REE, Y, Sc, and Li Partition between Aluminosilicate and Aluminofluoride Melts, Depending on Pressure and Water Content in the Model Granite System

Abstract

Experiments on REE, Y, Sc, and Li partition between aluminosilicate (L) and aluminofluoride (LF) melts in the granite system at 800°C and 1, 2 kbar, containing up to 18 wt % F and 2 to 13 wt % H2O, show that all REE, Y, Sc, and Li are preferably distributed into the aluminofluoride melt, regardless of the experimental conditions. The partition coefficients of the elements Kd REE = $$C_{{{\text{REE}}}}^{{LF}}$$/$$C_{{{\text{REE}}}}^{L}$$ between these phases depend on pressure. The first data are obtained indicating that a pressure increase from 1 to 2 kbar at a temperature of 800°C leads to a significant decrease in Kd REE. The partition coefficients between the melts monotonously decrease from LREE to HREE at both 1 and 2 kbar. No clear relationships were found between Kd REE and the water concentration in the system. It is shown that Li strongly impacts the distribution of REE, Y and Sc, because Li, similar to F, causes the onset of liquid immiscibility in the system and facilitates REE, Y, and Sc enrichment in the salt melts. All of the experiments show a positive correlation between the partition coefficients Kd Li and Kd REE, Y, Sc between the salt and silicate melts. The dependence of this REE behavior on pressure in the system may be explained by a change in the structure of silicate and salt melts when H2O and F are dissolved in them and by complexation under various experimental conditions.