drift prospecting for porphyry copper‐gold, volcanogenic … · 2019-04-22 · geoscience bc...
TRANSCRIPT
GeoscienceBCReport2013‐151
DriftProspectingforPorphyryCopper‐Gold,VolcanogenicMassiveSulphideMineralizationandPreciousandBaseMetalVeinswithinthe
QUESTProjectArea,CentralBritishColumbia(NTS093J)
BrentC.Ward,MatthewI.Leybourne,DavidA.Sacco,RaymondE.Lett,LambertusC.Struik
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INTRODUCTION.............................................................................................................................................3
Locationandphysiography.......................................................................................................................5
Bedrockgeology............................................................................................................................................5MineralOccurrences...............................................................................................................................................8RegionalQuaternaryGeology............................................................................................................................10
Methods.........................................................................................................................................................12Geochemistry...........................................................................................................................................................12HeavyMinerals........................................................................................................................................................13
QUALITYCONTROL...................................................................................................................................13
Results...........................................................................................................................................................14Au,As,AgandHginTill........................................................................................................................................17Cu,MoandSbinTill..............................................................................................................................................39Pb,Bi,ZnandCdinTill.........................................................................................................................................50RareEarthElements,U,Th,K,Ca,Mg,Na,Cr,Hf,Co,MnandNiinTill...............................................51HeavyMineralConcentrates:visiblegold,pyriteandcinnabar...........................................................51
TillGeochemicalExploration................................................................................................................52Preciousandbasemetalveins..........................................................................................................................52PorphyryCu‐Au.......................................................................................................................................................52VolcanogenicMassiveSulphideDeposits......................................................................................................53Mercury......................................................................................................................................................................54
HEAVYMINERALCONCENTRATEGEOCHEMISTRY........................................................................54
Conclusions..................................................................................................................................................54
Acknowledgments.....................................................................................................................................55
REFERENCES................................................................................................................................................56
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DriftProspectingforPorphyryCopper‐Gold,VolcanogenicMassiveSulphideMineralizationandPreciousandBaseMetalVeinswithintheQUESTProjectArea,
CentralBritishColumbia(NTS093J)
BrentC.Ward1,MatthewI.Leybourne2,DavidA.Sacco1,RaymondE.Lett3,LambertusC.Struik4
1DepartmentofEarthSciences,SimonFraserUniversity,Burnaby,BCV5A1S6;[email protected],2103DollartonHwy,NorthVancouver,BCV7H0A73BCGeologicalSurveyEmeritus3956AshfordRd,Victoria,BCV8P3S5
4GeologicalSurveyofCanada,NaturalResourcesCanada,1500‐605RobsonStreet,Vancouver,BCV6B5J3
INTRODUCTION ThisreportsummarizestheresultsofregionaltillgeochemicalandmineralogicalsurveysandQuaternarystudiesconductedintheheartoftheQUESTProjectarea(GeoscienceBC’sprogramtoattractnewexplorationinanunder‐exploredportionofcentralBritishColumbia,initiatedin2007;http://www.geosciencebc.com/s/Quest.asp)(Figure1).TheQUESTProjectareahasgoodpotentialforCu‐Auporphyryandvolcanogenicmassivesulphide(VMS)mineralization,butmineralexplorationactivityhasbeenhinderedinsomeareasduetothethickcoverofsurficialdeposits.Regional‐scaletillsamplingfollowedbydetailedsurveysaroundsampleswithelevatedoranomalousvalueswascarriedouttoassessmineralpotentialofthisarea.Tillisthepreferredsamplingmediumforgeochemicalandmineralogicalsurveysinglaciatedterrainbecauseitiscommonlyconsideredafirstderivativeofbedrock(Dreimanis,1989;Levson,2001).Thismethodologyhasbeenshowntoaidinidentifyingpotentiallymineralizedbedrockunitsinareascoveredwiththickglacialdeposits(Levson,2001;McClenaghanetal.,2002;McClenaghan,2005).TheQuaternarygeology,specificallythedistributionofsurficialdepositsandtheice‐flowhistory,includingthedominanttransportdirection,wereusedtoplanthesurveysanddeterminethetransporthistoryoftillgeochemicalandmineralogicaldata.Theprimarygoalofthisstudyistouseregional‐scalemajor‐,minor‐andtrace‐elementtillgeochemicaldata,goldgraincountsandheavymineralseparationandidentificationtoidentifymineralizedbedrock.Thegeochemicalandmineralogicaldatapresentedherehighlightnewexplorationtargetsand,incombinationwiththearea’sglacialhistory,provideasurficialgeologicalcontextforcompaniestointerprettheirowngeochemicalandbedrockgeologydatasets.
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LOCATIONANDPHYSIOGRAPHYThestudyarea,locatedinwest‐centralBritishColumbia,comprisessix,1:50000‐scalemapsheets(NTS093J/05,06,11,12,13,and14;Figure1).Highway97,whichlinksPrinceGeorgetoFortSt.John,runsalongsidetheeastsideofthestudyareaandHighway16,whichlinksPrinceGeorgetoFortSt.James,runstothesouth.AmoderatelydensenetworkofForestServiceroadsprovidesaccesstomostpartsofthestudyareaforfieldworkbasedoutofPrinceGeorge,FortSt.James,McLeodLakeandMackenzie.ThemajorityofthestudyarealiesintherelativelylowreliefoftheInteriorPlateau(Holland,1976;Mathews,1986),includingitssubdivisions,theNechakoPlainandtheFraserBasin.Theseareasarecharacterizedbydrumlinizedtill,glaciofluvialoutwashandeskerdepositswithglaciolacustrinedepositsoccurringinthesouthernregions.ThenorthwesternpartofthestudyareaoccurswithintheNechakoPlateauandischaracterizedbytillmantlesandexposedbedrock.
BEDROCK GEOLOGY ThestudyareastraddlesfouroftheterranesthatmakeuptheCanadianCordillera(CacheCreek,SlideMountain,Quesnel,Kootenay)whilethemostnortheasterncornerofitextendsintotheRockyMountainAssemblage(Figure2).AcomplexassemblageofintrusiveandextrusiverocksoftheSlideMountainterraneoccursintheeast.TheCacheCreekterraneisrepresentedbyPennsylvanianandPermianlimestoneinthesouthwesternportionofthestudyarea,withbasaltsoccurringjusttothesouth.TheRockyMountainassemblageinthenortheasterncornerofthestudyareacomprisesSiluriantoDevoniansandstoneandquartzite.TheQuesnelterranedominatesthestudyareaandiscomposedprimarilyofLateTriassictoEarlyJurassicarcvolcanicrocksoftheWitchLakesuccessionandvolcaniclasticrocksoftheCottonwoodRiversuccession,bothpartoftheNicolaGroup(Loganetal.,2010).TheNicolaGroupwaspreviouslyreferredtoastheTaklaGroup(Struik,1994),followingfirstusage.ItwascorrelatedwithTaklaGrouprockstothewestwithintheStikineterrane.TheNicolaGroupcomprises:a)mainlybasaltictodaciticvolcaniclasticrocksandsubordinatecoherentvolcanicrocks,eachwithaugite‐porphyrytextures(particularlycharacteristicoftheQuesnelterrane),whichformaneasternfaciesofalkalinetosubalkalineaugite‐phyricbasalticandesite;b)coevalandpartlycomagmaticplutonsrangingfromcalcalkaline(inthewest)toalkaline(intheeast);andc)sedimentaryrocks,includingshale,limestoneandepiclasticdeposits.StratigraphicallyoverlyingtheseterranesareaseriesofoverlapassemblagesrangingfromUpperCretaceoustoMiocenesedimentaryrocksandCretaceoustoPliocenevolcanicrocks.ThelatterincludesthedominantlyMioceneChilcotinbasaltsandEocenefelsicvolcanicrocks.Intrusiverocks,paragneissandmetasedimentaryrocksoftheWolverinemetamorphiccomplexwereexposedduringEoceneextension.ThemetamorphismandplutonismoccurredinthelateCretaceousandPaleogene,andtheprotolithfortheparagneissand
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metasedimentaryrocksarelikelyPrecambrianandEarlyPaleozoic(Struik,1994).RecentcompilationhasassignedtheserockstotheKootenayterrane(Loganetal.,2010).
