Sedimentary facies and their controls over mineralization of sandstone type uranium deposits in Nanlin Formation in Lianghe Basin, Western Yunnan, China

Based on the first hand drilling data of uranium exploration project in Langpuzhai area, Lianghe Basin, western Yunnan, the characteristics and evolution process of Pliocene in Lianghe Basin are analyzed, and the sedimentary system, sedimentary facies type and favorable ore-bearing microfacies combination of Nanlin Formation are determined. On this basis, the ore-controlling regularity of sedimentary evolution sequence on the vertical spatial distribution of ore-bearing layers is analyzed, and the favorable ore-bearing locations are predicted by reconstructing the lithofacies and paleogeography pattern of ore-bearing ancient alluvial fan body, trying to provide scientific basis for the exploration of sandstone type uranium deposits in the area. The study shows that the alluvial fan system of mountain discontinuous basin is mainly developed in Nanlin Formation of Lianghe Basin, including three subfacies and five microfacies. Fine sedimentological analysis of borehole cores shows that the host beds of sandstone-type uranium deposit are mainly developed in the fan sub-facies, especially in the Gravelly braided river microfacies. The host lithofacies are mainly containing gravel feldspathic sandstone and containing gravel lithic feldspathic sandstone. The lithofacies palaeogeographic pattern before and during the ore-bearing sedimentary period shows that the relative water level rises during the sedimentary transition period from fan root to middle fan, and the study area presents a regressive evolution as a whole, the area of middle fan facies enlarges, and the gravelly braided channel microfacies becomes more developed, which provides more favorable conditions for the formation of good uranium reservoir. It is considered that the central sub facies distribution area of the fan east of the Jiazhai-Langpuzhai line is a favorable exploration area for sandstone type uranium deposits.