内蒙古林西水头萤石矿床成矿流体特征及成矿过程

Characteristics of ore-forming fluids and mineralization processes of the Shuitou fluorite deposit in Linxi,Inner Mongolia Autonomous Region

内蒙古林西县水头大型萤石矿床位于索伦—林西缝合带北侧,产于二叠系火山-沉积岩中,矿体主要受NNE向断裂破碎带控制。文中从流体包裹体和H-O-S同位素研究出发,讨论了该矿床成矿流体的特征、演化与成矿过程。萤石中主要发育液相H2O包裹体,包裹体均一温度集中在140~220℃,盐度变化于0.4%~2.8%NaCleqv,密度平均为0.87g/cm3。包裹体成分以H2O为主,其次为CO2、H2,含有CH4、C2H6和C3H6等有机组分。成矿流体属中低温、低盐度、中低密度的NaCl-H2O体系。成矿流体的δDH2O-SMOW值为-140.1‰^-120.5‰,δ18 OH2O-SMOW值为-6.7‰~2.3‰,主体属大气降水热液;矿石中黄铁矿的δ34S值为1.2‰~3‰,指示硫的来源可能与岩浆活动有间接联系。综上推断,成矿热液主要来源于被加热的大气降水和地下水,水-岩反应很可能是萤石沉淀的主要机制,矿床属断裂控矿、中低温热液裂隙充填型萤石矿床。

The Shuitou large fluorite deposit is tectonically located at the north side of Solonker-Linxi suture zone in Inner Mongolia. The Linxi Shuitou deposit occurred in the Permian volcanic-sedimentary strata. Ore bodies are mainly controlled by NNE-trending faults and fracture zone. Based on the study of fluid inclusions and H-O-S stable isotopes, this paper focuses on the characteristics and evolution of the ore-forming fluids and the mineralization process. Fluid inclusions in the fluorite are mostly mono-phase H2O liquid fluid inclusions with a homogenization temperature of 140 - 220 ℃, a salinity approximately of 0.4 - 2.8 wt% NaCleqv, and a density of 0.87 g/cm3. Compositions of the fluid inclusions are dominantly H20 with subordinately CO2, H2 and some organic components （such as CH4, C2 H6, Ca H6 ）. Ore-forming fluids are characterized by medium- low temperature, low salinity and medium-low density. The δDH2O-SMOW values of the ore-forming fluids ranges from -120.5%ο to -140. 1%0 while δ18 OH2O-smow values range from -6. 7%0 to 2. 3%0, suggesting that ore- forming fluids were mainly derived from meteoric water. δ34 Sv-cDT values of pyrite range from 1.2%0 to 3%0, indicating a source related with magmatic activation. Water/rock reaction is suggested to be the main mechanism for fluorite precipitation in this deposit. Hence, it can be inferred that the Shuitou fluorite deposit is a fault-control, medium-low-temperature hydrothermal, fracture-filling type deposit.