江西科学

相山铀矿田是我国最大的火山岩型铀矿田,碎斑熔岩是其主要赋矿岩性之一。绿泥石化作为关键蚀变类型,对铀成矿过程具有重要指示意义。通过岩相学观察及电子探针分析,系统研究了碎斑熔岩3个亚相带中绿泥石的化学组成、形成温度及氧逸度特征。结果表明:1)绿泥石富Fe O(31.36%～37.40%)、低Mg O(4.90%～9.22%),Al2O3含量由边缘(18.38 wt.%)向中心亚相(15.53 wt.%)递减,指示还原环境; 2)绿泥石以蠕绿泥石和铁镁绿泥石为主; 3)母岩为泥质岩及铁镁质岩,可能与外来角砾有关;4)边缘至中心亚相绿泥石形成温度(323℃→236℃)及氧逸度(-43.09→-44.61)逐渐降低,反映热液活动减弱。研究成果揭示了热液蚀变的空间分带性,为铀成矿过程的热液演化提供了地球化学证据。

The Xiangshan uranium field, the largest volcanic-hosted uranium deposit in China, has brecciated lava as one of its principal ore-hosting lithologies. Chloritization, identified as a critical alteration type, is considered to hold indicative significance for uranium mineralization processes. In this study, the chemical composition, formation temperatures, and oxygen fugacity characteristics of chlorite within three subfacies zones of the brecciated lava were systematically investigated through petrographic observations and electron probe microanalysis. The key results are summarized as follows:1)Chlorite was characterized by Fe O enrichment(31.36%～37.40%) and Mg O depletion(4.90%～9.22%). Decreasing Al_2O₃ contents from the marginal subfacies(18.38 wt.%) to the central subfacies(15.53 wt.%) were interpreted as indicating reducing conditions; 2)The chlorite was mainly chamosite and ferro-magnesian chlorite;3)Parent rocks were inferred to be argillaceous and mafic materials, possibly related to exotic breccias;4)A progressive decline in chlorite formation temperatures(323 ℃→236 ℃) and oxygen fugacity(-43.09→-44.61) from the marginal to the central subfacies was observed, reflecting waning hydrothermal activity. This research elucidates the spatial zonation of hydrothermal alteration and provides geochemical constraints on the hydrothermal evolution during uranium mineralization.