Genesis and Age of the Ore Thickness of the Tomtor Deposit of Niobium and Rare-Earth Elements (Northeast Siberian Platform)

Abstract

In the northeast of the Siberian Platform (Republic of Sakha (Yakutia)), there is the Udzha province of alkaline ultrabasic massifs with carbonatites of the final phases of the evolution of the magmatic system, forming its central “carbonatite core” and containing increased concentrations of Fe, Al, P, and a complex of rare and rare-earth elements. The massifs have a lateritic weathering crust with a thickness of up to 400 m. In the weathering crust of carbonatites, the contents of phosphates, Nb, Y, Sc, and TR are significantly higher compared to unaltered rock varieties. However, they reach maximal values in the thickness of peculiar sedimentary deposits formed as a result of the deposition of products denudation of the crust of ore-bearing carbonatites in small lake depressions and their intensive chemogenic transformation in a hot humid climate. They are uniquely rich ores, which in terms of the set and content of useful components have no analogues in world practice. These rocks are sometimes their natural concentrates with average contents of Nb₂O₅ 7.21%, Y₂O₃ 0.578%, Sc₂O₃ 0.045%, and TR₂O₃ 10.16%. The rocks that make up the ore-bearing stratum have characteristic features of sedimentary genesis: well-defined layered texture and facies zoning, as well as the presence of carbonized plant detritus and bacteriomorphic aggregates. This gives grounds to consider the complex of these formations as an independent stratigraphic unit—the Tomtor strata. Geological data suggest that it was formed in the range of 340–280 My. The Tomtor strata can serve as an important search criterion when searching for rare and rare-earth elements.