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Petrology, structure and origin of the Copper Mountain intrusions near Princeton, British Columbia Montgomery, Joseph Hilton 1967

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The U n i v e r s i t y o f 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 JOSEPH HILTON MONTGOMERY" BL, Sc., U n i v e r s i t y of B r i t i s h Columbia, 1959 R.' Sc., U n i v e r s i t y of B r i t i s h Columbia, 1960 WEDNESDAY, JUNE 7, 1967 AT 3:30 P.M. IN ROOM 102, GEOLOGY AND GEOGRAPHY BLDG. COMMITTEE IN CHARGE ; Chairman: B.N. MoyLs K.C. McTaggart W.H. Mathews W.H. White A.J. S i n c l a i r R.E. Delavault L.G.R. Crouch External Examiner: K,D. Watson Department of Geology •University of C a l i f o r n i a Los Angeles, C a l i f o r n i a , U.S.A. Research Supervisor: K.C. McTaggart THE PETROLOGY, STRUCTURE, AND ORIGIN OF THE COPPER MOUNTAIN INTRUSIONS, PRINCETON, B„C ABSTRACT The Copper Mountain i n t r u s i o n s , which i n c l u d e the Voigt and Smelter Lake d i o r i t i c s t o c k s , Armstrong B l u f f s monzonite-syenite complex, and the d i f f e r e n -t i a t e d Copper Mountain stock are p a r t of a continuous a l k a l i - c a l c i c rock s e r i e s ranging i n composition from pyroxenite to p e r t h o s i t e pegmatite. The s e r i e s i s b e l i e v e d to be der i v e d from a s i n g l e parent magma of b a s i c d i o r i t e composition and to have formed through c r y s t a l l i z a t i o n d i f f e r e n t i a t i o n 0 The age of the s e r i e s , determined by potassium-argon methods, i s about 195 myy. Parent magma was in t r u d e d i n t o N i c o l a group (Upper T r i a s s i c ) rocks by f o r c e f u l i n j e c t i o n w i t h s t r u c t u r a l readjustment of the country rock. The Voigt and Smelter Lake stocks ( d i o r i t e ) c r y s t a l l i z e d without apparent d i f f e r e n t i a t i o n . - Armstrong B l u f f s monzonite-syenite complex i s b e l i e v e d to have formed by repeated tapping of a d i f f e r e n t i a t i n g magma x:'..'. ;\\ which was emplaced at i n t e r v a l s a f t e r c r y s t a l l i z a t i o n of d i o r i t e i n Voigt and Smelter Lake stocks„ In Copper Mountain stock, a f t e r c r y s t a l l i z a t i o n of a d i o r i t i c roof and outer zone, magma d i f f e r e n t i a t e d to form a continuous s e r i e s from pyroxenite to p e r t h o s i t e pegmatite. D i f f e r e n t i a t i o n r e s u l t e d through a combination of thermal c o n v e c t i o n , chemical d i f f u s i o n , c r y s t a l armoring and c r y s t a l s e t t l i n g . D i f f e r e n t i a t i o n began w i t h the formation of gabbro and was i n i t i a t e d by convection c u r r e n t s which were formed as a r e s u l t of temperature gradients i n a mobile, v o l a t i l e -charged magma. When the composition of the magma approached the Ab-Or si d e of the Ab-Or-An te r n a r y system, subsolvus c r y s t a l l i z a t i o n was succeeded by hypersolvus c r y s t a l l i z a t i o n and the development of p e r t h o s i t e pegmatite. Feldspars from the Copper Mountain intrusions, studied by X-ray powder technique, exhibit a range of thermal state from intermediate to low temperature types» Feldspar geothermometry suggests a range of crystallization from above 820 C to about 500°C. AWARDS 1957 California Standard Co c Undergrade Schol. 1958 California Standard Graduate Fellowship 1960 Queen Elizabeth Scholarship 1961 National Research Council Studentship 1962 National Research Council Fellowship GRADUATE STUDIES F i e l d of Study: Geology Advanced S t r u c t u r a l Geology-Advanced Mineralogy Petrology Reading Course Cartography Mineral Deposits Mining 4-50 Petrology (Queen's Univ.) Crystallography (Queen's Univ.) J.V. Ross R.M. Thompson K.C. McTaggart Dept. of Geology J.R. MacKay W.H. White L.G.R. Crouch H.R.. Wynn-Edwards L.G. Berry PETROLOGY, STRUCTURE AND ORIGIN OF THE COPPER MOUNTAIN INTRUSIONS NEAR PRINCETON, BRITISH COLUMBIA by J O S E P H HILTON MONTGOMERY M.Sc, University of B r i t i s h Columbia, I960 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of GEOLOGY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1967 I n 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 of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t c h e 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 reference and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t copying or 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 not be allowed without my w r i t t e n permission„ Department of The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada ( i i ) ABSTRACT The Copper Mountain intrusions, which include the Voigt and Smelter Lake d i o r i t i c stocks, Armstrong Bluffs monzonite-syenite complex, and the d i f f e r e n t i a t e d Copper Mountain stock are part of a continuous a l k a l i - c a l c i c rock series ranging i n compo-s i t i o n from pyroxenite to perthosite pegmatite. The series i s believed to be derived from a single parent magma of basic d i o r i t e composition and to have formed through c r y s t a l l i z a t i o n d i f f e r e n -t i a t i o n . The age of the series, determined by potassium-argon methods, i s about 195 m.y. Parent magma was intruded into Nicola group (Upper T r i a s s i c ) rocks by f o r c e f u l i n j e c t i o n with s t r u c t u r a l readjust-ment of the country rock. The Voigt and Smelter Lake stocks ( d i o r i t e ) c r y s t a l l i z e d without apparent d i f f e r e n t i a t i o n . Arm-strong B l u f f s monzonite-syenite complex i s believed to have formed, by repeated tapping of a d i f f e r e n t i a t i n g magma which was emplaced at i n t e r v a l s . a f t e r c r y s t a l l i z a t i o n of d i o r i t e i n Voigt and Smelter Lake stocks. In Copper Mountain stock, after c r y s t a l -l i z a t i o n of a d i o r i t i c roof and outer zone, magma d i f f e r e n t i a t e d to form a continuous series from pyroxenite to perthosite peg-matite . D i f f e r e n t i a t i o n resulted through a combination of thermal convection, chemical d i f f u s i o n , c r y s t a l armoring and cr y s t a l s e t t l i n g . D i f f e r e n t i a t i o n began with the formation of gabbro and was i n i t i a t e d by convection currents which were formed as a re s u l t of temperature gradients i n a mobile, v o l a t i l e -charged magma. When the composition of the magma approached the Ab-Or side of the Ab-Or-An ternary system, subsolvus c r y s t a l l i z a -( i i i ) t i o n was s u c c e e d e d b y h y p e r s o l v u s c r y s t a l l i z a t i o n a n d t h e d e v e l -o p m e n t o f p e r t h o s i t e p e g m a t i t e . F e l d s p a r s f r o m t h e C o p p e r M o u n t a i n i n t r u s i o n s , s t u d i e d b y X - r a y p o w d e r t e c h n i q u e , e x h i b i t a r a n g e o f t h e r m a l s t a t e f r o m i n t e r m e d i a t e t o l o w t e m p e r a t u r e t y p e s . F e l d s p a r g e o t h e r m o m e t r y s u g g e s t s a r a n g e o f c r y s t a l l i z a t i o n f r o m a b o v e 8.20°C t o a b o u t 5 0 0 ° C . (iv) Table of Contents  CHAPTER I - INTRODUCTION page General Statement 1 Location, A c c e s s i b i l i t y and Outcrop 1 Previous G e o l o g i c a l . Work and Mining History 4 Present Investigation 5 Physiography and Pleistocene and Recent Geology 6 Climate and Vegetation- . . . 1 1 Acknowledgments 1 1 CHAPTER II - GENERAL GEOLOGY Introduction 1 3 Table of Formations .. 1 4 Description of Formations 1 5 (a) Nicola G r o u p 1 5 Introduction . 15 Petrology 16 Structural Relations 2 1 Age and Correlation 2 1 (b) Copper- Mountain Intrusions 2 2 Introduction 2 2 Petrology . . •• • • «... • 2 4 Structural Relations .. 2 4 Age and Correlation 2 5 (c) Dykes ........ . • 2 6 Introduction 26 "Mine Dykes" 26 Hornblende Andesite 2 7 Lamprophyre ........ ... 2 7 L a t i t e Porphyry. . ... . . ... . . . ..... . 2 8 (v) (d) Princeton Group . . 28 Introduction 28 D i s t r i b u t i o n 28 Lower Volcanic Formation 2 9 Allenby Formation 33 Structural Relations ... . 36 Mode of Origin 3 7 Age and Correlation 38 (e) Geology of the Copper Mountain Mine 38 CHAPTER III - COPPER MOUNTAIN INTRUSIONS General: Statement 4 0 Previous Work 4 0 PART A: Petrography and Mineralogy Introduction . . 4 2 Mineralogical Composition 4 2 (a) Introduction 4 2 (b) Modal Analyses 4 2 (c) Rock Nomenclature 53 Texture 5 5 (a) Introduction 5 5 (b) Texture of Voigt and Smelter Lake Stocks .............. 5 5 (c) Textures of Armstrong B l u f f s Complex 5 7 (d) Textures of the Copper Mountain Stock 6 1 Out e r Z one ,. . » . ..... . o . . ... » . . . . . . . . » .. « ... .. . 6 1 Intermediate Zone 7 1 Inner Zone 73 (vi) Feldspars . .. 78 (a) Introduction 78 (b) Method of Separation 79 (c) Plagioclase 80 Plagioclase Composition 80 Structural State 82 (d) A l k a l i Feldspars 89 X-ray Study of Perthite 89 t Perthite Composition 90 A l k a l i - f e l d s p a r Series 95 Obliquity of A l k a l i Feldspars . . 97 (e) Coexisting, Feldspars 100 (f) Feldspar Geothermometers 102 (g) Analcite-Perthite Equilibrium- ..... ., . 104 Pyroxenes 106 (a) Introduction ... . ..... ... . 106 (b) X-ray Parameters of Pyroxenes ............... . 107 (c) Optical Determinations of Pyroxenes ..... . , . 109 (d) Pyroxene Composition and C r y s t a l l i z a t i o n Trend I l l PART B: Chemistry Introduction 112 Description of Analyzed Rock Specimens 112 Chemical Analyses and Norms 112 C l a s s i f i c a t i o n of the Copper Mountain Rock Series 118 V a r i a t i o n : i n the Copper Mountain Rocks 123 Oxidation •. . 131 ( v i i ) PART C: Structure of the Copper Mountain Intrusions Introduction ... . . . . ..... . . ... . ... . • • •• • • 135 Size and Shape of the Intrusions 135 External Contacts .......................................... 1 3 6 Internal; Structures 139 PART D: Origin of the Copper Mountain Intrusion^ Introduction. ......... . ............... . . ..... ... ........... ..... ..... .-. . 1 4 2 History of the Magma 144 (a) Introduction. . . ......... . . ....... . ......... ... . . . . ..... ... .-. ............ . 144 (b) Emplacement of the Magma ........................................ 144 (c) Evidence for Differentation- ..... ....... . ..... ... ... . . 147 (d) Chemistry of D i f f e r e n t i a t i o n 151 (e) Temperature of C r y s t a l l i z a t i o n 1 5 6 (f) Mechanics of D i f f e r e n t i a t i o n .. 157 ' Summary and . Sequence of Events . 161 BIBLIOGRAPHY 166 ( v i i i ) Plates page I. Steep-walled canyon of Similkameen River 3 I I . Old gold placer workings in.Similkameen River v a l l e y . . 4 I I I . Abandoned channel of Similkameen River (right) entering Smelter Lake v a l l e y (lower l e f t ) ............ 9 IV. Stream-worn bedrock and boulders 400 feet above present l e v e l of Similkameen River ....... 1 0 V. Andesitic feldspar porphyry of the Nicola group. Plagioclase phenocrysts have a subparallel alignment i n a groundmass -of fine-grained feldspar and horn-blende . Crossed n i c o l s , 2 4 X 17 VI. Pseudomorph of c h l o r i t e and c a l c i t e after pyroxene (or o l i v i n e ) i n Nicola andesite porphyry. The ground-mass contains altered plagioclase, c h l o r i t e , c a l c i t e and magnetite. Crossed n i c o l s , 24X 18 VII. Bedded l i t h i c t u f f from the sedimentary belt west of Copper Mountain stock. Fragments of lava, d e v i t r i f i e d glass, feldspar and limestone are present i n a dust matrix. Plane polarized l i g h t , 2 4 X 2 0 VIII. Steep b l u f f s of Lower Volcanic formation on east bank of Similkameen River 29 IX. Hornblende andesite from the Lower Volcanic forma-t i o n . The phenocrysts of plagioclase and b a s a l t i c hornblende are i n a matrix of glass and plagioclase m i c r o l i t e s . Crossed n i c o l s , 65X 30 X. Hornblende andesite from the Lower Volcanic forma-t i o n . The large c r y s t a l i s b a s a l t i c hornblende (with opague r e c r y s t a l l i z e d borders) and i s i n a matrix of glass and plagioclase m i c r o l i t e s . Plane polarized l i g h t , 65X ., ..... . . 30 XI. Hornblende andesite from the Lower Volcanic forma-t i o n . A plagioclase phenocryst shows o s c i l l a t o r y zoning (Angi to An^) i n a matrix of glass and plagio-clase m i c r o l i t e s ( A ^ ^ ) , Crossed n i c o l s , 65X 31 XII. Hornblende-andesite porphyry of the Lower Volcanic formation. 32 XIII. Z e o l i t i c andesite from the Lower Volcanic formation. The white amygdules contain a mixture of analcite and n a t r o l i t e . ..... ..... . . ....... . . ..... . . 32 ( i x ) XIV. C o a l measures t y p i c a l of those found i n the A l l e n b y f o r m a t i o n . These are 15 m i l e s northwest of Copper Mountain near Blakeburn, B.C. The dark l a y e r s are c o a l and carbonaceous sha l e and the l i g h t l a y e r s are c l a y and s h a l e 33 XV. L i t h i c t u f f from the A l l e n b y f o r m a t i o n . The rock c o n s i s t s of angular fragments of p l a g i o c l a s e , l a v a and shards i n a g l a s s y matrix. P l a n e - p o l a r i z e d l i g h t , 65X ... . 34 XVI. Tuffaceous bedded shal e from the A l l e n b y f o r m a t i o n . Fine fragments of f e l d s p a r and l a v a are present i n an i n d e f i n i t e m atrix. Plane p o l a r i z e d l i g h t , 6 5 X 34 •>XVII. D a c i t e o f the A l l e n b y f o r m a t i o n . 35 XVIII. Flow b r e c c i a s of the A l l e n b y f o r m a t i o n n o r t h of Smelter Lake . . . ........ ... ... . ... . . . 35 XIX. D a c i t e b r e c c i a of the A l l e n b y f o r m a t i o n 36 XX. S e r i c i t i z a t i o n of c a l c i c c ores of zoned p l a g i o c l a s e from V o i g t s t o c k d i o r i t e . Grossed n i c o l s , 65X ......... 56 XXI. Angular fragment of d i o r i t e i n c l u d e d i n the l a t e r monzonite of the Armstrong B l u f f s i n t r u s i v e com-p l e x . Arrows show the p o s i t i o n of the con t a c t be-tween the two rock types 57 XXII. Secondary b i o t i t e with i n t e r l e a v e d p l a t e s of e p i -dote i n monzonite of the Armstrong B l u f f s complex. Plane p o l a r i z e d l i g h t , 6 5 X 58 XXIII. C o n c e n t r a t i o n of magnetite c r y s t a l s p o i k i l i t i c a l l y e n c losed by and adjacent t o pyroxene c r y s t a l s from the Armstrong B l u f f s complex. Plane p o l a r i z e d l i g h t , 65X-......'. ... . . 59 XXIV. Monzonite b r e c c i a cemented with c a l c i t e and s c a p o l i t e . 59 XXV. Monzonite b r e c c i a with fragments cemented by s c a p o l i t e and c a l c i t e 60 XXVI. Photomicrograph .oof s c a p o l i t e - d i p p s i d e - c a i c i t e " s k a r n" from b r e c c i a zone i n Armstrong B l u f f s com-p l e x . Crossed n i c o l s , 65X 60 XXVII. D i o r i t e from the outer zone of the Copper Mountain stock 61 X X V I I I . B i o t i t e with e p i d o t e l a m e l l a e has r e p l a c e d horn-blende and pyroxene. Plane p o l a r i z e d l i g h t , 6 5 X ... 62 (x) XXIX. M u l t i p l e ( 1 0 0 ) t w i n n i n g i n pyroxene i n d i o r i t e from the outer,;; zone ©of the Copper Mountain s t o c k . Crossed n i c o l s , 65X 6 3 XXX. O s c i l l a t o r y zoning i n pyroxene i n d i o r i t e from the outer zone of the Copper Mountain s t o c k . Crossed n i c o l s , 65X . . . . . ;.6.3 XXXI. N e e d l e - l i k e i n c l u s i o n s of i l m e n i t e ? i n pyroxene c r y s t a l s i n d i o r i t e from the outer zone of the Copper Mountain s t o c k . Plane p o l a r i z e d l i g h t , 65X . . . . . . . . . . . 6 4 XXXII. N e e d l e - l i k e i n c l u s i o n s i n pyroxene show a zonal arrangement being c o n c e n t r a t e d i n a zone w i t h i n the c r y s t a l and p a r a l l e l t o i t s outer rim. Plane p o l a r i z e d l i g h t , 65X 6 4 XXIII. O s c i l l a t o r y zoning i n p l a g i o c l a s e i n d i o r i t e from the outer zone of the Copper Mountain s t o c k . The c a l c i c core has been completely s e r i c i t i z e d . Crossed n i c o l s , 6 - 5 X . . . . . . . . . 6 5 XXXIV. I n t e r s t i t i a l m i c r o p h r t h i t e i n d i o r i t e from the outer zone of the Copper Mountain s t o c k . Crossed n i c o l s , 6 5 X . . . . . . . . . . . . . . . . . . . . . . . . . 6 6 XXXV. P o i k i l i t i c m i c r o p e r t h i t e e n c l o s i n g p l a g i o c l a s e and pyroxene i n d i o r i t e from the outer zone of the Copper Mountain s t o c k . Crossed n i c o l s , 6 5 X 6 6 XXXVI!.; Pink p e r t h i t e v e i n i n d i o r i t e from the outer zone of the Copper Mountain s t o c k 6 7 XXXVII. Pink p e r t h i t e v e i n i n d i o r i t e from the outer zone of the Copper Mountain s t o c k . Plane p o l a r i z e d l i g h t , 24X . . . . . . . . . . . . . . 6 7 XXXVIII. A l t e r a t i o n rims of green hornblende ( u r a l i t e ) on pyroxene c r y s t a l s i n d i o r i t e from the outer zone of the Copper Mountain s t o c k . Plane p o l a r i z e d l i g h t , 6-5X • . . 6 8 XXXIX. P a r t i a l rims of magnetite on pyroxene c r y s t a l s i n d i o r i t e from the outer zone of the Copper Moun-t a i n stock., Plane p o l a r i z e d l i g h t , 65X 6 9 XL. P y r o x e n i t e from F r i d a y Creek. The rock i s pyroxene ( l i g h t grey) with a l i t t l e i n t e r s t i t i a l b i o t i t e (dark grey) and magnetite ( b l a c k ) . Plane p o l a r i z e d l i g h t , 24X 7 0 XLI. Gabbro from F r i d a y Creek, I t c o n t a i n s pyroxene (medium grey) which p o i k i l i t i c a l l y e n c l o s e s b i o -t i t e and magnetite and a l s o i n t e r s t i t i a l p l a g i o -c l a s e , b i o t i t e and magnetite. Plane p o l a r i z e d l i g h t , 24X 7 0 (xi) X L I I . Monzonite from the intermediate zone of the Copper Mountain stock 7 1 X L I I I . Monzonite from the contact adjacent to the pegmatite core. 72 XLIV. Microperthi te (P) i n monzonite from the i n t e r -mediate zone of the Copper Mountain stock. Small blebs of exsolved a l b i t e are v i s i b l e . Grossed n i c o l s , 65X 7 2 XLV. Red, i s o t r o p i c inc lus ions (black) and small gas bubbles (grey) i n apati te from monzonite of the intermediate zone of the Copper Mountain stock. Plane po lar i zed l i g h t , 65X 73 XLVI. V a r i a t i o n i n gra in s ize of microperthite i n perthosi te from the inner zone of the Copper Mountain stock 74 XLVII . Exsolved a l b i t e i n microperthite from the inner zone of Copper Mountain stock. Crossed n i c o l s , 24X , . 75 XLVIII . Radia l arrangement of per th i t e c r y s t a l s i n per-thos i te from the inner zone. Crossed n i c o l s , 24X. . . 75 XLIX. Leucoxene pseudomorphous after sphene i n pertho-s i t e from the inner zone of the Copper Mountain stock. Plane po lar ized l i g h t , 65X 76 L . . Complex o s c i l l a t o r y zoning i n per th i t e pheno-crysts from the inner zone of Copper Mountain stock. Crossed n i c o l s , 24X 77 L I . A l b i t e rims around zoned p lag ioc lase (Anry to An£^) c r y s t a l s from monzonite close to the pegma-t i t i c core of the Copper Mountain stock. Crossed n i c o l s , 6 5 X . ... 7 8 L I I . Late minor d i f f e r e n t i a t e of Copper Mountain rock ser ies cons is ts of ana lc i te ( i s o t r o p i c and black fleeted with s e r i c i t e ) and p e r t h i t e . I l l i t e i s an a l t e r a t i o n product of a n a l c i t e . Crossed n i c o l s , 24X . . . . 1 0 4 L I I I . Metasomatized sch l i eren i n d i o r i t e from the outer zone of the Copper Mountain stock. Note the t h i n mafic-free areas adjacent to the tabular s c h l i e r e n . . 1 4 0 LIV. Metasomatized s ch l i eren i n d i o r i t e from the outer zone of the Copper Mountain stock 1 4 1 ( x i i ) Figures 1. Geological Map of the Copper Mountain Stock and 3. Map of southern B r i t i s h Columbia showing location of Copper Mountain map-area. Scale 1 inch to 30 miles , 2 4. Map showing location of Copper Mountain intrusions (compare with Figure 1) 23 5. Flow structure i n hornblende andesite of Lower Volcanic formation. The f o l d axis plunges 70 de-grees at north 45 degrees east. Scale: 1 inch to 10 feet 37 6. Map showing location of modally analyzed specimens ... 44 7. A plot of the ess e n t i a l minerals (modal volume %) of 13 analyzed rocks against Wt. % S1O2 45 8. A ternary plot of the es s e n t i a l minerals (modal . volume %) of 99 modally analyzed specimens . . ... ....... 52 9. The compositions of plagioclase from 13 analyzed rocks plotted against optic angles, (after Slemmons, 1962), Specimen 95 (early plagioclase) was not chemically analyzed. 81 10. Angular separations (20(131)-29(131)) plotted against Ani (after Smith, 1956) 85 11. Angular separations ( 29 (13 2 ) - 20 (1.31) ) plotted against Ani (after Smith, 1956) . . . . . 86 12. Angular separations (20(220)A29(131) plotted against Ani (after Goodyear and Duffin, 1954) 86 13. Angular separations of V =29(131)+29(220)-49(ljl) plotted against An•% (after Smith and Gay, ,1958) 88 14. Angular separations of S =29 (111)-29 ("201) plotted against An % (after Smith and Gay, 1958) . . . . . . . . . . . . . . 89 15. The 201 spacings curve for synethetic a l k a l i f e l d -spars (after Bowen and Tuttle, 1950). Natural potassic and sodic phases for Copper Mountain per-t h i t e s . are plotted 93 16. Graphic representation of the compositions of the phases of natural and annealed perthites from the Copper Mountain intrusions 94 ( x i i i ) 17. Optic angles of potassic phases of Copper Mountain perthites plotted against t h e i r compositions (after T u t t l e , 1952) 96 18. Diagramatic representation of disorder-temperature relationships i n potash feldspars (modified after Goldsmith and Laves, 1954a) 98 19. Tie l i n e s j o i n i n g coexisting plagioclases and a l k a l i feldspars. The s o l i d l i n e s connecting s o l i d c i r c l e s are experimentally determined t i e l i n e s (Yoder, et a l , 1956) and the dashed l i n e s j o i n i n g open c i r c l e s represent coexisting Copper Mountain feldspars 101 20. Barth's feldspar geologic thermometer with Copper Mountain feldspars plotted (after Barch, 1962) 103 21. A plot of a s i n fZ against b on the pyroxene composi-t i o n trapezium (after Brown, i960) 109 22. The series index curve for the Copper Mountain rock series. (after Rittman, i960) 119 23. A l k a l i - l i m e index for the Copper Mountain rock series (after Peacock, 1931) 121 24. Contoured diagram for the 5000 analyses i n Wash-ington's Tables (after Thornton and Tuttle, i960), .... 122 25. S i l i c a v a r i a t i o n diagram for the Copper Mountain rock series . . . ... .... . . . ....... .... 125 26. Larsen v a r i a t i o n diagram for the Copper Mountain rock series (after Larsen, I938) 127 27. Major oxides plotted against Larsen position (l/3Si02+K20)-MgO-CaO-SFeO) 128 28. Larsen triangular diagram for the Copper Mountain rock series (after Larsen, 1938). Solid c i r c l e s represent the normative feldspars (An, Ab, Or) and open c i r c l e s t o t a l feldspar, quartz and femics as defined i n the text . . 130 2 9 . FMA triangular plot for the Copper Mountain rock series (after Yoder and T i l l e y , 1962) .. 131 30. Oxidation r a t i o s of several rock series and Osborne's (1959) experimental data (dashed l i n e s ) compared with those of the Copper Mountain series (after Osborne, 1959) 132 31. State of oxidation during c r y s t a l l i z a t i o n of the Copper Mountain rock series . . . 134 (xiv) 32. Diagramatic cross-section of the Copper Mountain intrusions. The dotted l i n e represents the zone at which d i f f e r e n t i a t i o n began i n the Copper Mountain stock and the dashed l i n e , the approximate present l e v e l of exposure ..... I 4 6 33« Subtraction v a r i a t i o n diagram. Gabbro-specimen 1. Pegmatite-average of specimens 11, 12 and 13. Voigt-Smelter-average of specimens 2 and 3. Monzonite-average of specimens 5, 6, 7, 8 and 9 149 34. Plot of normative compositions of 13 analyzed Copper Mountain rocks on the ternary diagram, An-Ab-Di; (after Bowen, 1915) 152. 35. Diagramatic i l l u s t r a t i o n of how fractioned cry-s t a l l i z a t i o n may lead to sy e n i t i c residua (after Barth, 1962) . 153 36. Diagramatic i n t e r p r e t a t i o n of the system Ab-An-Or (after Tuttle and Bowen, 1958) with Copper Moun-t a i n bulk compositions ( c i r c l e d dots), homogenized perthites (open c i r c l e s ) , and plagioclases (dots). Soli d curves are for Tuttle and Bowen's dry system and dashed curves represent an estimation of t h e i r p o s i t i o n i n the Copper Mountain magmas as PH2O i n -creased ... ... . ... . ... ... ... . 154 37. Diagramtic int e r p r e t a t i o n of convection c e l l sug-gested for Copper Mountain stock. Arrows represent d i r e c t i o n of magmatic movement. Density of descending magma equals that of lower magma-- at point A thereby l i m i t i n g v e r t i c a l size of c e l l 158 38. Diagramtic i n t e r p r e t a t i o n of the relati o n s h i p between d i f f u s i o n and convection during c r y s t a l -l i z a t i o n . V e r t i c a l arrows represent d i r e c t i o n and magnitude of convection. See text for explanation.... 160 39- Diagramtic representation of c r y s t a l l i z a t i o n d i f -f e r e n t i a t i o n of Copper Mountain stock. See text for explanation ... . . 163 Tables I. Geological formations of the Copper Mountain area 14 I I . Modal analyses (volume percent) of Copper Mountain intrusions 47 I I I . Optic angles and compositions of plagioclases from 13 analyzed rocks. More than one value i s given for zoned plagioclases 80 (xv) IV. X-ray powder-camera r e f l e c t i o n s (©Cr) f o r p l a g i o -c l a s e s from the Copper Mountin i n t r u s i o n s . F i l t e r e d chromium r a d i a t i o n was used . . . 84 V. X-ray powder-camera r e f l e c t i o n s (OCr) f o r n a t u r a l p e r t h i t e s from the Copper Mountain i n t r u s i o n s . F i l t e r e d chromium r a d i a t i o n was used 91 VI. X-ray powder-camera r e f l e c t i o n s (OCr) f o r annealed p e r t h i t e s from the Copper Mountain i n t r u s i o n s . F i l t e r e d chromium r a d i a t i o n was used 92 V I I . The d ( 2 0 1 ) spacings of both n a t u r a l and annealed p e r t h i t e s from the Copper Mountain i n t r u s i o n s 93 V I I I . O p t i c angles and compositions of p o t a s s i c phases Of Copper Mountain p e r t h i t e s ., , . 96 IX. Values of A f o r Copper Mountain p e r t h i t e s . ( A = 1 2 . 5 ( d l 3 1 - d l 3 1 ) . . . . 99 X. R e s u l t s of a n n e a l i n g p e r t h i t e s at 1 0 5 0 degrees C. f o r 48 hours . . . . . ....... 99 XI. X-ray powder-camera r e f l e c t i o n s (OCr) f o r Copper Mountain pyroxenes. The numbers A l A 2 , e t c . c o r -respond t o the p r e v i o u s specimen numbers 108 X I I . Values of a sin/3 and b f o r Copper Mountain pyroxenes 1 0 9 X I I I . Values of 2Vz and ZAc f o r the Copper Mountain pyroxenes 110 XIV. Chemical analyses of Copper Mountain rocks analyzed by H. Wiik of H e l s i n k i , F i n l a n d . (analyses marked x aretakedn from Dolmage, 1 9 3 4 ) 113 XV. Norms of Copper Mountain rocks 114 XVI. Chemical analyses of n a t u r a l m i n e r a l s used i n the c a l c u l a t i o n of the chemical content of a t h e o r e t i c a l rock with a modal composition of the average of specimens 2 and 3 1 1 7 XVII. C a l c u l a t e d chemical composition f o r the average mode of specimens 2 and 3 compared with the average of t h e i r a c t u a l chemical analyses 1 1 7 XVIII. S e r i e s i n d i c e s f o r the Copper Mountain rock s e r i e s . . 118 XIX. C l a s s i f i c a t i o n of rock s e r i e s , Rittman, i 9 6 0 119 (xvi) XX. Calculated Larsen pos i t ions for the Copper Mountain rock ser ies . . . . . . . . . ...126 XXI. The ca lcu la ted values for a Larsen t r i a n g u l a r plot for the Copper Mountain rock ser ies . . . . . . . . . . . 129 XXII. S o l i d i f i c a t i o n indices for the Copper Mountain rock ser ies ' . . . , , . . . . ' . . . . 134 XXIII . Weight percent metal oxides fo^ those rocks p l o t t e d . i n Figure 33. Pegmatite - average of specimens 11, 12 and 13. Gabbro - specimen 1. Vbigt-Smelter - average of specimens 2 and 3. Monzonite - average of specimens 5, 6, 7, 8 and 9 . • • . 150 CHAPTER I  INTRODUCTION General,Statement: The Copper Mountain stock, l y i n g just south of Prince-ton, B.C., i s well known to geologists because of i t s close association with the Copper Mountain mine, a major producer of copper for several decades. The purpose of t h i s t h e s i s i s to provide a modern account of the petrology, structure, and o r i g i n of the Copper Mountain stock and related igneous bodies. The research on which t h i s thesis i s based includes the prepara t i o n of a new and detailed geological map of the intrusions and the surrounding area and laboratory study of rock and mineral specimens from the various formations shown on t h i s map. Location. A c c e s s i b i l i t y and Outcrop: The map-area i s approximately 4 miles by 7 miles and i centered on the Copper Mountain stock which i s about 1 0 miles south of Princeton, B.C. (Figure 3 ) . The area i s divided into two parts by the Similkameen River. A c c e s s i b i l i t y i s excellent for most parts of the map-area. The western part of the area can be reached e a s i l y from the Hope-Princeton highway which roughly p a r a l l e l s the Similkameen River and the western border of the map-sheet. Good logging roads leave the highway at various points and provide access to t h i s section of the map-area. The larger eastern section, i n which the old Copper Moun t a i n mine workings are situated, can be reached by a good road which leaves the highway about a quarter of a mile east of Princeton and runs south to the mine. The entrance to the mine property i s presently blocked by locked gates, but permission t igure 3 ; Map of southern B r i t i s h Columbia showing l o c a t i o n of Copper Mountain map area. Scale 1 inch to 30 miles . 