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Mineral Occurrences
WithinthestudyareaaretwelveCushowings,sixAushowings,oneplatinumgroupelements(PGE)showing,twoHgshowingsandtwopast‐producingAuandPtdeposits(MINFILE;BCGeologicalSurvey,2010;Figure2).ThetwopastproducersaretheMcDougallRiverandMcLeodRiverplacerdeposits(MINFILE093J007and012;BCGeologicalSurvey,2010).Bothdepositsoccurinthenortheasternpartofthestudyarea,underlainprimarilybytheMississippianSlideMountainGroup.CaribooNorthernDevelopmentCo.Ltd.andNorthernReefGoldMinesLtd.workedtheMcDougallRiverplacergolddepositfromaround1931to1935,withtotalreportedproductionofapproximately1750gAu(62oz).From1981topresent,theareahasreceivedrenewedinterest,includingheavymineral,soil,siltandrocksampling;geologicalmapping;airborneverylowfrequency(VLF)andmagnetometersurveys;andgroundVLFandmagnetometersurveysbyavarietyofcompanies.AtMcDougallRiver,AuandPtwereextractedfromshallowgraveldepositsonbothbanksoftheriver,withadditionalclastsretrievedfromcracksandcrevicesinthebedrock.LocallyshearedrocksandquartzveinsmaybethesourceoftheplacerAuandPGE.HeavymineralsampleshaveyieldedhighAuandAgcontents,andmanyoftheplacerGoldgrainsrecoveredareangulartowiry,consistentwithminimaltransportfromalocalbedrocksource.Thecoincidentelectromagnetic(EM)andmagneticanomaliescouldrepresentthelocalsourceforAu.ThetwoHgshowings(MountPrinceSoutheastandNorthwest,MINFILE093J010,093J011)inthesouthwesternpartofthestudyareaareassociatedwiththePinchifault.Bothshowingsarecharacterizedbysmallvolumesofcinnabarhostedbycarbonate‐alteredandshearedNicolaGroupmaficvolcanicrocks,commonlyassociatedwithquartzstringers.Mostoftheothermineralshowingsinthestudyareaaresmallwithminimalassociatedexplorationactivity.MountMilligan(MINFILE093N194)isaCu‐AuporphyrydevelopedprospecttothenorthwestofthestudyareainQuesnelterrane.Inthisarea,TriassictoLowerJurassicvolcanicandsubordinatesedimentaryrocksofNicolaGroupareinterpretedtobetheextrusivephaseoftheHogemintrusivesuite.ManyCu‐AumineralshowingsareassociatedwiththeHogembatholithandsmallercoevalintrusions(LeFortetal.,2011).TheNicolaGroupintheMountMilliganareaisinformallysubdividedintoalower,predominantlysedimentaryInzanaLakesuccession,andanupper,predominantlyvolcaniclastic,WitchLakesuccession.TheWitchLakesuccessionhoststheMountMilligandepositandischaracterizedbyaugite‐phyricvolcaniclasticandcoherentbasalticandesite,withsubordinateepiclasticbeds.RegionalmappingandpetrographicstudiesintheMountMilliganareaindicatethattheWitchLakebasalticandesiteandassociatedsedimentaryrockshavebeensubjectedtostrongpotassicalterationdetectableforupto4kmfromthedeposit.WitchLakesuccessionvolcanicrockswereintrudedbysyn‐andpost‐depositionalgabbro,diorite,granodiorite,monzoniteandsyenite(Loganetal.,2010).RecentworkhasshownthatmineralizationatMountMilligan
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isdominatedbyanearlyCu‐richporphyrystage,withlatermineralizationcharacterizedbyenrichmentsinAu,PGE,As,Sb,Bi,TeandB(LeFortetal.,2011).
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Regional Quaternary Geology
TheCordilleranIceSheethasrepeatedlycoveredBritishColumbiaandportionsofYukon,AlaskaandWashingtonoverthelasttwomillionyears(Armstrongetal.,1965;Clague,1989).Atitsmaximumextent,theCordilleranIceSheetwasupto900kmwideandupto2000–3000mthickovertheInteriorPlateau,closelyresemblingthepresent‐dayGreenlandIceSheet(Clague,1989).AmorecomprehensivehistoryoftheCordilleranIceSheetcanbefoundinJacksonandClague(1991)andClagueandWard(2011).ThemajorsourcesofregionalicethatcoveredcentralBritishColumbiaadvancedfromaccumulationcentresintheCoast,Skeena,OmenicaandCariboomountains(Tipper,1971a,b;LevsonandGiles,1997;Plouffe,1997,2000,Wardetal,2009).Thestudyareaoccursneartheconvergenceofthesethreeadvancingicefronts,makingitdifficulttodeterminewhichicecentre(s)hadthemostinfluenceoniceflowdirectionanddispersalintheearlypartsoftheLateWisconsinan.Previouslyreportedice‐flowindicators(Tipper,1971a;PaulenandBobrowsky,2003),incombinationwithdatafromthisstudy,suggestthatitwasmainlyicefromtheCoastMountainstothewestandtheCoastandCariboomountainstothesouththataffectedthearea.Absolutechronologicalinformationonthemovementand/orconfluenceoficefrontsthroughthestudyareaislimited.AlthoughitisknownthaticewasadvancingoutoftheCoastMountainsby28.8ka(GSC‐95,Clague,1989),itisnotclearwhenthisadvancereachedthecentralInteriorPlateau.Ice,possiblysourcedfromtheCaribooMountains(PaulenandBobrowsky,2003),coveredtheBowronValleysometimeafter19.9ka(AA44045,Wardetal.,2008).AccordingtoBobrowskyandRutter(1992),iceadvancingfromtheOminecaMountainsintowhatisnowthenortharmofWillistonLakeoccurredsometimeafter15180±100BP(TO‐708).Thedominanticeflowinthestudyareaisrelativelyeasytodemonstrateusingtheorientationsofthenumerousmacro‐forms.Themacro‐formswereinitiallycompiledfromexistingmaps(Tipper1971)andtheresolutionwasincreasedwithobservationsmadeduringmappingforthisproject(Figure3).Thedominanticeflowindicatorsgenerallyconsistofdrumlins,flutings,cragandtails,andstreamlinedbedrock(Figure3).Theinteractionofthetwosourcesresultedinageneralnortheasterntransportdirectionwithminorvariationacrossthe6sheets;thelargestreamlinedformsareapproximatelyENEinthesouthwestportionofthestudyareaandcurvenorthward,beingNNEinthenorthofthestudyarea.Small‐scaleiceflowindicatorsweremeasuredinthefieldsuchasgrooves,striationsandrat‐tails.Thesemicro‐flowindicatorsweremeasuredatatotalof22sites(Figure3).Atsomeofthesesites,multipleiceflowdirectionswererecorded,atothersonlyonedominantdirectionwasobserved.Findingmicro‐flowindicators(e.g.,striations,rat‐tails)waschallengingduetothelackofbedrockexposuresinpartsofthefieldarea,andtheweatherednatureofsomeoftheoutcropspresent.Inmostcases,exceptforsomefreshroadcuts,micro‐flowindicatorswereonlyfoundaftersediment,usuallytill,wasscraped,brushedorwashedoffbedrocksurfaces.
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Theorientationofelongateclastsintillweremeasuredat12sites.Thesetillfabricscanbeusedtointerpretthegenesisofatillunitandthedirectionoficeflowthatdepositedit.FabricsandstriationswereusedtoadddetailandarelativechronologytotheiceflowhistorythatisdescribedinSaccoetal.(2012).
