o n t a c t  Between the two b r e c c i a s  which d i p s  steeply  i s a complex zone  about t e n f e e t wide c o n s i s t i n g o f numerous dark and l i g h t veins all  o f p o r p h y r y , and v e i n s  of magnetite-bearing  o f which are c u t t i n g Murray Several  length  breccia.  w i d e l y spaced f r a c t u r e s  of Breccia  ridge  breccia,  trending  a c r o s s the  appear to have broken the Murray  b r e c c i a i n t o b l o c k s which have moved v e r t i c a l l y r e l a t i v e t o one  another. A system o f j o i n t s v e r y s i m i l a r t o those on the summit  of C o n s t i t u t i o n into nearly The  Hill,  b r e a k s the b r e c c i a at some  equant b l o c k s  localities  (plate X V I ) .  exposures o f b r e c c i a i n the G l a c i e r c r e e k a r e a a r e  s i m i l a r i n appearance and c o m p o s i t i o n t o some o f the Murray breccia of Breccia  ridge.  The lower c o n t a c t  zone o f b r e c c i a appears t o d i p 3 5 ° S. abrupt change a t the c o n t a c t hornblende q u a r t z p l a g i o c l a s e breccia containing argillite, similar  o f the lowest  A l t h o u g h t h e r e i s an  from the u n d e r l y i n g  grey-green  porphyry t o s i m i l a r  a n g u l a r o r rounded p o r p h y r y ,  coloured  quartzite,  and a n d e s i t e ( ? ) fragments, the m a t r i x o f one i s  i n appearance t o the m a t r i x o f the o t h e r as seen i n  61.  P l a t e X V I I - S h r i n k a g e ( ? ) j o i n t s i n the q u a r t z d i o r i t e p o r p h y r y on the summit o f C o n s t i t u t i o n H i l l .  62.  the o u t c r o p .  A l s o , t h e r e i s no  d i s c o n t i n u i t y between the two  s u r f a c e o f p a r t i n g or  abrupt  rocks.  Microscopic Description.  D e s p i t e t h e i r wide  variations  i n megascopic appearance, the m i c r o s c o p i c s t r u c t u r e s of the v a r i o u s Murray b r e c c i a s are almost  identical.  On B r e c c i a  r i d g e most o f them are h i g h l y b i o t i t i z e d , but altered  or a n g u l a r fragments of porphyry,  volcanic  r o c k s are p r e s e n t , but are v e r y r a r e . approximately  one  s u b - c a t a c l a s t i c porphyry generally h i g h l y b i o t i t i z e d than those obscure.  indicative The  and  one  h a l f inches i n t o be  diameter.  somewhat comminuted  However, because i t i s  (p.77) i t s c h a r a c t e r i s t i c s ,  fragments, ragged  fragments to e x t r e m e l y  The porphyry.  some q u a r t z c r y s t a l  XX,  and  other  and  fragments,  shreds o f p o i k i l i t i c  hornthe  fine grained material (plates  XXI).  m a j o r i t y of the l a r g e r fragments are q u a r t z  diorite  Most such fragments have an a p h a n i t i c m a t r i x . fragments w i t h q u a r t z i n t h e i r m a t r i x e s  more common than those w i t h q u a r t z p h e n o c r y s t s . these fragments t r a c h i t i c parallel  fragments  There i s a complete g r a d a t i o n i n s i z e from  X V I I I , XIX,  and  of i t s c a t a c l a s t i c n a t u r e , are r a t h e r  i n most c a s e s , a few  blende.  (p.45).  The  m a t r i x c o n s i s t s m a i n l y of a n g u l a r r o c k  plagioclase crystal  Porphyry  siltstone,  Fragments of T r i a s s i c  In some specimens the m a t r i x appears  largest  to c o n t a i n rounded  sandstone,  s h a l e , i n t h a t o r d e r o f abundance.  and  less  specimens s t u d i e d are d e s c r i b e d h e r e .  In t h i n s e c t i o n the r o c k i s observed  average  the  o n l y , are In some of  s t r u c t u r e i s e x h i b i t e d by the  arrangement of p l a g i o c l a s e .  One  fragment  sub  contains  63.  P l a t e XIX - Same as p l a t e X V I I I but t a k e n w i t h c r o s s e d n i c o l s  64.  a c r y s t a l o f p l a g i o c l a s e at i t s margin which i s o n l y  slightly  rounded where i t p r o j e c t s i n t o  and  Many o f the s m a l l e r porphyry  the m a t r i x  ( p l a t e s XX  fragments are composed of  XXI).  single  p l a g i o c l a s e c r y s t a l s w i t h s m a l l amounts o f porphyry  matrix  adhering  porphyry  matrix  to them.  Other s m a l l fragments c o n s i s t  of  only.  Plagioclase oscillatory  ( 26-52^ An  zoning.  One  e x h i b i t s approximately  i  n  P  t t i e  o r  P y y fragments shows; n  c r y s t a l s t u d i e d under the  nine d i s t i n c t  f i v e e x h i b i t normal type z o n i n g and 2 6  _  5 2  respectively.  ,  An  3 8  _  5 2  microscope  c o n c e n t r i c zones, a l l o f  which are o f the same o r d e r o f s i z e .  imately A n  r  The  o u t e r zones, one  t h e i r ranges are  , An^^g, An  4 4 - 5 2  'and  A*  4 8  to  approx-  _  5 2  Zone s i x i s zoned r e v e r s e l y w i t h a range o f  o n l y about An^ __^Q. 2  Zones seven,  are not d i s t i n c t l y zoned, but  e i g h t , and  together  core zone n i n e  they form a d i s c o n -  tinuous; zone of the r e v e r s e type whose t h r e e p o r t i o n s are composed o f a p p r o x i m a t e l y  An^,  An^g  and  An^  There are u n c o n f o r m i t i e s between zones two and  s i x , and  and  three,  p o s s i b l y a l s o between zones seven and  zones e i g h t and The  respectively.  g  eight  and  nine.  comminuted m a t r i x o f the b r e c c i a s generally c o n s t i t u t e s  approximately  50%  of the r o c k .  I t s components show  of s w i r l i n g and much of i t i s s t r e a m l i n e d around the fragments ( p l a t e XX). blende,  five  larger  B e s i d e s p l a g i o c l a s e , q u a r t z , and  there i s considerable b i o t i t e ,  chlorite.  evidence  Hematite, magnetite,  epidote, s e r i c i t e  p y r i t e , and  hornand  sphene are a l s o  present• An o s c i l l a t o r y - z o n e d p l a g i o c l a s e c r y s t a l  (An,,- u ? ) from  65  P l a t e XX - P h o t o m i c r o g r a p h o f Murray b r e c c i a from B r e c c i a r i d g e showing p l a g i o c l a s e c r y s t a l o f p o r p h y r y fragment p r o j e c t i n g i n t o comminuted m a t r i x , (plain l i g h t , xl6)  P l a t e XXI - As p l a t e XX  only taken w i t h crossed  nicols.  66  the m a t r i x  o f the b r e c c i a c o n t a i n s f o u r d i s t i n c t  similar size. The  third  one, A n  Only  zones o f  the o u t e r N o . l zone shows r e v e r s e  zoning.  zone c o n t a i n s many s m a l l e r zones w i t h i n i t .  Zones  two, t h r e e , and f o u r have ranges o f a p p r o x i m a t e l y  43-38»  ^35-40•  A n  36-52»  i s a sharp u n c o n f o r m i t y  a  n  d  An  46-50:  r e s  P ctively.  There  e  between zones one and two.  Another p l a g i o c l a s e c r y s t a l  i n the m a t r i x i s f a i r l y  smoothly zoned i n a normal manner and i t s range i s about A n  28-65*  3.  Washington B r e c c i a Field  outcrops  Occurrence  Washington b r e c c i a  a l o n g the e a s t s i d e o f B r e c c i a r i d g e f o r a l e n g t h o f  about 1200 f e e t fairly  and D e s c r i p t i o n .  sharp  i n at l e a s t  (maps 1 and 2 ) . On i t s west s i d e i t i s i n  and near v e r t i c a l c o n t a c t w i t h Murray b r e c c i a one l o c a l i t y  (see p . g o ) .  To the east i t s  c o n t a c t s w i t h the b r e c c i a t e d r o c k s o f the b o r d e r are i n d i s t i n c t  and may be g r a d a t i o n a l .  l i m i t s are f a i r l y The  o f the s t o c k  To the south i t s  closely established.  b e s t exposure o f Washington b r e c c i a i s a p i p e - l i k e  body a p p r o x i m a t e l y  250 f e e t h i g h at the n o r t h e a s t  Breccia ridge (plate XXII). are common i n t h i s mass.  spaced  horizontal joints  On i t s n o r t h edge i t c o n t a i n s  spaced  to  i t s unexposed c o n t a c t w i t h the sediments and p o r p h y r i e s immediately  t r e n d s NNW  s h e e t - j o i n t s t r e n d i n g ENE p r o b a b l y  close-  ly  found  vertical  Widely  end o f  t o the n o r t h .  parallel  the Murray b r e c c i a . approximately  t o those Vertical  E-W a r e p r e s e n t  parallel  Another s i m i l a r s e t o f j o i n t s  found sheet  a l o n g i t s west c o n t a c t  with  joints trending  at the south edge o f t h i s p i p e -  67.  Plate  XXII  Outcrop o f part o f the p i p e - l i k e mass o f Washington b r e c c i a on the n o r t h e a s t edge o f Breccia ridge. Looki n g s o u t h w e s t . Snowc o v e r e d t a l u s and fractures.  Plate  XXIII  Close-up of boulder of Washington b r e c c i a on t a l u s s l o p e shown i n p l a t e X X I I . Strewn o u t fragments along bottom. Most f r a g m e n t s a r e s l a b shaped b u t some p o r phyry fragments are rounded.  68  l i k e mass o f Washington  breccia.  The huge b o u l d e r s and the c l i f f  o u t c r o p s o f the p i p e -  l i k e mass a r e composed o f s l a b - l i k e and rounded fragments o f light  g r e y p o r p h y r y and b l e a c h e d sediments ( p l a t e X X I I I ) .  many i n s t a n c e s the two t y p e s o c c u r s i d e by s i d e . the  In  In g e n e r a l  a n g u l a r s l a b - s h a p e d fragments a r e b l e a c h e d sediments  whereas the p o r p h y r y fragments are equant, and a r e at l e a s t inpart  rounded.  They a r e v a r i o u s s i z e s and a r e s e t i n a  dark b l u i s h g r e y h i g h l y magnetic m a t r i x c o n t a i n i n g a n g u l a r p a r t i c l e s o f p o r p h y r y o r sediment. p r o b a b l y average about but  The fragments  t h r e e i n c h e s i n d i a m e t e r or l e n g t h  one p o r p h y r y fragment  talus boulder.  finer  t h r e e f e e t wide was o b s e r v e d i n a  Many spaces between many fragments a r e  f i l l e d w i t h green amphibole.  C l o s e p a c k i n g o f the s l a b - l i k e  and rounded fragments i s common.  Between assemblages o f  these c l o s e packed fragments, m a t r i x m a t e r i a l and s m a l l e r a n g u l a r o r rounded fragments a r e strewn out i n p a r a l l e l arrangement  (plate XXIII).  f a i r l y massive.  Most specimens o f the b r e c c i a a r e  Many c o n t a i n c h a l c o p y r i t e and m a l a c h i t e a l o n g  f r a c t u r e s or on the edges o f f r a g m e n t s . Material similar b r e c c i a but d e f i c i e n t  to the m a t r i x e s o f the Washington i n magnetite c o n t a i n s r a r e  rounded  p o r p h y r y fragments, and o c c u r s on the n o r t h and s o u t h edges of  the p i p e - l i k e mass.  I t i s strewn out p a r a l l e l  j o i n t s which t r a v e r s e i t and which a r e s i m i l a r nearby i n the Washington fairly  breccia.  t o sheet  to those  There appears t o be a  sharp but g r a d a t i o n a l c o n t a c t between the V/ashington  b r e c c i a and t h i s f i n e r  material.  6 9  Microscopic Description.  In the porphyry fragments the  plagioclase phenocrysts are of similar composition to those of the normal porphyries.  They are generally s l i g h t l y altered  to epidote, kaolin(?), and c a l c i t e , in certain zones and along irregular fractures and cleavage planes.  Fine curved  stringers of hematite which join one another criss cross the porphyry fragments.  Hornblende crystals are completely  replaced by magnetite. The angular bleached sediment fragments studied are extremely fine grained but a few scattered angular grains of quartz are s t i l l v i s i b l e (plate XXIV).  These fragments  appear to be highly altered to clay minerals or pale c h l o r i t e . Around their edges i s a narrow halo of limonite which fades out inward away from the magnetite-rich matrix of the breccia. Magnetite clearly replaces the finer material of the matrix and the fringes of the fragments.  In some places the  matrix i s almost" completely replaced by magnetite. also completely f i l l  It may  the intervening areas between close-  f i t t i n g , straight-edged  fragments, or i t may occur fringing  the fragments, with a c t i n o l i t i c hornblende in the cores of the areas between the fragments.  In some specimens the only  mineral in such inter-fragment areas i s a c t i n o l i t i c hornblende. Magnetite also occurs as small veinlets composed of strings of interlocking globules.  These veinlets may cross  an entire fragment or may wedge out part way through the fragment.  They possess halos of limonite which join with  those around the edges of the fragments.  • • 70.  