GondwanaResearch16(2009)264–271
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GondwanaResearch
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ARe–OsstudyofmolybdenitesfromtheLanjiagouModepositofNorthChinaCratonanditsgeologicalsigni?cance
ChunmingHana,?,WenjiaoXiaoa,GuochunZhaob,MinSunb,WenjunQuc,AndaoDucabcStateKeylaboratoryofLithosphericEvolution,InstituteofGeologyandGeophysics,ChineseAcademyofSciences,Beijing,100029,ChinaDepartmentofEarthSciences,TheUniversityofHongKong,PokfulamRoad,HongKong,ChinaNationalResearchCenterofGeoanalysis,Beijing,100037,China
articleinfoabstract
TheLanjiagouModepositislocatedintheeasternpartoftheNorthChinaCraton.RheniumandosmiumisotopesinmolybdenitesfromtheLanjiagouporphyryModeposithavebeenusedtodeterminethetimingofmineralization.Molybdenitewasanalyzedmainlyfromgraniteporphyry,whichischaracterizedbymoderatetostrongsilici?cation.Rheniumconcentrationsinmolybdenitesamplesarebetween33and48μg/g.Analysisofelevenmolybdenitesamplesyieldsanisochronageof181.6±6.5Ma(2σ).Basedonthegeologicalhistoryandspatio-temporaldistributionofthegranitoids,itisproposedthattheModepositsintheeasternpartoftheNorthChinaCratonwererelatedtothesubductionofthePaleo-Paci?cplateduringJurassictime.
?2009PublishedbyElsevierB.V.onbehalfofInternationalAssociationforGondwanaResearch.
Articlehistory:
Received15October2008
Receivedinrevisedform15December2008Accepted4January2009
Availableonline7January2009Keywords:Re–OsstudyModepositLanjiagou
NorthChinaCraton
1.Introduction
TheNorthChinaCratonbearsthemostimportantmolybdenummetallogenicprovinceinChina,whichconsistsoftheYanshan–LiaoningmolybdenumorebeltonthenorthernmarginandtheEasternQinlingmolybdenumorebeltonthesouthernmargin(Huangetal.,1996).LocatedonthenorthernmarginoftheNorthChinaCraton(NCC),theYanshan–Liaoningmolybdenumorebeltisoneofthecentralizedareasofimportantmolybdenumdeposits,aswellasoneofthemajormolybdenumproducersinChina.Thetimeandspaceofthesedepositsareassociatedwithintermediate-acidgranites.Themolybdenum(copper)depositsareusuallydistributedalongtheendo-orexo-contactzonesofgraniteporphyries,andbelongtoporphyry-type(e.g.Lanjiagou),porphyry–skarn-type(e.g.Xiao-jiayingzi,DawanandXiaochigou)andskarn-type(e.g.YangjiazhangziandShouwangfen)oredeposits(Table1;Fig.2).
TheLanjiagouModepositislocatedintheeasternpartoftheNCC(Figs.1and2).Regionallyandtectonically,itoccursintheeasternpartoftheMesozoicYanshanfoldbelt.ItwasdiscoveredbytheLiaoningBureauofGeologyandGeneralCorporationofNon-ferrousMetallur-gicMetalsinthe1950s.Presently,theminingexplorationisstillbeingperformedbythelocalgovernment.Thereserveofmolybdenummetalinthedeposithasbeenestimatedtobemorethan216,800tonsMo(Huangetal.,1989).
SincethediscoveryoftheLanjiagouModeposit,manyscienti?cstudieshavebeenconducted,especiallyonthegeologyand
?Correspondingauthor.
E-mailaddress:cm-han@mail.igcas.ac.cn(C.Han).
geochemistryoftheMoores(AiandFeng,1985;YeandWang,1985;Luoetal.,1991;Yu,1992;Daietal.,2007;Tian,1999),includingstudiesonradiogenicisotopicdatingandstableisotopes(Huangetal.,1996;AiandFeng,1985),andtheore-formingenvironments(Huangetal.,1996;Peietal.,1998;Maoetal.,2003;Daietal.,2006;Geetal.,2007).However,muchofthedocumentationoftheLanjiagoudeposithasbeenreportedintheChineseliterature,andtheinternationalgeologicalcommunityknowslittleaboutthisdeposit.
