Mineralogical, fluid inclusion, and stable isotopic study of the Shangshan'gang Au deposit, southeast China: Implications for ore formation and exploration

The Shangshan'gang Au deposit is located in the Cretaceous Dongkeng volcanic basin of northern Fujian Province in southeast China. The deposit is hosted by altered intermediate to silicic volcanic rocks along NE–SW- and ENE–WSW-trending faults. The main types of wall-rock alteration are silicification, sericitization, argillization, and chloritization. Ore mineralization occurred in three stages, which were the base metal, AuAg, and post-ore stages. Electrum and kustelite are the main AuAg minerals. Laser ablation–inductively coupled plasma–mass spectrometry analyses revealed different compositions for the two stages of pyrite, galena, and sphalerite, which reflect changing mineralization conditions. Fluid inclusions revealed an epithermal mineralization environment with low–moderate temperature and salinity. Mixing of ore fluids is the main ore-forming mechanisms which occurred from the early to late stages, as evidenced by the H and O isotopic compositions of the ore-forming fluids. The proportion of meteoric fluid in the ore-forming hydrothermal fluid gradually increased with time. Fluid boiling may have locally occurred in the early stage and promoted ore precipitation. Our results show that the Shangshan'gang Au deposit is an intermediate-sulfidation-type epithermal deposit that gradually changed to a low-sulfidation-type during late mineralization. Given the close temporal and spatial relationship between intermediate-sulfidation-type and porphyry deposits, there is potential for porphyry deposits to exist in the Zhenghe–Jian'ou area.