P l a t e XXIV - P h o t o m i c r o g r a p h o f W a s h i n g t o n b r e c c i a . Angular b l e a c h e d s h a l e ( ? ) f r a g m e n t s on r i g h t , porphyryfragment on l e f t , b l a c k i s m a g n e t i t e , g r e y i s a c t i n o l i t i c hornblende. V e i n l e t of c a l c i t e , c h l o r i t e , e p i d o t e , ( p l a i n l i g h t , xl6)  P l a t e XXV  - S i l i c i f i e d W a s h i n g t o n ( ? ) b r e c c i a from t r e n c h e s SE o f p i p e - l i k e o u t c r o p shown i n p l a t e X X I I . F a i n t s i l i c i f i e d f r a g m e n t s i n c e n t e r , q u a r t z vug upper r i g h t , ( c r o s s e d n i c o l s , xl6)  71.  In one and  section studied, a veinlet  of c h l o r i t e ,  e p i d o t e c r o s s e s the e n t i r e r o c k , and  across every other mineral XXIV).  calcite,  i n so d o i n g  or fragment i n the r o c k  cuts  (plate  Where i t c r o s s e s the groundmass o f a p o r p h y r y  fragment i t i s composed of a l l t h r e e m i n e r a l s , but where i t crosses p l a g i o c l a s e c r y s t a l s i t contains only c a l c i t e epidote.  In b l e a c h e d  o n l y , and  s m a l l b l o b s of c a l c i t e  s h a l e fragments i t c o n s i s t s o f o c c u r r i n g i n the  near the v e i n l e t g r a d u a l l y d i m i n i s h i n s i z e and from i t .  Where i t i n t e r s e c t s a c t i n o l i t i c  composed of c h l o r i t e  and calcite  fragment  numbers away  hornblende i t i s  o n l y , and where a c t i n o l i t i c  hornblende  and m a g n e t i t e o c c u r r i n g s i d e by s i d e are d i s s e c t e d by veinlet  i t c o n t a i n s o n l y c h l o r i t e and  veinlet  c r o s s - c u t s every m i n e r a l  epidote.  this  Although  i n the r o c k , at one  i s cut o f f by a magnetite s t r i n g e r .  this  place i t  Narrower v e i n l e t s  t r a v e r s i n g the groundmass of the p o r p h y r i e s c o n t a i n o n l y chlorite. In t r e n c h e s silicified 4-.  to the s o u t h  of the p i p e - l i k e mass  and vuggy W a ^ g M ? ) b r e c c i a i s found  F r a c t u r e d and the Mt.  B r e c c i a t e d Rocks A l o n g  Washington  extremely  (plate  the West Contact  irregular  volcanics. Along  of P y r r h o t i t e c r e e k  feet  t h e r e i s an  shaped zone c o n s i s t i n g of d i s c o n t i n u o u s  h i g h l y f r a c t u r e d and  of  Stock.  From G l a c i e r Lake n o r t h to a l o c a t i o n about 700 east o f the upper end  XXV).  areas  b r e c c i a t e d p o r p h y r i e s , sediments,  T h i s zone i s a p p r o x i m a t e l y  300  feet  of and  wide.  the west s i d e of t h i s zone on the f r i n g e s of  s t o c k , t h e r e are numerous systems of net v e i n l e t s .  The  the  72. v e i n l e t s are about fe i n c h wide and  are composed o f p o r p h y r y  i n v o l c a n i c r o c k s , or of a c t i n o l i t i c porphyry.  hornblende i n the  stock  Some x e n o l i t h s of c o u n t r y r o c k which appear to  have been o n l y s l i g h t l y d i s p l a c e d from t h e i r p o s i t i o n s are found i m a t e l y 200  feet  i n the b o r d e r s  original  of the s t o c k .  Approx-  from the e a s t s i d e o f the zone, the  r o c k s are h i g h l y f r a c t u r e d , but generally l i t t l e d i s t u r b e d .  various  the b l o c k s so formed  are  As a r e s u l t , t h e r e are net  l e t s of p o r p h y r y , a c t i n o l i t i c magnetic b r e c c i a w i t h  vein-  angular  fragments a v e r a g i n g  l e s s than fe i n c h i n l e n g t h , q u a r t z  sericite, chlorite,  s u l p h i d e s , or c o m b i n a t i o n s of  and  these  m a t e r i a l s , c r i s s - c r o s s i n g the p o r p h y r i e s , sediments,  and  volcanics. F u r t h e r west a l o n g a l i n e c o i n c i d i n g w i t h extension of P y r r h o t i t e creek brecciated, s i l i c i f i e d ,  and  the  t h e r e i s a zone of  southward  finely  m i n e r a l i z e d r o c k s of v a r i o u s  types.  F.  Metamorphism and  1.  General The  is cut  Alteration  Statement  o n l y type  of metamorphism d e a l t w i t h  the v e r y l i m i t e d c o n t a c t or thermal by  the d i o r i t i c  heat  T h i s metamorphism i s caused  o f the i n t r u s i o n s and  and m i n e r a l o g i c a l changes i n the host contacts.  I t s e f f e c t s are d i f f i c u l t  hydrothermal  metamorphism of  rocks  i n t r u s i o n s , or o f i n c l u s i o n s i n the  i n t r u s i o n s or b r e c c i a s . gases and  in this thesis  alteration.  i s expressed  by  r o c k s near the to d i s t i n g u i s h  by chemical intrusive from  73. The  r e s u l t s o f magnetic p r e s s u r e — i n d u r a t i o n and  f o l i a t i o n o f the host r o c k s a l o n g i n t r u s i v e been d e s c r i b e d p r e v i o u s l y under headings  contacts—-have  C, D and E o f t h i s  chapter. A l t e r a t i o n s c o n s i d e r e d f o r the most p a r t t o be d e u t e r i c , 1. e.  - p l a g i o c l a s e p a r t i a l l y r e p l a c e d by s e r i c i t e  have been d e s c r i b e d p r e v i o u s l y (p«4-l of  ).  Intense  or quartz, alterations  the r o c k s i n a r e a s which do not n e c e s s a r i l y c o i n c i d e w i t h  the zones o f metamorphosed r o c k s a l o n g i n t r u s i v e c o n t a c t s a r e found  i n the C e n t r a l arm-West arm a r e a o f Mt. Washington, an  area of copper-gold m i n e r a l i z a t i o n . d e s c r i b e d under the h e a d i n g  These a l t e r a t i o n s a r e  "Alteration".  They i n v o l v e  c o n s i d e r a b l e a d d i t i o n o f new m a t e r i a l as w e l l as r e d i s t r i b u t i o n and r e c r y s t a l l i z a t i o n o f o r i g i n a l m a t e r i a l i n the altered rocks. due  The f o r m a t i o n o f p y r i t e and magnetite  may be  i n p a r t t o a l t e r a t i o n but t h i s s e c t i o n d e a l s o n l y w i t h  the common a l t e r a t i o n s which a r e g e n e r a l l y c o n s i d e r e d t o be of  hydrothermal Although  origin.  a l l the i n t e n s e a l t e r a t i o n s o c c u r i n c l o s e  p r o x i m i t y t o the c o p p e r - b e a r i n g r o c k s o f the West arm, silicification,  and p o s s i b l y s e r i c i t i z a t i o n ,  o n l y , show c l o s e  g e n e t i c r e l a t i o n s h i p s " t o c o p p e r - g o l d m i n e r a l i z a t i o n i n the sir© £t o 2.  Metamorphism Thermal metamorphism i s pronounced o n l y i n the immediate  vicinity  o f the Mt. Washington s t o c k , but even here  distinct  changes i n the appearance o f the i n t r u d e d r o c k s are generally visible  f o r l e s s than t e n f e e t .  Dykes and s i l l s  emanating  74.  from the s t o c k appear rocks.  t o have had  little  effect  on t h e i r host  However, most o f the Upper G r e t a c e o u s sediments are  i n d u r a t e d and intrusions.  t h i s may  nearby  C o n v e r s i o n o f sandstones to q u a r t z i t e s and o f  s h a l e s to a r g i l l i t e s  (p.'34-) may  e f f e c t s caused by the The  have been p a r t l y caused by  f i n e r grained  be due  i n part  to t h e r m a l  intrusions. sediments a r e more g r e a t l y a f f e c t e d  the i n t r u s i o n s t h a n are the c o a r s e - g r a i n e d s e d i m e n t s .  by  Thermal  e f f e c t s caused by the p o r p h y r y of the Summit are shown by the dark r i m s i n the sandstones a l o n g t h e i r c o n t a c t s w i t h porphyry. and  The  dark zone  i s generally l e s s than f i v e  i s caused by the r e c r y s t a l l i z a t i o n  m a t r i x e s o f the sandstones to b i o t i t e argillite,  and  siltstone  o f the  and c h l o r i t e .  ities  especially,  q u a r t z , up to 1 / 8 " original  scattered d e t r i t a l  In two  i n the  to rounded  of B r e c c i a ridge  One (map  o f these l o c a l i t i e s i s 2)  and  the o t h e r i s at  the l a r g e b l o c k o f Upper C r e t a c e o u s sediments which the Murray  and  Other g r a i n s o f the same  m i n e r a l s appear t o be u n a f f e c t e d .  into  local-  grains of f e l d s p a r  i n d i a m e t e r , which were d e p o s i t e d  c l o t s or to s i n g l e c r y s t a l s .  breccia,  breccia  a r g i l l a c e o u s sediment, are r e c r y s t a l l i z e d  on the west s i d e  Shale,  fragments w i t h i n the Murray  i n a s i m i l a r manner.  wide  argillaceous  and s i m i l a r r o c k s at the p e r i p h e r y o f the Murray ( p l a t e XV), a r e darkened  feet  b r e c c i a on the southwest  s i d e o f the  projects ridge.  The m a t r i x e s o f such r o c k s , as seen under the m i c r o s c o p e , are l a r g e l y composed o f mosaics o f f i n e l y biotite  and c h l o r i t e .  Feldspathic  i n t e r l o c k i n g grains of  s a n d s t o n e s . o v e r l y i n g the  a r g i l l a c e o u s r o c k s at b o t h l o c a l i t i e s  are h a r d l y a f f e c t e d  by  75 the heat At  o f the igneous  rocks.  the lower c o n t a c t s o f a s i l l  Main s i l l  i n the East  i n Ice creek  s a d d l e , the f i n e g r a i n e d  have been v i s i b l y b l e a c h e d  and o f the  sandstones:  f o r a d i s t a n c e o f o n l y a few  inches. Sandstones and s h a l e s i n t r u d e d by q u a r t z  diorite  p o r p h y r y on the west s i d e o f C o n s t i t u t i o n H i l l are n o t i c e a b l y b l e a c h e d  (plate VII)  f o r a d i s t a n c e o f o n l y a few f e e t  from the c o n t a c t . Magnetite selvedges contacts of d i o r i t i c MacKay creek over  are found  i n p l a c e s a l o n g the  dykes w i t h T r i a s s i c v o l c a n i c r o c k s .  the v o l c a n i c r o c k s c o n t a i n up to 20% magnetite  a w i d t h o f about f i f t e e n f e e t a d j a c e n t  c h i l l e d border An o u t c r o p  to the s l i g h t l y  o f the s t o c k . p o s s i b l y r e p r e s e n t i n g a b l o c k o f matamorph-  osed T r i a s s i c v o l c a n i c m a t e r i a l o c c u r s about 600 f e e t MW G l a c i e r Lake. (ZAC  In  I t i s composed o f a c t i n o l i t i c  of  hornblende  = 1 6 ° ; p l e o c h r o i s m - X = medium p a l e brown, Y - medium  brown green, plagioclase  Z = deep green;; a b s o r p t i o n - Z Y X ) , >  (about  >  A n ^ ) , and some a p a t i t e ( ? ) . Q  clear The h o r n -  b l e n d e has been p a r t i a l l y r e p l a c e d by p y r r h o t i t e , m a g n e t i t e , and c h a l c o p y r i t e . The by  replacement o f the f r i n g e s o f p l a g i o c l a s e  f i n e i n t e r l o c k i n g r e c r y s t a l l i z e d ( ? ) g r a i n s o f q u a r t z and  unzoned p l a g i o c l a s e o f the groundmasses i n some near the s t o c k may be due i n p a r t t o the thermal the q u a r t z d i o r i t e 3.  phenocrysts  porphyries e f f e c t s of  stock.  Alteration Si l i e i f i cat ion.  Silic.if ication, like  sulphide  mineral—  76.  ization, rocks;.  o c c u r s most  c o m m o r x l y i n the v i c i n i t y  of f r a c t u r e d  There appear to be two major o v e r l a p p i n g "zones" o f  r o c k s showing v a r i o u s degrees  of s i l i c i f i c a t i o n .  The f i r s t  zone i n c l u d e s the C e n t r a l arm and the i n n e r and c e n t r a l p o r t i o n s o f the West arm e x c l u d i n g B r e c c i a r i d g e . cides approximately (now  w i t h the p o s i t i o n , o r former  It coinposition  o c c u p i e d by i n t r u s i v e r o c k s or b r e c c i a s ) o f the  T r i a s s i c - U p p e r Cretaceous  unconformity.  The second  c o i n c i d e s w i t h P y r r h o t i t e c r e e k and extends the south o f N o . l f a u l t .  zone  south o f i t t o  In both zones most o f the r o c k s a r e  fractured or b r e c c i a t e d . W i t h i n these flat-lying  zones and on the West arm t h e r e a r e s e v e r a l  s h e e t - l i k e o r i r r e g u l a r - s h a p e d b o d i e s o f white  q u a r t z c o n t a i n i n g some s u l p h i d e s . s e v e r a l f e e t wide. veins:.  They a r e a few i n c h e s to  There a r e a l s o some s t e e p l y d i p p i n g q u a r t z  The r o c k s e n c l o s i n g such v e i n s o r b o d i e s o f q u a r t z are  highly s i l i c i f i e d ,  e s p e c i a l l y near  t h e i r c o n t a c t s w i t h the  quartz. Net  v e i n s o f quartz' a v e r a g i n g about  wide t r a v e r s e  r o c k s o f a l l t y p e s a l o n g the b o r d e r s o f the s t o c k . Washington(?) b r e c c i a i s found  on the West arm ( p l a t e XXV).  On the C e n t r a l arm c h e r t y s i l i c i f i e d ified  sandstones  Most o f the sheared of  argillites,  (p.36) a r e common near  s i m i l a r r o c k s a r e found  Silicified  and s i l i c -  the u n c o n f o r m i t y , and  at v a r i o u s l o c a t i o n s on the V/est arm. and b r e c c i a t e d r o c k s i n f a u l t  zones  the Mt. Washington a r e a a r e s i l i c i f i e d . The  source  o f the s i l i c a  i n the a l t e r e d  zones p r e s e n t s  77.  