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The geology of part of the Shulaps ultramafite, near Jim Creek, southwestern British Columbia Nagel, Joe Jochen 1979

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THE GEOLOGY OF PART OF THE SHULAPS ULTRAMAFITE, NEAR JIM CREEK, SOUTHWESTERN BRITISH COLUMBIA by JOE JOCHEN NAGEL Sc., University of California at Los Angeles, 1972 A THESIS SUBMITTED IN PARTIAL FULFILLtffiNT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August 1979 © Joe Jochen Nagel, 1979 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t 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 n o t 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 . D e p a r t m e n t Of G^nlogi na.] .Sn.i fitipps The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 August 20, 1979 ABSTRACT The Shulaps ultramafite l i e s at the eastern edge of the Coast Plutonic Complex approximately 150 miles from Vancouver, B.C. It i s one of the largest "alpine-type" p e r i d o t i t e s in B r i t i s h Columbia, consisting primarily of harzburgite and subordinate dunite l y i n g i n an elongate zone trending northwest. Irregular bodies of gabbro and clinopyroxenite occur on the western side of the ultramafite associated with pillowed volcanic rocks. The ultramafite i s bounded on the northeast by the Yalakom f a u l t , a major regional structure, and on the southwest by rocks on the Fergusson Group, an assemblage of chert, c l a s t i c and volcanic rocks, probably of T r i a s s i c age. This study outlines the d i s t r i b u t i o n of p e r i d o t i t e , gabbro and other rocks i n the area just west of Shulaps Peak, a major topographic feature in the area. The p e r i d o t i t e i s almost completely serpentinized and pervasively sheared. It i s in tectonic contact with a l l other rock types, and contains i s o l a t e d i n l i e r s , ranging from a few feet to over 500 feet, of gabbro, greenstone, chert and c l a s t i c rocks. Within the area mapped, the serpentinite could be termed a tectonic melange. An i n t e r e s t i n g feature of the serpentinite i s the irr e g u l a r occurrence of o l i v i n e porphyroblasts, formed by the reaction serpentine + brucite =olivine. The gabbro i s f o l i a t e d and in places layered, although no cumulate textures were observed. It i s in gradational contact with pillowed volcanic rocks and in tectonic contact with serpentinite. The evidence gathered by previous workers and during this study argues strongly for the hypothesis that the Shulaps ultramafite, and perhaps some of the associated rocks, are an allocthonous piece of oceanic crust (ophiolite) which has been emplaced into i t s present position by plate-tectonic processes. This emplacement probably took place between Middle T r i a s s i c and Lower Jurassic time. iv. TABLE OF CONTENTS INTRODUCTION 1 STRATIGRAPHY 10 DESCRIPTION OF UNITS 14 SEDIMENTARY ROCKS 14 EAST LIZA VOLCANICS 19 SHULAPS PEAK VOLCANICS 21 EAST LIZA GABBRO 21 MAIN GABBRO 26 SMALL BODIES, PODS AND DIKES OF GABBRO 28 DIORITE AND QUARTZ DIORITE 32 REACTION ZONES 34 MYLONITE 34 ULTRAMAFIC ROCKS 35 STRUCTURE 56 SPECULATION ON ORIGIN AND EMPLACEMENT 64 V. LIST OF FIGURES 1. Index map of the Jim Creek area 2 2. View of the central part of the Jim Creek area 3 3. Geological map of the Jim Creek area >M poukis.1; m MapC«.tinet 4. Geological map of the Shulaps Range (after Leech, 1953) 7 5. Outcrop of clastic rocks with interbedded chert, near 15 middle fork of Jim Creek 6. Ribbon chert near East Liza Basin 15 7. Photomicrograph of feldspathic wacke from East Liza 17 Basin (#N706)~ 8. Pillowed volcanic rock near East Liza Creek 17 9. Pillow breccia near East Liza Creek 18 10. Photomicrograph of pillowed volcanic rock from near 18 East Liza Creek (;W598) 11. Photomicrograph of volcanic rock from near East Liza 22 Basin (#NbIl) 12. layering in gabbro from southwestern part of map area 22 13. Layering in gabbro from southwestern part of map area 23 14. Stereonet summary of poles to layering and foliation 23 in gabbro 15. Contact of East Liza Gabbro and sheared serpentinite, with 25 central zone of pumpellyite-rich rock 16. Photomicrograph of pumpellyite from contact zone shown : 25 in Figure 15 (#N551) 17. Typical outcrop of Main Gabbro near the head of Jim Creek 29 18. Dike completely altered to rodingite, near the southern 29 part of the map area 19. Summary of optically determined pyroxene compositions 30 20. Exotic inclusion of granitic rock in serpentinite nea.r 33 Shulaps Peak V I . LIST OF FIGURES (CONT) 21. Quartz diorite intrusion and hornfels, near triple fork 33 in Jim Creek 22. Photomicrograph of mylonite from contact of East Liza 36 Gabbro and serpentinite (#N586) 23. Mylonite stringers at contact of sedimentary rocks and 36 serpentinite on centre fork of Jim Creek 24. Sheared serpentinite near centre fork of Jim Creek 38 25. "Roundstone Breccia" near triple fork of Jim Creek 38 26. Layered peridotite near western tributary of Jim Creek 40 27. Photomicrograph of relict olivine in peridotite, showing 40 deformation lamellae (#N35) 28. Relict grains of clinopyroxene and clinopyroxene exsolution 41 lamellae in serpentinized peridotite (#N45) 29. Inclusion trains of magnetite in sheared serpentinite (#N245) 41 30. Serpentinite with olivine porphyroblasts, from east of 45 the map area 31. Serpentinite with olivine porphyroblasts, found as float 45 32. Elongate olivine porphyroblast with pyramidal termi- 46 nation (#N215) 33. Regenerated olivine layers in outcrop near Shulaps Peak 46 34. Rim of magnesite enclosing olivine porphyroblast 47 35. Olivine porphyroblasts showing 120 degree grain 47 boundaries (#N312) 36. Mesh texture preserved in regenerated olivine (#N711) 48 37. Mesh texture preserved in regenerated olivine (#N711) 48 38. Regenerated olivine (#N710) 49 39. Regenerated olivine replacing serpentine vein (#N215) 49 40. Olivine porphyroblast almost completely serpentinized (#N440) 51 v i i . LIST OF FIGURES (OONT.) 41. Schematic T-X^ diagram for the system MgO-Si02-R20-C02 at 52 elevated pressures and temperatures. 42. Isobaric equilibrium curves at low C0? content for the system 53 MgO-SiOg-RgO-COg. 43. Summary of structural measurements 58 44. Sections A-A' and B-B' 60 45. Section C-C 61 46. Section D-D' 62 47. Hypothetical, schematic cross-section through the Shulaps 68 Range in the vicinity of Shulaps Peak. v o tl 48. Sample locations -i-n-pocket h0tu*+ ACKNOWLEDGEMENTS Thanks are due to Drs. H. J. Greenwood, K. C. McTaggart and P. B. Read for help in the field and in many subsequent discussions. H. J. Greenwood, K. C. McTaggart and J. V. Ross were also instrumental in helping the author overcome his considerable writers' inertia by way of their encouragement and patience. I would also like to thank my wife Sharon for her support at a l l times. 1. INTRODUCTION Purpose The aim of the present study i s to examine a part of the Shulaps alpine-type ultramafite, especially with respect to i t s contact relationships with other rock types. Alpine-type u l t r a -mafites are r e l a t i v e l y common in the Canadian C o r d i l l e r a , and the Shulaps body represents one of the large examples. Although descriptions of many of these may be found in the l i t e r a t u r e , comparatively l i t t l e work has been published since the advent of the theory of plate tectonics. In t h i s study, the author w i l l describe the geology of part of the western flank of the u l t r a -mafite, and interpret the features observed in terms of the plate tectonic model. Location and A c c e s s i b i l i t y The map area covers a part of the Shulaps Range, which i s located approximately 100 miles north of Vancouver, B.C., near the town of L i l l o o e t ( F i g . l ) . Marshall Lake, just outside the map area, i s accessible by sixty miles of good gravel road from L i l l o o e t . On the eastern side of Marshall Lake, a mining road branches into the drainage basin beneath Shulaps Peak. The road i s passable to a four-wheel drive vehicle. The eastern branch extends to 6000 feet and the western branch to 7000 feet. Although i t may snow at any time of the year at the higher elev-ations, the area i s r e l a t i v e l y clear from the end of June to the beginning of September. Figure 1: Index map of the Jim Creek area Figure 2. View of the central part of the Jim Creek area. Shulaps Peak i s to the right, just off the picture. The prominent outcrops on the right hand side of the photograph are gabbro. Most of the foreground i s underlain by serpenti-nite. 4. Physiography The map area l i e s on the western flank of the Shulaps Range immediately northeast of Marshall Lake. It i s bounded on the northeast by a prominent ridge which incorporates Shulaps Peak, and which forms the crest of the range. G l a c i a l action has formed a number of small valleys and basins which are drained by small creeks. The range-crest i s at approximately 9500 feet and local r e l i e f exceeds 5000 feet. Tree l i n e i s at 6500 feet and, because exposure i s poor below tree l i n e , most mapping was done above th i s elevation. Topography r e f l e c t s the geology; the steep ridges are primarily resistant gabbro, and the basins and lower elevation are underlain mainly by more e a s i l y eroded serpentinite or sedimentary rocks (Fig.2). Previous Work The e a r l i e s t work in the v i c i n i t y of the Shulaps Range was done by Drysdale (1916,1917). He made a general reconnaissance of an area which included a part of the Shulaps ultramafic rocks. McCann (1922) continued t h i s work with an emphasis on the economic aspects of the region. Both authors considered the Shulaps ultramafites to be volcanic. Cairnes (1937,1943) mapped the area around the Bridge River mining camp and northward, and established a regional stratigraphy. He determined the u l t r a -mafic rocks in the area to be intrusive rather than volcanic, but his mapping did not extend into the Shulaps Range. Leech (1953) mapped the Shulaps Range in d e t a i l at a scale of one inch to one mile. His major interest was the ultramafic body, but his map includes a small marginal area of the surround-ing rocks. Although Leech's mapping did not overlap with that of Cairnes, the l i t h o l o g i e s in the two areas were very similar and he correlated the s t r a t i f i e d rocks found in the Shulaps Range with the units Cairnes had defined i n the Bralorne area. Some of the units, however, he was unable to correlate. In agreement with Cairnes, he found the ultramafite to be intrusive rather than volcanic, but found i n s u f f i c i e n t evidence for correlation with the ultramafic rocks Cairnes had mapped to the west. Present Work This thesis area i s centered on the area around Jim Creek and includes ultramafic, gabbroic, volcanic, and sedimentary rocks (Fig.3). During the summer of 1973, approximately six square miles were mapped at a scale of 1000 feet to one inch. Of the 709 specimens:; col l e c t e d during mapping, 125 were chosen for more detailed study. Ninety-seven thin sections were examined in conjunction with forty-one X-ray diffractograms. X-ray fluores-cence data were collected for six representative gabbros to determine th e i r s u i t a b i l i t y for Rb/Sr dating. Because the t o t a l rubidium content was low (approx.30 ppm) and the spread in Rb/Sr ratios quite narrow, no analyses were performed. Regional Geology The Bridge River region l i e s on the eastern edge of the Coast Plutonic Complex, just west of the Intermontane Belt (Monger,et a l . 1972). An "eugeosynclinal" assemblage of basic volcanics, a r g i l l i t greywacke, ribbon chert, and minor limestone and conglomerate underlies most of the area. Igneous rocks include ultramafites, 6. gabbros, and g r a n i t i c rocks. The g r a n i t i c rocks are mainly of Cretaceous age. A large proportion of the rocks in the Bridge River area belong to the Fergusson Group. These are characterized by sequences of ribbon chert and greenstone, with minor quartzite and limestone. F o s s i l s are scarce, but conodonts col l e c t e d in a limestone approximately four miles southwest of the thesis area indicate a Middle T r i a s s i c age (Cameron and Monger, 1971). Similar rocks make up the Hurley and Noel Groups, defined by Cairnes in the Bralorne area. The problems involved in correlating these to rocks found in the Shulaps Range are dealt within a la t e r section. The main st r u c t u r a l trend of the region i s northwesterly, with numerous f a u l t s lying along t h i s trend. The most important of these i s the Yalakom Fault, which l i e s on the eastern flank of the Shulaps Range. This f a u l t i s a northerly extension of the Fraser River f a u l t system ( D u f f e l l and McTaggart, 1952) and marks a major regional s t r u c t u r a l discontinuity. The pre-Cretaceous rocks of the region have been complexly folded and faulted and subjected to a low grade of regional metamorphism. Ultramafic rocks are scattered throughout the Bridge River region. They consist of podiform to lensoidal masses ranging from tens of feet to miles across, usually elongate along the regional structural trend. Many of them are fault-bounded on at least one side (Cairnes, 1943). The Shulaps ultramafite, underlying approx-imately 150 square miles, i s by far the largest of these. LEGEND (after Leech, 1953) QUATERNARY Quaternary Cover Q CRETACEOUS (?) AND TERTIARY TAYLOR GROUP: Micaceous arkosic sandstone and grit, chert-pebble conglomerate, shale 8 UPPER TRIASSIC OR (?) LATER 5 I Gabbro and diopside-pyroxenite Shulaps Ultrabasic Rocks: peridotite, minor enstatite pyroxenite UPPER TRIASSIC HURLEY GROUP: Argillaceous and tuffaceous siltstone and sandstone, conglomerate, limestone, chert TRIASSIC AND/OR EARLIER Greenstone, argillite, chert, chloritic phyllites; minor limestone A Greywacke (tuffaceous in part), argillite, siltstone, grit, conglom-erate; limestone, chert; probably Jurassic and Lower Cretaceous P3 Undifferentiated sedimentary and volcanic rocks; probably Mesozoic Greenstone-gabbro complex; andesite and/or basalt, diorite, gabbro. The extrusive part is probably Triassic in age. 9. Local Geology The thesis area l i e s on the southwestern flank of the Shulaps ultramafite, and includes many of the rock types found on a regional scale. Leech (1953) recognized sedimentary rocks of the Hurley Group, a greenstone-gabbro complex, gabbro and diopside-pyroxenite, and some undifferentiated Mesozoic sedimentary rocks (Fig.4). Rocks mapped as Fergusson Group by Leech outcrop just south and east of the thesis area. The remainder of rock outcrop-ping within the thesis area consist of ultramafic and gabbroic rocks. The st r a t i g r a p h i c nomenclature adopted by Leech for the area w i l l not be adhered to i n t h i s report for reasons outlined i n a subseq-uent section. Sedimentary, gabbroic, and ultramafic rocks display a complex outcrop pattern, with "islands" of gabbroic and sedimentary rocks t o t a l l y surrounded by sheared serpentinite. These islands range in size from only a few feet across to masses over 500 feet across, and appear to be randomly distributed. In d e t a i l , the rock d i s t -ribution appears to be chaotic. 10. STRATIGRAPHY Ambiguity of L i t h o l o g i c Units Correlation of rock units mapped in thi s work with those described by Leech and by Cairnes presents d i f f i c u l t i e s . Similar d i f f i c u l t i e s were experienced by both of those authors in c o r r e l -ating rock units within t h e i r own respective areas. These problems center around the four factors discussed below. An obvious problem i s the d i f f i c u l t y of obtaining detailed s t r u c t u r a l information. Cairnes (1937,p.9) described the Fergusson series as, " ... highly deformed both by folding and f a u l t i n g and lacking recognizable horizons such as might f a c i l i t a t e interpreta-tions and Leech (1953,p.12) said, " . . . (they) are some thousands of feet thick, but deformation, the lack of marker horizons, and the d i f f i c u l t y of determining the tops of beds prevent accurate measurement.". Cairnes (1937,p.15) made a si m i l a r statement about the Noel Formation. These c h a r a c t e r i s t i c s have hampered detailed s t r u c t u r a l mapping, leaving the r e l a t i v e s t r u c t u r a l positions of the rock units some doubt. A serious factor making correlation d i f f i c u l t i s the ov e r a l l s i m i l a r i t y of rock types in the various units. The Fergusson Group, Noel Formation, Pioneer Formation, and Hurley Group are said by Cairnes to contain s i m i l a r l i t h o l o g i e s , d i f f e r i n g only in r e l a t i v e proportions of each. Cairnes (1937, p.14) said of the Noel Form-ation, "At a few places within the outcrop areas of t h i s formation narrow belts or lenses of cherty sediments, much resembling those of the Fergusson series, were noted.", while of the Hurley Group (1937, p.18), "many of the Hurley beds are banded, l i g h t and dark grey, argillaceous and tuffaceous rocks indistinguishable in appearance from the banded Noel s t r a t a . " . The same problem i s encountered in working with volcanic and intrusive rocks. Cairnes (1937, p.16) noted of the Pioneer Formation, "The formation i s es s e n t i a l l y volcanic, but includes intrusive phases and ... i n places i t was not possible to d i f f e r e n t i a t e between Pioneer extr-usives and related rocks and the l a t e r Bralorne intr u s i v e s . " . Also of the Pioneer Formation (1943,p.3), " D i f f i c u l t i e s were experienced in making everywhere an e f f e c t i v e separation between the Pioneer volcanic rocks and those of the Fergusson Group Although the units as defined by Cairnes are mappable in the Bralorne and Tyaughton Lake area, the o v e r a l l l i t h o l o g i c s i m i l -a r i t y of the various units make correlation tenuous where sedimen-tary outcrops occur as i n l i e r s within serpentinite. Stratigraphic relationships among the rock units are not well defined. Cairnes (1937,p.15) said of the Noel Formation, "Contact relations with the underlying Fergusson series were noted at a couple of widely separated points and yielded contrad-ic t o r y interpretations.". Also (1937,p.17),"The contact r e l a t i o n s of the Pioneer greenstone with the underlying Noel Formation are d i f f i c u l t to interpret.". Of the Bralorne intrusions (1937,p.21), "The rock may vary within the l i m i t s of a hand specimen or over narrow or broad outcrop areas from coarse to fine-grained, and the l a t t e r types may be indistinguishable from associated green-stone formations.". Cairnes (1937,p.20) also experienced some d i f f i c u l t i e s in interpreting the relationships among the Bralorne intrusions, Hurley Group and the Pioneer Formation, the l a t t e r which conformably underlies the Hurley Group. In places, Pioneer greenstone grades into the coarser-grained Bralorne augite-d i o r i t e . This and other relationships noted by Cairnes indicate that the Bralorne intrusions and the Pioneer greenstone are closely related i n o r i g i n . However, the Bralorne intrusions cut the overlying Hurley Group, which suggests that the Pioneer green-stones are considerably older; than the Bralorne intrusions (Cairnes 1937,p.24). These relationsups were interpreted by Cairnes as evidence that Bralorne intrusions