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Geology and petrogenesis of the Serb Creek intrusive complex near Smithers, British Columbia Sellmer, H. W. 1966

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GEOLOGY AND PETROGENESIS OP THE SERB CREEK INTRUSIVE COMPLEX NEAR SMITHERS, BRITISH COLUMBIA H. W. Sellmer B. Sc. University of B r i t i s h Columbia, 196^ A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n 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 , 1966 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t of the requirements fo 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 that the 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 that permiss ion fo r e x -t e n s i v e 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 . It i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n -c i a l gain s h a l l not be a l lowed wi thout my w r i t t e n p e r m i s s i o n . Department of GEOLOGY • The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date MAY 9TH. • 1966 ABSTRACT The Serb Creek molybdenite property is 26 miles west-northwest of Smithers, B. C. on the northeast flank of the Howson Range of the Coast Range physiographic province. The property l i e s within an upper mesozonal to lower epizonal batholithic offshoot of the Coast Range Intrusive Complex. Small irregular plutons and a series of northwesterly-striking dykes intrude the batholith. The rocks are quartz monzonitic and, in texture range from coarse-grained granitic to porphyritic. Plots of optic angle against composition show that feldspars are of intermediate structural type indicating an increasingly rapid rate of cooling from the oldest to the youngest intrusive body. This increase in the rate of cooling i s ascribed to smaller size of intrusive body with decreasing age. Plots of normative Q:AbOr ratios suggest that, i f one believes the magma to have formed "by anatexis, high pressures of volatiles, HC1, or of both were present during crystallization. Two general attitudes—N20° W to N^5° w and N75° E~control the emplacement of intrusive bodies, hydrothermal alteration, and, to a large extent, molybdenite mineralization. Hydrothermal alteration and molybdenite mineralization appear to be related to igneous activity because they are closely associated in time and space. - 1 -TABLE OF CONTENTS Page INTRODUCTION 2 Nature and Scope of the Study 2 Methods 2 Field Work 2 Laboratory Studies 2 History 4 Previous Work 4 Location and Accessibility 4 Physiography 6 Climate 6 Vegetation 8 Acknowledgments 8 GENERAL GEOLOGY 10 THE SERB CREEK INTRUSIONS 14 Distribution of Rock Types 14 Coarse-grained Quartz Monzonite 14 Fine-grained Quartz Monzonite 14 Porphyritic Quartz Monzonite 14 Early Quartz Monzonite Porphyry Dykes 15 Late Quartz Monzonite and Quartz Latite Porphyry Dykes.15 Altered Latite Dykes 15 Basic and Andesitic Dykes 15 Petrographic Descriptions 16 Coarse-grained Quartz Monzonite 16 Fine-grained Quartz Monzonite 22 Porphyritic Quartz Monzonite 27 Early Quartz Monzonite Porphyry Dykes 34 Quartz Latite and Quartz Monzonite Porphyry Dykes 38 Altered Latite Dykes 42 Basic and Intermediate Dykes 42 Thermal Histories of the Feldspars 42 Introduction 42 The Alkali Feldspars 43 Introduction 43 Determination of 2VX 43 Determination of Composition 46 Results of the Alk a l i Feldspar Study 55 Plagioclase Feldspars . . . . . 5 5 Introduction 55 Determination of Optic Angle (2VZ) 56 Composition Determinations 56 Thermal State of the Feldspars of the Serb Creek Complex.... 68 Structural Geology 69 Hydrothermal Alteration 70 Introduction 70 Groups of Alteration Assemblages 70 Group I Alteration 70 Group II Alteration 71 Group III Alteration 71 - i i -Sulphide Mineralization 75 Secondary Oxide Mineralization 76 Paragenesis 76 ORIGIN OP THE SERB CREEK INTRUSIVE COMPLEX 78 Sequence of Events 78 Origin of the Parent Magma 79 Environment of Emplacement 82 SUMMARY AND CONCLUSIONS 85 BIBLIOGRAPHY 88 LIST OP TABLES TABLE I: A2© of (201)Or before and after heating shown with corresponding weight per cent of orthoclase. Relative size of albite peaks, (20l)Ab, remaining after heating is also shown ^5 TABLE II: Composition of cryptoperthites of Serb Creek intrusive complex rock types. The correction is for the amount of albite l e f t in residual albite peaks which are listed in table I. A single average value is given for the corrected value ^7 TABLE III: Optic angle (2V X), composition, and types of crypto-perthites of the Serb Creek intrusive complex rock types. Composition is the corrected value taken from table II. Values of optic angle (2VX) are average values for rock types 53 TABLE IV: Optic angles (2VZ) and composition of plagioclase feldspars of the Serb Creek intrusive complex. Grains and zones studied in them are shown.... 58 LIST OF PIGURES FIGURE I; Modes of two specimens of coarse-grained quartz monzonite based on point-count thin-section analysis 17 FIGURE II: Modes of two specimens of fine-grained quartz monzonite based on point-count thin-section analysis 23 FIGURE III: Modes of two specimens of porphyritic quartz monzonite based on point-count thin-section analysis 28 - i i i -FIGURE IV: Modes of two specimens of early quartz monzonite porphyry dyke rock based on point-count thin-section analysis 35 FIGURE V: A2Q = 20.201 Feldspar minus 20.101 KBrO-3 plotted against weight per cent orthoclase (after Parsons) 48 FIGURE VI: Diagrammatic representation of diffractometer patterns of A, unheated (solid lines) and B, heated (dashed lines) a l k a l i feldspar 51 FIGURE VII: Plot of weight per cent orthoclase against optic angle (2VX) 54 FIGURE VIII: Thermal state of plagioclase from coarse-grained quartz monzonite (black squares) and transition varieties (circles) between i t and fine-grained quartz monzonite 62 FIGURE IX: Thermal state of plagioclase from fine-grained quartz monzonite (black squares) and transition varieties (circles) between i t and coarse-grained quartz monzonite 63 FIGURE X: Thermal state of plagioclases from porphyritic quartz monzonite 64 FIGURE XI: Thermal state of plagioclases from early quartz monzonite porphyry dyke 65 FIGURE XII: Thermal state of plagioclases from quartz l a t i t e porphyry dykes 66 FIGURE XIII: Composite of lines of best f i t taken from figures VIII to XII 67 FIGURE XIV: Geologic history of the Serb Creek molybdenite showing 80 FIGURE XV: Normative Q:Ah:0r ratios of eutectic points in granitic systems and experimentally produced anatectic melts at water pressure = 2000 bars ...81 LIST OF PLATES PLATE 1 3 Figure 1: View of the Serb Creek property from the north-west showing the rugged terrain in which the property is located. (The picture was taken in the earlier half of June.) Figure 2: Lateral view of the east half of the Serb Creek property looking to the east. - i v _ PLATE I I 5 F i g u r e 1: View to the n o r t h w e s t from Serb Creek p r o p e r t y i n e a r l y June. Sawtooth r i d g e i n the background i s comprised o f H a z e l t o n Group v o l c a n i c s . F i g u r e 2: View to the n o r t h e a s t l o o k i n g down Serb Creek from the p r o p e r t y i n e a r l y June. Note the U-shape o f t h e v a l l e y . PLATE I I I 7 F i g u r e 1: View to the southwest l o o k i n g up Serb Creek t o the Serb G l a c i e r i n mid-August. Note the U-shape o f the v a l l e y . F i g u r e 2 : Mid t o l a t e summer f l o r a o f the Serb Creek a r e a . PLATE IV 9 F i g u r e 1: Moraine Creek g l a c i a l f e a t u r e s w i t h p a r t o f Serb Creek p r o p e r t y i n the f o r e g r o u n d d u r i n g mid- June. F i g u r e 2: Toe o f Moraine Creek g l a c i e r w i t h l a t e r a l moraines i n t he f o r e g r o u n d . PLATE V 20 F i g u r e 1: E u h e d r a l sphene a s s o c i a t e d w i t h m a f i c m i n e r a l s i n c o a r s e - g r a i n e d q u a r t z monzonite (see page 19) . (x36, p l a i n l i g h t ) F i g u r e 2: P l a g i o c l a s e showing o s c i l l a t o r y z o n i n g , a l b i t e t w i n n i n g , and ragged a l b i t e - r i c h m u t u a l b o u n d a r i e s w i t h i n t e r s t i t i a l o r t h o c l a s e ( l a r g e l y a t e x t i n c t i o n ) . (x36, c r o s s e d n i c o l s ) , (see page 16) . PLATE V I 21 F i g u r e 1: P l a g i o c l a s e g r a i n showing two d i s t i n c t b r e a k s i n c r y s t a l l i z a t i o n and s t r o n g o s c i l l a t o r y - n o r m a l z o n i n g (see page 16) . (x36, c r o s s e d n i c o l s ) F i g u r e 2: Com b i n a t i o n t w i n n i n g i n p l a g i o c l a s e g r a i n s w i t h unmatched zones i n c o a r s e - g r a i n e d q u a r t z monzonite (see page 16) . (x36, c r o s s e d n i c o l s ) PLATE V I I ; 25 F i g u r e 1: T e x t u r e o f f i n e - g r a i n e d q u a r t z monzonite (see page 2 7 ) . Note the e u h e d r a l sphene j u s t l e f t o f c e n t r e . (x36, p l a i n l i g h t ) F i g u r e 2: E u h e d r a l p l a g i o c l a s e w i t h p a r t l y a l t e r e d c o r e s i n f i n e - g r a i n e d q u a r t z monzonite (see page 2 7 ) . (x36, c r o s s e d n i c o l s ) PLATE V I I I 26 F i g u r e 1: S u b - t r a c h y t i c t e x t u r e o f f i n e - g r a i n e d q u a r t z monzonite (see page 2 4 ) . (x36, c r o s s e d n i c o l s ) F i g u r e 2: S u b - p o i k i l i t i c o r t h o c l a s e g r a i n w i t h a l b i t e e x s o l u t i o n l a m e l l a e and i n c l u s i o n s o f q u a r t z and p l a g i o c l a s e (see page 2h). Rock type i s f i n e -g r a i n e d q u a r t z monzonite. ( x l 0 6 , c r o s s e d n i c o l s ) - V -PLATE IX 31 Figure 1: Texture of porphyritic quartz monzonite (see page 2 9 ) . (x3&, plain light) Figure 2: Texture of porphyritic quartz monzonite (see page 29). f x 3 6 , crossed nicols) PLATE X 32 Figure 1: Oscillatory zoning, combination twinning, and albite-rich rims in plagioclase phenoerysts of porphyritic quartz monzonite (see page 29). (x36, crossed nicols) Figure 2 : Chilled contact between fine-grained quartz monzonite and porphyritic quartz monzonite (see page 3 0 ) . (x36, plain light. PLATE XI 33 Figure 1: Texture of porphyritic quartz monzonite near chilled contact (see page 3 0 ) . (x36, plain light) Figure 2: Texture of porphyritic quartz monzonite near chilled contact (see page 3 0 ) . (x36, crossed nicols) PLATE XII 37 Figure 1: Texture of early quartz monzonite porphyry dyke rock—medial zone (see page 3 4 ) . (x36, crossed nicols) Figure 2: Large p o i k i l i t i c euhedral orthoclase phenocryst in early quartz monzonite porphyry dyke rock— near contact (see page 3 4 ) . (x36, crossed nicols) PLATE XIII 40 Figure 1: Texture of quartz l a t i t e porphyry (see page 3 9 ) . Note sphene upper right of centre. (xlOe?, crossed nicols) Figure 2: Texture of quartz l a t i t e porphyry. Note lack of well defined oscillatory zoning in plagioclase phenocryst largely at extinction (see page 3 9 ) . (x36, crossed nicols) PLATE XIV 41 Figure 1: Texture of quartz l a t i t e porphyry dyke rock. Note laths of plagioclase and euhedral hornblende (see page 3 9 ) . (x36, plain light) Figure 2: Texture of intermediate dyke. Note laths of hornblende and grains of biotite in a groundmass of plagioclase (see page 42). ( x l 0 6 , plain light) PLATE XV 72 Figure 1: Cryptoperthite vein (Group III alteration zone) (see page 75)• Note dusty inclusions of iron oxide. (x36, plain light) Figure 2 : As above. (x36, crossed nicols) - v i -PLATE XVI 73 F i g u r e 1: A l t e r a t i o n o f p o r p h y r i t i c q u a r t z monzonite w i t h development o f c h l o r i t e , s e r i c i t e , K - f e l d s p a r , and c a r b o n a t e . Group I I I c e n t r a l zone a l t e r a t i o n (see page 71) . (x36, p l a i n l i g h t ) F i g u r e 2: Carbonate, c h l o r i t e , s e r i c i t e a l t e r a t i o n o f Group I I I , c e n t r a l zone (see page 71) . (x36, c r o s s e d n i c o l s ) PLATE X V I I 7^ F i g u r e 1: Group I K - f e l d s p a r a l t e r a t i o n o f f i n e - g r a i n e d q u a r t z monzonite. D u s t y i n c l u s i o n s o f i r o n o x i d e a re c h a r a c t e r i s t i c o f secondary K - f e l d s p a r . (x36, p l a i n l i g h t ) (see page 71) F i g u r e 2: K - f e l d s p a r , e p i d o t e , and c h l o r i t e a l t e r a t i o n (Group I ) o f f r a c t u r e d c o a r s e - g r a i n e d q u a r t z monzonite. (x36, p l a i n l i g h t ) LIST OF MAPS MAP I : L o c a t i o n Map on page 1 MAP I I : G e o l o g i c a l Map o f the Serb Creek Area (1" = 1000') i n f o l d e r MAP I I I : G e o l o g i c a l Map (1" = 2 0 0 ' ) i n f o l d e r MAP IV: A l t e r a t i o n D i s t r i b u t i o n Map (1" = 500 ' ) i n f o l d e r S E R B C R E E K P R O J E C T O M I N E C A M D B C. Road — LOCATION M A P Helicopter Landing 8 3 5 miles Staked Area <(/ S C A L E 1=250,000 1 VANCOUVER — W.S -2-INTRODUCTION Nature and Scope of the Study This thesis i s concerned with the geological history of the Serb Creek intrusive complex. Both f i e l d and laboratory methods are used in this study and are described in detail below. The intrusive rock types in the area are shown on the geological map (map IV, in folder). This paper discusses their distribution, petrography, mineralogy, structure, alteration, and sulphide mineralization. A special study of a l k a l i and plagio-clase feldspars was undertaken with the object of clarifying the crystallization and cooling history of the various magmas and rocks. Methods Field Work A reconnaissance geological map was prepared on a 1"=500' base map prepared by Huntings Surveys. Locations in the f i e l d were plotted with the aid of airphotos. A detailed geological map was made on a scale of 1"=100' based on a topographic map, also prepared by Huntings Surveys. An area of about 6,500' by 2,500' was covered by this map. Control was provided by stations established by open stadia traverses run from permanent survey points. Chain and compass measurements were taken from temporary stadia points. Laboratory Studies  Laboratory work included thin-section study, point counts for modal composition, and analysis of the thermal state of a l k a l i and plagioclase feldspars using the universal stage and -3-PLATE I Figure 1 : View of the Serb Creek property from the northwest showing the rugged t e r r a i n i n which the property i s located. (The picture was taken i n the e a r l i e r h a l f of June.) - 4 -X-ray d i f f r a c t o m e t e r methods. H i s t o r y A l a r g e r u s t y zone w h i c h marks t h e m i n e r a l i z e d area, a t Serb Creek was f i r s t n o t i c e d by J . P. A l l a n i n 1964 i n e a r l y August. B e f o r e w i n t e r , 151 c l a i m s (see l o c a t i o n map, page 1) were s t a k e d , and mapping, c h i p s a m p l i n g , and pack-sack d r i l l i n g were u n d e r t a k e n . The w r i t e r p a r t i c i p a t e d i n a d e t a i l e d mapping programme o f the a r e a i n the 19^5 summer season. P r