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Geology of the Strachan Creek area, British Columbia Lee, Randolph 1958

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GEOLOGY OF THE STRACHAN CREEK AREA, .BRITISH COLUMBIA by RANDOLPH LEE 13.A., B„Sc, University of Western Ontario, 1956 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i i i the Department of GEOLOGY We accept t h i s -thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1958 i ABSTRACT The Strachan Creek area i s on the east shore of Howe Sound about three miles north of the town of Horseshoe Bay, B.C. The rocks of the area consist of migmatite of the Bowen Island group, volcanic rocks of the Gambier group, plutonic rocks of the Coast Intrusions,, and l a t e basic and acidic dykes. These rocks are described and t h e i r relationships discussed, A s t r i k i n g feature of the Strachan Creek area i s the banding i n the d i o r i t e , one of the units of the Coast Intrusions,. Each complete band i s a couplet composed of one l i g h t - and one dark-coloured layer, one layer grading into the other.. The light-coloured layer i s composed mostly of plagioclase, whereas the dark-coloured layer i s composed mostly of hornblende and magnetite. Generally, the r a t i o of hornblende (plus magnetite) to plagio clase decreases downward from a sharp contact, the couplets thus resembling inverted "graded-bedding". The author t e n t a t i v e l y concludes that the banding i n the d i o r i t e originated by a process of d i f f e r e n t i a t i o n and cr y s t a l r i s i n g within a cooling d i o r i t e magma. I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e 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 Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r 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 purposes may be g r a n t e d by t h e 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 . 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 olumbia, Vancouver 8, Canada. Date A p r i l 15, 1958 i i TABLE OF CONTENTS Page ABSTRACT i LIST OF ILLUSTRATIONS i i ACMOWLEDGMENTS i v CHAPTER I INTRODUCTION I- Physiography. 1 CHAPTER I I GENERAL GEOLOGY k CHAPTER I I I GEOLOGY OF THE STRACHAN CREEK AREA 8 Bowen Island Group. 9 Gambler Group « . . • 16 Diorite 20 Banding i n the Di o r i t e 2J> Origin of the Banding . . . » 29 Granodiorite. . . . . . . . . . . . 38 Small. Inclusions i n Granodiorite i j l Granite 143 Dyke Rocks k& LIST OF ILLUSTRATIONS Figure Page Banded Migmatite 1 10 Granitic lens i n amphibolite 2 11 Gneissic amphibolite band containing g r a n i t i c lens. . . . 3 11 Granitic material surrounding blocks of amphibolite « • • h 12 Thin-section of gneissic amphibolite. . . . . . . . . . . 5 13 Attitude of migmatite i n the road cut near Strachan Creek NO., l . e e e . . . . 6 llj. Road cut just north of Newman Creek 7 17 i i i Figure Page Sections exposed i n the road and r a i l r o a d cut shewing attitude of conglomerate bed i n volcanics 8 19 Pyrite surrounded by epidote . . • . . . . . . . . . . . . 9 21 Faulted contact between d i o r i t e and granodiorite . . . . . 10 22: Pegmatitic lenses i n d i o r i t e . . . . . . . 1 1 23 Orthoclase-epidote v e i n l e t s i n granodiorite 12 23 A p l i t e vein i n banded d i o r i t e 13 21+ Epidote vein following f a u l t plane i n d i o r i t e .11+ 2JU Banding i n the d i o r i t e i n the road cut . . . . . . . . . . 1 5 27 Graphs of the orientation of plagioclase . . . . . . . . . . 1 6 28 Gradation contacts of balding i n d i o r i t e . . . . . . . . . 1 7 29 Banding that Gilbert describes from the Si e r r a Nevada pluton, Calif... 18 30 Thin-section of dark band of the d i o r i t e showing r e l a t i o n  ship of hornblende to plagioclase . . . . . . . . . . 19 36 Elongated i n c l u s i o n i n granodiorite . . 20 i+l Oval incl u s i o n i n granodiorite . . . . . . . . . . . . . . 21 i i l Round i n c l u s i o n i n granodiorite 22 i j l Road cut near Strachan Creek No. 1 showing granite dykes i n d i o r i t e • 23 hh Granite-diorite contact i n road cut. . • 21+ 1+1+ Network of black veinlets i n granite . . 2 5 1+5 Road cut near Sunset Creek showing the various dykes . . . 26 1+7 Apl i t e vein containing epidote 27 1+9 TABLES Comparison of the mineral composition of the main plutonic rocks and of the components of the migmatite • Table ,. 1. Page 15 ACKNOVttEDGEMENTS The w r i t e r acknowledges h i s indebtedness td the B.C. Department of Highways f o r supplying the base map (100' to 1") on which the geology was plotted and to Marwell Construction Ltd. f o r t h e i r co-operation and a s s i s  tance i n allowing the author to use the Upper Levels Highway while s t i l l i n construction.- Thanks to Dr.. K.C. McTaggart, R.H. Dawson, and Min-Min Wei f o r t h e i r invaluable assistance i n the f i e l d work,. Helpful suggestions during the laboratory work and preparation of the manuscript were given by Dr.- K.C. McTaggart and Dr* J.V.. Ross.. The w r i t e r g r a t e f u l l y acknowledges the assistance of S. Zajac f o r the t r a n s l a t i o n of a German paper. 1 CHAPTER I INTRODUCTION The area mapped i s on the east shore of Howe Sound about four miles north of Horseshoe Bay, B.C. The area extends from Sunset Creek to Newman Creek and from the sea shore inland about a mile. I t forms a considerable part of the western slope of Mt. Strachan. The area i s r e a d i l y accessible by car, boat or t r a i n . The P a c i f i c Great Eastern Railway runs p a r a l l e l to the coastline at an elevation of about 100 feet above sea l e v e l . The Upper Levels Highway, a new road, i s being b u i l t p a r a l l e l to the r a i l r o a d and about 75 feet above i t . F i e l d work was done by the author during the 1957-58 u n i v e r s i t y winter session.- I t was l m L t e d mostly to the weekends* Much of the area was d i f f i c u l t to explore as the slopes are either covered with dense growth or are steep rock cliffs» Physiography The map-area i s i n a t y p i c a l l y rugged section of the Coast Mountains of B.C. The mountains r i s e abruptly from Howe Sound to elevations of more than 5000 feet.. Five creeks cut through the area. A l l of them are i n the youthful stage of development as they show V-shaped valleys and many rapids and water f a l l s i n places many tens of feet high. The larger creeks are floored with huge boulders of granodiorite several feet i n diameter most of which are smooth and f a i r l y w e l l rounded.. The large size of the boulders attest to the 2 great competency of the spring floods i n moving material down stream.. In the interstream areas, t a l u s i s abundant and i n many places a l i t t l e digging revealed t a l u s below a t h i n s o i l and vegetative cover* The talus p i l e s are mostly covered by vegetation and only at the base of a c t i v e l y eroding rock c l i f f s i s there any exposed talus.. The inter-stream areas are cov ered with dense forest growth whose continuity, i n many places, are broken by steep, high rock c l i f f s . C l i f f s were encountered mostly at elevations of around 700, lUOO, and 3U00 f e e t . The c l i f f s around lij.00 feet coincide with the approximate position of a contact between granodiorite and d i o r i t e . 3 LOCATION MAP Scale: One Inch t c 6 Miles h CHAPTER I I GENERAL GEOLOGY The general geology of the Vancouver North area i s summarized i n the following table which i s based on Armstrong's work (195U)« PLEISTOCENE and RECENT CENOZOIC MESOZOIC Terti a r y Miocene or l a t e r Upper Eocene Eocene Main Plutonic rocks ? Tr i a s s i c ? and/or l a t e r Gambier Group Bas a l t i c flows, dykes, s i l l s , tuff.. K i t s i l a n o formation — conglomerate, sandstone, shale. Burrard foimation — sandstone, shale, conglomerate, minor t u f f and ba s a l t . Tuff, breccia, agglomerate, slate,, andesite, a r g i l l i t e , arkose, grey- wacke, quartzite, conglomerate. angular unconformity Plutonic rocks ? Tr i a s s i c ? and/or e a r l i e r Bower Island Group Volcanic and metamorphic rocks,., minor sedimentary rocks. The rocks i n the area north of Vancouver consist of g r a n i t i c rocks of the Coast Range b a t h o l i t h , metamorphic and volcanic rocks of the Bowen Island group,, sedimentary and volcanic rocks of the Gambier group, and Ter t i a r y sediments and minor i n t r u s i v e s * In areal extent the g r a n i t i c rocks of the Coast Range b a t h o l i t h predominate. Nevertheless, large areas of Mesozoic rocks (Bowen Island and Gambier groups) are found throughout the Vancouver North area, i e . the head of Lynn Creek, Mt. Strachan and Mt.. Hollyburn, along the east shore of Howe Sound, Bowen Island, Gambier Island, and some of the smaller islands i n Howe Sound, (see Location Map, p.3)» The Bowen Island group has two main d i v i s i o n s , one consisting of mainly b a s a l t i c and andesitic lavas and the other of interbedded t u f f s and sedimentary rocks.. A l l the rocks of this group have been r e c r y s t a l l i z e d t o some extent, but primary structures are generally preserved. In some areas, however, these rocks have been extensively metamorphosed and metasomatized such that the o r i g i n a l textures have been oblitera t e d , i e . the summits of Mounts Strachan and Hollyburn.. In most places the Gambier group consists of pyr o c l a s t i c rocks and lavas with minor interbedded sedimentary rocks.. On Mount Brunswick, however, the section i s at l e a s t 6000 feet t h i c k of which 2000 feet i s composed of sl a t e , a r g i l l i t e , quartzite, and arkose. The age r e l a t i o n between the Bowen Island group and the Gambier group has been w e l l established by an angular unconformity which separates the two groups. Armstrong (l°f>i+, P»- 2) states that, During the i n t e r v a l represented by t h i s unconformity the Bowen Island group rocks were folded, metamorphosed, and p a r t l y granitizedj some of the plutonic rocks were formed; and the land was u p l i f t e d and eroded. Furthermore, at the base of the Gambier group there i s a basal con glomerate which has rounded and subrounded boulders l i t h o l o g i c a l l y s i m i l a r t o the rock types of the Bowen Island group and t o the older plutonic rocks. The b a t h o l i t h i c rocks of the Vancouver North area consist of granite, grandiorite, quartz d i o r i t e , d i o r i t e , and minor gabbro. Grandiorite and quartz d i o r i t e are, by f a r , the most abundant of the plutonic rocks mentioned above.. 