Inthepresentstudy,wecarriedoutRe–OsdatinginvestigationsonmolybdenumoresfromtheLanjiagoudepositsinordertofurtherconstrainthetimingofmineralization.Inaddition,wealsodiscussthegeodynamicenvironmentsandprocessesthatcontrolledtheoreformation.AnunderstandingofthesemineralizingprocessesandgeodynamicenvironmentshasimportantimplicationsfortheMoexplorationprogramsintheeasternpartoftheNCC.2.Geologicalsetting
TheNCCistriangularinshapewithanareaofapproximately1,500,000km2,andisboundedbyfaultsandyoungerorogenicbelts(Fig.1;Zhaoetal.,2001).TheEarlyPaleozoicQilianshanOrogenandtheLatePaleozoic–LateMesozoicTianshan–InnerMongolia–Daxin-ganlingOrogenboundtheNCCtothewestandthenorth,respectively(Fig.1;Ren,1980;Zorinetal.,2001;Zhaoetal.,2001),andtheQinling–Dabie–Suluultrahigh-pressuremetamorphicbeltseparatestheNCCfromtheYangtzeCratontothesouthandeast(Fig.1).Recently,manynewresultsfrominvestigationsofmagmatism,metamorphism,structureandtectonics,geochronology,andmajor,trace,andisotopegeochemistryonrocksrelatedtotheNCChavebeen
1342-937X/$–seefrontmatter?2009PublishedbyElsevierB.V.onbehalfofInternationalAssociationforGondwanaResearch.doi:10.1016/j.gr.2009.01.001
C.Hanetal./GondwanaResearch16(2009)264–271
Table1
SummaryofgeologicalandmineralogicalfeaturesofmolybdenumandcopperdepositsintheYanshan–Liaoningmetallogenicbelt.Deposits
Genetictypes
EconomicHostrocksmetalsMo
Middle-UpperCambrian-Ordovi:limestone,
shaleandskarn
Intrusiverocks
Wall–rockalteration
Reserve,grade26.2×104MoMo:0.14%
OrebodysizeLength:300–800mThickness:3–10mDepth:200–250m
Sul?de
assemblages
265
ReferencesHuangetal.,1989
YangjiazhangziSkarn
Porphyriticgranite,Silici?cation,granite–porphyrypyritization,
chloritization,carbonization
k-feldsparalteration,greisenization,silici?cation,pyritization,chloritization,carbonizationSkarnization,
k-feldsparalteration,pyritization,carbonization,sericitization,chloritization
K-feldsparalteration,silici?cation,pyritization,sericitization,chloritization
K-feldsparalteration,silici?cation,skarnization,Serpentinization,carbonizationK-feldsparalteration,pyritization,skarnization,Serpentinization,sericitizationSkarnization,chloritization,Sericitization,silici?cation,serpentinization
LanjiagouPorphyryMo
Xiaojiayingzi
Porphyry–Mo–Feskarn
PorphyriticgraniteSinian:Dolomitic
limestone,
chert–dolomiticlimestone;
Cretaceous:pyroclasticrock
PorphyriticdioriteSinian:Dolomitic
limestone,
chert–dolomiticlimestone
21.68×104MoMo:0.13%
10.5×104MoMo:0.28%;296.3×104FeFe:33.4%
DazhuangkePorphyryMoSinian:CarbonaterockKjelsasite
1.04×104MoMo:0.08%;
Dawan
Porphyry–Mo–Cu–skarnZn–AgSinian:Dolomitic
limestone
Rhyoliteporphyry
25.9×104MoMo:0.12%
Xiaosigou
Porphyry–Mo–Cuskarn
Sinian:Dolomiticlimestone,
chert–dolomiticlimestone
Granodiorite–porphyry
5.98×104MoMo:0.09%;1.85×104CuCu:0.74%
ShouwangfenSkarn
Cu–Mo–FeSinian:Dolomite,chert–dolomiteicPorphyritic–granodiorite
0.22×104MoMo:0.31%;1.62×104CuCu:0.72%
Molybdenite,pyrite,
Chalcopyrite,galena,
zincblende
Length:360–1280mMolybdenite,Thickness:13–31mpyrite,Depth:200–550mchalcopyrite,
galena,magnetite,argentite
Length:150–800mMolybdenite,Thickness:7–21mpyrite,Depth:150–600mmagnetite,
chalcopyrite,galena,
zincblende
Length:350–1000mMolybdenite,Thickness:20–95mpyrite,Depth:350–500mzincblende,
ilmenite,chalcopyrite,
Length:n×1000mMolybdenite,Thickness:n×10mpyrite,Depth:n×100mpyrrhotite,
zincblende,galena,
chalcopyrite
Length:2000mChalcopyrite,Thickness:30–100mChalcocite,Depth:300–500mpyrite,
molybdenite,bornite,tetrahedrite
Length:200–500mChalcopyrite,Depth:150–300mbornite,
molybdenite,magnetite,zincblende,galena
Huangetal.,1989
Daietal.,2006
Daietal.,2006
Daietal.,2006
Daietal.,2006
Daietal.,2006
obtained(Houetal.,2008a,b;Kuskyetal.,2007;Pengetal.,2007;Santoshetal.,2007a,b;Zhaietal.,2007;Suetal.,2008).