no problem.  Some was  likely  s i l i c e o u s sediments. Mt.  V/ashington  Much appears  always p r e s e n t  Sericite  a l s o as c l e a r white  (muscovite)  i s nearly  f l a k e s up to 1"  quartz i n f a u l t  i n diameter  zones and  i n the  larger  i r r e g u l a r quartz bodies c o n t a i n i n g s u l p h i d e s .  Intense porphyry  the  i n n o t i c e a b l e q u a n t i t i e s i n n e t - v e i n l e t s of  s c a t t e r e d throughout v e i n s and  to have emanated from  In most c a s e s , s e r i c i t i z a t i o n i s c l o s e l y  to s i l i c i f i c a t i o n .  q u a r t z and  from  stock.  Sericitization. related  locally redistributed  sericitization  from a d r i l l The  occurs i n a  hole c o l l a r e d  "sub-cataclastic"  a few  hundred f e e t  of  No.l saddle.  p l a g i o c l a s e and m a t r i x e s  of  t h i s r e g i o n are p a r t l y r e p l a c e d by f a i r l y  east  of the p o r p h y r i e s : coarse  shreds  of  sericite. Biotitization. immediate v i c i n i t y , ified  The  r o c k s of B r e c c i a r i d g e and i t s  e x c l u d i n g the zone o f b r e c c i a and  r o c k s a l o n g i t s e a s t e r n edge, are i n t e n s e l y  silic-  biotitized.  Much of the f i n e l y comminuted m a t r i x of the Murray b r e c c i a i s flooded with f i n e f l a k e s of b i o t i t e . aceous m a t r i x e s  and  Upper C r e t a c e o u s Some porphyry  due  argill-  l e s s s t a b l e m i n e r a l s i n the fragments o f  sediments are r e p l a c e d i n a s i m i l a r manner.  fragments i n the Murray b r e c c i a ,  c r o p s of p o r p h y r y  The  i n the v i c i n i t y  to p a r t i a l b i o t i t i z a t i o n .  p l e t e l y r e p l a c e s hornblende  and  a l l out-  of the b r e c c i a are brown  In these r o c k s b i o t i t e com-  c r y s t a l s and  cores of p l a g i o c l a s e phenocrysts  c e r t a i n zones or the  ( p l a t e XXVI).  It also  occurs  as v e i n l e t s or replacements  of f i n e r g r a i n s of hornblende  the p o r p h y r y  C h l o r i t e a l t e r a t i o n i s present i n  groundmasses.  in  78  c o n s i d e r a b l e q u a n t i t y i n the l e s s i n t e n s e l y b i o t i t i z e d Chloritization. alteration.  C h l o r i t i z a t i o n i s the most  rocks.  widespread  However, i t does not appear to o c c u r w i t h n e a r l y  the same degrees  of l o c a l  i n t e n s i t y as do the o t h e r  ations.  A l s o , i t seems to be  in their  zones of  s u p p l a n t e d by o t h e r  alter-  alterations  intensity.  Most o f the hornblende partially chloritized.  i n the d i o r i t i c  Some porphyry  intrusions i s  fragments  i n the  bio-  t i t i z e d Murray b r e c c i a e x h i b i t pseudomorphs o f c h l o r i t e hornblende  (plate  XXVII).  R e c r y s t a l l i z e d m a t r i x e s of the Upper C r e t a c e o u s c o n t a i n much c h l o r i t e .  T h i s i s almost  p r i m a r y m a t e r i a l i n the Argillization. p o r p h y r y was  after  c e r t a i n l y d e r i v e d from  sediment.  A zone of extreme a r g i l l i c  uncovered  sediments  alteration  by b u l l d o z i n g i n N o . l s a d d l e .  At  two  o t h e r l o c a t i o n s , s i m i l a r but much l e s s i n t e n s e a l t e r a t i o n observed. c r e e k and  One  locality  of  was  i s i n the upper p a r t s of P y r r h o t i t e  the o t h e r i s 3000 f e e t west o f No.l s a d d l e .  t h r e e o c c u r r e n c e s are w i t h i n f a u l t  All  zones.  In N o . l s a d d l e the zone i s exposed over an a r e a o f a p p r o x i m a t e l y 100  f e e t EW  by 20 f e e t NS.  The  c o n t a c t s of  this  zone w i t h u n a l t e r e d r o c k s are not exposed but o u t c r o p s o f contaminated  and b i o t i t i z e d p o r p h y r y  o c c u r about  thirty  to the s o u t h , and  o u t c r o p s of o n l y s l i g h t l y b i o t i t i z e d  phyry o c c u r about  100  feet  t o the n o r t h .  r o c k i n the b u l l d o z e r cut has been reduced m i l k y - w h i t e mass. but the odd let,  No  Some of the to a  feet por-  altered  crumbly,  f e r r o m a g n e s i a n m i n e r a l s are p r e s e r v e d  s m a l l g r e y q u a r t z g r a i n or q u a r t z - s e r i c i t e  vein-  or c h o c o l a t e brown p a t c h of i r o n o x i d e , are p r e s e n t .  At  79.  P l a t e XXVI - P h o t o m i c r o g r a p h of b i o t i t i z e d Murray b r e c c i a . M a t r i x e s of sandstone fragments (lower r i g h t and l o w e r c e n t e r ) , m a t r i x o f t h e b r e c c i a , and cores of p l a g i o c l a s e phenocrysts i n porphyry f r a g m e n t s a r e r e p l a c e d by b i o t i t e . (plain l i g h t , xl6)  P l a t e X X V I I - P h o t o m i c r o g r a p h o f Murray b r e c c i a showing pseudomorph o f c h l o r i t e a f t e r h o r n b l e n d e i n a p o r p h y r y f r a g m e n t . S m a l l c r y s t a l s a r e sphene. (plain light, xl6)  80.  some l o c a t i o n s where the r o c k i s l e s s h i g h l y a l t e r e d i t s dioritic  appearance  i s c l e a r l y seen.  possess s u b - c a t a c l a s t i e  Most o f these r o c k s  structure.  G.  Major S t r u c t u r e s (see maps 1 and 2; c r o s s s e c t i o n s 1 and 2 )  1.  General There  Statement a r e two major systems o f s t r u c t u r e s i n the Mt.  Washington-Constitution H i l l system a r e found throughout r e g i o n a l NNW  area.  the a r e a and c o i n c i d e w i t h the  t r e n d o f the r o c k s .  l a r g e s c a l e o r o g e n i c movements. the v i c i n i t y local  S t r u c t u r e s of the f i r s t  They owe t h e i r p r e s e n c e t o The second  system  i s found i n  o f Mt. Washington and owes i t s o r i g i n t o more  f o r c e s caused  at l e a s t  i n p a r t by the i n t r u s i o n o f  d i o r i t i c magma. E x t e n s i v e f r a c t u r i n g was accompanied by the i n t r u s i o n o f p o r p h y r y at many l o c a l i t i e s near the Mt. Washington s t o c k . A l s o , many p r e v i o u s l y e x i s t i n g f r a c t u r e s were l i k e l y i v a t e d by the i n t r u s i o n o f the s t o c k . structural  F o r these  reasons  i n t e r p r e t a t i o n at many p l a c e s i n the v i c i n i t y o f  the s t o c k i s v e r y  difficult.  On a e r i a l photographs-,  many s t r u c t u r e s w i t h i n the T r i a s s i c :  v o l c a n i c rocks are i n d i s t i n c t ance and massive  because  o f the s i m i l a r  n a t u r e o f these r o c k s .  i s necessary.  o b s e r v a t i o n i n the  S t r u c t u r e s w i t h i n the g e n t l y d i p p i n g  l a y e r e d Upper C r e t a c e o u s sediments b o t h i n the f i e l d  appear-  For i d e n t i f i c a t i o n  i n them o f a l l but the major f a u l t s , d i r e c t field  react-  and on a e r i a l  are more c l e a r l y  photographs.  observed,  81.  2.  Folds The  are  on the  fold is and  rocks  of the Mt.  Washington-Constitution H i l l  eastward d i p p i n g limb  (Clapp,  shown by  1917,  p.23)  of the P a c i f i c  The formity  and  map  2 — e s p . East  unconformity  and  arm).  the  rocks  s t r u c t u r a l l y elevated,  o f the  i n the v i c i n i t y  and  t h a t they are  show t h a t  tilting  and  outward towards the  outer  the west end  at v a r i o u s  the  elevated  to the  2). localities  T h i s dome f l a t t e n s  f r i n g e s of Mt.  are n e a r l y  o f the E a s t  Washington where  the  flat-lying. arm  downward i n a m o n o c l i n a l ( ? ) f a s h i o n  the  sediments are  (plate  folded  IV).  Fractures  the b a s i s of f i e l d  observations  s t u d i e s , the w r i t e r b e l i e v e s t h a t center  Mt.  f l e x i n g , combined w i t h f a u l t i n g , have  Upper C r e t a c e o u s r o c k s  F a u l t s or  of  s t o c k near MacKay Lake ( c r o s s s e c t i o n  produced a complex domed s t r u c t u r e .  On  uncon-  of s e v e r a l hundred f e e t d i r e c t l y over  A t t i t u d e s o f the Upper C r e t a c e o u s r o c k s  3.  cross  of the l a y e r e d Upper C r e t a c e o u s sediments at  t h e i r maximum h e i g h t  At  (see  c o n f i g u r a t i o n o f the Upper C r e t a c e o u s - T r i a s s i c  are  center  This  the a t t i t u d e s o f the Upper C r e t a c e o u s sediments  Washington i n d i c a t e s t h a t stock  Coast down-  which o c c u p i e s G e o r g i a S t r a i t .  of the Upper C r e t a c e o u s - T r i a s s i c  s e c t i o n 2,  area  the  and  aerial  photograph  r o c k s near the  west  and  o f the mountain are cut by numerous f r a c t u r e s of a l l  o r i e n t a t i o n s , but  many of which b e l o n g to two  steeply-dipping  s e t s , most of whose v e r t i c a l components o f d i s p l a c e m e n t l e s s than f i f t y f e e t .  The  members of one  of these  are  sets  g e n e r a l l y tend to converge towards MacKay Lake whereas members  82.  of  the o t h e r s e t f o l l o w a N-S  direction.  Throughout  this;  e n t i r e a r e a of the mountain former f r a c t u r e s b e l o n g i n g the two  s e t s appear to be now  o c c u p i e d by porphyry  to  dykes.  L a r g e r s c a l e f r a c t u r e s than most o f those d e s c r i b e d above form a r a d i a l  p a t t e r n about the Mt.  such f r a c t u r e s , No.l and No.2 and  one  o t h e r , No.3  known f a u l t , No.4 i s probable  Washington s t o c k .  faults,  f a u l t , almost  f a u l t , may  are known to be  certainly  belong  to the r a d i a l  that s e v e r a l other large r a d i a l  presence  i s not  obvious.  photograph i n t e r p r e t a t i o n , Veerman has faults  i n the T r i a s s i c  radial  f r a c t u r e s are as f o l l o w s :  No.l f a u l t — a E-W  through  On  Another  pattern.  saddle.  The  Cretaceous  the b a s i s of  aerial  d i s t i n g u i s h e d two  r o c k s n o r t h of the  distribution  stock.^  The  However, a r g i l l i t e  seen a p p r o x i m a t e l y  approximately  of Upper  Cretaceous  places t h i s occupied  m i n e r a l i z e d , b r e c c i a t e d , and  v e r t i c a l l y dipping fault  NW-SE a l o n g the n o r t h end  1  running  of the West arm.  seen as a lineament  on i t  can  (map  be  2).  fracture  i n many p l a c e s by s u b - c a t a c l a s t i c porphyry,  fault—a  clearly  saddle  " f a u l t " appears to have been a g a p i n g  which i s sheared, No.2  a b u t t i n g porphyry  3000 f e e t west of N o . l  such  large  sediments on e i t h e r s i d e of i t shows t h a t d i s p l a c e m e n t i s very small.  It  f r a c t u r e s are a l s o  v e r t i c a l l y dipping f r a c t u r e running  No.l  present,  exists.  p r e s e n t , but because they are not w i t h i n the Upper rocks t h e i r  Two  In now  some o f  altered. approximately  This fault i s  on a e r i a l p h o t o g r a p h s .  I t , or a  Veerman, H., 1957, "Report on the Mount Washington P r o p e r t y Courtenay, Vancouver I s l a n d , B.C. ( u n p u b l i s h e d p r o p e r t y r e p o r t o f Noranda Mines L i m i t e d ) .  83.  lineament  parallel  e a s t of i t ,  to i t and more than 1000  feet  t o the n o r t h -  can be t r a c e d f o r more than twenty m i l e s to the  s o u t h e a s t , and p o s s i b l y a few m i l e s to the northwest Washington.  The  at l e a s t 100  f e e t and  of  v e r t i c a l component of d i s p l a c e m e n t  on i t i s  i s l i k e l y much g r e a t e r than 100  f o r i t c o m p l e t e l y c u t s o f f the Upper C r e t a c e o u s  Ho.3  and p o s s i b l y a l s o on the E a s t  "fault"—a  feet,  sediments  the p o r p h y r y b o d i e s w i t h i n them to the s o u t h o f i t on West arm,  Mt,  and  the  arm.  s t e e p l y d i p p i n g f r a c t u r e whose presence i s  not proven but which may  t r e n d SSW  along G l a c i e r creek,  j u s t n o r t h of the Summit, and c o n t i n u e t o the SSW Summit where i t may or the Main s i l l .  o f the  d i e out w i t h i n Upper C r e t a c e o u s Shearing, f r a c t u r i n g ,  pass  sediments  and b r e c c i a t i o n of  r o c k s a l o n g G l a c i e r c r e e k , and p o s s i b l y some o f the p r i s m a t i c j o i n t i n g i n the v i c i n i t y of the Summit may on t h i s  "fault".  