A possible hypothesis for the formation of rare-metal cryolite-containing granites

DOI: 10.47765/0869-5997-2026-10013

Abstract

In the studied model granite system at 700–800°C, 1 kbar, and water content 2–50 wt. %, a liquid immiscibility is consistently observed between the aluminosilicate and salt melts. In the experiments at 700°C and 1 kbar, large cryolite crystals (more than 70 μm) crystallize from a salt alkali-aluminofluoride melt. The coefficients of separation of rare earth elements between the alkali-aluminofluoride and aluminosilicate phases increase with increasing the water content of the melt both at 700 and 800°C and 1 kbar. When comparing the experimental results in the model granite system with natural data on rare-metal granites of the Katugino ore deposit, it was found that cryolite in the rare-metal granites could have formed at the late magmatic stage of formation of a large granite massif as a result of separation of silicate-salt melts rich in fluorine, lithium and rare earth elements from the magma at a temperature of 700–800°C. The formation of the rare-metal Katugino deposit in paragenesis with cryolite should be attributed to the magmatic stage. To understand the process of formation of the cryolite-containing rare-metal granites, this work presents the model by M.I. Schvadus, that demonstrates the relationship between silicate-salt immiscibility (fluid-melt) and cryolite formation in fluorine-rare metal ore deposits.