Fluid Inclusion and Sulfur Isotope Study on the Donggualin Gold Deposit in the Ailaoshan Gold Belt

Fluid inclusions and sulfur isotopes can reveal the characteristics of ore-forming fluid and the origin of ore-forming materials, which are important indicators for ore genesis. The Donggualin gold deposit is located in the Zhenyuan gold orefield of the Ailaoshan gold belt. Only a few studies have been carried out on this deposit and thus the ore genesis remains unsolved. Microthermometry of fluid inclusion in veins from two mineralization stages and sulfur isotope analyses of pyrite from ores has been studied, in order to unravel the ore genesis. Fluid inclusion results show that the ore-forming fluids belong mainly to the NaCl-H₂O system and the homogenization temperatures range from 100℃ to 400℃, with two peak values of 160-190℃ and 280-310℃. The salinities peak at 6%-9% NaCl_eqv. The densities have two peaks of 0.7-0.8 g/cm³ and 0.9-1.0 g/cm³. These results suggest that the gold-forming fluids are characterized by mid-low temperature and low salinity. The δ³⁴S values of pyrite from the two stages are 0-1‰ and -4.7‰-3‰, respectively, which are generally consistent with those of the lamprophyre wallrock (-0.44‰-0.54‰). The lamprophyre is very close to gold mineralization and lamprophyre-hosted ore is the most common. It can be inferred that the ore materials are probably related to the lamprophyre derived from mantle related to minor crustal contamination. In conclusion, the Donggualin deposit was possibly formed by mantle-derived gold-bearing fluids involved in meteoric water and wall rocks. This research provides an important clue for the ore genesis of the Donggualin gold deposit and gold deposits in the Ailaoshan gold belt.