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Geology of the Upper Triassic Nicola group in south central British Columbia Schau, Mikkel Paul 1968

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GEOLOGY OF THE UPPER TRIASSIC NICOLA GROUP IN SOUTH CENTRAL BRITISH COLUMBIA  by KEKKEL PAUL SCHAU B.Sc., University of B r i t i s h Columbia, 1 9 6 4  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of GEOLOGY  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA December, 1968  In p r e s e n t i n g  this  thesis  an a d v a n c e d d e g r e e a t the I  the U n i v e r s i t y of  L i b r a r y s h a l l make  f u r t h e r agree  for  of  thesis  written  for  It  of  GEOLOGY  T  DECEMBER 23,  E  t  Columbia  1968  shall  the requirements  Columbia,  I agree  r e f e r e n c e and copying  of  this  that copying  or  for  that  Study. thesis  t h e Head o f my D e p a r t m e n t  understood  f i n a n c i a l gain  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, Canada  A  is  permission.  Department  D  for extensive  may be g r a n t e d by  representatives.  this  British  it freely available for  that permission  s c h o l a r l y purposes  by h i s  in p a r t i a l f u l f i l m e n t of  or  publication  n o t be a l l o w e d w i t h o u t my  ABSTRACT  The rocks of the Upper T r i a s s i c Nicola Group represent the altered broken remnants of a volcanic i s l a n d archipelago.  About 23,000 feet  of Upper T r i a s s i c sediments and volcanic rock are present i n the thesis area.  The group i s the product of two cycles of deposition d i s t i n g u i s h -  able on the basis of r e l a t i v e abundance of phenocrysts i n the volcanic members.  Rocks of the lower cycle (p), characterized by abundant feldspar  phenocrysts, are separated i n t o a lower, 6,000 foot thick assemblage of flows, breccias, and t u f f s composed mainly of b a s a l t i c andesite;  and an  upper, heterogeneous, 8,000 foot thick assemblage composed of andesitic and rarer b a s a l t i c or d a c i t i c agglomerates, breccias, t u f f s , flows, and associated  sediments as well as c o r a l reef bodies.  Rocks of the upper  cycle (A), characterized by abundant augite phenocrysts, are separated into a lower assemblage about 7,500 feet thick composed of flows, breccias, t u f f , and greywacke with rare limestone; and an upper assemblage about 1,600 feet thick composed of t u f f , a r g i l l i t e s , and cherts. During the Lower Jurassic, the group was gently folded, v a r i a b l y fractured, and intruded by a sequence of plutons culminating surface emplacement of huge batholiths.  i n the near-  Metamorphism and metasomatism  associated with batholiths altered the rocks so that they are now composed of low-grade metamorphic mineral assemblages.  By mid-Mesozoic time, the  plutons were exposed and a conglomerate l a i d down.  Faulting along  previous zones of weakness affected area during l a t e Mesozoic time. Eocene deposits formed i n an environment of h i l l s and swamps.  By l a t e  Miocene, a f t e r some j o s t l i n g of f a u l t s blocks, the main topographic  iii  features of the I n t e r i o r Plateau were f i x e d .  Subsequent outpouring of  Plateau and Valley basalts as well as g l a c i a l erosion and deposits have only mildly affected the main topographic features. The Nicola Group provides a chapter on the evolution of the C o r d i l l e r a . The r e l a t i o n s h i p s provide c e r t a i n l i m i t s to events that occurred the thesis area.  outside  Equally, relationships within the thesis area cannot  a l l be answered without reference  to larger areas.  iv TABLE OF CONTENTS CHAPTER I INTRODUCTION page General Statement  1  Location and Accessibility  1  Previous Work  •  Present Investigation  1 •  Acknowledgement  4 •  4  CHAPTER II GENERAL GEOLOGY Introduction  5  Sedimentary and Volcanic Rock  6 6  Cache Creek Complex Nicola Group  12  "Clapperton Conglomerate"  13  Kamloops Group  17  Arkose  17  Volcanic Rocks  19  Conglomerate  19  Plateau Basalt  20  Valley Basalt  21  Physiography and Glacial Geology  ..  Plutonic Units Dacite Plugs Quartz Diorite Stocks  22 24  .  26 28  V  page Batholiths  .  33  Penask B a t h o l i t h  36  Central Nicola Batholith  36  Douglas Lake P l u t o n  38  Summary  38 CHAPTER I I I NICOLA GROUP  Stratigraphy  •  40  G e n e r a l Statement  40  Assemblage P^  40  D i s t r i b u t i o n and T h i c k n e s s  40  Lithology  42  Internal Structures Indicators  and S t r a t i g r a p h y  44  o f Age and C o r r e l a t i o n  45  Assemblage P £  47  D i s t r i b u t i o n and T h i c k n e s s  47  Lithology  47  Internal Structures  and S t r a t i g r a p h i c V a r i a t i o n  ...  Age and C o r r e l a t i o n  59 62  Assemblage A^  64  D i s t r i b u t i o n and T h i c k n e s s  64  Lithology  64  Internal Structures Age and C o r r e l a t i o n  and S t r a t i g r a p h i c V a r i a t i o n  ...  67  ...  68  vi  Assemblage A  2  page 70  ..  D i s t r i b u t i o n and Thickness  70  Lithology  70  Internal Structures and Stratigraphic V a r i a t i o n  ...  Age and C o r r e l a t i o n  72 72  O r i g i n of the N i c o l a Group Introduction  70  •  72  Assemblage P]_  74  Assemblage P£  75  Volcanic Centers  75  Shallow-water Reefs  76  N e r i t i c Environments  •  78  Islands  •  Stratigraphic V a r i a b i l i t y  80 ..  Assemblage A^ Assemblage A  2  81 81  •  Conclusion  *  82 83  Chemistry of the N i c o l a Group Metasomatism Evidence of Metasomatism  83 85 85  Textural and Mineralogical Evidence  85  Chemical Evidence  86  Chemical Changes Effected by Metasomatism  91  General Statement  91  Changes Incurred by Metasomatism  92  vii Classification of Volcanic Rock of Nicola Group  ........  Mineralogical and Textural Criteria  page 97 97  Chemical Criteria  101  Nomenclature  104  Origin of Volcanic Rocks in the Nicola Group  104  Diversity of Volcanic Rocks  104  The Parent Magmas  107  Summary ..•••••••••••••••••.••••............*........... Structure  Ill Ill  Introduction Folds  Ill ...  HI  Meander Hills Syncline  Ill  Folds at Nicola Lake  114  Foliation  118  Faults  124  Longitudinal Faults  124  Introduction  124  Glimpse Lake Fault  124  Quilchena Fault Zone  126  Nestor Creek Fault System  127  Clapperton Creek-Howarth Creek Fault Zone Cross-faults  ....  129 130  Lineaments  133  Minor Structures  134  Conditions of Deformation  140  Stress Environment  143  viii page 146  Metamorphism Mineral Assemblages  146  Textural Changes  146  Mineralogic Changes  152  D i s t r i b u t i o n of Mineral Assemblages  •  155  Tests f o r Equilibrium  156  Environment of Metamorphism  164  Age of Metamorphism  169  O r i g i n of Metamorphism  170  Conclusion  171 CHAPTER IV THE NICOLA GROUP IN PERSPECTIVE  Introduction  •  .«  172  H i s t o r i c a l Geology of the N i c o l a Group  172  Upper T r i a s s i c Paleogeography of South Central B r i t i s h Columbia  175  N i c o l a Group i n World View of Upper T r i a s s i c  177  The Bearing of Sequence of Events i n Thesis Area on the Evolution of the C o r d i l l e r a  177  Regional A l t e r a t i o n  178  Geophysical  180  Speculations  Suggestions f o r Further Work REFERENCES CITED  4  180  *  APPENDIX 1:  Chemical Analyses of Nicola Group  APPENDIX 2:  Descriptions of F o s s i l L o c a l i t i e s  APPENDIX 3:  Spectrographs Methods  182 191 „  201 208  LIST OF ILLUSTRATIONS Figures 1.  Geology of the Nicola Group  in pocket  2.  Cross-sections  in pocket  3.  Fossil localities of the Nicola Group  in pocket  4. Oblique view of the thesis area 5.  2  Sketch map of Douglas Lake region  11  6. Distribution of "Clapperton Conglomerate"  14  7.  16  Distribution of Tertiary units  8. Distribution of plutons  27  9. Variation of specific gravity in South Nicola stock ..  29  10.  Variation of specific gravity and grain size in northwest corner of South Nicola stock  29  11.  Summary of plutonic activity  39  12.  Assemblage P]_  41  13.  Generalized section of Assemblage Pi  14.  Assemblage ?2  15.  Sections of Assemblage P  16.  Geology of area south of Nicola Lake (a volcanic center) Sketch map of edge of a reef (fossil locality 13) in Assemblage P •  61  18.  Assemblage A-j_  65  19.  Generalized section of Assemblage A^  69  20.  Assemblage A  71  21.  Generalized sections of Assemblage A  22.  Harker diagrams  87  23.  Na20 vs. K 0 in volcanic rocks of the Nicola Group ...  89  17.  ................  48 51  2  2  2  46  2  2  60  73  X  • ' page 24.  Harker diagram for modified values  ..................  102  25.  Oxidation ratio of the Nicola Group ..................  103  26.  Silica vs stratigraphic height  106  27.  The simplified basalt tetrahedron (modified after Yoder and Tilley, 1962)  108  28.  Distribution of fold elements In the Nicola Group ....  112  29.  Local folds at Nicola Lake  116  30.  Cross-section near Nicola Lake (see Fig. 29)  31.  Axes of minor folds along Nicola Lake  32.  Minor fold with east-plunging axis  119  33.  Variable plunge of the Meander Hills syncline .......  120  34.  Dispersion of poles to bedding from a recent volcano .  121  35.  Distribution of foliated area  122  36.  Poles to foliation  123  37.  Longitudinal faults  125  38.  Map showing local bend by Nestor Creek fault  39.  Cross-faults  131  40.  Non-glacial lineaments in thesis area  135  41.  Rose diagram of lineaments longer than one mile ......  136  42.  Variation of fault elements on one small portion of a non-planar fault surface (cutting South Nicola stock) Lines perpendicular to slickensides along faults of  43.  .. ........  116  ...............  117  .........  many different attitudes 44.  Poles to veins  45.  "Fault V from one locality showing the migration of intermediate stress component Proportions of metamorphic minerals besides albite in feldspars from 90 thin-sections in Nicola Group ..  46.  128  138 139 141 144 154  xi 47. Distribution of metamorphic facies in Nicola Group ....  page 157  48. Metamorphic environment (after Turner, 1968) .........  168  49. Summary of events in thesis area  173  .....................  50. Late Karnian-Early Nprian paleogeography of south central British Columbia .  176  51. The Nicola Group in relation to Phanerozoic in Canadian Cordillera  179  52. Working curve for Sr/Ba pair  ........................  211 (Appendix 3)  TabJ.es 1. Table of formations  7  2. Relations between units  9  3.  Fragments in overlying units  9  4.  Measured sections of Kamloops Group arkose  18  5.  Modal values of Valley basalt  18  6. Interglacial section from Coldwater River (Fulton, 1965) 7. Rock analyses, Nicola Group 8. Norms of completely analysed specimens, Nicola Group ..  25 195 (Appendix l ) 199 (Appendix l)  9. Insoluble residue/of limestones of Assemblage Pg  58  10. Fauna of deep-water reefs (after Teichert, 1958) 11. Variations of K 0 with distance from batholiths and Si0 content  58 90  12. Precision of chemical analyses of rocks of the Nicola Group  93  13. Copper in Nicola rock in comparison with other regions (from Prinz, 1967)  96  14. Rough adjustments to correct for local metasomatism in selected analyses ................................  96  2  2  xii 15. Modified selected chemical analyses calculated according to Table 14 ............................ 16. Norms of modified selected chemical analyses compared with original norms  page 98 99  17. Difference in aluminum content between Cycles A and P  110  18. Way-up criteria used to trace overturned folds 19. Minerals of Nicola Group found in type area  .....  ........  HO 147  20. A classification of Nicola Group rocks according to Turner and Verhoogen (i960; 21.  Mineral assemblages of calcareous rocks  149 ..........  22. Mineral assemblages of quarteofeldspathic rocks 23.  ....  149 150  Main mineral assemblages of basic sedimentary rocks..  150  24. Main mineral assemblages of basic effusive rocks .... 25. Ferric iron in epldote determined by method of  151  Myers (1965)  159  26. Variation of aluminum in chlorite 27. Strontium content of calcite from reef (Fig. 3 , loo. 14) 28. Strontium content from calcite in country rock ...... 29.. Qualitative modes of analysed rocks;, of Nicola Group 30. Summary of reef faunas, Nicola Group  159 162 162 191 205 (Appendix 2)  Plates I. Handspecimen showing distinctive porphyritic texture of dykes associated with South Nicola stock ....... II.  Negative print of thin-section of volcanic breccia, Assemblage P2  III. Negative print of thin-section of tuff, Assemblage P ?  53 53 54  xiii page IV.  Colonial corals (Astreid), Assemblage P  54  2  V. Negative print of thin-section of algal pisolites, Assemblage P2 VI.  77  Negative print of thin-section of algal crust, Assemblage P  77  2  T i l . Replacement mass of epidote near Nicola Lake  ........  84  VIII. Conglomerate with elongate fragments in limestone matrix IX. Holocene joints near Merritt, British Columbia .......  84 142  X. Fossils of the Nicola Group  2 0  ?  1  CHAPTER I INTRODUCTION  s  GENERAL STATEMENT This thesis deals with the stratigraphy, structure, petrology, and origin of the Upper Triassic Nicola Group in its type area in south central British Columbia. The study is part of the Cordilleran Structural Project (Wheeler, 1968) and this account of the geology of a small segment of the Interior Plateau provides a chapter in the history of the evolution of the Cordilleran mountain belt.  LOCATION AND ACCESSIBILITY The area mapped i s about 430 square miles centered on Quilchena, a small settlement about 10 miles east of Herritt, British Columbia, (Fig. 1, map in pocket). Highway 5 passes through the area and numerous logging roads and cattle trails join in to provide access to most parts of the area. Outcrop areas underlie about one-quarter of the region, but outcrops are generally rare.  PREVIOUS WORK The general geological framework of southern British Columbia was outlined by Dawson (1877). Greenish volcanic rocks that occur south of Nicola Lake he included in the Nicola Series and on the basis of some fossils in an associated limestone, determined them to be Upper Triassic in age.  These, as well as other units, are intruded  by plutonic rocks and overlain by Tertiary rocks. Dawson (1896) later  F I G U R E 4.  O B L I Q U E VIEW OF THESIS A R E A . LAKE,  HC - HAMILTON CREEK,  N - NICOLA VILLAGE, VILLAGE, LAKE,  M - MERRITT,  NC - NESTOR CREEK,  QC - Q U I L C H E N A C R E E K ,  (5) - H I G H W A Y  5.  GC - GODEY  LL - LUNDBLOM LAKE,  CREEK,  GL -  CC - C L A P P E R T O N  NL - NICOLA LAKE,  H M - HAMILTON MOUNTAIN,  GARCIA CREEK,  Q - QUILCHENA DL -  DOUGLAS  3 mapped the Kamloops sheet, which inoludes the northern part of the thesis area, on a scale of 8 miles to the inch. He enlarged his definition of the Nicola Series at this time to include the rocks from Meander Hills as the youngest member. Ells (1904a, 1904b) studied the Merritt and Quilchena coal basins in great detail.  He separated a Mesozoic  conglomerate from Tertiary coal-bearing beds, assigned rocks on Iron Mountain to the Nicola Series, and modified the boundaries between various units.  Some small mining prospects in the area have been studied by  Cole (1913), Young and TJglow (1926), Spence, (1928), White (1950), and Young (1962). Cockfield's (1944, 1948) map of the Nicola Sheet closely resembles Dawson's maps and he reassigned the Mesozoic conglomerate mentioned above to the Tertiary. New units in the map area were correlated with units exposed to the south and vest (Rice, 1947;  and McTaggart, 1952).  Duffell  Many mining prospects have recently been explored  in the Nioola Group, but none has yet proved economic (Kelly, 1962, unpublished report; Ashton, 1967, unpublished report; Mitchell, 1966, unpublished report). A generalized regional synthesis (Carr, 1962a) stressed graben structures in southern British Columbia. The results of a regional study of the Nicola Group were presented orally by Hillhouse (1964). His study demonstrated the possibility of subdividing the Nicola Group, the presence and importance of regional faults, and the lateral variation from sedimentary fringes to a volcanic center near the type area. He-concluded that i f the structure there were solved* the relationships between units could best be shown in the type area.  Mathews (1944) and  Pulton (1962, 1965) hav# studied glacial and post-glacial features of  the area. Bachelor theses at the university of British Columbia (Lambert, 1963; Campbell, 1966) have been concerned with Pleistocene Valley basalt.  PRESENT INVESTIGATIONS The present study i s based on 7 months' f i e l d work during the 1965* 1966, and 1967 seasons, as v e i l as laboratory work during the intervening periods. The f i e l d work inoluded geological mapping of about 430 square miles centered on Qollchena village.  Happing was done on half-mile to  the inch base maps and 1:50,000 scale maps made available by the Geological Survey of Canada and on half-mile to the inch a i r photographs contributed by Canex Aerial Explorations Limited. Laboratory investigations have inoluded examination of thin-sections under the mioroscope, optical and X-ray determinations of minerals, determinations of bulk speoific gravity, and chemical analyses of specimens by rapid methods.  ACKNOWLEDGEMENT Field vork for this thesis was financed largely through an I.N.CO. Fellowship and a grant i n aid of research to Sr. K.C. McTaggart provided by the Geological Survey of Canada. I am grateful to the Geological Survey and to the International Nickel Company for their assistance. I am especially indebted to Dr. K.C. McTaggart of the University of British Columbia for his guidance and his many helpful suggestions during the vriting of the thesis.  Dr. N. Hillhouse helped plan the work*  Drs. J.W. Murray, R.E.  Garrison, and H. Williams v i s i t e d i n the f i e l d .  Drs. R. Beerbower,  G. Westermann, D. Squires, T. Tozer, and N. S i l b e r l i n g helped to determine and make use of f o s s i l c o l l e c t i o n s .  Drs. J.A. Souther of the  G.S.C. and J . Payne of Anaconda provided chemical analyses.  Mr. Ed  Montgomery made and i n s t r u c t e d the writer i n making thin-sections and gave much t e c h n i c a l assistance.  Many other members of the Departments  of Geology and Metallurgy of the U n i v e r s i t y of B r i t i s h Columbia and many graduate students, i n c l u d i n g T. Richards, G. Payerle, and the l a t e J.A. Coates, gave f r e e l y of t h e i r time to discuss problems. Local ranchers and mining men, e s p e c i a l l y the l a t e P. Schutz, also helped a great deal with t h e i r knowledge of the thesis area. I thank them a l l f o r t h e i r help and co-operation. I would also l i k e to thank my wife, Ann, f o r her help as f i e l d a s s i s t a n t i n the summers of 1965 and 1966, her typing of the numerous drafts of t h i s t h e s i s , and her continual encouragement.  CHAPTER I I GENERAL GEOLOGY  INTRODUCTION The t h e s i s area l i e s within the Quesnel trough (Roddick et a l , 1967), a eugeosynclinal region within the Alaska-Canada segment of the North American C o r d i l l e r a (King, 1966).  In the southern part of the  trough, that i s i n the Thompson Plateau (Holland, 1964-), e a r l y Mesozoic, s l i g h t l y metamorphosed, eugeosynclinal rocks (Takla or Nicola Groups)  6  are composed mainly of basalt and andesite flows, pyroclastic rocks, and occasional limestones. Plutons were emplaced at high crustal levels in early mid-Mesozoic time. During and after mid-Mesozoic faulting, the deformed eugeosynclinal rocks were partly buried by midMesozoic conglomerate and later by early Tertiary arkose and volcanic rocks. These accumulated in successor basins (King, 1966) and were then themselves somewhat deformed. Undeformed late Tertiary Plateau and Valley basalts overlie the older rocks. The rock units in the thesis area are summarized on the main map (Pig. 1, in pocket) and in the table of formations (Table l ) . Relations between units are summarized in Table 2. An entry on the lefthand side of this table is considered younger than an entry in the top row; thus, 3-down-7-across means Kamloops Group was seen to unconformably overlie the Penask batholith and 3-down-3-across means that the rocks of Kamloops Group are faulted against themselves.  Table 3 shows the  occurrence of fragments of older units in younger beds. The column at the left is the containing unit; thus, 3-down-5-across means Kamloops Group contains fragments from batholiths.  SEDIMENTARY AND VOLCANIC ROCKS Cache Creek Complex Rocks tentatively assigned to the Cache Creek Complex (Danner, 1968) are found in the eastern part of the thesis area (Fig. 5 ) . Most of these rocks are steeply dipping, dark grey to black argillite or phyllite with light-coloured, arenitic interbeds, fine-grained slate,  7  Era  Period or Epoch  Formation and Thickness (feet)  Lithology  Recent  Colluvium 0-200+  Lacustrine s i l t , gravel, sand  CENOZOIC  UNCONFORMITY Till  T i l l 0-100+  UNCONFORMITY Pleistocene  Valley basalt (VB) 0-150+  Olivine basalt  UNCONFORMITY Interglacial sediments 0-100+  Sands i  UNCONFORMITY Pliocene  Plateau basalt (PB) 0-200+  UNCONFORMITY  Miocene Eocene  Basalt  Kamloops Group (KG) 0-1,000  Conglomerate, rhyolite, arkose  UNCONFORMITY Middle .Jurassic to Middle Cretaceous  "Clapperton Conglomerate" (CC) 0-3,800 (-)  Conglomerate, sandstone, siltstone  j  UNCONFORMITY Lower Jurassic  MESOZOIC  Central Nicola batholith (B2), Penask batholith (B3),  Granodiorite, minor quartz monzonite  Douglas Lake pluton (Bl)  INTRUSIVE CONTACT South Nicola stock,  i  East Guichon stock ( s )  Quartz d i o r i t e , minor  granodiorite and gabbro  INTRUSIVE CONTACT Dacite plugs ( P )  Table of formations.  i  '  Dacite  INTRUSIVE CONTACT Table 1;  j  j  The characters i n brackets are  |  8  Era  Assemblage A N I C  Upper Triassic  Lithology  Formation and Thickness (feet)  Period or Epoch  0  L A Gr  R  Fine-grained sediments and t u f f with minor limestone  2  1,600  Basalt flows, and associated p y r o c l a s t i c and e p i c l a s t i c sediments  Assemblage A. 7,500  Andesites, andesitic basalt and rare dacite, and abundant pyroclastics and sediments including limestone  Assemblage P~ 8,000  0  U P  B a s a l t i c andesite and associated pyroclastic and e p i c l a s t i c sediments  Assemblage P-j 6,000  UNCONFORMITY Cache Creek Complex (CCK) (unknown thickness)  Devonian to Permian  PALEOZOIC 1  Table 1 (cont.);  "  =  Table of formations.  A r g i l l i t e s , phyllites, hornfels, and amphibolites  *  OS  c  o  -p  •  rH CU f-t  O  P  o  I M P=< M  I  I  I  I  | PH  I  1 0 -  PH OJ PH  I p  I  ,o  a>  cd E-<  I 0" I H  I H  I  I O  fr<  ti  $  i-H  •H Tl  rH  I  P P  I M  I H H H  I O Pt  P  .21 •  I P  PH  I  I  i M r H W r — I r H r H O P M  P P I  rH PH  ti •rl  I H I  I M  10-  I  I H  I H  | fx, h  s  o Xi  CD rH  fit>  OJ  0) • H  PH  m a CQ u CO o *H <H +» ctf ti0 o •rl CQ o a> M  rH  a o P a *> -O ti  P  I  I P  I M  M  M PH  ID I I  P OJ  P  P I  I o o  a PH  I  I  p  I  I P  I  I  I H  I  I h  I pt,  I pt|  I M  SI  •H • H ed - p ti- p ti P fn o cu o W f\- p  P  I  PH  I h  1 l  I  1  1 1 1 1  © a 1  ©  1  ra1 1  1  <l> •  a a •  o  © a  1 1 SB cu  1  1 1  PH  .  1 1  o o raw  « •  a a «H  3 ti c a>  C>€>•  © •• a » •  1 0-  CO  1 1  o  o raCO  P=.  o  o  ra  cu <D  a a  o  raraH> - p - P .13  *  pp  o o  M  p  >  o  o  1 1 rara 1 1  0 "1  • 0) • I 1 <H • • 1 1 • •  • • • • 1 • • • • • • • • • • •  >  •  «  l raI I !  c U  m  •ri H U C cfl •H a>  u  o o  o  (Q 03 CQ cu cd U -ri  a  CO <D  a  cd  fH EH  c  flo -p  rH  i : :  •3 P ft  • • * • « •• • • • •  O 0} ra ti 0) - p 5 rH ti 0J  1  C"  o  © • *• 0 • •• o • ••  © © a  rati -p 3  •H g  o 0 "m  © S a  • I M  P n i i O H C J I O i S OJ H « H O p » PH w o m m w p m ^ ^ p » p* O  1 1  a>  I  S St CD 0) <rt «H  •ri  a  a>  0)  H  cd CO  1 1 1 1 l  ra O  d  P  u  -P  P^  P  M o  x> u  •H  P  r-t PH  •  *  *  i i*  • • • • • • • • • •• * • • « * • •• • • • • • • ••  *  : ** • • ••  • i *  i i*  • • • • • • • • •• • i i i • • • • • *• • • 0 • « • • « • « • •  o OJ H N H O  PHMO<I)«J!PHPHO  ra •rl TH t>> rH U 0) o ti •rl ra -p ti cu  CO 0) .ti •p  ti  •H T) CP N •H  g, O o CU rH  -p. rH Cd O PH EH ti cd  0) cd E-i  10 •rare hornfels, and dark green to black amphibolite. A steeply dipping, east-trending cleavage i s seen in most outcrops. Under the microscope, fine-grained beds are seen to be formed of brown biotite, epidote, quartz, albite, chloritelcalciteiwhite mica, and opaques including hematite.  Coarse-grained beds contain small clasts  composed of mosaics of elongate quartz and albite with undulatory extinction. The metamorphic brown biotite is seen to lie along and sporadically across the cleavage. The amphibolite, probably representing altered flows or dykes, is composed of chloritized hornblende and actinolite in a mosaic of quartz and albitelepidoteibrown mica, and leucoxene.. These amphibolites may have been retrogressively metamorphosed. Beddii^.^.,cleavage, and undifferentiated planar structures are plotted in Figure 5.  Their orientations suggest that the rocks were  folded about steeply dipping, east-striking axial planes. Cockfield (1948) has presented indirect evidence for an unconformable relationship between the younger Nicola Group and the Cache Creek Complex. In the writer's area, the two groups are believed to be separated by faults. Brown biotite is found in argillites, arenites, and amphibolites of the Cache Creek Complex. It is clearly metamorphic and was formed during and perhaps after structural adjustments,  in contrast, rocks of  the Nicola Group neither contain brown biotite nor show a cleavage in the vicinity of these Cache Creek rocks. Although earlier workers (Dawson, 1896; Cockfield, 1948) tentatively assigned these unfossiliferous rocks to the Paleozoic Cache Creek Complex, later workers (Hillhouse, 1964, pers. comm.; Preto, 1964; Campbell, 1966;  NICOLA  Hi  GROUP  70  - ^GLIMPSE  LAKE  CACHE  CREEK  C O M P L E X ( •?)  NICOLA  GROUP  LEGEND  <2>  Plateau  Basalt  Intrusive Unspecified planar from  structure  C o c k f i e l d (1944)  Bedding Cleavage FIGURE  5  SKETCH MAP  OF DOUGLAS L A K E  REGION,  K e l l e r h a l s , 1967, pers. comm.) suggest that these rocks belong to a postPaleozoic group such as the Nicola Group. the type area of the Nicola Group.  These rocks do not appear i n  Because of t h e i r s t r u c t u r a l r e l a t i o n s  and metamorphic condition they are not here considered  to be part of  the Nicola Group.  Nicola Group Much of the map area i s underlain by rocks of the Upper T r i a s s i c Nicola Group (Pig. 1, i n pocket). 4 assemblages.  The Nicola Group i s here divided into  A lower volcanic assemblage ( P i ) , about 6,000 feet  thick, i s composed of flows and breccias of altered b a s a l t i c andesites with abundant feldspar phenocrysts.  An overlying assemblage (P2) i s  composed o f c l a s t i c and p y r o c l a s t i c rocks whose fragments range from f i n e ash p a r t i c l e s to coarse rounded pebbles of volcanic debritus.  Limestone  beds, some reef.old', others c l a s t i c , are i n t e r c a l a t e d with the c l a s t i c beds.  This assemblage i s up to 8,000 feet thick.  A second volcanic  assemblage (A^) i s about 7,500 feet thick and consists of b a s a l t i c flows and breccias characterized by augite phenocrysts.  Lenses of t u f f ,  tuffaceous greywacke, and volcanic breccia are scattered through the assemblage.  Breccias with fragments of coarse-grained  l i e near the top of t h i s assemblage.  plutonic rock  Associated with.these beds are  scattered patches of reefoid limestone.  An overlying sedimentary  assemblage (A2) i s composed of 1,600 feet of fine-grained s i l i c e o u s argillite.  Relations with other units are summarized i n Table 2.  13 "Clapperton Conglomerate" The name "Clapperton Conglomerate" i s here, introduced informally to denote conglomerates  exposed on h i l l s north of Highway 5 west of  Nicola v i l l a g e and i n a b e l t stretching south from Lundblom Lake.  This  u n i t has hitherto been included i n the T e r t i a r y Coldwater beds, established by Dawson i n 1896. E l l s (1904a) separated these rocks from the Coldwater beds.  Cockfield (1948) reassigned these conglomerates  Coldwater beds which he included i n the Kamloops "Group".  to the  I t how appears  that the "Clapperton Conglomerate" i s mid-Mesozoic i n age. The beds consist of conglomerates shale.  and intercalated sandstone and  Coarse pebbles of hornblende-biotite granodiorite; f o l i a t e d  b i o t i t e granite; porphyritic rocks with feldspar phenocrysts; t u f f ; limestone fragments; and l i g h t grey, fine-grained, s i l i c e o u s cobbles occur i n the section.  E s p e c i a l l y higher i n the section, the cobbles are  set i n a b i o t i t e - b e a r i n g , arkosic but badly preserved, l o c a l l y c h l o r i t i z e d matrix.  Arkose interbeds may contain prominent white spots  up to \ inch i n diameter.  These consist of areas free of c h l o r i t e  and contain abundant fine-grained quartz i n contrast to the generally c h l o r i t i c matrix.  The s i l i c e o u s c l a s t s are commonly set i n an ochrous,  unconsolidated, fine-grained matrix. The beds d i p moderately eastward.  They are l o c a l l y intensely  fractured and fractures go through some cobbles, although other cobbles are complete and show s l i c k e n s i d i n g .  In one l o c a l i t y ( F i g . 6), some  large, p a r t l y weathered, g r a n i t i c cobbles have smaller pebbles i n t o t h e i r surfaces.  impressed  14  15 The maximum thickness of t h i s probably l e n t i c u l a r unit i s not known.  Measurements from cross-section ( F i g * 2, i n pocket) allow an  apparent maximum estimate of 3,800 feet but t h i s i s c e r t a i n l y too high because the section used f o r t h i s estimate has been thickened by shearing associated with the Clapperton Creek-Howarth Creek f a u l t zone. actual maximum i s probably not more than 1,000  The  f e e t , but accurate  determinations are not possible. The mid-Mesozoic age of the "Clapperton Conglomerate" i s postulated on the basis of s t r u c t u r a l and meager paleontological data.  The  con-  glomerates were deposited a f t e r the Jurassic (?) a c i d i c plutons of the area were exposed.  The conglomerates  contain no fragments of Kingsvale,  an Albian (?) volcanic group that crops out over hundreds of square miles and whose eastern outcrop l i m i t i s about 10 miles to the west. The beds were deposited, broken, and t i l t e d before deposition of the mid-Eocene Kamloops Group ( F i g . 