6 There i s apparently more than one period of i n t r u s i o n of the plutonic rocks.. Granitic pebbles i n the volcanic rocks of the Bowen Island group indicate that some plutonic rocks were formed p r i o r to the deposition of t h i s group, but no bodies of plutonic rocks were recognized as belonging to t h i s r e l a t i v e age, Armstrong (1954, P» 5) notes that some plutonic rocks formed before the deposition of the Gambier group whereas others formed after.. For example, the granodiorite mass i n the southern part of Gambier Island i s unconformably overlain by the Gambier group rocks,, whereas the hornblende d i o r i t e and quartz d i o r i t e of Mt.. Hanover and Mt. Harvey, about 3 miles north of the Strachan Creek area, appear to intrude the Gambier group. Since the contact between the plutonic rocks and the Gambier group over most of the Vancouver North area generally i s not exposed, the age relationship of these rocks can not be d e f i n i t e l y established. However, by using the potassium-argon method, Folinsbee (1957) has determined an absolute age of 10J? m i l l i o n years f o r the Coast Range bathol i t h at Vancouver. No mention i s made of the type of rock used f o r the age determination, but probably a sample of granodiorite or quartz d i o r i t e was used since these are the most abundant plutonic rocks.. This would place the main period of plutonic intrusion i n the Middle Cretaceous. T e r t i a r y rocks of the area consist of the Burrard formation, the K i t s i l a n o formation, and minor intrusions and volcanic rocks of Miocene age or l a t e r . The Burrard formation i s composed of about 2000 feet of sandstone, shale, conglomerate, and minor t u f f and basalt. I t dips gently to the south. I t i s mostly of continental o r i g i n and f o s s i l , plants within i t are of Eocene age, (Berry, 1926).. 7 The K i t s i l a n o formation consists of about 2000 feet of conglomerate, sandstone, and shale mostly of continental o r i g i n resting on the eroded sur face of the Burrard formation. I t also dips gently to the south and f o s s i l plants within i t are of Upper Eocene age, (Berry, 1°26).. The minor intrusions and volcanic rocks of Miocene age or l a t e r consist of b a s a l t i c dykes and s i l l s , and minor t u f f s . B a s a l t i c dykes are seen to cut the K i t s i l a n o and Burrard formations and the plutonic rocks. At Sentinal H i l l and L i t t l e Mountain, l a c c o l i t h - l i k e bodies of basalt crop out.. Tuff i s found on the south side of False Creek, 8 table. CHAPTER i n GEOLOGY OF THE STRACHAN CREEK AREA The geology of the Strachan Creek area i s sham i n the following PLEISTOCENE and RECE1JT TERTIARY ' Late dykes Plutonic rocks: MESOZOIC Granite, Granodiorite D i o r i t e Gambier Group Bowen Island Group- The oldest rock exposed i n the Strachan Creek area i s migmatite which underlies a small area and i s bordered by granite, granodiorite, and d i o r i t e * This mass of migmatite i s w e l l exposed along the road cut near Strachan Creek No. 1. and i s correlated with the Bowen Island group because of i t s s i m i l a r i t y i n l i t h o l o g y to the Bowen Island group rocks of the summits of Mounts Strachan and Hollyburn., This correlation i s at best only the most reasonable assumption as there i s the p o s s i b i l i t y that the migmatite belongs to the Gambier group. The Gambier group wit h i n the Strachan Creek area i s composed mostly of volcanic rocks, i . e . t u f f , agglomerate, and porphyritic basalt. -A bed of volcanic conglomerate wi t h i n the sequence of volcanics s t r i k e s Nl4.0°W and dips hO° to the NE. I t s attitude probably represents the general attitude of the volcanics. The contact between the Gambier group and the Bowen Island group i s not exposed i n the Strachan Creek area. Elsewhere, however, Armstrong 9 recognized an angular unconformity separating the two groups, Bowen Island below and Gambier above.. The plutonic rocks of the area consist of granite, diorite, and granodiorite. The age relationships of these rocks are not definitely established because outcrops of their contacts are scarce. However, ex posures of the granite-diorite contact indicate that granite probably formed later than diorite. Granite dykes i n the v i c i n i t y of Strachan Creek No. 1 contain inclusions of diorite suggesting that the granite magma stoped off parts of the diorite during intrusion (see Figure 21;, p. hli). Diorite, just south of Strachan Creek No. 2, i s cut by what appears to be an apophyse of granodiorite which suggests that the granodiorite is younger than the diorite. The age relationship between granodiorite and granite, however, is not deter minable because exposures of the contact of these rocks do not reveal con clusive evidence. A l l the plutonic rocks exposed in the Strachan Creek area appear to have formed after the deposition of the Gambier group. If the Gambier group rocks were younger than the plutonic rocks, then the contacts of these rocks would be conformable. However, i t i s seen that both the diorite and the grano diorite truncates the general strike of the Gambier group rocks which i s repre sented by the attitude of the conglomerate bed. Many late dykes, acidic and basic, are found i n the area. The basic dykes are of d i o r i t i c and basaltic composition. Some are porphyritic and others are non-porphyritic. The acidic dykes are of granite and aplite.. Bowen Island Group Within the Strachan Creek area, migmatite of the Bowen Island group crops out only along and near the road cut in the v i c i n i t y of Strachan Creek 10 No.. I . This body of migmatite extends up the slope of the mountain to an elevation of approximately 600 feet and extends to the north of Strachan Creek No. 1 f o r about 600 f e e t . I t s southern contact follows the creek and i s against granite, and i t s northern contact i s against granodiorite. A few miles to the south, outside of the Strachan Creek area, : there i s a large mass of migmatite which extends from the shore-line to approximately a half mile inland. I t appears to be s i m i l a r to the migma t i t e of the area under investigation i n both l i t h o l o g y and structure. Armstrong (l°51+) shows a small mass of migmatite on Strachan Creek No. 2 at an elevation of 1000 f e e t , but the author did not encounter i t during a traverse up t h i s creek.. I t i s probably a much smaller mass than i s indicated on the map. Migmatites are rocks composed of both g r a n i t i c and metamorphic parts and here, the migmatite consists of a metamorphic host rock which i s streaked and veined with g r a n i t i c material. . The migmatite, i n general, consists of gneissic amphibolite and g r a n i t i c rock alternating i n bands ranging from a few inches to a foot or more i n width. Generally, the bands and f o l i a t i o n of the amphibolite s t r i k e N 1+0° E and dip northwest 25° to 85°» At different i n t e r v a l s , the dark amphibolite bands are interrupted by light-coloured, quite coarse-grained, g r a n i t i c rock, (see Figure 1 ) , Figure 1. Banded migmatite. Dark amphibolite band interrupted by g r a n i t i c material. 11 In some places, the g r a n i t i c part consists of i r r e g u l a r patches and streaks of whitish rock rather than regular bands,, (see Figures 2 and 3) . In general, however, the streaks seem to be stretched out p a r a l l e l to the f o l i a t i o n within the amphibolite. These g r a n i t i c streaks, i n many places, contain areas of coarse, pink orthoclase and small patches of green, radiating c r y s t a l s of epidote.. Figures 2 and 3»- Gneissic amphibolite bands containing g r a n i t i c streaks which are stretched out p a r a l l e l to the f o l i a t i o n . The g r a n i t i c part i s composed mostly of coarse, anhedral grains of pink orthoclase, white plagioclase, and clear transparent quartz i n approxi mately equal amounts. The pink orthoclase commonly occupies the central part of the g r a n i t i c streaks. In other places i n the same outcrop, the l i g h t material i s the matrix which surrounds and cements large and small angular blocks of am ph i b o l i t e , (see Figure k)» In some specimens, the banding within the amphibolite blocks l i n e up with each other, but i n others, the blocks do not have a common orientation. In a few places, l o c a l areas of oriented and unoriented blocks of amphibolite occur within ten feet of each other. 