Genetic model of tabular orebody in Nalinggou uranium deposit, Ordos Basin: Constraint from clay minerals studies

Significant advancements have been achieved in the field of Uranium (U) exploration within the Ordos Basin. As a result, a sequence of U deposits characterized by tabular orebodies has been successfully identified. Extensive research has been conducted by scholars on the morphological characteristics, occurrence location, and control factors of the tabular orebody. However, a comprehensive understanding of its genesis and specific formation process remains elusive. Samples of sandstone from various geochemical zones in the Nalinggou U deposit were gathered for the purpose of microscopic observation, electron probe analysis, scanning electron microscopy, clay X-ray diffraction, and U elements analysis. Coffinite often occurs on the surface of particles and in association with other adsorbents such as organic matter, clay minerals, and titanium oxide, indicating strongly that sequential adsorption-reduction could be involved in the formation of U minerals. The clay minerals found in ore-bearing layers exhibit distinct characteristics. Specifically, there is a noticeable boundary between the content of kaolinite in the paleo-oxidation zone and the ore zone. This boundary aligns with the abrupt change in U content, indicating a consistent pattern. Moreover, the ore-bearing layer has undergone multiple stages of fluid transformation. These stages include the early U-bearing oxidizing meteoric precipitation and organic acidic fluids, as well as the late basin brine containing hydrocarbon. The formation of the tabular orebody can be attributed to the prolonged and stable interaction between weakly alkaline U-bearing oxidizing meteoric precipitation and the organic acidic fluid migrating towards the discharge area. This interaction leads to sequential adsorption-reduction processes, which occur due to the decrease in pH and the presence of reducing agents. These processes are responsible for the production of U mineralization on the interface where the two fluids interact. U metallogenic model of the tabular orebody in U deposits in the northern Ordos basin was established. This study presents an analysis of the metallogenic mechanism and evidence of fluids interaction interface for the tabular orebody. The findings of this study can be utilized as exploration guides for sandstone-type U deposits in the central-eastern basins of China