e v i o u s Work Other t h a n i n f o r m a t i o n c o n t a i n e d i n the 1964 Serb Creek r e p o r t ( p r i v a t e r e p o r t by J . P. A l l a n and J . N. S c h i n d l e r , 1964), some o f w h i c h has been m o d i f i e d "by t h i s s t u d y , l i t t l e i s known about the g e o l o g y o f the a r e a . The o n l y g e o l o g i c a l map o f the a r e a i s a c o m p i l a t i o n map p r e p a r e d by the G e o l o g i c a l Survey o f Canada i n 1944 ( P r e l i m i n a r y Map #44-23, J . E. Armstrong e t a l . ) on a s c a l e o f 1"=2 m i l e s . The l o c a t i o n o f the v o l c a n i c -i n t r u s i v e c o n t a c t i n the Serb Creek a r e a was found t o be i n a c c u r a t e on t h i s map. L o c a t i o n and A c c e s s i b i l i t y The Serb Creek m o l y b d e n i t e showing i s 26 m i l e s west-southwest o f S m i t h e r s , B r i t i s h Columbia on the n o r t h e a s t e r n e x t e n s i o n o f the Howson Range. The showing i s a t the head-w a t e r s o f Serb Creek (see l o c a t i o n map, page 1) on the n o r t h s i d e o f a 7»500-foot mountain. The a r e a i s a c c e s s i b l e o n l y by h e l i c o p t e r . A 2 5 - m i l e - l o n g -5-PIATE II Figure Is View to the northwest from Serb Creek property i n early June. Sawtooth ridge i n the background i s comprised of Hazelton Group volcanics. Figure 2: View to the northeast looking down Serb Creek from the property i n early June. Note the U-shaoe of the vall e y . -6-road leads from Smithers past McDonnell Lake to a helicopter landing f i e l d which is 15 miles from the showing. Although two other roads lead to points just as close to the area as the one described, the McDonnell Lake route i s the most practical be-cause i t involves the least vertical l i f t with the helicopter. Physiography The Howson Range, within which the Serb Creek property i s located, i s a narrow, rugged, north trending range within the eastern boundary of the Coast Range physiographic province. Serb Creek and Moraine Creek valleys are U-shaped (see figure 2 of plate II and figure 1 of plate III, on page 7 )• Glaciers (see plate IV, on page ^) that s t i l l occupy their heads are remnants of extensive glaciers that mantled valley floors with moraine and carved U-shaped valleys during the Pleistocene Epoch. The mountain slope (see plate I on page 3 ) on which the showing l i e s i s mainly outcrop and is divided into four some-what irregular zones: an upper bed-rock slope (up to elevation 6000 feet above sea level), an upper talus slope "below i t , a lower bed-rock slope, and a lower talus slope which leads onto the valley floor (elevation 3500 feet above sea level). The lower slope i s deeply dissected by northwesterly-trending gullies which act as funnels for snowslides and rock f a l l s . Climate Annual precipitation at Serb Creek i s 60-80 inches per year. Heavy snowfalls are common in winter and summers are cool with moderate r a i n f a l l . Snow patches remain a l l summer long in draws and much snow - 7 -PLATE III Figure 1: View to the southwest looking up Serb Greek to the Serb Glacier i n mid-August. Note the U-shape of the val l e y . Figure 2: Hid to late summer f l o r a of the Serb Creek area. -8-c o v e r s u r v i v e s u n t i l mid-June o r even l a t e r (see p l a t e I I on page 5 ) . The f i r s t heavy s n o w f a l l can be ex p e c t e d as e a r l y as mid-October. Old s l i d e s c a r s (see p l a t e I I , on page s ) suggest t h a t s l i d e s a r e a common f e a t u r e i n e a r l y s p r i n g . V e g e t a t i o n Balsam, s p r u c e , hemlock, and some y e l l o w c e d a r a r e found i n c r e e k v a l l e y s . S t u n t e d growth i s p r e s e n t (see p l a t e I , on page 3 ) up t o an e l e v a t i o n o f 4000 f e e t i n s l i d e - a r e a s and g u l l i e s and 4500 f e e t on r i d g e s and s p u r s between g u l l i e s . The u n d e r b r u s h i s a t h i c k t a n g l e o f s l i d e a l d e r , buck-b r u s h , and s a l a l i n l e s s d e n s e l y - f o r e s t e d a r e a s . Acknowledgments The w r i t e r acknowledges a. debt o f g r a t i t u d e t o Dr. K. C. McTaggart who a c t e d as s u p e r v i s o r f o r t h i s t h e s i s and gave much h e l p f u l a d v i c e . Acknowledgments are t e n d e r e d t o M e s s r s . R. A. B a r k e r and J . P. S. A l l a n o f Amax E x p l o r a t i o n I n c . who gave m a t e r i a l a i d and p e r m i s s i o n t o use i n f o r m a t i o n c o m p i l e d i n the summer as a b a s i s f o r the t h e s i s . Mr. H. P i r e s o f the same Company draughted the f i n a l copy o f f i e l d maps p r e p a r e d by the w r i t e r and A. G-ambardella. The w r i t e r w i s h e s t o thank Dr. E. H. Gardner f o r use o f the X-ray d i f f r a c t o m e t e r * i n S o i l S c i e n c e s . Acknowledgments are a l s o due t o Dr. A. J . S i n c l a i r o f the Geology Department f o r t e c h n i c a l a d v i c e and t o gr a d u a t e s t u d e n t s i n the Department who gave a d v i c e and encouragement i n t h i s s t u d y . * The d i f f r a c t o m e t e r u n i t was purchased by the Department o f S o i l S c i e n c e s w i t h a g r a n t from the N a t i o n a l R e s e a r c h C o u n c i l . -9-PLATE IV Figure 1: Moraine Greek g l a c i a l f e atures w i t h part of Serb Creek property i n the foreground during mid-June. Figure 2: Toe of Moraine Creek g l a c i e r w i t h l a t e r a l moraines i n the foreground. -10 -GENERAL GEOLOGY The Serb Creek m o l y b d e n i t e showing i s s i t u a t e d i n a q u a r t z monzonite i n t r u s i v e complex thought t o be o f l a t e Mesozoic age ( J . E. Armstrong e t a l . , 1944). The i n t r u s i o n s c u t dark g r e e n , medium- t o f i n e - g r a i n e d , massive b a s a l t i c and a n d e s i t i c f l o w s o f the Mesozoic H a z e l t o n Group. Two s m a l l q u a r t z monzonite p l u t o n s a r e l o c a t e d w i t h i n the main i n t r u s i v e body i n the a r e a o f the m o l y b d e n i t e showing. A l l o f the above r o c k t y p e s a r e c u t by numerous n o r t h w e s t e r l y - t r e n d i n g dykes. Three phases w h i c h comprise the i n t r u s i v e complex a r e d i s t i n g u i s h e d on the b a s i s o f t e x t u r e and f i e l d r e l a t i o n s h i p s . These a re (see f i g u r e XIV, on page s o ) c o a r s e - g r a i n e d q u a r t z monzonite, w h i c h comprises a l a r g e p a r t o f the complex; f i n e -g r a i n e d q u a r t z monzonite, w h i c h i n t r u d e s c o a r s e - g r a i n e d q u a r t z monzonite i n the form o f a 1-g—mile-long by -g--mile-wide p l u t o n w i t h a sharp t o g r a d a t i o n a l c o n t a c t ; and p o r p h y r i t i c q u a r t z monzonite, w h i c h o c c u r s as a s m a l l , 1 9 0 0-feet-long "by 500-feet-wide, h i g h l y i r r e g u l a r p l u t o n w i t h a c h i l l e d t o a b r u p t u n c h i l l e d c o n t a c t a g a i n s t b o t h o f the above r o c k t y p e s . C o a r s e - g r a i n e d q u a r t z monzonite i s h o l o c r y s t a l l i n e e q u i -g r a n u l a r , l o c a l l y h o l o c r y s t a l l i n e s u b - p o r p h y r i t i c . I n sub-p o r p h y r i t i c specimens, w h i t e f e l d s p a r s a r e c o n s p i c u o u s l y l a r g e a g a i n s t groundmass m i n e r a l s a l t h o u g h a l l a r e p h a n e r i t i c . S m a l l d i f f e r e n c e s i n modes are m a i n l y o f r e l a t i v e p r o p o r t i o n s o f hornblende and b i o t i t e . Sphene i s a c o n s p i c u o u s , macro-s c o p i c a l l y v i s i b l e a c c e s s o r y m i n e r a l . I n the a r e a o f the m o l y b d e n i t e showing two o t h e r phases o f the i n t r u s i v e complex have been r e c o g n i z e d . The more abundant - l i -on these i s fine-grained quartz monzonite whose distribution roughly delimits the area of molybdenite mineralization. Fine-grained quartz monzonite i s sub-porphyritic to sub-equigranular. Porphyritic appearance becomes pronounced near the contact with coarse-grained quartz monzonite. The unaltered rock i s grey, with a foliation expressed by biotite, the only mafic mineral, and has a "salt and pepper" appearance. The third phase is porphyritic quartz monzonite. It differs from fine-grained quartz monzonite in mafic content and porphyri-t i c texture. Porphyritic quartz monzonite has a chilled contact against fine-grained quartz monzonite and in some places contains inclusions of fine-grained quartz monzonite. Porphyritic quartz monzonite i s found mainly in the central part of the showing. Offshoots in the form of dykes and irregular apophyses intrude the surrounding fine-grained quartz monzonite. These rock types are older than sulphide mineralization (see figure XIV, on page so). A rock type which occurs in the map area (see map III, in folder) as a small elongate pluton and also as a large dyke, contains disseminated molybdenite and pyrite as well as quartz-molybdenite veins. Although this rock type is similar in composition and texture to the younger dyke rocks described below, i t has been distinguished as "Intra-mineral" or "Early quartz monzonite porphyry" because of i t s close temporal association with the period of molybdenite mineralization. A swarm of acid porphyry dykes and occasional andesitic and basaltic dykes striking between N 2 0°W and N^5°W with a steep southwesterly dip (see maps II & III, in folder) cut the -12-e a s t e r n p a r t o f the map a r e a . I n the f i e l d , a c i d dykes were c l a s s i f i e d i n t o f o u r t y p e s : 1. Q u a r t z - f e l d s p a r p o r p h y r y dykes. 2. Grey f e l d s p a r p o r p h y r y dykes. 3. H o r n b l e n d e - b e a r i n g f e l d s p a r p o r p h y r y dykes. 4. "Brown" dykes. L a b o r a t o r y s t u d i e s have shown the f i r s t t h r e e t y p e s t o be v e r y s i m i l a r i n t e x t u r e and c o m p o s i t i o n . These have been grouped under " l a t e q u a r t z monzonite and q u a r t z l a t i t e p o r p h y r y dykes". The "brown" dykes, a l t h o u g h p r o b a b l y s i m i l a r i n c o m p o s i t i o n t o the o t h e r t y p e s , a r e d i s t i n g u i s h e d by t h e i r c h a r a c t e r i s t i c a l t e r a t i o n w h i c h has r e s u l t e d i n a g r e e n i s h -brown c o l o u r and a f i n e - g r a i n e d t e x t u r e . The "brown" dykes have been renamed " a l t e r e d l a t i t e d ykes". A n d e s i t e dykes, l a b e l l e d " i n t e r m e d i a t e dykes" on the maps, have a f i n e - g r a i n e d to a p h a n i t i c t e x t u r e , d a r k - g r e e n t o medium-g r e e n c o l o u r , and a r e g e n e r a l l y found i n the same a r e a as q u a r t z monzonite and q u a r t z l a t i t e p o r p h y r y dykes. B a s a l t i c dykes have "been found o n l y o u t s i d e the r u s t -s t a i n e d zone (see map I I , i n f o l d e r ) . They are d a r k g r e y t o b l a c k w i t h a p h a n i t i c t e x t u r e and g e n e r a l l y a r e l e s s than two f e e t wide. The c o n t a c t between the i n t r u s i v e complex and v o l c a n i c r o c k s o f the H a z e l t o n Group was mapped a t the head o f Moraine Creek and i n the n o r t h w e s t e r n c i r q u e o f Serb Creek (see map I I , i n f o l d e r ) . The c o n t a c t , w h i c h d i p s away from the complex a t a n g l e s r a n g i n g from kQ t o 80 d e g r e e s , i s a b r u p t i n most p l a c e s . A d j a c e n t t o c o n t a c t s , v o l c a n i c s , l o c a l l y i n t e n s e l y - 1 3 -s i l i c i f i e d , have been metamorphosed t o h o r n f e l s . Subsequent h y d r o t h e r m a l a l t e r a t i o n has d e v e l o p e d e p i d o t e , s i l i c a , and c h l o r i t e i n the h o r n f e l s . B a r r e n q u a r t z - v e i n s t o c k w o r k s e x i s t near the c o n t a c t i n the v o l c a n i c s . M i n e r a l i z a t i o n a t the c o n t a c t c o n s i s t s o f minor amounts o f h e m a t i t e , m a g n e t i t e , p y r i t e , p y r r h o t i t e , and c h a l c o p y r i t e . These m i n e r a l s a r e commonly found i n v e i n s and f r a c t u r e s w i t h e p i d o t e and q u a r t z . C o a r s e - g r a i n e d q u a r t z monzonite i s c h i l l e d t o an a p h a n i t i c q u a r t z l a t i t e over a w i d t h o f s e v e r a l f e e t or more a t the c o n t a c t and shows a f o l i a t i o n and s w i r l s o f m a f i c m i n e r a l s caused by f l o w p a r a l l e l t o the c o n t a c t . G r a i n s i z e o f c o a r s e -g r a i n e d q u a r t z monzonite d e c r e a s e s p r o g r e s s i v e l y and the r o c k becomes p o r p h y r i t i c towards th e c o n t a c t . A p l i t i c and p e g m a t i t i c apophyses from c o a r s e - g r a i n e d q u a r t z monzonite a r e common i n the v o l c a n i c s . -14-THE SERB CREEK INTRUSIONS D i s t r i b u t i o n o f the Rock Types Rock t y p e s i n the a r e a where d e t a i l e d mapping was done (see maps I I & I I I , i n f o l d e r ) a r e v a r i o u s phases o f the Serb Creek i n t r u s i v e complex. I n t r u s i v e forms i n c l u d e s m a l l i r r e g u l a r p l u t o n s and dykes. S i n c e the s i z e and shape o f t h e s e b o d i e s i s o f importance i n c o n s i d e r i n g t h e i r h i s t o r y , the d i s t r i b u t i o n o f each r o c k t y p e , and the r e l a t i v e time o f emplacement w i l l be d i s c u s s e d . C o a r s e - g r a i n e d Quartz Monzonite C o a r s e - g r a i n e d q u a r t z monzonite i s the main i n t r u s i v e mass. I t i s the e a r l i e s t phase o f the i n t r u s i v e complex and i n t r u d e s v o l c a n i c r o c k s o f the H a z e l t o n Group. I t u n d e r l i e s some s c o r e s o f square m i l e s i n the a r e a s u r r o u n d i n g the m o l y b d e n i t e showing. F i n e - g r a i n e d Quartz Monzonite F i n e - g r a i n e d q u a r t z monzonite, w h i c h u n d e r l i e s most o f the map a r e a examined i n d e t a i l (see map I I I , i n f o l d e r ) o c c u r s as an i r r e g u l a r i n t r u s i v e body w h i c h t r e n d s n o r t h e a s t e r l y and has a l e n g t h o f 1-g- m i l e s and a w i d t h o f -§• m i l e . F i n e - g r a i n e d q u a r t z monzonite i s i n t r u s i v e i n t o c o a r s e - g r a i n e d q u a r t z monzonite and i s c o n t a i n e d e n t i r e l y w i t h i n i t . P o r p h y r i t i c Quartz Monzonite The t h i r d i n t r u s i v e body, p o r p h y r i t i c q u a r t z monzonite, i n t r u d e s the above two phases and has b o t h a b r u p t u n c h i l l e d and c h i l l e d c o n t a c t s a g a i n s t them. I t s shape i s e x t r e m e l y i r r e g u l a r . Many p o r p h y r i t i c q u a r t z monzonite apophyses i n t r u d e o t h e r r o c k t y p e s . P o r p h y r i t i c q u a r t z monzonite o c c u r s