Рисунок 1. Location of ultramafic-alkaline magmatic complexes of Udja Province

(after Shpount et al., 1991, modified)

At each point in the sequence, the massif's geological evolution is characterized by two contrasting rock series: nepheline and alkaline syenite on the one hand and carbonatite, ijolite-jacupirangite-urtite, alkaline gabbro, and picrite on the other. The massif’s magmatic evolution typically produced monomineral rocks—apatitolite, magnetitolite, francolitite, and carbonatite. Rare-metal ores of lower ore horizons are attributed to both hydrothermal infiltration and multistage formation of lateritic weathering crusts. Coal-bearing Permian deposits that acted as filters helped to form unusual concentrations of scandium, rare earths, yttrium, and niobium.