湘西花垣铅锌矿田成矿物质来源的C、O、H、S、Pb、Sr同位素制约

C,O,H,S,Pb and Sr Isotope Constraints on the Metals Sources of Huayuan Pb-Zn Deposits in Western Hunan

花垣地区铅锌矿床有望成为中国最大的铅锌矿床,也是铅锌矿资源储量超过千万吨的世界级超大型矿床之一。文章通过碳、氧、氢、硫、铅和锶同位素地球化学特征研究,探讨了成矿流体和成矿金属来源。测试结果显示,花垣地区铅锌矿床主成矿期方解石样品的δ^(13) CPDB值范围为-2.71‰~1.21‰,δ^(18) OSMOW值范围为16.09‰~22.48‰,该地区铅锌矿床成矿流体中的碳主要来源于海相碳酸盐岩的溶解作用。花垣矿区的围岩的δ^(13) CPDB值范围为0.29‰~1.05‰,δ^(18) OSMOW值范围为21.33‰~23.89‰,为沉积成因海相碳酸盐岩。矿石中硫化物的δ^(34) S变化于24.93‰~34.66‰之间,重晶石δ^(34) S为32.78‰~34.22‰,表明还原硫主要来自地层中海相硫酸盐的还原。矿石硫化物的铅同位素组成均一,^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb和^(208)Pb/^(204)Pb分别为17.999~18.919、15.554~15.798和38.088~38.576,铅模式年龄为437~534Ma,成矿金属可能主要来源于奥陶系—寒武系。方解石和闪锌矿样品中流体的δD_(SMOW)变化于-91.1‰^-15‰之间,δ^(18) Ofluid变化范围为-4.1‰~8.75‰,矿床成矿流体的主要来源是建造水和大气降水。成矿流体与围岩的水-岩反应是导致该区铅锌矿床中方解石和闪锌矿矿物沉淀结晶的主要机制。成矿流体^(87)Sr/^(86)Sr为0.70906~0.71022,高于赋矿围岩寒武系清虚洞组灰岩锶同位素比值0.70886~0.70921,表明成矿流体流经了清虚洞组下伏地层,并与其中具有高锶同位素比值的碎屑岩、页岩和泥岩等进行了水岩反应及同位素交换。

The Huayuan lead-zinc deposit is expected to become the biggest Pb-Zn deposit in China,and one of the world-class super-large ore deposits with more than ten million tons of lead and zinc resource reserves.In this paper,C,O,H,S,Pb and Sr isotope geochemistry were analyzed in this paper in order to understand comprehensively the source of the ore metals and ore fluids.The analysis results show thatδ^13CPDB values of calcite samples display a range of 2.71 ‰ to 1.21 ‰,theδ^18 OSMOW values in a range of16.09 ‰ to 22.48 ‰.In the Huayuan lead-zinc deposit,the carbon in the ore-forming fluid is mainly derived from marine carbonate dissolution.Theδ^13 CPDBvalues of surrounding rock in Huayuan lead-zinc deposit range of 0.29‰to 1.05‰,theδ^18 OSMOWvalues range of 21.33‰to23.89‰,the surrounding rock is sedimentary marine carbonate.Theδ^34SV-CDTvalues of sulfides are 24.93‰-34.66‰,and the 34 S values of barite are 32.78‰ - 34.22‰,suggesting that the sulfur should be derived from the insitu thermochemical reduction of sulfates from the sedimentary strata.The ^206Pb/^204Pb,^207Pb/^204Pb and208Pb/^204Pb values of the ores are in the range of 17.999-18.919,15.554-15.798 and 38.088-38.576 respectively,and the normal Pb model ages are 437-534 Ma,so the ore metals were likely derived from the Ordovician-Cambrian strata.TheδD_（SMOW）of fluid in calcite and sphalerite changes from 91.1‰to 15‰,theδ^18 Ofluidrange of 4.1 ‰ to 8.75 ‰,TheδD_（SMOW）-δ^18 Ofluiddiagram shown that,the main source of oreforming fluid is formation water and atmospheric precipitation.Water-rock reaction between ore-forming fluid and wall rock is the main mechanism leading the precipitation and crystallization of calcite and sphalerite in Huayuan Pb-Zn deposit,west Hunan.The initial^87Sr/^86Sr values of the ore-forming fluid are0.70906-0.71022,higher than ^87Sr/^86Sr values（0.70886-0.70921）of the host rock Cambrian limestone,implying that the ore-forming fluid probably migrated through the underlying formation of Qingxudong Group,and experienced water-rock reaction and isotope exchange between the ore fluid and the shale,clastic rocks and mudstones which had high ^87Sr/^86Sr values.