NEW DATA ON RARE-METAL MINERALIZATION IN THE GULI MASSIF CARBONATITES, ARCTIC SIBERIA

The composition of rare-metal mineralization of carbonatites of the Gu li Massif was investigated. In the course of the carbonatite magma dif ferentiation; considerable accumulation of Nb, Ta, Th, U, Hf occurred, which manifests itself by the crystallization of U-rich Th-pyrochlore , containing up to 16.42% ThO2, and baddeleyite with up to 4.78% Hf. I n all likelihood, the decomposition of zirconium-bearing minerals as a result of increasing activities of volatile constituents in carbonati tes is typical, and proceeds according to reactions: CaZr3Ti,NbO9 + F- ,OH- calzirtite = Ca-2(Ti,NbO3)(2)OH,F + ZrO2 pyrochlore baddeleyite C aTi,NbO3 + F-,OH- = Ca-2(Ti,NbO3)(2)OH,F, perovskite pyrochlore.