and Pioneer green-stone were derived from one magma chamber, with periods of i n t r u -sive and extrusive a c t i v i t y interrupted by a period of r e l a t i v e quiescence, during which the Hurley Group was deposited. Whatever the interpretation, the s t r a t i g r a p h i c relations between rock units are poorly defined. The limited age data on the ages of the rock units further hampers successful c o r r e l a t i o n . F o s s i l s within the sedimentary rocks are scarce, and radiometric dates for the igneous rocks are not available. Paleontologic dates have been established only for the Fergusson and Hurley Groups, and indicate Middle and Late T r i a s s i c - ages, respectively (Cairnes, 1937; Cameron and Monger, 1971). Because f o s s i l l o c a l i t i e s are few, and t h e i r s t r a t i g r a p h i c relations in doubt, these ages may not be representative of the rock units in question. For these reasons, age relationships are of limited p r a c t i c a l use in c o r r e l a t i o n . Correlation Leech, mapping the Shulaps Range, correlated his units on l i t h o l o g i c grounds with those of Cairnes. For reasons given above, these correlations are not unequivocal. Within the thesis area the problem i s aggravated in that most of the sedimentary rocks 13. are very similar, and i n many places occur as i s o l a t e d i n l i e r s within serpentinite, or in areas of poor exposure. Therefore, no attempt i s made here to correlate the sedimentary and volcanic rocks with previously established units. Detailed descriptions are made on the basis of location rather than under formation names. DESCRIPTION OF UNITS The most common rocks of the area include sedimentary rocks, volcanic rocks, gabbroic rocks with associated clinopyroxenite, and ultramafic rocks. In addition, quartz d i o r i t e , rodingite, and mylonite underlie small areas. 1 Sedimentary Rocks Sedimentary rocks crop out in East Li z a Basin, on the prominent ridge at the southwest corner of the map area, and as small bodies scattered throughout the rest of the map area. They consist of argillaceous and arenaceous rocks, ribbon chert, and minor amounts of limestone. Ribbon chert and argillaceous rocks are interbedded but in most exposures one of the other rock type i s dominant. The ribbon chert and c l a s t i c rock sequences commonly form r e l a t i v e l y resistant; dark brown to black outcrops (Fig.5). Where ribbon chert i s absent bedding i s commonly d i f f i c u l t to f i n d . Ribbon chert consists of one to two inch beds of chert separated by thin argillaceous partings, and forms d i s t i n c t i v e outcrops (Fig.6). The chert layers commonly show ir r e g u l a r folding and are dark grey, white, or more commonly a rusty brown. Arenaceous rocks are l i g h t grey and are commonly interbedded with black argillaceous rocks. This combination forms rather d i s t i n c t i v e banded outcrops i n East L i z a Basin, the bands measuring one to two inches. Outcrops of l i g h t grey l i t h i c wacke with angular black fragments were found near the southwest corner of the map area. The majority of the sedimentary outcrop, however, consists of f i n e -Figure 6. Ribbon chert near East Liza Basin. grained, black, argillaceous rock. Most of the fine-grained rocks have a steeply dipping f o l i a t i o n which trends northwesterly. In many places where th i s f o l i a t i o n i s well developed, the rock has a slat y or p h y l l i t i c appearance. Microscopically, the chert consists of micro-crystalline aggregate of quartz which i s cut by coarser veins of quartz. In one specimen, ir r e g u l a r patches and stringers of argillaceous mater i a l with pale green a c t i n o l i t e needles was noted. Most of the fine-grained c l a s t i c rocks are feldspathic wackes, consisting of angular grains of quartz and plagioclase feldspar averaging .1 to .2 millimeters in a fine-grained matrix which const itutes approximately 25% to 60% of the t o t a l rock (Fig.7). Some of these rocks also contain abundant chert fragments. Minor amounts of a c t i n o l i t e , epidote, carbonate, c h l o r i t e , and white mica are usually present. Bedding i s marked by thin laminae of argillaceous or carbonaceous material and most of the samples examined show evidence of deformation, often with extreme disruption of bedding. Although some of the rocks may be tuffaceous, no d e f i n i t i v e tex-tu r a l evidence of py r o c l a s t i c o r i g i n was found. One of the coarser l i t h i c wackes consists of grains averaging .5 to 1.0 millimeters. L i t h i c fragments include chert, fine-grained volcanic rocks, sand-stone, and a r g i l l i t e , in addition to quartz, plagioclase, and potassium feldspar grains. Limestone i s blue-grey to white, and occurs both as sporadic, discontinuous beds(?), and as a few isola t e d blocks in East L i z a Basin. Most of the outcrops in the head of the cirque facing East Liza Basin consists of a black volcanic rock with c a l c i t e amygdules 17. Figure 8. Pillowed volcanic rock near East Liza Creek. Figure 10. Photomicrograph of pillowed volcanic rock from near East Liza Creek. Amygdules are partially f i l l e d with pumpelly-i t e (#N598). 19. associated with abundant ribbon chert and limestone rubble. Very sim i l a r outcrops near a small i n l i e r of a r g i l l i t e and ribbon chert approximately 1000 feet to the west. Abundant rubble of the same volcanic rock occurs near the base of Shulaps Peak, the only out-crop being a three foot inclusion in serpentinite. The r e l a t i o n -ship between the sedimentary rocks and t h i s volcanic rock i s unclear, but small amounts of limestone associated with the volcanic rock suggest they are related. Serpentinite i s in tectonic contact with these rocks and where the contact i s exposed, the volcanic rocks are strongly deformed. East L i z a Volcanics Volcanic rocks underlie part of the eastern side of the area, in the v i c i n i t y of East L i z a Basin. These rocks grade into gabbro to the southeast. Both fine-grained, pillowed extrusives, and medium- to fine-grained volcanic rocks were recognized i n the f i e l d . The d i s t r i b u t i o n of the two types i s ir r e g u l a r , however. A sub-ordinate amount of tuffaceous rock i s also associated with these volcanic rocks. Volcanic pillows are recognizable in some weathered outcrops as rather vague, e l l i p s o i d a l shapes, but very l i t t l e d e t a i l i s v i s i b l e . Most pillows are one to two feet across. The best exp-osures are seen on certain planar j o i n t surfaces (Fig.8); here, the c h i l l e d margins of the pillows are c l e a r l y v i s i b l e . Most of the pillowed rocks are grey-green with rusty weathering surfaces. Loc-a l l y , they are brecciated with angular fragments of pillows held in dark green matrix (Fig.9). The s t r a t i g r a p h i c orientation of the pillow lavas could not be determined. A thin section from one of the pillows shows an amygdaloidal, s l i g h t l y porphyritic texture (Fig.10). Phenocrysts make up less than 5% of the rock and consists of plagioclase and minor augite. Most are smaller than 2 millimeters. Amygdules are generally less than 1 millimeter in size and consist of mixtures of c h l o r i t e , carbonate, and i r o n - r i c h pumpellyite, usually in r a d i a l aggregates. The groundmass consists of a fine-grained aggregate of plagioclase laths, up to approximately .3 millimeters, and smaller grains of a c t i n o l i t e , probably derived from augite. Scattered veins of ch l o r i t e , epidote, z o i s i t e , and carbonate are also present. The plagioclase i s a l b i t i c , with N 1.54. Alteration of the primary mineralogy precludes an exact name for these rocks, but the texture and composition suggests basalt or andesite. The coarser-grained rocks associated with the pillowed v o l -canics are characterized in the f i e l d by a more regular weathering pattern, and darker green color than the pillowed extrusives. Mafi grains averaging 1 millimeter and constituting 30% to 40% of the rock are p l a i n l y v i s i b l e in hand specimen.. These rocks occur near both gabbro and pillowed volcanics in scattered locations and may represent small flows or dikes. Microscopically, the rocks consist of 60% to 70% a l b i t i z e d and saussuritized plagioclase laths, and 30% to 40% t i t a n i f e r o u s augite with o p h i t i c texture (Fig.11). The average grain size i s approximately 1 millimeter. Sphene, p a r t i a l l y altered to leucox-ene, and patches of c h l o r i t e are abundant. The composition of one of the pyroxenes, determined o p t i c a l l y , i s approximately C a 4 1 M g „ 1 21. Shulaps Peak Volcanics Volcanic rocks associated with small bodies of gabbro outcrop near the base of Shulaps Peak. These rocks are very s i m i l a r to the East Liza Volcanics, although in general they are more deformed and lack pillowed v a r i e t i e s . A.thin section consists of approximately 50% a l b i t i z e d plagioclase, with the remainder composed of actino-l i t e , z o i s i t e , and c h l o r i t e , along with abundant sphene and patches of carbonate. The grain size ranges up to 1 millimeter, but the o r i g i n a l texture has been completely disrupted by deformation and a l t e r a t i o n . Although the petrographic evidence i s inconclusive, the general s i m i l a r i t y of these rocks with those near East L i z a Basin, and the fact that both volcanic units are associated with gabbro, suggests they may be part of the same sequence. East L i z a Gabbro The East L i z a Gabbro forms the eastern part of the Greenstone-Gabbro Complex mapped by Leech (1953). The