UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Metamorphism in the Fraser Canyon, British Columbia Bremner, Trevor John 1972

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1973_A6_7 B75.pdf [ 7.39MB ]
Metadata
JSON: 831-1.0052780.json
JSON-LD: 831-1.0052780-ld.json
RDF/XML (Pretty): 831-1.0052780-rdf.xml
RDF/JSON: 831-1.0052780-rdf.json
Turtle: 831-1.0052780-turtle.txt
N-Triples: 831-1.0052780-rdf-ntriples.txt
Original Record: 831-1.0052780-source.json
Full Text
831-1.0052780-fulltext.txt
Citation
831-1.0052780.ris

Full Text

M E T A M O R P H I S M I N T H E F R A S E R C A N Y O N , B R I T I S H C O L U M B I A . b y T R E V O R J O H N B R E M N E R B S c . ( H o n s ) 1 9 6 9 , O t a g o , N e w Z e a l a n d . A t h e s i s s u b m i t t e d i n p a r t i a l f u l f i l l m e n t o f t h e r e q u i r e m e n t s f o r t h e d e g r e e o f M a s t e r o f S c i e n c e i n t h e D E P A R T M E N T O F G E O L O G Y W e a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A A p r i l 1972 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h . . C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f GEOLOGY The U n i v e r s i t y o f B r i t i s h C o l umbia V a n c o u v e r 8, Canada Date 12 March, 1973 i ABSTRACT. The northerly trending Hozameen, Yale and Hope faults transect the northwesterly trending Custer Gneiss and Hozameen, Ladnef and Jackass Mountain Groups. Yale Fault separates gneisses of the Hozameen Group to the east from Custer Gneiss to the west. The Custer Gneiss, as herein restricted, i s cocvpos-i t i o n a l l y distinct from the Hozameen Group and shows a period of early deformation not present in the Hozameen Group. During the Cretaceous, regional deformation and greenschist facies metamorphism of the biotite zone affected rocks between the Yale and Hozameen faults. These rocks grade into gneisses of the hornblende hornfels facies within a few hundred yards of the Spuzzum Quartz Diorite and Yale Intrusions. This restricted contact metamorphism contrasts with the widespread, high temper-ature and pressure metamorphism found in this and other areas around the Spuzzum Quartz Diorite on the west side of the Hope faul^;. i i TABLE OF CONTENTS. P a g e ABSTRACT i TABLE OF CONTENTS i i LIST OF TABLES i v LIST OF FIGURES V CHAPTER I INTRODUCTION 1 CHAPTER I I GENERAL GEOLOGY •a) I n t r o d u c t i o n k b ) S t r a t i g r a p h y 7 ( i ) Custer Gneiss 7 ( i i ) Hozameen Group . 1 3 ( i i i ) Ladner Group 1 5 ( i v ) Jackass Mountain Group 15 c) I n t r u s i v e rocks ( i ) E a r l y b a s a l t i c dykes 16 ( i i ) Green andesite porphyry ............... 17 ( i i i ) Spuzzum Quartz D i o r i t e ................ 18 ( i v ) S e r p e n t i n i t e along the Hozameen f a u l t . 19 (v) Yale I n t r u s i o n s « . . « - . e . . * . . 19 ( v i ) A p l i t e dykes 2 2 . ( v i i ) Late b a s a l t i c dykes .»..,.....»..<**.** 2 2 ( v i i i ) Needle Peak P l u t o n 2 2 CHAFTER I I I STRUCTURE a ) I n t r o d u c t i o n 2k b ) F o l d i n g 24 ( i ) S t r u c t u r e w i t h i n the Custer Gneiss .... 2k ( i i ) S t r u c t u r e w i t h i n the Hozameen Group ... 2 5 ( i i i ) S t r u c t u r e w i t h i n the Ladner Group ..... 2 6 c) F a u l t i n g ( i ) The Hozameen f a u l t 2 ? ( i i ) Yale f a u l t 2 8 ( i i i ) Hope f a u l t ........ .« 2 8 CHAPTER IV METAMORPHISM a ) Custer Gneiss 3 9 b ) Hozameen Group 4 5 c) Ladner and Jackass Mountain Groups 51 d) Comparison wit h other areas 5 6 CHAPTER V SUMMARY AND CONCLUSIONS ......... 6 6 , i i i Page REFERENCES 6 8 APPENDICES I. PETROGRAPHIC SUMMARY 73 I I . KEY TO SPECIMENS 8 9 Map (A poclieJr LIST OF TABLES. Page I . TABLE OF ROCK UNITS 6 I I . COMPARISON OF ROCK UNITS 58 I I I , MAIN IGNEOUS, METAMORPHIC AND STRUCTURAL EVENTS ... 63 V LIST 0 ? FIGURES. Page 1. LOCATION MAP if 2. POLES TO S FOLIATION - CUSTER GNEISS JO 3. FOLD AXES *ND LINEATIONS - CUSTER GNEISS 31 k. POLES TO AXIAL PLANES (S ) - CUSTER GNEISS 32: 5. HOZAMEEN GROUP - POLES TO BEDDING 33 6. HOZAMEEN GROUP - FOLD AXES . 3k 7. HOZAMEEN GROUP - POLES TO AXIAL PLANES 35 8. LADNER GROUP - POLES TO BEDDING 36 9. LADNER GROUP - FOLD AXES 37 10. LADNER GROUP - POLES TO AXIAL PLANES 38' 11. POSSIBLE REACTIONS FORMING SILLIMANITE ^Z. 12. CUSTER GNEISS - CONDITIONS OF METAMORPHISM kk 13. APPROXIMATE POSITION OF THE OLIGOCLASE ISOGRAD SOUTH OF SPUZZUM CREEK ^ 14. APPROXIMATE POSITION OF THE OLIGOCLASE ISOGRAD SOUTH OF EMORY CREEK 15. ' SOME STAGES IN THE METAMORPHISM OF SILICEOUS DOLOMITES ^9 16. EXPERIMENTAL DATA FOR THE REACTION:-. Muscovite + c h l o r i t e + quartz —> c o r d i e r i t e + phl o g o p i t e + water 17. DIAGRAM SHOWING THE REACTION : Muscovite + c h l o r i t e + quartz -> c o r d i e r i t e + phlog o p i t e + water 55 18. DIAGRAM COMPARING BULK COMPOSITIONS OF CUSTER GNEISS AND HOZAMEEN GROUP 57 1 I. INTRODUCTION. The map-area straddles the Lillooet and Northern Cascade L mountain ranges, approximately 50 miles north of the Inter-national Border, and 120 miles by road east from Vancouver (fig.1). Attention was centred on the Fraser Canyon between Yale and Spuzzum, and mapping was extended outwards into the mountains to the east and west to cover a total area of about 110 square miles. Elevations in the area range from about 200 feet on the Fraser River at Yale to about 65OO feet on the highest ridge crests. The area i s wet, and the precipitous valley sides are heavily forested. Good access to both sides of the Canyon i s provided by the Trans-Canada Highway and the Canadian National and Canadian Pacific railway lines. Logging roads and British Columbia Hydro trans-mission lines have improved the access to the remoter parts of the area. The purpose of the study was to investigate the nature and grade of metamorphism within the Custer, Hozameen, Ladner and Jackass Mountain Groups and to determine i f the Custer Gneiss could have been derived from the Hozameen Group by migmatisation as suggested by McTaggart and Thompson ( 1 9 & 7 ) . A sudden change in metamorphic grade of rocks of the Hozameen Group i s best explained by contact metamorphism during 2 the emplacement of the Spuzzum b a t h o l i t h and Yale I n t r u s i o n s . The o l d e s t u n i t i n the map-area, the Custer Gneiss, shows more than one phase of f o l d i n g . Rocks of the Hozameen, Ladner and Jack-ass Mountain Groups show only one phase of mesoscopic f o l d s . Selwyn ( 1 8 7 2 ) and Dawson ( 1 8 7 9 ) made the e a r l i e s t recon-naissance i n the area on t h e i r way to the i n t e r i o r . Cairnes ( 1 9 2 4 ) i n c l u d e d the southeast corner of the present area i n h i s Coqui-h a l l a map. The o r i g i n a l f o u r - m i l e map of the Hope area (west h a l f ) of Cairnes ( 1 9 4 4 ) , reconnaissance mapping along the Fraser R i v e r F a u l t Zone by McTaggart and Thompson ( 1 9 6 7 ) » new four-mile mapping by Roddick and Hutchison ( 1 9 6 9 ) i n the northwest p a r t of the Hope sheet and the most recent map of the west h a l f of the Hope map-area by Monger ( 1 9 6 9 ) have a l l c o n t r i b u t e d to the present r e g i o n a l , p i c t u r e . D e t a i l e d work to the south has been done by Read ( i 9 6 0 ) , and f u r t h e r d e t a i l e d work by Pigage i s under way i n an adjacent area to the southwest. Ei g h t v/eeks v/ere spent i n the f i e l d between l a t e September and mid-December 1971» and a f u r t h e r two weeks were spent between February and May 1 9 7 2 . Thanks are due to Dr P. B. Read f o r suggesting and super-v i s i n g the p r o j e c t and to Dr K. C. McTaggart f o r the use of some t h i n s e c t i o n s . F i e l d work was supported by the N a t i o n a l Research c o u n c i l , (grant if 6 7 - 7 9 7 3 ) . I am g r a t e f u l to the U n i v e r s i t y of B r i t i s h Columbia f o r a UBC Graduate Fe l l o w s h i p and to the Geology Department f o r use i n the f i e l d of a Honda t r a i l b i k e . My wife 3 Sally and Fay Miner kindly helped type the thesis. N. Wilson and B. Wilson assisted with the preparation of figures. Imperial Oil Limited has provided considerable encouragement and has done the duplicating of maps, figures and text. 5 I I . GENERAL GEOLOGY« a) I n t r o d u c t i o n The area i s cut by three major n o r t h - s t r i k i n g f a u l t s . (Map, i n p o c k e t ) . The eastern-most Hozameen f a u l t has been traced southwards w e l l i n t o northern Washington, and extends many miles to the n o r t h . The Hope and Yale f a u l t s extend southwards across the I n t e r n a t i o n a l Border, and merge north of the map-area before j o i n i n g the o l d e r Hozameen f a u l t south of Boston Bar. The Hope, Yale and Hozameen f a u l t s together make up p a r t of the Fraser R i v e r F a u l t System (Tipper, ( 1 9 7 2 ) ) -On the east s i d e of the map-area, E a r l y Cretaceous conglom-erat e s and sandstones of the Jackass Mountain Group o v e r l i e s l a t e s : and sandstones of the E a r l y to Middle J u r a s s i c Ladner Group, which are separated by the Hozameen f a u l t from the cherts and green-stones of the u n f o s s i l i f e r o u s Hozameen Group. On the west side o f the Fraser R i v e r , d i o r i t e , g r a n o d i o r i t e and quartz d i o r i t e d i s c o r d a n t l y i n t r u d e rocks of the Hozameen Group. F a r t h e r west, the Yale f a u l t cuts o f f these r o c k s , and west of the Yale f a u l t , g r a n i t i c rocks i n t r u d e pegmatite and q u a r t z o f e l d s p a t h i c b i o t i t e -garnet gneiss which are c o n s i d e r a b l y a l t e r e d . The pegmatite and gneiss belong to the Custer Gneiss^ of u n c e r t a i n age, which 1 Reasons f o r a s s i g n i n g these rocks to the Custer Gneiss rather than i n c l u d i n g them i n the Hozameen Group as was done by McTaggart and Thompson ( 1 9 6 7 ) are given on page 9 -6 Post-Eocene(?) Late Eocene (39 m.y.) 5^ m.y.' Late Cretaceous 76 to 103 m.y/ TABLE I. TABLE OF ROCK UNITS. MYLONITE FROM YALE FAULT NEEDLE PEAK PLUTON LATE BASALTIC DYKES PINK APLITE DYKES YALE INTRUSIONS: granite (a) (b) SPUZZUM QUARTZ DIORITE SERPENTINITE FROM HOZAMEEN FAULT Lower Cretaceous JACKASS MT. GROUP b.iotite granodiorite diorite coarse-grained hornblende-biotite quartz diorite greywacke and conglomerate Lower to Middle Jurassic Mid-Triassic? Pre-Jurassic GREEN ANDESITE PORPHYRY LADNER GROUP BASALTIC DYKES HOZAMEEN GROUP slate and feldspathic greywacke CUSTER GNEISS greenstone, meta-argil-l i t e , chert, biotite gneiss and amphibolite. biotite-garnet gneiss pegmatite Baadsgaard et a l . (1961) 5Mattinson (1970) "Richards and White (1970) +Mattinson (1972) 7 extends southwards to the I n t e r n a t i o n a l Border, Custer Gneiss near Spuzzum Creek i s cut by the Hope f a u l t , which to the south sets the Spuzzum Quartz D i o r i t e of Late Cretaceous age against the gneiss and Yale d i o r i t e r o c k s , b) S t r a t i g r a p h y ( i ) Custer Gneiss The Custer Granite-Gneiss was f i r s t mapped by Daly ( 1 9 1 2 ) near the I n t e r n a t i o n a l Border as the 'Custer B a t h o l i t h ' because i t appeared to c o n s i s t of h i g h l y sheared g r a n i t i c m a t e r i a l . Misch ( 1 9 6 6 ) traced the c o n t i n u a t i o n of the Custer Gneiss, which he r e f e r r e d to as the 'Skagit Gneiss} from the I n t e r n a t i o n a l Border f o r t y m i les south i n t o Northern Washington. Misch, too, was impressed by the l a r g e amount of igneous m a t e r i a l , but noted the presence of subordinate but exceedingly numerous remnants of more or l e s s i s o c h e m i c a l s u p r a c r u s t a l r o c k s . Of these, he r e p o r t e d , the most widespread are commonly g a r n e t i f e r o u s b i o t i t e s c h i s t s , and more r a r e l y g a r n e t i f e r o u s a m p h i b o l i t e s . McTaggart and Thompson O 9 6 7 ) reported the Custer Gneiss south of Hope to c o n s i s t l a r g e l y of a s t r i k i n g l y banded gneiss c o n s i s t i n g of a l t e r n a t i n g l i g h t p l a g i o c l a s e - r i c h l a y e r s , and dark b i o t i t e - or hornblende-rich l a y e r s . They a l s o noted that g a r n e t i f e r o u s amphibolite makes up about 10 per cent of the u n i t . Read ( i 9 6 0 ) found that the bulk of the Custer Gneiss between Hope and Emory Creek c o n s i s t e d of l a y e r e d hornblende- and / or b i o t i t e - r i c h gneiss and white pegmatite g n e i s s . Two features of the Custer Gneiss were s t r e s s e d by a l l f i v e 8 authors. Almost everywhere the Custer Gneiss exhibits varying degrees of cataclasis, and the layered gneiss i s almost invariably cut by discordant pegmatites. Evidence of shearing i s preserved in the form of plagioclase augen, poikiloblastic garnets with trains of inclusions lying at various angles to the foliation, elongated quartz crystals with undulatory extinction which show strong preferred orientation, and shreds of partly chloritised biotite which curve around plagioclase augen. Misch (1966) commented on the development of pegmatites in the Skagit Gneiss: Features indicating small scale mobilisation of crystalline material are common in the Skagit Gneiss. . . . Widespread pegmatitic material, mostly trondjhemitic and locally granitic, ranges from synkinematic gneissose layers and lenses. . . . to post-kinematic pods and dykes. Late-metamorphic minor igneous components suggest anatexis did occur at depth. McTaggart and Thompson (1967) described most of the Custer Gneiss as being migmatitic, with bodies of pegmatite ranging from layers of single plagioclase augen to irregular masses of almost massive plagioclase pegmatite and coarse- to medium-grained trond-jhemite in areas up to 1/3 mile across. Read (i960) described pegmatite gneiss forming part of the Custer Gneiss as a white-weathering rock composed of coarse grains of plagioclase surrounded by quartz and biotite, and stated: "Because the pegmatite gneiss i s so intimately related with the foliated and layered gneiss. . . . i t i s not possible to map the actual limits of the pegmatite gneiss." 