Metallogenesis of uranium deposits in China: Perspectives from uraninite chemistry

Uraninite is generally the most principal component of uranium ores and can record the significant information about uranium mineralization processes. Here, chemical compositions of uraninites from thirty-five uranium deposits of nine types (including granite-related, sandstone-hosted, volcanic-related, black shale-hosted, Na-metasomatite-hosted, peralkaline syenite-hosted, pegmatite-hosted, carbonatite-hosted, and leucocratic dyke-hosted) in China were examined, with the aim to investigate the chemical variations of uraninite from each deposit type and fingerprint uranium metallogenesis. Uraninites from the last five types contain significant abundances of ThO₂ (median = 3.81 wt%), Y₂O₃ (0.96 wt%), and ∑REE (typically ≥ 1 wt%) and low concentrations of Si, Fe, and Ca (SiO₂ + CaO+FeO typically < 1 wt%) and have middle rare earth elements (MREE)-enriched chondrite-normalized REE patterns with pronounced negative Eu anomalies, although the carbonatite-hosted type shows insignificant Eu anomaly. These characterize the affinity of intrusive-related deposits that formed at high temperatures. Uraninites from granite-related deposits generally contain negligible abundances of Th and Y, the highest CaO (up to 9.89 wt%), and highly variable ∑REE concentrations. Their chondrite-normalized REE patterns typically resemble those of the host granites, suggesting that the REE signatures were mainly controlled by the sources of REE (U). Uraniferous phases from sandstone-hosted deposits have the lowest concentrations of UO₂ (median = 66.87 wt%) and the highest SiO₂ (up to 21.63 wt%), FeO (15.72 wt%), Y₂O₃ (10.35 wt%), and P₂O₅ (9.69 wt%) and generally show LREE-enriched REE patterns, which are indicative of the predominant role of LREE-rich sources in the mineralization. In contrast, those particles characterized by flat REE patterns probably suggest the involvement of hydrothermal fluids in the mineralization. Although uraninites from black shale-hosted uranium deposits have a LREE-rich source-controlled REE pattern, they are poor in P and Y and rich in W, which can discriminate them from the sandstone-hosted type. Uraninites from volcanic-related uranium deposits have variable REE signatures, suggesting the various formation conditions from which the uraninites form. Our study indicates that uraninite chemistry can help constrain the genesis of uranium deposits and discriminate deposit types.