近几年,鄂尔多斯盆地北部下白垩统铀矿找矿取得重大突破,在特拉敖包及其外围发现了多个产于环河组下段的厚大铀矿孔。有机质是砂岩型铀矿化的重要因素之一,环河组下段赋矿砂岩中缺乏肉眼可见的有机质,在铀矿化过程中起主导作用的有机质类型目前还缺乏研究,铀成矿作用过程还不清楚。本文以特拉敖包铀矿产地赋矿砂岩为研究对象,通过岩心观察与室内研究,厘定了赋矿砂岩中的有机质类型,探讨了有机质的来源及其与铀成矿的关系。研究结果表明:赋矿砂岩中几乎不含炭屑有机质,有机质主要为顺层沿砂岩孔隙充填、具有流动特征的浸染状有机质,它是一种具有与沥青相似的复杂结构、低演化程度的大分子物质,具有高等植物和低等水生生物混合来源的特点。铀矿化与固体炭屑有机质关系不大,主要与浸染状有机质密切相关,特拉敖包铀矿产地的成矿特征契合“渗出”砂岩型铀矿成矿模式的特点,深灰色、灰褐色铀矿石的形成可能主要与深部渗出的有机流体有关。成矿元素可能主要以有机质络合物的胶体形式迁移,物理化学条件的变化可能是导致成矿流体发生分解并沉淀成矿的主要因素。

In recent years, significant progress has been achieved in uranium exploration within the Lower Cretaceous strata of the northern Ordos Basin. Notably, numerous large-scale industrial drill holes, revealing substantial ore bodies, have been unearthed within the lower segment of the Huanhe Formation in the Tela’aobao area and its vicinity. Organic matter serves as a pivotal factor in sandstone-type uranium (U) mineralization. Despite the absence of visible organic matter in U-mineralization sandstone, there remains a dearth of research on the specific organic matter types influencing the U-mineralization process, thus leaving the uranium mineralization process ambiguous. This study focuses on the sandstone-type U-deposit in Tela’aobao area, located in the northern region of the Ordos Basin. Through comprehensive observation of drill cores and subsequent laboratory analyses, we have delineated the organic matter types present in the U-mineralization sandstone and investigated the relationship between organic matter sources and U-mineralization. Our findings indicate that the organic matter in U-mineralization sandstones is primarily disseminated and exhibits flowing characteristics within sandstone pores. This macromolecular organic matter, akin to bitumen, possesses a complex structure and low evolutionary degree, suggesting a mixed origin from both higher plants and lower aquatic organisms. The formation of dark gray and gray-brown uranium ores may be linked to exuded organic fluids. Ore-forming elements are likely transported primarily in colloidal form via organic matter complexes. Moreover, changes in physical-chemical conditions may constitute the primary driver behind the differentiation and mineralization of ore-forming fluids.