FLUID INCLUSION, ZIRCON U-Pb AGE AND GENESIS OF THE KAIFENGGOU GOLD DEPOSIT IN LIAONING PROVINCE

The quartz vein type of Kaifenggou gold deposit in Liaoning Province is situated in the Qingyuan granitegreenstone terrain of North China Craton. The NEE-trending Hunhe fault and its secondary faults in the area are the main ore-controlling structures. The fluid inclusions in quartz crystals can be classified into gas-liquid two-phase, CO₂-bearing three-phase and pure CO₂ types. The bubbles (gas-phase) are dominated by CO₂. The salinities range from 0.35% to 19.55%(NaCl), with an average of 6.55%. The homogenization temperatures range from 110℃ to 390℃, averagely 247℃, suggesting a mesothermal deposit. The ore-forming pressures of the deposit range from 26 to 91 MPa, with an average of 61 MPa, corresponding to depths of 2.7 to 8.2 km, averagely 5.7 km. In the early mineralization stage, the fluid inclusions are characterized by low salinity, high-temperature and rich CO₂. In the major mineralizing stage, the CO₂-rich fluid inclusions and gas-liquid two-phase inclusions coexist. Because of the immiscibility or boiling characterized by CO₂ escaping, the salinity increases in the residual fluid. Fluid inclusions in the later mineralization stage are of gas-liquid two-phase. The stable isotope analyzing results show that the metallogenic fluid is originated from the magmatic hydrotherm after the differentiation of mantle-derived C-H-O fluid. The granite porphyry closely related to mineralization has a zircon U-Pb age of 200.1±1.5 Ma, with seven zircon concordia age of 200.2±0.84 Ma, showing that the deposit was formed in early Yanshanian period. Comprehensive studies suggest that the Kaifenggou gold deposit belongs to orogenic type.