7).  E l l s (l904a) described a f o s s i l  l o c a l i t y containing ammonites and pelecypod s h e l l s .  Cockfield (1948)  reported fragments of soft f r i a b l e rock that contained incomplete ammonites i n the conglomerate.  He wondered how  such a soft rock could have  t r a v e l l e d very f a r from it's source with well-rounded chert cobbles as companions.  I t seems possible that the ammonite fragments were contained  i n contemporary muds.  No f o s s i l s were found i n t h i s unit by the writer.  In summary, the "Clapperton Conglomerate" contains ammonites, probably contemporary, and i s therefore considered Mesozoic; i t lacks fragments of the nearby Kingsvale Group and i s probably pre-Albian; and i t contains fragments of probably. Jurassic plutonic rocks and i s thus considered to be post-early Jurassic i n age.  FIGURE 7.  DISTRIBUTION  OF  TERTIARY  oP o 7  UNITS  LEGEND V B V a l l e y B a s a l t (H - hollow boulders) x  Interglacial Sediments  P  Plateau Basalt (1 - Palagonite)  K G Kamloops Group c conglomerate v volcanic r o c k a arkose S C A L E l» MILC9  17 Kamloops Group Rocks assigned to the Kamloops Group are found i n two basins and small o u t l i e r s (?) ( F i g . 7 ) .  The term, Kamloops "Group", includes arkosic  Coldwater beds as well as thick sections of volcanic rocks (Cockfield, 1948).  In t h i s report, the term, Coldwater beds, i s dropped because the  "Clapperton Conglomerates" previously assigned to the group have been removed from i t .  Instead, a l l of the Eocene rocks are referred to as  belonging to the Kamloops Group. Arkose Arkose of the Kamloops Group underlies the M e r r i t t and coal basins ( E l l s , 1904a, 1904b; C o c k f i e l d , 1948;  Quilchena  H i l l s , 1965).  The  M e r r i t t coal basin i s about 12 miles long and from 1 to 3 miles wide. The Quilchena basin i s about 7 miles long and 2 miles wide. The arkose consists of yellowish, medium-grained, moderately sorted, s i l i c e o u s or arkosic sandstone and dark brown, s i l t y or sandy, commonly f o s s i l i f e r o u s shale with rare interbeds of l i g n i t i c coal, ironstone, and bentonite.  Complete sections are r a r e l y exposed.  Some  4.  measured sections are summarized i n Table  The beds generally dip gently southwest i n the M e r r i t t basin and northeast i n the Quilchena basin.  Open f o l d s and, near margins of  basins or near f a u l t s , tight f o l d s have v a r i a b l y but gently plunging f o l d axes.  The contact of these T e r t i a r y rocks with those of the  Nicola Group i s i n most places disturbed. north-south f a u l t separates the groups.  West of Coal G u l l y , a steep  Along Quilchena Creek, the  beds dip gently to the northeast and terminate against N i c o l a rock along a lineament which probably represents a f a u l t .  18  Lithology  (ft.)  Year  Coal  Dawson  1896  Merritt  424  Sandy shale with sandstone and shale 4 coal seams  Ells  1904b  Quilchena  700  Mostly shale with coaly and s i l t y interbeds, occasional conglomerate and sandstone lenses  Cockfield  1948  Quilchena  400  5C$ conglomerate, 4C$ sandstone, 10$ shale  Measured  sections  Table  4  :  -  of Kamloops Group  arkose.  Average  Olivine Pyroxene Plagioclase Ar$ Volcanic glass (n 1.596) Opaques and a l t e r a t i o n  Table  Basin  Thickness  Author  5  :  10 14 45 64 28 3  Modal values (volume percent) of Valley basalt 1963; Campbell, 1966; S c h a u ).  Range 5-11 0-30 70-30 62-70 70-05 0-10  (Lambert,  and  ; i  19 This arkose contains plant fossils, microfossils, shell fragments, and a few fish remains a l l of which suggest correlation with the Kitsilano Formation in Vancouver, the Tranquille beds of Kamloops Group, and the mid-Eocene Green River beds of Utah (Penhallow, 1905; Whiteaves, 1905; Cockfield, 1948; Hills, 1965).  K/Ar dates on sanidine from Quilchena  give a date of 48.9 million years (Hills, 1965) or 62.9 million years (Hills and Baadsgaard, 1967), whereas glass shards give a date of 21.9 million years. Hills concludes that glass shards are not suitable for K/Ar dating. The arkose i s considered to be mid-Eocene. Volcanic Rocks Rhyolites of the Kamloops Group are found southwest of Merritt near the west limit of the thesis area and in outcrops east of Nicola Lake north of Nicola River (Fig. 7 ) . Thin-sections of typical mauve rhyolite show i t to be composed of small round grains of feldspar and widely scattered acicular resorbed hornblende crystals or very rare biotite flakes set in a very finegrained matrix composed of fine-grained hematite, quartz, and feldspar. The flows appear relatively flat-lying.  The flow north of Nicola  River rests unconformably upon a thin layer of detrital material which includes fragments of Nicola rock. The lack of clasts of mauve rhyolite in the arkose of the Kamloops Group and the presence of mauve rhyolite at a higher topographic level than the arkose suggest that the rhyolite south of Merritt is younger than the arkose. Conglomerate Small outcrops of conglomerate lie southwest of Merritt (Fig.7).  20 This u n i t i s distinguished by abundant sub-angular to sub-rounded pebbles of mauve r h y o l i t e .  I t occurs i n a small (200 feet x 200 feet)  outcrop l y i n g north of the mauve r h y o l i t e of the Kamloops Group volcanics. I t i s composed of poorly sorted sub-angular to sub-rounded c l a s t s up to 6 inches i n diameter which consist mainly of feldspar porphyry with s i l i c e o u s matrix, Kamloops Group arkose, and mauve r h y o l i t e . The conglomerate  appears to be f l a t - l y i n g .  About 400 yards to the  north of the outcrop, N i c o l a volcanics appear west of a f a u l t p a r a l l e l i n g Coal G u l l y and topographically above the conglomerate.  No  volcanic c l a s t s a t t r i b u t a b l e to the N i c o l a Group were found i n the conglomerate  suggesting that the N i c o l a rocks to the north were elevated  along the f a u l t a f t e r deposition of the conglomerate.  Plateau Basalt Plateau b a s a l t s crop out along and cover the contact between N i c o l a Group rocks and Cache Creek Complex rocks south of Douglas Lake along the eastern edge of map sheet.  Small outcrops are also found on the  h i l l east of the head of N i c o l a Lake ( F i g . 7 ) . The basalt i s black, dark brown weathering, occasionally v e s i c u l a r and sparsely p o r p h y r i t i c with phenocrysts of o l i v i n e .  At l o c a t i o n 1  ( F i g . 7), basalt i s palagonitized near i t s lower contact.  In t h i n -  section, the rock i s composed of rare phenocrysts of o p t i c a l l y negative o l i v i n e surrounded by small p i l o t a x i t i c feldspar c r y s t a l s (40$, 1 mm. long) set i n a matrix of very fine-grained intergranular o l i v i n e and/or pyroxene and c h l o r i t i c material with small blebs of opaque oxides scattered  throughout.  <  21 A lower contact i s seen at the palagonite locality where the basalt rests on coarse plutonic rocks of the Penask batholith. The rocks are correlated with the late Miocene-early Pliocene Plateau basalts (Mathews, 1964) because they resemble them in being aphanitic, vesicular, deposited late in the history of the area, and relatively undeformed.  Valley Basalt Cockfield (1948) first distinguished a young, suite of basaltic rocks which he named Valley basalt. They are found along the Nicola River a short distance east of Merritt, north of Monck Park on the north shore of Nicola Lake, in 3 patches along Quilchena Valley (2, 6 and 10 miles south from mouth of Quilchena Creek), to the east of Courtney Lake, and in a small patch about 3 miles north of Courtney Lake and half a mile east of Highway 5. These generally flat-lying flows form scarps facing the valleys in which they occur, but elsewhere glacial debris covers them. The average thickness of the unit i s 150 feet made up of 5 or 6 flows (Lambert, 1963). The sub-porphyritic and variably vesicular rock has phenocrysts of olivine and rare feldspar set in a greyish aphanitic or fine-grained matrix. In thin-section, i t i s seen to be a vesicular olivine basalt with about 10$ phenocrysts of olivine and 4$ feldspars in a matrix rich in feldspar laths, intergranular pyroxene, and glass. A modal analysis is shown in Table 5. According to Lambert (1963), magnetite and ilmenite are more common near the bottom of the flows than in the upper parts. The flows are vesicular and glassy near their tops and bottoms.  22 The Valley basalts are undeformed. Primary features include columnar jointing, surface structures similar to pahoehoe, vesicular tops, and peculiar inverted Y-shaped vesicules that indicate a northward direction of flow immediately east of Merritt (Lambert, 1963). Curious hollow boulders of Valley basalt are found in abundance on the surface of the outcrop east of Merritt, as well as on and by the outcrops in Quilchena Valley. Their hollows are due to some secondary or weathering action (Campbell, 1966). Similarly hollowed boulders of agglomerate l i e east of Stump Lake. The flows are generally horizontal but the lower flows have an i n i t i a l dip corresponding to the surface along which they were extruded. For instance, 2 miles south of Quilchena, the lower basalt flow rests upon weathered unconsolidated greenstone talus and the contact between talus and basalt dips 25° south. The flows above Monck Park also dip about 20° southward and down the presently existing side-hill. The flows rest upon Nicola rock, plutonic rocks, and arkose of the Kamloops.Group with obvious unconformity and lie along north-south fault zones.  East of Merritt, coarse gravel with interbedded sand is overlain  by basalt (Lambert, 1963). South of Merritt along the Coldwater River these basalts rest upon interglacial sediments (Fulton, 1965). Pleistocene rubble covers most Of the flows and boulders of Valley basalt have been moved south of existing Valley basalt outcrops.  Physiography and Glacial Geology The map area lies within the Thompson Plateaux of the major physiographic region called the Interior Plateau (Holland, 1964).  23  The topography of this region is characterized by a high rolling "upland dissected into blocks by linear, deep, occasionally wide valleys (Fig. 4 ) .  The rolling uplands are composed mostly of hard Mesozoic  rocks whose regional slopes are about 160 feet/mile (Reinecke, 1915). Irregular drainage elements in the map area, the Nicola River and its tributaries, l i e in steep-sided and straight valleys formed along zones of shearing or faulting.  The regional grade from Douglas Lake to Merritt  is about 20 feet per mile. The upland surface of the Interior Plateau is the oldest geomorphic surface preserved (Mathews, 1967). The rolling upland surface has a local relief of 1,500 to 2,000 feet but the valleys cut into i t as illustrated in Figure 4 and provide relief up to 3»500 feet. It truncates folded Eocene rocks and is overlain by relatively flat-lying Pliocene Plateau basalts. It is probably the counterpart of the "Entiat" surface which dips below the Columbia River lavas of central Washington (Mathews, 1967). The Plateau basalts and the upland surface are found at various altitudes throughout the southern interior from 3,000 to 6,500 feet. This difference in altitude is used to support a hypothesis of warping about north-south axes (Mathews, 1967). In the map area, outcrops of Plateau basalts, which are rare, range in altitude from 2,500 to 4,000 feet. Here, the variation is thought to be primary rather than due to warping. After the Pliocene, streams incised the floors of earlier broad valleys. A new erosion cycle started with a lower base level but i t was disturbed by Pleistocene glaciation.  24  Evidence of glaciation prior to the last Wisconsin episode i s rare and in the thesis area limited to interglacial sediments preserved high on the vest bank of the Coldvater River just south of Merritt (Fulton,  1962,  1965).  A composite section compiled by Fulton  (1965)  from  these exposures i s given in Table 6 . Subsequent to the deposition of interglacial beds, Valley basalts vere extruded near or along north-south fracture zones. Evidence for erosion during the last period of glaciation i s seen in rounded, polished, and striated outcrops, erratics, t i l l sheets, and crag and t a i l features which mark former glacial action even over the highest summits (Mathevs,  196?).  Tongues of waning ice sheets and subsequent morainal and fluvio— glacial deposits interfered with surface drainage and led to the present disorganized drainage pattern. Some meltvater streams filled preexisting valleys such as the Nicola Valley vith alluvium, forming flatfloored valleys across which small modern misfit streams now meander. Temporary ice—dammed lakes are recorded by abandoned shorelines and deltas and by bottom sediments of jointed varved silts.  Three phases of  a large glacial lake occupied an area centered on its modem remnant, Nicola Lake (Mathews,  1944,  1967;  Fulton,  1962,  1965).  Erosion and recent  colluvium have modified the Pleistocene lake bottoms and natural changes in drainage patterns are s t i l l occurring (Davson,  1877).  PLUTONIC UNITS Post-Nicola Group plutons underlie much of the thesis area. Dacite plugs and quartz diorite stocks were followed by Lower Jurassic  25  Description  Feet  Silt  5  Till  15  Silt  10  Unoxidized grey gravel, sand, and silt . with pebbles of Valley basalt  40  UNCONFORMITY Interglacial red s i l t and sand with occasional gravel beds with angular pink rhyolite fragments  95  Layer of tuffaceous sand is found 65 feet above the base as well as occasional layers of fossil pelecypods dated (C14 method) as 37,200 BP UNCONFORMITY White glaciolacustrine s i l t  Table 6  35  Interglacial section from Coldwater River (Fulton, 1965).  26 batholiths mainly of granodiorite. The plutons were emplaced in shallow, relatively cool rocks. Deformation accompanying plutonism led to formation of local folds in the Nicola Group at Nicola Lake.  Low-  grade metamorphism and metasomatism accompanied the intrusion of the batholiths.  Dacite Plugs Prominent porphyry plugs are scattered mainly in Assemblage P of 2  the Nicola Group (Fig. 8.). Light-coloured, locally glomeroporphyritic dacite contains phenocrysts of albite and rare, glassy quartz set in a siliceous, rarely vesicular or miarolitic, aphanitic matrix. In thin-section, the phenocrysts of clear albite are speckled with a few epidote and sericite grains. Rectangular phenocrysts of quartz occasionally show resorbed edges. Scattered clots of albite generally have leucoxene, magnetite, or chloritized mafic mineral associated with them. The matrix is composed of small albite laths set in a quartz, albite, and potash feldspar mosaic with veinlets of iron-rich chlorite. The irregularly shaped, discordant plugs are generally homogeneous although quartz veins and irregular stylolite-like surfaces defined by opaque material cut the rock. However, at one locality (Fig. 8, S8), bodies of a quartz-rich porphyry phase cut a feldspar-rich body. The plugs lie along and are sheared by north-south faults. Near pings, lithologically similar dykes lie along steep east-west fractures. Dacite plugs commonly lie near more basic stocks with which they have conflicting age relationships. At locality SI (Fig. 8), a dyke of  ISTRIBUTION PLUTONS  FIGURE 8. CENTRAL NICOLA  OF  " k  DOUGLAS A LAKE^ \PLUJON  V  i  ///£  'A  / \  p  A IRON MT.  t  SCALE  CORBET LAKE OF M I L E S  LEGEND EZ2 Country Rock CE3 (O South Nicola Stock and (*) East Quichon Stock Batholith Porphyritic Dykes with South Nicola Stock Dacite Plugs Breccia Dykes associated with batholiths  28  dacite cuts the chilled phase of the South Nicola stock. Elsewhere, the porphyry i s cut by quartz diorite (Fig. 8, S2) and dykes of the South Nicola stock (Fig. 8, S4). The youngest layered rocks cut by the plugs belong to Assemblage A^ of the Nicola Group. Mineralization associated with the Fenask batholith lies along shear zones (Fig. 8, S7) which cut a dacite plug. Thus, the plugs were emplaced after Norian time, are approximately contemporaneous with the South Nicola stock, and were emplaced earlier than the Fenask batholith. The felsitic matrix suggests that the country rock was cool when the crystal-bearing magma was intruded. Vesicles and miarolitic cavities suggest that a fluid separated from the magma as a discrete phase. This most commonly happens at relatively shallow depths.  Quartz Diorite Stock The latest Triassic and earliest Jurassic South Nicola stock and an eastern outlier of the Guichon batholith, composed of tonalitic rock of variable composition and grain size, provide useful information in the delineation of structural episodes and in estimation of depth of cover at the time of their emplacement. The elongate, north-trending, Y-shaped South Nicola stock crops out over 30 square miles south of Nicola Lake and west of Quilchena Creek. Only a small part of the eastward extension of the Guichon batholith (Cockfield, 1948; White et al, 1967) lies within the map area (Fig. 8). The South Nicola stock shows much variation in grain size, specific gravity (Fig. 9), and composition.  The main part is composed of medium-  grained quartz diorite with small but variable amounts of potash feldspar.  29  u  z  w a w  I -  2.68  •  2.17  SPECIFIC  F I G U R E 9.  £.86  £.9 5"  3.04  GRAVITY  VARIATION OF SPECIFIC GRAVITY N I C O L A S T O C K (n = 3 3 )  IN S O U T H  o CVi  H a  oo  u  i—i  k  u w  O  'A  I  2. •  A V E R A G E GRAIN D I A M E T E R (MM) [one t r a v e r s e a c r o s s other s a m p l e s f r o m  FIGURE  10.  contact region  VARIATION OF SPECIFIC GRAVITY S I Z E IN N O R T H W E S T NICOLA  STOCK  CORNER  AND GRAIN  OF SOUTH  30 A western part i s gabbro or diorite with coarse, altered, partly zoned feldspars, sporadically poikilitio clinopyroxene, abundant magnetite, and small interstitial areas of quartz and sodic plagioclase. Near the contact, along the west prong to the north, a chilled pyroxene-feldsparmagnetite-quartz phase occurs. This grades through a sub-porphyritic phase into the main phase. The pyroxene in the chilled part i s mantled and partly altered to hornblende similar to that in the main mass. The specific gravities of the chilled phase and the nearby coarse phase are the same (Fig. 10) and presumably the phases have very similar compositions. At locality Dl (Fig. 8), the main phase is porphyritic with large feldspar phenocrysts crowded together to show local trachytoid textures. This general region was perhaps the feeder to dykes mentioned below. Rusty-weathering porphyritic dykes with inch-long phenocrysts of feldspar are found in various parts of the area marked D (Fig. 8). About 5$ of the phenocrysts are cross-shaped (Plate i ) .  The matrix is  magnetite-rich and generally fine-grained to aphanitic, consisting of feldspar and fine mafic materials. The feldspars are altered and are now mainly saussurite. Dykes up to 20 feet thick may contain foot-long inclusions of Nicola rock resembling that of outcrops nearby. These dykes are very important in distinguishing age relationships of various events.  One cuts the chilled phase of the South Nicola stock  (Fig. 8, D2) and several are closely associated about the intrusive contact at locality D3 (Fig. 8). Farther from the stock, the dykes cut rocks assigned to Assemblages A]_, Pi, and ?2  o f  *ke Nicola Group. At  locality D4, a s i l l is now bent, faulted, foliated, and pumpellyite-  31 bearing. Brown, rusty, extremely altered and sheared dykes cut rock of Assemblage A± (Fig. 8, D5, D8). At locality D6, nearly flat-lying rock with a lower chilled surface and cross-cutting borders occurs on the same level on both sides of the valley marking the Nestor Creek fault. There, faulting seems to have preceded the dyke emplacement.  At locality  D7, laumontite is found in vesicles of this dyke rock emplaced there as an irregularly shaped s i l l or small laccolith-like body. These relations show that the dykes are probably a late phase of the stocks, that some faulting and folding preceded dyke formation, and that some;, folding, foliation, faulting, and metamorphism occurred after the intrusion of the dykes. The suggested uppermost Triassic or Lower Jurassic age of the South Nicola stock is based on geologic evidence. The stock intrudes rocks of the lower part of. Assemblage A^ of the Nicola Group and is intruded by the Penask batholith. It i s conceivable, but unlikely, that plutonic debris in the upper part of Assemblage A^ was eroded from the South Nicola stock. The similarity of composition between stock and fragments favours such an hypothesis but structural concordance of Assemblage Aj> and A , the lack of pebbles of Assemblage P^ and P in the angular debris, 2  2  the greater number of plutonic fragments to the east rather than west a l l contradict the hypothesis. The stock and its dykes are cut by some north-trending faults, show inconsistent intrusive relations with dacite plugs, are locally foliated near Nicola Lake, have been affected by metamorphism believed to be associated with the Penask batholith, have been intruded by the Penask batholith, and are overlain by the "Clapperton Conglomerate". No K/Ar dates have been determined for this  32 stock but i t is mineralogically and texturally like the eastward extension (Cockfield, 1948) of the 200 million year old Guichon batholith (White et al, 1967, Northcote, 1968). The contact relations of the South Nicola stock include a chilled border, dykes with fine-grained matrix, and sporadic development of vesicles. Rare epidosites and small bodies of hornblende pegmatite along borders suggest that fluid pressures at the end of crystallization were slightly higher than fluid pressure in country rock. The shallow depth of cover can also be deduced from experimental data on the behaviour of basaltic melts in the presence of water at high pressures (Yoder and Tilley, 1962). A pyroxene-labradorite assemblage is unstable at water pressures above about 1.5 kilobars. Minor quartz and somewhat more sodic plagioclase in the system i s not expected to alter this estimate of water pressure much. To translate water pressure into a depth estimate involves an estimation of the extent to which the water in the pile of sediment i s in contact with the surface. If the permeability in the sedimentary pile was high, which i s unlikely, then the water pressure would be about l/2 to l/3 of the total pressure. The greatest depth at which a pyroxene-bearing mafic body would crystallize in a wet, permeable, sedimentary pile, assuming the same PH20 3-  n  nagma and country rock, is about 35,000 feet below the surface.  The permeability in thick geosynclinal piles is probably low (Tkhostov, 1963) and therefore the water pressure would approximate total pressure and the depth estimate could be reduced to 15,000 feet. Because the interior of the stock contains hornblende and because hornblende replaces a few of the pyroxenes, the water pressure within the stock must  have b u i l t up to allow c r y s t a l l i z a t i o n of t h i s hydrous phase.  The ri  paucity of skarn about the stock suggests that v o l a t i l e pressure was never much higher than water pressure i n surrounding rock.  These  considerations suggest that the stock might well have been emplaced about 15,000 feet beneath some l a t e s t T r i a s s i c surface.  I t seems worthwhile  mentioning at t h i s point that about 7,000 feet of N i c o l a rocks were deposited above the youngest rocks now invaded by the South N i c o l a stock. Hence, the amount of material removed by erosion from the core of the. Meander H i l l s syncline must have been l e s s than 28,000 feet and probably l e s s than 8,000 f e e t . The eastern extension of the Guichon b a t h o l i t h shows many features s i m i l a r to those of the South N i c o l a stock. Rock types and dykes are the same. Dykes cut s i l i c e o u s plugs and both l i e along east-west planes. Only topographically high points show exposures of fine-grained d i o r i t e so that the present surface seems to be near the roof of t h i s pluton. The mode of o r i g i n , emplacement, and age of the eastern extension of the Guichon b a t h o l i t h are probably s i m i l a r to those of the South Nicola stock. Batholiths Small parts of the map area are underlain by the Penask batholith, the Central N i c o l a b a t h o l i t h , and the Douglas Lake pluton ( F i g . 8). Penask B a t h o l i t h Part of the Penask b a t h o l i t h occupies the southeast corner of the map area and extends west beyond Quilchena Creek.  I t s northern border  is irregular and within the map area i t extends from Douglas Lake to Teenamilst Creek. In Figure 8 the area shown underlain by the Penask batholith is larger than that shown by Cockfield (1948). In this poorly exposed region granitic rock surrounds the small areas of sheared and foliated rock noted by Cockfield. The batholith is composite (Cairnes, 1940. Rice, 1947; Mathews, 1968, pers. comm.). Away from contacts in the map area, the rock is uniform biotite-hornblende granodiorite, cut by rare aplite dykes and shear zones and containing large xenoliths of foliated amphibolite. A porphyritic heterogeneous phase (B) and associated dykes (d) occur along and near the northern border of the batholith (Fig. 8). This porphyritic phase may be crowded with inclusions of country rock and rare granite and hornblendite, especially at the contact (Fig. 8, Bl). The border phase i s characterized by large hornblendes rimmed with opaque minerals and rarer pyroxene phenocrysts set in a felsic, fine-grained aggregate of feldspar grains, interstitial quartz, and altered mafic minerals.  The dykes have fever mafic but more feldspar phenocrysts than  the border phase. In thin-section, feldspars of the heterogeneous phase are seen to be altered to saussurite. The hornblende and pyroxene phenocrysts are relatively fresh but the matrix and veinlets contain epidote, calcite, chlorite and albite. A secondary foliation in the country rock consisting of closely spaced fractures is associated with the walls of the pluton but, near the roof, discordant non-foliate contacts prevail. Beginning in that area,of the South Nicola stock intruded by the Penask batholith, foliated tuffs and sheared sections of the stock trend in a mile-wide zone north-  35 ward to Nicola Lake, projecting the line formed by the inferred western contact of the batholith (Fig. 8). This peripheral foliation i s not found along the northern boundary of the batholith. There, the batholithic contact i s thought to dip shallowly northward. The mode of emplacement i s composite.  A few inclusions of  recognizable country rock are found within the pluton, so that some stoping may have taken place. Shearing along the western border suggests that forceful intrusion played a part whereas the irregular northern border suggests permissive emplacement. The environment of emplacement of the Penask batholith i s transitional from epizone to mesozone (Buddington, 1959).  The fine-  grained matrix, chilled selvage, irregular inclusions, and irregular shapes of the fractures occupied by dykes (Fig. 8, dl) are evidence for emplacement at a shallow depth, The low-grade alteration of this heterogeneous phase suggests that i t i s an early chilled phase of the Penask batholith. Few aplite dykes and much low-grade metasomatism of the surrounding rocks suggest that much water was available during the cooling of the intrusion. The age of the composite Penask batholith is uncertain. Rice (1947) concluded that i t was Jurassic to the south of the map area. To the west at Brenda mines in another part of the batholith, White and Carter (1968) reported 180 million year old K/Ar dates on hornblende and also reported K/Ar biotite dates of 140 million years. In the thesis area, the age i s limited by the following considerations. The batholith i s younger than Assemblage A of the Nicola Group. It i s 2  younger than the north-south folding because i t truncates the Meander Hills syncline. Rocks of lithology similar to that of the Penask  36 batholith but not connected to i t by continuous outcrop show intrusive relations with the more altered South Nicola stock. Nearby mid-Mesozoic "Clapperton Conglomerate" contains quartz diorite and granodiorite fragments. The batholith is overlain by the Kamloops Group and is sheared by the Quilchena fault. Since the region was above sea level for most of the Mesozoic (Campbell, 1966), since the batholith probably was exposed by mid-Mesozoic time and certainly by Eocene time, and since the pluton was intruded a few kilometers below some past surface, i t follows that the most likely time of emplacement was prior to emergence; that i s , lower Jurassic time. Central Nicola Batholith The Central Nicola batholith extends into the map area from the north, underlying a 4-6 mile vide belt. This composite body contains a western heterogeneous phase cut by an eastern homogeneous phase. The heterogeneous phase consists of uniform granodiorite; medium-grained dioritic rocks, sometimes foliated, sometimes layered; mylonitic gneiss; and sheared diorite and granodiorite. The heterogeneous phase is apparently related to the South Nicola stock, but the occurrence of a chilled margin in the stock indicates that i t was emplaced at a different time (probably earlier).  The relatively  homogeneous phase is a medium-grained biotite-hornblende quartz monzonite with a colour index of about 20.  