GEOLOGY AND MINERAL OCCURRENCES OF THE YALAKOM RIVER AREA* (920/1, 2, 92J/15, 16) By P. Schiarizza and R.G. Gaba, M. Coleman, Carleton University J.I. Garver, University of Washington and J.K. Glover, Consulting Geologist

KEYWORDS:Regional mapping, Shulaps ophiolite, Bridge REGIONAL GEOLOGY River complex, Cadwallader Group Yalakom fault, Mission Ridge fault, Marshall Creek fault. The regional geologic setting of the Taseko- projectarea is described by Glover et al. (1988a) and Schiarizza et al. (1989a). The distributicn and relatio~uhips of themajor tectonostratigraphic assemblages are !;urn- INTRODUCTION marized in Figures 1-6-1 ;and 1-6-2. The Yalakom River area covers about 700 square kilo- The Yalakom River area, comprisinl: the southwertem metres of mountainous terrain along the northeastern margin segment of the project area, encompasses the whole OF the of the . It is centred 200 kilometres north of Shubdps ultramafic complex which is interpreted by hagel and 35 kilometresnorthwest of .Our (1979), Potter and Calon et a1.(19901 as a 1989 mapping provides more detailed coverageof the north- (1983, 1986) dismembered ophiolite. 'The areasouth and west (of the em and western ShulapsRange, partly mapped in 1987 Shulaps complex is underlain mainly by Cjceanic rocks cf the (Glover et al., 1988a, 1988b) and 1988 (Schiarizza et al., Permian(?)to Jurassic €!ridge Rivercomplex, and arc- 1989d, 1989b). and extends the mapping eastward to include derived volcanic and sedimentary rocksof the UpperTri %sic the eastem part of the ShulapsRange, the Yalakom and Cadwallader Group. These two assemhkgesare struclurally Bridge River valleys and the adjacent . In interleaved over a broad area extending from west of #Gold addition, several weeks were spentre-examining critical Bridge eastward to the slopes northeast (sfthe Yalakon and areas in the area and traversing the area Bridge rivers. In the Bralome- area th,-. are south of Gun Creek in an effort to mesh work with the -v our imbricated with the Permian Bralome diorite complex and maps produced by B.N. Church during his mineral deposit associated ultramafic rocks. studies of theBridge River mining camp (Church, 1987; Church and MacLean, 1987a: Church et ul., 1988a, 1988b: Sedimentary rocks exposed north and west of the 13-idge Church and Pettipas, 1989). River-Cadwallader belt range from Late Triassic to mid- Cretaceous in age. The ba.se of the section comprises L'pper Mapping in the Yalakom River area was carried out in Triassic clastic rocks and limestone of the Tyaughton Croup cooperation with Meg Coleman of Carleton University who and overlying Lower to Middle Jurassic ,sandstone and shale extended her 1988 mapping of theMission Ridge area of the Last Creek formation (Tipper, 1970: Umhoefer, I'B9). (Coleman, 1989) northwestward to Shulaps Creek:. It also These rocksare not seer in depositional contact w~ththe incorporatesdetailed mapping of the Shulaps ultramafic slightly older Cadwallader Group but a-e inferred to r:pre- complex in the Jim Creek-East Liza Creek area, begun in sent a continuation of thc: same arc-derlved sedimentition, 1988 by Tom Calon and continued this field seasonby Calon, and are included within the Cadwallader Terrane of Rusmore John Malpas and Rob Macdonald, all from the Memorial etal. (1988). University of Newfoundland (Calon ef al., 1990, this vol- ume). Geological mapping and sampling by D.A. Archibald Younger sedimentary rocks within the region are assigned of Queen's University extends a geochronology study begun tothe Tyaughton basin (Jeletzky and Tipper, 1968; in 1987 andcontinued in 1988 (Archibaldetal., 1989, 1990, Kleinspehn, 1985).Southwest of the Yalakom fault '.hese this volume). include shallow-marine clastic rocks of the Middle Jurassic to Lower Cretaceous Rehy Mountain Croup together with This is the final year of a4-year regional mapping project, conglomerate and associated finer grained clastics and vol- initiated east of Taseko Lakes in 1986 and funded by the canic rocks of the Albiart Taylor Creek Group. The Relay CanaddBritish ColumbiaMineral Development Agreement. Mountain Group outcrops most extensively in the Mmer Open File geology and mineral potential maps covering this Pass and Noaxe Creek map areaswhere it is locdly in season'sstudy area will be released in February, 1990. A depositional contact with the underlying. Last Creek fcnna- final report covering the entire .?-year program, including tion (Umhoefer, 1989). To the south and southeast the Relay updated 150 000 maps, will he prepared during the 1990191 Mountain Groupoccurs as localfault-.hounded slivers in fiscal year. contact with eitherthe Cadwdllader Group or the Bridge __ * This project is a contribution to the CanadaiBrilish Columbia Mineral Development Agreement Geological Fieldwork 1989, Puper 1990-1 53 54 Geological Survey Branch Figure 1-6-2. Tectonostratigraphic assemblages of the Taseko-Bridge River area

River complex. Synorogenic deposits of the Taylor Creek slivers within this belt, but were not observed in stratigraphic Group sit stratigraphically above the Relay Mountain Group contact with the Jackass Mountain Group. in the Relay Mountain area, andabove deformed Bridge Mesozoicstrata throug:hout theregion are intruded by River rocks in the Taylor Creek area (Gamer ef a/., 1989a). felsic to intermediate stocks and dikes ranging from Late Clasts within the Taylor Creek Group providethe first Cretaceous toOligocene in age(Archibald et al., 1989). evidence of regional uplift and erosion of the Bridge River Locally the strata are unconformably overlain by Ehcene complex volcanic and sedimentary rocks and by h4iocene to Plic'cene Upper Cretaceous andesiticbreccias and flows of the plateau lavas of the Chilcotin Group (Mdhews, 19891.Late Powell Creek volcanics are widespread in the northwestern Cretaceous granite to quartz diorite of the Coast plutonic part of the area, where they sit above the Taylor Creek Group complexintrudes the Mesozoic strata in thesouthwestem and older rocks with pronounced angular unconformity. To part of the Warner Pass map area and along the western edge the southeast Upper Cretaceous deposits of the nonmarine of the Brdlorne map area (Figure 1-6-1). Silverquick conglomerate rest unconformably above theTay- lor Creek Group and pass gradationallyupward into andesitic volcanicbreccia correlated to the Powell Creekvolcanics LITHOLOGY (Gamer et al., 1989a). Northeast of the Yalakom fault Mesozoicsedimentary SHULAPSULTRAMAFIC COMPLE:X rocks are distinctly differentfrom those to the southwest. The The Shulapsultramafic complex covers most of the north- base of the succession comprises Middle Jurassic volcanic- em half of the study area (Figure 1-6-3). It is bounded ty the rich sandstonesand associated shale and conglomerate. Yalakom fault to the northeast, and is juxtaposed ag,ainst These are overlain by a thick succession of arkosic sand- Bridge River and Cadwallader Group rocks across thru!.t and stone, conglomerateand shale of the Lower Cretaceous high-angle faultson thenorth,west, soutln andsoutheast. The JackassMountain Group. Andesitic volcanic and vol- complex was first studied in detail by Leech (1953). who caniclastic rocks,similar to the Powell Creekvolcanics concluded that it was an intrusive body, emplacedin thr. Late southwest of the Yalakom fault, occur locally as fault-bound Triassic or Early Jurassic, and later redistributed along fault Geologicul Fieldwork 1989, Puprr 1990.1 55 .*.. . ..f.. ..

A D

Figure 1-6-3. Generalized geology map and cross-sections. Yalakom River map area, zones to the west and northwest. Later workers (Monger, harzburgite is locally layered, with layering defined by 1977; Nagel, 1979;Wright er al., 1982; Potter, 1983, 1986) centimetre-widebands of orthopyroxeniteand rarely by suggested that the Shulaps and Bridge River complexes wider bands of dunite, orthopyroxenite and harzburgite. A togetherconstitute a dismembered ophiolite.The present penetrative mineral foliation and lineation are locally evi- study, and in particular the detailed mapping by Tom Calon dent; the foliation is typically parallel, or at a low angle to, and coworkers along the southwesternmargin of the complex compositional layering. This foliation is interpreted by Calon (Calon et al., 1990) has confirmed this interpretation. et a/.to be a mantle tectonite fabric. A spectacular mylonitic The structurally and topographically highest portionof the foliationdisplayed by harzburgite 2 kilometresnorth- Shulapscomplex comprises variably serpentinized northeast of Serpentine Lake is also thought to be a mantle harzburgite with lesser dunite and orthopyroxenite.The fabric.Dunite withinthe upper harzburgiteunit locally 56 Brirish Columbia Geological Survey Branch defines layering,but is more common asunoriented pods and ophiolitic serpentinite melange at this lower structural level lenses, some of which crosscut layering and foliation within suggests that emplacement and imbrication of the Shllaps the harrburgite. This may reflect an upper mantle origin for complex was a complex processinvolving some lou-of- the harzburgite unit, in the lower part of the transition zone to sequence thrusting or folding. overlyingultramafic-mafic cumulates (T. Calon, personal communication, 1988). Where the harrburgite unit sits Struc- BRIDGE RIVERCOMPLEX turally above cumulate-derived serpentinite melange, it does so across a sole of harzburgite-derived foliated serpentinite The Permian(?) to Jura:;sic Bridge Riber complex includes that can generally be distinguishedfrom the underlying variably metamorphosed and structurally imbricated chert, cumulate-derived serpentinite (Calon er al., 1990). The thick mafic extrusive and intrusive rocks, limestone, clastic rocks harzburgite unit itself is apparently imbricated across thrust and serpentinite (Potter, 1983,1986; Schiarizza e' al., contacts defined by similar foliated serpentinite, but these 1989a, Garver et a/., 1989a). It underlies much of' the area have not been mapped in detail. southwest of the Yalakom fault, where it is structurally A well-exposedbelt of cumulate-derivedserpentinite interleaved with rocks of the CadwalladerGroup and S'hulapr melangestructurally underlies the mantleharzburgite unit ultramaficcomplex. A centralblock of penetr:atively alongthe southwestern margin of the Shulapscomplex, deformed schists and phyllites exposedin the between East Liza and Hog creeks, It is in turn structurally is separated from lower grade rocks to thenortheast and underlain by Bridge River schistsand locally by Cadwallader southwest by the Mission Ridge and Marshall Creek fault: Groupmetasediments. This belt was studied in detail by respectively (Figure 1-6-3). Calon el al. and the following summary is based largely on Bridge River rocks southwest of the IMarshall Creel. faull their work. The melange comprises foliatedserpentinite are described by Potter (1983, 1986) and Schiarizza el al. containingblocks of ultramafic, gabbroic, volcanicand (1989a). They consist mhinly of prehnite-pumpellyitegrade sedimentary rock. The largest knockers, up to hundreds of chert and greenstone,together with lesseramounts 01 metres in size, derive from an igneous complex which argillite, limestone, tuff, chert and volcanic-rich sandstone, includes layered ultramafic cumulates, layered gabbro and pebble conglomerate,d,abase and gabbro. Similar rock! varitextured gabbro, all cut by swarms of mafic to intermedi- characterize the belt east of the Mission Ridgefault altllougk ate dikes. Gabbro at the base of the mklange in the western clasticrocks and limeslone are uncolnmon in thisarea part of the belt grades into a dike complex which in turn Structural slivers of serpentinite and diabase-gabbro-bt:arin~ grades into pillowed volcanic rocks. The melange thus con- serpentinite melange are commonin the area southwestof thc tains remnants of a plutonic-volcanic suite characteristic of Bridge and Yalakom rivers. Bridge River rocks northeast 0:' the upper part of an ophiolite complex. Volcanic and sedi- the BridgeRiver comprise chert and greenstone that arc mentary knockers occur throughout the melange and pre- structurally overlain by the Hurley Formation across a nloder sumably represent asampling of the footwall succession ately northeast-dippingfault. Similar northeast-dippint across which the Shulaps complex was emplaced. Sedimen- faults bound two persistent sliversof pillowed and brecziatec tary knockersinclude bedded chert,limestone, sandstone greenstone with lesser diabase, gabbro and serpentintile tha and pebble conglomerate.These in partresemble rocks occur within the Hurley belt farther to the northeast Thest found in the Bridge Rivercomplex, but in part may have been are tentatively assigned to the Bridge River complex, but ir derived from the Cadwallader Group or an unknown clastic part may be equivalent to thePioneer Formation imdio sequence. Shulaps serpentinite melange. Serpentinite also dominates the poorly exposednorth- The Bridge River complex between the Marshall Creel eastern part of the Shulaps complex.In exposures extending and Mission Ridge fault!. is represented mainly by phyllite:. from the northern tip of the complex southeastward to Per- and schists that were penetratively deformed under psedomi idotite Creek this serpentinite contains small knockers and nantlygreenschist-facie:; metamorphic conditions (i'ottet boudinaged dikes of diabase, amphibolite and gabbro. The 1983, 1986). The most common rock 1:ypes are medium t(' serpentinite melange exposed along upper Peridotite Creek dark grey phyllite, quam phyllite and biotite-bearin:g schis clearly sits structurally beneath mantle harrhurgite. The two (locally garnet-bearing) derived from argillite andche~ ant1t, serpentinite melange belts aretherefore inferred to be contin- chloritic schist (locally t~iotite-bearing:derived from mafic uousbeneath the intervening mantle harzburgite unit that volcanic rock. These ar: locally intercalated with crudel!, comprises the backboneof the Shulaps Range,indicating that foliated phyllosilicate-hc:aring metasandstone, mar'olc, ant1 the Shulaps complex is broadly synformal in nature. chlorite-actinolite-carbonate schists probably derive6 fron~ A separate belt of serpentinite melange outcropsbetween 4 impurecalcareous sediments. Serpentinite is coniinonl:? and 7 kilometressouth of the main part of the Shulaps interleaved with the schists for severalk~,lometres sou1.h of tb: complex and has been traced for about 12 kilometres east- Shulaps complex.Non-penetratively deformed rocks simila. ward from the Marshall Creek fault (Figure 1-6-31, Serpen- to thosewhich charac:erize the Bridge River comple:. tinite within this belt encloses knockers of ultramafic, gab- elsewhere within the map area occur locally in the dock. broic and dioritic rocks similarto those within the cumulate- particularly along the upper reaches of Hell and LaRochells: derived melange exposed between East Lira and Hog creeks. creeks. The lower melange belt is structurally overlain by penetra- The BridgeRiver schists are bounded by the ,Saulapi tively deformedBridge River rocks, and is underlain by ultramafic complex on the north; they sit structurally b'sneat I Cadwallader Group conglomerates and sandstones in the serpentinite melange on rhe west, but are juxtaposeddirect1 i west and Bridge River rocks in the east. The occurrence of against mantle harzburgite to the east (Figure 1-6-3). I'arther

