The Sources of Ore-forming Fluids from the Jinchang Gold Deposit, Heilongjiang Province, NE China: Constraints from the He-Ar Isotopic Evidence

The Jinchang gold deposit (more than 40 tons of gold) is located in the easternmost portion of the Central Asian Orogenic Belt. The gold mineralization types include mainly breccia, quartz vein and alteration rock types. Geological and geochemical characteristics suggest that the Jinchang gold deposit formed by the superposition of epithermal gold deposits and porphyry gold deposits. In this study, the helium and argon isotopic compositions of fluid inclusions in pyrites from the different ores are analyzed. The results show that He-3/He-4 ratios of fluid inclusions in pyrites range from 0.13 to 2.42 Ra, Ar-40/Ar-36 ratios are within 308.9-336.7, indicating that the ore-forming fluids of the Jinchang gold deposit were a mixture of crustal-derived fluids and partial mantle-derived fluids, and were contaminated by circum-flow meteoric water. From the early to the late mineralization stages, Jinchang gold deposit had a fluid evolution trend from more mantle fluid in the central area to crustal fluid in the outer area. Jinchang gold deposit is the result of superimposition of mineralization of magmatic fluids at different phases and nature.