Reconstruction of Provenance and Paleo-Sedimentary Environment of the Saihan Formation in the Manglai Uranium Deposit, Central-Eastern Erlian Basin, China.

The Manglai uranium deposit is located in the Tabei Sag within the Manit Depression, centrally positioned in the eastern Erlian Basin at the core of an ancient valley uranium metallogenic belt. This study analyzed the geochemical properties of 22 clastic and mudstone samples from the Lower Cretaceous Saihan Formation in the Manglai deposit to assess its tectonic setting, provenance direction, redox conditions, and paleoclimatic environment. Key findings reveal that (1) The primary sediment source of the Saihan Formation in the Manglai deposit consists of felsic igneous rocks, situated mainly in a passive continental margin setting. Subunits within the Saihan Formation show enrichment in light rare earth elements (LREEs) and relative depletion in heavy rare earth elements (HREEs), presenting a right-leaning rare earth element distribution pattern with high concentrations of large-ion lithophile elements such as Rb, U, and Sr. (2) Similarities in rare earth and trace element distributions between the Saihan Formation and the northern source region suggest that the sediments were derived from the Chaganaobao and Weijing regions to the north, where parent rocks predominantly consist of Early Cretaceous rhyolite and Permian biotite potassic granite. These origins are linked to late Paleozoic north-south compression between the Siberian and North China Plates, marked by cycles of oceanic crust subduction, continental crust accretion, and block collision, accompanied by recurrent granitoid magmatism involving crustal assimilation and contamination. (3) The Chemical Index of Alteration (CIA) and Index of Compositional Variability (ICV) indicate that the Saihan Formation underwent moderate to intense weathering during deposition with relatively low rock maturity. Coupled with trace element geochemistry, these findings point to an arid to semiarid, mildly saline, and oxygen-rich depositional environment for the Saihan Formation.