Characteristics of fluid inclusions in barite, witherite and barytocalcite from the Shiti barium deposit in southern Shaanxi and their genetic significance

Abstract：The Shiti barite-witherite deposit of Shaanxi occurs in an early Paleozoic large Ba metallogenic belt of southern Qinling region. Barite, witherite, barite-witherite and barytocalcite constitute major ore types, with barite being the main ore. Microthermometry reveals that homogeneous temperatures and salinities of fluid inclusions in barite are from 103.4℃ to 253.1℃ (main peak values 140～160℃) and from 0.35 wt％NaCl eqv. to 10.73wt％NaCl eqv., homogeneous temperatures and salinities of fluid inclusions in witherite are from 152℃ to 303.7℃ (main peak values200～220℃) and from 0.18 wt％NaCl eqv. to 9.73wt％NaCl eqv., and homogeneous temperatures and salinities of fluid inclusions in barytocalicite are from 107.8℃ to 260.0℃ (main peak values 160～200℃) and from 0.71 wt％NaCl eqv to 8.41wt％NaCl eqv., respectively. Laser Raman analyses show that gas phase compositions of fluid inclusions in these minerals are somewhat different： barite contains some N2, H2S and CH4, witherite contains abundant CO2 and N2, and barytocalicite contains some CO2, N2 and CH4. The relatively high temperature and abundant CO2 in fluids constitute conditions for witherite formation.