论东胜矿床油气逸散蚀变的地质地球化学特点及其意义

Geological and geochemical characteristics of escaped hydrocarbon epigenetic alteration in the Dongsheng mineral deposit and its significance

鄂尔多斯盆地东胜砂岩型铀矿的显著特点,首先是矿床存在明显的绿色蚀变控矿带以及漂白现象,其次是含矿层较广泛地分布有不连续透镜状碳酸盐化钙质胶结砂岩。经粘土矿物X射线衍射分析、扫描电镜鉴定、包裹体化学成分等项测试,认为绿色蚀变和漂白现象是在大范围还原性环境下形成的,而其中的还原性流体主要与油气逸散作用有关;经对含矿层罐顶气和碳酸盐碳同位素以及部分有机地球化学参数分析后认为,上述蚀变现象主要与上古生界来源的含CH4、H2S、CO、CO2等成分的煤成气向北东方向的逸散蚀变作用有关。故可认为,顺油气逸散方向的盆地边缘且位于绿色蚀变带前锋线的区域是铀矿成矿及找矿的有利地区。

This paper presents the following distinctive characteristics of the Dengsheng sandstone-type uranium deposit in the Ordos basin： （1） there exist a pronounced ore-controlling green alteration zone and the bleaching phenomenon in the deposit; and （2） discontinuous, lenticular, carbonated, calcareous-cemented sandstone is widespread in the ore horizon. X-ray diffraction analysis, SEM identification and analysis of the inclusion chemical composition of clay minerals indicate that the green alteration and bleaching phenomenon formed in an extensive reducing environment, and that the reducing fluids are mainly related to hydrocarbon escape. Carbon isotope analysis of fill-up gas and carbonates and analysis of part of organic geochemical parameters in the ore horizon indicate that the above-mentioned alteration is mainly related to NE-directed escaped hydrocarbon alteration of coal gases containing components such as CH4, H2S, CO and CO2. So, it can be thought that the basin margins in the direction of hydrocarbon escape and front of the green alteration zone are favorable areas for uranium mineralization and ore finding.