湘西地区铅锌矿成矿物质来源——来自S、Pb同位素的证据

    Sources of metallogenic materials of lead-zinc deposits in western Hu'nan Province:Evidence from S and Pb isotopes

    • 摘要: 湘西地区铅锌矿床位于湘西-鄂西成矿带西南段,具有良好的成矿地质背景和控矿条件,有望成为中国最大的铅锌矿基地。S和Pb同位素组成分析结果表明,湘西地区矿床的δ34S值变化范围为6.30‰~34.66‰,平均值为19.64‰,明显富重硫,具有双塔式分布特征,矿石硫主要来源于容矿地层中的海相硫酸盐类和海水。8个矿床矿石矿物的206Pb/204Pb值范围为17.689~18.295,207Pb/204Pb值变化于15.535~18.848之间,208Pb/204Pb值介于37.294~38.630之间。区内铅锌矿床Pb同位素成分具有造山带和上地壳Pb同位素特征,成矿物质来源于造山带和上地壳的混合作用,铅成因类型为上地壳和地幔因岩浆作用而混合的俯冲铅。提出了湘西地区铅锌矿成矿作用的两阶段演化模式,认为区内铅锌成矿作用经历了成矿流体形成和成矿流体迁移富集2个演化阶段。

       

      Abstract: Located in the southwest of the western Hubei to western Hu'nan metallogentic belt, lead-zinc deposits in western Hu'nan are expected to become the largest lead-zinc deposit basement, with good ore-forming geological background and ore-bear-ing conditions.In this paper, S-Pb isotope compositions of sulfide minerals separated from orebodies in the ore deposits were deter-mined so as to discuss the sources of ore-forming materials.Studies of sulfur and lead isotopic compositions show that the sulfur isoto-pic compositions δ34S in orebodies in western Hu'nan Province are in a wide range of 6.3‰~34.66‰, 19.64‰ on average, with obvi-ous rich heavy sulfur and the characteristics of the distribution of the Twin Towers.Sulfur of the ore mainly came from the marine sul-fate in the ore-bearing formation and seawater.The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for ore minerals from the eight depos-its are in the ranges of 17.689~18.295, 15.535~18.848 and 37.294~38.630 respectively.As for lead-zinc deposits in this area, lead isoto-pic composition has orogenic belt and upper crust Pb isotopic characteristics, sources of ore-forming materials were from the mixture of orogenic belt and upper crust, lead genetic types are the subduction lead resulting from mixture of upper crust and mantle magma-tism.The authors put forward the lead-zinc ore-forming model of two stages of evolution for deposits of western Hu'nan area.Leadzinc mineralization in the area went through two phases of evolution which included enrichment of ore-forming fluid and migration of ore-forming fluid.

       

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