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The geology of the Pioneer Ultramafite, Bralorne, British Columbia Wright, Robert Leslie 1974

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THE GEOLOGY OF THE PIONEER ULTRAMAFITE, BRALORNE, BRITISH COLUMBIA by ROBERT L, WRIGHT B.Sc, McHaster University, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of GEOLOGICAL SCIENCES -We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1974 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 lumbia, 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 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 Geological Sciences The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date J u n e 6> 1974 i ABSTRACT The Pioneer Ultramafite, south of Bralorne, B r i t i s h Columbia, i s a fault-bounded lens of alpine-type peridotlte enclosed in lower greenschlst facies sediments and volcanics of the middle Triassic Fergusson Group and late T r i -assic Noeli Pioneer and Hurley Formations. The body consists of a core of well layered harzburgite, dunite and orthopyroxenlte, rimmed by serpentinite and talc-carbonate alteration zones containing tectonic inclusions of sediments, volcanics and rodingite. Foliated harzburgite forms approximately 80 per cent of the ultramafitei dunite, as dikes, s i l l s and Irregular pods in harzburgite, comprises about 17 per cent} and orthopyroxenlte as layers ( l to 15 cm thick), p a r a l l e l to the f o l i a t i o n , ln harzburgite, constitutes the remaining 3 per cent. Electron microprobe analyses of the primary minerals indicate olivine composition ranges from Fo 90.2 to 92.5» orthopyroxene from En 89.2 to 90.2 and clino-pyroxene averages C a ^ gMgj^ if • Co""? 0 8!*! 0 0 8 o f coexisting primary minerals indicate a temperature of equilibration of about 950°C a t an unknown pressure. Alteration assemblages in the serpentinized contact zone indicate migration of ^ 0 , C0 2, CaO, MgO and S i 0 2 resulting in metasomatism of the ultramafite and country rocks, producing rodingite, nephrite (jade) and t a l c -carbonate. Serpentinization apparently occurred during emplacement of the ultramafite into the surrounding country rocks. Plastic deformation and recrystallization of the peridotlte produced the pervasive planar f o l i a t i o n or layering, which has been disrupted by several later episodes of folding and fracturing. Country rocks show evidence of two phases of deformation prior to emplacement of the ultramafite, A strong fo l i a t i o n of serpentinite and country rocks, near the contact, was produced during emplacement. The ultramafite and country rocks are interpreted as a partial, dismembered ophiolite which was emplaced in the late Triassic or early Jurassic by obduction of oceanic crust onto the continental margin. i i TABLE OF CONTENTS INTRODUCTION 1 REGIONAL GEOLOGY 7 STRATIGRAPHY 11 Fergusson Group , 11 Noel Formation f 14 Pioneer Formation 15 Hurley Formation 17 INTRUSIVE ROCKS 18 Bralorne Intrusions 18 Other Intrusions 19 ULTRAKAFIC ROCKS 30 General Description and Distribution 30 Petrography 33 Harzburgite 33 Orthopyroxenite 33 Dunite 42 Chemistry 45 Alteration 49 I. Pervasive Serpentlnization 49 II. Contact Zoning 53 a. Serpentinite 56 b. Talc-Carbonate 60 c. Nephrite (jade) 63 d. Rodingite 63 e. Quartz-Talc-Serpentine 75 f . Quartz-Magnesite 75 i i i III. Fault Zones IV. Later Intrusions STRUCTURAL GEX)LOGT Introduction Ultramafite Structures Country Rock Structures Interpretation Cross Sections DISCUSSION Pioneer Ultramafite Textures Petrogenesis Ultramaf i t e Alteration Chromite Alteration Serpentinization Talc-Carbonate Alteration Nephrite (jade) Rodingite Quartz-Magnesite Contact Ketaraorphisa Metamorphism of Country Rocks The Ophiolite Assemblage Geological History BIBLIOGRAPHY APPENDIX I Electron Probe Analyses APPENDIX II Estimated Modes from Thin Sections APPENDIX III Measured Sections of Ultramafite APPENDIX IV Geothermometry-Geobarometry APPENDIX V Alteration Zoning, Sample 306 75 77 80 80 80 84 8^9 97 100 100 100 1 0 2 104 104 1 0 7 110 112 1 1 3 114 114 116 117 119 121 126 144 1 5 7 167 176 Iv LIST OF TABLES Page 1 Table of Formations. *8 2a Chemical Analyses of Bralorne Diorite, Greenstone-diorite and Soda Granite •...••....20 2b Reported Average Analyses of Diorite and Gabbro .,21 2c Reported Average Analyses of Granites, Trondhjemite and Keratophyre 22 3 Classification of Intrusive Rocks............... ,.24 4a Summary of Primary Mineral Analyses from Pioneer 46 4b Reported Analyses of Primary Minerals from Alpine Ultramafites.••...•••• ....47 5 Summary of Deforraational History of F i e l d Area.. 81 6 Summary of Estimates of P,T Conditions of Equilibration of the Pioneer Ultramafite 10J LIST OF FIGURES Figure "^g® 1 Location Hap of Thesis Area 2 2 Topography....... • •••3 3 Regional Geology..... 9 4 Local Geology . . . . . . . .10 5 Provisional Classification Scheme for Ultramafic Rocks (after Irvine and Findlay, 1972) .........40 6 Modal Classification of Ultramafic Rocks (after Jackson, 1968) 41 7 Distribution of Alteration Types 54 8 Sections through Contact Zone..... .55 9 Rodingitized Gabbro Dike .67 10 F i e l d Relations of Samples 553a and 553b . . . . . . . . . . . . . . 6 9 11 Dunite Dike Crosscutting Peridotite Layering .....83 12 Sigmoidal Fold i n Peridotite Layering, S a ..85 13 Peridotite Layering, S a 87 14 S3 in Serpentimites and Talc-carbonates ...88 15 S^ in Sediments and Volcanies from North Side..........90 16 S i i n Sediments and Volcanies from South & West Sides..91 17 S i in A l l Sediments and Volcanies..... 92 18 Cross Sections of Pioneer Ultramafite.... .98 19a Cheraographic Diagram: Ca0-Mg0-Si02-C02-R*20 System 105 b Chemographlc Ddbagram 1 MgO-Si02-H20 System 105 20 Equilibria in the System Ca0-Mg0-Si02-H20-C02 ....106 21 Equilibria in the System CaO-MgO-S^^O. 108 22 Fe4"*" and Mg4* Partitioning i n Olivine and Opx '....168 23 Fe 4 4 , and Mg44" Partitioning in Olivine and Cpx. .......170 v i LIST OF FIGURES (continued) 24 Fe**^ and Mg"^ Partitioning i n Opx. and Cpx. 171 25 P-T Estimates Based on Clinopyroxene Composition. . . . . . .174 26 Modal Analyses of Alteration Zoning of Sample 306 178 27 Mg/Fe Ratios i n Sample 306... ...179 Maps t 28 Geology of the Pioneer Ultramafite in pocket -29 Sample Location Map. in pocket — LIST OF PLATES. v i i 1 -View of f i e l d area from north side of Cadwallader Creek. 2 View of north contact area, looking northward, from u l t r a m a f i t e . 3 View of south contact area, looking southward, from u l t r a m a f i t e . 4 View, from Peak 1, of ridge east of Crazy Creek. 5 R e l a t i v e l y undeformed Fergusson ribbon cherts. 6 Sheared, l e n s o i d a l Fergusson ribbon cherts. 7 Breccia, Noel Formation : Thin section (PPL) 8 Pioneer Greenstone : Pumpellyite. Thin section (X n i c o l s ) 9 S i l l of T e r t i a r y amygdaloidal v o l c a n i e s . 10 T e r t i a r y volcanies i Thomsonite. Thin section (X n i c o l s ) 11 Zoned Group C i n t r u s i o n of- d i o r i t e . 12 Closeup of Plate 11 : Kspar blebs and zoning. 13 Group D keratophyre s i l l along serpentinite-country rock contact. 14 Sample (267) of Group C i n t r u s i o n s . 15 Well-layered harzburgite itfith orthopyroxene lenses. 16 Layered p e r i d o t i t e : orthopyroxene and dunite l a y e r s . 17 Harzburgite;showing well-defined l a y e r i n g o f orthopyroxenes. 18 Enlargement of Plate 1?. 19 Harzburgite with discontinuous l a y e r s o f orthopyroxene. 20 Enlargement o f Plate 19. 21 Massive harzburgite with randomly d i s t r i b u t e d orthopyroxenes. 22 Thinly-layered harzburgite. 23 Orthopyroxenite : Thin section (X n i c o l s ) . 24 S t r i n g e r of orthopyroxenes, bordered by dunite, i n harzburgite; 25 Fracturing i n orthopyroxenite l a y e r . 26 Enlargement of Plate 25. 27 Chromite disseminated i n dunite. v i i i 28 Chromite stringer i n dunite. 29 Irregular layers of massive chromitite i n dunite. 30 Chromitite : Thin section (PPL). 31 Chromite grain rimmed by chlorite in serpentinized dunite. (PPL) 32 Enlargement of Plate 31. Thin section (X nicols). 33 Serpentinite developed along joint i n harzburgite. 34 Outcrop of serpentinite showing contorted fo l i a t i o n . 35 Mesh texture in serpentinite : Thin section (X nicols). 36 Magnetite islands in serpentinite : Thin section (PPL). 37 Sample (343) of serpentinized harzburgite with spots of brucite 38 Patches of brucite in serpentinite : Thin section (X nicols). 39 Sample (288) of serpentinized dunite 40 Brucite stringers (sample 288) : Thin section (X nicols). 41 Talc-magnesite veins crossing serpentinite f o l i a t i o n . 4-2 Sample (35^) °f talc veinlets in serpentinite. 4-3 Sample (350) of talc-serpentine schist. 4-4 Sample (I78) of massive talc-ma gne site rock. 45 Sheared tremolite-albite rock from contact of ultramafite. 46 Enlargement of Plate 45. 47 Sample (264) of sheared tremolite-albite rock. 48 Breccia (338) from along fault contact of ultramafite. 49 Botryoidal jade 1 Thin section (X nicols). 50 Rodingite replacing coarse-grained gabbro. 51 Small rodingite pod in serpentinite. 52 Large rodingite pod in serpentinite. 53 Rodingite (352) s idocrase veinlets in diopside-hydrogrossular. 54 Rodingite 1 zoned idocrase. Thin section (X nicols). 55 Rodingite : plagioclase phenocryst. Thin section (X nicols). ix 56 Rodingite : Zoisite replacing plagioclase. Thin section (X nicols). 57 Rodingite-serpentinite contact. Sample 2 7 6 . 58 Rodingite : hydrogrossular veinlets. 59 Rodingite : hydrogrossular and diopside. Thin section (X nicols). 60 Rodingite : clinozoisite i n calcite. Thin section (X nicols). 61 Shear zone in peridotite. 62 Sample (258) from shear zone in peridotite. 63 Crosscutting orthopyroxenite stringers.. 64 Closeup of crosscutting stringers. 65 Fractures offsetting orthopyroxenite stringers. 66 Flow fold in layered harzburgite. 67 Fractured dunite in undeformed harzburgite. 68 Contorted orthopyroxenite layers in dunite. 69 Peridotite with S 2 f o l i a t i o n . 70 Elongated rodingite pod i n serpentinite. 71 Alteration along joints i n peridotite. 72 Contact of talc-carbonate alteration zone with fresh peridotite. ACKNOWLEDGEMENTS This study was supervised by Drs. H. J. Greenwood, K. C. McTaggart, and P. B. Read, whose advico and direction are greatly appreciated. The writer wishes to thank Dr. Bernard Evans for the use of the electron microprobe at the University of Washington, Seattle, and Edmund Mathez for his helD with the analyses and computer work. The writer also wishes to thank P. Morton, D. Milne, and D. Wright who assisted with f i e l d work. The technical assistance of E. Montgomery and B. Cranston in preoaration of thin sections is greatly appreciated. Helpful discussions with Dr. J. Monger (G.S.C., Vancouver) and Dr. E. P. Meagher (UBC) are gratefully acknowledged. The manuscript was typed by Josephine Swayne. This, work-was. supported by a . National. Research Council 1967 Science. Scholarship. INTRODUCTION 1 Location and Access The Pioneer Ultramafic Body i s about 3 miles southeast of Bralorne, B.C. in the Pacific Ranges of the Coast Mountains (Holland, 1964). The ultramafite forms a 7600-foot peak at the northwest end of the Cadwallader Range (Fig. i ) . The area can be reached by good highway from Lillooet or by rough track from Pemberton. Access to the ultramafite i s by means of a t r a i l leading south from the road at the Pioneer Mine. Topography The area consists of sharp, rocky ridges separated by d r i f t - f i l l e d cirque; and valleys. Tlreeline i s at about 65OO feet, which roughly corresponds with the lower contact of the ultramafite, so that these rocks are generally well-exposed. Many of the topographic features of the area are unnamed. For refer ence in this discussion, various peaks and cirques are a r b i t r a r i l y numbered (Fig. 2). Previous Work Although gold prosDectors explored the area around Bralorne as early as the late I850*s, the f i r s t geological reports did not appear until 1911 when Camsell (1911) and Bateman (1912) reconnoitred the Bridge River-Cadwallader Creek area. Drysdale (1915) f i r s t mentioned the ultramafic rocks of the present map-area, and McCann (1922) later described them. Cairnes (1937) made a detailed study of the geology immediately north of the ultramafite, in the Cadwallader Creek valley. His report contains an annotated bibliography of a l l previous work in the area, up to 1937« Roddick and Hutchison (in press describe the broad structural, metamorphic and plutonic character ofthe region The name ' Pioneer' Ultramafite, assigned by the present writer, i s taken 1 from the nearby Pioneer Mine, a gold-quartz deposit f i r s t staked i n the 1890 s 2 FIG. 1 LOCATION MAP 3 Figure 2' Although the Pioneer body i s the type l o c a l i t y of Cairnes' (1937) President VIntrusives' (since i t is drained by President Creek), a more specific name is needed for the area under study. Hence the name Pioneer i s used, to d i s -tinguish this body from other President lIntrusives', l i k e the larger Copp Creek body (Cairnes, 1937; Roddick and Hutchinson, in press) about 8 km to the southeast. Present Investigation The purpose of this study was to map the Pioneer Ultramafite and sur-rounding country rock, and through study of structure and petrology to work out the geological history of the area. Field mapping at a scale of lslO,000 was completed during the summers of 1972-73- Laboratory work included stan-dard petrographic and X-ray diffraction techniques, as well as electron microprobe analyses. PLATE 1. View of f i e l d area from north side of Cadwallader Creek, looking southward. PLATE 2 . View of north contact area, looking northward, from peridotite (brown) across serpentinite (grey-green) Large valley i s Cadwallader Creek. 6 1 PLATE 3« View of south contact area, looking southward from peridotite (brown) across serpentinite (grey-green) talus, towards country rocks (black). I PLATE 4. View, from Peak 1, of ridge east of Crazy Creek. Left end of ridge is 3ralorne Intrusions. 7 REGIONAL GEOLOGY The f i e l d area i s located on the eastern edge of the Coast Plutonic Complex of British Columbia, just west of the Intermontane Belt. The region (Fig 3) i s underlain by eugeosynclinal sediments and volcanics of Early Mesozoic age. Ribbon cherts, a r g i l l i t e s , pillowed volcanics, and greenstones, with minor limestone comprise the Fergusson Group and Noel, Pioneer, and Hurley Formations (Cairnes, 1937)• These rocks are commonly highly deformed, with the predominant structural 'grain' being northwest-southeast, along the axis of the Plutonic Complex. Major fault zones, trending northwesterly, possibly with large horizontal movements, occur along the Yalakom River valley (Leech, 1953) and possibly i n the Cadwallader Creek valley. Numerous f a u l t -bounded ultramafic bodies are distributed throughout the region. These range from small pods, with maximum dimensions of a few metres, generally located along shear zones in the sediments and volcanics, to very large bodies l i k e the Shulaps (Leech, 1953) which i s over 30 km long. In the Cretaceous, a number of batholiths and associated dikes of inter-mediate composition intruded the eugeosynclinal sediments and volcanics. The nearest of these i s the Bendor batholith, which forms the core of the Bendor Range, to the northeast of the thesis area. Metamorphism in the Cadwallader Creek area i s generally of lower green-schist facies, except where contact metamorphism around the larger batholiths has resulted i n quartz-biotite schists, andalusite schists, and sericite schists (Cairnes, 1937). The thesis area i s near the northern end of a chain of Cenozoic volcanic centres. Noel Mountain, about 5 km west of this area, i s capped by these volcanic rocks. Glacial deposits, stream deposits, and a Recent scoriaceous ash or pumice (Nasmith et a l , 19$7) form a thin veneer over much of the area. 8 TABLE 1 i Table of Formations (after Cairnes, 19371 1943, and Roddick and Hutchison, 1974) QUATERNARY PLEISTOCENE and RECENT Ash Deposits Glacial Deposits, Alluvium 8 TERTIARY MIOCENE (?) Basalt to rhyolite t flows, plugs, sills LOWER TERTIARY Rexmount Porphyry, minor extrusive rhyolite and dacite IC and CRETACEOUS Taylor Creek, Jackass Mountain, and Relay Mountain Groups TRIASSIC Hurley Formation - thin-bedded limy argillite, phyllite, tuff, limestone, conglomerate, andesite, chert* Pioneer Formation - greenstone derived from andesitic flows and pyroclastic rocks. Noel Formation - thin-bedded argillite, chert, greenstone. Fergusson Group (Bridge River Group) - chert, argillite, phyllite greenstone, limestone, also biotite schists. PLUTONIC ROCKS (age not known) Granite Granodiorite Quartz diorite 1 B U Diorite including Bralorne Intrusions t diorite, gabbro, minor soda granite. Gabbro Ultramafic rocks - peridotite, pyroxenite Serpentinite FIGURE 4: o STRATIGRAPHY 1 1 The predominant lithology in the area i s a eugeosynclinal assemblage of ribbon chert, pillow lava, a r g i l l i t e , greenstone, and minor limestone. After mapping large regions north and northwest of the Pioneer Ultramafite, Cairnes (1937) worked out a stratigraphic sequence which i s generally accepted. The units are defined by the dominant rock type of the several that compose the unit. For example, the Fergusson Group is predominantly ribboned and massive cherts, with lesser amounts of volcanic rocks and limestone; the Noel Formation is dominantly a r g i l l i t e and greywacke, with minor chert, volcanic rocks, etc. Consequently, where exposures of' such rocks are small, i t may be impossible to assign the rocks to a particular unit. On the north side of the Pioneer Ultramafite, this stratigraphic sequence is mappable, Noel a r g i l l i t e s and greywackes being readily distinguished from Pioneer greenstones and Fergusson cherts and volcanies. In some areas on the south side, where structural deformation i s apparently more intense, these rock units cannot be mapped. Hence a number of areas have been mapped as 'cherts, a r g i l l i t e s and volcanies' representing, presumably, a tectonic mixture of Cairnes' Fergusson Group and Noel Formation. Despite these d i f f i c u l t i e s in mapping, Cairnes' stratigraphy is valuable, and i s probably the best that can be developed i n the area because of the struc-tural complexity and poor exposure of large areas. FERGUSSON GROUP The Fergusson Group i s the oldest unit recognized in the f i e l d area, form-'ing most of the undifferentiated unit along the west contact of the ultramafite. Excellent exposures of this unit, i n a relatively undeformed state occur along the north shore of Carpenter Lake, about 2 0 km north of the area. These include pillowed and massive volcanies, ribbon cherts (Plate 5 ) a n c^ limestone pods up to 2 5 m across. Within the present f i e l d area, however, these rocks are more 12 deformed, so that pillowed volcanics were not recognized and ribbon cherts tend to be lensoidal in character (Plate 6 ). In thin-section, the cherts are an equigranular fine-grained aggregate of strained quartz grains transected by numerous veinlets of coarser-grained, less strained quartz. The argillaceous partings of the ribbon cherts consist of fine-grained quartz with traces of albite, clinozoisite, chlorite and muscovite in an opaque carbonaceous matrix. Individual chert beds vary in thickness from 1 cm to 10 cm or more, but average about 2 to 3cm.In some places, massive dark grey chert occurs, without argillaceous interbeds. Such material i s relatively pure, as indicated by an analysis reported by Cairnes (1937, P« 11) which shows 97«7 percent Si0 2 with minor amounts of A l , Fe, Ca, Mg, Mn, and H20.. Limestone forms l i g h t to dark grey pods, usually in cherts, ranging from about 20 cm to as much as 10 metres in diameter. Locally, limestone beds, about 1 m thick, continue up to 30 m in length. The limestones are a very fine-grained (<0.1 mm) equigranular aggregate-of • calc ite and traces of quartz- cut by medium- to coarse-grained patches and stringers of calcite. The fine-grained part contains small amounts of i n t e r s t i t i a l carbonaceous material, producing the grey colour of the rock. Most recrystallized stringers are l i g h t grey or white due to a lesser amount of these impurities. Aragonite and dolomite were not detected by optical or X-ray diffraction techniques. Volcanic rocks of the Fergusson Group are generally dark green to black, fine-grained and massive, commonly with calcite or quartz-filled amygdules. Although Cairnes (1937) reported that pillows are common in these rocks, no definite pillow structures could be seen in the small area of Fergusson exposed i n the f i e l d area. Typical material consists of laths of albite with brownish pyroxene and minor chlorite, carbonate, tal c , and leucoxene. Because no diagnostic fossils could be found, Cairnes (1937) tentatively correlated the Fergusson with the Permian Cache Creek Group to the east, on lithologic s i m i l a r i t i e s . Recently, Cameron and Monger (1971) reported on an 13 PLATS 6. Sheared, lensoidal Fergusson ribbon cherts from west side of Pioneer Ultramafite. « • 10 cm. 14 assemblage o f conodonts c o l l e c t e d from a l i m e s t o n e pod on the n o r t h shore o f Carpenter L a k e , a t Tyaughton Creek . These f o s s i l s i n d i c a t e a L a d i n i a n - C a r n i a n age (Middle t o Late T r i a s s i c ) . The Fergusson Group p o s s i b l y c o r r e l a t e s w i t h the P a v i l i o n Group, a sequence o f c h e r t s , a r g i l l i t e s , v o l c a n i c s , l i m e s t o n e s , and conglomerates i n the L i l l o o e t a rea to the e a s t , a s s i g n e d a probable Midd le T r i a s s i c ( T r e t t i n , 1 9 6 1 ) . The undated Hozameen Group (McTaggart and Thompson, 1967) t o the s o u t h e a s t , a c r o s s the F r a s e r R i v e r F a u l t system, may represent a metamorohosed e q u i v a l e n t o f the Fergusson (Cameron and Monger, 1971) based on l i t h o l o g i c s i m i l a r i t i e s . NOEL FORMATION The Noel Format ion i s the dominant sedimentary u n i t i n the f i e l d a r e a , e x t e n d i n g a l o n g the e n t i r e n o r t h c o n t a c t o f the u l t r a m a f i t e (w i th the p o s s i b l e e x c e p t i o n o f a few areas o f i n t e r m i x e d Fergusson) and r e p r e s e n t i n g a major p a r t o f the sediments on the south c o n t a c t . The f o r m a t i o n as d e f i n e d by C a i r n e s (1937) c o n s i s t s p redominant l y o f a r g i l l i t e s , w i t h c h e r t s i d e n t i c a l t o those o f the Fergusson Group, g reenstones , conglomerate and b r e c c i a . A u n i t o f greywacke was mapped and a s s i g n e d t o the Noel Format ion by the w r i t e r . A r g i l l i t e s are t y p i c a l l y dark grey to b l a c k , and here and there w e l l - b e d d e d , c o n s i s t i n g o f a l t e r n a t i n g 1 mm t h i c k dark grey a r g i l l a c e o u s m a t e r i a l and l i g h t grey s i l t r a n g i n g from 1mm to 2 o r 3 cm i n t h i c k n e s s . In t h i n - s e c t i o n , unde -forraed rocks c o n s i s t o f f i n e - g r a i n e d ( < 0 . 