Characteristics Of Ore-forming Fluids And Its Evolution In The Wushan Copper Deposit,Jiangxi Province

Wushan copper deposit is one of the most important skam-type deposits along the Middle and Lower Yangtze River metallogenic belt.By a systematic study in the deposit of ore-forming fluids,the author analyzes the ore-forming fluid nature,source and evolution,explore its mineralization mechanism.Field investigation and petrographic observation indicate existence of two epochs of mineralizations,i.e.,pneumatolytic-hydrothermal and hydrothermal ones.The first includes early skarn,late skarn and magnetite stages,and the latter consists of quartz-sulphide and carbonate stages.As a main mineralization stage,the quartz-sulphide stage can be divided into three sub-stages,including quartz-molybdenite,quartz-pyrite-chalcopyrite and quartz-pyrite ones.Four types(LV,VL,SL and V)of fluid inclusions are observed in minerals of the deposit.Type(SL)consists of three-phase(vapor-liquid-solid)inclusions with daughter minerals,type(LV and VL)of two-phase(vapor-liquid)inclusions,and type(V)of one phase(vapor)inclusions.Fluid inclusions are rarely distributed in garnet formed during the pneumatolytic-hydrothermal epoch and include types(LV,VL,SL and V).In eontrast,fluid inclusions widely occur in quartz and calcite formed during the hydrothermal epoch and predominated by type(LV and VL).From the early skam stage to the carbonate stage,temperature and salinity of ore_forming fluids continuously decreased from 378.3?518.2?and 17.26?45.14%NaCleq to 112.6?249.9? and 3.39?11.93%NaCleq,respectively.Fluid boiling and mixing of magmatic hydrothermal fluid with meteoric water occurred during this evolution.The hydrothermal mixing in the early and late skarn stages was related to the formation of skarn.The hydrothermal boiling and mixing in the quartz-sulfide stage may be a significant mechanism for the formation of the copper deposit.Hydrogen and oxygen isotopic studies indicate that the ore-forming fluids during the formation of the deposit were predominated by magmatic water,with increasing of meteoric water in them from early to late.