3 enter may be obtained from the owners, Granby Consolidated, Ltd., of Vancouver, B.C. Access to the mine property may also be had by way of the abandoned Copper Mountain branch of the Kettle Valley Railway, which i s accessible by car as far south as Smelter Lake val l e y . Beyond t h i s point, many t r e s t l e s have collapsed and sev-era l tunnels are partly caved. From the mine buildings and townsite, narrow roads and t r a i l s provide access to most parts of the eastern section of the map-area. Similkameen River canyon cuts through the area from south to north and provides almost continuous exposure through-out i t s length. In the late summer, i t i s possible to traverse the length of the canyon with only an occasional crossing being necessary to get around steep b l u f f s such as those shown i n Plate I. Plate I Steep-walled canyon of Similkameen River. Many of the side roads have been and are presently being improved and extended by companies engaged i n exploration and 4 development work i n several places i n the area. The amount of outcrop i s small i n many parts of the map-area, p a r t i c u l a r l y where slopes are gentle. There i s , however, almost continuous exposure along Similkameen River and i n the open p i t s of Copper Mountain mine. In addition, rock cuts are found along some of the access roads. Previous Geological Work and Mining History: The history of mining a c t i v i t y i n the Copper Mountain area i s a long one and, since detailed accounts have been pub-lished by Camsell ( 1 9 1 3 ) , Dolmage ( 1 9 3 4 ) , and Rice ( 1 9 4 7 ) , only a b r i e f summary w i l l be presented here. The f i r s t i nterest i n the d i s t r i c t followed the d i s -covery of placer gold i n Similkameen River i n i 860 , but since the deposits were not r i c h , the miners soon moved on. Plate II shows old placer workings. Plate I I : Old gold placer workings i n Similkameen River v a l l e y . 5 Interest i n the Copper Mountain copper deposit was f i r s t aroused i n 1 8 9 2 when R.A. (Volcanic) Brown staked the f i r s t claim. Development work was undertaken without success by various com-panies during the period between 1 9 0 0 and 1 9 2 2 . In 192,2, the Granby Consolidated Mining, Smelting and Power Company acquired the property and began successful operations i n 1926. The property was dormant from 1 9 3 0 to 1 9 3 6 , then reopened i n 1 9 3 7 and operated u n t i l 1 9 5 7 . Total production of the mine was 6 1 3 , 1 3 9 , 8 4 6 l b s . of copper, 1 8 7 , 2 9 4 oz. of gold and • 4,3_8_4,097 oz. of s i l v e r from 34,775,010 tons of ore. Many other attempts to make producing mines of neighbour-ing copper deposits have proven unsuccessful. Some of the more notable of these are the Voigt property situated at the eastern end of Lost Horse Gulch, the Red Buck property and the Armstrong Bluffs property both of which are i i i Similkameen Canyon, and the Friday Creek property. These are only a few ni the larger opera-t i o n s . There have been dozens of smaller enterprises as attested to by the numerous old adits, trenches, and shafts scattered throughout the map-area. Early geological investigations include those of Dawson ( 1 8 7 7 ) , Bauerman ( I 8 8 4 ) , Camsell ( 1 9 0 6 , e t c . ) , Cairnes ( 1 9 2 0 , e t c . ) , Daly ( 1 9 1 2 ) , Dolmage ( 1 9 3 4 ) , Rice (1947),Fahrni ( 1 9 5 1 ) , and others. The more important of these w i l l be d i s -cussed i n Chapter II (General Geology). Present Investigation: The present inves t i g a t i o n consists of eight months' f i e l d work during the 1 9 6 1 , 1 9 6 2 , and 1963 seasons and labora-tory investigation and research during the intervening periods. 6 The f i e l d work included detailed geological mapping of a twenty-eight square mile area centered on the Copper Mountain stock near Princeton, B.C. Several hundred rock specimens, about sixt y of them oriented specimens, were coll e c t e d for labora-tory i n v e s t i g a t i o n . Mapping was done on enlarged a e r i a l photo-grphs and on a base map with a scale of 1 inch to 5 0 0 feet which was made by McElhanney Air Surveys, Ltd. The v e r t i c a l control for the map was supplied by a barometric survey conducted by the writer using e x i s t i n g bench marks as control points. Horizontal control was obtained from e x i s t i n g highway and railway,surveys, Laboratory i n v e s t i g a t i o n has included microscopic examination of t h i n sections, mineral separations, o p t i c a l and X^ray determinations, study of oriented specimens, and rock anal-yses. A great deal of time has been spent investigating the s t r u c t u r a l and compositional variations i n feldspars i n the hope that such work would y i e l d information about the environment and history of the Copper Mountain intrusions. The work has been financed lar g e l y through National Re-search Council scholarships and a National Research Council grant-i n - a i d of research. Physiography and Pleistocene and Recent Geology: The Copper Mountain map-area l i e s at the southern end of Thompson Plateau which i s the most southerly of the Inte r i o r Plateaux system. It i s situated between the Hozameen Range on the west and the Okanagan Range on the southeast, both of which are part of the Cascade Mountain system. The topography of the map-area i s t r a n s i t i o n a l between that of the plateaux to the north and the mountain ranges to 7 the south. The area i s characterized by broadly rounded summits with gently sloping sides and deeply incised v a l l e y s . Camsell (1913) has stated that the plateau summits have an average eleva-t i o n of 5000 to 6000 feet above sea l e v e l i n the Tulameen area, which l i e s about 30 miles to the north of Copper Mountain. In the general area surrounding the map-sheet, the plateau summits have an elevation of about 6800 feet above sea l e v e l . In t h i s t r a n s i t i o n zone between the plateaux and moun-t a i n ranges, there i s a topographic unconformity above which there i s a mature topography and below which the slope steepens into the deep valleys which cut the plateau. The elevation of the topographic unconformity increases from north to south. Camsell (1913) has placed the elevation of unconformity at 4500 feet above sea l e v e l i n the Tulameen area. It i s somewhat higher i n the area surrounding Copper Mountain, where i t i s close to 5500 feet above sea l e v e l . . The main physiographic feature within the map-area i s Similkameen River which flows from south to north through deep canyons cut into the bottom of a V-shaped v a l l e y . The gradient of the r i v e r through the map-area i s 55 feet per mile as com-pared to 38 feet per mile above the Pasayten River to the south. There are several east-west trending valleys which j o i n Similkameen v a l l e y with those of Wolfi Creek and W i l l i s Creek (which l i e s two miles east of the map-area) and whose elevations become progressively lower towards the north. These east-west valleys were meltwater channels which drained Similkameen Valley during late Pliestocene. Much of the topography has been modified to some 8 degree by g l a c i a t i o n . D eposits of g l a c i a l and f l u v i o g l a c i a l o r i g i n are found i n many of the higher p a r t s of Similkameen V a l l e y . These are exposed i n road c u t s and e x p l o r a t i o n trenches and reach t h i c k n e s s e s of over 50 f e e t . They are commonly com-plex and r e f l e c t r a p i d l y changing c o n d i t i o n s d u r i n g g l a c i a l r e -t r e a t . They are made up of f l u v i a l sands and g r a v e l s , unsorteu g l a c i a l d e b r i s c o n t a i n i n g an assortment of m a t e r i a l commonly of P r i n c e t o n b a s i n sediments from the n o r t h , and l a y e r e d s i l t s of l a c u s t r i n e o r i g i n . The s i g n i f i c a n c e of the many meltwater channels, t e r r a c e s , s t r a n d l i n e s , d e l t a s , m i s f i t streams, and la k e remnants w i l l be d i s c u s s e d i n the f o l l o w i n g paragraphs. S e v e r a l processes and events have c o n t r i b u t e d t o the formation of the present topography. Evidence f o r these have been g i v e n by Dawson ( 1 8 7 7 ) , Camsell ( 1 9 1 3 ) , C a i r n e s ( 1 9 2 3 ) , Mathews ( 1 9 4 4 ) , H i l l s ( 1 9 6 2 ) , and o t h e r s . The f i r s t p rocess, p e n e p l a n a t i o n d u r i n g a l o n g p e r i o d of s t a b i l i t y , f o l l o w e d the Laramide r e v o l u t i o n and r e s u l t e d i n a mature topography c h a r a c t e r i z e d by well-developed drainage and low r e l i e f . The evidence i s seen i n the broadly-rounded p l a t e a u summits and the wide g e n t l y - s l o p i n g v a l l e y s of the main streams. The second process, one of u p l i f t , i n i t i a t e d a r e -j u v e n a t i o n of drainage which i s r e f l e c t e d i n the topographic unconformity at e l e v a t i o n s from 4500 t o 5500 f e e t above sea l e v e l . The age of g e n e r a l u p l i f t may be as l a t e as P l i o c e n e when the Cascade mountains were formed. Camsell ( 1 9 1 3 ) s t a t e s t h a t g e n e r a l u p l i f t of the p l a t e a u system began at the end of the Oligocene and culminated i n the P l i o c e n e but Mathews ( 1 9 6 4 ) believes that diastrophism may have been s l i g h t or lacking during the period from Middle Eocene to Pliocene. Glaciation has had a strong influence on the present topography mainly through d i s l o c a t i o n of drainage during the l a t e -Pleistocene. The late-Pleistocene history of the area has been well documented by Dolmage (1934), Mathews (1944) and H i l l s (1962). During t h i s time, a series of ice-dammed lakes were formed at the front of the retreating ice sheet i n Similkameen v a l l e y . The r i v e r was diverted f i r s t through Lost Horse Gulch and l a t e r through Smelter Lake valley as the i c e sheet retreated to the north. Plate III shows the western end of Smelter Lake and an abandoned channel of the Pleistocene Similkameen River and Plate IV shows an area of stream-worn bedrock and boulders which i s situated at an elevation of 2800 feet, about 400 feet above the present r i v e r l e v e l . Smelter Lake and Victor Lake, which l i e s 3000 feet east of Lost Horse Gulch, occupy parts of former meltwater channels and have resulted from damming of the channels by alluvium and Plate I I I : Abandoned channel of Similkameen River (right) entering Smelter Lake va l l e y (lower l e f t ) . 10 Plate IV: Stream-worn bedrock and boulders 400 feet above present l e v e l of Similkameen River. t a l u s . Further evidence of late-Pleistocene lakes i s found i n the many terrace remnants reported by Cairnes ( 1 9 2 3 ) i n the upper Similkameen and Sunday Creek basins. Some of these are as much as 1 1 0 0 feet above the present stream l e v e l . H i l l s ( 1 9 6 2 ) , i n an unpublished M.Sc. thesis, has reported delta remnants and strand l i n e s at an elevation of 4 2 5 0 feet i n Copper Creek and Friday Creek v a l l e y s . The f i n a l process, which affected present topography, began after the ice withdrew and drainage was re-established. This process resulted i n the formation of p o s t - g l a c i a l canyons such as those i n Similkameen River and Whipsaw Creek. Dolmage ( 1 9 3 4 ) , and Cairnes ( 1 9 2 3 ) attribute these deep canyons to post-g l a c i a l u p l i f t or t i l t i n g , but the fact that the canyons exist i s not necessarily evidence of recent u p l i f t . It i s also pos-11 s i b l e that i f the o r i g i n a l Pliocene u p l i f t was r a p i d , that down-cut t ing of the streams might not have kept pace with i t and that , t h i s being the case, downcutting may have been interrupted by g l a c i a t i o n and renewed after the ice re treated . An argument i n favor of post-Ple is tocene u p l i f t might be developed i f t i l t e d strand l i n e s or s i m i l a r evidence were found i n Similkameen River v a l l e y . However, t h i s would require a very c a r e f u l and de ta i l ed study since only remnants of these features presently ex i s t and c o r r e l a t i o n would be extremely d i f f i c u l t . I t seems poss ible that both rapid Pliocene u p l i f t and p o s t - g l a c i a l rebound have contributed to the formation of these canyons. Climate and Vegetat ion; The Copper Mountain map-area l i e s within the Inter ior A r i d c l i m a t i c d i v i s i o n . The mean monthly temperature for Janu-ary i s 1 0 - 2 0 ° F and for July i s 5 5 - 6 0 ° F and the mean annual p r e c i p i t a t i o n i s 15-25 inches. The f l o r a i n t h i s area i s t y p i c a l of the Southern I n t e r i o r of B r i t i s h Columbia. Coniferous trees include ponderosa pine and lodgepole pine as the most common v a r i e t i e s with lesser amounts of spruce, hemlock, Douglas f i r , and jun iper . Deciduous trees include p o p l a r , b i r c h , and a lder . Much of the area around Princeton i s grass land. Acknowledgments: The work for t h i s thes i s was financed l a r g e l y through National Research Counci l scholarships and a g r a n t - i n - a i d of r e -search awarded to Dr. K . C . McTaggart for t h i s purpose by the National Research C o u n c i l . I would l i k e to express my grat i tude to t h i s organizat ion for t h e i r help . I am indebted to Dr. K . C . McTaggart of the Univers i ty of B r i t i s h Columbia for h i s guidance and h i s many h e l p f u l sug-gestions during the w r i t i n g of t h i s t h e s i s . I would l i k e to thank the many other members of the Faculty and s t a f f i n the Geology and Metallurgy departments at the Univers i ty of B r i t i s h Columbia for t h e i r w i l l i n g help . I would also l i k e to acknowledge the able assistance given by my wife, , S h e i l a , who acted as f i e l d ass is tant during the summers of 1961, 1962,and I 9 6 3 . The Granby Consolidated Mining, Smelting and Power Company generously permitted me to obtain copies of t h e i r a e r i a l , photographs and allowed access to t h e i r mine maps. F i n a l l y , I wish to thank the B . C . Department of Mines and the technic ians of the Department of Geology at the Univ-e r s i t y of B . C . for making t h i n sec t ions . CHAPTER II GENERAL GEOLOGY Introductions The oldest rocks i n the Copper Mountain map-area are those of the Nico la group. These consist almost e n t i r e l y of green andesites and a u g i t e - d i o r i t e s with minor sedimentary and t u f f a -ceous rocks . The Nico la rocks are intruded by the Copper Mountain in trus ions which are made up of a d i f f e r e n t i a t e d ser ies of rocks ranging i n composition from gabbro to per thos i t e , a rock con-s i s t i n g almost e n t i r e l y of p e r t h i t e . This rock ser ies i s bel ieved to have formed by d i f f e r e n t i a t i o n of a s ingle magma of d i o r i t i c composition. The copper ores, for which the area i s wel l known, are associated with these i n t r u s i o n s . The youngest rocks , which cover much of the northern part of the map-area, belong to the Princeton group of rocks . These are made up of a vo lcanic formation of hornblende andesite and basalt which i s over la in by shale , conglomerate, s i l t s t o n e , and coal of Middle Eocene age. These sedimentary rocks are p a r t l y interbedded with and p a r t l y over la in by daci te t u f f s and brecc ias . There are many dykes i n the area. Perhaps the most i n t e r -es t ing are the Mine Dykes (Dolmage, 1934), a swarm of f e l s i t i c dykes adjacent to the north contact of the Copper Mountain stock. Their age i s uncertain but they cut both Nico la and i n t r u s i v e rocks. Other dykes i n the area are re lated e i ther to the Copper Mountain in trus ions or to T e r t i a r y volcanic rocks, Much of the map-area i s over la in by Pleistocene and 14 Table of Formations: Era Period or Epoch Group or Formation Lithology CENOZOIC Pleistocene and Recent G l a c i a l ; t i l l , sands and grave l , l acus tr ine s i l t s UNCOMFORMITY Middle Eocene Allenby formation Shale, sandstone, daci te t u f f Lower Volcanic formation Hornblende .andesite, basa l t , brecc ia UNCONFORMITY CENOZOIC? Dyke rocks F e l s i t e , hornblende-andesite,lamprophyre l a t i t e porphyry INTRUSIVE CONTACT MESOZOIC Lower Jurass ic Copper Mountain Intrus ions Monzonite, syenite Pegmatite: syenite and perthosi te Monzonite Gabbro, pyroxenite D i o r i t e INTRUSIVE CONTACT MESOZOIC Upper T r i a s s i c Wolf Creek formation (Nicola group) Andesite flows and brecc ias , augite-d i o r i t e , a r g i l l i t e , t u f f , minor limestone and conglomerate Table I : Geologica l formations of the Copper Mountain area. 15 Recent deposits which include g l a c i a l t i l l s and lacustrine or f l u -v i a l material. These have not been mapped. Description of Formations: (a) Nicola Group Introduction: The Nicola group was f i r s t named by Dawson ( 1 8 7 7 ) , the type section being on the south side of Nicola Lake. It i s an extremely complex succession of volcanic rocks with several i n t e r -bedded belts of sedimentary and tuffaceous rocks. The sequence occupies a large region on the eastern side of the Coast Range Batholith extending over an area 20 to 50 miles wide and 140 miles long i n a northerly d i r e c t i o n . Much of the group has been intruded or overlain by l a t e r igneous rocks. It has been mapped and variously named by several authors, notably Dawson ( 1 8 7 7 ) , Dolmage ( 1 9 3 4 ) , Camsell ( 1 9 1 0 ; 1 9 1 3 ) , Bostock ( 1 9 4 0 ) , Rice ( 1 9 4 7 ) , Cock-f i e l d ( 1 9 4 8 ) , and Fahrni ( 1 9 5 1 ) . The following i s a l i s t of Nicola formations as compiled by Rice ( 1 9 4 7 ) s Wolf Creek formation- mainly volcanic rocks of andesitic composition. Henry formation- a r g i l l i t e , t u f f , and impure limestone. Hedley formation- consists of a lower member made up of limestone and quartzite and an upper member con-s i s t i n g largely of t h i n l y banded fine-grained, black and white quartzite and breccias. Sunnyside formation- thin-and thick-bedded limestones. Redtop formation- thin-bedded, banded, grey and white quartzites intercalated with limestone and argillaceous and volcanic bands. The Nicola rocks within the Copper Mountain map-sheet have been named the Wolf Creek formation by Dolmage ( 1 9 3 4 ) and were 16 c o r r e l a t e d w i t h t h e N i c o l a g r o u p b y h i m . F a h r n i ( 1 9 5 1 ) d i d a d d i -t i o n a l d e t a i l e d w o r k o n t h e W o l f C r e e k f o r m a t i o n ( s e e p a g e 38) . R o c k s o f t h e N i c o l a g r o u p u n d e r l i e t h e e n t i r e a r e a e x -c e p t w h e r e t h e y h a v e b e e n i n t r u d e d b y t h e C o p p e r M o u n t a i n i n t r u -s i o n s . I n t h e n o r t h e r n p a r t o f t h e map a r e a , t h e N i c o l a r o c k s a r e o v e r l a i n b y t h e P r i n c e t o n g r o u p . The N i c o l a r o c k s t o t h e n o r t h o f t h e C o p p e r M o u n t a i n s t o c k a r e l a r g e l y o f a u g i t e - d i o r i t e a n d a n d e s i t i c p o r p h y r i e s . B e l t s o f s e d i m e n t a r y a n d t u f f a c e o u s r o c k s l i e t o t h e w e s t a n d i m m e d i a t e l y s o u t h o f t h e s t o c k . S m a l l e r e x p o s u r e s o f s e d i m e n t a r y s e q u e n c e s a r e a d j a c e n t t o t h e n o r t h e r n c o n t a c t o f t h e s t o c k . T h e r e m a i n i n g N i c o l a r o c k s a r e l a r g e l y a n d e s i t i c f l o w s a n d b r e c c i a s . T h e t h i c k n e s s o f t h e N i c o l a s e q u e n c e i s u n k n o w n . P e t r o l o g y : The m o s t common t y p e o f N i c o l a v o l c a n i c r o c k i s a n d e s i t e p o r p h y r y . I t i s c o m m o n l y g r e e n o r g r e y - g r e e n a n d a p h a n i t i c i n a p p e a r a n c e b e c a u s e a l t e r a t i o n t e n d s t o o b s c u r e i t s p o r p h y r i t i c n a t u r e . M o s t o f t h e p o r p h y r i e s h a v e p h e n o c r y s t s o r a u g i t e , p l a -g i o c l a s e o r b o t h m i n e r a l s b u t i n a f e w , l a r g e e u h e d r a l c r y s t a l s o f h o r n b l e n d e a r e a l s o p r e s e n t . T h e g r o u n d m a s s i s c o m p o s e d o f f i n e - g r a i n e d a u g i t e a n d p l a g i o c l a s e w i t h t h e a c c e s s o r y m i n e r a l s m a g n e t i t e , a p a t i t e , b i o t i t e , s p h e n e , a n d a l i t t l e i n t e r s t i t i a l K - f e l d s p a r . T h e s e m i n e r a l s a l s o o c c u r p o i k i l i t i c a l l y e n c l o s e d b y p y r o x e n e p h e n o c r y s t s . The p o r p h y r i e s a r e c o m m o n l y t r a c h y t o i d w i t h a w e l l -d e v e l o p e d a l i g n m e n t o f p l a t y f e l d s p a r c r y s t a l s ( P l a t e V ) . 1 7 Plate V: Andesitic feldspar porphyry of the Nicola group. Plagioclase phenocrysts have a subparallel alignment i n a groundmass of fine-grained feldspar and horn-blende. Crossed n i c o l s , 24X. Plagioclase, both i n the groundmass and phenocrysts, i s subhedral to euhedral. I t i s commonly zoned and twinned and has the com-position of andesine i n the range An^ Q to An^<.. Pyroxene pheno-crysts are subhedral but have corroded surfaces even i n r e l a t i v e l y unaltered rocks. Some of them show compositional zoning. Almost a l l of the Nicola volcanic rocks within the map-area have undergone at least some a l t e r a t i o n . Magmatic and deuteric processes have probably caused corrosion of the pyroxene phenocrysts and some a l t e r a t i o n to amphibole and c h l o r i t e . Some s e r i c i t i z a t i o n of plagioclase has also resulted from deuteric a l t e r a t i o n . In the more highly altered rocks, plagioclase may be completely replaced by s e r i c i t e with epidote or c a l c i t e . Pyroxene i s commonly altered to green amphibole and, i n some rocks, has been completely replaced by f e l t e d masses of fine-grained 1 8 a c t i n o l i t e . C h l o r i t e i s also present i n many of the rocks as an a l t e r a t i o n product of pyroxene. One rock contains pseudomorphs of a mixture of c a l c i t e and c h l o r i t e which appears to have r e -placed pyroxene or o l i v i n e phenocrysts (Plate V I ) . The h ighly Plate V I ; Pseudomorph of c h l o r i t e and c a l c i t e after pyroxene (or o l i v i n e ) i n Nico la andesite porphyry. The ground-mass contains a l tered p lag ioc lase , c h l o r i t e , c a l c i t e and magnetite. Crossed n i c o l s , 24X. altered rocks contain unusually large amounts of sphene which may be formed from the a l t e r a t i o n of t i t a n i f e r o u s pyroxene or magne-t i t e . Many of the rocks contain secondary c a l c i t e , p a r t i c u l a r l y as a replacement of p lag ioc la se . In addi t ion to the above described a l t e r a t i o n , there i s a widespread potassium metasomatism of Nico la vo l can ic s . A mottled or patchy appearance of some of the andesite i s due to the addi -19 t i o n of b i o t i t e and K- fe ldspar . Dark grey areas contain only a l i t t l e pyroxene but a large amount of b i o t i t e and K- fe ldspar . Pink or salmon-colored veins of K-fe ldspar are found i n many places , some of them with copper m i n e r a l i z a t i o n . In the area to the north of the Copper Mountain stock, much of the rock of the Nico la group i s medium-grained to coarse-grained a u g i t e - d i o r i t e . This rock i s s imi lar minera log ica l ly to the previous ly described andesite porphyries but has the texture of an i n t r u s i v e rock. I t var ies a great deal i n co lor and tex-ture as a r e s u l t of various degrees of hydrothermal a l t e r a t i o n . I t i s bel ieved that these rocks are one of the types of Lost Horse in trus ions described by Dolmage ( 1 9 3 4 ) that are mentioned on page 2 2 , Their exact r e l a t i o n s h i p i s not known but t h e i r composition and texture suggest that they may be feeders or dykes re la ted to Nico la volcanism. The a u g i t e - d i o r i t e i s a b lack, medium-grained rock .'com-posed of zoned andesine p lag ioc lase , augite , magnetite, and apa-t i t e . Secondary minerals include s e r i c i t e , b i o t i t e , epidote, c h l o r i t e , sphene, hornblende, epidote, and K- fe ldspar . The most intense ly a l tered type i s yellow-grey i n c o l o r , the pyroxene having been almost e n t i r e l y replaced by hornblende, c h l o r i t e , c a l c i t e , and sphene. Some of the p lag ioc lase c r y s t a l s , poss ib ly as a r e s u l t of r e c r y s t a l l i z a t i o n under shearing s tress , have been bent or twisted and have feathered ends. Several be l t s of tuffaceous and normal sediments are present within the map area. On i t s western edge, a r g i l l i t e , l i t h i c t u f f , and limestone occur i n an a n t i c l i n a l s tructure which underl ies the main body of Nico la andesites (Wolf Creek formation) (Plate V I I ) , A r g i l l i t e of t h i s formation i s grey or black, and 20 Plate V I I ; Bedded l i t h i c t u f f from the sedimentary be l t west of Copper Mountain stock. Fragments of l a v a , d e v i t r i -f i ed g lass , fe ldspar and limestone are present i n a dust matrix . Plane po lar ized l i g h t , 24X. thin-bedded or massive. L i t h i c t u f f i s a grey rock made up of angular fragments of f e ldspar , l ava , d e v i t r i f i e d g lass , and l ime-stone. Limestone i s f ine -gra ined , grey i n c o l o r , and i s made up of mosaic- l ike c a l c i t e . None of the rocks i n t h i s succession has undergone any metamorphism. Another be l t of sedimentary rocks l i e s immediately to the south of Copper Mountain stock i n Similkameen V a l l e y . This succession i s mainly of very f ine-grained tuffaceous sediments interbedded with s i l i c e o u s p e l i t e s and minor conglomerate. A small area underla in by metamorphosed sedimentary rock i s found on the north contact of the Copper Mountain stock i n Similkameen canyon. The rock i s well-bedded, f ine -gra ined , has a t y p i c a l hornfe l s i c texture , and belongs to the pyroxene hornfels f a c i e s . One assemblage, quartz -d iops ide -p lag ioc lase , 21 suggests an o r i g i n a l impure or calcareous sandstone. An adjacent band contains pale-green c h l o r i t e , p lag ioc lase and quartz sug-gest ing an o r i g i n a l p e l i t i c assemblage which has been subjected to retrograde metamorphism. Considerable secondary c a l c i t e i s also present. Another rock, taken from a point 200 feet north of the contact , i s a quartz i te brecc ia composed of fragments of quartz with minor p lag ioc lase and b i o t i t e . The fragments are out-l i n e d by f ine-gra ined b i o t i t e which i s probably metamorphic. S t r u c t u r a l Re la t ions : The d i s p o s i t i o n of flows within the Nico la group remains obscure within the map-area. The vo lcanic rocks are mostly mas-s ive and, p a r t i c u l a r l y i n a l tered rocks , i t i s d i f f i c u l t to d i s -t i n g u i s h one flow from another. In the v i c i n i t y of the Copper Mountain mine, Fahrni ( 1 9 5 1 ) has mapped north- trending gentle fo lds i n repeated sequences of vo lcanic rocks and marine sediments. Several at t i tudes on bedding obtained from the western sedimentary be l t suggests an a n t i c l i n e s t r i k i n g about north 15 degrees east and plunging 40 degrees to the north . The other sedimentary bodies are steeply dipping and have probably been strongly af-fected by the i n t r u s i o n of the Copper Mountain stock. Several major fau l t s and many minor f a u l t s w i l l be discussed i n the sect ion on s t r u c t u r a l geology on p a g e l 3 5 . Age and C o r r e l a t i o n : Most of the Nico la rocks within the map-area belong to the Wolf Creek formation as defined by Dolmage ( 1 9 3 4 ) . The wes-tern be l t of sedimentary rocks appears l i t h o l o g i c a l l y very s i m i l a r to the Henry formation (Bostock, 1 9 4 0 ) which i s the uppermost formation i n the sedimentary succession at Hedley and which i s there over la in by the Wolf Creek formation (Rice, 1 9 4 7 ) . The other sedimentary bodies which are adjacent to the Copper Mountain stock belong to Wolf Creek formation. (b) Copper Mountain Intrusions Introduct ion: A de ta i l ed account of the Copper Mountain in trus ions i s o f f e r e d . i n a l a t e r chapter and, therefore , only a b r i e f d e s c r i p -t i o n w i l l be given i n t h i s s ec t ion . Dolmage ( 1 9 3 4 ) used the name Copper Mountain stock for the main .d i f f erent ia ted i n t r u s i o n i n the cen tra l part of the map-area (see Figure 4 ) . The stock to the west of Smelter Lake he c a l l e d the Smelter Lake stock and that on the eastern border of the map-sheet, the Voigt stock. Rice ( 1 9 4 7 ) used the term Copper Mouhtain in trus ions to include these three and the "Lost Horse Intrus ions". The Lost Horse Intrusions were mapped separately by Dolmage ( 1 9 3 4 ) who stated: "The age or ages of these (Lost Horse) i n t r u -s ives are not known, but they are i n places mineral ized by so lut ions that apparently or ig inated i n the magmas that formed the Copper Mountain and other stocks, and are, therefore , somewhat o lder . Their composition, however, i s so s i m i l a r to that of the stocks that they may be c lose ly re la ted to them i n time as wel l as o r i g i n . " He described two types: ( 1 ) a very l i g h t - c o l o r e d , acid a u g i t e - d i o r i t e ; and ( 2 ) a p inki sh-grey , b i o t i t e monzonite or syeni te . I t i s bel ieved by the present wri ter that the f i r s t type i s re la ted to Nico la volcanism and that the second type i s part of the Copper Mountain in trus ions as i t i s c l e a r l y in t rus ive in to Nico la rocks and i s c l o se ly s i m i l a r i n composition to the 2 3 Ii Smeltery Lake ^ i v - - ' Figure 4 Map showing loca t ion of Copper Mountain: in trus ions (compare with Figure 1 ) . 