METHODS
Geochemistry
Basaltillsampleswerecollectedatapproximately760siteswithinthestudyarea,duringthesummersof2008,2009,and2010.Thereareslightlydifferentnumbersofsamplesforthedifferentsizefractionsanalyzedowingtoasmallnumberoflostormislabeledsamples(seeAppendices).Basaltillinthestudyareaistypicallyadense,darkgrey,sandytoclayeysiltmatrixsupporteddiamictoncontaining25‐40%gravelsizedmaterial(clasts).Theaveragesampledensityisapproximately1sampleper8km2,buttherearesomezoneswithnosamplesandsomezoneswithhigherdensity.Insomeareassamplingwasnotpossiblebecauseofaccessproblems,roaddeactivationandlackofroads,orlackofsuitablesamplemedia,suchasareasofeolian,glaciofluvialandglaciolacustrinedeposits.Inaddition,nosamplingoccurredinCarpLakeProvincialPark.Ateachsamplesitethreeseparate~900gsampleswerecollectedfor:1)analysisoftheclay‐sizefraction(<0.002mm)byinductivelycoupledplasmamassspectrometry(ICP‐MS),followinganaquaregiadigestion,atAcmeAnalyticalLaboratoriesLtd.(Vancouver,BC);2)analysisofthesilt‐plusclay‐sizedfraction(<0.063mm)byinstrumentalneutronactivationanalysis(INAA)atActivationLaboratoriesInc.(Ancaster,ON);and3)forarchiveattheGeologicalSurveyofCanada.Thesearchivesampleswillbeavailableforfutureanalysisforeitherimproveddetectionlimitsordifferentelements.Clay‐sizedseparationswereproducedbycentrifugeatAcmeAnalyticalLaboratoriesLtd.(Vancouver,BC).Typically,between0.5–0.8kgoftillwereprocessed,whichonaverageyieldedapproximately5gofclay.TheclaysplitswereanalyzedbyICP‐MSfor36elements(analyticalpackage1DX)followingleachinginahot(95°C)aqua‐regiadigestion(detectionlimitsarelistedintheappendixeswiththedata).Upto5gofclayisanalyzedtoovercomepotentialnuggeteffectsforAu.Thesiltplusclay‐sizedfraction(<0.063mm)oftillsamples(onaverage,24gofmaterialwasused)wereanalyzedfor35elementsbyINAA(analyticalpackage1D,enhancedoption)(detectionlimitsarelistedintheappendixeswiththedata).Hoffman(1992)describestheanalyticalprocedureasfollows.Analiquotandaninternalstandard(oneforeveryelevensamples)areirradiatedwithfluxwiresatathermalneutronfluxof7x1012·n·cm‐2·s‐1.Afteraseven‐daydecay,thesamplesarecountedonahighpurityGedetector.Usingthefluxwires,thedecay‐correctedactivitiesarecomparedtoastandardcalibrationcurve.Thestandardincludedisonlyacheckonaccuracyandisnotusedforcalibrationpurposes.From10–30%ofthesamplesarerecheckedbyre‐measurement.
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Heavy Minerals
Bulktillsamples(>10kg)werecollectedatevery4–5sitessampledforgeochemicalanalysis.Intotal,152sampleswerecollected.Heavymineralconcentrates(HMCs)wereseparatedatOverburdenDrillingManagementLimited(Nepean,ON)andwerepannedforgoldgrains,platinumgroupmetals(PGM)anduraninite.Bulksamplesweredisaggregated,followedbyseparationofthe>2mmand<2mmfractions.The<2mmfractionwasthenpreconcentratedonashakingtable,withthefinest,heaviestfractionbeingpanned.Gold,uraninite,andplatinumgroupelements(PGEs)werethenexaminedunderopticalmicroscopetoprovidegraincountsaswellasgrainmorphology.MoredetaileddescriptionsofthemethodsareprovidedinAverill(2001).Sulfideandcinnabargraincountswerealsomade,althoughwheren>20,thesecountsareestimates.Thetableconcentratewasthensievedandthe<0.25mmfractionsubsequentlyseparatedusingheavyliquidat3.2g/cm3.This<0.25mmfractionwasthenanalyzedbyINAAatBecquerelLaboratories(Mississauga,ON)usingtheirBQ‐NAA‐1package(withtheadditionofHgfor2009and2010samples).Theconcentrateisplacedinvials,whicharestackedintoone‐foot(30cm)longbundlesforirradiationattheMcMasterNuclearReactor,whichhasfluxof8x1012·n·cm‐2·s‐1.Afteratypicaldecayperiodofsixdays,theirradiatedsamplesareloadedontoahighresolution,coaxialgermaniumdetectorthatconstructsaspectrumofgamma‐rayenergiesversusintensities.Thecountingtimeistwentytothirtyminutespersample.Quantitativeelementalcontentsarederivedbycomparisonofpeakpositionsandareawithlibrarystandards.Forthe2009and2010samples,severalelements,suchasHg,Ni,Zr,Rb,Au,hadvariableandhigherthanusualdetectionlimitsbecauseofelevatedCr,REEandThcontents(SteveSimpson,pers.comm.,2011).Forexample,Auusuallyhasadetectionlimitof2ppbbuthereitrangesfrom5to42ppbdependingonthesample.However,thesamplestakenin2008didnothavethisissue.
QUALITY CONTROL Discriminatinggeochemicaltrendscausedbygeologicalfeaturesfromvariationduetospurioussamplingoranalyticalerroriscriticalforassessingthereliabilityofregionalgeochemicalsurveydata.Acombinationoffieldduplicates,analyticalduplicatesandreferencestandardsareusedtoestimatetheaccuracyandprecisionoftheseanalyticaldata.Every20samplegroupsubmittedforcommercialanalysiscontainafieldduplicate,ananalyticalduplicate(splitandinsertedintothesamplesequenceatthelabafterpreparation),andareferencestandard(eitheranin‐houseBCGeologicalSurveystandardoracertifiedCanadaCentreforMineralandEnergyTechnology[CANMET]standard).Nofieldoranalyticalduplicatesweredonefortheheavymineralsamples,owingtothelargesamplesizesrequired.Scatter‐plotsoftheanalyticalandduplicatepairsweregeneratedandaselectionisshowninFigure4and5,withtherestoftheanalysisinAppendix1.Precisionfortheaquaregia(clayfraction)ICP‐MSanalysesistypicallymuchbetterthanfortheINAA(silt+clay)analyses.For
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theICP‐MSanalyses,correlationcoefficientsforthefieldduplicatesaretypicallyhigherthanthosefortheanalyticalduplicatesandaregenerallyabove+0.9.Morethan80percentofthetotalvariationamongtheduplicatesisaccountedforbytheFieldDuplicate1–FieldDuplicate2correlation.CorrelationcoefficientsfortheINAAduplicatesaregenerallymuchlower,withbetterprecisionforCo,Cr,ThandtheREEthantheotheranalytes.ThehigherprecisionfortheICP‐MSdataisinpartrelatedtolowerdetectionlimitsandlessvariationingrainsize,butalsolikelyreflectsbetterinstrumentcapabilities.FourCANMETtillstandards(TILL1,2,3and4),BCGeologicalSurveysediment(RD29)andtillstandards(SM,Till99),andtwoquartzblanksampleswereanalysedwiththesurveysamplestomeasureanalyticalaccuracyandprecision.AllofthestandardsdataiscompiledinAppendix1.TheINAAquartzblanksampleresultsrevealamountsofAs,Br,Co,Cr,La,Ce,ThandScinthe1to10ppmrangeandlessthan0.2%Fe.Traceamounts(<than1ppm)ofCu,Pb,Co,Mn,SrandBaintheblanksaredetectablebytheaquaregiadigestion‐ICP‐ESanalysis.Elementconcentrationsdetectedintheblanksamplesmayreflecttracesinthequartzandnotnecessarilysamplecontaminationduringtheanalysis.Precisionisbelow+/‐8%RSDforAs,Cd,Co,Cr,Cu,Hg,Mn,Mo,Ni,Pb,Sb,VandZninstandardsanalysedbyaquaregiaICP‐MSandbelow+/‐8%RSDforAs,Br,Co,Cr,Fe,La,Ce,ThandScinGSBTill99.Accuracycanbeaccessedfromthenear‐totalINAAanalysesandmeasuredamountsformostelementsarewithin5%oftherecommendedvalue.PrecisionandaccuracyforelementsatdifferentconcentrationisbestshownbytheCANMETstandardsdata(Appendix1).TheINAAanalysesofCANMET.Goldshowsconsiderablevariationalthoughthemeanandrecommendedvaluesareverysimilar.ThelargemeasuredBadifferencescomparedtotherecommendedvaluearedifficulttoexplain.Table2listsprecisionandCANMETrecommendedvalues(hotaquaregiaanalyses)forCANMETTill1,2,3and4.Goldprecision(%RSD)forthreeofthestandardsisbelow+/‐30%andmostotherelementshaveaprecisionbelow+/‐8%RSD.Lowerprecision(i.e.above8%)commonlyreflectsalowelementconcentrationsmeasuredinthestandard.
