Sr-Nd-Pb Isotope Systematics of U-Bearing Albitites of the Central Ukrainian Uranium Province: Implication for the Source of Metasomatizing Fluids

Sodium metasomatites are relatively widely distributed throughout the world and often contain uranium mineralization that occasionally may reach an exploitable scale. Uranium concentrations in deposits of this type are rather low but resources can be quite large, especially in the areas where sodium metasomatites attain wide distribution. Deposits of this type are significantly underexplored and may represent a promising target for further exploration. This is especially true as sodium metasomatites often contain complex mineralization that, besides U, includes Sc, V, Nb, HREE and Ag. The Central Ukrainian Uranium Province (CUUP) hosts several large deposits and numerous subeconomic deposits and occurrences. Production started in 1951 and since that time two deposits have been completely exhausted. The remaining U resources of the CUUP exceed 300 000 tU with grades varying between 0.05 and 0.20 wt% U. In spite of the long history of exploration and exploitation of Na-metasomatite type U deposits in Ukraine, many questions regarding their origin still remain unanswered. The main questions that were debated over decades related to the source of the metasomatic fluids and the source of the ore components. Numerous studies focused on the geological structure of U deposits in the CUUP, on their mineralogical and chemical compositions, and on stable isotope systematics. However, high quality geochemical data regarding these deposits were absent until recently, whereas radiogenic isotope data are still absent, which hampers a reasonable discussion about the origin and evolution of the Na-metasomatites and about the source of ore components. Current ideas regarding the origin of metasomatic fluids and their ore load are controversial. The main problems are: 1) The source of the very large volumes of high temperature hydrothermal solutions (with meteoritic waters, basin waters and magmatic fluids being the main alternatives) and complex sources evolving over time have also been invoked; 2) A source of U and Na, as large volumes of these elements cannot be derived from low crustal and mantle lithologies, and middle to upper crustal sources have been considered. However, simple calculations indicate that hydrothermal leaching of the host upper crustal rocks cannot produce such enrichment as these rocks are relatively poor in both U and Na, and huge volumes of leached rocks are unknown in the area; 3) The association of elements typical for this type of deposit includes elements that are more typical for mafic alkaline igneous complexes rather than for felsic crustal rocks. This contribution presents new Sr-Nd-Pb isotope data obtained for Na-metasomatites in the CUUP and for a large variety of host rocks and discusses the possible contribution of different sources to the origin of this type of U deposit.