ThebasementoftheNCChasbeendividedintotheEasternandWesternBlocksseparatedbythePaleoproterozoicTrans-NorthChinaOrogen(Fig.1;Zhaoetal.,2001).TheEasternBlockconsistsoftheArcheanbasementandthePaleoproterozoicJiao-Liao-JiBelt(Fig.1;Zhaoetal.,2005),andtheWesternBlockcanbesubdividedintotheOrdosandYinshanBlocksseparatedbythePaleoproterozoicKhonda-liteBelt(Fig.1;Zhaoetal.,2005).ThereisabroadconsensusthatboththeKhondaliteBeltintheWesternBlockandtheTrans-NorthChinaOrogeninthecentralpartofthecratonrepresenttwoPaleoproter-ozoiccontinent–continentcollisionalbelts(Zhaoetal.,2001,Wildeetal.,2002;Kr?neretal.,2005,2006).ThePaleoproterozoicKhondaliteBeltisconsideredtohaveformedbytheamalgamationoftheYinshanBlockinthenorthandtheOrdosBlockinthesouthtoformtheWesternBlockat1.95–1.92Ga(Zhaoetal.,2005;Wanetal.,2006;Santoshetal.,2007a,b),andsubsequentlytheWesternBlockcollidedwiththeEasternBlockalongtheTrans-NorthChinaOrogentoformthecoherentbasementoftheNCCat~1.85Ga(Zhaoetal.,2000,2001,2005;Guoetal.,2005;Liuetal.,2006).
TheEarlyArcheanbasementrocksareonlyreportedfromtheEasternBlock,representedby3.5–3.85Gadetritalzirconsandfuchsite-bearingquartzitesand~3.5GaamphibolitesintheCaoz-huangareaoftheEasternHebei,andthe3.3–3.8GagranitoidsandmetasedimentaryrocksinAnshanarea(Liuetal.,1992;Songetal.,1996).MiddleArcheanbasementrocksalsomainlycropoutintheEasternBlock,ranginginagefrom3.5to3.0Ga(Huangetal.,1986;Jahnetal.,1987;Kr?neretal.,1988;Wuetal.,1991;ShenandQian,1995),andoccurringasenclaves,boudinsandsheetswithinthe2.6–2.5Gatrondhjemite–tonalite–granodiorite(TTG)and2.5Gasyn-tectonicgraniteswhichmakeupmuchoftheNCC(Wuetal.,1991;Kr?neretal.,1988;Zhaoetal.,2001).ThelateArcheanbasementrocksarewidespreadinboththeEasternBlockandtheYinshanBlockandconsistpredominantlyof2.8–2.5Gatonalitic–trondhjemitic–grano-dioritic(TTG)gneisses,ultrama?ctoma?cigneousintrusions,dykesandminoramountsofsupracrustalrocks.Oftheserocks,TTGgneissesmakeup70%ofthetotalexposureoftheNeoarcheanbasement(Wuetal.,1991;Zhaoetal.,1998),andthesupracrustalrockscomprisesedimentaryandbimodalvolcanicrocks(Zhaoetal.,1998).Alltheserocksweredeformedandmetamorphosedtobetweengreenschistandgranulitefaciesat2.48–2.50Ga(Jahnetal.,1987;Wuetal.,1991;Zhaoetal.,1998;Geetal.,2003).
Sincethe?nalcratonizationat~1.85Ga(Zhaoetal.,2001;Kuskyetal.,2007),theNCCwassubsequentlycoveredbythicksequencesofMeso-NeoproterozoicandPaleozoicsediments(Luetal.,2008),withintrusionsofdiamondiferouskimberlitesinShandongandLiaoningProvincesduringmiddleOrdoviciantime.TheeasternpartoftheNCCbecametectonicallyactiveagainduringLateMesozoictime,withlarge-scalemagmatism,basindevelopment,ductiledeformationandmovementonlarge-scalefaultswhichtookplacefromtheLateJurassictoEarlyCretaceous(Yangetal.,2003).IntheCenozoic,alkalibasalts(manycontainingxenoliths)andminortholeiiticbasalts
266C.Hanetal./GondwanaResearch16(2009)264–271
Fig.1.TectonicsubdivisionoftheNorthChinaCraton(afterZhaoetal.,2005).Fig.2isoutlined.