9 North of Yale, a belt of quartz-plagioclase-biotite gneiss, garnetiferous amphibolite, and a large proportion of quartz-plagioclase-biotite pegmatite extends between the Hope and Yale faults as far north as Spuzzum Creek. Pegmatite, although i t i s particularly abundant near Yale and Spuzzum Creek where i t appears: to form small irregular intrusions as well as the ubiquitous dykes, i s intimately mixed with the gneiss i t intrudes and i s d i f f i c u l t to map separately, but generally i t shows considerable evidence of shearing. The gneiss and amphibolite have also been sheared. Garnet porphyroblasts have been shattered; quartz, chlorite, biotite and plagioclase show extreme undulatory extinction, and i n one specimen large plagioclase crystals were found forming clots in a much finer quartz-rich matrix, a texture described from the Custer Gneiss by Read (1960). •-The rocks described above have been intruded by dykes of Spuzzum Quartz Diorite, and by a three-mile-long body of diorite, the older of the two main Yale intrusions. McTaggart and Thompson (1967) recognised these rocks immediately north of Yale as Custer Gneiss, but assigned identical rocks from the same belt near Saw-mill Creek to the Hozameen Group. The Hozameen Group in the present map-area i s represented by large quantities of greenstone, micaceous quartzite, and lesser chert and marble. Near their contact with the Spuzzum batholith, rocks of the Hozameen Group show a sharp increase of metamorphic grade, but nowhere does pegmatite form a significant part of the lithology. The high-grade rocks formed tend to be more quartzose or more amphibolitic 10 than those of the Custer Gneiss and garnet i s a very i n s i g n i f i c a n t component. Close to both the Hozameen and the Yale f a u l t s , rocks of the Hozameen Group have a c a t a c l a s t i c texture l i k e the Custer Gneiss, but the c a t a c l a s i s i s not evident i n rocks more than a quarter of a mile from the major f a u l t zones and i s c e r t a i n l y not a c h a r a c t e r i s t i c of the u n i t . Chert was found w i t h i n the mylonite zone a s s o c i a t e d with the Yale f a u l t immediately south of Sawmill Creek. The f a c t that there i s no evidence of chert west of the Yale f a u l t anywhere i n the map-area suggests that the Yale f a u l t forms the western boundary of the Hozameen Group. In the map-area i t i s proposed that a l l rocks w i t h extensive pegmatites are Custer" Gneiss, and that a l l metamorphic rocks w i t h l i t t l e or no pegmatite be excluded from the Custer Gneiss. On t h i s b a s i s , the b e l t of b i o t i t e - g a r n e t gneiss and pegmatite between the Hope and Yale f a u l t s i s regarded as Custer Gneiss. A l l metamorphic rocks i n the map-area immediately east of the Yale f a u l t are regarded as belonging to the Hozameen Group. This i n c l u d e s q u a r t z o f e l d s p a t i c b i o t i t e gneiss exposed immediately south of the Yale road t u n n e l , which has been intrude d by e a r l y b a s a l t i c dykes and by Yale d i o r i t e but l a c k s the extensive pegmatite development found i n adjacent rocks west of the Yale f a u l t . Garnet i s a l s o t o t a l l y l a c k i n g i n the gneiss a t the Yale t u n n e l . West of the Hope f a u l t at Spuzzum Creek, a roof pendant - extends f i v e miles i n t o the Spuzzum b a t h o l i t h . The l i t h o l o g y i s s i m i l a r to that of the gneiss east of the Hope f a u l t except that the rocks are unaltered and show no signs of p o s t - c r y s t a l l i s a t i o n 1 1 8 t r a i n . Discordant pegmatite veining i s extensive. Garnet i s common and a p e l i t i c gneiss contains the assemblage quartz-b i o t i t e - s i l l i m a n i t e - g a r n e t . At the head of Spuzzum Creek, grey s i l l i m a n i t e - b e a r i n g gneiss of the Breakenridge Formation (Reamsbottom, 1 9 7 1) has a very s i m i l a r l i t h o l o g y and appearance to the rocks of the roof pendant farther downstream, and was correlated with the Custer Gneiss and Skagit Gneiss by Reams-bottom. In the absence of further evidence, the gneiss west of the Hope f a u l t exposed i n Spuzzum Creek w i l l be regarded as Custer Gneiss, or at l e a s t as c o r r e l a t i v e with the Custer Gneiss. S t r u c t u r a l evidence tends to support the assignment of a l l metamorphic rocks i n the map-area immediately east of the Yale v f a u l t to the Hozameen Group, and a l l metamorphic rocks west of the v a l e f a u l t to the Custer Gneiss. As shown i n Chapter I I I , rocks from between the Yale and Hope f a u l t s show evidence of one episode of f o l d i n g about a shallowly southeast-plunging a x i s . Rocks between the Yale and Hope f a u l t s have apparently been co-a x i a l l y folded twice about an axis plunging at a moderate angle to the northwest. The Yale f a u l t must be an important s t r u c t u r a l break and i n the map-area o f f e r s an a l t e r n a t i v e to the migmatite . front proposed by McTaggart and Thompson ( 1 9 6 7 ) to explain the fact that the Hozameen-Custer Gneiss contact cuts across the s t r i k e of both f o l i a t i o n and bedding. McTaggart and Thompson ( 1 9 6 7 ) reported that north of Hope, the Custer Gneiss outlines a crude northwest-plunging a n t i f o r m , a 1 2 broad arch plunging northwest, superimposed on small i s o c l i n a l overturned to recumbent folds plunging northwest. The i s o c l i n a l folds probably correlate with the F^ folds recognised north of Yale between the Hope and Yale faults, and the large antiform i s probably associated with the open F^ folds. If so, the entire belt of gneiss between the Hope and Yale faults i s structurally continuous with Custer Gneiss to the south. The axial trace of the large antiform was shown by Read (i960) to l i e north-south along the Fraser River south of Emory Creek. There i s evidence in the form of a vergence boundary north of Sawmill Creek that a large northwest-plunging antiformal structure most l i k e l y passes through the present map-area; this structure i s now truncated by the Yale fault but i s probably the northward continuation of the structure shown by Read (i960). A l l available evidence suggests that rocks mapped, by McTaggart and Thompson (1967) a s Hozameen Group between the Hope and Yale faults, and a roof pendant of gneiss west of the Hope fault at Spuzzum Creek belong to the Custer Gneiss, while a small volume of gneiss at the Yale tunnel, previously regarded as Custer Gneiss, probably belongs to the Hozameen Group. These conclusions more or less agree with those of Monger O969) who restricted the Hozameen Group between Yale and Spuzzum to the east side of the Fraser River. Monger, however, regarded amphibolite and biotite. gneiss west of Stout and east of Yale fault as Custer Gneiss, but the author prefers McTaggart and Thompson^ interpretation and regards i t as Hozameen Group. 13 A uranium-lead study of zircon and sphene from the correlative Skagit Gneiss of Northern Washington by Mattinson (1970) gave the zircons an absolute age of 1600 million years. Further studies (Mattinson, 1972) indicated that the zircons were involved in an episode of regional metamorphism and migmatisation between 60 and 90 million years ago, and that while not indicated by zircons from the Skagit Gneiss, there i s evidence that some rocks in the Northern Cascade terrain underwent an additional period of regional metamorphism and migmatisation 415 million years ago. Unfortunately the age of the zircons, which are probably detrital in origin, may not reflect the age of deposition of the Custer Gneiss. The Custer Gneiss could have been derived at any time before the Jurassic from a Precambrian source, and may or may not have been involved in the 415 million year metamorphism. ( i i ) Hozameen Groupp. Socks of this unit are found in a belt about five miles wide on both sides of the Fraser Kiver between the Yale and Hozameen faults. They consist predominantly of green meta-volcanic flows and tuffs which comprise units up to about 2000 feet thick, interbedded with lesser thicknesses of micaceous quartzite and chert. There are also rare limestone layers about 10 to 20 feet thick and up to several miles i n length. The greenstones of the Hozameen Group are largely massive:, with r e l i c t p o r p h y r i t i c t e x t u r e common. One specimen wit h a r e l i c t pyroclastic texture indicates that some of the greenstones 14 were originally tuffs. In thin section the greenstones are very fine-grained and consist mainly of albite (in phehocrysts and groundmass), pale green amphibole and bi o t i t e . Large porphyro-blasts of clinozoisite are common, and chlorite i s abundant in the groundmass and in large patches that appear to pseudomorph pyroxene. The rocks are cut in places by thin veinlets of quartz and calcite. The micaceous quartzites are brownish-weathering strongly-foliated rocks consisting mostly of fine-grained quartz, with up to 10 per cent brown biotite, and from 1 to 20 per cent albite. Within these quartz-mica schists there are pure quartzite horizons about twenty feet thick, one of which was followed over five miles-Cherts from near the Hozameen fault show a north-south foliation which i s seen in thin section to be caused by cataclasis. Marble layers about five to twenty feet thick consist of pure white calcite with clots (1-2cm) of quartz and feldspar that stand out on a weathered surface. The Hozameen group i s unfossiliferous but has been correl-ated on the basis of lithologic similarity with the Cache Creek Group north of the map-area (Daly, 1912; Monger, 1969), and the Fergusson Group i n the Bridge River area, 100 miles north-northwest of the map-area (Monger, 1969). Recent discovery of a Mid-Triassic conodont fauna within the Fergusson Group suggests that the Hozameen Group may be Middle Triassic (Cameron and Monger, 1 9 7 1 ) . 1 5 ( i i i ) Ladner Group. The Ladner Group occupies most of the map-area to the east of the Hozameen fault. It consists of grey-black to dark blue-grey pyrite-bearing slates and minor interbedded sandstones. The slates are very fine-grained. X-ray study shows that they contain the assemblage quartz-albite-muscovite-chlorite, locally calcite or dolomite, and pyrite. A sandstone, typical of twelve examined in thin section, consists of 3 0 per cent angular frag-ments of albite (up to 3 m m ) , 5 per cent subangular quartz crystals and 6 5 per cent groundmass ( 0 . 0 1 m m ) consisting of angular plagio-clase (of indeterminable composition), quartz, muscovite and calcite. As albite i s the dominant constituent of a l l the Ladner Group sandstones, they can be described as feldspathic greywackes* Fossils found elsewhere in the Ladner Group indicate an age of Early to Middle Jurassic ( Bajocian, Toarcian and possibly Sinemurian according to Coates, 1 9 7 0 ) . (iv) Jackass Mountain Group. This unit overlies the Ladner Group and occupies the north-east corner of the map-area in the vicinity of Anderson River Mountain. The contact was not observed, but Monger ( 1 9 6 9 ) pro-posed that the contact between the Ladner and Jackass Mountain Groups near Boston Bar i s an unconformity or a fault because rocks of the Jackass Mountain Group dip more shallowly. A similar change in dip across the contact is noticeable in the present map-area. At the boundary the lithology changes abruptly from well-16 cleaved dark blue-grey slate of the Ladner Group to massive grey-wacke and thin beds of dark a r g i l l i t e . The Jackass Mountain Group consists of blue-grey feldspathic greywacke, a r g i l l i t e and greenish volcanic-derived conglomerate. A typical greywacke consists mostly of angular fragments of plagioclase which have been altered to albite, muscovite and calcite. Quartz, calcite and fragments of fine-grained volcanic rock are present in minor amounts; apart from the plagioclase, most of the remainder of the rock consists of fine-grained, very chlorite-rich matrix. The main difference between the sandstones of the Ladner and Jackass Mountain Groups i s that the angular feldspar fragments form 70 to 85 per cent of a Jackass Mountain sandstone, and only 20 to kO per cent of a sand-stone from the Ladner Group. A Jackass Mountain conglomerate consists almost entirely of sub-rounded fragments of porphyritic volcanic rock. It also contains a few rounded fragments of quartz arenite, and others of a feldspathic greywacke (coarse angular plagioclase crystals in a fine groundmass) which were pro-bably derived from the Ladner Group. Hock fragments make up about 87 per cent of the conglomerate, and the rest consists mainly of a very fine-grained matrix and a few large crystals of calcite, epidote and recrystallised quartz. Calcite veining i s extensive in rocks of the Jackass Mountain Group. X-ray studies show that the matrix contains muscovite and chlorite, and dolomite occurs instead of calcite in one specimen. The Jackass Mountain Group i s known to be Lower Cretaceous in age. (c) I n t r u s i v e Rocks. (i) Early Basaltic Dykes. 