Fluid Inclusions in the Zhaxikang Pb-Zn-Sb Polymetallic Deposit, South Tibet, and Its Geological Significance

Abstract

Abstract:

The Zhaxikang PbZnSb polymetallic deposit, which is located in the south Tibetan detachment system, is one of the few large PbZnSbAg symbiotic deposits in Tibet that characterized by great variety of sulfosalt minerals. The deposit occurs in Lower Jurassic Ridang Formation, with the rocks being carbonbearing calcareous slate, calcareous slate, sericite slate, shale and quartz sandstone. The ore bodies in Zhaxikang deposit are mainly controlled by SN and NE-SW striking tensional faults. The deposit was subjected to two stages: medium low temperature hydrothermal period and hypergenesis period. The inclusions in siderite, calcite and quartz of the medium low temperature hydrothermal period are dominantly vapor liquid two phase inclusions, including a small amount of pure vapor inclusions, pure vapor CO₂ type inclusions and CO₂-H₂O three phase CO₂ inclusions. In the medium low temperature hydrothermal period, homogenization temperatures of inclusions vary from 184 to 329 ℃ with peak temperature of 255 ℃, the salinities from 2.07% to 12.05%, the densities from 0.65 to 0.86 g/cm³. The ore forming fluid is a medium low temperature, low salinity, low density H₂O-NaCl system, with minor or trace amounts of CO₂ and CH₄.The δDV-SMOW and δ¹⁸OH₂O values of the fluids in quartz and calcite inclusions varied from －165‰ to －131‰ and from－13.7‰ to 10.21‰, respectively, therefore, the water in the ore forming fluids derived from precipitation. The immiscibility which was marked by the escape of gases from the fluid occurred during the mineralization, whereas this immiscibility resulted in sulfide mineralization. The genesis of this deposit belongs to medium low temperature hydrothermal type formed during groundwater convection cycle driven by sedimentary structural geothermal activity.

Key words: Pb-Zn-Sb polymetallic deposit, fluid inclusion, mineralization, Zhaxikang, south Tibet

SHU Li-Kuan, GU Xue-Xiang, LI Guan-Qing, ZHANG Yong-Mei, CHENG Wen-Bin, BIAN Xiao-Dong. Fluid Inclusions in the Zhaxikang Pb-Zn-Sb Polymetallic Deposit, South Tibet, and Its Geological Significance[J]. Geoscience, 2012, 26(3): 453-463.

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