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近十几年来,在鄂尔多斯盆地北部伊盟隆起东胜及其以西杭锦旗一带,相继发现了东胜等系列大型-特大型砂岩铀矿,目前已成为中国砂岩铀矿发现潜力最大的地区。矿床的主要特征是矿体受直罗组砂岩绿色蚀变带控制;同时,在容矿层及其附近伴生有砂岩白色化、后生碳酸盐化及方解石脉、黄铁矿化等蚀变现象。通过后生蚀变的C、H、O、S等稳定同位素方面研究、示踪和探讨了蚀变的形成过程和成因及其与铀矿化的关系。镜下特征显示,铀矿石中存在的大颗粒结核状黄铁矿与铀矿物共生,两者为同时期的产物;该类样品S同位素表现为较大的负值,表明硫质来源的微生物作用特征明显;与盆地内可能提供硫源的直罗组煤屑、延安组煤层、延长组和延安组原油、上古生界煤系地层等有机S同位素对比,发现铀矿与上古生界煤系烃源岩的有机硫源关系密切。延安组顶部大规模白色化砂岩的高岭石H、O同位素表明,其成因与低温热液作用有关;容矿层后生方解石C、O同位素表明,其形成主要是有机质作用提供了碳源,且其碳质来源主要为上古生界气源岩,而与奥陶系及延长组油气的碳源无关。后生作用流体包裹体的测温及其H、O同位素组成表明,成矿流体以低温的大气降水为主,且与上古生界天然气一起形成低温热液的气-水混合流体;正是这一特点的流体作用形成了本区与铀矿化关系密切的上述各类后生蚀变现象。各类后生蚀变的稳定同位素特征表明,东胜铀矿床形成过程中存在后生低温热液和油气还原改造作用两大特点。本次研究结果为东胜铀矿区的成因认识提供了证据。
In the recent decade, a series of large-large sandstone uranium deposits such as Dongsheng have been discovered in the east of the Yimeng Uplift and its west peninsula in the Ordos Basin. So far, it has become the region with the highest potential for discovering sandstone-type uranium deposits in China. The main feature of the deposit is that the orebody is controlled by the green alteration zone of Zhiluo Formation sandstones. At the same time, white sandstone, epigenetic carbonate and calcite veins and pyrite alteration occur in and near the ore-bearing layer. Through the post-eclogic alteration of C, H, O, S and other stable isotope studies, tracing and discussing the formation of alteration process and its relationship with uranium mineralization. Microscopic features show that the large-granular nodular pyrite present in uranium ore is symbiotic with uranium minerals, both of which are products of the same period. The S isotopes of these samples show a large negative value, indicating that the sulfur-derived microorganisms act The characteristics are obvious. Comparing with the organic S isotopes of Zhiluo Formation, Yan’an Formation, Yanchang Formation, Yan’an Formation and Upper Paleozoic coal measures strata that may provide sulfur source in the basin, it is found that the uranium deposits and Upper Paleozoic coal series hydrocarbons Source of organic sulfur sources are closely related. The H, O isotopes of kaolinite from the large-scale white sandstone at the top of the Yan’an Formation show that its genesis is related to the low-temperature hydrothermal fluids. The C and O isotopic compositions of the calcite in the ore-bearing layer indicate that the formation of carbon isotopes mainly contributes to the organic matter and that The carbonaceous source is mainly Upper Paleozoic gas source rocks, but not related to carbon source of Ordovician and Yanchang Formation hydrocarbons. The epithermal fluid inclusions and their H, O isotopic compositions suggest that the ore-forming fluid is dominated by low-temperature atmospheric precipitation and forms a gas-water mixture with low temperature hydrothermal fluids in the Upper Paleozoic. It is this Characteristics of the fluid formed the formation of the region and uranium mineralization are closely related to the various types of epigenetic alteration. The stable isotopic characteristics of various epigenetic alterations indicate that there are two major characteristics of the epithermal hydrothermal fluids and the retrogressive transformation of petroleum during the formation of the Dongsheng uranium deposit. The results of this study provide evidence for the genesis of Dongsheng uranium deposit.