2 4 Copper Mountain intrusions. In t h i s t h esis, the term Copper Mountain intrusions w i l l be used to include a l l of those intrusive rocks believed to have formed from the same magma or period of magmatic a c t i v i t y as that which formed the main d i f f e r e n t i a t e d stock. The names used by Dolmage ( 1 9 3 4 ) w i l l be used i n describing p a r t i c u l a r bodies except for the term Lost Horse intrusions. In addition, the name Armstrong Bluffs complex w i l l be used to describe the group of i n -trusive masses including the body immediately southwest of the Smelter Lake stock and the monzonites and syenites north of the main stock. This complex includes Dolmage's type ( 2 ) Lost Horse intrusions. Armstrong Bluffs i s the name which i s used l o c a l l y to designate the steep b l u f f s on the west side of Similkameen River and immediately south of Smelter Lake stock. Petrology: The rocks of the Copper Mountain intrusions are diverse i n composition ranging from pyroxenite to syenite and perthosite pegmatites. Although a l l intermediate types are present, the rocks have been divided into f i v e main groups or mappable units as shown i n Figure 1 . It i s believed that the rocks of the Copper Mountain intrusions consitute a rock series which has been formed by c r y s t a l l i z a t i o n d i f f e r e n t i a t i o n of a single parent magma. Detailed descriptions of the various rock types are reserved.for a l a t e r chapter. Structural Relations: The Copper Mountain intrusions are int r u s i v e into rocks of the Nicola group and are i n turn cut by many dyke rocks. Their 25 erosion surface has been over la in i n part by sediments and v o l -canic rocks of the Princeton group. The Armstrong B lu f f s complex intrudes the Smelter Lake and Voigt stocks and the Nico la vo l can ic s . Gradational contacts separate the main masses of the d i f f e r e n t i a t e d Copper Mountain stock. A f o l i a t i o n which i s e r r a t i c a l l y developed i n a l l of the in trus ions plunges steeply i n the main stock and suggests for i t a c y l i n d r i c a l form. The Copper Mountain stock i s bounded on i t s western edge by a major f a u l t which s t r i k e s about 25 degrees east of north . Age and C o r r e l a t i o n : The age of the Copper Mountain in trus ions as defined by geologic methods i s known only within wide l i m i t s . They intrude the Upper T r i a s s i c Nico la group, are cut by in trus ions of Upper Cretaceous or ear ly T e r t i a r y age (Rice, 1 9 4 7 ) , and they are over-l a i n , unconf ormably by the Middle Eocene Princeton group. These data place them between the Jurass i c and ear ly Upper Cretaceous. Prel iminary K-Ar age dating (White, S i n c l a i r and Harakal, 1 9 6 7 ) gives an age of about 1 9 5 m i l l i o n years for the monzbnites from the intermediate zone of the Copper Mountain stock, and b i o t i t e associated with the copper ore of Copper Mountain mine. According to the phanerozoic time scale published by the Geo-l o g i c a l Society of London ( I 9 6 4 ) , t h i s date f a l l s very close to the T r i a s s i c - J u r a s s i c boundary. The Copper Mountain rocks , i n t h e i r v i r t u a l absence of quartz or fe ldspatho id , are quite d i f f eren t from any other i n -t rus ive rocks i n the immediate v i c i n i t y . A number of other s i l i c a - p o o r i n t r u s i v e complexes are known i n southern B r i t i s h 26 Columbia. Some of these are: Tulameen complex (Findlay , 1 9 6 3 ) ; dior i te -gabbro complex at Hedley (Camsell , 1 9 1 0 ) ; S e l i s h Moun-t a i n , d ior i te -gabbro (Rice, 1 9 4 7 ) ; Iron Mask Batho l i th (Cockf i e ld , 1 9 4 8 ) ; small s y e n i t i c bodies at Independence Mine (Cairnes, I 9 2 4 ) ; C o r y e l l syenites ( L i t t l e , I 9 6 0 ) ; Kreuger Mountain a lka l ine com-plex (Krauskopf, 1 9 4 1 ) . Although many of these igneous bodies have phases which are s imi lar in . charac ter to c e r t a i n phases of the Copper Mountain i n t r u s i o n s , none has both the continuous gradation from pyroxen-i t e to perthos i te and the concentric zonal arrangement of the Copper Mountain stock. The ages of the above mentioned in trus ions range from Jurass i c to Eocene. (c) Dykes Introduct ion: Dykes i n the Copper Mountain area range from r h y o l i t e to lamprophyre i n composition. Four types of dykes have been d i s -t inguished and only the largest have been mapped. "Mine Dykes": The most important of the dykes are the "Mine Dykes" which are abundant i n the v i c i n i t y of the Copper Mountain mine on the northeast side of the main stock. Their d i s t r i b u t i o n , on Figure 1, i s modified from that shown on maps loaned by Granby Consol idated. These are pale buff or cream i n c o l o r , and show both p o r p h y r i t i c and aphanit ic textures . The p o r p h y r i t i c types have phenocrysts of quartz and a l b i t e i n a f ine-gra ined mass of the same minerals . C h l o r i t e and leucoxene are apparently pseudomorphous after amphibole. One aphanit ic type i s a f i n e -2 7 grained fe ldspath ic mass containing c lo t s of b i o t i t e , c h l o r i t e and epidote. The age of the "Mine Dykes" i s not known. They cut the Nico la group and the Copper Mountain in trus ions and are cut by andesite dykes which are bel ieved to be re la ted to T e r t i a r y v o l -canism. The "Mine Dykes" trend i n a northwesterly d i r e c t i o n and dip v e r t i c a l l y . They are bel ieved to be unrelated to the Copper Mountain i n t r u s i o n s . Hornblende Andesite: A second type of dyke, hornblende andesite, i s much less common than the "Mine Dykes" and i s considered to be re la ted to the abundant T e r t i a r y lava flows. The rock i s grey-brown and com-monly p o r p h y r i t i c with phenocrysts of hornblende and p lag ioc la se . The amphibole occurs as ragged, greenish-blue , elongate prisms. Plagioc lase i s euhedral to subhedral and i s commonly s e r i c i t i z e d . Plagioc lase phenocrysts have e i ther normal or o s c i l l a t o r y zoning with cores as c a l c i c as l abrador i t e ( A n ^ ) . The groundmass i s composed of andesine (An^) with minor K-fe ldspar and quartz . Accessory minerals include magnetite, apat i t e , and sphene. Horn-blende andesite dykes are very s i m i l a r i n texture and composi-t i o n to the T e r t i a r y vo lcanic flows which are described i n a l a t e r sec t ion . Lamprophyre: A t h i r d type of dyke or minor in t rus ive i s a pyroxene lamprophyre which occurs at the southern contact of the Copper Mountain stock. I t i s a medium-grained, melanocratic porphyry 28 with phenocrysts of pyroxene p a r t l y a l tered to greenish-blue amphibole and b i o t i t e . The groundmass i s composed of f ine-grained b i o t i t e , amphibole, p lag ioc lase (An ) , and quartz . A few larger 3 2 c r y s t a l s of p lag ioca l se have been completely s e r i c i t i z e d except for a narrow outer r im. L a t i t e Porphyry: A fourth type of dyke rock i s grey and white l a t i t e por-phyry . Large white phenocrysts of p lag ioc lase ( A n ^ ) are i n a very f ine-gra ined fe ldspathic groundmass. P lagioc lase has been s e r i c i t i z e d and hornblende has been pseudomorphed by c h l o r i t e and magnetite. The porphyry dykes cut the Copper Mountain i n t r u -sions but t h e i r composition suggests a r e l a t i o n to them. (d) Princeton Group Introduct ion: Rice (1947) included the sedimentary and volcanic rocks of T e r t i a r y age i n a s ingle uni t termed the Princeton group. H i l l s (1962) subdivided the group in to the Lower Volcanic forma-t ion .and the Allenby formation. H i l l s ' subdiv i s ion w i l l be used i n . t h i s t h e s i s . D i s t r i b u t i o n : The Princeton group of vo lcanic and sedimentary rocks occupies basins both to the north and south of the Copper Moun-t a i n i n t r u s i o n s . The Lower Volcanic formation, which underl ies the predominantly sedimentary Allenby formation, l i e s unconform-ably over a part of the Copper Mountain in trus ions i n the northern.part of the map-area. Lower Volcanic Formation: The Lower Volcanic formation forms b lu f f s as a r e s u l t of erosion (Plate V I I I ) . steep, i r r e g u l a r The most common rock Plate V I I I : Steep b l u f f s of Lower Volcanic formation on east bank of Similkameen River . type i n the formation i s a hornblende andesite porphyry which i s a grey or grey-brown color where fresh but, depending upon the degree of weathering, may be yellow-brown, pink or red . In a few places , e spec ia l l y i n the lower va l l ey of Wolf Creek, there are remnant knobs of dark brown or black, flaggy basa l t s . The re la t ionsh ip of these rocks i s not c l ear but they have been i n -cluded with the Lower Volcanic formation. Some of these basal t s have a planar arrangement of ves i c l e s s i m i l a r to that found i n the adjacent porphyries , but lack the c h a r a c t e r i s t i c a l t e r a t i o n . On the i r r e g u l a r ridges and steep c l i f f s to the south of Smelter Lake, the rock i s a dark brown, blocky, b a s a l t i c ag-glomerate which has undergone intense red weathering and may be close to a vo lcanic vent. 30 The hornblende andesite porphyry contains phenocrysts of zoned plagioc lase ( A n ^ to A n 2 j ) , pyroxene and b a s a l t i c hornblende i n a matrix of glass and feldspar m i c r o l i t e s (Plates IX, X, X I ) . Plate IX: Hornblende andesite from the Lower Volcanic formation. The phenocrysts of p lag ioc lase and b a s a l t i c hornblende are i n a matrix of glass and p lag ioc lase m i c r o l i t e s . Crossed n i c o l s , 6 5 X . Plate X: Hornblende andesite from the Lower Volcanic formation. The large c r y s t a l i s b a s a l t i c hornblende (with opaque r e c r y s t a l -l i z e d borders) and i s i n a matrix of glass and plagioc lase m i c r o l i t e s . Plane po lar ized l i g h t , 6 5 X . 31 Plate XI: Hornblende andesite from the Lower Volcanic formation. A p lag ioc lase phenocryst shows o s c i l l a t o r y zoning (An^to A n ^ ) i n a matrix of glass and plagioc lase m i c r o l i t e s ( A n ^ ) . Crossed n i c o l s , 65X. In some parts of the flows, the b a s a l t i c hornblende phenocrysts are large and commonly with a preferred or i en ta t ion but i n other places they are inconspicuous or absent. Blocks of reddish horn-blende andesite porphyry are found included i n a groundmass of the grey-brown type. I t i s bel ieved that a l l of the flows are of very s imi lar composition and that the wide v a r i a t i o n i n co lor i s a re su l t of d i f f erent degrees of weathering or a l t e r a t i o n . Plate XII i l l u s t r a t e s a t y p i c a l hornblende andesite porphyry. Many of the rocks have a mottled appearance. I t appears that a planar arrangement of f lat tened ves i c l e s has resul ted from flow and sub-sequently has led to the unusual patterns of co lor through contro l of a l t e r a t i o n and subsequent weathering. In some of these rocks , the planar pattern of c a v i t i e s i s accentuated by white amygdules which contain a mixture of ana lc i te and n a t r o l i t e (Plate X I I I ) . 32 Plate XII : Plate XIII: Z e o l i t i c andesite from the Lower Volcanic forma-t i o n . The white amygdules contain a mixture of analcite and n a t r o l i t e . 33 Allenby Formation: L o c a l l y , the Allenby formation cons is ts mostly of brown f i s s i l e shales . These are interbedded with coal seams (Plate XIV) and also with minor amounts of arkosic sandstone, conglomerate, and tuffaceous sediments (Plates XV, XVI) . formation. These are about 15 miles northwest of Copper Mountain near Blakeburn, B . C . The dark layers are coal and carbonaceous shale and the l i g h t layers are c lay and shale . Dacite t u f f s and minor flows are also interbedded with sediments i n the Allenby formation. The t u f f s are massive, l i g h t - c o l o r e d , and f ine -gra ined . Minute phenocrysts of b i o t i t e , p lagioclase (An^^ to A n ^ ) and quartz are present i n a glassy matrix i n the flows. Plate XVII shows a t y p i c a l daci te of the Allenby formation. 3 4 Plate XV: L i t h i c t u f f from the Allenby formation. The rock consists of angular fragments of p lag ioc lase , l ava , and shards i n a glassy matrix. Plane po lar ized l i g h t , 65X. Plate XVI: Tuffaceous bedded shale from the Allenby formation. Fine fragments of fe ldspar and lava are present i n an i n d e f i n i t e matr ic . Plane po lar ized l i g h t , 6 5 X . 35 Plate XVII Dacite of the Allenby formation, D a c i t i c brecc ias and t u f f s , which over l i e the sediments have formed steep, i r r e g u l a r b lu f f s i n Similkameen canyon and along the ridge north of Smelter Lake (Plate XVIII ) . Plate XVIII: Flow brecc ias of the Allenby formation north of Smelter Lake. 3 6 These rocks are l e u c o c r a t i c , pale-pink to buff colored t u f f s and brecc ias which contain angular fragments and blocks up to 18 inches i n diameter. The matrix, i n some of the rocks , i s made up of f iner fragments and dust which has weathered a rusty brown color probably as a re su l t of rapid oxidat ion of the smaller p a r t i c l e s (Plate XIX) . Plate XIX: Dacite brecc ia of the Allenby formation. S truc tura l Re lat ions: Many of the i n t e r n a l s tructures observed i n the Lower Volcanic formation are due to flow. The most common of these i s a planar arrangement of f lat tened v e s i c l e s . A second com-mon flow structure i s a f o l i a t i o n or l i n e a t i o n caused by a l i g n -ment of hornblende phenocrysts. Fold s tructures are present wi th in the Lower Volcanic formation. A s t r i k i n g example, which resembles a large over-turned d r a g - f o l d , i s found i n the canyon of Whipsaw Creek ( F i g -ure 5). It i s believed to be a flow s t ruc ture . 37 Figure 5: Flow structure i n hornblende andesite of Lower V o l -canic formation. The f o l d axis plunges 70 degrees at north 45 degrees east . Scale: 1 inch to 10 feet . Internal s tructures i n the Allenby formation are v i s i b l e mainly i n the sedimentary rocks . In general , the beds dip norther ly or towards the center of the Princeton bas in . Minor fo lds about 15 feet across and with northwest-trending axes plunge gently i n t h i s d i r e c t i o n (Figure 1) . Mode of O r i g i n : The Lower Volcanic formation i s composed of andes i t ic and b a s a l t i c lava flows and agglomerates. The agglomeratic mass south of .Smelter Lake suggests that a volcano was nearby. Dykes and minor in trus ions of andes i t ic composition are considered.to be the feeders of the flows. Most of the at t i tudes of these lava flows are bel ieved to be i n i t i a l d i p s . After volcanism, sediments f i l l e d the fresh-water basin to the north of the map-area. The source of these sediments i s considered by H i l l s (1962) to be l a r g e l y north of the Princeton bas in . Towards the end of t h i s period of depos i t ion , there was intermit tent explosive v o l -canism which pr'oduced the p a r t l y interbedded and p a r t l y over ly ing 38 d a c i t i c t u f f s and brecc ias . Age and C o r r e l a t i o n : The sedimentary sequences of the Allenby formation have been dated by H i l l s ( 1 9 6 2 ) by means of plant and insect f o s s i l s as Middle Eocene. The age of the underlying Lower Volcanic f o r -mation i s not known. The Princeton basin i s s i m i l a r to other basins of T e r t i a r y sedimentary and volcanic rocks i n southern B r i t i s h Columbia. (e) Geology of the Copper Mountain Mine Fahrni ( 1 9 5 1 , 1 9 6 6 ) , ch ie f geologist for Granby Con-so l idated Mining, Smelting and Power Company Limi ted , was mine geologist at Copper Mountain from 1 9 4 5 to 1 9 5 7 - During t h i s per iod , he undertook an extensive program of de ta i l ed mapping i n the mine area and, since he&has a far more comprehensive understanding of the complex mine geology than does the present author, a b r i e f summary of h i s i n t e r p r e t a t i o n i s given here. In general , the orebodies l i e along theinortheastern contact of Copper Mountain stock but within Nico la vo lcanics (Wolf Creek formation) . The Wolf Creek formation cons is ts of repeated sequences of coarse andes i t i c brecc ias , shallow water, marine bedded t u f f s , and cherts , limestones and marine s ed i -ments. Structure i s obscure but the beds.appear to be gently folded into a north- trending open a n t i c l i n e that passes through the mine workings. Wolf Creek volcanics have been i n -truded by pre-ore fe ldspar porphyry dykes and s i l l s , Copper Mountain i n t r u s i o n s , and post-ore quartz-porphyry dykes. Faul ts and j o i n t s i n the Wolf Creek formation are of several types. Northeasterly trending "ore fractures" range i n width from a few hundredths of an inch to several inches and are f i l l e d with b i o t i t e - K - f e l d s p a r pegmatite i n which bornite occurs. S imi lar i n s t r i k e to the v e r t i c a l "ore fractures" , but less steeply d ipp ing , are fau l t s or "breaks" which cut a l l formations and contain up to 8 feet of gouge. A northwesterly trending v e r t i c a l f a u l t (Main f a u l t ) l i e s immediately north of the Copper Mountain stock and runs throughthe mine workings. This f au l t i s said to have 150 feet of v e r t i c a l of fset and there i s a sub-p a r a l l e l s c h i s t o s i t y and development of b i o t i t e i n the adjacent vo l can ic s . Ore minerals include born i t e , cha lcopyr i te and minor t e t rahedr i t e and c h a l c o c i t e . Gold and s i l v e r are present i n recoverable q u a n t i t i e s . P y r i t e , magnetite, hematite, b i o t i t e , K- fe ldspar , epidote and c a l c i t e are associated with the ore minerals . Fahrni (1966) states that the orebodies correspond i n part to Lindgren's pyrometasomatic deposits but are s i m i l a r to the "porphyry coppers" of the American:Southwest. A l t e r a t i o n i s of two types: (a) potash metasomation with resu l tant bleaching, b i o t i t i z a t i o n , and f e ldspath iza t ion ; (b) post-ore s i l i c i f i c a t i o n and c h l o r i t i z a t i o n associated with the quartz-porphyry dykes. 40 CHAPTER III  COPPER MOUNTAIN INTRUSIONS General Statement: This chapter i s d iv ided into four parts i n which the petrography and mineralogy, chemistry, s t ruc ture , and o r i g i n of the Copper Mountain in trus ions are considered. In the f i r s t par t , an account i s given of the textures and mineral -o g i c a l compositions of the various rock types. P a r t i c u l a r emphasis i s l a i d on the s t r u c t u r a l and chemical v a r i a t i o n s of the fe ldspars and t h e i r r e l a t i o n to the process of d i f f e r -e n t i a t i o n . This i s followed by cons iderat ion of the chemical composition and v a r i a t i o n s of the i n t r u s i o n s . The sect ion on s tructure i s concerned with the r e l a t i o n between i n t e r n a l and external s tructures and the mode of emplacement of the i n t r u -s ions . In the f i n a l part of t h i s chapter ah attempt i s made to re la te a l l of the various data to an hypothesis for the o r i g i n of the Copper Mountain i n t r u s i o n s . Previous Work: Ear ly work i n the Copper Mountain area was undertaken mainly by Dolmage ( 1 9 3 4 ) and l a t e r by Rice ( 1 9 4 7 ) . The f o r -mer recognized the genetic r e l a t i o n s h i p between the d i f f e r e n t igneous bodies comprising the Copper Mountain i n t r u s i o n s . Dolmage (1934 )pos tu la t ed a parent magma of syeno-gabbro composition (basic d i o r i t e of the present author) , and suggested that t h i s main body of magma occupied a "main magma chamber" beneath the present surface . He further suggested that the Voigt and Smelter Lake stocks and the Lost Horse 4 1 in trus ions were d i f f e r e n t i a t e d produces in jec ted from t h i s cham-ber . He states that the Copper Mountain stock i s an upward projec t ion which l i e s at the top of the main magma chamber and i n which v o l a t i l e s c o l l e c t e d . He suggests ..that t h i s stock d i f -ferent iated i n place with poss ible la te upward or downward move-ment of the core magma. He did not, however, suggest a mechanism of d i f f e r e n t i a t i o n . Rice ( 1 9 4 7 ) , mapping on a reconnaissance sca le , d id not elaborate on the work of Dolmage but d id map for the f i r s t time the western part of the Copper Mountain s tock. - He did not recog-nize the f a u l t that l i e s along the western border of the main stock. Fahrni ( 1 9 5 1 , 1 9 6 6 ) mapped the Copper Mountain mine area i n great d e t a i l . He worked out some of the s tructure of the Wolf Creek formation and postulated ore controls which were used i n the search for add i t i ona l ore. 4.2 PART A: Petrography and Mineralogy Introduct ion: The Copper Mountain in trus ions are made up of a wide var ie ty of rock types which vary minera log i ca l l y , t e x t u r a l l y , and chemical ly . M i n e r a l o g i c a l l y , the rocks range i n composi-t i o n from gabbro to per thos i t e . Although a l l poss ible grada-t ions e x i s t , i t was found,possible to group the rocks in to f ive main uni t s for mapping purposes. These are: (a) d i o r i t e , (b) .pyroxenite, gabbro, (c). monzonite, (d) pegmatite: perthosi te and syeni te , (e) monzonite, syeni te , .minor trachyte and l a t i t e (See Figure l ) . Texture ranges from:aphanit ic to :pegmatitic. Chemically, the Copper Mountain in trus ions belong, i n a general sense, to a suba lka l i c fami ly . Minera log ica l Composition: (a) Introduct ion The mineralogy of the Copper.Mountain in trus ions i s r e l a t i v e l y s imple. The rocks are composed e s s e n t i a l l y of p lag ioc lase , pyroxene, and per th i te with lesser amounts of the accessory minerals , magnetite, sphene, apat i t e , and quartz . Secondary minerals include hornblende, b i o t i t e , s e r i c i t e , e p i -dote, s c a p o l i t e , leucoxene, i r o n oxides, and "pseudoleucite". Perhaps the most s t r i k i n g feature of these rocks i s the almost complete absence of quartz or fe ldspathoid . There i s a complete mineralogica l gradation from the most, basic to the least basic rock type. (b) Modal Analyses Modal analyses of 99 specimens were made with the use 43 of a point counter. Locations of these specimens are given i n Figure 6. For each modal determination, an area of 1 0 0 mm. was traversed at a grid spacing of 0.33 nun. making a t o t a l of 9 6 1 points per section. No attempt was made to maintain uniformity of a n a l y t i c a l , error by any method such as that of Chayes ( 1 9 5 6 ) whereby a number of t h i n sections per specimen are analyzed, the number of sections being determined by the coarseness of the rock (IC number) and the area of measurement. It i s believed by the writer that such an approach would not be j u s t i f i e d for the Copper Mountain intrusions because of t h e i r heterogeneity and because the d i s t r i b u t i o n of the available specimens i s not random (see Figure 6 ) . Instead, a q u a l i t i a t i v e approach was used and a r e l a t i v e l y large number ofssamples from many parts of the intrusions were analyzed. The use of three s i g n i f i c a n t figures (Table II) ^ implies that degree of accuracy only for t h i s p a r t i c u l a r set of analyses. A rough estimate of the repro-d u c i b i l i t y error was obtained by a dozen repeat analyses on di f f e r e n t areas of the same sections. Major minerals (plagio-clase, pyroxene, perthite) d i f f e r e d by an average of 3.5 per-cent; accessories (magnetite, b i o t i t e ) d i f f e r e d by an average of 1.0 percent; perthites i n pegmatite d i f f e r e d by an average of 1.5 percent. Thirteen. chemical analyses are given on page 113. Eight of these were made by H. Wiik for the present work and the remaining f i v e are from Dolmage ( 1 9 3 4 ) . For modal analysis and other detailed work, f i v e specimens were chosen to repre-sent as nearly as possible the location and type of Dolmage fs analyzed specimens. 44 Figure 6 : Map showing l o c a t i o n of modally analyzed specimens. Plagioclase determinations were made for specimens 1 to 1 3 with the un iversa l stage and for the remaining specimens by the Car l sbad-a lb i t e method and by measurement of X* A 0 1 0 i n sect ions J - a . In most cases, where p lagioc lases are zoned, v i s u a l estimates of average anorthite content were made. These r e s u l t s and the modes, which are ca lcu la ted i n volume percents , are given i n Table I I . A l l of the various rock types of the Copper Mountain in trus ions are composed e s s e n t i a l l y of d i f f eren t proportions of augite , p lag ioc lase and p e r t h i t e . In general , where augite and plagioc lase are dominant, per th i te i s correspondingly scarce and where per th i t e i s dominant, augite and plagioc lase are dim-in i shed . (See Figures 7 and 8 ) . 100 75 -5 0 -c 0) 4) o. o o 25 0 -O Plagioclase A Pyroxene • Perthite Gabbro Diorite Monzonite Pegmatite 1 1 1 i i I 4 0 4 5 5 0 „.«55 Weight percent 5 i O , 60 65 Figure 1: A plot of the e s s e n t i a l minerals (modal volume^) of 1 3 analyzed rocks against Wt, % Si02. DIORITE - Voigt Stock No. PI Cp K Am Bi Mt Ap Sp pLc Lx Sc Qz Ct An % 2 5 5 . 8 2 2 . 8 6.6 4-5 4.8 4-8 0.6 0.2 - t r 3 2 - 5 8 ( 4 4 ) 18 4 2 . 8 2 3 - 3 19.7 5-3 . 3.7 4-5 0.3 0.2 - - - . - 0.2 47 1 0 7 4 6 . 6 2 4 . 1 23-0 - 2.5 3-3 0.2 - - - - - 0.2 47 1 1 1 4 5 - 3 25.6 22.3 - 0.6 4-7 l . S 0.1 4 7 - 5 7 ( 4 9 ) 112 4 4 - 6 2 1 . 3 22.6 1-7 3.0 3-4 0.6 - - 1.5 1.5 4 5 - 4 8 ( 4 7 ) DIORITE - Smelter Lake Stock 3 6 0 . 3 19 -0 10 . 2 - 5.1 5-5 t r . - - 3 2 - 6 6 ( 4 6 ) 98 66 .0 21.2 2.1 - 4.8 4.5 o . l 0.8 0.5 43 103 5 3 . 6 2 6 . 3 3.0 - 1 0 . 7 5.8 0.5 - 3 2 - 6 5 ( 4 7 ) 1 0 4 4 5 - 7 1 8 . 7 1 6 . 8 - 1 4 . 3 4-5 o . l _ _ _ _ _ - 48 ( 4 9 ) 105 5 6 . 5 25.0 3-5 - 8.6 6.1 0.2 _ _ _ _ _ - 4 3 - 5 8 106 4 6 . 6 2 4 - 1 23-0 2.5 3-3 •0.2 0.2 47 DIORITE - Copper Mountain Stock (outer zone) 17 6 0 . 8 3 2 . 3 _ _ 2.0 4-5 0.2 0.2 - 0.1 4 0 - 6 0 ( 4 5 ) 19 5 8 . 9 1 4 . 6 1 3 . 7 - 6.1 6.0 0.3 0.3 - 3 8 - 4 4 ( 4 2 ) 20 6 3 - 7 1 3 - 3 3-9 - 14.2 4- 5 0.3 0.1 - - - t r . 0.1 3 8 - 4 7 ( 4 2 ) 50 39-2 2 6 . 8 1 8 . 9 1.0 9.5 3.9 0,4 0.2 - • - 3 2 - 3 5 ( 3 4 ) 57 4 4 - 4 23-9 1 4 . 2 • — 1 1 . 1 5.8 0.4 0.1 — 3 0 - 5 0 ( 4 8 ) Table I I : Modal analyses (volume percent) of Copper Mountain intrusions. PI - plagioclase, Cp - clinopyroxene, K - perthite, Am - amphibole, B i - b i o t i t e , Mt - magnetite, Ap - apatite, Sp - sphene, pLc - pseudolencite, Lx - leucoxene, Sc - s e r i e i t e , Qz - quartz, Ct - c h l o r i t e . Average An % i n brackets. DIORITE - Copper Mountain Stock (outer zone -- cont * d. ) No. PI Cp K . Am Bi Mt Ap Sp pLc Lx Sc Qz Ct An % 58 58.6 17.9 5.1 _ 13.9 4.0 0.5 42-52 (47) 64 64.5 19.6 7.1 - 4.7 4.1 0.1 - - t r . 28-55 (46) 65 65.5 23 .0 0.5 - 5.6 5.2 0.1 0.1 43-57 (48) 66 57.3 17.6 12.1 - 6.3 6.6 0.1 - - - 38-52 (48) 68 53.9 .17.4 16.3 - 6.7 5.3 0.4 - - - 38-60 (49) 69 51.9 24 .0 8.6 - 10.3 4.4 0.6 t r . - - 0.1 39-55 (46) 70 44.6 27. 2 14.7 - 8 .0 5.2 0.3 - - - 35-55 (43) 71 45.6 24.6 15 .4 - 9,5 4.6 0.4 - - - 42 72 45.6 ,34.7 8.3 - 5.1 5.3 1 .0 - - - 38-40 (39) 73 45.9 28.0 12.2 - 6.1 3.7 1 .0 - 3 .0 - - 33 74 .3-9.3 27.1 19.8 - 9.7 .•3.3 0.8 - - - 35 75 48.6 25.8 15 .4 - 6.1 3.6 0.1 _ . - 29-35 (33) 77 41.7 27.9 14.6 - 11.2 4.1 0.5 - - - 32 78 40.8 23.1 19.6 - 5 .0 3 .0 0.9 - - 31-38 (34) 79 38 .4 34 .4 9-9 - 12 .0 4.7 0.6 - - . - 32 80 58 .4 23.9 4.9 • - 6.5 4.6 1.8 - - - 33 81 40 .0 29.1 18.1 - 9.1 ,2.9 0.6 0.1 - - 33 83 59 .4 16.1 9.8 1.8 2.5 5 .0 0.3 0.9 - t r . 4.2 32-42 (36) 84 57.8 23.9 1.2 - 12 .0 4.5 0.6 - - - 42-57 (47) 85 73 .0 24.8 - - - - 0.8 1.3 - - 35-48 (45) Table II ( c o n t ' d . ) : Modal analyses (volume percent) of Copper Mountain i n t r u s i o n s . DIORITE - Copper Mountain Stock (outer zone -- cont 'd . ) No. PI Cp K Am Bi Mt Ap Sp pLc Lx Sc Qz Ct An % 87 46.1 23.6 19-1 6.0 3.7 0.9 0.3 0.1 33 88 52.4 18.0 17.7 - 5.2 5.4 1.2 - - 38 (49) 90 52.7 15.6 22.3 - 5.9 2.7 0.7 0.1 - 25-71 91 48 .2 19.5 24.0 0.1 2.3 4.5 1.1 - - - 0.3 - 25-63 (44) 92 40.2 24.2 20.2 - 9.5 5.3 0.6 27-75 (50) 93 60 .7 24.1 — - 9.3 5.4 0.4 0.1 - - - 43-50 (44) 94 43.6 27.4 6.5 12.9 4.6 4.6 0.3 0.2 43-50 (44) GABBR0 - Copper Mountain; Stock (outer zone) 1 44.3 36.0 - 0.4 10.9 7.3 14 56.6 19-4 - 1-7.5 - 5.6 15 44.5 25.2 0.1 18.6 2.1 8.6 16 23.5 48.4 - . 8.4 10.8 7.9 47 63.4 14.8 13.9 - 3.7 4.2 48 55.7 21.5 .8.1 - 8.5 5.9 53 36.0 45.0 - 3-4 7.5 7.3 56 41.6 38.9 - - 11.1 7.2 60 43.6 36.6 - 9.4 1.6 7.4 82 56.5 12.9 0.5 17.1 12.4 0.3 89 57.5 25.8 - - 7.8 7.9 1.0 - - - - - 66 0.3 - - - - - 0.6 56-60 (58) 0.6 - - - - - 0 .2 65 0.9 - - - - - 68 t r . - - - 33-70 (55) 0.1 o . l - - - - - - - 25-70 (50) 0.8 - - - _ _ - 66 1.1 68 1.5 - - - - - - 65 0.3 - - - - - - 25-71 (64) 0 . 8 0 . 1 - - - - - 55 Table II ( c o n t ' d . ) : Modal analyses (volume percent) of Copper Mountain i n t r u s i o n s . MONZONITE - Copper Mountain Stock (intermediate zone) No. PI r.p K Am Bi Mt A D Sp pLc Lx Sc Oz Ct An t 5 2 6 .9 27.3 2 6 . 8 1 0 . 5 4 . 1 0.7 3.6 _ 3 0 - 3 5 ( 3 3 ) 6 2 0 . 4 22.7 3 5 . 1 0.5 9.1 3.9 0.6 1.0 5.7 - - 0 1 5 3 0 - 3 6 ( 3 3 ) 7 3 9 . 5 2 0 . 7 29.1 - 6.5 3.0 1.1 - - - - 2 7 - 4 0 ( 3 4 ) 8 4 8 . 7 7.0 3 1 . 9 6.9 1.7 2 . 8 0.4 0.3 0.3 - — 2 5 - 4 2 ( 3 8 ) 9 3 1 . 6 1 5 . 8 4 6 . 5 0 . 4 2 . 2 3.0 0.1 0.3 - - - — 2 7 - 3 6 ( 3 4 ) 27 3 9 . 4 1 2 . 1 4 1 . 1 - 4.3 2.6 t r . - 0.5 - - 3 3 - 3 5 ( 3 4 ) 28 3 1 . 3 2 8 . 1 23.8 - 4 . 9 4.5 0.3 0.3 6.8 - - — 3 2 - 3 9 ( 3 3 ) 29 4 1 . 8 1 3 . 3 28.0 - 1 3 . 7 2.0 1.1 - - . — - - — 34 33 4 2 . 9 1 9 . 9 25.4 - 7.0 2.7 2.0 0.1 - - - - - 33 34 4 8 . 0 1 2 . 5 29.8 - 7.3 2 . 4 t r . 0.1 - - _ . _ - 2 5 - 3 8 ( 3 D 35 4 3 . 3 22.2 21.0 0 . 5 4 . 8 4 . 7 1.1 0.1 2.3 - - - 3 4 - 3 8 ( 3 5 ) 36 4 9 . 4 5.0 3 5 . 9 3 . 0 3 . 2 2.8 0.2 0.4 - - - - t r . 3 1 - 3 8 ( 3 4 ) 37 4 4 . 5 8.0 40 .6 - 3.3 2.2 0.6 0.6 -- — - - — 34 38 3 5 . 8 8.5 4 6 . 5 - 5.6 2.8 t r . 0.2 - — - - — 2 7 - 3 5 ( 3 2 ) 3 9 4 2 . 0 1 0 . 2 3 7 . 4 3.5 2.2 2.4 0.6 0.4 1.2 - - — 2 5 - 4 7 ( 4 0 ) 40 4 3 . 1 1 9 . 0 2 6 . 8 - 3-9 5.1 1.6 0.5 - — - - - 3 5 - 4 0 ( 3 8 ) 42 5 2 . 4 4.9 39.4 2 . 1 0.8 0.1 0.2 — — - — _ 3 5 - 4 0 ( 3 8 ) 43 4 8 . 9 9.8 34.8 3 . 4 0.6 1.8 t r . t r . 0.7 - - — 3 0 - 4 0 ( 3 8 ) 44 4 3 - 6 1 7 . 5 3 1 . 1 - 4 . 9 2.5 0.2 0.2 — — — — — 2 8 - 3 6 ( 3 4 ) 45 5 1 . 9 1 0 . 7 28.3 - 3.6 2.0 3.1 0.2 — — — — _ 3 5 - 4 2 ( 3 8 ) 46 5 4 . 5 7.3 3 4 . 3 0.3 1.1 2.2 t r . 0.2 — — 3 6 - 4 6 ( 4 0 ) Table I I ( cont 'd . ) : Modal analyses (volume percent) of Copper Mountain i n t r u s i o n s . M 0 N Z 0 N I T E - Copper Mountain Stock (intermediate zone -- cont 'd No. PI C D K Am B i Mt A D S D D L C Lx Sc Oz Ct An. % 4 9 4 1 . 4 2 5 . 0 2 2 . 0 ' • - 5 . 7 5 . 1 0 . 8 t r . - - • — 33-36 (35) 51 2 7 . 3 2 3 . 2 4 0 . 8 0 . 4 4 . 1 2 .7 0 . 8 0 . 2 - -• - - 0 . 5 33-36 (35) 55 3 6 . 3 2 6 . 1 27.5 - 5 . 8 4 . 0 0 . 3 - - - - - 2 8 - 3 9 ( 3 4 ) 61 3-3.9 2 9 . 7 23 .4 - 7 .3 5 . 4 0 . 3 - - - 36 62 2 9 . 9 3 1 . 7 27 .9 - 7 .2 2.7 0 . 6 - - - - - 32 63 3 8 . 7 ,24.2 27.7 - 3 . 4 5 . 0 0 . 9 - — — — — — 35 PEGMATITE : SYENITE and PERTHOSITE -- Copper Mountain Stock (inner zone ) 11 _ 9 6 . 1 _ . — . _ _ 2.1 0 . 9 0 . 8 _ 12 - - 9 6 . 4 - - - - 0 . 5 2 . 9 0 . 2 - -13 • - ' - 9 8 . 3 - - _ - 0 . 4 1 . 0 0 . 3 : - • -21 - - 97.6 - ' - - - - 1.1 0 . 7 0 . 5 - -22 - 9 7 . 0 - 0 . 6 - - 0 . 4 1 .8 0 . 2 - ' . -23 - 9 9 . 4 - . - • . - 0 . 