东胜地区直罗组砂岩型铀矿包裹体特征与铀矿成因研究

Characteristics of fluid inclusions in sandstone-type uranium deposit and origin of uranium mineralization in Zhiluo Formation of Dongsheng area

鄂尔多斯盆地东胜地区直罗组含铀矿层位中流体包裹体均一温度和成分的测定及荧光分析表明,东胜地区至少存在三期有机流体充注与运移,流体特征总体反映出烃类从早期到晚期由低成熟到高成熟的演化过程。包裹体成分中含有大量CO2、烃类物质(CH4与C2+)和还原性气体(H2S与H2),含矿砂岩中有丰富的碳酸盐胶结物。这说明还原环境为铀的沉淀、富集提供了有利的成矿介质环境条件,CO2与碳酸盐对东胜地区铀的迁移与沉淀起了重要作用,烃类与铀成矿具有密切的联系。包裹体均一温度及其他证据显示,本区曾经历过明显的热事件。该热事件的发生与早期铀矿形成的时间相近,对铀矿的形成有重要贡献。

The measurement of homogeneous temperature and chemical component and the fluorescence analysis of fluid inclusion in the uranium-bearing sandstone and diagenetic sequence indicated that there were at least three phases of hydrocarbon-related fluid injection and migration in Zhiluo Formation of the Dongsheng area in Ordos Basin. The characteristics of the fluid demonstrated an evolution process of hydrocarbon from low maturity in the early phase to high maturity in the late phase. The fluid inclusions contained a large amount of CO2 ,hydrocarbons （CH4 and C2^＋ ） and reduction gas（H2 S and H2 ）. The uranium-bearing sandstones contained rich carbonate cement. Reduction gases provided a favorable condition for uranium precipitation and accumulation. The depositions of CO2 and carbonate cement in the formation had an important positive impact on uranium precipitation and accumulation. Hydrocarbon injection and emplacement had a close relationship with the origin of uranium mineralization. The homogeneous temperature of fluid inclusions and other related evidences showed that the tectonic thermal events once occurred in this area. The occurrence of the tectonic thermal events coincided with the uranium mineralization in the early stage,thus the thermal event had contribution to the uranium mineralization.