Geologicrrl Fieldwork 1989, Poper 1990-1 5:' south they enclose an imbricate belt of serpentinite melange workers, although Leech (1953) describes the rocks,includ- and Hurley Formation which was traced for more than 12 ing the distinctive conglomerate lenses, where they outcrop kilometres eastward from the MarshallCreek fault. The along the Yalakom River north of Shulaps Creek, and Rod- schists are intruded by foliated granodiorite of the Eocene dick and Hutchison (1973) mapped a small patch of Hurley Mission Ridge pluton, which crosscuts the imbricate belt, as Formation at the mouth of Antoine Creek. Coleman (1989) well as by undeformed to foliated and foldeddikes andsills of noted the similarity between sedimentary rocks northwest of similar composition. They, together with the Mission Ridge Applespring Creek and the CadwalladerGroup described by pluton,are also intruded by theundeformed Rexmount Rusmore (1987), but tentatively included them in the Lillooet porphyry and associated dikes. Group. We presently map the Hurley Formation within abelt up to 4 kilometres wide andmore than 30 kilometres long that extends from Beaverdam Creek southeastward to at least CADWALLADERGROUP Applespring Creek. This belt includes rocks assigned to an The Upper Triassic Cadwallader Group, as redefined by unnamed Lower Cretaceousunit by Leech (1953), to the the Rusmore (1985, 1987). comprises mafic volcanic rocks of Relay Mountain and Jackass Mountain groups by Roddick the Pioneer Formation and conformably overlyingclastic and Hutchison (1973) and tothe Lillooet Group by Coleman sediments of the Hurley Formation. These rocks, inferred to (1989). The HurleyFormation within this belt is strongly be volcanic-arc related, are the same age as parts of the deformed by southwesterly overturned folds and northeast- Bridge River complex with which they are structurally inter- dipping transpressionalfaults. Itis imbricatedwith two leaved over a broad area extending from the Coast plutonic mappable lenses of pillowed greenstone, volcanic breccia, complex west of Gold Bridge to the Yalakom River valley diabase and gabbro tentatively assigned to the Bridge River (Figure 1-6-1). The Pioneer Formation consists of green to complexand with one or more slivers of Buchia-bearing purplish weathering, commonly amygdaloidal,pillowed and Relay Mountain Group (Figure 1-6-3). massive greenstone and greenstone breccia. The overlying The Hurley Formation within this belt consists largely of Hurley Formation consists mainly of thin-bedded sandstone grey siltstone to fine-grained sandstone that occurs as thin, and siltstone turbidites, but commonly includes distinctive commonly gradedand crosslaminated beds intercalatedwith pebble to cobble conglomerates containing limestone. mafic dark grey mudstone.These areinterbedded with thin to to felsic volcanic and granitoid clasts. thick, locally graded beds of sandstone, calcareous sand- Within the study area, the Cadwallader Group is exposed stone and gritty sandstone, and rare thin to medium beds of in two areas onthe northeast sideof the Marshall Creek fault, laminatedand crosslaminated limestone. Conglomerate as well as within an extensive, but previously unrecognized occurs locally as lenticular beds several metres to more than belt along the northeastern slopes of the Yalakom and Bridge 10 metres thick that commonly cut into underlying beds. It rivers(Figure 1-6-3). Cadwallader rocks northeast of the consists of angular torounded pebbles, cobbles and blocksof MarshallCreek fault are structurallyimbricated with the lightgrey weathering limestone that occur with variable Shulaps complexand Bridge River phyllites. They were proportions of rounded felsic to intermediate volcanic and penetratively deformed underlower greenschist(?)facies plutonic clasts within a limy matrix. These conglomerates, metamorphic conditions suchthat fine-grained sediments are togetherwith all of the other associated lithologies,are typicallycleaved andclasts in conglomerate arelocally typical of the Hurley Formation elsewhere in the region, and highly flattened. Themost extensiveexposures arein the East form the basis for our correlation. Collections of limestone Liza Creek area, where the Hurley Formation is structurally are presently being processed for conodonts in an attempt to overlain, across a gently dipping and locally folded thrust confirm the inferred Late Triassic age of the rocks. contact, by a pillowed volcanic-dike-gabbro complex at the base of the Shulaps serpentinite mtlange. Pillowed green- RELAYMOUNTAIN GROUP stone that contactsthe Hurley tothe north is tentatively Middle Jurassic to Lower Cretaceousshallow-marine sedi- asigned to the Pioneer Formation,although the nature of the mentary rocks of the Relay Mountain Group outcrop exten- contact has not been established. The greenstones are jux- sively in the Warner Pass andNoaxe Creek map areas(Figure taposed againstthe Shulaps harzburgite by a steeply dipping 1-6-1). There, they are locally in depositional contact with east-northeast-trending fault that defines a prominent left- the underlying Last Creek formation and are in turn overlain stepping jogin thewestern boundary of the Shulaps complex. by the Taylor CreekGroup (Figure 1-6-2). Within the The Hurley Formation also outcrops 12 kilometres southeast Yalakom River area, Upper Jurassic and Lower Cretaceous of the East Liza Creek exposures,where it occurs as a narrow Buchiu-bearing rocksoutcrop locally nearOre Creek (Leech, lens structurally overlain by the lower serpentinite dlange 1953; Jeletzky, 1967). These fossiliferous rocks apparently and underlain by Bridge River schists (Figure 1-6-3). This led Roddick and Hutchison (1973) to mapmost of the lower thrust-imbricated package is truncated on the west by the slopes northeast of the Yalakom and Bridge rivers between Marshall Creek fault; the Hurley lens pinches out 7 kilo- Applespring and Junction creeksas Relay Mountain Group. metres southeast of the fault, whereas the overlying serpen- Most of these rocks are now interpreted as Hurley Formation tinite milange belt was traced an additional7 kilometres on thebasis of thelithologic correlation discussed in the eastward before apparentlypinching out within Bridge River previous section. TheRelay Mountain Group is thought to be schists. restricted to one ormore narrow fault-bound sliversof mainly The extensive belt of Hurley Formation sedimentary rocks shale and siltstone structurally interleaved with the Hurley mapped along andnortheast of the Yalakom and Bridge rivers Formation northeast of the Yalakom River between Ore and (Figure1-6-3) was largely unrecognized by previous Junction creeks (Figure 1-6-3). 58 British Columbia Geological Survey Brunch MIDDLEJURASSIC VOLCANICSANDSTONE mentary rocksthat sit strat~graphicallyabove Middle Jurassic UNIT strata along the northeastern margin of the study area. This area is part of the southwesxern margin of a continuousbelt of Middle Jurassic rocks outcrop along the northeastern side Jackass Mountain Group ,exposures that extends from south of the Yalakom River area where they form a continuous belt of Lillooetnorthwestward almost 150 kilometres to Big bounded on thesouthwest by the Yalakom fault (Figure Creek. Rockswithin this belt have yielded sparse collections 1-6-3). They comprise a steepto moderately dipping (locally of EarlyCretaceous fossils ranging from Barremim to overturned along the Yalakom fault) east to northeast-facing Albian in age (Duffell anmj McTaggart, 1952; Trettin, 1961; succession of volcanicsandstones intercalated with lesser Jeletzky and Tipper, 1968; Roddick and Hutchison, 1'373). amounts of granule to pebble conglomerate, siltstone and Only the lower part of the Jackass Mountain Grou[N was shale. To thenortheast, these rocks sit stratigraphically examined in the Yalakom River area(Figure 1-6-3). It beneath the Jackass Mountain Group with no apparent angu- consists mainly of olive-green to blue-greenmedium to lar discordance. coarse-grainedfeldspathic-lithic wackes,commonly with The Middle Jurassic section consists mainly of coarse to sparselyscattered granules to small pebbles of volcanic, medium-grained, locally gritty, green to grey volcanic-lithic sedimentary and plutonic rock fragments. The sandstones sandstone. The volcanic grains are commonly accompanied are typically massive, wi?h bedding onl:y locally defincd by by lesser amounts of feldspar and fine-grained sedimentary pebble concentrations or trains of siltstone intraclasts. lnter- rock fragments, and locally by several per cent glassy quartz vals of siltstone and shale, ranging from less than a metre to grains. Thesandstone commonly occurs asmedium to thick, as much as 300 metres thick, occur locally and are ctarac- locally graded beds with relatively thin caps or interbeds of terized by distinct thin beds that may be ;graded or crosslami- grey shale. Locally it is massive and apparently unbedded nated. Pebble to cobble conglomerates were observed only at over intervals of several tens of metres. Thick beds of granule or nearthe contact with theunderlying Middle Jurassic to small-pebble conglomerate are not uncommon and contain section. These comprisepredominantly rounded cla;ts of mainly volcanic and fine-grained sedimentary clasts, includ- mainly volcanic and granitic to dioritic plutonic rocks. with ing lenticular clasts of grey argillite and siltstone that were relativelyminor proportions of sedimentaryand meta- probably local rip-ups. Thin-bedded, commonly laminated morphic clasts. or crosslaminatedsiltstone and mudstone locally define intervals up to several tens of metres thick within the coarser The basalcontact of the Jackass Mountain Group was rocks.These arecommonly carbonaceous. asare some observed at one locality, 5 kilometres east of the mouth of portions of the coarser grained intervals. Brown-weathering Blue Creek, and was closelyapproached in several other beds of calcareoussandstone, conglomerate or siltstone places to the southeast. No angular discordance is apparenl occur locally, and thin to medium beds of silty limestone between Jackass Mountain Group and underlying rocks in were noted rarely. any of theselocations. The contact is typicallymarked. The rocks described in the previous paragraph are in part however, by a thin conJlomerate unit at thebase of the Middle Jurassic in age on the basis of Aalenian and Bajocian Jackass MountainGrouF; the conglomerate, together witt ammonites collectedfrom the lower part of the exposed overlying sandstones, containsabundant plutonic &:tritu, interval near the mouthof Blue Creek (Leech,1953: Frebold that is nowhere seen in the underlying section. This ob:;erva- et al., 1969; Tipper, 1978). The upper part of the succession tion, in combination with the Middle Jurassic age of a leas! has not been dated,but is lithologicallysimilar to the the lower part of the underlying unit as compared 10 the underlying Middle Jurassicrocks and thereforemay be Barremian to Albian age of the Jackass Mountain Group separatedfrom the overlyingLower Cretaceous Jackass suggests that the contact is a significani. disconformit). Mountain Group by a significant disconformity. Correlative rocks in the None Creek map area were mapped as Unit 3%. EOCENEVOLCANIC AND by Glover er al. (19XXa, 1988b). and tentatively assigned to the lower part of the Jackass Mountain Group; ammonites SEDIMENTARYROCKS collectedfrom the unit along Dash Creek, however, were Sedimentary and volcanic rocks of probable Eocere agc subsequentlyidentified as Bajocian(T. Poulton, written outcrop in two areas within the map areB. On Mission Ridgf communication, 1988) supportingthe present correlation. they comprise sedimentary rocks exposed in a northwest. The Middle Jurassic sandstones are lithologically similar to plunging synclinethat is lruncated on the west by the Missior theLillooet Group described by Duffelland McTaggart Ridge fault (Figure 1-6-3). They apparently lie unconfmna. (1952) andTrettin (1961)along the near bly upon low-grade Bridge River rocks In the hangingwall o Lillooet, and occupy the same stratigraphic position beneath the fault, although the contact is poorly exposed. Eocene(? the Jackass Mountain Group. The rocks near Lillooet were rocks exposed 15 kilometres to the west-northwest, on tht assigned a Lower Cretaceous age by Duffell and hlcTaggart slopes northeast of , apparently also lit, (1 952) but an ammonite recently discovered within them may unconformably above low-grade Bridge River rocks. Thesf be Middle Jurassic (J.W.H. Monger, personal communica- comprise gently northeast-dipping intermediate volcanicant1 tion, 19891, supporting their correlation. at least in part, with volcaniclastic rocks with lesser sediments that are truncatell the Middle Jurassic sandstone unit described here. to the northeast by the hlarshall Creek fault. The sedimentary rockson Mission Ridge comprise several JACKASS MOUNTAINGROUP hundredmetres of thick-bedded, moderately well sorted, The Jackass Mountain Group (Selwyn. 