Аннотация:In the model high-fluoride lithium-containing granite system Si-Al-Na-K-Li-F-O-H, when the temperature decreases from 1250 °C to 400 °C at 1 kbar, a certain order of crystallization of mineral phases from coexisting aluminosilicate (L) and salt alkali-aluminofluoride (LF) melts is observed. At 1250 °C and CH2O = 0-50 wt. % silicate melt is homogeneous. In experiments at 1000°C at a water content of ~ 10 wt. % there are signs of silicate-salt immiscibility in the form of spherical secretions of aluminofluoride composition. Starting from 800 °C and CH2O = 2-15 wt. % liquid immiscibility is stably presented in the system, and at 700 °C and CH2O = 2-50 wt. % partial crystallization of the salt melt begins with the formation of K-Na cryolite (Crl). In the silicate melt, quartz is the first to crystallize in the temperature range from 700 to 600 °C. With a further decrease in temperature, the crystallization of Li-mica of the polylithionite type occurs (at CH2O = 15 wt. % in the system) at the boundary of the silicate and salt melt. The cryolite continues to crystallize in the salt melt, but there is also a melt saturated with REE, Y, and Sc, which were introduced into the system. In the range between 600 and 500 °C, orthoclase and Na - and Na-K cryolite crystallize in the system along with quartz in the form of separate phases. The silicate melt remains in the system up to 400 °C, being in a metastable, supercooled state. In salt globules, the residual melt is presented at 500 °C, and at 400°C it completely crystallizes. The observed Na - and Na-K cryolite secretions inside large quartz grains (~200 microns) are similar to those found in cryolite-containing granites (for example, the Madeira deposit). The simultaneous crystallization of two compositions of Na-and Na-K-cryolite indicates the decomposition of a homogeneous solid solution of cryolite and the coexistence of two phases – cryolite and elpasolite, starting from 600-500 °C.