17 Discordant dark dykes a few inches to a few feet thick intrude Custer Gneiss and rocks of the Hozameen Group at Spuzzum Creek and Yale. The dykes are strongly foliated parallel to the regional f o l i a t i o n . At Yale they appear to have been metamorph-osed by the Yale diorite intrusion and now consist of hornblende, plagioclase, and some bioti t e . A medium-grained green diabase dyke about thirty feet wide discordantly intrudes Custer Gneiss west of the Hope fault in Spuzzum Creek. The dyke now consists of 60 per cent strongly zoned plagioclase ( A n ^ (core) to (rim)), 15 per cent brown hornblende and 25 per cent yellow-green chlorite. This dyke appears to have undergone the same retrograde metamorphism as the rocks i t intrudes. ( i i ) Green Andesite Porphyry. A;striking green porphyry found as dykes, s i l l s and as a small stock within the Ladner Group in the northeast of the map-area, has 1cm euhedral plagioclase phenocrysts which make up kO per cent of the rock. The phenocrysts show very strong o s c i l l -atory zoning with a composition between An_, and An„, and have been almost completely altered to sericite around the margins. Chlorite and epidote pseudomorph hornblende (a l i t t l e of which remains) to form 5 per cent of the rock. The rest of the rock consists of a fine-grained (0.04mm) groundmass of chlorite, albite, muscovite, and quartz. "^These dykes are too small to show on the map. They occur at specimen l o c a l i t i e s 91 and 1 respectively. 18 ( i i i ) Spuzzum Quartz Diorite. Spuzzum Quartz Diorite forms a large batholith to the west of the Hope fault, and occupies a large block north of Sawmill Creek on the east side of the Yale fault, where i t discordantly intrudes rocks of the Hozameen Group and forms vertical cream-coloured c l i f f s . Spuzzum Quartz Diorite i s characteristically coarse-grained. West of the Hope fault i t i s unfoliated, but east of the Yale fault there i s a rough foliation and lineation defined by horn-blende-rich layers and the alignment of the large hornblende crystals. These structures are concordant with the regional struc-ture within the Hozameen Group> At places near the margin the foli a t i o n i s contorted and disrupted, suggesting that deformation was taking place before the rock had s o l i d i f i e d completely. In thin section the foliation i s not evident. Plagioclase (60 per cent) i s only slightly zoned with cores of An^Q and slightly more sodic rims. Green hornblende (20 per cent) p o i k i l -i t i c a l l y encloses golden brown bi o t i t e . Biotite makes up 15 per cent of the rock, and quartz 5 per cent. Accessory minerals include epidote, sphene, zircon, opaques, and a l i t t l e chlorite replacing bio t i t e . A range of absolute ages (K-Ar) was obtained for different parts of the Spuzzum Quartz Diorite, from 76 million years near the margin to 103 million years near the core (Richards and 19 White, 1970). These ages were obtained twenty miles south of the present map-area, near Hope. McTaggart and Thompson (1967) reported an absolute age of 76 million years for a specimen of Spuzzum Quartz Diorite taken from Sawmill Creek. (iv) Serpentinite along the Hozameen fault. In places, the contact between the Ladner Group and the Hozameen Groups i s marked by pods of serpentinite. One of these was found in thin section to consist of 95 per cent serpentine pseudomorphs after olivine and orthopyroxene, and about 5 per cent of olivine and clinopyroxene. Clinopyroxene lamellae within the orthopyroxene pseudomorphs had remained intact. Serpentine-f i l l e d fractures define a rough fo l i a t i o n . The rock must have originally been a coarse-grained peridotite, with crystals up to 8mm. The emplacement of the serpentinite i s presumed to be re-lated to the Hozameen fault which i s probably older than 8k million years (Cbates, i n Wanless et a l . (1967)) t but younger than the Ladner Group, which i s Lower to Middle Jurassic in age. McTaggart and Thompson (196?) suggested an age of late Early Cretaceous as the age of the Hozameen fault. (v) Yale Intrusions. From Yale, an intrusive complex extends northwards on both sides of the Yale fault. The principal rock type, which can be seen on the highway from Yale almost to Sawmill Creek i s a dark medium-grained diorite, in which the plagioclase occurs as subhedral randomly oriented laths, and the hornblende i s i n t e r -20 s t i t i a l . The rock i s weakly foliated or unfoliated, and fractures into small fragments when weathered. In thin section, the elongated subhedral crystals of plagio-clase (An^) about 1.5mm long are surrounded by i n t e r s t i t i a l pale brown hornblende. Plagioclase makes up 55 per cent of the rock, hornblende 40 per cent, and opaques 5 per cent. This rock differs from the Spuzzum Quartz Diorite in that i t contains no quartz, no biotite, the plagioclase i s much more anprthite-ri-ch, and the grain size i s half as great. North of Sawmill Creek on the east side of the Yale fault* a foliated f e l s i c granodiorite discordantly intrudes the Spuzzum Quartz Diorite and i s found extensively as dykes and' s i l l s within the diorite to the south. The granodiorite at the contact against Spuzzum Quartz Diorite i s cut by a fault. The attitude of the fault plane i s 172 x 75°E, and slickensides on the fault surface plunge 7 ° northwards implying horizontal movement. Protoclastic texture throughout the granodiorite suggests that the rock was partly s o l i d i f i e d at the time of emplacement, and faulting at the contact with the Spuzzum Quartz Diorite may have accompanied em-placement of the granodiorite intrusion. The contact against the diorite to the south follows the regional strike, and i s marked by a line of elongated inclusions of Hozameen chert and amphibolite. At one place on the contact, an inclusion striking 1 ^ 2 ° , dipping 50°SW, has weathered leaving an overhanging c l i f f of diorite. 100 yards long. The granodiorite i s cut off to the west by the Yale fault. 2 1 The rock has a protoclastic texture, with a foliation defined by flakes of biotite and chlorite. The foliation i s not always parallel to the regional foliation, but in small dykes i t runs parallel to the walls of the dyke. Ragged crystals of plagio-clase (about 0.5mm) show strong oscillatory zoning, with cores of A n ^ which are partly altered to chlorite and sericite, and rims of An^. The large crystals of plagioclase l i e within a matrix of smaller crystals (average grain size 0.5mm). Plagioclase makes up 50 per cent of the rock, quartz 30 per cent, potash feldspar 20 per cent, and pale brown biotite and chlorite together make up only about 1 per cent. The biotite i s "pre-shearing". Accessory minerals include apatite, zircon and opaques. Inclusions of Yale diorite within the Yale granodiorite show clearly that the granodiorite i s the younger of the two intrusions. Characteristic of both the intrusions i s the presence of abundant elongated inclusions of Hozameen Group rocks up to 100 yards or more long, which have structures in them concordant with the regional structure. The inclusions are particularly abundant in a zone along the contact between the two intrusions. The age of the Yale Intrusions i s not known exactly. As the older diorite i s not well foliated, i t i s probably younger than the Spuzzum Quartz Diorite. The granodiorite i s clearly younger than the Spuzzum Quartz Diorite, which i t has intruded. The Yale Intrusions are therefore younger than 76 million years. They are both cut by the Yale f a u l t , which i s presumed to be post-Eocene, and the Hope fault, which i s known to be post-Eocene. McTaggart 22 and Thompson (196?) suggested a Late Cretaceous or Early Tertiary age. A' K-Ar age determination on a "Yale Granodiorite" by Richards and White (1970), gave an absolute age of 59 million years, though i f this sample has been severely sheared like the granodiorite near Sawmill Creek, the age would probably reflect the time of shearing. Richards and White (1970) suggested that the Yale Intrusions may be the sheared equivalents of Lower Eocene plutonic rocks (Hells Gate pluton and older parts of the Hope plutonic complex). ( v i l Aplite Dykes. Fink or white aplite dykes containing faint streaks of bio-t i t e discordantly intrude Spuzzum Quartz Diorite and cut across l i g h t grey dykes of granodiorite near Sawmill Creek. The dykes are foliated parallel to their margins. i ( v i i ) Late Basaltic Dykes. Dark, very fine-grained basaltic dykes'*" were observed in two places cutting Yale granodiorite discordantly. The age of these i s unknown, but as none was found cutting the Needle Peak Pluton they are assumed to be older. ( v i i i ) Needle Peak Pluton. This large granite batholith has intruded slates and sand-stones of the Ladner Group in the southeast corner of the map-area, ^"These dykes, too small to show on the map, were: found 100 yards south of Sailor Bar tunnel, and 0.5 miles north of Yale t u n n e l . T h e i r mineralogy was not determined. 23 forming a contact aureole about 200 yards wide. The bulk of the pluton consists of coarse-grained unfoliated albite granite con-taining about 55 per cent microcline perthite, 20 per cent quartz, 20 per cent albite (An^), 5 per cent biotite and a l i t t l e horn-blende. Unlike some of the other granitic intrusions in the map-area, the granite shows no sign of cataclasis and the quartz has sharp extinction. A quartz diorite dyke near the intrusive con-tact i s coarse-grained and consists of 58 per cent plagioclase (An^j.); 33 per cent hornblende, which has been partly replaced by biotite; 5 per cent large p o k i l i t i c biotite crystals; i n t e r s t i t i a l quartz and a l i t t l e apatite. A K-Ar age determination on a part of Needle Peak Pluton gave an absolute age of 39 million years (Baadsgaard et a l . , 1961). 2f III. STRUCTURE a) Introduction. The map-area i s cut by three north-striking faults. The Hope and Yale faults together belong to the Fraser River Fault System, which may be traced 50 miles south and 130 miles north of Yale. The Hozameen fault has been traced southwards into northern Washington. The faults divide the map-area into three domains, each of which has undergone regional metamorphism and deformation. / • b) Folding. (i) Structure within the Custer Gneiss between the Hope and Yale faults. Bedding within the Custer Gneiss has been obliterated and there i s a lack of marker horizons. In two outcrops, quartzite layers that w i l l be referred to as S^  surfaces, were found iso-c l i n a l l y folded about axes that plunge about 20° northwest. These folds w i l l be referred to as F„. Poles to axial planes (S, sur-faces) of a few folds l i e in a plane perpendicular to the F^ fold axis. (Fig. 4) The F 1 folds have been refolded by open folds (shown in Fig. 3) which plunge at a moderate angle northwest. The pole to the S_-pole girdle of Fig. 2 defines the same northwest-plunging 25 f o l d a x i s . A vergence boundary marking a change from northeast vergence to southwest vergence as one proceeds north of Sawmill Creek i s probably the trace of the a x i a l plane of a major a n t i -form which plunges a t a moderate angle to the northwest. The F^ f o l d s i n the Custer Gneiss are most l i k e l y contemp>-oraneous with the f o l d s i n the Hozameen and Ladner Groups. No F^ f o l d s were found i n the Hozameen and Ladner Groups. ( i i ) S t r u c t u r e w i t h i n the Hozameen Group, between the Yale and Hozameen f a u l t s . Bedding i n the Hozameen Group i s defined by marble and chert h o r i z o n s . F o l i a t i o n i n most p a r t s of the Hozameen Group i s w e l l developed, s t r i k i n g northv/est and mostly dip p i n g at high angles to the northeast or southwest. I t i s i n v a r i a b l y p a r a l l e l to bedding except near the Hozameen f a u l t , where a n o r t h - s t r i k i n g f o l i a t i o n a s s o c i a t e d w i t h m y l o n i t i s a t i o n has developed i n chert s and green-stones. Axes of minor f o l d s plunge at a low angle to the south-ea s t . ( F i g . 6). The f o l d s are open and have westerly vergence, w i t h a strong mineral l i n e a t i o n or c r e n u l a t i o n p a r a l l e l to the axes of the mesoscopic f o l d s . A.plot of poles to bedding ( F i g . 