1872; Duffell and volcanic and chert-rich conglomerates interbedded with silt- McTaggart, 1952) comprises Lower Cretaceous clastic sedi- stone and sandstone in afining-upwards sequence.Low- Geological Fieldwork 1989. Paper 1990-1 5! angle cross-stratification and basal scour in some of the Pettipas, 1989). Fresh hornblende separatesfrom hornblende conglomerates, andthe presence of wood fragments and feldspar porphyry that intrudes serpentinite melange along Mefasequoia leaf fossils in the fine-grained intervals, indi- the Yalakom fault, 4 kilometres to the northwest, however, cate that deposition probably occurred in a fluvial environ- yieldedwAr-3yAr total fusion andstep-heating dates of ment. The composition of the sandstone and conglomerate 7.5.622.8 and 77.0?10.7 Marespectively (Archibald el suggest that two different source terrains supplied detritus to al., 1989, 1990).These mineral-separatedates may be a this sequence; one rich in chert and another rich in felsic more reliable estimate of the cooling age or, alternatively, volcanics. Mixing of the two typesof detritus is common, but rocks included within the Blue Creek porphyries may repre- the felsic volcaniclastic detritus also occurs undiluted. Thin sent more than one intrusive suite. sections reveal that these white-weathering sandstones are Although they are most abundant within the northern part replete with felsic volcanic clasts, beta quartz, plagioclase of the Shulapscomplex, dikes of hornblendefeldspar andbiotite. Minoramounts of strained quartz, feldspar, porphyry and porphyritic diorite to quartz diorite alsooccur muscovite and sedimentary rock fragments are present and within the southern Shulaps complex and structurally under- may represent partial input from a plutonic and sedimentary lying Bridge River schists. These include a suite of horn- source. Chert-richsandstones and conglomerates contain blende 5 feldspar porphyry dikes that intrudes the melange minor amounts of felsic volcanicastic material but are domi- belt and caused local synkinematic metamorphism (Archi- nated by clasts of veined and unveined chert and metachert bald et a/.. 1989, 1990; Calon rr ul., 1990). These may be with lesser quantities of volcanic rock and sandstone. related to the Blue Creek porphyries since “JAr-ioAr step- The Eocene(?) rocks northeast of Carpenter Lake com- heating of an amphibolite knocker within the same mClange prisenearly 1000 metres of light grey to buff-weathering belt suggests cooling of the mklange at about 73 Ma (Archi- volcanic flows and breccias locally underlain by several tens bald et ol., 1989). of metres of sedimentary rocks.The volcanicrocks are mainlyhornblende, biotite, quartz and feldspar-phyric MISSION RIDGE PLUTON dacites. The sediments comprise conglomerate, sandstone The Mission Ridgepluton (Potter, 1983) is amarkedly and shale, locally with narrow seams of lignite. Clasts in the elongate body of coarse-grainedbiotite granodiorite that conglomerate include chert with lesser amounts of granitic extends from 5 kilometres south of the study area (Coleman, and felsic volcanic rock. 1989) for about 30 kilometres northwestward to the head of The chert-rich detritus within both the Mission Ridge and HolbrookCreek (Figure 1-6-3). Itintrudes Bridge River Carpenter Lake sedimentary sections was probably derived schists within the belt of metamorphic rocks that is bounded from the Bridge River complex. Theintimate mixing of chert by the Marshall Creek and Mission Ridge faults. Uranium- and felsic volcanic detritus, together with the presence of lead dating of zircon and monazite fractions from the pluton exclusively volcanic-derived interbedson Mission Ridge and indicates an age of 47.5 ?0.2 Ma (Coleman, M.Sc.thesis in the thick volcanic successionalong Carpenter Lake, suggests progress) which is slightly older than a previously reported that volcanism was contemporaneous with deposition and K-Arbiotitedateof44Ma(Woodsworth, 1977).TheMission comprised periodic eruptions that punctuated the erosion of Ridgepluton displays strongly foliated margins and is the BridgeRiver complex. Both the Mission Ridge and accompanied, within the Bridge River schist belt, by both Carpenter Lake sections are cut by normal faults that record deformed and undeformed dikes of similar composition.It is relative uplift of an intervening belt of relatively high-grade inferred to he synkinematic with respect to the latest stagesof metamorphicrocks duringa complex period of Tertiary deformation within the belt. strike-slipand extensional faulting. Bridge River detritus within the Eocenesediments is, however, derivedalmost REXMOUNT PORPHYRY exclusively from low-grade parts of the complex, although Rexmount porphyry (Drysdale, 1916; Leech, 1953)refers rare clasts of quartz-biotite schist in one thin section from to a light grey weathering rock comprising phenocrysts of Mission Ridge may have been derived from Bridge River hornblende, biotite, quartz and feldspar in an aphanitic to schists. Thissuggests that thepresently exposed Eocene fine-grained groundmass. It outcrops mainly in the Shulaps sediments were deposited relatively early in the uplift his- Range between LaRochelle and Hog creeks (Figure 1-6-3) tory, prior to unroofing of the higher grade rocks. and may he an intrusive equivalent of the dacitic volcanics that occur on the other side of the Marshall Creek fault, 3 INTRUSIVEROCKS kilometres to the southwest (Drysdale, 1916; Roddick and Hutchison, 1973). Although many earliermaps (Roddick and BLUE CREEK PORPHYRIES Hutchison, 1973; Potter, 1983; Schiarizza er al., 1989b) do Hornblende feldspar porphyry, diorite and quartz diorite not differentiate between the Rexmount porphyry andcoarse- that occur in and adjacent to the Blue Creek drainage area grained granodiorite of the Mission Ridge pluton, our 1989 were referred to as Blue Creekporphyries by Leech (1953). mappingindicates that the porphyry is a discrete,later They occur as abundant dikes and small plugs that intrude intrusive phase, as indicated by Woodsworth (1977). In the both mantleharzburgite and serpentinite mklange in the southwestern part of the belt it occurs mainly as dikes and northern part of the Shulaps complex. Twoof the largest sills cutting Mission Ridge granodorite and adjacent Bridge plugs cut the harzburgite unit 6kilometres west of the mouth River schists along the northeastern margin of the pluton. of Blue Creek and host the Elizabeth and Yalakom gold- The poungerporphyry becomesthe dominant intrusive phase quartzveins. One of thesehas recently been dated at to the northwest, and extends from the head of Holbrook 58.4 ? 2.0 Ma by the whole-rock K-Ar method (Church and Creek 10 kilometresnorthwestward as a moderately 60 British Columbiu Ceologirul Survey Branch northeast-dippingsheet cutting,from south tonorth, the has also been postulated (Potter, 1986; Rusmore er al. 1981 I southern serpentinite mklange belt, Bridge River schists and and is inferred to markthe juxtaposition of Cadkalladv part of the main Shulaps serpentinite mklange belt. Separate Terrane with the Bride River and Shulapscornolexe:., bodies of porphyry make up the Hog Creekstock to thewest Structures that can he unequivocallyassigned a ~Midd 15 (Figure 1-6-3) as well as a series of small plugs extending Jurassic age have not been found, however, and it is possib I: several kilometres to the east (Leech, 1953). Hornhlende- that amalgamationof these tectonostratigraphicelementswi.:; phyric felsite that intrudes both hangingwall and footwall amid-Cretaceous event (Schiarizza df al., 1989;Garver, rocks along the Mission Ridgefault south of the Bridge River 1989). (Coleman, 1989) may also he correlative. TYAUGHTONCREEK - CASTLE: PASS STRUCTURE FAULTSYSTEMS OVERVIEW Mapping in the Gold Bridge area was aimed at estatlishir ;; The regional structure is dominated by a system of north- the southern extensions of the Tyaughton Creek and Cast,,: west to north-trending faults that reflect a complex history of Pass fault systems. The!;e are important through-goin: stru:- mid-Cretaceous to Tertiary compressional, strike-slipand tures that had previously been traced from the Warner Pas extensionaldeformation (Figure 1-6-1). Our earlier inter- map areathrough the southwesterncorner oftheNoaxe Cree,'< pretationsattributed most of thethrough-going faults to area and into the Bralornemap area as farsouth as Gun Crec< dextral strike-slip in Late Cretaceous time (Glover ef al., (Glover er al., 1988a,1988b; Garver et al., 19893; 1988a; Schiarizza er a/., 1989a). Sysfems of folds and thrust Schiarizza et al., 1989a. 1989h). Within this area ,he tv) faults which are preserved locally were attributed mainly to faults enclose a lens of Cadwallader and vaughton Grol~J an earliercompressional event of mid-Cretaceous age, rocks and juxtapose them against younger Jura-Cre:aceo IS reflected in apronounced angular unconformity in the north- strata (Figure 1-6-4). Our 1989 mapping suggests thlt the;- western part of theproject area (Gloverand Schiarizza, fault systems were the locusof early Late Cretaceoust:inistld 1987). Our 1989 mapping suggests, however, that many of transpressional deformation, and that the uplifted block :'f the important faults in the region, including the Tyaughton older rocks they enclos'? is separated Srnm adjacent I'oungrr Creek and Castle Pass systems, have a history of sinistral rocks by predominantlyinward-dipping reverse..sinistrd transpressionaldeformation. This deformation probably faults. occurred in early Late Cretaceous time and produced both The structure near Gold Bridge (Figure 1-6-4) i!; don - sinistral strike-slip faults and compressional structures. nated by a complex system of mainly northwest tcm nortr: Dextral strike-slip is recorded along the Marshall Creek- trending faults (Cairne!;, 1937, 1943; Church er al., I988t1) Relay Creek and Yalakom fault systems and is, at least in informally referred to as the fault zone (F:usmolt,, part, Tertiary in age. Southwesterly directed thrust emplace- 1985;Leitch, 1989). Previousdetailed work has Iconcerl- ment of the Shulaps ophiolite complex occurredprior to and/ trated along a northwestto north-trend.ing belt of stru:turally or during the LateCretaceous, and apparently predated most interleaved Bralome diorite,Cadwallader Group and Bridge Rivercomplex that hosts the Bralorne, Pione':r, a1d or all of the dextral strike-slip faulting. Northerly trending oblique normal faultswithin thewestern Shulaps complex are numerous smaller gold-quartz vein systems. These studies related to a transfer zone linking the Marshall Creek and have established a complex history of faulting that i.1clud:d Yalakom fault systems along the southeastern margin of an west-directed thrusting of the Bridge River comple,. cover t :e extensionalstrike-slip duplex. Farther to thesoutheast, Cadwallader Group along the Ferguson thrust fault; ohliq :e extensionalfaulting is reflected by the gentlynortheast- thrusting alongthe north to north-northeast-dippillg r; bbon:d dipping Mission Ridge normal fault (Coleman, 1989) andby gold-quartz veins; and later dextral and vertical offset alo ~g later vertical displacement on theMarshall Creek fault. steeply dipping north-trendingfaults (Cairnes, 1937; Jouhin, These normal faults truncate Tertiary rocks and structures, 1948; Leitch, 1989). Observations made along the rlorthern including fabrics related to dextral strike-slip faulting. part of this system, near Gold Bridge (Figure 1-6-4;1, support the proposed west-directed thrusting of Bridge Riv,:r COIII- The mid-Cretaceous to Tertiary structures which dominate plex over Cadwallader Group; these include westerly ov,:r- the map pattern of the region aresuperimposed on older turned folds in footwall Cadwallader Group, asynmet - c structureswhich are not well understood. Triassic west-verging mesoscopic folds in hangingwall Bridge Ri1 <:I subduction-relateddeformation and metamorphism is complex, and shear bands in foliated rocks along the fallt reflected in penetratively deformed hlueschist-facies Bridge itself. Kinematic indicators were also observed along tx\o Riverrocks which occur locally (Garver ef al., 1989a, northwesterly trending faults, one that apparently marks the 1989b;Archibaldefal., 1990).1mbricationoftheblueschist- northern termination 01 the Cadwallader Group and Ilralorrle facies rocks with greenschist and prehnite-pumpellyite grade diorite panels, and one that separates the Bralomc~dior1:e rocks occurred sometime after Late Triassic metamorphism from adjacent Bridge River rocks neM Gold Bridge. The :;e and prior to (or during) mid-Cretaceous uplift and erosion are northeast-dipping Siructures along which the hani:ingw:ll when the metamorphic rocks were incorporated as clasts in has moved to the west; this sinistral transpressionis the sa~ne Alhian Taylor Creek conglomerate. The brittle faulting and as the documentednlovements along the Bralorne arid lenticularity of lithologic units that characterizes the Bridge Pioneer vein systems farther south. River complex elsewhere may also be attributed to an earlier deformational history, perhapsin a subduction zoneor accre- The northeast-dipping transpressionalfault that cresses t he tionary prism setting. A Middle Jurassic deformational event Bridge River at Gold I3ridge apparently extends northweit- Geological Fieldwork 1989, Paper 1990-1 51 Figure 1-6-4. Generalized geology of the Tyaughton Creek and Castle Pass fault systems.

