Abstract:

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.

Key words: organic matter, uranium mineralization, Lower Cretaceous, sandstone-type uranium deposit, Ordos Basin