Dual Control of Depositional Facies on Uranium Mineralization in Coal‐bearing Series: Examples from the Tuanyushan Area of the Northern Qaidam Basin, NW China

Abstract

AbstractThe uranium deposits in the Tuanyushan area of northern Qaidam Basin commonly occur in coal‐bearing series. To decipher the U‐enrichment mechanism and controlling factors in this area, a database of 72 drill cores, including 56 well‐logs and 3 sampling wells, was examined for sedimentology and geochemistry in relation to uranium concentrations. The results show that coal‐bearing series can influence uranium mineralization from two aspects, i.e., spatial distribution and dynamic control. Five types of uranium‐bearing rocks are recognized, mainly occurring in the braided river and braided delta sedimentary facies, among which sandstones near the coals are the most important. The lithological associations of sandstone‐type uranium deposits can be classified into three subtypes, termed as U‐coal type, coal‐U‐coal type, and coal‐U type, respectively. The coal and fine siliciclastic rocks in the coal‐bearing series confined the U‐rich fluid flow and uranium accumulation in the sandstone near them. Thus, the coal‐bearing series can provide good accommodations for uranium mineralization. Coals and organic matters in the coal‐bearing series may have served as reducing agents and absorbing barriers. Methane is deemed to be the main acidolysis hydrocarbon in the U‐bearing beds, which shows a positive correlation with U‐content in the sandstones in the coal‐bearing series. Additionally, the δ13C in the carbonate cements of the U‐bearing sandstones indicates that the organic matters, associated with the coal around the sandstones, were involved in the carbonation, one important component of alteration in the Tuanyushan area. Recognition of the dual control of coal‐bearing series on the uranium mineralization is significant for the development of coal circular economy, environmental protection during coal utilization and the security of national rare metal resources.