Fluid inclusions and H-O-S-Pb isotopic characteristics of the Jiagantan gold deposit in Gannan, West Qinling

Jiagantan gold deposit is the largest gold deposit discovered in Xiahe-Hezuo area of West Qinling in recent years. The gold ore bodies occur in the fine clastic rocks of the Middle and Upper Triassic. The gold ore body occurs in the Middle and Upper Triassic fine clastic rocks. The occurrence of the ore bodies is strictly controlled by the NW thrust faults and its secondary structure, and they are distributed in echelon and pinnate forms, and the ore bodies are in vein, plate and bifurcated forms. Main mineral assemblages in the main ore-forming stage of the hydrothermal stage are quartz-pyrite -arsenite -stibnite -natural gold. In order to identify the source of ore forming materials and analyze the genesis of the deposit, a systematic fluid inclusion and H-O-S-Pb stable isotopic testing analysis was conducted based on the geological survey of the deposit. The quartz inclusion type in the main mineralization stage of the Jiagantan gold deposit is gas-liquid two-phase inclusion, and liquid-rich two-phase inclusions are the most common. The average temperature of ore-forming fluid is 248.67℃, and the average salinity is 3.78% NaCl, which is characterized by low temperature and low salinity. On the δD - δ¹⁸O_H2O diagram, the samples are close to the primary water range of the primary magma and mantle. The δ³⁴S value of sulfide (-13.4‰~-7.5‰) is characterized by obvious negative value and narrow range of variation. The Pb isotopic compositions of pyrite and arsenopyrite are similar. The lead is mainly from orogenic belt, and some of the lead from upper crust and mantle is added. The genetic type of the Jiagantan gold deposit is a wide-range low-temperature hydrothermal gold deposit far away from the ore-forming geological bodies. Its formation is closely related to the deep magmatism produced by the subduction of the oceanic crust in the Indosinian period.