1 mm) a n g u l a r q u a r t z , c l i n o z o i s i t e and a l b i t e , and c h l o r i t e f l a k e s i n a v e r y f i n e - g r a i n e d m a t r i x o f quar t z and i n t e r s t i t i a l c a r b o n . Bedding ( S 0 ) i s d e f i n e d by f i n e - g r a i n e d s t r e a k s o f s e r i c i t e and c h l o r i t e f l a k e s , and quar t z g r a i n s , and by t h i n s t r i n g e r s o f carbonaceous m a t e r i a l . Deformed samples t y p i c a l l y have f r a c t u r e s u r f a c e s , coated w i t h c a r b o n , p a r a l l e l to S 0 . The b r e c c i a c o n s i s t s o f a n g u l a r t o rounded quar t z aggregates (from 0 . 1 t o 10 mm d iameter ) i n a m a t r i x o f f i n e - g r a i n e d ( 0 . 0 1 mm) q u a r t z , c h l o r i t e , s e r i c i t e , 15 albite and carbonaceous material. Grain size within the fragments varies from submicroscopic to about 1 mm diameter, but is uniform within each fragment. This unit develops i n a few isolated outcrops. It i s not certain whether i t i s a tectonic breccia, derived perhaps from ribbon cherts, or a sedimentary (intraformational) breccia. No f o s s i l s have been found i n any Noel rocks in the area, but Cairnes (193?) tentatively correlated the Noel with rocks to the north in which McCann (1922) found Late Triassic f o s s i l s . PIONEER FORMATION The Pioneer Formation, as defined by Cairnes (1937)» i s a unit of andesite, meta-andesite, tuff and breccia. The main occurrence in the f i e l d area is a large lens, about 1 km thick, immediately north of the Noel Formation, on the north side of the ultramafite, where i t i s intimately associated with and gradational into the Bralorne Intrusions. A second occurrence of volcanics and tuffs on the south side of the ultramafite i s tentatively assigned to the Pioneer Formation because i t also grades into a greenstone-gabbrp complex of the Bralorne Intrusions. The volcanic rocks are highly variable in texture, but typically are l i g h t to dark olive green, fine-grained, massive, commonly amygdaloidal, and only rarely pillowed (cf Fergusson). In thin-section, they consist of a fibrous mat of tremolite-actinolite with patches of albite, clinozoisite, and pumpellyite (?). Small amounts of chlorite, sphene, ilmenite, pyrite, calcite and quartz are disseminated throughout the tremolite matrix. A sample of interlayered a r g i l l i t e and crystal t u f f (Append.II) from the southern occurrence, consists of anhedral to subhedral, up to 0.5 mm, albite crystals x^ith chlorite patches, set i n a fine-grained matrix of quartz, albite, clinozoisite, chlorite and sphene, a l l cut by irregular patches and stringers of carbonate. The argillaceous interlayers consist essentially of fine-grained PLATE 7« Breccia, Noel Formation : Angular clasts of fine-te) ™ grained recrystallized chert in a matrix of quartz and carbonaceous matter. Plane-polarized lig h t (PPL). 17 quartz with streaks of carbonaceous material and are indistinguishable from Noel a r g i l l i t e s which occur nearby. Indirect evidence suggests that the Pioneer Formation i s Late Triassic, probably Carnian-Norian, in age. Cairnes (194-3) reported that i t appears to intrude the Noel, and is therefore younger. In the map area, the Pioneer Formation i s conformably overlain (?) by the Hurley Formation which, i n the Eldorado Creek area to the northwest, contains f o s s i l s indicating a Triassic age, probably Lower Norian (Cairnes, 1937; Shimer, 1926). HURLEY FORMATION Although no rocks of the Hurley Formation were definitely identified with-in the f i e l d area, the following summary i s given to il l u s t r a t e the similarity of this unit to previously described units and the possi b i l i t y that some rocks mapped as Noel and Pioneer could in fact be Hurley. Cairnes (1937) mapped a large lens of Hurley Formation, partly enclosed in'(contemporaneous with ?) Pioneer volcanics, immediately north of the present f i e l d area (see Fig. 4). The unit consists of a r g i l l i t e , tuff, andesite, conglomerate, limestone, agglomerate and chert. Cairnes (1937) noted that the tuffs and a r g i l l i t e s are indistinguishable from Noel strata and that the ande-site flows much resemble Pioneer greenstones. The main distinguishing charac-t e r i s t i c s are apparently the more limy nature of the sediments, impurity of the limestones, and the presence of more siliceous (rhyolite and dacite) volcanics. As previously stated, rocks i n the Tyaughton Creek Area to the northwest (Cairnes, 1943) which have been mapped as Hurley Formation, y i e l d a Lower Norian age. 18 INTRUSIVE ROCKS BRALORNE INTRUSIONS The Bralorne Intrusions are an extremely heterogeneous mixture of basic to acidic rocks consisting of pyroxenites, gabbros, anorthosites, diorites, granites, and their altered equivalents. The relations among these different rock types are not clear, although several contacts were seen in the f i e l d , including sharp intrusive contacts of medium-grained gabbro against coarse-, grained gabbro, and gradational contacts between gabbro and anorthosite. Because these rock types occupy an area too small to show on the scale of the map, the intrusions are mapped as a single unit, except around Bralorne, where Cairnes (1937) w a s able to distinguish a body of 'soda granite', based on information from extensive underground workings. This unit was of particular interest to early investigators because of i t s apparent relation to gold minera-l i z a t i o n i n the area. Bralorne Intrusions and the Pioneer Formation are spatially related (Fig. 4). This relation i s further supported in the f i e l d by gradational con-tacts between the two units, and by large areas of what Cairnes (1937) called "indistinguishable Pioneer greenstone and Bralorne intrusives: mainly fine-grained diorite and (or) greenstone , here abbreviated as simply greenstone-diorite or greenstone-gabbro complex. Because of the heterogeneity of this unit, i t i s not possible to give a meaningful vaverage sample' description. Modes of some of the rock types are included in Appendix LTf. Common features of these rocks include abundant albite and r e l i c t more calcic plagioclase, f i l l e d with minute zoisite inclusions, lack of potassic feldspar, even in the vgranites', scarce clinopyroxenes and biotite, abundant chlorite and r e l i c t hornblende (except i n anorthosite) and small amounts of carbonate, sphene, and magnetite. Several parts of the unit are well-layered, the layering being produced by slight variations in mafic 19 content, and by a preferred orientation of plagioclase laths. Veinlets of zoisite and carbonate are common. The names * Soda Granite' and x D i o r i t e ' were applied to these rocks by Cairnes (1937)» apparently largely on the basis of thin-section work. A comparison (Table 2) of his reported analyses with average analyses of appro-priate rock types, reported by Nockolds (1954) and Turner andVerhoogen (i960), indicates that the names Quartz Keratophyre and Gabbro, respectively, are more suitable. These two rock types are common constituents of the ophiolite assemblage (P.117). Although the intimate association of Pioneer greenstones and Bralorne Intrusions suggest a common origin, the intrusions cut the Hurley Formation, which i s younger than the Pioneer Formation. A possible explanation, proposed by Cairnes (1937) i s that the Hurley represent a period of sedimentation just after the Pioneer volcanism, and that the Bralorne Intrusions, although pre-dominantly associated with the volcanies, continued to, migrate upward into the overlying sedimentary pile of Hurley, so that intrusion continued after volcanism had a l l but ceased. The Hurley does contain some volcanies. The age of the Bralorne Intrusions i s effectively bracketed by the older Fergusson Group of Ladinian to Carnian age and the synchronous or younger Hurley Formation of Norian age. The Bralorne Intrusions must, therefore, be of Late Triassic, Carnian to Norian age (about 200 my - Van Eysinga, 1971). OTHER INTRUSIONS A large variety of intrusive rocks, in the form of dikes, s i l l s , plugs, and pads occur in the contact zone of the ultramafite and i n the enclosing country rocks. These range in composition from acidic to basic and include aphanitic to coarse-grained, porphyritic, amygdaloidal and vesicular types. Based on regional studies, Cairnes (1937) c l a s s i f i e d these rocks, on the basis of relative age, into six groups. Although many of the intrusive rocks TABLE 2a Chemical Analyses o f B ra lo rne D i o r i t e , Greenstone-d i o r i t e and Soda Gran i te ( a f t e r C a i r n e s , 1937) I I I I l l IV V Si02 48.07 52.15 50.69 74.36 75-87 Ti02 0.16 0.88 0.34 0 .14 0.31 A1203 21.61 15.05 18.61 12.87 12.42 Fe 2 0 3 0.87 2.30 1.51 0.61 0.66 FeO 5.16 6.35 7.45 1.96 2.03 MnO t r 0.10 0.11 t r -MgO 8.56 8.31 6.05 1.27 0.11 CaO II .85 10.14 8.30 1.12 1.59 Na20 1.40 2.48 3.80 5.27 5.06 K20 O.36 0.07 0.80 O.36 0.46 P 2 0 5 - 0.22 0.07 0.07 0.28 co 2 - - - 1.32 0.47 S 0.37 0.61 0.02 0.61 0.26 Ha0 + 1.09 0.77 2.89 1.21 0.31 H 2 0~ 0.09 0.10 0.16 0.10 0.10 C r 2 0 3 0.06 0.12 - - -99.52 99.42 100.70 100.95 99.36 I F resh m i l e s B r a l o r n e nor th o f d i o r i t e from d r i l l core , on B r a l o r n e . U ra l c l a i m s , about I I G r e e n s t o n e - d i o r i t e , a few f e e t from I,' same c o r e . I I I F resh u n a l t e r e d B r a l o r n e a u g i t e d i o r i t e , B r a l o r n e Mine (McCann, 1922, P. 63 ) IV B r a l o r n e Soda Gran i te - f rom P i o n e e r Mine V B r a l o r n e Soda Gran i te - f rom Empire ( Ida May) M i n e , p a r t o f B r a l o r n e M i n e s . 21 TABLE 2b Reported Average Analyses of Diorite and Gabbro (after Nockolds, 1954) I II III IV V sib 2 51.86 48 .55 48.36 48.01 50.78 T i 0 2 1 .50 1.91 1 .32 1 -55 1 .13 A1 2 0 3 16.40 1 6 . 5 2 16.84 17.22 1 5 . 6 8 Fe 2 0 3 2.73 3.16 2 -55 2.90 2.26 FeO 6.97 8.00 7 .92 7.68 7.41 MnO 0.18 0.22 0.18 0.15 0.18 MgO 6.12 6.71 8.06 7.45 8.35 CaO 8.40 9.49 11.07 10.80 10.85 Na20 3 . 3 6 3.10 2.26 2.28 2.14 K 20 1 .33 0.95 O .56 0.53 O .56 P 2 0 5 0.35 0.28 0.24 0 .33 0.18 C0 2 - - - - -S - - - - -H 2 0 + 0.80 1.11 0.64 1.10 0.48 H 20~ - - - - -C r 2 0 3 - - - - -100.00 100.00 100.00 100.00 100.00 I Average Diorite II Average Hornblende (- Augite) Diorite III Average Gabbro IV Average Hornblende Gabbro V Average Pyroxene Gabbro TABLE 2c Reported Average Analyses of Granites, Trondhjemite and Keratophyre (after Nockolds, 1954 and Turner and Verhoogen, I960). I II III IV 5 i0 2 72.08 73.86 69.30 75.07 T i 0 2 0 .37 0.20 0 .23 0.16 A1 2 0 3 13.86 13-75 16.81 13.12 Fe 2 0 3 0.86 0.78 0.28 1.15 FeO 1 .6? 1.13 1 .26 1.36 MnO 0.06 0.05 t r 0.05 MgO 0.52 0 .26 1.08 0.24 CaO 1 .33 0 .72 3 . 3 ^ O.36 Na20 3.08 3-51 . 6.00 5.74 K 20 5.46 5.13 1 .39 1 .55 P 2 0 5 0.18 0.14 0 .03 0 .06 co2 - - 0 .15 0 .07 S - - -H 2 0 + 0 .53 0.47 0 .50 1.01 H 2 0~ - - - 0 .26 C r 2 0 3 - - - -100.00 100.00 100.37 100.20 I Average C a l c - a l k a l i Granite (Nockolds, 1 9 5 ^ ) II Average A l k a l i Granite (Nockolds, 1 9 5 4 ) III Trondhjemite, from Trondhjem, Norway (Turner and Verhoogen, I 9 6 0 , P. 3 4 4 ) IV Quartz Keratophyre - average of 2 reported analyses (Turner and Verhoogen, I960, P. 262) 23 mapped by the present writer f i t into Cairnes' cla s s i f i c a t i o n , a substantial number do not. Consequently, a modified classification was made, based on chemical, textural, and structural c r i t e r i a . This new cla s s i f i c a t i o n differs from Cairnes ' , particularly with regard to his designation of rodingites as being * related to the President Intrusives Clearly, they are not related i n the same sense that granite dikes are related to the Bendor Batholith - the ultramafite i s a host, not a parent. The intrusive rocks can be divided into two major groups depending on thei age relative to the emplacement of the ultramafite. Although emplacement w i l l be discussed later (Structural Geology, P. 80), in essence, the ultramafite was emplaced as a solid mass, with intensive deformation occurring in a 50-metre wide zone of serpentinite schist, along the contact viith the country rocks. Many of the intrusive rocks occur in this zone, so they can be cl a s s i f i e d as: pre-emplacement boudins and irregular pods or post-emplacement dikes, s i l l s , and plugs. Further distinctions on the basis o f mineralogy and texture result in the classification scheme in Table 3« The rodingites, altered equivalents of Group E and H rocks, are considered separately in the following chapter. Group Age Rock Type Tertiary (?) Andesite (+ basalt?) post-emplacement post-emplacement (related to Bendor ?) Plagioclase Porphyry: Gabbro and Quartz Gabbro post-emplacement (related to Bendor ?) Hornblende Porphyryj Diorite t see Appendix II, Sample Locatio * see Plates TABLE 3 Classification of Intrusive Rocks Description vesicular amygdaloidal (cThomsonite) columnar jointing f.g black matrix, trachytic texture phenocrysts of olivine, augite patches of kspar in matrix m.e; dark grey allotriomorphic granular plagioclase relatively fresh An60-70 diopside-»biotite, chlorite myrmeckitic qtz-plag inter-growths skeletal ilmenite-»sphene f.g to e g medium grey characterized by: - mineral zoning (Plate 11 ) - acicular hornblende - kspar blebs plag relatively fresh An 3 0_ 4 0 euhedral diopside overgrown by hornblende Occurrence Cairnes (1937) class i f i c a t i o n s i l l s II S 2 in serpentinite plugs in serpentinite (between cirque 1 and cirque 2) plugs i n peridotite 3a(?) dike along fault zone in peridotite s i l l along serpentinite country rock contact s i l l s II S 2 in 3b(?) ssrpentinite irregular pods Sample  Numbers. 341* 342* 261 275 280 301 359 366 265 299 267 337 * 188 270 Map (Fig.29), and Reference Collection ro GrouD D E(.a) E(b) Age post-emplaceinent pre-emplacement post-emplacement pre-einplaceraent Rock Type Keratophyre (Albitite) variable: basalt gabbro diorite rodingite rodingite Basic volcanic, porphyritic TABLE 3 continued Description - lig h t greenish grey - f. g to rn. g - mafics (hornblende?)-*chlorite - abundant plag (An 0_ 3 0) - minor muscovite, sphene, quartz - variable: a group of pre-emplacement dikes, caught up in serpentinite - usually rodingitized at margin - see also Alteration, P 63 - see Alteration, P 63 highly altered, dark greenish grey mixture of chlorite, sericite and sphene mafic phenocrysts-»chlorite Occurrence Cairnes (1937)  classification s i l l s along serpentinite - country rock contact s i l l || S x i n sediments cutting Ultramafite contact dike cutting Bralorne Intrusions tectonic inclusions (subspherical pods) in serpentinite 2a? 4? 6b? - s i l l I I3 2 in serpentinite - in cherts and a r g i l l i t e s - contemporaneous with Noel or Fergusson (?) 5 (in part) 5 (in part) 4? Sample  Numbers 175 277 191 326 252 545 174 363 189 179? 316 179? 333 ro TABLE 3 continued Group Acce Rock Type Description G post- Keratophyre emplacement? large white albite (An0) phenocrysts in f.g grey-green matrix of zoisite, albite, hornblende, chlorite, sphene no kspar H pre- gabbro emplacement anorthosite rodingite - e g white plag (An 5 0) with minor diopside, chlorite - dunite inclusions - altered in part to rodingite Occurrence Cairnes (1937) Sample  classification Numbers s i l l along contact 2a? 5^ 3b between greenstone- 6b? gabbro complex and a r g i l l i t e s possibly related to Group D dikes and irregular 364 pods in peridotite 271 one dike truncated by serpentinite zone ro ON PLATE 11. Group C intrusion J strongly 5 c m > zoned s i l l i n serpentinite. PLATE 1 3 . Group D k e r a t o p h y r e s i l l a l o n g s e r p e n t i n i t e -c o u n t r y rook c o n t a c t . O v e r l y i n g r o c k i s s t r o n g l y 3 0 cm. s h e a r e d c h e r t s and s e r p e n t i n i t e . PLATE 14. Sample o f Group C i n t r u s i o n s showing k s n a r b l e b s , 1 cm. a c i c u l a r h o r n b l e n d e , and m i n e r a l z o n i n g , (sample number 267) 30 - ULTRAMAFIC ROCKS Definition of * Alpine-type ' The term xAlpine-type' has been applied to bodies of peridotite and derived serpentinite which occur, usually as fault-bounded lenses, sheets, or irregular masses, in orogenic fold belts (Hess, 1955)' The association of these rocks with s p i l i t e s , cherts, and gabbros has been referred to as the ophiolite suite (Steinmann, 1905) which has important implications i n view of current theories of Plate Tectonics. This l a t t e r term w i l l be discussed more fu l l y in a later chapter (P.117). General Description and Distribution The ultramafic rocks of the f i e l d area occur as: the large Pioneer Ultramafite, underlying most of the area; the * north s i l l ' which extends across the northern part of the map-area; a widespread group of highly altered pods along faults; and a number of inclusions with the Bralorne Intrusions. Only the Pioneer Ultramafite i s relatively unaltered. The others consist of rocks similar to the most altered parts of the Pioneer body and therefore possibly derived from the same unaltered parent rock as the Pioneer body. The less altered part of the Pioneer Ultramafite consists predominantly of harzburgite, with minor orthopyroxenite and dunite, and rare chromitite. The relations among these rock types are rather complex. The bulk of the ultramafite shows well-defined layering, which i s produced by discontinuous layers of orthopyroxene grains in an olivine-rich matrix (Plate 15 )• Many of these pyroxene layers are of sufficient thickness to be considered a separate rock type - orthopyroxenite. On the weathered surface, these orthopyroxenite layers apparently have sharp contacts with the adjacent peridotite, but in thin-section, this boundary is transitional over a centimetre or more. Orthopyroxenite layers range in thickness from less than 1 cm to more than 15 cm and are completely gradational PLATE 15. Well-layered harzburgite : layering defined by lenses of orthopyroxene. (diameter of scale i s 54 mm). PLATE 16. Layered peridotite sequence consisting of orthopyroxene layers (dark) and dunite streaks (light) in harzburgite. 32 into typical layered harzburgite. The distribution of these layers in a typical section of the ultramafite i s shown in Appendix III. Note that the orthopyroxenite layers occur in clusters, which are continuous along strike over distances of 40 m or more, but individual layers within a cluster do not persist. In several places a 2 to 3 cm layer decreases in thickness over a length of about 1 m to a string of pyroxene grains which merge with the surrounding layered harzburgite fabric (App. I l i a ) . In a few l o c a l i t i e s , stringers of orthopyroxene grains cut across the harzburgite layering (Plate 63). Although these stringers appear identical to stringers which parallel the layering, only 1- or 2-grain thick stringers (less than 1 cm) crosscut layering. No thick layers of orthopyroxenite transect the peridotite layering. Based on shape and sharpness of contacts, the dunites form two groups. In the f i r s t group, harzburgite grades, across strike, into dunite layers that range in thickness from a few millimetres, in the olivine-rich parts of the layered harzburgite, to more than two, metres. These, layers,.-with, gradational, contacts, may have formed by the same process which produced the layering in the harzburgite (See P. 8 9 ) . A second group of dunite bodies, characterized by sharp, commonly discordant contacts accounts for most of the dunite in the ultramafite body. It occurs as s i l l s , dikes, and irregular pods. S i l l s , with sharp contacts, are from 5 to 20 cm thick, and many contain stringers of chromite grains in the centre. Rare dikes from 5 to 10 cm thick, crosscut layering, usually at a high angle (60-90°) and l o c a l l y cause bending of pyroxene layers at the contacts (Fig. 11). Large, irregular pods of dunite, up to 20 m thick and as much as 40 m long, have both concordant and discordant contacts with surrounding harzburgite. Poor exposure prevents a detailed examination of contact relations and interpretation of mode of origin. The s i l l s and dikes, hoxirever provide ample evidence (P. 83) to suggest that they were intruded, by plastic deforma-tion along layering and crosscutting fractures respectively. 33 Petrography Harzburgite. A typical sample of unaltered harzburgite consists of the assemblage olivine-orthopyroxene-clinopyroxene-chromian spinel. In thin-section, the rock consists primarily of equant interlocking grains of olivine and orthopyroxene averaging about 5 mm in diameter. Orthopyroxenes may be aligned in distinct layers or may be randomly distributed throughout the rock. The harzburgites contain up to 40 percent orthopyroxene but the bulk contains about 20 to 25 percent orthopyroxene. Clinopyroxene occurs as discrete grains (1 to 2 mm dia) either between olivine grains or enclosed within olivine or orthopyroxene, and as exsolution lamellae i n the orthopyroxene. Although generally less than 5 percent i n abundance, clinopyroxene l o c a l l y exceeds 5 percent i n several samples, which are therefore lherzolites (Jackson, 1968). Chromite or chromian spinel i s a minor constituent (less than 1 percent) disseminated throughout the rock. It is typically translucent orange to reddish brown, forms anhedral grains 0.1 to 0.5 mm in diameter,, and. commonly has,con-cave grain boundaries against equant olivine grains. The macroscopic layering of harzburgite i s produced by small variations in the proportion of olivine and orthopyroxene, the distance between successive olivine-rich layers ranging from 3 to 10 mm. Pyroxene-rich layers commonly form elongate lenses (approx 0.5 cm x 3 cm) enclosed in an olivine-rich matrix (Plate 17 )• Rocks with this texture grade into those having randomly d i s t r i -buted pyroxenes with no detectible elongation of grain clusters (Plate 21 ). In outcrop, these textures are intimately intermixed with massive material grading into well-layered material over distances of a few centimetres. Orthopyroxenite. Unaltered orthopyroxenite layers consist of the assemb-lage orthopyroxene-olivine-clinopyroxene-chromian spinel. Orthopyroxene consti-tutes more than 70 percent, olivine up to 25 percent, clinopyroxene averages 5 percent, and chromite or chromian spinel i s less than 1 percent. Therefore, these rocks are not s t r i c t l y speaking, only orthopyroxenites, but include PLATE 19« Harzburgite with discontinuous layers of orthopyroxene. 2 era. u I PLATE 20. Enlargement of Plate 19. 1 era. 36 PLATE 21. Massive harzburgite showing randomly d i s t r i b u t e d orthooyroxene grains.(diameter o f scale s 1.9 cm.) 37 h a r z b u r g i t e s and p o s s i b l y even w e b s t e r i t e s and l h e r z o l i t e s . F o l l o w i n g the example o f Loney e t a l (1971) these o r t h o p y r o x e n e - r i c h rocks are d e s i g n a t e d s i m p l y as o r t h o p y r o x e n i t e s , s i n c e the a r b i t r a r y boundar ies o f J a c k s o n ' s (1968) c l a s s i f i c a t i o n ( F i g . 