on e i t h e r vertical No.4  The  fault—a  fault  fault  sediments t h e r e b y  have o c c u r r e d i n a somewhat  t r e n d s a p p r o x i m a t e l y N-S. ment i n the o r d e r of 400  may  little  extends producing  f l e x u r e s i n these r o c k s w i t h i n the E a s t  f a s h i o n to t h a t d e s c r i b e d by Buckham ( f i g . 4 ) .  displacement  that  i n the T r i a s s i c basement which  the d i s p l a c e m e n t s and F l e x i n g may  indicate  rocks  has o c c u r r e d on i t .  upward i n t o the Upper C r e t a c e o u s  saddle.  t o movements  p o s i t i o n s of the Upper C r e t a c e o u s  s i d e of the proposed displacement  be due  similar  This fault  A v e r t i c a l component of d i s p l a c e feet  i s i n d i c a t e d by the downward  of Upper C r e t a c e o u s r o c k s a l o n g i t (map  t r e n d n o r t h past the n o r t h end of the C e n t r a l arm  e a s t e r n f r i n g e s of the Mt. Washington s t o c k .  In the  2).  It  to the Triassic  84;  r o c k s to the south of Mt. Washington i t i s not d i s t i n c t may  but  p o s s i b l y continue f o r several m i l e s . A positively identified fault—No.5 fault—follows  P y r r h o t i t e c r e e k and  appears  s i d e of B r e c c i a r i d g e . f e e t northwest n o r t h of No.2 the T r i a s s i c  to extend  s o u t h a l o n g the east  I t becomes i n d i s t i n c t  a few  hundred  of the Summit and a l s o i n the T r i a s s i c fault.  However, a d i s t i n c t  and b r e c c i a t e d  Movement on No.5  rocks  linear feature i n  r o c k s s o u t h of the mountain may  southward c o n t i n u a t i o n .  along  represent its-  f a u l t has d i s t u r b e d  r o c k s f o r some d i s t a n c e on e i t h e r s i d e of i t .  S h e a r i n g i n a few p l a c e s i n d i c a t e t h a t d i p s moderately  this fault  or s t e e p l y t o the e a s t .  probably  Because i t i s  c r o s s e d by s e v e r a l o t h e r f r a c t u r e s , t h r e e of which are 1,  2, and 3 f a u l t s ,  and because these f r a c t u r e s appear to have  formed, or to have been r e a c t i v a t e d , when i t was movement on i t i s c o m p l i c a t e d . at the n o r t h end e l e v a t e d at l e a s t  formed,  Between N o . l and No.2  faults  of P y r r h o t i t e c r e e k the e a s t s i d e has been 100  f e e t , but complex f r a c t u r i n g of the  r o c k s i n t h i s a r e a makes d i s p l a c e m e n t difficult.  No.'s  determinations  As i s shown on c r o s s s e c t i o n 1, the sediments  the west of No.5  f a u l t near  the headwaters o f P y r r h o t i t e  c r e e k are at lower e l e v a t i o n s than those to the e a s t . i s p a r t l y due to be due and  to movement on No.5  f a u l t , but  i s also  i n p a r t to f l e x i n g of the s e d i m e n t s .  i n t r u s i o n of p o r p h y r y  This believed  Fracturing  i n the a r e a e x t e n d i n g s o u t h of  P y r r h o t i t e c r e e k to N o . l f a u l t make d i s p l a c e m e n t  determin-  a t i o n s almost  faults  impossible.  to  Between N o . l and No.3  d i s t r i b u t i o n o f Upper C r e t a c e o u s  and  brecciated rocks  the  may  85.  i n d i c a t e that  the main movement on  the  fault  i n t h i s area  was  dilational• The  Upper C r e t a c e o u s - T r i a s s i c  have been a s u r f a c e of the  rocks  along  a l o n g which t h r u s t i n g o c c u r r e d .  Shearing  i t or near to i t , i n c l u d i n g some c r o s s -  c u t t i n g i n t r u s i o n s on previously  u n c o n f o r m i t y appears to  (p.29).  the West arm,  Within  has  the o u t e r  been p a r t l y  part  of the  described  stock  a p p r o x i m a t e l y 4400 f e e t i n e l e v a t i o n i n G l a c i e r c r e e k is  a n e a r l y f l a t - l y i n g zone of sheared and  T h i s p o r p h y r y may aside  have been caught up  o f Upper C r e t a c e o u s r o c k s by  former f l a t - l y i n g f r a c t u r e s are now or  at  there  gouged m a t e r i a l .  during  the  and  the  stock.  occupied  thrusting  In many c a s e s by  quartz  veins  porphyry. F l a t - l y i n g tension  l o c a l i t i e s and C e n t r a l arm One s i d e has exist that  j o i n t s are w e l l developed at many  i n a l l r o c k t y p e s o f the West arm-Summit-  area.  NNW-trending, s t e e p l y - d i p p i n g moved upward r e l a t i v e  to the  fault east  at Ice c r e e k ( c r o s s s e c t i o n 2 ) . s e v e r a l s i m i l a r f a u l t s are p r e s e n t  Constitution H i l l  and  fault  along  s t r i k e s ENE  Mt.  Washington.  Ice c r e e k .  shearing,  i n t r o d u c t i o n of c a l c i t e ,  projected  eastward, the  The  on which the west  s i d e , i s known to writer  i n the Another  a r e a between steeply-dipping  Both f a u l t s e x h i b i t and  silicification.  second f a u l t would cut  near the west end  sill  of p o r p h y r y e x h i b i t s a maximum development o f It could  mentioned p r e v i o u s l y  o f Wolfe Lake at a p o s i t i o n where  f i t the  If  Constitution  Hill  jointing.  believes  the  prismatic  r e q u i r e m e n t s of the p o s s i b l e  ( p . 5 ( ) because the Upper C r e t a c e o u s  fault  86.  sediments that  are found to the s o u t h e a s t o f i t o n l y , s u g g e s t i n g  the s o u t h e a s t s i d e was  the northwest  side.  d i s p l a c e d downward r e l a t i v e  If this fault  Washington i t might  Mineral Deposits  I.  G e n e r a l E x t e n t and G e n e r a l  have been found  Mt.  be c o n s i d e r e d an e x t e n s i o n of No.4  H.  Copper-gold  i s p r o j e c t e d to  d e p o s i t s o f p o s s i b l e economic i n the West a r m - C e n t r a l arm  have a l s o been found i n T r i a s s i c  significance  area.  They are  Copper d e p o s i t s  r o c k s of the lower Murex  b a s i n and copper m i n e r a l i z a t i o n i s known to e x i s t  in Triassic  r o c k s at some l o c a l i t i e s between Mt. Washington and  Constitut-  Hill. Q u a n t i t a t i v e c h e m i c a l a n a l y s e s f o r copper,  zinc,  molybdenum were made i n the u n i v e r s i t y g e o c h e m i c a l a t o r i e s on the sediments streams The  fault.  Description  m a i n l y i n Upper C r e t a c e o u s or i n t r u s i v e r o c k s .  ion  to  labor-  from s e v e r a l e a s t w a r d - d r a i n i n g  and r i v e r s of the Campbell  sediments  and  taken from streams  River-Cumberland  o f the Mt.  region.  Washington-  I  Constitution H i l l of  area g e n e r a l l y possess a higher percentage  copper and h i g h e r copper  to z i n c r a t i o s than do  those  taken from the streams  d r a i n i n g r e g i o n s s o u t h e a s t or n o r t h -  west of the a r e a .  sediments  The  a c q u i r e d from MacKay c r e e k  c o n t a i n twelve p a r t s per m i l l i o n of molybdenum whereas those of  Murex c r e e k c o n t a i n l e s s than one  molybdenum.  Furthermore,  any o f the o t h e r streams  p a r t per m i l l i o n  none of the sediment c o n t a i n s more than one  of  samples from part  per  87.  m i l l i o n o f molybdenum. As a r e s u l t almost  o f the c h e m i c a l a n a l y s e s alone  c e r t a i n t h a t the Mt. W a s h i n g t o n - C o n s t i t u t i o n  a r e a i s one o f d i s t i n c t ation.  i t appears Hill  and c o n s i d e r a b l e copper m i n e r a l i z -  The molybdenum c o n t e n t  i s p r o b a b l y h i g h o n l y i n the  MacKay c r e e k sediment because MacKay c r e e k f l o w s a c r o s s the Mt. Washington s t o c k w i t h which molybdenum i s c l o s e l y associated• Because they were d e p o s i t e d i n two u n l i k e  environments,  the m i n e r a l d e p o s i t s i n the upper West a r m - C e n t r a l  arm r e g i o n  of Mt. Washington are m i n e r a l o g i c a l l y and p h y s i c a l l y different  from  somewhat  those i n the Murex b a s i n .  D e p o s i t s on the West arm are d e s c r i b e d i n g r e a t e r d e t a i l than the o t h e r d e p o s i t s o f the a r e a s i n c e they a r e the most complex, have been more f u l l y  s t u d i e d by the w r i t e r , and are  most p e r t i n e n t t o the f o l l o w i n g s e c t i o n s o f t h i s 2.  West Arm-Central  thesis.  Arm Deposits';  P h y s i c a l Forms and T e n o r s .  A system o f c o p p e r - g o l d  b e a r i n g q u a r t z v e i n s and o f i r r e g u l a r and minor s u l p h i d e replacements  shaped b o d i e s o f q u a r t z  i s present  i n rocks of various  t y p e s a l o n g the i n n e r c e n t r a l p a r t o f the West arm and on p a r t of the C e n t r a l arm.  The system c o i n c i d e s a p p r o x i m a t e l y  with  the o u t e r f r i n g e s o f the s t o c k and w i t h the p o s i t i o n o f the Upper C r e t a c e o u s - T r i a s s i e u n c o n f o r m i t y .  Most o f the l a r g e r  d e p o s i t s o f the system appear t o be g e n t l y d i p p i n g , and the i n f o r m a t i o n from  several d r i l l  h o l e s i n d i c a t e s t h a t some o f  the g e n t l y d i p p i n g q u a r t z o u t c r o p s n o r t h o f N o . l f a u l t form a p a r t l y eroded  but o t h e r w i s e  may  c o n t i n u o u s v e i n 250 f e e t  88.  wide, 600 f e e t l o n g , and seven to f i f t e e n f e e t t h i c k . assumption t h a t t h e r e that  On the  i s such a v e i n i t has been c a l c u l a t e d  i t a s s a y s an average o f a p p r o x i m a t e l y 2% copper, l e s s  than 1 o z . Ag p e r t o n , and a t r a c e o f g o l d . several c h a l c o p y r i t e - r i c h outcrops occur,  A zone i n which  and which  includes  t h i s v e i n , o r v e i n s , i s over 100 f e e t wide and f o l l o w s No.5 fault  from P y r r h o t i t e c r e e k t o N o . l f a u l t where a r i c h a r e a o f  copper m i n e r a l i z a t i o n i s exposed. Comb q u a r t z  and vugs w i t h i n the q u a r t z  in f l a t - l y i n g deposits. the m i n e r a l s enclosing  a r e v e r y common  In some zones o f massive  are layered p a r a l l e l  sulphides  t o the b e d d i n g o f the  sediments.  Scattered  small deposits  of m i n e r a l i z e d b r e c c i a , s e d i -  ments, and p o r p h y r y a r e found at e l e v a t i o n s o f 4400' t o 4500' i n a r e g i o n which extends a l o n g fault 2).  and c o n t i n u e s  p a r t way a l o n g  No.l v e i n i s a quartz  ington^) parallel  the West arm s o u t h o f N o . l  v e i n which i s i n s i l i c i f i e d  b r e c c i a of t h i s region. quartz  lenses  the C e n t r a l arm (maps 1 and  I t c o n s i s t s of s e v e r a l  i n a t a b u l a r zone which d i p s 30° NW and  i s a p p r o x i m a t e l y 100 f e e t l o n g by t h r e e shows i t c o n t a i n s 0. 8$  Wash-  f e e t wide.  Sampling  0.42 o z . Au p e r t o n , 0.34 o z . Ag p e r t o n ,  Cu, 0.5% Pb, 0.5% Zn, and 4.1% A s .  1  No.2 v e i n on the  west s i d e o f the C e n t r a l arm i s a f o u r i n c h wide q u a r t z p  which a s s a y s 1.14 oz,. Au p e r t o n .  1,  2  I t b e g i n s w i t h i n the  F o w l e r , H.S., (1946), "Domineer", Nanaimo M i n i n g D i v i s i o n , B.C. ( u n p u b l i s h e d c o n s u l t a n t ' s r e p o r t on the g o l d - q u a r t z v e i n s o f upper Mt. Washington).  vein  89,  o f the s t o c k where i t d i p s 50°E, and c a n be f o l l o w e d  border  d i s c o n t i n u o u s l y up the C e n t r a l arm where i t i s i n Upper Cretaceous  sediments.  C l o s e l y spaced  joint  s u r f a c e s between fragments i n  c r a c k l e d p o r p h y r i e s , sediments,  and v o l c a n i c s at some  l o c a t i o n s around the f r i n g e s o f the s t o c k o r a l o n g s i d e f a u l t s , are coated with t h i n f i l m s of s u l p h i d e s . may a l s o be d i s s e m i n a t e d at  throughout  no l o c a l i t y has e x t e n s i v e copper  type been f o u n d .  Sulphides  the fragments.  However,  m i n e r a l i z a t i o n of this  In the c r a c k l e d p o r p h y r i e s o n l y the mafic  m i n e r a l s a r e h i g h l y impregnated  with sulphides.  v e i n l e t s which c o n t a i n s u l p h i d e s a r e a l s o found  Some n e t i n these  regions of crackled rock. Disseminated found  p y r i t e , p y r r h o t i t e , and c h a l c o p y r i t e a r e  at some l o c a t i o n s near f a u l t s .  silicified  fault  Magnetite  Many o f the sheared and  surfaces contain sulphides.  d e p o s i t s i n the Washington b r e c c i a have been  described previously ( p . C 8 ) . p r o b a b l y averages  The i r o n c o n t e n t  of t h i s b r e c c i a  l e s s than 20%.  