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Geology of the White Lake Area Church, Barry Neil 1967

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The U n i v e r s i t y of B r i t i s h Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY of NEIL CHURCH B.Sc, McMaster Uni v e r s i t y , 1959 M.Sc „, McMaster University, L963 FRIDAY, MAY 26, 1967 AT 10.30 A.M. IN ROOM 102, GEOLOGY BUILDING. COMMITTEE IN CHARGE Chairman: I. McTaggart Cowan A. L. Farley W. H. Mathews K. C. McTaggart J. V. Ross G. E. Rouse W. F. Slawson Research Supervisor: W. H. Mathews External Examiner: Howel Williams Professor Emeritusj Department of Geology, Un i v e r s i t y of C a l i f o r n i a , Berkeley. GEOLOGY OF THE WHITE LAKE AREA ABSTRACT The object of this study i s to e s t a b l i s h the stratigraphy, structure and petrology of early T e r t i a r y rocks i n the White Lake area near Penticton, B r i t i s h Columbia. T h i s ' i s achieved by f i e l d mapping and laboratory work. Ear l y T e r t i a r y rocks of the White Lake area, thought to be mainly Eocene age, consist of f i v e main s t r a t i g r a p h i c d i v i s i o n s : 1,.- discontinuous beds of basal breccia and conglomerate; 2. a thick and widely d i s t r i b u t e d succession of volcanic rocks of diverse composition - mainly phonolite, trachyte, and andesite lavas; 3. discontinuous volcanic beds - mainly rhyodacite lava; 4. l o c a l l y thick volcanic sandstone and conglomerate beds i n t e r d i g i t a t e d with lahar and p y r o c l a s t i c deposits; 5. l o c a l deposits o f - s l i d e b reccia and some volcanic rock overlain by fanglomerate beds. Each d i v i s i o n rests with some angular or erosional unconformity on older rock. Aggregate thickness of the T e r t i a r y s t r a t a , where best- developed,- i s about 12,000 f t . These rocks are r e g i o n a l l y downfaulted accounting, i n part, for t h e i r preservation from erosion,, Greatest downward movement i s near the Okanagan Val l e y where, i n places, i t i s estimated that basal beds exceed depths of -5000 feet (m.s.l.). In general, beds are t i l t e d e a s t e r l y as i f rotated downward forming a trap-door-l i k e structure. L o c a l l y , folds are developed but these are without regional pattern and may be the re s u l t of simple'flextures i n the basement rocks. Petrographic and chemical data indicates a three-fold d i v i s i o n of igneous rocks: 'A' series - mainly plagioclase porphyries: lavas of rhyodacite and andesite composition; 'B- series - mainly two feldspar porphyries with cO-existing plagioclase and sanidine; lavas of tr a c h i t e and trachyandesite composition; 'C' series - mainly anorthoclase porphyries: lavas of phonolite composition;and some te p h r i t e . Phase diagrams and subtraction plots indicate that rocks of 'A1 and 'C' series were probably formed by c r y s t a l f r a c t i o n a t i o n . In the case of 'A' ser i e s , p r e c i p i t a t i o n of mainly plagioclase and pyroxene from andesite produces r h y o l i t e ; and for 'C' ser i e s , p r e c i p i t a t i o n of mainly pyroxene and some b i o t i t e from tephrite produces phonolite. j Rocks of 'B' series are intermediate i n com-po s i t i o n to 'A' and 1G' and were probably formed by mixing of magmas. GRADUATE AND RELATED STUDIES X-ray Mineralogy Spectrochemical Analysis Igneous Petrology Advances Geochemistry Paleobotany Advanced Igneous and Metamorphic Petrology S t r u c t u r a l Analysis Geomprphology AWARDS The C a l i f o r n i a Standard Company Scholarship The E.S. Moore Prize i n Geology The National Research Council Studentship The S h e l l Company Grant-in-aid The U n i v e r s i t y of B r i t i s h Columbia Fellowship s PUBLICATIONS Gra v i t a t i y e S e t t l i n g of O l i v i n e i n Pillows of an Icelandic Basalt: American Journal of Science, 1964. Reply to Discussion: American Journal of Science, 1965. B.J, Burley . D.M.. Shaw T.N. Irvine R.E. Delavault G.E. Rouse K.C. McTaggart J.V. Ross W.H. Mathews 1957- 58 1958- 59 1960-61 1964 1965-67 GEOLOGY OF THE WHITE LAKE AREA by BARRY NEIL CHURCH B.Sc.,McMaster University, 1959 M.Sc.,McMaster University, 1963 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 May, 1967 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h a L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a nd s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s , I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a i i ABSTRACT The object of this study i s to e s t a b l i s h the stratigraphy, structure, and petrology of early T e r t i a r y rocks i n the White Lake area near Penticton, B r i t i s h Columbia. This is achieved by f i e l d mapping and laboratory work. Ea r l y T e r t i a r y rocks of the White Lake area, thought to be mainly Eocene age, consist of f i v e main s t r a t i g r a p h i c d i v i s i o n ; 1. discontinuous beds of basal breccia and conglomerate, 2. a thick and widely d i s t r i b u t e d succession of v o l c a n i c rocks of diverse composition - mainly phonolite, trachyte, and andesite lavas, 3. discontinuous v o l c a n i c beds - mainly rhyodacite lava, 4. l o c a l l y thick v o l c a n i c sandstone and conglomerate beds i n t e r -d i g i t a t e d with lahar and p y r o c l a s t i c deposits, 5. l o c a l deposits of s l i d e breccia and some vo l c a n i c rock o v e r l a i n by fanglomerate beds. Each d i v i s i o n rests with some angular or erosional unconformity on older rock. Aggregate thickness of the T e r t i a r y s t r a t a , where best developed, is about 12,000 feet. These rocks are r e g i o n a l l y downfaulted accounting, i n part, for t h e i r preservation from erosion. Greatest downward movement i s near the Okanagan V a l l e y where, i n places, i t i s estimated that basal beds exceed depths of -5,000 feet (m.s.l.). In general, beds are t i l t e d e asterly as i f rotated downward forming a trap-door-like s t r u c t u r e . L o c a l l y , folds are developed but these are without regional pattern and may be the r e s u l t of simple flextures i n the basement rocks. Petrographic and chemical data indicates a t h r e e - f o l d d i v i s i o n of igneous rocks: 'A' ser i e s - mainly plagioclase porphyries; lavas of rhyodacite and andesite composition; 'B1 series - mainly two feldspar porphyries with co-existing plagioclase and sanidine; lavas of trachyte and trachyandesite composition; 'C1 series - mainly anorthoclase porphyries; lavas of phonolite composition and some te p h r i t e . Phase diagrams and subtraction plots i n d i c a t e that rocks of 'A' and 'C1 series were probably formed by c r y s t a l f r a c t i o n a t i o n . In the case of 'A' s e r i e s , p r e c i p i t a t i o n of mainly plagioclase and pyroxene from andesite produces r h y o l i t e ; and for 'C1 s e r i e s , p r e c i p i t a t i o n of mainly pyroxene and some b i o t i t e from t e p h r i t e produces phonolite. Rocks of 'B1 series are intermediate i n composition to 'A' and 'C1 and were probably formed by mixing of magmas. i v TABLE OF CONTENTS Page CHAPTER I: INTRODUCTION 1 SCOPE AND CONTENT 1 LOCATION AND ACCESS 1 NATURE OF MAP-AREA 1 PREVIOUS WORK 4 FIELD WORK 6 GEOLOGICAL SETTING 6 CHAPTER I I : GENERAL GEOLOGY AND STRUCTURE 14 PRE-TERTIARY ROCKS 14 TERTIARY ROCKS 14 1. BASAL TERTIARY SURFACE 15 2. DETAILED DESCRIPTION OF FORMATIONS 17 A. SPRINGBROOK FORMATION 17 a. D i s t r i b u t i o n and Thickness 17 b. Lithology 20 c. Structure 20 d. Age 25 e. C o r r e l a t i o n 25 B. MARRON FORMATION 26 Yellow Lake Porphyry Member 28 a. D i s t r i b u t i o n and Thickness 28 b. Lithology 29 Clot-Porphyry Member 29 a. D i s t r i b u t i o n and Thickness 32 b. Lithology 32 Page B a s a l t i c Andesite Member 34 a. D i s t r i b u t i o n and Thickness 34 b. Lithology 34 Rosette-Porphyry Member 34 a. D i s t r i b u t i o n and Thickness 36 b. Lithology 36 Park R i l l Andes i t e Member 36 a. D i s t r i b u t i o n and Thickness 38 b. Lithology 38 Structure 38 Co r r e l a t i o n and Age 41 C. MARAMA FORMATION 44 a. D i s t r i b u t i o n and Thickness 44 b. Stratigraphy and Lithology 46 c. Structure - 49 d. C o r r e l a t i o n 49 D. WHITE LAKE FORMATION 51 a. D i s t r i b u t i o n and Thickness 51 b. Stratigraphy and Lithology 51 Sedimentary Rocks 51 Volcanic Rocks 54 Structure 58 Source 59 Age and C o r r e l a t i o n 59 E. SKAHA FORMATION 66 Lower Member 66 v i Page 'Basal Breccias' 67 a. D i s t r i b u t i o n and Thickness 67 b. Lithology 67 'Augite-Porphyry' 70 'Granite Breccia' 75 a. D i s t r i b u t i o n and Thickness 75 b. Lithology 78 Upper Member 85 a. D i s t r i b u t i o n and Thickness 85 b. Lithology , 85 Structure 88 Age and C o r r e l a t i o n 93 3. RESUME OF GENERAL STRUCTURE 93 GLACIAL GEOLOGY 100 Ice Thickness and Movement 101 Meltwater Drainage^and G l a c i a l Deposits 101 CHAPTER I I I : IGNEOUS PETROLOGY 104 MAIN PETROGRAPHIC FEATURES 104 CHEMICAL VARIATION 106 PETROGRAPHIC PROVINCES 114 PETROGENESIS 119 CHAPTER IV: SUMMARY AND CONCLUSIONS 128 GEOLOGICAL HISTORY 128 PETROLOGY 131 SUGGESTIONS FOR FUTURE WORK 134 BIBLIOGRAPHY 135 v i i Page APPENDIX 'A1: CHEMICAL ANALYSES 143 APPENDIX 'B1: CALCULATION OF NORMS 147 APPENDIX 'C': PETROGRAPHIC DESCRIPTIONS 150 ROCKS OF 'A' SERIES 150 1 - B a s a l t i c Andesite 150 2 - Andesite 151 3 - Rhyodacite 155 4 - Rhyolite 159 ROCKS OF 'B' SERIES (Trachytes, Trachyandesites) 161 1 - Clot-Porphyries 161 2 - Rosette-Porphyries 161 3 - White Lake Feldspar-Porphyries 169 ROCKS OF 'C' SERIES. . . 170 1 - Rhomb-Porphyry (Phonolite) 170 2 - Augite-Porphyry (Tephrite) 179 v i i i LIST OF TABLES Table Page 2.0 T e r t i a r y Formations 16 2.1 Summary of Lithology of Springbrook Formation and Lower Marron Formation 21 2.2 Composition of Yellow Lake Porphyries 30 2.3 Composition of Clot-Porphyries 35 2.4 Composition of Rosette-Porphyries 37 2.5 Composition of Park R i l l andesite 39 2.6 C o r r e l a t i o n of Marron Formation and Midway Group . . 43 2.7 Composition of Marama Rocks " 48 2.8 Composition of Augite-Porphyry 77 2.9 Description of Common Boulders i n Upper Member (Skaha Formation) 89 3.0 Key to Analyses, Figure 3.1 . 108 3.1 Key to Analyese, Figures 3.2, 3.3, and 3.4 . . . . 112 3.2 Composition of Main Phases of C o r y e l l B a t h o l i t h and S i m i l a r Rocks of 'B1 and 'C1 Series 118 3.3 Normative Cal c u l a t i o n s , 'y' as Pyroxene, B i o t i t e , and Potash Residuals 124 4.0 Outline of Cenozoic Geological Events 129 A . l Chemical Composition of Rocks, White Lake Map-area . 143 A.2 P a r t i a l Analyses of Rocks, White Lake Map-area . . . 144 A.3 Chemical Analyses from Other Studies 145 A. 4 Average Analyses from Other Studies 146 B. l Normative Compositions 149 C l Feldspar X-ray D i f f r a c t i o n Data 175 C. 2 Analyses of Rhomb-shaped Anorthoclase 180 i x LIST OF FIGURES Figure Page 1.1 Location of Map-Area 2 1.2 Plot of Reconnaissance Traverses i n Map-Area . . . . 7 1.3 Location of Early T e r t i a r y Bedded Rocks 10 1.4 Refractive Index Frequency for Lavas in the White Lake, Kelowna, and Midway Areas 11 1.5 Grabens of Southwestern B r i t i s h Columbia and Northern Washington State 12 1.6 L i s t r i e Normal Faults i n South-Central B.C 13 2.1 Inferred Configuration of Basal T e r t i a r y Surface . . 18 2.2 Grain Analyses of Springbrook Sediment 23 2.3 Size Frequency Cumulative Curves of Springbrook Sediment 24 2.4 Glass Bead Ref r a c t i v e Indices of Marron and Marama Lavas 47 2.5 Trout Lake Graben 50 2.6 Generalized Columnar Sections of White Lake Beds . . 55 2.7 Structure Section of White Lake Beds on North Limb of Syncline 60 2.8 Compos it i o n o o f White Lake Sandstones 61 2.9 Ref r a c t i v e Index V a r i a t i o n of White Lake Volcanic Rocks 62 2.10 Resultant Vector Diagrams for Dip of White Lake Beds Measured from D.D.H. Core 63 2.11 Diagrammatic Structure Section of Concentric Folds and Related Faults 64 2.12 Cross-Bedding Directions i n White Lake Sediments . . 65 2.13 Comparison of Refractive Indices of Pulakite Dikes and Trachyte - Trachyandesite Lavas 71 2.14 Size D i s t r i b u t i o n of Skaha Chert Breccia 72 2.15 Internal Structure of Part of Granite Breccia Unit . 80 X 2.16 Composition of Skaha Sandstones 91 2.17 Some Late Structures i n Rocks East of White Lake . 94 2.18 Equal Area Diagrams 95 2.19 Possible Stress Scheme for Late Movement, Area near White Lake 96 2.20 S t r u c t u r a l Subdivisions of Map-Area and Adjacent Region 97 2.21 Cross-Section of White Lake Basin 99 2.22 Plot of Ice Movement i n Area East of White Lake . . 101 2.23 Topographic Section Showing G l a c i a l Features i n V i c i n i t y of the Hole 103 3.1 E a r l y T e r t i a r y Igneous Rock Series 107 3.2 V a r i a t i o n Diagram, 'A' Series 109 3.3 V a r i a t i o n Diagram, 'B1 Series 110 3.4 V a r i a t i o n Diagram, 'C1 Series I l l 3.5 Some Minor Element Variations 115 3.6 Cenozoic Petrographic Regions of Southern B r i t i s h Columbia and Washington State 117 3.7 Phase Diagrams 121 3.8 Subtraction Diagram, 'A' Series 122 3.9 Subtraction Diagram, 'C' Series 123 3.10 Coexisting Plagioclase and Potassic Feldspar i n Two Feldspar Rocks 125 3.11 Mixing Diagram 127 4.1 Generalized Columnar Section 130 C l I l l u s t r a t i o n of Habit and O p t i c a l O r i e n t a t i o n of Rhomb-shaped Anorthoclase 174 x i ; LIST OF PLATES Plate Page 2.1 Springbrook Formation, i n west part of map-area south of Highway 3 19 2.2 Springbrook beds, two miles west of Green Ranch . . . 22 2.3 Contact between Marron and Springbrook beds, near Yellow Lake 27 2.4 Blocky top of rhomb-porphyry lava flow 31 2.5 Slabby p i l l a r s , clot-porphyry lava 33 2.6 Conformable clot-porphyry and Yellow Lake porphyry lavas, north of Yellow Lake 40 2.7 Conformable Park R i l l andesite and rosette-prophyry lavas, south of Park R i l l near T.L. Ranch . . . . 40 2.8, 2.9, and 2.10 Gravity f a u l t displacement of Marron rocks north of Yellow Lake 42 2.11 Marama Formation, west of Highway 3 near Marama Creek 45 2.12A, B Small i n f i l l cycle, White Lake sediments, south limb of White Lake syncline 56 2.13 Interbedded lahar and p y r o c l a s t i c deposits, White Lake vo l c a n i c rocks near White Lake 57 2.14 B l u f f s of White Lake v o l c a n i c rocks, near White Lake. 57 2.15 'Basal breccias' (mainly dark chert) overlying White Lake beds (mainly l i g h t coloured p y r o c l a s t i c rocks) 68 2.16 Conglomerate zone immediately below 'basal breccias' Indian Head 68 2.17 'Basal breccias' (highly fragmented bedded chert breccia) overlying White Lake v o l c a n i c rocks, canyon of Kearns Creek west of The Hole 69 2.18 Highly fragmented chert breccia, 'basal breccias' . . 69 2.19 Intr u s i v e chert breccia i n conglomerate beds, lower member Skaha Formation 73 2.20 Augite-porphyry lava (tephrite) overlying crossbedded sandstone, near The Hole 74 x i i Plate Page 2.21 Augite-porphyry dike and i n t r u s i v e chert breccia i n conglomerate, lower member Skaha Formation . . 76 2.22 P o r p h y r i t i c granite 79 2.23 Aphanitic granite 79 2.24 Uncrushed granite t y p i c a l of large slabs, 'granite breccia zone' 81 2.25 Granite 'autobreccia' with crushed dike 82 2.26 Internal structure of 1autobrecciated' dike 82 2.27 ' F r i c t i o n a l breccia', layered deposits of mobilized granite and dike rock breccia, east of The Hole . 83 2.28 Granite-block conglomerate cemented by arkose . . . . 84 2.29 Arkosic sandstone bed i n granite-boulder conglomerate 84 2.30 Igneous i n t r u s i o n i n breccias, lower member Skaha Formation 86 2.31 Skaha beds east of The Hole 87 2.32 Boulder of arkosic sandstone i n upper member, Skaha Formation 90 2.33 Chert block i n upper member, Skaha Formation . . . . 90 2.34 Channel deposit i n upper member, Skaha Formation . . 92 2.35 Hoodoo structure i n conglomerate, upper member Skaha Formation 92 C l Hand specimen of t y p i c a l b a s a l t i c andesite 152 i C.2 Photomicrograph of b a s a l t i c andesite 152 C.3 Photomicrograph of merocrystalline andesite 156 C.4 Photomicrograph of v i t r i c andesite 156 C.5 T y p i c a l platy habit of rhyodacite lava 158 C.6 Photomicrograph of rhyodacite 158 C.7 F l i i i d a l banding i n r h y o l i t e 160 C.8 Photomicrograph of r h y o l i t e 160 C.9 Photomicrograph of clot-porphyry trachyte 164 x i i i Plate Page C.10 Photomicrography of clot-porphyry trachyandesite . . 164 C . l l T y p i c a l massive rosette-porphyry lava 167 C.12 Photomicrograph of rosette-porphyry trachyandesite . 168 C.13 Photomicrograph of rosette-porphyry trachyte . . . . 168 C.14 Photomicrograph of White Lake feldspar porphyry trachyte 171 C.15 T y p i c a l rhomb-shaped anorthoclase phenocryst from Yellow Lake lava 176 C.16 Photomicrograph of Yellow Lake lava 177 C.17 Photomicrograph of w e l l cleaved a p a t i t e i n rhomb-porphyry lava 177 C.18 Photomicrograph of (010) section of anorthoclase . . 178 C.19 Photomicrograph of (001) section of anorthoclase . . 178 C.20 Hand specimen of White Lake augite-porphyry (tephrite) charged with granite xenoliths 183 C.21 Photomicrograph of Skaha augite-porphyry lava . . . . 183 ACKNOWLEDGEMENTS The wri t e r wishes to convey his sincere thanks to Professor W.H. Mathews who sponsored the study and supervised preparation of the manuscript. Gratitude is extended to Professor W.H. White, Professor R.M. Thompson, and Dr. R.V. Best for use of U.B.C. Geology F i e l d School and for advice on geology of the map-area. Special thanks are owing Dr. K.C. McTaggart, Dr. J.V. Ross, and Dr. A.L. Farley for h e l p f u l c r i t i c i s m of the work, and Professor Howel Williams who, through the courtesy of Anaconda American Metal Brass Co., was able to v i s i t the f i e l d - a r e a with the w r i t e r . Also, Dr. G.E. Rouse k i n d l y a s s i s t e d i n i d e n t i f i c a t i o n of some plant f o s s i l s . The w r i t e r is obliged to o f f i c e r s of the Geological Survey o f Canada, e s p e c i a l l y Dr. H.W. L i t t l e and Dr. J.W.H. Monger for constructive suggestions, and Dr. J.G. Souther for chemical analyses. Assistance provided by other s t a f f members of the Un i v e r s i t y of B r i t i s h Columbia, fellow graduate students, and technicians, i s g r a t e f u l l y acknowledged. F i n a n c i a l assistance was provided by the S h e l l O i l Co. and the U n i v e r s i t y of B r i t i s h Columbia. CHAPTER I INTRODUCTION SCOPE AND CONTENT The object of t h i s study i s to e s t a b l i s h the s t r a t i g r a p h i c suc-cession, s t r u c t u r a l h i s t o r y , and petrology of early T e r t i a r y v o lcanic rocks i n a t y p i c a l , well exposed, and accessible area of southern B r i t i s h Columbia. F i e l d descriptions are amplified with d e t a i l e d laboratory data i n c l u d i n g rock and mineral determinations and chemical studies. LOCATION AND ACCESS White Lake map-area i s i n south-central B r i t i s h Columbia, approxi mately 150 miles due east of Vancouver and 8 miles south of Penticton i n the southern Okanagan region. It covers about 65 square miles l y i n g roughly between l a t . 49° 17' and 49° 23' N. and long. 199° 34' and 119 ° 48' W. P r o v i n c i a l Highway 3 passes through the area on the northwest and 97 on the east. An excellent gravel road turns west from Highway 97 near junction with Highway 3 and passes south to the Dominion Radio Astrophysical Observatory, branching west here to Twin Lakes and south past White Lake. D i r t farm and logging roads provide good access to parts remote from secondary roads and highways (see Figure 1.1). The v i l l a g e of Okanagan F a l l s i s located i n the east part of the map-area and provides l o c a l e s s e n t i a l s e r v i c e s . This i s also a s t a t i o n on the Okanagan branch l i n e of the Canadian P a c i f i c Railway. The Geology F i e l d School of the University of B r i t i s h Columbia l i e s about 6 miles south of the map-area and i s accessible on good gravel roads. NATURE OF MAP-AREA The White Lake map-area i s characterized mainly by a low mountainous t e r r a i n bounded on the east by the Okanagan and t r i b u t a r y 2 Figure I.I Location of Map-Area v a l l e y s ( l o c a l base l e v e l about 1,100 feet m.s.l.), and on the west by v a l l e y s t r i b u t a r y to the Similkameen draingage system ( l o c a l base l e v e l about 1,800 feet m.s.l.). Shales eroded from a b a s i n - l i k e g e o l o g i c a l structure underlie a dish-shaped topographic depression i n the east-central part of the map-area. Slopes r i s e gently from White Lake, a small ephemeral body of water near the center of the depression (about 1,750 feet m.s.l.), to an almost complete ri n g of h i l l s . Concordant summits northwest and southwest of White Lake underl i e a remnant of a once c o n t i -nuous upland surface, about 4,500 feet m.s.l., known as the Thompson Plateau (Holland, 1965). To the east the depression i s separated from Okanagan V a l l e y by numerous small knobs and ridges and by Mt. Hawthorn which r i s e s to 2,750 f e e t . The basin rim i s breached by several v a l l e y s containing small intermittant streams. Low parts and south-facing slopes i n the map-area are open ranch lands with p l e n t i f u l bunch-grass, sage brush, and cactus. Summits and north-facing slopes have forests of pine and f i r of s u f f i c i e n t density to support several logging operations. C l i m a t i c conditions are severe, the area being i n a dry b e l t . The t o t a l annual p r e c i p i t a t i o n , combined r a i n and snow, i s only about 11 inches (heaviest p r e c i p i t a t i o n i s during winter months). Temperatures are re-corded i n excess of 100 degrees Fahrenheit for short periods during mid-summer. Some ponds and larger bodies of open water i n the area are s a l i n e or stagnant and are not considered drinkable. Animal l i f e i s abundant and markedly v a r i e d . Bear, deer, and grouse are hunted by l o c a l sportsmen. Poisonous spotted p r a i r i e r a t t l e -snakes inhabit talus slopes and rocky ledges and are considered hazardous by ranchers and surveyors. Brown mud t u r t l e s l i v e i n Mahoney and Green lakes i n the southeast part of map-area and are a t o u r i s t a t t r a c t i o n . Also, a popular magazine reports (Western Homes and L i v i n g , June 1966, p. 42): "White Lake basin is of great i n t e r e s t to o r n i t h o l o g i s t s , who come here to explore one of the few remaining nesting s i t e s i n B r i t i s h Columbia of the Long-billed Curlew. In early sum-mer, lucky b i r d watchers may hear the f l u t e - l i k e tones 'curl-e-e-e-e-e-u-u-u-u' d r i f t i n g across the open p l a i n . ' i t never ceases to sadden' one n a t u r a l i s t wrote, 'for this c a l l with i t s mournful q u a l i t y i s the symbol of our vanishing grass lands' ." I* PREVIOUS WORK The presence of T e r t i a r y rocks i n the White Lake area was reported by Dawson (1879) during a reconnaissance survey of southern B r i t i s h Columbia. No geological information on t h i s area was published u n t i l l o c a l gold mining a c t i v i t y created a market for cheap blacksmithing coal. The f i r s t geological report, prepared by Camsell (1913), was e n t i t l e d White Lake Coal Area. This account i s b r i e f but accurate i n broad aspect, providing the basis, i n part, for l a t e r mapping by Bostock and for the present study. The following i s an extract from Camsell's report (p.215): "In general the structure of the White Lake coal area i s that of a s y n c l i n a l basin, the s t r i k e of which i s east and west. In d e t a i l , however, there are often wide var i a t i o n s from t h i s d i r e c t i o n , e s p e c i a l l y on the eastern side of the area where apparently there has been consider-able disturbance since the deposition of the coal-bearing beds. The dips range 0° to 50° and average about 20° . Some f a u l t i n g has taken place, e s p e c i a l l y i n the disturbed region on the east. The rocks of the coal-bearing formation (White Lake Formation) appear to have been l a i d down i n a gradually subsiding basin on the western edge of a region i n which volcanism was active at i n t e r v a l s throughout the whole period of t h e i r deposition. The eruptions at this focus were of the explosive type and great volumes of t u f f were blown out and deposited i n the basin. In parts of the basin these t u f f s were water worn to form true sandstones; but i n other parts they have not been so worn and they r e t a i n the same angularity of the grain when f i r s t ejected. (p.216) Overlying the coal-bearing rocks on the east i s a ser i e s of volcanic breccias and t u f f s and some flows of an andesite or more acid nature. In places the overlying volcanic rocks succeed the coal-bearing rocks conformably; but i n other places there i s a marked angular unconformity between them. I t i s probable, however, that t h i s un-conformity does not indicate any great time i n t e r v a l between the two s e r i e s . The upper volcanic rocks occupy an exceedingly i r r e g u l a r and broken country to the east of the coal basin, which no doubt i s the source from which t u f f s were derived. This broken country i s apparently the locus of an ancient T e r t i a r y volcano which was active at i n t e r v a l s during and a f t e r the deposition of the c o a l -bearing rocks. I t has a l l the c h a r a c t e r i s t i c s of an ancient, denuded volcanic crater about a mile i n diameter, the bottom and sides of which have slumped i n leaving a s e r i e s of steep-sided h i l l s and deep sinkholes now often f i l l e d with water." Camsell's d e s c r i p t i o n of the coal-bearing beds w i l l be given i n chapter two of t h i s report. A report by Dowling (1915), e n t i t l e d 'Coal F i e l d s of B r i t i s h  Columbia', contains a d e s c r i p t i o n by McEvoy of coal-bearing beds crop-ping out along Kearns Creek, about a h a l f mile north of White Lake. The f i r s t comprehensive geological survey of the area was com-pleted by Bostock (1941). He c l e a r l y delineated the T e r t i a r y deposits on 15 minute quadrangle maps 627A and 628A (Geological Survey, Canada) on a mile to an inch scale. The T e r t i a r y rocks were divided into a lower sedimentary unit, the Springbrook Formation, o v e r l a i n by a suc-cession of lavas, the Marron Formation, o v e r l a i n i n turn by volcanic rocks and f l u v i a l and la c u s t r i n e sediments, White Lake Formation, and an upper unnamed volcanic and sedimentary sub-unit. Cairnes (1937) presented an account of the mineral deposits of the K e t t l e River area, west h a l f ; map 538A (Geological Survey, Canada) by Cairnes shows Bostock's geology of the White Lake area unmodified. Map 15-1961 (Geological Survey, Canada) by L i t t l e , amplifies the s t r u c t u r a l data of the