广西373铀矿床微量元素地球化学特征及其成因探讨

The Trace Element Geochemical Characteristics and Genesis Analysis of the 373 Uranium Deposits in Guangxi

373铀矿床是我国南方典型碳硅泥岩型铀矿床之一,主要发育一套黑色弱硅化泥岩、粉砂岩,硅化生屑灰岩及其过渡型岩类地层,矿床明显受断裂发育影响,铀矿化于次级断裂带中。通过系统地球化学研究表明:3组不同期次脉体普遍亏损过渡元素Ti、Sc、Cr、Cu、Zn和高场强元素Nb、Ta、Zr和Hf;相对较富集Mn、Ni、As、Sr、Mo、Sb、Tl和U等微量元素。后期热液活动使脉体Ba、Sb、As和Mo等元素异常富集。后期热液叠加改造,使得岩石普遍亏损过渡元素Sc、Ti、Cr和高场强元素Nb、Ta、Zr、Hf,普遍富集Co、Ni、Zn、As、Sb、Mo、Cd、W、Tl、Pb、Bi和U,其中As、Sb、Mo、Tl和U尤为富集,富集系数平均达到100左右,U与W、As、Sb和Pb相关系数都在0.9左右,具有高度同源性,铀成矿与热液活动有关。典型剖面微量元素富集与硅化密切相关,当硅化达到一定程度后微量元素富集出现反转,即随着硅化强度增加而富集能力反而降低。V/Cr、V/Sc、Ni/Co、V/(V+Ni)、U/Th、δU、δEu和δCe等特征元素比值反应铀预富集形成于缺氧的古海洋环境。高丰度的As、Sb和Ba等元素,以及U-Th关系图解和Zn-Ni-Co三元图解均显示热水沉积成因。微量元素特征表明碳硅泥岩形成于缺氧的还原环境,铀预富集与热水沉积有关,铀成矿与热液叠加改造有关,后期热液沿运移通道上升进入储集空间,与铀预富集地层热液叠加成矿。

The 373 uranium deposits, as a typical carbonanceous-siliceous-pelitic rock type uranium deposits in South of China which has developed in a sequence including the weakly silicified black mudstone, silicified bioclastic limestone and the gradational rocks between them. The 373 uranium deposits is characterized with faults at which the uranium was mineralized widespread. Based on the geochemistry studies, it suggest that, （a） three episode veins has a distinct feature in trace element of geochemistry, with deficient of Ti, Sc, Cr, Cu, Zn elements and of Nb, Ta, Zr, Hf element, while it relatively enriched As, Sb, Mo, T1 and U elements. Furthermore, there are distinct features o{ hydrotherm effects in the deposits, the enriched Ba, Sb, As and Mo etc. elements are related with hydrotherm intrusion in three episode veins, （b） the enriched Co, Ni, Zn, As, Sb, Mo, Cd, W, T1, Pb, Bi and U elements, in particular As, Sb, Mo, T1 and U elements, are with enrichment coefficients of ～100, and the correlation coefficient between the U element relative to W, As, Sb and Pb elements is ～0.9. All indicate relative homology of uranium mineralization, related to hydrothermal activity. （c）There is a positive relationship between concentration of trace elements and silicifieation in strata in our typical profiles. However, after the maximum of concentration of trace elements, the relationship becomes to be negative. （d）It is indicted that the uranium mineralization was deposited under an anoxic and deoxidated setting by the ratios of V/Cr, V/Sc, Ni/Co, V/（V-FNi）, U/Th, ￡U, ￡Eu and ￡Ce, with much hydrothermal influence by the diagram of U-Th and graphic of Zn-Ni-Co, respectively. （e） characterization of trace element and characteristic element ratio reflect that carbonanceous-siliceous-pelitic rock formed in anoxic reducing environment which joined into hydrothermal fluid, Pre-enrichment of Uranium was related to the hydrothermal sediments, and Uranium mineralized was related to hydrothermal superimposed. Upward later hydrothermal fluid into reservoir bed through migrated channel,which react with Pre-enriched uranium bed and superimposed mineralization.