4 0 . 1 0 . 1 - ' -24 - - . 9 9 . 3 • - • - - • - 0 . 1 0 . 1 0 . 5 • -25 8 . 1 - 8 7 . 1 - - 0 . 2 - - 1.1 1.5 0 . 2 - 0 26 6 . 2 8 7 . 2 - _ 0 . 6 - - 1.1 3 . 4 . .' - . - 0 95 2 . 0 - . 93.3 - - •0.3 • - 2 . 8 — 0 . 2 — 0 PYROXENITE - GABBR0 -- Copper Mountain; Stock H 3 - 9 2 . 1 - - 3 . 1 4 . 8 - - t r . - - - -114 3 8 . 9 4 9 - 8 - - 6 . 0 4 . 0 1 . 0 - - - - - 53 Table I I (cont'd..): Modal analyses (volume percent) of Copper Mountain i n t r u s i o n s . MONZONITE - Armstrong B lu f f s Complex No. PI Cp K Am Bi Mt Ap Sp pLc Lx Sc Ct An % 4 4 8 . 2 1 7 . 1 27.3 0.3 1.2 5.7 0 . 2 _ _ — — _ — 4 0 - 5 0 ( 4 7 ) 10 4 2 . 2 8.1 4 7 . 7 1.5 0.3 0.3 - - - - - 3 0 - 3 2 ( 3 D • 96 4 5 . 5 1 8 . 4 30.7 - 3.4 0.8 1.1 - - - - - 47 ( 4 4 ) 97 3 3 . 8 1 7 . 2 43.5 2.6 1.9 0.5 - - 0.1 - - - 4 0 - 5 5 99 5 1 . 9 1 6 . 1 26.5 2.4 0 . 6 0.5 - - - 2.0 - 3 2 - 4 3 ( 3 8 ) 1 0 0 4 1 . 1 1 9 . 4 30.3 - 4.8 3.5 0.7 0 . 2 - - - - - 3 1 - 6 3 ( 4 5 ) Table II ( cont 'd . ) : Modal analyses (volume percent) of Copper Mounta in i in trus ions . 52 PI Figure 8: A ternary p lot of the e s sen t ia l minerals (modal volume %) of 99 modally analyzed specimens. In Figures 7 and 8, the mineralogica l gaps between mon-zonites and pegmatites might suggest a magmatic d i s cont inu i ty but, when i t i s considered that the pegmatites c r y s t a l l i z e d from ak la -l i n e f l u i d s of a r e s i d u a l nature, the v i r t u a l absence of p lag io -clase and pyroxene in . them i s expected. I t i s apparent ( in the f i e l d ) , from the nature of the gradat ional contact between mon-zonite and pegmatite, that i f a ser ies of c losely-spaced specimens was taken across the contact , then the gap would be f i l l e d . (c) Rock Nomenclature It i s d i f f i c u l t to choose mappable uni ts for the Copper Mountain in trus ions because there i s a continuous grada^-t i o n from one type to another. A l s o , . r o c k s of s imi lar chemical composition show a wide var i e ty of textures as a r e s u l t of d i f -ferent environments of c r y s t a l l i z a t i o n . In add i t ion , the wide range of zoning i n the p lag ioc lase of. these rocks makes choosing a "pigeon-hole" somewhat a r b i t r a r y . The uni ts chosen were based, as much as poss ib l e , on:mineralogy and, i n part , on chem-i c a l composition and texture . The rocks of the Copper Mountain in trus ions a l l belong to the family of d i o r i t e s , monzonites, and syenites with a somewhat greater proport ion of potassium than i s noramlly found i n such rocks . Five map uni ts are d i s t ingui shed . 1. D i o r i t e : Both the Voigt and. Smelter Lake stocks (Figures 1, 4 ) are d i o r i t i c (Table I I ) . The former contains approximately 47 percent, p lag ioc lase (about A n ^ ) , 24 percent cl inopyroxene, and 1 9 percent per th i te with the remaining 10 percent comprising the accessory minerals , b i o t i t e , magnetite, apat i t e , and sphene. The l a t t e r stock contains approximately 56 percent p lag ioc lase (about A n ^ ) , 21 percent cl inopyroxene, and 9 percent per th i t e with the remaining 14 percent comprising the same accessory minerals . The rock of the Voigt and Smelter Lake stocks was named syenodiori te by Dolmage ( 1 9 3 4 ) , but since the anorthite content of the p lag ioc lase i s about 47 percent, the term d i o r i t e i s pre ferred . Rock of d i o r i t i c composition also occurs i n the outer zone of the Copper Mountain stock. The average modal composition of t h i s rock i s 51 percent p lag ioc lase (about A n , , ) , 54 23 percent cl inopyroxene, and 12 percent per th i te with the r e -maining 14 percent comprising the accessory minerals b i o t i t e , magnetite, apat i te and sphene and the secondary minerals 'amphir bole a n d . c h l o r i t e . 2. Pyroxenite. gabbro: Bodies of gabbro are i r r e g u -l a r l y d i s t r i b u t e d through the outer zone of Copper Mountain stock (Figure 1 ) . The average composition of gabbro i s 48 per-cent p lag ioc lase (about An^)> 30 percent clinopyroxene and 2 percent p e r t h i t e . The remaining 20 percent consists of accessory b i o t i t e , apat i t e , magnetite, sphene, and secondary amphibole. I t i s bel ieved that the rock analys is (No. 1, page 1 1 3 ) given:by Dolmage ( 1 9 3 4 ) represents t h i s rock type. Dolmage named the outer zone of the Copper Mountain stock syenogabbro but i t ap-pears that only a small part of i t has such a composition, the major part of i t being d i o r i t e . A small body composed of pyroxenite and gabbro i s ex-posed i n Friday Creek V a l l e y (Figure 1 ) . - The pyroxenite con-t a i n s about 92 percent cl inopyroxene, 5 percent magnetite and 3 percent b i o t i t e and the gabbro contains about SO percent cl inopyroxene, 39 percent p lag ioc lase ( A n ^ ) , 4 percent mag-n e t i t e , 6 percent b i o t i t e and 1 percent apat i t e . 3- Monzonite: The intermediate zone of the Copper Mountain stock i s monzonite with the composition 40 percent p lagioc lase (about A n ^ ) , 17 percent cl inopyroxene, and 32 percent p e r t h i t e . The remaining 1 1 percent i s comprised of b i o t i t e , magnetite, apat i te and sphene with the secondary minerals amphibole and "pseudoleucite".(?) , 4. Pegmatite: syenite and perthos i te : The inner 55 zone of the Copper Mountain stock i s composed of s y e n i t i c and p e r t h o s i t i c pegmatites. Syenite pegmatite contains about 89 percent perth i te with 5 percent a l b i t e and minor amounts of leucoxene or sphene, quartz , and f ine-gra ined co lor l e s s micas. Perthosi te pegmatite contains about 97 percent per th i t e with the same accessory and secondary minerals . Dolmage (1934) named the rocks of the inner zone or thoc lase -a lb i t e pegmatite, but since they have s y e n i t i c and p e r t h o s i t i c compositions, the names syenite and perthos i te pegmatite appear more s u i t a b l e . 5 . Monzonite. syeni te , minor trachyte and l a t i t e : The Armstrong B luf f s i n t r u s i o n (see Figure 4, page 2 3 ) . i s a complex of dykes, s i l l s , and i r r e g u l a r bodies of various rock types. The major rock type i s monzonite with an average com-p o s i t i o n of 44 percent p lag ioc lase (about An ) , 16 percent 4 — cl inopyroxene, and 34 percent p e r t h i t e . Accessory minerals i n -clude b i o t i t e , magnetite, apat i t e , sphene, quartz and amphibole. Many of the smaller in trus ions (dykes and s i l l s ) have the com-p o s i t i o n of syeni te . Narrow dykes of trachyte and l a t i t e cut the e a r l i e r monzonites. Texture: (a) Introduct ion Although many of the i n t r u s i v e bodies which make up the Copper Mountain rock ser ies have compositions of monzon-i t e s or d i o r i t e s , i t i s poss ib le to d i s t i n g u i s h them and to determine t h e i r age r e l a t i o n s h i p s by t h e i r wide v a r i a t i o n i n texture . (b) Texture of Voigt and Smelter Lake Stocks D i o r i t e s of the Voigt and Smelter Lake stocks are 56 medium-grained (l-3mm), equigranular, and grey-green. Some phases, which are f ine-grained (0.5-2mm), appear dark i n co lor but have about the same mineral composition as the medium-grained types. In a few places , pyroxene and p lag ioc lase c r y s t a l s are a l igned, r e s u l t i n g i n a s teep ly-d ipping f o l i a t i o n . Most of the rock, how-ever, i s homophanous and consequently the i n t e r n a l s tructure of these two stocks i s obscure. The clinopyroxene c r y s t a l s are dark green subhedral prisms and are commonly p a r t l y replaced by'green amphibole and b i o t i t e . Plagioc lase c r y s t a l s are also subhedral and are almost i n v a r i a b l y twinned, usual ly according to the a l b i t e or Car l sbad-a lb i t e laws. Plagioc lase i s zoned i n the normal way with c a l c i c cores and sodic r ims. S e r i c i t i c a l t e r a t i o n of p lag io -clase i s common with many c r y s t a l s having t h e i r more c a l c i c cores completely replaced as shown i n Plate XX. Plate XX: S e r i c i t i z a t i o n of c a l c i c cores of zoned p lag ioc lase from Voigt stock d i o r i t e . Crossed n i c o l s , 65X. A l k a l i fe ldspar i s e n t i r e l y i n t e r s t i t i a l and i s com-monly charged with f ine hematite dust which gives i t a character-i s t i c pink color i n hand specimen. Accessory minerals include euhedral apatite and sphene and anhedral magnetite. The l a s t i s commonly p o i k i l i t i c a l l y enclosed by pyroxene. Green hornblende 57 (ura l i t e ) occurs as p a r t i a l rims on pyroxene and b i o t i t e occurs both as a late magmatic or deuteric a l t e r a t i o n of pyroxene and as separate c r y s t a l s . Small amounts of c h l o r i t e , c a l c i t e and e p i -dote are also present as a l t e r a t i o n products of p lag ioc lase and pyroxene. (c) Textures of Armstrong Bluf f s Complex The Armstrong B luf f s monzonite i s f ine-gra ined to medium-grained (0.5-3mm) and i s of a l i g h t e r color than the Voigt or Smelter Lake stocks. I t has a pink or reddish color that i s due to the r e l a t i v e abundance of a l k a l i f e ldspar . This i n t r u s i v e body i s a complex made up of a great number of small i r r e g u l a r i n -t r u s i o n s , dykes and s i l l s . Plate XXI shows a specimen of monzon-i t i n which an angular fragment of d i o r i t e i s enclosed. Plate XXI: Angular fragment of d i o r i t e included i n the l a t e r monzonite of the Armstrong Bluf f s i n t r u s i v e com-plex. Arrows show the pos i t i on of the contact be-tween the two rock types. The pyroxene c r y s t a l s i n the monzonite are mostly anhe-d r a l and ragged or corroded. In p laces , the c r y s t a l s appear to have been dissolved along cleavages or part ing d i r e c t i o n s leaving small rounded fragments which are scattered throughout the i n t e r -s t i t i a l K- fe ldspar . Pale-green, anhedral, elongate blades of 58 hornblende are present as an a l t e r a t i o n product of pyroxene. B i o t i t e occurs as i r r e g u l a r or ragged c r y s t a l s with inter leaved plates of co lor l e s s epidote (Plate XXII) . I t appears that t h i s Plate XXII. Secondary b i o t i t e with inter leaved plates of e p i -dote i n monzonite of the Armstrong B luf f s complex. Plane po lar ized l i g h t , 65X. b i o t i t e i s secondary after some mineral such as pyroxene i n whic calcium i s a major const i tuent . Fresh rocks have no hornblende and only a small amount of b i o t i t e . Anhedral magnetite c r y s t a l s are present throughout the rock, but appear to be concentrated i n the v i c i n i t y of pyroxene grains as shown i n Plate XXIII . Euhedral apat i te i s also present i n most of the rocks . P lag io -clase i s euhedral and i s commonly completely s e r i c i t i z e d . Nor-mal zoning over a wide range (An^Q to An2^) i s common. A l k a l i feldspar i s e n t i r e l y i n t e r s t i t i a l to pyroxene and p lag ioc lase and i s r e l a t i v e l y unal tered . In the more a l tered rocks , c a l c i t e c h l o r i t e , and epidote are common. In one area (Figure 1) , the complex has been sheared, brecciated and hydrothermally a l t e r e d . Feldspars have been large ly replaced by s c a p o l i t e , c a l c i t e , Plate XXIII: Concentration of magnetite c r y s t a l s p o i k i l i t i c a l l y enclosed by, and adjacent t o , pyroxene c r y s t a l s from the Armstrong Bluf f s complex. Plane po lar i zed l i g h t , 65X. s e r i e i t e , and epidote probably by the in troduct ion of CC^-bearing hydrothermal so lut ions (Plates XXIV, XXV and XXVI). Plate XXIV: Monzonite brecc ia cemented with c a l c i t e and s c a p o l i t e . 60 Plate XXVI: Photomicrograph of s c a p o l i t e - c a l c i t e - d i o p s i d e "skarn" from brecc ia zone i n Armstrong Bluf f s complex. Crossed n i c o l s , 65X. 61 Many small dykes of the Armstrong Bluf f s complex have the composition of l a t i t e and a l b i t e - t r a c h y t e . They are com-monly pink i n color and of f iner gra in than the other rocks . Most are p o r p h y r i t i c with phenocrysts of p lag ioc la se , pyroxene, hornblende or b i o t i t e . (d) Textures of the Copper Mountain Stock Outer Zone: The outer zone of the Copper Mountain stock i s a f ine to medium grained (0.5-3mm.), mesotype to melanocratic rock of compositions ranging from d i o r i t e to gabbro. The gabbroic bodies occur i r r e g u l a r l y d i s t r i b u t e d with in the outer zone (Figures 1 and 6) and have gradat ional contacts with d i o r i t e . Gabbro and d i o r i t e d i f f e r p r i m a r i l y i n the amount and composi-t i o n of the minerals , pyroxene, p lag ioc lase , and perth i te (page 46). Consequently, the fo l lowing general d e s c r i p t i o n of texture may be applied to a l l of the rock types i n t h i s zone. A t y p i c a l specimen of d i o r i t e i s shown i n Plate X X V I I . . Plate XXVII: D i o r i t e from the outer zone of the Copper Mountain stock. 62 Pyroxene i s subhedral, and i n a l tered rocks , i s p a r t l y replaced by green hornblende and brown b i o t i t e (Plate XXVIII) . In some specimens, the pyroxene i s anhedral with i r r e g u l a r embay-ments which appear to be the re su l t of so lut ion by magma. Pyrox-ene has also been replaced, i n part , by c h l o r i t e . In many rocks, Plate XXVIII: B i o t i t e with epidote lamellae has replaced horn-blende and pyroxene. Plane po lar ized l i g h t , 65X. pyroxene i s both zoned and twinned. The twinning i s of the (100) type and i s commonly mult ip le (Plate XXIX). Zoned c r y s t a l s common-ly show an increase i n ZAc towards the margin, but o s c i l l a t o r y zoning i s also f a i r l y common (Plate XXX). Many of the pyroxene crys ta l s contain two sets of b lack , or iented , need le - l ike i n c l u -sions as shown i n Plates XXXI and XXXII. P lagioc lase c r y s t a l s are subhedral and commonly show a preferred o r i e n t a t i o n . In a l tered rocks, they may be com-ple te ly replaced by s e r i c i t i c mica with some epidote and c a l c i t e . C a l c i c cores have been e s p e c i a l l y susceptible to a l t e r a t i o n . Plagioclase i s i n v a r i a b l y zoned commonly with a c a l c i c core 63 Plate XXIX: Mul t ip le (100) twinning i n pyroxene i n d i o r i t e from the outer zone of the Copper Mountain stock. Crossed n i c o l s , 65X. enveloped i n an outer r im of normally-zoned p lag ioc lase . A few examples of o s c i l l a t o r y zoning were found (Plate XXXIII) . 64 Plate XXXI: Needle-like inclusions of ilmenite? i n pyroxene c r y s t a l s i n d i o r i t e from the outer zone of the Copper Mountain stock. Plane plarized l i g h t , 65X. Plate XXXII: Needle-like inclusions i n pyroxene show a zonal arrangement being concentrated i n a zone within the c r y s t a l and p a r a l l e l to i t s outer rim. Plane polarized l i g h t , 6 5 X . 65 Plate XXXIII: O s c i l l a t o r y zoning i n p lag ioc lase i n d i o r i t e from the outer zone of the Copper Mountain stock. The c a l c i c core has been completely s e r i c i t i z e d . Crossed n i c o l s , 65X. Plagioclase i s most commonly twinned according to the Car l sbad-a lb i t e or a l b i t e twin laws, but more complex types such as ac l ine and a l b i t e - A l a B are also found. A l k a l i fe ldspar i s microperthite of the exsolut ion type. The r e l a t i v e proport ion of a l k a l i f e l d -spar to p lagioc lase i s quite var iab le even within one hand spec i -men. In p laces , only a l i t t l e perth i te i s present,and here i t i s e n t i r e l y i n t e r s t i t i a l to p lagioc lase and pyroxene (Plate XXXIV). In other places perth i te i s the dominant f e ldspar , and here i t p o i k i l i t i c a l l y encloses the smaller c r y s t a l s of p lag ioc lase and pyroxene (Plate XXV). Perth i te concentrations may be i r r e g u l a r i n shape or may occur as layers which are s u b p a r a l l e l to the general f o l i a t i o n of the rocks . Microperthi te i s r e l a t i v e l y free of a l t e r a t i o n . Perthi te also occurs as veins and dykes cut t ing the outer rocks of copper Mountain stock (Plates XXXVI 66 and XXXVII). B i o t i t e i s not abundant i n t h i s zone. I t occurs as greenish brown or brown ragged plates and commonly i n assoc iat ion Plate XXXIV: I n t e r s t i t i a l microperthite i n d i o r i t e from the outer zone of the Copper Mountain stock. Crossed n i c o l s , 65X. XXXV: P o i k i l i t i c microperthite enclos ing p lag ioc lase and pyroxene i n d i o r i t e from the outer zone of the Copper Mountain stock. Crossed n i c o l s , 65X. 67 Plate XXXVII: Pink perthite vein i n d i o r i t e from the outer zone of the Copper Mountain stock. Plane polarized l i g h t , 2 4X. 68 with pyroxene as p a r t i a l r ims. I t commonly contains t h i n plates of epidote i n i t s cleavage planes. There seem to be two types of b i o t i t e i n many of the rocks . One i s primary, brown, and occurs as separate c r y s t a l s . The other type, which i s an a l t e r a -t i o n product of pyroxene, i s a greenish brown and commonly con-ta ins epidote i n the manner described. Sphene i s commonly present i n small amounts but appears to be more abundant i n h ighly a l tered rocks and may be large ly a secondary mineral . Apatite i s present i n almost a l l of the rocks as smal l , euhedral prismatic c r y s t a l s . The only amphibole present i s a green hornblende, an a l t e r a t i o n product of pyroxene. I t commonly forms p a r t i a l rims on pyroxene c r y s t a l s (Plate XXVIII) . Commonly, a l i t t l e c h l o r i t e i s associated with hornblende. Magnetite occurs as separate anhedral c r y s t a l s or Plate XXXVIII: A l t e r a t i o n rims of green hornblende ( u r a l i t e ) on pyroxene c r y s t a l s i n d i o r i t e from the outer zone of the Copper Mountain stock. Plane po lar ized l i g h t , 65X. 69 as narrow p a r t i a l rims on pyroxene (Plate XXXIX). Plate XXXIX: P a r t i a l rims of magnetite on pyroxene c r y s t a l s i n d i o r i t e from the outer zone of the Copper Mountain stock. Plane po lar ized l i g h t , 65X. S e r i c i t e , epidote, and c a l c i t e are common a l t e r a t i o n products of p lag ioc lase i n a l l the Copper Mountain rocks . The small i so la t ed body of mafic and ul tramafic rock which i s found i n Friday Creek va l l ey (Figure 1) i s composed of pyroxenite and gabbro. Pyroxenite i s a medium-grained, melano-c r a t i c , dark green rock which contains mainly augite of s i m i l a r character to that found i n other parts of the Copper Mountain intrus ions (ZAC = 45 degrees, 2V"Z = 59 degrees). This rock has the texture of a cumulate (Plate XL) with subhedral augite and i n t e r s t i t i a l magnetite, b i o t i t e , apat i te and sphene. Gabbro (Plate XLI) contains , i n addi t ion to the above minerals , i n t e r -s t i t i a l p lagioc lase ( A n ^ ) . Pyroxene has been p a r t l y replaced by a nearly opaque mass of f ine-grained c a l c i t e , epidote, and 70 Plate XL: Pyroxenite from Friday Creek. The rock i s pyroxene ( l i gh t grey) with a l i t t l e i n t e r s t i t i a l b i o t i t e (dark grey) and magnetite (b lack) . Plane po lar ized l i g h t , 24X. Plate XLI: Gabbro from Friday Creek. It contains pyroxene (medium grey) which p o i k i l i t i c a l l y encloses b i o t i t e and magnetite and also i n t e r s t i t i a l p lag ioc lase , b i o t i t e and magnetite. Plane po lar ized l i g h t , 24X. n c h l o r i t e . Plagioc lase has been s e r i c i t i z e d and considerable pink K-feldspar and a l i t t l e bornite have been introduced. Intermediate Zone: Rock of the intermediate zone i s monzonite, medium to coarse-grained (2-6mm.) and l i g h t grey-green i n c o l o r . It con-ta ins a smaller percentage of mafic minerals than rocks of the outer zone but the minerals are very s i m i l a r . Plate XLII shows a t y p i c a l specimen of monzonite and Plate XLIII shows a coarser-grained var ie ty taken from the contact between the intermediate zone and the pegmatite core. In the monzonite, pyroxene i s sub-hedral to euhedral, 4 pr i smat ic , and i s commonly oriented i n a s teeply-d ipping f o l i a t i o n or l i n e a t i o n . I t i s a l t e r e d , i n par t , to hornblende and b i o t i t e with inter leaved epidote. The p lag io -clase i s s trongly zoned but i s l ess c a l c i c than that of the outer zone. S e r i c i t i z a t i o n , e spec ia l l y of the c a l c i c cores, i s common. Microperthi te i s i n t e r s t i t i a l and i n greater abundance Plate XLII : Monzonite from the intermediate zone of the Copper Mountain stock. 72 Plate XLIII : Monzonite, from the contact adjacent to the pegmatite core . than i n the d i o r i t e of the outer zone. The exsolved sodic phase i s more not iceable than i n the d i o r i t e and the blebs are s t ruc -t u r a l l y contro l l ed (Plate XLIV) . Magnetite i s anhedral to Plate XLIV: Microperthi te (P) i n monzonite from the i n t e r -mediate zone of the Copper Mountain stock. Small blebs of exsolved albite are v i s i b l e . Crossed n i c o l s , 65X. 73 subhedral and i s found throughout the monzonite. Euhedral apa-t i t e prisms are common throughout the monzonite. One c r y s t a l contains bright reddish-orange i s o t r o p i c inc lus ions (Plate XXV). Sphene i s present as euhedral to subhedral c r y s t a l s . S e r i c i t e , epidote,and c a l c i t e occur as a l t e r a t i o n products of p lag ioc lase . Plate XLV: Red, i s o t r o p i c inc lus ions (black) and small gas bubbles (grey) i n apat i te from monzonite of the intermediate zone of the Copper Mountain stock. Plane po lar ized l i g h t , 6 5 X . Some monzonite of the intermediate zone contains equant "knots" of a f ine-gra ined mixture of c o l o r l e s s mica and an un-i d e n t i f i e d i s o t r o p i c mineral . These "pseudoleucites" may be a mixture of s e r i c i t e and analc i te s i m i l a r to that found i n a n a l c i t e - p e r t h i t e pegmatites described on page 104. Inner Zone: The syenite and perthos i te pegmatite of the inner zone i s almost maf ic - free . It i s pale buff to pale pink and i s extremely coarse-grained. Gra in - s i ze i s quite var iab le (5-50mm.) 74 and, i n some places , very coarse perthos i te i s found adjacent to f iner -gra ined perthosi te (Plate XLVI) . Microper th i t e , which i s the main constituent of these rocks , i s i n v a r i a b l y clouded with " a r g i l l i c " a l t e r a t i o n . S t r u c t u r a l l y contro l l ed exsolut ion blebs of sodic p lagioc lase are coarse enough to d i sp lay vague a lb i t e twinning (Plate X L V I l ) . Many of the large per th i t e c r y s t a l s are Plate XLVI: V a r i a t i o n i n gra in s ize of microperthite i n perthosi te from inner zone of Copper Mountain stock. twinned according to the Carlsbad law. In some specimens, per-t h i t e c r y s t a l s show r a d i a l arrangement (Plate XLVIII ) . Leucoxene pseudomorphs euhedral sphene i n the pegma-t i t e core (Plate XLIX). P lagioc lase of a l b i t i c composition occurs mainly as coarse exsolut ion blebs within potass ic host crys ta l s but also as uncommon separate i r r e g u l a r c r y s t a l s . A very small amount of i n t e r s t i t i a l quartz i s v i s i b l e i n a few 75 Plate XLVII: Exsolved a l b i t e i n microperthite from the inner zone of Copper Mountain stock. Crossed n i c o l s , 2 4 X . Plate XLVIII: Radia l arrangement of per th i te c r y s t a l s i n perthos i te from the inner zone. Crossed n i c o l s , 2 4 X . 76 Plate XLIX: Leucoxene pseudomgbfribus after sphene i n pertho-s i t e from the inner zone of the Copper Mountain stock. Plane po lar ized l i g h t , 65X. t h i n - s e c t i o n s . In some of the rocks, pale yellow c l o t s of f ine-grained mica are present which may be pseudomorphous after b i o t i t e . Some large phenocrysts of pale grey perth i te are present in a matrix of coarse, pink perth i te and a l b i t e . They are twinned and show complex o s c i l l a t o r y zoning (Plate L ) . The minerals , c a l c i t e , cha lcopyr i te , and pyr i t e are l o c a l l y present i n vugs. According to Tut t l e and Bowen (1958), there are two fami l ies of rocks r i c h in a l k a l i f e ldspar: subsolvus types which contain both potassium fe ldspar and p lag ioc lase c r y s t a l s and hypersolvus types which are character ized by the absence of p lagioc lase except as a component of p e r t h i t e . The mineralogy and texture of most of 77 Plate L: Complex o s c i l l a t o r y zoning i n perth i te phenocrysts from the inner zone of Copper Mountain stock. Crossed n i c o l s , 24X. the pegmatites suggests that they are hypersolvus types. The only p lagioc lase pt?esent i n these i s a l b i t e and i t i s appar-ently an exsolved phase of p e r t h i t e . A number of pegmatite specimens, however, contain separate c r y s t a l s of a l b i t e whose texture suggests that they are early-formed plag ioc lase and not a product of exso lut ion . These may be subsolvus rocks i n which p lag ioc lase has been made over to a l b i t e during c r y s t a l -l i z a t i o n of the magma. This p o s s i b i l i t y w i l l be discussed i n the sect ion on fe ldspars (page 1 5 5 ) . In the contact zone between the pegmatite and i n t e r -mediate monzonite, p lag ioc lase phenocrysts (zoned An^_ to A ^ ^ ) have rims of a l b i t e (Plate L I ) . The rims are present only where the p lagioc lase c r y s t a l s adjoin a l k a l i fe ldspar and not where they adjoin pyroxene or other p lagioc lase c r y s t a l s . These rims may have formed by react ion with a l k a l i - r i c h 78 c r y s t a l s from monzonite close to the pegmatitic core of the Copper Mountain stock. Crossed n i c o l s , 65X. res idua l f l u i d s . A rock type which may be re la ted to the inner pegma-t i t e s , an a n a l c i t e - p e r t h i t e pegmatite, i s found as small dykes cut t ing rocks of the outer zone. A deta i l ed d e s c r i p t i o n of t h i s rock i s given i n a l a t e r sect ion (page 104 ) . Feldspars: (a) Introduct ion A deta i l ed study, inc lud ing o p t i c a l and X-ray tech-niques, was made of the compositional and s t r u c t u r a l v a r i a -t ions i n the f e ldspars of the analyzed rocks (Table I I ) . Because of the probable hypabyssal emplacement and small s ize of the Copper Mountain i n t r u s i o n s , i t was thought that , be-cause of r e l a t i v e l y rapid coo l ing , the fe ldspars might 79 preserve, i n t h e i r s t ruc tures , some evidence of the environment;of t h e i r formation. (b) Method of Separation Only the freshest rocks were used for chemical analy-s i s and de ta i l ed study. Thin sections were prepared and materia l set aside for chemical analys is for each specimen. The remaining mater ia l was crushed, ground, and cleaned for X-ray determinations. The procedure followed was a modif icat ion of that out l ined by Gates and Glabaugh ( 1 9 5 3 ) . The rock was f i r s t crushed i n a small jaw-crusher with the jaws set j inch apart and then screened on a -80 mesh screen, to remove f ines ,and any,soft a l t e r -at ion products present. The mater ia l was then ground i n a rotary pu lver i zer with the plates set about 1 mm. apart . This mater ia l was screened to obtain a - 1 0 0 + 1 5 0 mesh f r a c t i o n for magnetic and heavy l i q u i d separat ion. Strongly magnetic mater ia l was f i r s t removed with a hand magnet to prevent f o u l i n g of the separator. The non-magnetic mater ia l was then passed through a Franz Isodynamic separator at 0.6 amperes with the trough set at 15 degrees cant and 20 degrees s lope. This operation.served to separate the l i g h t from the dark minerals . The former were again passed through the machine at 0.75 amperes and resul ted i n a product which contained only f e ldspars , apat i t e , and fe ldspar-mica composite gra ins . Bromoform and methanol so lut ions were used to ob- ' t a i n clean concentrates of p lag ioc lase and a l k a l i f e ldspars , Constant adjustment of the so lut ions with the use of ca l ibra ted standards was necessary to.esnsure reasonably clean separat ions. 80 (c) P lagioc lase Plagioc lase Composition: Compositions of p lag ioc lases were determined with a four -ax i s un iversa l stage using the methods described by Slemmons ( 1962 ) , For each analyzed specimen, the opt ic angle and composition were determined and are tabulated i n Table I I I . No. 2 V z An% Average An% 1 77 66 66 2 79,94 5 0 i , 3 2 i - 44 3 79,94 57,32 46 4 78,78^,84 4 6 ^ , 5 0 , 4 0 ^ .47 5 95 30 33 6 99 30 33 7 88,97 40 , 2 7 34 • 8 98,88 . 25 ,34^ 38 9 9 7 , 9 2 , 27,36 34 .10 95 30 31 1 1 * • 8 o £ 3 . 3 . 1 2 * 83 2 ,2 1 3 * 82 4 4 Table I I I : Optic angles and compositions of p lag ioc lases from 13 analyzed rocks . More than one value i s given for zoned p lag ioc lase s . A l l values are p lot ted i n Figure 9- (* - exsolved Ab.) The composit ion.of p lag ioc lase from Copper Mountain in trus ions ranges from A n ^ to A n 2 i n those specimens selected for ana lys i s . Plagioc lase i n the range An^ to A n ^ was not found i n any of the Copper Mountain i n t r u s i o n s . A plot of 2yz against An% i s shown i n Figure 9. From t h i s diagram i t can be seen that Copper Mountain p lag ioc lases apparently range from high temperature types (specimen 1) to low temperature exsolved a l b i t e s (specimens 11 , 12 , 1 3 ) . Most of the p lag ioc lases are close to Van der Kaaden's "low temperature" curve. Ear ly albite , (specimen 95) i s apparently of a higher temperature type 81 140 120 2Vz 100-Plutonic High Temperature Van der Kaadens {low temp.) Ab 20 40 60 80 An Figure 9 MoJ °/ The compositions of p lag ioc lase from 13 analyzed rocks p lo t ted against opt ic angles (after Slemmons, 1962). Specimen 95 (early plagioclase)was not chemically analyzed. than.the exsolved a l b i t e s . I t i s bel ieved by the author that such p lag ioc lases may have been completely transformed to a l b i t e by i n t e r a c t i o n between c r y s t a l and magma during c r y s t a l l i z a t i o n . Such transformation would be poss ible under equ i l ibr ium condi-t ions f a c i l i t a t e d by the slow coo l ing of a magma highly charged w i t h . v o l a t i l e s . The absence of p lag ioc lase i n the range An, to kn^^, at f i r s t glance, might seem to indicate the e f fect of the p e r i s -t e r i t e i n t e r v a l . I f i t i s considered, however, that the pegma-t i t e s c r y s t a l l i z e d from r e s i d u a l a lka l ine f l u i d s depleted i n calc ium, then:there i s no reason to expect p lagioc lase i n that range of composition any more than one would expect to f ind i t within i n t e r s t i t i a l . p e r t h i t e i n monzonite or d i o r i t e . 