12 F i g u r e k» Amphibolite b l o c k s surrounded by g r a n i t i c m a t e r i a l . The amphibolites are dark, medium- t o f i n e - g r a i n e d rocks composed mostly of hornblende and p l a g i o c l a s e separated i n t o d i s t i n c t laminae t h a t s i m i l a t e bedding* G e n e r a l l y , the dark bands are t h i c k e r than the l i g h t bands. P y r i t e i s f a i r l y abundant i n the migraatites, but t h e r e i s no apparent c o n t r o l f o r i t s occurence. I t i s found as l e n s e s or s m a l l pods both i n and c u t t i n g across the dark and l i g h t bands.. In t h i n s e c t i o n s of the dark bands, p l a g i o c l a s e ( A n ^ t o An^g) f>0$, and hornblende h.0% are seen to be the dominant minerals and c h l o r i t e , o r tho- c l a s e , e p i d o t e , q u a r t z , magnetite, p y r i t e , b i o t i t e , and a p a t i t e occur i n sma l l e r amounts.. The t e x t u r e of the dark band i s a U o t r i o m o r p h i c , : e q u i g r a n u l a r , and medium-grained. The p r e f e r r e d o r i e n t a t i o n of the hornblende and the separa t i o n of the hornblende and p l a g i o c l a s e i n t o d i f f e r e n t laminae are e a s i l y d i s  c e r n i b l e i n t h i n - s e c t i o n , (see F i g u r e 5). C h l o r i t e i s s t r e t c h e d out i n the d i r e c t i o n of f o l i a t i o n . . The p l a g i o c l a s e g r a i n s of the d a r k bands are mostly untwinned and occur as somewhat s p h e r i c a l g r a i n s predominantly of one s i z e * Quartz i s i n t e r s t i t i a l , f i l l i n g the space between hornblende and p l a g i o c l a s e * Hornblende i s g e n e r a l l y f r e e of i n c l u s i o n s , but i n some places encloses s m a l l , round g r a i n s of a p a t i t e , p y r i t e , magnetite, and p l a g i o c l a s e . , R e l a t i v e l y l i t t l e 13 a l t e r a t i o n of the minerals has occurred, although b i o t i t e i s p a r t l y altered to c h l o r i t e , e s p e c i a l l y along the cleavage traces.. In the light-coloured bands, the mineralogy i s e s s e n t i a l l y the same as that of the dark bands except that the r e l a t i v e proportions of the minerals are d i f f e r e n t * Plagioclase and quartz occurs i n approximately equal amounts and make up approximately 90 per cent of the rock. Hornblende makes up about 8 per cent of the l i g h t bands. Quartz occupies large i n t e r s t i t i a l areas be tween plagioclase and hornblende and generally shows wavy extinction.. A small quantity of b i o t i t e i s present, but i t i s mostly altered to c h l o r i t e and zoisite.. Hornblende occurs as scattered grains, regular i n outline, and showing s l i g h t p o i k i l i t i c texture having inclusions of plagioclase and i r o n ore* Cataclastic texture i s apparent i n thin-section as most quartz grains show wavy extinction and f i n e l y crushed grains are found between large grains. The general s t r i k e of the banding and f o l i a t i o n of the migmatite i s N 70° E to N k0° E and the dip 30° to 50° to the northwest, (see Figure 6 ) . The dip may vary from 30 to 50 degrees i n a very short distance., Epidote veins are rather abundant and cut the rock i n many di r e c t i o n s . These migmatites could have originated i n several ways, (1) by i n  je c t i o n of magma along surfaces of weakness of pre-existing rocks,, (2) by p a r t i a l replacement of host rock by i o n i c exchange of material between host Ik rock and f l u i d , or (3) by d i f f e r e n t i a l fusion of host rock of varied composi tion.. « 200 fect Figure 6. Attitude of the migmatite i n the road cut near Strachan Creek No. 1. In some places the g r a n i t i c component appears to have originated by i n j e c t i o n of g r a n i t i c magma in t o amphibolite such that the light-coloured g r a n i t i c material encloses and surrounds angular blocks of amphibolite and, i n general, acts as the cementing matrix, (see Figure Here, the g r a n i t i c material forms sharp contacts with the amphibolite* In other places the g r a n i t i c material appears to have formed by p a r t i a l replacement of the dark material probably by magmatic emanations, or some active f l u i d of unknown o r i g i n . Ionic exchange of material between the host rock and the f l u i d s which penetrate the host rock along paths of minimum resistance would r e s u l t i n the formation of migmatite.. In places where there are numerous regular alternating bands of l i g h t and dark material which show uniform width and sharp contacts f o r several tens of f e e t * (see Figure 1), i t seems l i k e l y that the banding i s due to p a r t i a l replacement as i t i s d i f f i c u l t to v i s u a l i z e such regular i n j e c t i o n . There arises also the p o s s i b i l i t y that the migmatite originated by 15 d i f f e r e n t i a l fusion of host rock of uniform composition, y i e l d i n g a low- melting g r a n i t i c or pegmatitic l i q u i d (magma) di s t r i b u t e d through the rock as discontinuous streaks and veins.. To te s t t h i s p o s s i b i l i t y , a sample of the g r a n i t i c part of the migmatite was taken of an i s o l a t e d lens of the l i g h t material w i t h i n the dark material.. I f the l i g h t material were formed by d i f f e r e n t i a l fusion, then i t s components possibly could have been derived from the melting (fusion) of parts of the amphibolite. A comparison of the mineral composition of the is o l a t e d lens of g r a n i t i c material and of the amphibolite i s i l l u s t r a t e d i n Table I * TABLE I COMPARISON OF MINERAL COMPOSITION OF THE MAIN PLUTONIC ROCKS AND OF THE COMPONENTS OF THE MIGMATITE Minerals Amphibolite Isolated Granodiorite D i o r i t e Granite lens of g r a n i t i c material. Plagioclase A n l ^ ^ho ^1x0 mkh A n 2 0 50 % h$% 60 % 40-60 % 1 % Quartz 3 hS 10-15 2-15 30 K-feldspar 4 l 5-io 60 Hornblende ho 8 5 30-40 B i o t i t e 1 1 15 5-8 I t i s seen that the plagioclase has approximately the same average composition i n both the amphibolite and the i s o l a t e d lens of g r a n i t i c material.. However, i f the g r a n i t i c material i s the resul t of p a r t i a l fusion of the amphibolite, then the plagioclase of the g r a n i t i c material would be more 16 sodic i n composition than the plagioclase of the amphibolite,. The phase diagram of the albite-anorthite system as determined from a r t i f i c i a l melts by N.L. Bowen shows that i f a c r y s t a l of plagioclase of a given composition (eg, An)^) i s heated to i t s melting point, the f i r s t l i q u i d to form i s of much more sodic composition,, i e , an a l b i t i c l i q u i d would be formed by p a r t i a l fusion of more c a l c i c c r y s t a l s . Thus, the is o l a t e d lens probably i s not the r e u l t of p a r t i a l fusion of amphibolite* A comparison of the estimated mineral composition of granite, granodiorite, and d i o r i t e with the i s o l a t e d lens of g r a n i t i c material, i s i l l u s t r a t e d i n Table I,. I t i s seen that the mineral composition of neither the granite, ; granodiorite, nor the d i o r i t e i s s i m i l a r t o the composition of the i s o l a t e d l e n s * The granite contains much more K-feldspar and much less plagioclase than the i s o l a t e d l e n s * The d i o r i t e has much more hornblende and much less quartz than the i s o l a t e d l e n s * The granodiorite has more K-feldspar and b i o t i t e , and much less quartz and hornblende than the i s o l a t e d lens. Thus, the evidence i s inconclusive as to whether the magmatic emanations or active f l u i d s came from the granite, d i o r i t e , or granodiorite magma,. In conclusion i t seems to the author that the migmatite of the Strachan Creek area formed possibly p a r t l y by replacement and p a r t l y by in j e c t i o n of magma. The source of the magma or of the active f l u i d s i s not known, but could possibly have been derived from the granite,, granodiorite, or d i o r i t e magma,. The Gambier Group The Gambier group of rocks i s found i n the northern portion of the Strachan Creek area. These rocks occupy an area extending from the shore of Howe Sound to an elevation of about 2000 f e e t . The eastern contact of the 17 Gambier group i s against granodiorite, whereas i t s southern contact i s against diorite., The Gambier group consists of t u f f s , b a s a l t , volcanic agglomerate, porphyritic basalt, and volcanic conglomerate. The s t r a t i - graphic sequence of these rocks, however, has not been worked out i n d e t a i l . The best exposures of these rocks are found i n the road and r a i l r o a d cuts just north of Newman Creek. The sequence of rocks at th i s l o c a l i t y i s i l l u s t r a t e d i n the sketch i n Figure 7. t -toff Y< / ^ •' Y ftoo4 J .: , \'.' ••• Road s Figure 7.- Section exposed i n the road cut just north of Newman Creek. Porphyritic basalt i s found adjacent to a f a u l t contact with d i o r i t e . The basalt i s a greenish rock containing small white phenocrysts of plagioclase scattered throughout a dark, aphanitic groundmass. Pheno crysts make up approximately 15 per cent of the rock. In thin-sections of porphyritic basalt, the essential minerals are seen to be c h l o r i t e 35%3 plagioclase 30%, s e r i c i t e 10$, and epidote 20%. Accessory minerals are p y r i t e , c a l c i t e , and augite. The plagioclase i n the groundmass i s of labradorite composition. S e r i c i t e i s more abundant near the contact with d i o r i t e . On the other hand, epidote i s evenly d i s t r i b u t e d and always quite abundant.. The rock has marked tr a c h y t i c texture.. Tuff i s by f a r the predominant rock type of the Gambier group within the Strachan Creek area. I t i s found adjacent to and north of the 18 porphyritic basalt. In general appearance i n hand-specimen, the t u f f r e  sembles an altered greywacke, but the presence, i n thin-section, of c h l o r i t e pseudomorphs af t e r shards suggests that i t i s a t u f f . The t u f f i s green and fine-grained. As seen i n thin-section, the main constituents of the t u f f are l i t h i c fragments 60%, epidote 30$, and c h l o r i t e 10%» The ground- mass consists of c h l o r i t e and epidote and a very minor amount of feldspar. Broken fragments of plagioclase are present as medium-sized grains embedded i n the fine-grained groundmass. Most of the l i t h i c fragments show textures of volcanic rocks* A small proportion of quartz i s present as i r r e g u l a r , small grains or as aggregates of small grains set i n the groundmass* Volcanic agglomerate occurs as a bed within the t u f f . In outcrop the agglomerate i s a purplish rock with prominent c l a s t i c texture. Most of the angular fragments of volcanic rock are less than an inch across. However, many large, angular blocks over a foot i n diameter are also present* On a weathered surface, the angular blocks are conspicuous because they are whit i s h , whereas the groundmass i s purplish. Epidote occurs as small clumps scattered throughout the rock. I t also occurs as t i n y v e i n l e t s ( l / 8 " to l/klt thick) cutting the agglomerate* In thin-sections of the volcanic agglomerate i t i s seen that l i t h i c fragments of varying sizes and shapes make up about °5 per cent of the rock* Most of the l i t h i c fragments are angular and so close l y packed that the groundmass i s distinguished only with d i f f i c u l t y . A l l the fragments are of volcanic rocks and many of them have tr a c h y t i c texture. The groundmass con s i s t s of minute grains of feldspar which, i n some places, appear as d i s t i n c t , separate grains, but i n other places, appear to be welded so that individual- grains are not distinguishable. The l a s t feature suggests that the rock has 19 been somewhat re crystallized*. A bed of volcanic conglomerate i s found within the t u f f s i n the Strachan Creek area. This conglomerate bed i s exposed i n the road cut approximately 2000 feet north of Newman Creek. Here, i t i s about one foot t h i c k , (see Figure 8). The same bed i s exposed i n the r a i l r o a d cut nearby and here the s t r i k e of the conglomerate bed i s N k0° ¥ and the dip about hO° to the northeast. The attitude of the conglomerate bed probably r e  presents the general attitude of the volcanics of t h i s area.. The conglomerate consists of large boulders, cobbles,, and pebbles embedded i n a matrix of fine-grained rock d e t r i t u s . The boulders are variable i n s i z e , but average k inches i n diameter. The largest ones are about two feet i n diameter. The boulders and pebbles are w e l l rounded. The majority of the pebbles and boulders are of volcanic rocks, i e . basalt, andesite, t u f f , porphyritic basalt and andesite* One pebble of quartz and one of quartz d i o r i t e occurs i n the conglomerate* Figure 8. Sections exposed i n the road and r a i l r o a d cuts north of Newman Creek. 