相山铀矿田成矿作用的地球化学模拟

GEOCHEMICAL MODELING OF MINERALIZATION PROCESSES FOR XIANGSHAN URANIUM ORE-FIELD

相山铀矿田是我国最大的火山岩型热液铀矿田，在地质地球化学和高温高压实验研究的基础上，利用地球化学模式程序EQ3／6模拟了成矿热水溶液的形成过程和减压排泄区铀成矿作用。计算机模拟结果表明，通过大气除水与碎斑熔岩相互作用，可以形成富含F和SiO2等矿化剂的含铀热水溶液；由于铀以UO2F3和UO2(CO3)等配合物形式存在，非常稳定，即使在深部强还原环境中仍然能够迁移；酸性和碱性环境，尤其是强酸性介质有利于铀迁移；随着CO和F-含量的增高以及温度的提高，铀的迁移性能增强；在水热系统排泄区发生的降温、减压脱气（脱碳酸）和混合作用等造成铀沉淀富集，形成沥青铀矿、方柱石、萤石、方解石和赤铁矿组合，与相山矿田萤石-水云母型铀矿化特征相一致。地球化学模式程序不仅能够按天然条件模拟地球化学作用，而且还能阐明地球化学作用的反应途径和反应动力学问题，是研究铀成矿古水热系统中地球化学作用的有力手段。

Xiangshan uranium ore-field is the largest volcanic rock type hydrothermal uranium deposit in China. Based on the study of geology, geochewistry and experiments athigh pressures and temperatures, the authors have modeled the formation of ore-forminghydrothermal solution and the mineraization in discharge zones of Xiangshan fossilhydrothermal system using EQ3 / 6. The modeling shows tha F and CO2-richeduranium-bearing hydrothermal fluids could be generated by means of the intefactionbetween local meteoric water and porphyro-clastic lava, UO2F3, UO2(CO3)2 andother uranium complexes could be very stable even in strong reducing enviommenturanium tending to be more mobile with the increase of F CO2 and temperature, indischarge zones of hydrothermal systems, uranium could be precipitated by temperaturedropping, degassing and mixing, forming the mineara assemblage of uraninite,thorianite, fluorite, calcite and hematite, which is in accordance with thefluorite-hydromica type of Uranium deposit. Therefore, geochemical medeling codes areeffective meassures to approch the geochemical processes in hydrothermal system,which can be used not only for modeling of geochemical processes under naturaconditions, but also for exploring the reaction path and dynamics of geochemicalprocesses.