Experimental study of trace element distribution between calcite, fluorite and carbonatitic melt in the system CaCO3 + CaF2 + Na2CO3 ± Ca3(PO4)2 at 100 MPa

Abstract

Here we present an experimental study of the distribution of a broad range of trace elements between carbonatite melt, calcite and fluorite. The experiments were performed in the CaCO3 + CaF2 + Na2CO3 ± Ca3(PO4)2 synthetic system at 650–900 °C and 100 MPa using rapid-quench cold-seal pressure vessels. Starting mixtures were composed of reagent-grade oxides, carbonates, Ca3(PO4)2 and CaF2 doped with 1 wt% REE–HFSE mixture. The results show that the distribution coefficients of all the analyzed trace elements for calcite and fluorite are below 1, with the highest values observed for Sr (0.48–0.8 for calcite and 0.14–0.3 for fluorite) and Y (0.18–0.3). The partition coefficients of REE gradually increase with increasing atomic number from La to Lu. The solubility of Zr, Hf, Nb and Ta in the synthetic F-rich carbonatitic melts, which were used in our experiments, is low and limited by crystallization of baddeleyite and Nb-bearing perovskite.