Comparison of Supercontinent Cycles in the Metallogeny of Niobium

The distributions of niobium mineral deposits and their resources on the geological time scale are analyzed. The sampling list includes 45 mineral deposits with their individual resources estimated not less than 10 5 tons of Nb 2 О 5 . The classification of deposits used includes three types, namely, alkaligranitic, foidic, and carbonatitic. The geohistorical variability in niobium metallogeny is presented through comparison of supercontinent cycles. To date, no deposits belonging to the Kenoran cycle, which are of interest for the targeted extraction of niobium, have been identified. The Columbian cycle is the oldest among the significant cycles in niobium metallogeny, but its resources are relatively small. The most significant resources of niobium are related to alkaline igneous complexes of the Rodinian, Pangean, and Amasian cycles. The resources of carbonatitic deposits are sharply predominant among all resources generated in the cycles of geological history considered. A consistent increase in the share of resources of such deposits is established through the chronological sequence of supercontinent cycles. The maximum amount of resources of the foidic type is concentrated in the deposits of the Rodinian cycle, while a much smaller amount is in those of the Columbian and Pangean cycles, and no foidic deposits have been identified in the Amasian cycle. The alkaligranitic type demonstrates the smallest fluctuations in niobium resources among the cycles compared; however, its relative contribution to the total resources of all cycles is very small, except for the low-productive Columbian cycle. Despite the close relationships between niobium and tantalum in the mineral-forming processes, these elements do not always show mutually comparable ore concentrations in terms of economic value in the same deposits. Such a coincidence chiefly takes place in mineral deposits of the foidic and alkaligranitic types, which are not yet of great importance in real extraction of both niobium and tantalum. In terms of economic value, carbonatites are almost always specialized exclusively in niobium, while rare-metal pegmatites and granites are specialized in tantalum. These types of mineral deposits are formed in completely different geodynamic environments from magmas of contrasting composition that originated in different lithospheric layers. Therefore, the revealed differences in the historical metallogeny of these two metals have a logical explanation.