Post-crystallization alteration of natural uraninites: Implications for dating, tracing, and nuclear forensics

Geochronology and Geochemistry of Uraninite and Coffinite: Insights into Ore-Forming Process in the Pegmatite-Hosted Uraniferous Province, North Qinling, Central China

“…Note that the uraninite-A were widely distributed in the Chenjiazhuang, Xiaohuacha, and Guangshigou biotite pegmatites, whereas the uraninite-B were only found in the Guangshigou biotite pegmatites. Other elemental impurities can be integrated into the uraninite lattice though primary incorporation at the time of initial crystallization and elemental substitutions during the fluid-driven post-crystallization alterations [11,19]. The sums of SiO 2 , CaO, and FeO of uraninte-B are restricted and lower than 0.5 wt.%, while those of the uraninite-A are relatively scattered (0.01-1.69 wt.%, Figure 5d).…”

“…Thus, Pb is typically excluded in primary growth, whereas varying amounts of radiogenic Pb produced by radioactive decay of U can be retained in the crystal structure [8]. Combined with high U abundance, it has been demonstrated that uraninite is an ideal proxy for dating [17,19].…”

“…Based on rapid self-annealing kinetics, uraninite is known to a radiation-resistant phase [18]. Thus Pb-loss of uraninite (Figure 7) may be not caused by metamictization but can result from the following four processes: (I) removal of radiogenic Pb compensated by chemical substitutions of Ca, Si, and Fe during post-magmatic interactions with fluid [8,56], as evidenced by high sum of Si, Ca, and Fe for some analyses (>0.5 wt.%) and by the presence of galena, pyrite, and calcite ( Figure 2); (II) substitution of radiogenic Pb by water (magmatic fluid and late hydrothermal fluid, [19]); (III) hydrothermally-enhanced volume diffusion [65]; and (IV) replacement of uraninite by coffinite [9], as evidenced by the close association of uraninite and coffinite ( Figure 2). Partially released Pb from uraninite, being not migrate long distances, are thought to have reprecipitated as secondary galena by sulfofication at high fS2 (Figure 2d,g, [66]).…”

“…Alexandre et al [74] argued that in addition to the degree of alteration, there are additional factors that control the mounts of these elements in uraninite. Due to ionic radius of Ca (1.06 Å) being close to that of U (1.00 Å), Ca can be integrated into the uraninite lattice though primary incorporation at the time of initial crystallization [19,52], such as fresh uraninites from the Dörrmorsbach pegmatite-related deposit (ca. 10.5 wt.%, [52]) in Germany and Guérande granite-related hydrothermal deposit (as high as 9.55 wt.%, [17]) in France.…”

“…For pegmatite-type deposits, uraninite is mainly concentrated by magmatic process, but being one of the most sensitive mineral phases to post-magmatic hydrothermal processes due to geochemical instability to readily dissolve in the presence of later oxidizing fluids [15][16][17]. Uraninite is capable of retaining the imprints of the earlier magmatic event and capturing the footprints of subsequent hydrothermal events [18,19]. On the other hand, recent researches suggest that mobilized U can be subsequently reprecipitated as coffinite during later silica-rich fluid circulation events [10,20].…”