6) would d i v i d e a s i n g l e rock type i n t o 3 o r 4 sub types , thereby o b s c u r i n g t h e i r c l o s e a s s o c i a t i o n , and l e a d i n g to c o n f u s i o n w i t h the more common o l i v i n e - r i c h v a r i e t y o f h a r z b u r g i t e . In t h i s r e s p e c t , the p r o -v i s i o n a l c l a s s i f i c a t i o n scheme o f I r v i n e and F i n d l a y (1972) i s more s u i t a b l e , s i n c e i t r eco gn i zes the e x i s t e n c e o f a l a r g e f i e l d o f 1 o l i v i n e o r t h o p y r o x e n i t e ' w h i c h , t o g e t h e r w i t h the o r t h o p y r o x e n i t e f i e l d would encompass a l l o f the v a r i a t i o n seen i n the * o r t h o p y r o x e n i t e ' l a y e r s ( F i g . 5 ) . The c l a s s i f i c a t i o n o f I r v i n e and F i n d l a y (1972) i s t h e r e f o r e adopted i n p re fe rence to J a c k s o n ' s (1968) . In a d d i t i o n t o s i m p l i f y i n g the o r t h o p y r o x e n i t e c l a s s i f i c a t i o n , note t h a t I h e r z o l i t e i s a l s o d e f i n e d d i f f e r e n t l y , so t h a t l h e r z o l i t e , as d e f i n e d by I r v i n e and F i n d l a y (1972) does not o c c u r i n the P i o n e e r body. A t y p i c a l o r t h o p y r o x e n i t e (sample 35S, Appendix H a ) c o n s i s t s o f equant , i n t e r l o c k i n g g r a i n s o f o r thopyroxene , from 0.3 mm to 1 cm i n d i a m e t e r , w i t h g r a i n boundar ies commonly d e v e l o p i n g 120° a n g l e s , and about 10 pe rcent equant o l i v i n e , from 0.3 to 1 mm i n d i a m e t e r . As i n the h a r z b u r g i t e s , c l i n o p y r o x e n e (about 5 pe rcent ) occurs e i t h e r as s m a l l e r (0.05 to 0.5 mm) subequant g r a i n s , as i n c l u s i o n s i n , and i n t e r s t i t i a l to o r thopyroxene , o r as e x s o l u t i o n l a m e l l a e i n o r thopyroxene . Chromite occurs as d i s s e m i n a t e d , a n h e d r a l , i n t e r s t i t i a l g r a i n s t y p i c a l l y about 0.1 mm i n d i a m e t e r . In o u t c r o p , o r t h o p y r o x e n i t e l a y e r s range from l e s s t h a n 1 cm to more than 15 cm i n t h i c k n e s s . T h i c k e r l a y e r s commonly deve lop a system o f i n t e r n a l f r a c t u r e s , c o n s i s t i n g o f a f r a c t u r e a long each c o n t a c t and a se t o f i n t e r s e c t i n g f r a c t u r e s p e r p e n d i c u l a r t o the c o n t a c t s ( P l a t e 25 ) . These l a t t e r f r a c t u r e s commonly show a p r e f e r r e d o r i e n t a t i o n which may be r e l a t e d t o some d e f o r m a t i o n a l e p i s o d e . The o r i g i n o f these f r a c t u r e s , which penet ra te the sur rounding h a r z b u r g i t e f o r o n l y a few m i l l i m e t r e s , i s u n c e r t a i n (see P.102). PLAT'S 2 3 . Orthonyroxenite : Equant orthonyroxene (grey and O .5™ y e l l o w ) w i t h i n t e r s t i t i a l c l i n o n y r o x e n e and o l i v i n e (blue and orange). (X n i c o l s ) d u n i t e , i n h a r z b u r g i t e . Diameter o f s c a l e i s 5.4 cm 40 FIGURE 5 8 Provisional classification scheme for Ultramafic Rocks (after Irvine and Findlay, 1972) showing estimated positions of Pioneer Ultramafite rocks. Adopted for this study in preference to Jackson's (1968) classification (Fig.6). FIGURE 6 : Modal classification of Ultramafic Rocks (after' Jackson, 1968) showing estimated positions of Pioneer Ultramafite rocks. 42 Another feature which probably bears on the origin of these pyroxenite layers i s the occurence of a narrow zone of dunite on either side of a pyroxenite stringer (Plate 24 ). This feature, although not common, i s believed to be more than fortuitous. Possibly material for the pyroxene grains of the stringer was concentrated from the harzburgite, resulting in the symmetrical depletion zone of dunite (see P.102). Dunite. Typical dunite consists of olivine and chromian spinel. Although Irvine and Findlay's (1972) classification included as much as 5 percent clinopyroxene and/or orthopyroxene in dunite, a l l dunite bodies of the second group contain essentially no pyroxene. In mapping the layered sequences, i t i s d i f f i c u l t to distinguish a 5 percent pyroxene content in the rocks, and thus dunite (of the f i r s t group) and harzburgite were distinguished as being pyroxene, free and pyroxene-bearing, respectively. The amount of rocks containing up to 5 percent pyroxene is much.less than the amount of 'pure, end-member' dunite. and certainly much less than the amount of xtrue' harzburgite, so that the assignment of a name to this group, in view of the gradation between dunite and harzburgite, is not c r i t i c a l . A typical sample of dunite (sample 300, Appendix Ila) consists of an equi-granular aggregate of olivine grains. It i s d i f f i c u l t to determine an original grain size i n some of these rocks because of the strong fracturing and sub-parallel crystallographic orientation of adjacent fragments. Nevertheless, individual domains, having a single crystallographic orientation, range from 0.5 to 8 mm i n diameter., Chromite occurs as anhedral or subhedral, i n t e r s t i t i a l grains about 1 mm in size. In outcrop , dunite i s readily distinguished by i t s smooth weathered surface (Plate 27 ). Concentrations of chromite or chromian spinel greater than 1 percent are associated with dunite. Disseminated chromite content in dunites ranges from traces up to 2 or 3 percent (Plate 27 )• Greater concentrations develop as ... v.- • • *1 LW. Av j» • * V • ! >v_ ^ PLATE 27. Chromite disseminated i n dunite. Note smooth weathered surface o f dunite (cf Plate 21). 2 cm i s 1 . 9 cm. PLATE 30. Chromitite (sanrole 362) : Anhedral brown chromite with black spinel margins i n c h l o r i t e (white) replacing o l i v i n e (yellowish). (PPL). 0.5 mm. 45 stringers and not in disseminated form. These stringers range in thickness, from those previously described along the centres of dunite s i l l s , generally only a few grains wide (Plate 28 ), to rare occurrences which are over 10 cm thick (Plate 29 ). This l a t t e r occurrence of chromite is referred to as chromitite. A sample of this material (362, Appendix LTa) consists of about 80 percent anhedral, subequant grains of chromite, from 0.5 ram to 1 cm diameter, i n a matrix of chlorite replacing olivine. The significance of chlorite, which occurs in v i r t u a l l y a l l rocks containing significant chromite concentrations, w i l l be discussed under Alteration. Chemistry Partial chemical analyses of olivines and pyroxenes were obtained, by electron microprobe, from several dunites, orthopyroxenites and harzburgites (Appendix I ) . Averaged analyses of olivine, orthopyroxene and clinopyroxene in these samples are presented in Table 4, along with reported analyses of these phases from other ultramafites in the North American Cordillera. These include Burro Mountain, California (Loney et a l , 1971); Red Mountain, California (Himmelberg and Coleman, 1968); and Southwest Oregon (Medaris, 1972). For a comprehensive survey of world-wide l o c a l i t i e s , the reader i s referred to Irwin and Coleman (1972), and Green (1964). An examination of these analyses indicates the remarkable uniformity of mineral compositions from the four bodies; forsterite content of olivines ranges from 89.7 to 92.5, with similar narrow ranges for orthopyroxene and clinopyroxene compositions. These restricted ranges of mineral composition in alpine-type peridotite have been noted on a world-wide basis. For example, olivines from harzburgite and dunite typically range from Fo 8 6 to Fo 9 3 (Green, 1964, and Challis, I965). This feature distinguishes alpine peridotites from stratiform complexes (such as Skaergaard and Bushveld) which typically contain more iron-rich olivines and pyroxenes, extending over a larger range of compositions - for example, Fo 8 1 9 0 for olivines from Stillwater, Montana (Wager and; Brown, 1968). TABLE 4a Summary o f P r i m a r y M i n e r a l A n a l y s e s f r o m P i o n e e r U l t r a m a f i c Rocks Sample t 300 323 358 356 285 306 D u n i t e D u n i t e O r t h o p y r o x e n i t e i H a r z b u r g i t e * H a r z b u r g i t e H a r z b u r g i t e M i n e r a l : 01* 01 01 O p x * 01 Opx C p x * 01 Opx 01 Opx Cpx number o f a n a l y s e s s 10 10 4 8 5 7 2 8 3 9 7 1 S i O , 4 1 . 4 40.8 40.6 55-7 41.5 56.8 53.8 4 1 . 1 56.3 41.2. 56.3 53-2 T i 0 2 nd nd". nd nd nd nd nd nd nd nd nd nd A 1 2 0 3 0.26 0.39 0.49 2.8 0 .31 2.1 2.2 0.25 2.9 0.13 2 .4 1.9 nd nd nd nd nd nd nd nd nd nd. . nd nd F e O * * 7.5 9.6 8 .4 5-8 8.7. 5.8 2.1 9.2 6.1 9.1 5-8 2.2 MnO nd . n d nd nd nd nd nd nd nd nd nd nd MgO 51.2 49.4 49.8 34.1 50.1 34.4 17.8 49.6 33.8 49-7 34.0 17.5 CaO 0.06 0.20 0.03 0.61 0 .04 0.73 23.2 0 . 0 4 0.92 0.02 1 . 1 23.2 H 2 0 + nd nd nd nd nd nd nd nd nd nd nd nd C r 2 0 3 nd n d nd nd nd nd nd nd nd nd nd nd NiO nd n d nd n d nd nd nd nd nd nd nd' nd TOTAL 1 0 0 . 4 1 0 0 . 4 99.3 98.9 100.7 99.9 99.0 100.3 99.9 100.1 99.5 98.1 F o " * * 92.5 90.2 . 91.3 - 9 1 . 1 - - 90.6 90.7 - -E n - - 90.2 - 90.0 49.9 - 89.2 - 89.4 49.5 Wo . - - - 1.2 - 1 . 4 46.8 - 1.8 - 2.0 47.0 Fs - - - 8.6 - 8.6 3.3 - 9 .0 - 8.6 3-5 Mg/(Mg+Fe) 0.925 0.902 0.913 0 . 9 1 4 0 .911 0.913 0.938 0.906 0.909 0.907 0.913 0.934 * 01= o l i v i n e , Orac = o r t h o p y r o x e n e , Cpx = c l i n o p y r o x e n e * * * Fo = 100 x Mg/(Mg+Fe+Mn) * * FeO i s t o t a l i r o n , f o r m i c r o p r o b e a n a l y s e s En * 100 x Mg/(Mg+Fe+Ca) Wo = 100 x Ca/(Mg+Fe+Ca) A n a l y s t i R L W r i g h t Fs = 100 x Fe/(Mg+Fe+Ca) TABLE 4b R e p o r t e d A n a l y s e s o f P r i m a r y M i n e r a l s f r o m A l p i n e U l t r a m a f i t e s L o c a l i t y : Sample• B u r r o M o u n t a i n (Loney e t a l , , 1971) H a r z b u r g i t e O r t h o - D u n i t e * * Red M o u n t a i n * * * H a r z b u r g i t e D u n i t e SW Oregon ( M e d a r i s , 1972 P e r i d o t i t e M i n e r a l » number o f a n a l y s e s > f 01* 4 Opx 4 Cpx 4 01 Opx 1 1 01. A * 4 01.B 7 01 3 Opx 3 Cpx 1 01 4 1 01 4 Opx 7 \ Cpx 7 S i O s . 40.86 55-1 52.9 40.8 57.0 41.00 40.9 40.5 56.6 52.5 4o ; l 40.9 55-1 52.0 T i O a 0.00 n d nd nd nd 0.00 nd nd nd 0.02 nd nd 0.08 0.31 A1203 0.06 2.2 2.2 nd 1.3 0.02 nd nd 2.0 nd nd 3-9 4.8 F e 20, 0.48 nd nd n d n d 0.47 nd nd nd nd nd nd: nd nd ' FeO 7.98 5-5 1.9 8.6 5-5 6.86 8.4 9-7 6.0 2.0 10.2 9.4 6.4 2.5 MnO 0.08 nd nd n d n d 0.07 nd 0.1 0.1 nd 0.1 0.1 .0.2 0.1 MgO 49.86 34.9 17.7 49.8 34.8 50.95 50.1 49.6 35-5 17.9 49.7 49.2 33.9 16.3 CaO 0.04 0.9 23.9 nd 0.7 0.09 nd nd 0.6 24.8 nd nd O.65 22.9 HjO"* - 0.22 nd nd n d nd 0.25 nd nd nd nd nd nd nd nd C r 20, nd nd nd n d . n d n d n d nd 0.4 0.02 nd nd 0.53 0.90 NiO 0.35 nd n d n d n d 0.37 nd 0.3 nd nd 0.3 nd nd' nd TOTAL 99.93 98.6 98.6 99.2 99.8 100.06 99.4 100.5 100.4 99.8 100.4 99.7 100.7* 100.5 Fo 91.3 - - 91.2 - 92.5 91.4 90.0 - - 89.7 90.2 - -E n - 90.3 49.3 90.9 - - - 90.4 48.6 - - 89.3 47.7 Wo - 1.7 47.7 - 1.0 - - - 1.1 48.4 - - 1.2 48.2 Fs - 8.0 3.0 - 8.1 - - - 8.5 3.0 - - 9.5 4.1 Mg(Mg+Fe) 0.913 0.92 0.94 0.912 0.92 0.925 0.914 0.900 0.916 0.941 0.897 0.902 0.904 0.921 * w e t c h e m i c a l and s p e c t r o g r a p h ! © a n a l y s e s ; a l l o t h e r s a r e m i c r o p r o b e a n a l y s e s * * 0 1 . A r e f e r s t o Type I i r r e g u l a r d u n i t e b o d i e s , 0 1 . B r e f e r s t o Types I I and I I I d i k e s a d s i l l s ( L o n e r e t a l . 1971) -0 * * * (Himmelberg and C o l e m a n , 1968) 1 i n c l u d e s 0 . 0 3 N a . O , 0 . 0 3 K , 0 * i n c l u d e s 0 . 6 4 N a , 0 , 0 .02 K , 0 48 Closer examination of the data reveals a number of small, but significant, variations in composition. As pointed out by Loney et a l (1971) at Burro Mountain, olivine from dunite in large irregular pods (their Type I) i s significantly more magnesian, averaging Fo 9 2 > 5, than olivine from dunite s i l l s and dikes (their Types II and III) which averages Fo 9 1 < lf. Analyses from Pioneer confirm this (although sampling i s insufficient for s t a t i s t i c a l proof) since sample 300, from a large pod, averages F o 9 2 j S A O , a whereas sample 323» from a s i l l , averages F o 9 0 2 ± o . , . Olivines from Pioneer contain small amounts of alumina (0.1 to 0.4 percent) which, unfortunately, i s usually not determined by other authors, so that comparison cannot be made. Small amounts of calcium are also noted in the Pioneer analyses. In the orthopyroxenes, calcium content ranges from 0.6 to 1.1 percent both at Pioneer and at the reported l o c a l i t i e s . These values are lower than reported wet chemical analyses of orthopyroxene because the clinopyroxene exsolution lamellae are, at least in part, excluded by the microprobe. Alumina content in orthopyroxene from Pioneer averages about 2.4 percent as compared with values of about 2.0, 1.5 and 4.0 from Burro Mountain, Red Mountain, and Southwest Oregon respectively. This i s an indicator of the conditions of peridotite formation, as w i l l be discussed l a t e r (P . 1 0 2 ) . At Pioneer, the ratio X*.= Mg/(Mg+Fe) shows a small but consistent variation between coexisting olivine, orthopyroxene and clinopyroxene, which i s ^Mo- X >^Mg* >^Mg" ^ i s relation i s also apparent in the reported analyses, although i t should be noted that these are averages of several rock samples, and individual samples may not necessarily show this trend. This magnesium/iron fractionation can be used as a geothermometer (Medaris, 1972; Saxena and Ghose, 1968), which w i l l be discussed later. Both orthopyroxene and clinopyroxene compositions are consistent with analyses reported from other alpine-type ultramafites by Green (1964) and Challis (1965). 49 Alteration Alteration of the ultramafite and enclosed related rocks can be divided into four types: a pervasive serpentinization affecting v i r t u a l l y a l l ultramafic rocks; a well-marked mineral zonation at the contact with the country rock; development of talc-carbonate alteration along fault zones within the ultramafite; and alteration of peridotite in contact with later intrusive rocks. Although, on the basis of petrography, some similarities exist among the types, they d i f f e r in age and conditions of formation. I. Pervasive Serpentinization The zone of pervasive serpentinization constitutes the core of the ultramafite, extending to within about 50 metres of the contact T" the country rock. Within this zone, the degree of serpentinization varies accord-ing to location and rock type. Generally, the dunites are more serpentinized than the harzburgites, and the orthopyroxenites are relatively fresh. Because olivine i s more susceptible to alteration than orthopyroxene, the degree of serpentinization i s related to the olivine content of the rock. Intensity of serpentinization also varies with location, so that some dunites are much less serpentinized than harzburgites from other l o c a l i t i e s . The amount of serpentine ranges from less than 1 percent, in some orthopyroxenite layers, to about 50 percent, averaging 25 to 30 percent. Recent work (Whittaker, 1971) has indicated that a large number of serpentine ^polymorphs' can be distinguished on the basis of single-crystal X-ray work. Using. X-ray powder diffraction techniques outlined by Aumento (1969), an attempt was made to study the distribution of antigorite, l i z a r d i t e and chrysotile within the ultramafite. In spite of d i f f i c u l t i e s in interpreting the X-ray data, serpentine in the. Pioneer body i s probably l i z a r d i t e , with small amounts of chrysotile. Antigorite i s absent. Page (1968), Aumento (1969) and others pointed out that the serpentine ^polymorphs' are probably not true polymorphs, but that small differences in chemistry exist among the different types. 50 Petrography In less serpentinized peridotites, serpentine occurs as thin (0.05 to 0.1 ram) veinlets along grain boundaries and along fractures within grains of olivine and orthopyroxene. The size and number of fractures in olivine i s generally greater. In detail, these veinlets consist of blades of l i z a r d i t e radiating outward from a median line of very small (<0.001 mm) grains of an opaque mineral, presumably magnetite. This median line may represent the original fracture along which serpentinizing fluids migrated, with l i z a r d i t e replacing the material on either side of the fracture. Several ages of l i z a r d i t e veinlets are differentiated on the basis of crosscutting relationships and differences i n colour, grain size, and magnetic content. The degree of alteration of chromites i s highly variable, and apparently not related to the degree of serpentinization. Unaltered chromite i s a trans-lucent dark reddish brown i n colour. Alteration results in development of an opaque, black mineral at the margin of the chromite grain, which lo c a l l y replaces the entire chromite grain. This black mineral may be a spinel, although i t i s not certain which type. The term * black spinel' distinguishes i t from magnetite associated with the serpentinization process. Most chromite grains are rimmed by a thin (0.1 mm) fine-grained halo of chlorite, which merges with the surrounding olivine and serpentine. The chlorite also develops i n veinlets which radiate out from this halo. Chlorite develops most strongly around chromite grains having a black spinel margin, and only weakly or not at a l l around chromites which are unaltered. This suggests that both the black spinel and the chlorite are products of the alteration of chromite. Large chromite grains commonly have two generations of fractures: an early group f i l l e d with chlorite and bordered by black spinel replacing chromite, and a later l i z a r d i t e -f i l l e d group, without the black spinel, which commonly crosscut the chlorite halo and merge with the l i z a r d i t e veinlets of the peridotite matrix. These PLATE Jl, Chromite grain rimmed by c h l o r i t e (white) i n n c serpentinized dunite. Note veinlets of c h l o r i t e U • ^mm • r penetrating olivine-serpentine matrix (PPL). PLATE 3 2 . Enlargement of Plate 3 1 . Chromite and black spinel (black) rimmed by c h l o r i t e (brown)in o l i v i n e (pink, 0. 1mm orange, and blue) veined by l i z a r d i t e (grey and white). (X nicols) PLATE 33. Serpentinite developed along joint in harzburgite. Note chrysotile 1 cm. 1 veinlets i n centre of black serp-entinite . PLATE 34. Outcrop of serpentinite showing contorted f o l i a t i o n , along the SE contact of the ultramafite. 53 relations suggest that the alteration of chromite to produce chlorite and black spinel occurred before the pervasive serpentinization. II Contact Zoning Contact zoning i s confined to the area of the ultramafite within about 50 m of the contact with the country rocks, and i s partly developed i n smaller ultramafic bodies. Figure 7 i s a sketch map showing areas of well-exposed contact, and the approximate distribution of the rock types described. Because complete sections of contact zones are uncommon, the following discussion represents a compilation of information from many sections. Figure 8 i s a selection of well-exposed sections across the contact area, showing the relative location and variation i n magnitude of the various zones. At least six zones or alteration types are present in the contact areas of the ultramfite, although usually only three or four are presents in a given l o c a l i t y . From the ultramafite core outward, these arej-a. Seroentinite: A zone of highly sheared, up to 100 percent serpentinized, material averaging about 45 m in width. b. Talc-carbonate: Near the contact, seroentinite grades into t a l c - , carbonate schist which i s highly variable in width and intensity of development. c. Nephrite (Jade): Tremolite occurs as isolated pods at the contact, and grades into mylonitized country rock. d. Rodingite: Scattered pods occur within the serpentinite zone. e. Quartz-talc-seroentine: A few isolated l o c a l i t i e s of chalcedony veinlets, with a talc margin, cutting serpentinite, were noted. f. Quartz-magnesite: A single l o c a l i t y of massive magnesite with chalcedony veinlets was noted in the serpentinite near the southeastern contact. 54 exposed approximate inferred Contact s "\ Fault zone with talc-carbonate, serpentinite J N r r r sr.. u r K -'Sj:peak2 u V S ^ ^ ' " ? b S U T j . r . Bruclte locality Serpentinite Peridotite (<50% serp.) Talc-carbonate Nephrite jade locality Rodingite locality N \V N \ ir s. tii'. \ QM. Quartz-magnesite locality QTS. Quartz-talc-serpentine Figure 7 Simplified sketch map of Pioneer Ultramafite showing distribution of alteration types. 55 R0DING3TE 3 2 m. fffj SorDentinite Schist J'l'i Talc-serpentine ***' Schist Talc-nagne s i t e J Meohrite (Jade) y\ Intrusive Rocks Cherts I'i D Kylonite ! chert + t r e n o l i t e + a l b i t e FIGURE 8 : Sections through contact zone. See Fig 7 for location. 56 The petrography of each of these types of a l t e r a t i o n i s summarized i n the following section. Estimated modes of representative samples are presented i n Appendix I I . a. Serpentinite Towards the outer edge of the pervasively serpentinized zone, the per i d o t i t e develops a blocky character, with intense serpentinization along j o i n t s (Plate 33 ; Chrysotile commonly develops i n these j o i n t s as narrow (<0.5 cm) cross-fibre v e i n l e t s . The remainder of the serpentinized portion, averaging about 3 to 4 cm i n width i s a mat of l i z a r d i t e blades with a few r e l i c t ortho- or clinopyroxenes, i n d i c a t i n g that the l i z a r d i t e , at l e a s t , formed by replacement of p e r i d o t i t e , not by f r a c t u r e - f i l l i n g . ' than This blocky, jointed zone grades over less A 10 m into the sheared, highly serpentinized zone. This change i s readily recognizable i n the f i e l d because of the markedly d i f f e r e n t character of outcrops and t a l u s . The less altered p e r i d o t i t e i s l i g h t brown on the weathered surface and t y p i c a l l y forms blocky outcrops and coarse bouldery t a l u s , whereas the serpentinite i s dark green and forms highly sheared, rounded outcrops and smooth talus slopes composed of gravel-sized fragments (Plate 3 )• A t y p i c a l sample of serpentinite (eg 351, Appendix II) consists of about 9 8 percent l i z a r d i t e , 1 percent chrysotile and 1 percent magnetite. Li z a r d i t e usually forms a mesh texture (Plate 35 ) with a network of l i z a r d i t e v e i n l e t s enclosing ^islands' of platy l i z a r d i t e and magnetite. The magnetite concen-t r a t i o n i n these islands i s commonly very high, with some up to 100 percent (Plate 36 ). Orthopyroxene grains are completely replaced by serpentine ( c h r y s o t i l e ? ) , but the o r i g i n a l cleavage i s preserved. Chromite i s preserved i n the cores of anhedral black spinel grains. Brucite occurs l o c a l l y at the inner margin of the serpentinite zone, as i r r e g u l a r patches and stringers associated with magnetite (Plate 38 ). PLATS 3 5 « ^ e s h t e x t u r e i n s e r p e n t i n i t e produced by i n t e r s e c t i n g l i z a r d i t e v e i n l e t s (X n i c o l s ) . 