The amounts of hornblende and biotite  vary over short distances and in some rocks the mafic mineral is biotite. In the south, the phase is sub-porphyritic with large phenocrysts of perthitic potash feldspar and occasional grains of idiomorphic quartz. Rare aplite dykes, quartz veins, and late chloritic shears cut the mass.  37 Near the heterogeneous phase, xenoliths and mineral grains have their long axes lying along surfaces parallel to the intrusive contact surface. The contact between the two phases i s blurred to the north; near Nicola Lake, i t i s clear. The intrusive contact i s best exposed at locality A (Fig. 8) where quartz monzonite of the homogeneous phase intrudes a darker quartz diorite of the heterogeneous phase. The Central Nicola batholith contains rocks of two different ages. The heterogeneous phase cuts rocks of the Nicola Group. It i s variably foliated by surfaces outlined by mafic minerals whose orientation i s similar to the fractures in the bordering metamorphic rocks. It was thus emplaced prior to the formation of the foliation and probably preceded the Penask batholith. The homogeneous phase intrudes the heterogeneous phase. Early inch-vide aplitic dykes in the heterogeneous phase with weakly aligned biotite parallel to the foliation show dilation offsets where they have been cut by later inch-vide aplite dykes indicating that the later dykes formed after the heterogeneous phase had been foliated. The foliation has been molded about the homogeneous phase of the Central Nicola batholith to form looal folds at Nicola Lake indicating that the homogeneous phase post-dates the foliation and probably the Penask batholith. Hydrothermal veins thought to be associated with the homogeneous phase of the Central Nicola batholith cut foliation but are themselves sheared by later faulting along Nicola Lake. Within the map area, very l i t t l e evidence as to the environment of emplacement for this batholith is available. Tourmaline and , idiomorphic quartz in the homogeneous phase suggest shallower rather than deeper emplacement. The country rock is affected by low temperature metamorphism and low temperature hydrothermal mineral assemblages formed  38 from late emanations. The homogeneous phase of the Central Nicola batholith vas thus probably emplaced in some transitional epizonemesozone environment similar to that of the Penask batholith. Douglas Lake Pluton The Douglas Lake pluton consists of medium-grained grey granodiorite.  Its southern contacts are sharp, whereas farther north foliated  contact phases are perhaps part of the Cache Creek Complex. The pluton and associated dykes cut the country rock of Cycle A of the Nicola Group. The Douglas Lake pluton lies along an inferred fault which separates the Nicola Group from the Cache Creek Complex and is probably younger than the main north-south faulting.  Soon after the newly formed volcanogenic Nicola Group had been partly folded and faulted, dacite plugs and quartz diorite stocks were emplaced at shallow levels.  Then, the Lower Jurassic Penask batholith  was emplaced in an epizone—mesozone environment and a foliated belt was formed along its western edge. This foliation was soon deformed by the emplacement of the homogeneous phase of the Central Nicola batholith. The batholiths were then uncovered and boulders of them became incorporated into the mid-Mesozoic "Clapperton Conglomerate". The plutons are a l l considered to be of latest Triassic or early Jurassic age (Fig. 11).  39 i  DACITE; PLUGS !  (STRATIGRAPHIC  PLUTONS  DIORITE  PENASK.  QUARTZ  BATHOLITH  STOCKS  '  i UNITS A N D  CENTRAL  ^.STRUCTURAL  jNICOLA  ^EVENTS  i BATHOLITH  CLAPPERTON CONGLOMERATE  v  ^  "Homogeneous phase LOCAL  FOLDS  , LOCAL phase  . . .  1  7" .' - " I b y k e s t .;]  FOLIATION  IB o r d e r iphase. )yke  si  n \-  Main phases  Heterogeneous phase  Chilled •phases  If  MEANDER  SYNCLINE  NICOLA  FIGURE  11.  SUMMARY  OF PLUTONIC  HILLS  ACTIVITY.  GROUP  40  CHAPTER III NICOLA GROUP The Nicola Group i s the main subject of this thesis. The stratigraphy, environment of deposition, chemistry, origin, structure, and metamorphism of the rocks of the Nicola Group are discussed in turn.  STRATIGRAPHY General Statement The volcanogenic Nicola Group is divided into two cycles on the basis of stratigraphy.  Each cycle contains lavas and oogenetic  intrusions as well as volcaniclastic and calcareous rocks.  This approach  has been championed by Clark (i960) and Dickenson (1968). It would be labelled "preliminary" stratigraphy by Stj&rmer (1966) who has critically reviewed the various kinds of stratigraphy practised today. The cycles, P and A, are each represented by a lower (l) predominantly volcanic assemblage and an upper (2) heterogeneous but mainly sedimentary assemblage. The lower cycle (P) is characterized by single and clotted plagioclase phenocrysts in the volcanic members, whereas the upper cycle (A) is characterized by augite phenocrysts.  Assemblage P-; Distribution and Thickness Assemblage Pi is best exposed in a belt stretching south from Nicola village.  It is repeated by faulting on the lower and west slopes  of Iron Mountain and to the east of the mouth of Nestor Creek (Fig.12). The lower boundary of the assemblage is not exposed and the gradational  41  F I G U R E  12.  A S S E M B L A G E  P  42  upper boundary is marked by the change from mainly porphyritic flows interbedded with breccia to mainly sedimentary interbeds in breccia. The unit has an apparent thickness of a l i t t l e over 6,000 feet. Lithology Assemblage Pi i s composed mainly of altered porphyritic flows of andesitic basalt and abundant, altered, relatively coarse pyroclastic rocks. Flows and feeder dykes are generally porphyritic. Although the rocks are altered and generally poorly exposed, i t i s possible to outline areas of similar lithology which show that flows are less than 100 feet thick and extend along strike for at least hundreds of feet. Flows range in texture from strongly porphyritic or glomeroporphyritic to completely aphanitic. Generally, the glomeroporphyritic rocks have about 20-40$ equant, seriate, up to 7 mm. long feldspar phenocrysts set in a fine-grained to aphanitic matrix. The matrix i s greenish or bluish black at the base of the volcanic pile, black in the middle, and purple at the top of the section. In thin-section, the feldspars are seen to be altered to albite, white mica, clinozoisite, and calcite. Pseudo— morphed zones contain inclusions of chlorite, opaque material, and, rarely, pumpellyite (?). Opaque grains such as hematite, magnetite, and pyrite, and leucoxene are spotted through intersertal chlorite, microlites of albite (?), and grains of epidote of the matrix.  Scarce  clinopyroxene i s altered incompletely to calcite, epidote,and chlorite. Sporadic amygdales are mainly chlorite and epidote and contain very rare laths of albite.  Chemical analyses of these rocks are given in Table 7,  Appendix 1 (l,2,3,4,5*6,9, and 10) and the norms of completely analysed specimens are given i n Table 8, Appendix 1.  Detailed descriptions of  the analysed rocks also appear i n Appendix 1. Less abundant, inconspicuously p o r p h y r i t i c flows contain feldspar phenocrysts up to 7 mm. of  i n length, set i n a l i g h t grey matrix composed  p i l o t a x i t i c m i c r o l i t e s of a l b i t e and i n t e r s e r t a l c h l o r i t e sparsely  spotted with opaque minerals.  Brownish purple, microporphyritic, flow-  layered, aphanitic flows or dykes (?) are even less abundant.  These  are described i n more d e t a i l under Assemblage ?2I t i s d i f f i c u l t to estimate abundance of dykes and s i l l s because contacts are r a r e l y exposed.  The textures of dykes are not uniform as  one dyke has two sizes of phenocrysts (3 mm.  and 5 mm.)  set i n a  microporphyritic matrix, whereas other dykes are generally aphanitic. Flow breccias with p o r p h y r i t i c fragments set i n a s i m i l a r matrix occur near tops of flows.  Although these breccias may be r e l a t i v e l y  common, they are hard to d i s t i n g u i s h i n weathered outcrops of altered rock.  P y r o c l a s t i c breccias are composed of i r r e g u l a r l y shaped fragments  up to 5 inches across with p o r p h y r i t i c , amygdaloidal, aphanitic, or flowlayered textures set i n a reddish matrix that generally contains small lapilli.  Many l a p i l l i have red borders and dark red cores.  These  breccias are most common i n the upper h a l f of Assemblage P]_. Other volcanic breccias have moderately sorted porphyritic fragments with angular shapes and few l a p i l l i set i n a sparse fine-grained matrix. L a p i l l i - b e a r i n g , c r y s t a l , and l i t h i c t u f f s are a l l abundant near the top of Assemblage P^ and throughout the assemblage as interflow  44  layers. The crystals are mainly broken feldspar; the lithic fragments are from previously described flows; the l a p i l l i are irregular fragments of red to purple, finely and abundantly amygdaloidal, devitrified glass. Light-coloured tuff, mostly of devitrified pumice shards, some collapsed (?), of various sizes, with fragmented quartz and albite phenocrysts, occurs at the bottom of the assemblage. The tuff forms a marker unit (Fig. 12). Chemical analyses of this rock are given in Table 7 , Appendix 1 (7 and 8). Sedimentary intercalations such as well-sorted calcareous arenite, fossiliferous greyvacke, recrystallized limestone, fine-grained limestone, and conglomerate with calcareous matrix occur as isolated lenticles in Assemblage Pj_. Fossiliferous limestone blocks up to 40 feet in length are caught up in flows. Internal Structures and Stratigraphy Assemblage P\ shows primary structures mostly dipping east with moderate to steep angles. Calcareous, clastic, or pyroclastic bedded rocks are found scattered through the assemblage. Flow layering i s found in the aphanitic flows. Only few of the rare layers of vesicles in porphyritic flows show a consistent orientation across an outcrop. Aerial photographs show lithologically similar masses have a regional north-northeast strike with steep southeast dip. The vertical variation of a well-exposed part of the volcanic pile south of Nicola village i s shown in Figure (13). Repetition due to faulting i s probably not important on the scale of this section. In the section, flows are succeeded by breccias and tuffs.  Pyroclastic  beds occur closer together near the top of the section, marking a change  45 from mainly effusive to explosive volcanic activity.  The upper contact  of the assemblage i s drawn at the first appearance of agglomerate which marks the f i r s t , subaerial volcanic ejectamenta and perhaps widespread emergence of volcanic islands. A very fine-grained, bedded, siliceous tuff with interbeds of aphanitic limestone crops out at the bottom of the section west of Nestor Creek (Fig. 13). East of Nestor Creek, the tuff unit i s coarser and more clearly tuffaceous, indicating that the source for these beds i s closer to the mount of Nestor Creek than to the section. The marker horizon was not noted in the block on Iron Mountain west of the Clapperton Creek-Howarth Creek fault by the author, but siliceous volcanic rocks are said to be exposed in cuts one-half mile southwest of Iron Mountain (McKechnie, 1962). Interbedded tuffaceous and rarely calcareous clastic rocks are more common south of this section. Indicators of Age and Correlation The few poorly preserved fossils (Fig. 3, in pocket} Appendix 2) from Assemblage  are more useful as indicators of environment than of  age. The relative age of Assemblage P]^ with respect to P2 i s indicated by the occurrence of fragments of Assemblage P^ in overlying, concordant, volcanic breccias; the assemblage is probably only slightly older than the overlying Assemblage P 2 . It i s not known whether lithologic boundaries and time surfaces are parallel. Flows and breccias become less abundant to the south so the lithologic boundaries may lie at some angle to time surfaces but because the siliceous marker horizon remains 6,000 feet below the top of Assemblage P]_ in the main outcrop area, this angle cannot be large. Correlation of this Assemblage with units of Nicola Group described elsewhere in British Columbia is difficult and is not attempted here.  46  6600' A A. A A A .  Assemblage  LEGEND a A A A-A *  5280'  A  4  a 4  breccia  / \ ' \ •»  -o o  agglomerate  T  TTT  tuff  A  39^0'  T  T  T T T  ' V T  T  T  V T  T  A V A V  2640'  feldspar  v  porphyry  flow-layered  T  andesite  poorly exposed  AV  feldspar  >\ • \  p o r p h y r y and g r a y w a c k e  TT T T t T  greywacke  A7A?Ay  limestone  1320'  *\  FIGURE  13.  '  \ '  GENERALIZED  SECTION  OF ASSEMBLAGE  P  1  Assemblage P? Distribution and Thickness The rocks of Assemblage P2 crop out along a broad belt from Nicola Lake south-southwest.  This belt and other areas of outcrop of  Assemblage P2 are shown in Figure 14.  South of Nicola Lake, the whole  section i s about 5,000 feet thick; near Sugarloaf Mountain, i t i s about 6,000 feet with no top found, and in the Iron Mountain block, i t i s about 8,000 feet thick with no top found, but here i t is thickened by faulting. The base of the assemblage i s taken at the first occurrence of an agglomerate and, where this is lacking, at the point where tuffs and volcanic breccias become interbedded with tuffaceous sediments just above purple flows of Assemblage P]_. The top of the assemblage i s taken to be the contact between calcareous rooks and overlying olivine- and augitebearing porphyritic basalts. Lithology Flows of porphyritic and flow-layered amygdaloidal andesite are less abundant than compositionally equivalent agglomerates, breccias, and tuffs.  Wackes and calcareous rocks, including thick reef masses, are  locally abundant. Conspicuously porphyritic, basaltic andesite flows, resembling those of Assemblage Pi, with abundant feldspar phenocrysts and few augite phenocrysts have generally a black or green matrix except near their tops where a purple or mixed green and purple matrix predominates. Northeast of Courtney Lake, thin flows are extremely amygdaloidal at their tops. Under the microscope, the rock is seen to be composed of abundant, altered phenocrysts and laths, now albite, set in a mainly  FIGURE  14.  ASSEMBLAGE  P  49 intersertal matrix. In thin-sections of a fev less altered flows, normal oscillatory-zoned feldspar phenocrysts are seen to be labradorite in the center and oligoclase on the rims. Most of these calcic cores are replaced by some combination of calcite, chlorite, epidote, zoislte, albite, pumpellyite, prehnite, or white mica. The few augite phenocrysts are partly replaced by calcite and chlorite showing anomalous blue birefringence as does a l l the chlorite in Assemblage P . 2  Irregular,  sporadically abundant amygdales consist of chlorites, epidote, calcite, pumpellyite, or prehnite. Chemical analyses are presented in Table 7, Appendix 1 (l4 and 20) and norms in Table 8, Appendix 1. Inconspicuously prophyritic and microporphyritic flows are similar to the above except that the matrix contains pilotaxitic microlites of sodic plagioclase. Flow-layered andesites, abundant near the top of Assemblage ?2t form flows and dykes up to 45 feet thick. Flow layers are irregularly oriented near tops of flows, where they are parallel to elongated amygdales. Bear the base of some flows, a prominent, convex upwards . sheeting parallel to the base i s seen. These andesites are mainly interbedded with agglomerates or breccias, but may occur as dykes i  cutting Assemblages ?i and P 2 . In one place, a dyke of flow-layered andesite cuts through a flow of similar rock. The andesites are sparsely porphyritic with euhedral feldspar phenocrysts in either a pilotaxitic matrix or a matrix which i s mainly a mosaic of quartz blebs about  mm. across in which small sodic plagioclase laths and opaque.!  materials, mainly hematite, are set. The hematite becomes more abundant near elongate amygdales (up to 40 mm. long) of chlorite, calcite, chalcedony, and quartz. Chemical analyses of such rocks are  listed in Table 7 , Appendix 1 ( l l , 1 7 , 1 8 and 1 9 ) and norms in Table 8 , Appendix 1 . The specific gravity decreases regularly from the conspicuously porphyritic flows to flow-layered ones. Beds of agglomerate are found mainly north of the head of Nestor Creek and on Iron Mountain (Figs. 1 , 1 5 , 1 6 ) .  Eared, red, vesicular or  amygdaloidal bombs (Fig. 1 6 ) and "cored" bombs with oenters of angular fragments up to 1-J- feet across consisting of underlying porphyritic or flow-layered rooks are set in the red tuff matrix*  Zoned, irregular  fragments with curved re—entrants of vesicular or amygdaloidal, colourzoned, red aphanite representing bombs are also found in the agglomerates. At the top of a bed. a porphyritic flow fragment 4 0 mm. long rests partly within a red matrix composed of amygdaloidal aphanitic l a p i l l i .  Within  the l a p i l l i adjacent to the fragment, slightly elongate amygdales are warped to follow its oontours, indicating that the fragment travelled through the air.  In thin-section, the bomb material and matrix are seen  to be made of similar material. Hematite i s so abundant as to make much of the slide opaque and i t obscures much of the fine-grained matrix which contains scattered microlites of albite. Amygdales are generally filled with chlorite, calcite, or epidote. Finer grained equivalents of these beds are l a p i l l i tuffs. A chemical analysis of agglomerate i s presented in Table 7 , Appendix 1 ( 2 4 ) . An agglomerate referred with doubt to Assemblage P i s made of: 2  hen's egg-sized bombs set in a tuff matrix. In thin-section, the bombs are seen to be microporphyritic with clots of feldspar, now albite and a prismatic mafic mineral, probably augite, now pseudomorphed by quartz,  51 j  il-1/2  COVCRCD  1/2  mile  5940'  ISA "S A " " 5  miles  5280' »T. A  V  A  A S A  S  AS  y y vv vvv 5. A S A 5 A  A * A S A a s ^ S A  f  1  COV€ft€ D  4620'  Cove B « D A T «f>  A  v vv y y vv Co v€ R€t>  T A T c s  Q  ^  3  C O V€ Re D  3960'  O O O °O o 1° ° O o o o • © O o ° i ° ° 'O 0 ° „ F T  CoV€ R£ D  i •L  T  CCV€R€D  AS  63. P  ASA.  ATO-TAT^TA 3300' SANA'S A A t A T A  AT A T i V V V V V AT A T A T V V V V  12640',  V  A A A A l L E G E N D  S A 5* SA JA  1  limestone  • OO  A  - •» • ?  graywacke S45  S  1980'  5  !  >« » »» »  sedimentary  breccia  C0V€ RCO  conglomerate  1320'  tuff  1*1 4/  tuffaceous  breccia 660'  p o r p y r i t i c flow aphanitic flow dyke  F I G U R E  rocks  15.  S E C T I O N S  O F A S S E M B L A G E  P .  52 uralite, and rarely chlorite, set in an amygdaloidal diabasic matrix. The matrix of the agglomerate i s composed of large crystals of albite, uralite, fine-grained epidote, leucoxene, and opaque materials set in and around clear areas of chlorite and quartz. The amygdales are filled mainly with a coarse mosaic of quartz and lesser amounts of chlorite, actinolite, epidote, and albite.  Veins of quartz, epidote,chlorite,  and albite cut both bombs and matrix. Volcanic breccias (Plate II) consist of angular fragments of porphyritic rock, flow-layered rock, and earlier volcanic breccias generally set in an amygdaloidal, hematitic, "devitrified" matrix. Fragments up to 10 feet long are found in one locality northeast of the head of Nestor Creek, but generally the angular to sub-angular fragments are about 10 cm. long. Another kind of volcanic breccia is composed of variably sorted, angular to rounded fragments, a few cm. long, of underlying volcanic rock which are set in a fine-grained, mainly purple matrix. Chemical analyses of such specimens are given in Table 7, Appendix 1, (l3, 15 and 16) and norms in Table 8, Appendix 1. Purple feldspar-bearing tuff (Plate III) and purple vitric tuff are less common than lithic tuff. A distinctive rock type that served as marker horizon i s a bedded quartz-bearing vitric tuff.  It contains  fragments of dacite in which square, partly resorbed, quartz phenocrysts and altered feldspar clots are set in a mosaic of quartz and albite dotted with hematite, other opaques, and sphene. Chemical analyses of such tuffs are given in Table 7, Appendix 1 (12 and 23) and norms in Table 8, Appendix 1.  53  PLATE I I .  Negative p r i n t of thin-section of volcanic breccia, Assemblage P_. x l  54  55 Volcanic wackes south of Nicola Lake are mauve and tan with small fragments of angular to sub-angular, red and black aphanite and bright green chloritized glass fragments set in a generally medium- to fine-grained matrix. Far from volcanic centers, the wackes are mainly green and may contain benthonic fossils and carbonized twigs. In thinsection, mauve volcanic wacke is seen to be composed of sub-angular, occasionally porphyritic scoria fragments; sub-angular altered feldspar crystals now mostly saussurite and albite (although very few have labradorite cores); chlorites; and much hematite dust. Epidote alteration is responsible for the green colour of some volcanic wackes. Tuffaceous wackes have, in addition, l a p i l l i or smaller tuff fragments with irregular shapes. Calcareous wackes are generally massive, dark, greenish-tinged rocks with small fragments of crinoid stems and pelecypod shells.  In thin-section, suoh rock is seen to be oomposed of calcareous  fragments, porphyritic scoria fragments similar to those in the agglomerates, altered feldspar crystals, a few sub-angular grains of clinopyroxene, and rare quartz grains set in a matrix of recrystallized calcite and chlorite. Medium-grained plagioclase wackes are composed of altered plagioclase now mainly albite, and a matrix of chlorite, albite, calcite, and quartz. They are Veil sorted in comparison with other rocks in the map area, but compared with greywacke sequences in other areas, such as those in the upper Cretaceous Nanaimo Group in the Gulf Islands, they are poorly sorted. Calcareous rocks are formed from crinoid columnals, spongiomorphs, coral debris, cidarid echinoid spines, pelecypod debris, algal mats, brachiopod debris, and many other organisms. These biogenic components  56  are mixed in various combinations with both pyroclastic and epiclastic debris. A tuff with inch-long, aggregated, pentagonal crinoid columnals and broken brachiopod and pelecypod shells, including oyster-like forms, is found at fossil looalities 9» 10, and 11 (Fig. 3, in pocket). Calcareous wackes have already been described. Some of these have layers of convex upward shell as at locality 13* * volcanic wacke contains algal pisolites with brachiopod and pelecypod shell fragment cores (Fig. 3, in pocket, loc.28). Lithic calcarenites are composed mainly of broken crinoid columnals, pelecypod fragments, assorted indeterminable calcareous fragments with altered volcanic fragments set in a fine-grained, usually  recry8tallized  matrix.  Reef masses are composed of rarely vuggy, occasionally bituminous, light-grey fossiliferous limestone. Frame-building organisms include sponglomorphs, corals, rare bryozoans (?), and algal mats. Secondary quartz has partly preserved organ-pipe spongiomorph masses spread over tens of feet. Heads and flat patches of colonial corals, such as Astreids (Plate IV), or smaller pieces of brain coral, such as  Th^TOfiftlffTi ^1  represented by partly recrystallized limestone or replaced by quartz. A poorly preserved coral seems to be tabulate. Irregular algal mats are usually outlined by quartz. They coat or replace framework organisms. Found between the frame-building organisms are poorly sorted rudites with fragments of cidarid spines; prismatic- and thick -shelled pelecypod debris; crinoid stems; brachiopods of globose, smooth form (Terebratulids), or plicate form (Rhynchonellids); as well as Michelinoceras (an orthocone cephalopod); high-spired snails with low apical angle; Lopha (an oyster); rare Dentalium; and other unidentified material. The matrix of both reef limestone and rudite is a partly recrystallized micrite which contains  57 small ovoids of concentrically-zoned algal pellets. The insoluble residues of limestone vary both in amount and in kind (Table 9). After digestion in 10# HC1, primary and two kinds of secondary residues oould be distinguished. In two specimens of calcarenite (Table 9), irregular, bright green, frothy, mostly chloritized tuff fragments occur with sub-rounded fragments of quartz and relatively clear feldspar grains. In general, silica seems to have replaced the outside of a fossil first, reproducing the exterior in minute detail.  The inside  detail of the fossil i s destroyed by later silica replacement. SpOngiomorphs are replaced along their outer walls by very fine-grained botryoidal clear quartz, whereas, in their centers, spongy white quartz has destroyed any previous internal texture. Occasionally the outside i s covered by a thin coating of limonite. The partial replacement of the outer surface of cidarid spines by quartz, followed by dissolution of the spine's remaining calcite, yields small, cup-shaped fossils which resemble dasyclasid algae. Specimens representing gradations from calcite spines to these quartz cups are present. Pyrite is commonly associated with and finely dispersed through quartz and in some places the pyrite has been oxidized to limonite. Acetic acid dissolves calcite differentially, favouring fine-grained material over coarsely crystalline material such as crinoid stems and echinoderm spines. Some of these spines have their center filled with limoriite, probably oxidized from pyrite. All specimens of insoluble residues contain small botryoidal fragments of clear or white quartz. Most of the insoluble material not bound up in the fossils is bound up in this quartz. Some brachiopods contain a partial white quartz f i l l i n g .  Cherty lumps with remnants of  58  Map Locality (Fig. 3 in pocket)  Per cent insoluble in 10% HC1  1  1.0  3b  17.0  4  55.5  5  2.0  15  22.4,  17  7.9  5.0,  Table 9 : Insoluble residues of limestones in Assemblage P . Subscript 1 indicates calcarenite specimens. 2  Organism Corals and hydrozoans Bryozoans' Brachiopods Spongoids Molluscs Crustacea Echinoderms  Number of species 32  •7 4 6  32 32  48  Table 10 ; Fauna of deep-water reefs (after Teichert, 1958).  28.0i, 3.9i  59 calcareous fossils occur very sparingly with the limestone. Grey-weathering, bluish-black calcilutites are well bedded and contain rare flat-ribbed pelecypods (Halobia) or globose, smooth forms of brachiopods (Terebratuloids). Cherty lumps occur in this limestone. A pelecypod coquina interbedded with arenitee was found near Nestor Creek. Fragments of corals, sponge-like material, spongiomorphs, and many other forms, including a nautiloid, are found in rare conglomerates. Internal Structures and Stratigraphic Variation Host clastic units are lenticular and change grain size along strike.  Siliceous tuffs form widespread thin beds. They occur in 4 fault  blooks and, in one block, the unit has been traced for about two miles (Fig. 14). Calcareous horizons are persistent but the individual lithofacies such as reef masses or inter-reef calcilutites within horizons vary along strike (Fig. 17). Flow layering is the most prominent primary igneous feature and i s characteristic of andesites (Fig. 16). Green flows show mixed purple and green tops. Amygdaloidal zones in lavas are generally at the tops of flows but also occur throughout thin flows. -One flow i s continuous for a few miles along strike but faulting generally makes individual correlation of flows difficult. Vertical and lateral heterogeneity of a sedimentary part of Assemblage P are shown in sections (Fig. 15). Detailed maps also show 2  lateral variations near a volcanic center (Fig. 16) and at the edge of a reef mass (Fig. 17). The assemblage has been tectonically thinned near Nicola Lake.  60  61  62 Age and Correlation Assemblage P contains poorly preserved but diverse fauna including 2  pelagic, shallow-water, reef-making, and benthonic forms (Pig. 3; Table 32; Appendix 2).  The pelagic forms include fragments of a juvavitid ammonite,  various forms of "Arcestes", a large nautiloid, some forms of Halobia. and a few unidentified belemnite forms. The juvavitid fragment places a lower limit on the age; the assemblage i s younger than the Velleri zone of the upper Kami an sub stage (Tozer, 1967). The Halobia fragments put an upper limit on the age, that is, older than the upper Norian substage (Tozer, 1967). Reef forms such a spongiomorphs, '^"rpi^fl'ff^^'rfiP - astreids, pentagonal and 5-pointed star-shaped crinoid ossicles, cidarid spines, and orthocones confirm a lower Mesozoic age for this assemblage. Spongiomorph- and coral-bearing reefs were once thought to have been formed in the Cordillera only during lower Norian time (Smith, 1927) but subsequent work has shown that these reefs have a long temporal range, (ttuller, 1936; Tozer, 1967). Brachiopods in this assemblage include ,  :  terebratulpids, rhynchonellids, and cyrtinid or spiriferinid forms. The benthonic epifauna includes ornamented "myophorias" including Mlnnetrjgonia (Silberling, 1967, pers. comm.) and forms resembling Mypphoria adornata. The latter has previously been assigned to upper Norian substage (Tozer, 1967), but because i t occurs in beds along strike of Halobia-bearing beds, the time range of Mypphoria must be extended: Halobia is considered a more reliable index fossil than Mypphoria (Silberling, 1965). Another form, Cassianella. a benthonic pelecypod, was reported from Iron Mountain (Cockfield, 1948). A particular species  of this genus characterizes a marker horizon in upper Norian beds in the Taseko Lakes area (Tozer, 1967). Cassianella may reflect similar environmental conditions in the enclosing beds but not temporal equivalence Hence, i t is not thought to indicate that the beds on Iron Mountain are upper Norian. No Halobia. however, have been found in the beds west of the Iron Mountain fault block to confirm that the beds are lower Norian. Thus, the rocks of Assemblage P probably are of uppermost 2  Kami an to upper middle Norian substages.  Benthonic forms, previously  recorded from upper Norian rocks in the Cordillera, are found with associated beds containing Halobia. or are correlated with Halobiabearing rocks on the basis of lithology. Although Assemblage P stratigraphically overlies Assemblage Pi, 2  i t is quite possible for reasons already discussed (p.45 ) that some lower parts of Assemblage P2 far from the volcanic centers are older than some parts of Pi near these centers. The general attitude of bedding and the time planes marked by the two quartz-bearing tuffaceous marker beds, however, are generally sub-parallel, so that litho-stratigraphic units are similar to the chronostratigraphic units. The thick upper i limestone reef and associated limestone debris also mark an easily recognized physical sheet which is parallel to a short time span. The general strike of the assemblage and fossil localities noted by Rice (1947) suggest that this assemblage continues south-southwest for some distance beyond the map area. Halobia-bearing rocks with similar lithology but. with fewer flows and abundant limestone have been described by Carr (i960) from Promontory Point, 10 miles west of the map area. Calcareous and siliceous sedmintary sequences at Ashcroft (Duffell and  McTaggart, 1952; Carr, 1962b) and near Hedley (Rice, 194?), and greywackes in the Chilliwack Valley (Monger, 1966) also contain fossils from this general time interval.  