RESULTS Elementswiththemostsignificancetopotentialeconomicmineralizationintheprojectareaarediscussedbelow.Notethatweanalyzeddifferentsizefractionsbydifferentanalyticalmethods.Insomecases,commodityelementsarenotanalyzedbybothmethods(e.g.,CuwasnotdeterminedbyINAA).Furthermore,dependingonwhereanelementissequesteredinasample,comparisonsbetweensizefractionsmayhavegreaterorlesserutility,asdiscussedbelow.Notealsothataquaregiadigestionisnottotal,silicateandresistantoxidesarenotdigestedtoanygreatextent.Bycontrast,INAAisatotalmethod.Thus,thedifferencesbetweenresultsfortheclay‐sizeversusthesiltplusclay‐sizefractionsarenotonlyafunctionofanalyticalmethod(partialversustotal),butalsoafunctionofwhereananalyteresideswithina
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sample.Forexample,Asshowsgoodcorrelationsforbothfieldandlaboratoryduplicatesforbothsizefractions,becauseAsisprimarilyassociatedwithadsorptiontoclay‐sizemineralsurfaces(Figure4).Bycontrast,Auismorepronetothenuggeteffectinthesiltplusclay‐sizefractionthanAuintheclayfraction(Figure5).Tillgeochemicaldata(ICP‐MSandINAAanalysis)isinappendix2.Heavymineraldata(Graincounts,INAAanalysisontheheavymineralfraction)isinAppendix3.Averagevaluesarepresentedbelowalongwithonestandarddeviationandsamplecount.Samplecountsarevariableasresultsbelowdetectionarenotincludedinthestatisticalcalculations.Thresholdvalues(percentile)aresetbasedoninflexionpointsonthecumulativefrequencyplots(Figure6);wehavenotdefinedasetbackgroundvalueowingtothevariabilityinthegeochemicallandscape.Wherecorrelationsarestated(rvalues),theserepresentPearsonProductMomentcorrelations,statisticallysignificantatleastatthe95%confidenceinterval.Insomecases,wealsoemployedR‐modefactoranalysis,astatisticalmethodtoinvestigateinter‐relationshipsbetweenanalytesinacorrelationmatrix.
Au, As, Ag and Hg in Till
Goldcontentsintheclayfractionrangefromlessthandetection(0.5ppb)to294ppb(average=5.1±11ppb,n=704).Goldcontentsintheclayfractionshowhighlyanomalousvaluesaroundthe98thpercentile(10ppb),althoughthereisalsoasubtlechangeinslopearoundthe90thpercentile,or8ppb(Figure6a).Inthesiltplusclay‐sizefraction,Aucontentsrangefrombelowdetection(2ppb)upto635ppb.Forthesiltplusclay‐sizefraction,anomalousAucontentsoccurabovethe80thpercentile(~8ppb;Figure6a);mostsamplesbelowthisthresholdwerebelowthedetectionlimitbythismethod(2ppb).AnomalousAucontentsoccurinthenortheasternandnorthwesternpartsofthemapareaforbothsizefractions(Figures7a,b),largelycoincidentwithknownAushowings.TherearealsoanomalousAucontents,inparticularinthesiltplusclay‐sizefraction,tothesouth,andtoalesserextent,totheeastofCarpLake.TherearenoknownAushowingshere.FortheclayfractionAushowsthebestcorrelationwithCu(r=0.410).ThehighestAucontentbybothmethodsoccursinthesamesample(Figures7aand7b)indicatingthatthisanomalousvalueisnottheresultofthenuggeteffect,consistentwiththisalsobeingthesamplewiththehighestAscontentsbybothmethods(Figures7cand7d).Alltillsamplesprocessedforheavyminerals(n=152)containvisiblegold(Figure8a).Notsurprisingly,thedistributionofAubyINAAontheheavymineralconcentratesmimicsthegoldgraindistribution(Figure8b)alongwiththesilt+clayfractionanalyzedbyINAA(Figure7b).FortheINAAanalysesoftheHMCs,goldrangesfrombelowdetection(5to42ppbdependingonthesample)to2,630ppb.Goldcontentsshowclearlyanomalousvaluesaroundthe95thpercentile(~750ppb),althoughthereisalsoasubtlechangeinslopearoundthe80thpercentile(~400ppb).
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ArsenicistypicallyconsideredapathfinderelementforAu.Inthisstudy,thresholdAscontentsintillare32and26ppm,atthe95thand98thpercentilesfortheclayandsiltplusclay‐sizefractions,respectively(Figure6a).Arseniccontentsareanomalousinboththenortheasternandnorthwesternsectionsofthestudyarea(Figures7c,d),largelycoincidentwithAuanomalies.However,AscontentsdonotappeartobeanomaloussouthofCarpLake;incontrast,thereareanomalousAscontentsinthewest‐centralpartofthestudyarea,primarilyinthesiltplusclay‐sizefraction.AuandAsshowamoderatepositivecorrelation(r=0.372)fortheclayfractionbasedontheR‐modefactoranalysis,statisticallysignificantatthe99.9%confidenceinterval.Bycontrast,thestatisticalcorrelationbetweenAsandAuforthesiltplusclay‐sizefractionispoor(r=0.112),despitetheevidentspatialassociation(Figures7b,d).Figure7(Next18pages):Proportionaldotmapsofselectedelementsfromtillgeochemicalanalyses,centralBritishColumbia:a)Aucontents(clay‐sizedfraction)byinductivelycoupledplasma–massspectrometry(ICP‐MS);b)Aucontents(clayplussilt–sizedfraction)byinstrumentalneutronactivationanalysis(INAA);c)Ascontents(clay‐sizedfraction)byICP‐MS;d)Ascontents(clayplussilt–sizedfraction)byINAA;e)Agcontents(clay‐sizedfraction)byICP‐MS;f)Hgcontents(clay‐sizedfraction)byICP‐MS;g)Cucontents(clay‐sizedfraction)byICP‐MS;h)Mocontents(clay‐sizedfraction)byICP‐MS;i)Sbcontents(clay‐sizedfraction)byICP‐MS;j)Pbcontents(clay‐sizedfraction)byICP‐MS;k)Bicontents(clay‐sizedfraction)byICP‐MS;l)Zncontents(clay‐sizedfraction)byICP‐MS;m)Cdcontents(clay‐sizedfraction)byICP‐MS;n)Lacontents(clayplussilt–sizedfraction)byINAA;o)Lacontents(clay‐sizedfraction)byICP‐MS;p)Crcontents(clay‐sizedfraction)byICP‐MS;q)Sbcontents(silt+claysizedfraction)byINAA;r)Thcontents(silt+claysizedfraction)byINAA.SizeofdotsareproportionaltothecontentwithAu‐ICPandAu‐INAAbeingrepresentedbylogplots.DataareoverlaidonthebedrockgeologymappresentedinFigure2.
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Arseniccontentsintheheavymineralfractionrangefrom9to414ppmandshowclearlyanomalousvaluesaroundthe95thpercentile(60ppb)(Figure6a).ThespatialdistributionofAscontentsmimicthoseofgoldandmostanomalousvaluesareinthenortheastpartofthestudyareawithslightlylowervaluesinthenorthwest(Figure8c).Silvercontentsfortheclayfractionrangefromlessthandetection(0.1ppm)to1.1ppm(average=0.21±0.14ppm,n=520),withanomalousvalues>0.5ppm(~95thpercentile;Figure6a).Silvershowsamoderatelypositive,statisticallysignificantcorrelation(r=0.313)withAu,withanomalousvaluesinthenortheasternandnorthwesternpartsofthestudyarea(Figure7e),beingcoincidentwiththeAuanomalies.Silverforthesiltplusclay‐sizefractionandtheheavymineralfractionwasbelowdetectionlimitforallsamples.Mercurywasonlydetectedintheclayfraction,althoughheavymineralconcentratedata(seebelow)indicatesmanysampleshavesignificantquantitiesofcinnabargrains.Intheclayfraction,Hgrangesfrom0.02to1.0ppm(average=0.29±0.13ppm).Inthecumulativefrequencyplottherearenomajorbreaksinslope,consistentwithaclosetonormaldistribution(Figure6a).Settingthethresholdatthe95thpercentile(0.51ppm),anomalousHgcontentsoccurinthewest‐centralportionofthestudyarea(Figure7f),northofthetwoknownHgshowings.SeveralanomalousHgcontentsoccurinthenortheasternandnorthwesternpartsofthestudyarea,coincidentwithAu,AsandAganomalies.Mercuryvaluesdonot,however,statisticallycorrelatewellwithAuvalues(r=0.083),butdostatisticallycorrelatemoderatelywithAsvalues(r=0.360).Cinnabarcountsrangefrom0to400grains.Anomalouscinnabargraincounts(>60grains)occurinthewesternpartofthestudyarea,andmarkthestartofatrendofdecreasingvaluestothesoutheast(Fig.8e).Becauseofthelargenumberofcinnabargrainsidentified,the2009and2010sampleswerealsoanalyzedforHgbyINAA;unfortunately,becauseofdetectionlimitissuesduetointerferencewithotherelements,only14sampleshavevaluesabovedetection.Thesesamplesareonthewestandeastsideofthestudyareaanddomimichighsinthecinnabargraincounts(Fig.8f).
