内蒙古额尔古纳地区431铀矿床地质特征与流体包裹体研究

GEOLOGIC FEATURES AND FLUID INCLUSIONS OF NO.431 URANIUM DEPOSIT IN ERGUNA AREA,INNER MONGOLIA

为确定额尔古纳地区铀矿特征及成因类型,选择431铀矿床,在矿床地质特征研究基础上,对与铀矿化成因关系密切的硅化石英脉进行了流体包裹体显微测温.研究结果表明,431矿床产于印支期花岗岩与新元古代额尔古纳群变质岩接触带部位,受断裂构造控制明显,围岩普遍发育硅化、绿泥石化、水云母化、高岭土化、碳酸盐化等蚀变现象,地表矿石中铀矿物主要为钙铀云母.硅化石英脉中含气液两相和含CO2三相两种类型包裹体,对应的均一温度分别为132.2～301.5℃和322.5～408.9℃,平均值为247℃;盐度分别为12.65%～2.73%和4.04%～16.94%,平均值为8.18%;流体密度分别为0.76～0.94 g/cm3和0.60～0.78g/cm3;成矿流体属中温、中低盐度、低密度的NaCl-H2O-CO2流体体系.利用相关公式估算该区铀矿的成矿深度介于0.4～1.7km.431铀矿床属浅成中温热液矿床,成因上与花岗质岩浆作用有关.

To recognize the metallogenic features and genetic type of the uranium deposits in Erguna area, No. 431 uranium deposit is adopted for case study. Based on geological features of the deposit, microthermometry of fluid inclusions is researched for silicified quartz veins closely related to the genesis of uranium mineralization. The results show that the deposit occurs in the contact zone between the Indosinian granite and the Neoproterozoic Ergun metamorphic rocks, obviously controlled by faults. The wallrocks of ore bodies are generally developed with such alterations as silicification, chloritization, kaolinization and carbonation. The uranium mineral is dominantly autunite in the surface. Comparison studies of this deposit with some typical granitic uranium deposits indicate that No. 431 deposit is associated with granitic magmatism. The silicified quartz veins contain two types of inclusions, i.e. gas-liquid two-phase and CO2-bearing three-phase inclusions, corresponding to homogenization temperatures of 132.2 - 301.5℃ and 322.5 - 408.9℃, salinities （NaC1） of 12.65% - 2.73% and 4.04% - 16.94%, and fluid densities of 0.76 - 0.94 g/cm3 and 0.60 - 0.78g/cm^3. It is concluded that the uranium ore-forming fluid belongs to a NaC1-H20-CO2 fluid system with medium temperature, mid-low salinity and low density. The mineralization depth of the uranium deposits in this area estimated by related formulas ranges from 0.4 to 1.7 km, which suggests a mesothermal deposit.