62 Brirish Columbia Geological Sltrvey Branch ward to GunCreek (Figure 1-6-4). From there it is continuous may in part continue a!; the Tchaikazan fault farthel. to It I: with the north-trendingsegment of the Tyaughton Creek northwest (Figure 1-6-1 ); a lower limit of about 8;' Ma firr fault, although an important splay continues northwestward major movement along the Tchaikazan fault is provided t :i to separate the Bridge River complex from younger strata to radiometricdating of theadjacent #Coast plutonic rocl.3 the north. This splay is truncated by theCoast plutonic (McMillan, 1976;Archiabald et al., 1989). The timir;: complex but may have been continuou~with the Tchaikazan constraints outlined above indicate that sinistral tran!;pressi(~- fault whichabuts the granitic rocks along strike to the nal deformation occurred in early Late Cretaceous I:ine ar ti northwest (Figure 1-6-1). produced steep regionally persistent iaults as well as folllj The southern extension of the Castle Pass fault is inferred and thrust faults. This requires a re-evaluation of the c.mpll.:( to be a southwest-dipping fault identified on the south side of network of anastomosing northwest-trending faults that pel- Carpenter Lake IO kilometresnortheast of Gold Bridge vades the area within and adjacent to the 'I)aughton Creel .- (Figure 1-6-4). It separates contrasting Bridge River pack- Castle Pass systems ~ISmost of these were preiious:i ages. comprising mainly greenstone and chert on the west, attributed to a wide band of dextral faulting related to tilt and variably foliated and sheared sandstone, chert, argillite Yalakom system. Although dextral offsets are locall) appil- and serpentinite on the east. It encloses a lens of conglome- ent in this area, they m,iy he of relatively minor impsrtanl:: rate and sandstone identified as Relay Mountain Group by compared to early Late Cretaceoustranspressiona stru:. Church and MacLean (1987b) on the basis of fossil Buchia tures. The dextral faults are presumably related to qounglr collected from a thin interbed of laminatedsiltstone and dextral faultingthat was concentrated along theRelq Creel .- argillite. Foliation and mesoscopic shear zones within the MarshallCreek and Yalakom systems farther to 111: BridgeRiver rocks on thenortheast side of the fault dip northeast. moderately southwestto west. Shear bands and outcrop-scale transpressional duplex structures indicate a top-to-the-east sense of shear. This segment of Castle Pass fault is therefore THRUSTFAULTS M'ITHIN THE SHULAPS inferred to have been the locus of oblique sinistral shear; the ULTRAMAFICCOMPLEX east-west movement direction is the same as that demon- Detailed mapping along the southwestern margin of t le strated for the Cadwallader-Tyaughton Creek system to the Shulaps ultramafic cornplex by Tom Calon and coworkels west, but it has the opposite sense of vergence because the indicates that the Shulaps harzburgite and underlyin:: serpe-- fault and associated shears dip in the opposite direction. tinite melangetogether define a ma,jor southwesr-vergillg The observations summarized here are consistent with the linked thrustsystem comprising a number of hin:erlan:- map-scale geometry of the Tyaughton Creek and Castle Pass dipping duplexes (Calon ef a/., 1990). The large-sde tw:" fault systems from CarpenterLake to the head of Tyaughton folddivision of the Shulaps complex, comprisin:: manlle Creek, as they enclose a composite lens of relatively old, harzburgite sitting structurally above serpentinite nelan !e presumably uplifted rocks and separate it from younger rocks derived from ultramafiwnafic cumulates,reflects !,tuctu~;d to both the northeast and southwest (Figure 1-6-4). Further- stacking of lower over higher stratigraphic elemencs of in more, east-verging folds and thrust faults are documented originalophiolite suite. A similar !;tacking order occkls directly east of the Castle Passfault while northwest to west- within theserpentinite melange itself, as upper stuctu~;~l verging thrust faults occur withinthe Cadwalhder and levelscontain knockers of ultramafic-maficcwnu1at:s Tyaughton groups along theTyaughton Creek fault. Theseare whereas a large block. of gabbro and pillowed vdcani:s consistent with the outward-directed vergence of structures linked by an intervening dike swarm occurs along the strut'- related to thisuplifted block implied by fault dips and turd base of the melange. Serpentinite forming the matrix of kinematics observed in the Gold Bridge area. The uplifted the mClange commorily displays a penetrative. steeFly lens enclosed by the Tyaughton Creek and Castle Pass faults northeast-dipping SI foliation cut by discrete, nlor? gently resembles the "positive flower" or "palm tree" structures northeast-dipping S, slip surfaces spaced several millimetr: s documented along numerous strike-slip fault systems (Syl- to several centimetres a.part; sigmoidal deflection of SI at I, vester, 1988). The uplift may have been localized by the boundaries typically suggest a top-to-the-southwesl. !sense of changefrom northwest to northerly trends of the faults shear. Mylonite, possibly synchronous with the SI serperl- between Tyaughton and Gun creeks since this corresponds to tinite foliation, commonly occurs within gabbro adserperm a restraining bend in a sinistral fault system (Woodcock and tinite along the margins of large knockers. These rnilonil:~ Fisher, 1986; Sylvester, 1988). display a variety of kinematicindicators, including S 12 The Castle Pass fault cuts the Albian Taylor Creek Group foliations, shear hands and rotated mineral grains, that inlll- and the overlying (Albian or Cenomanian ?) Silverquick cate a top-to-the-southwestsense of shear.Serpentin le conglomerate, and is itself cut by the 64 Ma Eldorado pluton melange along the northeastern margin of the Shulaps COIII- (Carver rf ul., 1989a). The Tyaughton Creek fault also cuts plex is not as well exposed as the belt to the southwest, hut s the Taylor Creek Group, and is apparently continuous with inferred to comprise pa:? of the same imbricate zone and to :,e the Bralorne fault 2one, within which reverse-sinistral miner- continuous with the southwestern melange beneath the int :r- alized shear veins probably formed between 86 and 91 Ma vening mantle harzburf:ite. S-C foliations within m'deratf ly (Leitch, 1989). Farther south within the Bralorne fault zone northwest-dippingserpentinite mylonite along the cont;cct penetrativedeformation and metamorphism of the Chism betweenserpentinite melange and overlying. man e Creek schists nccurred between 85 and 100 Ma (Rusmore, harzburgite near upper Peridotite Crtxk support this int:r- 1985). Important strands of the Bralorne-Tyaughton Creek pretation as they also indicate a top-to-the-westsense of fault system are truncated by the Coast plutoniccomplex, but shear.