area. Other information r e l a t i v e to the geology of the White Lake area stems from t h e s i s - s t u d i e s : concerning Marron volcanic rocks - Paterson (1960) B.Sc, Church (1963) M.Sc., Bird (1965) B.Sc., concerning White Lake sediments Ward (1964) B.Sc. The d i s t r i b u t i o n of T e r t i a r y bedded rocks of c e n t r a l and southern B r i t i s h Columbia and northwestern Washington state i s shown i n Figure 1.3. Geological information on t h i s region i s provided by many authors. Dawson (1896) gave a d e t a i l e d d e s c r i p t i o n of T e r t i a r y rocks i n the Kamloops area. This work was reviewed and brought up to date by C o c k f i e l d (1948). The most recent d e s c r i p t i o n of the T e r t i a r y succession at Princeton was given by H i l l s (1961). Daly (1912) f i r s t described the K e t t l e River sediments and Midway volcanic rocks near the v i l l a g e of Midway. Recently, L i t t l e and Monger (1966) revised and added to t h i s work. T e r t i a r y rocks, s i m i l a r to those near Midway, occur i n the Beaverdell area and were described by Reinecke (1915) . Drysdale (1915) reported on K e t t l e River type sediments and Midway type volcanic rocks at F r a n k l i n camp. Also, i n Washington state, s i m i l a r rocks occurring near the town of Republic were mapped and described by Parker and Calkins (1964), and Staaz (1964) Other works applicable to the T e r t i a r y rocks of the region are referred to i n following sections. FIELD WORK F i e l d work was done i n t e r m i t t e n t l y between October 1963 and September 1965; a t o t a l of 1\ months were required to complete the map-ping program. Previous to t h i s , the author v i s i t e d the area i n July 1959 while employed by the Geological Survey of Canada and again i n May 1963 to log d r i l l core on the Dominion Observatory S i t e . Also, volcanologist Howel Williams and o f f i c i a l s of the Anaconda American Brass Co. accompanied the author on a t r i p through the area i n August 1966. F a c i l i t i e s of the Geology F i e l d School of University of B r i t i s h Columbia were used during the summer of 1965. This reduced costs and added greatly to e f f i c i e n c y of the f i e l d work. Reconnaissance mapping was completed on the scale of approxi-mately 3,000 feet to one inch, boundaries of geological units being interpolated between points of i n t e r s e c t i o n on traverses with the aid of lineaments v i s i b l e on a i r photographs (see map 100). Figure 1.2 shows the p o s i t i o n of reconnaissance traverses i n the map-area. Also, a d e t a i l outcrop map, covering about eight square miles on the scale of one inch to 500 feet, was prepared f o r part of the geologically complex area east of White Lake (see map 200). Geographic positions were transferred from photographs to topographic maps using altimeter readings and r a d i a l - l i n e p l o t s . GEOLOGICAL SETTING The d i s t r i b u t i o n of early T e r t i a r y bedded deposits of south-western B r i t i s h Columbia and northern Washington state i s shown i n Figure 1.3. These deposits occur as scattered erosional remnants of what was probably a once continuous b e l t composed mainly of volcanic rocks extending from at least c e n t r a l Washington through the I n t e r i o r to c e n t r a l B r i t i s h Columbia. S p e c i f i c ages are few, however, Mathews (1964) assigned a Middle Eocene age for deposits within 110 miles of the White Lake area; Figure 1.2 Plot of Reconnaissance Traverses in Map-area to the north, near Kamloops, 45 to 47 m i l l i o n years; to the west, near Princeton, 48 m i l l i o n years; to the east, near Midway, 48 to 49 m i l l i o n years. Fourteen age-determinations on rocks from the Princeton and Kamloops areas, by H i l l s and Baadsgaard (personal communication 1966) range from 47 to 51 m i l l i o n years. The age of a vertebrate f o s s i l found i n the Princeton area, determined by Russell (1935), agrees well with the above potassium-argon determinations. T i l t i n g and, i n places, f o l d i n g of these rocks are commonly suf-f i c i e n t to d i s t i n g u i s h them from younger T e r t i a r y units which are almost everywhere f l a t l y i n g . Mathews (1964) gives ages 10, 12, and 13 m i l l i o n years for some of these younger rocks northwest of Kamloops. Basal T e r t i a r y rocks are t y p i c a l l y coarse breccias and conglo-merates. In many places these are o v e r l a i n by volcanic beds with l o c a l i n t e r d i g i t a t e d f l u v i a l and l a c u s t r i n e sediments. In the Princeton and Kamloops areas, early T e r t i a r y v o l c anic rocks are commonly dark coloured, probably of andesitic or b a s a l t i c composition, whereas, i n the southern Okanagan area and near Midway these rocks are generally l i g h t coloured having varied composition of acid or intermediate character (see Figure 1.4). Detailed data are scarce but regional studies show that these s t r a t a are r a r e l y more than a few thousand feet thick. Carr (1962) emphasizes the tensional character of structures i n southwestern B r i t i s h Columbia and northern Washington state. Figure 1.5, taken from Carr's report, shows a f a n - l i k e system of grabens r a d i a t i n g from an area covered by Columbia River basalts i n c e n t r a l Washington. White Lake area l i e s between the northerly-trending Republic graben, to the southeast, and the northwesterly-trending Methow and Chiwaukum grabens, to the west and southwest. Extensive areas of T e r t i a r y rock are downfaulted i n Republic and Chiwaukum grabens; however, Methow and other grabens to the north contain l i t t l e T e r t i a r y rock and are possibly Mesozoic structures. Carr also outlines the p o s i t i o n of northwesterly-trending T e r t i a r y grabens, not previously shown on government survey maps, i n areas near Princeton and Kamloops. According to Bailey et a l . (1966) tensional conditions and u p l i f t p revailed a f t e r Laramide thrusting and molasse-type deposition cased, during Paleocene times, i n the Rocky Mountain area of southeastern B r i t i s h Columbia and adjacent parts of A l b e r t a . U p l i f t was accompanied by large scale ' l i s t r i c normal' f a u l t movement which was instrumental i n formation of many l o n g i t u d i n a l l y oriented v a l l e y s of i n t e r i o r B r i t i s h Columbia. These v a l l e y s became important drainage routes to the P a c i f i c Ocean and favourable s i t e s for early T e r t i a r y deposition. Figure 1.6 shows the l o c a t i o n and cross-section of two ' l i s t r i c normal' f a u l t bounded basins near White Lake map-area. Figure 1.3 Location of Early Tertiary Bedded Rocks Figure 1.4 Refractive Index Frequency for Lavas in White Lake, Kelowna, and Midway Areas r h y o l i t e Refractive Index (Class i n t e r v a l f o r histogram i s R.I. 0.010) basalt after Church, 1963 Figure 1.5 Grabens of Southwestern Brit ish Columbia and Northern Washington State a f te r Carr, 1962 Figure 1.6 Listric Normal Faults in South-Central, B.C. M O 50 Location Map White Lake map-area 49 120 Structure Section (after Bally etal., 1966) Okanogan R. Kettle R early Tertiary deposits m.s.l. 16,000' 32,000' Arrow L pre-Tertiary metamorphic rocks Scale 0 10 miles CHAPTER II GENERAL GEOLOGY AND STRUCTURE The main object of t h i s chapter i s to set f o r t h the stratigraphy and structure of the T e r t i a r y rocks of the White Lake area i n more d e t a i l than previously offered. Discussion covers d i s t r i b u t i o n , thickness, l i t h o l o g y , l o c a l and regional s t r u c t u r a l r e l a t i o n s and c o r r e l a t i o n of rock u n i t s . B r i e f reference i s made to pre-Tertiary rocks and g l a c i a l geology. PRE-TERTIARY ROCKS Pre-Tertiary rocks are exposed i n several small areas mainly at the margins of the map-area. According to Bostock (1941), these are T r i a s s i c or older metasedimentary and metavolcanic rocks. South of the map-area they are extensively intruded by Cretaceous and some Jur a s s i c granites, granodiorites, and syenites (Cannon, 1966). Also, i n places, they are cut by pulaskite dikes, probably T e r t i a r y age. The Shoemaker Formation, mainly dark grey chert., and Old Tom Formation, mainly greenstone, are int e r l a y e r e d units well exposed i n area about a mile west of Yellow Lake and south along Highway 3, and i n t h e the area south of D o r f l e r Ranch. Old Tom rocks are also exposed on the west wall of Okanagan v a l l e y about one mile north of Green Lake. A small window of Shoemaker Formation, showing through T e r t i a r y rocks, i s located about three-quarters of a mile northwest' of Mahoney Lake. The Vaseaux Formation i s exposed i n southeast corner of the map-area near Mahoney Lake and immediately west of Highway 97, one and one-h a l f miles south of Okanagan F a l l s . These rocks are probably older than the Old Tom and Shoemaker rocks and consist mainly of s i l i c e o u s and p h y l l i t i c gneiss and some s c h i s t . TERTIARY ROCKS The present study leads to several important modifications of Bostock's (1941) seven-fold d i v i s i o n of T e r t i a r y rocks (map 621k, Geol. Survey, Canada). Bostock's scheme i s as follows: 7 -Unnamed conglomerate 6 -Unnamed agglomerate, conglomerate IS 5 -Unnamed and e s i t i c b r e c c i a , t u f f , and agglomerate 4 -White Lake Formation: conglomerate, sandstone, and shale; coal; t u f f , agglomerate, br e c c i a 3 -Marron Formation: mainly basalt and andesite; more fe l d s p a t h i c lavas i n northern part of map-area; related b r e c c i a , agglomerate, and t u f f ; conglomerate. 2 -Unnamed coarse granite porphyry, coarse feldspar porphyry 1 -Springbrook Formation: mainly conglomerate; shale, sandstone, t u f f , talus deposits. Table 2.0 shows a revised scheme based on f i v e - f o l d d i v i s i o n of the rocks (see map 100). Bostock's Springbrook Formation '1' and White Lake Formation '4' are retained with only minor changes i n d e s c r i p t i o n . Unit '2' i s not observed i n the map-area and, therefore, i s dropped from the Table of Formations. The name Marama Formation i s newly applied to rocks, mainly rhyodacite and r h y o l i t e , equivalent to the upper part of Bostock's Marron Formation '3' but found to be unconformable on the older succession. The Marron Formation, as now defined, consists of f i v e conformable volcanic members bounded below by the Springbrook Formation and above by the Marama Formation. The name Skaha Formation i s newly applied to conglomerate and volcanic rocks, units '6' and '7' of Bostock's scheme, and interbedded s l i d e b r e c c i a not recognized by Bostock. 1. BASAL TERTIARY SURFACE The basal T e r t i a r y surface i n the map-area appears to be markedly warped and f a u l t e d . The form of t h i s surface, according to the writer's i n t e r p r e t a t i o n , i s shown i n Figure 2.1. Structure contours are based on topographic data and estimated thicknesses of the volcanic and s e d i -mentary p i l e . Also, information obtained from a v e r t i c a l diamond d r i l l hole, 2,000 feet deep, located about three-quarters of a mile north of White Lake, provides some contour co n t r o l . The surface i s generally t i l t e d i n an ea s t e r l y d i r e c t i o n . Its r e g u l a r i t y i s broken by an east-trending syncline i n the east-central part, and a southeast-trending a n t i c l i n e i n the north part of the map-area. Also, near the east and southeast margins of the map-area, the surface i s truncated abruptly by gravity f a u l t s of the Okanagan system which generally show westerly or northerly downthrow. Where f a u l t s pass Table 2.0 T e r t i a r y Formations 16 Thickness Range i n Feet SKAHA FORMATION Upper member 0 to 600 es s e n t i a l l y a fanglomerate unit with large boulders and blocks of T e r t i a r y and pre-Tertiary rock Lower member 0 to 300 mainly s l i d e b r e c c i a with some i n t e r c a l a t e d con-glomerate and te p h r i t e (augite-porphyry) WHITE LAKE FORMATION Upper member 0 to 300 mainly l i g h t coloured p y r o c l a s t i c rocks, v o l c a n i c breccia (Indian Head breccia) and some sediments and tep h r i t e (augite-porphyry lava) Middle and lower members 0 to 3500 consi s t i n g of i n t e r d i g i t a t e d deposits, sediments (White Lake sediments) composed of vol c a n i c sand-stone, conglomerate, and some coal; and v o l c a n i c rocks (White Lake v o l c a n i c rocks) composed of feldspar-porphyry lavas, lahars, and pyroclastic, rocks MARAMA FORMATION Not subdivided 0 to 1000 predominantly r h y o l i t e and rhyodacite lava with some p y r o c l a s t i c rocks and l o c a l basal conglomerate MARRON FORMATION Park R i l l Andesite Member 200 to 1500 mainly merocrystalline and glassy lava Rosette-Porphyry Member 400 to 1000 mainly trachyte and trachyandesite lava B a s a l t i c Andesite Member 0 to 400 mainly pyroxene-rich v e s i c u l a r lava Clot-Porphyry Member .. mainly trachyte and trachyandesite lava 1000 Yellow Lake Porphyry Member 500 to 1800 mainly anorthoclase-, augite-porphyry lavas (phonolites) and p y r o c l a s t i c rocks SPRINGBROOK FORMATION Not "subdivided 0 to 700 mainly boulder conglomerate overlying v a l l e y talus with fragments of underlying pre-Tertiary rocks 17 s u b p a r a l l e l to structure contours, the general slope of the surface i s l o c a l l y increased or decreased depending on the d i r e c t i o n of downthrow. The base of T e r t i a r y s t r a t a northeast of White Lake and east of Skaha Lake i s estimated to be near -5,500 feet (m.s.l.) and the maximum thickness to be about 8,000 feet . In comparison, Shaw (1952) shows that rocks of s i m i l a r age i n a b a s i n - l i k e structure near Princeton have a base about -400 feet (m.s.l.) and a thickness about 3,000 feet . 2. DETAILED DESCRIPTION OF FORMATIONS A. SPRINGBROOK FORMATION The Springbrook Formation was named and described by Bostock (1941) i n marginal notes appended to Maps 627A, 628A, and 341A, G.S.C. The following d e s c r i p t i o n i s on Map 627A: "The Springbrook formation rests on a pre-Tertiary rock surface of steep r e l i e f . I t i s composed of s o i l s , alluvium, t a l u s , stream and lake deposits and tuffaceous materials that accumulated i n the v a l l e y s before and during the e a r l y extrusions of the Marron volcanic rocks. Where the Springbrook formation i s thick, the basal beds are of conglomerate containing large angular boulders. These beds grade upward into conglomerates composed of smaller, more rounded and better sorted materials. Uppermost s t r a t a include beds of polished pebbles, tuffaceous sandstones and s i l t s . " a. D i s t r i b u t i o n and Thickness The Springbrook Formation i s exposed only on the western extremity of the map-area and immediately north of Mahoney Lake i n the southeast corner of the map-area (see Map 100 and Plate 2.1). The thickness of Springbrook sediments varies markedly over short distances. Beds about 700 feet thick are exposed on b l u f f s 2 miles west of Green Ranch, whereas, three-quarters of a mile west of Yellow Lake, the beds are only 200 feet thick, and immediately south of southwest corner of the map-area, younger T e r t i a r y rocks rest d i r e c t l y on p r e - T e r t i a r y formations. Bostock's maps show about 60 percent of the exposed basal T e r t i a r y unconformity i n the region to be d i r e c t l y o v e r l a i n by the Springbrook Formation and 40 percent by younger T e r t i a r y rocks. 18 Plate 2.1 Springbrook Formation, i n west part of ma area south of Highway 3 20 b. Lithology A summary of data from the s t r a t i g r a p h i c section of lowest T e r t i a r y beds 2 miles west of Green Ranch i s given i n Table 2 . 1 (see Plate 2 . 2 ) . The base of the Springbrook Formation, at th i s l o c a t i o n , i s established at el e v a t i o n 2 , 1 5 0 feet where a small knob of br e c c i a and conglomerate rests on massive black chert of the pre-Tertiary Shoemaker Formation. A rough estimate of the compostion of the basal sediment gives: 7 0 7 o f e l d s p a r - r i c h andesite (probably Old Tom Formation) . 2 0 7 o grgy and black chert and a r g i l l i t e (Shoemaker F.). 1 0 7 , c h l o r i t e s c h i s t and other u n i d e n t i f i e d fragments. The top of Springbrook Formation here i s close to elevation 2 , 8 5 0 feet. The uppermost, about 2 5 0 feet thick, i s a well-bedded, c l i f f - f o r m i n g unit c o n s i s t i n g of alternate layers of large-pebble and small-pebble conglomerate with a few scattered boulders. Beds range from several inches to tens of feet thick. They are nearly h o r i z o n t a l low i n the section but dip as much as 2 2 degrees east near the top, suggesting giant cross-bed or slump structure. Data from analysis of a sample of conglomeratic sandstone from upper part of Springbrook beds (disaggregated by acid treatment f o r carbonate cement) are given i n Figures 2 . 2 and 2 . 3 . S i z e - s o r t i n g c o e f f i c i e n t (S\ (Folk, 1 9 6 1 ) i s found to be 1 . 8 0. This i s c l a s s f i e d as poorly sorted but f a l l s within the range 0 . 4 0 to 2 . 5 0 quoted f o r r i v e r sediments. The composition i s bimodal c o n s i s t i n g of about two-thirds buff coloured weathered feldspar and clay minerals and one-third grey chert and quartz. Accessory heavy minerals include epidote, apatite, ilmenite, and magnetite. c. Structure In the western part of the map-area Springbrook beds (dipping 1 0 to 1 5 degrees east) are overlain, with some angular unconformity, by Marron volcanic rocks (dipping 0 to 5 degrees east). It i s probable, however, that t h i s unconformity represents only a short time i n t e r v a l because the contact between the two formations i s generally smooth (see Plate 2 . 3 ) . Table 2.1 Summary of Lithology of Springbrook Formation and Lower Marron Formation (Location, Two Miles West of Green Ranch) El e v a t i o n i n Feet Description Formations , (m.s.l.) 3720 -- base of b l u f f and top -- a n a l c i t e porphyry of section mainly -- anorthoclase-augite lava Lower Part of porphyry; some Marron F. columnar j o i n t i n g 3200 -- contact _ _ _ _ _ _ _ _ -- augite porphyry brec.-.' mainly coarse c i a ; hoodoo s t r u c t - p y r o c l a s t i c ures rocks minor angular 2850 -- contact - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - unconformity -- well-bedded conglomerate; dips range from zero to Springbrook F. 22 east 2550 - - _ - - - _ - - - - - _ - - - - possible f a u l t poor 2390 - _ _ - _ _ _ _ - - _ _ _ _ _ _ _ chert breccia great o i c n exposure ° £ 2150 -- contact - - - - - - - - - - - - - - - - - - - - - r - - unconformity 1980 -- base of exposure massive black chert Shoemaker F. Plate 2.2 Springbrook beds, two miles west of Green Ranch Figure 2.2 Grain Analyses of Springbrook Sediment (A Typical Conglomeratic Sondstone) A. Size Frequency Histogram B. Composition of Sand Fraction -4 -3 -2 - i o I 2 Grain Size (Phi Scale) Wt.% 40 -altered feldspar quartz 30 -- 20 -10 -3 4 2.45 2.50 2.55 2.60 Specific Grovity 2.65 2.70 Figure 2.3 Size Frequency Cumulative Curve of Springbrook Sediment Typical Conglomeratic Sandstone) 0 Grain Size (Phi Scale) 2* d. Age Bostock published c o n f l i c t i n g information on the age of the Springbrook Formation. On map 628A (G.S.C.), he indicates thatuthe:_upper beds "contain plants of early T e r t i a r y , perhaps Paleocene age"; on map 341A (G.S.C.) he states that "these beds contain plants of presum-ably late Eocene age." Although both maps were published i n 1941, the former (628A) has a higher series number and i s , therefore, considered to be Bostock's most recent i n t e r p r e t a t i o n . U n t i l a more comprehensive study i s made, however, the present author t e n t a t i v e l y assigns middle Eocene age to the Springbrook Formation i n keeping with K-Ar dates obtained on s i m i l a r rocks i n southern B r i t i s h Columbia (Mathews, 1964). e. C o r r e l a t i o n The following basal T e r t i a r y sedimentary units of the region are t e n t a t i v e l y c o r r e l a t e d with the Springbrook Formation: Kettle River Formation (Daly, 1912; Midway area). Curry Creek Formation (Reinecke, 1915; Beaverdell area). Coldwater Formation (Dawson, 1878; Kamloops area). Allenby Formation (Rice, 1952; Princeton area). O'Brien Creek Formation (Muessig, 1962; Republic area). The K e t t l e River Formation i s one of the most widely d i s t r i b u t e d u n i t s . It was recently redescribed by L i t t l e and Monger (1966, p. 67): "The Ke t t l e River Formation of Middle Eocene age unconformably o v e r l i e s -- (pre-Tertiary rocks) --, and consists of a discontinuous basal conglomerate, above which i s a white to buff, l o c a l l y plant-bearing, arkosic sandstone, s i l t s t o n e , and minor shale and conglomerate, a l l l a r g e l y derived from acid volcanic and g r a n i t i c rocks. The sedimentary rocks grade upward into a grey-green volcanic sandstone, gradational with, and i n part con-temporaneous with, the lower part of -- (Midway lavas) -Nowhere i n the map-area does the Ket t l e River Formation appear to be missing, with overlying -- (Midway lavas) -- r e s t i n g d i r e c t l y upon basement, although i t shows considerable v a r i a t i o n i n thickness, from at le a s t 1,500 feet i n the northwest of the map-area, where i t i s coarse and conglomeratic, to a few hundred feet i n the east-central part of the map-area." Although the Ket t l e River Formation i s l i t h o l o g i c a l l y d i f f e r e n t , containing large volumes of fine-grained sediment not present i n the Springbrook Formation, these units are probably of s i m i l a r age since both are o v e r l a i n d i r e c t l y by thick deposits of markedly s i m i l a r volcanic rocks. 26 B. MARRON FORMATION The name Marron Formation was applied by Bostock (1941) to the early T e r t i a r y volcanic rocks underlying a large area i n the central part of combined 15 minute quadrangle maps, O l a l l a , B.C. (G.S.C. map 628A) and Okanagan F a l l s , B.C. (G.S.C. map 621k). His b r i e f d e s c r i p t i o n of these rocks on map 627A i s as follows: "The volcanic rocks of the Marron formation were extruded over h i l l s of pre-Tertiary rocks into v a l l e y s part-l y f i l l e d by the Springbrook 'formation. They f i l l e d these v a l l e y s and accumulated to a thickness over 4,000 feet and are believed to have covered a l l parts of the map-area. The formation consists mainly of lava flows 10 to 200 feet thick, but i n places there are large masses of agglomerate. In the northeast part of the map-area the lower flows are highly f e l d s p a t h i c . To the northwest some fine grained acid types were observed. In places, notably northwest of White Lake, there are thi n interbeds of conglomerate, sandstone and s o i l . " Mapping by the wr i t e r provides the basis for a s i x - f o l d d i v i s i o n of these rocks. The name Marron Formation i s used i n th i s study i n reference to the lowest f i v e d i v i s i o n s (members), a succession of con-formable or nearly conformable beds. The type-section of the Marron Formation i s located near Yellow Lake, p a r a l l e l to structure cross-section A-B (see map 100). At the base of this section, 0.8 miles west of Yellow Lake at elevation 3,000 feet, the lowermost member of the Marron Formation rests with s l i g h t angular unconformity on Springbrook conglomeratic beds (see Plate 2.3). At the top of the section, 0.7 miles west of 'B' at 3,700 feet, lavas of uppermost member of Marron Formation are ov e r l a i n unconformably by younger v o l c a n i c rocks. (In the type-section, Marron rocks dip 5 to 25 degrees e a s t e r l y . The aggregate thickness of the s t r a t a i s about 5,000 feet.) In the type section the lowermost Marron unit, here termed the 'Yellow Lake porphyry member', i s well exposed near 'A' (see map 100). At 0.8 miles west of Yellow Lake and elevation 3,000 feet, these rocks rest on the Springbrook Formation; at elevation 4,400 feet i n the same area, the Yellow Lake porphyry member i s ov e r l a i n by the 'clot-porphyry member' (see Plate 2.6). Clot-porphyry rocks are exposed i n the type-section between 'A', at elevation 4,600 feet, and at a point 2.5 miles west of 'B' at elevation 2,700 feet. The 'Basaltic andesite member' i s a r e l a t i v e l y t h i n unit near the middle of the Marron succession and 27 Plate 2.3 Contact between Marron and Springbrook beds, near Yellow Lake i s exposed about a h a l f mile east of Yellow Lake midway between points 'A' and 'B'. Younger rocks, here termed the 'rosette-porphyry member', are present near Trout Lake cropping out i n the area 0.5 to 1.8 miles east of Yellow Lake i n A-B section. The 'Park R i l l andesite member', the uppermost unit of the Marron Formation o v e r l i e s rosette-porphyry rocks one mile west of 'B' at an elevation of 3,300 feet and i s over-l a i n by a younger volcanic formation 0.7 miles west of 'B' at elevation 3,700 feet . The r e f r a c t i v e index of glass prepared from powdered rock samples i s h e l p f u l i n d i s t i n g u i s h i n g lavas c h a r a c t e r i s t i c of various Marron members. These data are shown i n Figure 2.Li. Complete chemical analyses of these rocks, including some data on minor elements, are tabulated i n Appendix 'A', and de t a i l e d petro-graphic descriptions are given i n Appendix 'C. Yellow Lake Porphyry Member The name Yellow Lake porphyry member i s applied to a l k a l i - r i c h Volcanic rocks that form the lowermost unit of the Marron Formation. ('Porphyry' i s used as a text u r a l term with no inference concerning the structure of the rocks.) The petrography of these rocks i s b r i e f l y described by Church (1963) and more f u l l y by Bird (1965). a. D i s t r i b u t i o n and Thickness Yellow Lake porphyries are well exposed on b l u f f s i n the western extremity of the map-area, i n the north near Marron Lake and the switchback i n Highway 3, and i n the southeast part of the map-area, near Mahoney Lake. Although these rocks form only about 10 percent of the t o t a l rocks exposed, probably they underlie an a d d i t i o n a l 80 percent of the map-area. The thickness of th i s member v a r i e s . Near Marron Lake and Mahoney Lake, i n the north and southeast parts of the map-area respec-t i v e l y , the unit i s at le a s t 1,000 feet thick. In the western part of the map-area the thickness varies from about 1,800 feet, near the west end of Yellow Lake, to about 500 feet, 1.5 miles northwest of Yellow Lake. 29 b. Lithology The appearance of these rocks varies greatly within the map-area but most, i f not a l l v a r i e t i e s can be broadly c l a s s i f i e d as anorthoclase-augite porphyry. Many rocks contain rhomb-shaped phenocrysts of anorthoclase which may serve as a useful guide for f i e l d mapping. Near Mahoney Lake, the rocks are r e a d i l y d i v i s i b l e into two sub-units; an upper small-rhomb-porphyry lava, and a lower large-anorthoclase-augite porphyry lava and bre c c i a . The lower unit contains many xenoliths of chert, a r g i l l i t e , granite, and other p r e - T e r t i a r y rocks, and t h i n discontinuous lenses of chert pebble conglomerate. East of Marron Lake large-anorthoclase-augite porphyry lavas are observed; i n the v i c i n i t y of switchback on Highway 3 and areas immediate-l y south small-porphyry lavas are present. Near Yellow Lake the rocks are not e a s i l y d i v i s i b l e into large-and small-porphyry u n i t s . Rhomb-porphyries are poorly-developed and the lavas are l i g h t e r coloured and more amygdaloidal than those found at other l o c a l i t i e s . On b l u f f s two miles west of Green Ranch, the rocks consist of about 350 feet of volcanic b r e c c i a o v e r l a i n by about 600 feet of lavas. In places these rocks are cut by columnar jointed rhomb-porphyry dikes. Where the rocks are amygdaloidal, as near Yellow Lake, they contain much c a l c i t e , n a t r o l i t e , some thomsonite, and, r a r e l y , brews-t e r i t e . Cracks and f i s s u r e s contain c a l c i t e , laumontite-leonhardite, and mordenite. The major oxide-composition of two specimens from Yellow Lake porphyries i s shown i n Table 2.2. The composition of average rhomb-porphyry rock published by Daly (1933) i s s i m i l a r to these analyses. Clot-Porphyry Member The clot-porphyry member consists of feldspar-porphyry lavas and minor p y r o c l a s t i c rocks, mainly of t r a c h y t i c and trachyandesitic composition, conformably overlying Yellow Lake porphyry member (see Plate 2.6). 