0. lmm PLATS 36. S e r p e n t i n i t e : M a g n e t i t e - r i c h i s l a n d s veined by l i z a r d i t e (PPL). rt . PLATE 37. Sande (343) of serpentinized harzburgite with ^ c n ! f white spots of brucite. Srey patches are serpentine after orthooyroxene. PLATE 38. Spherical patches of brucite (light brown) in mesh-textured serpentinite, sample 3^3.(X nicols) 0. 1mm. PLATE 3 9 . Se merit inized dunite ( 2 8 8 ) : Equant, fractured olivines with dark rims of seroentine and brucite 1 cm. in a matrix of serpentinite. PLATE 40. Thin section of sample 2 8 8 : stringer of brucite (light brown) and magnetite in l i z a r d i t e , between grains of fractured olivine (orange). (X nicols) . 0. 1mm. 60 With increased deformation, the serpentinite i s disrupted into lensoidal structures^ 1 to 5 cm thick and up to 20 cm i n diameter. These lenses have massive cores of randomly oriented l i z a r d i t e veinlets and smooth, slickensided margins ( l to 4 mm thick) of l i z a r d i t e blades aligned parallel tothe surface • b. Talc-Carbonate Between the serpentinite zone and the contact is a zone of talc-carbonate schist, which varies in width and intensity of development of t a l c . The tran-sition from serpentinite into talc-carbonate may be abrupt or gradational. A shear surface, or narrow shear zone marks the abrupt transition between essentially pure serpentinite and talc-carbonate withonly minor serpentine. The gradual transition occ\rrs through the development, in the serpentinite, of talc and talc-carbonate veinlets (Plates 41, 42 ) which increase in abundance as the contact is approached, producing a massive talc-carbonate schist. In several places, this passive part was not developed, the only occurrence of talc being thin veinlets along shear surfaces in the serpentinite. A tupical sample of this massive talc-carbonate unit (eg 177, Appendix l i e ) consists of about 45.percent magnesite as clusters of anhedral subequant grains (0.25 to 1.0 mm in diameter) in a matrix of very fine-grained talc and minor chlorite. Anhedral grains of chromite, rimmed by black spinel and traversed by t a l c - f i l l e d fractures, are common. The similarity in abundance, distribution and texture of these chromites to those in harzburgite suggests that they are r e l i c t s remaining from the alteration of that rock type. The distribution of talc i s not homogeneous. Subequant patches composed of talc and chlorite, but no carbonate, constitute about 25 percent of the volume of the rock (Plate44 ). Their size (about 5 mm dia) and distribution is similar to that of orthopyroxene in fresh harzburgite. The magnesite-bearing portions of the rock may represent the alteration of olivine in the original peridotite matrix. PLATE 4 1 . T a l c - m a g n e s i t e v e i n s c r o s s i n g s e r p e n t i n i t e f o l i a t i o n , a l o n g SE c o n t a c t o f u l t r a m a f i t e . PLATE 4 2 . Sample (354) o f t a l c v e i n l e t s 2 cm. i n s e r p e n t i n i t e ( d a r k ) . ON 62 PLATS 43 . Samole (350) o f t a l c - s e r p e n t i n e s c h i s t : l e n s e s o f J f i n e - g r a i n e d t a l c and s e r p e n t i n e i n a l i g h t t a l c 1 cm• 1 1 m a t r i x . PLATS 4 4 . T y p i c a l sample (178) o f massive t a l c - m a g n e s i t e rock 1 Dark patches o f t a l c and c h l o r i t e a f t e r 1 cm. o r thopy roxene , i n a m a t r i x o f t a l c and magnesite a f t e r o l i v i n e . 63 c. Nephrite (Jade) Within a few metres of the contact are a small number of occurrences of nephrite jade (tremolite). This material occurs a) as small pods, a few metres in diameter, in serpentinite or talc-carbonate, and b) as sheared material along the contact, grading into sheared cherts of the country-' rock ( P l a t e d ). Material from the pods is tremolite, with only minor amounts of serpentine, ta l c , magnetite and chromite, whereas the sheared contact material i s commonly a mixture of tremolite, albite, potassic feldspar, diopside and carbonate with minor magnetite and chromite. The presence of chromite suggests that the tremolite formed by alteration of ultramafic rocks, rather than country rocks or inclusions of intrusive rock. d. Rodingite The term 'rodingite' refers to rocks made up predominantly of calcium-rich s i l i c a t e s such as hydrogarnet, idocrase, and diopside, which are considered to be derived from gabbros and basalts associated with ultramafites (Coleman, 1 Q 6 7 ) . In this discussion, 'rodingite' w i l l include tectonic inclusions of sediments, as well as gabbros and basalts which have undergone metasomatism involving the addition, primarily, of water and CaO. Because of the large number of rodingites in the f i e l d area, and the great variety of textures and mineral assemblages involved, only some variations are discussed. The occurrences selected indicate the range of properties and probabls nature of the unaltered parent material. A 20-metre long by 1-metre wide rodingite dike crosscuts peridotite layering just inside the serpentinite zone (Fig 9 ) « The margin of the dike is a greenish-black zone of serpentine and chlorite, about 0 . 5 m thick, which grades into relatively fresh peridotite. In thin section the rodingite consists of- large ( l cm dia) anhedral to subhedral phenocrysts of green diopside altered extensively to chlorite, in a matrix of white hydrogrossular, veined by 64 PLATE 45. Sheared tremolite-albite rock along contact of ultramafite xvith cherts. * * PLATE 46. Enlargement of Plate 45 : lenses of albite and tremolite in a fine-grained tremolite matrix. 2 cm. • • (sample 315). PLATE 4 7 . Sannle (264) o f sheared t r e m o l i t e - a l b i t e rock 2 cm. from c o n t a c t o f u l t r a m a f i t e w i t h c h e r t s . Large wh i te augen i s a l b i t e . PLATE 4 8 . B r e c c i a (338) from a l o n g f a u l t c o n t a c t o f u l t r a m a f i t e : f ragments o f c h e r t , a l b i t e , and 2 cm. 1 1 t r e m o l i t e i n a t r e m o l i t e m a t r i x . PLATE 49. Botryoidal Jade : very fine-grained tremolite spherules with inter-0 . 5™n ' 1 s t i t i a l serpentine and magnetite (X nicols) PLATE 5 0 • Rodingitized gabbro : dark grey patches of chlorite replacing diooside in a l i g h t grey matrix of hydrogrossular after plagioclase ' ' 1 c m # FIGURE 9 '• Rodingitized gabbro dike i n p e r i d o t i t e , disrupted by shearing i n serpentinates, during emplacement of the u l t r a m a f i t e 68. vesuvianite and hydrogrossular. The similarity of this occurrence to fresh dikes of gabbro and anorthosite which occur within the core of the "ultramafite suggests that this rodingite was originally a gabbro composed essentially of diopside and olagioclase, now largely altered to chlorite and hydrogrossular, respectively. Rodingite pods range in size from less than a metre (Plate 51 ) to more than 10 metres (Plate 52 ) in diameter, averaging about 2 to 3 metres. Larger pods commonly show zoning from an altered margin to a less altered core. An example shown in Figure 10 has a core of medium-grained brown porphyritic gabbro with large altered albite, and minor sphene, biotite and zoisite (553 a , Appendix I l f ) . The margin of the pod consists of large white patches of zoisite, similar in size and distribution to the plagioclase phenocrysts in the core, in a lig h t brown matrix of diopside, zoisite and sphene (553b, Appendix Hd). Apparently the main reaction involved is the conversion of plagioclase to zoisite, since the abundance of diopside does not change. Rodingites also develop from post-tectonic : s i l l s and pods of sediment. A large (15 x 20 m) inclusion of ribbon cherts in the north contact serpentinite zone is extensively altered within about 2 metres of i t s margin. This altered material (296, Appendix lid) consists of 5 to 10 mm breccia fragments of fine-grained equigranular quartz in a pale grey fine-grained matrix of diopside, hydrogrossular and quartz. Much of the quartz shows undulatory extinction indicating strain related, presumably, to the brecciation process. In summary, the rodingites form a highly variable rock type due, i n part, to the diversity of parent rock types and metasomatic conditions. A l l examples studies contained diopside, with one or more of the following! grossularite (or hydrogrossular), zoisite/clinozoisite, idocrase, chlorite, tremolite-actinolite, albite, and sporadic prehnite, sphene, calcite, quartz, magnetite or bioti t e / phlogopite. FIGURE 10 i Schematic f i e l d relations of samples 553a and 553b. Boudinaged s i l l in serpentinite. Smaller pods are rodingite, largest pod is altered dior i te (?) with rodingite margin. ON vO PLATE 51. Small rodingite ood with black serpentine-chlorite skin, in serpentinite, about 1 m from ultramafite contact with cherts PLATE 52.. Larq;e (10 m long) pod of rodingite in serpentinite. Wooded ridge i s underlain by ribbon cherts. Valley in background i s Cadwallader Creek. PLATE 53. Rodingite (sample 352) : dark veinlets of idocrase (vesuvianite) in a matrix of diopside and hydro-1 cm.i grossular. From pod shown in Plate 52• I PLATE 54. Rodingite : zoned idocrase (light brown) i n a matrix of fine-grained diopside and hydrogrossular. 0.5mm ' Sample 352 cf Plates 52, 53. (X nicols). I PLATS 55' Core of rodingite pod : corroded plagioclase „ „ Dhenocryst in matrix of dunside and plagioclase. 0 .5mm Sample 553a (X nicols) I PLATE 56. Margin of rodingite pod : zoisite (blue) crystals completely replacing Dlagioclase, in matrix of 0. 5mm diopside and zoisite. Sample 553° (X nicols). 73 PLATE 57' Rodingite-serpentinite contact : black part i s serpentine, chlorite and brucite; white part i s 1 cm • * diopside, idocrase and chlorite. Sample 276. PLATE 58. Rodingite i extremely fine-grained albite, diooside and hydro grossular, veined by hydrogrossular. 1 cm • Sample 353• 74 PLATE 5 9 « Rodingite : zoned hydrogrossular (grey) with euhedral diooside. (X nicols) 0 . 5 n m . I PLATE 6 0 . Rodingite s zoned euhedral clinozoisite (blue) crystals i n calcite (yellow) replacing k-feldspar 0 . 5 ^ ' (light grey). (X nicols) 75 e. Quartz-talc-serpentine A small number of examples of quarts veins cutting serpentinite were noted. These are typically 1 to 2 cm wide and consists of banded agate (chalcedony) with thin margins of fine-grained talc adjacent to the serpentinite. These quartz-talc veins develop in serpentinite near the zone of talc-carbonate alteration. f. Qua rt z -ma gne s i te Granular magnesite cut by recrystallized chalcedony veins (2 mm to about 4 cm in t h i c k n e s s ) occurs in one l o c a l i t y . I l l Fault Zones At least four different alteration mineral assemblages are associated with the fault zones in the ultramafite. These are: a. Talc-magnesite-chlorite b. Serpentine c. Serpentine-dolomite d. Serpentine-calcite Along the major fault north of peak 1, talc-magnesite-chlorite rock develops near the fault, and grades into serpentinite then serpentinized peridotite. The thickness of this alteration zone ranges from a few metres to a few tens of metres. Calcite and dolomite are restricted to single l o c a l i t i e s from the serpentinite adjacent to a fault. a. Talc-magnesite-chlorite forms in massive and foliated rocks. The massive variety i s similar to material from the talc-carbonate zone along the ultramafite contact. The foliated variety, which occurs l o c a l l y along the fault zone i s characterized by strong shearing (Plate 61 ). An example of this material (258, Appendix t i c ) consists of chlorite patches (after orthopyroxene), veined by calcite and dolomite, in an extremely fine-grained matrix ( 0.01 mm) of talc and chlorite. PLATE 6 l . Shear zone i n peridotite, composed of t a l c , chlorite, magnesite, and dolomite PLATE 62. Sample (253) from shear zone in peridotite. Dark patches are chlorite, 1 cm ' after orthopyroxene, in a matrix of ON extremely fine-grained talc-carbonate. 77 b. Serperetinites are similar to those developed along the main ultramafite contact, highly foliated material near the faults grading into massive material, then into relatively fresh peridotite. c. From one l o c a l i t y , on the ridge east of peak 1, the serpentinite i s highly fractured and veined by white, fine-grained dolomite. No evidence of a reaction between the serpentine and dolomite at vein margins was noted. d. In the fault zone about 10 m from the serpentine-dolomite l o c a l i t y , serpentine-calcite forms a pod ( l m x 2 m) enclosed by serpentinite. The serpentine and calcite appear to coexist stably with no evidence of reaction between them. Although the pod may be limestone caught up in the fault zone, this i s unlikely because no other inclusions were noted in the fault zone, and limestone i s an uncommon country rock type. IV Later Intrusions Ultramafic rocks are altered i n aureoles around later intrusive plugs and in inclusions within larger intrusive bodies. In the v i c i n i t y of peak 2 and south of cirque 2, plugs have produced a zone of a few metres width of massive serpentinite veined by chrysotile (top of measured section, Appendix I l i a ) . On peak 1, the plug caused serpentinization and development of a narrow zone up to 5 ni thick of talc-carbonate from surrounding peridotite. This zone merges with talc and talc-magnesite alteration along the fault immediately to north. Evidence of an earlier thermal metamorphism, now largely obliterated by serpentinisation and talc-magnesite formation, can be seen i n one location. Sample 321 (Appendix Ha), serpentinized harzburgite collected about 1 metre from the intrusive contact, contains about 2 percent tremolite, now largely replaced by l i z a r d i t e . On the ridge east of Crazy Creek, the Bralorne Intrusions contain several ultramafic inclusions. A small pod, about 2 metres in diameter, surrounded by gabbro, consists of talc pseudomorphs after orthopyroxene (?) i n a matrix of dolomite, t a l c , l i z a r d i t e and magnetite. The proportion of orthopyroxene (?) pseudomorphs indicates that this rock was probably an orthopyroxenite. Its source could be ultramafic rocks like the Pioneer body or i t may be an ultramafic differentiate of the Bralorne Intrusions which has subsequently been altered. Cairnes (1937) reported such differentiated rocks as diallagite dikes intruding Bralorne gabbros. The identity of the pyroxenes has obvious implications with respect to the relative ages of the Pioneer Ultramafite and Bralorne Intrusions. If they are orthopyroxenes, then the rock i s probably orthopyroxenite derived from the Pioneer body, indicating that the Bralorne Intrusion i s younger. If they are clinopyroxenes, then the rock i s probably not related to the Pioneer body and hence the relative age relation i s uncertain. If the modal composition (40 percent t a l c , 40 percent serpentine, 20 percent dolomite) i s recalculated i t yields an orthopyroxenite of 75 percent enstatite, 10 percent diopside and 15 percent olivine (Fig 5). This calculation assumes that the system i s closed except to H20 and C0 2. Although i t would be possible to produce the observed alteration assemblage by removal of calcium from a clinopyroxenite, evidence of removal of calcium i s lacking. The inclusion was probably, therefore, orthopyroxenite altered from rocks l i k e the Pioneer ultramafite. A second inclusion of altered ultramafic (?) rock consists of 40 percent granoblastic dolomite and 20 percent quartz in a matrix of fine-grained chlorite (5l6a, Appendix He). It was not possible to recalculate a reasonable ultramafic protolith for this material partly because of the excess of alumina in the chlorite. Either extensive metasomatism has occurred, or the protolith was not ultramafic. Immediately south of cirque 2, an andesite plug contains small (up to 2 or 3 cm) inclusions of ultramafic rock. Inclusions of fresh peridotite show very l i t t l e effect from the surrounding magma, but several inclusions 79 consist of very fine-grained ( 0.05 mm) equigranular aggregates of olivine, a texture unlike any observed elsewhere in the ultramafite. This olivine may be regenerated from inclusions of serpentinite (P. 115)• 80 STRUCTURAL GEOLOGY Introduction Mapping of th© ultramafite and country rocks shows that some structures i n the ultramafite d i f f e r i n number and style from those i n the country rocks whereas other structures are common to both. Apparently, the ultramafite and country rock were deformed separately, then deformed together during emplace-ment, followed by a later, combined, deformation (Table 5)» The evidence for this interpretation i s presented i n the following sections. Ultramaf^e Structures The predominant structural feature of the fresh peridotite i s the layering, defined by stringers of orthopyroxene i n the olivine-rich ground-mass (P. 33)• These orthopyroxene grains commonly show a preferred orient-ation, the long axis of grains being p a r a l l e l to layering. In the absence of petrofabric studies, a preferred crystallographic orientation of ortho-pyroxenes i s uncertain. Preferred crystallographic orientation of olivine i s shown by the simultaneous extinction of large numbers of grains i n a thin-section. The distribution of layering i n a v e r t i c a l section i s shown i n Appendix III. Development of layering varies throughout the section from portions showing no vi s i b l e fabric to portions showing well-defined layering. A number of features distort the (presumably) originally-planar layering. The orthopyroxenite layers, which are generally par a l l e l to the layering i n peridotite, are, i n several places cut by orthopyroxene stringers (Plate 63). Where these orthopyroxenite layers cross harzburgite-dunite contacts and enter dunite pods, they become highly contorted (Plate 68). Similarly, bending of orthopyroxenite layers occurs along the margin of a dunite dike which crosscuts layering (Fig. 11). TABLE 51 Summary of Doformational History i n Field Area ULTRAMAFIC ROCKS plastic deformation -•strong tectonite fabric, S a (original attitude unknown), multiple plastic deformations —•flow folds, dunite pods and dikes, crosscutting opx. stringers large-scale warping of S a Model 1 t Dj. - folding about NW-SE subhorizontal axes —•»-v e r t i c a l axial planes jD2 - i s o c l i n a l folding about ve r t i c a l axes, with shear i n NW-SE direction -+-St COUNTRY ROCKS Model 2 1 Dj, - horizontal shear -»- St and folds, rodding with NE-SW axes. Da - folding or t i l t i n g toward ver t i c a l , about a NW-SE horizontal axis EMPLACEMENT Dj - emplacement of UM along S^—*-S3 i n cherts and serpentinites along the ultramafite contact. D, - possible combined deformation of ultramafite and country rocks folds i n sediments, UM contact, and north serpentinite s i l l . 82 3x4 M ^mmmmfm 3a * r f '•• • 3 $ : i :• A rr PLATS 63. Crosscutting orthopyroxenite stringers. Host prominent set of stringers i s p a r a l l e l to the layering i n the p e r i d o t i t e . PLATS 64. Crosscutting orthopyroxenite stringers i n poorly layered harzburgite. 1 83 Minor folding of peridotite layering developed locally. These folds have subhorizontal northwest-trending axes with southwestward dipping axial planes. The folds are generally confined to a few metres of layering, with overlying and underlying layers being undistorted. Interllmb angles range from 80° to almost 180° (Fig. 12). Serpentinite along the margin of the ultramafite shows strong foliation subparallel to the contact with the country rock. Along the north contact, this foliation strikes approximately northwestward and i s vertical to steeply southwestward dipping. Along the south contact, the foliation also has an average northwestward strike, but is vertical to steeply northeastward dipping (Fig. 14). Lenses of serpentinite locally show a marked elongation in one direction. This rodding is generally directed down dip. Rodingite pods also show elongation down dip in several localities (Plate 70). A single large fault zone, consisting of serpentinite and talc schist, crosses the ridges north and east of peak 1. This fault appears to be a continuation of the argillite-serpentinite contact on the ridge east of Crazy Creek (Fig. 28). Minor faults were noted in several areas. These faults, having displacements of several centimetres (Plate 65), show no consistent pattern of orientation. Country Rock Structures The predominant structural feature observed in the country rocks is a weak foliation which, in argillites, is produced by a preferred planar orientation of muscovite and chlorite flakes and by subparallel fractures and shear surfaces.' The attitude of the foliation is generally subparallel to the foliation in the serpentinites (Fig. 14 and 17), that i s , northwesterly striking and dipping steeply southwestward on the north side of the ultra-mafite and steeply northeastward on the south side. Along the western margin 85 PLATE 65. Fractures producing small offset of orthopyroxenite stringers i n massive harzburgite. 88 N 75 points •< 1 percent 1- 2 percent 2- 4 percent 4 4-6 percent 5 6-8 percent > 8 percent FIGURE 14 Stereographic Projection of poles to S3 in -serpentinites and talc-carbonates. of the ultramafite, i t appears that foliation in the country rock is not parallel to foliation in serpentinites, since the sediments maintain their northwesterly strike attitude, whereas the ultramafite contact and foliation in serpentinites, although obscured by drift, appear to diverge toward a northeastward strike. In this area, within 3 metres of the serpentinite contact, the ribbon cherts show strong foliation parallel to the contact. This foliation is not recognized elsewhere along the contact, presumably because i t is parallel to the pervasive foliation in the rock. The pervasive foliation appears to be generally subparallel to bedding, where visible, except where quartz-rich layers form rootless isoclinal folds. The axes of these folds plunge down the dip of ths foliation and range from northeasterly to southwesterly plunging, through vertical. Close to the contact with the ultramafite, rodding is locally developed in the ribbon cherts. The rods are generally 2 to 4 cm in diameter and as much as a metre long, with the axis of elongation being down the dip direction of the foliation and parallel to rootless fold axes in the argillites. Limestone occurs throughout the sedimentary sequence as continuous layers and as pods. The origin of these pods i s uncertaint they could be primary features such as concretions, or, assuming they were originally part of continuous layers, could be boudins or even sheared-out isoclinal fold noses. Inte rpretation In the absence of petrofabrlc studies, a preferred erystallographic orientation of orthopyroxenes and olivines in the Pioneer Ultramafite i s uncertain| however, the simultaneous extinction of large numbers of grains in thin-section suggests that such preferred orientation does exist. This feature, described from similar rocks by AveLallement (1967) a n <* others, is tentatively interpreted as a tectonite fabric, , resulting from an early 71 points <1 percent 1- 2 percent 2- 4 percent —r~ s 4-6 percent >6 percent rootless fold axes FIGURE 15 Stereographic Projection of Poles to in sediments and volcanics on the north side of the ultramafite. 