5) i n d i c a t e s that bedding has been f o l d e d about a h o r i z o n t a l south-e a s t - t r e n d i n g a x i s . A p l o t of poles to a x i a l planes of minor f o l d s "^Vergence was defined by Wood ( 1 9 6 3 ) as the d i r e c t i o n t h a t l i e s i n a h o r i z o n t a l plane normal to the trend of the f o l d a x i s , given by the sense of r o t a t i o n of the upper member of the r o t a -t i o n a l couple i m p l i e d by the asymmetry of the f o l d . On a map the vergence symbol i n d i c a t e s the d i r e c t i o n of cl o s u r e of the major s t r u c t u r e . £.0 (Fig. 7) shows a strong maximum suggesting that the rocks have undergone only one period of folding. Westerly vergence of mi-nor folds in the Hozameen Group suggests that the rocks are on the east limb of a large south-plunging antiform. The foliation found in the Hozameen Group i s also developed within the margins of the Spuzzum Quartz Diorite; in places i t i s found to be contorted. Minor folds and a strong mineral lineation in the Spuzzum Quartz Diorite are also found to be concordant with those in the Hozameen Group. This evidence suggests that the Spuzzum Quartz Diorite was emplaced during the episode of deform-ation which affected the Hozameen Group, and that the folding con-tinued after the intrusion had s o l i d i f i e d . ( i i i ) Structure within the Ladner Group, east of the Hozameen fault. Foliation i s well developed in the slates of the Ladner Group and i s mostly parallel to bedding which i s defined by sand-stone beds, by sandy layers or layers of pyrite cubes within the slates. Strong axial-plane cleavage i s developed in the slates in the cores of large mesoscopic folds. Foliation strikes north-west and dips steeply to the northeast or southwest. Lineations and axes of minor folds plunge at a shallow angle to the south-east. (Fig. 9). A plot of poles to bedding (Fig. 8) gives a s t a t i s t i c a l fold axis that plunges at a shallow angle to the southeast. Clustering of five poles to axial planes (Fig. 10) suggests that like the rocks of the Hozameen Group, the Ladner slates have probably undergone only one period of folding. A change 27 from southwesterly to northeasterly vergence between points 117 ^ d 123 on the map suggests that a large southeast-plunging synform, recognised by Cairnes (192*0 in the Coquihalla Valley, extends into the present map-area. Graded bedding on the west limb near the Hozameen fault indicates that the top of the sequence l i e s to the northeast and that the fold must be a syncline. c) Faulting, (i ) The Hozameen fault. The Hozameen fault was f i r s t mapped by Daly ( 1912) at the International Border and was extended north intoj the present map-area by McTaggart and Thompson ( 1 9 & 7 ) . In the present map-area, the Hozameen fault separates Lower to Middle Jurassic slates and sandstones of the Ladner Group from greenstone, chert and micaceous quartzite of the Hozameen Group. The contact i s sharp, with a few pods of serpentinite along i t . The "Serpentine Belt", however, i s by no means continuous in this area and nowhere exceeds f i f t y feet in width. Near the fault, cherts and greenstones are mylonitised and a north-striking foliation i s developed. Unlike the mylonite of the Yale fault, the cataclastic rocks near the Hozameen fault are not layered and do not show folding. South of the Inter-national Border, Misch ( 1 9 6 6 ) has shown that the fault i s f l a t lying, while just north of the border i t i s ver t i c a l . Immediately east of Yale the fault trace bends to the east, which i s taken to mean that the fault i s dipping shallowly. The apparently variable dip of the fault may mean that the fault has been folded and i s therefore older than the Hope and Yale faults. A small pluton that 28 cuts the Hozameen fault has given the fault a minimum age of Bk million years (Coates, in Wanless et a l . 1967). McTaggart and Thompson (1967) suggested an age of late-Early Cretaceous. ( i i ) Yale fault. The Yale fault i s marked along most of i t s length by a my-lonite zone up to J>00 yards wide. McTaggart and Thompson (1967) noted the presence of small garnets from the original gneiss within the well-layered mylonite. The layers strike parallel to the trace of the fault plane. The mylonite contains open mesoscopic folds which plunge at moderate to steep angles southwards. Mod-erately plunging folds 6how westerly vergence and suggest that the west side of the fault has moved relatively down. Structures in the mylonite are clearly discordant and unrelated to the structures in metamorphic rocks on either side, suggesting that both sides of the mylonite zone are fault bounded. The Yale fault i s evidently a major discontinuity, as axes of mesoscopic folds change from a southeast plunge on the east side to a northwest plunge on the west side. V McTaggart and Thompson (1967) suggested that the Yale fault: i s the same age as the Hope fault. Both are cut by the Silver Creek stock which gives them a minimum age of 35 million years (Richards and White, 1970). ( i i i ) Hope fault. The Hope fault was f i r s t recognised farther south by Read 2 9 (1960). An extremely conspicuous topographic lineament marks the fault trace which separates coarse unfoliated Spuzaum Quartz Diorite to the west from a zone of Custer biotite-garnet gneiss and finer-grained Yale Intrusions to the east. Within the map-area, l i t t l e evidence suggests a fault rather than an intrusive contact, except for the topographic lineament and some small pods of mylon-it e that consist of broken quartz and plagioclase crystals show-ing extreme undulatory extinction and large calcite crystals, in a fine-grained cataclastic matrix. Gneiss enclosed by the Spuz-zum Quartz Diorite i n Spuzzum Creek valley west of the Hope fault has a foliation discordant with the foliation of similar gneiss on the east side. Read (1960) stated that the fault plane dips steeply and that the last movement on the fault was probably dip> s l i p . Eisbacher and Tempelman-Kluit (1972) suggested that right-l a t e r a l movement has taken place along this fault. As the fault cuts an Eocene conglomerate south of Yale i t i s known to be post-Eocene in age. The fault i s cut to the south by the Silver Creek stock, radiometric dating of which gives the fault a minimum age of 35 million years (Richards and White, 1970). 30 Poles to foliation - Custer Gneiss approximately 329xCo" CONTOURS: Z% . 6%, 5% , 3% t2% per 1 % area. 3 1 Fold Axes - Custer Gneiss & LJNEATIONS N ( F 2 F O L D S ) T Maximum at 329x 65 CONTOURS-- 20%, 13%, 10% ,7%, 3% psr 1% areo. 32 33 Hozameen Group - Poles to b idd ing N CpjXOxilTiOtQly 146 x 0 . CONTOURS: 10%,Q%, 6%, 4%, 3%, 2%, 1 % per 1 % creo. 34 35 Hozameen Group-Poles to Axial Planes N CONTOURS: 25%, 20%, 12% , 8 % . 4%, 1% per 1% area. 3S pahts CONTOURS: 11%, 9%, 7%, 4%, 2% per Fbte to sx-pclQ circle approxin>3tQly U8x2(f 1% area. Maximum approximately 139x 70°NE 3 9 IV. METAMORPHISM a) Custer Gneiss. The Custer Gneiss consists of a f a i r l y uniform sequence of biotite-quartz-plagioclase gneiss with or without garnet, abun-dant pegmatite and about 5 per cent amphibolite^ with or without garnet. A typical biotite gneiss consists of 3 0 per cent quartz, hO per cent plagioclase (An^), 25 per cent biotite and 5 per cent garnet. In a l l the specimens taken from between the Hope and Yale faults, the quartz shows undulatory extinction, sericite and epi-dote partly replace plagioclase, and pale green chlorite largely replaces brown biotite. Garnet appears as large closely-fractured porphyroblasts containing inclusions of quartz and plagioclase. Shearing, alteration of feldspars and formation of chlorite at the expense of biotite and hornblende appears to be the result of an episode of retrograde metamorphism and deformation. Ubiquitous white pegmatite i s found as dykes cutting the gneiss and as large intrusive bodies within the Custer Gneiss. A-specimen found between the Hope and Yale faults shows evidence of having undergone the same retrograde metamorphism as the gneiss. It i s a medium to coarse-grained ( 3 - 5 m m ) unfoliated rock consisting of about 6 0 per cent albite (An^), 2 0 per cent quartz and 2 0 per cent chlorite which has almost completely replace orange-brown bio-40 t i t e . Accessory minerals i n c l u d e c l i n o z o i s i t e , muscovite, sphene, opaques, and garnets which p o i k i l i t i c a l l y enclose quartz and a l b i t e . A diabase dyke"*" w i t h i n the Custer Gneiss to the east of the Hope f a u l t near Spuzzum Creek appears to have been subjected to the same episode of retrograde metamorphism. West of the Hope f a u l t a t Spuzzum Creek, a r o o f pendant of Custer Gneiss f i v e m i les long l i e s w i t h i n the Spuzzum b a t h o l i t h . The l i t h o l o g y i s s i m i l a r to t h a t of the gneiss east of the Hope f a u l t except that the rocks are u n a l t e r e d and show no si g n s of p o s t - c r y s t a l l i s a t i o n s t r a i n . Discordant pegmatite v e i n i n g i s e x t e n s i v e . A p e l i t i c gneiss from t h i s area contains the assem-blage q u a r t z - b i o t i t e - s i l l i m a n i t e - g a r n e t . S i l l i m a n i t e i s i n the form of long prisms l y i n g w i t h i n l a r g e b i o t i t e f l a k e s , and aligned, p a r a l l e l to the f o l i a t i o n . Garnet occurs i n 1cm i d i o b l a s t i c c r y s t a l s showing no signs of c o r r o s i o n . Assuming that e i t h e r s t a u r -o l i t e or muscovite has been completely used up, p o s s i b l e r e a c t i o n s f o r the formation of s i l l i m a n i t e are: 1. 3 F e A l i t S i 2 0 1 Q ( 0 H ) 2 + 2 S i 0 2 —> s t a u r o l i t e quartz F e A l 2 S i 5 0 1 2 + 5 A l 2 S i 0 5 + 3H 20 garnet s i l l i m a n i t e Described on p.7-If1 2. ( M g , F e ) 5 A l 2 S i 3 0 1 2 + KA12( AIS^O^) (0H>2 — > almandine muscovite K(Mg,Fe) 3AlSi 50 1 Q + 2Al 2Si0 5 + S i 0 2 biotite sillimanite quartz Another reaction which i s not so l i k e l y to have formed s i l l i -manite i s the reaction: 3. 3FeAl i fSi 20 1 ( )(0H) 2 + KA1£( AISi 0 1 Q) (0H) 2 + S i 0 2 > staurolite muscovite quartz KFe 3(AlSi 30 1 ( ))(OH) 2 + 7 A l 2 S i 0 5 + 3H 20 biotite sillimanite Reaction 3 i s not so l i k e l y to have occurred because stauro-l i t e i s not observed anywhere in the area and muscovite i s not found in the area close to sillimanite-bearing rocks. If reaction 3 had occurred, either muscovite or staurolite would be found unless the proportions of muscovite and staurolite had been exactly as in the balanced equation. Idioblastic garnets which show no signs of corrosion suggest that garnet i s more l i k e l y to have been a product than a reactant, and that sillimanite i s most l i k e l y to have been formed by a reaction similar to 1 . Hollister ( 1 9 6 9 ) found reaction 1 to be the most important reaction forming sillimanite in meta-greywackes of the Kwoiek area, twenty-three miles north of Spuzzum, which had undergone contact metamorphism at high pressure at the margin of the Scuzzy Batholith. <t2 A SJLLIMANI TE The dot r e p r e s e n t s & composition i n the f i e l d of m u s c o v i t e - £ O r n e L -b i o t i t e b e f o r e ths r e MUSCOVITE a c t i o n and i n the f i e l d s i U l n a r , ite-" b i o t i t e - g a r n t t a f t e r the r e -ac t i o n . T i i u s c o v i t e + garnet —> biotite + silliinanite* GARNE T BSOTI TE s t a u r o l i t e - t q u a r t z garnet * s i l l i m a n i t e * H 20 STAUROLITE SILLIMANITE The dot represents a bulk composition i n ths f i e l d o.f. s>ta.uroli t e - b i o i i t a -gamet b e f o r e the r e -a c t i o n and i n the f i e l d of .silliTnan-i t e - b i o t i t e -garnet a f t e r the r e a c t i o n . GARNE T FIG. 11 Possible reactions BIO Tl TE form incj sillimanite h3 A calc-silicate assemblage found at the margin of the Spuz-zum Creek roof pendant consists of garnet, diopside, clinozoisite and quartz, with magnetite and sphene unusually abundant. Locally, green hornblende appears to be replacing diopside. Abundant f l u i d inclusions in the quartz and a total lack of calcite imply that the f l u i d phase was probably water-rich. The adjacent assemblages, sillimanite-almandine-quartz and clinozoisite-quartz, and the exten-sive development of pegmatite probably formed by partial melting of the gneiss set limits on the conditions of metamorphism (Fig.12). Conditions of metamorphism in the Spuzzum roof pendant must have been in the range 6 7 0 - ? 7 0°C, 4 . 8 - 8 . 8 k b . Because of the lack of index minerals in the Custer Gneiss east of the Hope fault, i t i s impossible to exactly specify the maximum grade reached during regional metamorphism. Extensive development of pegmatite indicates that the Custer Gneiss east of the Hope fault was probably metamorphosed under roughly the same conditions as the gneiss in the Spuzzum roof pendant. One per cent of primary muscovite coexisting with quartz in a sheared biotite-garnet gneiss from this zone indicates that conditions for the re-action: KAl 2(AlSi 30 1 0)(OH) 2 + S i 0 2 > muscovite quartz KAlSi^Og + A l 2 S i 0 5 + H20 K feldspar sillimanite were, not exceeded during^the metamorphism. _ i > ' / i i _ f r — 300 500 700 9 0 0 T E M P E R A T U R E C F I G . 