30 Table 2.2 Composition of Yellow Lake Porphyries 1 2 3 SiO 56.8 55.2 57.9 A1„0, 22.6 21.9 20.6 Fe6 5 5.3 5.5 4.7 MgO 1.0 2.5 1.2 CaO 4.7 5.0 2.8 Na 0 6.5 4.9 7 .8 K 2 d 3.1 5 .0 5.0 1. Columnar rhomb-porphyry dike, N64-B, ( s t a t i o n no.l, map 100) 2. Small rhomb-porphyry lava, N64-20-K, ( s t a t i o n no.2, map 100) 3. Average composition of rhomb-porphyry lava, Daly (1933) ( t o t a l i r o n i s calculated as FeO) Plate 2.4 Blocky top of rhomb-porphyry lava flow 32 a. D i s t r i b u t i o n and Thickness Clot-porphyry rocks are extensively exposed i n the western part of the map-area, p a r t i c u l a r l y on mountain-tops and r i d g e - c r e s t s . Smaller areas of exposure are to be seen at the north end of Marron Lake, near the junction of Highways 3 and 97 and to the south, and on the h i l l side west of K i t l e y Lake and the low h i l l s and v a l l e y s to the southeast. Other exposures of t h i s unit are found west and northwest of Mahoney Lake (see map 100). Approximately three-quarters of the map-area i s underlain by c l o t -porphyry rocks at varying depth, but less than 15 percent contains exposed rocks of t h i s unit. The clot-porphyry member has a more or less uniform thickness of about 1,000 feet. b. Lithology Clot-porphyry rocks form conspicuous, thick lava flows i n the lower part of the Marron Formation. In the western part of the map-area, where best exposed, the rocks are t y p i f i e d by v e r t i c a l s l a b - l i k e p i l l a r s which l o c a l l y form c l i f f s more than 100 feet high (see Plate 2.5). Lavas are commonly non-vesicular and yellowish where fresh; where badly weathered, they are mottled with brownish-red hues or dark grey with bleached white feldspar phenocrysts. The most widely d i s t r i b u t e d type of clot-porphyry rock contains discr e t e tabular c r y s t a l s and polygonal c l u s t e r s of feldspar phenocrysts measuring 3 to 6 millimeters i n diameter, some small pyroxene grains, and few b i o t i t e flakes embedded i n f i n e c r y s t a l l i n e matrix. Plagioclase i s the dominant feldspar but sanidine i s abundant i n some rocks, occur-r i n g as d i s c r e t e glassy laths or forming jackets on p l a g i o c l a s e . West of Mahoney Lake, the upper part of the formation i s a ' c l o t -l a t h porphyry' about 400 feet thick. This rock contains both laths and anhedral c l o t s of feldspar 2 to 6 millimeters i n diameter set i n a buff coloured, m i c r o - c r y s t a l l i n e matrix. Ferromagnesian minerals are v i r t u a l -l y absent. Also, at t h i s l o c a l i t y , the lower part of the formation consists of a t h i n zone of small-feldspar-porphyry. The rock i s characterized by a high content of small equant c r y s t a l s and c l u s t e r s of feldspar phenocrysts, 33 Plate 2.5 Slabby p i l l a r s , clot-porphyry lava 3U 2 to 4 millimeters i n diameter, embedded i n a fine-grained matrix. Many fractures i n the clot-porphyry rocks contain f i l l i n g s of c a l c i t e , some laumontite-leonhardite, and r a r e l y heulandite. Major oxide compositions of two clot-porphyry rocks, given i n Table 2.3, are bracketed by Daly's average trachyte and trachyandesite. B a s a l t i c Andesite Member B a s a l t i c andesite occurs, with apparent conformity, near the middle part of the Marron succession. a. D i s t r i b u t i o n and Thickness Although widely d i s t r i b u t e d , the b a s a l t i c andesite i s poorly exposed; outcrops form less than 2 percent of the t o t a l map-area. The largest area of exposure i s found on v a l l e y slopes south of T.L. Ranch; small exposures may be seen east of Yellow Lake and near Mahoney Lake (see map 100). The unit attains i t s maximum thickness, about 400 feet, west of Mahoney Lake. b. Lithology The unit consists mainly of b a s a l t i c andesite lava and flow breccia, commonly dark brown and markedly v e s i c u l a r . Most rocks contain abundant pyroxene phenocrysts and a few scattered laths of p l a g i o c l a s e . B a s a l t i c andesite i s e a s i l y weathered and eroded. Areas underlain by t h i s unit are generally low l y i n g and covered with a brown, granular r e g o l i t h . Most v e s i c l e s are f i l l e d with c h l o r i t e , some chalcedony, and minor c a l c i t e . F i r e opal found north of the map-area probably occur i n these rocks. Rosette-Porphyry Member The rosette-porphyries are chemically s i m i l a r to the c l o t -porphyries (trachyte and trachyandesite) but d i f f e r i n texture and s t r a -t i c g r a p h i c p o s i t i o n . They form the upper middle part of Marron Formation overlying the b a s a l t i c andesite unit with apparent conformity. Table 2.3 Composition of Clot-Porphyries 35 SiO A l 0-FeO MgO CaO Na 0 K„0 58.4 19.9 5.1 1.9 4.8 4.7 5.2 63.3 16.8 3.9 1.5 4.0 10.5 59.9 17 .9 7 .0 1.3 4.3 5.9 3.7 62.1 18.2 5.2 1.1 3.1 4.5 5.8 1. Feldspar porphyry, N64-21-5, ( s t a t i o n no.4, map 100) 2. Feldspar porphyry, CC-5, ( s t a t i o n no.5, map 100) 3. Average composition of trachyandesite, Daly (1933) 4. Average composition of trachyte, Daly (1914) ( t o t a l i r o n i s c a l c u l ated as FeO) 36 a. D i s t r i b u t i o n and Thickness Rosette-porphyry beds are exposed continuously for several miles on slopes southeast and north of T.L. Ranch, between points 0.5 and 3.5 miles east of Yellow Lake on Highway 3 and adjacent slopes, and on northeast-facing slopes located south of Highway 3 i n l i n e between Marron Lake and Prather Lake. Rosette-porphyry underlies roughly h a l f of the map-area, though less than 15 percent i s outcrop. Rosette-porphyry, about 1,000 feet thick, i s exposed on b l u f f s north of T.L. Ranch; i n a few places west of Mahoney Lake the unit appears to be less than 200 feet thick. b. Lithology Rosette-porphyries form b l u f f and bench-topography i n cent r a l part of the map-area where the thickest deposits are observed. B l u f f s vary i n height from 50 to more than 200 feet, each corresponding appro-ximately to the thickness of one or more lava flows. These rocks are commonly yellowish, where fresh, nonvesicular, and contain scattered small phenocrysts of pyroxene and r a d i a t i n g plagioclase glomerophenocrysts set i n a fine c r y s t a l l i n e matrix. Some flows contain minor b i o t i t e and sanidine. Most of the rocks are homogeneous; constituent minerals varying only s l i g h t l y i n composition and abundance. P y r o c l a s t i c deposits are generally t h i n and discontinuous; how-ever, near Prather Lake the unit contains abundant agglomerate and some t u f f . In places west of Mahoney Lake, rosette-porphyries are intermixed with l i g h t coloured, aphanitic volcanic breccias. The chemical composition of rosette-porphyry i s s i m i l a r to Daly's average analyses of t r a c h y t i c lavas (see Table 2.4). Park R i l l Andesite Member The name Park R i l l andesite i s applied to the uppermost member of the Marron Formation which rests conformably on the rosette-porphyry member (see Plate 2.7). The rock i s d i s t i n c t from the b a s a l t i c andesite unit i n 37 Table 2.4 Composition of Rosette-Porphyries 1 2 3 SiO 59.4 A l 0 18.9 FeO 5.0 MgO 1.1 CaO 4.3 Na„0 4.6 K„0 6.7 59.9 62.1 17.9 18.2 7.0 5.2 1.3 1.1 4.3 3.1 5.9 4.5 3.7 5.8 1. Rosette-porphyry lava, N64-24-2 ( s t a t i o n no. 6, map 100) 2. Average composition of trachyandesite, Daly (1933) 3. Average composition of trachyte, Daly (1914) ( t o t a l i r o n is c alculated as FeO) 38 s t r a t i g r a p h i c p o s i t i o n , t e x t u r a l appearance, and probably chemical com-po s i t i o n , (see Figure 2 .h) . a. D i s t r i b u t i o n and Thickness Park R i l l andesites are exposed mostly i n the c e n t r a l and southern parts of the map-area. Thick deposits are to be seen on slopes west and south of Stewart Ranch and west and east of Dor f l e r Ranch near Park R i l l . A r e l a t i v e l y t h i n but continuous deposit crops out high on the north flank of the h i l l between Prather Lake and T.L. Ranch. Other important exposures are present near Mahoney Lake, on the ridge east of Prather Lake, and southwest of Marron Lake (see map 100). The l a t e r a l extent of the Park R i l l andesite amounts to about 30 percent of the map-area, but less than h a l f of t h i s area i s occupied by bed-rock exposure. The unit varies markedly i n thickness. Near the south boundary of the>map-area and east of Prather Lake, these beds are about 1,500 feet thick, but only 200 feet thick on the h i l l side west of K i t l e y Lake. b. Lithology The Park R i l l andesite i s mostly dark brown, nonvesicular lava. The unit i s generally massive, and i n d i v i d u a l flows are distinguished only with d i f f i c u l t y . The rock i s t y p i c a l l y merocrystalline, containing about equal parts glass and c r y s t a l s measuring about one millimeter i n diameter. A phase of t h i s unit cropping out south and on the ridge east of Prather Lake i s e s p e c i a l l y glassy; some specimens containing less than f i v e percent c r y s t a l s . The composition of Park R i l l andesite i s comparable with that of average analyses of andesite given by Daly and Nockolds (see Table 2.5). Structure Marron rocks show important var i a t i o n s i n attitude throughout the map-area. On the west, the rocks are almost h o r i z o n t a l or dip gently east; i n the c e n t r a l and southeast parts, they underlie younger beds of the White Lake syncline; i n the north-central part, they are unwarped over a broad southeast-trending a n t i c l i n a l axis that forms a l o c a l s t r u c t u r a l high adjacent to the White Lake syncline. Table 2.5 Composition of Park R i l l Andesite 1 2 3 4 5 6 SiC-2 61.0 60.3 65.5 57.5 61.3 55 .8 AI2O3 16.2 16.4 15.9 17.3 17.8 17 .7 FeO 6.1 6.0 4.9 7.3 6.3 8.9 MgO 4.2 4.0 3.4 5.1 2.8 4.5 CaO 5.4 5.2 6.6 6.5 6.0 8.2 Na20 4.0 4.1 1 3 7 4.0 3.7 3.8 K2O 3.1 4.0 1 '7 2.3 2.1 1.1 1. Park R i l l andesite, merocrystalline lava, N64-25A-2a, ( s t a t i o n no. 8, map 100) 2. " " " " weathered lava, N64-11-15 ( s t a t i o n no. 10, map 100) 3. Park R i l l andesite, merocrystall ine lava, CC-7 (s t a t i o n no. 11, map 100) 4. Park R i l l andesite, v i t r i c lava, N64-3-1 (s t a t i o n no. 9, map 100) 5. Average composition of andesite, Daly (1933) 6. Average composition of andesite, Nockolds (1954) ( t o t a l iron is calculated as FeO) uo Plate 2.6 Conformable clot-porphyry and Yellow Lake porphyry lavas, north of Yellow Lake Plate 2.7 Conformable Park R i l l andesite and rosette-porphyry lavas, south of Park R i l l near T.L, Ranch la The dip of the Marron beds i n the map-area r a r e l y exceeds 30 degrees except i n areas of severe f a u l t disturbance such as west of Mahoney Lake where some beds are almost v e r t i c a l . The beds are cut by numerous f a u l t s many of which are of gravity-type and show large v e r t i c a l displacement. This i s exemplified immediately north of Yellow Lake (see Plates 2.8, 2.9, and 2.10). Here the main movement has been along three north-trending f a u l t s spaced across about a h a l f mile of gently dipping Marron beds. The t o t a l v e r t i c a l displacement i s more than 1,500 feet with r e l a t i v e downward movement on the east. In the ce n t r a l and southern parts of the map-area, s i m i l a r f a u l t s are present; here, however, the downthrows are on the west. Between south pasture of T.L. Ranch and D o r f l e r Ranch many f a u l t s run sub-p a r a l l e l to the s t r i k e of beds which dip about 30 degrees east. Relative downward displacement of beds i n up dip d i r e c t i o n causes r e p e t i t i o n of s t r a t a i n t h i s area. Between Do r f l e r Ranch and Mahoney Lake the f a u l t pattern i s somewhat complex. Here, north trending f a u l t s cut Marron beds at sharp angles. A few important f a u l t s immediately west of Mahoney Lake pass s u b p a r a l l e l to the s t r i k e of the beds causing r e l a t i v e downward displacement to the southwest. C o r r e l a t i o n and Age Marron beds are comparable with the Midway Group. Recent studies by L i t t l e and Monger (1966) of the T e r t i a r y rocks near Midway B.C. reveal much about the i n t e r n a l structure of the Midway Group. Three d i v i s i o n s composed mainly of p o r p h y r i t i c lava are recognized: a basal d i v i s i o n c o n s i s t i n g of 300 to 1,000 feet of rhomb-porphyry and related a l k a l i -r i c h rocks; a middle d i v i s i o n , 200 to 1,000 feet thick, with two parts -a lower discontinuous unit composed mainly of andesite and an upper, widespread unit composed of trachyte and trachyandesite; an upper d i v i s i o n , at least 800 feet thick, composed of andesite. This Midway succession bears a marked resemblance to the Marron Formation as shown i n Table 2.6. No s i g n i f i c a n t Midway unit i s without a Marron equivalent; however, rocks of clot-porphyry type are not recognized i n the Midway assemblage. 1*2 P l a t e 2.8 P l a t e 2.9 P l a t e 2.10 G r a v i t y f a u l t d i s p l a c e m e n t s o f M a r r o n r o c k s n o r t h o f Y e l l o w L a k e ( n u m b e r s i n d i c a t e g e o -g r a p h i c p o s i t i o n s ) Table 2.6 Cor r e l a t i o n of Marron Formation and Midway Group Marron Members Thickness Range Divisions of Midway Group Park R i l l Andesite Rosette-porphyry B a s a l t i c andesite Clot-porphyry Yellow Lake porphyry 200 - 1500 400 - 1000 0 - 400 1000 500 - 1800 800 200 - 1000 Upper D i v i s i o n andesite Middle D i v i s i o n trachyandesite andes i t e 300 - 1000 Lower D i v i s i o n rhomb-porphyries •r-hh Mathews (1964) gives two K-Ar ages for Midway rocks; 'pulaskite porphyry' 48 m i l l i o n years and Rock Creek ash 49 m i l l i o n years (Middle Eocene). Description of rocks and sample locations suggest that 'pulaskite porphyry' corresponds to Midway trachyandesite lava (equiva-lent to the rosette-porphyry member of Marron Formation); 'Rock Creek ash' immediately underlies the trachyandesite lava. Age c o r r e l a t i o n of Midway Group with volcanic rocks of the Kamloops and Princeton Groups i s established by Mathews (1964) on the basis of K-Ar work; however, d e t a i l s concerning the i n t e r n a l structure and composition of the Princeton and Kamloops deposits are unknown. C. MARAMA FORMATION The Marama Formation consists mainly of r h y o l i t i c and r h y o d a c i tic rocks. The type-section l i e s near the crest of the mountain south of Marama Creek, near point 'B' i n structure sections A-B and B-C (see map 100). At the base of type-section, 0.7 miles west of 'B' at e l e -vation 3,700 feet, Marama p y r o c l a s t i c rocks unconformably o v e r l i e Park R i l l andesite lavas. At the top of the type-section, 1.4 miles south-east of 'B' at elevation 2,700 feet, Marama lavas and flow breccias are o v e r l a i n unconformably by younger sedimentary rocks. (In the l i n e of section, the Marama rocks dip 10 to 25 degrees southeast and reach a thickness, mainly lavas, of 700 feet.) a. D i s t r i b u t i o n and Thickness The Marama Formation i s most widely d i s t r i b u t e d i n the c e n t r a l and northern parts of the map-area where they form precipitous b l u f f s several hundred feet high (see Plate 2.11). The thickest deposits cap the ridge northwest of Marama Creek, slopes north of Stewart Ranch, and the ridge northeast of Prather Lake. Other important areas of exposure are on slopes immediately west of Green Ranch near Twin Lakes, west of Skaha Lake, and east of Okanagan F a l l s . A t h i n broken b e l t of rhyodacite b r e c c i a and pebble conglomerate extends for about a mile i n an e a s t e r l y d i r e c t i o n from the main road near Dor f l e r Ranch. Also, small bodies of t h i s rock crop out near the base of the White Lake Formation northeast of the Observatory S i t e (see map 100). Two small Plate 2.11 Marama Formation, west of Highway 3 near Marama Creek U6 deposits of conglomerate and p y r o c l a s t i c rocks, 1.5 miles northeast of Prather Lake, are t e n t a t i v e l y assigned to th i s unit. The Marama Formation probably underlies about 30 percent of the map-area but less than h a l f of t h i s i s exposed below younger formations. The maximum observed thickness of the Marama Formation, on slopes northwest of Marama Creek, i s about 1,000 feet. However, beds are generally discontinuous and, i n places, younger volcanic and sedimentary rocks, such as found about 1.5 miles southeast of White Lake, rest d i r e c t -l y on Marron s t r a t a . b. Stratigraphy and Lithology The lowermost beds of the Marama Formation consist of conglomerate, minor sandstone and shale with seams of p y r o c l a s t i c rocks i n t e r c a l a t e d throughout. Such deposits, northeast of Prather Lake, are about 50 feet thick but crop out only a few thousand feet along s t r i k e . These beds rest on the clot-porphyry member of the Marron Formation and contain many pebbles of feldspar prophyry. The beds appear to be o v e r l a i n by rhyodacite v o l c a n i c b r e c c i a and massive lava to the east; contact between the units i s , however, obscured by s o i l and talus cover. Volcanic breecia and t u f f deposits form the lowermost Marama beds on the mountain slopes north of Stewart Ranch and the ridge north-west of Marama Creek. On the mountainside immediately west of Green Ranch, the lowermost beds consist of chalky white p y r o c l a s t i c accumulations and r h y o l i t e lava. Thick rhyodacite lavas constitute the upper part and bulk of the Marama Formation. Generally, the rocks are varicoloured i n shades of grey, l i g h t brown, and cream. Some weathered, l i g h t brown phases of rhyodacite resemble v i t r i c Park R i l l andesite, but determinations on glass beads show much lower r e f r a c t i v e indices f o r rhyodacite than f o r andesite (see Figure 2.U). Rhyodacite i s commonly b r i t t l e , nonvesicular, and tends to cleave into t h i n plates perpendicular to bedding surface. Most of the lavas are glassy but some contain as much as 30 percent m i c r o l i t e s , mainly feldspar, some quartz, and minor pyroxene and hornblende. The chemical composition of Marama lavas agrees well with Norkold's averages f o r rh y o l i t e , and rhyodacite (see Table 2.7). Figure 2.4 Glass Bead Refractive Indices of Marron and Marama Lavas 10 10 I o 10 -o 1 g o O O Q O O o — cvi to sr m <o in in io io 10 in m Marama rhyodacite Park Ril l andes i te Rosette - porphyries Basaltic andesite 10 _Q , Clot - porphyries 10 _o i Yellow Lake porphyries Refract ive Index (Open circle is average refractive index of glass, bar represents refractive index range) U8 Table 2.7 Compos i t i o n of Marama Rocki 1 2 3 4 Si02 69.3 75.6 67 .8 74.4 A 1 2 0 3 17.5 14.9 15.9 13.8 FeO 2.3 0.6 3.9 2.0 MgO 0.1 0.1 1.6 0.3 CaO 3.0 1.2 3.7 1.1 Na 20 4.7 4.6 3.9 3.0 K2O 3.1 3.0 3.2 5.4 1. Rhyodacite lava, N64-8-9 ( s t a t i o n no. 12, map 100) 2. Rhyolite lava, N64-2-8 ( s t a t i o n no. 13, map 100) 3. Average composition of rhyodacite, Nockolds (1954) 4. Average composition of r h y o l i t e , Nockolds (1954) ( t o t a l i r o n i s calculated as FeO) U9 c. Structure Marama rocks rest with angular unconformity on the Marron Form-ation. In the ce n t r a l and southeast parts of the map-area, the Marama rocks o v e r l i e Park R i l l andesite; i n the west and northeast parts, they o v e r l i e clot-porphyry rocks. Marron beds were undoubtedly subjected to marked erosion p r i o r to deposition of the Marama rocks. In the cen t r a l part of the map-area, north of Stewart Ranch, beds vary i n dip from nearly h o r i z o n t a l at the top of the mountain to about 30 degrees southeast near the contact with younger sedimentary rocks. In t h i s area, Marama and Marron rocks are cut by north-trending normal f a u l t s , some of which show downthrow of several hundred feet to the west. Northwest of Highway 3, between Trout Lake and Marron Lake, Marama rocks dip gently east and are downfaulted i n the northeasterly trending Trout Lake graben (see Figure 2.5). Immediately east of Prather Lake, Marama Formation i s i n contact with southeasterly dipping Marron rocks along an east-trending f a u l t zone. A northeasterly dipping b e l t of Marama rocks trends northwest about 3 miles from an area of exposure east of Okanagan F a l l s to a point west of Skaha Lake near the north boundary of the map-area. These rocks are o v e r l a i n by younger beds on the east and are i n f a u l t contact with the same beds on the west. (This f a u l t appears to have reverse move-ment and may be the r e s u l t of concentric f o l d i n g of thick volcanic deposits i n th i s area.) The b e l t appears to be o f f s e t about one-half mile to the west along an east-trending f a u l t near the north boundary of the map-area. Northeast of the Do r f l e r Ranch, a t h i n e a s t e r l y trending b e l t of Marama rocks shows l a t e r a l o f f s e t of about 2,000 feet along several south- and southeast-trending f a u l t s . Dips varying from 69 degrees north to 42 and 85 degrees northeast are determined on beds within t h i s b e l t . d. C o r r e l a t i o n Marama rocks are comparable to lavas cropping out on Mt. Boucherie near Kelowna. The Boucherie lavas are cut by basalt dikes, thought to Legend : Horizontal scale : Fault zone, approx. , .... (tick on downthrow side) " J m , , e Marama rocks Graben (see map 100 for complete geology) 51 feeders of Miocene 'Plateau' lavas, and they rest on conglomerate beds which i n turn appear to rest on a surface deeply eroded i n older lavas s i m i l a r to the clot-porphyry rocks of the Marron Formation. Also, Marama beds resemble the s i l i c a - r i c h 'Sanpoil Volcanics' i n northeastern Washington State, described by Muessig (1962), Staaz (1964), and Parker and Calkins (1964). D. WHITE LAKE FORMATION The White Lake Formation, named by Bostock (1941), consists of a thick succession of lake and stream sediments and volcanic rocks that overlap units of thesolder T e r t i a r y volcanic p i l e and, i n turn, are over-l a i n unconformably by younger sediments and breccias. a. D i s t r i b u t i o n and Thickness The White Lake Formation i s located i n the east-central and northeast parts underlying about 25 percent of the map-area. Most of the sediments l i e west and north of White Lake, whereas the volcanic rocks are centered east and northeast of White Lake and near Okanagan F a l l s . The thickest section of White Lake s t r a t a , about 3,500 feet thick, i s to be seen near Observatory S i t e . Between White Lake and Mahoney Lake the beds are t h i n , and, i n places, younger rocks rest d i r e c t l y on pre- T e r t i a r y formations. b. Stratigraphy and Lithology White Lake beds exposed near White Lake are d i v i s i b l e into three members (see map 200). The lower and middle members contain i n t e r -d i g i t a t e d sedimentary and volcanic deposits; the upper member consists mainly of volcanic rocks with some in t e r c a l a t e d sediments. Sedimentary Rocks The stratigraphy of the sedimentary rocks, cropping out near Kearns Creek on north limb of White Lake syncline, i s summarized by Camsell (1913, p. 214): (lower member) "A section along the v a l l e y of Prather creek (Kearns Creek) on the north side of the basin was measured, which gave a thickness of about 2,000 feet of beds. I t i s very 52 l i k e l y , however, that t h i s thickness i s not uniform through-out the whole area: but, because of conditions under which the beds were deposited, must vary greatly from one side of the area to the other. I t i s possible also that the 2,000 feet thickness i n the section represents more than the actual thickness of the beds f o r , while there i s no apparent d u p l i c a t i o n of the beds by f a u l t i n g , i t i s very probable that there has been some s l i p p i n g or f a u l t i n g along the planes of bedding so as to give to the section an apparent thickness greater than a c t u a l . A study of the measured section shows that the whole series can roughly be divided on l i t h o l o g i c a l grounds into three parts. The lowest t h i r d of the section contains a preponderance of black and grey shales with a minor amount of sandstone. The shales are associated i n places with seams of coal. The middle t h i r d contains c h i e f l y sandstones with some bands of grey shales. The uppermost t h i r d con-s i s t s wholly of tuffaceous sandstones. (middle member) In the ce n t r a l part of the area (south of Observatory S i t e near Kearns Creek?) some grey shales and two narrow seams of coal outcrop. These beds are not contained i n the section measured and probably o v e r l i e i t and constitute the topmost members of the s e r i e s . " Data compiled during the present study f o r section E-F (see Figure 2.6 and map 100), located immediately east of Kearns Creek, coincide well with Camsell's d e s c r i p t i o n of the lower member; thick beds of fine-grained sediments i n the lower part of the section are o v e r l a i n by equally thick deposits of coarse sediments, possibly i n d i -cating large-scale i n f i l l i n g of T e r t i a r y White Lake. However, the exposed section proves to be 2,400 feet thick - about 400 feet thicker than Camsell's estimate. Probably Camsell obtained his data from a section immediately west of Kearns Creek, on the side of the creek opposite E-F - here a bed of volcanic rock, thickening westward and occurring about 1950 feet above base of the formation, terminates the exposed section. This same volcanic bed can be traced to the south limb of White Lake syncline and serves as a good marker-zone for the top of the lower sedimentary member (see Figure 2.6). Data compiled from a diamond d r i l l hole i n lower sedimentary member are summarized and i l l u s t r a t e d i n Figure 2.7. Selected samples of core were petrographically described by Ward (1954). East of section E-F along s t r i k e , White Lake sediments pass into a predominantly volcanic succession (see map 200 and section W-X). 