91 N 150 points x 1 rootless f o l d axes 3. < 1 percent 1- 2 percent 2- 4 percent 4-6 percent 6- 8 percent 8-10 percent 10-12 percent 8 >12 percent FIGURE 16 Stereographic Projection of Poles to i n sediments and volcanies from south and west sides of ultramafite. 92 N < 1 percent 1- 2 percent 2- 4- percent 221 points 4-6 percent 6-8 percent > 8 percent FIGURE 17 Stereographic Projection of Poles to ln a l l sediments and volcanies. 95 d e f o r m a t i o n , . The f e a t u r e s which d i s t o r t the (presumably) o r i g i n a l l y p l a n a r S a p r o b a b l y r e p r e s e n t s e v e r a l d e f o r m a t l o n a l e p i s o d e s , but a re grouped t o g e t h e r because d a t a are not s u f f i c i e n t t o pe rmi t a c h r o n o l o g i c a l s e p a r a t i o n o f e v e n t s . T h i s second d e f o r m a t i o n , D b , i s represented by emplacement o f d u n i t e d i k e s and s i l l s , and by minor f a u l t s and f o l d s i n p e r i d o t i t e l a y e r i n g . The d i s t r i b u t i o n o f a t t i t u d e s o f S a ( F i g . 13) throughout the u l t r a m a f i t e i n d i c a t e s a l a r g e synform, w i t h a s o u t h w e s t e r l y p l u n g i n g a x i s (215/20SW) and a n o r t h e a s t e r l y s t r i k i n g and s t e e p l y d i p p i n g a x i a l p l a n e . T h i s synform i s c o n s i d e r e d t o be the r e s u l t o f a t h i r d phase o f d e f o r m a t i o n , D c , w i t h i n the u l t r a m a f i t e . The f o l i a t i o n w i t h i n the s e r p e n t i n i t e s a l o n g the f a u l t c o n t a c t v i t h the c o u n t r y rock i s everywhere p a r a l l e l t o the c o n t a c t and i s i n t e r p r e t e d as h a v i n g formed d u r i n g emplacement o f the u l t r a m a f i t e as a s o l i d mass i n t o the c o u n t r y r o c k s . T h i s f o l i a t i o n , S 3 , t r u n c a t e s S a i n the p e r i d o t i t e and t h e r e f o r e p o s t - d a t e s D a and p r o b a b l y D D and D c . The use o f the te rm S 3 d e r i v e s from c o n s i d e r a t i o n o f s t r u c t u r e s w i t h i n the c o u n t r y r o c k . To produce s u b v e r t i c a l f o l d axes i n S 0 r e q u i r e s a t l e a s t two phases o f f o l d i n g , D t and D 2 , The p e r v a s i v e f o l i a t i o n i n the c o u n t r y rock i s termed Sj, , a l t h o u g h i t i s u n c e r t a i n whether t h i s f o l i a t i o n formed d u r i n g Dt o r Dj . There a re a t l e a s t two p o s s i b l e models f o r p r o d u c i n g the d i s t r i b u t i o n o f p o l e s t o ( F i g . 15, 16, 17). S t a r t i n g w i t h o r i g i n a l l y h o r i z o n t a l b e d d i n g , S 0 , t he f i r s t model assumes an e a r l y d e f o r m a t i o n resulting i n f o l d s w i t h NW-SE s u b h o r i z o n t a l axes and s u b v e r t i c a l f o l d l i m b s , f o l l o w e d by a l a t e r ep isode o f i s o c l i n a l f o l d i n g w i t h s u b v e r t i c a l axes and h o r i z o n t a l shear i n a NW-SE d i r e c t i o n . T h i s l a t t e r phase o f d e f o r m a t i o n would account f o r , r o d d i n g i n c h e r t s , and r o o t l e s s f o l d s . By the second mode l , a s u b h o r i z o n t a l Sx would be produced by s h e a r i n g a l o n g a h o r i z o n t a l p lane i n a NW-SE d i r e c t i o n . T h i s would result i n r o o t l e s s f o l d s w i t h h o r i z o n t a l NE-SW a x e s . A subsequent d e f o r m a t i o n i n v o l v i n g f o l d i n g 93 PLATE 6 8 . Contorted orthopyroxenite layers in dunite. PLATE 6 9 . Peridotite with 3 2 f o l i a t i o n , from zone between foliated serpentinite and massive, unseroentinized peridotite. PLATE 70. Elongated rodingite pod in serpentinite. Hammer handle parallels axis of elongation, down dip of S 2 . 96 or t i l t i n g about a NW-SE horizontal axis would produce the present d i s t r i b -ution of poles to S A (Fig. 17). It i s not possible, on the basis of available data, to say with certainty which model i s appropriate. Although poles to S t i n country rocks (Fig. 17) and poles to S3 i n serpentinite have similar distributions on the stereonet, the two foliations are not equivalent since they appear to diverge along the western contact, and a strong f o l i a t i o n , S3 , which i s p a r a l l e l to Sj i n serpentinite, appears in the country rocks close to the contact. This S 3 i s believed to be the result of shearing during emplacement of the ultramafite mass. Other features produced during D 3 , the emplacement of the ultramafite, probably include » development of tectonic inclusions of rodingite, sediments and volcanics i n the serpentinite margin} emplacement of small pods of ultramafic rock along faults i n the country rock (Fig. 28) j and development of rodding i n the serpentinite and inrodingite pods (Plate 70). In at least three places i n the map area, large-scale folds are seen, which may represent a fourth phase of deformation, , post-dating the emplacement of the ultramafite. No small-scale features such as foliations , or minor folds could be found which relate to this deformationj i t i s seen only in outcrop patterns and by examination of stereographic projections of poles to Sk and S^ (Fig. 17 and 14, resp.). In the second cirque, the ribbon cherts and the ultramafite contact have been folded about an axis at 115/15SE with an axial plane at 110/30S. Along the north contact, a grey-waeke lens and the serpentinite s i l l show folding of the same style, about axes at 270/35W and 090/30E respectively, and axial planes at 090/vert. and O8O/5OS resp. A l l folds are open, with interlirab angles of about 145°. These folds may have been produced during emplacement of the ultramafite, i e . as part of . The evidence i s inconclusive. 97 Cross Sections Three cross sections were constructed to show the general configuration of the ultramafite and country rocks (Fig. 18). For their locations, see Figure 28. These sections show the style of possible folds (SW end of section CC') and the attitude of the ultramafite contact. Note that the south contact changes from near-vertical i n the east to less steeply dipping i n the west, whereas the north contact i s quite variable, going from north-ward dipping i n the east, through the v e r t i c a l at Crazy Lake, reaching i t s shallowest southward dip on the ridge northeast of peak 2, then steepening to near-vertical towards the west. This v a r i a b i l i t y of the contact attitudes makes i t d i f f i c u l t to predict the shape of the ultramafite at depthf i t does however, appear to be elongated, with i t s long axis plunging steeply eastward. FIGURE 18 Cross Sections of the Pioneer Ultramafite LEGEND 98 Glacial drift and extensive talus deposits Cenozoic andesite plug Small intrusive stocks i gabbro Bralorne Intrusions Serpentinite and talc-carbonate Peridotite t Harzburgite with minor orthopyroxenite, dunite. Lines indicate projection of S& onto section. /''tti/n //////> /'////' Pioneer Greenstone (with minor interbedded sediments) Greywacke with minor argillite Argillites Mixed ribbon cherts, argillites and minor volcanies and limestones. e~* Fault Gradational contacts PEAK 2 B ft m 900 -300 600- -200 300- -100 VERTICAL EXAGGERATION i 1.1 X 100 DISCUSSION PIONEER ULTRAMAFITE Textures i The origin of layering in ultramafic rocks has been ascribed to magmatic differentiation and crystal settling (Wager and Brown, 1967), and to deformation and solid flow (Loney e£ a i , 197D• Features ascribed to magmatic differentiation include cumulate textures, cryptic zoning, and sedimentary features such as graded bedding, slump structures and channel-f i l l structures. These have been described from layered and zoned intrusions, such as Bushveld and Skaergaard (Wager and Brown, 1967), and Duke Island (Irvine, 1967), which are believed to have formed by differentiation of a basic magma and accumulation of crystals i n a layered sequence. None of these features was recognized i n the Pioneer ultramafite, and this mode of origin for the layering i s therefore considered unlikely. The texture of the layered peridotite i s similar to that described for the Burro Mountain peridotite by Loney e£ al_ (1971), and interpreted, on the basis of detailed petrofabric analysis, as being due to plastic deform-ation and recrystallization. Common features include t equigranular texture, preferred optical orientation of olivine , flow folds with axial planes p a r a l l e l to fo l i a t i o n , and segregation of orthopyroxene into layers. The prominent layering within the harzburgite i s therefore believed to be a tectonite fabric resulting from plastic deformation and recrystallization (Carter and Ave Lallement, 1969) accompanied by metamorphic differentiation (Turner and Verhoogen, I960, P.581) producing alternate o l i v i n e - and orthopyroxene-rich layers. The origin of both conformable and crosscutting orthopyroxenite layers i s unknown. The gradational contacts of these layers with the enclosing peridotite suggests that they were not intruded as s i l l s of orthopyroxene 101 magma. I t i s conceivable, however, that recrystallization after emplacement could result i n diffusing of a previously sharp contact. An alternate explanation, analagous to Bowen and Tuttles(l949) suggestion of a replacement origin for dunites, i s also possible. Such a mechanism would involve intro-duction of water vapour containing excess Si 0 2 along fractures i n harzburgite resulting in the replacement of olivine by orthopyroxene in the rock adjacent to the fracture. This mechanism seems unlikely since replacement textures, such as orthopyroxene rimming olivine, are not seen, and a source for S i 0 2 -rich fluids i s unknown. For a discussion of Si 0 3 a c t i v i t y i n igneous rocks see Nicholls ej, a l (1971). Dunite bodies within the harzburgite may have formed in one of the following ways i by crystallization from intruded dunite magmaj by sol i d intrusion accompanied by recrystallization} by replacement, as suggested by Bowen and Tuttle (19^9)} and by metamorphic segregation. The f i r s t group of dunites,which are conformable with the Sa fo l i a t i o n and grade into enclosing harzburgite, are perhaps most readily explained by a replacement model because of these gradational contacts. Such a mechanism involves replacement of orthopyroxene by olivine along fractures containing S i 0 2 -undersaturated water vapour (cf. orthopyroxenite formation, above). Replacement textures are, however, not seen. The second group of dunites, characterized by sharp contacts, cannot be explained by such a replacement mechanism. Crosscutting dikes (Fig. 11) clearly show evidence of deform-ation of the enclosing rock, which suggests that the dunite was a plastic s o l i d , or possibly a viscous mush of olivine crystals i n a magma. Textural evidence of a magmatic origin, such as finer-grained i n t e r s t i t i a l o l i v i n e , i s lacking. Chromite stringers i n the centre of dunite s i l l s (P. 42) may result from chemical or mechanical processes. It i s conceivable that chromium-bearing flu i d s i n a central fracture could produce the observed pattern. 102 Alternately, mechanical sorting based on density and/or grain size could occur during the intrusion of the dunite s i l l , analagpus to concentration of pebbles and boulders at the centre of sandstone dikes. Concentration of orthopyroxene grains along the centre of dunite s i l l s (P. 42) could be explained by a mechanical sorting process as above, or by migration of Si0 2-rich fluid along a fracture in the dunite resulting in conversion of olivine to orthopyroxene in the material adjacent to the fracture. If one assumes that the dunite layer also formed by a replacement process, this would require first a Si0 2-deficient fluid to convert harz-burgite to dunite, then a Si0 2-rich fluid to convert part of the dunite back to orthopyroxene. This process could also be explained in terms of MgO concentrations, increased MgO resulting in the conversion of orthopyroxene to olivine, and so on. No central fracture for migration of fluids was observed, although this could be obliterated by later recrystallization. Fracturing of orthopyroxenite layers (P. 37) could possibly be explained by expansion of the enclosing peridotite during serpentinization, resulting in boudlnaging of the relatively unserpentinized orthopyroxenite layer. This does not, however,explain the preferred orientation of fractures (Plate 25) which implies a directional stress (Ramsay, 196?)• Data on distribution and orientation of these fractures throughout the body are needed before an analysis of a possible structural origin can be made. Petrogenesis i The compositions of coexisting olivine, orthopyroxene and clinopyroxene can be used to determine the P,T conditions of equilibration of the ultra-mafite. These geobarometers and geothermometers are discussed in Appendix IVj some are based on preliminary data, so that P,T estimates vary widely, depending on the mineral pair used (Table 6). 103 TABLE 6 t Summary of Estimates of P,T conditions of equilibration of the Pioneer Ultramafite. Method P T 1) (Fe/Mg) in 01 vs Opx (Medaris, 1972) - >900°C ? 2) (Fe/Mg) in 01 vs Cpx (Van Schmus and - >820°C Koffman, 1967) 3) (Fe/Mg) in Opx vs Cpx (Van Schmus and - >820°C Koffman, 1967) 4) Opx-Cpx solubility >22 kb 1350°C (Wood and Banno, in press) (Irvine and Findlay, 1972) 5) Opx-Cpx solubility - 950°C (Warner and Luth, 1974) 6) Clinopyroxene composition (0 Hara, 1967) 1 kb ? 1150°C 7) Garnet stability <Z0 kb (Irvine and Findlay, 1972) 8) Al a0 3 in orthopyroxene - > 800°C (Anastasiou.and Seifert, 1972) 104 In summary, the pressure of equilibration of the peridotite cannot be accurately determined, but is presumably less than 20 kilobars based on the absence of garnet, which becomes stable above this pressure (Irvine and Findlay, 1972) . Temperature estimates range from greater than 800°C up to 1350°C. The best estimate is 950°C, given by Warner and Luth's (1974) model, based on Blander's (1972) thermodynamic treatment of orthopyroxene-clinopyroxene solubility. ALTERATION Alteration of the ultramafite and enclosed related rocks represents a complex series of reactions under variable conditions of pressure, temp-erature and fluid composition. A reasonably complete discussion and representation of these reactions would involve a minimum of seven compon-ents 1 MgO, FeO, CaO, A1203, Si0 2, H20, and C02 . Other components such as ° 2 » Cr 20 3, K20 and Na20 , while locally significant in explaining the stability of certain phases, can be omitted from much of the discussion. Even so, a system with nine variables ( pressure, temperature and seven components) is most unwieldy, so in order to graphically represent the appropriate equilibria, certain assumptions must be made. In isobaric, temperature-composition plots the pressure is arbitrarily set at 2 kb, so that while temperature estimates may not be absolutely correct, such estimates will generally be relatively correct with respect to other equilibria. Chromite Alteration Alteration of chromite to black spinel or magnetite (P. 50) reportedly occurs at temperatures above the stability limit of serpentine (Fig. 21) by the reaction (Cerny, 1968) 1 Chromite + olivine —*• magnetite + Cr-chlorite This conclusion is supported, in the Pioneer Ultramafite, by the observation Si0 2 Quartz 1 05 Figure 19a Ghemographic Diagram showing phases in the CaO - MgO -Si02 - CO2 - H2O system. SiO? Enstatite Forsterite MgO Figure 19b Chemographic Diagram showing phases in the MgO - Si0 2 - H2O system. To.+, Fo_ S e r p Di i Diopside Tr Ta : Tremolite i Talc En i Enstatite An J Anthophyllite Fo i Forsterite Br j Brucite P t Perlclase M t Magnesite Dol i Dolomite Cal t Calcite Q » Quartz Fo Serp -800 \-600 T°C \-koo 2kb. H90 0.2 OA 0.6 — i — 0.8 XcOc —1-200 C0 2 Figure 20 T - X Diagram showing selected equilibria in the system CaO - MgO - Si0 2 - H20 - C02 . Shaded area is stability f i e l d of serpentine. that the degree of alteration of chromite to black spinel or magnetite is independent of the degree of serpentinization or talc-carbonate alteration, implying that the temperatures at which these reactions occur are too low to produce further alteration of the chromite. The conclusion that chlorite formation pre-dates serpentinization i s in contradiction to the textural evidence in the Pioneer ultramafite samples which show veinlets of chlorite cutting serpentine (Plate 31)• Cerny (1968) suggested that since antigorite originates in a higher temperature environment (Wenner and Taylor, 1971» and Page, 196?) the breakdown of chromite could occur at the same time as antigorite formation. Since antigorite was not recognized in the Pioneer Ultramafite, this implies that chlorite is veining lizardite which has replaced antigorite. Such an interpretation depends on the stability relations of the serpentine * polymorphs, which are not well understood. Serpentinization With decreasing temperature (and pressure ?) the primary mineral assem-blage olivine-orthopyroxene-clinopyroxene becomes unstable and serpentine is produced by reaction with water. For the purpose of this discussion, this primary assemblage is approximated by forsterite-enstatite-diopside, neglecting components such as FeO and A1 20 3 which would produce small shifts in equilibrium conditions deduced from the simplified system Ca0-Mg0-Si02-Ha0-C02 (Fig. 20). For example, Scarfe and Willey (1967) have shown that adding FeO to the system decreases the breakdown temperature of forsterite to serpentine. Serpentinization is initiated by the reaction (Fig. 20, 21) i Forsterite + water — S e r p e n t i n e + brucite 2Mg8Si04 + 3 H20 Mg3Si207.2H20 + Mg(0H)8 This reaction occurs at about 400°C (at 2 kb). The stability of brucite is limited by the composition of the fluid phase, being stable only at very 108 Figure 21 Pressure-temperature plot of phase relations in the system CaO - MgO - Si0 2 . P H 20 * p t o t a l (after Evans and Tromasdorff, 1970). low C02 contents - to about 0.5 mole percent C 0 2 at Pfiuid = 2 kb and 400°C (Johannes, 1969)* At higher C02 contents of the fluid phase, the breakdown of olivine occurs by the reaction (fig. 20) i Forsterite + water + carbon dioxide — s » serpentine + magnesite 2 Mg2S10* + 2 H20 + C0a —*- Mg 3Si 20 7»2H 20 + MgC03 In the Pioneer Ultramafite, the absence of magnesite from the serpentinites and sporadic occurrence of brucite indicate that the serpentinizing fluid had a very low C02 content. This, of course, assumes that the system was essentially closed except for the addition of necessary water. The formation of serpentinite has been attributed to two different situations i a closed-system, and a constant-volume, open-system. The closed system model (Hostetler e£ a l , 1966) involves addition of water only, with-out loss of components from the serpentinizing rock. For an average harz-burgite (75 percent olivine, 25 percent orthopyroxene) this would result in a volume expansion of about 45 percent, the final serpentinite containing about 10 percent brucitej a dunite would alter to serpentinite containing over 22 percent brucite (Fig. 2 in Hostetler et a l , 1966). The constant-volume open-system model (Thayer, 1966) involves the removal of large amounts of MgO and Si0 2 in solution, the serpentinization reaction being (Turner and Verhoogen, I960) t Forsterite + water — s e r p e n t i n e + solution 5 Mg2Si04 + 4 H 2 0 — 2 Mg3Si207-2H20 + 4 MgO + SiO a (704g.219cc) (552g. 220cc) Removal of reaction products would result in a shift of the equilibrium to higher temperatures. Serpentinization of the Pioneer Ultramafite probably occurred by a process somewhere between these two vend-member' models, since the amount of brucite is too small to justify the closed-system model, but evidence of 110 expansion during serpentinization (P. 102 ) suggests that volume was not perfectly constant. Enstatite i Textural evidence suggests that enstatite (opx) is stable (or metastable) to lower temperatures than olivine, since serpentinites commonly contain unaltered or partially altered orthopyroxene but no olivine and orthopyroxenite is the least altered rock type in the ultramafite. Textural evidence further suggests that orthopyroxene alters directly to serpentine + magnetite. Figure 21 indicates that enstatite is not stable below about 700°C at 2 kb, but breaks down to form anthophyllite and forsterite. Because no evidence of these intermediate products is found, enstatite probably remains in the system, ma ta stably s until a temperature below the upper stability limit of serpentine is reached. Reaction of enstatite + water directly to serpentine either generates excess sil i c a which must be removed in solution, or by introduction of excess MgO, perhaps as a product of the serpentinization of olivine, forms serpentine by the reaction t Enstatite + water + Mg°aq. ~ ~ s e r p e n t i n e 2 MgSi03 + 2 H20 + MgO — * Mg3Si207.2H20 Equilibrium P,T conditions of such a reaction would depend on the activity of Mg in the serpentinizing solution. In summary, serpentinization in a closed system at 2 kb i s restricted to temperatures below about 400°C and to water-rich fluid compositions, XC0 2 <0 , °05« Evidence from the Pioneer Ultramafite suggests that a closed system model i s not a good approximation, and therefore temperatures of serpentinization could be greater than 400°C. Talc-carbonate Alteration In the ultramafite, adjacent to the country rock, a narrow zone of talc-carbonate alteration commonly develops. Whether this alteration I l l developed from serpentinite or directly from peridotite i s uncertain, but the preservation of peridotite textures (Plate 44) and lack of serpentinite mesh-texture suggest that peridotite was dir e c t l y altered to talc-carbonate. Within the contact zone, the carbonate mineral i s magnesite. The alteration of forsterite to talc + magnesite i s expressed by the reaction (Fig. 20) i Forsterite + water + carbon dioxide -*- talc + magnesite 4 Mg2SiO, + H20 + 5 C02 — » Mg 3Si 40 1 1'H a0 + 5 MgC03 In a closed system, this reaction occurs between 500 and 600°C (at 2 kb). Such temperatures are inconsistent with the metamorphic grade of the country rocks which indicates a temperature of about 400°C (lowest greenschist facies). Since talc-magnesite alteration formed i n the ultramafite adjacent to these rocks, an upper l i m i t of about 400°C would seem appropriate for the alteration temperature. This implies a non-equilibrium, open-system reaction involving the addition of CO 2-bearing fluids to the peridotite along the contact with the country rock. Alteration of orthopyroxene produces t a l c , but no magnesite (Plate 44) apparently by a reaction l i k e t Enstatite + water — t a l c + excess magnesia 4 MgSi03 + H20 Mg 3Si 40 i t 8H 20 + MgO The slight excess of MgO apparently goes to form chlorite, which i s generally more abundant i n the pyroxene pseudomorphs than i n the matrix. This distribution of chlorite reflects greater A1203 concentrations i n the orthopyroxene relative to olivine (Appendix I ) . The source of C02 and H20 for these reactions i s presumably the surrounding country rocks, which contain limestones. Migration of H20 and C02 into the ultramafite would result i n a CC a gradient which would explain the transition from talc-carbonate at the contact (Xco .