Cryolite as a reference mineral for rare metal mineralization (experimental study)

The phase relationships and distributions of rare earth elements, Sc, Y and Li between aluminofluoride and aluminosilicate melts in the model granite system Si-Al-Na-K-Li-F-O-H at 700 °C, 1 and 2 kbar with a water content from 3 to 50 wt. %. were experimentally studied. Based on the obtained and available experimental data on phase relationships in a granite system saturated with water, fluorine and containing rare elements, a comparison was made with the parageneses of rare-metal cryolite-containing granites from three deposits in Eastern Siberia are Zashikhinsky, Katuginsky and Ulug-Tanzeksky. It has been shown that the processes of liquid immiscibility between granite and salt aluminofluoride melts, which manifest themselves at high contents of fluorine and lithium in the system, contribute to the accumulation of rare elements in salt cryolite-like melts. At a temperature of 700 °C and a pressure of 1 and 2 kbar, crystallization of the aluminofluoride melt occurs in the granite system, from which cryolite is formed. It is in association with cryolite and lithium micas that the considered natural objects contain minerals of rare and rare earth elements containing fluorine, such as pyrochlore, gagarinite, etc. As a result of a comparison of experimental and natural data, the hypothesis about the important role of liquid immiscibility in the formation of cryolite is confirmed. It is assumed that cryolite can serve as a reference mineral for rare metal-rare earth mineralization in granites with high lithium and fluorine content.