Ore-forming fluids in gold-telluride deposits in the Pingyi area, western Shandong, China

Abstract

The Au-telluride district of the Pingyi area, western Shandong, mainly comprises the Guilaizhuang and Lifanggou gold deposits. The former is hosted in cryptoexplosive breccia of the Tongshi complex with a zircon SHRIMP U-Pb weighted mean age of 175.7±3.8 Ma. The latter occurs in dolomitic limestone, micrite and dolomite of the Early Cambrian Zhushadong Formation. Fluid inclusion studies indicate that the inclusions of both Au telluride deposits are both of vapor-liquid two-phase NaCl-H2O type. Homogenization temperatures of the fluid inclusions vary from 103 to 250°C, and the ice melting temperatures range from −2.5 to −13.5 °C, corresponding to a salinity range of 4.65 to 17.26 wt.% NaCl equiv. The δ34S values of pyrite associated with gold mineralization exhibit a narrow range of −0.71 to 2.99‰, implying that the sulfur was probably derived from the mantle or magma. The δ18OSMOW values of vein quartz and calcite range from 11.5 to 21.5‰, corresponding to the δ18Ofluid values of −1.13 to 10.9‰, and the δD values of the fluid inclusions between −70 and −48‰. The isotope data suggest that the ore-forming fluids of the two gold deposits were derived from the mantle, and mixed with meteoric water at shallow levels. Pressure release and boiling of the fluids played an important role in the ore-forming processes of the two deposits.