Ore-Fluid Evolution of the Sizhuang Orogenic Gold Deposit, Jiaodong Peninsula, China

The Sizhuang gold deposit with a proven gold resource of >120 t, located in northwest Jiaodong Peninsula in China, lies in the southern part of the Jiaojia gold belt. Gold mineralization can be divided into altered rock type, auriferous quartz vein type, and sulfide-quartz veinlet in K-feldspar altered granite. According to mineral paragenesis and mineral crosscutting relationships, three stages of metal mineralization can be identified: early stage, main stage, and late stage. Gold mainly occurs in the main stage. The petrography and microthermometry of fluid inclusion shows three types of inclusions (type 1 H2O–CO2 inclusions, type 2 aqueous inclusions, and type 3 CO2 inclusions). Early stage quartz-hosted inclusions have a trapped temperatures range 303–390 °C. The gold-rich main stage contains a fluid-inclusion cluster with both type 1 and 2 inclusions (trapped between 279 and 298 °C), and a wide range of homogenization temperatures of CO2 occurs to the vapor phase (17.6 to 30.5 °C). The late stage calcite only contains type 1 inclusions with homogenization temperatures between 195 and 289 °C. With evidences from the H–O isotope data and the study of water–rock interaction, the metamorphic water of the Jiaodong Group is considered to be the dominating source for the ore-forming fluid. The ore-fluid belonged to a CO2–H2O–NaCl system with medium-low temperature (160–360 °C), medium-low salinity (3.00–11.83 wt% NaCl eq.), and low density (1.51–1.02 g/cm3). Fluid immiscibility caused by pressure fluctuation is the key mechanism in inducing gold mineralization in the Sizhuang gold deposit.