> 0.005) to serpentinite ( X c 0 2 <• 0.005) • Veins of talc-magnesite i n serpentinite (Plate 41) 112 r e p r e s e n t a l o c a l i n c r e a s e i n Xpn a l o n g f r a c t u r e s , r e s u l t i n g i n (Johannes, 1969J F i g . 20) t S e r p e n t i n e + carbon d i o x i d e — » • t a l c + magnesite + wate r 2 M g 3 S i 2 0 7 * 2 H 2 0 + 3 C 0 2 — ^ Mg 3 S i 4 0 1 1 » H a 0 + 3 MgC0 3 + 3 H 2 0 Zones o f i n t e r m i x e d s e r p e n t i n e and t a l c ( P l a t e 4 2 ) , w i t h o u t carbonate o r q u a r t z , suggest t h a t r e a c t a n t s o r p r o d u c t s have m i g r a t e d i n s o l u t i o n , s i n c e the p r e c e d i n g r e a c t i o n generates excess MgO, and the a l t e r n a t e p o s s i b i l i t y ( Johannes, 1969) 1 S e r p e n t i n e + q u a r t z — * T a l c + w a t e r r e q u i r e s the i n t r o d u c t i o n o f S i 0 2 i n s o l u t i o n . Because average p e r i d o t i t e c o n t a i n s 3*5 p e r c e n t CaO, and average s e r p e n t i n i t e c o n t a i n s o n l y about 0 . 0 8 p e r c e n t (Coleman, 1967), l a r g e q u a n t i t i e s o f CaO are l i b e r a t e d f rom u l t r a m a f i c r o c k s d u r i n g s e r p e n t i n i z a t i o n . A l o n g the c o n t a c t z o n e , much o f the e x c e s s CaO r e a c t s w i t h t e c t o n i c i n c l u s i o n s t o form r o d i n g i t e . A l o n g f a u l t zones w i t h i n the u l t r a m a f i t e , these i n c l u s i o n s are g e n e r a l l y absent and excess CaO goes i n t o d o l o m i t e , and i n one l o c a l i t y , c a l c i t e . The assemblages s e r p e n t i n e - d o l o m i t e , s e r p e n t i n e -c a l c i t e , and t a l c - m a g n e s i t e - d o l o m i t e ( P . 75) a l o n g f a u l t zones may r e s u l t f rom i n c r e a s e d a c t i v i t y o f CaO r e l a t i v e t o t h a t o f the c o n t a c t z o n e s . T h i s i n c r e a s e can be a t t r i b u t e d t o s e v e r a l causes 1 1) a s m a l l e r volume o f f l u i d a l o n g f a u l t s , and s lower f l o w r a t e s , r e s u l t i n g i n h i g h e r c o n c e n t r a t i o n o f r e a c t i o n p r o d u c t s , l i k e CaO, i n s o l u t i o n ? 2) a l a c k o f s u i t a b l e t e c t o n i o i n c l u s i o n s t o a l t e r t o r o d i n g i t e t h e r e b y d e p l e t i n g CaO i n s o l u t i o n j and 3) l o w a c t i v i t y o f S i 0 2 i n s o l u t i o n , t h u s p r e v e n t i n g the f o r m a t i o n o f t r e m o l i t e . A l l o c c u r r e n c e s o f t r e m o l i t e ( n e p h r i t e jade) a s s o c i a t e d w i t h the u l t r a m a f i t e o c c u r w i t h i n a few metres o f , and commonly d i r e c t l y o n , the c o n t a c t o f u l t r a m a f i c and c o u n t r y r o c k s . T h i s d i s t r i b u t i o n can be e x p l a i n e d by reference to Fig, 19a, The original ultramafic rock, plotting within the shaded area of the diagram, requires addition of Si0 2 to produce a raonomineralic tremolite rock. The source of this Si0 2 would be cherts and other siliceous sediments of the country rocks. Because the texture of the tremolite rock is unlike that of the serpentinite, talc-carbonate, or primary peridotite, the original rock type is uncertain. Possibly, some tremolite formed from siliceous country rock by addition of CaO and MgO derived from the ultramafite. Not knowing the reactants involved in the production of tremolite, i t is not possible to determine the conditions under which the process occurred. > Rodingite Rodingites or 'reaction zones' (Coleman, 196?) are developed in dikes and tectonic inclusions enclosed in serpentine. The diversity of Initial rock types and of final rodingite assemblages makes a generalized discussion of alteration processes impractical. Minerals which characterize rodingites include diopside, grossularite/ hydrogrossular, zoisite/clinozoisite, idocrase, chlorite. Less altered cores of several rodingite pods indicate that these minerals form from rocks which originally contained quartz, plagioclase, diopside, potassic feldspar, and amphiboles. Occasionally, reaction relations can be recognized from textural evidence. Replacement of albite phenocrysts by zoisite was noted in one locality (Plates 55, 56)» a possible reaction beingt Albite + CaOa(1 + water — - zoisite + Na20a(1 + Si0 2 aq 6 NaAlSi308 . + 4- CaO + H20 —>• 2 ^ Ca^l^S^O^OH + 3 Na20 + 12 Si0 2 assuming Al Is fixed. In a second locality, grossularite replaces plagioclase ^ n « ? o ) * n a coarse-grained gabbro. An approximate reaction for this process Ilk 1st Plagioclase (An^n) + CaOa^ —>• Grossularite + Na20aq + Si0 2 a < 1 2 NaALSi^Og.CaAlgS^Os + 7 CaO —*- 3 Ca-jAlgSi-jO^ + Na20 + Si0 2 again, assvuning Al is fixed. In "both examples, the formation of rodingite occurs by addition of CaO and Water from the surrounding serpentinite, and loss of Na20,SiOz in solution, to the serpentinite. As previously noted, the source of CaO is probably serpentinising peridotite. This implies that serpentinization and rodingite formation are at least in part contemporaneous. Coleman (196?), in a detailed study of rodingites, concluded that alter-ation is produced by a loss of s i l i c a and enrichment of calcium and magnesium. The P, T conditions during metasomatism were estimated, from the stability relations of rodigite minerals, to be greater than k kb and 250 to 500°C. A few localities contain the assemblage quartz-magnesite in association with talc-magnesite and serpentinite alteration. This assemblage results from the reaction (Fig. 2 l ) » Carbon Dioxide + Talc —>- Quartz + Magnesite + Water 3 C02 + Kg3Sii^Oi 1.H2O—>- k SiC^ + 3 MgC03 + H20 This reaction occurs under a wide range of conditions, from 300 C (at 2 kb) in H 20-rich fluids to almost 600°C in C0 z-rich fluids. The origin of these few occurrences may result from a decrease in temperature at fixed pressure and fluid composition or a local increase in X T J O 2 of the fluid, at fixed P and T, or a combination of both. Since the alteration zone and surrounding rock are likely to be at the same temperature, a change in Xrjo2 * s "the most likely cause. Two possible occurrences of contact metamorphism are recognized within the ultramafite, where late intrusive plugs have caused a localized increase in temperature. An andesite plug near the western margin of the ultramafite contains numerous inclusions of chert, peridotite, and fine-grained, granular 115 olivine. These olivine inclusions may result from regeneration of olivine from serpentinite inclusions by (Fig. 20)t Serpentine + Brucite — 2 Forsterite + 3 H20 (A) 5 Serpentine — * - 1 Talc + 6 Forsterite + 9 H20 (B) Reaction A requires brucite, which is not common in the serpentinites, and reaction B results in production of talc which is absent from these inclusions. Neither reaction adequately explains the observed mineral assemblages. A second occurrence of prograde metamorphism occurs in the contact aureole of the gabbro plug on peak 1. The assemblage serpentinized olivine-tremolite may result from (Fig, 22)« Serpentine + Diopside *- Tremolite + Forsterite + Water 5 Mg3Si205.2H20 + 2 CatfgSi205 —»- Ca 2Mg 5Si 80 2 2(0H) 2 + 6 Mg^iO^ + 9 H20 which occurs at about 400°C, at 2 kb (Evans and Trommsdorff, 1970). Alternately CaO could be supplied in solution from the intrusion, s6 that the reaction would be approximately i Serpentine + CaOaq —*• Tremolite + MgOa<1 + Water 4 Mg3Si205.2H20 + 2 CaO —*- Ca2Mg5Si8022(0H)2 + 7 MgO + 7 H20 with excess MgO being removed in solution. It is not possible to t e l l from textural evidence whether olivine is regenerated or not, so that the validity of the f i r s t reaction is uncertain. In summary, alteration assemblages within the ultramafite apparently formed by metasomatic (open-system) disequilibrium reactions. Equilibrium reactions shown in Figure 20 and 21 can be used omly as a guide and do not give accurate temperature estimates. Due to metastability, the sequence of reactions predicted by these diagrams apparently did not occurj phases such as enstatite remained in the system to temperatures well below their predicted lower stability limits. Many of the alteration reactions may have occurred by prograde metamorphism and metasomatism under lower greenschist facies 116 c o n d i t i o n s (about 400 *C. The l a c k o f a metamorphic a u r e o l e i n count ry r o c k s around the u l t r a m a f i t e I n d i c a t e s t h a t the u l t r a m a f i t e was emplaced a s a c o o l ( < 4 O 0 ° C ) mass. METAMORPHISM OF COUNTRY ROCKS The most d i a g n o s t i c m i n e r a l assemblage i s found i n the P i o n e e r g r e e n s t o n e s , which c o n t a i n t r e m o l i t e - a c t i n o l i t e , a l b i t e , c l i n o z o i s i t e , sphene, c h l o r i t e , c a l c i t e , q u a r t z , and p o s s i b l y p u m p e l l y l t e ( ? ) . T h i s assemblage i s c o n s i s t e n t w i t h the q u a r t z - a l b i t e - m u s c o v i t e - c h l o r i t e s u b f a c i e s o f the g r e e n s c h i s t f a c i e s o f B a r r o v i a n - t y p e metamorphism ( W i n k l e r , 1967, P . 95). The occur rence o f p u m p e l l y l t e i n t h i s assemblage i s i n d i c a t i v e of metamorphic c o n d i t i o n s t r a n s -i t i o n a l between the p r e h n i t e - p u m p e l l y i t e ( s u b - g r e e n s c h i s t ) zone and lowest g r e e n s c h i s t f a c i e s ( Tu rner , 1968, P.33). Gabbros and d i o r i t e s o f the B r a l o r n e I n t r u s i o n s c o n t a i n the assemblage a l b i t e - z o i s i t e - q u a r t z - c a l c i t e - c h l o r i t e - s p h e n e ( e x c l u d i n g r e l i c t phases) which i s a l s o c o n s i s t e n t w i t h l o w e s t g r e e n s c h i s t f a c i e s . The p e l i t i c sed iments c o n t -a i n q u a r t z , m u s c o v i t e , c h l o r i t e , a l b i t e , c l i n o z o i s i t e and a d u l a r i a ( i n v e i n s ) The c h l o r i t e s u b f a c i e s o f g r e e n s c h i s t f a c i e s metamorphism o c c u r s a t about 400°C . (Wink le r , 1967 , T u r n e r , 1968). THE OPHIOLITE ASSEMBLAGE The definition and interpretation of "ophiolite has undergone considerable evolution since the term was f i r s t used by Steinroann (1905) in referring to an association of peridotite (serpentinite), gabbro, diabase, spilite and related rocks (Church, 1972). A recently proposed definition ( G.S.A. Penrose Confer-ence on Ophiolites, 1972) 1st A completely developed ophiolite consists of mafic to ultramafic rocks in the following sequence from the bottom and working upj Ultramafic complex consisting of harzburgite, lherzolite and dunite, usually with a metamorphic tectonite fabric. Gabbroic complex ordinarily with cumulus textures and usually less deformed than the ultramafic complex. Mafic sheeted dike complex. Mafic volcanic complex, commonly pillowed. Associated rock typest - ribbon cherts, shale, minor limestones - sodic felsic intrusive and extrusive rocks. Most recent interpretations (Church, 1972 j Coleman, 19711 Dewey and Bird, 1971 ) view ophiolite suites as being transported oceanic crust and mantle, based on the following considerations, as summarized by Williams and Smyth, (1973) « 1. Similarities in gross physical characteristics of ophiolite suites with geophysical models of oceanic crust and mantle (LePichon, 19&9). 2. Transported on-land ophiolite is rooted in oceanic lithosphere at Papua, New Guinea (Davies and Smith, 1971). 3. Strong lithologic similarities between ophiolites and rocks of MacQuarie Ridge (Varne and Rubenach, 1972), 118 4 . Lithe-logical and chemical similarities of oceanic tholeiites and pillow lavas of ophiollte suites (Aumento et a l , 1 9 7 1 ) . 5. Models relating sea floor spreading to the formation of sheeted dike com plexes (Williams and Malpas, 1972 ) . 6. High pressure mineralogy of peridotites requiring mantle depths for conditions of crystallization (Medaris, 1972 ) . 7. Common occurrence of metamorphic tectonites in ophiolite peridotites, displaying textures like those experimentally reproduced under conditions representative of the mantle (Nicolas, 1969 ) . 8. Similar metamorphic mineral assemblages in oceanic rocks at mid-ocean ridges compared with those of ophiolites (Williams and Malpas, 1972 | Aumento, 1 9 7 2 ) . According to current Plate Tectonic theory (eg Coleman, 1971) fragments of oceanic crust and upper mantle are emplaced along continental edges by a process of obduction, whereby oceanic lithosphere is overthrust onto the continental margin. Comparison to Pioneer Area t Rocks of the Pioneer Area show a number of striking similarities to typical ophiolite : 1, Pioneer Ultramafite consists of harzburgite, pyroxenite and dunite, and has a tectonite fabric, 2, Bralorne Intrusions are a gabbroic complex showing cumulus textures and less deformation than the Pioneer body. Sodic Felsic intrusive rocks are also present, such as the 'soda granite* of the Pioneer Mine area, 3, Country rocks consist of pillowed volcanies, ribbon cherts, argillites and limestones. Sheeted dikes have not been observed, but the gabbro-greenstone complex may be a tectonized dike complex 119 Because of lithologic similarities, the Pioneer Ultramafite and associated rocks are Interpreted as a partial, dismembered ophiolite. GEOLOGICAL HISTORY Based on the interpretation of ophiolite as being tectonically transported oceanic crust and mantle, a geological history of the area can be inferredt Some time before the Middle Triassic, the ultramafic rocks and gabbros were differentiated at an ocean ridge, and during the Middle and Upper Triassic migrated toward the North American continent. During this time, the tectonite fabric and other pre-emplacement structures were developed in the ultramafite, and the Fergusson Group and Noel, Pioneer, and Hurley Formations accumulated in an oceanic environment. In the Late Triassic, a subduction zone developed along the present Fraser-Yalakom Fault zone (Monger et a l , 1972) and the oceanic crust fragment composed of Pioneer Ultramafite, Bralorne Intrusions and overlying sediments and volcanics were emplaced along the continental edge. The resulting compression produced folding and faulting which dismembered the ophiolite suite. A possible sequence of events (model 1 - p. 95 ) is an i n i t i a l phase of folding about horizontal NW-SE axes, followed by folding and associated transcurrent faulting in a NW-SE direction. Monger et a l (1972) proposed a -period of dextral strike-slip motion on the Fraser-Yalakom Fault during the Jurassic, Possibly, similar motion occurred in the Cadwallader Creek area,. . along a fault zone parallel to the Yalakom, The precise timing and mechanism of ultramafite emplacement are uncertain. Possibly the ultramafite was obducted over the folded sediments in a large mass including the Shulaps and Copp Creek bodies, then broken up by the period of strike-slip motion into smaller blocks which were emplaced into the sedimentary rocks along S_i • The emplacement of the Pioneer body probably occurred late in the development of S_i in the sediments, since minor structures in both sediments and serpentinite show common orientation. 120 Serpentinization and rodingite formation were, at le a s t i n part, post-tect o n i c , since undeformed dikes of rodingite cross the serpentinite zone. The r e l a t i o n of t h i s a l t e r a t i o n to regional metamorphism i s uncertain. The lower greenschist metamorphism may have occurred before empacement of the ultramafite, possibly on the ocean f l o o r (Aumento, 1972), or during emplacement, but probably not a f t e r , since there i s no evidence of a l a t e r deformation which could have produced the preferred orientation of c h l o r i t e and muscovite which i s observed. A f t e r emplacement, the ultramafite was intruded by several ages of igneous rocks. The gabbroic plugs and s i l l s may be r e l a t e d to the Intrusion of the Coast Plutonic Complex i n the Cretaceous(?), The por p h y r i t i c and amygdaloidal andesites are probably r e l a t e d to Tertiary volcanism. BIBLIOGRAPHY 121 Anastasiou, P. and Selfert, F., 1972. Solid solubility of A1 20 3 in enstatite at high temperatures and 1-5 Kb water pressure: Contr. Mineral, and Petrol., v. 34, p. 272-287. Aumento, F., 1969. Serpentine mineralogy of ultrabasic intrusions in Canada and on the Mid-Atlantic Ridget G.S.C. Paper 69-53* 51 p. 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Primary Minerals O l i v i n e s , orthopyroxenes and clinopyroxenes were analysed from the following samples: Sample 3 0 0 - Dunite from a large, i r r e g u l a r pod ( 2 0 m x 40 m) surrounded by harzburgite (Plate 2 9 ) . Sample 3 2 3 - Dunite from a 20 cm-thick s i l l , with chromite concentrated i n centre. Sample 3 5 ^ - Orthopyroxenite from a 1 5 cm-thick layer i n harzburgite (Plate 2 3 ) . Sample 2 8 5 - Harzburgite from a well-layered section of p e r i d o t i t e . Sample 3 5 ° - Harzburgite from a 2 cm-thick layer between orthopyroxenite lay e r s • Sample 3 0 6 - Harzburgite - r e l a t i v e l y unaltered core of per i d o t i t e surrounded by fractures along which talc-carbonate-serpentine a l t e r a t i o n has developed (Plate 7 2 ) . To avoid sample damage and overcome inhomogeneity within grains, each analysis represents an average of a number of analyses from d i f f e r e n t areas i n a single grain. Inhomogeneity among grains was examined by analyses of a number of grains of each phase i n each sample. Inhomogeneity among samples was examined by comparing averaged analyses f o r each sample. Standards were selected from synthetic and natural materials supplied by 127 Dr B W Evans o f the U n i v e r s i t y o f Washington. To av o i d l a r g e d r i f t c o r r e c t i o n s , samples and standards were analysed a l t e r n a t e l y f o r Fe, Mg, Ca, S i and A l . In a l l analyses Fe x-ras computed as FeO. A l l readings were c o r r e c t e d f o r d r i f t , dead time, and background, and analyses were computed usi n g the EMPADR computer program ( a f t e r Rucklidge and G a s p a r r i n i , 1969, w i t h s u b s t a n t i a l m o d i f i c a t i o n by G. A. MacICay, U n i v e r s i t y o f Oregon, and I . S. McCallum, U n i v e r s i t y o f Washington). Whenever p o s s i b l e , samples were compared ag a i n s t standards o f the same mineral phase, except f o r Ca, f o r which a. d i o p s i d e g l a s s was used, and A l , f o r which a s y n t h e t i c aluminous e n s t a t i t e was used f o r a n a l y s i s o f a l l phases. In a d d i t i o n to the f i v e elements analysed, c e r t a i n other elements may be present. O l i v i n e s may c o n t a i n as much as 0.4 percent NiO and MnC (Troxmnsdorff and Evans, 1972); orthopyroxenes commonly c o n t a i n T i 0 2 , C r 2 0 3 , KnO and NiO, and clinopyroxenes commonly c o n t a i n s i g n i f i c a n t Na 20, i n a d d i t i o n to T i 0 2 , C r 2 0 3 , MnO and NiO (Deer, Howie and Zussman, 1963). For t h i s reason, l o w . p a r t i a l t o t a l s , . p a r t i c u l a r l y i n clinopj^roxenes may be acceptable. Secondary M i n e r a l s Analyses o f serpentine and t a l c from the a l t e r a t i o n zone i n sample 306 gave unacceptably low t o t a l s around 97 percent f o r t a l c . The low t o t a l s are due to extremely small g r a i n size, poor c o n d u c t i v i t y and p o s s i b l y e l e c t r o n beam damage. Serpentine analyses gave acceptable t o t a l s , f o r p a r t i a l a n a l y s e s , when e m p i r i c a l r a t h e r than i d e a l water was added to the anhydrous oxide t o t a l s (Deer, Howie and Zussman, 1963). A n a l y t i c a l c o n d i t i o n s were t h e same as above. Due to a l a c k o f s u i t a b l e serpentine standards, the o l i v i n e and pyroxene standards were used.. Dead time, d r i f t and background c o r r e c t i o n s were made using the UvPROBE program which f i t s a polynomial curve, by l e a s t squares, t o the standard p o i n t s , then reads o f f p r e l i m i n a r y c o n c e n t r a t i o n s o f the unknowns from t h i s working curve. 128 The 3AEDR program, based on the correction procedure of Bence and Albee (1968) was then used to make fluorescence, absorption, and atomic number corrections, allowing for water. O l i v i n e Analyses from Sample 300 01 300-1 01 300-2 01 300-3 01 300-4 01 300-5 01 300 -6 S i 0 2 41.4 41 .3 41 .7 41 .3 41 .5 41.4 A 1 2 0 3 0 .31 0 .13 0 .35 0.03 0.13 0.43 FeO 7.4 7.4 7 .5 7.4 7 .5 7-5 MgO 51.1 51.2 51.2 51.4 51.1 51.1 CaO 0.07 0.06 0.06 0.06 0.05 0.05 TOTAL 100.2 100.2 100.7 100.2 100.2 100 .5 Number o f Ions on the Basis of 4 Oxygens S i 1.00 1.00 1.00 1.00 1.00 1.00 A l 0.009 0.004 0.010 0.001 0.004 0.12 Mg 1.84 1.85 1.83 1.85 1.84 1.84 Fe 0 .15 0 .15 0.15 0.15 0.15 0.15 Ca 0.002 0.002 0.001 0.002 0.001 0.001 Fo 92 .6 92 .5 92.4 92 .5 92.4 92.4 Fe/Mg 0.080 0.081 • 0.082 0.081 0.082 0.082 Fe/(Fe+Mg) 0.074 0.075 O . O 7 6 0.075 O.O76 O.O76 O l i v i n e Analyses from Sample 300 (contimiecl) 01 300-7 01 300-3 01 300-9 01 300-10 Average Range S i 0 2 41.5 41.1 41.3 41.2 41.4 41.1-41.? A 1 2 0 3 0.45 0.36 0.34 0.09 0.26 0.03-0.45 FeO 7-7 7.5 • 7-4 7.4 7-5 7.3-7.7 MgO 51.2 51.4 51.3 51.3 51.2 51.1-51.4 CaO 0.08 0.05 0.07 0.08 0.06 0.05-0.08 TOTAL 100.9 100.4 100.4 100.1 100.4 100.1-100.9 Number o f Ions on the Basis of 4 Oxygens S i 1.00 0.99 1.00 1.00 1.00 0.99-1.00 A l 0.01.3 0.010 0.010 0.003 0.008 0.001-0.013 Mg 1.83 1.85 1.85 I.85 1.84 1.83-1.85 Fe 0.16 0.15 0.15 0.15 0.15 0.15-0.16 Ca 0.002 0.001 0.002 0.002 0.002 0.001-0.002 Fo 92.2 92.4 92.5 92.5 92.5 92.2-92.6 Fe/Mg 0.084 0.082 •0.081 0.081 0.082 0.080-0.084 Fe/(Fe+Mg) 0.078 0.076 .0.075 0.075 0.076 0.074-0.078 O O l i v i n e Analyses from Sample 323 01 323-1 01 323-2 01 323-3 01 323-4 01.323-1 01 323-6 S i 0 2 40.8 40.9 40.9 41.0 41.0 40.7 A 1 2 0 3 0.32 0.22 0.53 0.58 0.40 0.49 FeO 9.6 9.4 9.6 9.6 9.6 9.6 MgO ' 49.5 49.5 49-5 49.4 49.4 49.4 CaO 0.25 0.15 0.19 0.20 0.19 0.20 TOTAL 100.4 100.2 100.8 100.8 100.6 100.3 Number o f Ions on the Basis o f 4 Oxygens S i 0.99 1.00 0.99 1.00 1.00 0.99 A l 0.009 0.007 0.015 0.017 c o n 0.014 Mg 1.80 1.80 1 .79 1.79 1.79 1.80 Fe 0.20 0.19 0.20 0.20 0.20 0.20 Ca 0.006 . 0.004 0.005 0.005 0.005 0.005 Fo 90.2 90.3 90.2 90.2 90.1 90.2 Fe/Mg 0.108 0.107 • 0.109 0.109 0.110 0.109 Fe/(Fe+Mg) ; 0.098 0.097 0.098 0.099 0.099 0.098 O l i v i n e A n a l y s e s from Sample 323 (cont inued) 01 323-7 01 323-8 01 323-9 . 01 323-10 Ave ra sre Ran?e S i 0 2 4 0 . 9 40 .6 40.7 40 .6 40.8 4 0 . 6 - 4 1 . 0 A 1 2 0 3 0 .25 0 . 3 9 0 . 4 8 0 . 2 4 0.39 0.22-0.58 FeO' 9.6 9.6 9.5 9.6 9.6 9.4-9.6 MgO 49.5 49.4 49.4 49.2 49.4 49.2-49 .5 CaO 0.19 0 . 2 2 . 0 ..22 0 . 2 2 0.20 0 .15 -0 .25 TOTAL 100.4 100.2 100.3 99.8 100.4 99 .8-100.8 Number o f Ions on the B a s i s o f 4 Oxygens S i 1 .00 0 .99 0 .99 1.00 1.00 0.99-1.00 A l 0.C07 0.011 0 . 0 1 4 0.007 0.011 O.OO7-O.OI.7 Mg 1.80 1 .80 1.80 1.80 1.79 1 . 7 9 - 1 . 8 0 Fe 0.20 0.20 0 . 1 9 0.20 0.20 0.19-0.20 Ca 0 .005 0.006 0.006 0.006 0.005 0.004-0 .006 Fo 90 .2 9 0 . 