Ore-forming Fluids Characteristics And The Separation Mechanism Of Molybdenum And Copper Of Relin Molybdenum-copper Deposit,Western Yunnan,China

Relin Mo-Cu deposit is a big porphyry deposit explored in recent years in the southern part of Yidun terrain.Taking the typical phenomenon “copper upside and molybdenum underside” of this deposit as the starting point,this paper differentiates the ore-forming stages based on systematic geological and petrographic observation,and discusses the source and evolution of ore-forming fluids as well as the separation mechanism of Mo and Cu in virtue of fluid inclusions(FI)microthermometry,laser Raman testing,and H-O isotopic studies.Research findings are as follows.1.The ore body of Relin Mo-Cu deposit exists in the monzonitic granite porphyry,and it has four ore-forming stages which are silicate-oxide stage,quartz-molybdenite stage,quartz-chalcopyrite stage,and carbonatite stage.2.There are four types of FI in Relin Mo-Cu deposit,they are liquid-rich FI(VL),vapor-rich FI(LV),multiphase FI containing halite(SL),and multiphase FI containing CO2(LC).The FI in silicate-oxide stage are VL,LV and LC,and most of them are LV;both quartz-molybdenite stage and quartz-chalcopyrite stage has all four types of FI,but the latter has more LC in quantitative terms;carbonatite stage has VL and LV,mostly VL.3.The ore-forming fluids homogenization temperature of the ore-forming stages are 374.8~501.7°C,290.7~482.3°C(mainly 380~440°C),268.2~462.8°C(mainly 320~380°C),and 182.3~279.5°C,respectively.The temperature and salinity of the ore-forming stages declines and overlaps with adjacent stages,indicating the continuity of fluid evolution.4.The ore-forming fluids of silicate-oxide stage are derived from the primitive magmatic fluid;in quartz-molybdenite stage,the ore-forming fluids are mainly magmatic water,and they boiled in this stage;magmatic water mixed with atmospheric water and boiled in quartz-chalcopyrite stage;the ore-forming fluids in carbonatite stage is a mixture of magmatic water and atmospheric water.5.The ore-forming fluids of silicate-oxide stage are alkali-rich and relatively oxidizing and have high temperature;in quartz-molybdenite stage,the ore-forming fluids are relatively reducing and have medium-high temperature and high acidity;in quartz-chalcopyrite stage,the ore-forming fluids are relatively oxidizing and have medium-low temperature and low acidity.Temporal changes in redox conditions,acidity,and temperature of the ore-forming fluids resulted in the temporal separation of Mo and Cu by selective sulfide precipitation in Relin Mo-Cu deposit;the temperature of the ore-forming fluids,the competition among Mo and Cu for sulfur in magmatic fluids,and vapor-brine immiscibility(fluid boiling)are the key factors that contributed to the spatial separation of Mo and Cu in Relin Mo-Cu deposit.