Ore M i n e r a l s , T e x t u r e s , and P a r a g e n e s i s .  An e x h a u s t i v e  study o f the s u l p h i d e - b e a r i n g r o c k s has not been made. ever, s e v e r a l p o l i s h e d surfaces of s e l e c t i n v e s t i g a t e d under the microscope  samples were  by the w r i t e r , and the  i n f o r m a t i o n so o b t a i n e d has proven most u s e f u l t o t h i s Numerous t e x t u r e s have been observed  thesis.  i n the samples but those  i n d i c a t i v e o f b r e c c i a t i o n and open space f i l l i n g common.  How-  a r e most  T e x t u r e s depend on the s i z e s o f the m i n e r a l g r a i n s ,  the shapes assumed by the g r a i n s , and the p a t t e r n i n which  9 0 .  the g r a i n s make c o n t a c t w i t h one another a result  i n aggregates.  As  d e s c r i p t i o n s o f them a r e i n c l u d e d i n the account o f  the o c c u r r e n c e s o f i n d i v i d u a l m i n e r a l s . The  f o l l o w i n g m i n e r a l s , n e a r l y a l l o f which a r e almost  c e r t a i n l y hypogene, a r e arranged  i n t h e i r approximate  order  of abundance i n the f o l l o w i n g l i s t : Pyrrhotite. all  ( P e ^ S ) - occurs i n l a r g e q u a n t i t i e s i n  but the massive q u a r t z v e i n s , and i s c l o s e l y a s s o c i a t e d  with c h a l c o p y r i t e .  I n some samples the two minerals; e x h i b i t  mutual boundary r e l a t i o n s h i p s but i n most c h a l c o p y r i t e replaces pyrrhotite.  P a r a l l e l alternating layers of p y r r -  h o t i t e and c h a l c o p y r i t e (banded t e x t u r e s ) a r e common. D i s s e m i n a t i o n s and s l i p  surface coatings of p y r r h o t i t e i n  v a r i o u s r o c k s a r e a l s o common near  i n t r u s i o n s or f a u l t s  ( p l a t e XXIX), and e s p e c i a l l y a l o n g No.5 f a u l t creek.  P y r r h o t i t e r e p l a c e s hornblende  p o r p h y r i e s and i n one l o c a l i t y hornblende  i n many o f the  i t replaces a c t i n o l i t i c  o f a metamorphosed v o l c a n i c fragment  Pyrite. except  i n Pyrrhotite  (FeSg) - p r e s e n t  (p.75).  i n a l l sulphide-bearing rocks  a v e r y few i n which i t i s c o m p l e t e l y r e p l a c e d by l a t e r  formed m i n e r a l s .  I t occurs i n c l o s e a s s o c i a t i o n  with  c h a l c o p y r i t e and i s e s p e c i a l l y common i n q u a r t z v e i n s and silicified  and b r e c c i a t e d r o c k s ( p l a t e  Magnetite,  XXVIII).  (Fe^O^) - s m a l l specks  a r e p r e s e n t i n many  of the q u a r t z v e i n s and i r r e g u l a r b o d i e s o f q u a r t z but i t o c c u r s i n q u a n t i t y o n l y i n the Washington b r e c c i a o r i n Triassic  r o c k s at i n t r u s i v e c o n t a c t s .  Chalcopyrite,  ( C u F e S ) - i s the o n l y major p  copper-  91.  bearing mineral.  It f i l l s  arsenopyrite-quartz  rocks  spaces i n b r e c c i a t e d  ( p l a t e XXVIII) where i t has been  observed c o a t i n g one i n c h l o n g q u a r t z occurs and  pyrite-  crystals.  I t also  i n a l t e r n a t e l a y e r s w i t h p y r r h o t i t e i n banded  i s present  i n disseminations  or v e i n l e t s throughout  v a r i o u s : r o c k s near some o f the i n t r u s i o n s o r f a u l t s XXIX).  I t i s also present  "ores"  (plate  i n s m a l l amounts i n f r a c t u r e s ; i n  the Washington b r e c c i a . Arsenopyrite,  (FeAsS) - i n abundance o n l y i n  b r e c c i a t e d o r e s ( p l a t e XXVII) o r i n q u a r t z v e i n s and irregular  shaped s u l p h i d e - b e a r i n g b o d i e s  Molybdenite,  of quartz.  (MoS ) - i s found as s l i p 2  surface  in  c r a c k l e d r o c k s . w i t h i n o r near the b o r d e r s  at  the head o f P y r r h o t i t e c r e e k ,  up  to one i n c h wide i n t i m a t e l y mixed w i t h c o a r s e l y  quartz  o f the s t o c k and  and i s a l s o found as f l a k e s crystalline  a few hundred f e e t n o r t h o f N o . l s a d d l e . Sphalerite,  and  coatings  (ZnS) - o c c u r s  No.2 v e i n s where i t f i l l s  arsenopyrite rock,  i n small q u a n t i t i e s i n No.l  fractures within quartz-pyrite-  and as s c a t t e r e d minute b l e b s  throughout  c h a l c o p y r i t e i n specimens from the m i n e r a l i z e d r e g i o n of N o . l f a u l t .  north  A specimen from N o . l v e i n e x h i b i t s e m u l s i o n -  e x s o l u t i o n t e x t u r e o f c h a l c o p y r i t e i n s p h a l e r i t e ( p l a t e XXX). Galena . (PbS) - s m a l l amounts o f i t a r e p r e s e n t i n No.l  and No.2 v e i n s and i n some o t h e r  i r r e g u l a r - s h a p e d bodies the f r a c t u r e d q u a r t z . Bornite,  q u a r t z v e i n s and  o f q u a r t z where i t f i l l s I t may c o n t a i n  spaces i n  silver.  (Cu^FeS^) - i s not v e r y common but i s present  r e p l a c i n g p y r i t e and c h a l c o p y r i t e i n v e i n s n o r t h  of No.l  92.  P l a t e XXVIII - Photomicrograph of a b r e c c i a t e d p o r t i o n of N o . l quartz v e i n . Brecciated p y r i t e (mottled grey) and a r s e n o p y r i t e ( w h i t e , bottom c e n t e r ) a r e h e a l e d by q u a r t z and o t h e r gangue ( d a r k g r e y ) and c h a l c o p y r i t e ( c e n t e r t o t o p . Dark p a t c h e s c a u s e d by s c o u r d u r i n g p o l i s h i n g ) . P y r i t e i s s l i g h t l y s t r e w n out f r o m l e f t c e n t e r t o t o p C e n t e r . ( field length approx. 15mm. )  P l a t e XXIX - P h o t o m i c r o g r a p h o f d i s s e m i n a t e d p y r i t e ( g r e y m o t t l e d c r y s t a l s upper r i g h t ) , and c h a l c o p y r i t e and p y r r h o t i t e ( n o t d i s t i n g u i s h a b l e from one a n o t h e r ) i n s a n d s t o n e 1 0 0 0 f e e t west o f N o . l saddle. Chalcopyrite i n v e i n l e t ( r i g h t , c e n t e r ) . (  field  taig+b  approx.  15mm.  )  93.  fault.  It i s replaced  i n t u r n by c h a l c o c i t e and c o v e l l i t e .  Some or a l l o f i t may be s e c o n d a r y . Tetrahedrite-Tennantite(?). S^  (Cu,Fe,Zn,Ag) (As,Sb) 12  4  - small grey blebs w i t h i n p y r r h o t i t e , c h a l c o p y r i t e , or  gangue i n many o f the p o l i s h e d s e c t i o n s s t u d i e d a r e b e l i e v e d to be t e t r a h e d r i t e - t e n n a n t i t e . able  silver  f o r most a s s a y s show t h a t a t l e a s t  of s i l v e r a r e p r e s e n t Wehrlite. present and  They l i k e l y p o s s e s  consider-  some t r a c e s  i n most o f the v e i n s .  (Bi^Te plus 2  Ag and S ) , and H e s s i t e ,  (AggTe)  i n a few s m a l l v e i n l e t s c u t t i n g "banded" c h a l c o p y r i t e  p y r r h o t i t e from a specimen taken from the m i n e r a l i z e d  region north  of No.l f a u l t  Gold(?),  ( p l a t e XXXI).  (Au) - no n a t i v e g o l d was i d e n t i f i e d  samples s t u d i e d but some i s l i k e l y p r e s e n t Pyrite  and/or a r s e n o p y r i t e  i n the  i n the v e i n s .  a r e b e l i e v e d t o be the main  c a r r i e r s of gold.^ Supergene m i n e r a l s  and/or a l t e r a t i o n p r o d u c t s o f the  previously l i s t e d minerals Chalcocite,  (Cu S) - occurs 2  l e t s or i r r e g u l a r - s h a p e d pyrite.  common.  They a r e :  f a i r l y commonly as v e i n -  g r a i n s m a i n l y i n c h a l c o p y r i t e and  Sooty c h a l c o c i t e i s a l s o found i n decomposed v e i n  material. pyrite  are f a i r l y  In some c a s e s i t has almost c o m p l e t e l y  replaced  so t h a t o n l y rounded r e s i d u a l s o f t h i s m i n e r a l  remain.  Some o f i t may be hypogene but much o f i t i s supergene. Covellite,  1  (CuS) - o c c u r s  as s m a l l b l a d e s i n  p e r s o n a l communication w i t h Gordon Murray, p r e s i d e n t o f Mt. Washington Copper Company.  94.  c h a l c o c i t e and b o m i t e  and as f r a c t u r e f i l l i n g s  throughout  the q u a r t z v e i n s . N a t i v e Copper, (Cu) - found at  some  on o x i d i z e d v e i n m a t e r i a l  localities. Malachite,  (Cu (C0^) (0H) ) 2  2  2  - has developed  i n small  q u a n t i t i e s o n l y because o f the d e f i c i e n c y o f c a r b o n a t e  i n the  r o c k s o f the mountain.  I t forms c r u s t s on some o f the v e i n  m a t e r i a l and i s p r e s e n t  on the s u r f a c e s o f c h a l c o p y r i t e -  m i n e r a l i z e d b o u l d e r s o f Washington b r e c c i a . MolybditeC?), product  ( F e g O ^ M o O j . S H g O ) - a yellow o x i d a t i o n  of molybdenite  which i s l i k e l y m o l y b d i t e  but may be  p o w e l l i t e i s found w i t h some o f the m o l y b d e n i t e . Realgar,  (AsS) and/or Qrpiment. ( A s S ^ ) - o c c u r ( s ) as 2  o x i d a t i o n p r o d u c t s i n some a r s e n o p y r i t e - b e a r i n g v e i n s . Paragenesis  o f the ore m i n e r a l s appears  many r e s p e c t s to those  o f most h y d r o t h e r m a l  Edwards (1954, p.136).  o c c u r s i n at l e a s t  The major gangue m i n e r a l  quartz  likely  most o f the p e r i o d o f m i n e r a l i z a t i o n  d u r i n g more than one phase o f b r e c c i a t i o n . The  important  probable  sequence o f d e p o s i t i o n o f the most  metal-bearing minerals i s l i s t e d  p o s i t i o n s o f molybdenite unknown. but  i s always an e a r l y m i n e r a l o f the  two g e n e r a t i o n s but i t was  d e p o s i t e d throughout and  o r e s as l i s t e d by  More than one g e n e r a t i o n o f p y r i t e  may be p r e s e n t but p y r i t e d e p o s i t i o n a l sequence.  t o be s i m i l a r i n  below.  The exact  and b o r n i t e i n the sequence are  B o r n i t e i s post c h a l c o p y r i t e and pre c h a l c o c i t e  i s t e n t a t i v e l y p l a c e d i n the f i f t h p o s i t i o n .  minerals l i s t e d  t o g e t h e r are at l e a s t  Those  i n p a r t contemporaneous,  95  P l a t e XXX - P h o t o m i c r o g r a p h o f a specimen from N o . l v e i n showing e m u l s i o n - e x s o l u t i o n t e x t u r e e x h i b i t e d by s p h a l e r i t e (medium g r e y ) and c h a l c o p y r i t e ( w h i t e ) , and s e g r e g a t i o n v e i n l e t s o f c h a l c o p y rite. Dark a r e a s , e x c e p t i n g t h e q u a r t z g r a i n i n the l o w e r r i g h t , a r e gouges formed d u r i n g p o l i s h i n g . ( field length approx. o5 m m . )  P l a t e XXXI - P h o t o m i c r o g r a p h o f a m i n e r a l i z e d specimen from a f l a t - l y i n g q u a r t z - s u l p h i d e body n o r t h o f N o . l f a u l t . Wehrlite v e i n l e t (white) cuts across p y r r h o t i t e and c h a l c o p y r i t e ( n o t d i s t i n g u i s h a b l e f r o m one a n o t h e r i n p h o t o g r a p h ) . The v e i n l e t c o n t a i n s p a t c h e s o f h e s s i t e ( g r e y , low r e l i e f ) , and o r i e n t e d i n c l u s i o n s o f p y r r h o t i t e ( d a r k r i m s , h i g h r e l i e f ) . ( field length approx. o.5 mm- )  96.  or e l s e t h e i r  i n t e r - r e l a t i o n s h i p s are unknown.  (1)  Magnetite,  (2)  Pyrrhotite  (3)  Molybdenite  (4)  Chalcopyrite, Sphalerite, Tetrahedrite-  tennantite(?),  Pyrite,  Arsenopyrite  - ?  Galena  (5)  Bornite - ?  (6)  Wehrlite, Hessite,  (?)  Chalcocite, Covellite  Genetic  Classification.  Gold(?)  I t i s of i n t e r e s t  the m i n e r a l d e p o s i t s i n the v i c i n i t y s t o c k are  of the Mt.  to note t h a t Washington  s i m i l a r i n a g r e a t many r e s p e c t s to the  copper d e p o s i t s of southwest U n i t e d  States.  These m i n e r a l d e p o s i t s were formed i n a environment.  Comb s t r u c t u r e s and  are common i n d i c a t i n g e x t e n s i v e  porphyry  near-surface  vugs i n the q u a r t z  veins  open space f i l l i n g .  This:  i s generally considered  compatable o n l y w i t h a near  environment.  f o r t h i s environment are a l s o  Evidences  deduced from the n a t u r e probable  of the i n t r u s i o n s and  surface  b r e c c i a s , and  t h i c k n e s s of o v e r l y i n g r o c k s d u r i n g f o r m a t i o n  the d e p o s i t s  (p.48).  High temperature m i n e r a l s deposits.  predominate w i t h i n  the  Exsolution chalcopyrite i n sphalerite indicates  temperatures o f above 350°-400°C d u r i n g d e p o s i t i o n o f minerals  of  (Edwards, 1954,  tellurides  ( w e h r l i t e and  considered  to be low  p.98).  The  these  deposits also contain  h e s s i t e ) which are g e n e r a l l y  temperature m i n e r a l s .  