2 90.3 9 0 . 1 90 .2 90.1-90.3 Fe/Mg 0.109 0.109 0 . 1 0 8 ' 0.110 0.109 0.107-0.110 Fe/(Fe+Mg) 0.098 0 . 0 9 8 Q.097 0.099 0.098 0 .097-0 .099 O l i v i n e A n a l y s e s from Sample 35$ 01 358-2 01 358-4 01 358-5 01 353-6 Average Range S i 0 2 40.3 40.6 40.7 40.7 40.6 40.3-40.7 A 1 2 0 3 0.63 0.3? 0.31 0.66 0.49 0.31-0.66 FeO 8.3 8.5 8.6 8.4 8.4 8.3-8.6 MgO 49.4 49.7 49.9 50.1 49.8 49.4-50.1 CaO 0.03 0.01 0.04 0.05 0.03 0.01-0.05 TOTAL 98.6 99.2 99.5 100.0 ' 99.3 98.6-100.0 Number o f Ions on t h e B a s i s o f 4 Oxygens S i 0.99 1.00 1.00 0.99 1.00 0.99-1.00 A l 0.018 0.011 0.009 0.019 0.014 0.009-0.019 Mg 1.81 1.82 1.82 1.82 1.82 1.81-1.82 Fe 0.17 0.17 0.18 0.17 0.17 0.17-0.18 Ca 0.001 0.000 0.001 0.001 0.001 0.000-0.001 Fo 91.4 91.3 91.2 91.4 91.3 91.2-91.4 Fe/Mg 0.094 0.096 0.096 ' 0.094. 0.095 0.094-0.096 Fe/(Fe+Mg) 0.086 0.087 0.088 0.086 O.O87 0.086-0.088 Orthopyroxene Analyses from Sample 358 Opx Opx Oox Opx Ofx Onx Opx Opx Average Range, 3 5 8 - 1 3 5 8 - 2 358-4 358-5 358-6 358-7 358-9 358-10 Si0 2 5 5 . 6 55-4 5 5 . 4 5 5 . 7 5 5 . 9 5 6 . 2 55-9 55-7 55-7 ' 5 5 . 4 - 5 6 . 2 Al aO, 3 . 1 3 . 2 3 . 3 2 . 3 2 . 4 2 . 9 2 . 4 2 . 4 2 .8 2 . 3 - 3 - 3 FeO 5-6 5-7 5-7 5 . 9 5 . 7 5-7 6 . 0 5 . 8 5 .8 5 . 6 - 6 . 0 MgO 3 3 . 8 3 3 . 8 3 4 . 0 3 4 . 4 3 4 . 1 3 4 . 1 3 4 . 2 3 4 . 4 3 4 . 1 3 3 . 8 - 3 4 . 4 CaO 0 .88 0.64 0 . 4 5 0 . 5 7 O.63 0.46 0 . 6 8 O.57 0 . 6 1 0 . 4 5 - 0 . 8 8 TOTAL 9 8 . 9 9 8 . 8 9 8 . 8 9 8 . 8 9 8 . 7 9 9 . 4 9 9 . 2 9 8 . 9 9 8 . 9 9 3 . 7 - 9 9 . 4 Number of Ions on the Basis of 6 Oxygens Si 1 . 9 3 1 . 9 3 1 . 9 3 1 . 9 4 1 . 9 5 1 . 9 4 1 . 9 4 1 . 9 4 1.94 1 . 9 3 - 1 . 9 5 Al™ 0 . 0 7 0 . 0 7 0 . 0 7 0 . 0 6 0 . 0 5 0 . 0 6 0 . 0 6 • 0 . 0 6 0 . 0 6 0 . 0 5 - 0 . 0 7 E 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 ' 2 . 0 0 2 . 0 0 2 . 0 0 2.00 2 . 0 0 Mg 1 . 7 5 1 .76 1 .76 1 .78 1 .77 1 .76 1 .77 1 .78 1.77 1 . 7 5 - 1 . 7 8 Fe 0 . 1 6 0.17 0 . 1 7 0 . 1 7 0.17 0 . 1 7 0 . 1 7 0 . 1 7 0.17 0 . 1 6 - 0 . 1 7 Ca 0 .03 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 . 0 2 0 .02 0 . 0 2 - 0 . 0 3 A l " 0 .06 0 . 0 6 0 . 0 6 0.04 0 . 0 5 0 . 0 6 0.04 0.04 0 . 0 5 0.04-0.06 2 . 0 0 2 . 0 1 2 . 0 1 2 . 0 1 2 . 0 0 2 . 0 0 2 . 0 1 . 2 . 0 1 2.01 2 . 0 0 - 2 . 0 1 En 90.0 9 0 . 2 9 0 . 6 9 0 . 2 9 0 , 4 9 0 . 6 89,-9 9 0 . 4 9 0 . 3 8 9 . 9 - 9 0 . 6 Wo 1 . 7 1 . 2 0 .9 1 .1 1 .2 0 . 9 1 .3 1.1 1.2 0 . 9 - 1 . 7 Fs 8 .3 8.6 8 .5 8 .7 8 . 4 - 8 . 5 8 . 8 8 . 5 8 . 6 8 . 3 - 8 . 8 Fe/Mg 0 .093 0 . 0 9 5 0 . 0 9 4 ' . 0 . 0 9 6 0.093 0 . 0 9 4 0 . 0 9 8 0 . 0 9 4 0 . 0 9 5 0 . 0 9 3 - 0 . 0 9 3 Fe/(Fe+Mg) 0.085 0.087 0.086 0.088 0 . 0 8 5 0.086 0 . 0 8 9 0.086 . 0 . 0 8 7 0 . 0 8 5 - 0 . 0 8 9 Olivine Analyses from Sample 285 01 01 01 01 Ol 01 01 Average Ra n ge 285-1 O O cT ^ 285-4 285-5 285-6 285-7 285-8 S i 0 2 41.2 40.9 '40.9 41.4 41.3 41.1 41.0 41.2 41.1 '40.9-41.4 A1203 0.14 0.08 0.31 0.44 0.26 0.21 0.33 0.22 0.25 0.08-0.44 FeO 9.3 9.2 9.2 9.2 9.1 9.5 9.2 9-0 9.2 9.0-9.5 MgO 49.8 49.5 49.5 49.6 50.0 49.4 49.5 49.8 49.6 49.4-50.0 CaO 0.04 0.03 0.05 0.03 0.04 0.05 0.05 0.04 0.04 0.03-0.05 TOTAL 100.4 99.8 100.0 100.6 100.7 100.2 100.1 100.2 100.3 99.8-100.7 Number of Ions on the Basis of 4 Oxygens Si 1.00 1.00 1.00 1.00 1.00 1.00 1.00 .1.00 1.00 1.00 Al 0.004 0.002 0.009 0.012 0.008 0.006 0.010 0.006 0.007 0.002-0.012 Mg 1.80 1.81 1.80 1.79 1.80 1.80 1.80 1.81 1.80 1.79-1.31 Fe 0.19 0.19 0.19 • 0.19 0.19 0.19 0.19 0.18 0.19 0.18-0.19 Ca 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Fo . 90.6 90.6 90.5 90.5 90.7 ' 90.3 90.6 90.8 90.6 90.3-90.8 Fe/Mg 0.104 0.104 0.105 0.105 0.102 0.107 0.104 0.101 0.104 0.101-0.107 Fe/(Fe+Mg) 0.095 0.095 0.095 0.095 0.093 0.097 0.095 - 0.092 0.094 0.092-0.097 O l i v i n e Analyses from Sample 356 01 356-1 01 356-2 01 356-3 01 356 -4 01 356 -5 Ave ra ge Range S i0 2 41.7 41.4 41.3 41.4 41.7 41.7 41.3-41.7 A1 2 0 3 0.28 0.66 0.31 0.00 0.28 0.31 0.00-0.66 FeO 8.8 8.8 8.8 8.8 8.6 8.7 8.6-8.8 MgO 49.8. 50.0 50.3 50.3 50.2 50.1 49.8-50.3 CaO 0.05 0.03 0.02 0.05 0.04 0.04 0.02-0.05 TOTAL 100.7 100.9 100.6 100.5 100.8 100.7 100.5-100.9 Number o f Ions on the Basis of 4 Oxygens S i 1.01 1.00 1.00 1.00 1.01 1.00 1.00-1,01 Al 0.008 0.019 0.009 0.000 0.008 0.009 0,000-0.019 M0, 1.79 1.80 1.81 1.82 1.81 1.81 1.79-1.82 Fe 0.18 0.18 0.18 0.18 0.17 0.18 0.17-0.18 Ca 0.001 OoOOl 0.001 0.001 0.001 0.001 0.001. Fo 91.0 91.0 91.1 91.1 91.3 91.1 91.0-91.3 Fe/Mg 0.099 0.099 0.098 0.098 0.096 0.098 0.096-0.099 Fe/(Fe+Mg) 0.090 0.090 0.089 0.089 0.087 0.089 0.087-0.090 Orthopyroxene Analyses from Sample 356 Opx 356-1 Opx 3 5 6 - 2 Opx 356-3 Opx 356-4 Oox 356-6 Opx 356-7 Opx 356 -a Average Range S i 0 2 5 6 . 7 5 6 . 8 5 6 . 4 57 .1 5 6 . 8 57 .2 5 6 . 9 5 6 . 8 5 6 . 4 - 5 7 . 2 A l a 0 3 2.1 2.1 2 . 0 1.9 2 . 0 2 .1 2 . 2 2 . 1 1 . 9 - 2 . 2 FeO • 5-7 5-7 5 . 9 6 . 1 5-8 5-8 5 . 8 5 . 8 5 - 7 - 6 . 1 MgO 3 4 . 3 3 4 . 5 3 4 . 2 3 4 . 5 3 4 . 4 3 4 . 6 3 4 . 4 3 4 . 4 3 4 . 2 - 3 4 . 6 CaO 1.06 0 . 6 0 0 . 7 7 O.56 0 . 8 7 0 . 5 1 0 . 7 4 0 . 7 3 0 . 5 1 - 1 . 0 6 TOTAL 99.9 9 9 . 7 9 9 . 4 Number 100.1 of Ions on 9 9 . 9 the Basis 100.2 of 6 Oxy: 100.0 gens 9 9 . 9 9 9 . 4 - 1 0 0 . 2 Si 1.95 1.96 1.95 1.96 1.96 1.96 1.96 1.96 1 . 9 5 - 1 . 9 6 A 1 C T 0.046 0.044 0.046 0 . 0 3 8 0.044 0 . 0 3 9 0.043 0.043 0.038-0.046 z 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 Mg 1.76 1.77 1.77 1.77 1.77 1.77 1.76 1.77 1 .76-1 .77 Fe 0 . 1 7 0 . 1 7 0 . 1 7 0 . 1 7 0 . 1 7 0 . 1 7 0 . 1 7 0 . 1 7 0 . 1 7 Ca 0 . 0 3 9 0 . 0 2 2 0 . 0 2 9 • 0 . 0 2 1 0 . 0 3 2 0.019 0 . 0 2 7 0 . 0 2 7 0.019-0.039 A1 V I 0.040 0.042 0 . 0 3 6 0 . 0 3 8 0 . 0 3 6 0.044 0.045 0.040 0.036-0.045 E 2 . 0 0 2 . 0 0 2 . 0 1 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 2 . 0 0 - 2 . 0 1 En • 8 9 . 6 9 0 . 5 8 9 . 9 9 0 . 1 8 9 . 8 9 0 . 5 9 0 . 1 9 0 . 1 8 9 . 6 - 9 0 . 5 Wo 2 . 0 1.1 1.5 1.1 1.6 1.0 1.4 1.4 1 . 0 - 2 . 0 Fs 8 . 4 8 . 4 8 . 7 8 . 9 8 . 5 8 . 6 8 . 5 " 8 . 6 8 . 4 - 8 . 9 Fe/Mg 0.094 0 . 0 9 3 0 . 0 9 7 0 . 0 9 8 0 . 0 9 5 0 . 0 9 5 0 . 0 9 4 0 . 0 9 5 0 . 0 9 3 - 0 . 0 9 8 Fe/(Fe+Mg) 0 . 0 8 6 0 . 0 8 5 0 . 0 8 9 0.090 0 . 0 8 7 0 . 0 8 7 0.086 0 . 0 8 7 0.035-0.090 Olivine Analyses from Sample 30° 01 306-1 01 306-2 01 306-3 01 306-4 01 306-51 01 306-52 S i 0 2 41.4 41.0 41.4 4 1 . 5 41.1 40.9 A1 20 3 0.27 0.22 0-35 0.25 0.00 0.01 FeO 9.1 9.2 9.1 9.0 9.0 9.1 MgO 50.0 49-9 50.0 49.9 50.3 49.3 CaO 0.01 0.01 0.03 0.04 0.04 0.03 TOTAL 100.7 100.4 100.9 100.5 100.5 99.3 Number of Ions on the Basis of 4 Oxygens Si 1.00 1.00 1.00 1.00 1.00 1.00 A l 0.01 0.01 0.01 0.01 0.00 0.00 Mg 1.80 1 . 8 1 1.80 1.80 1.82 1.80 Fe 0.18 0.19 • 0 . 1 8 0.18 0.18 0.19 Ca 0.000 ' 0.000 0.001 0.001 0.001 0.001 Fo 90.7 90.6 90.8 90.9 90.9 90.7 Fe /Mg 0.102 0.103 "0.102 0.101 0.101 0.103 Fe/(Fe+Mg) 0.093 0.094 0.092 0.092 0.091 0.093 O l i v i n e Analyses from Sample 306 (continued) 01 306-53 01 306-44 01 306-45 Average Range S i 0 2 • 4 1 . 1 40.9 41.0 41.2 40.9-41.5 A 1 2 0 3 0.03 0.00 0.00 0.13 0.00-0.35 FeO 9-0 9.1 9.0 9-1 9-0-9.2 MgO 49.9 49.7 48.6 49.7 40.6-50.3 CaO 0.03 0.00 0.02 0.02 0.00-0.04 TOTAL 100.1 99.7 98.6 100.1 98.6-100.9 Number of Ions on the Basis of 4 Oxygens S i 1.00 1.00 1 .01 1.00 1.00-1.01 A l 0.00 0.00 0.00 0.00 0.00-0.01 Mg 1.31 1.81 1.79 1.81 1.79-1.82 Fe 0.13 0.19 0.19 0.18 0.18-0.19 Ca 0.001 0.000 0.001 0.001 0.000-0.001 Fo 90.8 90.7 90.6 90.7- 90.6-90.9 Fe /Mg 0.101 0.102 0.104 0.102 0.101-0.104 Fe/(Fe+Mg) 0 . 0 9 2 0.093 0.094 0.093 0.091-0.094 Orthopyroxene Analyses from Sample 306 Oox 306-1 Opx 306-2 Opx* 306-51 Opx * 306-52 Opx* 306-53 O D X 306-44 Opx 306-45 Average Range Si0 2 56.3 56.3 56.4 56.3 56.4 56.4 55-9 56.3 55-9-56.4 Al aO, 2.4 2.4 2.2 2.2' 2.3 2.5 2.3 2.4 2.2-2.5 FeO 5-8 5-9 5-7 5.8 5.6 5.9 6.0 5.8 5.6-6.0 MgO 34.2 34.2 33.8 33-7 33-4 34.3 34.5 34.0 33.4-34.5 CaO O.65 0 .61 1.0 1.3 \ 2.5 0 .76 O.58 1.1 0.50-1.3 TOTAL 99-4 99-5 99.1 99.3 100.2 99.8 99-3 99-5 99-1-100.2 Number of Ions on the Basis of 6 Oxygens Si 1.95 1.95 1.96 1.95 1.94 1.94 1.94 1.95 1 .94-1 .96 A 1 W O.05 0 . 0 5 0.04 0 .05 0 .06 0 .06 0 .06 0 .05 0.04-0.06 s 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Mg 1.76 1.76 1.75 1.74 1.72 1.76 1.78 1-75 1.72-1.78 Fe 0.17 0.17 0.17 0.17 0.16 0.17 0.18 0 .17 0.16-0.18 Ca 0.02 0.02 0.04 0 .05 0.09 0 .03 0.02 0.04 0.02-0.09 A1 V I 0 . 0 5 0 .05 0 .05 0.04 0.04 0 .05 0 .03 0.04 0 .03-0 .05 z 2.00 2.00 2.00 2.00 2.01 2.01 2.01 2.01 2.00-2.01 En 90.2 90.1 89.6 88.9 87.1 89.9 90.1 89.4 87.1-90.2 Wo 1.2 1.2 2.0 2.4 4.8 1.4 1.1 2.0 1.1-4.8 Fs 8 .5 8.8 8.4 8.7 8.2 8.6 8.9 8.6 8.2-8.9 Fe/Mg 0.094 0 .097 0.094 0 .097 o'.094 0.096 0.098 0.096 0.094-0.098 Fe/(Fe-H4g) 0.086 0.089 0.086 0.089 0.086 0.088 0.090 0.088 0.086-0.090 includes clinopyroxene lamellae (?) Orthopyroxene and Clinopyroxene Analyses from Samples 2 8 5 , 306 and 356 Opx 285-1 Opx 285-2 Opx 285-3 Average Cpx 306-41 Cpx 356-I Cpx 356-2 S i 0 2 56.3 56.2 56.5 56.3 53.2 53.6 5 3 - 9 A1203 3-0 2.9 2.7 2.9 1.9 2.1 2.3 FeO 6.1 5-9 6.1 6.1 2.2 2.1 2.1 MgO 34.0 33-5 33.8 33-8 17.5 17.8 17.7 CaO 0.69 1.1 0.93 0.92 2 3 . 2 23.3 23.1 TOTAL 100.0 99.6 100.1 99.9 98.1 9 8 . 9 99.1 Number of Ions on the Basis of 6 Oxygens Si 1.94 1.94 1.94 1.94 1.96 1.96 1.96 A1 I V 0.06 0.06 0.06 0.06 0.04 0.04 0.04 z 2.00 2.00 2.00 2.00 2.00 2.00 2.00 Mg 1.74 1.73 1.74 l.?4 0.965 0.967 0.963 Fe 0.18 0.17 0.18 0.18 O.O69 0.063 0.064 Ca 0.03 0.04 0.03 0.03 0.916 0.912 0.901 A1 V I 0.06 0.06 0.05 0.06 0.046 0.052 0.060 2.00 2.00 2.00 2.00 2.00 1.99 1.99 En 89.7 89.0 89.2 89.3 ^9.5 4 9 . 8 . 4 9 . 9 Wo 1.3 2.2 1.8 1.8 47.0 47.0 46.7 Fs 9.0 8.9 9.0 9.0 3-5 3.2 3.3 Fe/Mg 0.101 0.100 0.101 0.101 0.071 - O.O65 0.067 Fe/(Fe+Mg) 0.092 0.091 0.092 0.091 0.067 0.061 0.063 Serpentine Analyses from Sample 306 Chrv 306-1 Chry 306-2 L i z 306-1 L i z 306-2 L i z 306-3 L i z 306-4 L i z 306-5 SiO 2 41.0 41.1 41.9 41.9 41.9 42.1 42.5 A 1 2 0 3 0.54 0.58 0 . 3 0 0.46 0.69 0 . 0 7 0.00 FeO 4.7 5.0 5.4 4.9 5.4 5.4 4.6 MgO 37.8 37-1 37.6 38.4 37-3 37.6 38.4 H 20 * 13.8 13.8 13.8 13.3 13.8 13.8 13.8 TOTAL 97.8 97.5 99.0 99-5 99.1 99.0 99.3 Number of Ions on the Basis o f 7 Oxygens S i 2.00 2.02 2.02 2.01 2.02 2.04 2.04 A l 0 . 0 3 0 . 0 3 0.02 0 . 0 3 0.04 0.00 0.00 Mg 2.75 2.71 2.71 2.74 2.68 2.71 2.74 Fe 0.19 0.20 0.22 0.20 0.22 0.22 0.19 Mg/Fe 14.5 13.6 12.3 13.7 1 2 . 3 12.3 14.4 average of re ported analyses i n Deer," Howie and Zussman (1963). ro Serpentine Analyses from Sample 306 (continued) L i z 306-6 . L i z 306-7 L i z 306-8 L i z 306-9 L i z 306-10 Average Range 42.4 42.1 42.7 42.5 42.1 42.2 41.9-42.7 0.89 0.15 0.28 0.10 0.19 0.31 0.00-0.89 4.3 4.1 3.1 3.0 2.8 4.3 2.8-5.4 38.3 38.0 40.0 40.3 40.1 38.6 37.3-40.3 13.8 13.8 13-8 13.8 13.8 13.8 13.8 99.7 98.3 100.0 99.7 98.9 99.3 98.3-100.0 Number o f Ions on the Basis of 7 Oxygens 2.02 2.04 2.02 2.01 2.01 2.02 2.01-2.04 0.05 0.01 0.02 0.01 0.01 0.02 O.OO-O.O5 2.72 2.74 2.82 2.84 2.86 2.76 2.68-2.86 0.17 0.17 0.12 0.12 0.11 0.18 0.11-0.22 16.0 16.1 23.5 23.7 26.0 17.5 12.2-26.0 average o f reported analyses i n Deer, Howie and Zussman (1963) 144 APPENDIX I I The f o l l o w i n g s e c t i o n summarizes the petrography, estimated modes from t h i n s e c t i o n s , and g e o l o g i c a l environment o f samples s e l e c t e d to represent the major rock types i n the area. These are d i v i d e d i n t o f i v e groups: A. Primary u l t r a m a f i c r o c k s , a r b i t r a r i l y d e f i n e d as being l e s s than 50 percent s e r p e n t i n i z e d . The p r e f i x ' s e r p e n t i n i z e d ' i s a r b i t r a r i l y used f o r rocks w i t h 30 to 50 percent s e r p e n t i n e . B. S e r p e n t i n i t e s , a r b i t r a r i l y d e f i n e d as having more than 50 percent s e r p e n t i n e , but no t a l c . S e v e r a l n e p h r i t e (jade) samples, w i t h o n l y minor s e r p e n t i n e , are a l s o i n c l u d e d . C. T a l c - b e a r i n g r o c k s , c o n t a i n i n g s i g n i f i c a n t amounts o f t a l c , - s e r p e n t i n e , - carbonate. D. R o d i n g i t e s , o c c u r r i n g as d i k e s o r pods i n s e r p e n t i n i t e , and c o n t a i n i n g garnet, d i o p s i d e , z o i s i t e / c l i n o z o i s i t e , and/or i d o c r a s e . Garnet c e l l edges were determined by X-ray powder d i f f r a c t i o n and r e f i n e d by l e a s t - s q u a r e s approximation (Evans, Appleman and Handwerker, 196>3) • E. Country r o c k s , i n c l u d i n g greenstone, l i m e s t o n e , c h e r t and a r g i l l i t e . F. I n t r u s i v e r o c k ? , i n c l u d i n g d i k e s , p l u g s , and l a r g e r bodies which have not been r o d i n g i t i z e d . Rock names are taken from T r a v i s (1955) c l a s s i f i c a t i o n . The i d e n t i t y o f many phases was checked by X-ray powder d i f f r a c t i o n , u s i n g the A3TM f i l e f o r standards (Berry, 1974). A l l f e l d s p a r - b e a r i n g rocks were s t a i n e d f o r K - f e l d s p a r u s i n g an HF-sodium c o b a l t i n i t r i t e technique (Reid, 1969). APPENDIX I l a Primary U l t <K Q) 0 CD rH C c - P • r i CD CD <D • r i • P •p c 1 X i X *"C» O • r i +> • r i O O o O JH w • r i > U c u cd h o O •rl - P >> • • H >> is! rH rH u a. H a. • r i x: fn O o O i - l u o CQ CD u H 0) H P p !>> 300 Dunite (85)* 15* t r 323 Dunite (80)* • 15* 1* 360 Dunite (53)* 30* 362 Chromitite (<l) <•! 15* 288 Serot Dunite (45)* 50* 1 3* 343 Serp. Dunite (45)* 49* 5* 285 Harzburgite (70) 15 5 8 2 * i d e n t i t y cheeked by X-ray d i f f r a c t i o n ( ) r e l i c t m i n e r a l t Serp. = s e r p e n t i n i z e d i a f i c Rocks 0) ffl • P 05 -p • r i - P ct) - P -ri c C D e 0 C O ,5 b" Location and Notes ctf •*1 l a r g e (20m x 40m) pod surrounded by h a r z b u r g i t e . 1 (3) from a 20 cm t h i c k s i l l w ith chromite grains i n centre . 1 (15) from a 6 m t h i c k dunite l a y e r i n ha r z b u r g i t e ; p o s s i b l y connected to pod of sample 3 0 0 . 2 (83) i r r e g u l a r c h r o m i t i t e s t r i n g e r i n dunite (sample 36o).See P l a t e 29 1 ( < l ) <1 sheared outcrou o f dunite and h a r z b u r g i t e , between s e r p e n t i n i t e and p e r i d o t i t e zones. 1 (*l) from t r a n s i t i o n zone between s e r p -e n t i n i t e and p e r i d o t i t e , along SW contact o f u l t r a m a f i t e . <-l <•! t y e i c a l l a y e r e d p e r i d o t i t e from centre of u l t r a m a f i c body. A P P E N D I X H a ( c o n t i <D fc rH <D P^,D . <D E g O Cu ci p o !>s (1) Q) © rH C -P •H 0> •H -P c 1 X • X -P O •H o o o p fc > X fc c fc cd •H -p •rH >j N fc rH fn p. rH •H Xi o o O o ( 7 0 ) * 1 5 * 5 * 10* 356a Harzburgite (63) 10 1 25 356b Ortho- (10)* 6 9 * 5 1 5 * p y r o x e n i t e 282 Ortho- ( 2 5 * 6 0 * 5 1 0 * p y r o x e n i t e 1 358 Ortho- io" 8 5 * 5 pyroxenite 160 Serp. (40)* (2) 7 5 0 * Harzburgite 287 Serp. (40 )* 17 ^ * 2 Harzburgite 321 Serp. . (60) (1 ) -38 Harzburgite d) Primary U l t r a m a f i c Rocks 0) 0) HJ Q) -p 0 •rl -P CS -p -P •rl c •rf CD s 0 O C 0 P i h n fn fc crj 0Q O O 1 ( t r ) 1 ( t r ) 1 ( t r ) " 1 * 1 *1 . <1 <1 1 <1 t r 1 (<1) 1 «D Location and Notes near f a u l t zone north of peak 1 ; a l t e r e d along f r a c t u r e s t o t a l c -carbonate-serpentine. P l a t e 7 2 . t y p i c a l layered p e r i d o t i t e w i t h orthopyroxenite s t r i n g e r s : a - from h a r z b u r g i t e m a t r i x b - from 3 cm t h i c k o r t h o -pyroxenite l a y e r from a 5 cm wide co n t o r t e d orthopyroxenite v e i n c u t t i n g dunite.. See P l a t e 6 8 . from a 15 cm t h i c k conformable l a y e r 'of orthopyroxenite i n l a y e r e d p e r i d o t i t e . s e r p e n t i n i z e d p e r i d o t i t e from t y p i c a l l a y e r e d sequence, near f a u l t i n u l t r a m a f i t e . s e r p e n t i n i z e d p e r i d o t i t e , about 30 rn from north c o n t a c t . + 2 'la t r e m o l i t e . About 1 m from contact of b a s i c i n t r u s i o n on peak 1 . £ APPENDIX l i b S e rpenti n i t e s ^ — ^ ^ — ' <D !D CD -P rH CD -P •H •H -p CD -P <D •rl fc -P • r l -P •r! -P Ti O O c 1—i •ri -p - r l fc tX? w •ri o fc CD S a •rH >, > • • V. O C O tS3 -P fc •ri X X <D rH br, fc •ri C rH P.. p.. fc ,C cu ,c tA < o O o O s o 99* 1 (<D -p •rl <D fc r-i r-i CD O ,£> -P ^ <D E g O O p. ci P fc O !>> n 2 a, cc; e-< 158 H a r z b u r g i t e ( ? ) 167 Harzburgite 74 * (15)* (5) (5) 1 ("D 228 U l t r a m a f i c 75* (23)* 1 t r 1 256 Harzburgite 33 66 1 ( t r ) 284 Harzburgite 97 * 2 1 ( < l ) 289 P e r i d o t i t e 98* 2 ( t r ) 295 P e r i d o t i t e 99 * L o c a t i o n and Notes s e r p e n t i n i z e d m a t e r i a l along j o i n t i n massive p e r i d o t i t e . i s o l a t e d occurrence of m a t e r i a l w i t h unusual mottled t e x t u r e . sheared s e r p e n t i n i t e from north s i l l . v e i n o f c r o s s - f i b r e serpentine from s e r p e n t i n i z e d p e r i d o t i t e zone around i n t r u s i o n on peak 2. Top o f measured s e c t i o n , Appendix I I I A . s e r p e n t i n i z e d zone around i n t r u s i o n on peak 2. small pods (20 cm t h i c k ) o f massive s e r p e n t i n i t e intermixed w i t h sheared s e r p e n t i n i t e along UM c o n t a c t . l a r g e (4m x. 2m) pod o f very f i n e -grained compact, massive s e r p e n t i n i t e surrounded by t y p i c a l sheared s e r p e n t i n i t e , north c o n t a c t . APPENDIX l i b (continued) S e r p e n t i n i t e s CD S-< E g C O £•< -P •H rH O -P 0) o. o p. fn Q Pi a, « £ - 4 0) •p •rl TJ U Ci (SI •H »-} -p rH CD CD o CD •rl • r i C C -p CD •P CD -P CD CD • r i -P • r i -P o O 1 X 1 X rH • r i -P • r i M • r i o O o o o U CD • r i > ,c u c g O C o -P ^ • r i -P >> • r i 0) hi 5 rH p.. rH P- hi Ma X O O o U CJ Ma o Location and Note: 368 Peridotite 344 Harzburgite 20 79 76' 10 3 (1) (<D 4 cm wide v e i n o f c r o s s - f i b r e serpentine c u t t i n g layered p e r i d o t i t e near i n t r u s i o n on peak 1. + 10$ b r u c i t e . From t r a n s i t i o n zone-between s e r p e n t i n i t e and p e r i d o t i t e along SW contact o f 014. 351 Harzburgite Nephrite (Jade): 264 ? 315 99 <1 15 78 70' t r t r t y p i c a l sheared s e r p e n t i n i t e from contact shear zone, massive core with smooth slickensi.ded s u r f a c e s . + 5$ kspar, Z't carbonate mylonite zone along contact between s e r p e n t i n i t e and t a l c s c h i s t , and c h e r t s . t r ( t r ) + 25$ a l b i t e , carbonate, tr.amphi-bole. Location same as 264. 348 99.' t r t r botryoidal jade from pod of sheared jade, i n s e r p e n t i n i t e , about 15 w from contact with c h e r t s . i d e n t i t y checked by HF-sodium c o b a l t i n i t r i t e s t a i n i n g technique. APPENDIX He T a l c - b e a r i n g Rocks <D C 0 -P (1) •H 0 -P 0 •H -P 0 -P -P •rt -P V. •H -P C •H -P •rl IS3 0 E •rt <D SH 0 E -P C 0 O 0- O C O b.1 r H r H U r H bP J-< cd cd O cd 0 vcd - C Pi C l O 10 0 O r 45* 1 1 r- *• 45 5* <1 (-1) 0 u H 0 1 1 5 ^ ^ 3 £ Sf £ 3 Location and Notes 9* 1 oale grey-green talc-rnagnesite from contact zone o f UM 1?8 50* 45*  <1 (*1) l i g h t brown talc-rnagnesite, 15m from 177, 85 m from UM contacl 303 100* *1 ( < l ) dark green t a l c s c h i s t from contact of i n t r u s i o n on peak 1. 304 40* 50* 10* <1 (-^l) s i m i l a r to 178, from contact zone o f i n t r u s i o n on peak 1. 305 50* 45* 5* <1 s i m i l a r to 177, same l o c a l i t y as 304. 258 60* 9* 1* 30* <1 (<1) from f a u l t zone i n p e r i d o t i t e ; see Plate 62. 350 ' 60* 40* ^ - l t a l c v e i n l e t s i n s e r p e n t i n i t e ; see Pla t e 43. 3524. 60 40 <1 t a l c v e i n l e t s i n s e r p e n t i n i t e ; see Plate 42. 515 40* 20* 38* 2* small (2m d i a . ) i n c l u s i o n i n gabbro of Bralorne I n t r u s i o n s . 516a 40* 4 0 * 20* l a r g e (15m d i a . ) i n c l u s i o n i n Bralorne I n t r u s i o n s . a - from dark grey-green matrix 5l6b 15 50 20 5 10 b - l a r g e , i r r e g u l a r patches w i t h i n 51°a matrix. 306a 15* 10* 75* 1^ ("1) a l t e r a t i o n along j o i n t s i n harzburgite (30oc, Appendix IIA) a - zone adjacent to the j o i n t . 306b 20* 60 10 * <1 (<1) b - zone between f r e s h h a r z b u r g i t e and zone a . . see Pla t e 71. uo uo uo UJ UO UO uo uo ro ro ro ro Sample & $ ^ & £ ^ ^ <§ oi ^ 2 Number < 3 S O Un S ^ "8 un" £ Garnet H to K • N vj uo .p- £ uo vo ro Diopside O Un O un Un O Un CO O un O O K * * * * * * * * * * * * Z o i s i t e / r+ UO UO u J - P - VO o vo o un uo 0 0 • C l i n o z o i s i t e 0 0 ^ Idocrase o o ^ S g £ C h l o r i t e un T r e m o l i t e / uo ro o °. A c t i n o l i t e £ \3 ' A l b i t e un ro ro ro K-spar Pre h n i t e Sphene C a l c i t e Quartz uo B i o t i t e / ^ ^ °^ Phlogopite £ £ p £ Opaques un l_A 1 k- 1 o b& b& ' oC3 b S b 2 C e l l S"& 2 ^ 0 ^ 3 o r o ouo E d ro ro 1+ r - 1+ M -I-1 ro O • 0 • O « • CO . 0 - .00 O U T 0 1—*• O U n 0 r  0 uo 0 -Ti-ro ro G a r n e t cn M cn c/i U J Cri" 4 O f 35 HJ 4 t U CD H - 43 UO ro H P H ( D p ' f j p o I I (—' r o O h - 1 I I 4 fi 3 H r» \ D • (-» CD 3 0 4 f» (- 1 CD 3 M "0 3 H - r - ' - O C O P - U n Q a 1 j , c+ <  3 rf M • H H* H* CD H* CD H ' CD co -p "d e r a i—' H* sj p-p 1 1 i" 3 3 CL a 1 o H - c+ O O 3 ; O fl) j q UO H - 1! O • r - 1 O .jq 3 CO H - O PC rt- 3 CD c+ £> O " d H - CD c + O fu . X H - H - O H - O H - »-j i~J O P-. >-J CD O , c+ H - 3 3 3 3 3 3 Hj 0) 3 CD p. CD p CD 3 O -c+ J> 1 >j H ' u ) ~ . . . CO CD 3 Cn oo pi ffl 4 a> O ;—' 1—w cn 3 O H-CD 'kj CD © O ffl u'Q CD 3 r- 1 - O C D !—1 1^ c+>-J H - 3 ' 4 O n o -0 "o • ' d 3 c "P I ' d M « «• • - • r - J S - • • • O S 3 • O CD H - i-J A " W fo H - O "3 Q , 4 ' 1 ~ c+ rf- -p ro - i o u G O CD CD I—' 3 0 O CL. • w • . 3 - 3 V_n un c + O Co t ro in H , o c+ CD U n CD 3 3 P . c+ « w H - c/> CD p , 3 CD CD H* H -<-t -0 CD CD • H-— 3 CO APPENDIX. l i d (continued) Rodingites CD U KB 553a 553b CD -P • r i - CD to CD -P CD \ -H CD CD •P • r i t J <D O 1/1 •P • r i H •p •rl -P IS) • r i rH O CD CO •rl O o S c O. 03 C O o • r i o •rl -H o rH CD -P C3 •rl O rH O a NI O H O E-< 30* 2 33* 65* <1 CD -P • r i ^3 rH «; (65) ri D-, CO I 0) •P • r i C Xi CD CD CD •a 2 a) j j • r i CD CD a CO -P N -P o <1> -P • r i H J • r i hf> ;3 o ?-< •P O cf c rH CD rH ri o H ri !U rH bO ni • r i X! a ri CD •n O CU o O ta L o c a t i o n and Notes 3 boudinaged pods o f r o d i n g i t e ( F i g . 10), l a r g e s t pod having d i o r i t e core(553a) and. f i n e - g r a i n margin: see P l a t e 55> 56. 296 5* 5* t r 90' 11,856 r o d i n g i t i a e d margin o f a + 0.002 l a r g e (15m x 20m) ribbon ch e r t i n c l u s i o n , i n serp. 293 25 71 f . g . s i l l i n S 3 o f serp. Nephrite (jade) formed along contact of s i l l w i t h s e r p e n t i n i t e . 