已有的铀成矿模式大多认为,砂岩型铀矿是浅表层含氧水从盆地周邻蚀源区析出携带的外源铀汇入盆地而成矿。本研究发现,鄂尔多斯盆地北部伊盟隆起东部砂岩型铀矿矿集区的地质演化、地貌特征和铀成矿与此成矿模式相悖。其中令人困惑的关键问题是铀成矿物质的来源。对研究区的代表性矿物铀石(形成于强还原环境)及其共生的矿物进行多种地球化学测试分析发现:铀矿区存在淡水低温和中高盐度热液两类截然不同的铀矿化环境;铀成矿年龄主体小于80 Ma。结合盆地煤系气源岩富铀、天然气耗散量巨大和在伊盟隆起发现大面积分布的多种与成熟煤型气耗散有关的蚀变产物和凝析油苗,综合相关模拟实验和测试分析,提出了铀源来自深部的铀成矿新模式:来自盆地中部深层富铀煤系地层中的溶气热流体,在向伊盟隆起东部高部位运移耗散过程中,萃取并携带母岩和沿途围岩富铀地层中的铀元素运移到浅层,随温压降低亮晶方解石与铀石相伴沉淀完成了热液成矿过程,被析出的大规模有机天然气则在浅表层低温成矿同时为铀矿的保存创造了还原环境。此铀成矿新模式拓展了盆地勘探铀矿的思路和领域,提升了多种能源矿产相互作用的成矿效应和综合评价预测的科学性。

Most existing metallogenic models maintain that sandstone-type uranium (U) deposits are formed by infiltration of exogenous uranium carried by near-surface oxygenated waters from erosion source areas into basins. However, this study finds that these traditional models fail to explain the geological evolution, geomorphological characteristics, and mineralization of sandstone-type uranium deposits in eastern Yimeng Uplift, northern Ordos Basin. The key issue is the material source of uranium mineralization. Geochemical analysis of representative minerals from this area, including coffinite (formed in a strongly reducing environment) and its associated minerals, reveal the existence of two distinct uranium mineralization environments: low-salinity meteoric waters and medium-high-salinity hydrothermal fluids, and primary uranium mineralization occurred less than 80 Ma. Considering the U-rich source rocks of coal-bearing strata in the basin, the enormous dissipation of natural gas, and the widespread distribution of various hydrocarbon alteration products and condensate oil traces related to the dissipation of mature coal-type gas in the Yimeng Uplift, a novel metallogenic model of large uranium deposits is proposed based on comprehensive simulation experiments and testing analysis. According to the new model, the uranium source originates from deep U-rich coal strata in the middle of the basin, where dissolved gases from thermal fluids migrate and dissipate towards higher elevations in the eastern Yimeng Uplift, extracting and carrying uranium from the source rock and uranium-rich strata along the way to shallower layers to cause sparry calcite and coffinite to precipitate as temperature/pressure decreases; meanwhile along with the near-surface, low temperature mineralization, massive exsolved natural gas creates a reducing environment for the preservation of uranium deposits. This new model of uranium mineralization opens up new horizons for uranium exploration in terms of exploration approaches and domains, and strengthens the scientific basis for polymineralization involving different mineral (metallic, non-metallic) and energy (hydrothermal, hydrocarbon) types, as well as prediction and evaluation of such polyminealization occurrences.