Ceologicul Fieldwork 1989, Paper 1990-1 5 .i Deformation within the Shulaps serpentinite melange was mesoscopic folds and is locally crenulated and folded about in partsynchronous withintrusion of asuite of dioritic later open to tight folds that are approximately coaxial with hornblende porphyrydikes. These dikescaused prograde theearlierones. Thefoliation within the schists isconcordant metamorphism of serpentinite to talc-serpentine-magnesite to foliation and thrust contacts within the overlying Shulaps schist, locally with regenerated olivine porphyroblasts. The serpentinite mtlange as well as to those within the southern dikes arelocally boudinaged within the serpentinitemklange imbricate zone of serpentinite melange and Hurley metasedi- matrix and locally occur inknockers wherethey are truncated ments. Where observed southwest of Rex Peak, the contacf at the contact with the enclosing serpentinite. They therefore between BridgeRiver schists and underlying milange is predate some movement within themtlange but because they marked by a mylonitic fabric which appears to gradeupward caused prograde metamorphism of previously serpentinized into the schistosity in the overlying schists, and is folded ultramafic rock, and at one locality cut thefoliation in a aboutlater upright, gently east-plunging, south-verging penetratively deformed metasedimentary knocker, are inter- asymmetric folds (Schiarizza et al., 1989). These relation- preted to have been intruded during the late stages of defor- shipssuggest that foliationand later deformationfabrics mation (Archibald et a[., 1989; Calon et al., 1990). These displayed by the Bridge River schists in the northern part of dikes in part resemble the Blue Creek porphyries; one which the belt relateprimarily to acomplex history of thrust occurs asaligned pods within serpentinitemelange along the imbrication and folding during south to southwest-directed northeastmargin of the Shulaps complexhas yielded a emplacement of the Shulaps complex. The timing of this qAr-x9Ar plateau age of 77 Ma (Archibald e? al., 1990). event is not well constrained but, asdiscussed in theprevious Heating of the mtlange at this time is also suggested by a 73 section, the lateststages of deformation may have occurred in Ma 40Ar-39Ar date obtained from an amphibolite knocker theLate Cretaceous. It predatedintrusion of the Eocene within the southwestern melange belt which may date cool- Mission Ridge pluton, which crosscuts the southern imhri- ingfollowing intrusion-related heating (Archibald et a/., cate zone (Figure 1-6-3). 1989). Farther south, foliationwithin the Bridge Riverschists has The Shulaps serpentinite mklange, comprising the struc- a consistent northwest strike with shallowto moderate north- tural base of the imbricated Shulaps ophiolite complex, sits eastdips. Stretching and intersectionlineations are sub- structurally above Bridge Riverschists in the area of Jim and horizontal and consistently trend northwest. as do the fold Hog creeks. Thecontact was not observed, but is apparently hinges of both early and late folds. Kinematic indicators, concordant to themoderately to steeply dipping foliation includingshearbands, S-C planesand rotated por- withinboth themtlange and underlying schists,and is phyroblasts,give a consistentupper-member-to-the- inferred to be a thrust contact, assuggested by Potter (1983). southeastsense of shear(Coleman, 1989). lbo late- To the east, along East Liza Creek,the serpentinite mtlange syntectonic granitic dikes which crosscut foliation in the was apparently thrust over the Cadwallader Group. In this enclosing schists hut have the same S-C mylonitic fabrics area, a greenstone-gabbro complex at the baseof the melange have yielded 47? I Ma U-Pb zircon ages (Coleman, M.Sc. sits structurally above theHurley Formation across a narrow thesisin progress). This suggests that the top-to-the- mylonitic zone which is deformed by east-verging folds and southeast kinematic indicators formed in the Eocene, proba- associatedslaty cleavage (Calon et al., 1990). Athrust bly during dextral strike-slip faulting, and are relatively late contactalso defines the northern margin of the Shulaps products of a protracted historyof ductile deformation within complex (Figure 1-6-3) where southerly dipping serpentinite the Bridge River schists. milange at the base of the complex overlies subgreenschist grade BridgeRiver rocks. Thecontact was not observed, but YALAKOMFAULT southerly dipping striated shear surfaces locally bounding a The Yalakom fault is the most prominent structural feature sigmoidal flattening(?) foliation within Bridge River rocks of theregion as it separates areas of sharply contrasting near the contact suggest southerly directed thrusting of the stratigraphyand structural style (Figure 1-6-1).A major Shulaps complex over the Bridge River complex. steeply dipping fault zone bounding the Shulaps complex along the Yalakom River was first described and named the INTERNAL STRUCTURE OF THE Yalakom fault by Leech (1953). It was traced northwestward BRIDGE RIVER SCHISTS through the Taseko Lakes and map areas by Tipper (1969, 1978) who postulated that it was the locus of The Bridge River schists comprise several kilometres of major right-lateral displacement. It extends southeastwardto structural thickness of foliated and heated schist and phyl- Lillooet, where it is truncated by the more northerly trending lite intrudedby abundant syntectonic topost-tectonic granitic Fraser fault system (Monger and McMillan, 1984),along to felsic porphyry intrusions.The schists are truncatedby the which it is separated by about 90 kilometres from its probable Mission Ridge fault on the northeast and by the Marshall offset equivalent,the Hozameen fault, to the south (Monger, Creek fault on the southwest. They are structurally overlain 1985). Dextral offset of more than 100 kilometres has been by the Shulaps complex to the north. and several kilometres postulated along the Yalakom fault based on a number of south of the Shulaps enclose an imbricate lens of Shulaps different piercing point correlations. These include: 130 to serpentinite mklange and penetratively deformed metasedi- 190 kilometres offset of Middle Jurassic volcanic rocks that mentary rocks of the Hurley Formation. outcrop within the Mount Waddington, Anahim Lake and Foliation in the northem pat of the Bridge River schist belt Bella Coola map areas (Tipper, 1969); 125 to 175 kilometres dips tothe north, beneath the structurally overlying Shulaps offset of similar submarine-fan facies within theAlbian complex. It is axial planar to gently east or west-plunging Jackass Mountain Group between the Camelsfoot Rangeand 64 British Columbia Geological Survey Branch Chilco Lake (Kleinspehn, 1985); and about 100 kilometres hornblende feldspar porphyry, granodi(xiteand diorite wer: separation between the Shulaps ultramafic complex and the noted at several localities along or nea.: its inferred 1:race. Petch Cieek serpentinite along the Horameen fault, after first accounting for85 kilometres of dextral offset along the Fraser BRIDGERIVER FAULT fault (Umhoefer, 1989). While none of these reconstructions TheBridge River fault apparently diverges from ths: is unequivocal, they are consistent with the dextral sense Yalakom fault between the mouths of Blue and Beavsrdanl inferred within the Taseko-Bridge River project area, and creeks, fromwhere it extznds southeastward alongthe slope; with the large offset implied by the juxtaposition ofcontrast- southwest of the Yalakom River to follow the lower come 0' ing Albian lithologies of the Jackass Mountain and Taylor the river and the adjoining Bridge River to the \,ici~~ityoi Creek groups. CamooCreek. Itbounds the imbricatedHurley--l3ridg~: During the presentstudy the Yalakom fault has been traced River wedge to the northeast and separates it from rocks n' southeastward across the Noaxe Creek map area (Glover et the Shulaps and Bridge River complexes to the southwest 7 a/., 1988a. 1988b), through the southwest comer of the Big The fault zone is locally markedby conspicuous exposures o~' Bar Creek sheet to the southeast corner of the Bridge River serpentinite melange alcsng the Bridge River; this mrllangl. map sheet (this report). Northwestof Blue Creek thefault is a includesknockersofperi~otite,gabbroanddiabasesiirilartr~ steeply dipping structure commonly marked by a zone of those seen within the melange zone at Ithe structural base o~' serpentinized to listwanite-alteredultramafic rocks up to the Shulaps complex. This suggests that the Shulaps ma!' several hundred metres wide. It juxtaposes broadly folded have been translated in a dextral sense along the fault zone and faulted MiddleJurassic and Jackass Mountain Group although the dip, timing and nature of movement hzie no. rocks on thenortheast against mnre complexly deformed been established.The relationship of this fault (ty[licall! Powell Creek, Taylor Creek, Bridge River and Shulaps rocks identified as the Yalakom fault by earlier workers:' to thr, tothesouthwest(Figure 1-6-1). Dextral strike-slipmovement major fault bounding the Middle Jurassic sandstone-Jackas is suggested by fibrous minerals and slickensides along fault Mountain Group succession farther northeast (and hew con surfaces within and near the fault zone and by east-trending sidered the main strand (of the Yalakom fault) is also mcer folds within the Middle Jurassic sandstone-Jackass Moun- tain, hut will be discussed further in the section dealin2 wilt tain Group succession that are truncated by the fault (Glover the Mission Ridge fault. eta/., I988a). Shear hands cutting foliated serpentinite along the fault zone near the mouth of Blue Creek also indicate dextral movement, as does the orientation of extensional NORTHEAST-DIPPINGFAULTS ALONG THE veinsand slickensided surfaces in listwanite-altered ultra- YALAKOM AND BRIDGE RIVERS mafite along the fault in the same area. The 4-kilometre-wide lens enclosed by the Yalakom an( Southeast of Blue Creek, the Yalakom fault apparently Bridge River faults southeast of Beaverdam Creek indude! splays into two sub-parallel strands that enclose a wedge of Hurley Formation, Bridge River complex and Relay Moun. imbricated Hurley Formation and Bridge River complex. The tain Group rocksdeformed by southwesterly overturnec northeastern strand separates theMiddle Jurassic sandstone- folds and northeast-dippmg faults. The contacts that bounc Jackass Mountain Group belt on the northeast from the the major lithologic packages were identified as mocleratel) imbricated Hurley-Bridge River wedge and is here consid- northeast-dipping faults lby Coleman (1989) who sugg:estec ered the extension of the Yalakom fault. The southeastern that they might be oblique thrusts. The orientation ,)f the strand separatesthe latter package from the Shulapsand faults was confirmed by #bur 1989 fieldwork, and spa.r;e bul Bridge River complexes to the southeast and is referred to as consistent kinematic evidence suggests that they record sin- the Bridge River fault (Figure 1-6-3). istral transpressional deformation. The kinematic inckatorr The northeasternstrand is most readily related to the include:sinistral shear Ihands cutting foliated serperltinitt Yalakom fault since it bounds the same package of struc- along a northeast-dipping: Hurley-Bridge River fault 'conlac! turally simple Middle Jurassic and Jackass Mountain Group west of Applespring Creek, outcrop-scale fault system:; with rocks that occur along the fault to the northwest, and jux- oblique east 10 east-northeast plunging striations preSeNed taposes it againstBridge River and Hurley rocks which on northeast-dipping fa,llts and top-to-the-westsense oi elsewhere in the region occur only on the southwest side of movement indicated by offsetmarker beds; and westtc the Ydlakom fault. This fault is not exposed and was not southwest-vergingfolds with axes locally trending more recognized by previous workers; its trace crosses the wooded northerly than the strike .of the northeast-dipping faulti. ridges northeast of the Yalakom and Bridge River valleys.Its The relationship of thr: northeast-dipping transpres:;ional presence is corroborated by contrasting structural styles since faults within this wedge to adjacent structures is not certain the Middle Jurassic sandstone and Jackass Mountain Group Coleman (1989) correlated the easternmost of these faults, comprise a structurallysimple, steeply dipping east- which separates pillowed greenstone, gabbro and diab.lse oi northeast facing belt, while the Hurley-Bridge River belt is the Bridge River complex from overlying Hurley Formation characterized by west to southwest-verging overturned folds (her Lillooet Group) with the Yalakom fault. OUI' 1989 and imbrication across northeast-dipping faults. Neverthe- fieldwork has established, however, that the Yalakom fault is less, the fault is in places poorly constrained because of poor farther tothe northeast, ahere it separates the Hurley 1--orma- exposure and the difficulty in differentiating between the tion from a structurally smpler Middle Jurassic sands:one-