82 S t r u c t u r a l State: Many authors have made e f f o r t s to corre la te the com-p o s i t i o n and s t r u c t u r a l state of p lag ioc lases with t h e i r various l a t t i c e parameters determined by X-ray methods. Notable c o n t r i -butions have been made i n . t h i s f i e l d by Goodyear and Duff in (1954), Smith (1956), Smith and Yoder (1956), and Gay (1958). Goodyear and Duff in (1954) were among the f i r s t to use X-ray powder tech-niques for the determination of p lag ioc lase composition and thermal modi f i ca t ion . They chose 7 l i n e s which var ied with com-p o s i t i o n and drew several determinative curves based on the measurement of angular separat ions. Perhaps the most useful of these i s 29Cu(220)A2c>(l'31). The authors used a 20cm. camera with copper r a d i a t i o n and claimed an accuracy of 0.01 degrees i n 0.' Smith (1956) used Geiger-counter methods for greater accuracy and made determinative curves based on the angular separations 29(131)A 26(131), 20(132)A 20(131), and 29(111)A 2 9 ( i l l ) . Smith and Yoder (1956) made a large number of measurements of the (131) and (131) spacings using an X-ray d i f fTactometer . Smith and Gay (1958) a l so used an X-ray d i f fTactometer and constructed determinative curves based on the v a l u e s ,T =29(131)+29(220)-40 (131) and B= 29( i l l ) -29(201) . They claimed an accuracy of 0.015 degrees i n 29 for the former value and 0,01 degrees i n 29 for the l a t t e r . The general opinion concerning X-ray studies of p lag ioc lase may be summarized as fo l lows . Both the composition and s t r u c t u r a l state of p lag ioc lase affect i t s X-ray parameters and consequently, the simple measurement of these parameters cannot be used to determine these proper t i e s . I f the com-83 p o s i t i o n i s known, however, an est imation of s t r u c t u r a l state can. be made by using X-ray powder techniques. The best method of accurately measuring X-ray para-meters' i s , of course, by the use of the X-ray diffractometer but t h i s method requires a rather large amount of clean f e l d -spar . In the present work, a powder camera was used with chromium K<*( r a d i a t i o n which has X = 2 . 2 8 9 6 2 as compared to X = 1 . 5 4 0 5 0 for copper. The use of chromium r a d i a t i o n r e s u l t s i n a 50 percent greater spread of the l i n e s and consequently, better r e s o l u t i o n and greater accuracy. The accuracy obtained i s about 0.02 degrees in, 9. The Copper Mountain p lag ioc lases are a l l zoned and, as a r e s u l t , give somewhat d i f fuse l i n e s . In each specimen, however, there i s a dominant narrow range of kn% which allows determination of a representat ive average. The chromium r a d i a -t i o n method would probably give far more accurate r e s u l t s for p lag ioc lases of uniform composition and s t r u c t u r a l s ta te . The X-ray parameters for 13 se lected plagioc lases from analyzed rocks are given i n Table IV. The values of 0 given have been.corrected for f i l m shrinkage by using a cor-rec t ion factor of 1 . 0 0 1 8 . Only the r e f l e c t i o n s up to about 27 degrees 9 are given s ince , beyond t h i s po int , the r e f l e c -t ions are f a i n t and d i f f u s e . Extraneous l i n e s due to admixed a l k a l i fe ldspar e tc . have been deleted. In the fo l lowing pages, the X-ray parameters of p lag ioc lases from the Copper Mountain in trus ions are com-pared with the published curves of those authors mentioned e a r l i e r . 84 hfcl I(av PI P2 P3 P4 P5 P6 P7 0 0 1 , 1 I 0 2 1 0 . 3 2 10 . 24 1 0 . 3 1 1 0 . 2 9 1 0 . 31 : 1 0 . 2 9 1 1 1 1 - - - - - 1 1 . 2 8 1 1 1 1 - - - 1 1 . 8 1 1 1 . 82 1 1 . 8 0 0 2 1 1 14 .08 14.11 14.18 1 4 . 1 5 - -2 0 1 6 16 .43 16.48 16.48 1 6 . 5 3 1 6 . 5 2 1 6 . 48 1 6 . 5 5 1 1 1 2 17 .04 17 . 1 9 1 7 . 1 8 1 7 . 1 9 1 7 . 2 3 1 7 . 2 1 1 1 1 6 17 .73 1 7 . 7 8 1 7 . 7 4 1 7 . 8 4 1 7 . 7 4 1 7 . 76 1 7 . 7 6 130 4 - - - 1 7 . 9 2 - 1 7 . 9 4 130 , 1 3 1 6 18 .38 18.33 1 8 . 3 3 1 8 . 3 8 1 8 . 2 6 1 8 . 26 1 8 . 2 7 112 2 19 .30 19 . 2 6 1 9 . 3 1 1 9 . 3 1 1 9 . 2 7 1 9 . 26 1 9 . 2 6 221 1 - - - 1 9 . 5 7 1 9 . 55 1 9 . 4 7 112 3 1 9 .98 1 9 . 8 5 2 0 . 0 9 1 9 . 9 5 2 0 . 0 6 2 0 . 04 1 9 . 9 2 040 1 0 21 .15 2 0 . 9 5 2 0 . 9 6 2 0 . 9 1 20 . 91 2 1 . 10 2 0 . 9 8 002 10 2 1 . 1 1 2 1 . 1 5 2 1 . 1 9 2 1 . 1 6 2 1 . 1 6 220 2 21 .34 2 1 . 3 9 2 1 . 4 0 2 1 . 4 0 2 1 . 4 1 2 1 . 36 2 1 . 3 6 131 3 22 .27 2 2 . 4 2 2 2 . 4 9 2 2 . 4 5 2 2 . 5 3 2 2 . 59 2 2 . 5 5 0 4 1 6 22 .89 2 2 . 9 4 2 2 . 9 8 2 2 . 97 23 .00 2 3 . 04 23.08 131 5 23 .85 23 . 8 1 2 3 . 8 6 2 3 . 8 2 2 3 . 7 9 23 . 72 23 . 8 2 132 4 25 .60 25 . 62 2 5 . 6 1 2 5 . 6 5 2 5 . 6 5 2 5 . 6 5 2 4 1 1 .27 .04 26.94 2 7 . 0 0 2 7 . 0 2 26 .96 -Table IV: X-ray powder-camera r e f l e c t i o n s (OCr) for p lagioc lases from the Copper Mountain i n t r u s i o n s . F i l t e r e d chro-mium r a d i a t i o n was used. hkl I (av.) P8 P 9 P 1 0 P l l P 1 2 P 1 3 0 0 1 , l l o 2 1 0 . 3 4 1 0 . 3 7 1 0 . 3 3 1 0 . 3 4 1 0 . 3 6 1 0 . 3 4 1 1 1 1 1 1 . 3 5 - - 11 . 2 6 _ 1 1 1 1 1 1 . 8 0 - - - _ 0 2 1 1 -16.54 - _ _ _ 2 0 1 6 1 6 . 5 3 1 6 . 5 2 1 6 . 5 5 16.55 1 6 . 5 4 1 1 1 2 1 7 . 2 1 1 7 . 2 4 1 7 . 28 1 7 . 3 4 • 1 7 . 3 4 1 7 . 2 8 1 1 1 6 1.7.71 1 7 . 7 4 1 7 . 7 2 1 7 . 7 2 1 7 . 7 3 1 7 . 7 2 130 4 1 7 . 9 2 1 8 . 2 7 - — -1 3 0 , 1 3 1 6 1 8 . 3 1 1 8 . 2 5 1 8 . 2 2 1 8 . 2 5 1 8 . 2 1 1 1 2 2 1 9 . 2 5 .19.28 1 9 . 1 2 1 9 . 1 2 2 2 1 1 - - - — 1 1 2 3 •19.95 2 0 . 0 0 2 0 . 0 7 2 0 , 0 9 2 0 . 0 9 2 0 . 1 1 0 4 0 -0 0 2 1 0 1 0 2 0 . 96 2 1 . 1 8 2 1 . 0 4 2 1 . 0 6 2 1 . 0 9 2 1 . 1 0 . 2 1 . 1 0 2 2 0 2 2 1 . 4 0 2 1 . 3 5 2 1 . 2 8 2 1 . 3 0 2 1 . 3 1 -1 3 1 5 2 2 . 5 7 2 2 . 5 8 2 2 . 6 0 2 2 . 6 7 2 2 . 7 0 2 2 . 7 4 0 4 1 . 6 2 2 . 9 7 23 . 0 2 2 3 . 0 1 2 3 . 0 5 2 3 . 0 8 23 .07 1 3 1 5 2 3 . 7 7 2 3 . 7 3 2 3 . 7 1 2 3 . 6 4 23 .72 2 3 . 6 7 1 3 2 4 2 5 . 6 3 - - 2 5 . 7 5 2 5 . 7 6 -241 1 - - - - - -Table IV ( c o n t ' d . ) : X-ray powder camera r e f l e c t i o n s (OCr) for p lag ioc lases from the Copper Mountain i n t r u s i o n s . F i l t e r e d chromium r a d i a t i o n was used. 85 Smith ( 1 9 5 6 ) suggests that for p lag ioc lase i n the range An„ to An that the'angular separation 2 9 ( 1 3 1 ) - 2 0 ( 1 3 1 ) «U . 4-0 be used and that for the range An^ to .An , . t h e angular separa-t i o n 2 0 ( 1 3 2 ) - 2 0 ( 1 3 1 ) be used. In Figure 1 0 , the angular separat ions , 29 ( 1 3 1 ) - 2 0 (13.1) for the Copper Mountain p lag io -clases and i n Figure 1 1 , the angular separations, 2 9 ( 1 3 2 ) - 2 9 ( 1 3 1 ) are compared with Smith's curves. Figure 1 0 : An % Angular separations ( 2 9 (131 ) - 2 9 (131 ) ) p lot ted against An^ (after Smith, 1 9 5 6 ) . Goodyear and Duff in ( 1 9 5 4 ) have sought to i d e n t i f y the composition and thermal modif icat ion of p lag ioc lases by measuring the angular separation 2 9 (220 ) A 2 9 ( 1 3 1 ) . The data for the Copper Mountain p lag ioc lases i s p lot ted i n Figure 1 2 . C r C u 86 4.2H 4.0-1 On h2.8 \ \ 012 1-27, H2.6 h 3.8H CO CD CM CM 3.6-CD CN 3.4H 3.2-•2.5 2.4 \ 6-C-4 -O— 3 1 o r-2.3 -2.2 ^l&W**"" " ~ ~ I I D 20 40 60 80 A- 0 / Figure 11 : Angular separations, (29(132)-29(131)) p lot ted against An^ (after Smith, 1956). . 1 1 3 T 2 l T "5 2H CD CM < 4k M.5 •O10 o H.O CM ' £N CD cs r-0.5 -jab Temperature 20 40 60 80 K y Figure 12 : Angular separations," 29 (220) A 20(131) p lot ted against kn% (after Goodyear and Duf f in , 1954) 87 Smith and Yoder ( 1 9 5 6 ) also used the angular separa-t i o n 2 0 ( 1 3 1 ) A 2 9 ( 1 3 1 ) i n t h e i r work with p lag ioc la se . They ob-tained curves s i m i l a r to those of Smith ( 1 9 5 6 ) but over the ent i re range of p lag ioc lase composition. They obtained two d i s -t i n c t s er i e s , one for : "dry" synethetic and one for natura l p lag ioc lases . The authors state the fact that i s now general ly accepted that most natura l p lag ioc lases f a l l on neither of these l i n e s but rather have probably approached an undefined s t a b i l i t y between the two. Smith and Gay ( 1 9 5 8 ) have done perhaps the most ex-haustive search for su i table r e l a t i o n s h i p s between the X-ray parameters and composition and thermal state of p lag ioc lases . They state that , given the composition, . the s t r u c t u r a l state of a p lag ioc lase may be determined by a measurement of the angular separations ( 2 9 ( 1 3 1 ) + 2 0 ( 2 2 0 ) - 4 9 ( 1 3 1 ) ) which i s termed J~ ( c a p i t a l gamma) and ( 2 9 ( l T l ) - 2 9 ( 2 0 1 ) ) which i s termed <3 ( c a p i t a l beta) . They bel ieve that t~ i s corre la ted with, the state of d isorder and that the state of d isorder i s a funct ion of coo l ing r a t e , pressure, and percent of v o l a t i l e s . Figure 13 shows a p lot of the ca lcu lated values of V for the Copper Mountain p lag ioc lases with the Smith and Gay ( 1 9 5 8 ) curve and Figure 14 a s i m i l a r plot for the values of fj). From the foregoing p lots of angular separations of various X-ray parameters, i t appears that most of the Copper Mountain p lag ioc lases are of the low temperature type. A few of the specimens ind icate a poss ible intermediate state since they f a l l a l i t t l e above the low temperature l i n e . I f Smith and Gay ( 1 9 5 8 ) are correct i n t h e i r b e l i e f concerning 88 Figure 1 3 : Angular separations of [" =20 ( 1 3 1 )+20 ( 2 2 0 ) - 4 0 ( 1 3 1 ) plot ted against kn% (after Smith and Gay, 1 9 5 8 ) . the r e l a t i o n s h i p between order-disorder and thermal s tate , i t follows that most of the Copper Mountain p lag ioc lases are wel l ordered and a few are s l i g h t l y d isordered. 89 0 20 40 60 80 100 A n % Figure 1 4 ; Angular separations of % = 2 9 (111)-20(201 ) p lot ted against An% (after Smith and Gay, 1 9 5 8 ) . (d) A l k a l i Feldspars X-ray Study of P e r t h i t e : A l l of the K-fe ldspars found i n the Copper Mountain in trus ions are e i ther crypto- or microperthites of the exsolut ion type. Since considerable information concerning the composition, t r i c l i n c i t y , and order-disorder re la t ionsh ips of such minerals 90 may be had from the use of X-ray powder techniques, X-ray pow-der photographs were taken of both natura l and annealed p e r t h i t e s . The l a t t e r were heated i n open platinum cruc ib l e s at 1 0 5 0 degrees C for 68 hours. X-ray photographs were taken using f i l t e r e d chromium r a d i a t i o n with a large camera and a f ine c o l l i m a t o r . An accuracy of 0.02 degrees i n 9 was obtained. X-ray parameters for the Copper Mountain per th i te s are given i n Table V and Table V I . The samples numbered with a K pref ix are natura l perth i tes and those with a Kh pre f ix are annealed. Perthi te Composition: Several authors have shown that the value of the 201 r e f l e c t i o n of a l k a l i fe ldspars i s contro l l ed by the 0 r / A b r a t i o . Since the Copper Mountain a l k a l i fe ldspars are a l l p e r t h i t i e , two 201 r e f l e c t i o n s are obtained for each specimen, one for the potass ic host and the other for the exsolved a l b i t e . In add i t ion , an attempt was made to determine the bulk composition of the a l k a l i fe ldspars by annealing the specimens to homo-genzie the two phases. In. t h e i r study of the system, NJaAISi ^  O ^ - K A l S i ^ - H 0, 3 o. 3 o 2 Bowen and Tut t l e ( 1 9 5 0 ) used.the d ( 2 0 l ) spacings to determine the composition of synthet ic a l k a l i f e ldspars . The d ( 2 0 l ) spacing was shown to vary l i n e a r l y when p lot ted against weight percent. The d ( 2 0 1 ) spacings for both natura l and annealed perth i tes from Copper Mountain are shown i n Table V I I . Using the d ( 2 0 l ) curve of Bowen and Tut t l e ( 1 9 5 0 ) shown.in Figure 1 5 , the compositions of both the sodic and potass ic phases of, natura l per th i tes and the compositions 9 1 hkl I (av . ) K2 KJ K4 K5 K6 K_7 110,001,020 2 10 .23 10 . 19 10. 26 10. 28 10. 19 10.. .18 iir l 2 11 .29 11. 30 11. 21 11. 28 11. 27 111 1 11 .83 11. 88 11. 81 11. 81 11. 78 021 1 2 - - 14. 34 201K 7 15 • 79 15. 78 1 5 . 77 15- 80 1 5 . 79 15. 82 201Ab 2 16 .54 16. 53 16. 49 16. 49 16. 49 16. 50 111 3 16 .95 16. 87 16. 91 16. 88 16. 93 16. 92 111 i 2 - 1 7 . 29 1 7 . 25 120 6 17 .68 17. 70 17. 72 17- 73 1 7 . 72 1 7 . 73 130 3 18 . 24 18. 20 18. 28 18. 27 18. 26 18. 32 131 2 - 18. 83 112,221 7 19 • 30 19. 26 19. 30 19. 32 19. 33 1 9 . 30 2 20 2 19 .90 19. 92 19. 94 19. 95 - 19. 90 202 4 20 • 31 20 . 35 20 . 32 20. 39 20 . 36 20. 34 ;220,040,002 10 20 .74 20 . 71 20 . 70 20 . 75 20 . 69 20. 74 l_Ll 5 22 • 57 22. 58 22 . 52 22. 59 22. 58 22. 58 131 1 23 .05 23- 02 23. 00 23- 04 23- 05 23. 00 222,041,022 5 23 .29 23- 27 23- 25 2 3 . 29 23- 29 2 3 . 30 132 3 24 • 47 24. 39 2 4 . 41 24- 48 24- 42 24. 51 Table V: X-ray powder-camera r e f l e c t i o n s (OCr) for natura l perthi tes from the Copper Mountain i n t r u s i o n s . F i l t e r e d chromium r a d i a t i o n was used. hkl K a v . ) K8 K9 K10 K l l K12 K13 110,001,020 2 10. 26 10. 26 10 .23 10 .19 10. 29 10 .29 1 1 T l . 2 11. 26 11. 18 11 .16 11 .26 11. 22 11 . 21 111 1 11. 82 021 1 2 1 4 . 31 14 .33 201K 7 1 5 . 78 1 5 . 75 15 .75 15 .74 15- 74 15 • 72 20l~Ab 2 16. 53 16. 52 16 .50 16 .52 16. 55 16 .50 111 ? 16. 92 16. 88 16 .87 16 • 92 16. 89 16 .87 111 l 2 - 1 7 . 33 1 7 . 37 17 .36 130 6 17- 73 17. 71 17 .68 17 .69 17. 71 17 .69 130 3 18. 32 18. 19 18 .28 18 .23 18. 28 18 .24 1 3 1 2 18. 81 - 18 .81 112", 221. 7 19. 35 19. 27 19 • 35 19 .32 1 9 . 27 19 .26 220 2 - 19. 95 20 . 26 20 .01 1 9 . 96 19 .94 202 4 20 . 36 20 . 34 20 .40 20 .34 20 . 35 20 .40 220,00 2 1 3 1 10 20 . 76 20 . 70 20 .74 20 • 75 20 . 72 20 .70 5 22. 60 22. 62 22 .58 22 .60 2 2 ? 5 8 . 22 • 75 1 3 1 1 2 3 . 05 2 3 . 03 23 .08 23 .09 2 3 . 10 23 .08 22(2,041,022 5 2 3 . 35 2 3 . 29 23 • 32 23 .28 23- 27 23 .29 132 3 24. 53 24. 47 24 • 43 24 .47 2 4 . 43 24 • 54 Table V ( c o n t M . ) : X-ray powder-camera r e f l e c t i o n s (OCr) for nat-u r a l per th i te s . f rom the Copper Mountain in tru -s ions. F i l t e r e d chromium rad ia t ion was used. 92 hkl K a v . ) Kh2 Kh3 Kh4 Kh5 Kh6 Kh7 110,001,020 2 10 .19 10 .22 10 .22 10 . 24 10. 24 10 • 23 111 l 2 11 .27 11 . 22 11 • 30 11 .27 11. 37 11 • 27 111? I 2 12 .27 12. 37 12 .26 201K 5 15 .93 15 .98 15 .99 16 .10 16. 09 15 .99 201Ab i 2 16 .44 16 .44 16 • 49 16 .50 16. 45 16 .44 111 5 16 .97 17 .01 17 .04 17 .11 17. 11 17 • 07 130 8 17 .77 17 .73 17 .77 17 .84 1 7 . 83 17 .78 170 1 - 18 .27 131 i 2 18 .47 18 .40 - 18 • 53 1.11,121 6 19 .35 19 • 31 19 .35 19 .46 19. 41 19 • 35 220 i 2 20 . 06 19 • 90 - 19 .90 040 8 20 .49 20 .54 20 .57 20 .65 20 . 64 20 • 50 002 10 20 • 79 20 .80 20 .87 20 .87 20. 82 20 .85 131 5 22 .60 22 .72 22 .64 22 • 70 22 . 74 22 .66 H I i 2 - 22 .93 222,041,022 5 23 .27 23 • 32 23 • 30 23 • 35 23- 37 23 • 30 1 23 .77 23- 72 23 .67 132 3 24 • 49 24 .58 24 • 52 2 4 . 51 24 .48 Table VI: X-ray powder-camera re f l e c t i ons (OCr) for annealed per th i te s from the Copper Mountain i n t r u s i o n s . F i l t e r e d chromium r a d i a t i o n was used. hkl I (av . ) Kh8 Kh9 KhlO K h l l Khl2 Khl3 1 1 U , 0 0 1 , 0 2 0 2 10 .18 1 0 . 22 10 . 21 10 .19 10 . 21 1 0 . 22 1 1 1 l 2 11 • 31 1 1 . 32 1 1 . 23 11 .25 11 .30 1 1 . 23 1 1 1 ? T 2 201K 5 15 • 93 1 6 . 02 1 5 . 93 15 .93 16 .03 1 6 . 07 2 0 1 A b i 2 1 1 1 5 16 .99 1 7 . 03 1 5 . 94 16 .99 17 .07 1 7 . 06 130 8 17 .76 1 7 . 74 1 7 . 62 17 .71 17 .73 1 7 . 64 130 1 1 7 . 99 1 7 . 99 18 .04 18 .04 1 8 . 09 1 3 1 i 2 18 .46 1 1 2 , 2 2 1 6 19 • 35 1 9 . 33 1 9 . 30 19 .31 19 • 31 1 9 . 31 220 I 2 - 2 0 . 09 20 .10 -040 8 20 .46 20 . 60 20 . 44 20 .45 20 .60 2 0 . 65 002 10 20 .80 2 0 . 79 20 . 71 20 .76 20 . 80 20 . 80 1 3 1 5 22 .58 22 . 62 22 . 60 22 .59 22 .63 22. 61 1 3 1 I 2 22 . 84 22. 78 22 .87 22 .80 22. 82 2 2 2 , 0 4 1 , 0 2 2 ? 5 23 .28 2 3 . 29 2 3 . 29 23 . 28 23 .33 23- 30 132 3 24 • 53 2 4 . 52 2 4 . 47 24 .48 24 • 51 -Table VI ( c o n t ' d . ) : X-ray powder-camera r e f l e c t i o n s (9Cr) for annealed perth i tes from the Copper Mountain i n t r u s i o n s . F i l t e r e d chromium rad ia t ion was used. 93 Natural Annealed .Specimen d(201)K d(201)Na d(201)K d(20l )Na 2 4.207 4.021 4.171 4^045 3 4.210 4.024 4.158 4.045 4 4.212 4.033 4.156 4.033 5 4.2.05 4.033 4.128 4.031 6 4.207 4.033 4.131 4.043 7 4.199 4.031 4.156 4.045 •8 4.210 4.024 4,171 9 4.218 4.026 4.148 10 4.218 4.031 4.171 11 4.220 4.026 4.171 . 12 4.220 4.019 4.146 13 4 .225 4.031 4.136 Table V I I : The d(201) spacings of both na tura l and annealed perth i tes from the Copper Mountain i n t r u s i o n s . Wt.% Orthoclase Figure 15 s The 201 spacings curve for synthet ic a l k a l i : f e l d -spars (after Bowen and T u t t l e 1 9 5 0 . ) . Natural potass ic and sodic phases fob Copper Mountain per-t h i t e s are p l o t t e d . of the homogenized phases of annealed perth i tes were obtained, The r e s u l t s are p lot ted i n Figure 16. 1 1 1 1 1 1 1 1 1 1 2 ©--<-o 3 O — - H -c ©-<<-o 4 o ->- --o o 5 o 6 - - © c-«o 7 o > - - © c-*-o 8 o >- #-9 — 10 11 12 13 O Or 100 1 80 1 1 1 60 1 1 40 1 20 1 l 0 Ab 1 1 Figure 16: Graphic representat ion of the compositions of the phases of natura l and annealed perth i tes from the Copper Mountain i n t r u s i o n s . A comparison of the 201 r e f l e c t i o n s with the deter-minative curve i n Figure 15 shows that the potass ic phases of the natural perthi tes vary i n composition from Org^.^ to 0 r ^- Q-Some of the 201 r e f l e c t i o n s for the sodic phases give a negative amount of contained orthoclase . According to Bowen and Tut t le ( 1 9 5 8 ) , t h i s discrepancy i s due p a r t l y to the d i f ference i n 201 spacings of synthet ic and natura l f e ldspars . They found that the d i f f i c u l t y arose i n crypto-perth i tes of the orthoclase-low a l b i t e ser ies but not i n the low sanidine-high a l b i t e ser ies and suggested that an " in ter -ac t ion" between the two phases might account for the anomalous r e s u l t s . The 201 r e f l e c t i o n s i n the annealed specimens show that the potass ic phase d isso lved a l b i t e more e a s i l y than the sodic phase d isso lved orthoclase . Specimens 8 to 13 show that complete homogenization took place with the bulk compositions varying from ®r ^2 ^ ° ^ r 6 9 5' O r v i l l e ( 1 9 5 8 ) also used 201 r e f l e c t i o n s to determine the compositions of a l k a l i fe ldspars by using the ( 1 0 1 ) peak of KBrOg(20Cu=20.205 degrees) as an i n t e r n a l standard. The re su l t s obtained with the use of O r v i l l e f s determinative curve were s l i g h t l y lower (Or ) than those obtained using that of Bowen - - 3 and Tut t l e ( 1 9 5 8 ) . A l k a l i - f e l d s p a r Ser ies : Tut t l e ( 1 9 5 2 ) has d iv ided the a l k a l i fe ldspars into four d i s t i n c t ser ies based on o p t i c a l propert ies and composi-t i o n . The opt ic angles of the potass ic phases of Copper Moun-t a i n perth i tes were measured on the un iversa l stage and com-pared with t h e i r compositions determined by X-ray powder methods 96 as described i n the previous sec t ion , i n Table V I I I . These data are tabulated Specimen 0r% 2Vx Specimen 0r% 2Vx 1 _ _ 8 89.5 66 2 87.5 54 9- 94 .0 68 3 89.5 59 10 94 .0 68 4 90 .0 59 11 94.5 69 5 . 86.5 58 12 94.5 64 6 87.5 66 13 •97.0 68 7 84 .0 64 Table VIII Optic angles and compositions of potass ic phases of Copper Mountain p e r t h i t e s . In Figure 17, the compositions of the potass ic hosts are p lo t ted against t h e i r opt ic angles. From t h i s f i g u r e , i t i s apparent that the potass ic phases of the Copper Mountain per-t h i t e s change progress ive ly i n composition and opt ic angle. Com-pos i t i on .var ies from Org^ to 0 r ^ and 2Vx var ies from 54 to 69 degrees. This also suggests that the potass ic hosts progress from a type intermediate between.orthoclase and microcl ine microperthite to microc l ine microperth i te . T 2Vx Figure 17 °° Optic angles of potass ic phases of Copper Mountain perth i tes p lot ted against t h e i r compositions (after T u t t l e , 1952 ) . 97 Obl iqu i ty of A l k a l i Feldspars: The value , A =12.5 ( d l 3 1 - d l " 3 l ) i s termed o b l i q u i t y or the A -value and i s contro l l ed by several f a c t o r s . D i e t r i c h ( 1 9 6 2 ) states that these are ( 1 ) a l u m i n a / s i l i c a ordervdisorder r e l a t i o n s h i p s , ( 2 ) composition, and ( 3 ) temperature, pressure, length of time of c r y s t a l l i z a t i o n , and bulk composition of the rock. Because of the many v a r i a b l e s , he bel ieves that A -values cannot be used as absolute paragenetic c r i t e r i a but he suggests that they may be corre lated with temperature i n a general way. The A -values were f i r s t used by Goldsmith and Laves ( 1 9 5 4 a ) , They found that the most t r i c l i n i c microc l ine examined by them had a spacing di f ference of 0 . 0 8 . To make the A . -value vary from zero to u n i t y , they m u l t i p l i e d by a factor of 1 2 . 5 . According to Goldsmith and Laves ( 1 9 5 4 a ) , the low and high temperature forms of potassium feldspar are t r i c l i n i c micro-c l i n e and monoclinic sanidine re spec t ive ly . They state that the microc l ine-sanid ine s t a b i l i t y r e l a t i o n s are explained by the assumption that A l - S i . d i s t r i b u t i o n i s disordered i n s a n i -dine and ordered i n m i c r o c l i n e . They state further tha t , since the disordered mater ia l i s monoclinic and the ordered materia l t r i c l i n i c , that a measure of the " t r i c l i n i c i t y " may be used as a funct ion of the degree of order. Figure 18 shows d iagramat ica l ly the r e l a t i o n s h i p between t r i c l i n c i t y (order-disorder) and coo l ing h i s tory according to the hypothesis of Goldsmith and Laves ( 1 9 5 4 a ) . In another paper ( 1 9 5 4 b ) , these authors state that sanidine i s stable and disordered only above a c e r t a i n temperature which may be as low as 500 degrees C. I f the coo l ing of 98 Sanidine Triclinic A = 12.5 (d131-dl3l) Monoclinic (order) (disorder) Figure 18: Diagramatic representat ion .of disorder-temperature r e l a t i o n s h i p s i n potash fe ldspars(modif ied after Goldsmith and Laves, 1954a). sanidine follows path A (rapid cool ing?) (Figure 18), disordered metastable sanidine r e s u l t s and i f path B (slow cool ing?) i s fol lowed, maximum mierocl ine which i s ordered and stable r e s u l t s . I f any path between A and B i s followed (most common natural m i c r o c l i n e s ) , intermediate p a r t l y ordered microcl ines r e s u l t . These are metastable and have intermediate values of In Figure 18, a l l of the Copper Mountain perth i tes are seen to have A - v a l u e s within a rather narrow range (0.63 to 0.80). These values may indicate that the Copper Mountain K-fe ldspars had a coo l ing h i s tory along paths intermediate be-tween A and B and that they are metastable, p a r t l y ordered i n t e r -mediate microc l ines . The values for ca lcu lated A - v a l u e s for Copper Moun-t a i n perth i tes are given i n the fo l lowing t a b l e , 99 Specimen A Specimen A 2 0.74 8 0.69 3 0.68 9 0.63 4 0.69 10 0.76 5 0.69 11 0.75 6 0.73 . 12 .0 .80 • 7 0.65 13 0.71 Table IX: Values for A for Copper Mountain p e r t h i t e s . A = 12.5 ( d l 3 1 - d ! 3 1 ) . Annealing the perth i tes at 1050 degrees C reduced t h e i r A - y a l u e s by p a r t i a l or complete s a n i d i n i z a t i o n . The annealed values range from 0 to 0.42 and are p lo t ted i n Figure 18. A tabula t ion of the r e s u l t s of annealing (Table X) shows the r e l a -t i o n between the degrees of homogenization and s a n i d i n i z a t i o n which were reached. Specimen Homogenization San id in i za t ion 2 "partial complete 3 tt tt 4 tt tt 5 . tt . tt 6 . tt . tt 7 . tt p a r t i a l • 8 complete complete 9 tt p a r t i a l 10 tt . tt 11 tt tt . 12 . tt tt 13 tt tt Results of anneal ing:perthi tes at 1050 degr< for 48 hours. Although composition and o b l i q u i t y both f a l l in to narrow ranges, i t i s quite apparent that those specimens which have the highest potassium content (specimens 8-13) were easily- homogenized by annealing and only p a r t l y san id in ized . On the other hand, those specimens which have a lower Or 1 0 0 content (specimens 2-7) were only p a r t l y homogenized and were completely san id in i zed . Laves ( 1 9 5 2 ) states that cryptoper-t h i t e s with exsolved low a l b i t e are d i f f i c u l t to homogenize while those with exsolved high a l b i t e homogenize e a s i l y at r e l a t i v e l y low temperatures. He concludes that the reason for t h i s i s that the A l - S i order-disorder r e l a t i o n s h i p i n the potass ic host i s d i f f e r e n t from that of the exsolved sodic ; phase. The perth i tes from Copper Mountain which homogenize most e a s i l y , however, (specimens 1 1 , 1 2 , 1 3 ) are known to have exsolved low a l b i t e and i t i s quite probable that a l l of the specimens have low a l b i t e . Therefore, a more accurate statement might be that the most e a s i l y homogenized perth i tes have s i m i l a r states of o r d e r - d i s -order and s i m i l a r o b l i q u i t y i n both potass ic and sodic phases. Thus, cryptoperthi tes with exsolved low a lb i t e may homogenize e a s i l y provid ing that the potass ic phase has s i m i l a r s t ruc ture . (e) Coexis t ing Feldspars The study by Yoder, et a l ( 1 9 5 6 ) of the ternary sys-tem Ab-Qr-An at a water pressure of 5 0 0 0 bars shows' how the compositions of coex i s t ing p lag ioc lases and a l k a l i : f e l d s p a r s may be diagramatical ly- re la ted to the temperature and pressure of t h e i r c r y s t a l l i z a t i o n . A p lo t of experimentally determined t i e l i n e s for various temperatures of formation at 5 0 0 0 bars PH2O i s shown i n Figure 1 9 . The t i e l i n e s for coex i s t ing Copper Mountain fe ldspars are superimposed for comparison. Yoder, et a l ( 1 9 5 6 ) found that a p lot of analyzed fe ldspars agreed f a i r l y c lo se ly with the experimental t i e l i n e s except for those for fe ldspars from vo lcanic rocks which have a 1 0 1 A n Figure 1 9 s Tie l i n e s j o i n i n g coex i s t ing p lagioc lases and a l k a l i , f e ldspars . The s o l i d l i n e s connecting s o l i d c i r c l e s are experimentally determined.t ie l i n e s (Yoder, et a l , 1 9 5 6 ) and the dashed. l ines j o i n i n g open c i r c l e s represent coex i s t ing Copper Mountain f e ldspars . steeper slope wi th . re spec t . to the Ab-Or base l ine . The authors bel ieve therefore that the slope of the t i e l i n e s i s re la ted to pressure and temperature and that , i n general , t i e l i n e s of steeper slope are re la ted to lower pressures and higher tempera-tures . In p l o t t i n g the Copper Mountain fe ldspars i n Figure 1 9 , neither the potassium content of the p lagioc lases nor the calcium content of the a l k a l i fe ldspars was known and, conse-quently, average. Values for natura l fe ldspars were used. This 102 procedure would cause only l i t t l e error i n the slope of the p lot ted t i e l i n e s . From the diagram, i t i s apparent that the Copper Mountain t i e l i n e s f a l l in to a group which cuts across the 720 degree l i n e and has a s l i g h t l y steeper slope than the experimental l i n e . This fact i s compatible with a pressure of formation lower than 5 0 0 0 bars but not so low as that for surface flows whichhave considerably steeper t i e l i n e s . Specimen 95 (syenite pegmatite)(page 5 0 ) contains co-e x i s t i n g ear ly a l b i t e and perth i te and, although the composi-t i o n of the perth i te has not been determined, i t i s obvious that a t i e l i n e for these fe ldspars would l i e nearly p a r a l l e l to the base l i n e . Such a l i n e would be compatible with a lower temperature and poss ib ly a higher pressure (PH 0 ) than the upper group. The a l k a l i fe ldspars from the d i o r i t e s and gabbros were not completely homogenized and, consequently, the t i e l i n e s for these rocks could not be p l o t t e d . However, an e s t i -mation of t h e i r p o s i t i o n i s poss ible and suggests t i e l i n e s with a s i m i l a r or s l i g h t l y steeper s lope. (f) Feldspar Geothermometers Barth ( 1 9 6 2 ) has used coex i s t ing p lagioc lase and a l k a l i fe ldspar i n a rock as ind ica tors of temperature of f o r -mation. He bel ieves that a chemical equ i l ibr ium i n v o l v i n g the d i s t r i b u t i o n of the Ab molecule between plagioc lase and a l k a l i fe ldspar i s establ ished at a d e f i n i t e temperature. Conse-quently, the geologic thermometer of coex i s t ing fe ldspars measures a previous ly e x i s t i n g temperature which i s not neces-s a r i l y the maximum. In rocks with strongly zoned p lag ioc lase , 103 such as those from Copper Mountain, i t i s doubtful that a true equ i l ibr ium would have been reached. I t i s poss ib le , however, that equ i l ibr ium would have been approached between the f i n a l p lag ioc lase formed and the a l k a l i f e ldspar . The compositions of homogenized perth i tes were p lot ted against the f i n a l or rim plagioc lase for several Copper Mountain rocks i n F i g u r e ,20. Figure 2 0 ; Barth's fe ldspar geologic thermometer with Copper Mountain fe ldspars p lot ted (after Barth, .1962) . From Figure 2 0 , values of 580 to ;820 degree C were obtained. These are of course the lowest temperatures of equilibrium:between; p lag ioc lase and a l k a l i f e ldspars . Another fe ldspar geothermometer, which:has been devised by C h r i s t i e ( 1 9 6 2 ) depends upon the order-disorder state of p lag ioc lases as represented by the angular separation between d!31 and d l 3 1 . Almost a l l of the Copper Mountain p lagioc lases measured, when plot ted on C h r i s t i e ' s diagram, f e l l below his lowest, temperature l i n e at 300 degrees C. 104 Barth ( 1 9 6 2 ) found that p lag ioc lases which are disordered give much lower temperatures by C h r i s t i e ' s method than by the two-feldspar geothermometer method. The fact that much of the