Ore-forming Fluid Evolution And Metallogenic Mechanism Of The Lamasu Large Copper Deposit In The West Tianshan

The Lamasu deposit is the first large skarn copper deposit in the West Tianshan.The exposed strata in the Lamasu deposit was mainly the Mesoproterozoic Kusongmuqieke Group.The copper ore bodies are controlled by intermediate acid intrusive rocks,carbonate rocks strata and fault system.Fluid inclusions studies show that three types of fluid inclusions are present,i.e.,liquid-rich two-phase,gas-rich two-phase and daughter mineral-bearing multiphase fluid inclusions in the Lamasu deposit.The homogenization temperatures of fluid inclusions in the garnet of the skarn stage vary from 290°C to 470°C,and their salinities vary from 5.4%to 22.4%NaCl eqv.For the early quartz-sulfide stage,the homogenization temperatures of fluid inclusions in the quartz range from 230°C to 350°C,and the salinities range from 4.2%to 17.9%NaCl eqv.For the late quartz-sulfide stage,the homogenization temperatures of fluid inclusions in the quartz range from 130°C to 230°C,and their salinities range from1.2%to 12.7%NaCl eqv.The?³⁴S values of metal sulfides are mainly between 5‰and 8‰,which is similar with the?³⁴S values of ore-forming granodiorite porphyry in the mining area,indicating that the sulfur source from deep magma fluid.The?¹⁸O_V-SMOW of quartz ranges from 11.1‰to 15.2‰,and the?¹⁸O_H2O of quartz ranges from4.2‰to 8.3‰.?D of quartz ranges from-97.3‰to-86.1‰.The?¹⁸O_V-SMOW of garnet ranges from 6.9‰to 7.5‰,?¹⁸O_H2O of garnet ranges from 3.9‰to 4.5‰,?D of garnet ranges from-110.3‰to-99‰,indicating ore-forming fluids are dominated by magma water,and later mixed with some atmospheric water.Ore-forming fluid immiscibility was critical for the formation of the Lamasu deposit.