53 McEvoy (1915) b r i e f l y describes White Lake beds near the coal mine s i t e about half-way between section E-F and W-X: (lower member) "In the lower part of the series the volcanic beds are f a i r l y thick and the interbedded sediments contain carbonaceous shales, but only t h i n seams of coal; so f a r no greater thickness than 12 inches of clean coal has been uncovered. Some portions of this lower part of the sec-t i o n have not been uncovered and may contain seams of importance; but this i s not probable. (middle member) In the upper part of the s e r i e s , for a thickness of 1,000 feet the shales and sandstones predominate. In the shales i n th i s part seven seams of coal were uncovered, four of which did not contain more than one foot of clean c o a l . " Lithology of White Lake sediments i s diverse. The sediments are i n t e r c a l a t e d with many lenses and layers of p y r o c l a s t i c rock. The tuffaceous layers are generally n o n - f i s s i l e and l i g h t coloured. Thinly bedded sediments are commonly folded and com-pressed below thick p y r o c l a s t i c deposits probably owing to sudden deposition and loading. Medium and coarse c l a s t i c sediments are prominently exposed on ridge-crests and b l u f f s . These rocks are commonly massive but l o c a l l y t h i n l y bedded or flaggy. Crossbeds, most commonly of festoon type, are well developed i n some sandstones. The modal composition of 10 White Lake sandstones i s shown i n Figure 2.8. These rocks contain a high percentage of volcanic fragments, commonly more than 10 percent argillaceous matrix, minor quartz, chert, qua r t z i t e , and feldspar. According to G i l b e r t ' s (1955) c l a s s i f i c a t i o n , the term 'volcanic wacke' best describes t h i s type of rock. Mudstones comprise much of the sedimentary facies of White Lake Formation but, because of t h e i r non-resistant nature, they are commonly poorly exposed. The rocks are t h i n l y bedded and range i n colour from l i g h t to dark grey - commonly dark colour i s i n d i c a t i o n of high content of carbonaceous matter. Some mudstones are turbid showing l i t t l e e v i -dence of planar f a b r i c ; on the other hand, well-laminated zones and graded beds are not uncommon. Small-scale i n f i l l i n g i s observed i n some places. A good example is near the 600-foot l e v e l of section 'G' on the south limb of White Lak syncline (see Plate 2.12, Figure 2.6, and map 100). A complete i n f i l l -cycle consists of about 55 feet of s t r a t a . L i t h o l o g i c a l change i n the cycle can be roughly broken down as follows: at the base massive sand-stone i s abruptly o v e r l a i n by 30 feet of t h i n l y bedded mudstone, followe by 10 feet of flaggy sandstone with i n t e r c a l a t e d mudstone, o v e r l a i n i n turn by 15 feet of massive sandstone. Wood, stems, and le a f f o s s i l s are abundant i n these rocks, espe-c i a l l y i n mudstones. Needle-bearing branches i d e n t i f i e d as Metasequoia  sp. are common, also some f e r n - l i k e Comptonia sp., a great v a r i e t y of broad-leaf f o l i a g e i s observed, legume pods, and an assortment of other f r u i t i n g bodies are present. Volcanic Rocks In the north limb of the White Lake syncline (see map 200 and accompanying W-X structure section) v o l c a n i c rocks have a t o t a l thick-ness of about 3,000 f e e t . The lowest member, about 1,500 feet thick, consists of t h i n feldspar-porphyry lava flows and abundant lahar and p y r o c l a s t i c deposits containing some accidental fragments of Marama rhyodacite. The middle member, about 1,200 feet thick, consists of a few feldspar porphyry lava flows and much lahar and agglomerate. Charac t e r i s t i c a l l y , the c l a s t i c rocks contain exotic fragments of Yellow Lake porphyry. The upper member, about 300 feet thick, consists mainly of brown augite-porphyry lava and bre c c i a containing small quartz xenoliths and a few blocks of granit e . Immediately southeast of White Lake the middle member shows compositional change. Here beds containing xenoliths of Yellow Lake porphyry i n t e r d i g i t a t e with lahars and p y r o c l a s t i c deposits containing blocks of Park R i l l andesite (see Plate 2.13). In the area 0.5 to 2 miles southeast of White Lake the lower and middle members wedge out so that the upper member laps d i r e c t l y onto Yellow Lake porphyries (see map 200 and accompanying S-T structure sec-tion) . Here the upper member consists of buff coloured v o l c a n i c debris, the 'Indian Head breccia', p y r o c l a s t i c rocks, and some v o l c a n i c sandstone. Figure 2.6 Generalized Columnar Sections of White Lake Beds N o r t h L i m b of S y n c l i n e South L i m b of S ync l i ne E - F M e a s u r e d S e c t i o n s 3 0 0 2 0 0 1 0 0 . 1 0 0 0 . 9 0 0 8 0 0 7 0 0 6 0 0 . 5 0 0 a> 4 0 0 3 0 0 2 0 0 1 0 0 L e g e n d M u d s t o n e M u d s t o n e , minor s a n d s t o n e S a n d s t o n e , m ino r muds tone i i S a n d s t o n e , i J C o n g l o m e r a t e P y r o c l a s t i c r o c k R h y o d a c i t e ( M a r a m a F.) I 1 I I C o r r e l a t e d h o r i z o n ( P o s i t i o n s o f m e a s u r e d s e c t i o n s are shown on map 100) Plate 2.12 A, B Small i n f i l l cycle, White Lake sediments, south limb of White Lake syncline Plate 2.13 Interbedded lahar and p y r o c l a s t i c deposits, White Lake volcanic rocks near White Lake, 1 - beds r i c h i n xenoliths of Park R i l l andesite, 2 - beds r i c h i n xenoliths of Yellow Lake porphyry Plate 2.14 B l u f f s of White Lake vo l c a n i c rocks, near White Lake Feldspar-porphyry lavas are interspersed throughout a l l members of White Lake volcanic succession. Commonly these rocks are l i g h t grey or yellowish coloured and contain many feldspar laths and glomeropheno-c r y s t s . B i o t i t e and pyroxene are the main ferromagnesian minerals. These rocks have a broad trachyte -- trachyandesite composition range, showing general trend from basic to acid character toward top of the formation (see Figure 2.9). Augite-porphyry i s very l i m i t e d i n d i s t r i b u t i o n , occurring only i n the upper member and, to some extent, i n the overlying younger beds. In addition to the t h i n zone of t h i s rock about a mile east of the Observatory S i t e ( i n W-X section) there are several small exposures about one-half mile southwest of The Hole (see map 200). Detailed petrographic descriptions are given i n Appendix 'C. Structure Except near Skaha Lake, where underlying Marama rocks are as much as several hundred feet thick i n places, White Lake beds appear to have been deposited on a deeply eroded surface. In places north of the Observatory S i t e and west of White Lake the sediments rest d i r e c t l y on Park R i l l andesite; about a mile northwest of Mahoney Lake they o v e r l i e Yellow Lake porphyries with pronounced angular unconformity. White Lake beds are folded and cut by many f a u l t s . Near White Lake i t s e l f the beds are folded into the broad 'White Lake s y n c l i n e 1 , plunging about 25 degrees east. These rocks are more or less detached from White Lake s t r a t a near Skaha Lake by a f a u l t zone along,the west side of Okanagan Va l l e y . White Lake beds are generally more steeply i n c l i n e d than older T e r t i a r y rocks i n adjacent areas. For example, measurements from surface exposure and diamond d r i l l core from north limb of syncline show the average dip of beds to be 50 degrees (see Figure 2.10), where-as Marron rocks cropping out north of d r i l l - h o l e s i t e dip 30 degrees or l e s s . These old e r rocks may have steep dips under White Lake beds, or a l t e r n a t i v e l y , the f o l d form changes with depth; shallow dips i n Marron rocks may p e r s i s t at depth i n s p i t e of steep i n c l i n a t i o n of the overlying White Lake beds i f the beds are c o n c e n t r i c a l l y folded. 59 White Lake beds are possibly accommodated i n the core of a concentric f o l d by reverse f a u l t i n g or thrust movement sub p a r a l l e l to bedding. Reverse f a u l t i n g i s observed on the north limb of the syncline. About one mile northeast of the Observatory S i t e , f o r example, a body of Marama rhyodacite i s thrust upward through several hundred feet of White Lake beds (see map 200). Evidence of important movement sub-p a r a l l e l to bedding near the base of the White Lake Formation i s also i n diamond d r i l l core (see Figure 2.7). Figure 2.11 shows a hypothetical structure section through con-c e n t r i c folds of east-trending a n t i c l i n e and syncline. Source Data presented i n a preceding section shows that most White Lake sediments are the product of erosion of T e r t i a r y volcanic rocks. Chert, quartz, granite, greenstone, gneiss, s c h i s t , and other p r e - T e r t i a r y debris are scarce. Observations by Camsell (1913) suggest that the sediments were deposited from east-flowing streams (p. 215); "The sandstones are a l l grey i n colour and vary i n the coarseness and angularity of grains from the east to the west side of the area. On the east the grains are more rounded and waterworn while on the west they are very angular, show-ing proximity to t h e i r o r i g i n a l source." However, cross-bedding measurements shown i n Figure 2.12 provide some evidence that streams flowed i n a northerly d i r e c t i o n . This i s sup-ported by the fa c t that numerous exotic blocks i n the middle member of White Lake volcanic succession were derived, at l e a s t i n part, from Marron rocks underlying the southeast part of map-area. Age and C o r r e l a t i o n The White Lake beds o v e r l i e Marron and Marama rocks with angular unconformity and are probably Eocene but may be Oligocene age. They bear marked s t r u c t u r a l and l i t h o l o g i c a l s i m i l a r i t y to the lower unit of the Klondike Mountain Formation north of Republic i n Washington State (Parker and Calkins, 1964). Some c h a r a c t e r i s t i c features of the lower part of Klondike Mountain Formation are as follows: 1 - Lower beds rest with angular unconformity on Sanpoil Volcanic and older rocks. Figure 2.7 Structure Section of White Lake Beds on North Limb of Syncline Mudstone Mudstone, minor sands tone Sands tone , minor mudstone Sandstone Conglomerate Pyroclast ic rocks Rhyodacite (Maramo F.) mean sea level A s sumed fault zone —• Vert ica l - Horizontal, Sca le 0 5 0 0 feet I i i i 1 1 (Position of section is shown on map 200) Figure 2.8 Composition of White Lake Sandstones 62 Figure 2.9 Refractive Index Variation of White Lake Volcanic Rocks Refractive Index of Samples 63 Figure 2.10 Resultant Vector Diagram for Dip of White Lake Beds Measured from D.D.H. Core Figure 2.11 Diagrammatic Structure Section of Concentric Folds and Related Faults 65 Figure 2.12 C ross -bedd ing Directions in White Lake Sediments i 66 2 - Strata are warped forming a shallow s y n c l i n a l structure. 3 - The rocks are composed mainly of tuffaceous conglomerate, sandstone, and mudstone; t h i n flows of p o r p h y r i t i c l a t i t e ; l o c a l concentration of older T e r t i a r y and pre-Tertiary fragments; also, l o c a l volcanic mudflow deposits . 4 - Plant f o s s i l s include Metasequoia o c c i d e n t a l i s , Pinus sp., and Comptonia columbiana, an assemblage considered by Brown (Parker and Calkins, 1964, p. 66) to be Oligocene. Allenby sediments near Princeton and Tranquille sediments near Kamloops are thick f l u v i o - l a c u s t r i n e deposits i n t e r c a l a t e d with volcanic rocks s i m i l a r i n general aspect to rocks of the White Lake Formation. Mathews (1964) has dated these as Middle Eocene. (Comptionia sp. i s included i n a c o l l e c t i o n of f o s s i l leaves from the Allenby Formation -Rouse, 1966, personal communication.) E. SKAHA FORMATION Skaha Formation i s the name given i n t h i s study to the youngest T e r t i a r y beds of the map-area. These rocks crop out i n about f i v e per-cent of the map-area) centered about 2 miles southwest of Skaha Lake. The following d e s c r i p t i o n , by Bostock (G.S.C. map 627A, 1941), applies to Skaha beds and, i n part, to Marron rocks west of Mahoney Lake and White Lake volcanic rocks immediately east of White Lake: "Volcanic rocks, co n s i s t i n g mainly of b r e c c i a and agglomerate, l i e unconformably over the southeastern part of the White Lake syncline. They are roughly s t r a t i f i e d and dip e a s t e r l y or southerly. In places a large propor-t i o n of the fragments are from the Old Tom, Shoemaker, and Vaseaux formations and from the g r a n i t i c i n t r u s i v e s of the map-area. The fragments are up to 20 feet long. North of Mahoney Lake i s a group of s t r a t a i n which there i s more evidence of s o r t i n g and s t r a t i f i c a t i o n and i n which vo l c a n i c materials are less abundant. Overlying them are beds of nearly f l a t l y i n g conglomerate." The present study shows that the Skaha Formation consists of two members, a lower one composed mainly of s l i d e - b r e c c i a and some volcanic rock, and an upper one composed of coarse boulder block-conglomerate (fanglomerate). The t y p i c a l s t r a t i g r a p h i c r e l a t i o n s of these members are shown i n section S-T (accompanying Map 200). Lower Member The lower member consists of three units ; % b a s a l breccias', 'augite-porphyry^ and'granite b r e c c i a ' The breccias appear to be the product of several s l i d e s o r i g i n a t i n g i n t e r r a i n underlain by pre-T e r t i a r y rock near the southeast part of the map-area. The cause of s l i d e s i s unknown but they may have been the r e s u l t of f a u l t disturbance and u p l i f t accompanied by eruption of augite-porphyry. 'Basal Breccias' 'Basal breccias' are composed mainly of fragments of Shoemaker, Old Tom, and Vaseaux Formations. These rocks r e s t with varying degree of angular unconformity on older T e r t i a r y and pre-Tertiary rocks. a. D i s t r i b u t i o n and Thickness 'Basal breccias' occur roughly w i t h i n the area lying between Observatory S i t e , Mahoney Lake, White Lake, and east boundary of map-area (see map 100). These rocks have a maximum thickness of about 300 feet on the ridge one-half mile east of White Lake; elsewhere they t h i n and wedge out under younger beds. b. Lithology 'Basal breccias' consist of a chaotic mixture of coarse and f i n e l y broken rocks, massive blocks of chert and greenstone, and some conglo-merate; the unit varies i n d e t a i l from place to place. At Indian Head, about one-half mile east of White Lake, blocks of dark chert, some greenstone, together with f i n e chert-breccia form a thick cap on l i g h t coloured White Lake p y r o c l a s t i c beds (see Plate 2.15). Generally, the contact between the'basal breccias' and White Lake rocks i s abrupt. In a few places, however, t h i n zones of boulder conglomerate are found immediately below the breccias (see Plate 2.16). Immediately east of Kearns Creek near The Hole, 'basal breccias' form a nearly h o r i z o n t a l layer, about 15 feet thick, overlying White Lake v o l c a n i c rocks. 'Basal breccias' are roughly bedded and consist mainly of intensely broken chert (see Plate 2.17). Si m i l a r deposits of chert breccia are '-.centered about 1,000 feet northwest - and 2,000 feet south of The Hole. In places, the rock has a rough and craggy habit with many holes and caves developed where loose p a r t i c l e s have been removed by erosion (see Plate 2.18). Fragments are commonly less than two inches i n diameter and are mostly 68 P l a t e 2.15 S k a h a ' b a s a l b r e c c i a s ' ( m a i n l y d a r k c h e r t ) o v e r l y i n g W h i t e L a k e b e d s ( m a i n l y l i g h t c o l o u r e d p y r o c l a s t i c r o c k s ) , I n d i a n H e a d a t I n d i a n H e a d Plate 2.18 Highly fragmented chert breccia, 'basal breccias' Plate 2.17 'Basal breccias' (highly fragmented bedded chert breccia) overlying White Lake volcanic rocks, canyon of Kearns Creek west of The Hole cemented together by s i l i c a , some carbonate, and minor i r o n oxides. A disaggregated sample of chert breccia shows l i t t l e s o r t i n g ; s i z e d i s t r i -bution of fragments resembles mechanically crushed quartz (see Figure 2.14) . A deposit of massive chert, some greenstone, and dike rocks underlies about one-half square mile east and southeast of White Lake. Although dikes and host rocks are l o c a l l y crushed and sheared, the deposit i s generally i n t a c t and could e a s i l y be mistaken for Shoemaker or Old Tom Formations i n place. However, evidence indicates that this body of rock a c t u a l l y consists of large ra f t e d s l a b s . For example, at many widely spaced points White Lake beds s t r i k e under this deposit (see map 200 and accompanying sections S-T and X-Y) . Pulaskite dikes are traced without appreciable o f f s e t along s t r i k e for hundreds of feet, i n d i c a t i n g the s i z e of some slabs . None of the dikes cut White Lake rocks. ( C o r r e l a t i o n of p u l a s k i t e dikes with White Lake or Marron trachyte-trachyandesite lava is inconclusive on basis of glass bead r e f r a c t i v e index work; see Figure 2.13). In areas north of The Hole and Mahoney Lake, 'basal breccias' consist mainly of large lumps of chert and greenstone i n matrix of s i m i l a r composition. Blocks of feldspar porphyry, limestone, and p h y l l i t e are l o c a l l y abundant. The exact s i z e of the blocks is d i f f i c u l t to determine because of i n t e r n a l shattering and i r r e g u l a r margins; however, many exceed 5 feet i n diameter. Some large blocks, which have survived curshing, contain deep embayments and fiss u r e s f i l l e d t i g h t l y with brecciated matrix. Mixed boulder conglomerate and coarse t a l u s - l i k e breccia beds are found southeast of The Hole. Boulders and blocks are mainly chert, greenstone, p h y l l i t e , quartz gneiss, feldspar-porphyries (including rhomb-porphyry), some rusty quartzite, and g r a n i t e . These beds are markedly disturbed and dip steeply i n places. L o c a l l y the rocks are sheared by f a u l t movement and are intruded by augite-porphyry dikes and tongue-l i k e bodies of f i n e chert breccia (see Plate 2.19). 'Augite-Porphyry' Augite-porphyry lava (tephrite) i s present i n a small area cen-tered between Kearns Creek and The Hole (see map 200), accompanied by Minor l i g h t coloured sediments and p y r o c l a s t i c rocks (see Plate 2.20). Figure 2.13 Comparison of Refractive Indices of Pulaskite Dikes and Trachyte-Trachyandesite Lavas -i »-34 _o | White Lake Feldspar-porphyries 10 10 -o 1 —i 1 1 1— o O o o — f\l to * w w m 10 Rosette - porphyries Clot-porphyries Pulaskite Dikes Refractive Index (Open circle is average refractive index of glass t bar represents approximate standard deviation) Figure 2.14 Size Distribution of Skaha Chert Breccia Grain Size (Phi Scale) 73 Plate 2.19 Intrusive chert breccia i n conglomerate beds, lower member Skaha Formation 71 Plate 2.20 Augite-porphyry lava (tephrite) overlying cross-bedded sandstone, near The Hole 75 The augite-porphyry i s massive, dense, dark brown and contains c h a r a c t e r i s t i c large euhedral augite c r y s t a l s embedded i n a fine-grained matrix. Structures such as columnar j o i n t i n g , flow breccia, and amygdales are only l o c a l l y w ell developed. In a few places dikes of s i m i l a r rock cut Skaha basal breccia u n i t and older deposits (see Plate 2.21) . Augite-porphyry has a basic a l k a l i - r i c h composition s i m i l a r to appinites analysed by Bowes et a l . (1963) - see Table 2.8, this study. High v o l a t i l e content of the o r i g i n a l magma is indicated by the abundance of b i o t i t e and apatite (see petrographic d e s c r i p t i o n of augite-porphyry, Appendix 'C'). Bowes et a l . f i n d c o r r e l a t i o n between basic a l k a l i rocks, l i k e the augite-porphyry of this study, and explosion b r e c c i a s . Although no d i r e c t evidence i s a v a i l a b l e , i t i s possible that the curious bodies of i n t r u s i v e chert breccia, described i n the preceding section (see Plates 2.19 and 2.21), are simply s l i d e debris remobilized by steam explosions which may have accompanied eruption of augite-porphyry following deposition of the basal breccia u n i t . 'Granite Breccia' The 'granite b r e c c i a ' u n i t consists of s l i d e debris, mainly slabs and blocks of granite and some a p l i t e , and a few beds of granite boulder conglomerate and arkose. These rocks r e s t discordantly on basal Skaha s l i d e debris. I t appears that 'augite-porphyry' was l o c a l l y removed by erosion before emplacement of 'granite b r e c c i a ' . a. D i s t r i b u t i o n and Thickness 'Granite breccia' forms only about one-quarter of the t o t a l outcrop area of Skaha Formation. The main body of 'granite b r e c c i a ' i s found on Mt. Hawthorn. East of The Hole the deposit i s about 200 feet thick and appears to f i l l a p r e-existing v a l l e y developed i n Skaha basal breccias (see Plate 2.31). Also, a t h i n veneer of crushed and h i g h l y fragmented granite blocks forms an i s o l a t e d deposit cropping out on the ridge crest immediately north and northwest of The Hole. 76 Plate 2.21 Augite-porphyry dike and i n t r u s i v e chert breccia i n conglomerate, lower member Skaha Formation 77 Table 2.8 Composition of Augite-porphyry 1 2 3 SiC-2 51.0 51.4 49.0 A 1 2 0 3 16.6 17 .2 14.9 FeO 7.6 10.5 10.9 MgO 6.9 4.2 10.3 CaO 9.2 10.4 9.5 Na20 3.4 2.7 2.9 K20 5.3 3.6 2.5 1. Composition of augite-porphyry 93C1 2. Average composition of tephrite, (Daly, 1933). 3. Average appinite, (Bowes et a l . , 1963) ( t o t a l iron is calculated as FeO) 78 b. Lithology The granite is l e u c o c r a t i c containing a somewhat v a r i a b l e per-centage of quartz (30 - 5%), plagioclase (45 ± 57=), perthite-orthoclase (20 — 57o), and accessory mica and magnetite. Two t e x t u r a l phases are commonly observed; a medium- to fine-grained, d e l i c a t e l y f o l i a t e d phase, and a non-foliated phase containing large potassic feldspar phenocrysts. Smoky quartz 'eyes' are observed i n both phases (see Plates 2.22 and 2.23) . A v a r i e t y of i n t e r n a l structures is found i n the 'granite breccia' u n i t . In places large granite blocks grade into zones of 'autobreccia' or ' f r i c t i o n a l b r e c c i a ' . I t appears that granite blocks several hundred feet i n diameter were r a f t e d into place on a highly comminuted and mobile mass of breccia (termed f r i c t i o n a l breccia) of s i m i l a r composition. Lo c a l l y , the granite blocks are i n t e r n a l l y shattered forming a mosaic of fragments as i f crushed under t h e i r own weight (autobreccia) . An example of these structures i s to be found i n the area north of The Hole (see Figure 2.15) where granite blocks several hundred feet i n diameter can be observed. In places f o l i a t i o n and quartz veins can be traced tens of feet along s t r i k e , t e s t i f y i n g to the r e l a t i v e l y un-broken character of the blocks (see Plate 2.24). Elsewhere i n the same area, granite i s intensely fractured and crushed. L o c a l l y , brecciated feldspar-porphyry dikes i n the granite pinch and swell i r r e g u l a r y i n d i -cating i n t e n s i t y of deformation and crushing (see Plates 2.25 and 2.26). A good example of ' f r i c t i o n b r e c c i a ' i s to be seen on b l u f f s about 1,500 feet east of The Hole, where granite and feldspar-porphyry dike rocks are markedly broken with fragments mobilized and arranged i n nearly h o r i z o n t a l layers (see Plate 2.27). A few t h i n seams and lenses of rusty material, possibly t u f f , are interbedded with the b r e c c i a s . North of Green Lake and near the crest of Mt. Hawthorn, the u n i t consists mainly of coarse granite s l i d e breccias, some granite boulder conglomerate, and t h i n beds of arkosic sandstones (see Plates 2.28 and 2.29). The conglomerate and sandstone probably re s u l t e d from stream re-working of s l i d e deposits. The granite breccia unit i s intruded by a few small, i r r e g u l a r igneous bodies. These intrusions are aphanitic and generally l i g h t Plate 2,22 Porphyritic granite; potassic feldspar (stained yellow), plagioclase (white), quarts (smoky). Plate 2,23 Aphanitic granite with quartz eyes (smoky) set in matrix of fine grained potassic feldspar (stained yellow) and plagioclase (white)j a weak foliation trends normal to length of the ruler. Figure 2.15 Internal Structure of Part of Granite Breccia Unit Scale 0 5 0 0 feet » — > — • . — ' 1 The Hole (see map 2 0 0 for geological setting) 81 Plate 2.24 Uncrushed granite t y p i c a l of large slabs, 'granite breccia zone' Plate 2.25 Granite 'autobreccia' with crushed dike Plate 2.26 Internal structure of 'autobrecciated' dike Plate 2.27 ' F r i c t i o n a l breccia', layered deposits of mobilized granite and dike rock breccia, east of The Hole (folder and hammer c i r c l e d for scale) 8u Plate 2.29 Arkosic sandstone bed i n granite-boulder conglomerate 85 coloured and mottled with rusty s t a i n s . The r e f r a c t i v e index of glass beads i s high (1.585) suggesting a basic composition. Wall rocks adjacent to these intrusions are somewhat c h l o r i t i z e d and show loss of primary textures probably owing to thermal metamorphism and metasomatism (see Plate 2.30) . The r e l a t i o n s h i p of these intrusions to t u f f s interbedded with granite breccia or augite-porphyry units is not known, however, there appears to have been continuous igneous a c t i v i t y ( i f not continuous volcanism) during deposition of the lower member of the Skaha Formation. Upper Member The upper member of the Skaha Formation is the youngest T e r t i a r y u n i t i n the map-area and consists of coarse c l a s t i c sediments of mixed provenance. I t rests on an erosion surface of moderate to low r e l i e f overlying Skaha 'basal breccias', 'augite-porphyry' unit, and upper beds of White Lake Formation. 