i n the -15-m i d d l e p a r t o f the map a r e a (see map I I I , i n f o l d e r ) where i t forms s e v e r a l i r r e g u l a r b o d i e s w h i c h range from 100 f e e t wide and 300 f e e t l o n g t o 500 f e e t wide and 1000 f e e t l o n g . E a r l y Q u a r t z Monzonite P o r p h y r y Dykes T h i s r o c k type o c c u r s as two d i s t i n c t b o d i e s i n the map a r e a (see map I I I , i n f o l d e r ) . E a r l y q u a r t z monzonite p o r p h y r y forms a v e r t i c a l dyke 100 t o 150 f e e t wide i n draw 200E*. I n draw 1400W i t o c c u r s as an a l t e r e d , i r r e g u l a r body w h i c h s t r i k e s n o r t h e a s t on i t s n o r t h e r n end and southwest a t i t s s o u t h e r n e x t r e m i t y . A s m a l l dyke w h i c h s t r i k e s n o r t h e a s t a l s o o c c u r s i n draw 2300W. L a t e Q u a r t z Monzonite and Quartz L a t i t e P o r p h y r y Dykes L a t e q u a r t z monzonite and q u a r t z l a t i t e p o r p h y r y dykes o c c u r as a s e r i e s o f n o r t h - n o r t h w e s t e r l y - s t r i k i n g dykes w h i c h range from s e v e r a l f e e t t o over 200 f e e t i n w i d t h . A l l a r e n e a r l y v e r t i c a l and o c c u r e a s t o f draw 200E w i t h two e x c e p t i o n s w h i c h o c c u r a t the head o f draw 2300W (see map I I I , i n f o l d e r ) . L o c a l l y , as i n draw 878E and a t the head of i t , t h e y form most o f the o u t c r o p and a t t a i n t h i c k n e s s e s i n e x c e s s o f 200 f e e t . A l t e r e d L a t i t e Dykes A l t e r e d l a t i t e dykes o c c u r i n the same a r e a as q u a r t z monzonite and q u a r t z l a t i t e p o r p h y r y dykes and have the same g e n e r a l a t t i t u d e . A l t e r e d l a t i t e dykes a r e younger t h a n q u a r t z monzonite and q u a r t z l a t i t e p o r p h y r y dykes w h i c h they i n t r u d e . T h e i r w i d t h s range from l e s s than 10 t o 100 f e e t . B a s i c and A n d e s i t i c Dykes B a s i c and a n d e s i t i c (named " i n t e r m e d i a t e " dykes on map I I I , * Draw 200E i s one o f many draws or g u l l e y s on the mountain s i d e . S e v e r a l draws a r e named i n t h i s way on map I I I and w i l l he r e f e r r e d t o i n subsequent pages. -16-in folder) dykes are found in the same general area as the other dyke rocks. They are commonly less than 10 feet wide and average 3 feet wide. At least two ages were noted. One group i s earlier than the quartz monzonite and quartz l a t i t e porphyry dykes; the other is later. Petrographic Descriptions  Coarse-grained Quartz Monzonite The mode of two specimens of coarse-grained quartz monzonite i s shown in figure I (see page 1 7 ) . The rock i s coarse-grained with scattered, conspicuously large grains of plagioclase. The mafic minerals—green hornblende and black biotite in variable proportions—are largely subhedral or anhedral. Biotite commonly has a ragged outline. Plagioclase is subhedral to euhedral or anhedral as small grains. Quartz and pink a l k a l i feldspars are largely i n t e r s t i t i a l (see figure 2, plate V, on page 20) and anhedral. Quartz uncommonly and cryptoperthite rarely form large anhedral to subhedral grains. In thin-section plagioclase is seen to be euhedral to subhedral (see figures 1 and 2, plate VI, on page 2.1). A l l grains show pronounced zoning which i s weakly oscillatory with a strong normal trend (see figure 2, plate V, on page 2.0). The cores of the large grains have a composition of An^^_^Q, the rims vary between An-^ to An^Q. One or two distinct breaks in the continuity of crystallization are evident in most crystals as narrow zones of alteration which occur between An-^ Q and An^ Q (see figure 1, plate VI, on page 2/). Combination twinning (Ross, J. V., 1957) and two distinct cores with unmatching zones covered by later zoning (see figure 2, plate VI, on page aJ) are -17-6 5 X S T - 5 8 50. 0> i/i o o CL 40. S 30. u a 20 i a. 10 41 •o 2 C M u O a> C M C o X o 5 in 0) O W cn 01 O o < C M 65XST - 93 50_ cn JS o o '5) r3 C u 40_ 30_ £ 2 0 j 10_ in JS o o N in >- C M « C M o DO 0) T3 C 0) . a c o I • in 0) o VI cn at u o < FIGURE I: Modes of two specimens of coarse-grained quartz monzonite based on point-count thin-section analysis. -18-f e a t u r e s shown by r e l a t i v e l y l a r g e p l a g i o c l a s e c r y s t a l s i n c o a r s e - g r a i n e d q u a r t z monzonite. P l a g i o c l a s e g r a i n s are n e a r l y f r e e o f p r i m a r y i n c l u s i o n s e x c e p t f o r r a r e hornblende i n some o f the s m a l l g r a i n s . Where p l a g i o c l a s e i s i n c o n t a c t w i t h a l k a l i f e l d s p a r s , an a l h i t e - r i c h mutual boundary i s p r e s e n t . A n h e d r a l a l k a l i f e l d s p a r s ( c r y p t o p e r t h i t e and a l b i t e ) a r e l a t e i n the o r d e r o f c r y s t a l l i z a t i o n . Some l a r g e , a p p a r e n t l y e a r l i e r , a n h e d r a l t o s u b h e d r a l g r a i n s o f c r y p t o p e r t h i t e p o i k i l i t i c a l l y e n c l o s e b i o t i t e , h o r n b l e n d e , p l a g i o c l a s e , a p a t i t e , m a g n e t i t e , sphene, and r a r e l y , q u a r t z . I t would seem t h e r e f o r e , t h a t b o t h a l k a l i f e l d s p a r s and q u a r t z a r e l a t e i n t h e o r d e r o f c r y s t a l l i z a t i o n . C r y p t o p e r t h i t e s have i r r e g u l a r , a l b i t e - r i c h m u t u a l b o u n d a r i e s w i t h p l a g i o c l a s e g r a i n s ; w i t h q u a r t z g r a i n s the b o u n d a r i e s a r e smooth and rounded. The b u l k c o m p o s i t i o n o f c r y p t o p e r t h i t e was found t o be Org-j^Ab^ by X-ray methods. Quartz i s abundant i n c o a r s e - g r a i n e d q u a r t z monzonite as a n h e d r a l i n t e r s t i t i a l g r a i n s o f v a r i o u s s i z e s . Quartz shows u n d u l o s e e x t i n c t i o n and i n c l u s i o n s o f a l l o t h e r m i n e r a l s . I t i s found i n b i o t i t e g r a i n s as l a t e r - f o r m e d i n c l u s i o n s a l o n g c l e a v a g e p l a n e s . M a f i c m i n e r a l s are h o r n b l e n d e and b i o t i t e i n v a r i a b l e p r o p o r t i o n s , but t o t a l m a f i c c o n t e n t i s r e l a t i v e l y c o n s t a n t . Hornblende i s commonly e u h e d r a l t o s u b h e d r a l and p r i s m a t i c w i t h p a l e brown t o g r e e n p l e o c h r o i s m . Much hor n b l e n d e shows r e s o r p t i o n e f f e c t s and i s r e p l a c e d by b i o t i t e . T w inning on (100) i s common. - 1 9 -B i o t i t e shows a l a r g e range i n g r a i n s i z e and i s commonly charged w i t h i n c l u s i o n s o f m i n e r a l s such as q u a r t z , h o r n b l e n d e , 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 s , and a c c e s s o r y m i n e r a l s . B i o t i t e may a l s o o c c u r as i n c l u s i o n s i n c r y p t o p e r t h i t e s . A t h i r d h a b i t i s as s m a l l i n t e r s t i t i a l a n h e d r a l g r a i n s . Much b i o t i t e appears l a t e i n the p a r a g e n e t i c sequence. Two v a r i e t i e s , g r een and brown b i o t i t e a r e p r e s e n t — t h e g r e e n v a r i e t y i n l e s s e r amounts as a re p l a c e m e n t o r a l t e r a t i o n o f brown " b i o t i t e . H o u r g l a s s e x t i n c t i o n and bent c l e a v a g e s a r e common i n l a r g e b i o t i t e g r a i n s . A c c e s s o r y m i n e r a l s i n c l u d e m a g n e t i t e , sphene, and a p a t i t e . M a g n e t i t e o c c u r s as p a r t l y r e s o r b e d g r a i n s a s s o c i a t e d w i t h m a f i c m i n e r a l s o r w i t h c l u s t e r s o f o t h e r a c c e s s o r y m i n e r a l s . Sphene, the most c o n s p i c u o u s a c c e s s o r y m i n e r a l , o c c u r s as l a r g e diamond-shaped e u h e d r a l g r a i n s . Sphene i s i n t e r s t i t i a l and commonly a d j a c e n t t o or as an i n c l u s i o n i n b i o t i t e o r ho r n b l e n d e (see f i g u r e 1 , p l a t e V, on page 20) . I t has i n c l u s i o n s o f an opaque m i n e r a l , p o s s i b l y i l m e n i t e . A p a t i t e o c c u r s i n two d i s t i n c t h a b i t s . E a r l y a p a t i t e o c c u r s as minute l a t h s i n f e l d s p a r s and m a f i c s . A l a t e r v a r i e t y i s e u h e d r a l , l a r g e , and a s s o c i a t e d w i t h c l u s t e r s o f o t h e r a c c e s s o r y m i n e r a l s o r w i t h m a f i c m i n e r a l s . I n some specimens e p i d o t e o c c u r s a p p a r e n t l y as a d e u t e r i c a l t e r a t i o n accompanied by metasomatic a d d i t i o n o f K - f e l d s p a r . E p i d o t e i s found a l o n g f r a c t u r e s , i n p a r t i n g s o f m a g n e t i t e , and i n c l e a v a g e s o f m a f i c m i n e r a l s . K - f e l d s p a r a l t e r a t i o n has r e n d e r e d p r i m a r y a l k a l i f e l d s p a r s d u s t y i n appearance. D e u t e r i c a l t e r a t i o n g rades i n t o and i s hard t o d i s t i n g u i s h from h y d r o -t h e r m a l a l t e r a t i o n . The t e x t u r e o f c o a r s e - g r a i n e d q u a r t z monzonite i s - 2 0 -P L A T E V Figure 2 : P l a g i o c l a s e showing o s c i l l a t o r y zoning, a l b i t e twinning, and ragged a l b i t e - r i c h mutual boundaries w i t h i n t e r s t i t i a l o r t hoclase ( l a r g e l y at e x t i n c t i o n ) (x.36, crossed n i c o l s ) , (see page 16). -21-PLATE V I Figure 1: Plagioclase grain showing two d i s t i n c t breaks i n c r y s t a l l i z a t i o n and strong oscillatory-normal zoning (see page is). (x36, crossed n i c o l s ) Figure 2: Combination twinning i n plagioclase grains with unmatched zones i n coarse-grained quartz monzonite (see page 16). (x36, crossed n i c o l s ) -22-h y p i d i o m o r p h i c g r a n u l a r . P l a g i o c l a s e ( A n ^ ) and hornblende were p r o b a b l y the f i r s t m i n e r a l s t o c r y s t a l l i z e . When p l a g i o -c l a s e r e a c h e d a c o m p o s i t i o n o f An-^g t o An£o an i n t e r r u p t i o n i n growth may have o c c u r r e d . Some c r y p t o p e r t h i t e was formed a t or n e a r t h i s t i m e . B i o t i t e , a l k a l i f e l d s p a r s , a l b i t i c p l a g i o -c l a s e , and f i n a l l y q u a r t z completed t h e i r c r y s t a l l i z a t i o n i n t h a t o r d e r . A c c e s s o r y m i n e r a l s a r e d i f f i c u l t t o p l a c e i n t h e i r p a r a -g e n e t i c sequence. M a g n e t i t e appears t o have formed e a r l y a l o n g w i t h some a p a t i t e . A second g e n e r a t i o n o f a p a t i t e and sphene were among the l a s t m i n e r a l s t o c r y s t a l l i z e . F i n e - g r a i n e d Quartz Monzonite Modes o f f i n e - g r a i n e d q u a r t z monzonite a r e shown i n f i g u r e I I (see page 23). The r o c k i s g r e y i n c o l o u r w i t h a " s a l t and pepper" appearance. The homogeneity o f f i n e - g r a i n e d q u a r t z monzonite i s br o k e n o c c a s i o n a l l y by l a r g e p l a g i o c l a s e o r b i o t i t e c r y s t a l s . I n g e n e r a l b i o t i t e i s f i n e - g r a i n e d and d e f i n e s a co n s p i c u o u s f o l i a t i o n . A l t h o u g h the amount o f b i o t i t e and p l a g i o c l a s e p h e n o e r y s t s i s v a r i a b l e — e s p e c i a l l y n e a r c o n t a c t s w i t h c o a r s e - g r a i n e d q u a r t z m o n z o n i t e — t h e y u s u a l l y form l e s s t h a n 10 p e r cent o f the whole r o c k . A l k a l i f e l d s p a r s and q u a r t z a r e n o t c o n s p i c u o u s i n t h i s r o c k t y p e . P l a g i o c l a s e i s seen t o range i n c o m p o s i t i o n from about An^Q i n c o r e s o f l a r g e r p h e n o e r y s t s t o An^Q on t h e i r r i m s . P l a g i o -c l a s e g r a i n s a r e g e n e r a l l y e u h e d r a l t o s u b h e d r a l l a t h s . Zoning i s o s c i l l a t o r y - n o r m a l w i t h weak o s c i l l a t o r y zones except i n l a r g e p h e n o e r y s t s w h i c h a r e s i m i l a r t o those o f c o a r s e - g r a i n e d q u a r t z monzonite. Some l a r g e g r a i n s show a r e v e r s e t r e n d i n FIGURE II: Modes o f two specimens o f f i n e - g r a i n e d q u a r t z monzonite based on p o i n t - c o u n t t h i n - s e c t i o n a n a l y s i s . -24-z o n i n g near t h e i r r i m s . T h i s t r e n d becomes normal a g a i n as the r i m i s approached. M u t u a l b o u n d a r i e s o f p l a g i o c l a s e and a l k a l i f e l d s p a r s a r e a l b i t e - r i c h . S m a l l l a t h s o f p l a g i o c l a s e a r e i n t r a c h i t o i d arrangement (see f i g u r e 1, p l a t e V I I I , on page 2 . 