unit i s heterogeneous and appears to grade into extrusive rocks to the west. Gabbro ranges from fine-grained to pegmatitic v a r i e t i e s , along with sub-ordinate amounts of pyroxenite. Much of the medium- to coarse-grained gabbro has a well devel-oped layering and/or f o l i a t i o n , defined by segregation and alignment of mafic grains (Fig.12,13,14). The layering i s commonly of a wispy nature; i n d i v i d u a l layers are discontinuous and could not be traced more than 5 to 10 feet. There i s commonly a difference in grain size between i n d i v i d u a l layers, so that medium-grained gabbro in many cases has pegmatitic layers within i t . The f o l i a t i o n and lay-22. Figure 12. Layering i n gabbro from southwestern part of map area. Figure 14. Stereonet summary of poles to layering and foliation in gabbro ( 24 points ). ering are p a r a l l e l , generally dipping steeply and s t r i k i n g westerly, although subject to l o c a l variations. The o r i g i n of the layering i s unknown, but rhythmic units and textures indicative of cumulate or i g i n were not found. The relationship between rocks of di f f e r e n t grain size i s un-clear. In some well exposed areas, the gabbro i s a confusing assemblage of pegmatitic pods and stringers, medium-grained f o l i a t e d gabbro, and fine-grained dikes. In places, the fine-grained rocks truncate the f o l i a t i o n in the coarser-grained v a r i e t i e s , but the relationship between the pegmatitic and medium-grained rocks i s less apparent. Some of the unfoliated pegmatitic pods appear to be the r e s u l t of replacement, but interpretation i s hampered by the f r a c t -ured and sheared condition of the rocks. In general, the gabbro averages 50% mafic constituents, but l o c a l l y t h i s l i m i t i s exceeded. In hand specimen, the mafic miner-als appear r e l a t i v e l y unaltered, but feldspar consists of a d u l l , greyish-white material in which cleavage faces and twin lamellae are usually absent. Microscopic examination shows the feldspar to be almost t o t a l l y altered to a fine-grained mixture r i c h i n a l b i t e , epidote, c l i n o z o i s i t e , a c t i n o l i t e , and c h l o r i t e . The common mafic mineral i s augite, i n part altered to a c t i n o l i t i c amphibole. Most grains show undulatory extinction, and i n some specimens granu-lation around grain edges. The pyroxene from one of the f i n e r -grained rocks has an approximate composition Ca^^Mg^^FegQ, determined o p t i c a l l y . In one specimen, the main mafic mineral was found to be a brown hornblende, perhaps a u r a l i t i c a l t e r a t i o n of primary pyroxene. Small veins in the gabbro usually contain a l b i t e , c l i n o z o i s i t e , and c h l o r i t e , with occasional white mica. Quartz was not detected in any of the rocks. Although the primary textures was p a r t i a l l y obsc-25. Figure 15. Contact between East Liza Gabbro and sheared serpentinite, with central zone of pumpellyite-rich rock. Figure 16. Photomicrograph of pumpellyite from contact zone shown in Figure 15 (#N551). 26. ured in many specimens by alt e r a t i o n and small scale shearing, the fine-grained rocks are diabasic, while the coarse-grained va r i e t i e s appear hypidiomorphic-granular. In the contact area between the ultramafite and the East L i z a Gabbro, which i s well exposed on the northern perimeter of the gabbro.., a zone of altered rock approximately f i f t y feet thick separates intensely sheared serpentinite from gabbro (Fig.15). The rock in this zone i s partly mylonitized and consists almost e n t i r e l y of pale-green pumpellyite and green hornblende, with some c h l o r i t e . Small veins i n t h i s rock are composed e n t i r e l y of pump-e l l y i t e (Fig.16). The zone of pumpellyite rock i s not l a t e r a l l y continuous; approximately 1000 feet to the west the serpentinite i s i n direct contact with the gabbro. Also near this l o c a l i t y are two blocks of medium-grained, f o l i a t e d amphibolite, composed of altered feldspar and green hornblende in equal proportions. One of these i s approximately 25 feet across, the other only a few feet. Both are within the serpentinite and appear to be i d e n t i c a l , although they are separated by 200 feet. Their source i s unknown, as no other rock resembling them was found within the map area. Main Gabbro What i s referred to in t h i s account as the Main Gabbro under-l i e s the northeast side of the map area, forming very prominent c l i f f s (Fig.17). This unit i s at least in part tabular in cross-section, dipping to the northeast at a moderate angle. In plan, the gabbro consists of northwest and southeast sections separated by a narrow segment that i s obscured by rubble. Sheared serpentinite s t r u c t u r a l l y underlies and overlies the southeast section and at least part of the northwest section. Although gabbroic rockgrpred-ominate, a sizeable part of the unit consists of clinopyroxenite. Layering and f o l i a t i o n were observed in only three l o c a l i t i e s . A l l contacts are tectonic within the map area but Leech states (1953, p.40) that the gabbro intrudes the Hurley Group to the north. Although less strongly layered and containing larger amounts of pyroxenite, the Main Gabbro i s l i t h o l o g i c a l l y s i m i l a r to the East L i z a Gabbro, and consists of a complex assemblage of altered gabbroic rock, ranging from fine-grained to pegmatitic. Two pyroxene compositions, determined o p t i c a l l y , one in each of the major extensions are CsL^^S^Q^^gi^) and Ca^Mg2gFe2g(NW) . Layered and f o l i a t e d rubble i s abundant, suggesting that these features may be more common than exposed outcrop would indicate. Of the three layering attitudes measured, two are at a high angle to the general trend of those in the East L i z a Gabbro. Clinopyroxenite occurs as lense-shaped masses at least several hundred feet in length, although exact boundaries are d i f f i c u l t to trace i n the f i e l d . It occurs on the perimeter and within the Main Gabbro, and also associated with some gabbro pods within the serpen t i n i t e . The contact between pyroxenite and gabbroic rock i s very ir r e g u l a r on a fine scale, suggestive of intrusion or possibly r e p l acement. Several specimens were collected across a well exposed contact near the head of the western tributary of Jim Creek, where the contact i s well exposed within a pod of gabbro and pyroxenite. Mic roscopic examination shows the pyroxenite immediately adjacent to the contact to be coarse-grained, the largest grains greater than 28. 5 millimeters with numerous stringers of granulated pyroxene. The pyroxenite two feet from the contact i s also coarse-grained, but lacks the granulated zones. In addition, scattered veins and patches of serpentine are present. The pyroxene in both specimens has strongly undulatory extinction, and numerous t r i p l e - g r a i n boundaries in the l a t t e r specimen indicate that some r e c r y s t a l l i z -ation may have taken place. Optical properties show the pyroxene composition to be approximately Ca^Mg^QFe^. The contact consists of a two-inch-wide zone of fine-grained, dark grey rock composed of equal proportions of a c t i n o l i t i c amphibole in a very fine-grained groundmass r i c h in pumpellyite and c h l o r i t e . This rock grades into a diabasic rock with an average grain size of 1 millimeter, consist-ing of a l b i t e , a c t i n o l i t e , and c h l o r i t e , with accessory sphene. The pumpellyite-rich contact zone i s c l e a r l y the res u l t of metasomatic reactions between the pyroxenite and gabbroic rock similar i n nature to the narrow zone between part of the East L i z a Gabbro and serpentinite, but the o r i g i n of the pyroxenite is: unknown. Contact relationships and d i s t r i b u t i o n of the pyroxenite suggest that i t i s genetically related to the gabbro. Small Bodies, Pods, and Dikes of Gabbro In addition to the East Li z a and Main Gabbrox, numerous smaller bodies of gabbro are found within the map area. The largest of these i s near the head of Jim Creek, but others are scattered throughout the area. With the exception of the small amount of gabbro associ-ated with volcanic rocks near Shulaps Peak, and some small outcrops Figure 18. Dike completely altered to rodingite, near the southern part of the map area. N 34: Pyroxenite N118: Gabbro N154: Gabbro N195: Gabbro N236: Pyroxenite N298: Gabbro N408: Pyroxenite N575: Gabbro N667: Gabbro N677: Volcanic N703: Gabbro Figure 19. Summary of optically determined pyroxene compositions. For locations, see Figure 48. near the t r i p l e ; fork in Jim Creek, a l l of these gabbro bodies are completely surrounded by sheared serpentinite. L i t h o l o g i c a l l y these bodies are indistinguishable from the gabbroic rocks found in the Main and East L i z a Gabbros, although most are medium- to fine-grained and unfoliated. In addition to the r e l a t i v e l y large i n l i e r s mentioned above, smaller l e n t i c u l a r pods of gabbroic rock are found throughout the sheared serpentinite. The sizes of these pods range from approx-imately 50 feet to only a few feet. Gabbroic dikes are also present, although subordinate in number to the pods. A l l show some meta-somatic a l t e r a t i o n and deformation along t h e i r borders, with the smaller pods and dikes, in most cases, completely altered to white rodingite (Fig.18). In general, however, t h i s zone i s only a few inches thick and the pods appear remarkably undeformed. O p t i c a l l y determined pyroxene compositions from a l l of the gabbroic and