Ore-forming Fluids Of The Xiangtanzi Gold Deposit, Liangdang, Gansu Province

The Xiangtanzi gold deposit is a intrusion-related gold deposit in the western Qinling belt,central China.Ore deposit geology and ore-forming fluids geochemistry studies have been carried out on this deposit in order to ascertain its fluid mineralization process.Based on veins cutting relation,ore texture and structure,and mineral assemblage,the mineralization process of the Xiangtanzi gold deposit is divided into the barren quartz?I?,quartz-pyrite?II?,quartz-polymetallic sulfide?III?,calcite-sphalerite?IV?,and carbonate stages?V?.Five types of fluid inclusions have been identified in the Xiangtanzi gold deposit,based on their characteristics at room temperature:three-phaseCO₂-rich,three-phaseCO₂-bearing,solid-bearing,liquid-rich,and vapor-rich types.The stage I contains mainly solid-bearing fluid inclusions;the fluid inclusions display homogenization temperatures of 370-390°C and salinities of 44-46wt%NaCl equiv..The stage II contains predominantly three-phase CO₂-bearing fluid inclusions,which yield homogenization temperatures of 350-370°C and salinities of 6-8wt%NaCl equiv..The stage III contains chiefly three-phase CO₂-rich fluid inclusions,which yield homogenization temperatures of270-290°C and salinities of8-10 wt%NaCl equiv..The stages IV and V contains primarily liquid-rich fluid inclusions,these fluid inclusions show homogenization temperatures of 210-230°C and 150-170°C,and salinities of 4-6wt%NaCl equiv.and2-4 wt%NaCl equiv.,respectively.Hydrogen and oxygen isotope data indicate that the ore-forming fluids were dominated by mainly magmatic water in the early stage,and that the magmatic water gradually mixed with circulating meteoric water during the late stages.Petrographic observation and microthermometry suggest that fluid mixing and fluid immiscibility occurred in the main metallogenic stages,which probably lead to gold deposition in the Xiangtanzi gold deposit.