6 ) , p a r t i c u l a r l y where i n c o n t a c t w i t h f i n e - g r a i n e d i n t e r s t i t i a l m a t e r i a l . C r y p t o p e r t h i t e i s l a r g e l y i n t e r s t i t i a l i n the groundmass. Some l a r g e a n h e d r a l g r a i n s a r e ragged i n o u t l i n e and have a s u b - p o i k i l i t i c t e x t u r e (see f i g u r e 2, p l a t e V I I I , on page 2 6 ) . I n the f i n e - g r a i n e d groundmass a l k a l i f e l d s p a r s and q u a r t z a r e commonly i n t i m a t e l y i n t e r g r o w n . C r y p t o p e r t h i t e has a b u l k c o m p o s i t i o n 0rygAb22* L i k e a l k a l i f e l d s p a r , q u a r t z i s i n t e r s t i t i a l and r a r e l y o c c u r s as l a r g e a n h e d r a l g r a i n s . I n t e r l o c k i n g b o u n d a r i e s and we a k l y u n d u l o s e e x t i n c t i o n a r e c h a r a c t e r i s t i c o f q u a r t z g r a i n s . B i o t i t e o c c u r s as a n h e d r a l , c h i e f l y i n t e r s t i t i a l g r a i n s o f the brown v a r i e t y . S m a l l amounts o f gr e e n b i o t i t e r e p l a c e brown b i o t i t e . Coarse g r a i n s o c c u r as p h e n o c r y s t s w h i c h a r e ragged i n o u t l i n e and have a somewhat undulo s e e x t i n c t i o n . A c c e s s o r y m i n e r a l s and p y r i t e a r e c l o s e l y a s s o c i a t e d w i t h b i o t i t e and commonly have r e p l a c e d i t . S m a l l n e e d l e s o f r u t i l e o c c u r i n some g r a i n s o f b i o t i t e . Some b i o t i t e i s e l o n g a t e s u g g e s t i n g a complete r e p l a c e m e n t o f p r e - e x i s t i n g h o r n b l e n d e . The c h i e f a c c e s s o r y m i n e r a l i s secondary p y r i t e w h i c h has r e p l a c e d m a g n e t i t e and, i n p a r t , " b i o t i t e . R u t i l e i s p r e s e n t i n s m a l l amounts. Sphene i s p r e s e n t as l a r g e diamond-shaped e u h e d r a l g r a i n s w i t h i n c l u s i o n s ( i l m e n i t e ? ) . A p a t i t e o c c u r s Figure 1: Texture of fine-grained quartz monzonite (see page t l ) . Note the euhedral sphene just l e f t of centre. ( x 3 6 , p l a i n l i g h t ) -26-PLATE Y I I I Figure 1: Sub-trachytic texture of fine-grained quartz monzonite (see page 24). (x^6, crossed n i c o l s ) Figure 2: S u b - p o i k i l i t i c orthoclase grain with a l b i t e ex-solution lamellae and inclusions of quartz and plagioclase (see page z-f). Hock type i s f i n e -grained quartz monzonite. (xl06, crossed n i c o l s ) - 2 7 -as i n c l u s i o n s and r e l a t i v e l y c o a r s e i n t e r s t i t i a l , e u h e d r a l g r a i n s . The t e x t u r e o f f i n e - g r a i n e d q u a r t z monzonite (see p l a t e V I I , on page 25", and f i g u r e 1, p l a t e V I I I , on page z&) i s t r a c h y t i c and s u b - p o r p h y r i t i c . P l a g i o c l a s e was formed f i r s t , p o s s i b l y a l o n g w i t h some e a r l y h o r n b l e n d e w h i c h was l a t e r r e s o r b e d and r e p l a c e d by " b i o t i t e . Q u a r t z and a l k a l i f e l d s p a r s a r e c h a r a c t e r i s t i c a l l y i n t e r s t i t i a l and l a t e i n the p a r a g e n e t i c sequence. The a c c e s s o r y m i n e r a l s sphene, a p a t i t e , and r u t i l e are d i s t r i b u t e d much as they a r e i n c o a r s e - g r a i n e d q u a r t z ' m o n z o n i t e . P y r i t e , as r e p l a c e m e n t o f m a g n e t i t e and p r o b a b l y some b i o t i t e , i s a l a t e r d e u t e r i c m i n e r a l r e l a t e d to m i n e r a l i z a t i o n and a l t e r a t i o n . P o r p h y r i t i c Q u a r t z Monzonite Modes o f two specimens o f p o r p h y r i t i c q u a r t z monzonite a r e shown i n f i g u r e I I I (see page z&). I n the handspecimen p o r p h y r i t i c q u a r t z monzonite i s d a r k e r t h a n f i n e - g r a i n e d q u a r t z monzonite. T h i s d i f f e r e n c e i n appearance i s caused by f i n e g r a i n - s i z e and s m a l l abundant b i o t i t e g r a i n s i n p o r p h y r i t i c q u a r t z monzonite. Large g r a i n s o f b i o t i t e and p l a g i o c l a s e a r e s c a t t e r e d t h r o u g h o u t as i n f i n e - g r a i n e d q u a r t z monzonite. A few g r a i n s o f c r y p t o p e r t h i t e a l s o o c c u r as p h e n o c r y s t s . T h i s r o c k does n o t have a f o l i a t i o n . D i s t i n g u i s h i n g f e a t u r e s i n the handspecimen a r e : f i n e g r a i n - s i z e , l a c k o f f o l i a t i o n , and d a r k c o l o r . I n t h i n - s e c t i o n , the c o m p o s i t i o n o f p l a g i o c l a s e c r y s t a l s w h i c h show s t r o n g o s c i l l a t o r y - n o r m a l z o n i n g , i s An^Q t o An, i n FIGURE III: Modes o f two specimens o f p o r p h y r i t i c q u a r t z monzonite based on p o i n t - c o u n t t h i n - s e c t i o n a n a l y s i s . - 2 9 -the core and A ^ Q or more sodic on the rims. Plagioclase in the fine-grained groundmass is probably more sodic than An-^. Plagioclase phenocrysts (see figures 1 & 2 , plate IX, on page 3*) of porphyritic specimens show embayed contacts with fine grains of the groundmass. Large grains of plagioclase with oscillatory-normal zoning also occur (see figure 1 , plate X, on page 3 2 ) . Evidence of a liquid magmatic stage is shown by the presence of combination twinning (Ross J. V., 1957) in plagioclase phenocrysts. In porphyritic quartz monzonite cryptoperthite i s found as large anhedral phenocrysts and as fine interlocking grains in the groundmass. In specimens taken from near the contact of porphyritic quartz monzonite with fine-grained quartz monzonite cryptoperthite does not appear as phenocrysts—an indication that i t is late in the paragenetic sequence. Where i t does occur i t is p o i k i l i t i c and has inclusions of most other minerals in i t , especially near the rims. These cryptoperthites also commonly show cores of slightly higher Or content than their rims. Alkali feldspars of the groundmass form inter-locking grains chiefly with quartz and a l b i t i c plagioclase. The bulk composition of cryptoperthites was found to be OrgQAbgQ by X-ray methods. The habit of quartz is similar to that of a l k a l i feldspars. It occurs both as serrated anhedral phenocrysts and as small interlocking grains in the groundmass. Quartz generally has few inclusions and is present as embayed and rounded phenocrysts in specimens taken from near contacts. Quartz phenocrysts show weak undulose extinction. - 3 0 -Mafic minerals are biotite and minor amounts of hornblende. Hornblende occurs in specimens taken from near the contact, as inclusions in p o i k i l i t i c cryptoperthites, and as partly replaced remnants in the rock. Biotite occurs as both brown and green biotite—brown biotite being by far the more common. Biotite is occasionally pseudomorphous after hornblende hut is most common as anhedral grains. Rutile occurs rarely as fine needles in biotite. Apatite commonly occurs as fine euhedral crystals included in the other minerals of the rock and rarely as coarse-grained euhedral i n t e r s t i t i a l crystals. Sphene contains inclusions that resemble ilmenite. Pyrite is the most common accessory mineral and i s most l i k e l y formed by deuteric and hydrothermal alteration. The texture of porphyritic quartz monzonite (see plates IX & X, on pages 31 and 3 2 ) varies from sub-porphyritic to porph-y r i t i c . Phenocrysts are plagioclase, quartz, biotite, and cryptoperthite in decreasing order of abundance. The groundmass is comprised of interlocking grains of quartz, a l k a l i feldspars, and some sodic plagioclase. Hornblende and plagioclase were f i r s t to crystallize. Most hornblende was later replaced "by biotite. Cryptoperthite and some quartz began to crystallize relatively earlier in this rock than in previously described rock types. Both a l k a l i feldspars and quartz outlasted the other minerals. Apatite, sphene, and rut i l e occur as primary accessory minerals in porphyritic quartz monzonite, and were probably formed throughout the entire process of crystallization. -31-PLATE IX F i g u r e 2: Texture o f p o r p h y r i t i c q u a r t z monzonite (see page 2 9 ) . (x36, c r o s s e d n i c o l s ) - 3 2 -PLATE X Figure 1: O s c i l l a t o r y zoning, combination twinning, and a l b i t e -r i c h rims i n plagioclase phenocrysts of porphyritic quartz monzonite (see page 2 9 ) . (x36, crossed n i c o l s ) Figure 2: Chilled contact between fine-grained quartz monzonite and porphyritic quartz monzonite (see page 30). Contact runs between the two arrows. (x3&, p l a i n l i g h t ) - 3 3 -PLATE XI -u si'-. ' i Figure 1: Texture of p o r p h y r i t i c quartz monzonite near c h i l l e d contact (see page J O ) . (x36, p l a i n l i g h t ) Figure 2: Texture of p o r p h y r i t i c quartz monzonite near c h i l l e d contact (see page 30). (x36, crossed n i c o l s ) - 3 4 -Pyrite was formed at the expense of magnetite and some mafic minerals as a deuteric or hydrothermal alteration product. Early Quartz Monzonite Porphyry Dykes Modal compositions for two specimens of early quartz monzonite porphyry dykes are shown in figure IV (see page 3 5 - ) . The texture of this rock type i s porphyritic (see plate XII, on page 3 . 7 ) . Phenoerysts comprise about 50 per cent of the rock and are, in decreasing order of abundance, plagioclase, rounded conspicuous quartz "eyes", and cryptoperthite. Quartz "eyes" are the most distinguishing feature of the rock. Biotite is also present as phenoerysts and is commonly euhedral. It is not as abundant as in previously described rock types. Specimens taken from chilled contacts have phenoerysts of hornblende, biotite, and plagioclase (see plate XI, on page 3 3 ) in a fine-grained, dark grey groundmass. Thin-sections reveal that plagioclase in early quartz monzonite porphyry i s of the composition -A*1^ ^° a^ > 0 V i^ from core to rim. Zoning i s oscillatory-normal in large pheno-erysts and normal without oscillations in small grains. Phenoerysts are euhedral to subhedral and show relatively smooth contacts with the fine-grained groundmass. Combination twinning is common in large phenoerysts. Plagioclase grains are found as inclusions in cryptoperthite indicating that some plagioclase crystallized before cryptoperthite. Cryptoperthite is characteristically p o i k i l i t i c (see figure 2, plate XII, on page 3 7 ) with abundant inclusions of plagioclase and quartz. One phenocryst was noted to have a more Or-rich rim with myrmekitic albite exsolution surrounding a cryptoperthite FIGURE IV: Modes o f two specimens o f e a r l y q u a r t z monzonite p o r p h y r y dyke r o c k based on p o i n t - c o u n t t h i n - s e c t i o n a n a l y s i s . - 3 6 -c o r e . Some l a r g e c r y p t o p e r t h i t e p h e n o e r y s t s show weak z o n i n g and a l m o s t a l l a r e a n h e d r a l . Except f o r c r y p t o p e r t h i t e pheno-e r y s t s w h i c h comprise 5 "to 10 p e r c e n t o f the r o c k , a l l a l k a l i f e l d s p a r s a r e c o n f i n e d t o the groundmass. The "bulk c o m p o s i t i o n o f c r y p t o p e r t h i t e s was found t o be Org^Ab-^ by X-ray methods. Quartz i s found as l a r g e , rounded, s u b h e d r a l p h e n o e r y s t s w h i c h a r e c o n s p i c u o u s i n the handspecimen. There i s a c o n t i n -uous s i z e g r a d a t i o n from l a r g e p h e n o e r y s t s o f q u a r t z t o s m a l l ones t o f i n e - g r a i n e d i n t e r s t i t i a l q u a r t z g r a i n s o f the ground-mass. Large q u a r t z p h e n o e r y s t s have smooth, o c c a s i o n a l l y embayed c o n t a c t s and have i n c l u s i o n s , c h i e f l y o f a c c e s s o r y and m a f i c m i n e r a l s . P a t c h y e x t i n c t i o n i s common. B i o t i t e i s the c h i e f m a f i c m i n e r a l . Near c o n t a c t s a n h e d r a l h o r n b l e n d e i s commonly p a r t l y r e p l a c e d by brown and/or g r e e n b i o t i t e . A c c e s s o r y m i n e r a l s i n c l u d e sphene, p y r i t e , and a p a t i t e . Sphene w i t h i n c l u s i o n s o f i l m e n i t e i s r a r e . A p a t i t e , as f i n e -g r a i n e d e u h e d r a l c r y s t a l s and i n t e r s t i t i a l c o a r s e - g r a i n e d ones, i s more abundant than i n the p r e v i o u s l y d e s c r i b e d r o c k t y p e s . Hornblende, c a l c i c p l a g i o c l a s e , and q u a r t z c r y s t a l l i z e d e a r l y i n the o r d e r l i s t e d . C r y p t o p e r t h i t e was g e n e r a l l y l a t e and the f i n a l groundmass o f m i c r o c r y s t a l l i n e specimens i s an i n t e r l o c k i n g m i x t u r e o f a l k a l i f e l d s p a r and q u a r t z . A c c e s s o r y a p a t i t e c r y s t a l l i z e d t h r o u g h o u t the e n t i r e order" o f c r y s t a l l i z a t i o n and i s more abundant t h a n i n e a r l i e r d e s c r i b e d r o c k t y p e s . Sphene i s l e s s common and c r y s t a l l i z e d a t an i n t e r m e d i a t e t i m e . The t e x t u r e o f e a r l y q u a r t z monzonite p o r p h y r y dyke r o c k -37 -PLATE XII Figure 1: Texture of early quartz monzonite porphyry dyke rock—medial zone (see page 34). (x36, crossed nicols) Figure 2: Large p o i k i l i t i c euhedral orthoclase phenocryst in early quartz monzonite porphyry dyke rock—near contact (see page 3*). (x3$, crossed nicols) -38-is porphyritic with a slight tendency towards cumulophyric aggregates of quartz and feldspar phenoerysts. Quartz "eyes", abundant accessory pyrite, and anhedral biotite are conspicuous. Quartz Latite and Quartz Monzonite Porphyry Dykes Quartz l a t i t e and quartz monzonite porphyry dykes are d i f f i c u l t to distinguish from each other and differ mainly in distribution, modal composition, and grain-size. In the f i e l d these rock types were classified as i s shown on page 12 and maps II and III (in folder). A thin-section study has revealed that differences noted in handspecimens are very minor. For this reason these rock types have been collectively named quartz l a t i t e or quartz monzonite porphyry depending on the ratio of groundmass to phenoerysts. The texture and mode of these rock types seems to be, at least partly, controlled by the size of the dyke in question. Hornblende and biotite are mafic minerals. In some large dykes biotite i s the only mafic mineral. Quartz, plagioclase, and rarely cryptoperthite are phenoerysts which comprise from 20 to 45 per cent of the rock. The composition of quartz l a t i t e and quartz monzonite porphyry dykes i s probably very similar to that of the other rock types of the complex. Plagioclase of the late dykes i s very similar in zoning and composition to that of the previous rock types. Two distinct composition ranges and types of zoning occur. Large phenoerysts have pronounced oscillatory zoning with composition ranging from about An^Q in the core to An-^ or more sodic on the rim. Small phenoerysts show l i t t l e or no oscillatory zoning but have a smooth normal decrease from An 2 8 i n the core to An-, , or more - 3 9 -sodic on the rims. Plagioclase is present to a minor extent in the groundmass but i s so fine-grained that i t s composition can not be determined with any certainty. Phenoerysts of cryptoperthite are subhedral to anhedral. and are ophitic with inclusions of quartz, mafic minerals, and plagioclase grains. One plagioclase grain near the outer edge of an ophitic cryptoperthite was found to have a composition of k&2j o n ^ ne rim. The groundmass of late dykes i s comprised of chiefly a l k a l i feldspars and quartz with some albite-rich plagioclase. Quartz is commonly in subhedral to anhedral grains. These are rounded and embayed and formed early in the sequence of crystallization. Quartz also occurs as fine grains in the groundmass. The predominant mafic mineral is biotite. Hornblende occurs in rapidly chilled varieties, generally as anhedral remnants of former euhedral grains. Accessory minerals include pyrite, sphene, apatite, and r u t i l e . They occur as described in previous rock types but, except for pyrite, are less abundant. Quartz l a t i t e and quartz monzonite porphyry dykes are porphyritic in texture (see plate XIII, on page 40 and figure 1, plate XIV, on page 41 ). Porphyritic texture i s well developed and indicates a rapid rate of cooling. First minerals to crystallize were hornblende and plagioclase. When plagioclase had reached the composition Angy cryptoperthite started to crystallize. Crystallization of a l k a l i feldspars, quartz, and minor amounts of a l b i t i c plagioclase outlasted other minerals - 4 0 -PLATE XI I I Figure 2: Texture of quartz l a t i t e porphyry. Note l a c k of w e l l defined 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 phenocryst l a r g e l y at e x t i n c t i o n (see page 39). (x36, crossed n i c o l s ) -41-PLATE XIV F i g u r e 1: 5 ;• 5 p | ?'