20 The conglomerate probably was l a i d down as either a t e r r e s t r i a l (stream) or marine (shore-line) deposit. The provenance of the conglomerate, judging by the abundance of volcanic boulders and pebbles, was a volcanic t e r r a i n containing small areas of plutonic rocks. D i o r i t e D i o r i t e forms an elongate body having a general N-S trend extending from Newman Creek to Strachan Creek No. 1, a distance of approximately one and a quarter miles. I t extends up the slope of the mountain generally to an elevation of 11+00 f e e t , where i t comes into contact with granodiorite. There are three types of d i o r i t e , i e . banded, non-banded, and potash-rich types. The banded d i o r i t e grades into the non-banded type and the two have e s s e n t i a l  l y the same mineral composition. The potash-rich d i o r i t e , on the other hand, contains a high proportion of pink K-feldspar and i s due to a l t e r a t i o n of non-banded d i o r i t e . In hand specimen, the unhanded d i o r i t e i s t y p i c a l l y greenish and medium-grained, allotrimorphic, and equigranular i n texture. The mafic minerals on the average form approximately 30-1+0 per cent of the rock. The d i o r i t e i s e s s e n t i a l l y a hornblende-plagioclase rock with appreciable mag netite., P y r ite i s rather abundant i n certain scattered l o c a l i t i e s i n a l l ' types of d i o r i t e . I t occurs as stringers, lenses, or pods of almost s o l i d p y r i t e . Stringers are generally a f r a c t i o n of an inch t h i c k , but some pods may be f a i r l y large, i e . 15 inches long by 3 inches wide. Epidote i s generally c l o s e l y associated with p y r i t e , (see Figure °)» In thin-sections of the unhanded d i o r i t e , plagioclase (average compo s i t i o n An^,) and hornblende are seen to be the essential minerals* Quartz 21 i s present i n very small amounts (2%), but i n a few samples i s as much as 15" percent of the d i o r i t e * The accessory minerals are apatite, zirc o n , i r o n ores (pyrite and magnetite), b i o t i t e , and augite* A l t e r a t i o n products are epidote, c h l o r i t e , s e r i c i t e , and minor serpentine and t a l c . Some c a l  c i t e veins occur i n f i s s u r e s i n the rock. Figure 9* Pyrite surrounded by epidote as seen i n an outcrop of diorite.. The plagioclase shows zoning which i s generally the normal type (labradorite cores, about An^, to andesine rims, about An^cj), but i n some thin-sections o s c i l l a t o r y zoning i s found* The boundary of the zones of many grains i s corroded indicating reaction, between the plagioclase and the melt during c r y s t a l l i z a t i o n . In some places, plagioclase laths are altered to s e r i c i t e and c h l o r i t e and are consequently quite cloudy. Generally, plagioclase forms from lj.0-60 per cent of the rock. Hornblende i s dark green i n thin-section and i s strongly pleo— chroic (yellow to l i g h t green to dark green on r o t a t i o n ) . I t i s p o i k i l i t i c , containing small roundish inclusions of plagioclase, i r o n ore, and apatite* In many sections i t i s p a r t l y altered to epidote and chlorite., The borders 22 of hornblende are almost i n v a r i a b l y ragged and i r r e g u l a r suggesting corro sion by the magma during c r y s t a l l i z a t i o n . Rarely, i t - i s found as f a i r l y euhedral c r y s t a l s . Quartz i s i n t e r s t i t i a l , c l e a r , and shows undulatory e x t i n c t i o n . Apatite i s ubiquitous. Orthoclase-rich d i o r i t e i s found just south of Strachan Creek No.. 2 along both the road and r a i l r o a d cuts. The southern contact of orthoclase-rich d i o r i t e i s against granodiorite which, near the contact, contains many veins of pink orthoclase, (see Figure 10). I t i s a f a u l t contact. Pink orthoclase occurs i n both the d i o r i t e and granodiorite ( l ) with epidote as t h i n veinlets less than a quarter inch wide, (2) as d i s  seminated grains, and (3) as pegmatitic lenses (or pods) composed.essen t i a l l y of orthoclase, quartz, and epidote, (see Figures 11 and 12). Within the granodiorite, the amount of pink orthoclase decreases away from the f a u l t contact f o r a distance of approximately 100 fee t , whereas i n the 1 clio>-iie L— vei*.le.(-s of l • / p'mK ortkocU.se o r- + U o c < ^ 1 IO f t - . Figure 10. Fault contact between granodiorite and d i o r i t e i n a road cut near Strachan Creek No. 2. L o c a l i t y has high amount of pink orthoclase. 23 d i o r i t e , pink orthoclase i s abundant f o r over 500 feet from the contact. . Figure 11,. Pegraatitic lenses i n d i o r i t e i n the road cut near Strachan Greek No. 2, Pegmatitic lenses; (usually with 60% or more pink orthoclase) are abundant i n d i o r i t e , and as a result gives the rock an ov e r a l l spotted appearance when viewed at a distance, (see Figure 11). These pegmatitic lenses and also the abundant orthoclase are probably the result of l a t e hydro-thermal solutions emanating from the granite when i t was c r y s t a l l i z i n g . . A t h i n - in© rft. o.b i A r t t i o \ " ^ . r *A4.ar \j let* Figure 12. Orthoclase-epidote v e i n l e t s i n granodiorite i n road cut near Strachan Creek No. 2. 2k section of orthoclase-rich d i o r i t e showed that i t i s highly altered and contains much c l i n o z o i s i t e 35$, s e r i c i t e 10$, and c h l o r i t e $%, Cataclastic texture i s apparently due to f a u l t i n g . The hydrothermal. solutions probably invaded the rock along the fault and permeated the country rock along the crushed zones. Figure 13. A p l i t e vein i n banded Figure lk» Epidote vein follow- d i o r i t e as seen i n road cut. ing f a u l t plane i n d i o r i t e . Epidote i s abundant i n a l l phases of the d i o r i t e . I t i s frequent l y associated with pyrite and forms the borders of a p l i t e veins, (see Figure 13).- I t may also occupy parts of f a u l t planes,, (see Figure lk)t j o i n t s , fractures, and may p a r a l l e l the banding.. Epidote occurs as disseminated grains only i n rather minor amounts* Armstrong (195k) thinks that the hornblendic and b i o t i t i c diorites- are border facies of granodiorite and may not be of igneous or magmatic o r i g i n . He states, Normally, the r a t i o of hornblende to b i o t i t e i n the plutonic rocks increases near the exposed areas of older volcanic and sedimentary s t r a t a , indicating the profound influence of these older formations on the composition of the plutonic rocks.. 25 The northern contact of the d i o r i t e of the map-area i s against volcanic rocks of the G ambier group, whereas i t s southern contact i s with granite.. To the east and up the mountain slope d i o r i t e gives way to grano d i o r i t e . The contact between these two rock types i s not exposed, so i t i s not possible to say whether the contact i s sharp or gradational.. Just north of Strachan Creek No.. 1 d i o r i t e appears to be cut by an apophyse of granodiorite suggesting that granodiorite i s younger than d i o r i t e . Masses of granodiorite bordered by d i o r i t e have been described from other parts of the world. Compton (1955), i n his study of the Bald Rock b a t h o l i t h , found a gradation from leucotrondhjemite to trondhjemite to granodiorite to t o n a l i t e from the core of the pluton out to the rim. The width of the t o n a l i t e border was of the order of 1000 f e e t , Akaad (1956) described the Ardara g r a n i t i c d i a p i r of Ireland i n which he also found a t o n a l i t e border surrounding a granodiorite core* The d i o r i t e of the Strachan Creek area possibly represent the border facies of the large granodiorite mass. However, exposures of the contact between d i o r i t e and granodiorite are very poor and much of the d i o r i t e and granodiorite i s covered such that t h e i r relationships are obscured. I t seems more l i k e l y that the d i o r i t e and granodiorite r e  present two separate (but perhaps related) intrusions, whereby the granodiorite was formed l a t e r and i n places cut through the d i o r i t e as can be seen i n the road cut near Strachan Creek No. 1. Banding i n the D i o r i t e Banding i s prominent i n the d i o r i t e i n the area just north of 26 the contact between granite and d i o r i t e , that i s , between Sunset Creek and Strachan Creek No, 1, and occurs i n both the road cut and the r a i l  road cut* Each complete band i s a couplet composed of one l i g h t and one dark-coloured l a y e r : one layer grading into the other* The ch a r a c t e r i s t i c s of the banding are l i s t e d below, (a) Across the s t r i k e , the banding may be interrupted by wide zones of massive, unhanded d i o r i t e which range i n width from 20 to 50 f e e t . In places the banding i s very f a i n t and d i f f i c u l t to di s t i n g u i s h , (b) The banding i s found only near the contacts of the granite and the migmatite,. (c) The banding strikes. N 1*0-70° E and dips about 