Effect of Palaeoclimate and Palaeoenvironment on Tabular Uranium Mineralisation: Insight from the Upper Cretaceous Qingshankou Formation in the Qianjiadian Area of Songliao Basin, NE China

ABSTRACT Several sandstone‐type uranium deposits were identified within the Upper Cretaceous red‐variegated strata in the Qianjiadian area of the Songliao Basin, NE China. However, a consensus regarding the genesis of multilayer tabular ore bodies within a sandstone reservoir remains elusive. This paper investigates the provenance, palaeoenvironment, and unique mineralisation characteristics of the Qingshankou Formation within the newly discovered Dalin deposit on the basis of lithofacies, element–environment–organic geochemistry and stable isotopes. The results indicate that the fragment provenance of the ore‐bearing strata is primarily composed of intermediate–felsic rocks, and the source areas are characterised by a complex tectonic background that encompasses both passive and active continental margins, as well as continental arcs. Its sedimentary environment shows a general (semi‐) arid and hot palaeoclimate, with ancient lacustrine water exhibiting both fresh and brackish properties. Pure grey mudstone (PGM) features low Fe 2 O 3 T but exhibits elevated levels of ferrous iron, uranium, molybdenum, Fe 2+ /Fe 3+ ratio and reduction capacity; pure red mudstone (PRM) displays contrasting characteristics; and certain geochemical indicators of mottled mudstone (MD) are intermediate between those of the above‐mentioned mudstones. Green alteration within the MD is identified as having a syn‐sedimentary origin, as opposed to the previously assumed secondary reduction of foreign hydrocarbons. The associated organic matter is classified as Type‐III kerogen, initially derived from aquatic plankton and herbaceous plants. Finally, a sedimentary model is proposed for the red‐variegated Qingshankou Formation in the study area, where the original interbedded architecture with varying geochemical properties is influenced by alternations in palaeoclimate and associated redox stratification of ancient lacustrine water. Some lenticular native grey beds, which were deposited in local low‐lying lands during semi‐arid and pluvial interphases, exhibit pronounced uranium pre‐concentration due to phreatic oxidation during the sedimentary stage. Subsequently, differential redox activities in the Cenozoic era led to the development of multilayer geochemical zoning and tabular ore bodies in a reservoir. This research offers valuable insights into the uranium mineralisation of oxidative red‐variegated strata within global basins and contributes to the development of uranium exploration strategies.