d u r i n g d e p o s i t i o n of the v e i n m i n e r a l s may  Temperatures have v a r i e d  97.  considerably. Because t h e y were formed  f o r the most p a r t at l e a s t , a t  h i g h temperatures, and i n a n e a r - s u r f a c e environment,  most  of t h e West a r m - C e n t r a l arm m i n e r a l d e p o s i t s c o u l d be classified  as Xenothermal  d e p o s i t s (Buddington, 1930, p.205).  Structural Controls. deposits  The d i s t r i b u t i o n o f the m i n e r a l  (see maps>1 and 2) s u g g e s t s t h a t many o f them may  have been l o c a l i z e d by o r near to the f o l l o w i n g (1) Dilational  The Upper C r e t a c e o u s - T r i a s s i e zones may have formed  structures:  unconformity.  at or near t o the uncon-  formity.  Impermeable l a y e r s i n the Upper C r e t a c e o u s  sediments  above i t may have h a l t e d  the a s c e n t o f h y d r o t h e r m a l  solutions. (2)  L a r g e , s t e e p l y - d i p p i n g f a u l t s or f r a c t u r e s , and  e s p e c i a l l y No.5 f a u l t . (3) part  The system o f f r a c t u r e s s m a l l e r than those o f  (2) which  s u r r o u n d s the s t o c k .  t h i s system were e s p e c i a l l y  P l a t - l y i n g fractures of  important  controls.  A c o m b i n a t i o n o f a l l t h r e e o f the above major appears t o be p r e s e n t i n the h e a v i l y m i n e r a l i z e d  controls  region  e x t e n d i n g south o f P y r r h o t i t e c r e e k t o N o . l f a u l t . Bedding i n the sediments determined of the f r a c t u r e s formed m i n e r a l i z a t i o n depending attitude.  and may have a i d e d o r h i n d e r e d on i t s c o n s i s t e n c y , w i d t h , or  Permeable sediments may have been m i n e r a l i z e d to  a g r e a t e r degree 3.  the n a t u r e o f many  than non permeable  sediments.  D e p o s i t s o f Murex Creek and V i c i n i t y , and o f I c e Creek I n Murex c r e e k , o u t c r o p s o f T r i a s s i c  rocks occurring  98. over a l e n g t h o f s e v e r a l hundred f e e t and at e l e v a t i o n s o f about 2400 f e e t t o 2700 f e e t are h i g h l y f r a c t u r e d and s p o t t i l y m i n e r a l i z e d w i t h p y r r h o t i t e and c h a l c o p y r i t e . of the f r a c t u r e s s t r i k e a t N50°E and d i p 55°SE. d i p p i n g p o r p h y r y dyke a p p r o x i m a t e l y along  the east  Many  A steeply-  100 f e e t wide f o l l o w s ;  s i d e o f the e n t i r e b e l t  of mineralized  Grade and economic p o s s i b i l i t i e s o f t h e s u l p h i d e  rocks.  mineral-  i z a t i o n i n the b e l t were d e s c r i b e d p r e v i o u s l y ( p . 4 ) . Slip  s u r f a c e s on fragments o f f r a c t u r e d v o l c a n i c s a t  one l o c a l i t y about 2000 f e e t i n e l e v a t i o n on the n o r t h e a s t end o f the E a s t  arm are c o a t e d  with  t h i n f i l m s o f p y r i t e and  chalcopyrite. Sm all  d e p o s i t s of arsenopyrite are present  zones o f Ice c r e e k Gunning  (p>85).  (1930, p.76A).  i n the f a u l t  These have been d e s c r i b e d by  99. V  The  STRUCTURAL DEVELOPMENT OF MT.  Puget orogeny of post-Upper C r e t a c e o u s  i n c l u d e d f o l d i n g and affected  WASHINGTON  times  f a u l t i n g a l o n g NNW-trending axes  and  s t r a t a as young as Miocene on Vancouver I s l a n d  (White, 1959,  p.96).  F o l d i n g and  f a u l t i n g during  this  orogeny appear to have been l a r g e l y r e s p o n s i b l e f o r e l e v a t i n g the Upper C r e t a c e o u s  sediments at Mt.  l e v e l or from below s e a l e v e l h e i g h t s o f g r e a t e r than At Mt.  stock ful  (p.82),  the  (cross section 2).  at l e a s t  one  transverse  fracture—No.5  system o f s m a l l e r f r a c t u r e s s u r r o u n d i n g  i n t r u s i o n of the  formed or r e a c t i v a t e d by  s e c t i o n 1 i n d i c a t e s t h a t the dome may  above the s t o c k . feet  the f o r c e -  of a p p r o x i m a t e l y  However, the r e l i e f was  1000  have had feet  probably  s i n c e i n the c r o s s s e c t i o n the  the s t o c k has  taken  whereas e x t e n s i v e p u n c h i n g up stock l i k e l y is  shown by  occurred.  That  greater  interpretation  only f l e x i n g i n t o  was  account  of b l o c k s o f r o c k above the such p u n c h i n g l i k e l y  took p l a c e  the e l e v a t e d p o s i t i o n of the n o r t h e r n p a r t o f  b l o c k o f r o c k s e n c l o s e d by the western edge of the s t o c k No.'s  1,  2, and  3  a  directly  of the p o s i t i o n of the eroded l a y e r of sediments which f o r m e r l y over  the  stock.  maximum s t r u c t u r a l r e l i e f  than 1000  to t h e i r p r e s e n t maximum  5000 f e e t  ( p . 8 l ) were l i k e l y  Cross  ...  Washington the s t r u c t u r a l dome ( p > 8 l ) , the l a r g e  radial faults f a u l t , and  Washington from sea  the and  faults.  When compared to the s t r u c t u r a l r e l i e f s o f many domes;, i n the western U n i t e d  S t a t e s which are known to be caused by  the  100  i n t r u s i o n of magma, the apparent s t r u c t u r a l r e l i e f dome at Mt. be  Washington i s s m a l l .  c o n c l u d e d t h a t doming by  the  of  the  Because of t h i s i t might stock  c o u l d not  have produced  the l a r g e r f r a c t u r e s s u r r o u n d i n g i t . However, Wisser who  has  performed s e v e r a l s c a l e model experiments on  c o n c l u d e s (p.||) t h a t producing r a d i a l  and  "The  degree o f doming c a p a b l e  concentric  fractures i s  (I960), doming  of  astoundingly  small". The the  r o l e played  by  l o c a t i o n o f the Mt.  a l s o not  known how  attributed  tectonic structures i n determining Washington s t o c k  much movement on f a u l t s of the  to t h e i r r e a c t i v a t i o n by  However, i t i s known t h a t movements o c c u r r e d  both b e f o r e  before  shown by  the u p - s t e p p i n g of t h i s s i l l  the  stock  ( p . 4 9 ) , and  that  i s cut  at No.4  i t took p l a c e the  formed by  i n h a l f by No.2  the That i t  i n t r u s i o n of the Main s i l l  i s w e l l demonstrated by  Washington dome which was stock  the  fault  be  Cretaceous  d i o r i t i c magma.  occurred  saddle  or d u r i n g  a r e a can  or d u r i n g , a n d a f t e r  of the  It i s  forcible intrusion.  some l a r g e p o s t - L a t e  i n t r u s i o n o f at l e a s t p a r t  East  i s unknown.  fault  i n the  a f t e r i n t r u s i o n of  f a c t that  the  is  the  Mt.  i n t r u s i o n of  the  or by a p a r a l l e l f a u l t  near  to i t . Noble (1952) d e s c r i b e s  the f o r c i b l e  i n t r u s i o n of  a  composite s t o c k near the Homestake mine i n South Dakota. stock  punched s e c t i o n s of the  o v e r l y i n g r o c k s ahead of i t such  t h a t h o r s t s were formed between p a i r e d overall  s t r u c t u r e formed was  significant  This  f a u l t s and  that o f a dome.  that  the  It i s  to note t h a t the domed r o c k s d e s c r i b e d  by  Noble  lor. are  steeply  d i p p i n g P r e c a m b r i a n s c h i s t s and e r o s i o n a l  of n e a r l y f l a t - l y i n g Cambrian  s t r a t a which overly  remnants  the  He s u g g e s t s t h a t were i t n o t f o r the p r e s e n c e o f t h e  schists. Cambrian  s t r a t a w h i c h a r e r e a d i l y o b s e r v e d t o be e l e v a t e d , the doming and o t h e r e v i d e n c e s f o r f o r c i b l e i n t r u s i o n would be n o t i c e a b l e so t h a t the s i g n i f i c a n c e  scarcely  of the p a r a l l e l f a u l t s :  and p o r p h y r y b o d i e s would a l m o s t c e r t a i n l y n o t be r e a l i z e d geologists explain  mapping the a r e a .  the e l e v a t e d a r e a i n the v i c i n i t y o f t h e  by d i f f e r e n t i a l e r o s i o n . at Mt. W a s h i n g t o n volcanics overlain  R a t h e r , the g e o l o g i s t s  would  intrusions  A somewhat s i m i l a r s i t u a t i o n  exists  where m a s s i v e and s i m i l a r a p p e a r i n g T r i a s s i c  whose a t t i t u d e s  are d i f f i c u l t  to determine are  by n e a r l y f l a t - l y i n g o u t l i e r s o f Upper C r e t a c e o u s  s e d i m e n t s and b o t h have been f o r c i b l y i n t r u d e d by the Mt. Washington  stock.  by  102 VI  ORIGIN OF THE PORPHYRY BODY AT CONSTITUTION H I L L  Although  t h e w r i t e r d i d n o t map C o n s t i t u t i o n H i l l ,  s e v e r a l t r a v e r s e s were made i n i t s v i c i n i t y .  The p o r p h y r y  i n t r u s i o n s a t and n e a r t o t h e h i l l appear t o be c l o s e l y r e l a t e d i n o r i g i n t o t h e i n t r u s i o n s a t Mt. W a s h i n g t o n . The  p o r p h y r y body a t C o n s t i t u t i o n H i l l  may have been  i n t r u d e d t h r o u g h a f e e d e r u n d e r l y i n g t h e h i l l so t h a t t h e o n l y r e l a t i o n s h i p e x i s t i n g between i t and t h e Mt. W a s h i n g t o n s t o c k may be t h a t t h e y l i k e l y emanated f r o m t h e same chamber containing quartz d i o r i t e  (p.52.).  C o n s t i t u t i o n p o r p h y r y may r e p r e s e n t of a s i l l - l i k e Mt.  On t h e o t h e r hand t h e the bulbous t e r m i n a t i o n  body ( c r o s s s e c t i o n 2) w h i c h o r i g i n a t e d a t t h e  W a s h i n g t o n s t o c k and formed i n a manner s i m i l a r t o many  of the s i l l  t e r m i n a t i o n s o f t h e Pando r e g i o n o f C o l o r a d o  (Tweto, 1 9 5 1 , p . 5 1 6 ) .  The body may have formed by a b u i l d - u p  o f magma w h i c h had become i n c r e a s i n g l y c o o l and v i s c o u s and had  been s u b j e c t e d  the p r o b a b l e  to i n c r e a s i n g l i t h o s t a t i c pressures  due t o  i n c r e a s e i n the t h i c k n e s s o f the sediments  l y i n g i t , as i t moved e a s t w a r d f r o m t h e s t o c k .  over-  A f t e r the  i n t r u s i o n o f p o r p h y r y had c e a s e d , t h e s e d i m e n t s betv/een t h e f e e d e r s t o c k and C o n s t i t u t i o n H i l l continuous  sheet-like s i l l  o r t h e y may have c o n t a i n e d  scattered lenses of porphyry. support  a only  There a r e s e v e r a l f a c t s w h i c h  t h i s second mode o f o r i g i n . (1)  may have c o n t a i n e d  They a r e :  as i s shown i n c r o s s s e c t i o n 2 t h e Upper  Cretaceous sediments are i n conformable contact w i t h the lower part of the s i l l  a t l o c a l i t i e s on b o t h t h e west and  103. east sides of Constitution H i l l but have been observed to dip 60°E 1000 feet east of the edge of the h i l l .  These facts  may indicate that the porphyry body is part of a s i l l which wedges out to the east. (2)  the only large magma feeder observed i n the entire  area by the writer is the Mt. Washington stock, and a few dykes are found in the Triassic rocks in the v i c i n i t y of the feeder whereas no porphyry intrusions i n Triassic rocks in the immediate v i c i n i t y of Constitution H i l l were observed. (3)  several thin erosional outliers or grabens of  Upper Cretaceous sediments lying on Triassic volcanic rocks and containing s i l l s may be present between Mt. Washington and Constitution H i l l .  These s i l l s may be remnants of the  former sheet-like body or lenses mentioned above.  Two such  outliers containing remnants of s i l l s are known to be present approximately 2500 feet west of Constitution H i l l .  Other  outcrops of porphyry oecuring in areas southeast of Mt. Washington which are almost certainly underlain by Upper Cretaceous sediments, have been observed by the writer. (4)  there is very l i t t l e contact metamorphism of the  Upper Cretaceous sediments in the two outliers mentioned in part (2),  and at Constitution H i l l where the sediments are  overlain by several hundred feet of porphyry, they are hardly affected (p.75).  The writer has also not observed any  intense hydrothermal alteration or copper mineralization at these outliers or at Constitution H i l l .  These facts would  appear to indicate that the feeder for intrusion of the porphyry was far removed from the H i l l and outliers, or else  104  t h a t i t was v e r y s m a l l and i s now c o m p l e t e l y c o v e r e d  by  p o r p h y r y , because i n t h e v i c i n i t y o f a known f e e d e r - t h e Mt. W a s h i n g t o n s t o c k - the r o c k s have been h i g h l y i n d u r a t e d , a l t e r e d , and i n many l o c a l i t i e s ,  intensely mineralized.  