60-70° NW. (d) The difference i n colour between the l i g h t and dark band i s due to the large difference i n the r a t i o of mafic minerals to feldspar i n each. The white bands have very l i t t l e hornblende and magnetite, whereas the dark bands have over 1*0 per cent mafic minerals. Iron ore (magnetite and pyrite) i s generally c l o s e l y associated with hornblende, (e) The l i g h t bands are generally one half an inch t h i c k , but are an inch or more i n a few places. The dark bands are generally over one inch t h i c k and i n some places are over 6 inches t h i c k . The dark bands f i n a l l y grade into unhanded d i o r i t e * The dark bands are generally much thicker than the l i g h t ones. The r a t i o i s approxi mately 3 s i but may be ..quite variable, (f) Over a distance of one foot at one l o c a l i t y there are ten couplets, (g) The bands are, i n many places, wavy and undulating and t h e i r attitude varies considerably over a short distance (a foot or so), but the 27 o v e r a l l trend remains constant, (see Figure 15)• Figure 15. Banding i n the d i o r i t e i n the road cut,. (h.) In some places the bands merge and look somewhat l i k e inverted "cross-bedding", (see Figure 15). Outside the map-area, near the Lookout Point on the Upper Levels Highway approximately a mile from the town of Horseshoe Bay, t h i s feature i s w e l l exposed. ( i ) Magnetite i s more abundant i n the dark bands and appears to be most abundant near the sharp contact from where i t gradually decreases i n abundance u n t i l , i n the l i g h t bands, i t becomes a very minor con stituent.. ( j ) The contact between the l i g h t and dark band i s not everywhere sharp. Both contacts maybe gradational, (see Figure 1 7 ) . (k) The plagioclase i n both bands i s zoned (Core An^g to rim An^) and generally has a rough lamination p a r a l l e l to the banding, (see Figure 1 6 ) . The orientation of plagioclase laths was measured on the f l a t -3o Frequency curve showing the orientation of plagioclase i n the y No. of grains l i g h t band of the -2o \ of plagioclase d i o r i t e / • J 1 1 - I O Angle of deviation of long axis of plag ioclase laths from lamination of banding Frequency curve showing the orientation of plagioclase i n the dark band of the d i o r i t e No. of grains of plagioclase I , , P , 1 1 1 , 1 , t o o S o 6o 4 o 2 o o « o -*o 6o Bo too Angle of deviation of long axis of plag ioclase l a t h s from lamination of banding Figure 16. Orientation of plagioclase i n the l i g h t and dark bands i n the diorite.. The measurements were made on the f l a t stage using.oriented thin-sections of both the l i g h t and dark bands of the d i o r i t e . 29 stage and i t was found that the plagioclase i n the l i g h t band i s _ better oriented than those of the dark band. Hornblende appears to be i n t e r s t i t i a l and i s not apparently oriented, (see Figure 19, p, 36). Figure 17, Gradational contacts of banding i n d i o r i t e , (1) The grains size of the minerals appears to be s l i g h t l y larger i n the dark band near the sharp contact. There seems to be a gradation i n grain size from dark to l i g h t band* In other words, i t i s very si m i l a r to inverted "graded bedding". Origin of the Banding i n the D i o r i t e The type of banding found i n the d i o r i t e has been described extensively. Cloos (1936) describes very s i m i l a r banding which he found i n the granodiorite of the Sierra Nevada pluton i n C a l i f o r n i a * He c a l l s the banding "blatterschlieren" ( b l a t t e r = pages)* I t should be noted, however, that i n the hands of the Sierra.Nevada pluton the r a t i o of mafic minerals to plagioclase decreases upwards from a sharp contact whereas i n the hands of the Strachan Creek area the r a t i o increases. G.K. G i l b e r t (1906) describes banding i n granite i n the S i e r r a Nevada pluton which i s quite s i m i l a r to b l a t t e r s c h l i e r e n and to the banding i n the d i o r i t e of the Strachan, Creek area* However, the banding wMch G i l b e r t describes has one 30 feature that i s not seen i n the Strachan Creek area. One series of bands i s truncated by another series of bands giving the appearance of an "unconforraity", (see Figure 18)* Figure 18. Banding i n granite which Gilbert describes from the Sierra Nevada pluton of C a l i f o r n i a . The b l a t t e r s c h l i e r e n , Gilbert's banding, and the banding i n the Strachan Creek area show a sharp contact at the base of the dark band, gradation i n colour, minerals, and grains s i z e from dark to l i g h t bands, and some alignment of feldspars p a r a l l e l to the bands.. Both the bl a t t e r s c h l i e r e n and the banding i n the Strachan Creek area are found near the contacts of older rocks, and are cut by a younger granite. The s i m i l a r i t i e s i n the characteristics of the banding i n the three areas described above suggest that t h e i r mode of o r i g i n i s similar.. There are at le a s t f i v e ways i n which the banding i n the Strachan Creek area might possibly have formed. These are grouped into non-magmatic and magmatic origins and are l i s t e d below. 1. Non-magmatic Origins. (a) Banding represents o r i g i n a l s t r a t i f i c a t i o n of sedimentary rocks which have since been replaced. The banding may have formed as a result of replacement of former steeply dipping, overturned, graded beds of sedimentary rocks* I f the 31 o r i g i n a l rocks were a series of alternating layers of sedimentary rocks of different composition (eg, arkose and t u f f ) , then t h i s would explain the compositional difference of the bands,. This hypothesis seems to f i t most of the features of the bands. I t accounts f o r the inverted "graded-bedding", the difference i n grain s i z e , the sharp contacts, the "cross-bedding", and the great number of bands, A strong argument f o r the g r a n i t i z a t i o n or r e  placement o r i g i n i s that the attitude of the banding i n the d i o r i t e and the attitude of the lamination, i n the migmatite roughly coincide, Armstrong (19$h) has noted that the lamination i n the Bowen Island group has the same general trend throughout the North Vancouver area and t h a t i t represents primary structures, Phemister (l9h5) also observed that the laminated type of pre-batholithic rocks (Bowen Island group) i n the v i c i n i t y of Vancouver are metasediments. The lamination i n these rocks represent bedding planes and i n the f i e l d show consistent s t r i k e and dip over considerable areas. Thus, i t i s l i k e l y that the lamination i n the migmatite of the Strachan Creek area i s a primary structure and represents o r i g i n a l bedding. Since i t s attitude i s congruent with the attitude of the banding i n the d i o r i t e , then i t i s possible that the banding i n the d i o r i t e also represents bedding planes. Thus, i t i s v i s u a l i z e d that, before d i o r i t i z a t i o n , the area now represented by d i o r i t e consisted of a series of steeply dipping sedimentary rocks. Gra n i t i z a t i o n then altered these rocks to d i o r i t e and the banding of the d i o r i t e i s the o r i g i n a l bedding of the sedimentary rocks which has been preserved. The migmatite would represent a knot resistant to the wave of g r a n i t i z a t i o n that formed the diorite.. There are, however, many d i f f i c u l t i e s with t h i s hypothesis. 32 I f , o r i g i n a l l y , the bands were graded beds, then i t seems l i k e l y that graded bedding would be present i n rocks surrounding the Strachan Creek area. However, graded bedding does not occur i n any of the sedimentary or metamorphic rocks of the North Vancouver area. Also, the migmatite of the Strachan Creek area does not show graded bedding. No metamorphic textures ( i e . f o l i a t i o n , s c h i s t o s i t y , and cataelastic texture) and no new t y p i c a l l y metamorphic minerals are present i n the d i o r i t e . The uniformity of mineral composition of the d i o r i t e and the universal occurrence of apatite, zircon, i r o n ore, and b i o t i t e as accessory minerals i s not e a s i l y explained by an o r i g i n through granitization.. I t seems most probably that the o r i g i n a l sediments would have variable composition and, when granitized, would not a l l be altered to d i o r i t e of uniform mineral composition* (b) Banding as a r e s u l t of metamorphism of d i o r i t i c rocks.. The p o s s i b i l i t y arises that the banding i n the d i o r i t e i s the result of p o s t - c r y s t a l l i z a t i o n metamorphism of pre-existing d i o r i t i c rocks where metamorphic d i f f e r e n t i a t i o n separated the minerals into l i g h t and dark bands to produce a gneissic rock.. There are various processes of metamorphic d i f f e r e n t i t a t i o n by which contrasted mineral assemblages may develop from an o r i g i n a l l y uniform parent rock. The separation of minerals may be pro duced by solution, by s o l i d d i f f u s i o n , and by the force of c r y s t a l l i z a t i o n . S o l i d diffusion i s the migration of ions through continuous c r y s t a l l a t t i c e s , but only through s t r i c t l y l i m i t e d distances (generally minute). The force of c r y s t a l l i z a t i o n i s vaguely defined (Turner 191*8, p. 137) as "the driving force causing d i f f u s i o n of appropriate chemical substances through a c r y s t a l l i n e mass towards a c t i v e l y growing porphyroblasts or other c r y s t a l s " . Most writers v i s u a l i z e metamorphic d i f f e r e n t i a t i o n as a 33 phenomenon e s s e n t i a l l y connected with solution and redeposition of chemical components of rocks during metamorphism.. There are, however, many facts -which can not be re a d i l y explained, by t h i s hypothesis. I f the banding of the d i o r i t e was formed by metamor phic d i f f e r e n t i a t i o n , then i t i s very l i k e l y that the bands would be sym metrical, i e . the l i g h t and dark bands would be of equal width and a l l . con tacts would be gradational. A strong argument against a metamorphic o r i g i n of the banding i n the d i o r i t e i s that the texture of the d i o r i t e , as seen i n thin-section and i n hand-specimen, c e r t a i n l y appear to be magmatic, i e . the crystals intermesh,. there are no r e l i c t minerals, and there are no new, t y p i c a l l y metamorphic minerals. 