Abstract:

 Based on the microthermometry and thermodynamic parameters of fluid inclusions in the Shuiyingdong Au deposit, we have studied the thermodynamic conditions of the immiscibility of the oreforming fluids. The results show that the fluid inclusions in quartz are divided into three categories: H2O inclusions, CO2 inclusions and CO2H2O inclusions. The CO2H2O inclusions can be further classified into H2Orich CO2H2O inclusions and CO2rich CO2H2O inclusions. When heated, the homogeneous phase state of H2Orich CO2H2O inclusions was the H2O phase, while that of CO2rich CO2H2O inclusions was the CO2 phase. Moreover, they have the same homogeneous temperature and pressure. This suggests that they were CO2 and lowsalt water immiscible fluid inclusions having been trapped in the same period. The thermodynamic conditions of their formation are the formation temperature of 236  ℃, pressure of 324 bar, lowsalt water phase density 0900 g/cm3, CO2 phase density 0314 g/cm3, the CO2 mole fraction of 00376 in lowsalt water phase and 07337 in CO2 phase, and aqueous solution salinity w(NaCl)≈13％.

Key words: Shuiyindong gold deposit, oreforming fluid, fluid inclusion, immiscible fluid