西秦岭铀矿床铀迁移形式的热力学研究

THERMODYNAMIC STUDY OF URANIUM MIGRATION FORMS IN THE WEST QINLING URANIUM FIELD

利用热力学方法计算了西秦岭铀矿床含矿热液中铀的迁移形式。结果表明，从含矿热液早阶段到主成矿作用发生之前，热液中的铀主要以［ＵＯ２（ＣＯ３）０］形式迁移；在晚阶段残余热液中，铀的迁移形式改变为以［ＵＯ２（ＳＯ４）０］为主。铀迁移形式改变的原因与大气降水中ＳＯ２－４离子的大量带入有关。

This paper has analysed constituents of fluid inclusions in quartz and calcite formed at different stages of uranium bearing hydrothermal solution in the West Qinling uranium field and,using thermodynamic method, calculated migration forms of uranium in uranium bearing hydrothermal solution. The results show that at the early ore forming stage, the uranium bearing hydrothermal solution mainly contains K +, Na +, Ca 2+ , Mg 2+ , Cl -, CH 4, CO 2- 3 and CO 2, and is deficient in SO 2- 4, and at the middle and late ore forming stages, with the elevation of the emplacement of uranium bearing hydrothermal solution and the variation of the environment, K + and Cl - tend to decrease, Na + somewhat increases, and Ca 2+ , Mg 2+ , CH 4, CO 2- 3, CO 2 and SO 2- 4 obviously increase. The mixing of the groundwater with the uranium bearing hydrothermal solution, as evidenced by the fact that the groundwater at the oxidation reduction interface is of SO 2- 4 HCO - 3 Ca 2+ and Mg 2+ types, and the water body is rich in Ca 2+ , Mg 2+ and SO 2- 4 ions. Thermodynamic calculation of uranium migration forms in uranium bearing hydrothermal solution demonstrates that at the early and middle ore forming stages uranium in the uranium bearing hydrothermal solution migrates mainly in the form of UO 2(CO 3) 0 ,whereas in the residual hydrothermal solution of the late stage, the migration form of UO 2(SO 4) 0 becomes dominant. It is therefore inferred that the change of uranium migration forms might be attributed to the entry of large quantities of SO 2+ 4 ions derived from meteoric water, and that the uranium bearing hydrothermal solution is derived from the depth instead of from meteoric water.