• • T e x t u r e o f q u a r t z l a t i t e p o r p h y r y dyke r o c k . Note l a t h s o f p l a g i o c l a s e and e u h e d r a l h o r n b l e n d e (see page 3 9 ) . (x36, p l a i n l i g h t ) F i g u r e 2: Texture o f i n t e r m e d i a t e dyke. Note l a t h s o f hornblende and g r a i n s o f b i o t i t e i n a ground-mass o f p l a g i o c l a s e (see page f a ) , (xl06, p l a i n l i g h t ) t o form the groundmass o f the r o c k . A l t e r e d L a t i t e Dykes The c o l o u r o f a l t e r e d l a t i t e r anges from p i n k t h r o u g h brown t o g r e e n i s h - g r e y . I t i s composed o f green a c c i c u l a r h o r n -b l e n d e n e e d l e s i n a groundmass o f f e l d s p a r s w h i c h seem t o be m a i n l y a l k a l i f e l d s p a r s . Quartz "eyes" a r e c o n s p i c u o u s l y r a r e . The t e x t u r e o f t h i s r o c k type i s medium- t o f i n e - g r a i n e d w i t h s c a r c e p h e n o c r y s t s o f f e l d s p a r and h o r n b l e n d e . I n t h i n - s e c t i o n , p l a g i o c l a s e and a l k a l i ; f e l d s p a r s a r e seen t o be l a r g e l y r e p l a c e d by s e r i c i t e . A l k a l i f e l d s p a r s p r o b a b l y formed a l a r g e p ercentage o f the r o c k . C h l o r i t e i s pseudo-morphous a f t e r o r i g i n a l h o r n b l e n d e . B a s i c and I n t e r m e d i a t e Dykes These r o c k s a r e a p h a n i t i c and gr e e n o r b l a c k . Some b a s i c dykes have v e s i c u l a r o r a m y g d a l o i d a l m e d i a l zones. P h e n o c r y s t s are r a r e t o absent. P y r i t e i s common as an a c c e s s o r y m i n e r a l . Under the m i c r o s c o p e , i n t e r m e d i a t e dykes a r e seen to c o n s i s t o f a f i n e mass o f f e l t e d l a t h s o f p l a g i o c l a s e , h o r n b l e n d e , and g r a i n s o f b i o t i t e (see f i g u r e 2, p l a t e XIV, on page Quartz i s uncommon and a l k a l i f e l d s p a r s a re r a r e t o ab s e n t . A r a r e p h e n o c r y s t o f p l a g i o c l a s e i s o f the c o m p o s i t i o n A n ^ t o An^^. Thermal H i s t o r i e s o f t h e F e l d s p a r s  I n t r o d u c t i o n I n f e l d s p a r s , aluminum and s i l i c o n atoms l i e a t c e n t r e s o f t e t r a h e d r a t h a t form the f e l d s p a r c r y s t a l l a t t i c e . I n d i s o r d e r e d v a r i e t i e s o f a l k a l i f e l d s p a r s (e. g. s a n i d i n e ) aluminum c e n t e r e d t e t r a h e d r a a r e d i s t r i b u t e d randomly t h r o u g h o u t the c r y s t a l l a t t i c e . I n h i g h l y o r d e r e d a l k a l i f e l d s p a r ( e. g. -43-microcline) the positions that aluminum centered tetrahedra may occupy are restricted, with a consequent difference in symmetry from the disordered form. It i s believed that slow cooling allows ordering ( i . e. diffusion of Al and Si atoms to specific positions) and that quenching prevents i t . Thus the degree of ordering indicates rate of cooling during the ordering temperature interval, and thus defines what is known as "thermal state". It i s l i k e l y that total pressure and water vapour pressure as well as rate of cooling through the ordering temperature interval affect the degree of ordering in feldspars. This possibility has not been investigated quantitatively by research and is not pursued further in this study. In both plagioclases and a l k a l i feldspars thermal state has a direct effect on optic properties. The thermal state can be readily determined, as was done in this study, by measuring the optic angle and plotting i t against composition (see figures VII to XIII). For a l k a l i feldspars components of a crypto-pethitic intergrowth (see figure 2, plate VIII, on page 26) can be determined. The Alkali Feldspars  Introduction - The study of a l k a l i feldspars (cryptoperthite and albite) involved determination of composition and optic angle (2V X). Both procedures are described below. Results are given in tables I (on page 45-), II (on page -77), and III (on page sz). Curves of figure VII (on page 5-4) are taken from Emeleus and Smith ( 1 9 5 9 ) . Determination of 2V Y _ 2 y 0 f a l k a l i feldspars was determined - 4 4 -with a four-axis Leitz Universal Stage using the extinction method. Glass hemispheres with a refractive index of I . 5 1 6 were used so that Pedorow's correction for difference in refractive index between the hemispheres and a l k a l i feldspars was insignificant and therefore not applied. Optic directions, X and Y, and one or two optic axes were plotted on a Schmidt net of diameter 2 0 centimetres. Z was found by construction and 2V' was measured about X in the XZ plane. As stated previously, a l k a l i feldspars of the Serb Creek complex are generally anhedral and untwinned. It was there-fore impossible to determine whether the XZ plane is nearly perpendicular or parallel to ( 0 1 0 ) . This distinction might be important because the distinguishing feature between high sanidine and other forms i s that in high sanidine the optic plane (XZ) l i e s parallel to ( 0 1 0 ) whereas in the others i t is approximately perpendicular to ( 0 1 0 ) . Although high sanidine i s known from quenched synthetic melts, i t has not been identified in natural lavas or in plutonic rocks. Therefore i t is safely assumed that none of the rocks under study belong to the high sanidine-high albite series. Albite-rich lamellae of cryptoperthites were not coarse enough to allow determination of 2V of exsolved albite in any •A. of the rock types. Results of optic angle measurements are given in table III (see page S3). It can be seen that there is a pronounced difference in 2V of coarse-grained quartz monzonite (2VX = 69 degrees) and younger rock types (2V = 52 to 49 degrees). A sample of cryptoperthite from a hydrothermal vein of Group III TABLE I A29 of (201)0r before and a f t e r heating shown with corresponding weight p cent of orthoclase. Relative size of a l b i t e peaks, (201)Ab, remaining a f t e r heating i s also shown. Rock Types A26(20l)0r Weight io Or Residual Ab peak heated- •unheated heated--unheated Coarse-grained quartz .952 .839 83 92.5 no peak monzonite .950 .882 83 88.5 medium peak • 951 .826 83 92.5 very small peak Transition "between coarse - .955 • 790 78 97 no peak and-fine-grained quartz .884 .832 87.5 92.5 strong peak monzonite .926 .817 84.5 93.5 medium peak Fine-grained quartz .970 .830 81 92.5 very small peak monzonite • 950 .860 83 91 medium peak .936 .837 83-5 92.5 medium peak .920 .845 85 92 small peak .979 .820 80 93 small peak Porphyritic quartz .964 .811 81. 5 94 no peak monzonite Early quartz monzonite .970 .830 81 92.5 very small peak porphyry .884 .837 88 92.5 no peak Cryptoperthite from .937 .823 83-5 93 no peak hydrothermal vein - 4 6 -alteration (see page 71 and plate XV, on page TZ) was analysed to see i f any difference existed between i t and a l k a l i feldspars of the igneous rock types. Cryptoperthite of the vein has an average 2VX of 84 degrees. This indicates distinctly lower temperature conditions during hydrothermal activity. Determination of Composition - Composition of cryptoperthites was determined by X-ray methods involving measurement of the angle between a known standard peak and the peak of the (201) reflection of a l k a l i feldspar. The standard peak used was the (101) reflection of KBrO^. Because the position of the (201) peak of a l k a l i feldspar varies linearly with weight per cent of orthoclase, the difference, A 2 Q which is then 20 .(201) Or minus 20. (lOl)KBrO-j, is directly proportional to orthoclase content (see figure V, on page -*<&). The graph used in figure V to determine composition is part of one by Parsons (1965). The solid line of the graph joins A20 for the sanidine-high albite series while the broken line joins -^ 20 of microcline and low albite. Parsons has plotted 15 feldspar compositions and found that they f a l l between the two lines. For this reason al k a l i feldspars in this study were also plotted between the two lines. They were plotted somewhat closer to the microcline-low albite line (see figure V, on page *e) because an environment characteristic of plutonic rocks (and the microcline-low albite series) seems appropriate. Optic angle (2VX) was measured for heated samples and found to be the same as before heating. It is concluded that heating has had l i t t l e effect other than to homogenize intergrowths of sodium-rich and potassium-rich phases of cryptoperthites. For this reason plots of heated and TABLE II Composition of cryptoperthites of Serb Creek intr u s i v e complex rock types. The correction i s f o r the amount of a l b i t e l e f t i n r e s i d u a l a l b i t e peaks which are l i s t e d i n table I. A single average value i s given for the corrected value, Rock Type Weight jo Or (by X-ray) Corrected Value Coarse-grained quartz monzonite 83 83 83 0 r 8 l A b 1 Q Pine-grained quartz monzonite 81 80 83 83.5 85 0 r 7 8 A b 2 2 P o r p h y r i t i c quartz monzonite 81 0 r o Ab 80 20 Early quartz monzonite porphyry 81 88 ° W b l 6 Cryptoperthite from hydrothermal vein 83-5 0 r 8 4 A b l 6 -48-FIGURE V: *2Q = 20 .201 Feldspar minus 20 .101 KBrOo plotted against weight per cent orthoclase (after Parsons). Triangles are unheated samples; circles represent samples after heating at 920+10 degrees Centigrade for 24 hours. Albite peaks are not shown and a l l samples are not plotted. Solid line = sanidine-high albite series (Orville, I 9 6 3 ) . Broken line = microcline-low albite (Orville, i 9 6 0 and Smith, 1956). -49-unheated cryptoperthites are on the same line in figure V. Alkali feldspars were separated by the procedure described below, heat-treated, and mounted. Heated and unheated concentrates of fifteen samples were analysed with the X-ray diffractometer. Crushing was done by f i r s t breaking the rock into small chips with a hammer and then grinding them in a large porcelain mortar. Crushed material was sieved and particles between 70 and 120 mesh were retained. These were washed to remove dust. Magnetite and other strongly magnetic minerals were removed with a hand magnet. Further magnetic separation was carried out with a Franz Isodynamic Separator operating at a dip of 15 degrees and an inclination of 4 degrees. Two runs were made of each sample; one at 0.40 amperes to remove mafic minerals, and a second at 1.3 amperes to leave a non-magnetic concentrate of plagioclase, a l k a l i feldspars, quartz, and pyrite. Heavy liquid separations were carried out with a bromoform-methyl hydrate mixed solution with a specific gravity of 2.59. The non-magnetic concentrate was passed through this solution twice. Alkali feldspars floated in this solution whereas plagioclase, quartz, and pyrite sank. The concentrate obtained in this way was tested by staining a balsam mounted fraction with sodium cobalti-nitrate after etching the grains with hydrofluoric acid fumes. The concentrate was found to be 80 to 90 per cent or more a l k a l i feldspars. A fraction (1 to | gram) of purified a l k a l i feldspar concentrate was heated in an electric furnace at 920+10 degrees - 5 0 -centigra.de f o r 2k hours t o homogenize low a l b i t e - o r t h o c l a s e c r y p t o p e r t h i t e s . C o n c e r n i n g h e a t t r e a t m e n t o f n a t u r a l a l k a l i f e l d s p a r s , T u t t l e and Bowen (1958) say the f o l l o w i n g : " N a t u r a l a l k a l i f e l d s p a r s b e l o n g i n g t o the s a n i d i n e -h i g h a l b i t e s e r i e s can be r e a d i l y homogenized by h e a t i n g f o r a few mi n u t e s a t a temperature between 700 and 1000 degrees c e n t i g r a d e . F e l d s p a r s o f the o r t h o c l a s e - l o w a l b i t e s e r i e s h a v i n g c o m p o s i t i o n s between a p p r o x i m a t e l y O r ™ and 0r , - t cannot be homo-g e n i z e d u n t i l t h e y have changed t o the s a n i d i n e m o d i f i c a t i o n w h i c h may ta k e s e v e r a l weeks a t 1050 degrees c e n t i g r a d e . " P h a i r and F i s h e r (1962) found t h a t h e a t i n g a t 920+10 degrees c e n t i g r a d e f o r p e r i o d s up t o one week d i d n o t change c o m p o s i t i o n a p p r e c i a b l y from t h a t o f tho s e heated f o r 2k h o u r s . A p p r o x i m a t e l y 0 . 5 grams o f unheated a l k a l i f e l d s p a r c o n c e n t r a t e and 0 .2 grams o f KBrO-^ were ground t o g e t h e r i n a s m a l l agate m o r t a r . About 2 / 3 o f the a r e a o f a s t a n d a r d t h i n -s e c t i o n s l i d e (27 x 64mm) was cove r e d w i t h n a i l p o l i s h l e a v i n g one end f r e e . The powdered m i x t u r e o f a l k a l i f e l d s p a r and KBrO^ was d u s t e d e v e n l y on the wet n a i l p o l i s h . When the n a i l p o l i s h has d r i e d (1 hour) the s l i d e i s r e a d y f o r use. One end o f the s l i d e was l a b e l l e d t o i d e n t i f y the sample. The same proce d u r e was used i n p r e p a r a t i o n o f heated samples. A l k a l i f e l d s p a r s were a n a l y s e d w i t h a P h i l l i p s 19^3 model X-ray d i f f r a c t o m e t e r w i t h a goniometer head. N i c k e l o x i d e f i l t e r e d copper r a d i a t i o n was used. The machine was r u n a t kO k i l o v o l t s , 20 m i l l i a m p e r e s , and a s c a n n i n g speed o f l/k degree per m i n ute. Time/counts r a t i o was 3 / 3 0 0 . The c h a r t speed was l/k degree p e r minute ( i . e. the c h a r t and the goniometer were moving a t the same speed). Each sample was scanned over a range o f 20 = 19.60 degrees FIGURE VI: Diagrammatic r e p r e s e n t a t i o n o f d i f f r a c t o m e t e r p a t t e r n s o f A, unheated ( s o l i d l i n e s ) and B, h e a t e d (dashed l i n e s ) a l k a l i f e l d s p a r . C O Standard Potassium-rich phase S o d i u m - r i c h phase Potassium-rich phase Standard - 5 2 -to 2© = 22.20 degrees at least two times. Results of both scans (see figure VI, on page s~i) were measured with a 50-scale rule and averaged to give one value. These values (A2Q) are given for the (201)Or peaks in table I (see page •*&-). The values of ^20 are plotted in figure V (see page 4 8 ) to give the composition. Peaks for (101)KBr03 and (201)Or were of an excellent quality with the above specifications and ^20 could easily he read to an accuracy of +.005 degrees. Phair and Fisher (1962) estimate the accuracy of their results to be within 2 per cent of Or. Their work was done more rigorously than the present work but they show no plotted values for composition determin-ations of a l k a l i feldspars. A comparison of accuracies from graphs could therefore not be made and the author is forced to conclude that accuracy of the present analysis is in the order of +5 per cent of Or ( i . e. the actual composition of the cryptoperthites probably l i e s between the two curves shown in figure V on page 4s). An anomalous result noted in the patterns was that unheated albite peaks plotted as having a "negative" amount of orthoclase molecule. After heating of samples, peaks i f s t i l l present were reduced in height and showed a "positive" amount of orthoclase molecule on the graph. This was also noted by Tuttle and Bowen (1958) and, although they offer no explanation, they state: "Despite the uncertainty, the (201) gave approximate compositions, and the heated materials behaved like the sanidine-high albite cryptoperthites—that is the potassium phase took up sodium, and the sodium phase became richer in potassium..." It is thought that i f the feldspars had been heated at TABLE I I I O p t i c angle ( 2 V ) , composition, and types of c r y p t o p e r t h i t e s of the Serb Creek i n t r u s i v e complex rock types. Composition i s the c o r r e c t e d value taken from t a b l e I I . Values of o p t i c angle (2V ) are average v a l u e s f o r rock types. Rock type 2VX Composition Coarse-grained quartz 6 9 monzonite O r 8 l A b 1 9 Type of f e l d s p a r C r y p t o p e r t h i t e s between the m i c r o c l i n e - l o w a l b i t e and o r t h o c l a s e - l o w a l b i t e s e r i e s . F i n e - g r a i n e d quartz monzonite 52 0 r78 A b22 Orthoclase-low a l b i t e c rypto-p e r t h i t e s . P o r p h y r i t i c quartz monzonite 4 9 Oro nAb 80 A U20 Orthoclase-low a l b i t e c rypto-p e r t h i t e s . E a r l y quartz monzonite 53 porphyry 0 r 8 4 A b l 6 Orthoclase-low a l b i t e c r y p t o -p e r t h i t e s . Quartz l a t i t e porphyry 49 not analysed (Orthoclase-low a l b i t e c r yptc p e r t h i t e s . ) C r y p t o p e r t h i t e from hydrothermal v e i n 84 0 r 8 4 A b l 6 M i c r o c l i n e - l o w a l b i t e c rypto-p e r t h i t e s . -54-FIGURE V I I : P l o t o f weight p e r cent o r t h o c l a s e a g a i n s t o p t i c a n g l e (2V X). A = h i g h a l b i t e , B = low s a n i d i n e , G = o r t h o c l a s e , D = m i c r o c l i n e , and E = low a l b i t e . V e r t i c a l l i n e s = range o f o p t i c a n g l e ; e l l i p s e s = average o p t i c a n g l e . 