Assemblage Ai Distribution and Thickness Rocks of Assemblage A^ underlie most of the map area east of Quilchena Creek and Nicola Lake and southwest of Quilchena (Fig. 18). They form the lower part of the second cycle (A). The base of the unit i s at the base of porphyritic basaltic flows that overlie the thick reef complex in Assemblage ?2*  ^  n e  *  o po f t n e  unit is marked by a breccia-conglomerate-limestone complex. Estimates of thickness of the assemblage are not accurate because attitudes are rare and structures are complex. Measurements from cross-sections yield a maximum estimate of about 7,500 feet. Lithology Typical flows, about 20 feet thick, are mainly of porphyritic and commonly amygdaloidal basalts characterised by large (up to 15 mm.) equant, euhedral pyroxene phenocrysts. Some varieties also contain small (up to 5 mm.), tabular phenocrysts of feldspar and a variety common near the base of the assemblage contains red blebs of hematite probably pseudomorphous after olivine.  The matrix i s generally green and fine-  grained, but near the base i t is predominantly grey and red.  Dykes of  similar rock contain two sizes of phenocrysts of both augite and small tabular feldspar. In thin-section, the basalt is seen to contain phenocrysts of relatively fresh oscillatory-zoned, hourglass-zoned augite  65  66  set in a matrix of epidote, saussuritized feldspar, albite, chlorite, calcite, and, rarely, green biotite. Feldspar phenocrysts are altered to saussurite, but rare unaltered remnants are normal - to oscillatoryzoned labradorite. Amygdales are filled with epidote, quartz, chlorite, calcite, potash feldspar, pumpellyite, minor sulphides, albite, and actinolite.  Chemical analyses of these altered basalts are given in  Table 7, Appendix 1 (25,26,27,29,30,31,32, and 33) and Table 8, Appendix 1, lists norms. Breccias are made of fragments of vari-coloured basalts in matrix similar to the fragments.  It i s difficult to distinguish flow breccias  from pyroclastic breccias because the matrix i s generally recrustallized. Agglomerates and l a p i l l i tuffs are found southwest of Quilchena where red, hematite-rich, commonly porphyritic fragments are set in hematite-rich matrix. These altered pyroclastic rocks are not as coarse as those of the underlying Assemblage P . 2  Lenses of altered crystalline  and lithic tuffs are found in Henader Hills.  There, pyroxene crystals  and fewer feldspar crystals are set in a recrystallized, epidote-rich  1  :  matrix. A chemical analysis of a hematite-rich l a p i l l i tuff is given in Table 7, Appendix 1, (28). A breccia with some partly rounded fragments mainly of basaltbut including altered quartz diorite and hornblende-bearing gabbro fragments, very rare pebbles of hornblende-bearing volcanic rock, and one fragment of schist (?) - is found to change along strike into a cobble conglomerate with a partly calcareous matrix. Conglomerate in part overlies and merges with the above breccia and underlies or merges with calcareous reefs. Well-rounded fragments of  67 augite-bearing volcanic rock, up to a foot in diameter, l i e in a commonly calcareous matrix that includes a considerable proportion of calcareous material. Poorly preserved thick-shelled pelecypods that resemble Megalodont in form and 1-^-inch long high-spired snails are among the fossils found in this bed, together with broken crinoids, belemnite fragments, and irregular mats of colonial corals up to one foot long. Volcanic wackes are red or green, poorly sorted, medium-grained rocks with small fragments of dark pyroxene and, less commonly, feldspar* Beds range from foot-thick units with l i t t l e variation to finely laminated, vari-coloured, medium- to fine-grained, ripple-marked, and cross-bedded units. Graded bedding of units -^-inch to a few feet thick occurs, but infrequently. Limestones are found in lenticular bodies at and near the top of the assemblage, associated with conglomerate. Grey, veined, variably recrystallized limestones locally contain irregular layers of green tuffaceous material or vague and fragmentary algae (?), colonial corals (?), horn corals, snails, orthocones, and heart-shaped cross-sections of pelecypods. Internal Relations and Stratigraphic Variation Primary structures are relatively rare in Assemblage A]_. Sedimentary structures including graded bedding, cross-bedding, scour; features, and planar beds occur in some of the wackes and tuffs. Beds are generally up to a foot thick. Contacts between breccias and fine-:: grained rock are generally sharp although some beds show gradational • contacts spanning several inches.  Local slumping along curved planes; has  68 affected certain inch-thick feeds. Primary igneous features include amygdales in flows and l a p i l l i in the pyroclastic beds. Fragments of underlying limestone are caught up in the basal flows of the assemblage. Lateral and vertical variations in Assemblage Aj are poorly understood.  Host units are lenticular and are also disrupted by later  faulting and folding. Ho persistent marker beds have been found except for the limy horizons at the top of the assemblage. The basal flows contain olivine, and flows higher in the section seem to have more abundant tabular feldspar phenocrysts. Figure 19 i s not a measured section but instead includes observations from many parts of the assemblage. It should only be considered a very general illustration of the vertical variation in the assemblage. Age and Correlation Assemblage A^ overlies Assemblage P2 and i s thus younger than middle Norian. The extrusion of basalt flows over the reef complex at the top of Assemblage P was probably accomplished relatively quickly. 2  Thus, lithologic and chronostratigraphic boundaries are probably parallel. The few fossils recovered from Assemblage A^ are "facies"fossils rather than "index" fossils.  However, the large, thick-shelled pelecypods  that resemble Megalodont in form, and the heart-shaped cross-sections of pelecypods, are found elsewhere in Norian rocks (Fischer, 1964; Tozer, 1967). Thus Assemblage A^ is probably in part upper Norian in age. Rocks of Assemblage A^ can be correlated with rocks north and south of the map area. North of Stump Lake, a conglomerate in rocks lithologically similar to Assemblage A^ contains in its matrix Monotis  Assemblage P  A.  O ©  0  A, A A O A T - - : •° A  TT  A A *"-•;•*. ".T • A A A A A A  LEGEND  A  A  _V • \/ \/ ? V V V V V V V V v V  V V  vv v  A 4 breccia O O  o o conglomerate  V  V  £g. g r a y w a c k e o r tuff  V  T T  V V  r r  agglomerate  A v  T T  T  JTT -T V V  graywacke  v  r  Y V Y V  1  V V v  V v  v  >  Assemblage P  FIGURE  19.  tuff l i m e s t o n e , r e e f , c a l . sec  y y A V  v  augite p o r p h y r y  2  GENERALIZED  SECTION OF A S S E M B L A G E  A  70 subcircularis. an index fossil for the upper Norian (Tozer, 1967). In road cuts near Savona, augite—bearing volcanic rocks and associated sediments also contain Monotis snbcircularis (McTaggart et al, 1968).  Assemblage A? Distribution and Thickness Rocks of Assemblage A  2  are found exposed in the Meander Hills,  by Stump Lake Creek, and in other localities noted on Figure 20. The base of the assemblage i s taken as the contact between medium- to fine-grained greywaoke and the underlying limestone— conglomerate-breccia complex previously described. The highest beds of the assemblage are exposed in the core of the Meander Hills syncline. The unit i s at least 1,600 feet thick. Lithology Assemblage A  2  consists of bedded greywacke and argillites.  Grey-green, medium-grained greywackes are composed of poorly sorted grains of pyroxene and feldspar set in a fine-grained, rarely calcareous matrix of similar material, now more or less altered to epidote, quartz, albite, and chlorite. The silty interbeds are of similar composition. Tan-weathering, light green to dark green or black, conchoidally fracturing argillites are composed of albite, chlorite, and quartz mosaics with minor relict pyroxene, epidote, pyrite and calcite. Internal Structures and Stratigraphic Variation Assemblage Ag i s thick- and thin-bedded with ripple marks, load casts, cross-bedding, scour marks, cut and f i l l structures, sedimentary  71  72  boudinage, and rare graded bedding. Some bedding surfaces show rectangular markings perhaps representing worm tracks. The vertical variation i s summarized in Figure 21.  Age and Correlation The, only fossils recovered from this unit are peculiar, flat, anastomosing, calcareous worm (?) tubes which lie mainly along bedding surfaces. Assemblage A2 conformably overlies Assemblage A^ and i s therefore probably upper Norian or younger in age. However, the beds cannot be classified accurately as to age until appropriate fossils are found. Beds that correspond to this assemblage are found north of Stump Lake and also in a belt extending from near Pothole Creek to Missezula Lake (Rice, 1947).  ORIGIN OF, NICOLA GROUP Introduction The rocks of the Nicola Group, when first laid down, resembled those produced within a modern volcanic archipelago. The rocks have since been metamorphosed, metasomatized, strongly faulted, and weakly folded. Fossils, primary structures, and textures provide the main evidence for the environment of deposition. Discussion of the origin of volcanic types is postponed until the nature of chemical alteration has been considered.  73  SOUTH  NORTH  SECTION  SECTION  2640'  2640' eftosioN  1320'  s o n Fact.  1320'  COVERED  • LEGEND  fine grained graywacke or tuffaceous a r g i l l i t e  •  c o a r s e grained °  O  O  °oo  B  FIGURE  graywacke  I c  onglom e rate  21.  G E N E R A L I Z E D SECTIONS  OF ASSEMBLAGE A  0  <74  Complex interactions of the provenance and depositional basins have led to an abundance of rock types. The source of rock material was within or below the depositional basin itself.  Constructive agents  such as volcanic activity and biologic activity and destructive agents such as erosion near islands have combined to form the large variety of rocks. Subaerial mud flows, current-winnowing of sands, and settling of grains are examples of the mode of transport of rock material. The material was deposited mainly in shallow, marine waters. Plutonic rock apparently existed in the region before the Nicola Group was deposited. Although the great majority of the rocks of the Nicola Group are volcanic or sedimentary, a few scattered plutonic fragments occur in the volcanic rocks. Quartz diorite and gabbro are most common in breccia of Assemblage A but quartz monzonite and grano2  diorite are present elsewhere (Fig. 1, in pocket). Because other allochthonous debris i s lacking, i t i s thought that the fragments were derived from coarse-grained rocks beneath the Nicola Group.  A§£gmbj£ge_P  1  The volcanogenic Assemblage P-^ was deposited in a mainly submarine environment. Interbeds of conglomerate with calcareous matrix between flows and breccias, limestone blocks within flows, and rare Interbeds of greywacke containing pelecypods point to a submarine environment. Algaebearing blocks in flows suggest that the blocks were once parts of reefs and that subsequent flows either carried them away from the reefs or that the blocks slipped down fore-reef slopes before they were engulfed by the lavas. Local slopes with some areas near sea level seem to be  75 indicated. The presence of conglomerates suggests that material was being locally eroded. The "cockle"-bearing greywacke indicates a neritic marine environment. The widespread dacitic tuff marker horizon suggests that most of the basin was submarine and the lateral variation in grain size suggests that the source of dacite tuff lay to the east of Nestor Creek. Thus, a sea with local reef patches and small volcanoes rising above the relatively shallow floor of the basin is envisaged.  Dacite  erupted, probably near Nicola Lake east of Nestor Creek. Lava extruded from fissures within the basin flowed over and around reefs. Blocks and ash were scattered by explosions.  Assemblage Po Bocks of Assemblage P show that subaerial volcanoes appeared 2  intermittently; fringing reefs formed during quiescent periods. Volcanic Centers South of Nicola Lake, coarse agglomerate beds contain bombs of various kinds, some of which have well-developed "ears" and some of which have cores of volcanic breccia. Blocks in volcanic breccia are of mixed upper and lower Cycle P rocks and probably represent debris associated with phreatic explosions. Beds of agglomerate and coarse breccia also occur south of Nicola Mountain as well as hear the summit of Iron Mountain. Farther from these regions, the same assemblage is composed of much finer tuffaceous material and volcanic and calcareous wackes. This lateral variation is a good indication of the location of volcanic centers (Dickenson, 1968). Flow-layered andesitic flows and dykes are common near the centers.  76  That the centers were in part subjected to subaerial oxidation is suggested by the red tops of some flows with generally green matrix; the generally hematite-bearing, now devitrified glass in most of the agglomerate; the eared bombs; and zoned l a p i l l i with redder outer zones and darker purple-red inner core. From these volcanic centers, quiescent flows and explosive magmatophreatic (illustrated by cored bombs) or phreatic (illustrated in part by mixed breccia with no lava matrix) material were emitted. The composition varied from basaltic andesite (?) through andesites to dacite. Shallow-water Reefs Limestone beds in Assemblage P organisms.  2  contain fossils of colonial  South of Nicola Lake (Fig, 17), a massive lenticle of limestone  grades into conglomerates along strike.  The lenticle contains echionderms,  few corals, gastropods, and rare brachiopods and the presence of a reef i s clearly indicated (Teichert, 1958). Reefs may be either shallow-water or deep-water, Teichert (1958) described the rich fauna that i s found in deep-water reefs (Table 10), and suggested that coralliferous limestone of late Triassic age in southern Alaska may have been formed in the same environment as presentday Norwegian deep-water coral banks. The fauna of the southern Alaska coral banks i s similar to that of other Upper Triassic banks in the Cordillera, including the main reef at the top of Assemblage P of the 2  Nicola Group. Calcareous algae, however, are restricted to shallow-water reefs. Algal pisolites (Plate V) and algal crusts (Plate VI) occur in Assemblage P2 reef limestone. Prominent, peculiar, flat, wavy structures  77  PLATE VI.  Negative p r i n t of thin-section of a l g a l crust, Assemblage P~. <2  78 are interpreted to be Lonha fragments with algal crusts and hydrozoans (?) related to stromes (Murray, 1966, pers. comm.). The reef and smaller patch reefs of Assemblage P  2  probably formed i n shallow water.  Because reefs are accumulations of organisms with certain ecological niches, some deductions about the environment can be made. Reefs indicate the presence of clear, warm, marine waters and the lack of nearby erosion (Davis, 1928). Neritic Environments Fossil collections from Assemblage P  2  (excluding reefs) indicate  a variety of neritic depositional environments. Neritic environments affected by strong currents are shown by aligned, convex-up pelecypod shells (Menard and Boucot, 1951; Boucot et a l , 1958), well-sorted coarse coquinas, conglomerates bearing reefderived f o s s i l s , and aligned orthocones (Schwarzacher, 1963). Neritic environments not noticeably affected by currents include oyster-bearing localities (Fig. 3 i n pocket) and cpckle-bearing localities (Fig. 3 i n pocket).  The oyster-bearing localities also contain plicate  brachiopods and pelagic pelecypods, which probably required circulating waters.  The movement of these waters, however, was not sufficient to  reorient the shells. Exterior casts of small, separated valves of ribbed pelecypods resembling cockles are very common at locality 12 (Fig. 3 i n pocket). Only 3 out of 110 of these pelecypods were articulated.  These numbers  suggest that after the pelecypods died, sufficient time elapsed to allow organic disintegration before the shells were buried beneath the 6-inch deep biologically active zone (Zobell, 1942).  A well-preserved  79  echinoderm plate demonstrates that abrasion due to wave action did not affect the animal remains here. The fauna from locality 12 (Fig. 3 in pocket; Appendix 2) i s essentially a neritic one with a few pelagic forms and land-derived carbonized twigs. At fossil locality 7 (Fig. 3 in pocket), a 6-foot thick lens of silty, poorly sorted sandstone contains abundant Lingula along with flat, irregular shapes which perhaps represent green algae (?). The Lingula are folded but the containing bed is not.  This folding of the shells  is thought to be due to soft sediment deformation of the chitinous rather than calcareous Lingula shells. Lingula lived mainly in a shallowand perhaps brackish-water environment (Craig, 1952). The pelagic forms Halobia. Posidonia (?), ammonites, and belemnites (?) are found rarely in fine-grained, black, calcareous siltstones. These accumulations contain graphite and probably mark relatively deep areas in an irregular inter-island basin. The fossil localities mentioned a l l represent shallow-water accumulations in a relatively quickly subsiding, quickly f i l l i n g basin. Also evident are traces of the catastrophic impact made on neritic life by detritus from the nearby volcanic centers. Carbonized twigs found in locality 12 (Fig. 3 in pocket) represent wave-distributed remains of burning branches carried seaward when lava inundated the land (?). Encrinitic tuffs at locality 11 (Fig. 3 in pocket) reflect sudden death and burial by (hot?) volcanic ash. are caught up in tuff.  There, 2-inch long crinoid stems  Elsewhere in the area, similar crinoids are  80  represented by widely separated plates and ossicles. At locality 6 (Pig. 3 in pocket), a very amygdaloidal lava has enclosed a belemnitelike shape. A cast of a 1-inch wide snail is caught up in a porphyritic flow at locality 42. Sedimentary structures also reflect a variety of depositional environments. Strong currents or waves acted locally to form crossbedded calcarenites, medium-sorted conglomerates, sorted calcareous tuff, and tuffaceous arenites. Volcanic wackes that are very poorly sorted are thought to represent cold mud flows (Fiske, 1963). In contrast, at Garcia Lake, well-sorted plagioclase-rich sandstone suggests much winnowing has occurred.  In some wackes, volcanic fragments are intensively  chloritized or carbonatized whereas in other wackes, fragments with similar texture look relatively fresh. Part of this difference in mineralogy i s thought to reflect the fact that fragments on the floor of the basin were exposed to seawater for different lengths of time. Islands Sub-aerial volcanic centers were probably established islands. Woody, branched twigs' (Fig. 3 in pocket, loc. 12) can come only from land plants. Lingula-bearing  muds intercalated with conglomerates suggest  that fresh water, in part, was responsible for transport of fragments. Lenticular conglomerate beds in general indicate land was nearby. Local unconformities and a regolith (Fig. 1 in pocket, loc. l) also suggest that parts of the area were above water.  81 Stratigraphic V a r i a b i l i t y The s t r a t i g r a p h i c v a r i a b i l i t y i s a function of the kind, quantity, and rate of supply of material, the amount of material removed from the region, the shape of the depositional basin, and the rate of subsidence of the basin (Sloss, 1962;  A l l e n , 1963).  The rate of supply of material varied while Assemblage P being deposited.  2  was  Thick beds of lava and t u f f can be formed i n a very  short time ( T a z i e f f , 1962), whereas the presence of reefs shows the i n f l u x of material to be n e g l i g i b l e (Davis, 1928). equally v a r i e d .  Erosion rates were  Poorly sorted conglomerate beds imply rapid erosion and  dumping; the r e e f s show the sedimentation  rate to be low.  The rate of  subsidence seems to have been r e l a t i v e l y high throughout the i n t e r v a l of time when Assemblage P  2  vas  deposited.  The amount of material transported away from t h i s general area cannot be accurately estimated but the great p i l e of volcanic wackes at Promontory H i l l s (Carr, I960) l i t h o l o g i o a l l y s i m i l a r to Assemblage  P  2  suggests t h e i r source could have been near the t h e s i s area. A balance between rates of i s l a n d b u i l d i n g , i s l a n d erosion, organic a c c r e t i o n , subsidence, and transport of material out of system seems to have been struck so that most of the rock of Assemblage P2 deposited i n a shallow  was  sea.  Assemblage AT The volcanogenic Assemblage A^ has been f a u l t e d and folded more intensely than Assemblage P . 2  locally  The s t r a t i g r a p h i c continuity  82 of individual beds is generally hard to establish and the environment of deposition is difficult to deduce. Lenticular tuff beds and volcanic breccias show that local explosive eruptions occurred, but the intercalations of volcanic wacke suggest that regions near volcanic centers are not exposed now. The early flows cover reef rock of Assemblage P and the latest 2  beds in Assemblage A^ are conglomerates, breccias, calcareous algae- and coral-bearing reef structures. Thus, at the beginning and end of the interval during which this assemblage was deposited, shallow-water environments prevailed. The variety of volcanic boulders of Assemblage Ai in the conglomerate suggests that part of the area was differentially eroded or that the different kinds of flows did not cover the entire region. Irregular bedding in a few places indicates the presence of currents but elsewhere bedding is generally planar. Assemblages A^ seems to have accumulated first in deepening then in shallowing waters. Early volcanic rocks of this assemblage have reddish matrices but later volcanic matrices are green. If the red colour is due to primary hematite, i t implies that the environment of deposition of lavas changed from oxidizing to reducing, or from subaerial to submarine conditions. Shallow marine or subaerial conditions were then established and are represented by the reef at the top of the assemblage.  Assemblage A? Assemblage A contains sedimentary structures (already discussed, 2  p. 70) which are common in shallow marine waters (Shrock, 1948), but which  can apparently also be found in the upper parts and distal ends of beds deposited by turbidity currents (Walker, 1967). Because the immediately underlying rocks were formed in shallow water, and in the absence of strong evidence to the contrary, i t i s concluded that Assemblage A  2  was  probably formed in the same environment.  During Late Triassic time, vents in rapidly accumulating piles of basaltic andesite eventually became subaerial and the lava emitted became andesitic and, rarely, dacitic. Around the resulting islands, coral reefs grew and calcareous as well as olastic debris accumulated in the shallow waters. The reefs were covered by later basaltic effusive material. The volcanic centers and islands in the area shrank as the basin continued its rapid rate of subsidence. Upper Norian (?) shallowwater reefs flourished for a short while after basaltic volcanism. The area was then covered by a thin blanket of volcanic sand, s i l t , and fine ash, presumably also deposited in shallow water.  CHEMISTRY OF THE NICOLA GROUP  Although volcanic rocks of the Nicola Group have retained their primary textures, their bulk compositions have been locally altered. Consideration of the nature of this metasomatism makes i t possible to estimate, within broad limits, the original chemical nature of the volcanic rocks. Metamorphism, probably contemporaneous with metasomatism and  PLATE VIII.  Conglomerate with elongate fragments i n limestone matrix.  85 partly controlled by structure, is discussed in a later section.  Metasomatism Evidence of Metasomatism Textural and Mineralogical Evidence Replacement masses, veins, disseminations, amygdales, and pyrogenic minerals pseudomorphed by new minerals of quite different composition are textural evidence for chemical alteration of volcanic rock. Replacement masses of epidote are common near Nicola Lake (Plate VTl), southwest of Quilchena, northwest of Merritt, on the summit of Iron Maountain, north of Garcia Lake, and east-northeast of Lundblom Lake. Locally, foliated augite-bearing basalt, basaltic andesite flows and breccias, and dacite are almost completely replaced by epidote. Quartz masses and irregular jasper veins and masses cut and replace basaltic andesites. Pyrite forms up to 5$ by volume of some rocks. Amygdales are composed primarily of calcite, chlorite, and quartz with occasional additions of epidote, white mica, actinolite, hematite, pumpellyite, and less widely distributed potash feldspar, laumontite, celadonite (?), sulphides, and other minerals (Table 21). Up to 8 different minerals may be found in the same amygdale. Some amygdales are surrounded by chlorite, pumpellyite, hematite, or epidote—rich haloes. Veins of calcite-quartz—epidote are common in altered volcanic rock. Local hydrothermal veins with complicated mineralogies (Table 21) are found southwest of Quilchena and along the south shore of Nicola Lake. Alteration haloes of vein minerals border some veins; other veins are bounded by sheared, hydrated, and carbonated  86  volcanic rock. Pyrogenic minerals may have been replaced by either similar but hydrous minerals or by minerals with a different composition. Calcite, hematite, and chlorite have replaced olivine.  Augite is replaced  either by mixtures of uralite and minor amounts of green biotite, epidote and quartz or by chlorite and calcite with minor amounts of epidote and uralite.  Feldspars, a few with relict labradorite cores, are replaced  by white mica, hydrated Ca-Al silicates, carbonate, and albite, and more rarely by quartz or laumontite. Associated sedimentary rocks have also been replaced by new minerals. Epidote replacement masses are found in greywacke, tuff, and limestone. Limestone and tuff are replaced by magnetite near Sugarloaf Mountain (Carr, 1961b). A few volcanic breccias and tuffs are almost wholly replaced by calcite.  Chlorite—rich areas are common in a l l rock  types. Limestones contain considerable amounts of several generations of secondary quartz. Fossils from the reefs, such as fragments of spongiomorphs, echinoid spines, brachiopods, and pelecypods are generally coated with, and in part replaced by, quartz. Fossil casts are lined by fine quartz druses or outlined by epidote. Chemical Evidence Chemical analyses of volcanic rocks of the Nicola Group, represented on an oxide vs. SiOg diagram (Fig. 22), plot near the average basalt-andeslte-dacite-rhyolite trend (Barth, 1952) but a large scatter of points i s evident. The usual KgO and Na 0 values expected from the 2  calc-alkaline trend are plotted on Figure 23.  These are compared with  values obtained from relatively fresh volcanic rocks of the Nicola Group.  Open symbols  "Cycle A  Closed symbols : Cycle P  ,0  •8 o O O*  15  10 % K  0 10 2  Q  F I G U R E 22.  0 5 %  HARKER  Na O z  DIAGRAMS  %CaO  0  80  Open symbols Closed  : Cycle A  symbols : C y c l e  P  « •  a  a  a  •  20  25 %A1 0 2  3  +  O Q  •  0  15  HARKER  5  10 %  •  F I G U R E 22.  +  +  4-  +  •  + + +  Fe 0 ^ 2  3  DIAGRAMS  0  % MgO •  CONTINUED  Percentage Na20 0  1  F I G U R E  _  23.  2  N a  4  3  O  vs  K  O  .  EST V O L C A N I C  5  R O C K S  6  O F  7  T H E  N I C O L A  8  G R O U P .  90  sio $ 2  •  more than 60  less than 1 mile  1 Distance from Batholith 1-2 2 or more more than miles miles 3 miles  4.13 (n-1)  1.4+1.2 (n-3)  Rock Type  Tuff  -  !  Plows  60-51  50-41  Tuff  -  Plows  -  Tuff  Plows  Table 11;  -  1.9 (n-l)  2.7+0.9 (n-7)  0.2  (n»l)  tr  (n-1)  2.8+1.5  -  1.6+0.9 (n-5)  0.5 (n«l)  tr (n=l)  -  -  3.1 (n-1)  1.0+0.2  (ni)  0.7 (n-1)  Variation of K^O with distance from batholiths and SiO, content.  0.9 (n-1)  91 The wide scatter of points this plot suggests that either some secondary process has induced the scatter or that these points represent a very variable and unusual rock series. ^0 values are higher nearer the batholiths than farther away (Table l l ) and i t is concluded that this difference i s due to metasomatism. Chemical Changes Effected by Metasomatism general Statement Detection of changes in bulk chemistry of the Nicola Group rocks depends partly on sampling methods and the precision and accuracy of the chemical analyses. Fresh-looking samples of volcanic rock of the Nicola Group were collected for chemical analyses. However, rocks that appear unaltered may have undergone some chemical alteration. For instance, a detailed study of an outcrop of a single basalt flow metamorphosed in the prehnite-pumpellyite-greywacke facies field shows a wide vatiation of chemical composition (Smith, 1968). There, small areas of Ca-rich lithology are set in a generally Ca-depleted lithology. The Ca-rich lithologies are green and obviously altered; the Ca-depleted areas are grey and not obviously altered. Vallance (i960) has suggested that the collecting of not obviously altered rocks (lime depleted ?) from lowgrade metabasalt terranes has resulted in too sodic estimates for such terranes. Thirty-three samples of relatively unaltered metavolcanic rock from the Nicola Group collected by the author from a 4-mile thick section exposed over about 200 square miles are probably biased in the above manner. Figure 22 shows CaO vs. Si0 for a l l analysed rocks of the Nicola 2  Group. Most CaO values lie below the calc-alkalic trend of Barth (1952). This probably illustrates a general CaO depletion of analysed rocks. Two different laboratories performed the chemical analyses. Samples 1,2,11,12,13,14,15,25,26,30,32, and 33 were analysed by rapid methods in the Geological Survey of Canada labs. Na 0 analyses were 2  performed by the writer at the Anaconda Research Laboratory (Britannia Beach).  The remainder of the oxides were analysed by rapid methods by  the Anaconda lab. The precision of the analyses i s shown in Table 12.  The relative  accuracy of the data i s more difficult to evaluate. Samples analysed by the G.S.C. were used to adjust some Anaconda Standard Curves prepared from standard rocks G^ and %  so that the values of the two labs are  comparable (Payne, 1967, pers. comm.). Precision of the Cu, Pb, Zn, and Ni values i s about 10$ of quoted value (Payne, 1967, pers. comm.). Changes Incurred by Metasomatism Within a metamorphio terrene in which the overall ratios of elements have not been altered, there may occur small domains in which the element ratios have been changed. This local metasomatism is difficult to distinguish from metasomatism caused by an external source such as a pluton. Redistribution of elements i s particularly effective at low temperatures in a strained rock whose initial mineral assemblage is not stable in the new environment. Various sizes of domains of rocks of the Nicola Group are clearly metasomatized. The largest domain in which element ratios have been altered is the size of the thesis area, the smallest about the size of a hand-  93  G.s . c .  