346 50 48' + 1% serp. dark green sheared, margin of l a r g e r o d i n g i t e pod (Plate"52) * i d e n t i t y checked by X-ray d i f f r a c t i o n ( ) r e l i c t m i n e r a l ** i d e n t i t y checked by HF-sodium c o b a l t i n i t r a t e s t a i n i n g technique. APPENDIX H e Sediments and Volcanies E g CO s ^ © o p. © -p © • H © i H © • r i -p O -p -p CO • H c u •ri a CO • r i a ,0 o •rl -P r H •rl O O < a 00 «; © -p •rl > O O CO 3 © © © -p -P © -P •rl • r i C •rl fn -P O © O O cd Xi rH H E f-l a, cd © cd CO u O U Location and Notes 281 limestone 1' 322 limestone t r 334 292 329 502 374 355 limestone ribbon chert ribbon chert sheared ribbon cherts chert b r e c c i a a r g i l l i t e t r t r 157 greenstone 99 97 1 97* t r 85* 10* 10' t r t r 4 99" 100 100 t r t r 25* 64 * 1 <1 *1 *1 <1 2 t r <1 1 t r t r 1 <1 <1 1 30 cm t h i c k bed of limestone i n r i b b o n c h e r t s . Im x Jm limestone pod i n sheared ribbon c h e r t s . Im x 15m limestone bed i n ribbon c h e r t s t y p i c a l r ibbon c h e r t ; 30 m from IM contact. t y p i c a l ribbon chert w i t h a r g i l l a c e o u s i n t e r b e d s . (+ t r a d u l a r i a i n v e i n s ) l e n s e s of chert i n a c h e r t b r e c c i a -a r g i l l i t e matrix. + t r . k-spar. . angular to rounded cher t fragments i n a r g i l l i t e matrix. t y p i c a l , a r g i l l i t e ; w e l l - d e f i n e d bedding p a r a l l e l s shear s u r f a c e s . 1'fo b i o t i t e . pale green Pioneer metavolcanics + 1% p u m p e l l y i t e ( ? ) . APPENDIX H e (continued) Sediments and Volcanies © tH CD P - , , 0 6 § M © O On 333 greenstone 522 t u f f 554 mylonite ~ 40 1 © •H -P © © Ti rH •H © -p •p tsJ CD •H •p o > © -p •H •rl c -P •P CO •H C o •ri -P o T, •H a co • •H O © O o cd X> q •rl -P CO rH H it H •H o O a Ci x: © cd < CO o o c_> 1 39 10 50 35 37 20 t r *1 2 5 1 t r *1 -40* L o c a t i o n and Notes p o r p h y r i t i c hypabysal or v o l c a n i c rock enclosed i n ribbon c h e r t s . 2m t h i c k l a y e r of fragmental v o l c a n i e s i n t e r l a y e r e d with greenstones and a r g i l l i t e . m y l o n i t i z e d cherts w i t h i n a few metres of UM contact ( i n f e r r e d ) . + 20$ k - s p a r * * * i d e n t i t y checked by X-ray d i f f r a c t i o n t r t r a c e ** i d e n t i f i e d by HF-sodium c o b a l t i n i t r i t e s t a i n i n g . UO r o r o r o u o r-* u o u o -o -o ~o O N O N -o o U n UO -P- -P-o a a a a > ?=> > H- r-> 3 3 O o O o o P C+ CL O <-i >-s cr CD CD <~i H" H" H- H' H- 05 c+ r+ c+ c+ C+ c+ 4 CD H- 3 ' 0 CD CD CD CD o p. c+ O ^— CD 01 s H---O c+ CD u n ^ s r o U n O N r o -p- U n UO NO O -P" u o -P- • O V n O v - ' ^—' UO UO -P- H-* o u o U l O r o u n o o U n -o o u n u n 1 1 1 1 NO u n •p-U n d-ro o ro o u n U n ro u n u o o r o o ro o U n u n ro o u o o uo o ro t->- 1—^  !->• Un c+ C+ 4 --d P CL M ro O fu © ro o o o o cr H- ' I 53 01 3 + l-l. 3 • r-1 r-1 3 o CL o CL 0 0 3 fo un O H-1 3 3 3 r-r 0 - i CL. ON O c+ 3 3 1 c+ c+ c+ 2j o 0 "O H* '<-> 0 X P3 3 03 3 0 01 o CD P O o 0 3 •p 3 • O 0! Ul. C3 O O r+ 01 c+ 01 3 c+ o d- h J H- un rt CD 3 ?r CD CD fl) CL J-J. -d H- O I—' 3 N iSI M 3 O 3 O <! 3 s« O CD O -d O 'd 0 c+ ul. H- CL H- M d O CL 3 CD 3 CD iii 3 rl- 3 - 2l O 3 CD 3 CD 3 P M N 0 O 0 M- CL rl- 05 O H « c-»- c+ O O 01 Hj H- C+ O H- •—^ H" 3 3 Q O 3 3^ O O 3 H- 3 "0 3 S> CQ 0 I-IJ CL C+ r-1 c+ 3 1—1 H- 3 • P H- •d CL • S» 'c+ 'as c+ CL 0 r-< A 0 O 01 CD c+ 0 ;3 CD ~i 3 ^ 3 C+H CD O rr H* LJ. H--d O O s o o >1 CL 'rr c+ •<~> 01 O '~b f-"3 0 o 3 o o O 0 0 f" 3 !— •~J. 3 O rt-c+ 4 (—• v y c : c+ c+ CT ; v ui. O CD -d o •M » 01 (U 0 P> c+ • • 3* • O O 0 I - 1 CD c+ O c+ 3 • • ^—' c+ • 00 Sample Number Rock Type Quartz P l a g i o c l a s e An content K-soar B i o t i t e Muscovite C h l o r i t e Cpx. Amphibole Z o i s i t e / C l i n o z o i s i t e Carbonate Sphene Opaques b o fa c+ i_i. b 3 fu 3 P. O 0 CO APPENDIX H f (continued) I n t r u s i v e Rocks CD P.$ X. CO B g O P . A 53 « E-n CD las ent o -p <D o c •P -p •H o ciS •H ?H bO O P- -P cfl nS CO o rH c 1 •H c? (X m 543b A l b i t i t e 359 A l t e r e d Gabbro 301 A l t e r e d Quartz Gabbro 511a A l t e r e d Gabbro(?) 5Hb A l t e r e d Gabbro(?) 513 A l t e r e d Gabbro 514 A l t e r e d A n o r t h o s i t e 543 Amphibolite 70 (40) 5 71 ~70 366 Quartz Gabbro 10 60 58 (39) 40 (53) 42 (25) ? (50) ? (33) 5 t r CD c CD CD -P •ri CD O CD 0] CD -P CD H - r i H— • r i •P >> • O CD O cti > • r i a ,Q -P N C CD O in O • r i •ri O O C O O c W P. ,0 CD CO rH • r i rv •ri - r i .C rH § ' O rH 03 P. O O rs3 O O cn 3 5 (5) 16 • 1 10 * i (15) 5 15 20 5 2 15 5 5 15 20 30 25 (20) 10 5 50 5 4 (1) 40 5 1 1 5 <1 55 5 CO 0 p' CX1 c.S p.. o 4 t r 1 <1 2 1 (<D 2 t r Location and Note; 2 m wide s i l l II Sx i n a r g i l l i t e s ; south contact o f greenstone- gabbro comolex. plug(?) on peak 2; 25m d i a . 1 (2) plug on peak 1 ; 30ra diameter. dike along f a u l t north o f peak 1 ; s i m i l a r to 301. Bralorne I n t r u s i o n s : e. g. gabbro i c rock (a,) cut by f. g. dike ( b ) , about 3m wide. Bralorne I n t r u s i o n : layered gabbro Bralorne I n t r u s i o n : a n o r t h o s i t i c p o r t i o n . from greenstone-gabbro complex UO -P" r o ••d > o 3 w C L d CD -J-01 *<J •<->• w C+ H -CD c+ H" O >• CD 3 01 Q , i - l" CD O 01 •pj c+ P* CD 4 r o ON > o 3 4 C L - d co 3 " < H" CD r+ H" O U n •P" NO cr > P c+ a' CD ' - j CD O C L U n -P" N O CT) M c r CD cc --j -j o o C L Sample Number Rock Type H" H" 3 C L C L CD F" O CD c+ CD 01 Ps1 1 01 ' d fD 01 —r P ;_!. 3 I H* R3 3 <<: + £--> L« t-i" 01 CD fD o M 3 b CD 3 C+ '< CD f» U n o ro o r o o u n O r o U n CO O Quartz g" P l a g i o c l a s e o o An content. i i K-spar B i o t i t e Muscovite £ S C h l o r i t e Clinopyroxene § Amphibole ^ Z o i s i t e / -P" ° C l i n o z o i s i t e Carbonate i H H H i o O 3 CD C L H 3 c+ f i 0! H" < CD o p n e n e CJ o u.) r o ro w o a a u e s - r H u n 3 H) - f r o •f' d P v'Q o r-1 o 3 v.n 3 o u o p • o C o CD O c+ O uq AS 0 H } H * C L i-j- 3 O 01 01 U>" '. 3 CO ;—1 o , o I i O 3 CD CD f+ •~" ^  "d 1—i -i b ^ ;—' O -"• 01 v« 3 H " • fD 3 M C+ <l 3 p 0 3 C+ 01 H" H - 4 01 .--^  1 :D CD O H O 3 -a r r •Jl • r o O * 3 M 3 •3) CD 0 fo ' . J ' ^ N O O r—'* 01 v» P 6 bb • c r r-1" O w bb cr -~r CD 3 3 R O U J " c i b D ' -Lo »* i—- " < i A 3 C L o O o CQ r-1 CD 3 CD o 71 -. o 4 -D T- P 3 o o T r V ~ • 4 CO r t - Ui 3 3 o >« o ' 3 0 u5 3 CD r-1 'c+ CD H 1 CT 3 0 fD H" C~f~ • H j >N U n q £-01 3 05 ui- UT. H j o P O - r r CD 3 3 3 o a . • p H" O 3 3 C L 157 APPENDIX I I I D e t a i l e d s e c t i o n s were measured i n order to study the h o r i z o n t a l and v e r t i c a l extent of p e r i d o t i t e l a y e r i n g , and t o provide a rough estimate of the p r o p o r t i o n s o f h a r z b u r g i t e , d u n i t e , and orthopyroxenite i n t h e l a y e r e d p o r t i o n s o f the u l t r a m a f i t e . I l l A i s a 115-metre v e r t i c a l s e c t i o n measured along the ridge northwest o f peak 2, where the a x i s of the ridge i s e s s e n t i a l l y p e r p e n d i c u l a r tothe p e r i d o t i t e l a y e r i n g and the outcrop i s continuous. I l l B i s a s e r i e s of f i v e s e c t i o n s measured on a 40 metre l i n e along s t r i k e . The s e c t i o n s show t h a t the sequence o f orthopyroxenite l a y e r s i s continuous over a c o n s i d e r a b l e d i s t a n c e , but i n d i v i d u a l l a y e r s w i t h i n the sequence do not p e r s i s t . The f o l l o w i n g terminology a p p l i e s to the s e c t i o n s : Pyroxenite l a y e r s - l a y e r s of orthopyroxenite having sharp boundaries, on the weathered s u r f a c e , w i t h the e n c l o s i n g p e r i d o t i t e . The contact i s g e n e r a l l y marked by a f r a c t u r e (eg Photo G) . Pyroxenite s t r i n g e r s - t h i n l a y e r s of orthopyroxene having g r a d a t i o n a l contacts as seen on the weathered s u r f a c e . Dunite - p e r i d o t i t e w i t h no pyroxene on weathered s u r f a c e . Contacts are i n d i c a t e d by s o l i d l i n e where sharp, or by dashed o r dotted l i n e where g r a d a t i o n a l . Harzburgite - p e r i d o t i t e w i t h pyroxene on weathered s u r f a c e . Pyroxene content ranges t o a maximum of 40xpercent. The p r o p o r t i o n of: pyroxene i s shown q u a l i t a t i v e l y by the i n t e n s i t y o f s t i p p l i n g on the s e c t i o n s . 158 S e c t i o n I I I A i n d i c a t e s the f o l l o w i n g p.rooortions o f the major rock types: Dunite - 7 percent Orthopyroxenite - 3 percent Harzburgite - 90 percent (of which about 10 percent i s ( d u n i t i c ' , i e l e s s than 5 percent pyroxene on the weathered surface) 159 Photo A t 3 n , chromite grains in centre of dunite layer, in harzburgite. Light diagonal streak is dunite. APPENDIX III A i Detailed section of layered peridotite. 160 24m. 21 15 18 Photo D i 18 m , V-shaped orthopyroxenite layer terminates in harzburgite. Two dark streaks are orthopyroxenite fading out in the upper left corner of photo. Pho^o C t Orthopyroxenite layers i n harzburgite, at 12 m. 12 161 ., r36m. orthopyroxenite, and dunite. Photo E i 29 m , Orthopyroxenite layer terminates abruptly in poorly layered harzburgite. Lenscap diameter is 5*^  OB» 24 162 r 48m. Photo H i 45 ra , O r t h o p y r o x e n i t e l a y e r s i n p y r o x e n e -poor ( ' d u n i t i c ' ) h a r z b u r g i t e . • .•.•.•'.'•••'•*',U Photo G j 38 m , O r t h o p y r o x e n i t e l a y e r s and s t r i n g e r s i n v d u n i t i c ' h a r z b u r g i t e . 36 163 . • . . . ^ — • - . . I K -60m. 57 moderately well-layered 54 massive U 8 72 m. 69 66 63i 60 84 m. 96 m. 164 • 81 73 75 Photo I j 92 ra , extremely well-layered peridotite with many orthopyroxene stringers and layers. Orthopyroxenite layer pinches and swells. \ 93 90 72 84 165 1-108 114 m. hl05 -102 55 a CO o OS 111 108 \ / Phofo J » 110 m , chrysotile veinlets in serpentinite. (xl) , Chromite LEGEND Dunite Harzburgite i massive h99 Harzburgite t moderately well-layered. Harzburgite t very well layered. Orthopyroxene stringer Orthopyroxenite layer II M M l I I I Sharp contact L 0 6 Gradational contact 166 APPENDIX III B « Series of sections measured along strike of orthopyroxenite layers. Intervals between sections covered by talus. Photograph is of layering at section 4 location. 167 APPENDIX IV PlStrlfrrtlon <?£ ^  &ni Fo frg&feen, CoexlsJ^or.Sjj.Jlca-tos. Because a l l of the mineral analyses were done by microprobe, total iron being reported as FeO, the amount of Fe*'''' is not known. Reported analyses of minerals from similar rocks (Table 3) indicate that Fe is relatively low, and the assumption that total iron is FeO does not lead to significant errors. Olivine-Orthopyroxene » The distribution of iron and magnesium between olivine and orthopyroxene is shown in Figure 22. Four samples from the Pioneer Ultramafite are compared with other alpine peridotites, stratiform basic intrusions and chondritic meteorites. Experimental studies (Modaris, 1969) have established that distribution of iron and magnesium between coexisting olivine and ortho-pyroxene is relatively insensitive to temperature. The degree of fractionation is expressed by Krj , the distribution coefficient, defined by i KD = (XFe /%g)olivine / (XFe /xMg)orthopyroxene The experimental distribution curve, determined at 900°C and 0.5 kbars, is shown in Figure 22. The fractionation in meteorites is in close agreement with the experimental curve, whereas other rock types plot slightly below, due perhaps to disequilibrium or higher pressures (Medaris, 1969). Note that these points are centred on the line of no fractionation, ie Kp = 1.0. Alpine peridotites, including the Pioneer samples, show l i t t l e variation in Fe/Mg ratios, in contrast to stratiform intrusions. 168 FIGURE 22 P a r t i t i o n i n g of Fe and Kg between coexisting o l i v i n e and orthopyroxene. Log-log pl o t of /Xp e\ v g / xFe\ I X M g / o l i v i n e \xM j orthopyroxene 169 Olivine-Clinopyroxene i The distribution of Fe and Mg between coexisting olivine and calcium-rich clinopyroxene (Fig. 23) has not been calibrated by experiment. Preliminary data have, however, indicated that the fractionation is temp-erature dependent and might be useful for geothermometry (Medaris, 1972). The upper curve in figure 23 represents compositions of coexisting olivine and clinopyroxene from chondritic meteorites estimated to have equilibrated at about 820°C (Van Schmus and Koffman,1967), based on the opx-cpx geothermometer (Kretz, 196l). The lower curve, Kn = 1.0, represents no fractionation or infinite temperature. Compositions of olivine-clinopyroxene pairs from Pioneer and other alpine ultramafites plot in a small area between the two curves, indicating that the temperature of equilibration was greater than 820°C. Analyses from Emigrant Gap, a zoned ultramafic complex (James, 1971) and the Duluth Gabbro, a stratiform complex (Snyder, 1959), are included for comparison. Both examples are more iron-rich, and show a wider compositional range, than Alpine ultramafites. Orthopyroxene-Clinopyroxene i Distribution of Fe and Mg between coexisting orthopyroxene and calcium-rich clinopyroxene (Fig. Zk) has not been calibrated by experiment, but Kretz (1961) has shown that there is a systematic change in KJJ with geologic occurrence, ranging from 1.85 in metamorphic rocks to 1.37 in igneous rocks. These KQ values, combined with temperature estimates, constitute a serai-quantitative geothermometer. Analyses from Pioneer and other alpine peridotites form a tight cluster between the = 1 (T = °°) and KQ = 1.37 ('igneous'temperatures) lines.These Kn. lines are not isothermal distribution lines, since KQ is a function of composition as well as temp-erature (O'Kara, 1967). Wood and Banno (in press) have recently proposed an empirical model relating solubility of enstatite in diopside coexisting with orthopyroxene 170 T = 820°+ 50°C (Van Schraus and Koffman,) 1967 0 — DULUTH GABBRO 1.0 XFe| XM g/01. K D - 1.0 © Pioneer Ultramafite + Red Mountain • Southwest Oregon 0 New Zealand ^ Lizard, Cornwall A Chondritic Meteorites (Van Schmus and Koffman, 1967) iJS/ Duluth Gahhro (Snyder, 1959) , y Emigrant Gap (James, 1972) J0.01 0.01 \XKg/Cpx. 0.1 1.0 FIGURE 23 Partitioning of Fe and Mg between coexisting olivine and clinopyroxene. Log-log plot of / xFa\ X M f f /olivine v s * VX M /clinopyroxene 'Mg' MgJ 171 FIGURE 2k Partitioning of Fe and Mg between coexisting orthopyroxene and clinopyroxene. Log-log plot of /Xpe\ v s ^ /%e\ Ix^/Opx lx H g J c p x . 172 to temperature of equilibration. The Pioneer analyses, assuming Mn, Na, Fe , Ti, and Cr = 0 , yield the following temperature estimates j Sample 306 T = 1370°C Sample 356 T = 1365°C The effect of using partial analyses was examined by substituting average values for Mn, Na, Fe , Ti, and Cr from pyroxene analyses from alpine peridotite reported in the literature (Table 4b). The result is a lowering of temperature estimates by about 25 C°, which is insignificant since Wood and Banno (in press) indicate that their geothermometer is only accurate to + 50 C°. Davis and Boyd (1966) have shown that the solubility of enstatite in diopside is virtually independent of pressure. A second orthopyroxene-clinopyroxene geothermometer was recently . developed by Warner and Luth (1974) from an experimental investigation of the diopside-orthoenstatite system. Temperature estimates from Pioneer clinopyroxenes are as follows 1 Sample 306 T - 9k0°C Sample 356" T = 955°C The large discrepancy between these two sets of values is puzzling, since Warner and Luth (1974) claimed that up to 3 or k percent A1 20 3 , and a few weight percent FeO (<6 percent FeO at Pioneer) do not significantly affect their geothermometer, and Wood and Banno (in press) claim to have taken Fe and Al into account in theirs. The problem may be explained by thermodynamic considerations. Blander (1972) concluded that the temperature dependence of the relative compositions of coexisting clino- and orthopyroxene is much smaller than their dependence on calcium content. The model of Warner and Luth (1974) which takes Ca content into account is probably more reliable than the model of Wood and Banno (in press) which emphasizes relative compositions, for example Fe/Mg ratios, but not total Ca content. The temp-erature estimate of 1350°C, based on Wood and Banno (in press) indicates a 173 pressure of greater than 22 kb, the position of the peridotite solidus (Irvine and Findlay, 1 9 7 2 ) . Clinopyroxene Composition t A summary of recent experimental work on the stability relations of high pressure mineral assemblages in ultramafic rocks (O'Hara, 1967) showed that the distribution of calcium and aluminum in and between coexisting pyroxenes can be used as a guide to their conditions of equilibration. O'Hara (I967) devised a tentative petrogenetic grid based on the composition of clino-pyroxene coexisting with olivine, orthopyroxene, and an aluminous phase, such as plagioclase, spinel, or garnet. The parameters o<c and |3C , which aire based on the CaSi03 and A 1 2 0 3 content, respectively, of clinopyroxene, are determined from chemical analyses and plotted on the grid (O'Hara, 1967, P. 3 9 6 ) . Experimental control of the grid is more precise at high pressures, so that P,T estimates on plagioclase and spinel peridotites (lower P) will be subject to revision as experimental data become available. Three clinopyroxene analyses from the Pioneer Ultramafite are plotted on Figure 25 which is based on 0'Haras (1967) pyroxene grid. These analyses indicate a temperature of 1100 to 1200°C and a pressure of about 1 kbar. Since the ultramafite is a spinel peridotite, without plagioclase, the pressure estimate is apparently low. The position of the reaction Anorthite + Forsterite —«• Aluminous enstatite + Aluminous diopside + Spinel (MgAl 20J defines the boundary between plagioclase and spinel peridotites. It is strongly affected by Cr a0 3 and Fe 30 3 , which act to stabilize the spinel phase, and at high Cr/Al ratios, plagioclase-free spinel peridotite may be stable to pressures as low as one bar (Irvine and Findlay, 1972 ) . In the absence of suitable chromite analyses for the Pioneer samples, the position of this reaction boundary is uncertain. 1 7 4 150<H PERIDOTITE + LIQUID 1000-t T°C 5004 / ALPINE TYPE j Pioneer B Beni Bouchera, Morocco (Kornprobst , 1 9 6 9 ) L- Li z a r d , Cornwall (Green, 1 9 6 4 ) 2- New Zealand ( C h a l l i s , 1 9 6 5 ) E Etang de Lherz, Pyrenees (O'Hara, I967) .B Bushveld ") A Basalts © Kiiaberlite compiled by O'Hara, 1967 0 10 20 30 P kbars—*-4 0 Figure 25 Pressure-temperature estimates based on clinopyroxene composition ( a f t e r O'Hara, 1967 ). 175 Orthopyroxene Composition » The solubility of A1 20 3 in orthopyroxene has been suggested as a geobarometer-geothermometer (Banno, 1964), but, as with the clinopyroxene geobarometer, estimates depend on total chemistry, not just A1203 content. Anastasiou and Seifert (1972) have shown that Al a0 3 solubility in ortho-pyroxene is not strongly pressure dependent. According to their data, Pioneer orthopyroxenes, which range in A1 20 3 content from 1.9 to 3*3 percent and average 2,4 + 0.4cr percent (25 analyses), could form under conditions ranging from 800°C at 1 kb to 1200°C at 50 kb. This range could be further limited by consideration of the stability of other phases in the rocks. Irvine and Findlay (1972) for example, concluded that the upper limit for equilibration pressures in alpine-type peridotite is 16 to 20 kb, based on the appearance of garnet (which does not occur in alpine peridotite) at higher pressures. According to Anastasiou and Seifert (1972) this upper pressure limit corresponds to a temperature of 800°C, for opx, having 2.4 percent Al 20 3.This is a minimum temperature estimate since the orthopyroxene is not coexisting with A1 20 3 as in their experiments, but coexists with chromite, in which the A1 20 3 activity is less than unity. Without analyses of chromite, the temperature estimate cannot be corrected for A1203 activity. i 176 APPENDIX V Adjacent to the fault zone north of peak 1, talc-carbonate and serp-entine alteration have developed along intersecting fractures in the peridotite (Plate 71)» resulting in an ellipsoidal structure. The core of these ellipsoids is typical serpentinized harzburgite with lizardite veining equant olivine, orthopyroxene and clinopyroxene grains. About 7 cm from the fracture, the mineral assemblage alters abruptly (Plate 72) to magnesite, dolomite, talc and serpentine. Texture of the peridotite is preserved in this zone with fine-grained talc pseudomorphs of orthopyroxene and magnesite-talc pseudomorphs of olivine. Serpentine veinlets occur between magnesite-talc pseudomorphs. X-ray diffraction work Indicates that about 10 percent of the carbonate is dolomite. This zone is too fine-grained to permit identification of the dolomite, although dolomite and talc probably replace clinopyroxene, whereas magnesite and talc replace olivine. Transition into the third zone, adjacent to the fracture, is marked by a decrease ln carbonate content and corresponding increase in lizardite content. The lizardite content of about 60 percent, remains fairly constant throughout this zone, except near the fracture surface where chrysotile occurs in 0.4 cm wide veins, Microprobe analyses of serpentine from the alteration zones show a systematic change ln Mg/Fe ratios. In peridotite, MgtFe is about 25*1, whereas in the more altered zones, MgjFe is fairly constant at about 14:1 . Iron enrichment in serpentine from more altered zones may be related to oxygen fugacity. In peridotite, high f 0 2 during serpentinization would result in oxidation of iron to produce magnetite, whereas in more altered zones, low fg would cause iron to remain in the reduced, divalent state and to substitute for magnesium in the serpentine structure. PLATE 71. A l t e r a t i o n along j o i n t s i n p e r i d o t i t e , producing e l l i p s o i d a l s t r u c t u r e s w i t h h a r z b u r g i t e c o r e s . PLATE 72. Contact o f ta l c - c a r b o n a t e a l t e r a t i o n zone w i t h f r e s h h a r z b u r g i t e . 1 1 Mote p a r t i a l replacement o f orthopyroxene -v) (orange) g r a i n . Sample 306 (X n i c o l s ) ~° 178 LIZARDITE MAGNESITE PYROXENE — * OLIVINE Figure 26 Variation of Mineral Modes in Alteration Zoning of Sample 306. Figure 27 Kg/Fe Ratios from serpentine in alteration zoning of sample 306 • ' B i o g r a p h i c a l I n f o r m a t i o n NAME: Robert Leslie Wright PLACE AND DATE OF BIRTH: Montreal, Canada Sept. 24, 1948 EDUCATION ( C o l l e g e s and U n i v e r s i t i e s a t t e n d e d , d a t e s , degrees) McMaster University, Hamilton, Ontario 1967-1971 B.Sc. P05ITlONS HELD: PUBLICATIONS: AWARDS: National Research Council 1967 Science Scholarship. T h i s form i s to be completed by c a n d i d a t e s f o r the M a s t e r ' s o r h i g h e r degree and s u b m i t t e d to the U n i v e r s i t y L i b r a r y S p e c i a l C o l l e c t i o n s D i v i s i o n w i t h the t h e s i s . •5 i I ^ 3 u»*gf m All (A*76 c.i FIGURE 29 i i LEGEND 8 Quaternary-drift & talus TRIASSIC: Pioneer Fm. Greenstone Noel Fm. Argillite I Greywacke Fergusson Gp. Ribbon Chert, predominantly M mixed chert, argillite, greenstone CENOZOIC: Andesite, basalt POST-TRIASSIC Gabbro, diorite, keratophyre B TRIASSIC (?): Bralorne Intrusions Peridotite Serpentinite Talc-carbonate J u Fault Limestone ^ Observed / Foliation Approximate Inferred J Geologic / Rodding / Layering Rootless fold axis contour interval: 100 ft. .40 .45 60 N 8 0 ^80 M A G N E T I C NORTH N 6 3 v.73 78 M \ 6 0 0 0 60 62 0.5 mile GEOLOGY OF THE PIONEER ULTRAMAFITE BRALORNE, B.C. FIGURE 28 


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