'Granite breccia' beds are not found i n contact with the upper member and were probably topographically high standing during deposition of these younger beds. a. D i s t r i b u t i o n and Thickness The main deposit occurs near Mahoney Lake capping the south spur of Mt. Hawthorn. Here beds form prominent b l u f f s and have a maximum thickness of about 600 feet (see Plate 2.31). Small exposures of si m i l a r rock are present near Kearns Creek and northeast of The Hole. b. Lithology The unit i s a thick-bedded mixed boulder- and block-conglomerate. I t contains fragments measuring as much as 6 feet i n diameter, but commonly less than one foot, composed of older T e r t i a r y and pre-Tertiary rocks. The mean s i z e of the fragments varies considerably between beds; however, fine-grained sediments are scarce. The general aspect of the deposit i s that of an a l l u v i a l fan developed near a f a u l t scarp or r e l a t i v e l y high standing t e r r a i n . Chert and greenstone boulders are most common and were probably derived from Shoemaker and Old Tom Formations to the south. The presence of a few lumps of chert breccia suggests that some material was eroded from the lower member of Skaha Formation. Lumps of augite-Plate 2.30 Igneous i n t r u s i o n i n breccias, lower member Skaha Formation 87 88 porphyry are present, some very large, petrographically i d e n t i c a l with augite-porphyry from the Skaha and White Lake Formations from which they were almost c e r t a i n l y eroded. (A complete d e s c r i p t i o n of the boulders i s given i n Table 2.9). These fragments are enclosed i n r e l a t i v e l y clean pebbly and sandy matrix cemented by carbonate and some iron oxide (see Plates 2.32 and 2.33). Sandstone beds are generally very t h i n and discontinuous. The rock i s grey and speckled with black chert; i t i s best described petro-g r a p h i c a l l y as a l i t h i c a renite (see Figure 2.16). Although about 10 percent of the fragments i n the upper member are of vo l c a n i c o r i g i n , primary v o l c a n i c deposits are not found i n this u n i t . Except f o r l o c a l pebble imbrication and channel features (see Plate 2.34) l i t t l e i n t e r n a l structure is found i n the upper member, at lea s t when viewed c l o s e l y . T y p i c a l l y , the rock i s only moderately w e l l indurated and j o i n t fractures tend to pass around pebbles and boulders rather than through them. Generally, the rocks weather e a s i l y forming hoodoo structures and caves on steep h i l l sides (see Plate 2.35). Structure The Skaha beds have undergone marked deformation. They l i e north of The Hole, dip to the south and are roughly p a r a l l e l to the north limb of the White Lake s y n c l i n e . Reverse f a u l t i n g along a northeast trending zone (probably r e l a t e d to concentric folding) has severed the northern part of the formation, mainly chert breccia beds, from the main body of s i m i l a r rock l y i n g immediately to the south (see structure section X-Y) . South of The Hole, the Skaha beds dip eas t e r l y . (In this area- T e r t i a r y beds are r e l a t i v e l y t h i n and are not simply r e l a t e d to f o l d structures to the north where beds are thick.) Here, Skaha beds are displaced by steep northerly-trending gravity f a u l t s s i m i l a r to those found i n southern and western parts of map-area (see de s c r i p t i o n of Marron Formation and structure sections C-D on map 100 and S-T accompanying map 200). Slickensides and cleavages are l o c a l l y w e l l developed east of White Lake providing evidence of r e l a t i v e l y l a t e movement. These structures occur i n Skaha, White Lake, and Marron rocks with some 89 Table 2.9 Description of Common Boulders i n Upper Type of Fragment Des c r i p t i o n Chert and Greenstone Angular and subrounded fragments up to four feet i n diameter, very common occurrence, probably derived from lower s l i d e complex or Shoemaker F. and Old Tom F. Feldspar-porphyries Angular fragments up to f i v e feet i n diameter, very common occurrence, probably derived from Marron c l o t -porphyries and White Lake feldspar-porphyries . Arkose Rounded fragments up to s i x feet i n diameter, l e u c o c r a t i c granite source possibly from upper s l i d e complex. Vein quartz Angular fragments up to eight inches i n diameter, probably derived upper s l i d e complex. Augite-porphyry Angular blocks up to s i x feet i n diameter, derived from augite-porphyry unit of upper White Lake F. or Skaha F. P h y l l i t e Sub-rounded fragments up to two feet i n diameter, probably derived from lower s l i d e complex or Vaseaux F. Granite and A p l i t e Sub-rounded fragments up to three feet i n diameter, probably derived from upper s l i d e complex. 90 Plate 2.33 Chert block i n upper member, Skaha Formation 91 Figure 2.16 Composition of Skaha Sandstones c o I— a. 80 6 0 40 20 Average of 3 Samples a £ "5. < § a) a. CL _> o O 80 60 40 20 Average of 2 Samples » Cv •e | < ° w — O OT a a. o o a: a o o o O a a. o to c o" u > a a> I Plate 2,35 Hoodoo structure in conglomerate, upper member Skaha Formation Plate 2,3U Channel deposit in upper member, Skaha Formation 93 d i r e c t i o n a l consistency. Generally, cleavages s t r i k e northeast and dip steeply; s l i c k e n s i d e l i n e a t i o n s plunge, at low angeles, i n two main dire c t i o n s - northeasterly, approximately coincident with mean cleavage plane, and southeasterly roughly p a r a l l e l to s t r i k e of main f a u l t s of the Okanagan system (see Figures 2.17 and 2.18). Figure 2.19 shows a hypothetical r e l a t i o n of structures i n conjugate shear plan i n d i c a t i n g north as the approximate d i r e c t i o n of maximum s t r e s s . Age and C o r r e l a t i o n The Skaha Formation i s j u s t s l i g h t l y younger than White Lake Formation; this i s suggested by the f a c t that Skaha beds o v e r l i e White Lake rocks with minor unconformity and have undergone s i m i l a r deformation. The only other deposit described to date i n southern B r i t i s h Columbia resembling the Skaha rocks occurs i n the Flathead area, about 225 miles east of White Lake. This deposit, known as the Kishenehn Formation, consists p a r t l y of coarse conglomerate containing boulders commonly one foot and some as large as four feet i n diameter. According to P r i c e (1966), this material was eroded from high t e r r a i n underlain by Paleozoic rocks and deposited as a 1fanglomerate' on the downthrow, west side of Flathead f a u l t i n l a t e Eocene or early Oligocene time. 3 . RESUME OF GENERAL STRUCTURE T e r t i a r y rocks i n v i c i n i t y of White Lake map-area are i n t e r -sected by important gravity f a u l t s . The region i s divided into three s t r u c t u r a l zones by the Marron f a u l t system which follows Marron V a l l e y southeasterly to Marron Lake; here i t s p l i t s into a weak easterly-trending branch which passes into Okanagan Va l l e y , a n d ' a strong south-westerly-trending branch which passes near Twin Lakes and extends into Similkameen V a l l e y (see Figure 2.20). S t r u c t u r a l zone 'A1, the area west of Marron f a u l t and Twin Lake branch, i s r e l a t i v e l y simple. T y p i c a l l y , the s t r a t a here are thin, dip gently east, and are displaced mainly by northerly-trending gravity f a u l t s with easterly downthrow. Small grabens, such as Trout Lake graben (see Figure 2.4), occur along the eastern margin of the zone adjacent to the Marron f a u l t system, which shows a n t i t h e t i c displacement.. Figure 2.17 Some Lote Structures in Rocks East of White Lake A. Slickenside Pattern B. Cleavage Pattern i25 li5 V5 Snorl bar. lingl* cleavaga meosutmtnl Long bar, averag* of umilot cltovag* atiludes in tmal quadranli 'H' numbtr of m«ajuremint» c»«rog«d 'D' angular dliplrion of Ov«rog«d meojurtmtfi) (only itrihgi of Cl«avog«t *IIFI dipt grcdltr than 60"or* pfotld) DO" / DO' / X 015* 015' 1 D3S' 0 30" ^ 0 25' Y • / 0 15' 0 40' ' D30". 015". D KT D 30" / £ N8 , / NIB D25" / D 45' / OW / 0 35* N IT HZ / 0 *0' / 0 20' N B / NIO. D 35* / OK)' 0 13' ^ 0 20" 0 15' D5' . (Co-ordinats art tli* iams ai on mop 200) 4=" Figure 2.18 Equal Area Diagrams A. Plot of Slickensides B. Plot of Cleavages NO vn. 96 Figure 2.19 Possible Stress Scheme for Late Movement, Area Near White Lake Figure 2.20 Structural Subdivisions of M a p - a r e a and Adjacent Region 98 Zone 'B1, the area between Twin Lake branch and easterly-trending branch of Marron f a u l t system, is somewhat complex. In general, the s t r a t a here are folded to form 'White Lake syncline' which i s open and plunges gently to the east. The beds are cut by g r a v i t y f a u l t s of widely varying trends which show mainly westerly or northerly downthrow. Reverse f a u l t s , probably r e l a t e d to concentric folding, are developed where s t r a t a are e s p e c i a l l y thick such as on the north limb of White Lake s y n c l i n e . Some northerly-trending f a u l t s i n the southeast part of zone 'B' show s t r i k e - s l i p displacement. Rocks only i n the southern part of zone 'C1, the area east of Marron f a u l t and north of zone 'B1, were examined by the w r i t e r but some s t r u c t u r a l features are evident. In general, the T e r t i a r y p i l e is t h i n on the west along the axis of an a n t i c l i n e and thick near the south end of Skaha Lake, s i t e of the 'Okanagan F a l l s s y n c l i n e ' . Both folds are open and plunge southeastward. A northerly trending reverse f a u l t , immediately west of south end of Skaha Lake, i s possibly due to con-c e n t r i c f o l d i n g of thick s t r a t a . In summary, the main s t r u c t u r a l features are as follows: 1. The area underlain by T e r t i a r y rocks i s mostly bounded by gravity f a u l t s . 2. The T e r t i a r y p i l e i s thickest and s t r u c t u r a l l y lowest near the Okanagan V a l l e y . 3. Beds commonly dip i n an easterly d i r e c t i o n - westerly dipping beds are few. The structure section A-B-C-D (see Figure 2.21) across the main b e l t of T e r t i a r y rocks shows the t y p i c a l deformation. I t is proposed that a trapdoor-like downward r o t a t i o n along west-dipping f a u l t s of the Okanagan system produced easterly dips and marked subsidence of s t r a t a near Okanagan V a l l e y . Also, although d e t a i l s of the s t r u c t u r a l h i s t o r y are uncertain, this type of movement may have been i n f l u e n t i a l i n l o c a l i z i n g Skaha and White Lake beds i n the east part of the area, (see section on h i s t o r i c a l geology i n Chapter IV of this report,). Folds are only l o c a l l y important and are best developed where Te r t i a r y deposits appear to be t h i c k e s t . C o n c e n t r i c a l l y folded beds of White Lake and Okanagan F a l l s synclines probably r e f l e c t simpler underlying structures, possibly t i t l e d f a u l t blocks. Figure 2.21 C r o s s S e c t i o n of White Lake B a s i n (Looking Northeasterly) (see map 100 for tocation of cross section) NO 100 GLACIAL GEOLOGY Ice Thickness and Movement According to the G l a c i a l Map of Canada (1962), the Wisconsin i c e sheet moved southerly from an i c e divide north of Kamloops and attained a maximum elevation i n excess of 7,000 feet i n the southern Okanagan. Two sets of g l a c i a l s t r i a e are observed i n the map-area; a southerly trending set with presumably southerly sense, and an easterly trending set with sense of i c e movement unknown. East of White Lake, where the rocks were examined i n d e t a i l , 16 of a t o t a l of 18 s t r i a e measurements trend southerly, 2 trend east-e r l y . The presence of large blocks of granite breccia i n gravel deposits west of Mahoney Lake establishes a southerly sense for the most recent ic e advance, since the source of these blocks i s about 1.5 miles north, on the ridge north of The Hole (see Figure 2.22). A series of small closed depressions ( s i t e of ephemeral ponds) southeast of White Lake were probably formed by 'eddies' set up i n southerly flowing i c e i n response to l o c a l topographic features. These depressions are mostly located on the south sides of k n o l l s and b l u f f s where the thickest i c e would accumulate an erode i n a manner analogous to the formation of tarns and paternoster depressions such as commonly found i n g l a c i a t e d rugged t e r r a i n . Meltwater Drainage and G l a c i a l Deposits According to Nasmith (1962), during the r e t r e a t of the Wisconsin ic e sheet, meltwater discharging into the Similkameen v a l l e y excavated two s i g n i f i c a n t channels, one containing Yellow Lake and the other located southwest of Twin Lakes. P i t t e d outwash deposits near Twin Lakes were l a i d down during t h i s i n i t i a l r e t r e a t of the i c e . At a l a t e r stage, meltwaters flowed south and east through White Lake basin to Okanagan V a l l e y v i a Kearns Creek. S i g n i f i c a n t outwash deposits were formed at t h i s time i n the v i c i n i t y of Marron Lake and White Lake. Unable to pass d i r e c t l y south across the White Lake basin, probably because of i c e damming near D o r f l e r Ranch, the meltwaters flowed southeast of the Observatory S i t e downslope along a surface of r e s i s t a n t chert breccia beds of Skaha Formation. Between Indian Head and The Hole, the western margin of augite-porphyry u n i t 101 Figure 2 2 2 Plot of Ice Movement in Area East of White Lake 102 c l o s e l y p a r a l l e l s the present course of Kearns Creek suggesting that the contact between this rock and chert breccia beds l o c a l l y c o n t r o l l e d the course of a stream p r i o r to entrenchmentof meltwaters and formation of present v a l l e y i n this area (see Figure 2.23). Further south, the meltwater channel was co n t r o l l e d i n part by north trending f a u l t zone (see map 200). At a l a t e r stage, when Okanagan ice lobe retreated north of Okanagan F a l l s , the Kearns Creek course was abandoned and meltwaters flowed eastward to g l a c i a l Lake Penticton following the present course of Marron Creek. A considerable volume of white s i l t (delta deposit) was l a i d down by this stream west of Okanagan F a l l s . Figure 2.23 Topographic Section Showing Glacial Features in Vic in i ty of The Hole Indian Head .W. line of _ section 0 8 0 ' N.E. feet above Kearns m s l -L 1600 Horizontal Scale>: 0 5 0 0 i _ _ 1000 Feet i CHAPTER I I I IGNEOUS PETROLOGY The object of this chapter is to elucidate the petrographic and chemical nature and mode of o r i g i n of the T e r t i a r y igneous rocks of the White Lake area. MAIN PETROGRAPHIC FEATURES A v a r i e t y of early T e r t i a r y e f f u s i v e rocks i s found i n south-cen t r a l B r i t i s h Columbia and northern Washington State as shown by petrographic descriptions and chemical analyses of LeRoy (1912), Daly (1912), Drysdale (1915), Church (1963), Staaz (1964), and Bostock (1966). (A comprehensive tabulation of chemical analyses Is given i n Appendix 'A'.) The rock assemblage includes andesite, r h y o l i t e , trachyandesite, trachyte, tephrite (augite-porphyry), and phonolite (commonly with rhomb-shaped anorthoclase phenocrysts) . A s i m i l a r spectrum of rock types i s present i n the White Lake area. The order of extrusion of these rocks i s as follows: 8 tep h r i t e White Lake and Skaha.F. 7 trachyte, trachyandesite White Lake F. 6 r h y o l i t e , rhyodacite Marama F. 5 andesite Marron F. 4 trachyte, trachyandesite " 3 b a s a l t i c andesite " 2 trachyte, trachyandesite " 1 phonolite . " (The normative composition of analysed rocks i s given i n Appendix 'B1 and de t a i l e d petrographic descriptions of selected rocks are given i n Appen-dix !C' .) Trachytes and trachyandesites are found i n three s t r a t i g r a p h i c zones (2, 4, and 7). C h a r a c t e r i s t i c a l l y , these rocks contain two feldspars; plagioclase, which forms laths and clot s or star-shaped glomerophenocrysts, and potassic feldspar, which occurs mainly as thi n 105 rims or jackets on plagioclase c r y s t a l s , or less commonly as d i s c r e t e phenocrysts, and i n the fine-grained goundmass. Generally the most basic rocks of this group, the trachyandesites, contain some normative nepheline, whereas the trachytes have some normative quartz. Although feldspathoidal minerals have not been detected i n these rocks, quartz was observed i n the fine-grained matrix of some trachytes. The lowermost and uppermost lavas i n the succession, phonolites and tephrites respectively, are markedly undersaturated i n s i l i c a and contain important amounts of normative nepheline and o l i v i n e . X-ray analysis shows abundant a n a l c i t e i n the matrix of many of these rocks. Only a few grains of serpentine, pseudomorphic a f t e r o l i v i n e , are found. Potassic feldspar is abundant, occurring as d i s t i n c t i v e rhomb-shaped (anorthoclase) phenocrysts i n many lava flows. Plagioclase i s scarce and generally r e s t r i c t e d to the fine-grained groundmass of these rocks. In contrast, andesite and rhy o l i t e - r h y o d a c i t e rocks, which occur near the middle of the succession (3, 5, and 6), are r i c h i n normative quartz. Also, u n l i k e the rocks described above which are commonly h o l o c r y s t a l l i n e , the andesitesand rhyodacitesare v i t r o p h y r i c . Plagio-clase phenocrysts are abundant i n most of these rocks, whereas, phenocrysts of potassic feldspar are scarce and found only i n some r h y o l i t e s . In s p i t e ofthe many differences i n the f e l s i c composition of these rocks, the mafic minerals show l i t t l e v a r i e t y . D i o p s i d i c augite and b i o t i t e are widely d i s t r i b u t e d , varying only i n r e l a t i v e abundance. Except for r h y o l i t e and some trachytes, modal b i o t i t e is less abundant than pyroxene. Accessory minerals include magnetite, apatite, and hypersthene. Magnetite occurs as small grains disseminated i n the matrix of holo-c r y s t a l l i n e rocks or as small phenocrysts i n v i t r o p h y r i c rocks or constituent grains i n glomerophenocrysts. Apatite occurs i n the matrix of most rocks examined but i s e s p e c i a l l y abundant and forms unusually large c r y s t a l s i n tep h r i t e (augite-porphyry) and phonolite (rhomb-porphyry) . (Prismatic cleavage traces are commonly observed i n this apatite.) Hypersthene i s found i n some aridesites but only amounts to a small percentage of the t o t a l pyroxene content. 106 CHEMICAL VARIATIONS Murata (1960) has provided a graphical method of i l l u s t r a t i n g chemical v a r i a t i o n s i n igneous rock s e r i e s . Major oxides, such as lime and magnesia, are simply p o l t t e d against a l u m i n a - t o - s i l i c a r a t i o s . The u t i l i t y of Murata-type plots i s three-fold: 1- With these plots, rock ser i e s are r e a d i l y delineated, as demonstrated by Murata i n the case of Hawaiian t h o l o i i t i c and a l k a l i c b a s a l t s . 2- Only p a r t i a l chemical analyses are required. 3- Chemical v a r i a t i o n s are e a s i l y compared with important phase equi-l i b r i a diagrams. Important chemical differences i n the igneous rock groups of this study are brought out with the plo t - t o t a l i r o n oxide versus alumina-t o - s i l i c a r a t i o s (see Figure 3.1). Andesite - rhyodacite rocks, designated 'A' s e r i e s , have r e l a t i v e l y small a l u m i n a - t o - s i l i c a r a t i o s but large i r o n oxide range; high i r o n oxide values for andesites and low values for rhyodacites and r h y o l i t e s . Tephrite (augite-porphyry) and phonolite (rhomb-porphyry) rocks, designated 'C1 s e r i e s , t y p i c a l l y have large a l u m i n a - t o - s i l i c a r a t i o s and high i r o n oxide content. Iron oxide i s higher i n tephrite rocks compared to p h o n o l i t i c members of the series but range of values is less than exhibited by 'A' s e r i e s . Trachyte - trachy-andesite rocks, designated 'B1 s e r i e s , are intermediate i n composition between 'A' and 'C1 s e r i e s . Generally, the most basic members of the s e r i e s , the trachyandesites, have higher i r o n content than the acid members, the trachytes. I t i s i n t e r e s t i n g to note (see Figure 3.1) that the l i n e of s i l i c a - s a t u r a t i o n bisects the composition f i e l d of 'B1 s e r i e s , whereas, 'A' and 'C1 series f a l l , r e s p e c t i v e l y , on the oversaturated and under-saturated side of the l i n e . I t w i l l be shown i n a l a t e r s ection that the p o s i t i o n of this l i n e i s important i n considering the genesis of the rocks of each series . Refra c t i v e indices of glass of a r t i f i c i a l l y fused rocks of 'A1, 'B1, and 'C' serie s are found by Church (1963) to be a s u i t a b l e scale on which to base main chemical v a r i a t i o n s . The chemistry of analysed rocks i s i l l u s t r a t e d i n Figures 3.2, 3.3, and 3.4. Ref r a c t i v e index histograms for a t o t a l of 137 samples, representing the three s e r i e s , show r e l a t i v e abundance of the various rock types. 107 Figure 3.1 Early Tertiary Igneous Rock Series o o o a> 9 -• 8 -4 •-3 -2 -I --1 1-silica over saturated : under saturated v 16 tephrite (plagioclase-porphyries) \ (anorthoclase -ss porphyries) (san id ine - plagioclase porphyries) \ »-A l 2 0 3 / / S i 0 2 open circles, analyses of lavas of White Lake map-area solid circles, analyses of effusive rocks of south-central British Columbia and northern Wash, areas within solid lines indicate approximate composition range for rock series (see Table 3.1, key to analyses) Table 3.0 Key to Analyses, Figure 3.1 Analysis No. Description 1. Feeder dike to Midway andesite lava, LeRoy 1912 (see Appendix Table A-3, no. 5) 2. Park R i l l andesite, Marron F. (see Appendix Table B - l , no. 1) 3. Andesite, Midway lava, Church 1963 (see Appendix Table A-3, no. 1) 4. Rhyodacite, Kelowna area, Church 1963 (see Appendix Table A-3, no. 2) 5. Sanpoil lava, Staaz 1964 (see Appendix Table A-4, no. 2) 6. Sanpoil lava, Parker and Calkins 1964 (see Appendix Table A-4, no. 3) 7. Marama lava (see Appendix Table B - l , no. 2) 8. Shingle Creek porphyry (see Appendix Table A-3, no. 9) 9. Pulaskite dike, feeder to Midway lava, LeRoy 1912 (see Appendix Table A-3, no. 6) 10. Rosette-porphyry, Marron F. (see Appendix Table B - l , no. 3) 11. Marron lava, Bostock 1966 (see Appendix Table A-3, no. 10) 12. Clot-porphyry, Marron F. (see Appendix Table B - l , no. 4) 13. Trachyte, Midway lava, Drysdale 1915 (see Appendix Table A-3, no. 7) 14. Pulaskite dike, feeder to Midway lavas (see Appendix Table A-3, no. 3) 15. Trachyte, Kelowna area, Church 1963 (see Appendix Table A-4, no. 4) 16. Augite-porphyry, Midway lava, Drysdale 1915, (see Appendix Table A-3, no. 8) 17. Augite - porphyry lava, Skaha F. (see Appendix Table B - l , no. 5) 18. Marron lava, Bostock 1966 (see Appendix Table A-4, no. 1) 19. Rhomb-porphyry, Midway volcanic rocks, Daly 1912 (see Appendix Table A-4, no. 5) 20. Yellow Lake rhomb-porphyry, Marron F. (see Appendix Table B - l , no. 6) 21. Rhomb-porphyry, Midway lava, LeRoy 1912, (see Appendix Table A-3, no. 4) 22. Indian Head breccia (weathered), White Lake F. (see Appendix Table A - l , sample CC-18) O CD 109 Figure 3.3 Variation Diagram,'B1 Series open circles, analyses t h i 6 study (see Table 3.1) solid circles, analyses Church 1963 I l l open circles, analyses this study (see Table 3.1) solid circles, analyses Church 1963 112 Table 3.1 Key to Analyses (Figs. 3.2, 3.3, 3.4) Analyses F i e l d TIT ,, Description Nos. No. r 'A' 1. N64-3-1 andesite Series 2. N64-11-15 andesite 3. N64-25A-2 andesite 4. N64-8-9 rhyodacite 5. N64-2-8 r h y o l i t e 'B' 1. N64-24-2 trachyandesite Series 2. N64-21-5 trachyte 'C' .1. 93C1 augite-porphyry Series 2. N64-B rhomb-porphyry 3. N64-20-K rhomb-porphyry (Complete chemical data for these rocks i s given i n Appendix Table A-l) 113 In summary, the main chemical c h a r a c t e r i s t i c s of the series are as follows: 1- In a l l series s i l i c a increases with decreasing r e f r a c t i v e index; s i l i c a values are generally lower i n 'C 1 series showing smaller rate of increase than i n 'A1 or 'B' s e r i e s . 2- Alumina i s markedly v a r i a b l e ; 'C' series shows sharp increase i n alumina content passing from basic to acid rocks, however, the reverse i s true for 'B' s e r i e s . In contrast to both 'B' and 'C' se r i e s , the o v e r a l l alumina content i n rocks of 'A' series is low with l i t t l e v a r i a t i o n between basic and acid rocks. 3- Lime, magnesia, and i r o n oxide, the most re f r a c t o r y major c o n s t i -tuents, decrease with increasing a c i d i t y (decreasing r e f r a c t i v e index). 