Anaconda  Method  s  n  Si02  XRF  .6  12  Ti02  XRF  .025  12  XRF  XRF  .35  12  XRF  A1 0 2  3  Method XRF  Fe20j  by difference  .25  12  -  FeO  rapid chem.  .10  12  -  -  -  0  MnO  XRF  .10  12  MgO  XRF  .5  12  CaO  XRF  .15  12  .07  Fe as Fe 0j 2  s  n  ••1.0  21  .02 1.5  21 21  -•  0  • -  0  XRF  .5  21  XRF  .02  21  1.0  21  XRF  .6  21  12  At.A  .15  19  .05  12  XRF  .3  21  rapid chem.  .02  12  -  CG  rapid chem.  .05  12  -  total H2O  rapid chem.  .05  12  Na20 K0  XRF  2  p o 2  rapid chem.  5  2  S  Table 12  -  —  0  XRF, At• A  •  XRF  Precision of analysis of rocks of the Nicola Group, s standard deviation, n number of samples analysed, SRF X-ray fluorescence, At.A atomic absorption.  -  .1  0 0 0 33  94 specimen. Water, S, and C0 nave been added to volcanic rocks in the 2  thesis area. At least some of the H 0, S, and C0 was present in 2  2  surrounding sedimentary rooks since connate waters from porous pyroclastic sediments; oxidized organic sulphur; and C0 from oxidized organisms or 2  from dissolved limestone were available. As mentioned previously, K 0 2  is concentrated near batholiths*  Potash feldspar i s found in veins,  replacement masses and amygdales near plutons and white mica i s relatively more abundant near plutons than farther away. Whether the K 0 has been 2  added by the batholiths or whether the K 0 has been redistributed can be 2  determined only i f the original compositions of the lavas i s known. Whatever the process, the domain involved is a large one, including a l l of the volcanic rooks in the area i f redistribution occurred and one third of the area i f addition occurred. Lava and nearby tuff to not have the same amount of ^0 suggesting that different permeabilities played some part in fixing of the &>0. Small domains in which Ca-rich areas are set in Ca-depleted regions can be outlined. Epidote masses, carbonatized tuffs, and widespread epidote-calcite-quartz veins accompany the generally Ca-depleted rocks such as chloritized volcanic rock with chloritized clinopyroxene, albitized labradorite, and chloritized or silicified matrix. These variations are common in low-grade meta-basalt (Barth, 1952; Ramberg, 1952; Helson and Van Andel, 1966; Smith, 1968). They suggest that some CaO has been redistributed perhaps over domains of about a cubic meter. Hydrothermal veins that contain quartz, chlorite, epidote, salmonpink calcite, potash feldspar, albite, pyrite, copper sulphides, and  95  sulphosalts form small tabular domains composed of added material. Some of this vein material such as albite. potash feldspar, and perhaps sulphides was probably introduced by late emanations from nearby batholiths. Copper in many of the veins i s enriched by a factor of about 10^ over that in the country rock. The volcanic rocks in general seem to be impoverished in copper compared to other volcanic terranes (Table 13) so that depletion and subsequent redistribution of copper may have occurred. Some amygdales contain the same minerals as do veins. If material from an outside source formed the minerals, then the containing rock mass of at least a few cubic meters has been affected. These rocks contain uniformly saussuritized feldspar phenocrysts. Elsewhere rocks contain amygdales of variable composition and there, only smaller domains have been altered as suggested by local haloes around amygdales. In these rocks, feldspar grains in the same thin-section are variously altered. Local metasomatism has also affected domains of unknown size. Magnetite forms replacement masses of some cubic meters in limestone. Soda has been introduced as albite veins and as albite replacements of feldspars. Magnesium has been moved out of olivine phenocrysts but very l i t t l e can be deduced about its behaviour because the analytical data are not sufficiently precise. Aluminum-bearing minerals including epidote, albite, potash feldspar, and chlorite show that aluminum has been locally added. Although the source i s presumed to be nearby country rock (cf. Moorhouse, 1959), some aluminum is found in hydrothermal veins. Silicon introduction i s demonstrated by quartz in hydrothermal veins and amygdales; epidote-quartz-calcite veins and replacement masses; quartz replacing  96 Nicola Group frequency  ppm  Average of other regions  5 9 6 7 3  0-10 11-20 21-40 41-80 81-160  Mt. Hood Oregon (lowest)  0 . 1 1  161-320 321-640 641-1280  Table 15;  Aleutian volcanics, Alaska; average value for a l l basaltic rocks Kilauea basalts (highest)  Copper in Nicola rock in comparison with other regions (from Prinz, 1967).  Si02  No adjustment, perhaps too high  Ti02  No adjustment, probably stayed same  Al 0j  No adjustment, probably altered slightly  total Pe  No adjustment, random variation  MgO  No adjustment (precision poor)  CaO  No adjustment, although selected analyses depleted  2  with CaO Na 0  No adjustment, although probably too high  K0  Adjust values to average value far from batholith  H0  Adjust to 0  C0  Adjust to 0  2  2  2  2  S  Table 14;  Adjust to 0  Rough adjustments to correct for local metasomatism in selected analyses. After adjustment, recalculate sum to 100$.  .  97  microlites of feldspar in tuff fragments; quartz-coated fossils; and chert. Thus a l l the major oxides have been added locally to the rock in domains probably larger than handspecimen size. Because the analytical data are represented as percentage data, each addition requires a concomitant decrease in other .oxides. Thus, a l l the element ratios have been altered, especially in handspecimen size samples. Adjustments (Table 14) can be made to analyses of unveined, amygdale-free, but altered and albite-bearing lava in an attempt to obtain rough estimates of the compositions of the original rocks. Selected analyses adjusted according to the scheme in Table 14 are shown in Table 15 and their norms in Table 16. Although the ratio of analysed Cycle P rocks to analysed Cycle A rocks is about 2:1, approximately the same number of analyses have been recalculated. This disparity reflects the greater number of tuffs and altered and sheared volcanic rocks originally analysed from Cycle P.  The amount of alteration and  metasomatism appears to be a function of the granularity of the rocks. The matrix of Cycle P rocks is mainly aphanitic whereas the matrix of Cycle A rocks i s phaneritic.  Classification of Volcanic Rocks of Nicola Croup Mineralogical and Textural Criteria The two cycles of the Nicola Group can be classified by textures and relict minerals. Cycle P contains a variety of porphyritic rocks. The phenocrysts of these rocks were mainly altered, zoned, intermediate plagioclase. Leucocratic rocks may contain quartz phenocrysts; mesocratic  98 Cycle P 1  6  Cycle A  13  20  25  30  32  33  Si0  2  50.0  50.2  60.5  53.6  49.5  49.9  50.5  52.5  Ti0  2  1.0  1.2  1.2  0.9  0.8  0.7  0.7  0.8  22.0  16.2  18.5  17.2  16.5  14.4  18.5  8.1  5.6  3.7  5.3  2.4  4.7  7.0  5.2  A1 0  3  20.0  Pe 0  5  7.0  2  2  5.0  11.2  3.6  11.1  FeO + MhO  5.1  MgO  6.8  3.4  2.6  3.7  7.2  6.6  10.0  6.7  CaO  4.5  5.5  4.0  7.3  10.0  10.0  9.5  8.8  Na 0  4.9  5.5  5.4  3.8  3.2  3.0  1.7  K0  0.8  0.8  1.00  0.8  0.8  0.8  100.1  99.8  100.3  99.8  100.1  2  2  Table 15:  99.6  0.8  0.8  99.5  99.6  Modified selected chemical analyses calculated according to Table 14. Specimen numbers correspond to those of Table 7, Appendix 1.  99  Cycle P 6*  1 Quartz Orthoclaae Albite  -  (0.49)  -  ( " )  4.7  (3.21)  4.7  (8.0)  41.4  (56.40)  Nepheline  -  Anorthite  22.3  (-) (19.31)  Corundum  2.9 (0.96)  CaClinopyroxene  0.60 (-)  13.28 (16.08) 5.9  46.62 (43.69)  -  20*  13  (1.47)  8.92 (7.07) ! 4.7  (7.70)  45.91 (47.43) 31.43 (31.39)  -  (1.61)  (-)  -  (-)  17.09 (16.99) 31.62 (29.83)  27.34 (27.37) 2.09 (1.28)  «•>  (0.58)  -  (-)  ! :  MgClinopyroxene FeClinopyroxene Enstatite  10.2  2.0 (2.72) !  -  (-)  0.97 (-)  1.7  -  (-)  0.07 (-)  -  (-) (-) (8.17)  Ferrosilite  0.5  Forsterite  1.15 (-)  Fayalite  4.72 (-)  Magnetite  (-)  1.20 (~>  -  (-)  2.79 (-) -  5.3  0.43 (0.46)  (-)  3.99 (5.99) -  10.14 (8.20)  Hematite  -  (1.32)  11.2  Ilmenite  1.9  (1.56)  -  Rutile  0.01 (0.01)  (6.46)  .-  (-)  (-)  -  (-)  (-)  7.3  -  (10.93) (-)  0.02 (o.oi)  (7.23) (-)  2.3  (2.19)  -  (0.01)  +  (-)  7.54 (6.90) -  (-)  -  (-)  -  (-) (-)  11.14 (11.13) -  (-)  0.01 (o.oi)  Table 16: Norms of modified selected chemical analyses compared with original norms (in brackets). Specimen numbers correspond to those in Table 8, Appendix 1. * Fe /Fe* * not determined. ++  (2.34)  100  Cycle A  -  Quart2  jOrthoclase  4.7  Albite  32  30  25 (-)  0.28  (-)  (13.56)  4.82  (16.69)  32.06 (23.61) 27.52 (21.59)  Nepheline  0.08  Anorthite  ( 4.03)  ( 2.84)  27.56 (22.36) 28.86 (22.36) -  Corundum  (-)  (-)  4.75  33 (-)  (16.89)  25.5  (16.64)  -  ( 4.54)  23.55 (16.97) -  (-)  9o62  4.7  (l.l) (21.58)  14.34 (14.08) 40.33 (30.26) -  (-)  CaClinopyroxene  9.29  ( 8.59)  9.13  ( 9.67)  9.97  (11.10)  1.33  ( 3.18)  MgClinopyroxene  8.7  ( 7.39)  6.99  ( 7.31)  6.79  (7.66)  0.98  ( 2.37)  FeClinopyroxene  -  (-)  1.2  ( 1.32)  2.36  ( 2.48)  0.23  ( 0.48)  (-)  9.83  (-)  7.36  <-)  (-)  1.70  (-)  2.55  <-)  ( 6.30)  7.61  (11.90)  Enstatite Ferrosilite  -  Forsterite  6.99  Fayalite  -  ( 7.27)  -  .  (-)•  -  ( 1.26)  2.91 (•4.24)  ( 8.01)  5.4  Magnetite  5.43  ( 4.51)  8.29  Hematite  4.37  ( 4.74)  -  Ilmenite  1.5  ( 1.57)  1.36  -  ( 0.01)  Rutile  Table 16 (Cont'd.)%  /  -  (-)  ( 1.30) ( 0.01)  ( 5.33) (-)  1.3  15*66 (13.69) 3.61 «s  ( 2.77) (-) <-)  7.7  -  ( 7.39) (~)  ( 1.36)  1.5  ( 1.52)  ( 0.01)  -  ( 0.01)  Norms of modified selected chemical analyses compared with original norms (in brackets).  101  rocks contain very few augite phenocrysts.  These phenocrysts are those  expected from calc-alkaline rock suites (Barth, 1952; Moorhouse, 1959; Turner and Verhoogen, I960). feldspar phenocrysts.  Cycle A contains augite,olivine and few  In neither cycle are there any r e l i c t grains of  minerals diagnostic of alkaline rock suites. Chemical Criteria Although according to results of experiments with the simple system Fo-Di-Ne-Si02 (loder and T i l l e y , 1962) a thermal divide separates rock compositions of the alkalic suite from those of the t h o l e i i t i c suite at low pressures, recent work (Manson, 1967) nas shown that a continuous variation and overlapping of the various rock suites occur i n nature.  One method of distinguishing the suites previously used with  success i n certain regions (Kuno, I960; McDonald and Katsura, 1964), the total alkalis vs. S i 0 plor, seems not to apply to basaltic rocks i n 2  general (Hanson, 1967). Since the general validity of this plot i s suspect, and since the a l k a l i values have been changed during metasomatism and are highly erratic (Fig. 23) i n the rocks of the map area, this plot seems not to be relevant. Harker diagrams (Fig. 24) of the modified analyses suggest that the rocks of the Nioola Group are not very different from those of calcalkaline suites.  The volcanic rocks are thus tentatively classified as  calc-alkaline rocks.  Rocks of Cycle A, when plotted on the oxidation  ratio plot of Osborn (1959). l i e along the line of tholeiite basalt (Fig. 25). suite.  This cyole might be tentatively assigned to the tholeiite  In continental areas, t h o l e i i t i c and calc-alkaline suites are  intergradational (Barth, I960).  104  Although trace element data were collected (Table 7, Appendix l ) , i t i s not possible to distinguish between alkaline and tholeiitic differentiation trends using individual trace element data (Prinz, 1967). The conclusion that the rocks belong to calc-alkaline and tholeiitic suites seems at variance with the norms of the analysed rocks (Table 8, in Appendix l ) .  In these rocks, normative corundum and quartz are  present in Cycle P and normative nepheline i s present in Cyole A. Norms of the selected and modified analyses differ from those derived from original data (Table 16). Since the norms changed considerably with the very small change outlined in Table (l4), and sinoe the amount of alteration for each rock i s not known, the norms are not considered diagnostic of any rock series. Nomenclature The character of the volcanic rocks i s preserved in relict minerals, but new minerals have formed. A common mineral assemblage in these rocks i s albite phenocrysts and microlites, chlorite, and in some cases, augite. Such rocks are often called spilites.  The writer  does not apply the term spilites to the altered volcanic rocks of the Nicola Group because there are no generally accepted textural, mineralogical, or chemical criteria that distinguish spilites and the term has many different genetic connotations (Vallance, I960) and is thus not a suitable rock name. Origin of Volcanic Rocks in the Nicola Group Diversity of Volcanic Rocks Volcanic cycles, P and A, are the surface expression of the intricate interplay of various magmatic processes acting for different  105  lengths of time on a rising magma. The lower cycle, P, is made of Assemblage Pj of relatively homogeneous basaltic andesite overlain by Assemblage Pg of andesite, some basaltic andesite, and rare dacite. The upper cycle, A, contains a lower homogeneous basaltic Assemblage A  The amount of diversity in each assemblage, illustrated by  1#  plotting Si02 vs. approximate stratigraphic height (Fig. 26), may reflect the length of time that the magma rested in some shallow reservoir. Homogeneous assemblages (A^ and P^) were formed from magmas in a shorter time than that required to form the differentiated Assemblage P2.  Intercalated sediments in the assemblages support this view.  Coral reefs require clear water and stable environment over relatively long intervals and these, as well as abundant, occasionally well-sorted sediments derived from the assemblage itself, are plentiful in Assemblage P . The absence of i n situ coral reefs within Assemblages Pj^ 2  and A^ and the relative scarcity of sediments suggest that P^ and A^ were deposited over a relatively short time, and that magmas had l i t t l e time for differentiation. A greater percentage of the acid rock types than basic rocks are pyroclastic in Assemblage P2.  This increase in explosivity with  increasing differentiation is explained by Rittman (1962, p. 218). M  ... Hot undifferentiated basalt magma has a very great potential total  energy but only very limited eruptive energy. As i t cools and crystallizes the total energy diminishes but the eruptive energy increases. If differentiation occurs, the eruptive energy per unit volume in the lightest differentiates reaches very high values. The quantity of these partial magmas is, however, very small in comparison with that of the  F I G U R E 26.  SILICA  VS  STRATIGRAPHIC  HEIGHT  107  parent. Since they are, moreover, at a lower temperature than the parent, their total energy i s only a small fraction of the original content of the magma chamber . T h e increase of watery fluids in the magma chamber, especially i f some were added from the country rock, would tend to facilitate the development of the calo-alkaline differentiation trend of Assemblage P (Osborn, 1959; Hamilton and Anderson, 1967). 2  The Parent Magmas The "parent" magma that gave rise to the volcanic rocks of Cycle P was probably not of the same composition as that which formed Cycle A. The abundance of plagioclase phenocrysts in rocks of Cycle P compared with the preponderance of augite phenocrysts in volcanic rocks of Cycle A suggests that the melts from which these phenocrysts crystallized had different crystallisation histories.  These histories can best be  pictured in the simplified basalt tetrahedron (Toder and Tilley, 1962) (Fig. 27). For example, the initial composition of "parent" magma P may be represented by a point in volume 1. As the melt crystallized, plagioclase phenocrysts would form until the melt reached a composition on plane 1, at which time pyroxene phenocrysts would form.  Similarly,  the ''parent" magma A would have an initial composition in volume 2 and as augite crystallized, the melt would move towards plane 1. When the melt reached plan 1, plagioclase phenocrysts, and later, as line 1 was approached, olivine phenocrysts would form. The difference in composition between the parent magmas is further suggested by different chemical compositions of rocks from the two cycles. Although metasomatism has affected rocks of both cycles unequally, aluminum is not considered to be very mobile in either cycle. Thus, the  108  DI  AN  FIGURE  27.  T H E SIMPLIFIED BASALT T E T R A H E D R O N (MODIFIED A F T E R YODER AND T I L L E Y , SHOWING T H E COURSE OF  CRYSTALLIZATION  O F T H E P H E N O C R Y S T S IN T H E T W O P  A N D A.  1962)  FOR EXPLANATION, SEE  CYCLES, TEXT.  109  variation i n aluminum i s considered to be primary.  Volcanic rooks of  the two cycles with between 45-55$ S i 0 contain differing amounts of 2  aluminum; rooks of the feldspar-rich Cycle P contain more aluminum than rocks of augite-rich Cycle A (Table 17). The two parent magmas may have had a common origin and since have differentiated at deeper levels than those discussed i n the prior section.  On the other hand, the magmas may have formed i n different  regions of the deep crust or upper mantle.  In view of the considerable  controversy as to the mechanisms and sites of magma generation (Yoder and T i l l e y , 1962; Green and Ringwood, 1966, Kuno, 1967; Hanson, 1967, O'Hara, 1968) and because " ... the ultimate origin of magmas i s more a geophysical than a geochemical problem ... (Erauskopf, 1967, p. 41l), H  the deeper history of the magmas i s not further discussed here. The composition of parent melts seems to be unaffected by assimilation of rocks torn from the conduit walls. Rare granite and syenodiorite i n volcanic breccias were probably derived from deep conduit walls. The quartz diorite, diorite, and gabbro fragments that occur near the top of Assemblage A^ were probably torn from already crystallized but related dykes and stocks. Xenoliths of volcanic rocks of the Nicola Group are abundant i n breccias, agglomerates, and some flows and they suggest that the emerging lava plucked these fragments from wall rock at very shallow depths.  Since these fragments and the enclosing rocks are similar i n  composition, very l i t t l e assimilation seems to have taken place. Xenoliths of limestone engulfed by extruded lava may have locally modified the composition of the volcanic rock, although rapid cooling would have prevented widespread effects.  110 n  5  s  Phenocrysts  Cycle A.  6  14.9  1.8  Pyroxene, feldspar, and olivine  Cycle P  11  16.1  2.0  Feldspar  U  Table 17:  Difference in aluminum content between Cycles A and P. n number of specimens, s standard deviation, x mean. Difference between means is significant at 95$ probability level.  Locality (Fig. 29)  Evidence Red flow top, vesicular tops; overlying rocks containing underlying rocks; partially filled brachiopods; current-oriented shells; rare graded bedding. Flows immediately overlying limestone contain calcite amygdales that decrease going up section away from limestone. Interflow breccias contain fragments of underlying limestone.  Table 18:  Way-up criteria used to trace overturned folds.  Ill  SUMMARY Although metasomatism affecting domains of various sizes has been operative in the volcanic rocks of the Nicola Group, these rocks are referred to the calc-alkaline rock series on the basis of relict mineralogy and inferred original chemical composition. The diversity of the rock types i s explained by differentiation of magma at shallow levels as well as by some deeper process. Assimilation i s not thought to have been very important in modifying chemical composition of magma.  STRUCTURE  The main structural feature of the area is a north-striking syncline, the Meander Hills syncline, which is modified by local folds and by longitudinal and cross faults. Local faults, veins, joints, and lineaments contribute to the broken aspect of the rock (Fig. 1 in pocket). Evidence for several periods of deformation at shallow depths is present throughout.  Folds Meander Hills Syncline Beds of Nicola Group from as far west as Iron Mountain dip moderately to steeply eastward towards the Meander Hills, where a synclinal axial trace is clearly marked by the well-bedded Assemblage A  2  (Dawson, 1896). Local, superposed modifications of this syncline, occurring west of Quilchena, will be discussed separately (Fig. 28).  112  FIGURE  28.  DISTRIBUTION IN T H E N I C O L A  OF F O L D GROUP.  ELEMENTS  113  The fold has been traced from Stump Lake (Dawson, 1896; Cockfield, 1948) southward through the thesis area to a point just west of Princeton (Rice, 1947; Hillhouse, 1965, pers* comm.), a distance of about 60 miles. The geometrical elements that define this fold are generally well displayed.  The fold axis of the syncline i s subhorizontal and trends  northerly.  The axial surface probably dips steeply but i s d i f f i c u l t to  determine because the fold has a round hinge (Fig. 1, i n pocket), lacks axial plane cleavage, and has been subsequently warped (Fig. 32). Although the subhorizontal, upright, oylindroidal syncline was originally symmetrical, subsequent faulting has resulted i n apparent thickening of the western limb.  The structure has a wave length of at least 14 miles.  Well-preserved primary structures and a few secondary minor structures suggest that the syncline formed by flexural s l i p .  Abundant  sedimentary structures indicate that bedding i s right-side-up.  These  structures, as v e i l as the fossils i n the area, are undeformed, suggesting that flow within the beds was negligible and flattening was not importanto  A calculation on the basis of radius and thickness of the  folded structure (Donath and Parker, 1964) indicates that the maximum strain was less than 5$.  Rare minor folds and slickensides along bedding  planes provide the main evidence for differential s l i p on bedding survaces. The synoline formed i n response to a stress system with east-west max  p  8 2 x 4  vertical Pmin. Such a system could have formed by weak  compression or i n response to differential movement i n the basement. Low strain, flexural-slip folding, and faulting associated with the fold suggest that i t formed i n a near-surface environment.  114  The Meander H i l l s syncline i s post-dorian, since Norian rocks are folded into the syncline; but pre-lower Jurassic, since i t i s cut by the Fenask batholith, A fev minor folds with east-west axes (Fig. 32) and a variation i n the plunge of the Meander H i l l s syncline can be accounted for by at least three different hypotheses.  In the f i r s t place, the original bedding  may not have been horizontal.  An example of the extent of deviation from  the horizontal of beds around a volcano i s shown on a stereonet plot of poles to bedding from Tristan da Cunha (Hg. 34) (Baker et a l , 1964.). Folding such a texrane could possibly yield a highly dispersed pattern similar to Fig. 33.  Secondly, many areas affected by flexural-slip  folding show contemporaneous culminations and depressions.  A third  possibility i s that cross-folds were later superposed on the north-south folds.  To the south, Kingsvale rocks were folded about east-west axes  during late Cretaceous time.  Perhaps the structures i n question represent  this late fold episode.  Folds at Nicola Lake An upright fold (the Quilchena anticline and a pair of tight, overturned folds (referred to as the Nicola Lake anticline and the Quilchena syncline) l i e between the Central Nicola batholith to the north and the South Nicola stock and the Penask batholith to the south.  They  are best exposed i n north-facing slopes at Nioola Lake (Figs. 29. 30; Table 18) where beds including a dacitic tuff marker-bed have been traced around the overturn.  115  Geometrical elements of these folds are not well defined. Fold axes of the overturned folds have shallow to moderate southwest plunges marked by few minor folds (cf. Fig. 3l).  The axial trace of the Nicola  Lake anticline, in conjunction with the fold axis, defines an axial plane which strikes about 200° and dips 60° southeast. Axial planes of the other folds have similar or steeper dips as judged from outcrop pattern. The Quilchena syncline i s irregular and broken because the beds impinged on the older South Nicola stock and considerable adjustment took place by faulting in various directions. The crest of the Quilchena anticline has been modified by a longitudinal fault zone and i s oonoealed under alluvium and Tertiary rooks. The folds are not continuous along strike. These elongate, conical folds with small apical angles die out to the south against the South Nicola stock, and south and southwest of the stock, there i s no evidence that strata are repeated by folding. To the north, beyond a left-handed offset at Nicola Lake, the folds strike toward the Central Nicola batholith, but disappear under overburden far short of the contact. The inclined axial plane and the looal overturn suggest that the stress system in which the folds formed was oblique compared to systems in which gravity i s a principal component. The greatest principal component of this oblique system i s thought to have plunged northeast toward the site of the Central Nicola batholith, along a line normal to the axial plane of the fold. Corrugated minor folds, slickensides along a folded foliation, and lack of axial plane cleavage suggest that the folds were formed by  116  1  Nicola Lake  2  Quilchena  Syncline  3  Quilchena  Anticline  /  Marker  F I G U R E 30.  Anticline  Beds  CROSS-SECTION NEAR NICOLA ( S E E F I G . 29)  LAKE  118  flexural slip with the main slip occurring along the foliation and dyke contacts rather than bedding planes. The environment in which the oblique stress system acted i s thought to be relatively near-surface. Local folding near Nicola Lake i s thought to be related to the emplacement of the Central Nicola batholith. It i s younger than the secondary foliation which cuts dykes of the South Nicola stock since foliation i s affected by the fold. The folding i s older than hydrothermal veins and replacement masses associated with the Central Nicola batholith.  Foliated rocks underlie a narrow northerly-trending strip parallel to the western border of the Penask batholith (Fig. 3 5 ) . The foliation i s marked in many places by closely spaced fractures, between which lie rotated and broken phenocrysts and extended breccia fragments. A foliated conglomerate contains elongated fragments set in a foliated limestone mass (Plate VIII). Limy tuffs and tuffs are phyllitic whereas phenocrysts in porphyritic flows are intact. The foliation i s generally nearly vertical (Fig. 3 6 ) . In this local area, strain i s considerably more than 5 $ , the maximum value estimated for the region as a whole. Part of the chilled phase of the South Nicola stock, dykes associated with the South Nicola stock and the heterogeneous phase of the Central Nicola batholith are foliated. The foliation was imposed on Assemblages P and A^ after they had been folded into the Meander Hills 2  syncline and the angle between bedding plane and foliation i s about 25° in the few places where the relation was seen. Early epidote veins have  LEGEND  • Pole 8 to Bedding * Axis  FIGURE 32.  MINOR FOLD WITH EAST-PLUNGING AXIS  120  II  LEGEND ^  Plunging syncline P o l e s to bedding  ^  Fault  [23  Intrusive Rock  F I G U R E 33.  VARIABLE P L U N G E OF T H E MEANDER HILLS SYNCLINE.  121  fit  F I G U R E 34.  DISPERSION O F P O L E S T O B E D D I N G F R O M A R E C E N T VOLCANO.  122  123  F I G U R E 36.  POLES T O FOLIATION i  124  been flattened along the foliation.  The foliation is older than local  overturned folds at Nicola Lake and is cut by late hydrothermal veins associated with the Central Nicola batholith.  The foliation is probably  lower Jurassic in age. The origins of the foliation is not certain. Since the foliation constitutes the northward extension of the Penask batholith's western borderline, and was formed during the same timespan as that batholith (prior to folding associated with the Central Nicola batholith), i t seems reasonable that the foliation was related to emplacement of the Penask batholith.  Faults Longitudinal Faults  Longitudinal faults sub-parallel to the Meander Hills syncline are prominent in the thesis area (Fig. 37).  They are northern continua-  tions of longitudinal faults mapped by Rice (1947) and Hillhouse (1965? pers. comm.). Some are marked by physiographic lineaments. Stratigraphic separations are generally large, being the cumulative results of several periods of left-hand movement. Glimpse Lake Fault Assemblage A^ of the Nicola Group and the Cache Creek Complex are separated by a straight gully north of Glimpse Lake (Fig. 37). Structures typical of the Cache Creek Complex, including steep dips of bedding  and east-west Bteeply dipping axial planes, are found only on the  125  126  east side of the gully. A normal fault with the vest side dovn i s postulated. The main movement on this fault was post*JJorian but preceded the emplacement of the Jurassic (?) Douglas Lake pluton which cuts across the projected southerly strike of the fault. S#uth of the pluton, the projected fault and the contact between the Nicola Group and Cache Creek Complex are covered by Pliocene Plateau basalt. Quilchena Fault Zone The Quilchena fault ssone i s marked by a prominent southerlytrending lineament which enters the thesis area along Koore Creek in the north and extends aleng Quilchena Creek in the south (White. 1 9 5 0 ; McKechnie,  1963).  The fault zone i s about 2 - 3 miles vide and i s composed of many generally north-striking steeply dipping but intersecting faults. Individual faults are sliokensided; some l i e along previous calcite and hematite veins; and many contain wide calcite—cemented breccia zones. The adjacent strata are broken and the frequency of north-south faults decreases away from the zone. Many subsidiary north-striking faults and smaller cross-faults are exposed in the vicinity, as are poorly exposed, shattered outcrops in the valley bottom at Quilchena.  