Middle Jurassic rocks and Hurle)' Formation where only the Jackass Mountain Group panel. Although neither the(d p nor finer grained facies are represented.The fault was apparently kinematics along this secl.ion of the Yalakom fault have been the locus of igneous intrusion as quartz feldspar porphyry, established it is readily correlated with the Yalakom fault

Geological Fieldwork 1989, Puper 1990-1 65 farther northwest, which is a steeply dipping dextral strike- related to dextral strike-slip faulting. The Mission Ridge fault slip fault. Since the panel of imbricated Hurley and Bridge is in turn cut by the Fraser fault system, and was therefore River rocks containing these northeast-dipping transpressio- probably active in the Middle to Late Eocene. nal faults apparently pinches out between the Yalakom and The majordisplacement suggested by the contrast in Bridge River faults near BeaverdamCreek. they may be pre- metamorphic gradeacross the low-angle MissionRidge fault Yalakom structures isolated within this fault-bound wedge. It indicates that lithologic units and structures in its hanging- is noteworthy that the sinistraltranspressional movement wall have been displaced a considerable distance northeast- along these faults is similar to that documented along early ward relative to adjacent footwall rocks. If pre-normal- Late Cretaceous structures in the Gold Bridge area, and also faulting dextral shear recorded in footwall fabricsis related to that theimbricated Hurley-Bridge River-greenstone- movement on the Yalakom fault, then the Yalakom is an diabase-gabbropanels within the wedge bear a strong earlier structure that may have been cut by the Mission Ridge resemblance to imbricateslices associated with thelower fault.This suggests that thesoutheastern segment of the serpentinite melange south of the Shulaps complex and its Yalakom fault identified to the northeast of the Yalakom and possible offset equivalent west of the Marshall Creek fault. Bridge rivers represents only a relatively high-level expres- sion of an original Yalakom fault that was detached from its roots and translated eastward along the Mission Ridge fault. MISSIONRIDGE FAULT Perhaps continued orlater strike-slip(?) movement along the The Mission Ridge fault extends from 4 kilometres south- root fault broke through the overlying cover (hangingwall of east of Lillooet, where it is truncated by the Fraser fault, the Mission Ridge fault) at the position of the Bridge River northwest at least 40 kilometres to Shulaps Creek.It was first fault and generated the present fault configuration. recognized and named by Coleman (1989) who established the geometry. kinematics and relative timingof movement on the segment of the fault between Lillooet and the Bridge MARSHALLCREEK FAULT River canyon. TheMarshall Creek fault is a prominentnorthwest- The Mission Ridge fault strikes northwest and hasa dip of trending structure that separates Bridge River schists on the 25" to 30'northeast. South of the Bridge River it juxtaposes northeast from lower grade BridgeRiver rocks on the south- low-grade, non-penetratively deformed Bridge River com- west (Potter, 1983, 1986). It is a regionally persistent fault plex and Eocene nonmarine sedimentary rocks in the hang- that extends from the Fraser fault system, 35 kilometres south ingwall againstlower to uppergreenschist-grade Bridge of Lillooet (Monger and McMillan, 1984) for W kilometres River schist and phyllite. Assuming a normal geothermal northwestward to Marshall Lake. From there it extends an gradient, an estimated 12 kilometres of down-dip displace- additional 45 kilometres northwest as the Relay Creek fault ment is required to account forthe contrasting metamorphic system (Glover ef al., 1988a. 1988b) before apparently grade of hangingwall and footwall rocks (Coleman, 1989). mergingwith the Yalakom fault nearBig Creek (Tipper, The fault trace crosses the Bridge River about 1 kilometre 1978). west of the Yalakom River confluence and continues norrh- Withinthe study area theMarshall Creek fault zone westward, parallel to the Yalakom, to at least Shulaps Creek. comprisestwo steeply dippingstrands. The northeastern Between the Bridge River and LaRochelle Creek the fault strandseparates penetratively deformed greenschist-facies trace follows the base ofa distinctive planar slope. Theslope Bridge Riger complex and locally imbricated Cadwallader has the same orientation as the Mission Ridge fault, consists Groupand serpentinite mklange on the northeast from of footwall schists and phyllites. and is interpreted to be the prehnite-pumpellyite-gradeBridge Riverrocks on the south- exhumed fault surface. The contrast in metamorphic grade west. A parallel strand to the southwest juxtaposes the low- across the fault diminishes to the northwest and is evidence gradeBridge River rocksagainst a similar BridgeRiver for a decrease in the amount of normal displacement at this package and unconformdbly overlying Eocene(?) volcanics, end of the fault. Its continuation beyond Shulaps Creek is indicating a component of Eocene or later southwest-side- uncertain, butit may swing westward and mark the boundary down displacement. Thetwo strands apparently mergeto the between Bridge River schists and Shulaps harzburgite, per- southeast where,south of Carpenter Lake, the fault also cuts hapsaccounting for thepinching out of theintervening the Eocene MissionRidge pluton whichintrudes Bridge serpentinite melange (Figure 1-6-3). Alternatively, or in River schists on its northeast side. Farther to the southeast, addition, it may splay into a series of imbricate faults extend- beyond the limitsof the present map area, the Marshall Creek ing north and northwestward from Shulaps Creekas outcrop- fault truncates a low-angle fault on its southwest side which scale, predominantlyeast-side-down. low and high-angle juxtaposes footwall Bridge River schist against hangingwall normal faults were observed at several localities in this area. low-grade Bridge River rocks (Coleman, 1989). The low- The Mission Ridge fault truncates Eocene(?) nonmarine angle fault is interpreted by Coleman to bepart of the Mission sedimentary rocks in its hangingwall and the 47.5 Ma Mis- Ridgefault; its restoration gives approximately 3.5 kilo- sion Ridge pluton in its footwall (Coleman, 1989).Where the metres of sourhwest-side-down vertical displacement on the fault zone is exposed on the southeast sideof the BridgeRiver Marshall Creek fault (see Coleman, 1989, Figure 1-12-3). canyon, an anastomosing fracture cleavage parallel to the The Marshall Creek fault is also inferred to have been the fault is superimposed onfoliation of the Bridge River schists locus of significant dextral strike-slipmovement. This in a zone 5 metres wide. This confirms that brittle normal inference is based partly on the prominent system of north- movement on the Mission Ridge fault postdates penetrative erly trending faults that forms a transfer zone linking the strain in the Bridge River schists, part of which may be Marshall Creek with the Ydlakom strike-slip fault west of the 66 British Columbia Geological Survey Branch Shulaps complex (Figure 1-6-1). The regional fault pattern SUMMARY and distribution of lithologic units suggest that these north- erlytrending faults form the southeastem margin of an The Taseko-Bridge River project arm was the locls of i extensionalduplex within a dextralstrike-slip system complex history of mid-Cretaceous to mid-Tertiary deforma (Schiarizza etul., 1989a). Detailed mapping alongthe south- tion and intrusion that was superimposed on an carlie westernmargin of the Shulaps complex supports this deformationalhistory that in partincluded subduztion inference sincenortherly trending faults in thisarea are related deformation and metamorphism of the Bridge Rive typically transtensional (Calon er al., 1990). Dextral offset is complex. Themain conclusions drawn from our 1989field furthersupported by tentativecorrelation of thethrust- work are summarized as follows: imbricatedpackage of HurleyFormation, serpentinite The northwest to north-trending Tyaughton Creek an< melange and Bridge River schists that is truncated by the Castle Pass fault systems were the locus ofriinistra MarshallCreek fault IO kilometressoutheast of Marshall transpressionaldelhrmation. They wereprev ousl! Lake with a similar (but lower metamorphic grade) package attributed to Late Cretaceous dextral strike-slip relate1 truncated on the other side of the fault IS kilometres to the to the Yalakom system, and inferred to be dislinctl]. northwest at Lira Lake (Schiarizza et a/., 1989b). If strike- later thanmid-Cretaceous thrust faults they Iscall!. slip was synchronous with dextral shearalong horizontal truncate. Our revised interpretation suggests th,u steel' stretching lineations within the Bridge River schists, it pre- faults andcompres;sional structures formed tozethe' dates the southwest-side-down normal faulting documented during early LateCretaceous sinistral transpression along the southeastern segment of the Marshall Creek fault This provides a better explanation ]for several mapscall: features within the Taseko-Bridge River project areil including: the localization of compressional structure,: MINERAL OCCURRENCES along the north-trending fault segments associate'i wit11 the Tyaughton Creel<-Castle Pass s.ystems in the S;PNCI: Metallic mineral prospects within the Yalakom River area Lake-EldoradoMountain area, since these reflec: occur mainly between theMarshall Creek and Yalakom- restraining bends in a sinistral fault system;:old thl: Bridge River faults. These include mesothermal gold-quartz abrupt change in r.tructural stylewest ofBig: Creel. veins within stocks of Blue Creek porphyry,as well as veins, where relatively untieformed Upper Cretaceous Powell disseminations and stockwork containingmolybdenum, cop- Creek volcanics apparently rest unconformably abow: per and gold along the northeastern margin of the Mission both low and high-angle faults (Glover etal., 198 7) that Ridge pluton. In addition, ultramafic rocks of the Shulaps may be related to transpressionaldeformatio'n. Tht: complexcontain small chromite concentrationsand have Tyaughton Creek falllt is apparently continuous with th,: been prospected for nephrite jade, magnesite and chrysotile Bralorne fault zone: farther southeast, which was th,: (Figure 1-6-5). Cinnabaroccurs locally as disseminations locus of mesothernial goldquartz: veining durir g thi i and veinlets near the Bridge River fault. deformation. Gold-bearing quartz veins at the Yalakom and Elizabeth Imbrication and thrust emplacement of the Shulapi prospects occur within stocks of porphyritic quartz diorite ophiolite complex over the Bridge River complcx anll (Blue Creek porphyry) that cut Shulaps harzburgite north of CadwalladerGroup occurred along southwesterl:! Blue Creek (Figure 1-6-5). The veins are typically ribboned directedthrust faults. 40Ar-39Ar coolingdates fronl and occupy steeply dipping, northerly trending shears (Gaba dikes and knockers within the Shulaps serpentinit': etal., 1988). They contain visible gold andrarely more than a melange suggest a Late Cretaceous age for the latest few per cent sulphide minerals, mainly arsenopyrite. pyrite pulse of deformation (Archibald ,et al., 1990). 'Thrust and chalcopyrite. Theseveins are similar to the mesothermal faults that may be related to the Shulaps imbricatt: zons: veins at the Bralorne and Pioneer mines,which have yielded are also identified west of theMarshall Creel: fault most of the gold produced from the Bridge River mining where they separateslices of serpentinite rnilange, camp. CadwalladerGroup and Bridge River comple:: Most other metallicmineral occurrences areassociated (Schiarizza et al., 1989a. 1989b). West to southwest- with granodiorite of the Mission Ridgepluton. Theseinclude verging overturned folds and transpressional faults als1 high-sulphide auriferous veins at the Spokane and Broken occur east of the Shulaps complex where they imhricat~: Hill prospects as well as stockwork molybdenite at the Cub lenses of Cadwallader Group, Bridge River cornplex. showing, which was discoveredduring the course of our serpentinite-diabase-greenstone and Relay Mountai~~ mapping. These showings are described in a separate report Group between the Bridge River and Yalakoln fxults. by Gaba (1990, this volume). The structures d-scribed in the previous tmo para- Cinnabar veinlets and disseminationsat the Eagle andRed graphs may have all formed during a protracted perioll Eagle prospectsare withingreenstoneand greenstone breccia of late Early Cretaceous to early Late Cretaceous. com- of the Bridge Rivercomplex. Thecinnabar is associated with pressive to transpressivedeformation. Theearliest man- widely spaced carbonate veins that occupy shears parallel to ifestation of this ebent is the implied deformation an(l the adjacent Bridge River fault. Similar mercurymineralira- uplift related to deposition of the synorogenic Taylor tion occurs along the Yalakom fault 30 kilometres to the Creek Group (Garver, 1989). Although middle to earl i northwest (Glover etul., 1988a. 1988b),and along theRelay Late Cretaceous contractional deformation is recogn- Creek fault system north of (Schiarizza et ized throughout the region (e.g. Rusmore and Wood- al., 1988a. 1988b). sworth,1989: Joarneay and Ckontos, 1989). th: Geological Fieldwork 1989, Paper 1990-1 6' Figure 1-6-5. Mineraloccurrences, Yalakom River map area, MINFILE number precedes deposit or prospect name. Mineral abbreviations: apy = arsenopyrite. born = bornite, cinn = cinnabar, cpy = chalcopyrite, pa = galena. mo = molybdenite. py = pyrite, PO = pyrrhotite, sche = scheelite, sph = sphalerite, stib = stibnite. tetra = tetrahedrite.

