湘西凤凰民稿铅锌矿床流体包裹体地球化学特征

Geochemical characteristics of fluid inclusions from Mingao Pb-Zn deposit in Fenghuang County,Western Hunan

在总结前人研究的基础上,对民稿铅锌矿床成矿期方解石脉进行了流体包裹体均一温度、盐度、流体包裹体气相成分、流体包裹体群体液相成分和氢氧同位素测定及分析,进而明确该矿床的成矿机制。结果表明,成矿流体温度主要为150~200℃,盐度一般大于11%,密度约1 g/cm^3,成矿压力约(195.3~215.8)×105Pa,成矿深度在737~814 m,是以钠和钙的氯化物为主的高浓度溶液,属低温、高盐度、高密度的地下热卤水性质的含矿热水溶液。成矿流体气相成分主要为H_2O和CO_2,并含少量的CH_4和H_2;包裹体液相成分中阳离子以Ca^(2+)、Na^+为主,其次为Mg^(2+)和K^+;阴离子主要为Cl^-、SO_4^(2-),其次为F^-、NO_3^-。氢氧同位素指示成矿流体主要来自建造水,有变质水的混入,后期可能有雨水的渗入。成矿期流体包裹体气相成分中普遍含CH_4,表明成矿与有机质相关,控矿构造及容矿层中的有机质充当还原剂,使硫酸盐成为还原硫,从而使成矿流体中的铅、锌等组分从络合物中分离、沉淀,堆积形成矿床。

Fluid inclusions in the mineralization calcite were studied from the Mingao Pb - Zn deposit, based on predecessors researches. Through the analysis of homogenization temperature, salinity, gas compositions, liquid compositions by heating/freezing system, hydrogen and oxygen isotopic compositions, it shows that the tempera-ture of ore-forming fluid is mostly ranging from 150 to 200 ℃, the salinity is always greater than 11% , the den-sity is generally about 1 g/cm^3, the mineralization pressure is about （195. 3 -215. 8） ×10^5 Pa, and the miner-alization depth varies from 737 to 814 m. The ore-forming fluid is highly concentrated in solution containing mainly sodium and calcium chloride. It belongs to the low temperature, high salinity, high density and mineral-ized underground hot brine. The gas component of fluid inclusion is dominated by H20 and C02, and also has little CH4 and H2. The positive ions in fluid inclusions are mainly Ca^2＋ , Na^＋ and secondly Mg^2＋ , K^ ＋. The main negative ions are Cl^-, SO4^2- with a fraction of F^- , NO3^- . The results of hydrogen and oxygen isotopic compositions imply that the origin of ore-forming fluid is related to formation water, with possible infiltration of rainwater and metamorphic water. C02 and CH4 are widespread in the fluid inclusions, indicating that the min-eralization is probably related to organic matter. The organic matter in the ore-controlling structure leads to the reduction of sulfate and the deposition of lead and zinc ore.