Subsidiary gouge-bearing faults of  Quilchena fault zone are cut by mine-workings around Quilchena. The movement of the fault zone has been composite. Horizontal, oblique, and vertical slickensides occur on the same slip surface. The stratigraphic separation of the fault is unknown but thought to be small.  127  The zone i s best described as a strike-slip fault (Billings. I960) along vhioh multiple movements, either along strike or down dip. have occurred. The stratigraphic separation i s small but the intensity of deformation suggests considerable movement. The main movements on the fault occurred during the late Mesozoic. The fault zone affects the lover Jurassic Penask batholith to the south of the area and north-south shears are present i n the lover Jurassic Central Nicola batholith along the vest shore of Nicola Lake.  Arkose  of the Eocene Kamloops Group does not appear strongly affected by faulting.  Pleistocene Valley basalt crops out along the fault zone.  Evidence for early movement i s preserved as homfelsed sheared rooks at the contact of the Penask batholith.  The fault thus was active from  early Jurassic to Paleocene, with the possibility of some later Pleistocene movement providing conduits for Valley basalts. I f the fault i s mainly a strike-slip fault, then an intermediate stress direction vould be near vertical.  The main compressive component  would be from the north-northeast or north-northwest (Anderson, 1951). An environment of relatively low confining pressures i s suggested by the presence of breccia, gouge, and open:spaces found i n the fault zone. Nestor Creek Pault System Wide gouge zones (Cockfield, 1948), repeated strata, topographio lineaments, and a large drag fold are found along the Nestor Creek fault system. This fault system i s composed of several irregular surfaces which join toward the south to form the northward extension of the Allison fault  128  RELATION BETWEEN  F O L D AXIS, H Y P O T H E T I C A L  H Y P O T H E T I C A L SLICKENSIDE  FIGURE  38.  AND FAULT  "B",  TRACE  M A P SHOWING L O C A L B E N D BY FAULT  FAULT  NESTOR  CREEK  129  system (Rice. 1947).  A limonitic, clayey gouge zone about 100 yards  wide marks the fault zone near Nestor Creek, and to the south, strongly sheared rook l i e s along i t .  The strata bordering the fault have been  dragged into a large fold (Fig. 38) (Haman, 196l). The stratigraphic separation i s about 3,000 feet near the mouth of Nestor Creek.  South of Lundblom Lake, i t cannot be more than a fev hundred  feet because a prominent and thick lava unit which borders the fault on either side has not been much offset.  The strike-slip direction i s shown  by the drag fold (Fig. 38); the west side apparently moved north. Movements along this fault were multiple with various parts active at different times. The fault formed after the deposition of Assemblage P  2  and i n part prior to the intrusion of the South Nicola  stock (pg.3l).  At Nicola Lake, the faults seem to join the Nicola Lake  shear zone. Movement along parts of the Nestor Creek fault system took place as early as latest Triassic time. Subsequent movement post-dates the South Nicola stock. Although i n one place rock correlated with the "Clapperton Conglomerate" appears at the same elevation on both sides of the fault, i n other l o c a l i t i e s the conglomerate i s clearly affected by the fault. The stress systems involved i n this complex fault include a strike-slip component and a weak dip-slip component. This fault system formed i n a low-pressure, low-temperature environment. Clapperton Creek«*Howarth Creek Fault Zone The most westerly of the longitudinal fault sets i n the map area, the Clapperton Creek-Howarth Creek fault zone, i s marked by stratigraphic separation, by shear zones, and by lineaments.  130  The trace of the fault zone i s generally straight although i t i s possible that small en echelon offsets occur east of Iron Mountain. The movement zone i s 100 yards or more wide and contains strongly sheared rock.  Adjacent shears suggest that the fault i s steeply dipping.  The  net s l i p i s unknown. Apparent movement was such that the west moved down and northward, resulting i n a stratigraphic separation of 4,000 feet.  This fault zone, like the other longitudinal faults, contains  evidence for several movements within the same zone. The fault zone contains sheared porphyry plugs.  In Clapperton  Creek, granite of the Central Nicola batholith i s sheared (Cockfield, 1948). The moderately east-dipping "Clapperton Conglomerate" i s also sheared by this fault zone. The overlying arkose of the Kamloops Group i s relatively undisturbed and the overlying Valley basalt suggests that later movements allowed extrusion of basalt.  Thus, although the movement may have been  initiated during latest Triassic, i t was most prominent during midMesozoic or later Mesozoic time with only minor activity since Eocene times.  The stress f i e l d and environment of deformation are very similar  to those of the Quilchena fault zone. Cross-faults The Meander H i l l s syncline i s offset by the projection of a gouge-bearing cross-fault exposed at locality 1 (Fig. 39).  There, the  northern side moved down about 1,000 feet and westward about 3,3000 feet.  Recurrent activity has affected this oblique-slip fault.  A  faulted dyke, related to the Central Nicola batholith, i s emplaced i n the wide gouge. A dyke with chilled edges, probably a feeder to volcanic rock of the Kamloops Group, was later intruded into this faulted dyke  132  and subsequently fractured.  Thus, the main fracture was formed prior to  the Central Nicola batholith and subsequent to deposition of Assemblage A  2  i n latest Triassic or earliest Jurassic time.  Subsequent movement  occurred i n part after emplacement of the lower Jurassic Central Nicola batholith, prior to deposition of the Eocene Kamloops Group. The maximum principal stress component was probably directed at a small angle to the fault surface.  Wide gouge zones testify to low oonfining pressures.  Strong east-west shearing i n a few outcrops along the upper Nicola River (Fig. 3 9 , loo. 2) suggests that a cross-fault underlies the river bed. Along east-west gullies south of Nicola village (Fig. 3 9 , loc. 3 ) , the strata are offset so that the north side moved down or west. South of Lundblom Lake (Fig. 3 9 , loc. 4-), small cross-faults are common. The north side has moved down or west on a l l those faults along which relative movement can be deduced. These faults affect mainly Nicola Group strata and only on occasion do they cut the South Nicola stock.  Only one fracture displaces the "Clapperton Conglomerate".  West of Nicola village (Fig. 3 9 , loc. 5 ) , small cross-faults with left-handed offsets have been reported by Young ( 1 9 6 2 ) .  These faults  cut through limestone containing occasional undeformed fossils indicating that the environment i n which they formed was one favouring b r i t t l e fracture of limestone. The east-west trending part of Nicola Lake i s believed to l i e along a shear zone.  Outcrops providing information about the nature of  this zone are exposed along the shores of the lake.  An east-striking  fault surface with sub-horizontal slickensides i s exposed at locality 7  133  (Fig. 3 9 ) . A shear zone containing minor vertically plunging drag folds with amplitudes of about a foot i s found at locality 7 (Fig. 3 9 ) . Steeply dipping, near horizontal gashes, with varying strikes, kink bands, and irregular slip surfaces are found in road-cuts south of Nicola Lake.  Slickensides from this region plunge northwest.  Oblique slip is  apparent within the shear zone; the north side moved down and west relative to the southern block. Along the fault, movement has been recurrent. Late faults are slickensided surfaces but earlier faults are in part replaced by hydrothermal veins and minerals. The north tip of the South Nicola stock i s epidotized and shows evidence of being disrupted several times. It was epidotized, ruptured, veined, and broken in turn. Successive bending of foliation, breaking, gashing, and kinking are seen elsewhere in the road-cuts. The stresses involved were oblique to the gravitational field. Shearing in 10-foot-wide zones was followed by discontinuous, more localized shearing, and closely spaced shears are bent by kinks which usually occur in brittle environments (Ramsay, 1 9 6 7 ) .  The fault  zone i s probably a continued response to the stress system which caused the local folds at Nicola Lake.  The total movement may have been  relatively small.  Lineaments The map area is covered with lineaments that show well on aerial photographs of a scale of half-mile to the inch. These lineaments  134  were transferred to a half-alle base map and reduced i n scale (Fig. 4 0 ) . A l l lineaments longer than a mile are shown on Figure 1 (in pocket) and their distribution i n various rock types i s given i n Figure 41. Although many lineaments on the aerial photographs are obviously faults, others cannot be related to known structural features (cf. Brown. 196l).  The majority of lineaments i n the thesis area are thought  to be fault traces.  Some glacial striations may accidently have been  included i n the compilation (Fig. 41) but their number would be small compared to the total number of lineaments collected. The diagrams (Fig. 41) show that most lineaments parallel the direction of the longitudinal faults.  Successively younger units contain  fewer lineaments per square mile (Fig. 4 l ) .  Minor Structures Minor structures reflect the b r i t t l e nature of the rock during deformation.  Small faults, veins, joints, and shear zones are  abundant and contribute to the broken aspect of the country rock. Minor faults are sub-planar (Fig. 42).  Slickensided hematite  and crushed calcite mark s l i p surfaces along older vein walls. There seems to be no distinct differences i n the orientation of faults along veins variously f i l l e d with calcite, quartz, epidote, or hematite (Fig. 43). Slickensides and other linear features are found on fault surfaces parallel to the direction of movement (Tjia, 1967). Most slickensides i n the map area plunge northwest. The presence of two or more sets of slickenside directions on the same surface indicates either that the  FIGURE  40.  NON-GLACIAL. LINEAMENTS  IN T H E S I S  AREA  136 \C A C H E C R E E K  COMPLEX  ' 1% of t o t a l l i n e a r m i l e s o v e r • 3% of t o t a l t h e s i s  ;SOUTH NICOLA 12%  area  STOCK  CLAPPERTON 6%  area  CONGLOMERATE!  of t o t a l l i n e a r m i l e s o v e r 1 % of t o t a l t h e s i s  F I G U R E 41.  66%  GROUP  ©f t o t a l l i n e a r m i l e s o v e r 57%  of t o t a l t h e s i s  area  ! 11% of t o t a l l i n e a r m i l e s o v e r 25% of t o t a l t h e s i s  [TERTIARY  MILE.  area  ROCKS  ! 3% of t o t a l l i n e a r m i l e s o v e r 11% o f t o t a l t h e s i s  ROSE DIAGRAM O F LINEAMENTS ONE  area  j BATHOLITHS  of t o t a l l i n e a r m i l e s o v e r 2% of t o t a l t h e s i s  NICOLA  area  LONGER  THAN  137  block with slickensides rotated i n the fault or that more than one direction of movement occurred along the fault.  Typical variation i n  orientation of a fault surface, i t s slickensides. and "faults b" are shown i n Figure 4 2 . A "fault b" i s a line (cf• a, b, c of petrofabrics) along a given fault plane normal to the slickenside.  This line i s the axis of  rotation of the fault and the "fault b" has been interpreted by Price (1967) to define the intermediate stress vector. However* deWaard (1955) and Norris (1967) have shown that the correspondence i s not good i n gently folded areas and Oertel (1965) has provided an explanation for this divergence.  In experiments he showed that a mixture of clay and other  material, say sand, that together acts as a heterogeneous 2-phase material with one rough granular phase, does not, under low rates of strain, obey the Coulomb c r i t e r i a of fracture.  That i s , the fault plane does not  include the intermediate stress axis and the attitude of a fault i s dependent on the intermediate stress.  When grains and cement are similar,  the material w i l l act as a homogeneous body and obey the Coulomb criteria. The center of a concentration of "fault b" would thus be near an intermediate stress direction.  The spread of "fault b" w i l l reflect, i n part,  the heterogeneity of the rock that i s faulted.  I f different stress  systems have resulted i n multiple movement along faults, the "fault b" would be distributed i n an even more complex manner than that illustrated i n Figure 42 about each of the intermediate axes.  Figure 43 illustrates  the distribution of "fault b" i n a repeatedly faulted region of the thesis area.  The spread of "fault b" i n this figure i s much greater than that  in Figure 42 and suggests that the local stress environment varied extensively.  138  LEGEND X  x  P o l e to F a u l t  0, S l i c k e n s i d e b, F a u l t B  F I G U R E 42;  VARIATION PORTION  OF FAULT  ELEMENTS  ON ONE S M A L L  OF A NON-PLANAR FAULT  (CUTTING SOUTH NICOLA  STOCK)  SURFACE  139  3* \  F I G U R E  43.  L I N E S  P E R P E N D I C U L A R  F A U L T S ( F A U L T S S E N T E D  O F  M A N Y  W I T H B Y  T O  S L I C K E N S I D E S  D I F F E R E N T  T W O  A T T I T U D E S .  S L I C K E N S I D E S  N U M B E R S . )  A R E  A L O N G .  R E P R E -  140  In a region affected by one stress system, the majority of veins w i l l group around the local minimum compressive stress component (deWaard„ 1955). It can be seen from Figure 44 that a sequence of local stress systems i s required to explain the distribution of veins i n the thesis area.  The idea of a sequence i s supported by the common occurrence  of veins which cut and offset earlier veins. Some joints i n the map area may have had a geometrical relation to large structures (deWaard, 1955; Billings, I960} Secor, 1965)*  The  mixture of different kinds of joints formed at different times precludes detailed interpretation of the joints pattern.  Joints i n late Pleisto-  cene or early Holocene clays near Merritt are illustrated i n Plate IX and show that joints may form less than 8,000 years after deposition of rock.  In an area that has had a long history, with the development of  many joint sets (Figs. 44,45), the detailed history of fracturing may  be  impossibly complex.  Conditions of Deformation Different environments control the development of different structural styles. Experimental results show " ... that the ductility of a rock can change appreciably, depending on the environment, and, moreover, that ductility determines to a large extent the mode of deformation and hence, whether fracturing, faulting, folding or other types of deformation w i l l develop under a given set of conditions ..." (Donath, 1963, p. 87).  The ductility of most rocks i s increased by  increasing the pressure, the temperature, or lowering the strain rates. Thus, near the surface, most rocks tend to yield to the earth's stresses  141  •  Other cross-cutting  El  Early  LI  Late  F I G U R E 44.  veins  P O L E S T O VEINS  142  PLATE IX.  Holocene j o i n t s near Merritt, B r i t i s h Columbia.  143  by fracture, while at greater depts, deformation more commonly takes place by rock flowage (Holmes. 1965). The structures i n the thesis area include flexural s l i p folds and much faulting. These were formed i n shallow environments where rocks were b r i t t l e .  Only local structures associated with the batholiths i n  space and time show evidence of having been formed i n an environment that was conducive to formation of extended pebbles and some rook flowage along the local foliation and i t s later folding.  Stress Environment The geometry of a structure reflects the kind of stress system imposed on the rock. Folds are usually aligned so that their axial planes are normal to the maximum principal stress component. Along or nearly along their surfaces, faults usually contain the axis of rotation or "fault b" which i s parallel to the intermediate stress component (Friedman, 1 9 6 4 ) .  In Figure 4 3 , the dispersion of "fault b" i n  the area i s much larger than the variation on any one fault plane and perhaps reflects the various orientations of the Intermediate stress component i n any local region.  A pair of "conjugate" fault surfaces  near Quilchena show the local shifts i n the intermediate stress component (Fig. 4 5 ) . The various orientations of the smallest principal component of stress are reflected by the many orientations of veins (Fig. 4 4 ) . According to these c r i t e r i a , the thesis area has been affected by a variety of local stress fields.  Although the local stress fields may  have varied, i t i s not certain over how large a domain they acted.  Local  strains, offsets, fractures, and slickensides are not necessarily clearly  144  L A T E  x  2  0  (.)  2  2  E A R L Y (•)l  FIGURE  X J O J  45.  F A U L T  "B"S  MIGRATION  F R O M  ONE LOCALITY  OF INTERMEDIATE  SHOWING  STRESS  T H E  COMPONENT  145  geometrically related to the gross structural field, particularly in rocks previously broken or in heterogeneous terranes containing rocks of highly different mechanical properties. In the preceding discussion, the stress field i s assumed to have at least one component perpendicular to the earth's surface (Anderson, 1951; Holmes, 1965). Oblique stress systems are expected along the flanks of rising igneous bodies (Hedley, 1952; Holmes, 1965; Ramberg, 1967).  Stress  systems responsible for both the foliation and the Nicola Lake shear zone are thought to have been caused by emplacement of batholiths.  The  emplacement of the Penask batholith is believed to have caused the foliation. Most of the western border of the Penask batholith intrudes the South Nicola stock, a medium-grained igneous rock. Farther north, easily deformed vitric tuffs and associated debris are foliated.  The  emplacement of the Penask batholith i s believed to have produced the shearing of the stock and formation of the foliation.  The Penask batholith  is thought to extend northward towards Nicola Lake under the Nicola Group so that the foliation there i s due to shearing associated with the concealed part of the batholith. Very shortly thereafter, the Central Nicola batholith arrived at the crustal level now exposed and the foliated rocks were easily bent aside to make room for the batholith. This led to the formation of local folds and shearing along Nicola Lake. In this zone, oblique-slip faults suggest the stress field was oblique.  Within the  shear zone, kinks and gashes of several generations affect the rock. Small adjacent drag folds in a fault zone along Nicola Lake give contradictory senses of movement, showing that the zone was characterized by complex movement.  146  Gentle folds and abundant faults hare deformed the Nicola Group. The deformation has been more or less that to be expected from a shallow environment and although local stress systems have changed i n orientation, i t i s not known how and to what extent the gross stress f i e l d varied.  METAMORPRTSM The rocks of the Nicola Group have been metamorphosed.  Hydration  and carbonation of high-temperature minerals have yielded low-grade, disequilibrium, metamorphio mineral assemblages.  ftlflftiT*!! Assemblages A large number of mineral species have been found i n rocks of the Nicola Group (Table 19). Other minerals may be hidden i n fine-grained intergrown minerals forming saussurite or epidote-ohlorite-oxide-quartzalbite groundmass. Turner and Verhoogen (i960) have classified metamorphic rocks according to their compositions as p o l i t i c , quartzofeldspathic, calcareous, basic, and so on. Rocks of the Nicola Group are classified i n this way i n Table 20. Various mineral assemblages are summarized i n Tables 21, 22, 23 and 24.  Textural Changes Although primary textures of the Nicola Group are generally well preserved, mechanical disruption and recrystallization have locally altered the fabric of the rock.  Swirled skeletal microlites, oscillatory and  147  Occurrence  Minerals  Quartz  relict ign  relict sed.  recryst. met.  U  R  U  U-C  C-A  -  -  U  -  -  U-R  U  R  -  A  U  U  R  -  -  mm  -  R-U  R-U  R C .  Albite  -  Labradorite  R  Opal Orthoclase  Laumontite Leonhardite  -  open space amyg.  Chlorite  R?  ?  A  A  Celadonite  -  R  -  vR?  White mica  -  Biotite Serpentine  -  -  -  Uralite  ?  -  Actinolite  -  -  Tremolite  -  mm  Hypersthene  R  -  Augite  U-C  -  Tourmaline  -  -  Epidote Clinozoisite or Zoisite Sphene (Leucoxene)  Table 19;  -  -  u  -  "R  . - • .  U-C  -  -  R-U  R  R  R  Prehnite  Pumpellyite  C  veins+ gouge  R R  vR  -  ' -  -  -  -  R  U-R  U-R  -  C  C  C  c  -  —  u  —  —  -  -  -  Minerals of the Nicola Group found in the type area. A abundant, C common, U uncommon, R rare, vR very rare, ? uncertain, - not seen.  R  148 Minerals  Occurrence relict ign.  Garnet  relict sed.  recrhst. met.  -  R  -  _  -  -  R  V i v i a n i t e (?)  -  -  Apatite  R  -  Barite  -  -  Azurite  -  Ankerite  -  Dolomite  -  open space amyg.  veins+ gouge  -  R  -  -  R  R  -  -  R  R  -•  -  R  R'  -  -  R  -  A  C  C  C  ?  ?  -  R  R  Magnetite  .U  ?  u"  R  Ilmenite  U  -  U  -  -  -'  Hematite  C-U  -  -  -  c  Malachite  Calcite L i m o n i t e and o t h e r hydrous Fe o x i d e s  -  1  .. t  Tetrahedrite  -  -  Pyrite  -  -  R  Covellite  -  -  -  -  vR  Pyrrhotite  -  -  vR  -  Chalcopyrite  -  -  -  -  R  -  -  -  vfi  -  R  -  U  Galena  -  Bornite  -  -  -  -  Chalcocite  -  -  -  vR  Copper  -  -  vR  Gold  -  -  -  -  -  T a b l e 19 ( c o n t . ) :  M i n e r a l s o f the N i c o l a Group found i n type a r e a .  i.  vR  '- . vR  149 Assemblages Al  Classification PI  P2  Quartzofeldspathic  V  U  ns  ns  Calcareous  V  C  TJ  R  Basic: sedimentary and pyroclastic  C  A  A  A  Basic:  A  A  A  R  effusive  Table 20:  A c l a s s i f i c a t i o n of Nicola Croup rocks according to Turner and Verhoogen (i960). A abundant, C common, U uncommon, R rare, ns not seen.  Minerals  Metamorphic Facies Zeolite PI  Calcite Epidote Zoisite Chlorite Quartz Tremolite Muscovite Dolomite Magnetite White mica Limonite  Table 21:  A2  P2  PrehnitePumpellyite  P2  Al  HornblendeHornfels  P2  PI  --+ - + + + •— - - - - - - -  +  - - -  + +  + +  + +  + +  - — — - --  + +  -  + +  — —  — —  -  -  +  -  -  -  + +  Mineral assemblages of calcareous rocks. + - not present.  + +  PI  P2  Al  A2  --  _  — -  --  A2  PI  +  +  Greenschist  +  present,  -— -  -  150 Minerals  Metamorphic Facies Zeolite PI  Quartz Plagioclase An$ i n plag. Feldspar White mica Epidote Zoisite Magnetite Hematite Pumpellyite Calcite Chlorite Leucoxene Relict Minerals: Pyroxene Hornblende Biotite Labradorite Quartz Table 22:  P2  Greenschist  PrehnitePumpellyite P2  PI  P2  mm  an  + +  + + + + +  PI  0-10  —  —  —  —  m»  mm  mm  mm  -  mm  mm  —  _  +  mm  -  —  —  _ at  mm  + + + + + +  -  -  -  -  -  +  -  + +  —  —  —  -  —  —  —  mm  -  -  -  -  +  -  -  -  —  —  —  -  —  -  -  +  -  -  PI  P2  mm  mm  —  — -  -  —  -  mm  aa  —  mm  mm  mm  mm  — mm  — mm  — mm  —  mm  :  •»  mm  —  Mineral assemblages of quartzofeldspathic rocks. + present, - not present. Metamorphic Facie s  Minerals Zeolite PI Plagioclase An$ in plag. Epidote Actinolite Chlorite Pyrite Sphene Laumontite Biotite Magnetite Calcite Hematite White mica Quartz Leucoxene Table 23:  0-10  «•  —  HornblendeHornfels  P2 +  am —  -  -  0-10  +  -  + •>  -  -  mm  . —  +  Prehnite Pumpellyite P2 PI  -  -  +  0-10 +  -  +  - .+ +  -  -  +  -  —  Greenschist PI  P2  Al  A2  +  +  +  +  0-fl0 0-10 +  +  + + + + —  -  --  -  + + + +  -  +  0-10 0-10 + + + +  -  + + + + + +  +  +  +  + +  -  -  +  Main mineral assemblages of basic sedimentary rocks (such as greywacke and tuffaceous greywacke). + present, — not present. .  HornblendeHornfels Al A2 mm  -  --  -  -  -  mm  mm  —  -  -  -  -  -  -  mm  mm  151 Minerals  Metamorphic Facies Zeolite PI  Celadonite Pumpellyite Feldspar Prehnite Hornblende Diopside Limonite Relict Minerals: Augite Labradorite to Andesine  PrehnitePumpellyite  P2  PI  mm  +  —  —  -  — -  —  •  P2 + —  +  —  +  —  + +  mm  —  -  -  Greenschist PI _ —  _ —  P2 + —  — _ —  —  — mm  + +  _ _  _ «.  HornblendeHornfels  Al  A2  wm  mm  + +  -  mm  mm  mm  mm  mm  mm  +  Al  A2  _  —  .  —  - —  mm  mm  mm  mm  mm  mm  mm  mm  mm  mm  mm  Table 25 (cont): Main mineral assemblages of basic sedimentary rocks (such as greywacke and tuffaceous greywacke). Minerals Zeolite P2 Plagioclase An# in plag. Quartz Zoisite Epidote White mica Chlorite Hematite Magnetite Actinolite Green hornblende Prehnite Pumpellyite Calcite Diopside Garnet Leucoxene Green biotite Feldspar Laumontite Relict Minerals: Augite Labradorite Magnetite  mm  PrehnitePumpellyite PI  P2  +  +  0-10  0-10  +  +  mm  m.  —  + + + + +  + + + + +  —  +  — — — — mm  -  -  — m.  -  —  +  + + +  Metamorphic Facies Greenschist HornblendeHornfels  +  —  — —  + +  + +  —  -  — —  —  -  + + +  —  —  + + +  PI +  0-10 + —  + + + + +  P2 +  0-10 _  + + + + + + +  -  Al .  +  0-10 + + + + + + + +  —  —  — —  (+) +  (+) +  +  -  —  —  — —  — +  -  -  'mm  +  — —  -  (+) + (+) +  +  +  —  — —  f Table 24: Main assemblages of basic effusive rocks. + present, (+ ) ynlfp. - ? nnnprtain. — r\r\+. nrpgpnf:  Al +  25-30 + —  — —  —  +  ? ? mm  + + + —  + +  -  — —  —  152  hourglass zoning in augite, and shapes of phenocrysts are veil preserved. Primary colour zoning of l a p i l l i and scoriaceous textures are abundant. Delicate fossils and cavities have persisted. Mechanical disruption of textures includes veins, shear zones, joints, and local foliation. Some zones of sheared basaltic rock are now phyllonite composed of chlorite, quartz, calcite, and clay. Fine-grained recrystallized mosaics are developed locally near intrusions. In a vertical diamond d r i l l hole one mile southwest of Quilchena, the recrystallized texture becomes progressively more coarse-grained with increasing depth, possibly as the buried Penask batholith i s approached. Most of Assemblage A is 2  recrystallized to a very fine mosaic. Only epidote forms porphyroblasts in tuff, breccia, flows, and the South Nicola stock. Most other minerals are pseudomorphs of pyrogenic minerals or they have formed in groundmass, in amygdales, in veins, or inside phenocrysts.  Mineralogjc Changes New minerals were formed from olivine, pyroxene, intermediate plagioclase, iron ore, and groundmass minerals which constituted . volcanic rocks of the Nicola Group. Olivine phenocrysts are now represented by hematite skeletons filled with "chlorite", "serpentine", calcite, and, on occasion, quartz or epidote. In lower rocks of Cycle P, rare altered clinopyroxene phenocrysts are represented by sporadic equant areas of chlorite-epidote-iquartziron oxide, chlorite-actionolite, or chlorite-calcite-actinoliteliron oxide. In volcanic rocks of Cycle A, fresh and partly altered  153  clinopyroxenes occur in the same thin-section. Alteration of one of two kinds occurs: augite — -  uralite i green biotite i epidote i quarts  or augite —  chlorite t calcite i epidote t uralite.  Relict feldspar crystals occurring in sediments and flows of Assemblage P2 are zoned labradorite. The majority of the feldspars are now composed of some combination of hydrous Ca-Al-silicates, white mica, calcite, and albite (Fig. 46).  Less albite is found in the  cores of feldspar phenocrysts than in the associated microlites. The number of different metamorphic minerals in the phenocrysts is usually 2 or 3 in addition to albite.  Phenocrysts in a single thin-section show  2 or 3 different combinations and microlites usually show 2 different kinds of alteration. For instance, a thin-section may contain feldspar phenocrysts pseudomorphed by mica-epidote-albite and calcite-pumpellyitealbite and microlites pseudomorphed by clear albite. A more complicated example in thin-section shows plagioclase pseudomorphed by clinozoisite (?) -albite, clinozoisite-epidote-albite, epidote-albite, calcite-white mica-albite, white mica-albite, and saussurite; the microlites are clear albite except for a few with a few grains of epidote.  A large number  of minerals replacing plagioclase crystals is evident,although the different mineral assemblages observed in the same thin-section may be the result of viewing zoned crystals. Various hydrous Ca-Al-silicates are not equally distributed amongst the alteration products. Very fine-grained clinozoisite is most abundant in association with either calcite or white mica or both, whereas epidote occurs most commonly as euhedral crystals in albite.  154  MICROLITES n = 235  FIGURE  46.  microlites  PROPORTIONS  OF M E T A M O R P H I C MINERALS  B E S I D E S A L B I T E IN F E L D S P A R S , THIN-SECTIONS  FROM  OF NICOLA GROUP.  90  155  Pumpellyite accompanies saussuritized phenocrysts.  Less abundant  alterations include laumontization of feldspars and replacement of microlites by quartz. Magnetite-ilmenite (?) grains are surrounded by leucoxene or very fine-grained sphene. Pine hematite dust i s distributed throughout groundmass; at least some of this dust i s thought to be primary.  In  polished section, magnetite from the South Nicola stock shows r e l i c t ilmenite lamellae and i s now surrounded by leucoxene. The groundmass of flow rocks i s now generally a speckled mass of iron-titanium oxides, epidote, pumpellyite, chlorite, albite, quartz, and calcite. Minerals i n amygdales have been discussed previously (pg. 85 )• Laumontite-rich regions occur near Kane Lake, Courtney Lake, and northward, becoming less common towards Sugarloaf Mountain.  Typically,  only sedimentary rocks, matrices of extremely vesicular rocks, and vesicles are laumontized.  