pegmatite core i s a hyper-solvus rock containing an exsolved sodic phase and -a parent po-t a s s i c phase suggests that the rock formed at a temperature higher than the top of the solvus . This temperature has been de termined as 660 degrees C (Tutt le and Bowen, 1 9 5 8 ) . (g) A n a l c i t e - P e r t h i t e E q u i l i b r i u m An a n a l c i t e - p e r t h i t e pegmatite occurs as a minor la te phase of the Copper Mountain in trus ions and forms i r r e g u l a r peg matite dykes up to 3 inches i n width. These cut the main stock The contacts , although i r r e g u l a r , are sharp. The pegmatite con s i s t s of 82$ p e r t h i t e , 3% b i o t i t e , and 1 5 $ ana lc i t e and i l l i t e along with minor accessory minerals , magnetite, apat i t e , and sphene (Plate L I I ) . Plate L I I : Late minor d i f f e r e n t i a t e of Copper Mountain rock ser ies consists of ana lc i te ( i so trop ic and black f lecked by s e r i c i t e ) and p e r t h i t e . I l l i t e i s an a l t e r a t i o n product of a n a l c i t e . Crossed n ico l s ,24X. 1 0 5 The per th i te c r y s t a l s are subhedral to euhedral , 5 to 10 mm. long, and show a pecu l iar i n t e r l o c k i n g arrangement. The c r y s t a l borders appear to have bra id or patch p e r t h i t i e i n t e r -growths, but the patches are o p t i c a l l y oriented and c l e a r l y part of adjoining c r y s t a l s . The per th i te i s of the exsolut ion type as indicated by the fact that the exsolved a lb i t e i s s t r u c t u r a l l y c o n t r o l l e d , i s f a i r l y uniformly d i s t r i b u t e d i n d i f f e r e n t gra ins , and shows a somewhat greater abundance toward the center of the potass ic host c r y s t a l s . I n t e r s t i t i a l to the well-developed c r y s t a l s of per th i te are i r r e g u l a r patches of i l l i t e and a n a l c i t e . Both of these minerals were i d e n t i f i e d by. X-ray powder photographs. The analc i te grains are a pale tan color and commonly contain ran-domly oriented minute opaque i n c l u s i o n s . Ana lc i t e appears to be very s l i g h t l y b i re fr ingent and i s , i n places , e n t i r e l y replaced by i l l i t e . In some c r y s t a l s , "islands" of ana lc i t e remain i n a f i e l d of i l l i t e . The i l l i t e has a preferred or ientat ion ,and has probably replaced ana lc i t e along some s t r u c t u r a l d i r e c t i o n . Occurrences of s i m i l a r rock have been recorded by others . Stewart ( 1 9 4 1 ) described an occurrence of su lphat ic cancr in i t e and analc i te from A l l t a M h u i l l i n , Scotland i n pegmatitic patches and veins i n boro lan i t e , a var i e ty of melanite-nepheline syeni te . The a n a l c i t e , b i re fr ingent and twinned, i s associated with ortho-c lase , melanite, and a l l a n i t e . Brogger ( 1 8 9 0 ) describes s i m i l a r mater ia l from Laven i n south Norway. Coombs ( 1 9 5 5 ) discovered b i re f r ingent ana lc i t e from F l i n d e r s , A u s t r a l i a i n a steam cav i ty i n basalt which gave X-ray patterns almost i d e n t i c a l to that from Copper Mountain. He suggested that the b ire fr ingent 106 analc i te i s polymorphous with a s t r i c t l y cubic type which ex i s t s at elevated gemperatures i n the presence of water vapor and that invers ion to one or more lower symmetry forms takes place on coo l ing . He further suggestsLthat the invers ion i s s luggish.and that the t r a n s i t i o n may be a reconstruct ive pro-cess such as an order-disorder r e l a t i o n s h i p of S i and A l ions rather than a d i s p l a c i v e transformation as i n l e u c i t e . The F l inders analc i te i s nearly cubic , but with some anomalous X-ray r e f l e c t i o n s and the Laven mater ia l i s t r i g o n a l or nearly so, Mackenzie (1956) found that on heating a g lass of nepheline^-syenite composition i n the presence of water vapor (600 bars) at 625-800 degrees C, c r y s t a l l i z a t i o n of K-fe ldspar and nepheline took place but at 500 degrees C, K-fe ldspar and analc i te were formed. It appears that analc i te from Copper Mountain i s a primary const i tuent of the rock and that i t formed with micro-per th i te from a l k a l i n e - r i c h r e s i d u a l so lu t ions . The analc i te has been subsequently p a r t l y replaced by f ine-gra ined micas of the i l l i t e fami ly . Since i l l i t e micas are general ly r i c h i n potassium, t h i s suggests that the o r i g i n a l ana lc i te was also potassium-bearing. That the Copper Mountain analc i te has a^= 13*75A which i s intermediate between that of common sodium analc i te ( 1 3 » 7 0 A ) and synthet ic potassium analc i te (13.79A) supports t h i s suggestion. Pyroxenes: (a) Introduct ion Pyroxene i s the major mafic mineral found i n the rocks of the Copper Mountain rock ser ies and i s present i n a l l types 1 0 7 except the syenite and perthosi te pegmatites. Textural descr ip -t ions and photographs are contained i n a previous sect ion of t h i s chapter. This section, i s concerned with the composition and c r y s t a l l i z a t i o n : t r e n d of the pyroxenes. No chemical analyses of pyroxenes are ava i lab le but reasonable determinations have been made through i n t e r p r e t a t i o n . o f o p t i c a l propert ies and of s t r u c -ture as defined by X-ray parameters. (b) X-ray Parameters of Pyroxenes X-ray powder photographs of pyroxenes from 10 of the analyzed rocks have been made using f i l t e r e d chromium r a d i a -t i o n . The spacings are l i s t e d i n Table X I . A comparison of the Copper Mountain, pyroxene spacings with that of diopside (ASTM Index Card 11-654) showed that the s tructures of the two are very s i m i l a r . Brown (I960) has constructed determinative curves for pyroxenes using the values of a sin/3 and b which are r e a d i l y obtained from an: X-ray powder f i l m . Table XII l i s t s those values of a s i n /3 and b which have been determined for the Copper Mountain pyroxenes. Figure 21 shows a p lo t of these values superimposed on BrownTs determinative curves. hkl Kav.X A l A2 A3 A4 A5 A6 M A8 A9 AlO 110 1 ? 2 10 .23 10 .27 10. 27 10. 26 200 14 .05 14 .13 1 4 . 14 020 1 14. 88 14 .88 14 .89 14 .90 14 .90 14 .90 1 4 . 93 14 • 90 1 4 . 90 1 4 . 85 021 1 20 .04 20 .12 20 .01 20 .07 2 0 . 09 20 .04 20 . 04 20. 05 220 7 20. 77 20 • 74 20 .81 20 .81 20 .85 20 .82 20 . 86 20 .76 20 . 79 20. 74 221 10 22. 48 22 • 49 22 .51 22 .52 22 .57 22 .53 22. 58 22 • 54 22. 57 22. 50 310 8 22. 86 22 .83 22 • 92 22 .84 22 .92 22 .90 22. 94 22 .85 22. 90 22. 85 3 IT 4 23. 26 23 • 32 23 • 30 23 .32 23 • 32 23 • 32 23. 37 23 • 29 2 3 . 34 2 3 . 29 1 3 T 4 2 6 . 54 26 .51 26 .52 26 • 56 26 .59 26 .60 26. 64 26 • 57 26. 59 26 . 55 002,201 3 2 7 . 05 27 .04 27 .05 26 • 92 26 .91 26. 9 1 26 .91 26. 99 2 7 . 02 112,22T 5 27 .09 27 .17 27 .17 2 7 . 19 27 .10 2 7 . 09 311 2 29. 88 29 .84 29 .90 29 .93 29 .87 29 .88 29. 89 29 .84 2 9 . 83 2 9 . 84 112 2 3 1 . 11 31 .08 31 .14 31 • 13 31 .03 31 .07 3 1 . 07 31 .08 3 1 . 06 3 1 . 06 022,22"Z 1 3 1 . 43 31 .37 31 .49 31 .39 31 .41 31 .42 3 1 . 37 31 ,37 3 1 . 37 3 1 . 37 330 3 32. 14 32 .08 32 .15 32 .13 32 .22 32 .23 32. 26 32 .18 3 2 . 18 3 2 . 07 331 4 32. 51 32 .44 32 .50 32 .47 32 • 56 32 .56 3 2 . 58 32 • 50 3 2 . 52 32. 48 4 2 1 3 32. 98 32 .87 32 .88 32 .93 32 .98 32 .95 3 2 . 97 32 .92 3 2 . 92 3 2 . 88 041 3 34- 12 34 .12 34 .16 34 .19 34 .25 34 .25 •34. 29 34 .21 34. 20 34- 15 407, 240 1 34- 58 34 .66 34 .67 34 .60 34 .64 34. 71 34 .61 34. 72 34. 66 222 1 38b 57 38 .61 38 .66 38 .63 38 .69 38 .74 3 8 . 73 38 .63 .38. 62 3 8 . 63 150 4 40. 86 40 .72 40 .79 40 .83 41 .05 40 .97 4 1 . 00 40 .87 40 • 86 40. 82 Table XI; X-ray powder-camera re f l e c t i ons (OCr) for Copper Mountain pyroxenes. The numbers, A l , A2, etc . correspond to the previous specimen numbers. 1 0 9 Specimen b a slnfi A l 8 92 9 37 A 2 8 92 9 38 A 3 8 9 1 9 32 A 4 8 90 9 3 4 A5 8 90 9 3 4 A 6 8 90 9 3 4 A7 8 89 9 3 4 A 8 8 90 9 38 A 9 8 90 9 38 A 1 0 8 93 9 36 Table XII : Values of a s i n / ^ and b for Copper Mountain pyroxenes. Figure 2 1 ; A plot of a s i n /S against b on the pyroxene com-p o s i t i o n trapezium (after Brown, I 9 6 0 ) . The diagram suggests that the compositions of the Copper Mountain pyroxenes f a l l within the range Ca^gMg^F^Q to Ca^gMg^^Fe-^^ o According to the nomenclature of Poldervaart and Hess ( 1 9 5 1 ) , pyroxenes' of these compositions would be termed d i o p s i d i c a u g i t e s „ An i n d i c a t i o n that the determina-t i v e curves are not completely accurate i s suggested by the fact that one specimen ( A 7 ) f a l l s outside the boundaries of the composition trapezium. (c ) O p t i c a l Determinations of Pyroxenes Measurements of 2Vz and ZAc were made on twinned c r y s t a l s of pyroxene using those methods described by Hess 110 (1949) for the un iversa l stage microscope. Many of the Copper Mountain pyroxenes are zoned. The most common type of zoning i s that i n which rims of p leochroic green pyroxene mantle a paler green core mater ia l . The mantle pyroxenes have greater 2Vz and Z/\c values than the core mater ia l . O s c i l l a t o r y zoning and a complex, intermixed type of zoning have also been ob-served. In the instances where zoning i s pronounced, o p t i c a l measurements were made i n d i f f e r e n t parts of the c r y s t a l s . The r e s u l t s of the o p t i c a l measurements are given i n Table X I I I . Specimen 2Vz ZAc A l 534 55§ 42 A2 42 A3 42^ A4 56 42 A5 61^-60-62^ 48-46-53 A6 6 l £ - 6 9 £ 48-62 A7 60-64 49^-54 A8 59i 47 A9 57 44 A10 57 45 Table X I I I ; Values of 2Vz and ZAc for the Copper Mountain pyroxenes. The opt ic angles range from 5 4 ^ degrees (ZAc=41 degrees) to 6 I 5 degrees (ZAc=48 degrees) with the rims having values up to 6 9 2 degrees ,(ZAc=62 degrees). These values sug-guest pyroxene compositions s l i g h t l y more c a l c i c than those in ferred from the X-ray data. The compositional range sug-gested by the o p t i c a l data i s that from s a l i t i c augites to diopsides with rims of aegerine. Such compositions are com-monly found i n pyroxenes associated with hypabyssal rocks derived from a l k a l i basalt magmas according to Deer, et a l ( 1 9 6 3 ) . I l l (d) Pyroxene Composition and C r y s t a l l i z a t i o n Trend The compositions of the Copper Mountain pyroxenes, as determined by X-ray and o p t i c a l data, f a l l within the range of s a l i t i c or d i o p s i d i c augites with reac t ion rims of aegerine. It appears that the Ca/Mg r a t i o remains approximately the same i n a l l the pyroxenes and that the Fe var ie s from 0 to.16%, but no systematic v a r i a t i o n with rock type has been es tab l i shed . In order to e s t a b l i s h the d i r e c t i o n of the c r y s t a l l i z a t i o n trend of pyroxenes, that i s towards or away from i r o n enrichment, i t would be necessary to tes t a larger number of specimens. In ad-d i t i o n , i t i s probable that chemical analyses and s ing le c r y s t a l determinations would be necessary. 1 1 2 PART B: Chemistry Introduct ion: Thirteen chemical analyses of rocks from the Copper Mountain in trus ions are considered i n the fo l lowing sec t ion . Eight of these analyses are of rocks selected by the present wri ter and the remaining f i ve were made by Dolmage ( 1 9 3 4 ) . As far as poss ib le , rocks were chosen which are free of a l t e r a -t i o n and which would give information regarding the trends of chemical v a r i a t i o n . The chemical data are used i n several ways to c l a s s i f y the rocks and to show graph ica l l y the v a r i a -t ions i n composition, degree of ox idat ion , and normative minerals . Descr ipt ion of Analyzed Rock Specimens: The locat ions from which the t h i r t e e n analyzed rocks were taken are shown i n Figure 6. Since descr ipt ions of the f ive analyzed rocks taken from Dolmage ( 1 9 3 4 ) are not a v a i l -able, rocks co l l ec ted by the present wri ter as near as poss ible to Dolmage's locat ions are supplied for comparison and con-s istency i n treatment. Chemical Analyses and Norms: The chemical analyses of t h i r t e e n rocks are shown i n Table XIV. Those marked with an as ter i sk (#) are from Dolmage and the remaining eight rocks were analyzed by H Wiik of H e l s i n k i , F i n l a n d . The ca lcu la ted norms are found i n Table XV. These were ca lcu la ted according to the C . I . P . W . methods out l ined by Johannsen ( 1 9 3 9 ) . Note that , although neither appreciable fe ldspathoids Oxide i * 2 3 4 5 6* 7 8 9* 10 l l 1 2 * 1 3 * s i o 2 43 .12 46 .55 46 .83 48 .71 5 1 . 3 8 50 .60 53 .18 5 4 . 86 54- 40 57 .11 64 .29 62 .86 61 .84 T i 0 2 0 .50 0 .71 0 .68 0 .53 0.71 0 • 35 0 .60 0 . 58 0. 30 0 .46 0 • 45 0 • 35 0 .10 A 1 2 0 3 18 .19 16 .19 18 .42 18 .77 1 4 . 5 3 16 .15 17 .08 18. 43 1 9 . 05 18 .14 19 • 44 20 .41 19 .35 F e 2 0 3 6 . 20 5 .74 5 .65 -4 .61 6.51 5 .68 4 .86 3. 47 3. 55 3 .63 0 .16 0 • 35 1 .03 FeO 6 .43 4 .95 3 .48 3 . 20 2.73 2 • 50 2 .59 2 . 66 2. 86 1 .49 0 .29 0 .14 0 .53 MnO 0 .12 0 .17 0 .16 0 .16 0.08 0 .14 0 .19 0 . 19 • 0. 11 0 .08 0 .02 0 .01 0 .03 MgO 6 .52 5 .80 4 .90 3 .95 5-57 5 .06 4 .19 2. 59 2. 56 1 .84 0 • 37 0 . 20 0 .54 CaO 14 .00 11 .45 11 • 30 10 .05 9 . 4 4 8 .72 8 .10 6. 88 6. 96 5 .01 0 .65 1 . 20 1 .06 Na 20 2 • 49 3 .87 3 .82 3 .56 3-64 3 .86 3 .91 4 . 06 3- 88 5 .10 2 • 72 4 .87 6 .07 K 20 0 .81 2 . 22 1 • 77 2 .93 3.81 4 -54 4 .18 4 . 38 •5. 34 4 .61 9 • 51 7 • 35 7 .12 P 2 0 5 1 .00 0 .28 0 .38. 0 .01 0.49 0 .58 0 .50 0,. 41 0. 36 0 .02 0 .00 0 • 35 0 .17 H 20 0 .65 1 .50 1 .67 1 .02 1.34 1 .36 0 .95 1. 48 0. 66 1 .10 1 .41 0 .59 0 .76 H 20 0 .10 0 .10 0 .07 0 .18 0.00 0 .14 0 .05 0. 05 0. 04 0 • 35 0 .28 0 .04 0 .24 C 0 2 0 .05 0 .00 0 .25 0 .39 0.00 0 .10 0 .00 0 . 31 0. 00 0 .73 0 .00 1 .16 0 .92 s • 0 .05 0 .00 0 .00 0 .00 0.00 0 .02 0 .00 0 . 00 0. 02 0 .00 0 .00 0 .05 0 .00 Total 100 • 35 99 • 53 99 .38 98 .07 100. 23 99. . 80 100 .38 100 • 35 9 8 . 09 99 .67 99 .59 99 .93 99 .76 Table XIV; Chemical analyses of Copper Mountain rocks analyzed by H. Wiik of Hel s i n k i , Finland (analyses marked * are taken from Dolmage, 1 9 3 4 ) . Normative M i n e r a l s 1 * 2 3 4 5 6* 7 8 9* 10 11 1 2 * 1 3 * O r t h o c l a s e 5. .01 13. .36 10, • 57 17. .25 22, .26 26, .71 24. .49 26, .16 31. • 72 27. • 27 56 .21 43. .41 42, .29 A l b i t e 10 • 49 11, .53 19. .40 19. .66 22, .28 17. .83 28, • 3 1 34. .07 25. .43 42, .99 23 .07 41. .42 44. .30 Nepheline 5. .68 11, • 36 7. .10 5. .82 4. .69 7. • 95 2. .56 4. . 12 3. • 83 Quartz 9. .85 4. .32 A n o r t h i t e 35. .88 20, • 30 27. .81 26, .42 12, .23 13. • 35 16, .97 19. .19 18, .64 13. .07 3. • 34 3. .89 4. .45 D i o p s i d e 21, .02 27. • 45 18. • 75 16, .68 24. .68 19. .91 15. .18 9. .71 10, .49 5. • 41 Hypersthene 1, .71 1, .30 0. .50 O l i v i n e 8, • 91 3. • 45 3. .01 2, • 35 1. .69 2. • 32 2. ,48 2. • 34 2, • 44 0 . ,28 0. 9 1 A p a t i t e 2 , • 35 0. .67 1. ,01 1. ,01 1. • 34 1. • 34 1. ,01 0. .67 0 . 34 I l m e n i t e 0. .91 1. • 37 1. • 37 1, ,06 1. .37 0. ,61 1. ,21 1. ,06 0. ,61 0. ,91 0. • 30 0. 15 R u t i l e 0(. ,48 0. ,16 Magnetite 9-• 03 8. • 33 8. ,10 6. ,71 6. .94 7-.64 6. ^ 94 5-,09 5. ,09 3. ,70 0 . ,23 1. 39 Hematite 1. • 76 0. ,48 1. ,12 0 . 32 Corundum 3. .47 2. .96 C a l c i t e 0 . ,40 0 . ,60 0. 90 0 . .20 1. ,70 Table XV: Norms of Copper Mountain roc k s . 1 1 5 nor o l i v i n e were found i n the analyzed specimens (Table I I ) , both nepheline and o l i v i n e appear i n the norms p a r t i c u l a r l y i n the most basic rocks . The question ar ises as to how rocks with modes such as these could have unders i l i ca t ed norms. There are at l east three factors which might c o n t r i -bute to such an apparent c o n t r a d i c t i o n . The f i r s t of these i s poss ible error i n chemical analyses. Deer, et a l ( 1 9 6 3 ) has stated that i n the c l a s s i c a l method of s i l i c a t e analys is used for most fe ldspar analyses there i s an inherent tendency to y i e l d low values for SiO^ with compensating high values for A ^ O ^ . In the copper Mountain rock analyses, however, there i s no evidence to suggest that such errors are s i g n i f i c a n t . A second factor which could contribute to u n d e r s i l i -cated norms i s the discrepancy between the actual and theore-t i c a l s i l i c a content of rock minerals . Deer et a l ( I 9 6 3 ) has stated that a l k a l i fe ldspars may show e i ther excesses or de-f i c i e n c i e s of SiC>2 as compared to t h e o r e t i c a l values and that p lag ioc lases commonly show small d e f i c i e n c i e s of, S iC^ . Apparent.SiC^ de f i c i enc i e s i n rock minerals are a r e s u l t of i o n i c or molecular s u b s t i t u t i o n . Greig and Barth ( 1 9 3 8 ) have suggested that the carnegie i te molecule (Na2Al2Si20g) may sub-s t i t u t e , i n small amounts,for the a l b i t e molecule i n synthet ic preparat ions . Deer, et a l ( 1 9 6 3 ) bel ieve that FE , A l " and T i + + + may hold t e trahedra l pos i t ions i n pyroxenes. It seems reasonable to assume that some of the apparent s i l i c a def ic iency i n the Copper Mountain ser ies may be a r e s u l t of t h i s discrepancy between actual and t h e o r e t i c a l values of SiC^ content. 116 A t h i r d factor (probably the most important) which could r e s u l t i n f e ldspatho ida l norms i s the fact that minerals such as b i o t i t e or s e r i c i t e are not considered i n the norms. Both of these minerals , p a r t i c u l a r l y b i o t i t e , use less s i l i c a i n t h e i r c o n s t i t u t i o n than fe ldspars or pyroxenes. In order to tes t the second and t h i r d factors an at-tempt was made to determine whether or not the modal composition of the average of specimens 2 and 3 could have feldspathoids i n i t s norm. To do t h i s , i t was necessary to assign compositions to the modal minerals . Instead of using the t h e o r e t i c a l values which are used i n normative c a l c u l a t i o n s , chemical analyses of natura l minerals s i m i l a r to those from the Copper Mountain ser ies were used. In Table XVI,the analyses and t h e i r sources are given. Approximately 18 percent of the amount of p lagioc lase i s ca lculated as s e r i c i t e because at least t h i s amount of s e r i -c i t e i s present i n the analyzed rocks . There i s no obvious c o r r e l a t i o n between the amount of s e r i c i t e and normative f e l d s -pathoids i n i n d i v i d u a l specimens, but t h i s might be expected since s e r i t i c i z a t i o n of p lag ioc lase i s quite e r r a t i c ranging from 0 to 50 percent i n a s ingle t h i n sec t ion . The ca lcu la ted chemical composition for the.average mode of specimens 2 and 3 i s compared with the average of t h e i r actual chemical compositions obtained by analys is i n Table XVII. A comparison of the r e s u l t s shows that the ca lcu lated analys is i s s i m i l a r to the actual ana lys i s . I t i s poss ible to obtain a ca lcu la ted analys is almost exactly l i k e the actual one by adjust ing the modal content of magnetite, pyroxene, and plagioc lase only a few percent (probably much;less than the actual v a r i a t i o n i n the rocks ) . 1 1 7 Mode 2 3 . 1 4 8 . 0 10 .0 8.4 5-1 5-0 0.3 0.1 Oxide Pyr. Plag. Ser. Perth. Mag. Bio. Ap. Sphene S i 0 2 49 • 58 54 • 44 49 .16 64.66 0 .03 38. 22 - 30 .03 A1203 4 .60 28 .97 30 .81 20 .10 0 • 19 1 4 . 71 - l .65 T i 0 2 1 • 44 - 2. 96 - 40 .16 Fe203 1 • 92 0 • 51 - ) 0.35 68 • 95 3. 83 -FeO 6 • 55 1 • 4 3 ) 30 .82 1 3 . 44 -MnO 0 .18 t r 0 . 52 0. 07 MgO 14 . 21 0 .13 2 . 22 0.12 1 3 . 45 0. 10 CaO 20 .66 10 • 47 0.60 0 .02 1. 46 5 5 . 84 28 .46 Na 20 0 • 57 5 • 57 0 .48 4. 21 0 . 50 -K 20 0 .09 0 • 35 10 • 90 10.19 7. 90 -H 20 + 4 • 7 3 ) 0.11 j 0 .04 1. 89 1. 86 H 20" 0 .10 0 .15) 0 . 60 -P 2 O 5 — 4 2 . 05 Zr0 2 - - 0 .02 T o t a l 99 .90 100 •44 100 •07 100.34 100 •05 9 9 . 56 100 . 23 100 •32 Table XVI: Chemical analyses of n a t u r a l minerals used i n the c a l c u l a t i o n of the chemical content of a theoretical rock with a modal composition of the average of specimens 2 and 3-Pyroxene - specimen 23 , p .364,Yoder and T i l l e y (1962). P l a g i o c l a s e - a n a l y s i s 1, p.116, Deer et a l ( 1 9 6 3 ) . P e r t h i t e - a n a l y s i s 4, p.38, Deer et a l ( 1 9 6 3 ) . S e r i e i t e - a n a l y s i s 9, p.17, Deer et a l ( 1 9 6 3 ) . Magnetite - a n a l y s i s 1 1 , p.72, Deer et a l ( 1 9 6 3 ) . A p a t i t e - a n a l y s i s 2, p.325, Deer et a l ( 1 9 6 3 ) Sphene - a n a l y s i s 2, p.72, Deer et a l ( 1 9 6 3 ) B i o t i t e - a n a l y s i s 1, p.58, Deer et a l ( 1 9 6 3 ) . Oxide C a l c u l a t e d Average Composition Composition Specimens 2 and 3 S i 0 2 4 9 - 7 4 6 . 7 A1203 20.5 1 7 - 3 T i 0 2 0.5 0.7 F e 2 0 3 4-3 5.7 FeO 3.8 4.2 MgO 3-6 5-3 CaO 10 . 2 11.4 Na 20 3-2 3.8 K 20 H 20 + 2.6 2.0 0.6 1.5 T o t a l 99 .0 9 8 . 6 Table XVII: C a l c u l a t e d chemical composition f o r the average mode of specimens 2 and 3 compared with the average of t h e i r a c t u a l chemical analyses. 118 The norm of the ca lcu lated chemical composition con-ta ins both o l i v i n e ( 3 . 6 6 $ ) and nepheline ( 4 . 8 2 % ) . These r e -su l t s show that i t i s poss ible for a rock, which i s s l i g h t l y undersaturated chemical ly , to have c r y s t a l l i z e d with neither fe ldspathoid nor o l i v i n e . C l a s s i f i c a t i o n of the Copper Mountain Rock Ser ie s : There are several d i f f e r e n t methods of chemically c l a s s i f y i n g rocks or rock ser ies to be found i n the l i t e r a t u r e . Rittman (I960) has devised a system of rock c l a s s i f i -cat ion based on the proport ion of a l k a l i e s and the ser ies index (s) which i s ca lcu lated from s=(tfa20-K20) / S i 0 2 - 4 3 . The c a l c u -lated ser ies ind ices for the Copper Mountain rock ser ies are given i n Table XVIII . No. s No. s No. s 1 1 3 1 6 9 . 2 9 11 7.05 2 1 0 . 4 8 7 6.43 12 7.52 3 8.17 8 6.01 13 9.23 4 7.38 • 9 7.46 5 6 .62 10 6.70 Table XVIII: Series indices for the Copper Mountain rock s e r i e s . In Figure 22, the t o t a l a l k a l i weight percent i s p lot ted against weight percent s i l i c a on a diagram with superimposed curves corresponding to Rittman's s e r i a l i n d i c e s . A curve i s obtained with a value of approximately 7.7 which i s the average of the ca lcu la ted values after excluding the anomalously large value for Specimen 1. In. h is c l a s s i f i c a t i o n of rock s e r i e s , Rittman div ides rocks in to three broad groups; P a c i f i c or C a l c i c , A t l a n t i c or 119 SiO? Figure 2 2 : The ser ies index curve for the Copper Mountain rock ser ies (after Rittman, i 9 6 0 ) . Sodic, and Mediterranean or Potassic as shown i n Table XIX. The p lac ing of a rock ser ies i n h i s c l a s s i f i c a t i o n depends upon the s e r i a l index value and the proport ion of a l k a l i e s . The s e r i a l index for the Copper Mountain rock ser ies i s 7 . 7 , but the pro-port ion of a l k a l i e s i s not constant. In the basic end of the s e r i e s , N a 2 0 > K 2 0 and i n the acid end, N a 2 O ^ K 2 0 . Proport ion S e r i a l of A l k a l i e s & Character 1 extreme l , N a 2 0 ^ K 2 0 2 strong P a c i f i c 3 medium or 4=5 weak C a l c i c 4 t r a n s i t i o n a l 2 , N a 2 0 >K20 8 medium A t l a n t i c 17 strong or - 6 - 0 extreme Sodic 4 weak 3 .Na 2 0«C K 2 0 8 medium Mediter-14- strong ranean or neg. extreme Potassic Table XIX; C l a s s i f i c a t i o n of rock s er i e s , Rittman, i 9 6 0 . 1 2 0 This change might suggest that the Copper Mountain rock ser ies i t r a n s i t i o n a l between medium A t l a n t i c or Sodic and medium Mediter ranean or Potass ic . In any case, the Copper Mountain rocks are c l e a r l y not c a l c i c by Rittman's c r i t e r i a . Peacock ( 1 9 3 1 ) developed a f o u r - f o l d c l a s s i f i c a t i o n for igneous rock ser ies which i s based on the a l k a l i - l i m e index, i . e the percentage of s i l i c a taken at the i n t e r s e c t i o n of v a r i a t i o n curves for t o t a l a l k a l i e s and l ime. The c l a s s i f i c a t i o n d iv ides rock ser ies in to a l k a l i c , a l k a l i - c a l c i c , c a l c - a l k a l i c , and c a l c i c . The appropriate values for the Copper Mountain rock ser ies are p lot ted i n F igure . 23 and an a l k a l i - l i m e index of 5 2 . 3 i s obtained. This value places the rock ser ies i n the a l k a l i - c a l c i c group very near the border with.the a l k a l i c group. In comparison with those rocks given as examples by Peacock, the index of the T e r t i a r y vo lcanic rocks of Mozambique (Holmes, 1 9 1 7 ) has the c losest value ( 5 2 . 0 ) to that of the Copper Moun-t a i n rock s e r i e s . Peacock states that t y p i c a l rocks of the a l k a l i - c a l c i c group consist of soda-pyroxene, soda amphibole, a l k a l i - f e l d s p a r , and l i t t l e quartz or fe ldspatho id . In add i t ion , o l i v i n e , A l -pyroxene, b i o t i t e , i r o n and t i tanium ore, and plagioc lase may be present. Except for the soda-r ich pyroxene and amphibole, of which the Copper Mountain rocks contain only a l i t t l e , the mineralogy suggested by Peacock for the a l k a l i - c a l c i c group i s quite s i m i l a r to that of the Copper Mountain group. Another method of c l a s s i f i c a t i o n , based on the use of a d i f f e r e n t i a t i o n index, has been used by Thornton and 1 2 1 i I 1 1 1 1 1 1 1 r \ \ \ \ \ +/ + \ •10 o + o CN o z 8-5 \ + / o \ , V© h 5 / + N a 2 0 + K 2 ° O CaO \ \ \ \ 52.3 \ \ O d \ \ \ P \ Alkalic Alkali-Calcic Calc-Alkalic Calcic % S i 0 2 Figure 23 ° A l k a l i - l i m e index for the Copper Mountain rock ser ies (after Peacock, 1 9 3 1 ) . 1 2 2 T u t t l e (I960). The d i f f e r e n t i a t i o n index gives a measure of the "bas ic i ty" of a rock but not whether the rock i s a lka l ine or a c i d . In other words, i t i s a measure of how far the magma has pro-gressed toward "petrogeny's res idua system". The d i f f e r e n t i a t i o n index i s obtained by summing the weight percentages of normative quartz , orthoclase , a l b i t e , nepheline, l e u c i t e , and k a l s i l i t e , whichever three appear i n the norm. The values obtained i n t h i s way may be used as abscissae to show the chemical v a r i a t i o n of oxides i n a d i f f e r e n t i a t e d ser ies of rocks . In Figure 2 4 , for example, the weight per-centages of s i l i c a are p lot ted against the d i f f e r e n t i a t i o n i n -dices for Washington's 5 0 0 0 rock analyses. Superimposed on t h i s diagram i s the l i n e represent ing the d i f f e r e n t i a t i o n indices for Figure 2 4 : Contoured diagram for the 5 0 0 0 analyses i n Washington's Tables (after Thornton and T u t t l e , I960). 123 the Copper Mountain rock s e r i e s . The contours i n t h i s diagram out l ine the major trends of d i f f e r e n t i a t i o n but the dominant trend shown i s l arge ly a funct ion of the large number of gran-i t e s , r h y o l i t e s , basa l t s , e tc . p l o t t e d . Other important trends , such as that of under-saturated rocks , may be completely ob-scured by averaging , a l l rocks . Thornton and T u t t l e have broadly c l a s s i f i e d rock ser ies in to saturated, under-saturated, and over-saturated groups by drawing s tra ight l i n e s from the s i l i c a content of a l -b i t e and orthoclase at D . I . = 1 0 0 to the s i l i c a content of anor-t h i t e at D . I.=0. There may be some question as to the v a l i d i t y of . these l i n e s being used to demark areas of sa turat ion . The fe ldspars occur over the ent ire range of D . I . and vary con-s iderably i n s i l i c a content. Perhaps, s ince the Copper Mountain rock ser ies contains nei ther appreciable quartz nor fe ldspath-o ids , the D . I . l i n e for these rocks might be more usefu l than those l i n e s drawn by Thornton and T u t t l e i n demarking areas of over- or under-saturat ion . The concept of s i l i c a - s a t u r a t i o n as determined by the presence or absence of quartz or f e l d s -pathoids i s not a r igorous one. I f neither quartz nor f e l d s -pathoid i s present, a rock may be "saturated" or may be under-saturated. An under-saturated rock need not contain f e l d s -pathoids because various chemical subst i tut ions such as that of A l for S i may hide a def ic iency i n s i l i c a . V a r i a t i o n i n the Copper Mountain Rocks: Chayes ( 1 9 6 4 ) has stated that Harker diagrams are of l i t t l e use i n . d i s c r i m i n a t i n g between the e f fects of the various processes thought to be important i n the d i f f e r e n t i a t i o n of 1 2 4 volcanic rocks . He reasons that : "Any process which w i l l great ly expand the variance of s i l i c a r e l a t i v e to the other oxides w i l l also lead to strong negative c o r r e l a t i o n between s i l i c a and those of the other oxides which are major con-t r i b u t o r s to the t o t a l variance of the array ." Even though t h i s may,be t rue , i t appears that v a r i a t i o n d i a -grams may s t i l l be u s e f u l . Their use provides a graphic method of i l l u s t r a t i n g trends of d i f f e r e n t i a t i o n whatever process may be involved and allows convenient comparison with other pub-l i shed d i f f e r e n t i a t i o n trends . In add i t ion , v a r i a t i o n diagrams may be useful i n recogniz ing rock ser ies or rock f a m i l i e s . In Figure 2 5 , the weight percentages of the metal oxides are p lo t ted d i r e c t l y against weight percentage of s i l i c a i n order to show the v a r i a t i o n with in the rock ser ies of each component. The weight percentages used are those reported by the .analys t and have not been reca lcu la ted to equal 100 per-cent . A n a l y t i c a l error i s not introduced i n a uniform manner but rather on each component separately and i t i s bel ieved therefore that r e c a l c u l a t i o n might introduce even further error i n a majority of the reported values . The mafic oxides, CaO, MgO, FeO, and F e 20g a l l de-crease f a i r l y r e g u l a r l y with an increase i n s i l i c a . Alumina, although e r r a t i c , shows a s l i g h t increase with an increase i n s i l i c a . Perhaps the most i n t e r e s t i n g trend i s that shown by the a l k a l i e s . The sum of the a l k a l i e s (Figure 2 3 ) gives an approximately s t ra ight l i n e increas ing i n value with an i n -crease i n s i l i c a . Plot ted separately (Figure 2 5 ) , the potash curve begins at an ordinate point a l i t t l e lower thari that of the soda curve and crosses the l a t t e r at about 50% S i 0 9 . 