Cu, Mo and Sb in Till
Copperwasanalyzedonlyfortheclayfractionsamplesandrangesfrom33to408ppm(average=125±38ppm).Basedonthecumulativefrequencyplot,Cucontentsintheclayfractionareanomalousatthe90thpercentile(165ppm;Figure6a).AnomalousCucontentsoccurinthenorthwesterncornerofthestudyarea,withsmalleranomaliesinthenortheasternFigure8(next10pages):Proportionaldotmapsofselectedelementsandmineralsfor<0.25mmfractionoftillheavymineralseparatesforINAAgeochemicalanalysesalongwithselectedgraincounts.a)Goldgraincounts,b)Au,c)As,d)Sb,e)cinnabar,f)Hg,g)Ce,h)Th,i)Cr,andj)pyrite.SizeofdotsareproportionaltothecontentwithAu,Cinnabar,andpyritegrains,andAu,As,andThbeingrepresentedbylogplots.DataareoverlaidonthebedrockgeologymappresentedinFigure2.
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corner(Figure7g).ThereisapositiveconcentrationcorrelationbetweenCuandanumberofotheranalytessuchasFe(r=0.712),Sc(r=0.654),V(r=0.656),As(r=0.538),Au(r=0.410),Co(r=0.341)andMo(r=0.313).TheseelementassociationsindicatethatCuintheclayfractionofthetillinthenorthwesternandnortheasternpartsofthestudyareaisassociatedwithCu‐Aumineralization.Molybdenumwasanalyzedforbothsizefractions.AllclaysamplesreturnedMocontentsabovethedetectionlimit,rangingfrom0.3to12ppm(average=1.74±1.12ppm).Bycontrast,thesiltplusclay‐sizefractionhadonly137samplesabovedetectionlimit(1ppm),rangingfrom3to28ppm.Fortheclayfraction,theanomalousthresholdisaroundthe97thpercentile(3.5ppm;Figure6a),whereasforthesiltplusclay‐sizefraction,allsampleswithdetectableMocanbeconsideredanomalousatthe85thpercentile(≥3ppm;Figure6a).Thetwosizefractionsshowdifferentspatialrelationships.Fortheclayfraction,anomalousMocontentsoccurmainlyinthenortheasternsectionofthestudyarea;Mocontentsarenotanomalousinthenorthwesternsection(Figure7h).ThehighestMocontentisforasampleinthewest‐centralpartofthestudyarea.Bycontrast,thesiltplusclay‐sizefractionhasanomalousMocontentsscatteredovermuchofthestudyarea,withthemostconsistentlyelevatedcontentsintheeast‐centralandsouthernareas.Notably,Mocontentsinthesiltplusclay‐sizefractionarebelowdetectionforthenorthwesternareawherehighCu,AuandAsvaluesoccur.Antimonywasmeasuredforbothsizefractions,withclaycontentsrangingfrom0.1to5.6ppm(average=0.80±0.48ppm),andclay+siltcontentsrangingfrom0.5to13.1ppm(average=1.84±0.87ppm).Thresholdvaluesarearoundthe95thpercentileforbothfractions,at1.5and2.7ppmfortheclayandsiltplusclay‐sizefractions,respectively(Figure6a).Spatially,thetwosizefractionsshowsimilardistributions,withthemostanomalouscontentsoccurringinthenortheasternsectionofthestudyarea(Figure7i).AntimonyisalsoacommonpathfinderelementofporphyryCu‐AuandVMSmineralization.Antimonyintheheavymineralfractionrangesfrom1.2to26.3ppm,andisanomalousatthe90thpercentile(~7ppm)(Figure6a).ThetwohighestvaluesintheheavymineralfractionaretothesoutheastandnortheastofCarpLake,withintermediatevaluesinthenorthwest,thezoneofpotentialporphyryCu‐Austylemineralization.
Pb, Bi, Zn and Cd in Till
Leadwasonlyanalyzedintheclayfraction,andrangesfrom6.6to64ppm(average=15.0±5.21ppm).Leadshowsanearnormaldistribution,althoughthereisasubtleinflectioninthecumulativefrequencyplotnearthe85thpercentile(Figure6a);settingthethresholdvalueatthe95thpercentilegivesanomalousPbat>24ppm.ThestrongestcorrelationswithPbareshownbyK(r=0.591),La(r=0.501),Bi(r=0.668),Th(r=0.720)andU(r=0.621).ThespatialdistributionofanomalousPbconcentrationsisdistinctfromtheothercommodity‐relatedelements,withthehighestPbcontentsinthenorth‐centralpartofthemaparea,betweenthenortheasternandnorthwesternareasthatareanomalousinAu,CuandAs(Figure7j).Bismuth(Figure7k)showsasimilarspatialdistributiontoPb,alongwithU,Th
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andtherareearthelements(REE).Bismuthrangesfromlessthandetection(0.1ppm)to2.7ppm(average=0.33±0.26ppm),withathresholdaroundthe95thpercentile(0.8ppm;Figure6b).ZncontentswereanalyzedinbothsizefractionsandCdwasonlyanalyzedintheclayfraction.Zinccontentsinclayrangefrom83to531ppm(average=187±41ppm)comparedto60to400ppmintheclay+silt(average=167±49ppm,witharound280samplesbelowdetection).CadmiumshowssimilarspatialdistributiontoZn,andrangesfrom0.1to4.0ppm(average=0.75±0.48ppm).Bothmetalsshowthelargestanomalies(thresholdatthe95thpercentile=245ppmZnforclay,250ppmZnforclay+siltand1.6ppmCdforclay;Figure6b)alongtheeasternsideofthemaparea(Figure7l,m),althoughCdalsoshowsseveralanomalousvaluesinthewest‐centralportionofthestudyarea.BothZnandCdhavestrongpositivecorrelationswithMo(r=0.743and0.586,respectively),As(r=0.421and0.364,respectively)andSb(r=0.464and0.334,respectively),aswellaswitheachother(r=0.719).AlthoughZncorrelatespoorlywithmajorelements,CdisstronglycorrelatedwithCa(r=0.595).
Rare Earth Elements, U, Th, K, Ca, Mg, Na, Cr, Hf, Co, Mn and Ni in Till
BoththebasaltillgeochemicalresultsandtheINAAdeterminationsontheheavymineralfractionshowthatvaluesforrareearthelements(REE),U,Th,K,Ca,Mg,Na,Ni,andCr(onlyLa,ThandCrshowninFigure7asexamples)havespatialrelationshipsthatareconsistentwithchangesinthedominantunderlyingbedrocklithology(e.g.,Figures7n,o,p).Thus,incompatibleelementsthatareenrichedinfelsicrocks(i.e.,theREE,U,Th,KandHf)areelevatedinthenorthernpartofthestudyareacoincidentwiththeWolverinemetamorphiccomplex,whichcontainsfelsicrockssuchasgraniticpegmatite,granite,granodioriteandrhyolite(Struik,1994).InthelargeHMCsamplesfromthisareaofthemap,>33%oftheclaststhatare>2mmaregranitoid,indicatingagreaterprevalenceofalkalicvolcanicrocksandassociatedlatestageintrusiverocks.NickelandCrcontentsarehighestinthesouth‐southwestportionofthestudyareawheremaficandvolcaniclasticrocksoftheQuesnelTerraneoccur(Struik,1994).Conversely,whereasCoshowsastrongcorrelationwithMnintheclayfraction,CrandNi,whicharestronglyadsorbedbyMnoxidesandoxyhydroxides(NicholsonandEley,1997;Leybourneetal.,2003),showdistributionpatternsthatfollowthemajormaficvolcanicbedrockunitsinthesouthernpartofthestudyarea(Figure7p).HighTa,CeandThcontentsinthenorthtonortheastsuggestmorefelsicrocks,likelythegraniticpegmatite,granite,granodioriteandrhyoliteand/ormoreenrichedmaficrocks;whereashighCrcontentsinthesouthindicatesmoreprimitivemaficrocks(Figures7g,h,i,j).
Heavy Mineral Concentrates: visible gold, pyrite and cinnabar
Alltillsamplesprocessedforheavyminerals(n=152)containvisiblegoldgrains.Thenumberofgoldgrainsper~10kgofsamplerangesfrom1to91(Figure8a)andthecalculatedAucontentsrangefrom1to23,491ppb.Intotal,1584goldgrainswereclassifiedonthebasisofsizeandmorphology.Goldgrainmorphologiesaresubdividedintothreegroups:pristine,modifiedandreshaped,basedontheclassificationschemeofDilabio(1990).Themajorityof
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goldgrainsinthisstudyareclassifiedasreshaped(82.5%),withlesscommonmodifiedgrains(14%)andrarepristinegrains(3.5%).Thethresholdvalueforthetotalnumberofgoldgrainsisaround12–15(80–85thpercentile),basedonchangesinslopeofaprobabilitydistribution.Althoughtheyareonlyestimates,graincountsofpyriteandcinnabarareuseful.Pyritecountsrangefromzerotoahighof~10000grains.Mostofthetillsampleswithelevatedpyritegraincounts(whereanomalousvaluesareapproximately>50grains)occurintheeasternandsouthernpartsofthestudyarea(Figure8b),distinctlysouthoftheareawithanomalousmetalvalues(northeasterncornerofthestudyarea;Figures7a–i,k–m).Bycontrast,cinnabarcountsrangefrom0to400,withanomalouscinnabargraincounts(approximately>60grains)inthewesternpartofthestudyarea,withatrendofdecreasingvaluestothesoutheast(Figure8c).