4- T o t a l a l k a l i composition (soda plus potash) of 'B* and 'C 1 series is r e l a t i v e l y high showing l i t t l e d i f f e r e n c e between basic and acid rocks. A l k a l i composition of 'A' series increases somewhat with a c i d i t y but i s generally lower than 'B' or ' c ' l e v e l s . Average potash-to-soda r a t i o s of rocks analysed for the present study are as follows: 'A1 s e r i e s andesite 0.77 r h y o l i t e - rhyodacite 0.66 'B 1 series trachyte - trachyandes i t e 1.47 'C' series tephrite (augite-porphyry) 1.53 phonolite (rhomb-porphyry) 0.76 In general, 'A' series rocks are r e l a t i v e l y soda-rich, 'B' series rocks are r e l a t i v e l y potash-rich, and 'C 1 series rocks are mixed with basic rocks potash-rich and acid rocks soda-rich or intermediate. Data are also a v a i l a b l e for a few important minor elements. F i -gure 3.5A shows good c o r r e l a t i o n between t i t a n i a and i r o n oxide for analysed rocks. This c o r r e l a t i o n is not s u r p r i s i n g since one of GoldschmidtJs main rules of diadochy states (Mason, 1956, p. 114): "When a minor element has a s i m i l a r i o n i c radius but a higher charge than that of a major element, i t i s said to be captured by the c r y s t a l l a t t i c e containing the major element." Ionic r a d i i of "iron and titanium are very s i m i l a r ( i n s i x - f o l d co-ordination): divalent i r o n 0.74 A° t r i v a l e n t i r o n 0.64 A 0 t r i v a l e n t titanium 0.76 A° o quadrivalent titanium 0.68 A Twenty-eight strontium and barium determinations were made on these rocks for this study (see Appendix Table A-l) and by Church (1963, Table D . l ) . The average strontium-to-barium r a t i o s are s i m i l a r for these rocks: However, some differences i n concentration levels of strontium and barium are noted (see Figure 3.5B). Average concentration of these elements i n 'A' series is less than 2000 p.p.m. and i n 'B' series less than 3000 p.p.m. . C h a r a c t e r i s t i c a l l y 'C' series has high strontium and barium concentrations - greater than 3000 p.p.m. Figure 3.6 is a sketch map showing the main areas of v o l c a n i c rock i n southern B r i t i s h Columbia and Washington State. Waters (1962) distinguishes two petrographic provinces of early T e r t i a r y rock i n western Washington; (1) a s p i l i t e province centered on the Olympic peninsula and coastal areas to the south, and (2) an andesite province south and east of Puget Sound, extending east to the axis of the Cascades. The andesites are, i n part, o v e r l a i n by the younger Columbia River basalts to the east and the much younger rocks of the Cascade vo l c a n i c complex. As shown i n the preceding section the early T e r t i a r y v o l c a n i c assemblage of the White Lake map-area and, more generally, Okanagan and Boundary areas of southern B r i t i s h Columbia, have markedly mixed composition. Interlayering of diverse rocks, such as those of 'A1, 'B1, and 'C1 s e r i e s , i s probably due to overlapping of adjacent petrographic provinces. Rocks of 'A1 series examined by the author are mainly andesites and minor s i l i c a - r i c h a c i d types (see histogram Figure 3.2) and are possibly c o r r e l a t i v e with s i m i l a r early T e r t i a r y lavas of Kamloops and Princeton areas (see Stevenson, 1939, p.446, and d e s c r i p t i o n of Kamloops A series B 1 series C 1 series 0.50 0.52 0.57 PETROGRAPHIC PROVINCES Figure 3.5 Some Minor Element Variations (B) S r - B a Dispersion Series A -14 Sr B ° average / ^ r a n g e C - -o A - o 14 Ba B 4 c — 0 . 1 2 3 4 5 6 7 p.p.m. x IO 3 (data includes analyses by Church 1963) Group by Daly, 1915, p. 126-130; and d e s c r i p t i o n of Princeton lavas by Rice, 1947, p. 29, and Shaw, 1952, p. 6, Camsell, 1913, p. 83). This 'andesitic' s u i t e of v o l c a n i c rocks crop out i n a broad b e l t trending northward from northern Washington through south-central B r i t i s h Columbia. The b e l t may represent a p a r t l y eroded northerly extension of the andesite province (2) of the Puget Sound area. Rocks of 'B1 and 'C1 series are a l k a l i - r i c h and resemble the C o r y e l l b a t h o l i t h i n both composition and age. The inference by Daly (1912, p. 419) that the C o r y e l l intrusions are simply the plutonic equivalents of some of these early T e r t i a r y v o l c a n i c rocks i s now w e l l founded. Table 3.2 shows the average chemical composition of two phases of the main intrusions of the C o r y e l l b a t h o l i t h near T r a i l and Lower Arrow Lake, B r i t i s h Columbia. The most acid rocks of 'B' series (no. 15 of Figure 3.1) are s i m i l a r to the quartz syenite phase, and tephrite of 'C1 series (no. 17 of Figure 3.1) corresponds w e l l with the shonkinite phase of the C o r y e l l b a t h o l i t h . Also, the age of the Midway volcanic rocks determined by Mathews (1964), 48 and 49 m.y., i s s i m i l a r to the age of the C o r y e l l rocks determined by Baadsgaard et a l . (1961), 54 and 58 m.y. The area of thickest volcanic deposits and largest exposed intrusions of these rocks, termed the ' a l k a l i c magma province' (3), is roughly outlined i n Figure 3.6. Some early T e r t i a r y trachyte flows and a l k a l i - r i c h intrusions are reported to occur i n the Princeton and Kamloops areas to the west (Rice, 1929; Dawson, 1896) but these are comparatively small bodies possibly r e l a t e d to a l k a l i n e centers remote from the Okanagan - Boundary region. Knowledge of early T e r t i a r y v o l c a n i c o u t l i e r s and intrusions to the southwest and northeast is incomplete and the boundaries of province (3) are more or less a r b i t r a r i l y drawn. To the southeast, the 'Petrographic Province of Central Montana', made famous by the work of Pirsson (1905) and Larsen (1940), contains an assemblage of a l k a l i - r i c h T e r t i a r y intrusions (shonkinites) and v o l c a n i c rocks (mafic phonolites) bearing some Figure 3.6 Cenozoic Petrographic Regions of Southern British Columbia and Washington State 118 Table 3.2 Composition of Main Phases of C o r y e l l B a t h o l i t h and Similar Rocks of 'B1 and 'C' Series 1 2 3 4 5 FeO MgO CaO Na20 K20 63.2 17 .0 4.3 2.0 2.8 4.9 5.8 63.7 17.1 3.5 0.7 3.4 11.6 60.4 18.5 4.7 1.5 4,4 4.6 5.9 53.4 16.6 8.5 5.8 8.0 3.4 4.3 51.0 16.6 7.6 6.9 9.2 3.4 5.3 1. Average composition of C o r y e l l 'quartz syenite' (see L i t t l e I960, Table I, nos. K and L; Table I I I , no. 1) 2. Trachyte, Kelowna area (see Appendix Table A-4, no. 4) 3. Average trachyte-trachyandesite, Marron F. (see Table 2.4, no. 3; Table 2.5, no. 1) 4. Average composition of C o r y e l l 'monzonites and shonkonites 1 (see L i t t l e 1960, Table I nos. M and N; Table I I I , no. 2) 5. Augite-porphyry, Skaha F. (see Table 2.9, no. 1) ( t o t a l i r o n is calculated as FeO) 119 resemblance to the a l k a l i - r i c h rocks of the Okanagan - Boundary region. These are best developed i n the Highwood Mountains of Montana and are t y p i c a l l y potassic and r i c h i n strontium and barium. Alumina content, however, is generally less than that i n rocks of 'B1 and 'C1 series of the Okanagan - Boundary area and rhomb-porphyry rocks are not found. PETROGENESIS F r a c t i o n a l c r y s t a l l i z a t i o n of parental andesite and shon-k i n i t e magmas appears to account for the rocks of the 'A' and 'C' ser i e s , r e s p e c t i v e l y . Mixing of 'A' and 'C1 magmas best explains the 'B' series and the t r a n s i t i o n from undersaturated to oversaturated compositions. Migration of potash from 'C1 to 'B1 magmas may have accompanied this mixing process, possibly aided by v o l a t i l e t r a n s f e r . The magmas of the 'A1 and 'C1 series probably approached a s i l i c a - r i c h r h y o l i t e e u t e c t i c and a soda-rich phonolite (rhomb-porphyry) eutectic, respectively, along separate composition and thermal lines of descent. These l i n e s are diagrammatically represented i n the system d i o p s i d e - n e p h e l i n e - s i l i c a (see Figure 3.7A) which contains important normative minerals of the 'A' and 'C' s e r i e s . Subtraction diagrams, Figures 3.8 and 3.9, show q u a n t i t a t i v e l y how the acid magmas of 'A' and 'C* se r i e s , r e s p e c t i v e l y , may have been produced. In the case of the 'A' ser i e s , subtraction (f r a c t i o n a t i o n ) of a mineral aggregate, 'x' (composed mostly of plagioclase, some pyroxene, b i o t i t e , and minor magnetite), from Park R i l l andesite, '1', can produce a s i l i c a - r i c h composition s i m i l a r to average Marama lava, '2'. Roughly, f r a c t i o n a t i o n of andesite '1' y i e l d s 60 percent c r y s t a l accumulate 'x' and 40 percent r h y o l i t i c magma '2'. In the case of the 'C' s e r i e s , subtraction of aggregate 'y' (composed lar g e l y of pyroxene, some b i o t i t e , and minor potash) from Skaha augite-porphyry, '5', produces a composition s i m i l a r to average Yellow Lake lava, '6'. Rough calcu l a t i o n s show that f r a c t i o n a t i o n of augite-porphyry y i e l d s 40 percent c r y s t a l accumulate plus minor f u g i t i v e potash and 60 percent p h o n o l i t i c magma '6'. The magmas of 'B' ser i e s , as previously indicated, include s i l i c a - s a t u r a t e d and undersaturated types. The thermal divide between undersaturated and oversaturated magmas is breached, theor-e t i c a l l y , by f r a c t i o n a t i o n of undersaturated minerals or mixing of s i l i c a - p o o r and s i l i c a - r i c h magmas (see T i l l e y , 1958) . In consideration of the f i r s t case, that of separation of undersaturated minerals, b i o t i t e is present as phenocrysts i n some rocks of the 'B1 s e r i e s ; however, magnetite i s the only abundant undersaturated mineral. Osborn (1959) shows that f r a c t i o n a t i o n of magnetite from wet magmas with high p a r t i a l pressure of oxygen can lead to enrichment i n s i l i c a . Also, Bailey and Schairer (1966) show that c r y s t a l f r a c t i o n a t i o n i n highly oxidized undersaturated systems can y i e l d oversaturated iron-poor residuals (see Figure 3.7B). However, i n view o f the r e l a t i v e l y high i r o n content of even the most acid rocks of 'B1 s e r i e s (see Figure 3.1) i t seems u n l i k e l y that magnetite-fractionation played any important r o l e i n the generation of these rocks. Also, determination of co-existing plagioclase and potassic feldspars i n a number of rocks of 'B' series shows that feldspar pairs are joined by r e l a t i v e l y steep t i e lines (see Figure 3.10); this feature, according to Yoder et a l . (1957), is character-i s t i c of shallow-seated magmas (low pressure and high temperature). Escape of water through the roof of the magma chamber would reduce the oxygen content of the magma, thereby i n h i b i t i n g formation of magnetite. A more adequate explanation of the o r i g i n of the 'B1 series is simply mixing of 'A' and 'C1 magmas. V a r i a t i o n diagram, Figure 3.11, shows mostly regular chemical change from ' i ' , a composition intermediate i n 'C1 series (see Figure 3.9), through undersaturated and saturated rocks of 'B' s e r i e s , nos. *3l and '4.' and average 'k 1, average Kelowna trachyte (see Appendix Table A-4, no. 4), to no. '2.', average Marama lava. Roughly, rosette-porphyries and clot-porphyries of 'B1 series represent mixtures of ' i ' and '2.' of about 2:1; average Kelowna trachyte 'k' i s mixed about 1:2. Re l a t i v e l y high concentration of potash i n 'B' series shown i n 121 Figure 3.7 Phase Diagrams Si l ica Albite Nepheline Figure 3.8 Subtraction Diagram, 'A1 Series (see Table B-l) V Y y a) a) a) . . .2 x ~ c Park Rill av. Marama Jf | o o andesite lava a. a in 5 (total iron is calculated as FeO) 123 Figure 3.9 Subtraction Diagram, 'C'Series (see Table B-l) Skaha augite - porphyry av. Yellow Lake lava (total iron is calculated as FeO) 'y' consists of crystal accumulate clinopyroxene 6 8 % and biotite 2 7 % and fugitive potash 5 % (see Table 3.4) V composition intermediate in'c'series , see Figure 3.11 Table 3.3 Normative Calculations, 'y' as Pyroxene, B i o t i t e , and Potash Residual Formula positions of cations Z Y X W to t a l s 100.0 Composition of 'y', cation molecular percent S i A l Fe" Fe" Mg Ca K 39.7 8.5 8.2 19.9 15.3 8.4 Clinopyroxene (Wo^^En^^Fs^Q) %> general formula cation proportions W(X,Y)Z 20 6 charge 29.1 1.7 +6.8 4.9 0.3 +0.9 6. 0.3 +0.9 8 0.1 +0.2 11.9 0.7 +1.4 15.3 0.9 + 1.8 68.0% +12.0 B i o t i t e % general formula cation proportions W(X,Y) 3 Z 4 0 1 Q ( O H ) 2 charge 10.6 3.0 + 12.0 3.6 1.0 +3.0 1. 0.4 + 1.4 4 8.0 2.3 +4.6 3.5 1.0 + 1.0 27.1% +22.0 Residual "L 4.9 4.9% (Composition Wo. En„ Fs„ n i s determined o p t i c a l l y for pyroxene i n Skaha augite-porphyry) Figure 3.10 Co-existing Plagioclase and Potassic Feldspar in Two-Feldspar Rocks B Series ' A ' Series I. Rhyolite (Kelowna Area) 2. Trachyte (Kelowna Area) 3. Trachyandesite (Midway Area) 4. Trachyte (Midway Area) 5. Rosette - porphyry , Marron Gp. w 6. Clot-porphyry, Marron Gp. • determinations, this study o determinations, Church 1963 _ _ Join for De_e P_S_eate_d_Mogma (Yo_der_e_t _al 10 20 30 4 0 50 60 O r % in Potassic Feldspar (201 X-ray determinations) Figure 3.11, i s not accounted for by -the mixing hypothesis outlined above. Source of this extra potash may be 'C1 magmas since, as previously indicated, some potash is l o s t from 'C1 during magmatic evolution. High apatite content i n these rocks suggests that the magmas were v o l a t i l e - r i c h and that possibly transfer of potash from 'C1 to 'B1 magmas i s achieved by v o l a t i l e movement. Concentration differences of Sr and Ba i n rocks and minerals support the f r a c t i o n a t i o n and mixing hypotheses outlined above. Church (1963, Table 4.8) shows average p l a g i o c l a s e much r i c h e r i n Sr and Ba than clinopyroxene (plagioclase, 3300ppm. Sr and 1260 ppm. Ba, average of 4 analyses, clinopyroxene, 174ppm. Sr and 90ppm. Ba, average of 6 analyses). High Sr and Ba content of 'C' compared to 'A' series rocks (see Figure 3.5B) is possibly due to p a r t i t i o n i n g of these elements between c r y s t a l and l i q u i d phases such that marked f r a c t i o n a t i o n of pyroxene from 'c' magmas leaves r e s i d u a l l i q u i d enriched i n Sr and Ba, whereas, f r a c t i o n a t i o n of large amounts of plag i o c l a s e i n the case of 'A' series leaves r e s i d u a l l i q u i d s impoverished i n these elements. Average concentration of Sr and Ba i n 'B' series is intermediate to 'A' and 'c' supporting the mixing hypothesis . Figure 3.11 Mixing Diagram 127 (total iron is calculated as FeO) 128 CHAPTER IV SUMMARY AND CONCLUSIONS GEOLOGICAL HISTORY A summary of Cenozoic geological events i n southern i n t e r i o r of B r i t i s h Columbia i s given i n Table 4.0, based mainly on; publications by Schofield (1943), R u s s e l l (1954), Mathews (1964), and B a l l y et a l . (1966) . In the l i g h t of f o s s i l evidence and s t r a t i g r a p h i c c o r r e l a t i o n s , outlined i n preceding chapters, i t seems l i k e l y that most of the rocks of the White Lake map-area were deposited during a short i n t e r v a l of geological time, probably not extending much beyond the Eocene opoch. A generalized columnar section of the T e r t i a r y s t r a t a i s shown i n Figure 4.1. The e a r l i e s t recorded T e r t i a r y event i n the area was marked by deposition of Springbrook v a l l e y - t a l u s and stream gravels. This was followed by s l i g h t eastward t i l t i n g of the Springbrook beds and a period of intense v o l c a n i c a c t i v i t y , during which the Marron rocks were deposited. Five v o l c a n i c events are recognized i n the Marron succession, each marked by deposition of d i s t i n c t i v e rocks. The lowermost rocks are, t y p i c a l l y , anorthoclase porphyries. These are o v e r l a i n , i n order, by trachyte-trachyandesite, b a s a l t i c andesite, trachyte-trachyandesite, and, uppermost, andesite. These lavas, mostly products of f i s s u r e extrusions, buried p r e - e x i s t i n g v a l l e y s and h i l l tops to form thick s h e e t - l i k e deposits, so that l o c a l topographic r e l i e f was greatly reduced. Volcanic a c t i v i t y resumed with renewed vigor with extrusion of Marama r h y o l i t e and rhyodacite, but not before erosion had cut deeply into the upper Marron rocks. Viscous lavas flooded v a l l e y s burying t h i n gravel deposits and, l o c a l l y , overtopped r i d g e - c r e s t s . An i n t e r v a l of erosion and gravity f a u l t i n g followed. At t h i s time, Okanagan V a l l e y was probably a prominent geomorphological feature containing an important stream course. 129 Table 4.0 Outline of Cenozoic Geological Events Epochs K-Ar Age Main Events /Recent u p l i f t and downcutting of streams; development of r i v e r terraces, deposition of a l l u v i a l fans i n main v a l l e y s Pleistocene extensive g l a c i a t i o n , general beveling of topography and widing and deepening of v a l l e y s by ice action, formation of melt water channels; deposition of t i l l s and d r i f t , deposition of white s i l t s of Kamloops and Okanagan v a l l e y s 1 m.y. Pliocene u p l i f t and d i s s e c t i o n of landscape followed by l o c a l v o l c a n i c eruptions, 'valley basalt' 10 m.y. Miocene short period of widespread v o l c a n i c eruption "plateau b a s a l t s ' 25 m.y. Oligocene u p l i f t followed by development of l a t e mature erosion surface 38 m.y. Eocene extensive and prolonged v o l c a n i c eruption; deposition of lake and stream sediments and some coal 57 m.y. ; : Paleocene record i n Rocky Mountain area - end of imbricate thrusting and molasse-type deposition K-Ar dates for epoch boundaries, average from Holmes (1959), Kulp (1961), and Geol. Soc. London (1964) 130 Figure 4.1 Generalized Columnar Section Formations Main Deposits Erosional and Tectonic Events Scale: 3 0 0 0 ' -2000 ' -1000'-o' J Skaha F. White Lake F. Marama F. Marron F. ,_,or-« °o-, Springbrook F. - \ I y-l / - \ I \ - / I \ / I \ — / 0 O o O D T-+ + + + + + f + + + + + +• + + + + O o o O ( o 0 7 TJ p a a •9 ••aa?c9 A A A A glacial deposits fanglomerate slide breccias volcanic rocks interdigitated with sediments rhyolite - rhyodacite conglomerate  andesite trachyte - trachyandesite basaltic andesite trachyte - trachyandesite rhomb-porphyry conglomerate talus pre-Tertiary metomorphic rocks erosion - faulting - folding erosion faulting erosion - faulting faulting erosion - faulting -folding (maximum thickness of units shown) Deposition of White Lake sediments coincided with the eruption of trachyte and trachyandesite lavas from vents centered near the Okanagan V a l l e y . In th i s area, a northerly flowing stream was pro-bably dammed by vo l c a n i c debris forming a lake several miles i n diameter (T e r t i a r y White Lake). Large volumes of l a h a r i c and pyro-c l a s t i c material were p e r i o d i c a l l y ejected from w a t e r - f i l l e d vents s p i l l i n g debris into Okanagan V a l l e y and the nearby lake. The lake was f i l l e d by considerable thickness of shale, sandstone, and some co a l . Extrusion of a small amount of tephrite lava marked the climax of v o l c a n i c a c t i v i t y . Normal f a u l t i n g followed and continued during deposition of the Skaha beds. These consist, i n the lower part, of s l i d e - b r e c c i a s with i n t e r c a l a t e d tephrite lava and, i n the upper part, of coarse fanglomerates . I-The gross nature of the c l a s t i c rocks r e f l e c t s the dynamic conditions under which they were deposited. The s l i d e - b r e c c i a s were derived from high t e r r a i n , underlain mainly be Mesozoic chert, greenstone, and granite near the southeast part of map-area. The breccias were deposited on both T e r t i a r y and pre-Tertiary rocks, possibly at the base of a f a u l t scarp. They disrupted l o c a l drainage and were p a r t l y eroded and reworked by stream a c t i o n . The uppermost beds, the fanglomerates, were derived p a r t l y from older T e r t i a r y rocks and from the same high t e r r a i n that was a source f o r the s l i d e - b r e c c i a s This material rests on eroded s l i d e - b r e c c i a s and l o c a l l y onlaps White Lake rocks . Deformation postdating the events described above, include f o l d i n g (probably pre-Miocene), gravity and s t r i k e - s l i p f a u l t move-ment (age unknown). The l a t e mature erosion surface, t y p i c a l of c e n t r a l i n t e r i o r B r i t i s h Columbia, i s preserved, i n places, i n the western part of the map-areaj however, no Miocene Plateau Basalts o v e r l i e t h i s surface as they do elsewhere. PETROLOGY A wide spectrum of lavas i s present i n the T e r t i a r y s t r a t i g r a p h 132 succession of the White Lake area. Three rock series are recognized from mineral and chemical evidence; 'A1, rhyolite-andesite; 'B1, trachyte-trachyandesite; *C', phonolite (rhomb-porphyry) -' tephrite (shonkinite). Some important mineral differences are found. For example feldspar compositions vary markedly. T y p i c a l l y 'A' series rocks contain plagioclase phenocrysts i n the range An 0_ to An.^; potassic _,U oL) feldspar i s scarce. Commonly 'B' series rocks are two feldspar-bearing with coexisting andesine and sanidine phenocrysts. The rocks of 'C' series contain anorthoclase or, less commonly, sanidine; but very l i t t l e p l a g i o c l a s e . Apatite shown important v a r i a t i o n s . Apatite c r y s t a l s are generally small and scarce i n 'A* rocks, small but common i n 'B' rocks, and large and abundant i n 'C' rocks. Marked chemical differences are also found. The composition of 'A' rocks contrasts sharply with that of 'C' rocks; generally, 'B1 rocks are chemically intermediate to 'A' and 'C'. 'A' rocks commonly contain normative quartz and have small a l u m i n a - t o - s i l i c a r a t i o s , low strontium and barium content, and show a large range i n i r o n concen-t r a t i o n . In contrast, *C* rocks contain normative nepheline and have large a l u m i n a - t o - s i l i c a r a t i o s , high strontium and barium content, and are i r o n - r i c h . Details on the o r i g i n of these rocks are uncertain but probably they were derived from p l u t o n i c bodies formed from the melting of s i a l i c and possibly some carbonate substratum. Absence of basalt suggests that this rock played l i t t l e or no r o l e i n formation of the lavas of the White Lake area. Rocks of 'A' series form part of an early T e r t i a r y 'andesite 1 b e l t that extends through the central i n t e r i o r of B r i t i s h Columbia and northern and western Washington st a t e . These lavas were probably ex-truded from large granodiorite,batholiths f l a n k i n g the axis of the Cascade Mountains. Rocks of 'B' and 'C' series are probably derived from the C o r y e l l B a t h o l i t h (or s a t e l l i t e stock) which i s s i m i l a r i n age and 133 composition. The main lobe of the C o r y e l l B a t h o l i t h , near T r a i l i n south-central B r i t i s h Columbia, appears to be a high l e v e l i n t r u s i o n unroofted by erosion a f t e r l a t e T e r t i a r y u p l i f t . C o r y e l l intrusions together with the lavas of the 'B' and 'C' series form an a l k a l i c petrographic province centered immediately north of the International Boundary, extending from Okanagan V a l l e y area on the west to Kootenay Lake on the east. Evidence from experimental petrology suggests that two proces-ses were mainly responsible f o r genesis and d i v e r s i f i c a t i o n of these ro cks: 1- Rocks of the 'A' and *C' series were formed by c r y s t a l f r a c t i o n -a t i o n of a n d e s i t i c and s h o n k i n i t i c parent magmas, r e s p e c t i v e l y . 2- Rocks of the 'B1 series were formed by mixing of 'A' and 'C' l i q u i d d i f f e r e n t i a t e s . Removal of mineral aggregates s i m i l a r to actual phenocrysts of basic rocks of 'A' and 'C' series y i e l d s residuals s i m i l a r i n com-p o s i t i o n to acid rocks of the s e r i e s . For example, subtraction of mainly plagioclase and some pyroxene and b i o t i t e from t y p i c a l andesite of the 'A' series y i e l d s a r h y o l i t i c composition; a l s o , subtraction of the mainly pyroxene and some b i o t i t e from tephrite (augite-porphyry of the 'C' series) y i e l d s p h o n o l i t i c composition ( l i k e the rhomb-porphyry rocks of 'C series) . S i m i l a r l y , i t i s possible to show, using a mixing diagram, that 'B1 rocks have bulk compositions intermediate between the 'A' and 'C s e r i e s . D e t a i l s on the mixing process are uncertain, however; s c a r c i t y of country rock xenoliths i n 'B' lavas favours the view that l i q u i d mixing was achieved without much s o l i d a s s i m i l a t i o n . In view of the high apatite content of 'B1 and 'C' rocks i t i s l i k e l y that v o l a t i l e s were i n f l u e n t i a l i n t h e i r evolution. For example, the high potash content of 'B' rocks i s not accounted f o r by simple mixing of 'A' and 'C' magmas which are mostly soda-rich. Also, ca l c u l a t i o n s show that excess potash r e s u l t s from c r y s t a l f r a c t i o n -ations of *C' magmas - probably this excess potash was bo i l e d o f f with v o l a t i l e s , to be gained, i n part, by subjacent 'B.1 magmas. F i n a l l y , i n the l i g h t of recent work by Bowes and others, the 13U a s s o c i a t i o n of i n t r u s i o n breccias and basic a l k a l i - r i c h rock, such as found i n the Skaha Formation, may not be c o i n c i d e n t a l . Possibly v o l a t i l e s generated by c r y s t a l l i z a t i o n of augite-porphyry magma caused explosions and remobilization of bedded rocks, such as Skaha s l i d e debris, to form i n t r u s i o n b reccias. However, no conclusive e v i -dence was found to support t h i s theory during the present study. SUGGESTIONS FOR FUTURE WORK The present study provides a basis f o r future work on s t r a t i -graphy, structure, mineralogy, and chemistry of T e r t i a r y rocks of the White Lake area. The following studies are proposed to amplify s t r a t i g r a p h i c data f o r purposes of c o r r e l a t i o n : 1- Radiometric age-dating. Most lavas of the White Lake area contain fresh b i o t i t e s u i t a b l e f or potassium - argon determinations. 2- P a l i o b o t a n i c a l studies. Springbrook beds and e s p e c i a l l y White Lake beds contain abundant le a f f o s s i l s . Some m i c r o f o s s i l s , spores and p o l l e n grains were obtained from White Lake sediments. 3- Paleomagnetic studies. According to some authors, magnetic reversals serve as marker zones f o r c o r r e l a t i o n i n some otherwise u n d i f f e r e n t i a t e d lava successions. A d d i t i o n a l research i s suggested on the structure of the T e r t i a r y p i l e i n the complex area near White Lake. A wealth of information could be obtained from seismic records of the Dominion Observatory s t a t i o n at White Lake. Mineral studies might p r o f i t a b l y be extended to include major and minor element analyses using X-ray fluorescent or emission spectro-g r a p h s methods. Detailed information i s e s p e c i a l l y scarce on z e o l i t e s , a l k a l i f e l d s p a r s , and a p a t i t e , a l l of which are fresh minerals commonly occurring i n abundance i n the T e r t i a r y rocks of the White Lake area. F i n a l l y , to complete chemical data, i t i s suggested that major oxide analyses be obtained for Marron b a s a l t i c andesite and White Lake trachyte and trachyandesite l a v a s . 