12 C U S T E R G N E I S S - C O N D I T I O N S O F M E T A M O R P H I S M . D A T A F R O M : • (1 ) R I C H A R D S O N , G I L B E R T L B E L L ( 1 9 6 9 ) ( 2 ) H O L D A W A Y ( 1 9 G S ) (3) R O B E R T S O N & W Y L L I E ( 1 9 7 1 ) • (A)EVAN s ( I S G S ) . " ( 5 ) R ( C H A R D S O M ( 1 9 G 8 ) ±5 Hozameen Group. Within the map-area, the Hozameen Group consists of massive greenstones and foliated greenschists interbedded with micaceous quartzite and chert, and rare marble layers. Typical greenstones have r e l i c t porphyritic or locally pyroclastic texture. A common greenstone i s extremely fine-grained with r e l i c t phenocrysts of albitised plagioclase about 0.1mm, porphyroblasts of clinozoisite, and chlorite pseudomorphs after pyroxene in a very fine (0.002ram) groundmass of albite, quartz, chlorite., pale green biotite, actino-l i t e hematite and sphene. A typical micaceous quartzite contains 60 per cent quartz, 20 per cent albite, 10 per cent biotite, k per cent chlorite and 5 per cent hematite. Thus most of the Hozameen Group in the map-area reached equilibrium under conditions of the biotite zone of the greenschist faciesv The following assemblages were observed in a folded magnesium-rich siliceous carbonate layer in a marble collected by Dr. H. J. Greenwood 100 yards south of Sailor Bar tunnel: forsterite-clinohumite-calcite. diopside-quartz-calcite. tremolite-calcite. diopside-plagioclase (An^)-muscovite-calcite. The assemblage talc-calcite was observed, with talc forming at the expense of olivine. Two other rocks from the same place gave the assemblages:. S P U Z Z U M , C R E E K \rpfrocd\-o irdsx Isss than that \ \oi Concdo Bzlzcm .} B: Bio titc in T.5. APf'ROXH^'Jz POSITION OF- HIE GLIGOCiAi (dotted I S?u:h cfSpv::-jm fe. FIG. 13 i f i S ISC6RAD APPROXIMATE POSITION OF THE OLIGOCLASE ISOGRAD 48 hornblende-plagioclase-calcite-microcline-epidote. forsterite-calcite-plagioclase-epidote. forsterite-calcite-plagioclase-clinohumite. hornblende-quartz-calcite. clinohumite-epidote-calcite-plagioclase. calcite-epidote-quartz-microcline-diopside. The assemblage talc-calcite was observed once again with the talc this time forming at the expense of clinohumite. Clinohumite was identified by X-ray. The assemblage calcite-quartz i s stable so that conditions for the formation of wollastonite by the reaction:: CaCO, + SiO. CaSiO, + C0_ were not exceeded. (Fig. 15). The absence of dolomite (checked by staining) indicates that the reaction:: ~'\ ' Ca 2Mg 5Sig0 2 2(0H) 2 + 11CaMg(C03)2 > tremolite dolomite SMggSiO^ + 13CaC03 + 9C02 + H20 forsterite calcite went to completion. Experimental data on the reaction (Fig. 15) show that 48o°C would be a minimum temperature for the reaction at 2 kb. According to the work of Metz and Trommsdorf (1972) the reaction at 1 kb has a minimum temperature of 539°C when the mole fraction of CO in the fl u i d phase exceeds 0.9- The stable assem-•• J 5 Some stages in the m e t a tno r p h i_s_m of siliceous dolomites 50 blage tremolite-calcite-forsterite indicates that the reaction: 3Ca 2Mg 5Si g0 2 2(0H) 2 + 5CaC05 > tremolite calcite 11CaMgSi206 +'2Mg2SiO^ + 3H20 + 5 C 0 2 diopside forsterite has not taken place and sets a maximum temperature limit on the rock of 615°C at 2 k b . (Fig. 1 5 ) . Because the exact temperature at which these reactions takes place depends on the mole fractions of C0 2 and. H^ O in the f l u i d phase, i t i s impossible to set limits more precisely. However, the maximum temperature limit for the* metamorphism i s below the nfinimum melting temperature of a granite, and, no pegmatite would be expected in the Hozameen gneiss. This i s borne out by obser-vations in the f i e l d : the Hozameen Group i s generally devoid of pegmatite. The assemblage of talc-calcite about some forsterite or clino-huoite grains indicates that at a late stage of this episode of metamorphism the f l u i d phase had a mole fraction of at least 0 .5 water. The temperature at this stage would have been below 450°C at 2kb. (see Fig. 1 5 ) . Near Spuzzum Creek a skarn formed at the margin of the Spuz-zum Quartz Diorite contained the assemblages: 5 1 c a l c i t e - t r e m o l i t e - m u s c o v i t e . c a l c i t e - g r e e n hornblende-quartz. g a r n e t ( g r o s s u l a r i t e - a n d r a d i t e ) - c a l c i t e - q u a r t z f green hornblende -e p i d o t e - q u a r t z - c a l c i t e . Tremolite i s unstable a t the margin of the quartz-bearing l a y e r where i t i s a l t e r i n g to hornblende. As i n the marble from S a i l o r -Bar t u n n e l , the assemblage t r e m o l i t e - c a l c i t e sets an upper temper-ature of 615°C at 2 k b . The other assemblages are not d i a g n o s t i c . The Hozameen Group t h e r e f o r e shows the e f f e c t s of a low grade r e g i o n a l metamorphism under c o n d i t i o n s of the b i o t i t e zone of the gr e e n s c h i s t f a c i e s , and a probably contemporaneous episode of contact metamorphism under c o n d i t i o n s of the hornblende-hornfels f a c i e s a t the margins of the Spuzzum Quartz D i o r i t e (and f a r t h e r south, the-Yale I n t r u s i o n s ) . D i s t o r t i o n of f o l i a t i o n i n the Spuzzum Quartz D i o r i t e which corresponds to the f o l i a t i o n i n the h o r n f e l s and the b i o t i t e zone rocks of the Hozameen Group suggests that the Spuzzum Quartz D i o r i t e was not completely s o l i d i f i e d at the time of r e g i o n a l metamorphism. Concordance of f o l i a t i o n s and mineral l i n e a t i o n s i n the Spuzzum Quartz D i o r i t e , the h o r n f e l s , and the b i o t i t e zone rocks i m p l i e s that r e c r y s t a l l i s a t i o n was t a k i n g place i n a l l three zones during the one episode of deformation. c) Ladner and Jackass Mountain Groups. The s l a t e s of the Ladner Group have c l e a r l y been formed by low grade r e g i o n a l metamorphism, and a r g i l l i t e s of the Jackass Mountain Group d i s p l a y a moderately well-developed cleavage that i s 52 regarded by Coombs et a l . d 9 7 0 ) as a c h a r a c t e r i s t i c of some rocks of the preh n i t e - p u m p e l l y i t e f a c i e s . The Ladner Group and the Jackass Mountain Group have been subjected to r e g i o n a l metamorphism under c o n d i t i o n s of the lowest greenschist f a c i e s or lower. X-ray d i f f r a c t i o n s t u d i e s of whole rocks and study of t h i n s e c t i o n s f a i l e d to f i n d any calcium a l u m i n o s i l i c a t e or z e o l i t e index min-e r a l s , though they may have been present i n minute amounts or i n rocks not sampled. Coombs et a l . (1970) 1 found that only a few of the metamorphic rocks known to belong to the preh n i t e - p u m p e l l y i t e f a c i e s which they s t u d i e d contained index m i n e r a l s . According to Coombs et a l . , the development of calcium a l u m i n o s i l i c a t e s and calcium z e o l i t e s i s i n h i b i t e d by a high p a r t i a l pressure of CO^ r e l a t i v e to H^O. The occurrence of up to 5% c a l c i t e i n most of the Ladner Group and Jackass Mountain Group rocks supports the cont e n t i o n that a high p a r t i a l pressure of CO,, may be re s p o n s i b l e f o r the absence of p r e h n i t e , pumpellyite or z e o l i t e s . I n the case of the Jackass Mountain Group, the complete m i n e r a l o g i c a l recon-s t i t u t i o n of the greywackes (replacement of the matrix by c h l o r i t e and muscovite, a l b i t i s a t i o n of the p l a g i o c l a s e , and the develop-ment of epidote porphyroblasts) would be taken by Coombs et a l . (1970) as evidence that metamorphism has occurred. The metamorphic grade remains indeterminate, but at l e a s t the absence of b i o t i t e •^Coombs et a l . ( 1 9 7 0 ) described rocks from the prehnite-pum-p e l l y i t e f a c i e s of Northern Maine. Well developed cleavage was seen only i n the f i n e - g r a i n e d r o c k s . The rocks from Northern Maine showed l i t t l e macroscopic s i g n of metamorphism and i n t h i n s e c t i o n primary igneous or sedimentary textures were u s u a l l y found to be c l e a r l y preserved. The most common assemblage v/as q u a r t s - a l b i t e -c h l o r i t e - s e r i c i t e - c a l c i t e - s p h e n e , with calcium a l u m i n o s i l i c a t e s ab-sent from most of the ro c k s . M i n e r a l o g i c a l r e c o n s t i t u t i o n was taken to be the main i n d i c a t i o n that metamorphism had taken p l a c e . 5 3 east of the Hozameen f a u l t i s evidence that there i s a change of metamorphic grade at the f a u l t . At the margin of the Needle Peak P l u t o n , s l a t e s of the Ladner Group have been subjected to contact metamorphism. Within about 1 0 0 yards of the g r a n i t e c o n t a c t , the t y p i c a l rocks are h o r n f e l s e s c o n t a i n i n g quartz, p l a g i o c l a s e , b i o t i t and c o r d i e r i t e which occurs i n o v a l p o i k i l o b l a s t i c c r y s t a l s up to 5mm. The c o r d i e r i t e and b i o t i t e probably formed from muscovite, c h l o r i t e and quartz by the reaction:: muscovite + c h l o r i t e + q u a r t z — • c o r d i e r i t e + b i o t i t e + H.,0 which was recognized by Schreyer and Yoder O 9 6 D as one of the most important r e a c t i o n s producing c o r d i e r i t e i n p e l i t i c r o c k s . The r e a c t i o n : K A l 3 S i 5 0 1 0 ( 0 H ) 2 + - M g 5 A l 2 S i 3 0 1 0 ( 0 H ) 2 + 2 S i 0 2 > muscovite c h l o r i t e quartz K H g 3 A l S i 3 0 1 0 ( 0 H ) 2 + M g 2 A l 2 f S i 5 O l g + H 2 0 phlogopite c o r d i e r i t e water was s t u d i e d experimentally by S e i f e r t ( 1 9 7 0 ) . The r e a c t i o n curve i s given i n F i g . 1 6 . The e f f e c t of f e r r o u s i r o n s u b s t i t u t i n g f o r magnesium i n n a t u r a l c h l o r i t e , b i o t i t e : and c o r d i e r i t e i s unknown, but i t i s almost c e r t a i n that the temperature of metamorphism ex-ceeded 5 0 0°C. Conditions at the margin of the Needle Peak Pluton were therefore s u f f i c i e n t to form assemblages of the hornblende h o r n f e l s f a c i e s . FROM; SEIFERT (1970)' EXPERIMENTAL DATA FOR THE REACTION: m u s c o v i t e + c h l o r i t e + q u a r t z > c o r d i e r i t e + p h l o g o p i t e + w a t e r FIG. 16 FROM: SEIFERT ()9 70) A T h e m u s c o v i t e - ( p h e n g i t z ) - c h l o r i t e f i e l d s h r i n k s w i t h r i s i n g t e m p e r a t u r e . T h e e x a c t p o s i t i o n o f t h e t i e - l i n e ( d a s h e d ) v a r i e s , a c c o r d i n g t o P T c o n d i t i o n s , b e t w e e n d o t t e d l i m i t s . FI 6. 17 D I A G R A M S H O W I N G M u s c o v i t e + c h l o r i t e +• q u a r t z T H £ R E A C T I O N > p h l o g o p i t e +• c o r d 1 c r i t c * w c t 5 6 di) Comparison with other areas, and the age of metamorphism. A number of studies have been made of metamorphic rocks around the margins of the Spuzzum batholith. In the following table, some units that have been mapped outside the present map-area are compared and contrasted with the Custer Gneiss and the Hozameen Group north of Yale. Rocks of the Hozameen Group north of Yale are thought to belong to the uppermost of the four divisions of this unit recognised by McTaggart and Thompson ( 1 9 6 ? ) . There seems to be a distinct difference between the bulk compo-sit i o n of the Hozameen Group and that of the Custer Gneiss. The difference does not show up distinctly when representative spec-imens of both are plotted on an ACF diagram because the amounts of albite, potash feldspar and quartz are not represented in the dia-gram. (Fig. 1 8 ) . Biotite gneiss, commonly containing garnet, i s typical of the Custer Gneiss, whereas greenstone, a r g i l l i t e , chert and limestone are typical of the uppermost division of the Hoza-meen Group. In the present map-area, the bulk composition of the: Hozameen Group i s either amphibolitic or quartzose, while the rocks of the Custer Gneiss are mostly quartzo-feldspathic. Reamsbottom ( 1971) correlated the Breakenridge Formation with the Custer Gneiss. West of the Hope fault the gneiss exposed in Spuzzum Creek i s extremely similar in lithology and metamorphic grade to grey gneiss of the Breakenridge Formation described by Reamsbottom from the head of Spuzzum Creek, but i s not dissimilar enough from the Custer Gneiss east of the Hope fault to warrant drawing a distinction by naming i t Breakenridge Formation. In the HORNBLENDE Diagram shoving similar bulk compositions of tyoical rocks of •• ° Custer Gne.'ss from Spuzzum reef pendant A Hozameen gttiss (excluding mcrbte ). 58 TABLE I I COMPARISON OF SOCK UNITS (Rock types l i s t e d i n decreasing order of importance) CUSTER GNEISS IN PRESENT MAP-AREA, (present author) 55/o b i o t i t e gneiss kO% pegmatite 5% amphibolite +. garnet t r c a l c - s i l i c a t e CUSTER GNEISS SOUTH OF HOPE. (McTaggart & Thompson ( 1 9 & 7 ) ) b i o t i t e - h o r n b l e n d e gneiss pegmatitic gneiss 1056 amphibolite _+ garnet r a r e q u a r t z i t e & skarn BREAKENRIDGE FORMATION. (Reamsbottom ( 1 9 7 1 ) ) homogeneoxis grey gneiss ( b i o t i t e - q u a r t a - p l a g i o e l a s e gneiss garnet) abundant pegmatite amphibolite p e l i t i c gneiss migmatite minor skarn PELITIC SCHIST NORTHWEST OF HOPE. (Read ( 1 9 6 0 ) ) 95?