105 VII  ORIGIN OF THE BRECCIAS  AND FRACTURED AND BRECCIATED ROCKS  A.  Current Theories  on the O r i g i n o f B r e c c i a  Pipes  The o r i g i n o f b r e c c i a p i p e s has l o n g been the much c o n t r o v e r s y among g e o l o g i s t s . agreed that  genetic  subject  However, i t i s  relationships exist  between  generally  the  i n t r u s i o n o f magma and the f o r m a t i o n o f most b r e c c i a Gates  ( 1 9 5 9 , p p . 8 0 6 - 8 1 2 ) has made an e x c e l l e n t  current  beliefs  on the o r i g i n o f b r e c c i a  of  pipes.  summary of  the  pipes.  Burbank ( 1 9 4 1 , p . 1 7 7 ) e x p l a i n s the development  of  breccia  p i p e s i n t h e San J u a n M o u n t a i n s o f C o l o r a d o as f o l l o w s : "The i n f e r r e d h i s t o r y of p i p e f o r m a t i o n may be b r i e f l y summarized up t o the p o i n t o f c o m p l e t e development o f the pipe, • The passage o f magmatic e m a n a t i o n s up t h r o u g h f a v o u r a b l y j o i n t e d and f i s s u r e d r o c k may have c a u s e d c e r t a i n c h e m i c a l o r volume changes a l o n g some v e r t i c a l a x i s o f g r e a t e s t c o n c e n t r a t i o n , w h i c h i m p a i r e d the s t r e n g t h o f the r o c k and i n d u c e d l o c a l c r a c k l i n g and c r u m b l i n g . The zone o f d i s i n t e g r a t i o n s p r e a d outward f r o m the a x i s a l o n g g e n e r a l l y curved surfaces . As the b r e c c i a mass s p r e a d i n t o the s u r r o u n d i n g r o c k i t t e n d e d t o assume the f o r m e i t h e r o f a r i n g zone o r a c y l i n d r i c a l c o r e . When the b r e c c i a c o r e became partly displaced with intrusive rock, further external f r a c t u r i n g ensued as a r e s u l t o f u p t h r u s t i n g by the i n t r u s i v e body." I n d e s c r i b i n g the b r e c c i a p i p e s n e a r B a g d a d , A n d e r s o n , S c h o l z , and S t r o b e l l opinion that  (1955, p.42)  Arizona,  express  the  B u r b a n k ' s p r o p o s e d method o f o r i g i n (above)  as good an e x p l a n a t i o n as c a n be o f f e r e d and t h e y  is  further  state: "When gas p r e s s u r e was u n u s u a l l y g r e a t , gas e x p l o s i o n s p r o b a b l y c a r r i e d f r a g m e n t s u p w a r d , and abraded them d u r i n g transport. The p o s s i b i l i t y cannot be d e n i e d t h a t s u b s i d e n c e may have o c c u r r e d , p a r t i c u l a r l y i n the p i p e s t h a t a r e l a r g e l y  106. s h a t t e r e d h o s t r o c k , b u t n e i t h e r c a n i t be d e n i e d t h a t l o c a l upward movement h a s t a k e n p l a c e , and r o c k f r a g m e n t s have been rounded by a b r a s i o n . A g a i n a mass o f b r e c c i a might have been u p l i f t e d b o d i l y by t h e upward t h r u s t o f an u n d e r l y i n g p l u g o r d o m e l i k e i n t r u s i v e mass, a c c o u n t i n g f o r some p i p e s c o n t a i n i n g f r a g m e n t s d e r i v e d from r o c k u n i t s b e l o w . "  B.  Development o f t h e Murray  Breccia  The p i p e - l i k e shape o f t h e Murray b r e c c i a may be i n f e r r e d because i t i s i n n e a r v e r t i c a l c o n t a c t t o t h e n o r t h w i t h b i o t i t i z e d p o r p h y r y and t o t h e e a s t w i t h c l o s e - j o i n t e d Washington b r e c c i a . The Murray b r e c c i a was formed of  d u r i n g p a r t o f the p e r i o d  i n t r u s i o n o f p o r p h y r y a t Mt. W a s h i n g t o n .  I t s content of  p o r p h y r y f r a g m e n t s and i t s c r o s s - c u t t i n g r e l a t i o n s h i p w i t h b i o t i t i z e d p o r p h y r y o f t h e Main s i l l  i n d i c a t e that i t i s  younger t h a n much o f t h e p o r p h y r y , b u t because i t i s i n t r u d e d by dykes o f p o r p h y r y i t was formed magmatic The  before the f i n a l  stages of  activity. i n t r u s i v e n a t u r e o f much o f t h e b r e c c i a i s a p p a r e n t  because some o f i t o c c u r s as a s i l l  i n a foundered b l o c k of  Upper C r e t a c e o u s s e d i m e n t s and because i t c o n t a i n s numerous inclusions.  Many o f i t s c h a r a c t e r i s t i c s such as s w i r l e d  s t r e a k s o f d i o r i t i c m a t e r i a l , s h r i n k a g e (?) and i t s d i o r i t i c nature.  joints: (plate XVI),  composition are i n d i c a t i v e o f i t s igneous  These, and t h e p r e s e n c e o f a l i t t l e  abraded  p l a g i o c l a s e c r y s t a l p r o j e c t i n g from a p o r p h y r y fragment  into  t h e m a t r i x ( p l a t e s XX and X X I ) i n d i c a t e t h a t i t was h i g h l y m o b i l e when  formed.  R a p i d changes i n t h e appearance  and c o n t e n t o f t h e b r e c c i a  107.  may be the r e s u l t s o f d i f f e r e n t  c o n d i t i o n s e x i s t i n g at v a r i o u s  l o c a t i o n s i n the p i p e o r o f v e r t i c a l movements w i t h i n the pipe of blocks  o f b r e c c i a bounded by the t r a n s v e r s e f r a c t u r e s  shown on map 2.  Such movements o f b l o c k s may have been  caused by changes i n the magmatic p r e s s u r e stock.  o f the u n d e r l y i n g  I t s r e s u l t s c o u l d be t h a t d i f f e r e n t  formed at d i f f e r e n t  breccias  l e v e l s i n the p i p e a r e now seen s i d e by  s i d e , and because i n t e r m i n g l i n g o f these b r e c c i a s may have o c c u r r e d ations exist  appearing  among them.  Cretaceous roof rocks  different  appearing  d u r i n g movement o f b l o c k s  grad-  Slumping or s h a t t e r i n g o f the Upper  d u r i n g movement o f the b l o c k s  may  account f o r the l o c a l presence o f r u b b l y Murray b r e c c i a . The  presence o f w e l l rounded fragments such as those o f  the Murray b r e c c i a has been r e c o r d e d breccia pipes.  Rust  i n d e s c r i p t i o n s o f many  (1936, p.58) r e p o r t s t h a t the diatreme  b r e c c i a s of southeastern  M i s s o u r i are so s i m i l a r i n appear-  ance t o c o n g l o m e r a t e s t h a t they were mapped as such i n the e a r l y 1900's. The  m a j o r i t y o f the fragments i n the Murray b r e c c i a a r e  p o r p h y r y whereas T r i a s s i c  r o c k fragments a r e e x t r e m e l y r a r e .  T h i s may be due to the f a c t  t h a t most o f the rock  lying  d i r e c t l y under the p i p e when i t formed was p o r p h y r y . L a y e r i n g i s not uncommon i n b r e c c i a p i p e s . has  Hunt  (1958)  d e s c r i b e d l a y e r e d b r e c c i a p i p e s o f the L a S a l Mountains  i n Utah whose b r e c c i a s are s t r i k i n g l y s i m i l a r t o the Murray breccia. by  L a y e r i n g i n the Murray b r e c c i a may have developed  s e t t l i n g and subsequent s e g r e g a t i o n  which o c c u r r e d pipe.  during  of mobile m a t e r i a l  the s u b s i d e n c e o f b l o c k s w i t h i n the  I t s i r r e g u l a r nature  and c o n t o r t e d  appearance may be  108.  a r e f l e c t i o n o f many f a c t o r s such as unequal r a t e s and amounts o f s u b s i d e n c e o r the d i f f e r e n t manners i n which t h e b r e c c i a was i n t r u d e d The  writer  the  layered  at d i f f e r e n t l o c a t i o n s within  does n o t r u l e out the p o s s i b i l i t y  that  Murray b r e c c i a may be p y r o c l a s t i c  the p i p e . some o f  material  brought t o i t s p r e s e n t p o s i t i o n by s u b s i d e n c e . After considering features  the p o s s i b l e  o r i g i n s o f some o f the  o f the Murray b r e c c i a the w r i t e r has made the  following conclusions (1)  regarding  i t s formation:  the b r e c c i a formed a f t e r t h e i n t r u s i o n o f much  magma had o c c u r r e d  from the s t o c k  i n t o the Upper C r e t a c e o u s  sediments. (2)  the i n t r u d e d  from the s u r f a c e  magma may have s e a l e d  thereby forming a c l o s e d  o f f the s t o c k  system i n which  gases and magma accumulated such as was thought by Rust p.70)  t o have o c c u r r e d (3)  at the d i a t r e m e s o f M i s s o u r i .  gaseous and magmatic p r e s s u r e may have caused  formation of v e r t i c a l  f r a c t u r e s above the s t o c k which c o i n -  c i d e d w i t h the p r e s e n t p o s i t i o n o f B r e c c i a (4)  ridge.  the b r e c c i a was formed by p r o c e s s e s s i m i l a r t o  those d e s c r i b e d (p.los).  (1936,  by Burbank, and Anderson, S c h o l z ,  Much o f i t may have been i n t r u d e d  and S t r o b e l l  i n a manner some-  what s i m i l a r t o the i n t r u s i o n b r e c c i a a t K i l k e n n e y , ( P i t c h e r and Read, 1952), and the i n t r u s i o n b r e c c i a s  Scotland near  Horseshoe Bay, B r i t i s h Columbia, some c h a r a c t e r i s t i c s o f which have been d e s c r i b e d  1  t o the w r i t e r by R o s s .  D r . J.V. Ross, A s s i s t a n t Columbia  Professor,  1  University of B r i t i s h  109  I t s formation may have been accompanied by some vulcanism. (5)  i n t r u s i o n of porphyry into the b r e c c i a occurred  a f t e r i t s formation.  C.  Development  of the Washington B r e c c i a  The Washington b r e c c i a assumes a p i p e - l i k e shape.  It i s  almost c e r t a i n l y younger than the Murray b r e c c i a because veins of b r e c c i a which appear to be offshoots of i t are present w i t h i n the Murray b r e c c i a .  It may have formed soon  a f t e r the Murray b r e c c i a by b u r s t i n g and upthrusting or slumping of b r e c c i a t e d rocks within a d i l a t i o n a l f r a c t u r e , the No.5 f a u l t .  D i l a t i o n a l movement may have occurred on  the f a u l t when the block of rocks bounded by No.'s 1, 3, and 5 f a u l t s foundered into the stock underlying  it.  Bursting of close jointed rocks or of sediments which were e a s i l y s p l i t along t h e i r bedding planes may have cont r i b u t e d the high proportion of s l a b - l i k e fragments to the breccia.  Many of i t s rounded fragments may have been derived  from the Murray b r e c c i a .  Some rounding of fragments and the  strewing out of matrix between assemblages of angular and p a r t l y rounded fragments and along the edges of the pipel i k e outcrop may have been caused by gas streaming accompanied by f l u i d i z a t i o n , which i s believed by Reynolds (1954) to be an important g e o l o g i c a l process. Gates (1959, p.809) considers that rock b u r s t i n g , "perhaps deserves more consideration than has been granted i t heretofore."  He b e l i e v e s that a study of rock b u r s t i n g  w i t h i n mines could help to reveal the o r i g i n of b r e c c i a  110 pipes-.  Concerning  r o c k b u r s t i n g i n mines he s t a t e s (p.810,  811, 8 1 2 ) : "Large b o d i e s o f r o c k may be c o m p l e t e l y b r e c c i a t e d w i t h r e l a t i v e l y l i t t l e movement o f t h e body as a w h o l e . Rock b u r s t s c a n produce a v a r i e t y o f b r e c c i a s . Some a r e i n c o h e r e n t masses o f a n g u l a r f r a g m e n t s o f a l l s i z e s r a n g i n g from dust t o b l o c k s weighing t o n s . In a v o l c a n i c a r e a , e s p e c i a l l y where t h e r o c k s a r e b r i t t l e and siliceous r o c k b u r s t i n g m i g h t o c c u r i f f r e e f a c e s were formed." A c t i n o l i t i c h o r n b l e n d e i n t h e W a s h i n g t o n b r e c c i a may have been d e p o s i t e d by v o l a t i l e - r i c h s o l u t i o n s w h i c h emanated f r o m t h e u n d e r l y i n g s t o c k .  Magnetite  i n the matrix  may have been d e r i v e d f r o m t h e s t o c k by a p r o c e s s  similar to  t h a t d e s c r i b e d by M a c k i n (1948) f o r t h e m a g n e t i t e d e p o s i t s at I r o n S p r i n g s , Utah.  However, t h e n a t u r e  of the v e i n l e t  o f c a l c i t e , e p i d o t e , and c h l o r i t e d e s c r i b e d p r e v i o u s l y (p.7 I ) may i n d i c a t e t h a t much o f t h e m a g n e t i t e was d e r i v e d f r o m t h e b r e c c i a t e d r o c k s by a p r o c e s s D.  involving secretion.  Development and S i g n i f i c a n c e o f t h e F r a c t u r e d and B r e c c i a t e d Rocks: F o r c i b l e i n t r u s i o n o f t h e Mt. W a s h i n g t o n s t o c k accomp-  a n i e d by e x p l o s i v e a c t i v i t y c a u s e d by e x p a n s i o n accumulating  o f gases  above and w i t h i n t h e s t o c k may have c a u s e d t h e  f o r m a t i o n o f t h e zone o f f r a c t u r e d and b r e c c i a t e d r o c k s a l o n g t h e west b o r d e r The  of the stock.  