Isotope Systematics of Albitite-Type Uranium Deposits, the Central Ukrainian Uranium Province

The new whole-rock geochemistry and Sr-Nd-Pb isotope data obtained for U-bearing Na-metasomatites (albitites) in the Central Ukrainian Uranium Province (CUUP) are presented and discussed in terms of the possible contribution of different sources of elements to this type of uranium deposit. When compared with the host granite, albitites demonstrate a sharp decrease in the abundances of SiO₂ and K₂O, whereas most other major oxides show significant enrichment. Albitites have Sr isotopic signature typical for crustal rocks. Specifically, rocks of the Novokostyantynivka deposit have ⁸⁷Sr/⁸⁶Sr(1800) in the range 0.7087–0.7105, whereas rocks of the Novooleksiivka deposit show a variation from 0.7172 to 0.7207. Neodymium isotope compositions allowed construction of the Sm-Nd isochron that yielded an age of 1728 ± 110 Ma. The calculated εNd value of -4.8 indicates that a dominantly crustal source of the fluids was responsible for producing the metasomatic alteration. Lead isotope compositions indicate a prevalence of radiogenic Pb resulting from the decay of uranium, whereas 'common' Pb is negligible. Pb-Pb isochron yielded an age of 1810 ± 17 Ma. The isotope results can be compared with data available for the main rock types present in the area. Albitites of the Novokostyantynivka deposit plot between fields of the Novoukrainka massif and Korsun-Novomyrhorod anorthosite-mangerite-charnockite-granite (AMCG) complex. In contrast, albitites of the Novooleksiivka deposit plot entirely within the field defined by the Inhul granitoid complex. According to Sr-Nd isotope data, the initial fluids could have been derived from or equilibrated with the Palaeoproterozoic felsic rocks widely distributed in the area. However, trace element data indicate an important influence of mantle-derived material. Probably a mantle plume that was active in that area during formation of the albitites was responsible not only for the heating of area and formation of hot fluids but also provided some material necessary for the formation of the albitites. (author)