粤北大宝山多金属矿床成因研究

Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries,including porphyry deposits centered on intrusions;skarn,carbonate-replacement,and sediment-hosted Au deposits and so on. The distal skarn-type deposit that occured in layer, layer-likely shape of the orebodies, is difficult to distinguish from SEDEX or VMS deposit.In south China,some region or a single deposit coexist statiform/ massive sulphides with vein-,skarn,and porphyry-type orebodies,like as the Dabaoshan polymetallic deposit of nortern Guangdong.Their ore genesis is debated for a long time.In this study,after extensive field work and zircon SHRIMP U-Pb dating,Hf isotope,whole-rock major- and trace-elements as well as Sr-Nd-Pb isotopes, we attempt to investigate the intrusive age,petrogenesis,nature of source and tectonic setting of the intrusive rocks related to mineralization; After pyrite Re-Os dating,LA-ICP-MS and EMPA elements analysis,to obtain the ore-forming age,trace element composition,occurrence and genesis of pyrite and discuss the nature of ore-forming fluids of the statiform Cu-Pb-Zn ore. Furthermore, combined with S isotopic data and the previous study,a comparison on the trace-elements composition of pyrite, nature of ore-forming, ore-forming age between statiform Cu-Pb-Zn ore and porphy-,skarn-type Mo-W ore is to be carried out to decipher their ore genesis relationship, which will be linked with the redefined magmatisim for establishing model of ore genesis and related tectonic setting.Our study will guide the next prospecting in the Dabaoshan deposit and will prvide a mirror for ore genesis study of statiform/massive sulphide deposit in south China.

斑岩系统中发育的远矽卡岩矿床呈层状产出时，与海底喷流矿床较难区分。华南地区的一些层状/块状硫化物矿床就长期存在海底喷流和岩浆热液成因之争，粤北大宝山多金属矿床便是其中之一。本项目拟通过锆石U-Pb年龄、Hf同位素、全岩主量、微量元素、Sr-Nd-Pb同位素分析，探讨大宝山矿区成矿岩体的时代、成因、成岩过程及构造背景；通过黄铁矿Re-Os年龄、黄铁矿LA-ICP-MS和EMPA原位测定，探讨矿区层状铜铅锌多金属矿的成矿时代、黄铁矿中微量元素组成、赋存状态及不同类型黄铁矿成因，并与矿区已知时代、成因的斑岩钼（钨）矿和矽卡岩钼钨矿进行对比研究。结合硫同位素数据及前人资料，进一步探讨不同阶段的成矿流体特征，建立不同类型矿体之间的成因联系及与区内岩浆活动的关系，从而确定矿床成因，建立成矿模式。本研究将对该区进一步的找矿提供理论依据，并能为华南地区块状硫化物矿床成因厘定提供借鉴。

项目对大宝山矿区层状-似层状Cu-Pb-Zn多金属矿及区内岩浆岩进行了详细的研究，在层状-似层状Cu-Pb-Zn多金属矿的时代、成因这一关键科学问题上取得重要进展。（1）获得了大宝山矿区岩浆岩高精度的成岩年龄。SHRIMP和LA-ICP-MS锆石U-Pb定年结果表明，矿区火山岩中流纹岩和凝灰岩形成于437.1～439.1Ma、辉绿岩形成于209.8Ma、花岗闪长(斑)岩形成于164.3～165.2Ma；玄武岩基质的40Ar/39Ar坪年龄为146.7Ma。表明矿区至少存在三期岩浆活动：427～439Ma、～210Ma和167～147Ma。（2）揭示了岩浆岩的源区性质及形成的构造背景。元素地球化学及Nd-Hf同位素地球化学研究表明，流纹岩和凝灰岩源于华南元古宙(1.48～1.90Ga)地壳物质的部分熔融，可能与加里东期吴川-四会深大断裂活动有关；辉绿岩源于具亏损特征的地幔物质部分熔融，是印支期造山运动后伸展背景下基性岩浆底侵的产物；花岗闪长（斑）岩源于华南元古宙（1.01～1.31Ga）地壳物质重熔，并有少量幔源物质的加入，形成于太平洋板块俯冲引起的弧后伸展背景；玄武岩为弧后盆地后期阶段产物。（3）厘定了层状-似层状Cu-Pb-Zn多金属矿的形成时代。获得了具沉积改造特征的细粒磁黄铁矿423±18Ma的Re-Os等时线年龄，具热液特征的粗粒磁黄铁矿及与其共生的黄铜矿238±22Ma 的Re-Os等时线年龄。（4）利用电子探针、LA-ICP-MS等原位分析手段对层状-似层状矿体中硫化物进行了系统分析，获得一大批高精度数据，揭示磁黄铁矿从细粒具沉积改造特征→粗粒具热液特征→与其他热液硫化物共生的演化过程中的流体，是与基性岩浆活动有关的富Cu流体，从早到晚流体中Cu含量逐渐增加，且晚期流体富含Zn元素。（5）提出大宝山多金属矿床为多期叠加成矿的认识。第一期成矿作用与加里东期岩浆活动有关，形成了层状-似层状矿体中具沉积改造特征的细粒磁黄铁矿；第二期成矿作用与印支期辉绿岩岩浆活动有关，形成了层状-似层状矿体中的Cu-Pb-Zn矿，并对早期形成的磁黄铁矿进行了叠加改造，使其粒度变粗、品位增高；第三期成矿作用与燕山期花岗闪长(斑)岩有关，形成了矿区斑岩型-矽卡岩型Mo-W矿。