西藏驱龙超大型斑岩铜矿床_地质_蚀变与成矿_杨志明

20086June,2008MINERALDEPOSITS273Vol.27No.3:0258-7106(2008)03-0279-40:X杨志明1,侯增谦1,宋玉财1,李振清2,夏代详3,潘凤雏4(1,100037;2,100037;3,850000;4,850000),,,,,,,,2212Ma,PX1(1517?012)Ma2,,6Ma,,XHf,,70%,,-,EW,,,;SN,,,(UST)3,2,,:,;,,--,,,-,-,-,-;,-;,,,,;,,Ca2+;,();,Ca2+Fe2+;;;;;;;:P618.65:AX(:40730419)973(:2002CB412600),,1978,,E-mail:[e-mail]2008-02-26;2008-04-08QulongsuperlargeporphyryCudepositinTibet:Geology,alterationandmineralizationYANGZhiMing1,HOUZengQian1,SONGYuCai1,LIZhenQing2,XIADaiXiang3andPANFengChu4(1InstituteofGeology,ChineseAcademyofGeologicalScience,Beijing100037,China;2InstituteofMineralResources,ChineseAcademyofGeologicalScience,Beijing100037,China;3TibetZhongshengMineralResourcesCompany,Lhasa850000,Tibet,China;4TibetInstituteofGeologicalSurvey,Lhasa850000,Tibet,China)AbstractAlthoughsomeporphyrydepositsareseeninpost-collisionalextensionalsettingsandseeminglyhavenorela-tionshiptosubduction,suchdepositscommonlyoccurinarcsettingsinassociationwithsubduction-relatedcalc-alkalinemagmas,andtheircharacteristicsremainpoorlyunderstood.Inthispaper,theauthorsdescribeigneousgeology,alterationmineralogyandmineralizationhistoryofQulongdeposit,anewly-discoveredpost-collisionaltypeporphyryCudepositinsouthernTibet.ItisassociatedwithMiocenemonzogranite-granodioriteintrusionsandhostedpartlyinJurassicandesitic-daciticvolcanics.A1915MagranodioriteplutonwithdioriteenclavesseemtobetheearliestMioceneintrusiveunit,intowhicharegularly-shapedstock(Pporphyry)andthenathindike(XPorphyry)ofmonzograniteintrudedabout1717Maago1Themaincopper-molybdenummineralizationisassociatedwiththePporphyry.AbarrendioriteporphyryintrudedintothePandXporphyriesaround1517Ma.PetrologictrendsoftheintrusionssuggestthattheMioceneintrusionshadsimilaroriginandwereprobablyformedbyfractionationofaratherdeepmagmachamber.EmplacementofMioceneporphyries,controlledbyQulonganticline,wasadirectresponsetotherapiduplift/erosionofGangdesearcbatholithsinsouthernTibet.Miaroliticcavitiesandunidirectionalsolidificationtextures,thekeyevidenceforvolatileseparation,wererecog-nizedinthePandXporphyries,respectively.Earlypotassicalteration,characterizedbyquartz-Kfeldspar(?anhydrite),pervadesthePporphyryandgranodiorite.Laterally,thisalterationgradesintoquartz-biotite-anhy-drite(?Kfeldspar),whichhasaffectedallMioceneintrusionsexceptthelatestdioriticporphyry.WallrocksofgranodioriteandJurassicandesitic-daciticvolcanicswithin1~115kilometersfromtheporphyriesaredominatedbypotassicalteration.Anouterhaloofpropyliticalteration(epidote-chlorite?calcite)extendsupto2km.Feldspar-destructivealteration(sericite-chlorite?clayminerals)hasoverprintedmostofthepotassicandpartofthepropyliticalteration.Thealterationisstronglypervasiveintheinterioroftheporphyriesandoccursasveinhalosawayfromtheporphyries.Theearliestquartz-Kfeldsparalterationandveinsarebarren,whereasap-proximately60percentofthe7milliontonsofcoppertheycontainhavetodowithslightlylaterquartz-biotite-anhydritealteration.Barrenassemblagesarerelatedtoirregularquartz(-Kfeldspar?anhydrite)veins,whicharetruncatedbytheXporphyry.Cusulfide-bearingassemblagesareassociatedwithdiscontinuouschalcopyrite(?biotite)andcontinuousquartz-anhydrite-chalcopyrite(?molybdenum)veins.DepositionofCu-Mowithabundantanhydriteoccurredduringorbetweenemplacementsofcloselyrelatedporphyriesfromhightempera-turemagmatically-derivedfluids,andwasprobablycausedbyhydrolysisofSO2.Keywords:geology,alteration,mineralization,metallogeneticmodel,porphyrycopperdeposit,Qulong,Gangdese,Tibet(,2001;,2001),,,711Mt(Cu2802008015%),1986~1988,1:20,;1988~1994,,/0,2000,,()1998~2001(973)2000~2002(),;2001,,;2002~2005,,;2004,,(Cu111Mt,,2004)2006~2007,,(Cu711Mt)1998~2001,,/0,/0(,2001;,2001),,,(,2001;2003a;2003b;2004a;2005;,2001;2004b;2006;,2003;2004;2006;,2003;2004;2006;Houetal.,2004b;Gaoetal.,2003;2007;Quetal.,2004a;2007;,2004;,2003;,2005a;2005b;2006),,-,,(,2007),,,;,,,,1,-(1a)(Yinetal.,2000),--,70~80km1500km(,2005)4-,-,(30~24Ma,Yinetal.,2000)(21~18Ma,Copelandetal.,1987;Harrisonetal.,1992)(18Ma,Williamsetal.,2001)(14~1315Ma,Colemanetal.,1995;Blisniuketal.,2001)--(25~10Ma,Coulonetal.,1986;Turneretal.,1993;Milleretal.,1999)(,2005),),Cu-MoCu-Pb-Zn,350km30~50km(1b),;,1917~1212Ma,,16Ma(,2003;2004;Houetal.,2004b)281273::1-(a)(b)(Houetal.,2004b)Fig.1Simplifiedgeologicalmap(a)oftheHimalayan-Tibetanorogen,showingthelocationoftheGangdesePorphyryCuBelt(GPCB),andsimplifiedgeologicalmap(b)oftheGangdeseporphyrycopperbeltintheTibetanorogen(modifiedfromHouetal.,2004b)2,EW,3:-()(),,,,,-,,,,2.1,60%(2a),EW,,,3km,(174Ma),,,(,2006)3:,(3a),,;,(3b),,,,,();,28220082(a,,2004;,2008a)(b,c)X,,bc,Fig.2a.GeologicalmapoftheoredepositwiththesectionlinesA-AcandB-Bc(compiledfromZhengetal.,2004andYangetal.,2008a);b.CrosssectionalongsectionA-Acwithlitholigiesonthebasisofdatafroms6xdrillholesofthesection;c.CrosssectionalongsectionB-Bcbasedondatafrom12drillholesofthesectionXporphyryisaratherthinandirregulardyke,whichcannotbewelltracedbyavailabledataofdrillholes2.22.2.1西部斑岩(2a)(IIIIIIV,,2004),,115km2,,,(3c)(10%~15%)(8%~10%),15%~25%;,,,(