Melt inclusions as indicators of the magmatic origin of carbonatite rare metal and rare earth minerals

Carbonatite melts, originating in the course of crystallization or liquid differentiation of mantle-carbonatized alkaline magmas, could contain primary enhanced quantities of alkalis, phosphorous, and incompatible trace elements (Nb, Ta, Zr, REE, Sr, Ba). This statement, based upon experimental data relative to fractionation of carbonatite-forming systems and solubility of Nb and La in synthetic carbonate liquids, allows us to suggest magmatic nature of rare metal (RMM) and rare earth (REM) minerals in carbonatites. Crystallization of RMM and REM from carbonatite melts is supported by the results of the present melt inclusion study in minerals of carbonatites. We observe the: (i) presence of RMM and REM in the form of solid inclusions in magmatic host-minerals; (ii) microprobe analyses of daughter rare metal and rare earth phases, entering into composition of crystallized melt inclusions; and (iii) conservation by rare metal and rare earth minerals of melt inclusions with high temperatures of homogenization.