Laumontized rock shows muted and pastel  colours; i t i s friable, porous, and easily weathered. In thin-section, the laumontite i s seen to f i l l interstices, replace the goundmass of porphyritic fragments, and occasionally to replace parts of feldspars. Chlorites from laumontized regions show broad, poorly defined X-ray diffraction peaks. Pumpellyite i s relatively abundant; prehnite i s occasionally seen as an alteration of groundmass and feldspars. Distribution of Mineral Assemblages Mineral assemblages increase i n grade toward the batholiths. The laumontite-bearing assemblages occur far from the batholiths, but longitudinal faulting has down-dropped the eastern block so that  156  laumontite-bearing rocks occur much closer to the Penask batholith than elsewhere. Pumpellyite- and prehnite-bearing assemblages occur closer to plutons. Mineral assemblages of the greenschist facies are found near the plutons or their covered extensions. At the batholithic contact, rocks of Assemblage Al are metamorphosed to hornblende-hornfels facies (Fig. 47). Rocks differ not only in mineral assemblage but also in composition of veins and of gouge. Veins are more abundant near plutons, where they contain gold, tetrahedrite, bomite, and chalcopyrite in gangue of quartz, potash feldspar, salmon-pink calcite, and epidote. Further from plutons, chalcopyrite, pyrite, or galena are found with barren quartz, white calcite, or less commonly, barite gangue. Gouge are from the Penask batholith, in the Nestor Creek fault zone, i s a mixture of limonite and clay minerals. Near the Penask batholith, chlorite-quartz-calcite-clay mixtures form gouge.  Tests for the stability of mineral phases with respect to each other at some given pressure and temperature can be deduced from the phase rule (Zen« 1961; Turner, 1968). The first test involves enumerating the number of phases and comparing them with the number of components. The phase rule states that in a system in divariant equilibrium the number of phases must not be greater than the number of components. The usual number of constituents analysed in a silicate rock is about 14 (SiOg, Ti(>2, AI2O3, Fe2(>3, MnO, MgO, CaO, Na20, K 0, P2O5, %2°> 2> )« 2  C0  s  I f  F e 0  »  the chemical composition  158  sums to one hundred per cent, then a rock with more than 14 phases must be a disequilibrium assemblage. In the thesis area, the most phases that are found in a single thin-section are 13.  Amygdales carry up to  8 phases, most of them similar to those in the groundmass. Therefore, this test does not demonstrate disequilibrium although more phases are present than are usually encountered in metamorphic rocks. Fragments formed in various pressure-temperature environments when put into a new pressure-temperature environment will tend to form the new mineral assemblage stable at those conditions. Most rocks in the thesis area illustrate this principle of convergence.  In  conglomerate north of Hamilton Mountain (Fig. 49, loc. l ) , however, one finds relict hypersthene, relict primary hornblende, unaltered igneous fragments, fragments of unaltered clinopyroxene, fragments of Nicola volcanics with altered feldspars and others with unaltered feldspars, a l l in a low-grade metamorphosed matrix showing that at least there equilibrium was not attained. A second test involves searching for incompatible mineral pairs (Zen, 1963). Hematite and graphite have been found in the same handspecimen (Fig. 47, loc. 2,3), whereas the compatible pair i s magnetite and CO2. Chlorite and primary clinopyroxehe in presence of water are usually considered to be incompatible with respect to each other. Chlorite veins clinopyroxene extensively near Quilchena (Fig. 47, loc. 4 ) . Actinolite, calcite, quartz, and chlorite also coexist. Usually this assemblage would be interpreted to represent disequilibrium, but since another degree of freedom i s provided by the presence of aluminum in at least the chlorite, the coexistence of the minerals is possible in an equilibrium assemblage.  159 Locality (Fig.3 ) 1  Description  F e ^ (±:03)  Massive epidote from replacement in basalt Epidote from vein Massive epidote replacement in foliated basalt Epidote mas8 in basalt Epidote mass in greywacke Epidote mass Vesicule f i l l i n g in dacite plug Epidote mass from basalt Epidote-quartz vein in basalt Epidote amygdale Epidote amygdale Epidote from vein Epidote mass in tuff Epidote mass in basaltic andesite Epidote stockwork in breccia Epidote amygdale Epidote skarn  1 2 3 4 5 6 7 7 8 8 9 10 11 12 13 14  .21 .32  .16** .25 .25 .25  .25 .25 .28 .25 .21 .25 .30  .25 .25 .27 .35  Table 25; Ferric iron in epidote determined by method of Myers (1965). ** broad mixed peak, therefore determination not certain.  Specimen  d 001 A  Veins 1 2 Masses 3 Amygdales ' 4 • 5 6 7 8 Laumontitebearing rocks 9 10  Al atoms  14.07 14.07  3 3  14.07  3  14.03 14.22 14.22 14.28 14.23  2 (-) 2 1 2  14.07 14.27  5  Description of measured basalt peaks  M  3 1/8  1  Table 26;  Variation of aluminum in chlorite.  split peak ""  split peak (003, 004) split peaks (003, 004) split peaks (001, 002, 003, 004)  160  A third test i s based on the requirement that i n a given mineral assemblage comprising a system the solid solution species have the same composition.  One sign of disequilibrium i s to find different members of  the same solid solution series i n contact. Albite cuts labradorite (Pig. 47, loc. 4 ) .  Iron-rich chlorite veins iron-magnesium chlorite  (Pig. 47, loc. 5). Amygdales contain up to 3 chlorites i n contact with each other*  These relations indicate that these minerals are not i n  equilibrium with each other. Although many disequilibrium relations are found for domains smaller than a thin-section, some solid solution minerals of the same composition are widely distributed, indicating an approach to equilibrium. Most of the altered feldspar i s albite.  Because f l a t stage methods  (bisectrix, perpendicular to "a", Michel Levy) were used, the exact composition of the albite i s not known,but the extinction angles, low negative r e l i e f , and positive optical sign suggest i t to be mostly sodic and probably low-temperature. and i n different associations.  Epidote i s widespread, of different ages, The average epidote composition i n the  area - based on 20 scattered epidotes whose ferric iron has been determined using the method of Myer (1965)(Table 25) - i s Ca2Al 4 Pe|. 2  (SijOgKOH).  >  The precision of the method i s +.03 of the iron ratio and  the standard deviation of determinations from Table 25 i s .04, so that there i s no reason to suspect any systematic change across the area. Epidotes from the same locality may show slightly different compositions (Table 25). Other solid solution minerals do show variations i n composition. Chlorite, for instance, shows variations i n Al/Si(Table 26) and Pe/Mg  161  ratios. Single amygdales are seen to contain chlorites with different birefringence, optic sign, and basal spacings.  In general, chlorites  have anomalous blue to white birefringence colours, are optically positive, and have an n* around 1.62-1.60, but chlorites with yellow birefringence colour and both, optically negative and positive have been seen. Anomalous brown birefringence colours are less common. The birefringence and optic sign are an indication of Fe/Mg ratio (Albee, 1962) and basal spacings of Al/Si ratio (Albee, 1962; Deer, Howie and Zussman, 1962). Drummond (1966) concluded as a result of detailed work that birefringence, optic sign, and basal spacings are related to Fe/Mg and Al/Si ratios of chlorites in the Nicola Group at Craigmont. Turner (1968) contends that in chlorite schists of greenschist facies in New Zealand the phases have the same composition throughout, in domains from thin-section to cubic miles in size. In the map area, albite and epidote minerals seem to attain the requisite uniformity over large areas, but chlorite does not. Minor elements also show a general tendency towards equilibrium. Biogenic calcium carbonate i s aragonite, high-magnesium calcite, or lowmagnesium calcite.  Limestones from reefs in the Nicola Group are made of  low-magensium calcite (less than ^  Mg, determined by X-ray diffraction,  stains, chromatography, and spectroscopy on more than 100 specimens), although the organisms that constituted the reef were probably composed of aragonite (algae, pelecypods, gastropods, bryozoans, and anthozoans) and calcite (algae, pelecypods, gastropods, echinoidea, bryozoans, and brachiopods).  Strontium in calcium carbonate in modern reef material  varies; algae may contain 6,500 ppm.,  corals and hydrozoans, 4-6,000 ppm.  Description Calcite within a spongiomorph Groundmass outside same spongiomorph Unidentified recrystallized coral Matrix pooled sample Well-preserved Thamnasteria Groundmass near a spongiomorph Vein cutting the same spongiomorph Vein in reef Vein in reef  Sr (ppm) 670 470 1500+ 410 890 290 100 930 600  Table 27; Strontium content of calcite from reef (Fig. 3, loc. 14)  Description Calcite crystal from fault fillings (Fig. 3, loc. 12) Cardium (Fig. 3, loc. 12) Belemnite or orthocone in lava flow Heavily veined shattered grey limestone Limy matrix in deformed pebble conglomerate Limy matrix in undeformed pebble conglomerate Calcite from calcite-epidote vein from epidotized and chloritized pyroclastic  Sr (ppm) 550 1000 1500+ 1000 820 340 290  Table 28; Strontium content from calcite in country rock.  163  (Lowenstam, 1963). However, the distribution of strontium i n a limestone body that has been subjected to elevated temperatures would be homogeneous i f i t has reached "perfect" equilibrium with the system i n question.  Strontium content of calcite from the reef, determined by  spectroscopic methods (Appendix 3) i s not homogeneous (Table 29). Rather than providing a test of equlibrium, the variations i n strontium content of calcite i n the country rook (Table 28) may reflect variations i n the abundance of strontium i n the country rock i t s e l f , or i n the precipitating solution. A particular grain of a mineral should have the same composition throughout i f i t was formed under equilibrium conditions (Shaw and Cruft, 1962). Various zones of different composition i n a solid solution mineral are not i n equilibrium with each other.  In the Nicola Group,  both pyrogenic and metamorphic crystals are zoned. Clinopyroxenes are oscillatory-zoned and r e l i c t plagioclase grains are normally-zoned. Metamorphic epidotes and chlorite sheaves are zoned. One small sheaf of radiating chlorite fibers shows a change i n the optic sign along the fiber.  A few weakly zoned crystals of new albite are found. Most rocks of the Nicola Group contain low-grade mineral assemblages  belonging to either the zeolite facies or to the greenschist facies. That many of the mineral assemblages have nearly reached equilibrium over wide areas i s suggested by the regional homogeneity of some minerals. Certain mineral assemblages and trace element distributions demonstrate that i n domains as small as a thin-section, amygdale, or crystal, perfect equilibrium between various solids i n rock was not reached or, i n many cases, even approached.  Thus, i t i s not s t r i c t l y correct to say that the  164  rocks belong to metamorphic facies (Eskola i n Barth, 1952; Lambert, 1962; Turner, 1968). Barth (1952, p. 334) concluded, however, that i n rocks i n the greenschist facies  M  ... the low temperature and generally the  surface-near conditions have hindered the attainment of internal equilibrium; moreover, the equilibrium conditions are d i f f i c u l t to define and their interpretations exceptionally complicated...".  Turner  (1968, p. 77) also considered that crystallization of metastable phases i s " ... l i k e l y i n earliest stages of metamorphism, represented by the zeolite facies and rocks of the chlorite zone. Here low temperatures slow down metamorphic reaction rates ...  In such environments,  temperatures have to be considerably above "equilibrium" temperatures to allow reactions to proceed with appreciable velocity. Thus, the drop i n free energy i s relatively large for each of the potential reactions. The nature of the product w i l l then depend on such factors as minimal change i n entropy or favourable conditions of nucleation rather than on attainment of minimal possible free energy. Turner (1968, p. 77) concluded that " ... on these grounds one might expect considerable mineralogical variation among the zeolites, chlorites, micas, etc., that appear i n the earlier stages of metamorphism.  Some such variety i s  indeed encountered ... ".  Environment of Metamorphism Prior to metamorphism, the rocks of the Nicola Group were a mixture of minerals stable at high temperature (eg. olivine, pyroxene, calcic plagioclase) and minerals stable i n the environment of deposition (eg. calcite, weathering products).  These i n i t i a l assemblages were  165  subjected to new conditions under which neither group was stable. The new conditions can be deduced f r o * a consideration of environments implied by the stratigraphy, structure, and kinds of plutonism, as well as from the new minerals formed.  Stratigraphic evidence suggests  that sedimentation i n the area ceased with the deposition of the Nicola Group and that later, after invasion by plutons, the area was positive, that i s , rising.  Thus, the maximum pressures and temperatures deduced  from the thickness of section are relatively low.  Structures reflect the  b r i t t l e conditions under which they were formed. It has been previously mentioned (p. 3 9 ) that plutons were emplaced at shallow levels i n the crust.  Heat and some directed pressure accompanied the emplacement of  the plutons. The geologic history thus suggests that the metamorphism occurred i n a low temperature and pressure environment. The metamorphic minerals i n the Nicola Group must have formed within their stability f i e l d s but the limits of the fields of formation in nature are not necessarily those of their stability.  Experiments of  synthesis, destruction, or equilibrium reactions of chlorites and white mica cannot yield precise limits on the lower boundary of their stability i n rocks because factors such as pH, composition of f l u i d , P H 0 »  a  n  d  2  many other parameters are more important than temperature and pressure (Krauskopf, 1967; Turner, 1968).  Very l i t t l e green biotite i s found  i n the Nicola Group. Thus the majority of the rocks formed i n conditions which do not favour the appearance of biotite.  In a prograde metamorphic  terrane, the f i r s t appearance of biotite would, on the basis of experimental data, suggest water pressure of a few kilobars at temperatures betweem 300<> and 400° C. Since the reactions were retrograde, only a  166  small amount of energy was available to i n i t i a t e reactions. Strens (1963, 1965) has concluded, on the basis of f i e l d evidence and experimental data, that epidote with between 20 and 40 per cent, and especially about 26$, pistacite (a hypothetical iron epidote) end-member seems to be stable from about 630° C to below 200° C over pressure ranges from a few bars to several kilobars i n the presence of quartz. Reducing conditions and the addition of Ha, Fe, and Mg w i l l tend to decrease the stability range of epidote, especially i n the upper limits.  Iron-  poor epidote or clinozoisite reacts to form other Ca-Al minerals below 300°-3500 C.  Although solid solution between the pure aluminum epidote  and common iron epidote has been postulated (Beer, Howie, and Zussman, 1962), Strens (1965) has recently argued that an i a a i s o i b i l i t y gap occurs and that epidote-clinozoisite and clinozoisite-zoisite can coexist i n a stable manner. The lower limit of the range of coexistence of epidote and clinozoisite i s determined by the relative stability of lowtemperature Ca-Al-silicates; the upper limit, by the closure of the solvus postulated on the basis of indirect evidence to be about 550° C (Strens, 1965). Winkler (1967) considers pumpellyite to be stable i n the "pumpellyite-prehnite-quartz facies" which l i e s between the zeolitic facies . and the greenschist facies.  Pumpellyite, thought to have formed i i i situ,  has been recovered a few hundred meters below the earth's surface (White and Sigvaldason, 1962; Krauskopf, 1967).  Laumontite rather than lawsonite  suggests pressures of less than 34" kilobars (Turner, 1968) and slightly higher temperature (about 200° C) than that which forms the upper stability limit of heulandite.  The presence of albite rather than the  167  analcime-quartz pair suggests temperatures of over 200° C although because zoisite and albite or epidote and albite coexist, temperatures have remained relatively low (Barth, 1952).  Laumontite by i t s e l f i s  probably unstable above 400° C (Winkler, 1967); coupled reactions probably reduce this temperature significantly.  Hornblende-hornfels  facies at the batholithic contact i n the map area contain plagioclose as calcic as An 6-30 and reflect a higher temperature environment than 2  established above. The metamorphic conditions are summarized i n Figure 48. P  H  2  Q  and partial pressures of volatiles i n fluids that affected  rock i n the thesis area varied with time and space.  Considerable water  pressure and variable CO2 pressure are suggested by hydrated and occasionally carbonated assemblages. P o and P 2  S 2  varied, forming  different assemblages of iron sulphides and oxides. Eydrothermal veins i n the area are mesothermal according to Lindgren's classification (Dana, 1959; Krauskopf, 1967), and thus reflect temperatures of 200°-300° C and moderate pressures. These veins contain low-temperature,  potassium-bearing albite coexisting with pure, generally  untwinned, ordered potash feldspar.  The separation of the two phases  occurs at very low temperatures (Barth, 1952, I960). Minerals and assemblages show not only spatial distribution (eg. around plutons) but also temporal distribution; that i s , different minerals or mineral assemblages were formed at different times. contain alternating quartz and chlorite linings.  Some amygdales  Others contain chlorites,  the magnesium-rich ones usually having formed prior to the iron-rich ones. The chlorites are not of the same composition i n nearby handspecimens.  168  v u OB 0) V  4kb -.  u  2kb  — 1 —  150 Temperature °C  500  LEGEND Z PP  Zeolitic  Facies  Pumpellyite-PrehniteMetagraywacke Facies  G  Greenschist  Facies  A  Albite-Epidote Hornfels  H  Hornblende Hornfels P h y s i c a l C o n d i t i o n s of Metamorphism. Nicola  F I G U R E 48.  of  Lake  METAMORPHIC  ENVIRONMENT  (AFTER TURNER  1968)  169  The general tendency i s to have the same range of variation represented in a given region. For instance, Mg/Fe** ratios in chlorite vary in this way: chlorite from amygdales and groundmass of augite porphyry southwest of Quilchena varies from magnesium-rich to equal magnesium and iron. South of Nicola Lake, chlorites vary from generally magnesium-rich to generally iron-rich; by Sugarloaf Mountain, the chlorites vary from equally magnesium-rich to iron-rich. In a few amygdales, the complete range from magnesium-rich to iron-rich chlorites i s seen. Epidote was sometimes deposited during the middle or near the end of formation of the amygdale. The composition of the chlorite with which epidote appears is not the same everywhere. In general, amygdaloidal albite and potash feldspar are early. Pumpellyite i s generally late. Early calcite is slightly ferroan and salmon-pink; later calcite i s white, usually with hematite; and the latest i s clear calcite.  Age of Metamorphism The metamorphism can be dated with respect to age of deformation and plutonism. Metamorphism post-dates the emplacement of the South Nicola stock. Laumontite f i l l s vesicles in and has altered flows and tuffs of the Nicola Group and dykes of the South Nicola stock. Pumpellyite i s found as a feldspar alteration both in rocks of the Nicola Group and in dykes of the South Nicola stock. Some rocks of the South Nicola stock are saussuritized; others are altered to albite-quartz-actinolite-epidoteiron oxide assemblages. Foliated rock including sheared quartz diorite of the South Nicola stock is cut by hydrothermal veins. The early  170  chilled phase and dykes of the Penask batholith are also slightly degraded. The metamorphism preceded deposition of the "Clapperton Conglomerate"„ which contains metamorphic fragments of rocks of the Nicola Group. Metamorphism also precedes most shearing i n the thesis area. At Quilchena, late shears cut mineralized and altered rocks.  Throughout  the area, shearing has occurred along hematite-calcite, many epidotecalcite and epidote-quartz veins. The country rock i s similarly sheared and broken crystals are visible i n about one-fifth of the thin-sections of these rocks. The metamorphism occurred after emplacement of the South Nicola stock and preceded the deposition of the "Clapperton Conglomerate" and the occurrence of widespread shearing.  The crude zonal distribution of  mineral assemblages about the batholiths suggests a genetic relationship between the two.  Thus, the metamorphism may be lower Jurassic i n age.  Origin of Metamorphism It has been suggested that metasomatism and metamorphism of the rocks of the Nicola Group are linked to the emplacement of the plutons. The metamorphism i s thought to have been caused by heat and perhaps fluids supplied by the intruding and crystallizing batholiths. This i s supported by the general zonation of mineral assemblages around the batholiths, the high temperature ones occurring near the contact, the lower temperature ones farther away. The batholiths are probably not the sole contributor of energy or metasomatic material. The hydration and carbonation of anhydrous,  171  high temperature mineral assemblages are exothermic reactions and the reactions would tend to perpetuate themselves once started.  As already  explained i n the section on metasomatism, a large part of the added material may have been r e d i s t r i b u t e d along gradients caused by emplacement of the plutons. Hot, mostly r e c i r c u l a t e d waters, containing material dissolved from country rock as w e l l as juvenile materials, permeated the rock mass and flowed along f a u l t s and j o i n t s .  Thus, the a l t e r a t i o n of the  N i c o l a Group took place within a "hot spring" environment. Although z e o l i t e - and pumpellyite-bearing assemblages are commonly associated with b u r i a l metamorphism, the following evidence negates t h i s method of formation. the younger rocks; Assemblage P  2  The metamorphic grade increases i n contains laumontite—bearing rocks as  w e l l as t y p i c a l greenschist f a c i e s rocks; Assemblage A]_ contains greenschist f a c i e s rocks as w e l l as homblende—homfels; and a l l metamorphism i s l a t e r than emplacement of the South N i c o l a stock.  Conclusion The N i c o l a Group has been altered by b u r i a l , deformation, and e s p e c i a l l y by energy supplied by plutons.  The mineralogy of rocks i n  t h i s group has been reconstituted to form mineral assemblages c h a r a c t e r i s t i c of the lower grade metamorphic rocks. tions of the rocks have also been a l t e r e d .  The environment i n which  t h i s was accomplished i s thought to be approximated spring areas.  The bulk composi-  by present-day hot  The shallow and r e l a t i v e l y low-temperature environment  thus envisaged i s supported by arguments from stratigraphy, structure,  172  and plutonism, as well as silicate and sulphide mineral assemblages.  CHAPTER IV THE NICOLA GROUP IM PERSPECTIVE  INTRODUCTION Although the thesis area i s small, i t i s considered that the Nicola Group within i t s borders i s typical of Upper Triassic deposits of the Interior Plateau (Dawson, 1896; Rice, 1947; Cockfield, 1948; Hillhouse, 1965; pers. comm.). Generalizations about i t s subsequent history probably have widespread applications, especially to the history of the development of the Canadian Cordillera.  HISTORICAL GEOLOGY OP THE NICOLA GROUP The sequence of the events that played a part i n the formation of rocks of the Nicola Group i s outlined i n Figure 49. The Nicola Group represents the preserved remnants of an Upper Triassic island archipelago.  The earliest deposits (Assemblage P^)  represent the rapid submarine extrusion of basaltic andesite.  As the  volcanic pile was built closer to sea level, the effusions became increasingly explosive and eventually formed volcanic islands composed of basaltic, andesitic, and, rarely, dacitic rock (Assemblage Pg). Around these submerging, occasionally dormant volcanic centers grew coral reefs.  Between islands fine-grained, occasionally calcic  sediments accumulated. Continued submergence of the region was accompanied by extrusion of augite—rich basalts (Assemblage A i ) . New volcanic  173 Sedimentation  Volcanism  Plutonism  Metamorphism  Folding  Faulting  PB  30  :/0  KG  KG  60  m u ti  •w  90  g  B  120  :>CC  150  180  210  240  * A b b r e v i a t i o n s as T a b l e L> F I G U R E 49.  S U M M A R Y O F E V E N T S IN T H E S I S A R E A  174  islands arose and were eroded, becoming incorporated into conglomerate lenses near the reefs formed when volcanic activity ceased.  Pine ashes  and sediments from distant volcanoes formed thin, well-bedded sheets of fine-grained tuffaceous a r g i l l i t e s and tuffs  (Assemblage A ) .  No  2  younger assemblages of the Nicola Group occur i n the thesis area. The Nicola Group was then mildly folded about a north-south axis into a large syncline and locally fractured,  Dacite plugs and quartz  diorite stocks were emplaced along or near fracture systems.  Local  deformation accompanying granodioritic batholithic intrusions foliated the rock, bent strata into local folds, and displaced blocks. Rocks of the Nicola Group were then metasomatized and metamorphosed. Erosion uncovered batholiths and a brief submergent period followed during which the "Clapperton Conglomerate" was deposited.  Subsequently,  widespread north-south faulting provided the last major structural readjustments i n the region. The newly formed heights were eroded, although by Eocene time, when rocks of the Kamloops Group were deposited, the terrane was s t i l l rough enough to provide relatively cool climates above semitropical swamps which formed the coal basins (Hills, 1965).  Continued  erosion levelled these mountains and generated a rolling surface much like the present upland surface of the Interior Plateau. This surface was i n part covered by Pliocene Plateau basalts and subsequently exhumed by erosion by rivers following u p l i f t of the region and by glaciation. In one inter-glacial interlude, Valley basalts were extruded mainly along the previous fracture systems.  These flows were eroded by the last  glacier which, although i t polished and carried loose debris, does not seem to have much affected the region. A subsequent ice-dam allowed  175  considerable material to be deposited i n the Valleys. Misfit rivers are now removing this material.  UPPER TRIASSIC PALEOGEOGRAPHY OF SOUTH CENTRAL BRITISH COLUMBIA The Nicola Group and other Upper Triassic units contain rocks that reflect a variety of deposition environments (Rice, 1947; McLearn,  1953).  Figure 50 i s a map showing the general paleogeography of south  central British Columbia i n Late Karnian-Early Norian time.  Sections  of the Upper Triassic rocks are available from Asheroft (Dawson, 1896; Duffell and McTaggart, 1952; Carr, 1962b;), Promontory H i l l (Carr, I960), Kamloops (Daly, 1915), and Hedley (Rice, 1947). General knowledge i s available about Copper Mountain (Montgomery,  1967),  Craigmont (Carr,  1961a; Drummond, 1966), and Cultus Lake (Monger, 1966). Thesis-area deposits from volcanic islands with coral reefs give way i n the west, on Promontory H i l l , to medium-grained, mainly sedimentary rocks composed of fragments from volcanoes.  Farther west,  near Asheroft, l i e turbidite-like deposits of limy and volcanogenic detritus.  To the south, the rocks suggest that fewer volcanic islands  were present.  To the southeast, the carbonate and cherty-silt deposits  near Hedley probably represent a carbonate bank much like the present-day Bahama Bank. Far to the southwest, near Cultus Lake, fine-grained turbidite sequences suggest that deep troughs, far removed from volcanic rock, were also prominent features of the Upper Triassic topography (Monger, 1966). To the north, very few fossils of the Upper KarnianLower Norian age have been found.  To the east, no rocks of Upper  Triassic age are found for many miles.  There i s a possibility that land  F I G U R E 50.  L A T E KARNIAN— EARLY  NORIAN  PALEOGEOGRAPHY  OF SOUTH  C E N T R A L BRITISH  COLUMBIA.  177  lay to the east. General paleogeographic reconstructions favour such a scheme (Campbell j, 1966). but no good evidence has been found in the thesis area to support i t .  NICOLA GROUP IN WORLD VIEW OP UPPER TRIASSIC The Nicola Group lies within the Circumpacific linear mobile belt which throughout its extent received enormous quantities of volcanic material during the latter part of the Triassic. This mobile belt and the Tethyan belt were subsiding whereas cratons were continental. The belts were not affected by widespread orogenic movement during most of the Triassic. Near the end of Triassic times, disturbances started in southeast Asia, migrated to northeast Asia, then to North America, and during early Jurassic time began to affect Europe (Strakhov, 1962). Thus the events detailed from the thesis area are an integral part of the general evolution of the Mesozoic mountain belts and i t seems extremely likely that answers to many of the problems about the origin of magmas and stress systems must come from data dram from areas similar to but much larger than the thesis area.  THE BEARING OF SEQUENCE OF EVENTS IN THESIS AREA ON THE EVOLUTION OF THE CORDILLERA The sequence of events in the thesis area is similar to those from some nearby regions in the Interior Plateau. Deposition of upper Triassic volcanic rocks upon an eroded folded region was followed by several episodes of plutonism. Subsequent deposition was limited to a few conglomerates and later continental deposits. This sequence differs  178 drastically from the sequence of events to the east and west (Pig. 51) and serves to put some limits on the vexing problem of the age of the Shuswap metamorphic terrane (Leech, 1962; Price, 1967; Hyndman, 1968; Ross and Kellerhals, 1968). Either deep-seated regional stresses that formed east-west lineations in the Shuswap terrane were not reflected in shallowly buried rocks, suggesting a decollement between deep and shallow rocks; or the folds died out before getting that far west; or the Shuswap metamorphism i s older than the Nicola Group. A steeply dipping, east-striking cleavage unique to the older Cache Creek rocks near Douglas Lake tends to favour the third hypothesis.  