TILL GEOCHEMICAL EXPLORATION
Precious and base metal veins
Inthenortheasternpartofthestudyarea,thereareanumberofAuandCu‐Aushowings,aswellastwosmallpast‐producingplacerdeposits(discussedpreviously).Historicgoldrecoveredfromtheplacerdepositswasdescribedaswirytoangular(MINFILE093J007),suggestingthattheplacergoldhadnotbeentransportedfarfromsource.Samplesoftheclayfractionwereanalyzedbyaqua‐regiadigestionfollowedbyICP‐MS,whereasthesiltplusclay‐sizefractionwasanalyzedbyINAA,thustheICP‐MSresultswillbelessbiasedbythenuggeteffect.Goldintheclayfractionoccurseitherasclay‐sizedgoldgrains,mostlikelyaresultofglacialcomminutionand/orsmall‐scalehydromorphicgolddispersionandadsorptiontoclayandoxyhydroxidemineralsurfacesintheclayfraction.Otherthanasmallnumber(~3)ofhighlyanomalousAuvaluesintheICP‐MSresults,thereisarelativelystrongcorrelation(r=0.410)betweenCuandAu;thissuggeststhatmuchoftheAuisassociatedwithCu‐sulphideminerals.Thepathfinderelementalassociationspresentedhere(i.e.,Sb,As,Se,Tl,Cd,Zn)areconsistentwiththisstyleofmineralization(Taylor,2007).Thisassociationiscoherentwithdescriptionsofmanyoftheshowingsinthenortheasternsectionofthestudyarea;showingsofquartzveinswithAu,Cu±Agand/orPGE(MINFILE093J007,093J012,093J027,093J037),likelyofepigeneticorigin.Themainclusteroftillsampleswithanomalousvaluesisessentiallyspatiallycoincidentwithmanyoftheshowings.Thedominanticeflowtowardsthenortheastcanbeusedasavectortoguidefurtherprospecting.
Porphyry Cu‐Au
ThereispotentialforporphyryCu‐Au–stylemineralizationinthestudyareabasedonthepresenceoftheMountMilliganporphyryCu‐Audevelopedprospectincorrelativerockstothenorthwestofthestudyarea.ThetillgeochemicaldatashowselevatedvaluesofCuandAuandanumberofpathfinderelements(e.g.,As,Hg,Sb)inthenorthwesternpartofthestudyarea(Figures7a,b,c,d,f,g,i).Theseanomaloustillsamplesstronglyindicatesourcesofmineralizationup‐ice,towardsthesouthwest.ThereareanumberofCuandCu‐Aushowings
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coincidentandup‐iceofthisareaofelevatedgeochemicalvalues(Figure2).Forexample,attheTsilshowing(MINFILE094C180),inthenorthwesterncornerofthestudyarea,therearereportsofoutcropsofintermediatehornblendeandfeldsparporphyriticrocksexhibitingquartz‐carbonatealterationwithpyrite,pyrrhotiteandrarechalcopyriteveins.ThemainclusterofCuandAuanomaliesinthenorthwesternpartofthestudyareadirectlyoverliethemainclusterofCuandAushowingsinthisarea(Figure2).ThehighestheavymineralcontentscorrespondtotheareaidentifiedashavingpotentialporphyryCu‐Austylemineralization(cf.Wardetal.,2011).
Volcanogenic Massive Sulphide Deposits
Volcanogenicmassivesulfideshowingsoccurtothesoutheastandtothenorthwestofthestudyareaalongthetrendofthemajorbedrockunits.Giventhepresenceextensivevolcanicrocks,thereshouldbesignificantpotentialforVMSmineralizationinthestudyarea,eventhoughtherearenoVMSshowingsordepositslistedinMINFILE.However,thisstudyindicatesthereisrelativelylittlespatialcorrelationbetweenthecommodityelementsassociatedwithVMSmineralization.LeadanomaliesareclearlydistinctfrombothCuandZn.TherelativelylowPbcontentsinthetillinthestudyarea,comparedtootherareasofVMSdeposits(cf.,Halletal.,2003;ParkhillandDoiron,2003),couldberelatedtothreefactors: GiventhepreponderanceofmaficvolcanicrocksinthispartofBC,VMSmineralization,if
present,wouldlikelybelead‐poorgiventhegenerallyjuvenilenatureofthesourceofthevolcanicrocks(Smithetal.,1995;PatchettandGehrels,1998;Dostaletal.,1999;Erdmeretal.,2002;Rossetal.,2005).Furthermore,VMSdepositsassociatedwithoceanfloorandoceanicarcsettingsarelead‐poorcomparedtothoseassociatedwithcontinentalmargins(Franklinetal.,1981;Galleyetal.,2007).
OnlytheclayfractionwasanalyzedforPb,byaqua‐regiadigestionfollowedbyICP‐MS,anditispossiblethatPbispresentinalesslabileformorinacoarsersizefraction.
ItispossiblethatthethicktillunitsofthestudyareahavedilutedthegeochemicalsignatureofunderlyingbedrocklithologiesresultinginsubduedanomaliesforPb.
DespiteanapparentlackofgeochemicalresponseforPbintillsamplesthereisstillpotentialforVMS‐stylemineralizationinthestudyarea.ThegenerallackofspatialcorrelationbetweenanomalousCuandZnmaysimplybeafunctionofVMS‐relatedCuanomaliesbeingmaskedbyanomaliesassociatedwithporphyryCu‐Auandpreciousandbasemetalveinmineralizationorbydilutionduetothicktill.ZincshowspoorcorrelationswithNi,CrandMgindicatingthatanomalousZncontentsinthetillarenotsimplyafunctionofweatheringofmaficvolcanicrocks.InadditiontoanomalousZnalongtheeasternportionofthestudyarea(Figure7l),therearecoincidentanomaliesforCd,BiandTl,suggestingthepotentialforconcealed,presentlyunrecognized,Znmineralization.TheHMCsampleswiththehighestpyritegraincountsarealsofromtheeast‐centralpartofthemaparea(Figure8b),furthersuggestingthepresenceofVMS‐stylemineralizationinthisarea.MoredetailedworkfollowingupthesourceofanomalouspyritegraincountsandZn,Cd,BiandTlcontentsinthetilliswarranted.
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Mercury
PinchiLakemercurymine(MINFILE093K049)islocatedonthePinchifaultapproximately45kmtothenorthwestofthetwoHgoccurrencesinthesouthwesternportionofthestudyarea(Figure2).ThePinchiLakemineoperatedfrom1940to1944and1968to1975,andwasoneofonlytwomercury‐producingminesinCanada(Plouffe,1998).ThetwoHgshowingswithinthestudyareaareassociatedwiththeextensionofthePinchifault,butanomalouscinnabarcountsandHgcontentsintheclayfractionarenotspatiallyassociatedwiththeseshowings(Figures7f,5c).Elevatedcinnabargraincountsoccurtothenorthoftheshowings,suggestingadditionalsourcesoffault‐associatedHgmineralizationupicefromthecinnabargrains.ModeratelyelevatedHgintheclayfractionalsooccursintheareaofhighcinnabargraincounts.Follow‐upworkthatincludesananalysisofthesiltplusclay‐sizefractionusingananalyticalmethodwithlowerdetectionlimitsforHgiswarranted.
