Vol 69, No 8 (2024)

The effective solubilities (maximum contents) of Ta and Nb in acidic magmatic lithium-fluoride melts of varying alkalinity and alumina content were experimentally determined at the dissolution of Ta–Nb and Nb minerals: pyrochlore, microlite, ilmenorutile and ferrotapiolyte at T = 650–850 °C and P = 100 and 400 MPa, and also the partitioning of Ta and Nb in mineral–melt systems was studied. When pyrochlore is dissolved in granitoid melts at P = 100 MPa and T = 650–850 °C, the highest effective solubilities of Nb (0.7–1.8 wt. %) are obtained in alkaline melt; they decrease significantly (up to 0.03–0.5 wt. %) in subaluminous and peraluminous melts. Increasing the temperature increases the solubility (content) of Nb in the melt. When dissolving microlite, similar dependences of Ta solubility were obtained. In peraluminous granitoid melt microlite remains stable, while pyrochlore becomes unstable. It has been established that in alkaline and subaluminous melts, a decrease in pressure from 400 to 100 MPa does not have a significant effect on the dissolution of microlite and pyrochlore, while in the peraluminous melt the Ta and Nb contents noticeably decrease. The dependences of the solubility of Nb and partitioning of Nb between granitoid melts and ilmenorutile on the alkalinity–alumina content of the melt are similar to those for the dissolution of columbite and tantalite. The dependences obtained by dissolving ferrotapiolyte, pyrochlore and microlite differ from them.

Drilling cores from peat deposits of the Vydrinsky bog with a thickness of 4.4 m and an age of 13,100 cal. years, composed of lowland, transitional and high-moor types of peat, were studied in detail. The processes of post-sedimentary transformations of swamp sediments during early diagenesis are considered, the distribution of elements, the formation of authigenic minerals and the chemical composition of swamp waters are studied. The destruction of organic matter begins already in the upper intervals of peat at the early stages of diagenesis. Pyrograms do not have clearly defined high-temperature peaks, “rudiments” of the macromolecular structure of kerogen, which indicates a low degree of transformation of peat organic matter. A high number of organotrophic, ammonifying, nitrifying, phosphate-mobilizing microorganisms, a small number of Fe- and Mn-oxidizing microorganisms, and sulfate-reducing bacteria were revealed. The presence of organotrophic microorganisms throughout the section indicates that the biogeochemical processes of the carbon cycle cover the entire thickness of the peat deposit. A small amount of S (II) indicates a low intensity of sulfate reduction processes. Lowland peat is characterized by high contents of Si, Al, Fe, Ca, Sr, Ba, Zr, La and anomalous contents of Cu, Zn, which is a consequence of the formation of the bog under conditions of rich mineral nutrition. In the ash part of the transitional peat, a decrease in the contents of Si, Fe, Sr, Br, K Si, Ca, Ba, Cu, Zn and La is noted, which reflects the gradual weakening of the connection of the peat deposit with the underlying rocks. In the near-surface horizon of high-moor peat, there is an increase in the contents of K, Mn, Zn, Hg, Pb and As, which is associated with an increase in atmospheric dust and anthropogenic impact on the bog ecosystem in the 20th and 21st centuries. Bog waters of low-lying peat are characterized by high contents of the main ions, Al, Fe, Mn, Sr, while transitional peat is characterized by a decrease in DOC, SO₄^2–, HCO₃^–, Al, Fe, Ni, Ca, Mg. The oligotrophic strata is characterized by the development of Fe oxides and hydroxides, the presence of vivianite is noted for transitional peats, and the eutrophic part of the peat deposit includes rhodochrosite and sulfides of Fe, Cu, and Zn.

The results of long-term studies of the conjugate distribution of concentrations of methane (CH ₄ ) and sulfide sulfur (S _sulfide ) in bottom sediments of streams of the steppe zone of the European part of Russia are analyzed. In addition to CH ₄ and S _sulfide , Eh and pH values, humidity and density were determined in various sediment horizons; CH ₄ , dry residue and pH values were determined in water. Concentrations of CH ₄ in the water of watercourses vary from <0.1 to 2007.0 µl/l (median 24.3 µl/l), with the largest number of values (72 %) in the range 10.1–100.0 µl/l. The concentrations of CH ₄ and Ssulfide in the bottom sediments of watercourses are quite high and vary, respectively, from <0.01 to 51.0 µg/g of wet sediment (median 1.35 µg/g) and from <0.001 to 4.50 mg/g of wet sediment (median 0.813 mg/g). Usually, there is an increase in CH ₄ and S _sulfide from the surface layer to the subsurface horizons, after which their concentrations decrease. The difference between the distribution of sulfides and the distribution of CH ₄ is the more frequent occurrence of maximum concentrations of sulfides in less deep sediment horizons. Seasonal changes in the distribution of CH ₄ and S _sulfide along the vertical of sediments were recorded not only in terms of their concentrations, but also in the location of maximum and minimum values. There is a weak direct relationship between the concentrations of CH ₄ and S _sulfide , which indicates synchronous processes of formation of these gases in separate layers of sediments of the studied watercourses. The direct relationship established between the concentrations of CH ₄ in water and the 0–2 cm layer of bottom sediments indicates sediments as an important source of CH ₄ entering water and its emission into the atmosphere.