1 2 5 20 15 10 40 23 4 6 5 7 98 10 II I 13 12 11 50 55 Wt. % S i Q 2 • I"" • • - A l 20 3 • - C a O O - Fe 20 3 -+ - FeO X - MgO A - K20 A _ Na 20 Figure 25 S i l i c a v a r i a t i o n diagram for the Copper Mountain rock s e r i e s . At about 62% Si02, the two curves diverge rather abruptly with potash increas ing r a p i d l y and with ,a corresponding decrease i n soda. Larsen ( 1 9 3 8 ) has devised a type of v a r i a t i o n diagram i n which the abscissa points are determined, on the basis of the major oxides, S i 0 2 , CaO, MgO, t o t a l i r o n , and K£0. Alumina and soda are disregarded, the former because of i t s general ly e r r a t i c nature, and the l a t t e r because of i t s common uniformity, 126 The advantage of t h i s type of p lot as compared to ah abscissa of the weight percent of a s ingle oxide such as s i l i c a , i s that the e f fect of any a n a l y t i c a l error for a s ing le oxide i s consider-ably diminished. The abscissae points are determined by l /3Si0 2 +K 2 0-MgO-CaO- FeO. The c a l c u l a t i o n i s made by adding MnO to FeO and BaO plus SrO to CaO. The major oxides S i 0 2 , A 1 2 0 3 , FeO plus 0 .9Fe 2 0 3 ,MgO, CaO, K 2 0 , and Na 20 are adjusted to a sum of 100. These adjusted values are used to determine the abscissa points or Larsen p o s i t i o n s . The ca lcu la ted Larsen p o s i -t ions for the Copper Mountain rock ser ies are shown i n Table XX. No. f o s . N o . Po s . No. P o s . i - 1 8 . 0 6 -0.4 11 30.1 2 - 1 0 . 2 7 2.4 12 2 7 . 2 ' 3 -7 . 8 8 7.3 13 2 5 . 3 4 - 2 . 6 9 7 . 8 5 - 2 . 9 10 1 2 . 4 Table XX: Calculated Larsen pos i t ions for the Copper Mountain rock s e r i e s . Figure 26 shows a v a r i a t i o n diagram with femics (MgO, FeO, CaO) p lot ted as ordinates against Larsen pos i t ions as abscissae. The r e s u l t i s a s t r a i g h t l i n e which r e -sembles very c lo se ly that given by Larsen (1938) for the San Juan Mountains, Colorado and the southern C a l i f o r n i a b a t h o l i t h rock s e r i e s . These are c l a s s i f i e d as "ldnte-alkalic" rocks by Larsen. In Figure 2 7 , the major oxides are p lot ted against the Larsen pos i t ions for the Copper Mountin rock s e r i e s . The oxides, with the exception of the a l k a l i e s and alumina, p lot i n such a manner that they may be best represented by s tra ight l i n e s . The femic oxides, CaO, FeO, and MgO, a l l decrease i n a 1 2 7 -20 -10 0 10 20 1/3 S i0 2 +K20+MgQ-CaO-FeO Figure 26 ; Larsen v a r i a t i o n diagram for the Copper Mountain rock , ser ies (after Larsen, 1938). regular manner with an. increase i n p o s i t i o n number while s i l i c a increases i n a regular manner. Alumina i s somewhat i r r e g u l a r but a s l i g h t increase , with increas ing p o s i t i o n number, i s ind ica ted . The p lot Of the a l k a l i e s shows a rather abrupt increase i n K2O with a corresponding decrease i n Na20 at a Larsen p o s i t i o n of about 2 5 . In general , the slopes ,and pos i t ions of the curves suggests a s i m i l a r i t y to the l i m e - a l k a l i c rocks described, by Larsen ( 1 9 3 8 ) . Another type of v a r i a t i o n diagram developed by Larsen, a t r i angu lar , p l o t , shows the r e l a t i v e proportions of ft^O, K 20, and CaO, the over-saturat ion or under-saturat ion of the rock, and the proportion, of femic minerals i n the rock. Two points are ca lcu la ted from each .rock ana lys i s . The f i r s t point 128 -30 -10 0 10 20 1/3 S iQ 2 + K 2 0 - M g O - C a O - ^ F e O 30 Figure ,27 Major oxides p lot ted against Larsen pos i t i on ( l /3Si0 2 +K 2 0-MgO-CaO- FeO). 1 2 9 represents the normative fe ldspars and feldspathoids reca lculated to 1 0 0 $ . The normative nepheline i s m u l t i p l i e d by 1 . 8 4 5 and added to a l b i t e before r e c a l c u l a t i n g to 1 0 0 $ . The second point i s obtained by adding the normative femic minerals (after ca l cu -l a t i n g o l i v i n e to pyroxene). This sum, and the quartz and f e l d -spar sum are adjusted to 1 0 0 $ . I f there i s a s i l i c a de f i c i ency , the femic and fe ldspar t o t a l s are ca lcu la ted to 1 0 0 $ and the s i l i c a def ic iency i s the amount of Si02 required to convert nepheline to a l b i t e and o l i v i n e to pyroxene. The ca lcu lated values for the Copper Mountain rock ser ies are shown i n Table XXI and the r e s u l t s p lot ted i n Figure 2 8 . No. Or Ab An F e l d . Femic Qtz . 1 8.1 3 3 . 9 5 8 . 0 5 7 . 6 4 2 . 4 -S.3 2 20.2 4 9 . 1 3 0 . 7 60.8 39.2 - 1 1 . 0 3 1-5.0 45.8 39.2 67.8 32,2 - 7.3 4 23.4 4 1 . 0 35.6 7 2 . 7 2 7 : 3 - 5 . 9 5 3 4 . 1 4 7 . 2 18 .7 63-2 .36 . 8 -4 . 8 6 36.8 44.8 I 8 . 4 68.6 3 1 . 4 - 7 . 7 7 3 2 . 9 44.3 2 2 . 8 7 4 . 5 .28.1 -3.3 8 3 3 . 0 4 2 . 8 24.2 7 9 . 8 20.2 - 1 . 3 9 3 8 . 1 3 9 . 6 2 2 . 3 8 0 . 2 1 9 . 8 -4 . 5 10 3 2 . 7 5 1 . 6 1 5 . 7 86.3 1 3 . 7 - 0 . 1 1 1 68.0 28.0 4.0 •87.4 2.1 1 0 . 5 12 4 9 . 0 46.7 4.3 9 3 . 4 2.1 4.5 13 43.1 52.3 4.6 • .96.8 3.2 -3 . 6 Table XXI: The ca lcu la ted values for a Larsen t r i a n g u l a r plot for the Copper Mountain rock s e r i e s . In the t r i a n g u l a r diagram i n Figure 28, there i s a progressive decrease i n normative anorthite and femic miner-als with an increase i n normative orthoclase and a l b i t e . The rate of increase i n normative orthoclase becomes greater to -wards the bottom of the diagram and, correspondingly, norma-t i v e a l b i t e decreases. The t r a n s i t i o n from under-saturat ion to over-saturat ion i s also shown. The plot shown i n Figure 1 3 0 Qtz. Ab Feld. Figure 28: Larsen t r i a n g u l a r diagram for the Copper Mountain rock ser ies (after Larsen, 1938). S o l i d c i r c l e s represent the normative fe ldspars (An, Ab, Or) and open c i r c l e s t o t a l f e ldspar , quartz and, femics as defined i n the t ex t . 28 i s not c lo se ly s i m i l a r to any of those published by Larsen ( 1 9 3 8 ) . Yoder and T i l l e y ( 1 9 6 2 ) have plot ted t r i a n g u l a r d i a -grams to show the f r a c t i o n a t i o n trends of b a s a l t i c magmas. The diagram i s of the f a m i l i a r FMA type with the coordinates being MgO, t o t a l i r o n as FeO, and t o t a l a l k a l i e s . The t o t a l i r o n i s ca lcu la ted as Fe0+ 0 . 9 F e 2 0 3 . Figure 29 shows an FMA plot for 1 3 1 ><Ps ' ' " 3* .-•*2 7 ( 6 ) A M Figure 29 ' FMA t r i a n g u l a r p lot for the Copper Mountain rock ser ies (after Yoder and T i l l e y , 1 9 6 2 ) . 1. Skaergaard l i q u i d s , 2., T h o l e i i t e s e r i e s , 3. Cascades, 4. C a l c - a l k a l i s e r i e s , 5. Hawaiin a l k a l i s e r i e s , 6. Oslo d i s t r i c t , 7. Coppier Moun-t a i n ( in part coincident with No. 6 ) . the Copper Mountain rock s e r i e s . The f r a c t i o n a t i o n trend for the Copper Mountain rock ser ies i s e n t i r e l y one of a l k a l i en-richment. There i s no apparent ear ly i r o n enrichment as i s observed. in many rock s e r i e s . Oxidation% Var ia t ions i n the oxygen.pressure (PO^), of a c rys t a l -l i z i n g magma may inf luence strongly the trend of d i f f e r e n t i a -t i o n . In Figure 3 0 , the Copper Mountain rock ser ies i s com-pared, with other well-known rock ser ies .and with experimental data (Osborne, 1 9 5 9 ) on oxidat ion r a t i o s . 132 Wt. % s.o2 Figure 30 '• Oxidation r a t i o s of several rock ser ies and Osborne's ( 1 9 5 9 ) experimental data (dashed l ines ) compared with those of the Copper Mountain ser ies (after Osborne, 1 9 5 9 ) • The oxidat ion r a t i o curve for the Copper Mountain rock ser ies c lo se ly resembles that for the c a l c - a l k a l i ser ies of Nockolds ( 1 9 5 4 ) . The curve has a slope which indicates s i l i c a enrichment and perhaps s l i g h t l y increas ing PO2. Osborne has shown experimentally that two possible trends of d i f f e r e n t i a t i o n ex i s t i n s i l i c a systems which contain FeO and ¥ 6 2 ^ 2 ° "*~n n ^ s ^yP e -*-n w n i - c h the bulk composition remains constant, the l i q u i d becomes enriched i n i r o n , while i n h i s Type I I , i n which the p a r t i a l pressure of oxygen remains con-s tant , the l i q u i d becomes r i c h i n s i l i c a . The curve for the Copper Mountain rock ser ies suggests that the p a r t i a l pressure of oxygen may have increased s l i g h t l y during the c r y s t a l l i z a t i o n 133 process. Since i s probably l a r g e l y contro l l ed by the amount of water i n a s i l i c a t e melt, i t fol lows that water pressure and poss ib ly also that of other v o l a t i l e s has increased during the c r y s t a l l i z a t i o n process. Further information with respect to the state of oxida-t i o n of the c r y s t a l l i z i n g Copper Mountain magma i s obtained by p l o t t i n g the F e 0 / F e 202 r a t i o s against the s o l i d i f i c a t i o n indices (SI) . The l a t t e r value was devised by Kuno et a l ( 1 9 5 0 ) who found that i t appears to decrease at about the same rate as the percentage of r e s i d u a l l i q u i d of a c r y s t a l l i z i n g magma. They bel ieve that curves based on t h i s value should give a f a i r l y accurate measure of the magma state at various stages of i t s s o l i d i f i c a t i o n . The SI value i s ca lcu la ted from (MgOxlOO/ M g O - F e O-Fe203 - N a 20 - K 20) . The SI values for the Copper Mountain rock ser ies are given i n Table XXII . Rather than plot the trend of oxides against the SI , s ince these trends are already f a i r l y wel l e s tab l i shed , the F e 0 / F e 203 r a t i o s are p lo t ted as ordinates i n Figure 3 1 . The r e s u l t i n g curve shows a s l i g h t i n i t i a l decrease i n the oxida-t i o n r a t i o followed by a f a i r l y constant r a t i o to completion of s o l i d i f i c a t i o n . I t might be in ferred that the pressure of oxygen was constant, after an i n i t i a l increase , throughout the course of c r y s t a l l i z a t i o n . 134 No. SI No. SI No. SI 1 2 9 . 1 6 2 3 . 4 11 2 .8 2 2 5 . 7 7 2 1 . 3 12 . 1 .55 " 3 2 5 . 0 8 1 5 . 1 13 3 . 5 4 21 .6 9 1 4 . 1 5 2 5 . 0 10 1 1 . 0 Table XXII: S o l i d i f i c a t i o n indices for the Copper Mountain rock s e r i e s . i i i 1 1 1 1 1 T JL O o _L X X X X X 3 0 2 5 10 2 0 15 S o l i d i f i c a t i o n Index Figure 3 1 : State of oxidat ion during c r y s t a l l i z a t i o n of the Copper Mountain rock s e r i e s . 1 3 5 PART C: Structure of the Copper Mountain Intrusions  Introduct ion: The Copper Mountain in trus ions include four apparently separate igneous bodies within the map-area and several other smaller i n -trus ions of s i m i l a r composition.which have been mapped by Rice ( 1 9 4 7 ) and which l i e northeast of the present map-area. This sec-t i o n w i l l be concerned with a d e s c r i p t i o n of the i n t e r n a l and ex-t e r n a l s t r u c t u r a l elements of those in trus ions within the map-area. Size and Shape of the Intrus ions: The Copper Mountain stock, which i s the largest of the i n t r u s i o n s , i s e l l i p t i c a l i n plan with the long ax is , which s t r i k e s north 60 degrees west being about 3.8 miles long. The stock occupies an area of approximately 6.5 square mi les . The western contact i s a f a u l t , the northern and southern contacts are apparently nearly v e r t i c a l , and the eastern.contact dips inward (westerly) at an. angle of about 45 degrees. The Armstrong B lu f f s complex i s made up of numerous dykes, s i l l s , and i r r e g u l a r bodies. A n o r t h - s t r i k i n g f a u l t forms the western.boundary of the westernmost of the i n t r u s i v e masses, The contacts show much v a r i e t y , some being sharp and e a s i l y defined and others being t r a n s i t i o n a l . The Smelter Lake stock i s i r r e g u l a r i n shape and oc-cupies less than one square mile of area. The exposed.contact zones are complicated by f a u l t i n g and the southern end i s i n -truded i n part by the Armstrong B luf f s monzonites. The Voigt stock i s only p a r t l y within the map-area. I ts f u l l s ize i s approximately 5.5 square miles with about 136 one-quarter of, i t within the map-area. I t i s i r r e g u l a r i n shape and the at t i tudes of i t s contacts are not known. It i s intruded on the east by the Otter in trus ions and on the west by Armstrong B lu f f s i n t r u s i o n s . External Contacts : The northern contact ,o f the Copper Mountain stock ap-pears to be v e r t i c a l or nearly so with one exception. The 1000 feet long body of dibrite east of the mine bui ld ings (Figure l ) appears to be a f l a n g e - l i k e , f l a t - f l o o r e d northward p r o j e c t i o n . I t i s separated from the main.stock by a f a u l t and i t s exact r e -l a t i o n to the stock i s not known but i t i s probab ly , s imi lar to l o b e - l i k e project ions on the east side of. the stock (page 138). S trata of the Nico la group adjacent to the Copper Mountain stock dip s teeply . Beds of the sedimentary block s i tuated at the nor-i thern contact where i t crosses Similkameen River dip v e r t i c a l l y and.show a blocky contact with the i n t r u s i v e mass. A f a u l t , l o c a l l y known as the Main f a u l t , l i e s adjacent to the northern contact: i n Nico la rocks . I t s t r i k e s at about north 45 degrees west and appears to be nearly v e r t i c a l . This f au l t i s probably a fau l t zone rather than a simple f a u l t , par-t i c u l a r l y at the northwestern end. Fahrni (1966) states that the Main f a u l t has a v e r t i c a l displacement of 150.feet. Assoc ia-ted with the Main fau l t i s - a swarm of r h y o l i t i c dykes, the so-c a l l e d "mine-dykes". These are approximately v e r t i c a l , and s t r i k e about north at an average of 40 degrees to the f a u l t . The "mine-dykes" are probably re la ted to the Main fau l t and poss ib ly to the Otter in trus ions which l i e east of the map-area. I f the Main f a u l t and the Mine HykeS-are re la ted to a 1 3 7 s t r a i n e l l i p s o i d or s tress i n d i c a t r i x and the dykes are con-sidered to l i e along tension f r a c t u r e s , then the fau l t would be d e x t r a l . On the other hand, i f they are release f rac tures , which form perpendicular to compression, the f a u l t would be s i n i s -t r a l . In the second case, the f a u l t which borders the west side of the westernmost Armstrong B l u f f s i n t r u s i o n (page 1 3 8 ) could be a d i s located extension of the f a u l t which cuts the west side of the Copper Mountain stock. The western contact of the stock i s a f a u l t that s t r i k e s at north ,25 degrees east and dips about 75 degrees west. The Nico la group on.the west side of the f a u l t includes the a n t i -c l i n e of a r g i l l i t e , t u f f and minor limestone mentioned e a r l i e r . These rocks are t e n t a t i v e l y corre la ted with the Henry formation. The a u g i t e - d i o r i t e s and vo lcanics to the north of the stock and the tuffaceous and andes i t ic beds to the south and east are con-sidered to be part of the Wolf Creek formation (Polmage, 1 9 3 4 ) which. i s known to over l i e the Henry formation elsewhere (Rice, 1 9 4 7 ) . This arrangement suggests that the f a u l t i s a steep r e -verse fau l t and that the western block has moved up with respect to that on the east . No i n d i c a t i o n of the amount of s t r i k e movement was found. Age of the f a u l t movement i s not known except that i t followed emplacement of Copper Mountain stock and preceded the erosion which produced the pre-Eocene uncon-formity . The v e r t i c a l displacement was perhaps s u f f i c i e n t to ra i s e the west end of the Copper Mountain stock and allow subse-quent removal by eros ion . The southwest contact i s apparently almost v e r t i c a l and there are s teep ly -d ipping s u b p a r a l l e l f a u l t s i n the 138 adjacent Nico la rocks . Where at t i tudes are a v a i l a b l e , the Nico la rocks are also seen to be s teep ly -d ipp ing . These facts are com-pat ib l e with the suggestion that considerable s t r u c t u r a l readjust -ment of the Nico la rocks may have taken place during i n t r u s i o n of the stock. Much of the southeastern, eastern and northeastern con-tact i s sinuous or lobate . The trend of t h i s contact suggests that there may have been some l a t e r a l i n t r u s i o n of the magma and tha t , i n t h i s area, the contacts dip inward at shallow angles. Diamond d r i l l i n g i n the area about one mile southeast of the mine workings showed an. inward-dipping contact of 40 degrees or less (Fahrni , 1 9 5 1 ) . The contacts of the Armstrong Bluf f s i n t r u s i o n show much v a r i a t i o n . In general , the small bodies have r e l a t i v e l y sharp contacts whereas the large bodies , which have been accom-panied by potash metasomatism, hydrothermal a l t e r a t i o n and m i n e r a l i z a t i o n , commonly have t r a n s i t i o n a l contacts . The largest and westernmost of these i n t r u s i v e com-plexes i s faul ted at i t s western contact with Nico la group rocks . This f a u l t i s s i m i l a r to that l y i n g along the west side of Copper Mountain stock i n that i t s s t r i k e i s northerly and that the same older formation of Nico la rocks ex i s t s on i t s west s ide . In several areas within and adjacent to the western-most Armstrong B l u f f s i n t r u s i o n , the rocks have been sheared and brecciated (page 5.8 ) . The s ize of the zone or zones i s unknown but i n one place , the shearing and b r e c c i a t i o n was observed over an area 2 0 0 0 feet by 200 feet (Figure 1 ) . The 1 3 9 main d i r e c t i o n of shearing i s at north 60 west with a dip 70 degrees south. In the most intense ly brecciated parts the f r a c -tures are healed with c a l c i t e and the rock i s a l tered to scapo-l i t e and d iops ide . The small i so la t ed body of pyroxenite and gabbro which cuts across the contact between the outer and intermediate zones of Copper Mountain.stock i n Friday Creek v a l l e y (Figure 1 ) i s bounded on i t s west side by a f a u l t . Other parts of i t s contact are obscured by overburden but i t s composition, texture , l o c a -t i o n and i t s faul ted western contact a l l suggest that the body may be a faulted-up segment from a lower l e v e l of the stock. Internal S tructures : The Copper Mountain stock i s composed of three major rock types which are arranged more or less c o n c e n t r i c a l l y with an inner core of perthos i te and syenite pegmatite, an i n t e r -mediate zone of monzonite, and an outer zone composed of d i o r i t e and gabbro. Contacts of the small gabbroic bodies i n the outer zone are gradat ional with d i o r i t e . The contact between the outer and intermediate zones i s t r a n s i t i o n a l over distances up to 200 feet . The contact between the intermediate and core zones i s , for the most p a r t , s i m i l a r l y gradat iona l . Small peg-matite dykes with sharp contacts are found i n many parts of the intermediate and outer zones. They range from frac t ions of an inch to several feet i n . w i d t h . In one area just west of Deep Gulch Creek and about 150 feet north of the contact between the inner and intermediate zones, the pegmatite i s i n sharp contact with monzonite. This contact i s bel ieved to be that of an apophyse or large dyke. 140 There are three types of f o l i a t i o n i n the Copper Moun-t a i n i n t r u s i o n s . The most common type, due to an alignment of p lagioc lase and pyroxene c r y s t a l s , i s bel ieved to be a primary flow structure formed when the magma was moving. The f o l i a t i o n i s well-developed i n some parts of the Copper Mountain stock and i s , for the most part , subpara l l e l to the contact of the sto No f o l i a t i o n or other flow structures were observed i n the pegma t i t i c core . F o l i a t i o n was observed only i n a few places i n the Voigt and Smelter Lake stocks and consequently l i t t l e i s known about the i n t e r n a l s tructure i n those stocks. A second type of flow structure consists of t h i n l y tabular s ch l i eren up to one foot long (Plates L I I I and LIV) . Plate L I I I : Metasomatized sch l i eren i n d i o r i t e from the outer zone of the Copper Mountain stock. Note the t h i n mafic-free areas adjacent to the tabular s c h l i e r e n . These are found only i n a few places i n the outer zone of the Copper Mountain stock. They are r i c h i n mafic minerals , par t i cu 141 Plate LIV: Metasomatized sch l i eren i n d i o r i t e from the outer zone of the Copper Mountain stock. l a r l y hornblende, and the adjacent igneous rock i s depleted i n mafics. They are bel ieved to be metasomatized and stretched out fragments of Nico la vo lcanic rock or , poss ib ly , cognate i n c l u -sions . A t h i r d type of f o l i a t i o n i s a r e s u l t of a planar con-centrat ion of b i o t i t e i n some of the rocks , p a r t i c u l a r l y i n the outer zone of the Copper Mountain stock and the Armstrong Bluf fs complex. The b i o t i t e occurs i n segregations with the plates oriented i n a plane and i t i s bel ieved that the b i o t i t e might have been deposited by deuter ic so lut ions on surfaces along which movement occurred la te i n the emplacement of the body. 142 Part D: O r i g i n of the Copper Mountain Intrusions  Introduct ion: In t h i s s ec t ion , a summary and in terpe ta t ion of ev id -ence r e l a t i n g to the o r i g i n of the Copper Mountain rock ser ies are given. The evidence, which i s drawn from the pre-vious sect ions on texture , mineralogy, chemistry and s t ruc ture , i s discussed and re la ted to the various petrogenetic processes which contributed to the formation of the s e r i e s . The f i n a l part i s a summary of the h i s tory of the i n t r u s i o n s . Three general-petrogenetic processes could lead to formation of a ser ies such as the Copper Mountain i n t r u s i o n s : metasomatic replacement, a s s i m i l a t i o n , or magmatic d i f f e r e n t i a -t i o n . The f i r s t p o s s i b i l i t y , metasomatic replacement (whe-ther by s o l i d d i f f u s i o n , permeation by f l u i d s or soaking by a s y e n i t i c magma) i s re jec ted . Although some potash metasomatism has taken place i n rocks of the Nico la group near the stock, sharp contacts , compositions, textures and mineralogy a l l point to a magmatic o r i g i n for the Copper Mountain i n t r u s i o n s . The second p o s s i b i l i t y , that a magma was modified by as s imi la t ion of country rock as Compton ( 1 9 5 5 ) suggested for Bald Rock b a t h o l i t h i n C a l i f o r n i a , does not seem to be a pro-mising one . I f the o r i g i n a l magma was considered to be of the composition of the central .pegmat i te , magma of the composition of the intermediate zone could be produced by as s imi la t ion of Nico la group andesites . On the assumption that the rock uni ts are of nearly c y l i n d r i c a l form (Figure 3 2 , the volume of rock 143 ass imi lated would have to be larger than the volume of pegmatite magma and i t seems impossible that such large amounts of basic rock could be d isso lved i n such a magma unless i t was super-heated. There i s no evidence of unusually high temperatures. I f , on the other hand, a b a s a l t i c magma was the parent and ex-tensive a s s imi la t ion of more ac id mater ia l i s assumed, i t might be possible to form magmas of the necessary intermediate com-p o s i t i o n . This would not exp la in , however, the compositional zoning of the stock with i t s r e l a t i v e l y bas ic margin and f e l d s -pathic core. In add i t i on , the country rock i s almost e n t i r e l y of andes i t i c composition. Compton ( 1 9 5 5 ) c i t ed the concentr i -c a l l y zoned arrangement of t rondhjemite -granodior i te - tona l i t e i n the Bald Rock b a t h o l i t h as evidence of a s s i m i l a t i o n but, as pointed out by Larsen and Poldervaart ( 1 9 6 1 ) , Heimlich ( 1 9 6 5 ) and others, such zoning could r e s u l t from other processes. I f a s s imi la t i on had been of importance i n the genesis of Copper Mountain stock, there should be some evidence, e s p e c i a l l y i n the marginal areas, of xenol i ths in the various stages of d i -gest ion. In a few areas, small inc lus ions were observed but these were metasomatized and not digested (page 1 4 0 ) . Conse-quently, i t seems highly u n l i k e l y that a s s imi la t ion has played an important part in the formation of t h i s rock s er i e s . There seems l i t t l e doubt that the Copper Mountain rock ser ies has formed by magmatic d i f f e r e n t i a t i o n . The we l l -defined petrogenetic sequence of gabbro-diorite-monzonite-syenite i s that which would be expected by c r y s t a l l i z a t i o n d i f f e r e n t i a t i o n with a l k a l i enrichment of a basic magma. In add i t i on , mineralogy, texture and s tructure a l l support the 1 4 4 idea of magmatic d i f f e r e n t i a t i o n . Moreover, i t i s bel ieved that d i f f e r e n t i a t i o n occurred after emplacement of the magma i i t s present p o s i t i o n rather than by d i f f e r e n t i a t i o n at depth followed by successive i n j e c t i o n s of already d i f f e r e n t i a t e d magma or by a s ing le i n j e c t i o n of a heterogeneous magma. This b e l i e f i s supported by the gradat ional contacts within the sto His tory of the Magma: (a) Introduct ion The Copper Mountain in trus ions are bel ieved to have formed by d i f f e r e n t i a t i o n . i n : p l a c e of a singled basic magma. The Voigt and Smelter Lake stocks and a large part of the outer zone of the Copper Mountain stock are considered to be of unmodified parent magma composition. Pyroxenite, gabbro, monzonite, syenites and perthos i tes of Copper Mountain stock and Armstrong B lu f f s complex are considered to be d i f f e r e n -t i a t e s of the same magma. D i f f e r e n t i a t i o n i s bel ieved to have been effected by a combination of convection and d i f f u s i o n . In the fo l lowing sect ions these points are d i scussed . in d e t a i l (b) Emplacement of the Magma Several, hypotheses: have been advanced for the em-placement of c o n c e n t r i c a l l y zoned igneous bodies. Larsen and Poldervaart ( 1 9 6 1 ) , i n t h e i r i n t e r p r e t a t i o n of the Bald Rock b a t h o l i t h of C a l i f o r n i a , posulated a f o r c e f u l i n j e c t i o n of migma-magma separated in to a cen tra l l i q u i d of trondhjemite composition and a marginal mobile mixture of c r y s t a l s and l i q u i d of granodior i te and t o n a l i t e composition. Such an hypothesis does not appear compatible with the arrangement 1 4 5 of rocks found i n Copper Mountain stock (Figure 1 ) because i t does not explain the gabbroic bodies within the d i o r i t e of the outer zone. Heimlich ( 1 9 6 5 ) suggested a c r y s t a l mush i n t r u -s ion for the r e l a t i v e l y basic outer part of the F l o r a Lake stock and a l a t e r granite magma for the core . He c i t e s flow s tructure as evidence for c r y s t a l mush i n t r u s i o n but such s t r u c -tures could also r e s u l t from convective movement during c r y s t a l -l i z a t i o n . Another theory, that of mult ip le i n t r u s i o n and cauldron subsidence, has been postulated for the r i n g complexes of Scot-land. According to t h i s hypothesis , d i f f e r e n t i a t i o n takes place at depth and d i f f eren t magmas are supplied at i n t e r v a l s to a higher l e v e l . There i s l i t t l e to support such a suggestion for Copper Mountain stock since gradat ional contacts separate the various zones within the stock and since there i s an absence of s tructures i n d i c a t i n g cauldron subsidence. I t i s be l i eved , by the author, that f o r c e f u l i n j e c -t i o n and d i f f e r e n t i a t i o n i n place of a s ingle parent magma was the means by which Copper Mountain stock was formed. Sup-port for f o r c e f u l i n j e c t i o n i s seen i n the d i s t o r t i o n of the reg ional trend i n Nico la rocks . Fahrni ( I 9 6 6 ) states that gentle north- trending fo lds character ize volcanic sequences at Copper Mountain mine. In some areas adjacent to the stock (Figure 1 ) , however, s tructures are s teep ly -d ipping and at large angles to t h i s t rend . In add i t i on , f a u l t i n g and shearing such.as that at the southwest contact of the stock may be due to s t r u c t u r a l readjustment of Nico la rocks during i n t r u s i o n . Planar flow structures i n Copper Mountain stock 146 suggest that there has been some l a t e r a l i n t r u s i o n of the magma. The l o b e - l i k e project ions (page 1 4 6 ) on the northern and east-ern extremit ies of the stock appear to have inward dips of about 40 degrees. The shapes of the various in trus ions are suggested i n Figure 3 2 . That the Copper Mountain stock c r y s t a l l i z e d at the margin f i r s t , and that the pegmatite core c r y s t a l l i z e d l a s t , i s suggested by several l i n e s of evidence. In some places , pegma-t i t e has been in jec ted into outer parts of the stock (page 1 3 9 ) . In add i t ion , the coarse gra in of pegmatite suggests that i t has formed i n the presence of a r e l a t i v e l y large amount of v o l a t i l e s such.as would be found i n la te d i f f e r e n t i a t e s . F i n a l l y , the sequence from gabbro to syenite f i t s a reasonable order of d i f -f erenta t ion . Figure 3 2 ; Diagramatic cross - sec t ion of the Copper Mountain i n t r u s i o n s . The dotted l i n e represents the zone at which d i f f e r e n t i a t i o n began i n the Copper Mountain stock and the dashed l i n e , the approxi-mate present l e v e l of exposure. 