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SiO '74.9 -67.6 53.8 54.6 58.1 49.7 54.9 55.0 51.7 52.0 • 46.8 TiO-2 0.18 0.41 1.46 0.94 0.86 0.60 0.90 0.98 0.78 0.94 1.04 AI 2 6 14.7 17.2 16.2 14.8 15.4 17.5 18.8 17 .5 20.5 20.6 15.3 MnO 0.07 0.06 0.14 0.08 0.11 0.09 0.10 0.18 0.11 0.10 0.14 FeO 0.63 2.3 6.8 5.5 5.9 3.2 4.9 4.6 5.1 4.8 7.0 MgO 0.5 0.5 4.8 3.7 4.1 2.8 1.8 1.0 2.3 0.9 6.3 CaO 1.2 2.9 6.1 4.8 5.2 6.7 4.6 4.0 4.7 4.3 8.5 Na20 4.6 4.6 3.7 3.8 3.9 4.1 4.5 4.3 4.6 6.0 3.2 K20 2.97 3.08 2.11 3.70 2.95 5.21 4.94 6.17 4.73 2.86 4.90 SrO 0.015 0.045 0.070 0.130 0.118 0.177 0.390 0.189 0.602 0.402 0.580 BaO 0.202 .0.224 0.0965 0.269 0.224 0.560 0.615 0.415 0.850 0.808 0.965 H 20 0.6 0.9 2.7 3.3 1.7 1.8 2.0 1.6 2.7 4.9 2.0 C O 2 0.1 0.3 0.1 3.0 0.1 7 .8 0.1 0.3 0.4 1.1 3.5 To t a l 100.7 100.1 98.1 98.6 98.7 100.2 98.5 96.2 99.1 99.7 100.2 R.I. 1.499 1.508 1.553 1.549 1.539 1.541 1.535 1.584 1.555 1.556 1.582 1. Rhyolite, Marama F. ( f i e l d no. N64-2-8; Map 100 loca t i o n no. 13) 2. Rhyodacite, Marama F . ( f i e l d no. N64-8-9; Map 100 l o c a t i o n no. 12) 3. Park R i l l andesite, Marron F, ( f i e l d no . N64-3-1 ; Map 100 l o c a t i o n no. 9) 4. Park R i l l andesite, Marron F. ( f i e l d no . N64-11-15; Map 100 l o c a t i o n no. 10) 5. Park R i l l andesite, Marron F. ( f i e l d no . N 6 4 - 2 5 A -a; Map 100 lo c a t i o n no. 8) 6. Trachyandesit e (weathered), White Lake F. ( f i e l d no. CC-18; Map 100 1 l o c a t i o n no. 14) 7. Clot-porphyry , Marron F. ( f i e l d no. N64 -21-5; Map 100 l o c a t i o n no. 4) 8. Rosette-porphyry, Marron F. ( f i e l d no. N64-24-2; Map 100 lo c a t i o n no. 6) 9. Yellow Lake porphyry , Marron F . ( f i e l d no. N64-20-K; Map 100 l o c a t i o n no. 3) 10. Yellow Lake porphyry , Marron F . ( f i e l d no. N64-B ; Map 100 l o c a t i o n no. 1) 11. Augite-porphyry, Skaha F. ( f i e l d no. 93C1; Map 100 l o c a t i o n no. 15) ( t o t a l i r o n i s calculated as FeO) Analyses by Geological Survey of Canada, Rapid Method Table A-2 P a r t i a l Analyses of Rocks, White-Lake Map-area i . 2. 3. a. S i 0 2 61.79 63.68 T i 0 2 0.74 0.91 AI2O3 16.52 15.47 MnO 0.05 0.07 FeO 3.78 4.81 5 .20 4.30 MgO 1.50 3.30 3.30 2.40 CaO 3.90 6.40 6.20 4.20 SrO 0.15 0.15 0.165 0.310 BaO 0.28 0.16 0.260 0.550 trace 0.30 H 20 1.19 1.19 Tota l 89.90 96.44 R.I. 1.517 1.538 1.529 1.532 1. Clot-porphyry, Marron F. ( f i e l d no. CC-5; Map 100 l o c a t i o n no. 5) 2. Park R i l l andesite, Marron F. ( f i e l d no. CC-7; Map 100 l o c a t i o n no. 11) 3. Rosette-porphyry, Marron F. ( f i e l d no. CC-6; Map 100 l o c a t i o n no. 7) 4. Yellow Lake porphyry, Marron F. ( f i e l d no. CC-1; Map 100 l o c a t i o n no. 2) Table A-3 Chemical Analyses from Other Studies 1. 2. 3. 4. 5. 6. 7 . 8. 9. 10. Si02 59.7 65.6 63.8 55.9 58.4 58.7 61.4 53.0 72.5 59.5 A1 20 3 15.4 15.4 18.1 22.0 16.2 17.8 18.4 15.8 15.1 20.4 FeO 6.2 3.5 3.5 4.7 6.7 5.7 4.1 8.1 1.7 4.2 MgO 5.1 1.8 1.0 1.7 4.9 2.8 1.4 8.1 0.8 1.8 CaO 8.6 4.2 1.8 4.2 6.1 4.3 1.8 8.2 1.5 3.9 Na 20 ) S 0 > 9 5 4.9 5.1 3.0 4.6 5.4 2.9 4.1 4.3 K 20 ) J . VJ ) 9 ' 5 6.9 6.4 4.7 6.1 7 .5 3.9 4.3 5.9 (major oxides recalculated to 100 ] percent; t o t a l i r o n as FeO) 1. Average andesite, Midway Gp. (Church, 1963, Table D-3 analysis A^ ^) 2. Rhyodacite, Kelowna area (Church, 1963, Table D-3 no. A.7) 3. Pulaskite dike, Midway area (Daly 1912, Table XXVII no. 1) 4. Rhomb-porphyry, Midway Gp. (LeRoy 1912, analysis no. I, p.46) 5. Feeder dike to Midway andesite (LeRoy 1912, analysis no. I, p.49) 6. Trachyandesite, Midway Gp. (LeRoy 1912, analysis no. I, p.51) 7. Trachyte, Midway Gp. (Drysdale 1915, analysis p.126) 8. ' A l k a l i c b a s a l t 1 (augite-porphyry), Midway Gp. (Drysdale 1915, analysis p.128) 9. Average composition of Shingle Creek porphyry (Bostock 1966, Table LX, no.5) 10. Trachyandesite, Marron Gp. (Bostock 1966, Table IX, no. 8) vn. Table A-4 Averaged Analyses from Other Studies 1. 2. 3. 4. 5. FeO MgO CaO Na20 K 2 O 56.2 18.9 6.0 4.5 3.5 5.1 5.8 68.1 15.8 3.3 1.9 3.8 4.0 3.1 64.8 16.8 4.5 2.7 4.7 4.1 2.8 63.7 17.1 3.5 0.7 3.4 11.6 56.0 20.5 5.8 2.6 4.5 6.1 4.5 (major oxides recalculated to 100 percent; t o t a l i r o n as FeO) 1. Average 'rhomb-porphyry', Marron Gp. (Bostock 1966, Table IX, nos. 6 and 7) 2. Average lava, Sanpoil Volcanics (Staatz 1964, Table 5, nos 1, 2, and 3) 3. Average lava, Sanpoil Volcanics (Parker and Calkins, 1964, Table 3, nos. 1 and 2) 4. Average trachyte, Kelowna area (Church 1963, Table D-3, nos. B-5 and B-7) 5. Average rhomb-porphyry, Midway Gp. (Daly 1912, Table XXVI no. 3; no. 1064 p. 414) APPENDIX 'B' CALCULATION OF NORMS Norm calculations are performed using a method adapted from Barth (1959). B r i e f l y , the procedure is as follows: Major oxide composition i s recalculated to cation proportions according to the following example for A^O^ : molecular proportion = Wt.%/ Mol. Wt. = 18/ 102 = 0.176 cation proportion = 0.176 x 2 = 0.352 Cation proportions are summed and recast as percentages, then assigned to mineral molecules according to the schedule given below. F i n a l l y , constituent cations of each mineral are summed giving normative mineral composition expressed as molecular mineral percent. Schedule for Assignment of Cations: !. Orthoclase IK, 1A1, 3Si 2. A l b i t e INa, 1A1, 3Si 3. Anorthite ICa, 2A1, 2Si 4. Residual A l as corundum 5. Residual Ca i n d i o p s i d i c augite ICa, l(Mg + Fe), 2Si 6. Residual Mg i n hypersthene lMg, lFe, 2Si 7. Residual Fe as magnetite 8. Residual S i as quartz 9. If there is a deficiency of S i , r e c a l c u l a t e part or a l l of a l b i t e to nepheline (INa, 1A1, ISi) i n the proportions: x ( a l b i t e ) + y(nepheline) = a v a i l a b l e Na 3x(albite) + y(nepheline) = a v a i l a b l e S i 10. I f there i s s t i l l a deficiency of S i a f t e r step 9 then r e c a l c u l a t e part or a l l of hypersthene to o l i v i n e (lMg, lFe, ISi) i n the proportions: x(hypersthene)+ y ( o l i v i n e ) = a v a i l a b l e Mg, Fe x(hypersthene)+%y(olivine) = a v a i l a b l e Mg, Fe For purpose of s i m p l i f i c a t i o n , minor rock constituents, including water, are ignored i n c a l c u l a t i o n s . As a r e s u l t , b i o t i t e which i s a common modal hydrous mineral, is normatively represented by some of the orthoclase (or k a l s i l i t e ) - a n d i r o n oxide, and most o 1U8 the o l i v i n e and corundum. S i m i l a r l y , a n a l c i t e which is present i n some undersaturated rocks of this study, is represented mainly by normative nepheline. The norms of rocks of 'A1, 'B1, and 'C1 s e r i e s , occurring i n the White Lake area, are given i n Table B - l . Abbreviations for normative minerals are as follows: Qtz quartz Or orthoclase Ab a l b i t e An anorthite Ne nepheline Cor corundum Di d i o p s i d i c augite Hy hypersthene Olv o l i v i n e Mg magnetite 11*9 Table B - l Normative Compositions 1. 2. 3. 4. 5. 6. SiO 61.0 72.4 59.4 60.9 51.0 56.0 A l 6 16.2 16.2 18.9 18.4 16.6 22.3 F e d 3 6.1 1.5 5.0 4.5 7.6 5.4 MgO 4.2 0.1 1.1 1.7 6.9 1.8 CaO 5.4 2.1 4.3 4.4 9.2 4.8 Na 0 4.0 4.7 4.6 4.8 3.4 5.7 K26 3.1 3.0 6.7 5.3 5.3 4.0 Qtz 5.5 26.9 1.9 Or 18.2 18.1 39.1 30.8 30.7 23.0 Ab 35.5 41.9 35.0 42.3 2.0 38.0 An 16.9 , 10.0 11.0 12.8 14.0 22.9 Ne - - 3.5 - 16.7 7.1 Cor - 1.5 - - - -D i 7 .7 - 8.1 7.0 24.5 0.3 Hy 15.3 0.6 - 2.3 - -Olv - - - 9.5 7.0 Mg 0.9 1.0 3.3 2.9 2.6 1.7 1. Fresh Park R i l l andesite ( f i e l d no. N64-25A-2) 2. Average Marama lava ( f i e l d nos. N64-2-8, N64-8-9) 3. Fresh rosette-porphyry ( f i e l d no. N64-24-2) 4. Average clot-porphyry ( f i e l d nos. N64-21-5, CC-5) 5. Fresh Skaha augite-porphyry ( f i e l d no. 93C1) 6. Average Yellow Lake lava ( f i e l d nos. N64-20-k, N64-B) ( t o t a l i r o n i s calculated as FeO) APPENDIX 'C1 PETROGRAPHIC DESCRIPTIONS The following petrographic descriptions of d i s t i n c t i v e lava types supplement data given i n Chapters I I and I I I . Descriptions are arranged according to the main rock s e r i e s , as defined i n Chapter I I I , then i n order of r e l a t i v e s t r a t i g r a p h i c p o s i t i o n of the rocks. Rock colour-names and symbols are adapted from the 'rock-color chart 1 d i s t r i b u t e d by Geological Society of America (1963). Textural terms are those suggested by Williams, Turner, and G i l b e r t (1955) . Methods used for determination of main minerals are as follows: Potassic feldspar - 201 X-ray method (Tut t l e and Bowen, 1958, p. 13) Plagioclase - cleavage flake o i l immersion method by Tsuboi (Winchell and Winchell, 1956, p. 281) - r e f r a c t i v e indices of p l a g i o c l a s e glass (Slemmons, 1962, Plate 12) Clinopyroxene - o p t i c a x i a l angle and r e f r a c t i v e index method (Deer et aL, 1963, v o l . 2, p. 132) ROCKS OF 'A' SERIES 1. B a s a l t i c Andesite This rock occurs near the middle of the Marron Formation and is conveniently exposed i n a road cut 0.4 miles east of Yellow Lake on Highway 3. The rock i s t y p i c a l l y a pyroxene-porphyry and varies i n colour from brownish grey (5YR4/1) on fresh surfaces to moderate brown (5YR3/4) where weathered. Although no chemical analyses are a v a i l a b l e , r e l a t i v e high r e f r a c t i v e indices of glass a r t i f i c i a l l y prepared from several samples suggest a s l i g h t l y more basic composition than that of t y p i c a l andesites of 'A' series (see Figure 2.4). 151 The following modal composition i s determined from four t h i n sections: Phenocrys ts Clinopyroxene Plagioclase 10% 1% Groundmass Feldspar C h l o r i t e 60% 15% Magnetite B i o t i t e Apatite Quartz accessory Clinopyroxene composition i s about Wo,„En„ qFs (2V^- 51°, ny - 1.693). Grains are commonly subhedral, s l i g h t l y elongate i n prismatic section, and r a r e l y exceed 3.5mm. i n maximum diameter. Alternate medium and pale green ( o s c i l l a t o r y ) zones are developed i n many large c r y s t a l s . Inclusions of small apatite rods, magnetite granules, and glass blebs are common i n some phenocrysts. Plagioclase phenocrysts range i n composition between o l i g o -clase and andesine ( r e f r a c t i v e index determinations on glass from fused plagioclase, n - 1.513, gives the composition Ab^^An.^). Large c r y s t a l s are generally lath-shaped (as much as 4mm. long) but as a r u l e with some embayments or rounded o u t l i n e . The groundmass i s composed of small (less than %mm. i n diameter) i n t e r l o c k i n g equant grains of plagioclase, potassic f e l d -spar, and c h l o r i t e . Magnetite granules are disseminated throughout the groundmass and are i n t e r s t i t i a l to s l i g h t l y larger s i l i c a t e minerals. Quartz i s scarce and i s mainly concentrated i n amygdales and along cracks . Secondary a l t e r a t i o n has severely affected plagioclase pheno-crysts and groundmass constituents; however, primary textures are not destroyed. Plagioclase i s replaced, i n part, by mixtures of mica, clay minerals, and possibly some c a l c i t e . C h l o r i t e has replaced a few small phenocrysts of pyroxene and almost a l l of the groundmass pyroxene and b i o t i t e . 2. Andesite T y p i c a l andesite forms the uppermost u n i t of the Marron 1*2 Plate C.2 Photomicrograph (crossed n i c o l s ) of b a s a l t i c andesite showing plagioclase (PI.) and clinopyroxene (Cpx.) phenocrysts set i n m i c r o c r y s t a l l i n e groundmass Formation and i s given the l o c a l name-'Park R i l l andesite'. Two text u r a l phases can be distinguished i n the f i e l d , a merocrystalline and a v i t r i c phase. Me r o c r y s t a l l i n e andesite is d i s t r i b u t e d widely throughout the map-area but i s most conveniently exposed immediately north of the gravel road about 0.8 miles northwest of Stewart Ranch. V i t r i c andesite, s t r a t i g r a p h i c a l l y equivalent to merocrystalline andesite, i s observed only on the north limb of the White Lake syn c l i n e . A fresh and r e a d i l y accessible exposure of v i t r i c andesite i s located immediately east of the gravel road 1.1 miles north of Observatory S i t e . The colour of these rocks i s somewhat v a r i a b l e . M e r o c r y s t a l l i n e andesite i s commonly dusky yellowish brown (10YR2/2) where fresh but moderate brown (5YR3/4) on rusted weathered surfaces. A l t e r e d ( c h l o r i t i z e d ) andesite observed on the ridge south of Stewart Ranch i s commonly greenish grey (5GY6/1) flecked with small white a l t e r e d feldspar c r y s t a l s . V i t r i c andesite i s dark grey (N3) where fresh but yellowish brown (10YR4/2) on weathered surfaces. Chemical analyses show merocrystalline andesite to be s l i g h t l y more a c i d i c i n composition than v i t r i c andesite (see Table 2.6). This is i n keeping with s l i g h t differences noted i n r e f r a c t i v e indices of glass beads prepared from rock samples (average R.I. = 1.541, 4 samples of merocrystalline andesite; average R.I. = 1.548, 8 samples of v i t r i c andesite). Smaller average density of v i t r i c andesite (av. S.G. = 2.656, 15 samples) compared to merocrystalline andesite (av. S.G. = 2.669, 21 samples) i s probably due to c r y s t a l - t o - g l a s s r a t i o d i f f e r e n c e s . Modal composition of fresh merocrystalline andesite, determined from eight t h i n sections, is as follows: Glass Plagioclase Clinopyroxene Magnetite B i o t i t e Orthopyroxene Apatite 60% 25% 157= 17= - 17= trace trace Plagioclase c r y s t a l s commonly show o s c i l l a t o r y zoning and have a composition-range of An^. - An^-j (Tsuboi method) - (R.I. of plagioclase glass i s 1.533 giving the approximate composition Ab^g An^) • Crystals are commonly s o l i t a r y with rectangular habit of subhedral or euhedral o u t l i n e . Crystals with diameters 0.5 to 1mm. are most abundant and few exceed 3.5mm. Most commonly, pla g i o c l a s e i s clear and contains a few apati t e grains or glassy bleb i n c l u s i o n s ; also, c r y s t a l s are r i d d l e d with vermicular glass or blebs and grains of foreign material arranged c o n c e n t r i c a l l y i n layers p a r a l l e l to o s c i l l a t o r y zoning. A l b i t e and Carlsbad type twinning i s w e l l developed i n almost a l l plagioclase grains. Clinopyroxene shows some o s c i l l a t o r y zoning and has the approximate composition Wo^ ^ 3 3 F S2Q = 57°> n y = 1.697). Crystals are commonly s o l i t a r y with stubby prismatic sections and anhedral or subhedral o u t l i n e s . Most c r y s t a l s are w i t h i n the s i z e range 0.25 to 0.5mm., few are greater than 3mm. i n diameter. Crystals are pale green and clear; a few contain small a p a t i t e rods or magnetite grains . Accessory minerals include magnetite, b i o t i t e , orthopyroxene, and a p a t i t e . Magnetite i s r e l a t i v e l y abundant forming anhedral grains (less than 0.25mm. i n diam.) scattered randomly throughout the glassy groundmass or occurring i n clusters with pryoxene. B i o t i t e i s less abundant and is observed as dark brown strongly pleochroic books (oxybiotite) ranging greatly i n s i z e from less than 0.5mm. to more than 3mm. i n maximum length. Commonly, b i o t i t e i s p a r t l y corroded and charged with magnetite dust but also occurs as fresh euhedral c r y s t a l s . Apatite i s not abundant and is found mainly as inclusions i n s i l i c a t e minerals. A strongly pleochroic v a r i e t y of orthopyroxene, probably hypersthene (large o p t i c a x i a l angle) forms about 5 percent of the pyroxene concentrates separated from t h i s rock. Glass, which forms the bulk volume of this rock, is medium brown coloured and has a lower r e f r a c t i v e index than Canada Balsam (1.540). S t r u c t u r a l l y , the glass has flow banding and, i n some samples, is charged with t i n y m i c r o l i t e s . V i t r i c andesite composition, estimated from 12 t h i n sections of fresh rock, i s as follows: Phenocrysts - Clinopyroxene 57, Orthopyroxene 1% Plagioclase 1% Groundmass - Glass plus micro 1 i t e s 957= Clinopyroxene composition is estimated Wo^g ^ n39 ^s]_2 (2V^ = 59°, ny = 1.688). These c r y s t a l s are clear, almost colourless, anhedral, and commonly 0.25 to 0.5mm. i n diameter. Orthopyroxene is distinguished from clinopyroxene with some d i f f i c u l t y . The mineral has pale green and pink pleochroism suggest-ing hypersthene composition, although no det a i l e d o p t i c a l data are av a i l a b l e for p o s i t i v e i d e n t i f i c a t i o n . The composition of plagioclase phenocrysts i s i n the range A n ^ - An^ ,_ ( r e l a t i v e l y high r e f r a c t i v e index; p o s i t i v e o p t i c a x i a l angle). Phenocrysts are lath-shaped and small, generally less than 0.5mm. long. Twinning i s not highly developed. The groundmass is composed mostly of grayish brown glass but is commonly charged with small, s u b p a r a l l e l plagioclase laths (less than 0.2mm. long) forming t y p i c a l m i c r o l i t i c texture. Intergranular pyroxene and magnetite i s disseminated throughout. Secondary a l t e r a t i o n of andesite, p a r t l y due to weathering, re s u l t s i n replacement of pyroxene by c h l o r i t e and of plag i o c l a s e by white mica, clay minerals, and c a l c i t e . Chemical analyses of both weathered and fresh merocrystalline andesite (see Appendix Table A - l , nos. 4 and 5) shows high t o t a l water and carbon dioxide i n the weathered rock. Fresh and weathered rocks are almost chemically i d e n t i c a l when major oxides, excluding water and carbon dioxide, are r e c a l c u l a t e d to 100 percent (see Table 2.6, nos. 1 and 2). Normally, textures are w e l l preserved even i n the most severely a l t e r e d rocks . 3. Rhyodacite Rhyodacite lava comprises most of the Marama Formation and is intermixed with minor r h y o l i t e lava and b r e c c i a . The rock i s conveniently exposed i n a road cut immediately east of Prather Lake. 106 Plate C.3 Photomicrograph ( p l a i n l i g h t ) of merocrystalline andesite showing plagioclase (Pl.)> pyroxene ( P x ) , and minor magnetite (opaque) phenocrysts set i n glass Plate C.4 Photomicrogrpah ( p l a i n l i g h t ) of v i t r i c andesite; the rock i s composed lar g e l y of glass containing small laths of plagioclase and a few pyroxene (Px.) subhedra The rock i s varicoloured i n tones of grey on fresh surfaces ( N 3 to N 6 ) and brown ( 1 0 Y R 6 / 2 , 5 Y R 5 / 2 , and 5 Y R 6 / 4 ) where weathered. T y p i c a l l y , p a r t l y weathered samples are mottled medium grey ( N 5 ) and dark yellowish brown ( 1 0 Y R 4 / 2 ) . ) The rock has v i t r o p h y r i c texture and is e a s i l y confused with v i t r i c andesite i n the f i e l d . However, rhyodacite is chemically d i s t i n c t i v e (see Appendix Table A - l , no. 2 ) and has low r e f r a c t i v e index (average R . I . on glass beads is 1 . 5 0 8 , 1 0 samples) and s p e c i f i c gravity (average S.G. = 2 . 5 3 8 , 1 4 samples). Study of twenty t h i n sections shows that the rock consists of more than 8 5 percent glass, d e v i t r i f i e d glass, and m i c r o l i t e s . Pheno-crysts are mainly plagioclase (less than 1 5 7 o ) , some clinopyroxene (less than 5 7 o ) or, r a r e l y , hornblende. Pla g i o c l a s e shows some normal and o s c i l l a t o r y zoning but has an average composition of approximately Ab,.^  ^-n43 (based on deter-mination of plagioclase glass, R . I . = 1 . 5 2 5 ) . Crystals are mainly lath-shaped with euhedral outlines and show complete s i z e range between phenocrysts 1mm. i n maximum length to cryptomicrolite dimens ions. Clinopyroxene c r y s t a l s are observed only i n about h a l f the t o t a l t h i n s e c t i o n examined. The exact composition of this mineral is unknown but a large o p t i c a x i a l angle and almost colourless appearance suggests that i t may be d i o p s i d i c augite. Crystals are small, less than 0.5mm. i n diameter, with equant habit, and commonly subhedral or anhedral o u t l i n e . Hornblende i s observed i n only one t h i n s e c t i o n . Crystals are small, mostly less than 0.5mm. i n length, and show subhedral o u t l i n e s . Margins of some c r y s t a l s are corroded and charged with opaque magnetite dust. Pleochroism i s so strongly developed (commonly dark brown and greenish brown) that e x t i n c t i o n angles and opti c axis figures are d i f f i c u l t to measure, although Z to C values are small, i n keeping with common hornblende compositions. The glassy groundmass of rhyodacite i s commonly l i g h t coloured and charged with p l a g i o c l a s e m i c r o l i t e s and magnetite grains. 158 P l a t e C»6 P h o t o m i c r o g r a p h ( c r o s s e d n i c o l s ) o f r h y o d a c i t e s h o w i n g p l a g i o c l a s e p h e n o c r y s t s ( P I . ) s e t i n g l a s s y g r o u n d m a s s - f e r r o m a g n e s i a n m i n e r a l s a r e s c a r c e Most samples of rhyodacite show signs of secondary a l t e r a t i o n . The groundmass i s commonly b i r e f r i n g e n t i n d i c a t i n g d e v i t r i f i c a t i o n and replacement by m i c r o c r y s t a l l i n e minerals. C a l c i t e and minor c h l o r i t e have replaced phenocrysts and patches of groundmass i n some of the rock. 4. Rhyolite Rhyolite was observed only i n the Marama Formation and i s w e l l exposed on the h i l l side immediately north of Green Ranch. The rock i s t y p i c a l l y a l i g h t coloured (yellowish grey 5Y8/1) quartz-feldspar-porphyry. Chemical analysis (see Appendix Table A - l , no. 1) shows unusually high s i l i c a content of r h y o l i t e compared to other lavas of this study. Also, s p e c i f i c gravity and r e f r a c t i v e index of r h y o l i t e i s r e l a t i v e l y low (S.G. 2.33; R.I. 1.499). Examination of one t h i n s e c t i o n of r h y o l i t e shows the following modal composition: Phenocrysts - Plagioclase 107o Quartz 57, B i o t i t e 1% Groundmass - mainly de-v i t r i f i e d glass 857o Plagioclase shows marked normal zoning; cores of large pheno-crysts have the approximate composition Ab^,. An^,., m i c r o l i t e s and outer zones of phenocrysts are about Abyg A n 2 4 (determinations are based on the Tsuboi o i l immersion method and e x t i n c t i o n methods). Crystals are rectangular or polygonal i n habit with subhedral outlines and vary i n s i z e from 4mm. i n maximum length to less than 0.5mm. Quartz c r y s t a l s are water-clear and have equant habit showing rounded and embayed o u t l i n e s . Inclusions are few and consist mainly of small rods of apatite, r u t i l e ( ? ) , and vacuoles p a r t l y f i l l e d with l i q u i d . C r y s t a l sizes are v a r i a b l e but commonly range between 0.5 and 3mm. i n diameter. Plate C.7 F l u i d a l banding i n r h y o l i t e Plate C.8 Photomicrograph (crossed n i c o l s ) of r h y o l i t e showing plagioclase (PI.), quartz (Qz.), and b i o t i t e (Bio.) set i n groundmass of p a r t l y d e v i t r i f i e d glass B i o t i t e i s pleochroic i n deep_browns and appears f r e s h . Books are subhedral i n o u t l i n e and commonly less than 2mm. i n diameter. Inclusions are few and consist mainly of magnetite and apatite grains. The groundmass of this rock i s composed almost e n t i r e l y of quartz and feldspar. These c r y s t a l s are interwoven i n a mat-work of feathery c r y p t o c r y s t a l l i n e c l o t s . The clot s are about 0.2mm. i n diameter and may represent patches of d e v i t r i f i e d and r e c r y s t a l l i z e d glass . Magnetite and other accessory heavy minerals are scarce. Except for some rusted surfaces r h y o l i t e is commonly fresh and appears to be more r e s i s t a n t to weathering than other lavas i n the map-area. ROCKS OF 'B' SERIES j . Clot-Porphyr ies The f i e l d name 'clot-porphyry' is a c o l l e c t i v e term used i n reference to t r a c h y t i c and trachyandesitic rocks with lath-shaped phenocrysts and glomerophenocrystic ' c l o t s ' of feldspar having equant or stout rectangular h a b i t . These rocks occur i n the lower middle part of the Marron Formation. Clot-porphyry rocks are multicoloured, commonly dark yellowish brown (10YR4/2) and o l i v e gre.y (5Y4/1) where fresh and brownish gre,y (5YR4/1) and medium grey (N-5) on weathered surfaces. Some severely weathered rocks have a blackish red matrix (5R2/2) and bleached white feldspar phenocrysts. The chemical composition of two samples is given i n Appendix Table A - l (no. 7) and Appendix Table A-2 (no. 1), and the r e f r a c t i v e index-range of glass of a r t i f i c i a l l y fused samples is shown i n Figure 2.4. The most common v a r i e t y of clot-porphyry rock i s conveniently exposed i n roadcuts along Highway 3 near the east end of Yellow Lake and near the junction of Highways 3 and 97. This rock also forms the middle part of the clot-porphyry section west of Mahoney Lake. Its 162 approximate mode i s as follows: Phenocrysts - Plagioclase i 0. anidine I Clinopyroxenel ^ B i o t i t e I Magnetite Apatite 1% accessory Groundmass - Feldspar - 6 0 $ Magnetite B i o t i t e Pyroxene C h l o r i t e Apatite Quartz The composition of plagioclase phenocrysts determined from two samples is A b c o An and Ab An (nx 1 - 1.553, nx' - 1.551; 5Z 4o 55 MO Tsuboi method). Zoning i s s l i g h t . S o l i t a r y c r y s t a l s have tabular or lath-shaped habits, commonly \ to 3mm. i n maximum diameter, with rounded or embayed o u t l i n e s . Glomerophenocrysts commonly consist of f i v e or s i x unsymmetrically arranged c r y s t a l s joined along sinuous contacts. These ' c l o t s ' range from 3 to 7mm. i n diameter. Minor pyroxene, b i o t i t e , and magnetite are observed i n some aggregates. The texture of the feldspar c l o t s suggests a x e n o l i t h l c o r i g i n . Possibly the clot s were derived from loose crystal-accumulates i n a magma chamber. Xenoliths of country rock are uncommon i n c l o t -porphyry lavas. Sanidine phenocrysts are generally scarce. The compositions of s l i g h t l y zoned c r y s t a l s from two trachytes are (Ab + An) r Or... _ 6 94 and (Ab +An).„ Or (201 X-ray method). The sanidine i s commonly H - / . 5b fresh and r e l a t i v e l y free from inclusions and occurs as s o l i t a r y laths as much as 2cm. long or as jackets on p l a g i o c l a s e . The clinopyroxene, determined from two samples, is Wo^ <. En F s 2 Q and Wo 4 2 E n ^ F s ^ (2V, = 51°, ny = 1.693; 2V^ = 54°, ny = 1.696). Phenocrysts are pale green, s l i g h t l y zoned, and commonly have equant habits with subhedral o u t l i n e s . Generally i n d i v i d u a l pyroxene c r y s t a l s are small, \ to 2mm. i n diameter, however, a few glomerophenocrysts are. as much as 4mm. i n diameter. 