volc-anic rocks are summarized in Figure 19. The o r i g i n of these tectonic inclusions i s uncertain. None of the dikes i s traceable for more than a few tens of feet before being truncated by serpentinite. Crude alignment of some of the smaller pods suggest that they may be dismembered dikes. Leech (1953) rep-orts gabbroic dikes of various sizes in Shulaps ultramafic rocks outside the map area, so some of the pods may be derived from such dikes. L i t h o l o g i c s i m i l a r i t y to the Main and East L i z a Gabbros suggest them as a possible source. However, in the v i c i n i t y of Shulaps Peak, at 8,400 feet, a tectonic inclusion approximately 15 feet across consists of 60% quartz, 40% a l b i t e , with minor tremolite (Fig.20). The grain size averages 2 millimeters. This rock i s a b r i l l i a n t white and none other resembling i t was found within the map area. This exotic inclusion suggests that the source of the gabbroic (tectonic) inclusions i s not necessarily close at hand. Di o r i t e and Quartz D i o r i t e A few small outcrops of grey, smoothly weathering d i o r i t e and quartz d i o r i t e occur just north of the t r i p l e fork in Jim Creek. Acicular hornblende prisms are prominent in hand specimen. In thin section this rock averages 50% brown hornblende prisms up to 3 m i l l -imeters in length, along with subordinate reddish-brown b i o t i t e ; strained quartz and plagioclase make up the remainder. Quartz content ranges from 5% to 25%. Hornblende i s altered to c h l o r i t e and c l i n o z o i s i t e , in some specimens almost completely, and small sheaves of muscoivite. • and c l i n o z o i s i t e are scattered as inclusions throughout the a l b i t i c feldspar. Accessories include t i t a n i t e , apatite, and zircon. Quartz and feldspar are commonly graphically intergrown and most of the o r i g i n a l texture has been obscured by r e c r y s t a l l i z a t i o n . Although the contact of the quartz d i o r i t e with the serpent-i n i t e i s not exposed in t h i s l o c a l i t y , i t i s intrusive into an associated i n l i e r of sedimentary rocks and has formed a narrow zone of hornfels (Fig.21). In addition, the outcrop pattern suggests that the quartz d i o r i t e truncates a narrow s l i v e r of f o l i a t e d gabbro l i t h o l o g i c a l l y i d e n t i c a l to the Main Gabbro, which also intrudes the sedimentary rocks i n t h i s l o c a l i t y . Therefore, the quartz dior-i t e i s probably younger than the East Li z a and Main Gabbros. A ten foot thick dike of altered quartz d i o r i t e very si m i l a r to the above occurs within a narrow sedimentary i n l i e r approximately 3000 feet to the northwest. Here, the dike i s c l e a r l y truncated by sheared 33. Figure 21. Quartz diorite intrusion and hornfels, near triple fork in Jim Creek. 34. serpentinite, suggesting an e a r l i e r age for the quartz d i o r i t e . Reaction Zones Reaction zones occur at a l l serpentinite contacts. In general, these zones are less than a few inches wide, but many small tecton-i c inclusions are completely replaced; such small pods are present throughout the serpentinite i n the map area. These rocks are usually white or pale green, fine-grained, and have been given the name "rodingite" after type l o c a l i t i e s near Dun Mountain, New Zealand ( B e l l , et a l , 1911; Grange, 1927). The rocks examined consist primarily of mixtures of diopside, tremolite, garnet of the grossular-hydrogrossular series, c h l o r i t e , and occas-ional vesuvianite. In a few instances, compositional zoning p a r a l l -e l to the serpentinite contact was noted. The serpentinite near major contacts i s in many places veined by ch r y s o l i t e . In a few places, talcose rocks are present near these major contacts. Some small scale mining a c t i v i t y i s centered on small deposits of neph-r i t e that develops in these reaction zones. Detailed studies of such rocks have been presented elsewhere (Coleman, 1967; Larrabee, 1969). Mylonite The term mylonite was o r i g i n a l l y defined by Lapworth (1885) to refer to intensely deformed rocks characterized by b r i t t l e f a i l -ure. The use and misuse of the mylonite terminology was summariz-ed by C h r i s t i e (1960,1963), and more recent work has shown that mylonites may actually be the result of du c t i l e processes (Ross, 1973; B e l l and Etheridge, 1973). Because of the disagreement as to 35. the exact mode of o r i g i n , B e l l and Etheridge (1973) have proposed the following more generalized d e f i n i t i o n of the term mylonite: "a mylonite i s a f o l i a t e d rock, commonly lineated and containing megacrysts, which occurs in narrow, planar zones of intense deform-ation. It i s often finer-grained than the surrounding rocks, into which i t grades.". Mylonite" as used here, adheres to the above d e f i n i t i o n . Mylonitic rocks occur sporadically along serpentinite contacts. Most of the mylonite i s confined to those contacts with larger gabbroic or sedimentary bodies, but occasional small mylonitic stringers can be found within the serpentinite. These may be devel-oped from the remnants of tectonic inclusions. Mylonites are most commonly pale green, with i r r e g u l a r banding and streaking. They consists of mixtures of tremolite, diopside, and c h l o r i t e , with occasional pumpellyite and brown spinel (Fig.22). In some places, small stringers are intercalated with serpentinite at the margin of the mylonite zone (Fig.23). These zones usually grade within ten feet into r e l a t i v e l y undeformed rocks with the t y p i c a l sedimentary or igneous mineral assemblages described previously. On the basis of the mylonite occurrences,it appears that the serpentinite margin in general has been a zone of intense deformation. Ultramafic Rocks The ultramafic rocks within the map area have been almost completely serpentinized; primary minerals were only found in one l o c a l i t y . In addition, many of the rocks have been deformed to such an extent that the o r i g i n a l textures are completely obliterated. 36. Figure 23. Mylonite stringers at contact of sedimentary rocks and ser-pentinite on center fork of Jim Creek. Serpentinite is on the right. 37. For these reasons, characterization of the p r o t o l i t h i s d i f f i c u l t . In other parts of the Shulaps Range, however, the rocks are less altered and have been described in d e t a i l by Leech (1953). He found that approximately 85% of the Shulaps ultramafic rocks were harz-burgite (10% - 20% pyroxene), the remainder consisting of dunite. In addition, approximately 10% of the ultramafic rock was found to be layered, the layers consisting of narrow, discontinuous layers of orthopyroxene. The ultramafite within the map area i s assumed here to have once had a sim i l a r composition. Textural evidence supports t h i s conclusion. The ultramafite consists of a complex mixture of two types of serpentinite. "Sheared serpentinite" i s l i g h t green and contains closely spaced, slickensided shear surfaces (Fig.24). Generally, this type of rock i s f i s s i l e , but i n places i s quite coherent, with a mylonitic texture. No r e l i c t textures remain i n this type of rock. "Blocky serpentinite" forms the bulk of the ultramafite, weathering i n shades of green and rusty brown. In most specimens serpentine pseudomorphs after pyroxene can be cl e a r l y seen on fresh surfaces. A l l gradations between these two serpentinite v a r i e t i e s are common. In occasional exposures the blocky serpentinite occurs as rounded masses up to ten feet i n diameter i n a matrix of sheared serpentinite (Fig.25). These "roundstone breccias" probably repres-ent l o c a l i z e d zones of d i f f e r e n t i a l movement, but none was mappable for any great distance. Although outcrops of the serpentinite mixtures are complex i n d e t a i l , with shear zones of many sizes and orientations bounding blocky serpentinite, most have a dominant, measurable f o l i a t i o n . The o r i g i n of thi s f o l i a t i o n i s discussed in a subsequent section. 3 8 . Figure 25. "Roundstone breccia" near triple fork of Jim Creek. 39. Layered pe r i d o t i t e was observed i n only three outcrops; two are near the fork i n the western tributary of Jim Creek, and the t h i r d within the narrow band of serpentinite separating the East Liza Gabbro from sedimentary rocks to the south. The layering con-s i s t s of thin stringers, only a few crystals wide, of pyroxene pseudomorphs which weather i n s l i g h t r e l i e f (Fig.26). The inconsis-tency in the orientation of layering and the very r e s t r i c t e d extent of the layered outcrop within sheared serpentinite suggest that these examples are i s o l a t e d blocks within the serpentinite complex. The three serpentine "polymorphs" c l i n o c h r y s o t i l e , l i z a r d i t e , and antigorite have been described i n d e t a i l by Whittaker and Zuss-man (1956) and Aumento (1970). Additional comments on i d e n t i f i c a t i o n were offered by Hostetler, et al.(1966). Aumento pointed out the d i f f i c u l t i e s i n making posit i v e i d e n t i f i c a t i o n of mixtures of these minerals using powder d i f f r a c t i o n techniques. Special sample prep-aration i s necessary i n most cases. Optical techniques are of limited usefullness because of t y p i c a l l y fine grain sizes and s i m i l -a r i t y of o p t i c a l properties. Although special sample preparation was not attempted, comparison of standard X-ray diffractograms of bulk samples with those of Aumento (1970), coupled with textures observed i n thin section, indicate that the Shulaps serpentinites probably consist of mixtures of c l i n o c h r y s o t i l e and l i z a r d i t e . Anti-gorite may be present in some specimens of dense, mylonitic serpen-t i n i t e . In any case, l i t t l e i s known of the genetic significance of the three serpentine v a r i e t i e s . The general term "serpentine" i s used here to refer to a l l serpentinites found in the area. Figure 27. Photomicrograph of r e l i c t olivine i n peridotite, showing deformation lamellae (#N35). 