REGIONAL ALTERATION The low-grade metamorphism reported from the thesis area i s common throughout the outcrop area of the Nicola Group. Instances of increases in grade occur along the borders of the Eagle granodiorite complex and, to the south, of the/Tulameen ultramafic complex (Pindlay, 1963). South of the thesis area, the feldspars are andesine (Rice, 1947; Montgomery, 1967). North of the thesis area, feldspars are generally albitized. In the entire region, clinopyroxene is generally unaltered, although in a given local area, i t may well be completely uralitized or chloritized, as i t i s near Stump Lake. These low-grade assemblages are distinct from the gneissic metamorphic complexes that bound the Interior Plateau (Gabrielse and Reesor, 1964; McTaggart and Thompson, 1967) and show either that heat sources were very local or that these metamorphic terranes were formed previous to Late Triassic time.  FIGURE 51.  t Uplift  THE NICOLA GROUP in relation to Phanerozoic in Canadian Cordillera (modified after Wheeler, 1967)  i s„ «i4»c< a  • "•*•»•••*•« Bj Cn-«M «f  plur.di  180  GEOPHYSICAL SPECULATIONS Data of a geophysical nature are rare from the region around Merritt,  A recent estimate of the depth of the crust i n this region i s  about 40 kilometers (Wheeler, 1967). The upper 6 kilometers of this are rocks of the Nicola Group which presumably overlie an unknown thickness of Cache Creek rock.  Granitic material and other material  capable of forming the extrusive and intrusive rocks on the surface i n this region must l i e below the Cache Creek Complex, Many speculations about the crust are derived from a consideration of magnetic data.  Using a small flux-gate type magnetometer, Thompson  (1968; pers. comm., 1968) showed that oriented specimens of 5 upper Triassic volcanic rocks and one early Jurassic dyke contained a normally oriented remanent f i e l d ,  Paleomagnetio pole determinations are not  available from this region and poles determined from the Triassic of North America are so widely scattered that no conclusion can be made as to the dipole position ( i f any) during Triassic time (Morley and Larochelle, 1964).  SUGGESTIONS FOR FURTHER WORK Many fascinating aspects of geology of the thesis area require detailed work. Of special interest to the writer i s the possibility of more accurately determining the size of the domains that acted as closed systems during metamorphism. The size of the domains could be determined from a statistical study of the chemical compositions of volcanic rocks from the Nicola Group  181 using the method of analysis of variance developed by Krumbein and Tukey (1956). The population to be studied would include a l l volcanic rocks of the Nicola Group within a large area.  This area would be  chosen so that one part of i t was near plutons, another part far away. Since not a l l volcanic rocks would be available for sampling, the sampled population would be the volcanic rocks exposed at the surface. The sampling plan would be a nested design.  That i s , the region chosen  would be divided into sets of successively smaller areas.  A certain  set of sub-areas would be randomized from each of the sets. In each of these sub-areas, channel samples would be collected. be analysed twice.  Bach sample would  This sampling scheme would allow determination of  the level at which the variances of the chemical analyses become homogeneous. This level, representing a given sample size, would then define the size of the domain.  The results would apply only to the  sampled population and extrapolation would be necessary to apply the results to the Nicola Group i n general.  References Cited  Albee, A.L. (1962), Relationships between the mineral association, chemical composition, and physical properties of the chlorite series; Am. Min.. 47: 851-. Allen, P. (1963), Sedimentological models; J. Sed. Pet.. 33: 289-293. Anderson, E.M. (l95l), The Dynamics of Faulting: 2nd edition, Oliver and Boyd, Edinburgh, 206 pp. Baker, P.E., Gass, I.G., Harris, P.G., and LeMaitre, R.W. ( 1 9 6 4 ) , The volcanological report of the Royal Society Expedition to Tristan da Cunha, 1962; Phil. Trans. Roy. Soc. 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(1905), Paleontology and zoology; G.S.C. Snmm, for 1905; 357.  RPT>*.  Winkler, H.G.P. (1967), Petrogenesis of Metamorphic Rocks; 2nd edition, Springer Verlag. Yoder, H.S. Jr. (1965), Diopside-anorthite water at five and ten kilobars and its bearing on explosive volcanism; Carnegie Inst.. Washington. Yearbook. 64; 82-89. and Tilley, C.E. (1962), Origin of basalt magmas: an experimental study of natural and synthetic rock systems; J. Petrol.. 3: 342-532. Young, G.A. and Uglow, W.L. (1926), Iron ores of Canada, Vol. 1; G.S.C. Econ. Geol. Ser. #3. Young, R.J. (1962), Geology of a sedimentary section in the Nicola Group near Merritt, British Columbia; unpubl. B.A.Sc. thesis, Geol. Dept., Univ. of B.C. Zen, E-an (l96l), The zeolite facies: 259: 401-409.  an interpretation; Am. J. Sc..  _______ (1963)» Components, phases, and criteria of chemical equilibrium in rocks; Am. J. Sc.. 261: 929-942. Zobell, C.E. (1942), Changes produced by micro-organisms in sediment after deposition; J. Sed. Pet.. 12: 127-137.  191 APPENDIX 1 CHEMICAL ANALYSES OP NICOLA GROUP PART A Assemblage P^  1  2  3  4  5  6  7  8  9  10  Plagioclase  Pm(a)  Pm  P  P  P  P  Pm  P  Pm  P  Ai$ i n p i g .  Ab  Ab  Ab  Ab  Ab  Ab  Ab  Ab  Ab  Ab  Epidote  (a).  p,m  m  m  m  •  m  m  -  P  Clinozoisite  P  -  P  P  -  P  -  -  -  m  -  m  m  m  Minerals  -  .  a  -  - •  m  m  p,m,a  m  -  -  -  -  Pumpellyite  mm  White mica  P  P  P  P  P  (p)  • -  '. -  Chlorites  Pm  P  P.m  m  m  a,m  m  -  -  —  -  Celadonite  -  -  Green b i o t i t e  -  -  -  -  -  -  -  -  -  --  Hematite  U)  m  m  m  m  (m)  (m)  (m)  m  m  Magnetite  m  m  -  • -  -  -  Pyrite  -  -  -  -  -  -  -  (m)  -  -  -  -  Leucoxene  (m)  (m)  m  m  m  m  m  m  m  m  Actinolite  P  p.m.a  -  -  -  -  -  Uralite  -  -  -  -  -  -  Clinopyroxene  (p)  -  -  -  -  -  -  -  -  Calcite  m  m  m  m  m  m,  v,a  m,a,v  Limonite  - •  oat  -  - •  -  -  -  -  Quartz  m.a.p  Clay Potash feldspar  Table 29;  -  -  m,  -  -  •-  m  m  m  m  m  Pm  Pm  m  v,a,m  -  -  -  -  -  -  -  -  -  -  —•  —  —  —  —  —  •—  —  —  —  Qualitative modes of analysed rocks of the Nicola Group. C a p i t a l l e t t e r = abundant, lower case = present, bracketed lower case = uncommon; ^,p phenocrysts, ^,m matrix, A,a amygdale, V,v vein, - not seen, Ab = a l b i t e .  192  PART A Minerals  Assemblage P2  17  18  19  20  P,A,M m  a  Pm  Pm  Pm  Ab  Ab  Ab  Ab  -  Ab  -  m  -  m  m  m  11  12  13  14  15  Plagioclase  m,a  M,P  Pm  a,Pm  An# in pig.  Ab  Ab  Ab  Epidote  m  p,m  Clinozoisite Pumpellyite  m  P  Am  White mica Chlorites  16  Am  -  m  -  -  p,m  p,m  p,m  -  : -'  P  P.m  pMa  Am  <•»  -  -  m  m  p,m  m  m  Vm  m  m  m  m  (m)  m  m  m  m  m  m  m  Celadonite Green biotite Hematite  p,m  Magnetite  m  pm  Pyrite Leucozene  m  m  Actinolite  m  m  Uralite Clinopyroxene Calcite  A  Pv  m  Limonite Quartz  Am  M,P,v m  p, a v m, a  m  a  m,a,v m,a  m  «.  m  -  m,a  -  -  V,a  m,a,v m  m  9  -  m,a,v m,p,A m  Clay Potash feldspar  Mm  Table 2 9 : Qualitative modes of analysed rocks of the Nicola Group. (cont.) Capital letter = abundant, lower case = present, bracketed lower case = uncommon; P,p phenocrysts, M,m matrix, A,a amygdale, V,v vein, - not seen, Ab = albite.  PART A  Minerals  21  22  Assemblage P2 23 24  Plagioclase  Pm  P  Mp  An$ i n p i g .  Ab  Ab  Ab  -  m  -•  Epidote  -  Clinozoisite  P  -  -  -  -  -  m  m  m  Clinopyroxene  -  m  -  -  Calcite  m  m  m  Limonite  m  m  m  -  Quartz  m  m  Mm  V  Clay  m  m  Potash feldspar  m  —  White mica  -  Chlorites  m  Pumpellyite  P  -  -  ?  -  m  m  a  -  Green b i o t i t e  -  -  -  Hematite  m  m  a,m  Celadonite  Magnetite  -  Pyrite Leucoxene Actinolite Uralite  -  —  Table 29: Qualitative modes of analysed rocks of the Nicola Group. (cont.) C a p i t a l l e t t e r = abundant, lower case = present, bracketed lower case = uncommon; P,p phenocrysts, M,m matrix, A,a amygdale, V,v vein, - not seen, Ab = a l b i t e .  194  PART A 25  26  Assemblage A^ 28 29 27  Plagioclase  P,m,v  m  m,a,v Am  Pm  P,m,v  Ar$ in pig.  Ab  Ab  Ab  Ab  Ab  Ab  Epidote  m  m  Am  (p),m  aMp,v  Clinozoisite  P  Minerals  Pumpellyite  -  White mica  p,m  Chlorites  Green biotite  -  Hematite  m  Magnetite  m  Celadonite  m  m  ?  p,a  a  en  Leucozene Actinolite  m  -  -  CE*  -  -  m  m  m  m  to  -  m  m  -  Uralite  mat  Clinopyroxene  P  Pm  m  CO  Calcite  a  a,p  m  Am  -  Limonite Quartz Clay  -  Potash feldspar  m  Table 29: (cont.)  -  m  -  -  m  -  Am  -  32  33  -  p,m  m,v  Ab  ?  m  m  mtm  ?  -  -  mat  P  m  m  —  m  P  -  ta  31  -  m  -  30  m  am  _  -  Pyrite  -  i  m.p m,v  -  -  -  m  (»)  -  p,a,m  -  m m  -  m,p,v  -  (m),v  -  m  —  (m)  mam  -  -  am  -  m  -  -  m,p  Pm  m  m  (m)  -  |  •**  m  -  -  m  i  m p,m  p  P  p  m  m  -  -  m  m,v  -  -  -  Qualitative modes of analysed rocks of the Nicola Group, Capital letter = abundant, lower case = present, bracketed lower case = uncommon; P,p phenocrysts, M,m matrix, A,a amygdale, V,v vein, - not seen, Ab = albite.  j  -  "!  195 PART B  Assemblage P i  SiC-2  1*  2*  3  4  5  6  7  8  9  10  48.5  53.2  60.8  42.0  55.9  48.3  78.5  77.2  47.5  46.4  0.96  TiC-2  0.80  19.4  19.1  Fe205  6.8  6.8  FeO  4.8  3.2  MnO  0.22  0.22  KgO  6.6  3.2  CaO  4.3  Na 0 K 0  A1 0 2  5  0.84  0.86  15.9  17.4  [9.4  (10.3  0.88  14.5  1.07 21.0  |l0.5  0.23  0.25  1.22  0.89  10.4  13.2  14.3  18.0  (.3.0  i«.  |l2.4  J9.6  0.19  0.10  0.24  0.11  0.09  0.14  0.28  ,2.6  4.1  3.0  3.3  1.5  1.4  5.4  5-7  4.0  1.5  10.2  4.2  5.3  3.8  1.0  4.7  6.9  4.7  6.5  6.0  1.9  5.8  5.3  1.5  3.9  5.6  3.2  0.73  0.53  tr  0.6  tr  1.3  1.3-  2.7  1.6  0.9  0.04  0.06  nd  nd  nd  nd  nd  nd  nd  nd  0.01  0.01  nd  nd  nd  nd  nd  nd  nd  nd  H0  3.6  1.3  nd  nd  nd  nd  nd  nd  nd  nd  Cu  7  23  23  65  725  48  18  15  78  50  Pb  56  40  28  31  33  40  39  20  40  40  Zn  136  80  50  64  37  96  28  47  105  76  Ag  0  0  tr  0  0  1  -  -  Ni  38  36  28  35  27  25  3  24  17  38  2  2  p o 2  C0 2  S  2  5  0.3  0.2  0.10  0.2  0.5  0.3  0.2  1  0.2  0.2  * G.S.C. Rapid Methods Table 7 : Rock analyses, Nicola Group, nd = not done.  t r , trace, - not present,  0.3  0.5  ;  196 PART B Assemblage P  Si0  2  Ti0  2  A1 0  2  11*  12*  13*  14*  15*  16  17  18  19  20  54.5  73.3  58.8  48.0  55.9  54.7  50.9  56.1  50.9  53.3  0.3  1.11  1.42  1.14  1.20  1.07  1.53  16.6  17.4  (13.4  (15.9  1.47  14.3  0.92  1.49  14.4  12.9  15.7  18.0  17.1  Pe205  5.9  1.1  4.8  5.2  9.9  FeO  4.3  0.6  3.4  6.6  0.8  MnO  0.15  0.02  0.14  0.20  0.15  0.19  0.18  0.21  0.12  MgO  3.2  0.6  2.5  5.4  1.7  3.0  4.0  5.5  4.4  CaO  12.4  1.2  3.9  4.1  2.8  4.3  4.3  4.6  5.1  7.3  3.7  2  5  (12.2  18.7  18.4  (14.9  |ll.l  0.30  :  3.7  Na 0  0.1  3.1  5.2  4.9  5.5  2.5  3.7  4.4  nd  K 0  0.2  4.13  0.24  0.62  1.89  4.3  1.6  2.0  2  ?2°5 •  0.5  0.7  0.4  2.9  2.8  nd  nd  nd  nd  nd  C0  5.0  1.6  2.9  5.2  1.7  nd  nd  nd  nd  nd  0.04  0.07  0.07  0.11  nd  nd  nd  nd  nd  2  2  2  H0 2  0.12  '5  1.3  Cu  438  67  43  28  12  18  55  60  10  31  Pb  48  36  28  42  56  44  64  30  52  38  Zn  84  22  52  70  70  130  70  120  68  Ag  -  -  -  107  Ni  35  26  22  S  0.3  0.2  0.2  -  -  24  26  0.2  0.2  -  31 0.3  1  28 0.2  nd 30 0.4  1  26 0.3  tr 32 0.2  j  * G.S.C. Rapid Methods  Table 7 : (cont.)  Rock analyses, Nicola Group, nd = not done.  t r , trace, - not present,  PART B  Assemblage P2  Si0  2  Ti0  2  A1 0 2  21  22  23  24  53.8  47.5  74.0  48.2  0.80 5  0.60  0.81  j  1.30  25.4  12.5  11.5  14.4  [l3.2  [l0.4  (6.7  [l5.1  Pe203 FeO MnO  0.03  0.23  0.12  0.14  MgO  2.3  6.9  2.0  3.6  CaO  1.5  7.1  1.8  5.2  Na 0  nd  2.4  4.7  3.7  K0  4.0  3.6  0.2  3.1  nd  nd  nd  nd  2  nd  nd  nd  nd  H0  nd  nd  nd  nd  Cu  7  20  15  10  Pb  45  54  24  49  Zn  37  95  81  Ag  -  64  Ni  20  41  21  27  2  2  po 2  co 2  S  5  0.3  -  0.4  -  0.2  -  0.3  * G.S.C. Rapid Methods  Table 7 : Rock analyses, Nicola Group, (cont.) nd = not done.  t r , trace, - not present,  198 PART B •  Assemblage A]_  Si0  2  TiC-2  25  26  27  28  29  30  31  32  33*  47.4  47.2  49.3  48.4  49.8  48.4  49.1  48.4  48.6  0.81  0.68  Al 0j  16.4  13.3  Pe203  7.7  6.7  2  PeO  2.1  3.0  MnO  0.17  0.16  MgO  7.0  CaO  0.70 17.4 (9.0  0.81 12.9  [ll.5  0.96 16.9  [ll.7  0.67  16.1 5.4  0.80 16.8 (9.8  4.5  0.70  0.77  13.9  17.1  3.6  4.9  6.5  4.6  0.19  0.20  0.32  0.14  0.21  0.19  0.18  10.5  4.0  4.7  5.4  6.4  3.5  9.7  6.2  9.8  11.0  7.9  8.5  5.5  9.7  7.4  9.1  8.2  Na 0  3.6  2.8  3.6  2.0  5.0  3.1  4.3  2.9  1.6  K0  2.25  2.10  4.7  1.9  1.0  2.76  2.3  2.80  3.51  0.43  0.24  nd  nd  nd  0.38  nd  0.30  0.56  0.6  0.4  nd  nd  nd  0.2  nd  0.1  0.1  3.1  2.4  nd  nd  nd  2.4  nd  2.8  4.0  2  2  p o 2  C0  2  H0 2  Cu Pb  5  56 76  Zn  25  Ag  _  Ni  56  S  56  25  45  31  48  24  56  48  76  57  77  145  84  62  84  84  7  97  17  18  20  120  130  30  tr  1  -  -  43  36  33  47  64  0.4  0.4  36  0.4  0.4  0.3  42 0.3  0.4  0.3  * G.S.C. Rapid Methods Table 7 : Rock analyses, Nicola Group, tr, trace, - not present, (cont.) d = °t done. n  n  s 41  0.3  PART C  199 Assemblage P_ 1  2  Assemblage P  I  2  11  12  13  28.22  38.71  16.08  5.90  12.79  14  15  Quartz  0.49  -  Orthoclase  3.21  4.45  1.22  24.9  1.47  3.78  5.48  56.40  41.02  0.87  26.76  47.43  42.77  48.51  Albite Nepheline  -  -  Anorthite  19.31  21.09  Corundum  0.96  3.49  Mg Clinopyroxene  -  Fe Clinopyroxene  -  Enstatite  8.17  39.41  -  -  1.60  13.79  2.85  0.58  8.98  2.34  -  -  0/57  13.67  1.46  1.52  6.46  13.87  1.34  0.12  0.46  6.13  -  -  8.36 6.75  -  Magnetite  8.20  Hematite  1.32  -  Ilmenite  1.56  1.88  2.78  Rutile  0.01  0.01  0.07  -  Apatite  0.15  0.10  0.30  Calcite  0.23  0.23  Ar$ i n plagioclase  25.50  Colour Index  20.22  10.17  -  _  -  -  8.82  1.09  7.23  -  2.30 0.25  - '  0.37  -  0.58  -  -  7.78  -.  ! f  -  16.99  Fayalite  Forsterite  -  1.49  -  Ferrosilite  -  -  -  Ca Clinopyroxene  -  j  |  mm  4.41  -  ;  mm  M  - ..  •  -  10.32  H  2.19  2.24  .1.76  ]]  0.01  0.01  0.10  0.17  0.17  0.27  |:  1.17  1.62  0.94  6.80  6.05  !  33.95  97.84  5.30  26.37  3.60  22.13  i !  33.12  28.87  6.42  16.93  39.00  18.9  ; j  J)  ii  * assumed no CO2 Table 8:  Norms of completely analysed specimens (G-.S.C. Rapid Methods), Nicola Group. The specimen numbers correspond to those i n Table 7.  206  PART C  Assemblage Al  Quartz  25  26  -  -  30 an*  32 mm  33 1.1  Orthoclase  13.56  12.67  16.69  16.89  21.58;  Albite  23.61  17.09  21.59  16.64  14.08  Nepheline  4.03  3.85  2.84  4.54  Anorthite  22.36  17.88  22.37  16.97  30.26  Corundum  ' mm  -  -  -  -  Ca Clinopyroxene  8.59  14.12  9.67  11.10  3.18  Mg Clinopyroxene  7.39  12.15  7.31  7.66  2.37  1.32  2.48  0.48  -  -  Pe Clinopyroxene Enstatite  -  -  13.69  Perrosilite  -  Porsterite  7.27  Payalite  _  -  Magnetite  4.51  7.86  Hematite  4.74  1.42  -  -  -  Ilmenite  1.57  1.32  1.30  1.36  1.52  Rutile  0.01  0.01  0.01  0.01  0.01  Apatite  1.05  0.59  0.93  0.73  1.40  Calcite  1.39  0.93  0.47  0.23  0.24  10.20  -  mm  2.77  6.30  11.90  1.26  4.24  -  8.01  5.33  7.39  An$ in plagioclase  49.0  51.0  51.0  51.0  68.0  Colour Index  34.0  47.0  35.16  44.0  31.0  * assumed no C 0 2 Table 8; Norms of completely analysed specimens (G.S.C. Rapid (cont.) Methods), Nicola Group. The specimen numbers correspond to those in Table 7.  201 APPENDIX 2 DESCRIPTION OP FOSSIL LOCALITIES F o s s i l s i n the Nicola Group (Plate X) are neither well-preserved nor abundant. L o c a l i t i e s where f o s s i l s have been found are noted on Figure 1 ( i n pocket). F o s s i l s are u s u a l l y not well enough preserved to be i d e n t i f i e d as to species (Tozer, 1965,  pers. comm.).  by N.J. S i l b e r l i n g (NJS). G. Westerman (GW)  The few Halobia and ammonite fragments were determined  The r e s t were i d e n t i f i e d by the writer with help from  and J.R. Beerbower (JRB).  I n s t i t u t e , Washington, D.C,  i n 1965  The writer v i s i t e d the  Smithsonian  to work with the type material of Smith'(1927)»  but the f o s s i l s are very poorly preserved.  At the same time, D. Squires offered  much help with the ecologic implications of reef faunas.  N. Hillhouse made  available h i s specimens and notes on f o s s i l l o c a l i t i e s found i n the region studied by the w r i t e r .  F o s s i l s i n Assemblage P] L o c a l i t y 41:  Poorly exposed greywacke i n a draw contains few small, poorly preserved, external casts of cockle-like pelecypods.  L o c a l i t y 1:  A well-exposed limestone block, measuring tens of feet i n length and width, i n feldspar-bearing b a s a l t i c andesite contains fragmentary and poorly-preserved corals, a l g a l material, s h e l l fragments and c r i n o i d stems.  L o c a l i t y 45:  A well-exposed limestone block i n feldspar-bearing b a s a l t i c andesite contains fragmentary and poorly preserved corals, a l g a l mat and s h e l l fragments. F o s s i l s i n Assemblage Po  L o c a l i t y 6:  A belemnite (?) or orthocone (?) fragment i s engulfed i n vesicular lava.  L o c a l i t y 42:  A cast of a s n a i l i s found i n feldspar-bearing p o r p h y r i t i c lava.  L o c a l i t y 12.  22: A well-exposed outcrop of coarse- to fine-grained t u f f and greywacke has yielded the best f o s s i l c o l l e c t i o n from the Nicola Group. A l i s t of organisms appears below.  202 Pelecypods: Very abundant "cockles" (indet. c a r d i t o i d pelecypod NJS) F a i r l y common "dams" ' Rare "mussels" Rare "scallops" Rare oysters, some forms l i k e Lppha (?) (GW) Rare indet. t r i g o n i i d pelecypods (NJS) Rare Minnetrigonia sp. (?) (NJS) Rare, other pelecypods with thick prismatic s h e l l Rare G e r v i l l e i a sp. (?) Rare f l a t , f i n e l y - r i b b e d pelecypod Gastropods:  turriform gastropod  Scaphopods:  common large and small dentaloids  Cephalopods: Abundant Arcestes (?) , Juvavites sp. (?) (NJS) Rare f l a t , ribbed, involute forms Rare indet. ammonite, possibly an Upper T r i a s s i c h a l o r i t i d (NJS) Rare "orthocone" Rare "belemnite" with l o n g i t u d i n a l s t r i a t i o n s Brachiopods: Rare Lingula sp. Rare terebratuloid Echinodeemata: F a i r l y common Isocrinus F a i r l y common Pentacrinus Rare echinoid debris, including a c i d a r i d spine and an ambulacral plate Chordata Rare f i s h bones (JRB) Carbonized wood, twigs and branches L o c a l i t y 11:  In a poorly exposed b l u i s h tuffaceous e n c r i n i t e , various f o s s i l s are poorly preserved. They include up to ^ - i n c h long pentagonal and s t e l l a t e c r i n o i d stems, a broken crenulated round brachiopod with well-defined sulcus, broken, f l a t , coarselyand f l a t - r i b b e d pelecypod, other s h e l l material, broken terebratuloid fragments, "oyster", and Meleagrinella (?) (GW).  L o c a l i t y 9:  A poorly exposed black aphanitic t u f f with interbeds of calcareous t u f f contains: Indet. s h e l l material Pentacrinus (?) Hazelnut-shaped brachiopods Isocrinus (?) Terebratuloids High-spired gastropod Flat-ribbed pelecypod Costate brachiopods (?) "Oyster" "Cockles" F i s h bone Indet. ammonite Wood Arcestes (?) Crinoid fragments Indet. t r i g o n i i d pelecypod s i m i l a r to Mvophoria adornata  203 L o c a l i t y 3:  A small l i t h o l o g i c a l l y complex area comprised of e n c r i n i t i c t u f f , tuffaceous greywacke, t u f f , and very l i t t l e e n c r i n i t e with occasionally some coquina contains terebratuloids, Isocrinus d e t r i t u s , other c r i n o i d stems, costate brachiopod s h e l l s , "cockles", sponge material, "oyster", indetermined s h e l l s , and "clams" with heart-shaped cross-sections.  L o c a l i t y 2;  Poorly exposed, steeply dipping beds a few hundred yards south of Highway 5 contain Halobia sp. indet. (NJS), flattened belemnite, Posidonia (?) (GW), r e t i c u l a t e network ( a l g a l mat ? ) , and indetermined ammonite.  L o c a l i t y 3:  Poorly exposed, well-bedded b l u i s h tuffaceous fine-grained limestone contains Halobia sp. indet. (NJS), Halobia c f . H. omatissima Smith (NJS), small pieces of carbonized material. Overlying limestone contains Thamnasteria. indetermined corals, and pelecypod fragments.  L o c a l i t y 27:  Poorly exposed, well-bedded, b l u i s h tuffaceous fine-grained limestone contains Halobia c f . H. omatissima Smith (NJS), belemnoid fragments, and other f l a t - r i b b e d pelecypods.  L o c a l i t y 25.24; Dark limy t u f f contains Halobia c f . H. c o r d i l l e r a n a Smith (NJS), c r i n o i d debris, and Arcestes. L o c a l i t y 10;  Tuff and dark blue fine-grained limestone contain a few terebratuloids, oyster, and broken pelecypod debris.  L o c a l i t y 47;**  Well-exposed outcrops of occasionally bituminous and argillaceous limestone on a steep h i l l s i d e y i e l d a, v a r i e t y of specimens:  Halobia c f . H. c o r d i l l e r a n a Smith (NJS) Arcestes sp. "(NJSj Hannaoceras (?) sp. (NJS) Indet. clam-shaped pelecypods. Grey limestones there y i e l d large c o l o n i a l corals, astreids, Halobia indet. sp., and f l a t , ribbed pelecypods. To the south of the 50°N l a t i t u d e , but not f a r from t h i s l o c a l i t y , Rice (1947) reported: Oxytoma c f . inaeauivalve var. intermedia Pecten c f . oleanus Mypphoria sp. "Arcestes" sp. L o c a l i t y 28:  Well-exposed, t h i n , limy layer contains a l g a l p i s o l i t e s with cores of indeterminate brachiopods and pelecypods.  L o c a l i t y 19:  This poorly-exposed and faulted region i s underlain by conglomerate with fragments of porphyritic rock of Cycle P set i n a limy matrix which i s f o s s i l i z e d (Halobia sp. indet. NJS ).  **  Reported by Hillhouse (1965, pers. comm.); l o c a l i t y v i s i t e d by writer.  204 L o c a l i t y 13: Well-exposed greywacke and breccia-conglomerate inter-bedded with the southern extension of the reef contain a d i v e r s i f i e d fauna: Pelecypods: Small "cockles", mostly disaggregated Large, thick-shelled "cockles" Indet. t r i g o n i i d pelecypod Gastropods: high-spired, thick-shelled gastropods Scaphopods: small dentaloids Cephalopods: A large n a u t i l o i d about 1 foot across Orthocone (?) Belemnite (?) Corals: astreids Spongiomorph Sponge debris A l g a l mats Pish bone L o c a l i t y 48:**  In scattered outcrops of light-grey, thick-bedded, fine-grained limestone with clay and occasional interbeds of coquina occurs a small varied fauna:  Delicate c o r a l (Halomitra ?) M o n t l i v a u l t i a sp. Pecten C y r t i n i d brachiopod Terebratuloids P l i c a t e brachiopods (perhaps Plectonconcha c f . P. aeauiplicata) L o c a l i t y 50:*** Along Clapperton Creek occurs limestone with poorly preserved astreid corals. L o c a l i t y 7:  In a poorly exposed greywacke interbed i n conglomerate Lingula sp., plant remains ( ? ) , and charcoal.  occur a few  L o c a l i t y 52:* Mypphoria (?) occurs i n a poorly exposed, p a r t i a l l y r e c r y s t a l l i z e d , evenly bedded limestone and skarn bed. L o c a l i t y 49:**  In limy conglomerate occur yophoria (?); a weathered, f l a t , ribbed, eared (?) pelecypod; spongiomorph; horn corals; and bryozoans ( ? ) . M  Cockfield (1948) has reported f o s s i l s from the thesis area: Paleocardita ? c f . buruca Boehm i n h i l l s south of Nicola Lake, and Cassianella sp. south of Iron Mountain. * ** ***  Pound by Young; reported by Hillhouse (1965, pers. comm.). Reported by Hillhouse (1965, pers. comm.); l o c a l i t y v i s i t e d by writer. Reported by Hillhouse (l965,» pers. comm.); l o c a l i t y not found by writer.  205 Various l o c a l i t i e s are found i n l i t h o l o g i c a l l y continuous reef limestones. The faunas i n each reef are summarized i n Table 3 2 .  Localities  Fossils  20,18, 17  51**  29,26,4, 31.32.5  16,36,15, 14.30  Spongiomorphs: 3 kinds  +  +  +  Astreids  -  +  +  +  -  -  +  +  +  +  Terebratuloids  -  +  +  +  -  P l i c a t e and costate brachiopods  -  +  -  +  -  A l g a l crusts  -  +  +  -  Pentacrinus  -  +  -  -  -  +  +  +  -  -  -  +  +  -  -  +  + .  +  • -  +  -  -  -  +  -  -  -  +  —  Thamnasteria  ST>.  Other c r i n o i d material C i d a r i d spines High-spired gastropods  -  -  Pelecypod fragments Orthocone, prob. Michelinoceras Belemnoid ?  Table 52:  -  -  —  44** +  53  +  i i j  —  i  —  + j  i  _ •  Summary of reef faunas, Nicola Group. L o c a l i t i e s are shown on Figure 5. + present, - not present. F o s s i l s i n Assemblage A-[  L o c a l i t y 58: A poorly exposed conglomerate contains fragments of Assemblage A]_ set i n a limy matrix with pelecypod s h e l l s . ** Reported by Hillhouse (1965, pers. comm.); l o c a l i t y v i s i t e d by writer.  206 L o c a l i t y 59:  A well-exposed limestone lense with interbedded t u f f contains a v a r i e t y of poorly-preserved forms: pelecypods with heart-shaped cross-sections, indeterminate s h e l l debris, indeterminate corals, and a l g a l mats.  L o c a l i t y 40:  A well-exposed limestone overlies a conglomerate with fragments of Assemblage A_ set i n a limy f o s s i l i f e r o u s matrix: large pelecypod with shape s i m i l a r to Megalodont. indeterminate s h e l l debris, and a l g a l mats.  207  HALOBIA  ORNATISSIMA  HANNAOCERAS  HALOBIA  ARCESTES  LOPHA  PLATE  X.  GERVEILLA  "COCKLE"  F O S S I L S OF THE NICOLA  GROUP.  208 APPENDIX 5 SPECTROGRAPHIC METHODS  To determine Sr and Mg contents of carbonates, a spectroscopic method was employed.  The following discussion i s divided i n t o 3 parts:  preparation, (2)  ( l ) sample  a tabular l i s t i n g of spectroscopic method, and (3)  discussion  of photometry, and s i g n i f i c a n c e of r e s u l t s .  Sample Preparation Preparation: out.  Outer 5 mm.  were removed by a dental d r i l l ; then sample was  drilled  Sample was weighed, and one part i n t e r n a l standard, two parts l i t h i u m  carbonate, and four parts b o r i c a c i d were added. hand, grinding under acetone f o r 10 minutes. heating under i n f r a r e d lamp. storage.  Sample was  This was  thoroughly mixed by  The l a s t acetone was  removed by  then transferred to a p l a s t i c v i a l for  Later, samples were fused i n graphite c r u c i b l e s at 900° C f o r 20 minutes,  then cooled on a stone bench.  The r e s u l t i n g blue beads were crushed and mixed  with an equal amount of s p e c i a l spec-pure graphite. Internal Standard:  3.9$  C02O3 : 16.1$  BaCOj : 80.0$ Li2C03 by weight were mixed  together and ground under acetone f o r h a l f an hour.  The material was  then  stored i n glass j a r t i l l needed. L i s t i n g of Spectroscopic Method Spectrograph:  JACO,.21-foot grating, Wadsworth mount with f i r s t order dispersion 5.24 A/mm.  Condensing Optics:  (distance from s l i t given f i r s t )  0 . 0 cm. c y l i n d r i c a l lens with horizontal axis and 25 cm f o c a l length 16.1  cm. c y l i n d r i c a l lens with v e r t i c a l axis and 6.7  27.5  cm. diaphragm with 5 nun.  aperature  58.1 cm. s p h e r i c a l lens with 10 cm. f o c a l length 72.5  cm.  arc  '  I  .  cm. f o c a l length  209 S l i t width;  30  S l i t Length; Arc Gap:  8 mm.  5  mm.  Intensity Reduction;  7-step sector at s l i t : log i n t e n s i t y r a t i o equals 2; 2 mesh screens f o r further reduction  Voltage:  225 v o l t s D.C. on open c i r c u i t  Current:  9.5 amps  Cooling: Gas Jet:  water at 18 gph Stalwood Assemblage using 79$ Ar : 21$ 0 A i r Co.) at 18 scfh  Electrodes:  2  (mixed tank, Canada Liquid  a) preformed l/8-inch rod with p l a i n crater l / l 6 - i n c h by 3/8-inch, by United Carbon Products Co. b) l/8-inch s p e c i a l graphite rod, by National Carbon Co.  Exposure:  70 seconds (time taken to burn to completion)  Emulsion:  Eastman Kodak SA 1 (2400-3700 A) ; Eastman Kodak I I I F (3700-5000 A)  Processing:  a) 3 min. i n E.K. D-19 Developer, with vigorous a g i t a t i o n b) 20 sec. i n stop bath, with gentle a g i t a t i o n c) 5 min. i n Ansco Liquid Rapafix, with sporadic a g i t a t i o n d) 20 min. i n running cold water, with l i t t l e  agitation  3) 5 sec. i n d i s t i l l e d water, then dried by sponge. ARL  Photodensitometry  The 2nd, 3rd, 4th, or 3rd, 4th, 5th steps were read whenever possible.  Many  times, the 1st or 6th step had to be used, but these usually f e l l o f f the c a l i b r a t i o n l i n e suggested by steps nearer the center.  The nonlinearity was a  r e s u l t of i r r e g u l a r i l l u m i n a t i o n of the s l i t (Payne, 1965» pers. comm.).  On some  Mg l i n e s , there seemed to be a break; that i s , steps with i n t e n s i t i e s above 50 plotted on one l i n e , those with i n t e n s i t i e s below 50 on another l i n e . the slope difference was small. consistent.  Fortunately,  Very weak or very intense l i n e s are probably not  210 Results  Sr The Sr 4215 and Ba 4528 l i n e s were intense and their i n t e n s i t i e s plotted on approximately p a r a l l e l straight l i n e s .  The Sr 4215/Ba 4528 p a i r was used because  the Sr 4607/Ca 4608.5 p a i r proved unwieldy.  Both these l a t t e r l i n e s are near the  r e l a t i v e l y sensitive l i n e L i 4605 which, because of the high L i content of the sample mixture,  was very intense and thus i n t e r f e r e d with background readings on  the Sr and Ca l i n e s near i t .  The variables which a f f e c t the Sr 4607 and  Ca 4608.5 l i n e s include variable Sr and L i concentration and variable of burn (the higher the temperature,  temperature  the stronger the Ca 4608.5 l i n e ) .  A plot of Y values of standards against composition y i e l d s a very s i g n i f i c a n t l i n e a r c o r r e l a t i o n ( F i g . 54). This l i n e was then compared to a mixture of one part NBS limestone #la and four parts spec-pure c a l c i t e .  Three r e p l i c a t e s  y i e l d 600, 600, and 720 ppm Sr f o r the 1:4 sample which contains 400 ppm Sr. These values are outside the confidence l e v e l s of the regression l i n e .  Three factors  may explain t h i s : ( l ) Ba content of clay, s i l i c a , and other minerals may a l t e r t h i s Sr/Ba pair; that i s , some Ba i n the limestone would give a spurious value; (2) there may be some unspecified matrix e f f e c t ; and (3) Ba was not mixed thoroughly. K_ A l l Mg values were lower than concentrations of the standards. .Mn Mn was present i n most samples i n variable amounts.  Qualitative results  showed that the Mn content of the samples was less than that of NBS limestone #la.  211  FIGURE  52.  WORKING C U R V E FOR S r / B a PAIR. INDICATED BY.POSITIONING P A R T N B S L I M E S T O N E #la: CALCITE.  A C C U R A C Y IS  OF A MIXTURE 3 PARTS SPEC  OF 1  PURE  

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