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IntroductiontoSediment-HostedPb-ZnDeposits:Part1:OverviewandComparisonofMississippiVelley-TypeandClasticDominated(SEDEX)OresDavidLLeachHonoraryProfessor,InstituteofGeology,ChineseAcademyofGeologicalSciencesAdjunctProfessor,CentreforExplorationTargeting,UniversityofWesternAustraliaConsultanttotheMineralsIndustrydleach5100@me.comPinePoint,NWTCanada沉积岩中赋存的铅锌矿第一部分:MVT和CD型矿床的概述和对比ModifiedfromCamAllen,2010Contrastingtectonicsettings:Attributes,survival,etcSediment-hostedZn-PbdepositsSkarn-DistalSkarn-PolymetallicVein-CRD-MVT矽卡岩有关的矽卡岩-多金属脉与MVT型矿床的区别ConfusionbetweenMVTZn-Pbandcarbonate-hosteddeposits:skarnminerals,geologicsetting,minorandtraceelements.MVT铅锌矿与碳酸盐岩容矿矿床的区别:矽卡岩矿物、地质背景、少量和微量元素的差别Carbonate-Hosted-notnecessarilyMVT!t碳酸盐岩容矿-但不是MVT的必须条件RecentSummariesofCarbonate-HostedPb-ZnDeposits碳酸盐岩容矿的铅锌矿综述MISSISSIPPIVALLEY-TYPELEAD-ZINCDEPOSITSMVT型铅锌矿床SUZANNEPARADIS,PETERHANNIGAN,ANDKEITHDEWINGFromYardley2005Concentrationvs.TemperatureinCrustalfluids各类地壳流体的温度和金属含量MVTandCDPb-ZnOresTransportandDepositionMVT与碳酸盐岩容矿矿床的迁移与沉淀•Extractionandtransport:Attemperatures250C,MobileinpresenceofOxidizedsulfurandimmobileinpresenceofReducedsulfur(thesulfurgod!).Requiresminimumsalinityof~10wt%•萃取与运移:低于250℃的温度,以氧化硫迁移,而还原硫不迁移。要求盐度至少~10wt%•Deposition:Mainlyincreaseinreducedsulfur(i.e.,localsulfatereductionorfluidmixingwithreducedsulfur).•沉淀:主要以还原硫形式,例如,局部硫酸盐还原或与还原硫的混合Sullivan:Hotandreduced:Carbonatepoorsequence,complexmetal,Metalconcentrationsinorefluidpossible.Uncommon.BHTlike?志留纪:热的还原的,贫碳酸盐地层,络合物金属,大于成矿流体中金属浓度,并不普遍。不常见。类BHT?MetalDeposition金属沉淀•200˚C•Salinityof15wt%NaCl•SS=0.02m•pH=5.5•温度:200℃•盐度:15wt%•总硫:0.02m•pH:5.5-Emsbo,2000REDUCING还原OXIDIZING氧化Temperature&pHlesseffectiveincarbonateaquifers@MVTconditionsSediment-hostedoresaredifficulttodate.沉积岩容矿的矿石定年困难Classification:DependenceonOreTextures.分类主要依据矿石结构ReocinSpainTunisiaN.Arkansas,USAJinding,YunanChinaClassifications分类“TakeHomePoints”要点•ISMYDEPOSITAMVTORCD?怎么判断一个矿床是MVT型还是CD型?•LAMINATEDORSYNGENETICTEXTURESCANBEMISLEADING(MVTorCD)纹层状或同沉积结构构造不可靠(可能是MVT型也可能是CD型)•CARBONATE-HOSTED–MVTORCDORSKARNORPOLYMETALICREPLACEMENT碳酸盐岩中赋存的矿床:可能是MVT型、CD型、矽卡岩型或多金属交代型•TECTONICSETTTING–THEFIRSTANDMOSTIMPORTANTCONSIDERATION大地构造背景–最先要考虑也是最重要的因素•BOTHFORMBYSIMILARFLUIDSATSIMILARTEMPERATURES形成两者的流体和温度相似•THETECTONICSETTINGSETSTHEMAPART大地构造背景将二者区分开来•CD:MAINLYPASSIVEMARGINSORPROTEROZICRIFT/SAGBASINSCD型:主要形成于被动大陆边缘或元古宙裂谷/下陷盆地中•MVTCARBONATEPLATFORMSEQUENCESINPASSIVEMARGINSMVT型:被动大陆边缘的碳酸盐岩台地层序•SKARNOFTENCONFUSEDWITHMVT矽卡岩型常被误认为是MVT型SEDEXDefinitionSEDEX型的定义•CarneandCathro(1982):Laminated,exhalativesulfidesinfine-grainedclastic,carbonate,andmetasedimentaryrocks.CarneandCathro(1982)定义:细粒碎屑岩、碳酸盐岩和变质沉积岩中赋存的纹层状喷流成因硫化物•“Exhalative”componentinherentinthetermSEDEX术语本身就说明喷流成因•Directevidenceofanexhalitenotrequired–includessub-seafloorsystems.