Geochemical studies of the Nanxiaoyao gold deposit in central Yishu fault zone, Shandong province, Eastern China

Abstract

The Nanxiaoyao gold deposit is located in the middle part of the central Yishu fault zone in Shandong Province, Eastern China. In this study, we examined its genesis based on detailed in-situ LA-ICP-MS analyses of pyrite trace element contents, sulfide (pyrite and galena) sulfur isotopes, and fluid inclusion (FI) He–Ar isotopes of the ore-related pyrite. The Nanxiaoyao pyrite have ns/nFe (1.81–2.27), Au/Ag (0.0012–0.2416) and Fe/(S + As) (0.81–0.89), with the latter two ratios indicating that the gold mineralization occurred at medium-/deep-level and under medium–high temperatures. The Co–Ni and Co–Ni–As discrimination diagrams indicate that the mineralization was magmatic-related, the gold ores may have undergone post-ore alteration, and that the ore fluids were mainly (sub)volcanic-derived. The pyrite FI He–Ar isotope data indicate that the ore-forming fluids were mainly crustal-derived, and had mixed with some mantle-sourced fluids and minor meteoric water. Sulfur isotopic evidence of the Nanxiaoyao sulfides (δ34S = −3.2 to 2.9‰) further supports a deep-level (probably mantle) source for the ore-forming materials. Therefore, we suggest that the Mesozoic magma and (sub)volcanic-sourced hydrothermal fluids may have ascended along the Yishu fault zone, bringing the ore-forming materials to the Nanxiaoyao-Qiansuozhuang fault and formed the Nanxiaoyao gold deposit.