Vinokurov and three co-authors reported in 2017 that three groups of industrial uranium deposits that differ in the distribution of lanthanides in U oxides have been recognized. A dependence of the REE distribution type on the Yttrium content and Yttrium index YI = (La + Ce)/Y that controls the formation of REE phases capable of selective accumulation of lanthanides has been discovered. This indicates the important role of crystal–chemical fractionation in the distribution of lanthanides. Preferable accumulation of Sm–Gd by U oxides has been found to occur at relatively low contents of Y. In Proterozoic uranium deposits, the yttrium specialization of oxides predominates, while in most Phanerozoic deposits the lanthanum–cerium specialization is typical. These results extend the possibilities of using REEs in ores for purposes of study of the genesis of various uranium deposits.
The authors concluded that the REE distribution in U oxides is mainly influenced by crystal–chemical fractionation. This conclusion is based on identification of the REE distribution dependence on the value of the YI, which determines the possibility of formation of minerals selectively incorporating REEs. The ability of U oxides to accumulate IREEs at different values of YP has also been demonstrated. Dominance of Y or (Ce + La) in the studied U oxides permitted recognition of two groups of deposits. The first has yttrium specialization (the first type of REE distribution) and is characteristic of ancient Proterozoic deposits, the second one with a cerium–lanthanum specialization (types two and three) is typical for most of the Phanerozoic deposits (Table 1).The causes for the differences are in various compositions of the ore-forming solution that determines formation of microphases of either xenotime or monazite. The dependence of the REE distribution in U oxides on the mineral-forming medium allows identification of possible sources of polychronous U deposits. These data can be used in the development of a genetic version for classification of uranium deposits.
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