Vol 69, No 7 (2024)

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.

In the northern regions, as a result of seasonal temperature changes, cyclic thawing and freezing of soils and rocks occurs, which is accompanied by dangerous natural phenomena, including landslides. Special conditions arise on the mountain slopes of many reservoirs due to fluctuations of water levels and the interaction of humified waters with rocks. The paper presents the results of an experimental study of the biotransformation of sodium humate (SH) and changes in the microstructure of the surface of silicate rock that is part of the body of the Bureya landslide under various conditions of cyclic freezing-thawing (CFT). Freezing of samples was carried out at a temperature of –18 °C, and thawing at different temperature ranges (+4 °C and +23 °C). The role of biogenic factor was played by 4 strains of microorganisms isolated from the surface and bottom layers of water in the Bureiskoe Reservoir above and below the landslide body. The nature of the biotransformation of SH during CFT was studied by spectral methods at different wavelengths (254 nm, 275 nm, 465 nm). Analysis of the composition of water-soluble forms of chemical elements in an aqueous environment during rock destruction was carried out with use of the ICP-MS method, and changes in the microstructure of its surface with use of scanning electron microscopy. It was found that the transformation of aromatic component of SH occurred most active. After CFT, the strain Actinomyces sp. 45 VD, isolated from bottom layers of water, showed maximum activity at a thawing temperature of +4 °C in relation to SH and leaching of elements from rock (Al, Ca, Mg, Mn). Its activity was comparable to the intensity of leaching of elements by a natural microbial consortium of non-sterile rock. For comparison, we used rocks subjected to CFT in deionized water; in this case, the content of water-soluble forms of many chemical elements (Fe, Ni, Cu, Zn, As, Mo, Ag, Cd, Tl, Bi, As) was below the detection limits of the device (<0.001). High biogeochemical activity of Actinomyces sp. 45 VD is confirmed by analysis of SEM-images of the microstructure of the silicate rock surface and the formation of a wide variety of isomorphic biominerals.