2, Magmatic Origins (a) Banding due to cooling effects near a cold contact. The banding may be the r e s u l t of d i f f e r e n t i a l cooling i n the v i c i n i t y of the margins of the d i o r i t e . During the cooling stage of the d i o r i t e , a thermal gradient would be set up at i t s margin. There would be a gradual increase i n the temperature of the magma from a cool margin i n  wards to a hot central core. At the margin of the d i o r i t e i n t r u s i o n , the magma would be against cool rocks. Thus, c r y s t a l l i z a t i o n would begin from the margin inward. Since plagioclase appears to be early, c r y s t a l l i z a t i o n would begin at the margin with plagioclase and would gradually move inward with increasing formation of hornblende and magnetite u n t i l one complete couplet i s formed* In order to get repeated bands, there must have been either periodic halts i n the cooling of the magma or periodic changes i n the thermal, gradient. The l a t t e r may be brought about by convection 3k currents which would bring i n new heat supplies and fresh magma from below or from the hotter central part of the magma. Localization of c r y s t a l l i z a t i o n along the cooling walls has f r e  quently been invoked to explain gradual v a r i a t i o n i n mineral constituents near the margin of intrusive bodies. There are many examples of c r y s t a l  l i z a t i o n from the margin inwards. In the Skaergaard i n t r u s i o n (Wager and Deer, 1933—39) the marginal border group has i n some places elongated f e l d  spars perpendicular to the contact, and everywhere shows a gradation of mineral composition from the margin inwards i n d i c a t i n g that the magma crys t a l l i z e d from the margin i n towards the centre. Another example i s that many pegmatite veins have crystals perpendicular to the walls of the vein which obviously began to form at the walls and grew inwards. Also many dykes and s i l l s have c h i l l e d margins and show a gradation i n mineral com posit i o n and i n the size of the minerals from the contact i n towards the centre suggesting that they c r y s t a l l i z e d from the walls inward. Thus, i t i s seen that c r y s t a l l i z a t i o n from the margin inwards i s not uncommon. I t seems probable that the banding resulted from cooling effects near a cool contact and c r y s t a l l i z a t i o n from the margin inward, but t h i s effect i s most probably subsidiary t o the greater changes that d i f f e r e n  t i a t i o n and c r y s t a l r i s i n g would produce., I t seems very u n l i k e l y that the multiple bands could have formed s o l e l y by d i f f e r e n t i a l - cooling. Some other process such as d i f f e r e n t i a t i o n , c r y s t a l s e t t l i n g , or d i f f u s i o n i s necessary to produce a separation of minerals.. (b) Banding through d i f f e r e n t i a l movements, (Cloos, 1936). Cloos argues that the bl a t t e r s c h l i e r e n of the Si e r r a Nevada pluton are due to d i f f e r e n t i a l movements i n the magma. Evidence that 3 5 movement occurred i n the d i o r i t e magma of Strachan Creek are possibly the waviness of some of the bands, the rough alinement of plagioclase p a r a l l e l to the banding, (see Figure 16, p. 28), and the presence of "cross-bedding". Cloos argues that the b l a t t e r s c h l i e r e n were formed where movements i n the magma were strong, and that areas of unhanded rock were areas of quiesence. Since the b l a t t e r s c h l i e r e n and the banding i n the d i o r i t e are s i m i l a r , there i s a p o s s i b i l i t y that they have s i m i l a r origins.. However, evidence that movements occurred i n the d i o r i t e magma are not common and signs of strong movement are absent. Thus, i t seems u n l i k e l y , though not impossible, that the banding resulted from d i f f e r e n t i a l movements i n the d i o r i t e magma, (c) Banding through d i f f e r e n t i a t i o n and c r y s t a l r i s i n g . I t i s possible that the banding i n the d i o r i t e resulted from the process of d i f f e r e n t i a t i o n and c r y s t a l r i s i n g . In t h i s process the r e l a t i v e densities of plagioclase and hornblende (plus magnetite) and the v i s c o s i t y of the magma would play an important r o l e . I t i s important to note that there i s a s i g n i f i c a n t and s u f f i c i e n t difference i n the densities of plagio clase and hornblende to bring about t h e i r separation through s e t t l i n g or r i s i n g i n an appropriate l i q u i d medium. Plagioclase has a density of 2.60-2,75 whereas common hornblende has a density of 3 , 0 5 - 3 , 1 * 7 (Dana, Textbook of Mineralogy). From the study of the paragenesis of the minerals i n the dark bands i t appears that hornblende formed simultaneously with and s l i g h t l y a f ter plagioclase, (see Figure 19). Hornblende occurs as i n t e r  s t i t i a l material f i l l i n g the spaces between laths of plagioclase, and i n places i s intergrown with plagioclase. There are many inclusions of plagio clase i n hornblende, but the reverse i s not true. The crystals, of plagio clase are subhedral, and i n many places are intergrown with one another. In 36 Figure 19• Dark band of diorite as seen i n thin-section tinder crossed nicols. Hornblende i s i n t e r s t i t i a l and contain inclusions of plagioclase and magne t i t e . X 100. some places they show corroded edges where they are i n contact with horn blende. Since the hornblende formed after the plagioclase, then i t could not have settled out to form the dark bands. It i s possible, however, that the plagioclase floated and consequently caused the separation of the light and dark minerals. The banding may have developed either on the floor or near the roof of the diorite intrusion. It seems improbable, however, that the banding developed on the floor of the intrusion because the plagio clase, on crystallization, would start to rise through the denser magma.. The plagioclase would not accumulate into a layer because there would be nothing to arrest their rise and consequently the plagioclase crystals would continue to move upwards u n t i l either the magma becomes too viscuous or the plagioclase i s stopped by a barrier. 37 The author v i s u a l i z e s the banding as a re s u l t of d i f f e r e n t i a t i o n near the roof of the d i o r i t e i n t r u s i v e -whereby the plagioclase separated out from the magma and rose to the roof where i t accumulated as a layer.. Consider the c r y s t a l l i z a t i o n of the f i r s t couplet at the roof of the i n  tr u s i o n . The composition of the magma forming t h i s couplet would be uniform before c r y s t a l l i z a t i o n started. C r y s t a l l i z a t i o n would begin with plagioclase crystals which, being l i g h t e r than the magma, would r i s e and accumulate against the roof. The separation of plagioclase from the melt forming the couplet would enrich the lower part of the couplet with heavy constituents. When an appreciable amount of plagioclase c r y s t a l s had accumulated at the roof, c r y s t a l l i z a t i o n of hornblende began and f i l l e d the spaces between the plagioclase l a t h s . Plagioclase and hornblende (and the other minor constituents of the d i o r i t e ) would then continue to crys t a l l i z e u n t i l the couplet i s s o l i d i f i e d . In t h i s way a separation of plagio clase and hornblende i s produced. After the f i r s t couplet had s o l i d i f i e d , convection currents would bring i n a new supply of magma of uniform compo s i t i o n s i m i l a r to that of the f i r s t couplet. C r y s t a l l i z a t i o n of plagio clase would begin and these crystals would r i s e and accumulate against the base of the dark band of the f i r s t couplet. The process of separation by d i f f e r e n t i a t i o n and c r y s t a l r i s i n g would be repeated u n t i l the second couplet i s produced. Many repetitions of t h i s process would resu l t i n multiple bands. The width of the l i g h t band (plagioclase band) would depend s i g n i f i c a n t l y on the rate of c r y s t a l l i z a t i o n of the plagioclase and the length of time that the plagioclase had to accumulate at the roof before c r y s t a l l i z a t i o n of hornblende and consequently the whole couplet.. The 38 variations i n the width of the couplets may be the r e s u l t of changes i n the temperature gradient as a re s u l t of convection currents. The rough lamination of the plagioclases i n the l i g h t bands r e f l e c t the tendency .of the plagioclase plates to f l o a t to the roof with t h e i r f l a t faces p a r a l l e l to the roof, or the effect of currents within the magma flowing p a r a l l e l to the roof. The variations i n the width of a single dark band may be the r e s u l t of convection currents which car r i e d away parts of the heavy c o n s t i  tuents or of the sinking of parts of the heavy constituents of the dark band to lower parts of the magma as a re s u l t of gravity. After s o l i d i f i c a t i o n of the d i o r i t e magma, the whole mass of d i o r i t e was overturned and the banding assumed i t s present attitude.. This i s a necessary inference and a major objection to the hypothesis as there i s no evidence to suggest that the d i o r i t e was overturned after consolida t i o n . In conclusion i t i s seen that none of the hypotheses f i t p e r f e c t l y the features of the banding, but possibly the o r i g i n of the landing through d i f f e r e n t i a t i o n and c r y s t a l r i s i n g i s the most reasonable and the easiest to v i s u a l i z e . Granodiorite A large part of the Strachan Creek area i s underlain by grano d i o r i t e . In general, the granodiorite covers most of the eastern half of the Strachan Creek area. Along the road and r a i l r o a d cut between Strachan Creek No. 1 and Strachan Creek No. 2, there i s a 500 foot section of grano d i o r i t e . Throughout most of the area, granodiorite i s bordered by d i o r i t e . To the northwest, however, granodiorite i s adjacent to the volcanic rocks of the Gambier group, and to the southwest i t i s i n contact with granite.. The 39 The granodiorite-granite contact i s exposed outside of the Strachan Creek area i n a road cut approximately a half mile to the south of Sunset Creek* Here, i t i s very sharp, and neither the granite nor the granodiorite shows signs of chilling..