Experimental data indicate that high F concentrations in leucocratic aluminosilicate melts (of granite and nepheline syenite composition) bring about the crystallization of F-rich minerals (topaz, villiaumite, and cryolite) on the liquidus. The crystallization of the minerals is controlled by the silicity, agpaitic coefficient, and proportions of alkalis in the system SiO₂-Al₂O₃-Na₂O-K₂O-F-H₂O. Our earlier experimental data on this system are compared with petrographic and petrochemical data on granites and nepheline syenites containing accessory topaz, cryolite, and villiaumite. The composition of topaz- and cryolite-bearing rocks is proved to correspond to the experimentally established equilibrium fields of F-rich aluminosilicate melt with these minerals. It is proved that the high-F minerals can crystallize from melt. The partial substitution of K and Na for Li modifies phase relations in the system, first of all, significantly expands the equilibrium field of aluminosilicate melt and alkaline aluminofluoride melts. The two melts are proved to be immiscible within broad compositional ranges in the SiO₂-Al₂O₃-Na₂O-Li₂O-F-H₂O system at 800–650°C and 1 kbar. Experimental data indicate that fluoride brine can coexist with aluminosilicate melts in nature. This finds support data on melt inclusions in granites and alkaline rocks whose contents of major components, water and fluorine are close to those in the experimental glasses. Our data lend support to the hypothesis that large cryolite bodies at the Ivigtut, Pitinga, Ulog-Tanzek, and other deposits were formed by fluoride salt melts that separated from F-rich aluminosilicate magmas late in the course of their differentiation. It is experimentally established that fluoride salt melts are able to concentrate valuable trace elements, such as Li, W, Nb, Hf, Sc, U, Th, and REE, which suggests that such melts can play an important role in the origin of rare-metal deposits genetically related to rocks that crystallize from magmas rich in F.

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 K_{d 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 K_{d 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 K_{d 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 K_{d Li} and K_{d 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.

Phase relations and the distributions of rare earth elements (REE), Sc, Y, and Li between aluminofluoride and aluminosilicate melts in the model granite system Si–Al–Na–K–Li–F–O–H were experimentally studied at 700°C, 1 and 2 kbar, and water contents of 3 to 50 wt %. Our original and available literature experimental data on phase relations in the granite system saturated with water and fluorine and containing trace elements are compared with the mineral assemblages of rare-metal cryolite-bearing granites from the Zashikhinsky, Katugin, and Ulug-Tanzek deposits in eastern Siberia. Liquid immiscibility between granite and salt aluminofluoride melts, which occurs at high contents of fluorine and lithium in the system, is proved to facilitate the accumulation of rare elements in salt cryolite-like melts. At a temperature of 700°C and pressures of 1 and 2 kbar, aluminofluoride melt in the granite system crystallizes and forms cryolite. Fluorine-bearing minerals of trace and rare earth elements, such as pyrochlore and gagarinite, occur at these deposits in association with cryolite and lithium micas. Comparison of experimental data and natural observations provides arguments in support of the hypothesis that liquid immiscibility should play an important role in the formation of cryolite. Cryolite is thought to be able to serve as a reference mineral for rare metal-rare earth mineralization in granites with high lithium and fluorine content.

The results of two experiments on the interaction of fluorine-bearing granite melt and calcite with the same initial composition of the dry charge and diff

A series of experiments were carried out in the peraluminous part of the haplogranite high fluorine system SiO2–Al2O3–Na2O–Li2O–F a