NEAR-SOLIDUS MELTS IN CARBONATIZED MANTLE PERIDOTITES WITH APATITE AND URANINITE

Liquids equilibrated with lherzolites at temperatures about 1100-degre es-C are characterized by the dominance of dolomite with increased pho sphate concentrations (almost-equal-to 20 wt% P2O5) and sodium carbona te. The ratio Ca/(Mg + Fe) in these melts decreased with decreasing te mperature and increasing pressure. Some of the compositions studied co ntained uraninite. Uranium distribution coefficient between apatite an d melt falls in the interval 0.15-0.3. These quantities are lower for clinopyroxene, orthopyroxene, and olivine, so the carbonate - phosphat e melts will extract uranium intensively from the rock-forming mineral s of mantle peridotites. Crystallization of these melts leads to urani um fixation in apatite in accordance with the fact that apatite is the main uranium concentrator in some metasomatized mantle rocks.