regional extent or significance of the sinistral compo- an extensional dextral-strike-slip duplex (Schiarizra et nent is at present uncertain. It is of interest, however, nl. , 1989a). Shear bands in foliated serpentinite along thatGreig (1989) hasrecently documented mid- the Yalakom fault near BlueCreek corroborate the Cretaceous sinistraltranspression along thePasayten dextral shear implied by these map-scale features. Top- fault to the southeast. to-the-southeastkinematic indicators associated with 0 Dextral strike-slip faultingalong the Yalakom and Relay subhorizontalstretching lineations within northeast- Creek-Marshall Creek fault systems postdates thecom- dipping Bridge River schists also indicate dextral shear pressionalto transpressional deformation described that may be related to movement along the bounding above. Dextralmovement along this system is sug- Yalakom and/orMarshall Creek faults. The same gested by east-trending folds within the Middle Jurassic kinematicindicators arefound in late synkinematic sandstone and Jackass MountainGroup northeast of the Eocene dikes, suggesting that dextral faulting was, at Yalakom fault (Glover et a!., 1988a), and by a transfer least in part, Eocene in age. The upper limit of dextral zone of northerly-trending faults that links the Relay movement is not well constrained, however, and it is Creek-MarshallCreek and Yalakomfault systems possible that the early stages of strike-slip faulting along northwest of the Shulaps ultramafic complex to define the Yalakom and/or Marshall Creek systems coincided 68 Geological Columbia BritishBrnnrh Survey with the final pulse of (Late Cretaceous) deformation theearly metamorphic pattern such that itsspatial documented within the Shulaps serpentinite mklange. relationship to the Shulaps ophiolite is unclear. 0 Miller (1987) conducted a detailed structural analysisof BridgeRiver schists throughout: most of lhe high Lillooet and Jackass Mountain Group rocks exposed grade belt, which ea.tends from the Shulaps conlplex between the Yalakom and Fraser faults directly northof more than 40 kilometres southwestward to the Fraser Lillooet.He concluded that structures within these River (Monger and McMillan, 1984: Coleman, 1989) rockssuggested a history of left-lateralfollowed by are intrudedby abundant synkinematicto postkinematic high-angle reverse movement along the Yalakom fault. MiddleEocene granitic rocks, and record Middle The panel of oblique-sinistral faults and related folds Eocene ductile deformation (Price et a/., 1985; Pfxter, documented here between the Yalakom andBridge 1986: Coleman, 1980). Mostof thebelt was therefore at River faults is more or less along strike from Miller's elevated temperatures during the Middle Eocene, per- study area, but contains distinctly different stratigraphic haps directly or indirectly related to the granitic intru- elements. Furthermore, these structures are inferred to sions localized along thebelt at that time. Later uplift of be mid-Cretaceous in age and unrelated to the Yalakom the belt was in partaccommodated by extensional fault which is hereinterpreted as ayounger dextral faulting along thegently northeast-dipping Mission strike-slipfault. Their relationship to thestructures Ridge fault (Coleman, 1989). Displacement alonf: this studied by Miller is therefore not readily apparent. fault seems to diminish to the north, suggesting that However, Greig (1989) has alsodocumented mid- uplift may have been greatest in the south and imparted Cretaceoussinistral transpression along the Pasayten a northward tilt to the block. This is consistent with fault, which marks the northeastern boundaryof a panel preservation of the structurally higher Shulaps ophiolite of Jackass Mountain Group and related rocks that is complex at the north end, and of structures related to its probablythe offset equivalent of the one studied by emplacementwithin Bridge Riverand Cadwallader Miller. Itis thereforesuggested that thestructures Group rocks directly beneath it. describedby Miller may reflectmid-Cretaceous sinistral transpression, and be unrelated to (younger) Metallic mineral occurrences within the Yalakom River movement along the Yalakom fault. area are concentrated within the bell: of relatively higher grade metamorphic rocks between the Marshall Creek 0 The BridgeRiver schists and phyllites between the and Yalakom fault!;. Theseinclude the Elira'3eth- MarshallCreek and Mission Ridge faults were Yalakom mesothermal gold-quartz veins within s:ocks penetrativelydeformed under lower to upper of Blue Creek porphyry, as well a:$ base and pre'ious greenschist-facies metamorphic conditions, in contrast metalbearing vein!; anddisseminations within and to the predominantly prehnite-pumpellyite-facies that adjacent to the Mission Ridge pluton. The metal pros- characterizesrocks to thenortheast and southwest. pects are thereforebroadly related to the inl:rusive Elevated metamorphic conditions along the north endof activity that Characterized the belt in Late Cret'lce:(Ius to the belt apparently prevailed duringimbrication and Eocene time. Mineralization associated with the Mis- southwesterlydirected thrusting of theShulaps sion Ridge pluton includes stockwork molybdenlo: that ophiolite complex over the Bridge river complex and was discovered during the coursc:of this surnner's Cadwallader Group. Metamorphism was in part syn- work; this type of mineralization was previousl:i un- chronous with intrusion of asuite of late-kinematic recognized and repr'?sents a new exploration tari:et in hornblende feldspar porphyry dikes of Late Cretaceous the Bridge River mining camp (Gaba, 1990). age, but earlierdeformation was also in part ductile and generatedmylonites and greenschist-facies meta- The stratigraphic succession northeast of the Yaltikom morphic mineral assemhlages prior to intrusion of the fault is represented by Middle Jurassic volcanic :sand- dikes(Archibalderal., 1989, 1990;Calonrtal., 1990). stone, granule to pebble conglomerate and lessconmon Potter (1983, 1986) suggested that the heat source for siltstone and shale, together with dlsconformahly over- thismetamorphism was hotupper mantle of the lying upper Lower Cretaceous arkosic sandstone. vol- obducted Shulaps complex. The present study has not canicand plutonic-clast conglomerate, siltstone and documented an inverted metamorphic gradient beneath shale of the Jackass Mountain Grc'up. These units are the Shulaps complex where locally, as along the north- lithologically distinct from age-equivalent strata on the ern margin of the complex, Shulaps rocks are in thrust southwest side of the: Yalakom fault, where the Middle contact with subgreenschistfacies rocks. However, a Jurassic is represented by mainly sheles and siltstonesof thickslice of serpentinite mklange occurs alongthe theLast Creek formation (Frebold et al., 1969; contact in areas where a thrust relationship between the Umhoefer, 1989) and the upper Lower Cretacecus is Shulaps and underlyingBridge River complex is represented by mainly volcanic an'd chert-rich chstics inferred or documented. Structures within and adjacent of the Taylor Creek Group (Carver, 1989). The Srati- to the melange record a complex deformational history graphic succession on the northeast side of the Yakkom that includes mixing of ophiolitic and lower to upper fault compares more closely to the stratigraphy ID0 to greenschist-faciessupracrustal elements within the 200 kilometres to the south, where the Jackass Moun- melange as well as later imbrication and/or infolding of tain Group is in part directly under'lain by the Lower to themklange and underlying Bridge River and Cad- Middle Jurassic Ladner Group, including lower Middle wallader rocks.This deformationand attendant late Jurassic volcanic sandstones and conglomerates. vol- metamorphism have clearly shuffled andoverprinted canictuff, breccia and local flows of theDewdney

Geological Fieldwork 1989. Puper 1990.1 69 Creek Formation (O'Brien. 1986). These rocks occur Church, B.N., Gaba, R.G., Hanna, J. M. and James.D.A.R. on the northeast sideof the Hozameen fault, the proba- (1988a): GeologicalReconnaissance in theBridge ble southern extension of the Yalakom fault. RiverMining Camp (921115, 16, IO; 920102): B.C. Ministry of Enerxy, Mines and Petroleum Resources, GeologicalFieldwork 1987, Paper 1988-1. pages ACKNOWLEDGMENTS 93.100. The authors wouldlike to thank R. Macdonald, M. O'Dea, Church, B.N., MacLean, M., Gaba, R.G., Hanna,1. M. and D.A. Archibald, T. Calon, J. Malpas, F. Cordey,P.J. James, D.A. (1988b):Geology of theBralorne Map Umhoeferand A. Till for their mapping contributions, Area (92J/15); B.C. Mini.rtry of Enel-gy, Minesand geological insights and good company during the course of Petroleum Resources, Open File 1988-3. this season's fieldwork. We also benefited from field trips Church,B.N. andPettipas, A.R. (1989):Research and anddiscussions with W.R. Smyth, R. Meyers, W.J. Exploration in the Bridge River Mining Camp (925115, McMillan andD. MacIntyre of this ministry, R. Parrish of the 16); B.C. Ministry oj Energy,Mines and Petroleum GSC, Ottawa, and R.L. Brown of Carleton University. Field Resources, Geological Fieldwork 1988, Paper 1989-1, and laboratory work by M. Coleman was funded by project pages 105-1 14. 850001 of the Geological Surveyof Canada (R. Parrish) and NaturalSciences and Engineering Research Council Sup- Coleman,M. (1989): Geology of MissionRidge, near porting Geoscience Grant No.86 awarded toR. Parrish. Bob Lillooet, British Columbia (921, 1); B.C. Ministry of Thurstonand Bob Holt of Cariboo-ChilcotinHelicopters Energy,Mines and Petroleum Resources, Geological Ltd. are thanked for safe and punctual helicopter service. Fieldwork 1988, Paper 1989-1, pages 99-104. Drysdale.C.W. (1916): BridgeRiver Map-area, Lillooet REFERENCES Mining Division: Geologicrd Survey of Canada, Sum- mary report for 1915, pages 75-85. Archibald, D.A., Glover, J.K.and Schiarizza, P. (1989): Preliminary Report on4"Ar139Ar Geochronology of the Duffell, S. andMcTaggart, K.C.(1952): Ashcroft Map Warner Pass, Noaxe Creek and Bridge RiverMap Areas Area. British Columbia;Geological Sumeyof Canuda, (92013, 2;921116); B.C. Ministry ofEnergy, Mines and Memoir 262, 122 pages. PetroleumResources, GeologicalFieldwork 1988, Frebold, H., Tipper, H.W. and Coates, J.A. (1969): Toarcian Paper 1989-1, pages 145-151. and Bajocian rocks and Guide Ammonites from South- western British Columbia; Geological Survey of Can- Archibald, D.A.,Schiarirra, P. and GaNer,J.I. (1990): uda, Paper 67-10, 55 pages. 40Ar-39Ar Dating and the Timing of Deformation and Metamorphism in theBridge River Terrane, South- Gaba, R.G. (1990): Stockwork Molybdenite in the Mission western British Columbia (92012;925115); B.C. Minis- Ridge Pluton: A New Exploration Target in the Bridge try of Energy, Mines and Petroleum Resonces,Geologi- River Mining Camp(92J116); B.C. Ministy ofEnergy, cal Fieldwork 1989, Paper 1990-1, this volume. Mines and Petroleum Resources,Geological Fieldwork 1989, Paper 1990-1. this volume. Cairnes, C.E. (1937): Geology and Mineral Deposits of the Bridge RiverMiningCamp, British Columbia; Geologi- Gaba,R.G., Hanna, M.J. and Church, B.N. (1988): The cal Survey of Canada, Memoir 213, 140 pages. Elizabeth-YalakomProspect, Bridge River Mining Camp (92012); B.C. Ministry ofEnerg?: Mines and ~ (1943):Geology and Mineral Deposits of PetroleumResources, GeologicalFieldwork 1987, Tyaughton LakeArea, British Columbia; Geological Paper 1988-1, pages 329-333. Survey of Canada, Paper 43-15, 39 pages. Garver, J.I. (1989): Basin Evolution and Source Terranes of Calon, T.J., Malpas, J.G. and Macdonald, R. (1990): The Albian-CenomanianRocks in theTyaughton Basin, Anatomy of the Shulaps Ophiolite; B.C. Ministry of SouthernBritish Columbia: Implications for Mid- Energy, Mines andPetroleum Resources, Geological CretaceousTectonics in theCanadian Cordillera; Fieldwork 1989, Paper 1990-1, this volume. unpublishedPh.D. thesis, University of Washington, Church, B.N. (1987): Geology andMineralization of the 221 pages. Bridge River Mining Camp (925115, 92012, 921110); Garver, J.I., Schiarizza, P. and Gaba, R.G. (1989a): Strat- B.C.Ministry ofEnergy, Mines aud Petroleum igraphy and Structure of the Eldorado Mountain Area, Resources, Geological Fieldwork 1986, Paper 1987-1, ChilcotinRanges, Southwestern British Columbia pages 23-29. (92012 and 925115); B.C. Ministry of Energy, Mines Church, B.N. and MacLean, M.E. (1987a): Geologyof the and Petroleum Resources, Geological Fieldwork 1988, Gold Bridge Area (921115W);B.C. Ministry $Energy, Paper 1989-1, pages 131-143. Mines and Petroleum Resources, Open File 1987-1 1. Garver, J.I., Till, A.B., Armstrong, R.L. and Schiarizza, P. Church, B.N. and MacLean, M.E. (1987b): Geology and (l989b): Permo-Triassic Blueschist in the Bridge River Mineralization in the vicinity of the Mary Mac Mine; Complex,Southern British Columbia; Geological B.C. Minisrryof Energy, Mines und Petroleum Society of America, CordilleraniRocky Mountain Sec- Resources, Exploration in BritishColumbia 1986, tions Annual Meeting,Spokane, Washington, Abstracts pages B33-B37. with Programs, page 82.

