Fluid Evolution Characteristics And Metallogenic Age Of Weiquan Silver Deposit,Eastern Tianshan Mountain

As the only large Ag deposit in Jueluotage polymetallic metallogenic belt in Eastern Tianshan,Weiquan silver deposit is characterized by complex mineralization.Previous work had done some preliminary discussions on geological characteristics,the lastest ore-forming age and prospecting direction.However,the research status of minerals symbiotic composition and relationship,ore-fluid temperature and evolution,mineralization stages and periods,and Ag occurrence is still poor.Based on our study,according to analysis of mineral electronic probe and energy spectrum,fluid inclusion thermometry,stable isotope tracing,zircon U-Pb dating,we reconstruct the fluid evolution characteristics and metallogenic epoch.By researching of energy spectrum,the occurrence of native bismuth was first observed in Weiquan silver deposit,which is texturally and temporally associated with Ag-Bi alloy and matildite.It is worth mentioning that the matildite in different characterastics perhaps formed in two generations with N_Ag:N_Bi=1:1 or N_Ag:N_Bi=3:1,respectively.The fluid inclusions in ore calcite veins,belonging to sample H₂O-NaCl system,develops two phases inclusions and is characterized bymedium-low homogenization temperature?240²00??,medium-low salinity?0.35%²3.18%NaCleqv?and medium-low density?0.690g/cm³¹.100g/cm³?.What's more,the salinity and density gradually increases with the decrease of temperature.Mineralization mainly occurs in hydrothermal period,which canbe divided into quartz-oxide stage????quartz-arsenopyrite-pyrite-magnetite is the major mineral assemblages,the fluid has a temperature section of 376²89??;Bi-bearing mineral and carbonate stage????native bismuth-matildite-calcite assemblages formed,the fluid islimited by the highest temperature of 271??;Ag-bearing mineral and sulfide stage????calcite-native silver-calcite-chalcopyrite-galena-sphalerite,hold the temperature from240?to 200??.The fluid has experienced the process,from high-sulfide,through low-sulfur,high-sulfide again,to finally low-sulfur.In order to investigate the source of ore-forming fluids,C-H-O isotope analysis results in calcite are performed as:?¹³C_V-PDB=-2.5⁺2.3‰,?D_V-SMOW=-115.6^-78.0‰and?¹⁸O_H2O=+4.0⁺8.1‰,which suggest that the ore-forming fluid are mainly derived from residual magma water and little meteoric water participate in during fluid evolution.Moreover,analysis result of sulfide(?^#S_V-CDT=-6.9⁺1.4‰)show that the ore-forming materials are mainly derived from magma which is a mixture of crust and mantle,with little sediment mixed.After accurate chronological analysis by zircon LA-ICP-MS U-Pb method,we focus the age of tuff and diorite-porphyrite on 326.5±4.5Ma?MSWD=0.87?and298.5±1.5Ma?MSWD=0.14?,which point the metallogenetic epoch mainly between326.5²98.5Ma,Late Carboniferous.