° p e l i t i c s c h i s t (dark grey with 20-30% of garnet, s t a u r o l i t e , muscovite and ky a n i t e ) 5?o amphibolite CAIRN NEEDLE FORMATION., (Reamsbottom ( 1 9 7 D ) p e l i t i c s c h i s t garnet-hornblende s c h i s t c a l c - s i l i c a t e s c h i s t limestone conglomerate HOZAMEEN GROUP. (McTaggart & Thompson ( 1 9 & 7 ) ) D i v i s i o n 1 (lowest) ribbon chert 2 5 % limestone 5 ^ greenstone 59 D i v i s i o n 2 100"?? greenstone limestone & chert lenses D i v i s i o n 3 100;$ ribbon chert & a r g i l l i t e D i v i s i o n k (North of Yale i n present map-area) (present author) 60% greenstone h0% chert & a r g i l l i t e minor limestone 60 present map-area there i s no equivalent of the Cairn Needle Form-ation which Reamsbottom correlated with a unit of p e l i t i c schists (the Settler Schist) mapped northwest of Hope by Read ( i 9 6 0 ) . Read ( i 9 6 0 ) , McTaggart and Thompson ( 1 9 6 7 ) , Hollister ( 1 9 6 9 ) , and Reamsbottom (1971) a l l concluded that the most recent episode of metamorphism in the region was in some way related to the em-placement of large quartz diorite plutons during the Late Cret-aceous. Read ( i 9 6 0 ) and McTaggart and Thompson ( 1967) believed that aluminosilicate minerals developed in the p e l i t i c Settler Schist: northwest of Hope were the product of regional metamor-phism contemporaneous with the emplacement of the Spuzzum Quartz Diorite. Hollister ( 1969) stated that metamorphic rocks in the Kwoiek area of Briti s h Columbia, 23 miles north of Spuzzum, have> undergone high pressure contact metamorphism at the eastern margin of the Coast Range batholith. Reamsbottom ( 1971) recognised an early phase of Barrovian-type regional metamorphism and stated that andalusite- and sillimanite-bearing schists to the west of the present map-area were produced in the contact aureole of the Scuzzy pluton. The present study indicates that such high pressure contact metamorphism i s restricted in the present map-area to the Custer Gneiss, which appears to have been subjected to two phases of metamorphism. Metamorphic conditions implied by stable mineral assemblages west of the Hope fault were sufficient to produce large amounts of pegmatite by partial melting, at least during 61. the second phase of high grade metamorphism. The d i s t r i b u t i o n of pegmatite i n the Custer Gneiss bears no r e l a t i o n s h i p to the pos-i t i o n of the Spuzzum Quartz D i o r i t e i n e i t h e r the present map-area or i n the area mapped by Read ( i 9 6 0 ) j u s t south of Y a l e . The Spuzzum Quartz D i o r i t e presumably occupied the reg i o n of highest temperature i n the t e r r a i n at the time of i t s emplacement and the pegmatite ought to be most abundant c l o s e to the margins of the b a t h o l i t h . That i t i s not suggests that a t l e a s t some of the pegmatite may have been formed during the f i r s t phase: of r e g i o n a l metamorphism and deformation which preceded the emplacement of the Spuzzum Quartz D i o r i t e . S i l l i m a n i t e forming i n aluminous rocks i n d i c a t e s t h a t second-phase :metamorphism of the Custer Gneiss probably took p l a c e under the c o n d i t i o n s envisaged by H o l l i s t e r and Reamsbottom (above). The Custer Gneiss between the Hope and Yale f a u l t s a l s o shows the e v i -dence of an episode of high grade r e g i o n a l metamorphism and deform- > a t i o n during which time pegmatites were produced from the g n e i s s . I t i s probable that metamorphic c o n d i t i o n s were roughly the same as those i n the Spuzzum roof pendant. There i s no reason to dispute the i d e a that second phase metamorphism of the Custer Gneiss was contemporaneous with emplace-ment of the Spuzzum Quartz D i o r i t e , at a depth and a temperature s u f f i c i e n t to produce a n a t e x i s , where isotherms were not i n v a r i a b l y c o n c e n t r i c around the b a t h o l i t h . In t h i s r e g i o n the d i s t i n c t i o n between contact and r e g i o n a l metamorphism becomes b l u r r e d and may not be worth making. 62 East of the Yale f a u l t , metamorphic c o n d i t i o n s were q u i t e d i f f e r e n t . The Spuzzum Quartz D i o r i t e , and l a t e r the Yale I n t r u -s i o n s , have metamorphosed a s t r i p of Hozameen rocks about h a l f a mile wide. Near the margin of the Spuzzum Quartz D i o r i t e , and f a r t h e r south near the margin of the Yale I n t r u s i o n s , rocks of. the Hozameen Group c o n s i s t of amphibolite, b i o t i t e - g a r n e t gneiss and marble. The o l i g o c l a s e i s o g r a d separating a l b i t e (An^ ^) from o l i g o c l a s e or andesine ( A n 2 £ ~ A n 3 ^ i i e s 6 ° ° t 0 8 0 0 yards east of the contact and r e f l e c t s the contact ( F i g s . 1J & I k ) . The develop-ment of i d e n t i c a l s t r u c t u r e s ( s o u t h e a s t e r l y - p l u n g i n g , open F., f o l d s and strong l i n e a t i o n s ) i n the Spuzzum Quartz D i o r i t e , and i n b i o -t i t e - z o n e r e g i o n a l l y metamorphosed rocks of the Hozameen Group where they are c l e a r l y r e l a t e d to the r e g i o n a l metamorphism, sug-gests that the i n t r u s i o n was s y n t e c t o n i c . I t i s thus proposed that the r e g i o n a l metamorphism of the Hozameen Group i s the same as the second phase metamorphism of the Custer Gneiss. The emplacement of the Spuzzum Quartz D i o r i t e a f f e c t e d the Custer Gneiss d i f f e r e n t l y from the Hozameen Group s o l e l y because the two t e r r a i n s were at a d i f f e r e n t depth: movement on the Yale f a u l t has juxtaposed the Custer Gneiss, metamorphosed at great depth, and the Hozameen Group, metamorphosed much nearer the s u r f a c e . The second phase metamorphism probably caused a l t e r a t i o n of p e r i d o t i t e along the Hozameen f a u l t to serpe n t i n e . Thus the meta-morphism must be younger than the Hozameen f a u l t which has been dated as older than Sk m i l l i o n years, the age of a small pluton 6 3 TABLE I I I . MAIN METAMORPHIC, IGNEOUS AND STRUCTURAL EVENTS. Post-Eocene? Major Events: : Movement on Yale and Hope f a u l t s . Retrograde ( 3 r d phase) metamorph-ism of Custer Gneiss. E f f e c t s : Formation of exten-s i v e mylonite zones, extensive shearing. Late Eocene ( 3 9 m.y.) 1 I n t r u s i o n of Needle Peak P l u t o n . Formation of contact aureole i n Ladner Group s l a t e s . Paleocene? ( 5 4 m.y.) T e r t i a r y to Late Cretaceous , ( 5 7 to 9 6 m . y . K Late Cretaceous. ( 7 6 to 1 0 3 m.y.)' Further contact meta-morphism of Hozameen Group r o c k s . Formation of F^ f o l d s I n t r u s i o n of Yale g r a n o d i o r i t e . I n t r u s i o n of Yale d i o r i t e . Second phase r e g i o n -a l metamorphism and deformation of Custer Gneiss. 1 s t r e g i o n a l metamorphism and def-ormation of Hozameen, Ladner and Jackass Mt Groups. Metamorphism and deformation at l e a s t p a r t l y contemp-oraneous w i t h i n t r u s i o n of Spuzzum Qtz D i o r i t e . I n t r u s i o n of Spuzzum Contact metamorphism Quartz D i o r i t e . of p a r t of the Hoza-(Mostly contemporaneous meen Group, with r e g i o n a l meta-morphism (above)). L a t e - E a r l y Cretaceous (84+ m.y.)^ Last movement on Hozameen f a u l t . Emplacement of s e r -p e n t i n i t e pods at or before t h i s time. P r e - J u r a s s i c ( 4 1 5 m.y?)^ ( 1 6 5 0 m.y?) 3 F i r s t phase metamor- Formation of F^ f o l d s phism of Custer Gneiss ' !: • Obscure igneous or metamorphic event. P o s s i b l y the 1 s t phase metamorphism above. O r i g i n of z i r c o n s i n Custer Gneiss. 1 2 % Baadsgaard et a l . ( 1 9D 1 ) Richards & White ( 1 9 7 0 ) "^Mattinson ( 1 9 7 0 ) Mattinson ( 1 9 7 2 ) 6k t h a t cuts i t (Coates, i n Wanless et a l . , 1 9 6 7 ) . The i n t r u s i o n of the Spuzzum Quartz D i o r i t e i n the map-area appears to have taken place 76 m i l l i o n years ago, although elsewhere ages of up to 103 m i l l i o n years have been obtained (Richards and White, 1 9 7 0 ) . Mattinson ( 1 9 7 0 ) gave an age of 57 to 92 m i l l i o n years f o r metamorphism of the S k a g i t Gneiss. I t seems necessary to pro-pose a pre-Lower J u r a s s i c episode of metamorphism as the f i r s t phase to a f f e c t the Custer Gneiss, as the equivalent of the i s o -c l i n a l f i r s t phase f o l d s were not formed i n the Hozameen, Ladner or Jackass Mountain Groups. This may have been the 1600 m i l l i o n year event forming the z i r c o n s , as the Custer Gneiss i s g e n e r a l l y thought to be sedimentary r a t h e r than igneous i n o r i g i n , and the z i r c o n s were probably formed i n the Custer Gneiss by metamorphism. The z i r c o n s may, however, be d e t r i t a l , d e r i v e d from a Precambrian source rock and the Custer Gneiss may be very much younger than the z i r c o n s . The f i r s t phase of the Custer Gneiss may then be the same as a *f15 m i l l i o n year episode of r e g i o n a l metamorphism and migmatisation s a i d by Mattinson ( 1972) to have a f f e c t e d some of the rocks of the Northern Cascade t e r r a i n . An episode of g r e e n s c h i s t facie6 r e g i o n a l metamorphism and deformation, the t h i r d phase of metamorphism to a f f e c t the Custer Gneiss, i s shown by the extensive a l t e r a t i o n of f e l d s p a r s and b i o t i t e , and by evidence of shearing. This a l t e r a t i o n and shearing i s only n o t i c e a b l e i n the zone between the Hope and Yale f a u l t s . Yale d i o r i t e from the same re g i o n i s c l o s e l y f r a c t u r e d and shows some evidence of a l t e r a t i o n : the p l a g i o c l a s e has been p a r t l y a l t e r e d 65 to ser i c i t e , and the hornblende has been partly altered to chlorite. Since the retrograde metamorphism i s younger than the Yale diorite and i s associated with cataclasis of some of the Custer Gneiss i t i s probably related to post-Eocene movement on the Hope and Yale faults. 66 V. SUMMARY AND CONCLUSIONS. The Yale f a u l t appears to separate two q u i t e d i f f e r e n t meta-morphic t e r r a i n s - to the west, a high grade t e r r a i n twice deformed about a northwest-plunging a x i s , and to the east a low grade t e r r a i n once deformed about a southeast-plunging a x i s . F i r s t phase i s o c l i n a l f o l d s w i t h i n the Custer Gneiss were produced during f i r s t phase r e g i o n a l metamorphism which d i d not a f f e c t the Hozameen Group. Monger ( 1 9 6 9 ) found no evidence w i t h i n the r e g i o n f o r a post-Late P a l e o z o i c , p r e - J u r a s s i c metamorphism envisioned by Misch ( 1 9 6 6 ) . The f i r s t phase r e g i o n a l metamorphism a f f e c t i n g the Custer. Gneiss may c o i n c i d e w i t h the;: formation of z i r c o n s i n i t , dated by Mattinson ( 1970) at 1600 m i l l i o n years. Or i t may c o i n c i d e with an episode of r e g i o n a l metamorphism and migmatisation which appears to have a f f e c t e d some rocks of the Northern Cascade t e r r a i n 415 m i l l i o n years ago (Mattinson, 1 9 7 2 ) . A.second phase of high grade r e g i o n a l metamorphism and deformation of the Custer Gneiss i s probably r e l a t e d to the em-placement of the Spuzzum Quartz D i o r i t e during the Late Cretaceous. Conditions exceeded those of the f i r s t s i l l i m a n i t e i s o g r a d and were s u f f i c i e n t to produce extensive p a r t i a l melting of the g n e i s s , implying metamorphism at a considerable depth. Movement on the Hope and Yale f a u l t s during the T e r t i a r y was a s s o c i a t e d w i t h r e t r o -67 grade alteration of the Custer Gneiss between the faults, and i s thought to have juxtaposed the Custer Gneiss against rocks of the Hozameen, Ladner and Jackass Mountain Groups which were also metamorphosed during the Late Crestaceous but at much shallower depths. East of the Yale fault, conditions of the biotite zone of the greenschist facies were reached in rocks of the Hozameen Group about the same time as the emplacement of the Spuzzum Quartz Dior-i t e , which was i t s e l f affected by regional deformation (correspon-ding to: the second phase in the Custer Gneiss) as i t metamorphosed Hozameen Group; rocks near the contact to the hornblende hornfels facies. Conditions were not sufficient to cause partial melting of the gneiss. At the same time, rocks of the Ladner and Jackass Mountain Groups were subjected to conditions of the lowest green-schist facies or lower. Emplacement of the Yale Intrusions caused further contact metamorphism of Hozameen Group rocks, extending the narrow zone: of hornfels almost as far south as Hope (Figs. 12 & 13). Emplacement of the Needle Peak Pluton caused contact metamor-phism of the Ladner slates to cordierite-biotite hornfels of the hornblende-hornfels facies. 68 REFERENCES. Baadsgaard, H., F o l i n s b e e , R.E., and L i p s o n , J . 1961: Fotassium-argon dates of b i o t i t e s from C o r d i l l e r a n g r a n i t e s ; B u l l . Geol. Soc. Am., v o l . 7 2 , pp. 6 8 9 - 7 0 2 . B o e t t c h e r , A.L. 1970: The system CaO-Al^^-SiO^-J^O at high pressures and temperatures; J . Pet. 11 : 3 3 7 - 3 7 9 . C a i r n e s , C.E. 1 9 2 4 : C o q u i h a l l a area, B r i t i s h Columbia; Geol. Surv. Can., Mem. 1 3 9 . 