| 西藏冈底斯三处斑岩铜矿床流体包裹体及成矿作用研究 |
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| 引用本文：.2005.Fluid inclusions and ore_forming processes of three porphyry copper deposits in Gangdese belt, Tibet[J].Mineral Deposits,24(4):398~408 |
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| 基金项目:国家重点基础研究发展规划项目（编号2002CB412600） |
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| 中文摘要:对西藏冈底斯斑岩铜矿带中的驱龙、冲江斑岩铜矿床和与斑岩有关的帮浦铜多金属矿床进行了流体包裹体岩相学、显微测温和激光拉曼探针分析。对斑岩中斑晶石英、硅化脉石英和热液矿物硬石膏内流体包裹体的观测表明，与成矿有关的流体包裹体可以分为气相包裹体、液相包裹体、含子晶的多相包裹体等3类。它们的均一温度变化较大（191～550℃），气相包裹体与含子晶多相包裹体的均一温度相近，主要集中于300～550℃之间。流体的盐度w(NaCleq)为1.91%～66.75%，含石盐子晶包裹体的盐度w(NaCleq)范围为32.70%～66.75%。激光拉曼光谱分析表明，子晶以石盐为主，并有较多的黄铜矿；气相包裹体和液相包裹体的气相中含有CO2。低密度的气相包裹体与高密度的液相包裹体、高盐度的含子晶包裹体共生，其均一温度范围一致，但盐度相差较大，指示成矿流体有不混溶作用或沸腾作用。成矿流体来自于岩浆的出溶；金属硫化物直接来源于岩浆。斑晶石英内流体包裹体中的不混溶作用与岩浆的初始沸腾有关；硅化脉石英捕获的流体包裹体与岩浆的二次沸腾有关；而硬石膏内流体包裹体的不混溶与两种不同性质流体的混合作用有关。斑晶石英中包裹体内的黄铜矿子晶是岩浆流体高金属含量的表征而不是矿化开始的标志。冈底斯成矿带内斑岩铜矿的成矿始于岩浆期后高温阶段，随后的高_中温热液阶段是流体大量沉淀矿质的重要时期。 |
| 中文关键词:地球化学 成矿作用 流体包裹体 激光拉曼光谱 斑岩铜矿 冈底斯 西藏 |
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| Fluid inclusions and ore_forming processes of three porphyry copper deposits in Gangdese belt, Tibet |
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| Abstract:Three copper deposits in Gangdese metallogenic belt of Tibet were selected for fluid inclusion studies. They include Qulong and Chongjiang, which are typical porphyry copper deposits, and Bangpu porphyry_related copper polymetallic deposit. Three types of fluid inclusions, namely gas_rich, liquid_rich and daughter mineral_bearing polyphase brine inclusions, were recognized according to their characteristics and the volume proportions of phases in quartz phenocrysts, vein quartz and anhydrite at the room temperature. The homogenization temperatures of the fluid inclusions are spread scatteredly in the range of 191℃～550℃. The homogenization temperatures of the gas_rich inclusions are similar to those of the daughter mineral_bearing polyphase brine inclusions, ranging from 300℃ to 550℃. The salinities w(NaCleq) of the three types of inclusions vary remarkably from 1.91% to 66.75%, with the high_salinity halite_bearing inclusions up to 66.75%. Single inclusion microanalyses by Laser Raman Spectroscope show that the daughter minerals in inclusions are mainly halite and chalcopyrite, and that CO2 is indwelled in some gas_ and liquid_rich inclusions, but with no evidence of petrography and microthermometry. The coexistence of low_density gas_rich inclusions, high_density liquid_rich inclusions and high_salinity halite_bearing inclusions with striking salinity differences in the same range of homogenization temperatures is attributed to the immiscible separation of fluids, boiling of magma or mixing of fluids. The halite_ and chalcopyrite_bearing polyphase high_salinity brine inclusions in quartz phenocrysts are interpreted as the most primitive magamtic fluid. Ore_forming fluids were derived from the exsolution of magmatic melts that introduced dominant ore metals into the porphyry copper deposits. The immiscibility of fluids inferred by the inclusions in quartz phenocrysts resulted from the first boiling of magma and that in vein quartz from the second boiling. The immiscibility of fluids in anhydrite, however, represented the result of mixing between magmatic fluids and meteoric water. The chalcopyrite crystals in quartz phenocryst fluid inclusions indicate the high concentration of ore metals in the inclusions rather than the beginning of copper mineralization. In the copper deposits of Gangdese belt, the copper mineralization began at high temperature in postmagmatic phase and mass copper precipitated in hydrothermal fluids at high to intermediate temperature.
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| keywords:geochemistry, mineralization, fluid inclusion, Laser Raman Spectra, porphyry copper deposit, Gangdese, Tibet |
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