- Instead, both rocks are coarse-grained right at the contact and here the c r y s t a l s interlock.. No conclusive evidence of the age relationship of granite and granodiorite i s present i n t h i s exposure* . Granodiorite appears to have formed l a t e r than the Gambier group.. The s t r i k e of the conglomerate bed of the Gambier group i s t r u n  cated by granodiorite. The granodiorite of the Strachan Creek area i s connected to the granodiorite of Mounts Harvey and Hanover three miles to the north, so as to form one large continuous mass related i n age. Armstrong (1954) notes that the granodiorite of Mounts Harvey and Hanover' originated a f t e r the deposition of the Gambier group. Thus, the granodio r i t e of the Strachan Creek area formed at the same time* In hand-specimen, a t y p i c a l sample of granodiorite i s greyish white and coarse-grained, inequigranular, and allotriomorphic i n texture. The mafic minerals constitute from 5 to 20 per cent of the rock. The granodiorite i s uniform not only i n mineralogical composition and texture, but also i n the constant presence of round dark inclusions.. These i n c l u  sions form approximately one to two per cent of the rock and are evenly d i s t r i b u t e d . The weathering of feldspar produces a white surface on the weathered surface of granodiorite* In thin-sections of granodiorite, i t i s seen that the e s s e n t i a l minerals making up the granodiorite are plagioclase (average, An^) 60%, b i o t i t e 15$, hornblende 5$, quartz, and orthoclase. Quartz forms from 10 to 15 per cent and orthoclase up to 10 per cent of the rock. The accessory minerals are apatite, sphene, and i r o n ore. A l t e r a t i o n products 1*0 are epidote, c l i n o z o i s i t e , and s e r i c i t e . Plagioclase shows marked zoning which i s generally of the o s c i l l a t o r y type, but normal zoning i s also present. Phemister (191,5, p* 65) has studied the zoning of plagioclase of a normal granodiorite of the b a t h o l i t h near Vancouver and describes plagioclase crystals with up to ten zones of the o s c i l l a t o r y type* These zones range i n composition from An gg to An^ 2 with an average composition of Anjp. Phemister also mentions that he observed reverse zoning i n grano d i o r i t e , but t h i s i s not found i n any specimens from the Strachan Creek area. Hornblende i s strongly pbochroic i n tones of green and has smooth grains boundaries, and i n places i s subhedral.- Many cr y s t a l s are twinned. Generally, hornblende contains inclusions of apatite, feldspar, and i r o n ore. B i o t i t e i s present as ragged grains p a r t l y altered to c h l o r i t e , e s p e c i a l l y along cleavage traces* Generally, i t contains round inclusions of plagioclase and iron ore (pyrite and magnetite).. Quartz i s mainly i n t e r  s t i t i a l , but i n places forms large, i r r e g u l a r l y bounded grains which show wavy extinction, i n c i p i e n t f r a c t u r i n g , and minute bubbles and inclusions.. Orthoclase occurs as clear, untwinned i n t e r s t i t i a l areas which i n some places surrounds plagioclase l a t h s * A l t e r a t i o n i s not prominent* In general, the granodiorite has.no d i r e c t i v e textures, but i n a few places the inclusions are roughly oriented* The presence of ( l ) an apophyse of granodiorite cutting d i o r i t e , (2) the uniform pattern i n the o v e r a l l texture of the granodiorite, and (3) the constant mineral composition of the granodiorite suggests a magmatlc o r i g i n of the granodiorite. Id Small Inclusions i n Granodiorite Small basic xenoliths are i n v a r i a b l y found i n the granodiorite. Generally, they form 1 to 2 per cent of the rock, but i n some places they make up to 5 per cent of the rock., They appear to be evenly d i s t r i b u t e d throughout the granodiorite regardless of contact relations.. In general, the inclusions are round to subround i n outline, but i n a few places sharp angles are noted. There are same elongated inclusions (see Figure 20) which have a r a t i o of length to width ranging from 2:1 to The largest inclu s i o n seen i n outcrop i s approximately 7 inches i n i t s longest d i r e c t i o n , but many boulders of granodiorite i n the creek beds contain inclusions over a foot or more i n diameter. The size of the inclusions grade from 7 inches to l e s s than a quarter of an inch across. The majority of the i n c l u s i o n s , however, are about 1 to 2 inches i n diameter. The contact between xenolith and granodiorite i s sharp, but generally, the c r y s t a l s intermesh across the contact, (see Figures 20, 21, and 22). In most places the xenoliths show random orientation.. Figure 20. Figure 21.. Figure 22. Small inclusions i n the granodiorite. Figure 20 i s of an elon gate inclusion with sharp contacts. A large feldspar c r y s t a l l i e s across the boundary. Figure 21 i s of an oval i n c l u s i o n which has sharp contacts without interlocking c r y s t a l s across the contact. Figure 22. i s of a round in c l u s i o n with phenocrysts or porphyroblasts. U2 Variations i n the type of xenoliths are observed. Most of them are of dark, fine-grained, e s s e n t i a l l y d i o r i t i c rocks, but a few are of very fine-grained, dark, b a s a l t i c rocks. The author found one xenolith of a meta morphic rock with d e f i n i t e f o l i a t i o n and with a composition of quartz, feldspar, c h l o r i t e , and epidote.. Some xenoliths of d i o r i t i c composition have f a i n t banding due to a preferred orientation and segregation of mafic minerals..- One type of xenolith i s c h a r a c t e r i s t i c and dominant i n granodio r i t e . I t i s a f i n e l y granular rock of d i o r i t i c composition composed mainly of hornblende and plagioclase. Ih places i t i s porphyritic or por- phyroblastic, having large white phenocrysts or porphyroblasts of plagio clase ranging from l/8 to l/l+ inches i n diameter i n a fine-grained, dark groundmass* In thin-sections of the most common ( d i o r i t i c ) type of xe n o l i t h , the minerals are seen to be plagioclase (zoned, rim A ^ Q t o core An^g) 55$, hornblende 30$, b i o t i t e 5$, quartz, c h l o r i t e , orthoclase, z o i s i t e , s e r i c i t e , sphene, and c l i n o z o i s i t e . Quartz i s i n t e r s t i t i a l , encloses w e l l formed laths of plagioclase and subhedral crystals of hornblende, and has undulatory ext i n c t i o n . There appears to be two stages i n the formation of hornblende. The e a r l y hornblende cr y s t a l s are subhedral t o euhedral and r e l a t i v e l y free of i n c l u s i o n s * The l a t e r hornblende appear as anhedral grains with ragged c r y s t a l outlines and p o i k i l i t i c texture, containing small inclusions of plagioclase, apatite, and iro n ore. Phemister (I9k5) proposes that the xenoliths represent fragments of pre-batholithic dykes and other country rocks which were caught up into the intruding magma and made over into basic patches which were i n e q u i l i  brium with the surrounding magma* A strong argument f o r t h i s hypothesis i s h3 i s that a chemical analysis (made by Phemister) of the composition of a common type of xenolith i n the granodiorite of the Caulfields area near Vancouver i s very s i m i l a r to that of the pre-batholithic dykes. Also, at Caulfields the inclusions show a l l stages of conversion to granodiorite. Granite The main mass of pink granite occurs i n the southern part of the Strachan Creek area and extends from the southern boundary of the area northward to approximately 1000 feet north of Sunset Creek and up the slope of the mountain to an elevation of more than 3000 f e e t . Armstrong (195k) shows t h i s mass to continue as an alongate body about h miles long and l / h to 1/3 mile wide, having a general northwesterly trend. Good exposures are found along the seashore, and along the road and r a i l r o a d cuts. To the south, just outside of the Strachan Creek area, granite i s i n contact with granodiorite. Just to the north of Sunset Creek the main mass of granite gives way to d i o r i t e . The contact here i s not exposed, but within a few feet of i t both the granite and granodiorite i s exposed. About 300 feet above the road cut, the contact i s occupied by a dark, p o r p h y r i t i c , dio r i t i c dyke* To the north of the main mass of granite many smaller dykes of granite are found.. They cut the d i o r i t e and range i n width from 20 to 300 fe e t , (see Figure 23) The contact of the granite dykes with the d i o r i t e i s generally quite sharp. In a few places the granite dykes con t a i n small, angular inclusions of d i o r i t e near the contact, (see Figure 2h)» This suggests that the granite magma stoped off parts of the walls of the d i o r i t e during i t s i n t r u s i o n . kh S+ro.cKqn Figure 23. Section exposed i n road cut near Strachan Creek No. 1. D i o r i t e cut by numerous dykes of granite* In hand-specimen, the granite i s t y p i c a l l y pale pink and coarse grained, allotriomorphic to hypidiomorphic, and inequigranular i n texture,. Mafic minerals make up less than 5 per cent of the rock and i n general are w e l l d i s t r i b u t e d throughout. The melanocratic minerals are generally much smaller than the leucocratic minerals. The pink colour of the granite i s due to the abundance of K-feldspar.. The rock i s w e l l jointed and has many fractures and j o i n t s * The granite i n the v i c i n i t y of Sunset Creek i s cut Figure 2 l i . Granite-diorite contact as seen i n road cut near Strachan Creek No. 1. Note the large inclusions of d i o r i t e i n granite* 16 by numerous t h i n , black vehlets approximately l / l O t h of an inch thick.. These veinlets form a sort of network or boxwork (see Figure 25) and appear to be related to the j o i n t i n g as the two are clos e l y associated. The veinlets are composed mainly of b i o t i t e with minor amounts of c h l o r i t e and s e r i c i t e . . These minerals are w e l l oriented p a r a l l e l to the walls of the veinlets.. In thin-section the mineral composition of the granite i s seen to be microperthite 60$, quartz 30$, b i o t i t e 5-8$, plagioclase A n ^ , apatite, magnetite, p y r i t e , s e r i c i t e , c h l o r i t e , z o i s i t e , c l i n o z o i s i t e , and andalusite. Microperthite and quartz are predominant and a l l the other minerals are present only i n rather minor amounts. Mafic minerals form from 1+-8 per cent of the rock.. Andalusite i s present only i n one thin-section. Here, i t occurs as subhedral, squarish crystals surrounded by a very t h i n rim of se r i c i t e . . Some andalusite crystals are enclosed i n quartz, while others are embedded i n a fine-grained, crushed matrix of quartz grains. The para- genesis of the minerals show that andalusite formed after the c r y s t a l l i z a -U6 t i o n of microperthite, plagioclase, and b i o t i t e , but before the formation of quartz. This suggests that the andalusite i s of primary origin.. That i s , the magma had an excess of alumina a f t e r having s a t i s f i e d the require ments of feldspar and mica, and t h i s excess was used up i n the formation of andalusite. In a l l thin-sections the granite shows c a t a c l a s t i c texture. The boundaries of large microperthite and quartz grains appear to be granulated. Large areas of the thin-sections show fine-grained, broken up crystals of quartz and K-feldspar. Many t h i n v e i n l e t s of fine-grained granulated material cut through the rock. The vei n l e t s are seen to weave between the large grains and i n places even cut through the large grains* Large microperthite grains are encircled by very fine-grained granular quartz. The cat a c l a s t i c action seems to have occurred a f t e r the c o n s o l i  dation of the rock because a l l the quartz has wavy extinction and there i s no i n t e r s t i t i a l quartz between the granulated grains.. The granite appears to be a t y p i c a l high l e v e l granite emplaced as magma.. A strong argument f o r t h i s hypothesis i s that the granite has a. uniform pattern i n i t s o v e r a l l texture and i t s mineral composition i s everywhere constant.. The presence of granite dykes containing blocks of d i o r i t e indicate that the magma stoped off parts of the d i o r i t e during i n t r u s i o n . The general occurrence of cata c l a s t i c texture i n the granite suggests that the granite suffered p o s t - c r y s t a l l i z a t i o n stresses. Perhaps i t wedged i t s way further after s o l i d i f i c a t i o n . Dyke Rocks Several v a r i e t i e s of dykes are found cutting the plutonic rocks of the Strachan Creek area. The dykes can be divided on the basis of com-1*7 position into two groups, basic dykes and acidic dykes* The basic dykes of the Strachan Creek area consist of gabbro, porphyritic and non-porphyritic d i o r i t e , and b a s a l t i c (or trap) dykes.. A l l the basic dykes, except f o r one gabbroic dyke, are found i n the main mass of granite. The best exposures of the basic dykes are found i n the road and the r a i l r o a d cuts near Sunset Creek. Only one dyke of gabbro occurs i n the map-area and i t i s found just north of Strachan Creek No. 1 at an elevation of about 1200 fe e t . I t has very sharp contacts with the adjacent d i o r i t e and i s f i n e r grain near i t s margin than towards i t s centre. In t h i n - section the essential minerals are seen to be plagioclase (An^) %0%f augite 20$, c h l o r i t e 15%, and quartz 5%» Accessory minerals are p y r i t e , magnetite, apatite, and calcite.. The porphyritic d i o r i t e dykes are exposed along the road cut just north of Sunset Creek, (see Figure 26). They are medium- to fine-grained, greyish green rocks which are spotted with large white pheno- crysts of plagioclase. The essential- minerals are plagioclase (average Anj^) 60%, hornblende 30%, and magnetite 5%, and the accessory minerals are quartz, c h l o r i t e , epidote, b i o t i t e , and apatite. Phenocrysts of plagioclase show o s c i l l a t o r y zoning. No dir e c t i v e textures are apparent i n either hand- specimens or thin-sections of the rock.. The non-porphyritic d i o r i t e dykes Figure 26. Section exposed i n road cut just north of Sunset Creek. Granite i s cut by numerous dykes* are also exposed along the road cut just north of Sunset Creek, (see Figure 26). One of these dykes i s found i n the granite at elevations of 12-llt00 f e e t . The d i o r i t i c dykes are grey and medium-grained, allotrioraorphic, and inequigranular i n texture* The mafic minerals occur as evenly d i s t r i b u t e d c l o t s or bunches composed mainly of b i o t i t e , . In hand-specimen, i t i s seen that plagioclase 60$, b i o t i t e 25%, hornblende Q%, and i r o n ore 3% are the e s s e n t i a l minerals. In a few places the mafic minerals show a preferred orientation. The trap dykes are very fine-grained, black rocks of b a s a l t i c composition. The basic dykes were intruded after the formation of the plutonic rocks. Strong evidence f o r t h i s i s that many of the basic dykes show c h i l l e d borders and are of f i n e r grain near t h e i r margins than i n the central, part of the dyke. Generally, the contacts of the dykes with the adjacent rocks are very sharp. The age relations between the various basic dykes i s not ce r t a i n . However, i t i s clear that the trap dykes are l a t e r than the porphyritic and non-porphyritic d i o r i t e dykes as the trap dykes cut both of these dykes, (see Figure 26). The acidic dykes are found i n the d i o r i t e at various i n t e r v a l s from Sunset Creek to Newman Creek.. A U of them are too small, and too i r r e g u l a r to be mapped. In the Strachan Creek area they are represented by a p l i t e and pegmatite dykes. In places they follow f a u l t planes, (see Figure 27).. Where a p l i t e occupies a f a u l t plane, i t i s bounded on one w a l l by the f a u l t and on the other by country rock, (see Figures 13 and 27). Both contacts are sharp,. In some places epidote occurs i n the a p l i t e only along the f a u l t w a l l , but i n other places epidote i s present along both . Figure 27* Epidote grading i n abundance from both walls of the a p l i t e vein toward the centre,. contacts, (see Figure 27)* In both of these instances, epidote i s more abundant near the contact and gradually decreases i n abundance towards the centre of the dyke,. In hand-specimen, the a p l i t e consists e s s e n t i a l l y of orthoclase 50%, plagioclase 25%, and quartz 15% • The accessory minerals are epidote, b i o t i t e , c h l o r i t e , magnetite, and hematite. The a p l i t e dykes probably represent the l a t e emanations of a consolidating g r a n i t i c magma,. 50 BIBLIOGRAPHY Akaad, M.K.. (1956), The Ardara granitic diapir of County Donegal, Ireland; Quarterly Jour.. Geol. Soc, London, vol . CXII, Dec , pt. 3 , p. 263-290. Armstrong, J.E.. (1951+), Preliminary map of Vancouver North, B.C.; Geol.. Surv.. Canada Paper 53-28. Balk, R.. (1937), Structural behaviour of igneous rocks;; Geol. Soc. Amer. Mem.. 5 , July. Berry, E.W. (1926), Tertiary floras from British Columbia; Geol.. Surv. Canada, Bulletin No.. i|2, Geol* Series No.. 1+5, p.91-116.. Cheng, Yu-chi (191+1+), The migmatite area around Bettyhill Sutherland, England; Quarterly Jour.. Geol. Soc London, vol., XCIX, pt.. 3 & U, Jan., p. .107-151+. Cloos, E. (1933), Structure of the Sierra Nevada Batholith;; 16th Int. Geol.. Congress, Guidebook 16, p* 1+0-1+5.. (1936), Der Sierra Nevada pluton in California; Neues Jahrbuch fur Min., Geol., und Paleo.. 76, Bai l * Bd., Abt. B. , 3$$rl&0+ Folinsbee, R.E. , Ritchie, W.D., Stansberry, G.F. (1957), The Crowsnest volcanics and Cretaceous geochronology;, Guidebook, 7th Annual Field Conference, Waterton; Alta. Soc of Petroleum Geol., Sept., p.. 20-26.. Gilbert, G.K. (1906), Gravitational assemblage in granite;; Geol. Soc. Amer. Bu l l . , vol. 17,. p.. 321-328. Gilluly, J* (191+8), Origin of granite;; Geol. Soc. Mar * Mem. 28, April. 10 . Larsen, E.S. Jr* (191+8), Batholith cf Southern Cal i f . : Geol. Soc. Amer.. Mem.. 29* Nockolds, S.R.,'(1932), The contaminated granite of Babette Head, Alderney; Geol.. Mag*. 69 , p.- 1*33-1+52. (1933), Some theoretical aspects of contamination of acid magma; Jour. Geol., vol.. 1+1, p* 561-589* Phemister, T .C . , (191+5), The Coast Range batholith near Vancouver, B.C.; Quarterly Jour. Geol. Soc. London, vol* C i , pt. 1 & 2, p* 37-88. Turner, F.J.. (1948), Mineralogical and str u c t u r a l evolution of the metamorphic rocks;; Geol. Soc. Amer. Mem.. 30, J u l y 28* Wager, L.R. (1953), layered intrusions;,'Meddelelser f r a Dansk Geologisk Forening, Bd* 12, Kobenhavn, August. Wager, L.R. and Deer, W.A. (1933-39), Petrology of Skaergaard Intrusion Meddelelser om Gronland udgivne af Kommissionen f o r Videnskabelige Undersogelser i Gronland, v o l . 105* ABSENCE REPORT Please report holidays i n terms of days and sick leave i n hours. Please do not report periods of less than a half hour. DIVISION WViSK ENDING SATURDAY LEAVE V/ITHOUT NAME SICK LEAVE PAY . VACATION APPROVED Divi s i o n Head. x in o m CJ o ro CM to 0 ro CM CM o ro CM CENOZOIC T E R T I A R Y 4 9 ° 26 H z 'A T R A P D Y K E B A S I C D Y K E S - G A B B R O , D I O R I T - E E S O Z O I C G R A N I T E G R A N O D I O R I T E -1 v D I O R I T E T R I A S S I C A N D / O R G A M B I E R ' G R O U P LATER V O L C A N I C S C O N G L O M E R A T E TRIASSIC A N D / O R B O W E N I S L A N D G R O U P E \^ R L. 8 EE! M I G M A T I T E 49° 25' H SO C O N T O U R S G E O L O G I C A L B O U N D A R Y A S S U M E D G E O L O G I C A L C O N T A C T S H O W I N G D I P S T R I K E A N D D I P O F B A N D I N G R O A D S H O R E - L I N . E 1/5 0 S C A L E 1/5 I : 1 0 , O O O 2/5 3/5 4/5 I M I L E 1 CONTOUR I N T E R V A L 2 0 0 G E O L O G I C A L A P V A N C O U V E R . D I S T R I C T B R I T I S H C O L U M B I A 

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