Tectonic setting and provenance analysis of the Wuyun Formation in the Zhanhe Depression, central Sunwu-Jiayin Basin, northeast China, and its relationship to uranium mineralisation

The Zhanhe Depression exhibits significant potential for uranium mineralisation, with the Paleogene Wuyun Formation as the primary ore-bearing layer. This formation consists mainly of greyish-white to greyish-yellow, gravel-bearing medium to coarse-grained sandstone. The rocks are characterised by a high content of SiO2 and Al2O3, along with low levels of MgO and CaO. They are enriched in Rb, Th, U, K and light rare earth elements and depleted in high-field-strength elements, similar to the composition of upper crustal rocks. Zircon U–Pb dating reveals that the zircon ages of the Wuyun Formation can be classified into nine distinct stages: 2653–2508 Ma, 2052–2024 Ma, 1896–1687 Ma, 520–470 Ma, 309–252 Ma, 229–177 Ma, 155–133 Ma, 114–89 Ma and 81–69 Ma. By integrating geochemical characteristics and the regional evolutionary history, it is hypothesised that the Wuyun Formation originated in an active continental margin environment. The clastic rocks within the Wuyun Formation primarily obtain their source materials from uranium-rich granite and felsic volcanic rocks in the Lesser Khingan Mountains. The paleoclimate was predominantly arid to semiarid. The elemental ratios of B, Sr/Ba, B/Ga, U/Th, V/(V + Ni), V/Cr and Ni/Co suggest that the paleowater medium during the deposition of the Wuyun Formation was oxygen-rich freshwater with moderate stratification and steady runoff, conditions that are favourable for uranium mineralisation.