THE TOMTOR ultramafic-alkaline ring pluton — geology, petrology and ore formation
This paper reviews the geology, petrology, and ore content of the Tomtor massif (northern Siberia), one of the greatest carbonate-bearing alkaline massifs in the world. Radiometric dates show that the massif was formed during the emplacement of a sequence of magmatic complexes (смотри рисунок 1).
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.