41. Figure 28. Relict grains of clinopyroxene and clinopyroxene ex-solution lamellae i n serpentinized peridotite (#N45). Figure 29. Inclusion trains of magnetite in sheared serpentinite (#N215). 42. Primary periodotite minerals were observed in only one set of outcrops in the south-central part of the map area. The rock i s grey-green in hand specimen with approximately 15% milky-green pyroxene pseudomorphs. Two specimens were co l l e c t e d from the out-crop, and thin section examination shows one to be 60% serpentin-ized and the other approximately 80%. The o r i g i n a l rock consisted of approximately 15% orthopyroxene, 10% clinopyroxene, 72% o l i v i n e , and 3% chromian spinel. The orthopyroxene occurs as large grains (2 mm) and i s completely altered to a brownish serpentine mixture, while the clinopyroxene i s in clusters of unaltered, smaller cry-s t a l s (1 mm). Olivine grains range in size from 0.5 millimeters to over 5.0 millimeters, and are a l l partly serpentinized. Most of the grains show d i s t i n c t deformation lamellae (Fig.27). Semi-quantitative microprobe analysis y i e l d s a composition of Fo (91). Chromian spinel occurs as anhedral grains averaging 2.0 millimeters and sheathed in a zone of colorless c h l o r i t e . The cores of these grains are translucent brown, while the remainder i s altered to an opaque material, probably magnetite. Veins of serpentine-brucite-magnetite are scattered throughout. In thin section, blocky serpentinites are quite variable in appearance. Most specimens contain some orthopyroxene pseudomorphs, which are recognizable because they are commonly replaced by serp-entine ( c l i n o c h r y s o t i l e ? ) with a s l i g h t l y higher birefringence than the groundmass. These pseudomorphs commonly show kink bands. In some specimens small exsolution lamellae and/or grains of clinopy-roxene have r e s i s t e d serpentinization, although the t o t a l clinopy-roxene i s generally less than 1.0% (Fig.28). Most of these rocks were o r i g i n a l l y harzburgites. Primary o l i v i n e i s completely absent from these rocks, and serpentinization and deformation have almost 4 3 . completely obscured o r i g i n a l textures. Serpentine grains are generally smaller than 0.2 mm, although the sheared v a r i e t i e s are usually finer-grained. "Mesh texture", islands of serpentine bounded by intersecting serpentine veinlets, i s commonly developed, but not the rule. Brucite was not detected. Both the sheared and the blocky serpentinites contain opaque minerals ranging to 10%. These occur i n two forms; large (1.0 mm) anhedral to subhedral grains, and smaller ( 1 . 0 mm) anhedral grains and stringers. The larger grains are probably magnetite derived from o r i g i n a l chromian spinel; they have occasionally retained a translucent brown core. In the more deformed serpentinites the smaller grains commonly occur as trains within the f o l i a t i o n plane (Fig.29). These are probably secondary magnetite, but may also be in part remnants of e a r l i e r chromian s p i n e l . Regenerated Olivine Olivine regenerated from serpentine i s present i n the area around Shulaps Peak, although the d i s t r i b u t i o n i s sporadic and un-predictable in d e t a i l (Fig.3). Buff-weathering o l i v i n e porphy-roblasts, ranging i n size from 0.1 mm to 10.0 mm, occur within both sheared and blocky serpentinite and give the rock a very d i s t i n c t i v e spotted appearance (Fig.30,31). Most porphyroblasts are ovoid, while some are elongate along (001) and occasionally show a pyramid-al termination (Fig.32). The direction of elongation i s d i f f e r e n t than that reported from elongate o l i v i n e s in talcose metamorphic rocks (Evans & Tommsdorff, 1974). Although i n most instances the grains are randomly distributed, some specimens of sheared serpent-i n i t e have small grains concentrated along f o l i a t i o n planes, and i n one outcrop near Shulaps Peak, the o l i v i n e i s concentrated in discrete layers up to 2 cm thick (Fig. 33). The porphyroblasts generally constitute from 20% to 50% of the rock, and magnesite i s a common accessory, usually as small grains in the serpentine matrix. In one specimen, however, a narrow rim of magnesite encloses the o l i v i n e grains (Fig. 31, 34). Grain boundaries between ovoid grains commonly form 120 degree angles (Fig. 35). In only two specimens do the o l i v i n e porphyroblasts show deformation lamellae, although most are fractured to various degrees. Small opaque inclusions are present in a l l grains, but in widely ranging concentrations. The most s t r i k i n g feature of the regenerated o l i v i n e s i s the r e l i c t mesh textures.which are preserved within them. These textures are outlined by small opaque inclusions (magnetite?) in the o l i v i n e . In some thin-sections the textures can be traced d i r e c t l y into the surrounding serpentine matrix (Fig. 36, 37), while i n others the relationship i s less clear (Fig. 38). Oliv i n e c l e a r l y replaces a serpentine vein on one specimen (Fig. 39). Semi-quantitative analyses of four regenerated o l i v i n e s performed with electron microprobe yielded three compositions of Fo 97 ± 1% and one of Fo 95.5 ± 1%. The l a t t e r sample i s one with a large concentration of inclusions, which may have affected the re s u l t . These compositions are more magnesium-r i c h than the compositions reported by Leech (1953) for primary o l i v i n e s , and are consistent with a metamorphic mode of o r i g i n (Trommsdorff and Evans, 1972). Figure 30. Serpentinite with olivine porphyroblasts, from east of the map area. Figure 31. Serpentinite with olivine porphyroblasts, found as float. In this specimen, each olivine grain i s enveloped i n a thin layer of magnesite. 46. Figure 32. Elongate olivine porphyroblast with pyramidal termi-nation (#N215). Figure 33. Regenerated olivine layers in an outcrop near Shulaps Peak. 1 mm Figure 34. Rim of magnesite enclosing olivine porphyroblast. Same specimen shown in Figure 31. 1 mm Figure 35. Olivine porphyroblasts showing 120 degree grain boundaries (#N312). Figure 37. Mesh texture preserved in regenerated olivine (#N711). Figure 39. Regenerated olivine replacing serpentine vein (#N215). A l l of the regenerated o l i v i n e s are affected by a second generation of serpentinization, which usually progresses along grain boundaries and fractures. Small amounts of brucite are commonly present in these rocks, usually associated with the second-generation serpentinization or in small veins close by. One sample which in hand specimen appears to have rather large porphyroblasts, i s seen'in thin section to have been almost completely serpentinized, and only small islands of r e l i c t o l i v i n e remain (Fig. 40). The assemblages present in rocks containing regenerated o l i v i n e are the following: F o r s t e r i t e + Serpentine ± Brucite F o r s t e r i t e + Serpentine ± Magnesite The reaction producing these assemblages can be described within the system Mg0-Si02-R"20-C02, which has been investigated in d e t a i l by Johannes (1969), and Greenwood (1967). A schematic diagram of the s t a b i l i t y ranges in t h i s system i s given in Fig . 41 and a detailed plot of the portion relevant to the Shulaps rocks in Fig. 42. Almost a l l of the regenerated o l i v i n e examined appears to be the re s u l t of the reaction: 1 serpentine + 1 brucite = 2 f o r s t e r i t e + 3 H 2 0 which takes place only under very low values of x Q Q 2 - A t 1000 o bars the reaction proceeds at approximately 360 C., r i s i n g to o 410 C at 4000 bars. With increase of X o r i f o r s t e r i t e breaks down by the reaction: 2 f o r s t e r i t e + 2 H2O + 1 CO2= 1 serpentine + 1 magnesite 51. Figure 40. Olivine porphyroblasts almost completely serpenti-nized (#N440). Uncrossed polars. adopttd from Johannts(l969) Figure 41. Schematic T-X^ diagram for the system MgO-Si02-H20-CD2 at elevated pressures and temperatures. Abbreviations: A=anthophyllite; B=brucite; E=enstatite F=forsterite; M=magnesite; P=periclase; Q=quartz S=serpentine; T=talc Figure 42. Isobaric equilibrium curves at low C0o content in the T-field for the system MgO-43i02-B^O-C02 See Figure 41 for abbreviations. Generally, the CO2 component appears to have been minimal, as the above reaction was i l l u s t r a t e d by only one specimen, found as f l o a t ( Fig. 3 4 ) . The highest values of X „ n reached in the are exemplified by talc-magnesite rock which i s l o c a l l y abundant. The o r i g i n of the regenerated o l i v i n e i s problematical. The very i r r e g u l a r d i s t r i b u t i o n of olivine-bearing outcrops, and absence of a l o c a l heat source suggest that the porphyroblasts were not formed in s i t u . (See F i g . 