不需要有喷流物或海底之下成矿体系存在的证据.AssumedAgeofmineralization“same”or“closeto”ageofhostrocks假定的矿化年龄与赋矿围岩的年龄相同或非常相似Sedex=ClasticdominatedPb-ZnSedex=碎屑状为主的铅锌矿CDOreTexturesCD型矿石的结构构造•Typicallyfine-grained,laminatedandstrataform典型矿石为细粒,纹层状或层状•Maybesub-seafloorreplacive可能由海床下的交代作用形成•Varietyofhostrocks:shale,carbonate,coarseclastics各种各样的围岩:页岩,碳酸盐岩,粗粒碎屑岩•Typicallyfine-grainedbutcanbecoarse-grained典型矿石为细粒,但也可呈粗粒状SEDEXClassificationsinLiterature文献中SEDEX型矿床的分类•Balmat-Edwards,UpperProterozoicCarbonate-hostedSedexBalmat-Edwards,晚元古代碳酸盐岩中赋存的SEDEX型矿床•ManySedexdepositsinTable1AaremetamorphosedSedexbutnoMVThasbeenmetamorphosed表格1A中的许多SEDEX型矿床是经过变质的,但MVT型矿床都未变质。•Problemwithclassifications!Layeredsulfides=SEDEX分类中存在的问题!层状硫化物=SEDEXMississippiValley-typePb-Zndeposits密西西比河谷型铅锌矿床•Diversefamilyofepigeneticores种类繁多的一大类次生矿床•Mainlyinplatformcarbonatesequences主要产在地台型碳酸盐岩层序中•Formedmainlyinextensionalfeatures主要形成于扩张环境•duringcontractionalorogenicevents;在挤压造山运动中•importantfaultcontrol断层控制很重要•Notassociatedwithigneousactivity与岩浆活动无关•Formedfromdensesedimentarybrines`10to35wt%形成于高浓度的沉积盐水中,盐度10to35wt%•Formedattemperatures200to250C形成温度200to250C•Oremainlyreplacementandopen-spacefill;dissolutioncollapsebrecciascommon大部分矿石为交代型和开放空间充填型;溶解崩塌角砾岩很普遍UN:UnclassifiedPM:PassivemarginBA:BackarcCS:ContinentalSagRF:ContinentalRiftTectonicClassificationsofCDDepositsCD矿床的构造背景分类太古宙元古宙显生宙被动边缘的数量被动边缘的数量年龄不是特别确定海水中硫酸盐的含量早元古代中元古代晚元古代Pb+Zn(百万吨)年龄次生氧气全球氧化事件UN:构造背景不明;BA:后弧;RF:大陆裂谷PM:被动边缘;CS:大陆下陷Modernpassivemargins现代被动大陆边缘•94,000kmaggregatelength总长94,000公里•oldestoneis~175m.y.r.最老的~175百万年ModifiedfromWarren2006World’sGreatestFactoryforEvaporitesandEvaporativefluids蒸发岩或喷气流体导致的世界最大的工厂被动大陆边缘的铅锌矿远离活动板块边缘。火山作用很少。例子:美国东海岸大陆边缘深海扇浊积岩深海平原洋壳大陆坡大陆隆大陆架水下峡谷陆架边缘大陆壳离散边缘(初始裂谷)的高角度正断层很厚的沉积物泥砂碳酸盐和硅质软泥蒸发岩PassiveMarginsandCDPb-ZnDeposits被动大陆边缘和碳酸盐容矿的铅锌矿Bradley,2008Passivemargins被动大陆边缘fromBradley,2008;Deposits矿床fromLeachetal.,2005MississippiValley-typePb-ZndepositsanddistrictsMVT型铅锌矿及时空分布TwobillionsyearsoftheWilsonCycleofoceanbasins威尔逊旋回中20亿年的海盆Evaporites,carbonateplatformstectonicsandstructure蒸发岩、碳酸盐台地大地构造和结构Crustalshorteninglinkedtoinboardextensionalzones与不宽广的伸展带有关的地壳缩短Enhancedpreservationoncontinentalcrust大陆壳的保存LifeCycleofPassiveMargins被动大陆边缘的生消轮回裂谷与宽广大洋相邻的被动边缘与新生的、正在扩张的大洋相邻的被动边缘弧逐渐靠近
本文标题:世界典型铅锌矿对比
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