1 = c o a r s e - g r a i n e d q u a r t z monzonite, 2 = f i n e - g r a i n e d q u a r t z monzonite, 3 = p o r p h y r i t i c q u a r t z monzonite, 4 = e a r l y q u a r t z monzonite p o r p h y r y dyke r o c k , 5= q u a r t z l a t i t e p o r p h y r y dyke r o c k , and 6 = h y d r o t h e r m a l v e i n f e l d s p a r . -55-9 2 0 + 1 0 degrees centigrade for a longer period of time only one peak would remain. Albite-rich peaks which remained after heating, (20l)Ab in figure V (see page -?&), are not plotted in figure VI (see page si) but their.presence is noted in table I (see page -**-) and a crude correction has been applied where the presence of an albite peak makes this desirable (see tables I & II, on pages +s- and tn). This correction is a visual estimate of albite content and is proportional to height of the albite peak remaining after heating. An average composition (after the correction has been applied) is shown for each rock type (see table II, on page - 4 7 ) . Results of the Alkali Feldspar Study - Alkali feldspars of coarse-grained quartz monzonite are cryptoperthites of composition Org-^ Ab-^ .^ Their average 2V X is 6 9 degrees (see figure VII, on page s+) with a range of 1 0 degrees from 64 to 74 degrees. The degree of ordering of these feldspars is intermediate between that of the orthoclase-low albite series and the microcline-low albite series. Cryptoperthites in the remaining rock types—namely fine-grained quartz monzonite, porphyritic quartz monzonite, early quartz monzonite porphyry, and late dyke rocks—ranges from Org^Ab^^ to OrygAb^. Average 2V X i s between 49 to 53 degrees in these feldspars. Composition of a microcline-low albite cryptoperthite from a hydrothermal vein (see page <H, and plate XV, on page 7z) was found to be Org^Ab-^ with an average 2V X of 84 degrees. Plagioclase Feldspars  Introduction - As in a l k a l i feldspars, i t has been suggested - 5 6 -that degree of ordering i n plagioclases indicates rate of cooling during the ordering temperature i n t e r v a l . Slemmons (1962) provides a plot of composition versus optic angle (see figures VIII to XIII, on pages 6z to 67) on which, fo r sodic plagioclase, "volcanic" and "plutonic" plagioclases are widely separated and e a s i l y distinguished. He believes that "volcanic" (quenched) plagioclase i s disordered and "plutonic" (slowly cooled) plagioclase i s highly ordered. Intermediate positions on the plot indicate intermediate degree of ordering and moderately rapid rates of cooling. Plagioclase feldspars were studied o p t i c a l l y with the L e i t z four-axis universal stage using extinction-angle methods. Determination of Optic Angle ( 2 V „ ) - Thin-sections of various rock types were examined on the f l a t stage for suitable grains. These grains were sketched, numbered, and marked for easy re-location. Using the four-axis universal stage and the revised Turner method (Slemmons, 1962) twin lammellae, cleavages, optic axes, and v i b r a t i o n directions were determined. Glass hemispheres used for t h i s work have a r e f r a c t i v e index of 1.559 which i s so close to that of plagioclase that Fedorow's corrections can be ignored without s i g n i f i c a n t loss of accuracy. Various components of plagioclase grains were plotted on a Schmidt net of 20 centimetres diameter, 2V was measured i n ' z the XZ plane, and twin axes found by construction. Twin type, and approximate composition were also determined f o r some grains using Slemmons' revised twin axis curves. Where possible, several zones were analysed i n t h i s fashion. Composition Determinations - Once the type of twin had been - 5 7 -determined an estimate of composition could be made by plotting X and Y against twin axis. This method was used successfully for some grains. In many thin-sections the twin axis method for determining composition was found to be unsatisfactory. This was especially true for zoned crystals in which twins were not continuous throughout a l l zones. Where albite twinning was identified and nearly correctly oriented the "section perpendicular to a" method was used to determine composition. Many albite twins could be oriented perpendicular to "a" using the universal stage and composition could be determined by measuring Xf against (010) for successive albite twin lamellae. In the composition range An„„ to An,lA the twin axis 20 *+u method commonly leads to ambiguous results. This is because the X^ and X 2 vibration directions of some twin types f a l l very close together with the result that twin axes can be determined with only low accuracy. In such a case the "section perpendicular to a" method was used i f albite twinning was present. Because of d i f f i c u l t i e s outlined above, accuracy of determination of 2V^ and composition are not as great as is desirable. An estimate of accuracy of 2VZ is +k degrees as a maximum and an average of +2 degrees. Composition error is thought to average +2 per cent An. Table IV (see page s-&) shows results of plagioclase feldspar studies which are plotted in figures VIII to XIII on pages 6z to 6 7 ) with lines of best f i t drawn through them. The last figure (see figure XIII, on page 6 7 ) is a composite of these TABLE IV Optic angles (2V Z) and composition of p l a g i o c l a s e f e l d s p a r s of the Serb Greek i n t r u s i v e complex rock types. Grains and zones studied i n them are shown. Rock Type Coarse-grained quartz monzonite T r a n s i t i o n between f i n e - and coarse-grained q u a r t z monzonite Grain 1 2 3 4 5 6 7 middle 8 core r i m 9 core 10 r i m 11 middle 12 r i m 13 r i m core 14 rim 1 i i i i i i i v 2 i i i 3 i i i Composition A n 2 8 A n 3 1 A-n27 A n 2 8 A n 3 0 An 27 A n 2 8 A n 2 y A n 2 1 ^ 2 4 A n 2 1 A n 2 4 A n 2 1 A n 3 1 A n 2 4 An^„ i n l n 3 3 A n 2 8 *4i 2Iz 96 96 96 100 96 96 99 9 7 . 5 102 .5 102 106 9 4 . 5 114 93 92 114 94 9 5 . 5 102 93 104 95 91 . 5 ' 100 .5 Rock Type Grain Transition between f ine- and coarse-grained quartz monzonite Fine-grained quartz monzonite 4 core rim 5 core middle rim 6 core middle rim 7 8 core rim 9 core rim 1 core middle rim 2 core rim 3 middle 4 middle 5 middle 6 core 7 8 9 10 1 1 core 12 core 13 middle Gomposition 2J_Z A n . , 9 5 AnJ2 100 A n 3 ? 100 A n ^ 9 5 Antl 102 A n ^ 95 An42 9 8 x2 An 2 Q 102 An^i 88 An^i 98 An 2 ^ 102 An2g 104 A n 2 2 102 A n 2 7 98 An2I 89 An2o HO An^3 96 An23 100 A n 2 1 110 A n 2 2 102.5 A n 2 0 108 An?z- 104.5 An^7 88 A n „ 89 An?l 84 A n28 1 0 1 An ° 101 A n ^ 9 2 A n ^ 95 Rock Type G r a i n C o m p o s i t i o n 2Y„ P o r p h y r i t i c q u a r t z monzonite 1 c o r e A n ^ 80 m i d d l e An^ 85 2 An£A 82.5 3 An^ 81.5 4 m i d d l e A n 2 8 1 0 0 5 c o r e A n 38 ^ r i m -^24 6 m i d d l e An-? 102 r i m An^° 112 7 c o r e A n ^ 100 8 c o r e An^g 92 r i m An 22 H O 9 c o r e A n 3 5 96 10 An££ 84 11 An.,!; 92 12 An:?' 97 13 A n ^ 99 14 An^rj 102 15 c o r e An-3^ 94 m i d d l e A n ™ 99 16 c o r e A n 3 3 97 m i d d l e An2? 104 r i m A i i ? o 114 17 A n t i 94 18 W ; 91 19 Anj3 92 E a r l y q u a r t z monzonite 1 r i m A n ? ? 102 p o r p h y r y c o r e - ^ I b 92 2 r i m Ardu 102.5 c o r e An 3 3 92 Rock Type G r a i n C o m p o s i t i o n 2V, E a r l y q u a r t z monzonite p o r p h y r y 3 4 r i m Quartz l a t i t e p o r p h y r y 8 c o r e 5 6 7 8 1 2 3 4 5 6 7 c o r e m i d d l e i i i i i i 9 10 11 12 13 14 15 m i d d l e c o r e 16 A n2 5 Anfg An y fit Anfg A n 3 l A n - „ ^42 An A n J 29 35 An' An An' An" ?, Hi A n ^ A n 3 2 An o ? kni An An An 38 * 3 2 Anj6 A n 3 4 100 108 93 89 110 107 102 104.5 106 87 85 107 106 98 106 103 100 91 101 105 104 99 100 94 103 96 102 - 6 2 -COARSE GRAINED QUARTZ MONZONITE & TRANSITION I 1 I 10 20 30 PER CENT ANORTHITE FIGURE V I I I : Thermal s t a t e o f p l a g i o c l a s e from c o a r s e - g r a i n e d q u a r t z monzonite ( b l a c k s q u a r e s ) and t r a n s i t i o n v a r i e t i e s ( c i r c l e s ) between i t and f i n e - g r a i n e d q u a r t z monzonite. -63-FINE GRAINED QUARTZ MONZONITE & TRANSITION I l ! 10 20 30 PER CENT ANORTHITE FIGURE IX: Thermal s t a t e o f p l a g i o c l a s e from f i n e - g r a i n e d q u a r t z monzonite ( b l a c k s q u a r e s ) and t r a n s i t i o n v a r i e t i e s ( c i r c l e s ) between i t and c o a r s e - g r a i n e d q u a r t z monzonite. -64-4 PORPHYRITIC QUARTZ MONZONITE 10 20 PER CENT ANORTHITE FIGURE X: Thermal s t a t e o f p l a g i o c l a s e s from p o r p h y r i t i c q u a r t z monzonite. -65-EARLY QUARTZ MONZONITE DYKE 10 2 0 PER CENT ANORTHITE FIGURE XI: Thermal state of plagioclases from early quartz monzonite porphyry dyke. -66-QUARTZ LATITE PORPHYRY DYKES 110-2 V Z 100-90 _ I I I 10 20 30 PER CENT ANORTHITE FIGURE XII: Thermal state of plagioclases from quartz l a t i t e porphyry dykes. -67-COMPOSITE OF ANALYSED ROCK TYPES FIGURE X I I I : Composite o f l i n e s o f b e s t f i t t a k e n from f i g u r e s V I I I t o X I I . 1 = c o a r s e - g r a i n e d q u a r t z monzonite, 2 = f i n e - g r a i n e d q u a r t z monzonite, 3 = p o r p h y r i t i c q u a r t z monzonite, 4 = e a r l y q u a r t z monzonite p o r p h y r y dyke r o c k , and 5 = q u a r t z l a t i t e p o r p h y r y dykes. - 6 8 -lines. Thermal State of the Feldspars of the Serb Greek Complex Alkali feldspars of coarse-grained quartz monzonite are cryptoperthites intermediate between the microcline-low albite and the orthoclase-low albite series. They show a relatively high degree of ordering and are therefore thought to have cooled slowly through the ordering temperature interval. Cryptoperthites of the remaining rock types (2 to 5» see figure VII, on page ) belong to the orthoclase-low albite series. They show a lower degree of ordering than those of coarse-grained quartz monzonite and are thought to have cooled more rapidly through the ordering temperature interval. Cryptoperthite from a hydrothermal vein belongs to the microcline-low albite series. It shows the highest degree of order and therefore the slowest rate of cooling through the ordering temperature interval or was formed within or below the ordering temperature interval. In a similar way, plagioclase of coarse-grained quartz monzonite shows an intermediate degree of ordering, whereas plagioclases of fine-grained quartz monzonite, porphyritic quartz monzonite, early quartz monzonite porphyry, and quartz l a t i t e porphyry show a much lower degree of ordering. Plagioclase of transition samples ( i . e. rock samples taken from the gradational contact between fine-grained and coarse-grained quartz monzonite) shows less ordering than plagioclase of either type, thereby indicating a more rapid rate of crystallization or cooling through the ordering temperature interval at the contact of the two rock types. Lines of best f i t of fine-grained quartz monzonite, porphyritic quartz monzonite, and early quartz monzonite porphyry - 6 9 -have s t e e p e r s l o p e s than t h o s e o f c o a r s e - g r a i n e d q u a r t z monzonite and q u a r t z l a t i t e p o r p h y r y . The s t e e p e r s l o p e s suggest t h a t e a r l y p l a g i o c l a s e (e. g. p h e n o e r y s t s ) i n a g i v e n r o c k type a r e more o r d e r e d t h a n l a t e f e l d s p a r s (e. g. groundmass). S i m i l a r l y , c a l c i c c o r e s o f zoned c r y s t a l s a r e more h i g h l y o r d e r e d than t h e i r s o d i c r i m s . I t i s suggested t h a t p h e n o e r y s t s and c a l c i c c o r e s formed b e f o r e emplacement o f the body, perhaps a t c o n s i d e r a b l e d e p t h , and were h e l d a t a temperature w i t h i n the o r d e r i n g temperature i n t e r v a l f o r a l o n g p e r i o d o f time and t h a t a f t e r emplacement c r y s t a l l i z a t i o n and c o o l i n g were r a p i d . An a l t e r n a t e e x p l a n a t i o n i s t h a t an i n c r e a s e i n r a t e o f c r y s t a l l i z a t i o n was caused by a de c r e a s e i n water p r e s s u r e . T h i s e x p l a n a t i o n i s l e s s a c c e p t a b l e t h a n the f i r s t because abundance o f w a t e r i s i n d i c a t e d by d e u t e r i c and h y d r o t h e r m a l a l t e r a t i o n . S t r u c t u r a l Geology The Serb Greek a r e a c o n t a i n s f a u l t s , s h e a r s , and f r a c t u r e s as w e l l as i n t r u s i v e b o d i e s o f d i f f e r e n t shapes t h a t comprise the Serb Greek complex. Two dominant a t t i t u d e s o f f a u l t s , s h e a r s , and dykes a r e N20°W to N45°W and N75°E w i t h n e a r - v e r t i c a l d i p s to southwest and s o u t h e a s t r e s p e c t i v e l y . Three p e r i o d s o f f a u l t i n g i n the Serb Creek a r e a a r e d i s c u s s e d below. The f i r s t p e r i o d o f f a u l t i n g , w h i c h o c c u r r e d b e f o r e m o l y b d e n i t e m i n e r a l i z a