Geochemical and isotopic insights into uranium mineralization in the Dongsheng Area (Ordos Basin, NW China): Implications for global uranium systems

Abstract

The Dongsheng region of the Ordos Basin (China) contains important sandstone-hosted uranium deposits that reveal an evolving interaction of geochemical evolution and tectono-sedimentary dynamics. The present work combines whole-rock and carbon‑sulfur isotopic compositions to understand the origin and formation of uranium metallogeny within the Middle Jurassic intracontinental Zhiluo Formation of the Ordos Basin. The δ¹³C values (−26.7‰ to −2.2‰) of calcite-cement indicate that the carbon mainly originated through biochemical remineralization. Negative and variable δ¹³C values indicate a strong biogenic carbon contribution, while positive excursions reflect mantle or inorganic inputs. Additionally, the δ³⁴S composition (−25.2‰ to 10.2‰) indicates the mutual inputs from bacterial sulfate reduction and Rayleigh fractionation. The broad δ³⁴S range of pyrite similarly points to multiple sources, with a strong bacterial sulfate reduction signal. Trace element patterns show Light Rare Earth Element (LREE) enrichment, Heavy Rare Earth Elements (HREE) depletion, and distinctive “W-shaped” anomalies (e.g., Nd, Nb, Zr), consistent with reductive immobilization under diagenetic conditions. Tectonic reconstruction and sedimentary provenance support a deposition along an active continental margin with felsic to intermediate source rocks. The Zhiluo Formation was deposited in arid to semi-arid settings, as evidenced by low Rb/Sr and high Sr/Cu and Sr/Ba ratios, reflecting high paleosalinity and strong evaporation. A revised genetic model is here proposed in which oxidized uranium-bearing groundwater interacts with both locally derived organic matter and hydrocarbon-charged reducing fluids (e.g., CH₄, CO, H₂S, CO₂) along structurally controlled fluid pathways, resulting in redox-driven uranium precipitation. This integrated isotopic–geochemical framework not only refines the mineralization model for the Dongsheng deposit but also provides a predictive approach for uranium exploration in analogous basinal settings worldwide. Our outcomes stress the wider role of microbial-hydrocarbon cycling in modulating uranium deposits across continental settings.