Abstract
On the basis of combined analysis of data on a geological survey on a scale of 1 : 200 000 (1959–1960) and exploration works (1980–1990), it was found that the zones of higher radioactivity and related rich La–Ce ores are localized along linear faults 10–15 km long parallel to the axis of the Udzha Anticline. The HREE mineralization of the Y–Yb group is concentrated in sandstones and gravelstones of the Vendian Tomtor Formation, which unconformably overlap the Udzha Anticline on its wings. This indicates that the volatile flow has a deep (transmagmatic) origin rather than separation from magma. A carbonatite body with sulfide veinlets and dissemination is described with respect to a zone of high contents of La–Ce ores. The complex character of the Tomtor ores is explained by the juxtaposition of mineralization phases of various ages and composition: Nb and Sc–Th mineralization paragenetically related to the central ring structure of the intrusion and to the external rischorrite zone, respectively.
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