1 9 4 4 : Geology of Hope area, B r i t i s h Columbia; Geol. Surv. Can., Map 737A. Cameron, B.E.B., and Monger, J.W.H. 1971: Middle T r i a s s i c conodonts from the Fergusson Group, north-east Pemberton map-area ( 9 2 J ) , B r i t i s h Columbia; Geol. Surv. Can. % Paper 71-1B, p. 9 4 . Coates, J.A. 1 9 7 0 : S t r a t i g r a p h y and s t r u c t u r e i n Manning Park area, southwestern B r i t i s h Columbia; Geol. Soc. Can., Spec. Paper no. 6 , pp. 1 4 9 - 1 5 4 . Coombs, D. S., Horodyski, R.J. & Naylor, R.S. 1 9 7 0 : Occurrence of p r e h n i t e - p u m p e l l y i t e f a c i e s metamorphism i n northern Maine; An. J . S c i . , v o l . 2 6 8 , pp. 142 - 1 4 6 . 69 Daly, R.A. 1 9 1 2 : Geology of the North American C o r d i l l e r a a t the f o r t y -n i n t h p a r a l l e l ; Geol. Surv. Can., Mem. 3 8 . E i s b a c h e r , G.H., and Tempelman-Kluit, D.J. 1972: Map of major f a u l t s i n the Canadian C o r d i l l e r a ; Geol. Assoc. Can., Symposium a b s t r a c t s , pp. 13-14. Evans, B.W. 1 9 6 5 : A p p l i c a t i o n of a r e a c t i o n r a t e method to the breakdown e q u i l i b r i a of muscovite and muscovite p l u s quartz Am. J . S c i . , v o l . 2 6 3 , pp. 647-667 Gordon, T.M., and Greenwood, H.J. 1970: The r e a c t i o n : dolomite + quarts + water — — ^ t a l c + c a l c i t e + CO^; Am. J . S c i . , v o l . 2 6 8 , pp. 225-242. Greenwood, H.J. 1967: M i n e r a l e q u i l i b r i a i n the system MgO-SiC^-H^O-CO^ i n : Abelson, P.H., ed., Researches i n Geochemistry, v o l . 2: John Wiley & Sons, N.Y., pp. 542 - 5 6 7 . Holdaway, M.J. 1 9 6 6 : Hydrothermal s t a b i l i t y of c l i n o z o i s i t e p l u s quartz; Am. J . S c i . , v o l . 264, pp. 643 - 6 6 7 . H o l l i s t e r , L.S. 1969: Metastable p&ragene-tic sequence of a n d a l u s i t e , k y a n i t e and s i l l i m a n i t e , Kvoiek area, B r i t i s h Columbia; Am. J . S c i . , v o l . 2 6 7 , pp. 3 5 2 - 3 7 0 . 70 Mattinson, J.M. 1 9 7 0: Uranium-lead study of z i r c o n and sphene from p r e - T e r t i a r y igneous and metamorphic rocks i n the northern Cascade Mountains; Geol. Soc. Am., A b s t r a c t s w i t h programmes, v o l , 2 . , p. 1 1 6 . 1 9 7 2 : Ages of z i r c o n s from the northern Cascade Mountains, Washington; B u l l . Geol. Soc. Am., v o l . 8 3 , pp. 3 7 6 9 - 8 4 . McTaggart, K.C. 1 9 7 0 : Tectonic h i s t o r y of the northern Cascade Mountains; Geol. Assoc. Can., Spec, paper, no. 6 , pp. 137-148. McTaggart, K.C, and Thompson, R.M. 1 9 6 7 : Geology of part of the northern Cascades i n southern B r i t i s h Columbia; Can. J . Earth S c i . , v o l . 4 , pp. 1 1 9 9 - 1 2 2 8 . Metz, P., and Trommsdorf, V. 1 9 6 8 : Phase e q u i l i b r i a i n metamorphosed s i l i c e o u s dolomites; Contr. M i n e r a l , and P e t r o l . , v o l . 1 8 , pp. 3 0 5 - 3 0 9 . Misch, P. 1 9 6 6 : Tectonic e v o l u t i o n of the northern Cascades of Washington State; i n Can. I n s t . Mining Met., Spec v o l . 8 , pp. 1 0 1 - 1 8 4 . Monger, J.W.H. 1 9 6 9 : Hope map-area, west h a l f , B r i t i s h Columbia; Geol. Surv. Can., Paper 6 9 - 4 7 . Pigage, L. 1 9 7 2 : Unpub. M.Sc. t h e s i s , Univ. B r i t i s h Columbia. 7 1 Read, P.B. 1 9 6 0 : The geology of the Fraser V a l l e y between Hope and Emory Creek, B r i t i s h Columbia; Univ. B r i t i s h Columbia, unpub. M.Sc. t h e s i s . Reamsbottom, S.B. 1 9 7 1: Unpub. M.Sc. t h e s i s , Univ. B r i t i s h Columbia. Richards, T., and White, W.H. 1 9 7 0: K-Ar ages of p l u t o n i c rocks betv/een Hope, B r i t i s h Columbia, and the 49th p a r a l l e l ; Can. J . Earth S c i . , v o l . 5, pp. 1 2 0 3 - 1 2 0 7 . Richardson, S.W. 1 9 6 8 : S t a b i l i t y of F e - s t a u r o l i t e + quartz; Carnegie I n s t . Washington Year Book 6 6 , pp. 398-402. Richardson, S.W., G i l b e r t , M.C. and B e l l , P.M. 1 9 6 9 : Experimental determination of k y a n i t e - a n d a l u s i t e -s i l l i m a n i t e e q u i l i b r i a : The aluminum s i l i c a t e t r i p l e p o i n t ; Am. J . S c i . , v o l . 2 6 7 , pp. 2 5 9 - 2 7 2 . Robertson, J.K. and W y l l i e , P.J. 1 9 7 1: Rock-water systems, with s p e c i a l reference to the w a t e r - d e f i c i e n t r e g i o n ; Am. J . S c i . , v o l . 2 7 1 , pp. 2 5 2 - 2 7 7 . Roddick, J.A. and Hutchison, W.W. 1 9 6 9 : Northwestern part of Hope map-area, B r i t i s h Columbia ( 9 2 H W/2); i n Report of a c t i v i t i e s , A p r i l to October 1 9 6 8 ; Geol. Surv. Can., Paper 69-1A, pp. 2 9 - 3 8 . 7 2 Skippen, G.B. 1 9 6 7 : ms. An experimental study of the metamorphism of s i l i -ceous carbonate rocks; Ph.D. Thesis, John Hopkins U n i v e r s i t y , B a l t i m o r e , Md. Tippe r , H.W. 1 9 7 2 : The ages, magnitudes, and types of f a u l t s i n the South-ern Coast Mountains and along t h e i r eastern f l a n k ; i n F a u l t s , f r a c t u r e s , lineaments and r e l a t e d m i n e r a l i z a -t i o n i n the Canadian C o r d i l l e r a ; Geol. Assoc. Can., symposium, Program 8c A b s t r a c t s , p. 4 0 . Wanless, R.K., Stevens, R.D., Lachance, G.R., and Edmonds, CM. 1 9 6 7 : Age determination and g e o l o g i c a l s t u d i e s ; Geol. Surv. Can., Paper 6 6 - 1 7 . Wood, B.L. 1963: S t r u c t u r e of the Otago S c h i s t s ; N.Z.J. Geol. Geophys., v o l . 6 , pp. 641 - 6 8 0 . 73 PETRCG3APUIC SUMMARY Abbreviations. Actinolite Ac Magnetite Mt Albite Ab Muscovite Ku Apatite Ap Olivine 01 Bioti t e Bi Opaques Op Calcite Cc Orthopyroxene Ox Chlorite CI Quartz Qz Clinoa^phibole Ca Phlogopite Ph Clinopyroxene Cx Potash Feldspar Ks Clinoaoisite Cz Prehnite Pr Cordierite Cd Pyrite Py Diopsido Di Rock fragments RF Dolomite Do Serpentine ^Se Epidote Ep Sillimanite Si Garnet Ga Sphene Sp Groundmass Gr Trenolite Tr Hematite He Tourmaline Tm Hornblende Hb Zircon Zr Matrix Kx 74 PD??0:.RAPHIC SUMMARY. I n the f o l l o w i n g t a b l e , t r s i g n i f i e s that the mineral makes up l e s s than one percent of the rock. For a rock vhere g r a i n s f a l l i n t o two s i z e c a t e g o r i e s , the l a r g e r a n d the s m a l l e r average g r a i n s i z e s are both given. F I E L D A V . • T E X T U R E - HIND2AL0GY NO. G/3 ( n m ) P l a g i o c l a s e Kspar Other CUSTEH GNEISS. A-85 3 Hornblende i s r e p l a c i n g Q z diopside i n one corner Hb of the s l i d e . E p i D i ' Op 5% s P 85A Abundant f l u i d i n c l u s i o n s J>0% An.,_half 5% i n q u a r t z . Coarse igneous a l t e r e ^ t o o r t h . t e x t u r e . euidote and s e r i c i t e . 50-;^  Qz 10vi Hb 2^ t r t r t r Ep Ku Sp Z r Ap Tin 85B 1.5 Igneous texture;abundant f l u i d i n c l u s i o n s and accessory minerals i n qua r t z . Q u •15# Ep • r.'o DI 15'w Ga t r Z r t r Ap 85H 1.5 F o l i a t i o n w e l l defined • 30;o An 30?6 Qz by b i o t i t e and horn- .7 '• o r t h . 7% Hb blende. t r F.p 10JS B i 75 FIELD AV. KG. G/G (mm) 86 TEXTURE K1KEHAL0GY Layered. E i o t i t e - r i c b . layer i s described, jjillir.'.anite i s found within b i o t i t e . P l a 5 i o c l a s e 15Ji A n ^ _ Ksnar Other 3<y/° Qz 1% C z 30,', B i 5;J- S i 15* Ga 2',o Op 89 Well f o l i a t e d 20% Untwinned ho;S Qz 15"u B i t r Op tr 2r 90 0.5. Igneous texture. Weakly f o l i a t e d . -•92 1 Gneissic f o l i a t i o n . J>0"/o n>balsan 5°/j Q Z •Largely 'al- 10'.', lib " . . tered to 2Ji i'p s e r i c i t e tr liu 2% B i t r CI tr Ga k% Un-twinned An 30$ Qz p 1 25?5 HD 206 o.k 20;J An 3? 8055 Kb t r Op t r Zr t r Ap 2 1 4 1 Weakly f o l i a t e d , 7% An^ 15:* Qz shows s t r a i n (garnets . 2,'i B i shattered, quartz and 5/o 01 c h l o r i t e show undu- J>',li Ga lose e x t i n c t i o n . Garnets porphyro-b l a s t i c , Jnr:. 217 1 Garnet porphyroblasts 30/S An 55/^ Qz 2nm. Hock has been ^ 5& B i sheared - quartz, . . 10:S Ga feldspars and b i o t i t e show extreme modu-la t o r y e x t i n c t i o n . Garnets shuttered. 76 FIELD 2,'U. 229 /.V. G/o (nc:) 1.2 THXTURS MINERALOGY Strongly f o l i a t e d . Quartz shows s t r a i n , B i o t i t e l p r g e l y a l t e r e d to c u l o r i t e . £lagioclftse k0% An-^ s l i ^ h t f y alteredC to kaolinite?) Kspar Other 25-u 3 i 5'i Ga 261 1 E q u i g r a n u l a r 3055 An 0 703 Qz l a r g e l y t r Ep untv/inned t r CI t r Op t r i>p 77 r iELD AV. NO. G/S (n.-a) HOZAMEEN GROUP. *t 0.8 T.2XTU32 l-'.INEiwiLOGY P l a g i o c l a s e Other 1005&C t r Qz 17 0.5 99% Cc t r Fh 19 1 0.1 C l o t s of quartz and f e l d s p a r i n f i n e grained marble. P a r t i a l l y twinned K f e l d s p a r . 29% untwinned k0% Qz An 33* 20% Cc VA Hu 10# Ks 37 1.5 0.005 C a t a c l a s t i c - chert fragments i n a -very f i n e matrix. Sough f o l i a t i o n d efined by l a y e r s of opaques. 100#?z t r Op 38 0.8 0.00V C a t a c l a c t i c . 5£, n<balsam 85% Qz 5% Ac 5% Op 0.3 0.01 C a t a c l a s t i c 100%Qz t r 3 i t r CI t r Op 55 0.16 Strongly f o l i a t e d , sorae 30% An h0% Qz rnyrmokite at f e l d s p a r 1 25% Ks margins. K f e l d s p a r shows 5% B i p a r t i a l rcicrocline twinning. t r Sp t r 2r t r Ap 13'*A 0.2 F o l i a t i o n d e f i n e d by b i o t i t e V,i untwinned f l a k e s . n<balsaa 9 ^ Qz % B i 13^S 1 100#Cc t r Qz 78 FIELD AV. TEXTURE MINERALOGY KO. G/S (am) P l a g i o c l a s e Other 1 3 7 0 . 2 0 . 0 0 2 P o r p h y r i t i c Untwinnod Cc Ac 1 3 8 0 . 5 Strong f o l i a t i o n defined by .elender. r a l e y.ellaw-grecn a c t i n o l i t e p r i s a s . ^0>o untwinned . .An_ 5 55% Ac 5tf Cz 1 ^ 2 0 . 8 90% Cc 5% Qz t r D i 1 ^ 3 A 3 0 . 3 P l a g i o c l a s e c o n s i d e r a b l y a l t e r e d ( t o k a o l i n i t e ? ) C a t a c l a s t i c , augen up to 5m'a« 6 0 > » An^ 7 2 5 % Qz 1C& Hb 5% B i t r Ep t r Ga 1 4 3 B 0.15 C a t a c l a s t i c , garnet porphyro-b l a s t e uj> to 2rr:a. ^ 5 ; i zoned 30,3 Qz 10^ B i 10^ Ga 5% Kb 1^5 0 . 3 23% n>balsaja 75% Hb 1 6 7 0.16 100%Qz 1 7 8 0.1 0 . 0 0 2 P o r p h y r i t i c - phenocrysts of c h l o r i t o , b i o t i t e , c p i d c t e , p l a g i o c l a s e wake up 15^ of the rock. 3 0 ^ 3 0 % Cz 20% CI 10?£ B i 5% Ke J>% Ac 2% Sp 180 0 . 2 T o t a l l y r e c r y s t a l l i c e d . No' r o l i c t t e x t u r e . 30;i A n 3 Q 55% Hb 10% Ep 5% Qz f 79 FIELD AV. TEXTURE MINERALOGY HO. G/S (inn) P l a g i o c l a s e Other 181 0.2 Graphite l a y e r s show f o l d i n g . Trace 100^Cc t r D i t r Gr 186 0.08 0.008 P o r p h y r o b l a s t i c 20j£ A n n . 60%" Qz 1 10% B i 5% He h% 01 1 8 7 0.03 S t r o n g l y f o l i a t e d . 20^, n<balsam 55%" 01 I d i o b l a s t i c e p i d o t e . 15% Cc 5% En 5# B*i t r Sp 188 0 . 0 2 A c t i n o l i t e i n the form of sho r t yellow-green p r i s m a t i c c r y s t a l s . 1 9 0 0 . 0 3 L a t e r v e i n i n g by coarser 9^% Qz grained quartz c r o s s cuts 5% Op and has almost o b l i t e r a t e d 1% B i f o l i a t i o n . 1 9 2 A 0 . 3 S t r o n g l y f o l i a t e d . Asiphibole porphyroblasts i n the c h l o r i t e l a y e r c r o s s cut the f o l i a t i o n . 6 ? ^ Cc 2$% CI 5% Qz 3% Hb 1 9 2 B OA S l i g h t l y f o l i a t e d . Epidote i n v e i n s . 15%* An 6 6 0 % Ac 25* E? 1 9 2 0 0 . 2 C h l o r i t e pseudomorphous a f t e r hornblende. 30%* zoned An,^ (cores) 3L> 70% Hb t r CI 1 9 3 0 . 6 0 . 0 1 A few l a r g e quartz c r y s t a l s , mostly f i n e g r a i n e d . -90%" Qz 1056 B i t r Ho 70?£ untwinned 3 0 ^ Ac ^ 0 - 1 80 FIELD NO. 195 AV. G/S (mm) 0.25 0.002 TEXTURE Sedimentary, l a r g e rounded quartz and f e l d s p a r g r a i n s i n f i n e grained matrix. C a l c i t e i n v e i n s . MINERALOGY P l a g i o c l a s e Other 5% l a r g e 5% Qz rounded 5% Cc g r a i n s . 2% 3 i 36/0 i n matrix. 2% He 200 0.02 kCT/j An. 50% Ac tr CI-221 2-5 Metamorphic l a y e r : G n e i s s i c f o l i a t i o n d e f i n e d by horn-blende and p l a g i o c l a s e . Garnet grew l a t e r , 2mm p o i k i l o b l a s t i c c r y s t a l s . Igneous vei-n.;.c,ttt.s- gneiss' d i s c o r d a n t l y . 50>J untwinned, a l t e r i n g to epidote, k a o l i n i t e ? p r e h n i t e . 8055 An 29 40% Hb 7% Qz 3% Ep 2% Ga tr Op tr Bp tr Ap tr Tm tr Pr 15% Qz 3% Hb 2^0 0.5' • S t r o n g l y l a y e r e d a l t e r n a t e hornblende and p l a g i o c l a s e l a y e r s , about 2ma t h i c k . 50%" An somewhat a l t e r e d to k a o l i n i t e ? 30% Hb 105S Qz 3% B i 2 4 1 0.3 Layered 50% A n ? 2 e x t e n s i v e l y a l t e r e d to e e r i c i t e . 3C# Qz 20% Kb t r Sp t r Ap 252A 5 3 Assemblages: Hornblende 90% Cc forming from t r e m o l i t e at the 5% Tr boundary between c a l c i t e r i c h 5% Mu l a y e r without quartz, and epidote r i c h l a y e r with quartz. 60% Ep • 20% Eb 10% Cc 10% Qz 86% Ga 5% Qz 5% Cc 2% Hb 2% Kt t r Mu 81 FIELD AV. TEXTURE MINERALOGY NO. G/S (inta) P l a g i o c l a s e Other Z^h C a t a c l a s t i c ; garnet porphyro- 60% An, Q 20% 3 i b l a s t s 3rja, p l a g i o c l a s e O.Jmn, 10% Qz b i o t i t e 0.05cm. 10% Ga 1% Ap BASALTIC DYKES INTRUDING CUSTER GNEISS AMD HOZAMEEN GROUP. 1G 0.15 Very s t r o n g l y f o l i a t e d due to 60% zoned 37% lib alignment of blue-green core An. 2% Op hornblende nrisms. r i m An„^ 1% 3 i 35 1E 1.5 R e l i c t p o r p h y r i t i c t e x t u r e . 55% zoned. 30% Hb 0.3 Cphene forms a d i s c o r d - P a r a l l e l 25% Qz ant v e i n , of Zmn. 2ircdn and o s c i l l a t o r y 15% 3 i a p a t i t e i n c l u s i o n s i n p l a g i o - zones. 1% Op c l a s e . A p a t i t e shows t y p i c a l core Ant-rim A n ^ g t r Ap igneous h a b i t - long slender t r 3 p prisms. t r Zr 91 0.8 U n f o l i a t e d igneous texture - 60% zoned . 