Fluid and ore-material source of the Xiajiaxiaohe gold deposit in central Yishu fault zone in Shandong, Eastern China

The Xiajiaxiaohe gold deposit is located in the middle section of the central Yishu fault zone in Shandong Province (Eastern China). Previous studies mainly focused on the relations between the fault zone and gold mineralization; yet, its mineralization process was rarely studied, which hinders further exploration and deposit model development. In this study, we analyzed the trace elements and He-Ar isotopes of the auriferous pyrite and determined the source(s) and nature of ore-forming fluids and materials. Rare earth element (REE) compositions of the pyrite indicate that the ore-forming materials at Xiajiaxiaohe were sourced from the Yishui Group wallrocks. The Co-Ni contents and Co/Ni ratios show that the Xiajiaxiaohe gold mineralization was formed under medium- to low-temperature conditions. Fluid inclusions in pyrite have 3He/4He (0.14–0.20 Ra) and 40Ar/36Ar (1038–1290) ratios reflecting a crust source for the ore-forming fluids. The fluids may have then undergone varying degree of interactions with a deep-mantle source, plus minor meteoric input during the Mesozoic Pacific subduction beneath the Eurasian plate.