鄂尔多斯盆地西南缘砂岩型铀矿“源-汇”系统研究

Analysis on Source to Convergence Systems of Sandstone Type Uranium Deposit in the Southwestern Margin of Ordos Basin

文章以鄂尔多斯盆地西南缘为例,将“源”到“汇”的研究思路应用到砂岩型铀矿成矿作用研究中来,提出将含铀物质从风化剥蚀到汇流、富集的整个物理化学过程看成一个完整“源—汇”系统,以此来探讨砂岩型铀矿的富集机理和成矿规律。鄂尔多期盆地西南缘下白垩统的铀源岩主要为北部、西南部的沉积岩、花岗岩,混杂了少量长英质岩和中性火成岩。沉积期富铀沉积岩和西南部富铀蚀源区为成矿提供了铀源条件,沉积期铀的预富集为铀成矿奠定了部分物质基础;盆缘古隆起区和下切沟壑古地貌单元是铀成矿时期的两种主要汇流通道,含氧含铀水在重力的驱使下沿着古隆起区和下切沟壑向盆内渗透性好的砂岩迁移流动,形成后生氧化蚀变,在氧化带前锋线附近,受有机质、黄铁矿等还原性物质作用富集成矿。砂岩型铀矿“源—汇”系统研究有助于对铀成矿规律的研究和总结,为鄂尔多斯盆地西南缘下一步铀矿地质勘查提供一定的理论依据。

Research ideas of"from source to convergence"was applied to study the metallization of sandstone type uranium deposits in the southwestern margin of Ordos Basin.The whole physical and chemical process of uranium source from denudation to confluence and enrichment were considered as a complete source convergence system for the enrichment mechanism of sandstone type uranium deposits.The Lower Cretaceous uranium source rocks in the study area are mainly sedimentary rock and granite in the southwestern parts of the study area,with a few felsic and neutral rocks mixed together.During the deposition period,sedimentary rocks and baserock fragments with rich uranium in the northwestern created the conditions for mineralization and the uranium pre-concentration provided a part of material foundation for uranium metallization.During the metallization period,the two pale geomorphic units,paleo uplift and lower incised gully,were the main confluence channels of uranous fluid on the basin margin,by which oxygenated uranium water moved down the paleo uplift area and through incised gully in the margin of the basin into the well permeable sandstone in the basin,resulted in the formation of epigenetic oxidation alteration.Uranium mineral were enriched by mineralization of organic matter,pyrite and other reducing substances near the front line of oxidation zone.The study of the source-convergence system of sandstone type uranium deposits is helpful for the study and summarization of uranium metallogenic regularity,and provides a theoretical basis for the next step uranium geological exploration in the southwestern margin of Ordos Basin.