t i o n , i s r e p r e s e n t e d by f a u l t s s t r i k i n g N20°W to N45°W and d i p p i n g s t e e p l y t o the southwest. B r e c c i a t i o n , m o l y b d e n i t e and p y r i t e m i n e r a l i z a t i o n , and q u a r t z , s e r i c i t e , K - f e l d s p a r , and c l a y m i n e r a l a l t e r a t i o n a r e commonly a s s o c i a t e d w i t h these f a u l t s . A second p e r i o d o f f a u l t i n g (H75°E, s t e e p l y d i p p i n g t o the -70-south) o c c u r r e d a f t e r m o l y b d e n i t e m i n e r a l i z a t i o n . A l a t e r s u l p h i d e m i n e r a l assemblage c o n s i s t i n g o f c h a l c o p y r i t e , p y r i t e , s p h a l e r i t e , and g a l e n a i n a gangue o f q u a r t z and c a r b o n a t e i s found i n t h e s e f a u l t s . The f i n a l p e r i o d o f f a u l t i n g i s a l o n g b o t h p r e v i o u s l y e s t a b l i s h e d d i r e c t i o n s and p r o b a b l y r e p r e s e n t s f i n a l r e a d j u s t -ments a l o n g them. There i s no s u l p h i d e m i n e r a l i z a t i o n and o n l y weak h y d r o t h e r m a l a l t e r a t i o n a s s o c i a t e d w i t h t h i s f i n a l p e r i o d o f f a u l t i n g . H y d r o t h e r m a l A l t e r a t i o n I n t r o d u c t i o n H y d r o t h e r m a l a l t e r a t i o n i s w i d e s p r e a d on the Serb Creek showing. P r o d u c t s o f h y d r o t h e r m a l a l t e r a t i o n i n c l u d e the f o l l o w i n g : s e r i c i t e , K - f e l d s p a r , c h l o r i t e , c a r b o n a t e , e p i d o t e , c l a y m i n e r a l s , and q u a r t z . A g e n e r a l i z e d map (see map IV, i n f o l d e r ) shows a r o u g h l y c o n c e n t r i c z o n a l d i s t r i b u t i o n o f a l t e r a t i o n t y p e s . Groups o f A l t e r a t i o n Assemblages H y d r o t h e r m a l a l t e r a t i o n m i n e r a l s a r e d i v i d e d i n t o t h r e e groups a c c o r d i n g t o t h e i r d i s t r i b u t i o n as f o l l o w s : Group I A l t e r a t i o n - K - f l e d s p a r , c h l o r i t e , e p i d o t e - Group I a l t e r a t i o n i s i n t e n s e west o f the a r e a o f d e t a i l e d mapping. I t i s a l s o found s o u t h o f the showing where i t i s l e s s i n t e n s e . Group I a l t e r a t i o n forms a zone t h a t i s r o u g h l y p e r i p h e r a l t o o t h e r zones on the showing. I t i s p o s s i b l e t h a t Group I a l t e r a t i o n i s due t o p a r t l y d e u t e r i c as w e l l as h y d r o t h e r m a l f l u i d a c t i v i t y and may n o t be d i r e c t l y a s s o c i a t e d w i t h s u l p h i d e m i n e r a l i z a t i o n . -71-Rock which is subject to Group I alteration is coloured pink by K-feldspar and has green chlorite-epidote f i l l e d fractures throughout (see plate XVII, on page 74). Group II Alteration - Clay minerals, sericite, chlorite - Group II alteration zone l i e s generally between the central map area and the outer zone of alteration. It is found in the western, south-central, and eastern areas (see map IV, in folder). It also occurs on the north slope of Serb Creek valley and Moraine Creek valley. Group II alteration is generally not intense except in the vicinity of fractures, faults, and shear zones. Rock which has been affected by Group II alteration is crumbly, with a white to pale yellow dusty appearance. Where alteration is pervasive the rock is coloured white to yellowish-white by clay minerals, and sericite with quartz grains remaining as the only original constituent. Mafic minerals, altered to chlorite, are visible as dark green specks throughout the rock. Group III Alteration - Sericite, K-feldspar, quartz, chlorite, carbonate - Group III alteration i s found in the central zone of the showing. In general, quartz veins are associated with i t . Sericite is the characteristic mineral of this zone. Alteration of this type, i f pervasive, reduces rock to a greenish-coloured mass of sericite with remnant quartz "eyes" or to an a p l i t i c -looking mixture of sericite, K-feldspar, and quartz. Chlorite and carbonate are also present in this zone (see figures 1 and 2, plate XVI, on page 7 3 ) , but these minerals are thought to represent, in part, a later, low-temperature metasomatism which accompanied sulphides such as chalcopyrite, pyrite, sphalerite, and galena. Areas of intense mineralization are associated with -72-P L A T E XV Figure I s C r y p t o p e r t h i t e v e i n (Group I I I a l t e r a t i o n zone) (see page 75"). Note dusty i n c l u s i o n s of i r o n oxide. (x36, p l a i n l i g h t ) -73-PLATE XVI Figure 1: A l t e r a t i o n o f p o r p h y r i t i c quartz monzonite w i t h development of c h l o r i t e , s e r i c i t e , K-feldspar, and carbonate. Group I I I central zone a l t e r a t i o n (see page 7 / ) . (x36, p l a i n l i g h t ) - 7 4 -P L A T E X V I I Figure 1: Group I K-feldspar a l t e r a t i o n of f i n e - g r a i n e d quartz monzonite. Dusty i n c l u s i o n s of i r o n oxide are c h a r a c t e r i s t i c of secondary K-feldspar. (x36, p l a i n l i g h t ) (see page 11) Figure 2: K-feldspar, epidote, and c h l o r i t e a l t e r a t i o n (Group I ) of f r a c t u r e d coarse-grained quartz monzonite. ( x 3 6 , p l a i n l i g h t ) . -75-pervasive Group III alteration. Group III alteration also occurs outside of the central zone along mineralized faults and veins. These contain quartz, pyrite, and molybdenite and are surrounded by a narrow alteration zone of K-feldspar, sericite, clay minerals, and chlorite. A photomicrograph of cryptoperthite from such a vein is shown in figures 1 and 2 of plate XV (see page 7 2 ) . Sulphide Mineralization Molybdenite occurs irregularly over the entire map area which i s stained by limonite formed from associated pyrite. Areas of more intense mineralization are exposed between the upper and lower talus slopes and bounded on the sides by draws 878E and 2 3 0 0 W . Molybdenite occurs with or without pyrite as smears on "dry" fractures (fractures which have no hydrothermal alteration or quartz associated with them), as fine dust-like grains in and along the selvage of quartz veins, as smears on shear surfaces in the intensely sericitized areas (Group III alteration), and as a cement in fault breccia zones. Disseminated molybdenite in the st r i c t sense is non-existent except for one very minor occurrence in early quartz monzonite porphyry at the foot of draw 200E. It is present in this rock type as fine-grained, isolated flakes with abundant anhedral grains of evenly distributed pyrite. A mineral assemblage of lesser economic importance is comprised of chalcopyrite, pyrite, sphalerite, and galena, in v uggy» steeply-dipping quartz-carbonate veins which strike N75°E. It is found between draws 1400W and 600W in the central map area - 7 6 -associated with chlorite-carbonate alteration of Group III (see page 7/). Combined sulphides in these veins rarely, i f ever, make up more than ten per cent of the vein matter. Sphalerite and chalcopyrite are also found in quartz-epidote veins over a large area which includes most of the showing. Secondary Oxide Mineralization Secondary oxide and rust stain i s found at the surface only, except in shear zones, faults, and highly altered areas where i t reaches depths of several tens of feet. Oxidation products include mixtures of iron oxides, jarosite, ferri-molybdite, manganese oxide, azurite, and malachite. Jarosite and ferri-molybdite were identified by X-ray powder diffraction patterns. Jarosite is widespread throughout the rust-stained zone. It occurs as a fine brown to yellowish-brown dust or a silky-looking coating lining cracks and cavities in rusty areas. Ferri-molybdite is found as a yellow coating associated with molybdenite mineralization. Paragenesis Paragenesis of various mineral assemblages was determined in the f i e l d . Molybdenite is so fine-grained that preparation of polished sections for microscopic study is very d i f f i c u l t . Pyrite is both earlier and later than molybdenite. The second mineral assemblage consists of pyrite, chalco-pyrite, sphalerite, and galena. It is distinctly later than molybdenite and is thought to be of a lower temperature type because late chlorite and carbonate alteration are associated with i t . This assemblage probably represents f i n a l activity of residual hydrothermal solutions. A decrease in pressure is -77-indicated by the veins which are coarsely crystalline with numerous crystal-lined vugs, a feature which i s not common in molybdenite-pyrite quartz veins. Deposition of quartz began before sulphide mineralization, as is indicated by barren quartz veins cut by later mineralized ones, and continued at least until chalcopyrite-sphalerite-galena mineralization was deposited. Hydrothermal alteration probably began soon after intrusion of fine-grained quartz monzonite, reached a maximum intensity during time of molybdenite mineralization, and then gradually declined. Oxidation minerals were probably formed after the last period of glaciation. -78-ORIGIN OF THE SERB GREEK INTRUSIVE COMPLEX Field relationships, textures, composition, and types of feldspars present in the Serb Greek intrusive complex are a l l indicators of i t s history and origin and form the basis of this discussion. Some statements concerning origin of parent magma which are highly speculative are discussed separately below. Sequence of Events The order of emplacement of various rock types is shown diagrammatically in figure XIV (see page so). The colours are those used on maps II and III (in folder). The sizes of the blocks in figure XIV gives a rough idea of the relative surface area of the various intrusive bodies encountered. There is probably a considerable time interval between emplacement of fine-grained quartz monzonite and later rock types which were probably emplaced in relatively rapid succession. Hydrothermal alteration probably began during emplacement of fine-grained quartz monzonite. It reached a maximum intensity at or near the time of molybdenite mineralization and then decreased gradually. Sulphide mineralization occurred in two stages, during and after the emplacement of early quartz monzonite porphyry. The earlier of these was the deposition of molybdenite and pyrite; in the later chalcopyrite, pyrite, sphalerite, and galena were deposited. Pyrite deposition probably lasted over a longer period of time than did deposition of the other sulphides. Faulting, fracturing, and shearing lasted throughout the entire episode with several periods of intense fracturing during that time. - 7 9 -Origin of the Parent Magma There can be l i t t l e doubt that the Serb Creek intrusive complex had a magmatic stage in i t s history. Both petrographic and f i e l d evidence presented in this paper strongly substantiate such a conclusion. The ultimate origin of such quartz monzonite magmas is a subject of much speculation. On reviewing the many and varied discussions of the origin of granitic magmas the author i s forced to conclude that c r i t e r i a for various hypotheses are inconclusive. A few common hypotheses include (a) d i f f e r -entiation from a parental gabbroic magma (b) modification of basic magmas by assimilation (c) formation by anatexis—melting of geosynclinal sediments and their metamorphic derivatives during orogeny. Winkler (1965) has provided new data on the last hypothesis, one which is currently popular among petrogenists. In considering the process of melting a rock by anatexis at a given water pressure (2000 bars) Winkler states: "As the temperature increases more melt is formed, the composition changing along that cotectic line, which, with the least possible temperature rise, leads toward the point representing the composition of the rock." It seems reasonable that i f the bulk composition of a granitic magmatic rock i s accurately determined and plotted in terms of Q:Ab:0r ratio, this information might indicate the pressure-temperature conditions at which the melt was formed, provided one assumes that i t was formed by anatectic melting. Compositions of Serb Creek intrusive rock types (see figure XV, on page 81) are compatible with those resulting from crystal and liquid equilibrium studies (Winkler, 19&5) a n d a r e thus compatible with either an origin by anatexis or by differentiation. - 8 0 -A L T E R E D L A T I T E D Y K E Cn •v. (fe — k I N T E R M E D I A T E D Y K E P O R P H Y R Y D Y K E S <3 ! M I N E R A L IZ A T I <b I N T E R M E D I A T E D Y K E Q / c h a l c o p y r i t e , s p h a l e r i t e , galena ( m o l y b d e n i t e , p y r i t e I N T R A - M I N E R A L P O R P H Y R Y D Y K E M I N E R A L I Z A T I O N { m o l y b d e n i t e , pyr i te P O R P H Y R I T I C Q U A R T Z M O N Z O N I T E F I N E G R A I N E D B I O T I T E Q U A R T Z M O N Z O N I T E U A P L I T E 3 B A S I C D Y K E Ql C O A R S E G R A I N E D H O R N B L E N D - B I O T I T E Q U A R T Z M O N Z O N I T E S E R B H A Z E LT O N V O L C A N I C S FIGURE XIV^ G E O L O G I C H I S T O R Y OF T H E C R E E K M O L Y B D E N I T E S H O W I N G H. P. -81-FIGURE X V : Normative Q:Ab:0r r a t i o s of eutectic points i n gr a n i t i c systems and experimentally produced ana-t e c t i c melts at water pressure = 2000 bars, dots - eutectic points i n water saturated systems with various Ab/An r a t i o s . c i r c l e s - eutectic points i n sjrstems with i n t e r -polated Ab/An r a t i o s . f i l l e d - i n and open triangles - eutectic points i n systems containing 0.05 m HC1. diamonds - anatectic melts above the eutectic temp-erature. At pressures greater than 2000 bars, the f i e l d bounded by the dashed l i n e i s shifted towards the Ab corner. The s o l i d l i n e shows the f i e l d of granite compositions taken from Winkler and v. Platen, 1961, Geochim. et Cosmochim. Acta, 24, 250ff. The s o l i d l i n e includes 86$ of the frequency d i s t -r i b u t i o n of the normative Q:Ab:0r r a t i o s of 1190 g r a n i t i c rocks. squares - composition of Serb Creek rock types calculated from point-count determinations. 