Deposit geology, fluid inclusion characteristics and ore genesis of the Matoushan Cu-Au deposit in Southwest Sichuan Province

The Matoushan copper-gold deposit is located in the Kangding-Jinping mountain metallogenic concentration area. It is located in the junction of the Jinping-kangding-Shuicheng fault. It is a one of medium-size copper gold deposit in Southwest Sichuan Province. Ore bodies was presented as sulfide quartz vein, which occur in Devonian carbonated mudstone limestone and Permian metamorphic basalt. They are obviously controlled by structures. Pyrite, bornite, chalcopyrite and galena are common sulfide minerals in the ore. The observation of primary fluid inclusions of quartz in the ore and Laser Raman spectroscopy analysis show that, the ore-forming fluid of Matoushan Cu-Au deposit is a system of H₂O-CO₂-NaCl, the average temperature of fluid inclusions ranged from 108.1 to 439.1℃, and the salinity ranged from 3.55% to 22.78% NaCleq with a density ranged of 0.51 to 1.12 g/cm³, the fluid inclusions at the major metallogenic stage has the characteristics of medium temperature, medium-low salinity, low density, and rich in CO₂. The δ³⁴S_V-CDT was -4.6‰ to 8.4‰ of sulfide minerals in ores, indicating that the characteristics of S isotopic are from the magmatic; the primary fluid inclusions in quartz veins are δD=-78.8‰—-48.7‰ and δ¹⁸O_H2O=-2.1‰-9.3‰, the carbon and oxygen isotopic compositions of the dolomite are δ¹³C_V-PDB=-5.3‰-1.7‰ and δ¹⁸O_V-SMOW=19.4‰-25.9‰, which indicates that the ore-forming fluid is magmatic water-mixed with meteoric water and formation fluid. Based on the geological features of ore deposit, fluid inclusions and the isotopic evidence of S, C, O and H, it can ben concluded that the Matoushan coppergold deposit belongs to the type of medium-low temperature-magmatic hydrothermal Cu-Au deposit.