Fig.2.SchematicgeologicalmapoftheYanshan–LiaoningmolybdenummetallogenicbeltonthenorthernmarginoftheNorthChinaplatform(modi?edfromHuangetal.,1996).
C.Hanetal./GondwanaResearch16(2009)264–271267
Fig.3.GeologicalmapoftheLanjiagouModeposit(modi?edfromDaietal.,2007).
eruptedatseverallocationsintheNCC(Basuetal.,1991;Tatsumotoetal.,1992).
TheoccurrenceofdiamondiferouskimberlitesinShandongandLiaoningProvincessuggeststhepresenceofathickandcoldlithosphericroot(ca.200km)oftheNCCatleastaslateasMiddleOrdoviciantime(Zhouetal.,1991,1994;Menziesetal.,1993;Grif?netal.,1998).However,constraintsfromxenolithsintheCenozoicbasaltsindicatethattheNCCisnowunderlainbyahotlithospherevaryingbetween120and50kmthick(Maetal.,1984),whichisconsistentwiththeavailableseismicandsurfaceheat?owdata.Therefore,itisevidentthattherewasstronglithosphericthinningduringPhanerozoictime,mostlyintheMesozoicandCenozoic(Menziesetal.,1993;MenziesandXu,1998;Grif?netal.,1998),whichiscon?rmedbytherecentOsisotopestudiesofGaoetal.(2002)andWuetal.(2003).3.LanjiagouMo(copper)deposit
TheLanjiagouintrusioniscomposedofcoarse-grainedgraniteand?ne-grainedgranite,thelargestofwhichoccupiesasurfaceoutcropof~20km2(Fig.3).Viewedfromthesurfaceoutcrop,theintrusionismostlyirregularinshape,butviewedfromtheverticalsection,theintrusionoccursasveinsoflargerbodies.Thecoarse-grainedgranitegenerallycontains40–45%orthoclase,15–20%plagioclase,30–33%quartz,and3–5%biotite,withminoramountsofcalcite,muscoviteandsericite.The?ne-grainedgranitegenerallycontains40–45%orthoclase,15–20%plagioclase,28–35%quartz,and1–3%biotite,withminoramountsofcalcite,muscoviteandepidote.Orthoclasecrystalsrangefrom0.36to3.5mminsize.Geochronologyofcoarse-grainedgraniterangesbetween178and186MaK–Armethod,andthe?ne-grainedgraniteyieldsaRb–Srwhole-rockisochronageof154±14Ma.
TheLanjiagoudepositcanbefurthersubdividedintotheupperLanjiagou,MiddleLanjiagou,LowerLanjiagou,Xiaomagou,Yuan-baoshanandXishandistricts.Totally101mineralizedbodieshavebeenidenti?ed,andtheyaredistributedinthemiddlesegmentofthe?ne-grainedgraniteandthecontactzonebetweenthecoarse-grainedand?ne-grainedgranites.Individualorebodiesvaryfrom76mto1288minlengthand3.1mto31.8minthickness.Inthedippingdirection,theexploredorebodiesextendover400mbelowthesurface.ThemainorebodiestrendinNWandNSwithadipangleabout45°.Thesizeofmolybdeniterangesfrom0.01mmto0.15mm.Theoresarecharacterizedbyeuhedralandsubhedratextures,veinlet-disseminatedandbrecciatedstructures.Principalmetallicmineralsaremolybdeniteandpyriteaswellasminorquantitiesofzincblende,chalcopyrite,galena,magnetiteandelectrum.Theganguemineralsincludemainlyorthoclase,plagioclaseandquartz,withlesseramountsofcalcite,muscoviteandchlorite.Wallrocksalterationismarkedbysilici?cation,sericitization,carbonatization,chloritization,potassicalterationandgreisenization(Luoetal.,1991).
Accordingtomineralassemblagesandcrosscuttingrelationshipsoftheoreveins,?vemineralizationstagescanbeidenti?ed(Fig.4).The?rstmineralizationstage(I)ischaracterizedbygas–liquidmetasoma-tism,accompaniedbypotassiumfeldspar,quartzandmuscovite.Thesecondstage(II)ischaracterizedmainlybyphyllicalteration,formingthequartz+sericite+magnetite+pyriteassemblagethatoccursasveins.Thethirdstage(III,mainmineralizationstage)isrepresentedbytheformationofveinscontainingquartz+molybdenite+pyrite+sphalerite.Thefourthstage(IV)ismarkedbytheformationofthe