Tectonic-basin evolution in Tengchong block, western Yunnan Province, and minerogenetic conditions of sandstone type uranium deposits

A new round exploration for sandstone type uranium deposits led by China Geological Survey focuses on the Tengchong block in western Yunnan Province at present. This paper mainly analyzes the relationship between tectonic-basin evolution and uranium mineralization in Tengchong block in three aspects, i.e., the sedimentology of host rocks, the uranium source and the oreforming process. A compound sedimentary system consisting of alluvial fan, fan delta, braided river, fluvial delta and lacustrine facies was formed in the small graben basins on Tengchong block during Pliocene epoch. The host rocks of uranium deposits were generally developed in special microfacies such as braided channel, delta front sheet sand and distributary channel. The acidic granites from Yanshanian orogeny and the metamorphic rocks in Gaoligongshan Group provided main uranium source for mineralization. Moreover, the neotectonic movements, either in host rocks depositional stage or in the post-depositional stage, drove the multiperiodic ore-forming processes, including phreatic oxidation and interlayer oxidation. Based on the above results, the authors hold that the study of microfacies, large-scale lithofacies paleogeography, uranium source capacity in different geological bodies and the analysis of mineralization types constitute the keys to present exploration in Tengchong block.