Characteristics of Fluid Inclusions in the Super-Large Wollastonite Deposit in Shizhushan, Western Jiangxi Province

The Shizhushan super-large wollastonite deposit, situated in the western segment of the Pingle Depression within the Qin–Hang metallogenic belt, represents the largest known wollastonite deposit in the world. The deposit formed mainly through contact metamorphism, followed by contact metasomatism. The ore bodies are hosted in the carbonate rocks of the Middle Permian Maokou Formation. The deposit consists of 12 ore bodies, which are controlled by the strata and occur as layered and lenticular bodies. The mineralization process is divided into an early contact metamorphism period (wollastonite–calcite and wollastonite–calcite–quartz stages) and later hydrothermal metasomatism period (wollastonite–garnet stage). This study examined the fluid inclusions in the contact metamorphic wollastonite ore bodies in this deposit. The results show that the types of inclusions are mainly liquid-rich two-phase inclusions, pure liquid-phase inclusions, and pure vapor-phase inclusions, with a small number of CO2-H2O three-phase inclusions. The homogenization temperature ranges of the different stages are 409.50~260.10 °C for the wollastonite–calcite stage and 283.60~132.40 °C for the wollastonite–calcite–quartz stage. The temperature and salinity of ore-forming fluids show an evolution from medium–high temperature and medium–low salinity to low temperature and low salinity. The minimum ore-forming depth of the deposit is 0.79~4.74 km, indicating a shallow, low-pressure environment. Based on the macrogeological characteristics, the tectonic fractures formed during the contact metamorphic period triggered decompression boiling of the ore-forming fluids, which led to the precipitation of mineralization materials and the subsequent mineralization. Based on a comprehensive analysis of the metallogenic geological setting, material sources, metallogenic process, and structural control factors, a trinity metallogenic model of the “carbonate rock + pluton + semi-open structural system” is established for the Shizhushan wollastonite deposit.