HEAVY MINERAL CONCENTRATE GEOCHEMISTRY TheINAAdeterminationsonheavymineralconcentratespresentedhereaddtothepreviouslypublisheddataandbegintobuildacoherentstoryonthepotentialformetallicmineralizationinthestudyarea.ThespatialdistributionofAu,AsandSbcontentsconfirmthepotentialforpreciousandbasemetalveinmineralizationandtoalesserextentporphyryCu‐Auinthenortheastandnorthwestareasofthestudyarea,respectively.Withgreaterthan30sampleshavingAucontentsgreaterthan400ppb,thereisthepotentialformineralizedbedrocktooccurthere.GoldanomaliescommonlycoincidewithanomaliesinotherpathfinderelementssuchasAsandSb.Althoughonlyalimitednumberofvaluesareabovedetectionlimit,thespatialdistributionsofHgvaluesintheheavymineralconcentratesdomimicthecinnabargraincounts.AreaswithelevatedINAAvaluesandgraincountsmaybeassociatedwithfaultssimilartothePinchiLakefault.ElevatedlightREEsandThinthenorthernpartofthestudyareaarecoincidentwith,andlocateddown‐icefrom,granitepegmatite,granite,andgranodioritesuggestingthepossibilityofREEmineralizationbeingassociatedwithfelsicporphyrybodiesinthearea.Ourpreviousstudiesontheclay+siltandclayfractionsofstudyareatillsandthepresenceoflargenumbersofpyrite/marcasitegrainsinsomeoftheHMCsamplessuggestpossibleVMSmineralization(Wardetal.,2011).However,theinherentlimitationsoftheINAAmethod(e.g.,lackofCuandPbdeterminationsandhighdetectionlimitsforZn,Cd,andAg)meanthatINAAdeterminationspresentedhereonheavymineralconcentratesdonotaddanyinsightintothepotentialforVMSstylemineralizationwithinthestudyarea.
CONCLUSIONS InpartoftheQUESTProjectarea,centralBC,approximately760tillsampleshavebeencollectedwherethickglacialdepositscoverbedrock,hinderingbothbedrockmappingandmineralexplorationprograms.ThestudyareaoccurswithintheQuesnelterrane,andisdominatedbymiddletoupperTriassicmaficvolcanicrocksandvolcaniclasticsedimentary
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rocksoftheNicolaGroup.TheMountMilliganCu‐Auporphyrydepositoccursjusttothenorthwestofthestudyareaincorrelativerocks,partofanearlinear,northwest‐trendingseriesofCu±Modepositsthatoccurwithinthisterrane.Tillgeochemicaldata(clayandclay+silt)andheavymineralgraincountdataandmetalcontentsofthe<0.25mmfraction,highlightfourareasthatwarrantfurtherwork:1) Inthenorthwesternpartofthestudyarea,thereisalargenumberoftillsampleswith
significantlyanomalousCuandAucontents(andcoincidentbutlesssignificantAsandAganomalies).TheunderlyingrocksarecorrelativewiththosethathosttheMountMilliganCu‐Auporphyrydeposit.ConsistentwiththepotentialforporphyryCu‐Austylemineralization,thereareanumberofshowingsassociatedwithalkalicvolcanicandporphyriticrocks.ThisareaalsohastillsampleselevatedinHf,REE,Th,Ti,FeandV,reflectingFe‐richalkalicigneousrocksintheunderlyingandup‐icebedrock.
2) Inthenortheasternpartofthestudyarea,thereareAu,Cu,As,Ag,SbandCdanomaliesintilloccurnearseveralpreciousandbasemetalveinshowingsandtwosmall‐scalepast‐producingAu(andPt)placermines.
3) Intheeast‐centralportionofthestudyarea,tillsampleshaveelevatedZn,CdandBicontents,aswellashighpyritegraincounts(upto10000grainsina10kgsample).TherearenoknownshowingsormineralizationinthispartofthestudyareabutthetillgeochemicalresultssuggeststhereispotentialforconcealedVMS‐typemineralization.
4) Inthewest‐centralportionandintothecentralportionofthestudyarea,Hgvaluesandelevatedcinnabargraincountssuggestthereisfault‐associatedHgmineralizationup‐ice(i.e.,tothesouthwest),perhapssimilartothePinchiLakemercuryminelocatedtothewestofthestudyarea.
Inthesefourareasincreasedtillsampledensitycouldprovidesomeinsightintocoveredbedrocklithologiesandthepotentialformetallicmineralization.Tillsamplingcanbecomemorechallenging,however,assampledensityincreasesappropriatesamplematerialcanbedifficulttofindandaccesstogoodsamplesitescanbelimited.Insuchcases,prospecting(includinganexaminationofclastsindrift)andtrenchingcouldbecarriedouttofurthertesttheseareas.
ACKNOWLEDGMENTS GeoscienceBCprovidedthemajorityoffundingforthisprojectandtheauthorsextendmanythankstoC.AnglinandC.Sluggettforhelpingtomakethisprojecthappen.TheMountainPineBeetle(MPB)ProgramunderthedirectionofC.Hutton(GSC,NaturalResourcesCanada)facilitatedbyAlainPLouffeprovidedfundingforaportionofthegeochemicalanalysesforsamplestakenin2008.AlainPlouffealsoarrangedforthearchivingofsamplesattheGSC.M.Casola,M.Dinsdale,K.Kennedy,V.Levson,J.McDonald,C.Pennimpede,S.Reichheld,I.SellersandD.Visprovidedableassistanceinthefield.AthoroughreviewbyT.Ferbeyhelpedtogreatlyimprovethemanuscript.
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REFERENCES Armstrong, J. E., Crandell, D. R., Easterbrook, D. J. andNoble, J. B. (1965): Late Pleistocene
stratigraphy and chronology in south‐western British Columbia and north‐westernWashington;GeologicalSocietyofAmericaBulletin,v.72,p.321‐330.
Averill, S. A. (2001): The application of heavy indicatormineralogy inmineral explorationwithemphasisonbasemetal indicatorsinglaciatedmetamorphicandplutonicterrains.GeologicalSocietySpecialPublicationsv.185,p.69‐81.
BCGeologicalSurvey(2010):MINFILEBCmineraldepositsdatabase;BCMinistryofForest,MinesandLands,URL<http://minfile.ca/>[August2010].
Bobrowsky,P.T.,Rutter,N.W.(1992):TheQuaternarygeologichistoryoftheCanadianRockyMountains.GeographiephysicetQuaternairev.46,p.5–50.
Clague, J.J. (1989):Chapter1:Quaternarygeologyof theCanadianCordillera; inQuaternaryGeologyofCanadaandGreenland,R.J.Fulton(ed.),GeologyofCanadaSeriesNo.1.,p.17‐96.
Clague J.J., Ward B.C. (2011): Pleistocene glaciation of British Columbia. In Quaternaryglaciations–extentandchronology,acloserlook,EhlersJ,GibbardPL,HughesPD(eds),DevelopmentsinQuaternaryScience15:563–573.
Dreimanis,A.,(1989):Tills:theirgeneticterminologyandclassification.In:Goldthwait,R.P.and Matsch, C. L. Eds.)Genetic Classification of Glacigenic Deposits. A.A. Balkema,Rotterdam.
Dilabio,R.N.W.(1990):Classificationandinterpretationoftheshapesandsurfacetexturesofgoldgrainsfromtill;inCurrentResearch,PartC,GeologicalSurveyofCanada,Paper90‐1C,p.323–329.
Dostal,J.,Gale,V.andChurch,B.N.(1999):UpperTriassicTaklaGroupvolcanicrocks,StikineTerrane,north‐centralBritishColumbia:geochemistry,petrogenesis,andtectonicimplications;CanadianJournalofEarthSciences,v.36,p.1483–1494.
Dreimanis,A.(1989):Tills:theirgeneticterminologyandclassification;inGeneticClassificationofGlacigenicDeposits,R.P.GoldthwaitandC.L.Matsch(ed.),A.A.Balkema,Rotterdam,p.17–83.
Erdmer,P.,Moore,J.M.,Heaman,L.,Thompson,R.I.,Daughtry,K.L.andCreaser,R.A.(2002):ExtendingtheancientmarginoutboardintheCanadianCordillera:recordofProterozoiccrustandPaleoceneregionalmetamorphismintheNicolahorst,southernBritishColumbia;CanadianJournalofEarthSciences,v.39,p.1605–1623.
Ferbey,T.LevsonandV.M.(2010):EvidenceofWestwardGlacialDispersalAlongaTillGeochemicalTransectoftheCopperStarCu+/‐Mo+/‐AuOccurrence,West‐centralBritishColumbia;BCMinistryofEnergyandMinesOpenFile2010‐04
Ferbey,T.Levson,V.M.andLett,R.E.(2012):TillGeochemistryoftheHuckleberryMineArea,West‐CentralBritishColumbia(NTS093E/11);BCMinistryofEnergyandMinesOpenFile2012‐02
GeoscienceBCReport2013‐1557
Franklin,J.M.,Lydon,J.W.andSangster,D.F.(1981):Volcanic‐associatedmasivesulfidedeposits;EconomicGeology,75thAnniversary,p.485–627.
Galley,A.G.,Hannington,M.andJonasson,I.(2007):Volcanogenicmassivesulfidedeposits;inMineralDepositsofCanada:ASynthesisofMajorDeposit‐Types,DistrictMetallogeny,theEvolutionofGeologicalProvinces,andExplorationMethods,W.D.Goodfellow(ed.),GeologicalAssociationofCanada,SpecialPublicationno.5,p.141–161.
