Metallogenic characteristics and models of sandstone-type uranium deposits in China

With the rapid development of nuclear power, the world demand for uranium is increasing year by year. Sandstone-type uranium deposits, as the primary target for uranium exploration and mining, have attracted more and more experts and scholars to conduct in-depth research with respect to ore morphology, metallogenic mechanism, metallogenic characteristics, and metallogenic models. In China, a lot of large and ultra-large sandstone-type uranium deposits were initially discovered by learning from international researches. However, these researches could not support operations on the sandstone-type uranium deposits with complex metallogenesis, resulting in no significant uranium breakthroughs in China over the past ten years. It is urgent to understand the metallogenic characteristics and models of sandstone-type uranium deposits. As the most popular deposits in China, sandstone-type uranium deposits are poor in southern China and rich in northern China - 88% of sandstone-type uranium resources are found in sedimentary basins in northern China, mainly in Jurassic and Cretaceous strata. Five elements of sandstone-type uranium metallogenesis are recognized, i.e., source, reservoir, barrier, migration, and accumulation. Analysis results show that the sandstone-type uranium deposits discovered in China are obviously source-controlled, and mostly distributed 50 km away from their sources. Uranium reservoirs are generally large braided river or large braided river delta deposits, and locally large meandering river and fan delta deposits. They appear evidently in zones, an oxidation zone, a transition zone, and a reduction zone, which are different in color, mineral composition, and element content. Usually, stable barriers are developed at the roofs and floors of uranium reservoirs, and they provide strong supports for the sustainable and steady progress of uranium metallogenesis. Fluids as the carrier for uranium migration can be divided into two types: surficial infiltration fluid and deep upwelling fluid. Uranium metallogenesis is mainly controlled by reductants and adsorbents. Moreover, changes in fluid pH and temperature can lead to changes in uranium solubility in the fluid, allowing uranium to precipitate and accumulate into ore. Uranium generally occurs in three states: uranium mineral, adsorbed uranium, and uraniferous mineral. Based on the style of fluid migration, the metallogenic models of uranium deposits are divided into three types: surficial infiltration fluid, deep hydrothermal metallogenic fluid, and superimposed metallogenic models. The surficial infiltration fluid metallogenic model have two types: phreatic infiltration-type and interlayer oxidation-type.