70 British Columhio Geological Survey Brunch Glover J.K. and Schiarirza. P. (1987): Geology and Mineral McMillan, W.J. (1976): Granite Creek Property, (92013W); Potential of the Warner Pass Map Area (92013);B.C. B.C. Ministry of .Energy,Mint.s and Petrureum Ministry of €nergy, Mines und Petroleum Resources, Resources, Geology in British Columbia, 1975, pages GeologicalFieldwork 1986, Paper 1987-1, pages 67-84. 157-169. Miller, M. (1987): Deformationnear Lillooet, British Glover, J.K., Schiarizza, P., IJmhoefer, P.J. and Garver, J.I. Columbia:Its Bearing on the SlipHistory OJ the (1987): Geology of the Warner Pass Map Area (92013); Yalakom fault; unpublished M.Sc. thesis, Uniwers:ryof B.C. Mini.Ttry of Energy, Mines and Petroleum Washington, 102 pap,es. Resources, Open File 1987-3. Monger, J.W.H. (1977): Upper Paleozoic Rocks of the West- Glover, J.K., Schiarizza, P. and Garver, J.I. (19X8a): Geol- em CanadianCordillera and theirBearing or1 Cor- ogy of the Noaxe Creek Map Area (92012): B.C. dilleranEvolution; CanadianJournal of €urr,'l Sci- Ministry of Energ?: Mines und Petroleum Resources, ences, Volume 14, pages 1832-1859.

GeologicalFieldwork 1987, Paper 1988-1, pages ~ (1985): Structural Evolution cl the Southwestem 105-123. IntermontaneBelt, Ashcroit and HopeMap Areas, Glover, J.K., Schiarizza, P.,Garver, J.I., Umhoefer, P.J. and BritishColumbia; in Current F!esearch, Part A, Tipper, H.W. (198Xb): Geology and Mineral Potential Geological Survey qf Canada, Paper 1985-lA, pages of the Noaxe Creek Map Area (92012); B.C. Ministryof 349-358. €nergy,Mines nnd Petroleum Resources, OpenFile Monger, J.W.H. and McMillan, W.J. (1984): Bedrock Geol- 1988-9. ogy of Ashcroft (921) Map Area; Ckological Survey of Greig, C.J. (1989): Geologyand Geochronometry of the Canada, Open File !>go. Eagle PlutonicComplex, Coquihalla Area, South- Nagel, J.J. (1979): The Geology of prt of the ShJlaps western British Columbia; unpublished M.Sc. thesis, Ultramafitenear Jim Creek, Southwestern Btitish The Univer.Tiry ofBritish Columbia, 423 pages. Columbia; unpub1ishedM.S~. thes~s,The UniverJiy of British Columbia, 74 pages Jeletzky,J.A. (1967): Stratigraphyand Paleontology of Lower Cretaceous and Upper Jurassic Rocks of Taseko O'Brien, J. (1986): JurassicStratigraphy of the Methow Lakes (92-0) andPemberton (92-J) MapAreas; in Trough,Southwestern British Columbia; in CLrrent Report of Activities, Part A, GeologicalSurvey of Research, Part B, Gdogical Survc.?. of Canada, Paper Canada, Paper 67-IA, pages 65-68. 86-1B. pages 749-756. Price,R.A., Monger, J.W.H. and Roddick,J.A. (1985): Jeletzky, J.A. and Tipper, H.W. (1968): Upper Jurassic and Cordilleran Cross-swtion, Calgary toVancouwr; in Cretaceous Rocks of Taseko Lakes Map Area and their Field Guides Geology and Mineral Deposits the Bearing on theGeological History of Southwestern to in SouthernCanadian Cordillera,D. Tempelman-Kluit, British Columbia; Geologicul Survey of Canada, Paper Editor, GeologicalSuciety ofAmerica, Cordillemr Sec- 67-54, 218 pages. tionAnnual Meel:ing, Vancouver, B.C., ages Journeay, J.M. and Csontos, L. (1989): Preliminary Report 3.1-3.85. on the Structural Setting along the Southeast Flank of Potter, C.J. (1983): Geology of the Bridge River Complex, the Coast Belt, British Columbia; in Current Research, Southern Shulaps Range, British Columbia: A 1L:cord Part E, Geological Survey ff Canada, Paper 89-IE. of Mesozoic Convergent Tectonics., unpublished 1'h.D. pages 177.187. thesis, University of Washington, 192 pages.

Joubin, ER. (1948): Structural Geology of the Bralome and ~ (1986): Origin, Accretionand Post-accretionary Pioneer Mines, Bridge River District, British Colum- Evolution of the Bridge River Terrnne, Southwest Brit- bia; Western Miner, July 1948, pages 39-50. ish Columbia; Tectonics, Volume 5, Pages 1027- 1041. Kleinspehn,K.L. (1985): CretaceousSedimentation and Roddick,J.A. and Hutchison, W.W. (1973): Petrkerton Tectonics,Tyaughton-Methow Basin, Southwestern (East Half) Map AIea, British Columbia; Geohgicai British Columbia; Carradian Journal of Earth Sciences, Survey of Canada, Paper 73-17. 2 I pages. Volume 22, pages 154.174. Rusmore, M.E. (1985): Geology and Rctonic Signilicance Leech, G.B. (1953): Geology and Mineral Deposits of the of the Upper Triassic Cadwallader Croup and its Bound- Shulaps Range; B.C. Mini.rtry of EnerR?: Mines and ing Faults, Southwest BritishColumbia; unpublished Petroleum Resources, Bulletin 32, 54 pages. Ph.D. thesis, Univerrity of Washinpton, 174 pagcs.

Leitch, C.H.B. (1989): Geology, Wallrock Alteration, and ~ (1987): Geology of the Cadwallader Group and the Characteristics of the Ore Fluid at the Bralorne Meso- Intermontane-Insular Superterrane: Boundary, South- thermalGold Vein Deposit,Southwestern British western British Columbia; Canadian Journal qr Farth Columbia; unpub1ishedPh.D.thesis, UniversityofBrir- Sciences, Volume 24, pages 2279-2291. ish Columbia, 483 pages. Rusmore,M.E., Potter, C.J. andUmhoefer, P.J. t.1988): Mathews, W.H. (1989): Neogene Chilcotin basalts in South- Middle Jurassic Terrane Accretion along the Western central British Columbia: Geology, Ages, and Geo- Edge of the Intermontane Superterrane, Southwesterr morphic History; Canadian Journal <$€arth Sciences, BritishColumbia, Geology, Volume 16, page! Volume 26, pages 969-982. 891-894.

Geologicul Fieldwork 19XY, Paper 1990-1 /I Rusmore, M.E. and Woodsworth, G.J. (1989): A Note on Tipper, H.W. (1969): MesozoicandCenozoic Geology ofthe the Coast-Intermontane Belt Transition, Mount Wad- NortheasternPart of MountWaddington MapArea dingtonMap Area, British Columbia: in Current (92N).Coast District, British Columbia; Geological Research, Part E, Geological Survey of Canada, Paper Survey ofCanada, Paper 68-33. 89-1E. pages 163-167. (1978): Taseko Lakes (920) Map Area; Geological Schiarizza, P.. Gaba, R.G., Glover,J.K. and Garver, J.I. Survey of Canada, Open File 534. (1989a):Geology and Mineral Occurrences of the Trettin,H.P. (1961): Geology of theFraser River Valley Tyaughton Creek area (92012, 92J115.16); B.C. Minis- between Lillooet and Big Bar Creek; B.C. Minisrn) of rry of Energy,Mines and Perroleum Resources, Energy, Mines and Petroleum Resources, Bulletin 44, GeologicalFieldwork 1988, Paper 1989-1, pages 109 pages. 115-130. Umhoefer, P.J. (1989): Stratigraphy and Tectonic Setting of Schiarizza,P., Gaba, R.G., Garver, J.I., Glover, J.K., theUpper Cadwallader Terrane and overlying Relay Church,B.N., Umhoefer,P.J., Lynch, T., Sajgalik, Mountain Group, and the Cretaceous to Eocene Struc- P.P., Safton, K.E., Archibald, D.A., Calon, T., Mac- tural Evolution of the Eastern naughton Basin, British Lean,M., Hanna, M.J., Riddell, J.L. and James, Columbia;unpublished Ph.D. thesis, Universiry of D.A.R. (1989b): Geology and Mineral Potential of the Washington, 186 pages. Tyaughton Creek area (92Ji15, 16; 92012);B.C. Minis- Woodcock,N.H. and Fischer, M. (1986): Strike-slip try of Energ)? Mines and Perroleum Resources, Open Duplexes; Journal of Strucrural Geology, Volume 8, File 1989-4. pages 725-735. Selwyn, A.R.C. (1872): Journal and Report of Preliminary Woodsworth,G.J. (1977): Pemberton Map Area (925); Explorations in British Columbia;Geological Survey of Geological Survey of Canada, Open File 482. Canada, Report of Progress I87I to 1872, pages 16-72. Wright, R.L.,Nagel, J.J. andMcTaggart, K.C. (1982): Sylvester,A.G. (1988): Strike-slip Faults; Geological AlpineUltramafic Rocks of SouthwesternBritish Society of AmericaBulletin, Volume100, pages Columbia; Canadian Journal of Earth Sciences, Vol- 1666.1703. ume 19, pages 1156-1173.

72 British Columbia Geological Survey Branch