1 = coarse-grained quartz monzonite, 2 = fine-grained quartz monzonite, 3 = porphyritic quartz monzonite, and 4 = early quartz monzonite porphyry. -82-Normative Q:Ab:0r ratios for Serb Creek rock types f a l l within the 86$ frequency boundaries of 1190 granitic rocks plotted by Winkler (1965). This includes rocks which were probably formed by both processes ( i . e. anatexis or di f f e r -entiation). In experiments with eutectic melts Winkler has shown how the eutectic point and the cotectic lines of the system Q-Ab-Or-R^O vary with varying pressures of RgO or of HC1 (see figure XV, on page 8 i ) . Evidence from thin-sections of Serb Creek rock types suggests that feldspar and quartz crystallized throughout the entire sequence of crystallization. This means that crystallization of the parent magma, assumed to have formed by anatexis, proceeded along the quartz-feldspar cotectic line towards the eutectic point. Position of Q:Ab:Or ratios of Serb Creek rock types (see figure XV, on page ei) indicate that the quartz-feldspar cotectic line and eutectic point are shifted towards the Ab corner of the ternary diagram—a feature attributed by Winkler to a high pressure of volatiles or HC1, or to both. Environment of Emplacement General conclusions concerning the level of emplacement of Serb Creek rock types can be drawn. Evidence drawn from distribution of rock types, textures, composition, and thermal state study of feldspars is summarized below. The Serb Creek complex is a discordant intrusive complex comprised of a series of cross-cutting, progressively smaller injections. Contacts of intrusive bodies with each other and with - 8 3 -v o l c a n i c s a r e s t e e p l y d i p p i n g and g e n e r a l l y a b r u p t u n e h i l l e d t o c h i l l e d . F i n e - g r a i n e d q u a r t z monzonite has a f o l i a t i o n e x p r e s s e d by b i o t i t e . F o l i a t i o n o f c o a r s e - g r a i n e d q u a r t z monzonite i s found near and p a r a l l e l t o c o n t a c t s w i t h the v o l c a n i c s . A p l i t i c and p e g m a t i t i c apophyses from the i n t r u s i v e s i n t o v o l c a n i c s a r e common. V o l c a n i c s have been baked t o h o r n f e l s a t the i n t r u s i v e -v o l c a n i c s c o n t a c t w i t h metasomatic a d d i t i o n o f s i l i c a , e p i d o t e , and c h l o r i t e . T e x t u r e s o f i n t r u s i v e r o c k t y p e s v a r y from p h a n e r i t i c t o p o r p h y r i t i c w i t h a p h a n i t i c groundmass. N o r m a l - o s c i l l a t o r y z o n i n g and c o m b i n a t i o n t w i n n i n g o f p l a g i o c l a s e i s p r e s e n t i n a l l i n t r u s i v e r o c k t y p e s . C o m p o s i t i o n shows l i t t l e o r no p r o g r e s s i v e change from the o l d e s t t o the youngest r o c k t y p e . Hornblende, p r e s e n t i n c o a r s e - g r a i n e d q u a r t z monzonite, i s r e p l a c e d by b i o t i t e i n younger r o c k t y p e s . Quartz and f e l d s p a r c r y s t a l l i z e d s i m u l t a -n e o u s l y i n the l a t e r r o c k t y p e s t h r o u g h o u t the e n t i r e sequence o f c r y s t a l l i z a t i o n . P l o t s o f n o r m a t i v e Q:Ab:Or r a t i o s i n d i c a t e a h i g h p r e s s u r e o f v o l a t i l e s , HC1, o r o f b o t h . Thermal s t a t e s t u d y o f b o t h a l k a l i f e l d s p a r s and p l a g i o -c l a s e s r e v e a l e d t h a t degree o f o r d e r i n g i n f e l d s p a r s d e c r e a s e s from the o l d e s t ( c o a r s e - g r a i n e d ) t o the youngest ( f i n e -g r a i n e d ) r o c k t y p e . Rates o f c o o l i n g i n t e r p r e t e d from t h i s s t u d y became p r o g r e s s i v e l y more r a p i d f o r s u c c e s s i v e l y younger and s m a l l e r i n j e c t i o n s . The e v i d e n c e summarized above i n d i c a t e s t h a t the Serb Creek complex was i n t r u d e d i n t o an upper mesozonal t o l o w e r -84-epizonal environment (Buddington, 1959). -85-SUMMARY AND CONCLUSIONS The Serb Creek intrusions form a small batholithic off-shoot of the Coast Range intrusive complex. They intrude volcanics of the Hazelton Group of Mesozoic age which are baked to a hornfels at the contact with the intrusions. Two minor phases, fine-grained quartz monzonite and porphyritic quartz monzonite, have intruded coarse-grained quartz monzonite, the main phase. These are in turn intruded by a series of quartz monzonite porphyry and intermediate dykes, as are coarse-grained quartz monzonite and volcanics of the Hazelton Group. Intrusive phases studied in detail are very similar in composition but vary in texture which becomes increasingly more porphyritic with decreasing relative age and size of the intrusive body. Plagioclase formed early in the sequence of crystallization and shows oscillatory-normal zoning from a core of composition An^ Q to An^ o r more sodic at the rim. Cryptoperthites are late and are of composition OrgQAb^. Quartz crystallized throughout the entire sequence of crystallization and shows mottled extinction in most rock types. Hornblende and biotite are mafic minerals in coarse-grained quartz monzonite and at chilled contacts of some rock types; biotite is otherwise the only mafic mineral. Sphene is a conspicuous accessory mineral in most rock types. Both plagioclases and a l k a l i feldspars were found to be of intermediate structural type indicating partial ordering, relatively rapid cooling, and probably a hypabyssal environment. - 8 6 -There i s e v i d e n c e t h a t the r o c k s were emplaced i n an o r i g i n a l l y l a r g e l y m o l t e n s t a t e . U n i f o r m i t y o f c o m p o s i t i o n o f the v a r i o u s r o c k t y p e s i n d i c a t e s t h a t l i t t l e d i f f e r e n t i a t i o n has o c c u r r e d between the magma chamber and the p o s i t i o n o f c r y s t a l l i z a t i o n o f the r o c k s . The a u t h o r s u g g e s t s t h a t the r o c k t y p e s have the same p a r e n t magma and t h a t t h e y r e p r e s e n t a s e r i e s o f p r o g r e s s i v e l y s m a l l e r i n j e c t i o n s i n t o c o u n t r y r o c k from a magma chamber. The r e s u l t i n g i n c r e a s i n g l y more r a p i d r a t e o f c o o l i n g o f i n j e c t e d b o d i e s would account f o r d i f f e r e n c e s i n t e x t u r e s from c o a r s e - g r a i n e d q u a r t z monzonite t o q u a r t z l a t i t e p o r p h y r y dykes. P l o t s o f n o r m a t i v e Q:Ab:0r r a t i o s suggest t h a t , i f one b e l i e v e s the p a r e n t magma t o have been formed by a n a t e x i s , a h i g h p r e s s u r e o f v o l a t i l e s o r HC1, o r b o t h was p r e s e n t d u r i n g c r y s t a l l i z a t i o n o f the l a t e r r o c k t y p e s . T h i s s u g g e s t i o n i s co m p a t i b l e w i t h the c l o s e a s s o c i a t i o n o f h y d r o t h e r m a l a l t e r a t i o n and igneous i n t r u s i o n on the Serb Greek m o l y b d e n i t e p r o p e r t y . F a u l t s , dykes, v e i n s , and f r a c t u r e s have two major a t t i t u d e s . The s t r o n g e r o f t h e s e , N20°W t o N45°W, i s b e s t shown by f a u l t s and by a t t i t u d e s o f dykes. The second, N75°E, i s c h a r a c t e r i s t i c o f c h a l c o p y r i t e , p y r i t e , s p h a l e r i t e , and g a l e n a v e i n s . H y d r o t h e r m a l m i n e r a l s i n c l u d e K - f e l d s p a r , s e r i c i t e , q u a r t z c l a y m i n e r a l s , c a r b o n a t e , c h l o r i t e , a,nd e p i d o t e . These show a r o u g h l y c o n c e n t r i c p a t t e r n o f d i s t r i b u t i o n and a r e grouped as f o l l o w s : Group I A l t e r a t i o n - K - f e l d s p a r , c h l o r i t e , e p i d o t e - o u t e r zone. Group I I A l t e r a t i o n - S e r i c i t e , c l a y m i n e r a l s , c h l o r i t e --87-m i d d l e zone. Group I I I A l t e r a t i o n - S e r i c i t e , K - f e l d s p a r , c l a y m i n e r a l s , c a r b o n a t e c h l o r i t e , q u a r t z - c e n t r a l zone. S u l p h i d e m i n e r a l i z a t i o n o c c u r r e d i n two d i s t i n c t p e r i o d s . I n the f i r s t w h i c h was more i n t e n s e , m o l y b d e n i t e and p y r i t e were d e p o s i t e d . I n the second minor amounts o f c h a l c o p y r i t e , p y r i t e , s p h a l e r i t e , and g a l e n a were d e p o s i t e d i n the c e n t r a l zone i n vuggy q u a r t z - c a r b o n a t e v e i n s . O x i d a t i o n m i n e r a l s , w h i c h were p r o b a b l y formed a f t e r the l a s t p e r i o d o f g l a c i a t i o n , i n c l u d e i r o n o x i d e s , j a r o s i t e , f e r r i -m o l y b d i t e , manganese o x i d e , a z u r i t e , and m a l a c h i t e . These a r e found a t the s u r f a c e o n l y , except i n f a u l t zones, s h e a r s , or h i g h l y a l t e r e d zones where they p e n e t r a t e t o depths o f s e v e r a l t e n s o f f e e t below the s u r f a c e . - 8 8 -BIBLIOGRAPHY Allan, J. F. and Schindler, J. N. , 1964, Final Report, Serb Creek Molybdenite Property: Private Report to Amax Explorations, Inc. Armstong, J. E. et a l . , 1944, Preliminary Map #44-23 Smithers, Coast District, British Columbia: Geological Survey of Canada. Bowen, N. L., 1940, Geologic Temperature Recorders: Science Monthly, Vol. 51, PP- 5 - 1 ^ Buddington, A. F., 1959, Granite Emplacement with Special Reference  to North America: Geological Society of America Bulletin #70, pp. 671-747., Butler, B. S. and Vanderwilt, J. W., 1931, Climax Molybdenum Deposit of Colorado: Colorado Scientific Society, Vol . 1 2 , #10. Deer, ¥. A., Howie, R. A., and Zussman, J., 1964, Rock-forming  Minerals, Volume IV, Framework Silicates: Longmans, Green and Co. Ltd., London. Emeleus, C. H. and Smith J. V., 1959, The Alkali Feldspars, IV  Sanidine and Orthoclase Perthites from the Slieve Gullion  Area, Northern Ireland: American Mineralogist, Vol. 44, pp. 1187-1209. Fleischer, M., 1959, The Geochemistry of Rhenium with Special Reference to i t s Occurrence in Molybdenite: Economic Geology, Vol. 54, pp. 1406-1414. Gilluly, J. A., 1948, The Origin of Granites: Geological Society of America Memoir 28. Jaeger, J. C., 1961, The Cooling of Irregularly Shaped Igneous  Bodies: American Journal of Science, Vol. 259, PP 721-73^-. Larsen, E. S. Jr., 1945, Time Required for the Crystallization  of the Great Batholith of Southern and Lower California: American Journal of Science, Vol. 243-A, pp. 339-416. Lovering, T. S., 1955, Temperatures in and Near Intrusions: Economic Geology 5°th Anniversary Volume, pp. 249-281. Mackenzie, W. S., 1952, Optical and X-ray Studies of Alkali  Feldspars: Carnegie Institute of Washington Yearbook, No. 51, PP- 50. Moorhouse, W. W., 1956, The Paragenesis of Accessory Minerals: Economic Geology, Vol. 51, pp. 248-263. Parsons, I., 1965, The Feldspathic Syenites of the Loch Alish Intrusion, Assynt, Scotland: Journal of Petrology, Vol. 6, No. 3 , PP. 365-395-- 8 9 -P h a i r , G. and F i s h e r , F. G., 1962, Laramide Comagmatic S e r i e s i n the C o l o r a d o F r o n t Range: The F e l d s p a r s : G. S. A. Budd i n g t o n Volume, pp. 479-522. Ross, J . V., 1957, Combination Twinning i n P l a g i o c l a s e F e l d s p a r s : American J o u r n a l on S c i e n c e , 255, pp. 650-655. Schwartz, G. M., 1947, H y d r o t h e r m a l A l t e r a t i o n i n the P o r p h y r y  Copper D e p o s i t s : Economic Geology, V o l . 42, pp. 319-352. Slemmons, D. B., 1962, D e t e r m i n a t i o n o f V o l c a n i c and P l u t o n i c  P l a g i o c l a s e s U s i n g a Three- or F o u r - A x i s U n i v e r s a l Stage: G. S. A. S p e c i a l Paper 69. Smith, J . V., 1959, Phase Diagrams f o r A l k a l i F e l d s p a r s : G. S. A. Memoir 52, pp. I85-I93. Stevenson, J . S., 1940, Molybdenum D e p o s i t s o f B r i t i s h Columbia: B. C. Dept. o f Mines B u l l e t i n 9. T u r n e r , F. J . , 1947, D e t e r m i n a t i o n o f P l a g i o c l a s e w i t h the F o u r - A x i s U n i v e r s a l Stage: American M i n e r a l o g i s t , V o l . 32, pp. 389-410. T u t t l e , 0. F. and Bowen, N. L., 1958, O r i g i n o f G r a n i t e i n L i g h t  o f E x p e r i m e n t a l S t u d i e s : G. S. A. Memoir 74. Vance, J . A., 1961, P o l y s y n t h e t i c T w i n n i n g i n P l a g i o c l a s e : American M i n e r a l o g i s t , V o l . 46, pp. 1097-1119. W i n k l e r , H. G. F., 1965, P e t r o g e n e s i s o f Metamorphic Rocks: S p r i n g e r V e r l a g , New York I n c . , pp. 176-208. Yoder, e t a l . , 1957, Annual R e p o r t o f the G e o p h y s i c a l L a b o r a t o r y : C a r n e g i e I n s t i t u t e o f Washington 56, No. 1277, pp. 206-216. L E G E N D NOTE — Topography after a map by Hunting Survey Corporation Limited. Geology after a map by H W Sellmer and A. Gambardella. Basalt dykes . Geology by H. W. Sellmer and A.Gombadella — 1965. Altered latite dykes Intermediate dykes S Y M B O L S Quartz feldspar porphyry dykes Grey feldspar porphyry dykes. Hornblende feldspar porphyry dykes Fine grained quartz monzonite . Quartz latite - Quartz monzonite porphyry dykes . — 7 0 Geological contact ( dip). Limit of geological mapping and/or outcrop. Fault or shear . Dry fracture with MoSg . S E R B C R E E K P R O J E C T O M I N E C A M I N I N G D I V I S I O N GEOLOGICAL OF T H E B R I T I S H C O L U M B I A MAP S E R B C R E E K A R E A Coarse grained quartz monzonite . Haze I ton Group volcanic rocks. 'S-28 Hand specimen location and number. &3378.51 Precise survey station (number, elevation) S C A L E r - 1,000' Vancouver H. C Plres 238,000 - N 237,000 - N 236,000 - N 235,000 - N 234,000 - N 238,000 - N 237,000- N 236,000 - N 235,000 - N y \ 234,000-N L E G E N D Altered latite dykes. Intermediate dykes Quartz feldspar porphyry dykes. Grey feldspar porphyry dykes. Hornblende feldspar porphyry dykes. Intra - mineral quartz monzonite porphyry dykes Porphyritic quartz monzonite. Fine grained quartz monzonite. Coarse grained quartz monzonite . ^ Quartz latite - Quartz monzonite porphyry dykes. Geological contact (defined, assumed). Limit of geological mapping and/or outcrop. Fault (defined, assumed) showing direction of movement i r i ; v ^ r ^ Mineralized fault. "eov ^ Shear zone showing direction of movement Mineralized shear zone . Barren to weakly mineralized quartz vein stock wor k Quartz - Mo S2 vein greater than vjg" wide . M B 0 A 2 9 2 c , Quartz- Mo S? vein less than '/2" wide Dry fracture with Mo Sp . s - 7 3 Hand specimen location and number Precise survey station. Inclined diamond drill hole showing hole number, dip at collar, and total depth ffos'ZfSsoP Vertical diamond drill hole showing hole number, dip at collar, and total depth NOTE Topography after maps by Hunting Survey Corporation Limited. Geology after a map by H W. Sellmer and A G a m b a r d e 11 a. Geology by H W Sellmer and A Gambardella — 1965 S E R B C R E E K P R O J E C T O M I N E C A M I N I N G D I V I S I O N B R I T I S H C O L U M B I A G E O L O G I C A L M A P S H O W I N G 1965 DIAMOND DRILL HOLES S C A L E 200 Vancouver H. C. Pi res 237,500 N » 33 .000 N 237,800 N 230,000 N NOTE L N D Topograph, attar a map of Hunting Surrtf C or poration 11*1*0*. Patttrm of occurrtnc* of alt*r a tlon art r er / gmntral i fd K-feldspar, chlorite, epidote Clay, sericite. Sericite, K-feidspor, quartz, carbonate K-feldspar, sericite, quorti, c'ay, chlorite along major faults and veins only Quartz reining (generally barren) S E R B C R E E K P R O J E C T OMINECA MINING DIVISION BRITISH COLUMBIA ALTERATION DISTRIBUTION MAP S C A L E I -- 5 0 0 r^ ~ Structural trends Vancouver H C P'rtM 

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