Hall,G.E.M.,Parkhill,M.A.andBonham‐Carter,G.F. (2003):Conventionalandselective leachgeochemical exploration methods applied to humus and B horizon soil overlying theRestigouche VMS deposit, BathurstMining Camp, NewBrunswick; in Massive SulphideDeposits of the Bathurst Mining Camp, New Brunswick, and Northern Maine,W.D.Goodfellow,S.R.McCutcheonandJ.M.Peter(ed.),EconomicGeologyMonograph11,p.763–782.
Hoffman,E.L.(1992):Instrumentalneutron‐activationingeoanalysis;JournalofGeochemicalExploration,v.44,p.297–319.
Holland,S.S.,(1976):LandformsofBritishColumbia–aphysiographicoutline;BritishColumbiaMinistryofEnergy,MinesandPetroleumResources,Bulletin48,p.138.
JacksonJr.,L.E.,Clague,J.J.(Eds.),(1991):TheCordilleranIceSheet,In:GeographiephysiqueetQuaternaire.45,261–377.
LeFort,Darren;Hanley,Jacob;Guillong,Marcel.(2011):SubepithermalAu‐PdmineralizationassociatedwithanalkalicporphyryCu‐Audeposit,MountMilligan,QuesnelTerrane,BritishColumbia,Canada.EconomicGeologyandtheBulletinoftheSocietyofEconomicGeologistsv.106,p.781‐808.
Levson, V.M. (2001): Regional till geochemical surveys in the Canadian Cordillera: samplemedia, methods and anomaly evaluation; in Drift Exploration in Glaciated Terrain;McClenaghan, M.B, Bobrowsky, P.T., Hall, G.E.M. and Cook, S.J., Editors, The GeologicalSociety,SpecialPublicationNo.185,p.45‐68.
Levson,V.M.andGiles,T.R. (1997):Quaternarygeologyandtillgeochemistrystudies in theNechako and Fraser Plateaus, central British Columbia in Interior Plateau GeoscienceProject: Summary of Geological, Geochemical and Geophysical Studies; Diakow, L.J.,Metcalfe,P. andNewell J.,Editors,BritishColumbiaGeologicalSurvey,Paper1997‐2,p.121‐145.
Leybourne,M.I.,Boyle,D.R.andGoodfellow,W.D.(2003):Interpretationofstreamwaterandsediment geochemistry in the Bathurst Mining Camp, New Brunswick: applications tomineral exploration; in Massive Sulphide Deposits of the Bathurst Mining Camp, NewBrunswick, andNorthernMaine,W.D.Goodfellow, S.R.McCutcheon and J.M.Peter (ed.),EconomicGeologyMonograph11,p.741–761.
Logan, J. M., Schiarizza, P., Struik, L. C., Barnett, C., Nelson, J. L., Kowalczyk, P., Ferri, F.,Mihalynuk,M.G.,Thomas,M.D.,Gammon,P.,Lett,R.,Jackaman,W.,andFerbey,T.(2010):BedrockGeologyoftheQUESTmaparea,centralBritishColumbia;.GeoscienceBCReport
GeoscienceBCReport2013‐1558
2010‐5,BritishColumbiaGeologicalSurveyGeoscienceMap2010‐1andGeologicalSurveyofCanadaOpenFile6476.
Mathews,W.H.(1986):PhysiographicmapoftheCanadianCordillera;GeologicalSurveyofCanada,“A”SeriesMap1710A,scale1:5000000.
McClenaghan,M.B.(2005):Indicatormineralmethodsinmineralexploration;Geochemistry:Exploration,Environment,Analysis,v.5,p.233–245.
McClenaghan,M.B.,Ward,B.C.,Kjarsgaard, I.M.,Kjarsgaard,B.A.,Kerr,D.E. andDredge, L.A.(2002): Indicator mineral and till geochemical dispersal patterns associated with theRanch Lake kimberlite, Lac de Gras region, NWT, Canada; Geochemistry: Exploration,Environment,Analysis,v.2,p.299–320.
Nicholson,K., andEley,M. (1997):Geochemistry ofmanganeseoxides;metal adsorption infreshwater andmarine environments. Geological Society Special Publications v. 119, p.309‐326.
Parkhill,M.A. andDoiron, A. (2003):Quaternary geology of theBathurstMining Camp andimplications for base metal exploration using drift prospecting; in Massive SulphideDeposits of the Bathurst Mining Camp, New Brunswick, and Northern Maine,W.D.Goodfellow,S.R.McCutcheonandJ.M.Peter(ed.),EconomicGeologyMonograph11.
Patchett,P.J.andGehrels,G.E.(1998):ContinentalinfluenceonCanadianCordilleranterranesfromNdisotopicstudy,andsignificanceforcrustalgrowthprocesses;JournalofGeology,v.106,p.269–280.
Paulen,R.C.andBobrowsky,P.T.(2003):MultiphaseflowofLateWisconsiniceintheQuesnelHighlands:piecingtogetherdiscordanticeflowindicators.Programwithabstracts,vol.28,p.132,2003GAC‐MAC‐SEG,Vancouver.
Plouffe, A. (1997): Ice flow and late glacial lakes of the Fraser Glaciation, central BritishColumbia;inCurrentResearch1997‐A,GeologicalSurveyofCanada,p133‐143.
Plouffe,A.(2000):QuaternarygeologyoftheFortFraserandMansonRivermapareas,centralBritishColumbiaGeologicalSurveyofCanada,Bulletin554,p.62.
Ross,G.M.,Patchett,P.J.,Hamilton,M.,Heaman,L.,Decelles,P.G.,Rosenberg,E.andGiovanni,M.K.(2005):EvolutionoftheCordilleranorogen(southwesternAlberta,Canada)inferredfromdetritalmineralgeochronology,geochemistry,andNdisotopesintheforelandbasin;GeologicalSocietyofAmericaBulletin,v.117,p.747–763.
Sacco,D.A.,Ward,B.C.,Maynard,D.,Geertsema,M.andReichheld,S.(2010):Terrainmapping,glacial history and drift prospecting in the northwest corner ofMcleod Lakemap area(part of NTS 093J), central British Columbia; in Geoscience BC Summary of Activities2009,GeoscienceBC,Report2010‐1,p.33‐42.
SanderGeophysicsLimited(2008):Airbornegravitysurvey,QuesnelliaRegion,BritishColumbia;GeoscienceBC,Report2008‐08,121p.
Smith,A.D.,Brandon,A.D.andLambert,R.S.(1995):Nd‐SrisotopesystematicsofNicolaGroupvolcanicrocks,Quesnelterrane;CanadianJournalofEarthSciences,v.32,p.437–446.
GeoscienceBCReport2013‐1559
Struik, L.C. (1994): Geology of theMcleod Lakemap area (93J), British Columbia; GeologicSurveyofCanada,Report:2439,18pp.
Taylor BE (2007) Epithermal gold deposits In: GoodfellowWD (ed) Mineral Resources ofCanada: A Synthesis of Major Deposit‐types, District Metallogeny, the Evolution ofGeologicalProvinces,andExplorationMethods.pp113‐139.
Tipper, H.W. (1971): Glacial geomorphology and Pleistocene history of central BritishColumbia;GeologicSurveyofCanada,Bulletin196,89p.
Ward,B.C.,Geertsema,M.,Telka,A.,andMathewes,R.W.(2008):Apaleoecologicalrecordofclimatic deterioration frommiddle to lateWisconsinan time on the Interior Plateau ofBritish Columbia, Canada. 33rd International Geological Congress, August 6–14, 2008,Oslo,Norway.
Ward,B.,Maynard,D.,Geertsema,M.andRabb,T.(2009):Ice‐flowhistory,driftthicknessanddriftprospectingforaportionoftheQUESTProjectarea,centralBritishColumbia(NTS093G,H[westhalf],J);inGeoscienceBCSummaryofActivities2008,GeoscienceBC,Report2009‐1,p.25–32.
Ward,B.C.,Leybourne,M.I.andSacco,D.A.(2011):DriftprospectingwithintheQUESTprojectarea(NTS093J):MineralpotentialforporphyryCu‐Au,VMS,andAu‐CuVeins;inGeoscienceBCSummaryofActivities2011,GeoscienceBC,Report2011‐1,p.73‐96.
Ward,B.C.,Leybourne,M.I.andSacco,D.A.(2012):HeavymineralanalysisfromtillsampleswithintheQUESTProjectArea,centralBritishColumbia(NTS093J);inGeoscienceBCSummaryofActivities2012,GeoscienceBC,Report2012‐1,p69‐78.