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GEOCHEMISTRY OF RARE EARTH ELEMENTS IN ALLANITE OF THE DANILOVSKOYE MANIFESTATION OF THE GORNYI ALTAI

A. I. Gusev

Altai State Humanities and Pedagogical University, Biysk, Altai Territory

Data are given on the geochemical pecularities and composition of allanite of the Danilovskoye pegmatite manifestation belonging to the Nb > Ta-Y-F (NYF) family and allanite (orthite)-monazite type enriched with light rare earth elements (REE). Allanite occurs in the large-block part and micropegmatite fringe of zonal pegmatites and it is closely associated with hydroxyl-containing minerals- muscovite, zoisite. Total concentrations of rare earth elements in mineral vary from 182163 to 189046 g/t. It is also characterized by increased contents of Ti, Y, Th, U, Mn. High ratios (La/Yb)N (from 278 to 375.7) indicate a highly diff erentiated type of REE distribution. The tetradic effect of the W-type REE fractionation in allanite is due to abnormal conditions of its crystallization at the transition stage to water enrichment of fluids and an increased alkaline regime of the mineral formation medium. This process contributed to manifestation of the effect of nonсonformity to charge-radius behavior of chemical elements during crystallization of allanite. Abundant mineral secretions contributed to its accumulation in placers of some rivers together with monazite.

Keywords: Gornyi Altai, rare-earth zoned pegmatites, allanite, rare earths, tetradic effect of fractionation of rare-earth elements, increased alkaline regime.

DOI 10.20403/2078-0575-2023-1-68-75

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