内蒙古林西地区小北沟萤石矿床成矿流体特征及矿床成因探讨

Characteristics of ore-forming fluids and genesis of Xiaobeigou fluorite deposit in Linxi area,Inner Mongolia

小北沟萤石矿床矿体赋存于中生代中酸性火山-沉积岩中,主要受近SN向、NNE向断裂破碎带控制。流体包裹体显微测温和激光拉曼分析结果表明:各成矿阶段主要发育气液两相H_2O包裹体,包裹体均一温度集中分布在160~200℃,盐度(w(NaCl_(eqv)))集中分布在0.2%~1.4%,流体密度0.77~0.93 g/cm^3;包裹体成分以H_2O为主,含少量C_3H_6等有机组分,成矿流体属于中-低温、低盐度、低密度NaCl-H_2O流体体系。野外地质特征及显微测温结果均表明,流体弱沸腾导致早阶段石英沉淀,水/岩反应是萤石的主要沉淀机制。小北沟萤石矿属于中低温热液充填型脉状矿床,成矿流体主要来源于被加热的大气降水和地层水。

The Xiaobeigou fluorite deposit is a newly discovered hydrothermal deposit in Linxi area,Inner Mongolia. The ore bodies are hosted in the Mesozoic intermediate-acid volcanic-sedimentary rocks and are mainly controlled by the nearby SN and NNE trending faults. The results of microthermometry and laser Raman analysis of fluid inclusions show that the fluid inclusions in different stages of mineralization are predominantly gas-liquid two-phase H2O fluid inclusions with a homogenization temperature of 160-200 ℃,a salinity of 0. 2%^-1. 4%NaCl（eqv）,and a density of 0. 77-0. 93 g/cm^3. The compositions of fluid inclusions are predominantly H2O and minor organic components,such as C3H6. The ore-forming fluid belongs to NaCl-H2O fluid system,which is characterized by medium-low temperature,low salinity and low density. The geological features and microthermometry results suggest that the quartz precipitation is due to the weak fluid boiling process. The water/rock reaction is one of the potential causes for the precipitation of fluorite. Hence,it can be inferred that the ore-forming fluid was mainly sourced from meteoric water and formation water,and the Xiaobeigou fluorite deposit is considered to be a medium to low-temperature hydrothermal,vein-type deposit.