3 7 ) Rather, they appear to be within small exotic blocks which are now incorporated in the serpentinite melange. The o l i v i n e s must have been formed between two events: ( 1 ) i n i t i a l serpen-t i n i z a t i o n of a p e r i d o t i t e p r o t o l i t h , and ( 2 ) a second episode of serpentinization and some deformation which has affected the secondary o l i v i n e . Given the lack of information on the early history of the Shulaps ultramafite, these are rather broad constraints, but a b r i e f consideration of the possible mode of o r i g i n of these i n t e r e s t i n g rock i s appro-priate . The metamorphic o l i v i n e could have been formed in one of the three ways: ( 1 ) regional metamorphism ( 2 ) f r i c t i o n a l heating associated with emplacement of the ultramafite ( 3 ) contact metamorphism by a nearby intrusion. Regional metamorphism i s precluded in that the rocks containing the o l i v i n e are found in only a small area. If a substantial area of serpentinite had been affected, one would expect to f i n d more i n evidence now, even after dismemberment. F r i c t i o n a l heating has been investigated by a number of workers (Minear & Toksoz, 1970; Mercier & Carter, 1975), and i s i n s u f f i c i e n t to produce the amount of heat required for s i g n i f i c a n t metamor-phism. The r e s t r i c t e d occurrence of the secondary o l i v i n e also argues against t h i s hypothesis. Contact metamorphism by a neighbouring i n t r u s i v e appears to o f f e r the best solution. Such an intrusion would produce porphyroblasts within a r e s t r i c t e d area which, after dismemberment, could assume the d i s t r i b u t i o n now observed. In addition, other cases of such contact metamorphism i n the c o r d i l l e r a have been well documented (Frost, 1975; Pinsent & Hi r s t , 1977). This contact metamorphism must have happened r e l a t i v e l y early, as there are no suitable intrusions in the immediate area. It should be mentioned that in addition to the area above, simi l a r olivine-bearing rocks were reported by Leech (1949, p. 150) near the head of Burkholder Creek. The t o t a l area underlain by such rocks was estimated to be 400 acres, consid-erably more than in the present area of study. Leech attributed the o r i g i n of the o l i v i n e to dynamothermal metamorphsim, the heat being furnished mechanically. STRUCTURE Introduction Obtaining detailed s t r u c t u r a l measurements in the map area i s hampered by a number of factors. Bedding in the sedimentary rocks i s d i f f i c u l t to fin d , and in most cases s t r a t i g r a p h i c top i s not apparent. Most of the ultramafic rock consists of sheared serpentinite with a chaotic array of shear planes. Also, i n d i v i d u a l measurements are subject to magnetic compass error. In most outcrops, however, a dominant f o l i a t i o n was measurable. Structural data obtained are summarized in Figure 43. Attitudes measured i n the area of East L i z a Basin are distinguished for reasons given below. Structural Relations Almost a l l ultramafite in the Jim Creek area i s pervasively sheared and serpentinized, making interpretation of contacts with other rock types d i f f i c u l t . A l l ultramafite contacts appear sheared, and are characterized by reaction zones. In addition, no metamorphic aureole was observed at any contact. For these reasons, the contact of serpentinite with a l l other rock types was interpreted to be tectonic, and defines a major s t r u c t u r a l boundary within the mapped area. The contact between the East Li z a Gabbro and the East Liz a Volcanic appears to be gradational. To the west, sedimentary rocks in East Liza Basin are in contact with the East L i z a Volcanics. This contact dips southeast at a moderate angle, conformable with the bedding attitudes in the argillaceous rocks. Although the contact i s not abrupt, the rock near i t i s severely distrupted and sheared, and was mapped as a f a u l t . This f a u l t must be an early feature, as i t has been folded p a r a l l e l to the regional trend. The Main Gabbro was not seen in contact with sedimentary rocks. Leech (1953) states that the gabbro i s the younger on the basis of sedimentary fragments within the gabbro to the east of L i z a Lake. This contact, however, i s a sheared one (Leech, 1949, p.116), and t h i s writer does not f e e l that the evidence i s conclusive. In the i n l i e r near the head of Jim Creek, however, a small body of gabbro l i t h o l o g i c a l l y i d e n t i c a l to the Main Gabbro i s intrusive into argillaceous sedimentary rocks. Although th i s contact i s within an exotic block, i t supports the view that the gabbro i s younger than the sedimen-tary rocks. Structural measurements on sedimentary rocks were obtained from two general areas; in and around East Li z a Basin, and around the west tributary of Jim Creek. The l a t t e r may give a misleading picture as the rocks may be exotic blocks. For t h i s reason, these two areas are distinguished in Figure 43. In general, the rocks, i n East L i z a Basin s t r i k e northwesterly, and have a pronounced sub-vertical f o l i a t i o n . In one outcrop, Poles to serpentine foliations Poles to foliations in country rocks A= western half of area •= East Liza Creek area • = eastern half of area * = Jim Creek area Lineations in country rocks Poles to bedding in country rocks. • = East Liza Creek area • •= East Liza Creek area A = Jim Creek area A = Jim Creek area • Figure 43. Summary of structural measurements 59. mesoscopic symmetrical folds of approximately f i v e inch amplitude were observed. The f o l d axis plunges nine degrees to the northwest, although other outcrops suggest gentle plunges to the southeast. Overall Structure The i r r e g u l a r i t y of many of the contacts in the Jim Creek area makes extrapolation to depth very speculative. Although some of the outcrop pattern shown on Leech's map just to the southeast suggests rather large-scale folds, such structures cannot reasonably be t i e d into the present mapping. For t h i s reason, the following remarks are r e s t r i c t e d to the area mapped for the present study. Cross-section A-A' to D-D' are shown in Figures 44 and 45. Although the cross-sections are of necessity rather schematic, a s t r i k i n g feature i s the serpentine melange zone seen in sections B-B' to D-D'. This zone consists of sheared serpentinite with inclusions of almost a l l other rock types encountered in the area. Serpentine f o l i a t i o n wraps around these inclusions, and the larger ones are surrounded by a rodingite reaction zone. Most of the inclusions are gabbroic, and are most abundant i n thearea around and west of Shulaps Peak. The cross-sections suggest thateven the Main Gabbro may represent a large i n c l u s i o n . B r i e f l y , the s t r u c t u r a l history of the area i s as follows. The sedimentary rocks, the oldest i n the area, were intruded by gabbro at some time before the Upper T r i a s s i c . These rocks then underwent some metamorphism and deformation before Figure 44. Sections A-A' and B-B' For legend, see Figure 3. Figure 45. Section C-C' For legend, see Figure 3. emplacement of the serpentinite. This i s c l e a r l y seen on the northeast side of the range, where i s o c l i n a l folding in the country rocks i s not observed i n the ultramafite (P. Mejstrick, Pers. Comm.). Emplacement of the ultramafite followed, probably during the Upper T r i a s s i c or the Lower Jurassic, although i t may not have been a single episode. Further work along the western flank of the ultramafite i s necessary to give a more complete picture. Speculation on Origin and Emplacement One of the aims of th i s study was to determine what place the Shulaps ultramafite has in the geological history of B r i t i s h Columbia, as examined in the l i g h t of plate tectonic theory. Knowledge of the processes of seafloor spreading and continental d r i f t has served to put alpine-type ultramafic rocks i n an important position with regard to understanding the evolution of continental margins. As yet, the processes taking place in the mantle which lead to seafloor spreading are poorly understood, and bodies such as the Shulaps ultramafite, thought to be mantle derivatives, may give some answers. A related problem i s that of the mechanics of emplacement of such large bodies of ultramafic rock. A number of writers have recently attempted to interpret the plate tectonic history of the Canadian C o r d i l l e r a (Monger, et a l , 1972; Ross, 1973; Godwin, 1975). The scope of the present study i s not broad enought for such a general discussion, but the place of the Shulaps u l t r a -mafite i n the t e c t i n i c regime of B. C. w i l l be outlined in view of present evidence. The term " o p h i o l i t e " i s currently used to refer to the suite of rocks commonly associated with and including alpine-type ultramafites such as the Shulaps body. The term has undergone some change since i t was f i r s t proposed, and recently was defined (G.S.A. Penrose Conference on Ophiolites, 1972) as follows: A completely developed o p h i o l i t e consists of mafic to ultramafic rocks i n the following sequence from the bottom and working up: (1) Ultramafic complex consisting of harzburgite, l h e r z o l i t e and dunite, usually with a metamorphic tectonite f a b r i c . (2) Gabbroic complex o r d i n a r i l y with cumulus textures and usually less deformed than the ultramafic complex. (3) Mafic sheeted dike complex (4) Mafic volcanic complex, commonly pillowed. (5) Associated rock types: - ribbon chert, shale, minor limestone - sodic f e l s i c i ntrusive and extrusive rocks Ophiolites are currently thought by most workers to represent pieces of oceanic crust and upper mantle, for reasons summarized by Williams and Smyth (1973). The Shulaps ultramafic complex possesses a l l of the features of an o p h i o l i t e , with the exception of the sheeted dike complex. It does not, however, represent the o p h i o l i t e succession; the