1 4 7 The apparent absence of d i f f e r e n t i a t i o n i n the Voigt and Smelter Lake bodies i s perhaps due to r e l a t i v e l y fast coo l ing and loss of v o l a t i l e s . Evidence for these condit ions i s seen i n the general f ine to medium-grained texture of these rocks which contrasts with coarser textures of d i f f e r -ent iated parts of Copper Mountain stock. I t may also be pos-s i b l e that d i f f e r e n t i a t i o n did occur i n Voigt and Smelter Lake stocks at some l e v e l not now exposed to view. The v a r i a t i o n s i n compositions and textures i n the dykes, s i l l s , and i r r e g u l a r in trus ions of the Armstrong Bluf f s complex suggest that i t formed from repeated tappings of a d i f f e r e n t i a t i n g magma. The complex i s c l e a r l y younger than d i o r i t e s of the other stocks but whether i t s magmatic source was a lower part of Voigt or Smelter Lake stocks or some other source i s not known. (c) Evidence for D i f f e r e n t i a t i o n The minera log ica l s i m i l a r i t y of a l l rocks of the Copper Mountain ser ies i s i n d i c a t i v e of a common o r i g i n . The same minerals are present i n each rock, there i s a v i r t u a l absence of quartz and fe ldspathoid i n a l l rocks , and there i s a minera log ica l gradation from one type to another (Figure 7 ) . S t r u c t u r a l and compositional var ia t ions of the f e l d -spars are compatible with the idea that the ser ies formed by d i f f e r e n t i a t i o n . P lagioc lase ranges i n composition from A n ^ to ^n2$ i - n intermediate and basic rocks while a l b i t e , both exsolved and primary, i s found i n pegmatite. Opt ica l and X-ray studies of p lag ioc lases have shown that they are 148 of low temperature s t r u c t u r a l state with the poss ible exception of a few from the more basic rocks which may be intermediate types. P lagioc lases show normal and o s c i l l a t o r y zoning, thus i n d i c a t i n g non-equi l ibr ium c r y s t a l l i z a t i o n or f r a c t i o n a t i o n . The a l k a l i fe ldspars i n the Copper Mountain rock ser ies are cryptoperthi tes or microperth i tes . The potass ic phases range i n composition from Org^ to O r ^ and the sodic phases are of a l b i t i c composition. Bulk compositions of perth i tes appear to be Or^Q to Or^Q . Opt i ca l and X-ray determinations suggest that per th i tes from the basic end of the ser ies are p a r t l y ordered intermediate mierocl ine and low a l b i t e and that those from the s y e n i t i c end of the ser ies consist of a more ordered and more " t r i c l i n i c " mierocl ine and low a l b i t e . The reason for the d i f ference i s bel ieved to be that the s y e n i t i c end of the ser ies c r y s t a l l i z e d much more slowly and i n the presence of a greater pressure of v o l a t i l e s than the basic end and conse-quently, the perthites'. were able to reach a more ordered s ta te . Tie l i n e slopes (Figure 19) for coex i s t ing fe ldspars suggest a range of pressure and temperature with la te d i f f e r e n t i a t e s c r y s t a l l i z i n g under lower temperatures and higher pressures than ear ly basic rocks . This i s compatible with the idea that the rock ser ies formed from a s ingle magma by d i f f e r e n -t i a t i o n with resul tant r e s i d u a l concentration of v o l a t i l e s . Further evidence of a common parent magma i s sug-gested by the chemical v a r i a t i o n s of the Copper Mountain rock s e r i e s . There i s a continuous v a r i a t i o n from one end of the ser ies to the other i n component oxides, the a l k a l i e s increas -ing with a corresponding decrease i n femic oxides (Figure 2 5 ) . 149 The trend of d i f f e r e n t i a t i o n (Figure 2 9 ) i s s imi lar to the trend of the a l k a l i c rocks of the Oslo d i s t r i c t in that i t i s toward a l k a l i enrichment, but there i s no apparent early enrichment i n i r o n . The oxidat ion r a t i o curve (Figure 3 0 ) suggests that there was s l i g h t l y increas ing pressure of oxygen (and probably water) with s i l i c a enrichment. Evidence that i s compatible with the idea of a s ingle parent magma i s also found in a subtract ion v a r i -at ion diagram. In Figure 33? the two extreme compositions, the gabbroic phase of the Copper Mountain stock (Specimen 1 ) and the c e n t r a l pegmatite (average of specimens 1 1 , 12 and 1 3 ) might represent the f i r s t (neglect ing pyroxenite) and f i n a l d i f f e r e n t i a t e s re spec t ive ly . Since the Voigt 20r 5 0 \ A , V 5 5 Wt./4 SiC»2 60 65 Figure 3 3 : Subtraction v a r i a t i o n diagram. Gabbro - specimen 1 Pegmatite - average of specimens 1 1 , 12 and 13" Voigt-Smelter - average of specimens 2 and 3» Monzonite - average of specimens S> 6, 7, 8 and 9-150 and Smelter Lake stocks are probably und i f f erent ia ted , f i n e -grained and appear to have c r y s t a l l i z e d with l i t t l e modif ica-t i o n , i t i s assumed that the o r i g i n a l magma was of t h i s composition. This composition (average of specimens 2 and 3) i s p lot ted on the v a r i a t i o n diagram (Figure 3 3 ) . It i s ap-parent that a close f i t to s tra ight l i n e s between the two extreme compositions i s obtained. This suggests that an o r i g i n a l magma of . the composition of the Voigt and Smelter Lake stocks could be modified by removal of gabbroic compon-ents and produce magmas approaching pegmatite composition. This s i m p l i f i e d view would require the formation of about f ive times as much gabbro (or less pyroxenite) as pegmatite, and would suggest the existence of much more gabbro at depth than shows on the geo log ica l map. The weight percents of the major oxides of those rocks p lot ted i n Figure 33 are given i n Table XXIII . Oxide Pegmatite Gabbro Voigt-Smelter Monzonite S i 0 2 63 .00 43 . 1 2 4 6 . 6 9 5 2 . 8 8 MgO 0.37 6 .52 5.35 3.99 CaO . 0.97 14 • 00 11.38 8 .02 Na 20 4.55 2.49 3.85 3.87 K 2 0 7.99 0.81 1.99 4.45 A 1 2 0 3 1 9 . 7 3 18 .19 1 7 - 3 0 1 7 . 0 5 FeO 0.78 12.01 9.34 7 .00 Table XXIII: Weight percent metal oxides for those rocks p lot ted i n Figure 3 3 . Pegmatite - average of specimens 1 1 , 1 2 and 1 3 . Gabbro - specimen 1. Voigt-Smelter - average of specimens 2 and 3. Monzonite - average of specimens 5 , 6 , 7 , 8 and 9. Rittman (I960) has suggested a method of determining the process of magmatic d i f f e r e n t i a t i o n . According to t h i s 1 5 1 scheme, which i s based on a study of d i f f e r e n t i a t e d magmas, i f c r y s t a l s e t t l i n g (or more properly c r y s t a l f rac t ionat ion) i s the dominant process, then the sui te index must remain constant with an increas ing s i l i c a content. In Figure 22, the su i te index curve for the Copper Mountain rock ser ies was shown to be approximately constant at 7-7 over the ent ire range of s i l i c a content. (d) Chemistry of D i f f e r e n t i a t i o n In the previous sec t ion , i t was concluded that the Copper Mountain rock ser ies formed by magmatic d i f f e r e n t i a t i o n of a s ingle magma of the composition of the Voigt and Smelter Lake stocks. The trend of d i f f e r e n t i a t i o n i n terms of chemical components has been shown to be (page 1 3 1 ) } toward a l k a l i and s i l i c a enrichment. In t h i s sec t ion , an attempt w i l l be made to determine the trend of d i f f e r e n t i a t i o n i n terms of the rock minerals . The Copper Mountain ser ies contains three major minerals; p lag ioc lase , c l inopyroxene, and a l k a l i f e ldspar . The various rock types i n the ser ies have d i f f eren t propor-t ions of these minerals and, i n add i t i on , the compositions of these minerals d i f f e r from one type to another. The establ ished chemical trend of a l k a l i enrichment and mafic deplet ion and the t e x t u r a l r e l a t i o n s h i p s of the minerals suggest that pyroxene and p lag ioc lase were the e a r l i e s t minerals to p r e c i p i t a t e . A p lot of normative compositions of the 13 analyzed specimens on the ternary diagram, An-Ab-Di (Figure 3 4 ) suggests that both pyroxene and p lag ioc lase may have prec ip i ta t ed s imultan-eously throughout a large part of the magmatic'history of the 1 5 2 An Ab Di Fi'guye 34 ' P lot of normative compositions of 13 analyzed Copper Mountain rocks on the ternary diagram, An-Ab-Di (after Bowen, 1 9 1 5 ) . s e r i e s . There i s a considerable scat ter of points but t h i s i s to be expected since the normative minerals Ab, An and Di make up less than 70 percent of a l l the rocks . A further i n d i c a t i o n of the trend of d i f f e r e n t i a t i o n with respect to s i l i c a sa turat ion may be seen (Figure 3 5 ) i n a diagram which represents a cross - sec t ion at the f i e l d boun-dary which separates pyroxene and o l i v i n e from p lag ioc lase , nepheline, and quartz i n the quaternary system, nepheline-anorth i te -quartz -d iops ide ( o l i v i n e ) . The p r e c i p i t a t i o n of "saturated" minerals (plagioclase and pyroxene) from composi-t i o n A leads to "saturated" or s y e n i t i c residua of composition A2. After i n i t i a l p r e c i p i t a t i o n of pyroxene and p lag ioc lase , the l i q u i d s move toward a l k a l i enrichment and, at some point , 153 Ne1 Figure 3 5 ' Diagramatic i l l u s t r a t i o n of how 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 may lead to s y e n i t i c res idua (after Barth, 1 9 6 2 ) . these ear ly minerals are joined by the p r e c i p i t a t i o n of a l k a l i f e ldspar . This part of the magmatic h i s tory might be i l l u s t r a t e d by the ternary diagram, Ab-An-Or (Figure 3 6 ) . In Figure 3 6 , the bulk compositions of 13 analyzed rocks are p lot ted at points representing t o t a l normative f e l d -spar ca lcu lated as described on page 1 2 9 - The Or content of a l k a l i fe ldspars (Specimens 8 to 1 3 ) was determined by X-ray methods and t h e i r An content was estimated. The pegmatites (Specimens 1 1 , 1 2 , 1 3 ) , which are one-feldspar rocks , would be expected to have fe ldspar compositions near that of t o t a l norma-t i v e feldspar compositions of the rocks from which they came. This assumption places t h e i r An content at approximately 5 per-cent. Since specimens 8, 9 and 10 contain two fe ldspars , t h e i r a l k a l i fe ldspars are assumed to f a l l on a so l idus (dashed l i n e ) somewhat above 5 percent anorthite but below the so l idus 1 5 4 An Ab Or Figure 3 6 : Diagramatic i n t e r p r e t a t i o n of the system Ab-An-Or (after Tut t l e and Bowen, 1 9 5 8 ) with Copper Mountain bulk compositions ( c i r c l e d dots ) , homogenized per th i tes (open c i r c l e s ) , and p lag ioc lases (dots) . S o l i d curves are for Tut t l e and BowenTs dry system and dashed curves represent an est imation of t h e i r p o s i t i o n i n the Copper Mountain magmas as PH2O i n -creased . ( so l id l i n e ) for dry systems. Plotted p lagioc lase compositions are outer rim compositions of zoned c r y s t a l s . Or content of p lag ioc lase i s estimated keeping i n mind that Or content would not increase with decreasing An content as i n the dry system (Figure 3 6 ) . The t o t a l normative fe ldspar compositions of specimens 1 to 10 f a l l wi thin the two fe ldspar f i e l d to the r i g h t or above the curve LKP. In t h i s reg ion , i f there i s equ i l ibr ium c r y s t a l -l i z a t i o n , an i n i t i a l p lag ioc lase p r e c i p i t a t e s and, as the l i q u i d composition moves toward the f i e l d boundary' C D t h e composi-t i o n of the p lagioc lase moves along the s o l i d curve (LK) 15 5 toward K. When the . f i e Id . boundary i s reached, p lag ioc lase i s j o i n -ed by an a l k a l i fe ldspar with a composition on the curve KP and then both fe ldspars change composition along the so l idus curve toward K u n t i l the l i q u i d i s used up. In the case of the Copper Mountain specimens ( l to 1 0 ) , c r y s t a l l i z a t i o n was of the non-equi l ibr ium type, but i t i s s t i l l poss ible to make a reasonable estimate of the c r y s t a l l i z a t i o n path. These specimens contain two fe ldspars and i t i s obvious from t h e i r textures that p lag io -clase preceded p e r t h i t e . The main point of d i f ference between the equi l ibr ium and non-equi l ibrium systems i s that p lag ioc lase d id not change in composition along the curve LK but rather succes-s ive layers prec ip i ta t ed which probably have compositions along the curve. Another important di f ference i s that l i q u i d was not used up i n transforming the fe ldspars as in equi l ibr ium c r y s t a l -l i z a t i o n , but rather was separated from the c r y s t a l s in the manner described in the fol lowing sec t ion . The r e s u l t of t h i s process of f r a c t i o n a t i o n was the formation of r e s i d u a l a l k a l i n e - r i c h l i q u i d s whose compositions l i e in the one-feldspar f i e l d below the curve KFP and which c r y s t a l l i z e d to form a one-feldspar pegmatite (specimens 1 1 , 12 and 1 3 ) . Tut t l e and Bowen ( 1 9 5 8 ) state that such compositions w i l l f i n i s h c r y s t a l l i z a t i o n as a s ingle homo-genous fe ldspar although plagioc lase may c r y s t a l i z e d e a r l i e r . This suggests that the minimum on the boundary curve CD might, under these p a r t i c u l a r condit ions of P and Ph^O, f a l l in the region of the bulk compositions of specimens 12 and 1 3 . It i s not poss ible to speculate on the type of termination of the three-phase region, p l a g i o c l a s e - a l k a l i - f e l d s p a r - l i q u i d , because both the compositions of the coexis t ing fe ldspars and the com-156 pos i t ions of the coex i s t ing l i q u i d are required (Stewart and Rqseboom, 1 9 6 2 ) . I t may be reasonable to say, however, that through d i f f e r e n t i a t i o n , large amounts of a l k a l i - r i c h l i q u i d s with a composition near that of specimens 12 and 13 were separa-ted and c r y s t a l l i z e d i n the one-feldspar or hypersolvus reg ion . On cool ing fur ther , the hypersolvus a l k a l i fe ldspars exsolved a l b i t e to form the cryptoperthi tes now present i n the rocks . It w i l l be noted that the pegmatites, e spec ia l l y spec i -men 1 1 , are more potass ic than might be expected. Their composi-t ions f a l l somewhat to the r i g h t of the boundary minimum deter-mined by Tut t l e and Bowen ( 1 9 5 8 ) . I t may be that some meta-somatic process such as r e c i p r o c a l a l k a l i t rans fer ( O r v i l l e , 1 9 6 2 ) has enriched the pegmatite perth i tes i n potassium or simply that they r e f l e c t the r e l a t i v e l y potass ium-rich character of the o r i g i n a l parent magma. (e) Temperature of C r y s t a l l i z a t i o n An i n d i c a t i o n of temperature of c r y s t a l l i z a t i o n i s ob-tained from some of the minera log ica l r e l a t i o n s h i p s . A compari-son of the coex i s t ing fe ldspars from Copper Mountain with the experimental work of Yoder, et a l ( 1 9 5 6 ) showed that the basic rocks may have c r y s t a l l i z e d at higher temperatures and lower pressures of v o l a t i l e s than the pegmatite core (see page 1 0 1 ) . A comparison of the Copper Mountain fe ldspars with Barth's ( 1 9 6 2 ) fe ldspar geothermometer suggested minimum temperatures of c r y s t a l -l i z a t i o n ranging from 820 degrees C for the basic rocks to 570 degrees C for the pegmatites. These temperatures appear to be somewhat low because the s y e n i t i c rocks of the inner zone are hypersolvus and thus must have c r y s t a l l i z e d at a temperature 157 greater than about 660 degrees G, the temperature of the top of the solvus i n the binary system NaAlSi^Og-KAlSi^Og (Tutt le and Bowen, 1958). I t i s poss ib le , however, that the top of the solvus i s lower than 660 degrees due to the e f fect of pressure of v o l a -t i l e s on the so lvus . T u t t l e and Bowen found that fe ldspars ob-tained i n t h e i r experimental determination of the pos i t ion of the solvus were metastable high temperature types. (f) Mechanics of D i f f e r e n t i a t i o n It i s bel ieved that d i f f e r e n t i a t i o n began large ly after the roof and walls of the stock had c r y s t a l l i z e d . In the Copper Mountain stock, c r y s t a l l i z a t i o n of d i o r i t e began i n the cooler per iphera l areas and, at a c e r t a i n . p o i n t , d i f f e r e n t i a t i o n began. This point i s bel ieved to be a t r a n s i t i o n a l one which resul ted from a gradual bu i ld -up of trapped v o l a t i l e s and a consequent i n -crease i n mobi l i ty of the magma. The process of d i f f e r e n t i a t i o n i s considered to be one of 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 effected through a combination of convection, d i f f u s i o n , c r y s t a l zoning and c r y s t a l s e t t l i n g . Thermal convection has been.c i ted as a factor i n d i f f e r -en t ia t i on i n d o l e r i t e s i l l s by Hess (i960). Here, cool and dense l i q u i d from the roof, region i s bel ieved to s ink and be r e -placed by hot r i s i n g l i q u i d s . In the Copper Mountain stock, i t i s bel ieved that l i q u i d s in per iphera l areas of the magma chamber were r e l a t i v e l y cool and therefore descended and were replaced by hot l i q u i d s from the c e n t r a l region of the chamber. During descent of the magma along the walls of the chamber, density of the magma would gradual ly decrease for two reasons. Higher temperatures i n lower parts of the magma chamber would cause an 158 increase i n temperature and consequent decrease i n density of the descending magma. In add i t i on , continuing c r y s t a l l i z a t i o n and r e -moval of mafic const i tuents i n descending magmas adjacent to the chamber walls would cause a decrease i n magma dens i ty . Hess (I960) has estimated that the density of a t h o l e i i t i c magma at 1 1 2 5 degrees C i s 2.65 before separation of mafic const i tuents and 2.58 afterward. As a r e s u l t of gradual ly decreasing density i n the descending magma, a point would be reached at which the density of the descending magma would equal that of the magma i n the lower and centra l part of the chamber and, consequently, downward movement would cease and thus the v e r t i c a l extent of the convection c e l l would be l i m i t e d . This idea i s i l l u s t r a t e d i n Figure 3 7 . Diffusion.must also have taken place during d i f f e r e n t i a -t i o n of Copper Mountain magma. There are several types of d i f -fusion mentioned i n the l i t e r a t u r e deal ing with magmas. The A Figure 27° Diagramatic i n t e r p r e t a t i o n . o f convection c e l l sug-gested for Copper Mountain stock. Arrows represent d i r e c t i o n of magmatic movement. Density of des-cending magma equals that of lower magmas at point A thereby l i m i t i n g v e r t i c a l s ize of c e l l . 1 5 9 Spret e f f e c t , i n which c e r t a i n disso lved molecules migrate to -ward cooler marginal areas, has been discounted by Bowen ( 1 9 2 8 ) as being too slow to be e f f ec t ive over reasonable d is tances . Another type of d i f f u s i o n which involves chemical equ i l ibr ium has been discussed by Hess ( i 9 6 0 ) . He states that , i n i n t e r -s t i t i a l l i q u i d i n bottom accumulations of c r y s t a l s i n the S t i l l w a t e r complex, d i f f u s i o n takes place upward over several feet i n order to maintain chemical e q u i l i b r i u m . It i s bel ieved that d i f f u s i o n of t h i s type may have been important i n d i f f e r -en t ia t i on of Copper Mountain stock and that i t occurred between the i n t e r s t i t i a l l i q u i d i n the c r y s t a l l i z i n g per iphera l areas and the adjacent descending magma rather than at the bottom of a magma chamber. C r y s t a l "armoring" and c r y s t a l s e t t l i n g were also important i n d i f f e r e n t i a t i o n of Copper Mountain stock. P lag io -clase i s commonly zoned with c a l c i c cores which have been e f f e c t i v e l y mantled against react ion with r e s i d u a l l i q u i d s . Zoning i s also apparent i n pyroxene c r y s t a l s with sodic r ims. Evidence of c r y s t a l s e t t l i n g i s seen i n pyroxenite cumulates described on page 6 9 . Hess ( i 9 6 0 ) has shown that the s e t t l i n g v e l o c i t i e s of c r y s t a l s i n a magma with a v i s c o s i t y of 3 0 0 0 poises and a density of 2.58 are such that pyroxene and p lag ioc lase c r y s t a l s could s e t t l e at rates up to several hundred meters per year depending on the s ize of the c r y s t a l s . Figure 38 i l l u s t r a t e s d iagramat ica l ly the r e l a t i o n -ship between d i f f u s i o n and convection during c r y s t a l l i z a t i o n . The l e t t ered zones represent c r y s t a l l i n e d i o r i t e (A), a v i s -cous mixture of p lag ioc la se , pyroxene c r y s t a l s and i n t e r s t i t i a l 160 ' 1 - " , B i - / an D - ' l • 'a o I D • « Dl. in / / Diorite / \ / diffusion _j increasing temperature  Figure 38; Diagramtic i n t e r p r e t a t i o n of the r e l a t i o n s h i p be-tween d i f f u s i o n and convection during c r y s t a l l i z a -t i o n . V e r t i c a l arrows represent d i r e c t i o n and magnitude of convection. See text for explanation. l i q u i d (B), and descending magma containing m i c r o l i t e s and some larger c r y s t a l s of p lag ioc lase and pyroxene (C) . The s o l i d l i n e (X) represents the t r a n s i t i o n a l zone i n which d i f f e r e n t i a -t i o n began. In zone C, magma descends because of a r e l a t i v e l y higher density than magma i n the center of the chamber but, as zone B i s approached, the l i q u i d becomes more highly charged with c r y s t a l s and more viscous and, consequently, descends at a lower r a t e . Rate and d i r e c t i o n of flow of the magma i s represented by v e r t i c a l arrows. Zone B i s composed of a v i s -cous c r y s t a l mush i n which l i t t l e or no movement occurs. It i s bel ieved that chemical d i f f u s i o n takes place i n the region between zones B and C, As i n t e r s t i t i a l l i q u i d of zone B i s 161 depleted i n mafic const i tuents , add i t i ona l mafic const i tuents migrate i n from zone C i n order to maintain chemical equ i l ibr ium. The reverse i s true for a l k a l i c and v o l a t i l e const i tuents . I t i s bel ieved that pyroxene c r y s t a l s s e t t l ed out and accumulated i n the lower part of the convection c e l l . Summary and Sequence of Events: The fo l lowing i s a summary of the h i s t o r y of the Copper Mountain i n t r u s i o n s : 1. Magma of d i o r i t i c composition was f o r c e f u l l y i n -jected into rocks of the Nico la group to form the Copper Mountain, V o i g t , and Smelter Lake stocks. C r y s t a l l i z a t i o n began while the magma was moving, r e s u l t i n g i n planar flow s t ruc tures . Some l a t e r a l i n j e c t i o n of magma took place forming l o b e - l i k e s tructures such as those on the northern and east-ern contacts of Copper Mountain stock. 2. The Voigt and Smelter Lake stocks c r y s t a l l i z e d without apparent d i f f e r e n t i a t i o n , forming d i o r i t e . Perhaps loss of v o l a t i l e s to the country rock pre-vented d i f f e r e n t i a t i o n . o r perhaps d i f f e r e n t i a t i o n occurred at some l e v e l not exposed to view. Copper Mountain stock c r y s t a l l i z e d from the out-side i n forming an outer zone of d i o r i t e . 3. When the roof and marginal parts of the Copper Mountain stock c r y s t a l l i z e d to form d i o r i t e , v o l a t i l e s , trapped within the remaining magma, lowered i t s v i s c o s i t y . At t h i s time, a tempera-ture and density gradient resul ted i n formation 162 of a convection c e l l (Figure 39a) i n which l i q u i d s from the roof and per iphera l regions of the magma chamber descended and were replaced by hot r i s i n g l i q u i d s from the centra l region of the chamber. V e r t i c a l extent of the convection c e l l was l imi ted as the density of descending magma decreased through reheating and removal of mafic const i tuents by c r y s t a l l i z a t i o n . 4. At t h i s po int , d i f f e r e n t i a t i o n began, the f i r s t d i f f e r e n t i a t e being gabbro. Chemical d i f f u s i o n between l i q u i d s of zones B and C (Figure 38) sup-p l i e d a d d i t i o n a l mafic const i tuents and resul ted i n c r y s t a l l i z a t i o n of a d i f f e r e n t i a t e (gabbro) more basic than the parent magma (Figure 39b). The sporadic development of these gabbros i s per-haps due to the fact that a balance between rates of convection and d i f f u s i o n was not everywhere reached. As d i f f e r e n t i a t i o n proceeded, composi-t i o n of the magma changed continuously toward one enriched i n a l k a l i e s . This process was aided by c r y s t a l armoring and c r y s t a l s e t t l i n g . A l k a l i and v o l a t i l e const i tuents tended to remain i n the upper part of the chamber while pyroxene c r y s t a l s tended toward the lower par t . 5. As the magma changed i n composition and c r y s t a l -l i z a t i o n progressed, less basic rocks were formed . ( F i g u r e 3 9 c ) . Increased v o l a t i l e content and poss ib ly a reduced coo l ing rate resul ted i n a 163 Figure 39 ; Diagramatic representat ion of c r y s t a l l i z a t i o n d i f -f e r e n t i a t i o n of Copper Mountain stock. See text for explanat ion. 164 coarser gra in s ize for monzonite of the interme-diate zone than for gabbro and d i o r i t e of the outer zone. 6. When r e s i d u a l l i q u i d s were completely depleted i n mafic const i tuents , i . e . , at the end of monzonite c r y s t a l l i z a t i o n , convection ceased or slowed con-s iderably (Figure 39d) . C r y s t a l l i z a t i o n of coarse-grained syenite pegmatite then proceeded. Be-cause of the very h i g h . v o l a t i l e content, c r y s t a l -l i z a t i o n then took place under nearly equi l ibr ium condit ions and ear ly p lagioc lase was completely transformed to a l b i t e . As the composition of the magma approached the Ab-Or side of the Ab-An-Or ternary system, subsolvus c r y s t a l l i z a t i o n was suc-ceeded by hypersolvus c r y s t a l l i z a t i o n and the development of the one-feldspar perthos i te pegma-t i t e . I t i s bel ieved that c r y s t a l l i z a t i o n of pegmatites took place i n a r e l a t i v e l y s t a t i c en-vironment except fpr poss ible a l k a l i ion exchange between a l k a l i fe ldspar c r y s t a l s and i n t e r s t i t i a l f l u i d s . 7. As c r y s t a l l i z a t i o n of core pegmatites progressed, the outer monzonite and d i o r i t e s h e l l f rac tured . This and adjacent Nico la rocks were permeated by f l u i d s carry ing v o l a t i l e s and potassium, forming b i o t i t e and K-fe ldspar veins and dykes,some of which are associated with copper m i n e r a l i z a t i o n . 8. The Armstrong Bluf f s complex i s bel ieved to have formed by repeated tapping of a d i f f e r e n t i a t i n g 165 magma which was emplaced at i n t e r v a l s after c r y s t a l -l i z a t i o n of d i o r i t e i n Voigt and Smelter Lake stocks. The west side of Copper Mountain stock i s bel ieved to have been faul ted upward and removed by subse-quent eros ion . 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F . , ( 1 9 5 2 ) , "Opt ica l studies on a l k a l i f e ldspars ," Amer. J o u r . C S c i . , Bowen v o l . T u t t l e , 0. F . , and Bowen, N. L . , ( 1 9 5 0 ) , "High temperature a l b i t e and contiguous f e ldspars ," Jour. G e o l . , v o l . 5 8 . 172 and Bowen, N. L . , ( 1 958 ) , "Orig in of granite i n l i g h t of experimental s tud ies ," G. S. A. Mem.. 74. Van der Kaaden, G . , ( 1 951 ) , "Opt ica l studies on natura l p lag io -clase fe ldspar with high-temperature and low-temperature o p t i c s , " D i s s e r t , Univ. Utrecht . Van der P las , L . , and T o b i , A. C . , ( 1965 ) , "A chart for judging the r e l i a b i l i t y of point counting r e s u l t s , " Amer. J o u r y S c i . , v o l . 263, No. 1. White, W. H . , S i n c l a i r , A. J . , and Harakal , J . , (1967) personal communications. Yoder, H. S . , Stewart, D. B . , and Smith, J . R . , ( 1956 ) , "Fe ld-spar i n v e s t i g a t i o n s . " Ann. Rept. D i r . Geoph. L a b . . Year Book 55 . Stewart, D. B . , and Smith, J . R. ( 1 957 ) , "Ternary f e l d -spars ," Ann. Rept. D i r . Carnegie I n s t . . Wash. and T i l l e y , C. E . , ( 1 962 ) , "Orig in of basalt magmas: an experimental study of natura l and synthet ic systems," Jour. of P e t . . v o l . 3, No. 3. F I G U R E 2 V e r t i c a l C r o s s - s e c t i o n s S c a l e : ! I nch t o 1 0 0 0 f e e t H-0 00 _, 3500 J 300(9 H 2500 H r 4ooo r- 3500 \-3000 \-2500 3500 A 3000 A 2500 A B 1 v • i \ h 3500 \-3000 \-2500 B' 5O0<? -4 4500 -J o^oo H 3500 H 3 0 0 0 H Deep Gulch C r e e k r rSSOO ysooo r^H-500 y HOOO V 3500 \- 3000 F i g u r e 1 GEOLOGICAL MAP OF THE COPPER MOUNTAIN STOCK A N D VICINITY Scale: 1 inch to 1000 feet 5 0 0 0 5 0 0 1 0 0 0 1 5 0 0 feet o z LU u 10 TERTIARY? 8 o - b - c I L E G E N D TERTIARY M I D D L E E O C E N E P R I N C E T O N G R O U P A l l e n b y F o r m a t i o n : 10. D a c i t e tu f f* , b r e c c i a s , f l o w s . 11. S h a l e , a rkose , c o o l , c o n g l o m e r a t e , m i n o r rhyol i te tu f f . Lower V o l c a n i c F o r m a t i o n : 9. N fa r ico lo red a n d e s i t e , a n d e s i t e p o r p h y r y , b a s a l t . D Y K E S 8 a , m i n e d y k e s ; 8b, h o r n b l e n d e andes i te ; 8c , l a m p r o p h y r e . C O P P E R M O U N T A I N I N T R U S I O N S 7. M o n z o n i t e , s y e n i t e , minor t r a c h y t e a n d l a t i t e . 6 . P e g m a t i t e : s y e n i t e , p e r t h o s i t e . 5. M o n z o n i t e . 4 a . P y r o x e n i t e . 4 b . G a b b r o . 3. D i o r i t e . JURASSIC TRIASSIC U P P E R T R I A S S I C N I C O L A G R O U P 1. M a i n l y a n d e s i t e , a u g i t e d io r i te , a n d m i n o r tuff. 2 . M a i n l y a r g i l l i t e . a n d minor cong lomerate . G e o l o g y b y J K M o n t g o m e r y (1961, 1962. 1963) 1 MAP SYMBOLS Geolog ica l boundary (defined, ctpproximote,assumed) Bedding ( inc l ined .ver t ica l ) P r i m a r y f l o w structures ( incl ined, v e r t i c a l ) Fo ld a x e s (anticl ine, syncl ine) L ineat ion (hor i zonta l , inc l ined) Fault (de f ined , a p p r o x i m a t e ) S h e a r z o n e O p e n p i t D u m p Roods : h i g h w a y s e c o n d a r y j e e p tracks troili _ P h o t o centers Spo t e levat ions C u t l ines ( t ransmiss ion , w a t e r , etc.) S t r e a m s (def in i te , d r y or intermit tent ) Marsh -R a i l w a y Trestle Tunnel M + WW X '•TO / \ \ \ \ J-L. 

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