Abstract:

Based on the petrography, micro-thermometry, REEs data, hydrogen and oxygen isotopes of the fluid inclusions in the Zhesang gold deposit in Yunnan Province，we discussed the characteristics of the ore-forming fluids. The results show that there are four types of fluid inclusions, which includes liquid inclusions, pure liquid inclusions, pure vapor inclusions and CO₂-bearing three-phase inclusions. Homogenization temperatures, salinities, densities and mineralization pressures of liquid inclusions are 83.4-248.2 ℃, 0.18%-6.45%, 0.85-1.0 g/cm3 and 10.9-59.4 MPa, respectively. Metallogenic depth which is calculated based on the above data ranges among 0.2-2.2 km. REEs data of quartz and calcite from different hydrothermal stages display that the Zhesang gold deposit formed in reducing environment. δ¹⁸O_H2O of the fluid inclusions ranges from -6.1‰ to 4.9‰ and the δD_V-SMOW ranges from -40.3‰ to -74.8‰, showing that the ore-forming fluid comes from atmosphere precipitation. When the ore-forming fluid flowed through the organic-rich sedimentary rocks, primitive mefeoric water would be contaminated by the organic substance, resulting in the drift of hydrogen isotope. Organic carbon content of the ores reaches 0.12%-0.45% and the Au grade is growing with the increase of organic carbon. The δ³⁴S_V-CDT values of pyrite and arsenopyrite range from 9.2‰ to 10.2‰. All these evidences proved the source of sulfur resulting from the reaction between organic matter and sulfate in wall-rocks. Preliminary analyses inferred that during the oozing process, the ore-forming fluid mixed with the construction water and was heated to recycle upward by magma and geothermal gradient. Gold mineralization occurred in interaction process between the thermal recycle and wall-rocks, and enriched in proper space.

Key words: fluid inclusion, ore-forming fluid, organic matter, Zhesang gold deposit, Funing County, Yunnan Province