elements are dismembered and no-longer in the proper sequence. In outline: (1) Most of the Shulaps ultamafite consists of harz-burgite, with subordinate dunite; tectonite f a b r i c has not been documented, but may be present. (2) The East L i z a and Main Gabbros represent part(?) of a gabbroic complex. Layering i s present, although d e f i n i t e cumulus textures were not ob-served. Although sheared in places, the gabbro i s not extensively deformed. (3) A mafic sheeted-dike complex was not observed. It can be noted that t h i s element of the o p h i o l i t e succession i s the one most commonly missing in other examples. (4) Pillowed mafic volcanic rocks are associated with the East L i z a Gabbro. (5) Associated with the Shulaps ultramafite are ribbon chert, greywacke and minor limestone. The regional setting i s much the same. A large part of the Bridge River area i s underlain by the Fergusson Group, through which are scatterd numerous ultramafites, although non nearly as large as the Shulaps body. One of these, the Pioneer ultramafite, was studied i n d e t a i l by Wright (1974). He concluded that the Pioneer ultramafite was a part of a dismembered o p h i o l i t e . The Shulaps ultramafite i s bounded on the east by the Yalakom Fault, which i s a northern extension of the Fraser River f a u l t system (McTaggart, 1967). This f a u l t i s sub-v e r t i c a l and sharply truncates the ultramafite. The western boundary of the ultramafite appears much more complex, however. Although the Jim Creek area may not be represen-t a t i v e , i t suggests, with i t s melange zone and pervasive shearing, that i t may represent a part of the base of the ultramafite, along which emplacement by t h r u s t - f a u l t i n g took place. The blocks of varied l i t h o l o g i e s scattered throughout the serpentinite melange could be pieces of country rock which were torn up during emplacement, with the predominant f o l i a t i o n i n the serpentine being produced during the same event. This would mean that the ultrmafite i n the Jim Creek area must have been largely serpentinized before f i n a l emplace-ment. The melange zone would thus represent the base of the ultramafite, along which i t was transported to i t s present po s i t i o n . A schematic cross-section of t h i s arrangement i s shown in Figure 46. A l a t e r f a u l t , shown just to the east of the crest of the range, may account for the fact that r e l a t i v e l y unaltered p e r i d o t i t e i s found in a topographic-a l l y low part of the body, and also for the sharp topographic break east of the range crest. It should be mentioned, however, that a reconnaisance to the northern t i p of the ultramafite, an area which appears to be i n the same struc-t u r a l p osition as the Jim Creek area, did not show an extensive serpentine melange zone. This problem can only be resolved by more extensive detailed mapping. SHULAPS PEAK MELANGE ZTj YALAKOM FAULT /DEXTRAL STRIKE-SLIP \ I S I N C E MIDDLE JURASSIC 1 JURASSIC 6 CRETACEOUS Figure 46. Hypothetical, schematic cross-section through the Shulaps Range in the vicinity of Shulaps Peak. ( 3x vertical exaggeration) There may have been some deformation after emplacement of the ultramafite, as suggested by some outcops on the central tributary of Jim Creek. Here, a small antiformal i n l i e r (?) of sedimentary rocks has serpentinite wrapped conformably around i t ; they may have been folded contemp-oraneously. If there was post-emplacement folding, some of the serpentinite may have been re-mobilized, accounting for some of the i r r e g u l a r serpentinite d i s t r i b u t i o n around East L i z a Basin. It appears there as i f the serpentinite may have been "squeezed" in and around some of the more competent rock units, possibly i n response to folding. The mode of emplacement of the Shulaps ultramafite i s thus presumably by thrust f a u l t i n g , associated with an active plate margin. This may be either by the process of obduction, as suggested by Coleman (1971), or by complex f a u l t i n g which appears to take place near a subducting li t h o s p h e r i c plate, as exemplified by the Franciscan complex in C a l i f o r n i a (Ernst, 1965 ; Suppe, 1972). The age of emplacement i s bracketed on the one hand by the age of the Fergusson Group, Ladinian to Carnian (Cameron and Monger, 1971), and on the other by d e t r i t a l chromite in c l a s t i c rocks of la t e Lower Jurassic age (Leech, 1953, p. 39). This i s in agreement with paleo-magnetic evidence from T r i a s s i c rocks in the insular belt and from the i n t e r i o r , which support the idea of an active suture zone during that period of time (Nelson, 1976). Literature Cited Aumento, F. (1970): Serpentine mineralogy of ultrabasic intrusions i n Canada and on the Mid-Atlantic ridge; Geol. Surv. Can. Paper 69-53, pp. 1-51. B e l l , et a l (1911): The geology of the Dun Mountain subdivi-sion, Nelson; New Zealand Geol. Surv. B u l l . 12. B e l l , T.H. & Etheridge, M.A. (1973): Microstructure of mylonites and t h e i r descriptive terminology; Lithos 6(4), pp. 337-348. Cairnes, C.E. (1937): Geology and mineral deposits of the Bridge River mining camp, B r i t i s h Columbia; Geol. Surv. Can. Memoir 213. (1943): Geology and mineral deposits of Tyaughton Lake map-area, B r i t i s h Columbia; Geol. Surv. Can. Paper 43-15. Cameron, B.E.B. & Monger, J.W.H. (1971): Middle T r i a s s i c . conodonts from the Fergusson Group, northeastern Pemberton map-area (92J), B r i t i s h Columbia; Geol. Surv. Can. Paper 71-lb, pp. 94-96. C h r i s t i e , J.M. (1960): Mylonitic rocks of the Moine thrust-zone i n the Assynt region, northwestern Scotland; Edinburgh Geo. Soc. Trans. 18, pp. 79-93. (1963): The Moine thrust-zone in the Assynt region, northwest Scotland; Univ. C a l i f . Publ. Geol. S c i . 40, pp. 345-440. Coleman, R.G. (1967): Low-temperature reaction zones and alpine ultramafic rocks of C a l i f o r n i a , Oregon and Washington; U.S.G.S. B u l l . 1247. (1971): Petrologic and geophysical nature of serpentinites; Geol. Soc. Amer. B u l l . 82(897-918). Drysdale, C.W. (1916): Bridge River map-area, L i l l o o e t mining d i v i s i o n ; Geol. Surv. Can. Summ.Rpt. 1915, pp. 75-85. (1917): Bridge River map-area; Geol. Surv. Can. Summ Rept. 1916, pp. 45-53. D u f f e l l , S. & McTaggart, K.C. (1952): Ashcroft map-area, B r i t i s h Columbia; Geol. Surv. Can. Memoir 262. Ernst, W.G. (1965): Mineral paragenesis i n Franciscan metamorphic rocks, Panoche Pass, C a l i f o r n i a ; Geol. Soc. Amer. B u l l . 76(879-914). Frost, B.R. (1975): Contact metamorphism of serpentinite, c h l o r i t e blackwall and rodingite at Paddy-Go-Easy Pass, Central Cascades, Washington; Jour:. Pet. 16(2), pp. 272-313. Godwin, C.I. (1975): Imbricate subduction zones and th e i r r elationship with Upper Cretaceous to Tertiary porphyry deposits in the Canadian C o r d i l l e r a ; Can. Jour. E. S c i . 12(8), pp. 1362-1378. Grange (1927): On the rodingites of Nelson; New Zealand Inst. Trans. 58, pp. 160-166. Greenwood, H.J. (1967): Mineral e q u i l i b r i a in the system MgO-SiC^-^O-CC^ ,in Researches in Geochemistry, Abelson, P.H., ed., John Wiley & Sons, pp. 542-567. Hostetler, P.B. et a l (1966): Brucite in alpine serpentinites Amer. Min. 51, pp. 75-98. Johannes, W. (1969): Ah experimental investigation o i the system Mg0-Si0 2-H 20-C0 2; Amer. Jour. S c i . 267, pp. 1083-. 1104. Lapworth (1885): On the stratigraphy and metamorphism of the rocks of the Durness-Eriboll D i s t r i c t ; Proc. Geol. Assoc. Vol. VIII, pp. 438. Leech, G.B. (1953): Geology and mineral deposits of the Shulaps Range; B.C. Dept. Mines B u l l . 32. McCann, W.S. (1922): Geology and mineral deposits of the Bridge River map-area, B r i t i s h Columbia; Geol. Surv. Can. Memoir 130. McTaggart, K.C. & Thompson, R.M. (1967): Geology of part of the northern Cascades in southern B r i t i s h Columbia; Can.' Jour. E. S c i . 4, pp. 1199-1228. Mercier, J. & Carter, N.L. (1975): Pyroxene geotherms; Jour. Geophy. Rsrch. 80 (23), pp. 3349-3362. Minear, J.W. & Toksoz, M.N. (1970): Thermal regime of a downgoing slab and new global tectonics; Jour. Geophys. Rsch. 8, pp. 1397. Monger, J.W.H. et a l (1972): Evolution of the Canadian C o r d i l l e r a : A p l a t e - t e c t o n t i c model; Amer. Jour. S c i . 272, pp. 577-602. Nelson, J.L. (1976): Origin of Georgia Depression; The Coast Plutonic Complex/Insular Belt Province Boundary on Hardwicke and West Thurlow Island, B.C.; Univ. B.C. M.Sc. thesis. Pinsent, R.H. & H i r s t , D.M. (1977): The metamorphism of the Blue-River ultramafic body, Cassiar, B r i t i s h Columbia, Canada; Jour. Pet. 18(4), pp. 567-594. Ross, J.V. (1973): Mylonitic rocks and flattened garnets i n the southern Okanagan of B r i t i s h Columbia; Can. Jour. E. S c i . 10, pp. 1-17. Suppe, J. (1973): Geology of the Leech Lake Mountain-Bell Mountain region, C a l i f o r n i a ; Univ. of C a l i f . Pub. Geol. S c i . V. 107. Trommsdorff, V. & Evans, B.W. (1972): Progressive metamorphism of a n t i g o r i t e schist in the Bergell t o n a l i t e aureole ( I t a l y ) ; Amer. Jour. S c i . 272, pp. 423-437. Whittaker, E.J.W. & Zussman, J. (1956): The characterization of serpentine minerals by X-ray d i f f r a c t i o n ; Min. Mag. 31, pp. 107-126. Williams, H. & Smyth, W.R. (1973): Metamorphic aureoles beneath o p h i o l i t i c suites and alpine p e r i d o t i t e s : tectonic implications with West Newfoundland examples; Amer. Jour. S c i . 273, pp. 594-621. 74. Wright, R.L. (1974): The geology of the Pioneer ultramafite, Bralorne, B.C.; U.B.C. M.Sc. thesis. 

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