s i g n i f i c a n c e o f t h e s e r o c k s , and t o a l e s s e r e x t e n t o f  the o t h e r b r e c c i a s , i s t h a t t h e y a r e f o u n d o n l y i n t h e v i c i n i t y o f t h e Upper C r e t a c e o u s - T r i a s s i e u n c o n f o r m i t y . may i n d i c a t e t h a t v e r t i c a l and l a t e r a l development o f t h e s t o c k was r e s t r i c t e d w i t h i n t h e T r i a s s i c r o c k s because o f  This  111. t h e i r m a s s i v e n a t u r e , b u t t h a t when t h e s t o c k had r e a c h e d near t o the unconformity  i t breached the surface o f the  T r i a s s i c rocks thereby causing extensive b r e c c i a t i o n i n i t s vicinity.  I t may t h e n have s p r e a d out l a t e r a l l y w i t h i n t h e  Upper C r e t a c e o u s porphyry  sediments t o form the Main s i l l  body a t C o n s t i t u t i o n H i l l .  and t h e  T h i s method o f i n t r u s i o n  i s so s i m i l a r t o t h a t p r o p o s e d by Gunning (1932) f o r t h e Nimpkish  " b a t h o l i t h " o f n o r t h - c e n t r a l Vancouver I s l a n d t h a t  the l a t t e r must be c o n s i d e r e d i n t h i s s e c t i o n . the i n t r u s i o n o f t h e N i m p k i s h  Concerning  " b a t h o l i t h " Gunning s t a t e s  (p.303): " t h e l i m e s t o n e i n t r u d e d by g r a n o d i o r i t e i s u n d e r l a i n by a m a s s i v e assemblage o f f l o w s and v o l c a n i c f r a g m e n t a l s , a t l e a s t s e v e r a l thousand f e e t t h i c k , known as t h e K a r m u t s e n v o l c a n i c s . These r o c k s f o r m a h a r d , competent member. The l i m e s t o n e i s about 1000 f e e t t h i c k and above i t i s a t h i c k n e s s o f about 400 f e e t o f a r g i l l i t e , impure l i m e s t o n e , q u a r t z i t e and t u f f . T h i s s u c c e s s i o n , and the s u b s u r f a c e . f o r m o f t h e g r a n o d i o r i t e a s w e l l a s t h e close f o l d s i n the limestone, suggest t h e f o l l o w i n g method o f i n t r u s i o n . The magma arose along a n o r t h w e s t e r l y t r e n d i n g l i n e o f weakness. I t ascended t h r o u g h the competent Karmutsen v o l c a n i c s i n r a t h e r r e s t r i c t e d f o r m but under g r e a t p r e s s u r e . E x c e p t i n so f a r a s s t o p i n g was o p e r a t i v e a t t h i s s t a g e , t h e magma f o u n d g r e a t d i f f i c u l t y i n e n l a r g i n g i t s chamber. But when t h e i n t r u s i v e had p i e r c e d t h r o u g h t h e v o l c a n i c s i t e n c o u n t e r e d t h e l e s s comp e t e n t l i m e s t o n e and a r g i l l i t e s w h i c h w o u l d y i e l d more r e a d i l y t o compressive f o r c e s than the u n d e r l y i n g v o l c a n i c s . Once i n t h e l i m e s t o n e t h e magma was a b l e t o e n l a r g e i t s chamber by l a t e r a l e x t e n s i o n . I t o v e r r o d e t h e u n d e r l y i n g v o l c a n i c s , p u s h i n g b a c k t h e l i m e s t o n e i n t o a s e r i e s o f more o r l e s s , t i g h t l y compressed f o l d s ? "  112. VIII  The  SEQUENCE OF GEOLOGICAL EVENTS  g e o l o g i c a l h i s t o r y o f t h e Mt. W a s h i n g t o n a r e a  during  the f o l l o w i n g e r a s , p e r i o d s , and epochs may have i n c l u d e d t h e following  events:  (1)  T r i a s s i c : - d e p o s i t i o n on t h e ocean b o t t o m o f  g r e a t t h i c k n e s s e s o f a n d e s i t i c and b a s a l t i c v o l c a n i c r o c k s . (2)  Late J u r a s s i c - E a r l y Cretaceous-Late  Cretaceous:  —  e l e v a t i o n t o above s e a l e v e l o f t h e T r i a s s i c rocks: accompanied  by t h e i r e r o s i o n and f o l l o w e d by t h e i r d e p r e s s i o n t o  below s e a l e v e l d u r i n g t h e f o r m a t i o n  o f the P a c i f i c  coast  downfold. (3)  Late Cretaceous:  - d e p o s i t i o n o f s e v e r a l thousand  f e e t of sediments i n c l u d i n g s h a l e s , sandstones, conglomerates and  c o a l beds, under c o n d i t i o n s ; d e s c r i b e d by M a c k e n z i e (4)  Cenozoic:  - accentuation of the P a c i f i c  d o w n f o l d by f o l d i n g and f a u l t i n g a l o n g NNW a x e s .  (1922).  coast  The i n l a n d  a r e a s were e l e v a t e d t o above s e a l e v e l and much o f t h e Upper C r e t a c e o u s s e d i m e n t s were e r o d e d .  During  e a r l y 01igocene(?)  d i o r i t i c magma was i n t r u d e d i n t o t h e r o c k s o f Mt. W a s h i n g t o n and  Constitution H i l l .  The i n t r u s i o n o f t h e Mt. W a s h i n g t o n  s t o c k c a u s e d t h e f o r m a t i o n o f t h e domed s t r u c t u r e i n t h e r o c k s o f t h e m o u n t a i n , t h e r a d i a l f r a c t u r e p a t t e r n , and t h e b r e c c i a s , and was f o l l o w e d c l o s e l y by t h e d e p o s i t i o n o f metallic minerals. in half.  L a t e r f a u l t i n g c u t t h e domed s t r u c t u r e  E r o s i o n o f much o f t h e f r a c t u r e d r o c k a t Mt.  Washington i n i t i a t e d the f o r m a t i o n basins.  o f t h e MacKay and Murex  At t h e same t i m e , e r o s i o n o f t h e c o v e r o f s e d i m e n t s  113  at  Constitution H i l l l i k e l y  o c c u r r e d so t h a t t h e p o r p h y r y  body a t t h e h i l l was exposed t o t h e s u r f a c e . (5)  P l e i s t o c e n e : - m o d i f i c a t i o n of the topography  d u r i n g two s t a g e s o f g l a c i a t i o n ( C l a p p , 1917,  p.350).  D u r i n g the c l i m a x e s o f t h e g l a c i a l s t a g e s t h e i c e on Vancouver I s l a n d was h i g h e s t a t an i c e d i v i d e a t B u t t l e Lake (fig.l), Mathews  and i t s s u r f a c e s l o p e d downward t o w a r d s t h e e a s t . has f o u n d e v i d e n c e t h a t t h e i c e r e a c h e d a maximum  1  e l e v a t i o n o f 6300 f e e t on Mt. A l b e r t Edward between B u t t l e Lake and Mt. W a s h i n g t o n .  , which i s :  T h e r e f o r e the i c e  was l i k e l y n e v e r much h i g h e r t h a n t h e Summit w h i c h i s a t an e l e v a t i o n o f 5215 f e e t . the  first  As a r e s u l t e r o s i o n a l f e a t u r e s o f  t h r e e phases o f g l a c i a t i o n p r o p o s e d by D a v i s and  Mathews (1944, p.409) were formed a t Mt. Washington the  during  advance and r e t r e a t o f t h e i c e . Such f e a t u r e s a r e the  Summit w h i c h i s domed, the rounded arms, and t h e U-shaped MacKay and Murex b a s i n s w h i c h the i c e a c c e n t u a t e d . In ice  t h e S t r a i t o f G e o r g i a and on t h e C o a s t a l p l a i n the  was much t h i c k e r t h a n i t was a t Mt. W a s h i n g t o n .  smoothed p r o m i n e n c e s s u c h as C o n s t i t u t i o n H i l l  It  as i t moved  southeast. (6) of  Recent: - l i t t l e  e r o s i o n , m a i n l y the f o r m a t i o n  s m a l l but s t e e p - w a l l e d r i v e r o r s t r e a m v a l l e y s i n s o f t  g l a c i a l m a t e r i a l o r a l o n g zones o f f r a c t u r e d  1 2  rock.  D r . W.H. Mathews, A s s o c i a t e P r o f e s s o r , U n i v e r s i t y o f B r i t i s h Columbia P e r s o n a l c o m m u n i c a t i o n w i t h W.H. Mathews.  114.  BIBLIOGRAPHY  B a l k , R.  (1937), " S t r u c t u r a l Behaviour o f Igneous Rocks", G e o l . Soc. Am. Mem. 5, pp> 27-40, pp. 97-129.  Buckham, A.F., "The Nanaimo C o a l F i e l d " , V o l . 50, pp. 460-472.  Can.  I n s t . Min.  Met.  Buddington, A.F. (1935), "High Temperature M i n e r a l A s s o c i a t i o n s at Shallow to Moderate Depth", Econ. G e o l . , V o l . 3 0 , p. 205. Burbank, W.S. (1941), " S t r u c t u r a l C o n t r o l o f Ore D e p o s i t i o n i n the Red Mountain, S n e f f e l s , and T e l l u r i d e d i s t r i c t s o f the San Juan Mountains", C o l o . S c i . Soc. P r o c , V o l . 14, p. 177. C a r r , J.M.  (1954), "Zoned P l a g i o c l a s e s i n L a y e r e d Gabbros o f the S k a e r g a a r d I n t r u s i o n , E a s t G r e e n l a n d " , M i n e r a l o g . Mag., London, V o l . 3 0 , No. 2 2 5 , pp. 367375.  C l a p p , C H . (1911), " G e o l o g i c a l Survey o f Canada, Summary R e p o r t " , 1 9 1 1 , p. 106. "  "  (1917), "Sooke and Duncan Map-areas Vancouver I s l a n d " , G e o l . S u r v . Can. Mem. 96, pp. 93-103, p . 304.  D a v i s , N.F.G. and Mathews, W.H. (1944), "Four Phases: of G l a c i a t i o n w i t h I l l u s t r a t i o n s from Southwestern B r i t i s h Columbia", J o u r n . G e o l . , V o l . 52, pp. 403413. Edwards, A.B. (1954), " T e x t u r e s of the Ore M i n e r a l s and T h e i r S i g n i f i c a n c e " , A u s t r a l i a n I n s t . Min. Met., 1954. F y l e s , J . T . (1955), "Geology o f the Cowichan Lake A r e a " , B r i t . C o l . Dept. Mines B u l l . No. 37, pp> 11-27. Gates, 0.  ( 1 9 5 9 ) , " B r e c c i a P i p e s of the Shoshone Range, Nevada", E c . G e o l . , V o l . 5 4 , pp. 790-815.  Greenwood, H.J. and McTaggart, K.C. ( 1 9 5 7 ) , " C o r r e l a t i o n o f Zones i n P l a g i o c l a s e " , Am. J o u r n . S c i . , V o l . 255, pp. 6 5 6 - 6 6 6 . Gunning,  H.C. (1931), " B u t t l e Lake Map-area Vancouver I s l a n d " , G e o l . S u r v . Can. Summ. Rept. f o r 1 9 3 0 , p t . A, pp. 5 6 - 7 8 .  it  ( 1 9 3 2 ) , "Form and Mechanics o f I n t r u s i o n of the Nimpkish ' B a t h o l i t h " , Trans:. Roy. Soc. Can., T h i r d S e r i e s , V o l . 26, S e c t i o n 4.  "  1  115 H i l l s , E.S. (1936), "Reverse and 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 F e l d s p a r s " , G e o l . Mag. V o l . 73, No. 2,  pp. 49-56.  Hunt, C B . (1958), " S t r u c t u r a l and Igneous G e o l o g y o f t h e L a S a l M o u n t a i n s , U t a h " , G e o l . S u r v . Am. P r o f . Pap. 294. Hunt, C.B., A v e r i t t , P., and M i l l e r , R.L. (1953), "Geology and Geography o f t h e Henry M o u n t a i n s R e g i o n , U t a h " , G e o l . S u r v . Am. P r o f . P a p . 228, pp. 36-166. M a c k i n , J.H. (I960), " S t r u c t u r a l S i g n i f i c a n c e o f T e r t i a r y V o l c a n i c Rocks i n S o u t h w e s t e r n U t a h " , Am. J o u r n .  S c i . , V o l . 258, p p . 114-119.  M a c k i n , J . 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(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 G r a n i t e s " , Am. J o u r n . S c i . , V o l . 252, p p . 577-614.  R i c h e y , J . E . (1937), "Some F e a t u r e s o f T e r t i a r y V o l c a n i c i t y i n S c o t l a n d and I r e l a n d " , B u l l . V o l c a n o l o g i q u e , S e r . 2, Tome 1, pp. 13-34. "  "  (1940), " A s s o c i a t i o n o f E x p l o s i v e B r e c c i a t i o n and P l u t o n i c I n t r u s i o n i n t h e B r i t i s h T e r t i a r y Igneous P r o v i n c e " , B u l l . V o l c a n o l o g i q u e , S e r . 6, Tome 2,  pp;. 157-175.  R i c h e y , J . E . and Thomas, H.H. (1932), "The T e r t i a r y R i n g Complex o f S l i e v e G u i l l o n ( I r e l a n d ) " , J o u r n . G e o l . Soc. Lond., V o l . 88, pp. 776-849. R u s t , G.W. (1936), " P r e l i m i n a r y N o t e s on E x p l o s i v e V u l c a n i s m i n S o u t h e a s t e r n M i s s o u r i " , J o u r n . G e o l . , V o l . 45,  pp. 48-75.  116  S i d w e l l , R. ( 1 9 3 1 ) , " E f f e c t s o f D i k e s and D i s p l a c e m e n t Movements on S e d i m e n t s i n C a p i t a n Q u a d r a n g l e , New M e x i c o " , Am. M i n . V o l . 3 1 , pp. 6 5 - 7 0 . Tweto, 0 .  (1951),  "Form and S t r u c t u r e o f S i l l s Near Pando C o l o r a d o " , G e o l . S o c . Am. B u l l . , V o l . 6 2 , pp. 5 0 7 532.  Waters:, A.C. ( 1 9 3 8 ) , " P e t r o l o g y o f t h e C o n t a c t B r e c c i a s o f the C h e l a n B a t h o l i t h " , B u l l . G e o l . S o c . Am., Vol.  49,  pp. 7 6 3 - 7 9 4 .  W h i t e , W.H. ( 1 9 5 9 ) , " C o r d i l l e r a n T e c t o n i c s i n B r i t i s h C o l u m b i a " , B u l l . Am. A s s o c n . P e t . G e o l . , V o l . 4 3 , No. 1 , J a n u a r y , 1 9 5 9 , p p . 8 1 - 9 9 . W h i t e , W.H., Thompson, R.M., and M c T a g g a r t , K.C. ( 1 9 5 7 ) , "The G e o l o g y and M i n e r a l D e p o s i t s o f H i g h l a n d V a l l e y , B.C.", Can. M i n . M e t . B u l l . , Aug. 1 9 5 7 , pp.  487-503.  W i s s e r , E . ( I 9 6 0 ) , " R e l a t i o n o f Ore D e p o s i t i o n t o Doming i n the N o r t h A m e r i c a n C o r d i l l e r a " , G e o l . S o c . Am. Mem. 7 7 .  

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