25% CI randomly o r i e n t a t e d plagio-. core Anj_ rita A n 2 J 15* Kb c l a s e l a t h s . Hornblende t r Cc l a r g e l y r e p l a c e d by r a d i a t i n g t r Ap aggregates of yellow-green t r Qz c h l o r i t e . Long p r i s m a t i c a p a t i t e s are abundant. 82 FIELD AV. TEXTURE MINERALOGY NO. G/S (ma) Matrix RF Other LADNER GROUP. 29 Massive sandstone. Ab Qz Mu CI 76 F o l i a t e d s l a t e . ' Ab Qz Ku CI 78 3 0.01 Angular plagioclase fragments have altered to s e r i c i t e and calcite". Quartz, subrounded. 65%: 80% angular a l b i t e . 15% s e r i c i t e . 5% angular quartz. 30% Ab 5%" Qz 80 F o l i a t e d s l a t e . Ab . Qz >;u c i 96 0.3 A l b i t e and quartz 1055: a l b i t e 2% 0.003 angular. P y r i t e i n c h l o r i t e vole. 85% Ab cubes up to 4ma. c a l c i t e 2% Cc Cal c i t e i n i r r e g u l a r quartz. 1% Qz c r y s t a l s . t r Py 100 f o l i a t e d s l a t e . Ab Qz Mu CI.. 117 F o l i a t e d s l a t e . Ab Qz Mu CI 8 3 FIELD AV. TEXTURE MINERALOGY NO. G/S (mm) Matrix RF Other 118 3 Large o v a l p o i k i l o b l a s t i c 80%: 20% Cd 0.02 c r y s t a l s of c o r d i e r i t e . quartz Ab Rock i s s t r o n g l y f o l i a t e d . b i o t i t e Qz p l a g i o c l a s e B i epidote Ep 120 O.O'f Massive h o r n f e l s c o n t a i n - Ab i u g p y r i t e lumps up to Qz 2mifl and cut by 0.25m-T> B i quartz v e i n l e t s . Op 121 0.12 Massive h o r n f e l s . 10% B i 10% Cd . • . 5% o P Ab . 125B F o l i a t e d s l a t e . Ab Qz Mu CI 128 0.8 0.0*f Unsorted, angular fragments. 38%, very c h l o r i t e r i c h . 15% 20%Ab che r t 15%Qz and . 5% Cc v o l e . 5% Do 2% Op t r CI 129 0.5 0.003 Very angular fragments. *t8%, very c h l o r i t e r i c h . 10% 20%0z f i n e 10%Ab gr. 2% Op porph.tr CI v o l e . 133 oA 0.00k Angular quartz, f e l d s p a r and reck fragments i n a very f i n e matrix. Fine • grained a l b i t e growing i n pressure shadows of l a r g e 1mm p y r i t e cubes. Few Ab Qz Mu CI Op 17^A 1 65% 30% Ab 5% Qz 17^B 1 35% c h l o r i t e . a o c t l y , some a l b i t e and c a l c i t e . 3# Fine vole 60% Ab 1% Qz t r Cc FIELD NO. AV. G/S (ma) TEXTURE MINERALOGY P l a g i o c l a s e GREEN ANDESITE PORPHYRY INTRUDING THE LADNER GROUP. 77 1.5 Extremely altex-ad look-f i n e i n g rock. L i t t l e or no quartz. Feldspars . s t i l l show zoning, but are very corroded l o o k i n g . ?0;i, r e l i c s of complex twinning. n<balsam. Other 30% CI t r Cc 8 P o r p h y r i t i c , l a r g e k0% euhedral pheno- 55% Gr: 0.0^ euhedral ohenocrysts c r y s t s up to 1cm. Ab of p l a g i o c l a s e , and Almost completely Mu hornblende which has a l t e r e d to s e r i c i t e Qz mostly a l t e r e d to around the margins. CI . c h l o r i t e and epidote. Tremendous o s c i l - 5% CI l a t o r y zoning. Cn/ 5/0 rib An„-An,.. 2;> 3.? t r Ep 85 FIELD AV. TEXTURE MINERALOGY HO. G/S ( n u n ) JACKASS MCUI!T/> .IN GROUP. 156 o.k Angular fragments of a l b i t o and cubes of 5% Ab 0.01 p y r i t e and c r y s t a l s of doloa;ite i n a Do ~ u s c o v i t e - r i c h matrix. Cut by a quartz- Hu c a l c i t e v ein O.^faa wide. Py Cc Qz 157 0.3 Angular a l b i t e and quartz and a few f i n e - 60% Ab grained rock fragments. I r r e g u l a r c a l c i t e 30% Mx veins and c r y s t a l s i n a f i n e - g r a i n e d matrix 5% Qz of muscovite and c h l o r i t e , f e l d s p a r has 3S Cc l a r g e l y a l t e r e d to s e r i c i t e and c a l c i t e . 1% Py t r HF 158 5 Most of the rock i s made up of sub-rounded 87,* RF rock fragments (mostly f i n e - g r a i n e d porphy- 8% Hx r i t i c v o l c a n i c s , a fev; rounded quartz sand- 3% Ab stcne and greywacke fragments) Voids between 3% Qz fragments are f i l l e d with a very f i n e - g r a i n e d 1% Cc matrix and la r g e c r y s t a l s of c a l c i t e , epidote t r Sp and r e c r y s t a l l ' i s e d quartz. Occasional l a r g e . angular f e l d s p a r fragments. 139 0.3 Highly angular fragments of a l b i t e , quartz, chert and f i n e - g r a i n e d v o l c a n i c s . . 80% Ab 10% RF 5% Vz 5% Kx 161 0.2 Poorly s o r t e d , angular quartz and a l b i t e 70% Kx fragments and patches of c a l c i t e i n a f i n e - 22% Ab grained matrix of c h l o r i t e , c a l c i t e , quartz 5% Cc and f e l d s p a r . 2% Qz 1% Ep t r Ku t r Py 164 1 . / e l l s o r t e d subangular f^a^ments of p l a g i o - 85% Ab cl a s e that has almost completely a l t e r e d to 5% Qz s e r i c i t e . O a l c i t e a c t s as a cement. 10% Cc 86 FIELD AV. TEXTURE .MINERALOGY NO. G/3 (nn) SERPENTINITE ALONG THE HOZAMEEN FAULT. i> 5 R e l i c t c r y s t a l s of augite end. f o r s t e r i t i c 95% Se o l i v i n e i n a.network of serp e n t i n e . CI Large serpentine pseudomorphs of o r t h - Ox pyroxene and o l i v i n e . Clinopyroxene Cx e x s o l u t i o n lamellae w i t h i n the ortho- Ht pyroxene pseudomorphs are not s e r p e n t i n i s e d . P a r a l l e l s e r p e n t i n e - f i l l e d f r a c t u r e s appear to define a p r e f e r r e d shearing d i r e c t i o n . t 8 7 FIELD AV. TEXTURE MINERALOGY NO. G/S (mm) P l a g i o c l a s e Kspar Other SPUZZUM QUARTZ DIORITE. 85A 2 Quarts contains abundant 30%, exten- 5% 50% Qz i n c l u s i o n s of a l l the s i v e l y a l t e r - o r t h . 10% Hb accessory minerals and ed to s e r i c i t e s i . 2% Sp myriad f l u i d i n c l u s i o n s . ( 5 % of p l a g i o - a l t . 2% Ep Sphene i s e x c e p t i o n a l l y c l a s e ) and 1% Mu abundant, makes up 10% epidote (25% t r 2r of a hornblende r i c h of plagioclase) t r Ap l a y e r i n the form of A**27 t r Tm l a r g e c r y s t a l s . Coarse igneous t e x t u r e . •z 3.5 Igneous texture. 60%, s l i g h t l y 22% Hb F o l i a t i o n weak; not zoned. 1556 B i eeen i n t h i n s e c t i o n . core An-_ rim A n ^ Cores a n t i -3% Qz t r Ep t r t r t r Sp Op C l p e r t h i t i c . YALE INTRUSIONS. 1.5 P l a g i o c l a s e forms elongated randomly o r i e n t a t e d subhedral c r y s t a l s . Pale brown hornblende forms an i n t e r s t i t i a l mess. F o l i a t i o n weak.; not n o t i c e a b l e i n t h i n s e c t i o n . 55% unzoned A%7' 4055 Hb 5 % Op 0.5 C a t a c l a s t i c t e x t u r e . 0.05 T o t a l mafics approx. 1%, b i o t i t e pre-shear-i n g , bent around l a r g e ragged p l a g i o c l a s e c r y s t a l s . 50% o s c i l l a t o r y zoning, core An T rim An2li. Cores p a r t l y a l t e r e d to epidote and s e r i c i t e . 20% 30% Qz t r B i t r C l t r Ap t r Op t r Zr 88 FIELD AV. NO. G/S TEXTURE MINERALOGY 252B 1.5 0.03 C a t a c l a c t i c . P l a g i o -c l a s e has micrographic i n c l u s i o n s of quartz. Most of the quartz i s ground up. Quartz, b i o t i t e , c h l o r i t e a l l show extreme undula-tory e x t i n c t i o n , and have not r e c r y s t a l -l i s e d s i n c e deforma-t i o n . A p a t i t e shows very long p r i s n a t i c h a b i t t y p i c a l of those found i n igneous rocks, P l a g i o c l a s e Kspar Other 35% ragged 5% 35% Qz augen,strong- occ. 5% B i l y zoned. micr. t r CI Core An--Rim A n ^ 20% i n l i n e tw. t r Op t r Zr t r Ap matrix. tr Sp NEEDLE PEAK PLUTON. 83 2 Igneous texture, 58% An^ 33% Hb undeforraed. Large 5%. B i orange-brown b i o t i t e 2% Qz c r y s t a l s p o i k i l i t i c a l l y 2% Op enclose and appear to be 1% Ep r e p l a c i n g pale green t r Sp hornblende. Epidotc t r Ap euhedral, quartz i n t e r -s t i t i a l . 125 A Coarse igneous t e x t u r e , f e l d s p a r s up to 1cm. A p a t i t e i n very long slender prisms. S i o t i t e i s the dark o x y b i o t i t e form. 20% An p A l i t t l e myrziekite developed. 55% perth-i t e . P a r t . m i cr. tw. 20% Qz 5% B i t r Hb t r Ap MYLOHITE FROM ALONG THE HOPE FAULT. 59 1.5 C a t a c l a s t i c , l a r g e 0.05 broken c r y s t a l s of quartz and p l a g i o c l a s i n a f i n e l i m o n i t e - • s t a i n e d n a t r i x . 5^% An sorr>evha{ a l t e r e d to k a o l i n i t e ? 25% Qz 20% Mx 10% Cc 89 KEY TO SPECIMENS Dept. F i e l d . T h i n Hand X ray Rock Type C o l l . No. Sect. Spec. No. CUSTER GNEISS. 1005-1 A-85 1 1 C a l c - s i l i c a t e gneiss 1005-2 853 1 1 C a l c - s i l i c a t e gneiss 1005-3 85H 1 1 B i o t i t e 6 c h i s t 1005-4 86 1 1 S i l l i m a n i t e - b i o t i t e - g a r n e t s c h i s t 1005-5 87 1 Hornblende gneiss 1005-6 89 1 1 C h l o r i t e - b i o t i t e - g a r n e t s c h i s t 1005-7 90 1 1 Hornblende gneiss 1005-8 92 1 1 Hornblende-garnet g n e i s s 1005-9 206 1 1 * Amphibolite 1005-10 214 1 1 B i o t i t e - g a r n e t gneiss 1005-11 217 1 1 G a r n e t - b i o t i t e gneiss 1005-12 229 1 1 ••' C h l o r i t e - b i o t i t e - g a r n e t s c h i s t 1005-13 261 1 1 Amphibolite HCZ.AMEE? f GROUP. 1005-14 4 1 1 Marble 1005-15 17 1 1 Marble 1005-16 19 1 1 Marble 1005-17 37 1 1 M y l o n i t i s e d chert 1005-18 38 1 1 M y l o n i t i s e d chert 1005-19 40 1 1 M y l o n i t i s e d chert 1005-20 55 1 1 B i o t i t e gneiss 1005-21 134A 1 1 Micaceous q u a r t z i t e 1005-22 134B 1 1 Marble 1005-23 137 1 1 Greenstone 1005-24 138 2 1 Greenschist 1005-25 142 1 1 Marble 1005-26 143A 1 1 Hornblende-aUgen gneiss 1005-27 14JB 1 1 Ga r n e t - b i o t i t e - h o r n b l e n d e gneiss 1005-28 145 1 1 Amphibolite 1005-29 167 1 1 Marble 90 Dept. F i e l d T hin Hand X ray Rock Type C o l l . No. Sect. Spec. No. 1005-30 178 1 1 Greenstone 1005-31 1o0 1 1 Araphibolite 1005-32 181 2 1 Marble 1005-33 186 1 1 Q u a r t z - b i o t i t e s c h i s t 1005-3^ 137 2 1 Greenstone IOO5.--35 188 1 1 Greenstone 1005-36 190 1 Chert 1005-37 192A- 1 1 - Impure marble 1005-38 192B 1 1 Greenstone 1005-39 192C 1 1 Greenstone .1005-40 193 1 1 Chert 1005-^1 195 1 1 * Greenstone ( t u f f ) 1005-4-2 200 1 1 Greenstone 1005-4-3 221 1 1 Garnot amphibolite 1005-44- 24-0 1 1 Amphibolite 1005-45 24-1. 1 1 Araphibolite 1005-46 252A 1 * 1 Skarn 1005-47 254- 1 1 B i o t i t e - g a r n e t gneiss BASALTIC DYKES IN TKUDING CUSTER GNEISS AND HOZAMEEN GROUP. 1005-^8 1E 1 1 Amphibolite 1005-^9 1G 1 1 Amphibolite 1005-50 91 1 1 A l t e r e d amphibolite LADNER GROUP. 1005 -51 29 1 X F e l d s p a t h i c greyv/acke 1005-52 76 1 X S l a t e 1005-53 78 1 1 .Feldspathic greyv/acke 1005-54- 80 1 X S l a t e 1005-55 96 1 1 F e l d s p a t h i c a r e n i t e 1005-56 100 1 X Sl a t e 1005-57 117 1 X Sl a t e IOO5-58 118 1 1 X C o r d i e r i t e h o r n f e l s 91 Dept. F i e l d Thin Hand X ray Rock Type C o l l . No. Sect. Spec. No. 1005-59 120 1 B i o t i t e h o r n f e l s 1005-60 121 1 1 X C o r d i e r i t e h o r n f e l s 1005-61 125B 1 X S l a t e 1005-62 128 1 1 X Greywacke 1005-63 129 1 1 F e l d s p a t h i c greywacke 1005-64 133 1 1 X Fine grained f e l d s p a t h i c greywacke 1005-65 173 1 X Sl a t e 1005-66 174A 1 1 F e l d s p a t h i c greywacke 1005-67 1?4B 1 1 X F e l d s p a t h i c greywacke GREEN ANDE5ITE' PC (RPHYRY INTRUDING LADN' ER GROUP. 1005-68 77 1 1 1005-69 95 1 1 JACKASS MOUNTAIN- GROUP. 1005-70 156 1 1 X A r g i l l i t e 1005-71 157 1 1 X F e l d s p a t h i c greywacke 1005-72 158 1 1 X L i t h i c conglomerate 1005-73 159 1 1 X Fe l d s p a t h i c a r e n i t e 1005-74 161 1 1 F e l d s p a t h i c greywacke 1005-75 164 1 1 Calcite-cemented f e l d s p a t h i c a r e n i SERPENTINITE ALON G THS : KOZAMEEN FAULT. 1005-76 S 1 1 X S e r p e n t i n i s e d p e r i d o t i t e SPUZZUM QUARTZ DIORITE. 1005-77 85A 1 Quartz v e i n 1005-78 Z 1 • Quartz d i o r i t e YALE INTRUSIONS. 1005-79 Y 1 1 1 D i o r i t e 1005-80 Y 2 1 1 M y l o n i t i s e d f e l s i c g r a n o d i o r i t e 1005-81 252B 1 . 1 M y l o n i t i s e d f e l s i c g r a n o d i o r i t e 92 Dept. F i e l d Thin Hand X ray Rock Type C o l l . No. Sect. Spec. No. APLITE DYKE. 1005-82 A 1 F e l s i t e NEEDLE PEAK PLUTON. 1005-83 123 1 G r a n o d i o r i t e dyke 1005-84 125A 1 Granite MYLONITE ALONG THE HOPE FAULT. 1005-85 59 1 1 Mylonite \ fed 20' R m L e g e n d LATE EOCENE (39 m.y.) Needle Peak Pluton granite LATE CRETACEOUS - EARLY TERTIARY ( 54-m.y.?) Yale Intrusions - foliated biotite granodiorite LATE CRETACEOUS-EARLY TERTIARY Yale Intrusions - Unfoliated dark fine - grained diorite LATE CRETACEOUS (76m.y.) Spuzzum Quartz Diorite -foliated hornblende -biotite quartz diorite LOWER CRETACEOUS Jackass Mountain Group feldspathic greywacke & minor conglomerate Green andesite porphyry intruding Ladner Group EARLY TO MIDDLE JURASSIC Ladner Group - slate and minor feldspathic greywacke . MID- TRIASSIC ? Hozameen Group - greenstone, amphibolite chert, argillite, gneiss limr Lone chert PRE - JURA S3 IC (PALEOZOIC?) Custer Gneiss- pegmatite, biotite - garnet gneiss 45, 210, S^iSample locations Geo log i ca I boundary ( defined, approxi m a t e ) Vergence boundary Bedding (inclined, vertical ) 6C V Metamor phic or igneous foliation (inclined , vertical ) 6E0L06Y OF PART OF THE SPUZZUM M A P - A R E A (WEST HALF) 7 0 2 3 miles 1000 n m u r r a J 0 0 0 LU_JJ_LLUL 4000 metres 4000 yards CONTOUR INTERVAL 100 FEET Sdso map: CANADA NATIONAL TOPOGRAPHIC SERIES 92 H / 11 WEST, EDITION 1 ASE SERIES A 721 SCALE 7 : 50,000 / / 16 16 Plunge of meso scopic fold axis Plunge of lineation or non - verging fold \ westerly, ^easterly vergence Fault trace ( defined, assumed ) Abundant gneissic inclusions Serpen t i n i t e My I o ni t e 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0052780/manifest

Comment

Related Items