163 B i o t i t e is strongly pleochroic i n shades of brown. Basal plates are generally darker than prismatic sections. Phenocrysts are commonly s o l i t a r y showing subhedral or corroded amoeboid-like o u t l i n e . The t h i n outermost s h e l l of b i o t i t e books i s usually charged with magnetite dust. Magnetite and ap a t i t e phenocrysts are few and less than %mm. i n diameter. Magnetite generally occurs as equant subhedral or anhedral grains, and a p a t i t e as subhedral prisms. Many of these minerals form p o i k i l i t i c inclusions i n pyroxene and b i o t i t e and, to a much lesser extent, i n feldspar phenocrysts. The groundmass i s composed mainly of f e l t e d feldspar micro-l i t e s with i n t e r s t i t i a l b i o t i t e , pyroxene, and disseminated magnetite grains. In a few rocks the m i c r o l i t e s are arranged i n s u b p a r a l l e l fashion suggesting flowage. The lowermost clot-porphyry beds, west of Mahoney Lake, are d i s t i n c t i v e and are mapped separately (termed small feldspar porphyry on map 200) . The modal composition of this rock is as follows: Phenocrysts: Plagioclase 207= B i o t i t e trace Groundmass: Feldspar 7 0 $ Magnetite C a l c i t e speudomorphic - accessory a f t e r pyroxene Apatite The low concentration of ferromagnesian minerals and r e l a t i v e l y small s i z e of feldspar-porphyry ' c l o t s ' (less than 4mm. i n diameter) are t y p i c a l of this rock, di s t i n g u i s h i n g i t from the 'normal' type of clot-porphyry described above. The anomalously high sodic composition of plagioclase i n t h i s rock, Ab,_ An., (determination on p l a g i o c l a s e glass, R.I. - 1.518) i s by 31 possibly due to deuteric a c t i o n . Most plagioclase examined is bleached white and charged with f i n e l y disseminated clay minerals. The upper part of the clot-porphyry rocks, west of Mahoney Lake, also forms a mappable u n i t (termed c l o t - l a t h feldspar porphyry on map I6h Plate C.9 Photomicrograph (crossed nichols) of c l o t -porphyry trachyte showing plagioclase glomerophenocrysts (PI.) with sanidine jackets (San.) set i n m i c r o c r y s t a l l i n e groundmass Plate C.10 Photomicrograph (crossed nichols) of c l o t -porphyry trachyandesite showing t y p i c a l plagioclase ' c l o t ' (xenolith) 16$ 200). The mode i s as follows: Phenocrysts - Plagioclase ^ 5 % B i o t i t e C a l c i t e pseudomorphic - trace a f t e r pyroxene Groundmass - Feldspar 25 to 75% Magnetite ^ 2% Ch l o r i t e Submicroscopic undetermined 20 to 70%, material - possibly d e v i t r i f i e d glass The rock generally contains markedly fewer feldspar phenocrysts and has a lower r a t i o of glomeroporphyroblasts to s o l i t a r y c r y s t a l s than does that of normal clot-porphyry described previously. Plagioclase occurs mainly as plates (1 to 6mm. i n diameter) with broad equidimen-s i o n a l (010) faces and thi n lath-shaped sections i n zones normal to (010). The rock i s commonly deeply weathered and fresh phenocrysts are scarce. Determination of p a r t l y s e r i c i t i z e d p l a gioclase using e x t i n c t i o n methods i s Ab"72 A.n2Q 2. Rosette-Porphyries The f i e l d name 'rosette-porphyry 1 applies to t r a c h y t i c and trachyandesitic rocks that t y p i c a l l y contain small glomerophenocrysts of r a d i a l l y oriented feldspar. These rocks occur i n the upper middle part of the Marron Formation and are conveniently exposed i n roadcuts along Highway 3 near Trout Lake. Rosette-porphyry i s t y p i c a l l y dark yellowish brown (10YR4/2) on fresh surfaces and commonly l i g h t o l i v e grey (5Y5/2) or greyish red (10R4/2) where weathered. Refractive indices and s p e c i f i c g r a v i t i e s of rosette-porphyry (R.I.= 1.527, av. of 10 samples; S.G.= 2.59, av. ;of 42 samples) and clot-porphyry (R.I. 1.526, av. of 10 samples; S.G.= 2.59, average 46 samples) are markedly s i m i l a r , as are t h e i r chemical compositions (see Appendix Table A - l , nos. 7 and 8). Examination of 25 t h i n sections of fresh rock shows the following average composition: - 8% Phenocrysts - Plagioclase Sanidine Clinopyroxene ~> 3% B i o t i t e - trace 166 Groundmass - Feldspar ~ 70% Glass ~-10% B i o t i t e Pyroxene Magnetite Apatite - accessory In view of the low phenocryst-to-groundmass r a t i o , shown above, d i s t i n c t i o n between trachytes and trachyandesites i s best made on the basis of chemical data. Since the most pronounced differences between rocks of t h i s s e r i e s i s s i l i c a composition (see Chapter I I I ) , rocks containing normative quartz are a r b i t r a r i l y c a l l e d trachytes and under-saturated rocks with normative nepheline are termed trachyandesites. Plagioclase phenocrysts are only s l i g h t l y zoned. Their com-p o s i t i o n range, based on determination of feldspar from two rocks, i s from Ab52 A n ^ to Abjjjj An£6 ( n v = 1.553, and ny = 1.558; Tusboi method). Individual c r y s t a l s are lath-shaped and most of them form glomeroporphyritic bursts 2 to 5mm. i n diameter. Carlsbad and poly-synthetic a l b i t e twinning i s displayed by most c r y s t a l s . Inclusions are few and consist mainly of small apatite rods. Sanidine i s a soda-rich v a r i e t y with compositions (Ab+An) J^ 2 OrcJQ and (Ab+An) ijg Or5b, (determined from two rocks by the 201 X-ray method). (The widely accepted boundary between sanidine and anortho-clase i s about Ab5$ Or35 based on the monoclinic - t r i c l i n i c inversion point of these feldspars - see Smith and Mackenzie 1958, p. 874). Sani-dine occurs as jackets on plagioclase or commonly as f r e e - f l o a t i n g laths 2 to 6mm. long. The c r y s t a l s are cl e a r , r e l a t i v e l y free from inc l u s i o n s and with subhedral or euhedral habits. The optic a x i a l plane i s oriented nearly p a r a l l e l to the basal cleavage; o p t i c a x i a l angles are generally large f o r sanidine, 50 to 60 degrees. Most laths show Carlsbad twinning; g r i d twinning, t y p i c a l of anorthoclase, i s not observed. o The clinopyroxene i s approximately WoJ^ rJ H v35 F s 2 0 (^VJJ = 54, ny= 1.696). Crystals are pale green i n thi n section and only s l i g h t l y zoned. Most commonly i t occurs as s o l i t a r y c r y s t a l s % to 1mm. i n diameter showing equant habits and subhedral o u t l i n e s . Apatite and magnetite inclusions are common. B i o t i t e phenocrysts are generally few. They are pleochroic i n yellowish browns, commonly corroded and charged with magnetite dust. 167 Plate C .11 T y p i c a l massive rosette-porphyry trachyte Plate C.12 Photomicrograph (crossed nichols) of rosette-porphyry trachyandesite showing t y p i c a l plagioclase glomerophenocryst Plate C.13 Photomicrograph (crossed n i c o l s ) of rosette-porphyry trachyte showing sanidine laths set in m i c r o c r y s t a l l i n e groundmass The goundmass i s composed mainly of f e l t e d feldspar mocrolites about 0.1mm. long. I n t e r s t i c e s are f i l l e d mostly with a dark brown substance, probably d e v i t r i f i e d glass, some b i o t i t e and pyroxene. Magnetite grains are disseminated uniformly throughout. 3. White Lake Feldspar Porphyries Feldspar-porphyries resembling 'clot-porphyry' rocks described previously, form the bulk of the volcanic f a c i e s of the White Lake Formation. These rocks are conveniently exposed i n roadcuts immediately southwest of the bridge on Highway 97, near the v i l l a g e of Okanagan F a l l and on the b l u f f s near Indian Head about h a l f a mile east of White Lake. The rocks are commonly weathered, perhaps due to t h e i r fragmented character (see Chapter I I ) , and they vary i n colour from medium grey (N7) to greenish grey (5GY6/1) and moderate yellowish brown (10YR5/4) on rust-stained surfaces. The r e f r a c t i v e index of glass prepared from the White Lake feldspar-porphyry rocks indicates a marked composition range (see Figure 2.8). The chemical analysis of a weathered sample obtained near Indian Head resembles trachyte i n composition except f o r low s i l i c a , and high lime and carbon dioxide (see Appendix Table A - l , no. 6) The r e l a t i v e frequency of phenocrysts i n these rocks i s as f o l -lows (based on binocular examination and thi n section s t u d i e s ) : Plagioclase Sanidine B i o t i t e Clinopyroxene Magnetite Apatite - 5 to 20% - less than 5% - trace The goundmass i s markedly v a r i a b l e i n composition and texture. In some of the most 'acid' rocks, such as those near Indian Head, the goundmass consists mainly of small feathery feldspar m i c r o l i t e s (~75%) , showing s u b p a r a l l e l 'flow' arrangement (trachyte texture", and i n t e r -s t i t i a l c h l o r i t e ( ~ 20%) , possibly replacing glass, and disseminated magnetite grains (^ 5%). On the other hand, some of the most 'basic' rocks of th i s assemblage, such as some i n the lower part of the White Lake Formation, are r e l a t i v e l y galssy; i . e . -Groundmass Glass and p a r t i a l l y d e v i t r i f i e d glass . - 70% Feldspar m i c r o l i t e s . . . . - 25% Ferromagnesian minerals 5%, Plagioclase i s commonly replaced by mica, c a l c i t e , or patches of sodic feldspar. Composition based on r e f r a c t i v e index of glass prepared from a sample of this a l t e r e d plagioclase i s about Abyn An3o (R.I. = 1.512). The mineral occurs both as single c r y s t a l s and glomerophenocrysts, usually less than 5mm. i n diameter, showing embayed and rounded o u t l i n e s . Sanidine amounts to less than % t o t a l modal feldspar phenocryst content i n rocks examined. Composition of phenocrysts determined from a trachyandesite are about (An+Ab) ij OTQCJ. (201 X-ray method). Crystals are c l e a r , except for minor a l t e r a t i o n products, and occur as jackets on plagioclase or s o l i t a r y l a t h s . B i o t i t e i s commonly present and i s the dominant ferromagnesian constituent i n trachytes and trachyte breccias near Indian Head. Generally b i o t i t e books are pleochroic i n browns and reddish brown, subhedral i n o u t l i n e , % to 2mm. i n diameter, and are r e l a t i v e l y free of i n c l u s i o n s except f o r some magnetite dust near resorbed margins and a few apatite c r y s t a l s . B i o t i t e a l t e r s to weakly b i r e f i n g e n t c h l o r i t e minerals and magnetite; also, i n some rocks b i o t i t e i s replaced by a bright green c h l o r i t e showing moderate birefringence. Clinopyroxene i s commonly replaced by c a l c i t e , c h l o r i t e , and i r o n oxide. The composition of fresh unzoned phenocrysts from a o trachyandesite i s Wo^ E n ^ F s l 8 (^V^ = ^4; ny= 1.695). Crystals generally range from \ to 2mm. i n diameter and show subhedral o u t l i n e s . Magnetite and apatite c r y s t a l s , which are less than %mm. i n maximum diameter and subhedral i n o u t l i n e , occur as s o l i t a r y c r y s t a l s or form glomeroporphyroblasts with pyroxene a l t e r a t i o n products. ROCKS OF 'C' SERIES 1. Rhomb-Porphyry (Phonolite) Lavas bearing d i s t i n c t i v e rhomb-shaped anorthoclase phenocrysts constitute most of the Yellow Lake porphyry beds, the basal unit of the Marron Formation. This rock i s conveniently exposed i n roadcuts on the north shore of Yellow Lake and near the switchback on Highway 3 about 1.7 miles west of Kaleden Junction. The best te x t u r a l develop-ment of t h i s rock i s displayed by basal Marron lavas i n the v a l l e y cut Plate C.14 Photomicrograph (crossed n i c o l s ) of White Lake feldspar-porphyry trachyte showing plagioclase (PI.) and sanidine (San.) phenocrysts set i n m i c r o c r y s t a l l i n e ground-mass 172 by Kearns Creek, about a h a l f mile northwest of Mahoney Lake. The rock, i s commonly l i g h t o l i v e grey (5Y6/1) or dark grey (N3) on f r e s h l y broken surfaces and l i g h t o l i v e grey (5Y5/2) where weathered. The large range i n r e f r a c t i v e indices obtained on glass beads prepared from rocks (see Figure 2.4) suggests marked chemical v a r i a t i o n ; however, two non-amygdaliodal samples analysed are quite s i m i l a r , showing r e l a t i v e l y low s i l i c a and unusually high alumina content (see Appendix Table A - l , nos. 9 and 10). Examination of 30 t h i n sections of fresh rock shows the following mineral: Phenocrysts -Groundmass -Anorthoclase (varying abundance) Clinopyroxene (varying abundance) B i o t i t e (minor abundance) Plagioclase (present i n some rocks) A n a l c i t e (uncommon as phenocrysts) Oli v i n e (uncommon; mainly a l t e r e d to bowlingit) Apatite (rare as phenocrysts) Magnetite (rar.e as phenocrysts) Feldspar (very abundant) Pyroxene (common) B i o t i t e (common) Apatite (common) Magnetite (common) An a l c i t e (common i n some rocks) Glass (scarce) The textures exhibited by rhomb-porphyry rocks are markedly v a r i a b l e . For example, the lowermost lavas i n the Yellow Lake succes-sion commonly contain large and often well-formed phenocrysts (some as long as 2cm.) of anorthoclase (5 to 15%), dark green clinopyroxene (10 to 20%), and minor b i o t i t e suspended i n a matrix composed mainly of f e l t e d feldspar m i c r o l i t e s and scattered magnetite granules. In contrast, the uppermost Yellow Lake lavas are commonly microporphyritic and composed mostly of small subhedral c r y s t a l s (mainly less than 2mm. i n diameter) c o n s i s t i n g mainly of anorthoclase (15 to 25%) and clinopyro-sene (about 5%); the goundmass i s commonly a f e l t e d intergrowth of feldspar and some pyroxene m i c r o l i t e s , a few b i o t i t e f l a k e s , and d i s -seminated magnetite granules. Some rhomb-porphyries are s i m i l a r to the 'shackanite' lavas of the Midway area described by Daly (1912, p. 411-415); t y p i c a l l y , the goundmass of these rocks contains many roundish or polygonal a n a l c i t e c r y s t a l s with average diameters of about 0.1mm. In 173 a few ' shackanites', there are an a l c i t e phenocrysts with diameters as large as 3mm. The composition of anorthoclase from microporphyry i s approxi-mately (Ab+An) go Or 2 0 (201 X-ray determination). This i s roughly i n agreement with X-ray fluoresence determination of large anorthoclase phenocrysts by Bostock (1966, p. 13) from basal Marron flows, Shingle Creek B.C. The usual habit of the anorthoclase i s i l l u s t r a t e d i n Figure C . l . Goniometric measurements on two large c r y s t a l s , obtained from basal lavas near Kearn's Creek, show that the c h a r a c t e r i s t i c rhomb-outline of (010) sections, faces, and cleavage plates i s due to modifications of the type (110), (110), and (201): 110 A 010 ^ 58° 110 A 001 * 68° 201 A 001 * 80° /?=116° a:b:c = 0.66 : 1 : 0.58 (see Daly 1912, p. 402). Optical data obtained on the same large c r y s t a l s are s i m i l a r to common anorthoclase (see Figure C . l and Deer et a l . , v o l . 4, p. 57). It should be pointed out, however, that examination of many thi n sections shows 2V^range of 38 to 80 degrees and e x t i n c t i o n angle with (001) cleavage trace on (010) plate s , 3 to 14 degrees. Many anorthoclase c r y s t a l s examined i n t h i n section show marked zoning. C o b a l t i n i t r i t e s t a i n - t e s t s indicate that the t h i n outer zones of some c r y s t a l s are r i c h i n potassium. This i s v e r i f i e d by X-ray determination on part of the outer s h e l l of a large rhomb-shaped c r y s t a l which gives Or QQ (201 method). Also, the X-ray d i f f r a c t i o n pattern of t h i s outer s h e l l i s comparable to that of hyalophane, suggesting a s i g n i f i c a n t content of barium (see Table C . l ) . (Since barium i s commonly divalent and i s markedly s i m i l a r to potassium i n i o n i c radius (Ba = 1.46, K=1.45 A ) i t i s not s u r p r i s i n g that t h i s minor element i s captured by potassium-rich zones i n f e l d s p a r ) . Grid twinning (combination of a l b i t e and p e r i c l i n e polysynthetic twinning) i s observed on some anorthoclase c r y s t a l s . S i g n i f i c a n t l y , sections showing good grid twinning also show (001) and (010) cleavage Figure C.l Illustration of Habit and Optical Orientation of Rhomb-shaped Anorthoclase 175 Table C l Feldspar X-ray D i f f r a c t i o n Data 1. 2. dA I dA I 6.48 5 6.53 30 5.90 5 5 .87 10 4.678 5 4.216 20 4.027 5 4.01 60 3.93 20 3.798 25 3.77 80 3.675 5 3.60 10 3.457 7 3.46 50 3.318 100 3.30 90 3.190 70 3.22 100 2.993 20 2.98 80 2.904 15 2.901 70 2.765 7 2.759 50 2.576 40 2.572 80 2.393 7 2.427 10 2.322 5 2.319 20 2.167 15 2.162 60 2.126 10 2.113 10 2.065 5 2.057 10 2.009 5 2.004 10 1.973 5 1.969 10 1.932 5 1.920 20 1.849 5 1.852 10 1.792 30 1.796 80 1.673 10 1.620 3 1.626 20 1.587 3 1.562 3 1.570 20 1.534 3 1.529 10 1.498 15 1.494 70 1. Potassic feldspar from outer s h e l l of large rhomb-shaped anorthoclase c r y s t a l . 2. 'Hyalophane' containing 3.8% BaO (Vermaas, 1953) 176 Plate C.15 T y p i c a l rhomb-shaped anorthoclase phenocryst from Yellow Lake lava Plate C.16 Photomicrograph ( p l a i n l i g h t ) of Yellow Lake lava with anorthoclase (Anorth.), clinopyroxene (Cpx.), b i o t i t e (Bi.)> and apatite (Ap.) phenocrysts. The ground-mass i s f i n e l y c r y s t a l l i n e and contains many round grains of a n a l c i t e . Plate C.17 Photomicrograph (crossed n i c o l s ) of apatite c r y s t a l , i n rhomb-porphyry lava, showing basal parting and well developed (1010) cleavage. Plate C.18 Photomicrograph (crossed n i c o l s ) of (010) section of anorthoclase showing rhomb-shaped o u t l i n e of c r y s t a l s and (001) cleavage trace. Plate C.19 Photomicrograph (crossed n i c o l s ) of (001) section ofanorthoclase showing grid-twinning and (010) cleavage trace. traces and generally squarish or equant rather than rhomb-shaped o u t l i n e s . Chemical compositions of rhomb-shaped anorthoclase c r y s t a l s from Midway area, B r i t i s h Columbia, and Mount Erebus, Ross Island A n t a r t i c a , are given i n Table C.2. Plagioclase phenocrysts are infrequent; however, when present they are commonly corroded and mantled with potassic feldspar. The estimated composition of the pl a g i o c l a s e , based on r e l a t i v e r e l i e f and e x t i n c t i o n angles, i s An • o The clinopyroxene composition i s WOCJQ Hy^£ ^ s l 5 (2V^J = 60, ny= 1.694; average of three s i m i l a r determinations). Phenocrysts show o s c i l l a t o r y zoning and v a r i a t i o n s i n l i g h t and medium green colours. Large c r y s t a l s are prismatic, commonly with euhedral o u t l i n e ; however, microporphyries generally contain stubby subhedral c r y s t a l s . Although some rhomb-porphyry rocks are soda-rich, sodic pyroxenes are not observed. B i o t i t e i s strongly pleochroic i n browns and orange-brown, and generally the margins of the b i o t i t e books show evidence of magmatic corrosion. Apatite and magnetite are r e l a t i v e l y abundant i n rhomb-porphyry rocks and from a few c r y s t a l s as large as 2mm. i n diameter. These minerals occur i n the goundmass and as inclusions i n feldspar, pyroxene, and b i o t i t e phenocrysts. Prismatic cleavage (1010) i s commonly well developed i n ap a t i t e . Fresh o l i v i n e i s not found i n rhomb-porphyries even though these rocks contain s i g n i f i c a n t normative o l i v i n e . A greenish-brown mineral (bowlingite?) was observed i n several t h i n sections pseudomorphic a f t e r a small equant mineral with well developed pyramid terminations - possibly o l i v i n e . 2. Augite-Porphyry (Tephrite) Augite-porphyry i s a basic a l k a l i - r i c h rock s i m i l a r i n composition to t e p h r i t e , the extrusive equivalent of shonkinite. I t occurs i n two s t r a t i g r a p h i c zones i n the map-area; at the top of the White Lake Formation and near the middle of the Skaha Formation. The rock from the White Lake Formation i s t y p i c a l l y a microporphyry containing many xenoliths (mainly quartz grains, and lumps of granite and shale). Skaha augite-porphyry i s r e l a t i v e l y coarse, fresh, and free from 3jo Table C.2 Analyses of Rhomb-shaped Anorthoclase 1. 2. SiO 56.16 62.61 TiO 0.62 -A l 6 22.80 21.98 F e 2 ° 3 2.06 0.33 F e 3 3 - 0.86 MgO 1.34 0.08 CaO 4.75 3.75 Na 0 4.59 7 .27 K 0 5.74 3.12 BaO 1.12 -SrO 0.82 -<h _ 1.536 - 1.541 2V 40° to 50°(-) 62°(-) x'001 2° to 14° 2° to 5° S .G. - 2.620 Mol.% (Ab+An) 6 ( )Or 4 0 (Ab+An) 2 20r 1 8 1. Anorthoclase from Rock Creek Chonolith, near Midway B.C. (Daly, 1912) 2. Anorthoclase from ash deposit, crater of Mt. Erebus, Ross Island A n t a r t i c a (Mountain, 1925) 18-1 xenoliths. A good exposure of th i s rock i s to be seen beside the logging road about a mile southeast of the Observatory S i t e . The rock i s o l i v e grey (5Y4/1) where fresh, and moderate brown (5YR4/4) or greyish brown (5YR3/2) on weathered surfaces. A xenolith-free v a r i e t y has r e l a t i v e l y high s p e c i f i c gravity ( ~ 2.820) and r e f r a c t i v e index of glass beads ( ^  1.580). These values decrease with increasing degree of xe n o l i t h contamination. The modal composition of fresh, xenolith-free rock (based on examination of three t h i n sections) i s comparable to the normative compo-s i t i o n c a l c u lated from chemical analysis of the same rock using the Barth method (see Barth 1959, p. 82; and Appendix Table B - l , no. 5). Mode Norm 63.4% f e l s i c Potassic Feldspar Or 3 0 . 7 7 c minerals (and Plagioclase) 5 0 7 c Ab 2 . 0 7 » 6 5 7 c An 1 4 . 0 7 c A n a l c i t e 1 5 7 o Ne 1 6 . 7 7 c Clinopyroxene 2 5 7 c Di 2 4 . 5 7 c B i o t i t e 4 7 c Olv 9 . 5 7 o Magnetite 4 7 c Mg 2 . 6 7 c Apatite 2 7 „ Clinopyroxene shows o s c i l l a t o r y zoning i n d i c a t i n g somewhat var i a b l e composition; however, many o p t i c a l measurements give an average of Wbj^ cJ En^0 F s2 Q • (2V^= 55° ; ny= 1.696). Crystals commonly have prismatic elongation, euhedral o u t l i n e , and range i n length between 0.25mm. and 1.5cm. They vary i n colour from medium to very pale green and dis p l a y high second order interference colours under crossed n i c o l s . Inclusions are mainly magnetite and apatite, some b i o t i t e , feldspar, and glass. The groundmass i s composed mainly of grains less than 0.5mm. i n di a -meter including the f e l s i c minerals, most of the b i o t i t e , and the acces-s o r i e s , magnetite and apatite. Potassic feldspar, p l a g i o c l a s e , and b i o t i t e occur as randomly oriented laths and plate Angular i n t e r s t i c e s between these minerals are f i l l e d mainly with a n a l c i t e and some glass (?). Rounded grains of magnetite and euhedral apat i t e , probably early-formed minerals, are scattered throughout the goundmass commonly occurring as inclusions i n other minerals. P a r t i a l replacement of plagioclase by secondary minerals prevents accurate determinations, however, r e l a t i v e l y high normative anorthite content of the rock suggests a c a l c i c composition. 182 Fresh o l i v i n e i s not observed i n augite-porphyry; however, a few patches of serpentine-like substance i n the goundmass appear to be pseudomorphic a f t e r t h i s mineral. The r e l a t i v e l y high normative o l i v i n e composition of the rock i s probably accounted for by the presence of b i o t i t e which i s , i n part, chemically equivalent to o l i v i n e . Plate C.20 Hand specimen of White Lake augite-porphyry (tephrite) charged with granite xenoliths Plate C.21 Photomicrograph ( p l a i n l i g h t ) of Skaha augite-porphyry lava showing large clinopyroxene euhedra (Cpx.) and some b i o t i t e (Bi.) plates set i n a groundmass of feldspar, a n a l c i t e , b i o t i t e , and magnetite. Geology of White Lake Basin ( M a p 100 ) 4 9° 23 Legend Earlly Ter t ia ry Rock s S k a h a Fo rmat i on 12 -15 9/8,10 Sed iment s / Vo lcan ic Rocks Ma rama Format ion Park R i l l A n d e s i t e Mbr. Rosette - Porphyry Mbr. B a s a l t i c Ande s i t e Mbr. Clot - Porphyry Mbr. Ye l low L a k e Porphyry Mbr Spr ingbrook Fo rmat i on White L a k e Formation Marron Formation P r e - T e r t i a r y R o c k s A A a , Old Tom F o r m a t i o n Ab, Shoemaker Fo rma t i on A c , V a s e a u x Format ion Symbol s Dr i ft - covered area Geo l o g i c a l boundary (approx imate) B e d d i n g (hor i zonta l , inc l ined) S y n c l i n e (plunging) Anticl ine Fault (approximate, a s s u m e d ) ' 3 o Topograph i ca l contour (interval 5 0 0 f ee t ) S t r u c t u r e sect ion Boundary of map 2 0 0 S t r e a m Ma in r o a d S e c o n d a r y r oad G l a c i a l s t r iae C h e m i c a l a n a l y s i s s t a t i o n r\s\S\/\S\ /"v 3000 • 0 8 Geology by N. Church, 1967 Structure Sect ions 5 0 0 0 4 0 0 0 3 0 0 0 2 0 0 0 \ 1 0 0 0 1 2 Trout Lake Graben 5 0 0 0 V 4 0 0 0 L 3 0 0 0 • «••' A* J . \ > . .'.'.'.'.'.'.WW'. -vA Detailed Geology near White Lake (map 2 0 0 ) Legend Glacial and Recent Deposits undivided sediments 10 Early Tertiary Rocks SKAHA FORMATION Upper Member 15, mixed boulder conglomerate . Lower Member (4, granite breccia', mainly brecciated granite and aplite , I4a, granite boulder cong lomerate and arkose , 13, 'augite-porphyry' (tephrite)•, 12, "basal breccias ' undivided , 12a, brecciated Old Tom F 12b, brecciated Shoemaker F. I2bb, intensely brecciated chert , )2c, brecciated Vaseaux F.j I2d, mixed conglomerate and breccia WHITE L A K E FORMATION Upper Member 10a, agglomerate, tuff, sediments , 10b, Indian Head volcanic b recc i a , 10c, augite - porphyry (tephrite) , lOd, mainly shale, possibly equivalent to 9 or 12 , Middle and Lower Members 9, White Lake sediments, mudstone, sandstone, cong lom-era te , coal , and pyroclastics ; Middle Member 8a, pyroclastic rocks and lahars with abundant xenoliths of 2 ; 8b, pyroclastic rocks and lahars with abundant xenoliths of 6 , Lower Member : 8, trachyte and trachyandesite lavas ond pyroclastic rocks -t MARAMA FORMAT ION 7, undivided rhyodacite and rhyolite, some basal conglomerate j MARRON FORMAT ION Park Rill Andesite Member 6, mainly merocrystal l ine andes i te ; 6a, v i t nc andesite , Rosette - Porphyry Member 5 , undivided trachyte and trachyandesite , 5a, aphanltic volcanic brecc ia, Basalt ic Andesite Member 4 , mainly vesicular lava ; C l o t - P o r p h y r y Member 3, undivided troc^to and trachyandesite j 3a , small teldspar porphyry , 3b , c l o t - l a t h feldspar porphyry j Yellow Lake Porphyry Member 2 , undivided rhomb - porphyries , 2a, small anorthoclase - augite porphyry ; 2b, large anorthoclase - augite porphyry , SPRINGBROOK FORMATION I , undivide conglomerate and basal breccia ; unclassified intrusive rocks augite - porphyry intrusive rocks undivided White Lake intrusive rocks feldspar - porphyry intrusive rocks Pre - Tertiary Rocks Aa, Old Tom Formation j Ab, Shoemaker Formation , Ac, Vaseaux Formation; v N Symbols Bedrock exposure Geological boundary Boundary of detailed mapping Bedding Fault (approximate position) minor displacement major displacement Topographical contour (interval, 50 feet) Structure section Diamond drill hole Coal mine Road Lake Morsh Stream Granite Agglomerate Limestone o o o 45 /VWWW\ — - m a — • s«-0 D.D.H. &> G aggtom Li • T Scale 1000 5 0 0 0 1000 feet Geology by N. Church, 1967 W-X-Y-Z s e c t i o n 3 0 0 0 2 9 0 0 2 8 0 0 2 7 0 0 2 6 0 0 2 5 0 0 2 4 0 0 2 3 0 0 2 2 0 0 2100 2 0 0 0 1900 1800 I 7 0 0 1600 1500 12 8a 10 w Q o 15 E 3 0 0 0 2 9 0 0 2 8 0 0 2 7 0 0 2 6 0 0 2 5 0 0 2 4 0 0 2 3 0 0 2 2 0 0 2 1 0 0 2 0 0 0 1900 1800 1700 1600 1500 Structure Sections to Accompany Map 2 0 0 Geology by N. Church, 1967 Horizontal Scale 1 0 0 0 5 0 0 0 1000 feet S-T s e c t i o n o 

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