Anastasia V. Sergeeva

Magmatogenic-hydrothermal formation model of fluid dynamic structures and rare metal brine deposits in Siberian Platform cover | Vakhromeev | Earth sciences and subsoil use Магматогенно-гидротермальная модель формирования флюидодинамических структур и месторождений редкометалльных рассолов в чехле Сибирской платформы | Вахромеев | Науки о Земле и недропользование

This study explores the training of a neural network to determine the mineral composition of complex mineral associations formed in the thermal fields of Kamchatka, which are associated with modern geothermal systems. Typical secondary minerals of productive reservoirs are key to characterizing the stages and conditions of the development of modern geothermal systems, the exploration of which is crucial for the advancement of geothermal energy. These typical secondary minerals include kaolinite, montmorillonite, quartz, opal, minerals of the alunite and jarosite groups, gypsum, calcite, and zeolite minerals. All of them possess individual infrared spectra and can be interpreted individually by an operator. However, in complex mixtures, the absorption bands overlap. To recognize the qualitative mineral composition in such cases, machine learning was applied. We utilized convolutional neural networks, and the training dataset contained approximately one thousand labeled spectra, which enabled the achievement of high accuracy in determining the mineral composition using the neural network.

The possibilities of using infrared spectroscopy for express characterization of the mineral composition of hydrothermally altered rocks are considered using the example of argillisites of the Yuzhno-Kambalny Central Thermal Field (Pauzhetsky district of South Kamchatka). The minerals that are indicators of sulfuric acid and carbon dioxide leaching zones of rocks have been identified, and the conditions for the transition of some mineral associations to others have been restored with changes in the temperature and geochemical regimes of the geological environment. Zones of ascending alkaline fluid are marked by carbonates and the change of feldspar into gel-like zeolite-like aggregates, with which ore minerals are often associated. To diagnose the latter, an additional method is used, that is, X-ray diffractometry. When taking a large number of core samples from geothermal deposits, this methodological approach is very relevant as it is quite reliable, rapid and economically feasible.

—The montmorillonite samples from shallow parts of the thermal fields within the Mutnovsky hydrothermal steam deposit (the Upper Mutnovsky thermal field and the Dachny site), along with the composition of salts in the clay pore solutions have been studied in the context of ion exchange between them. This aspect represents one of the topical problems due to geothermal clays (montmorillonite) enrichment with elements transferred by steam hydrotherms and concentrating in the near-surface horizons, while montmorillonite as a natural cation exchanger will absorb them, thus acting as a geochemical barrier. The composition of the interlayer cationic complex of montmorillonite samples was studied on isolated clay fractions and from the ion-exchange experiment to determine the salt composition of clay pore solutions and the mineral composition of clay fractions. Geothermally heated soils within the studied thermal fields are dominated by kaolinite-alunite-jarosite assemblage with subordinate amounts of montmorillonite, while montmorillonite prevailing in the mud-water pots is subjected to degradation when they dry out. Crystallization of salts from pore solutions in the near-surface horizons of the studied thermal fields can be exemplified by szomolnokite FeSO4‧H2O, metavoltine K2Na6Fe2+Fe3+6O2(SO4)12·18H2O, leonite K2Mg(SO4)2‧2H2O, polyhalite K2Ca2Mg(SO4)4‧2H2O, mikasaite Fe2(SO4)3, alum and amorphous aluminum sulfate hydrate. Interaction of such solutions with montmorillonite will trigger the cation exchange reactions in the interlayer space of the layered silicate with attendant formation of predominantly Al,Fe-intercalated forms. Alumina hydrates entering the interlayer space of the montmorillonite are reflected by the band at ~ 2500 cm–1 on the infrared spectra attributed to the water coordinated to aluminum. In addition to aluminum and iron, other cations which are concentrated in the uppermost parts of geothermal clay blankets and penetrate into the interlayer space of montmorillonite are: Li+, K+, NH4+, Mg2+, Ca2+, Sr2+, Ba2+, Hg2+, etc. As a result, in the thermal field conditions, montmorillonite is intercalated with easily extractable elements, including lithium, mercury, barium and strontium, ammonium, at the level of units (the first tens of grams per ton).

This paper considers the propagation of ash during the paroxysmal eruption of Sheveluch Volcano which occurred April 10–13, 2023, and its impact on the water resources of the affected area. We characterize ash thicknesses at various population centers and describe the grain-size composition of the ash. We show that the propagation of ash plumes is primarily driven by the eruption dynamics, but atmospheric circulation actually controls the spatial distribution of deposit thickness. The water-soluble salts contained in the ash and the dynamics of their washing out under natural conditions have been determined. The water-soluble part of fresh ash is dominated by calcium and magnesium sulfates, sodium chloride, with minor amounts of chlorides and fluorides of aluminum, potassium, and ammonium. The first substances to be washed out from ashes are well-soluble chlorides, to be followed by sulfates. As time goes on, the total concentration of soluble salts is decreasing, and their qualitative composition changes: hydrogen carbonates of calcium, magnesium, and sodium begin to dominate. Several months after the eruption, the impact of the ashfall on water resources of the settlements, including open springs at the ground surface, was leveled out.

The Pauzhetka geothermal field was surveyed to study the mineral deposits that were formed as thermal water was discharged from well separators. We studied the compositions, structure, and geochemical properties of these sediments along the flow and in vertical cross sections of manmade “sinters”. It was found that, at the beginning of thermal water discharges, the sediments were composed of X-ray-amorphous mordenite–opal mixtures; later on, the sediments became wholly siliceous. The zeolite component of the mineral deposits determines their high sorption properties in relation to Au, Ag, Hg, As, Rb, Sr, Ba, Cs and other elements; the mordenite matrix receives sulfides of iron, silver, and copper. It is shown that the mineral deposits which were formed at the ground surface of the Pauzhetka geothermal field constitute an indicator of alkaline mineral-forming and ore-forming environment in the lower horizons of the Pauzhetka geothermal system.

На Восточно-Паужетском термальном поле с помощью бурения скважин и проходки шурфов детально изучена толща аргиллизированных пород и гидротермальных глин. Выделены зоны, сложенные минеральными ассоциациями необычного состава, рассмотрены условия их образования. Показано строение основания толщи гидротермальных глин, исходные породы которого (брекчированные андезиты) изменены гидротермально-метасоматическими процессами и представлены смектит-хлорит-калишпат-цеолит-карбонат-кремнистым агрегатом с сульфидами, фосфатами, титано- и цирконо-силикатами и др. минеральными фазами, включающими редкие металлы. Построена концептуальная геолого-геохимическая модель формирования аргиллизитов и зон, содержащих минеральные рудные ассоциации. Предполагается, что современное минералообразование на Восточно-Паужетском термальном поле наследует эпитермальную рудообразующую систему, расположенную в зоне влияния глубинного флюида, дериваты которого разгружаются вблизи дневной поверхности в форме щелочных металлоносных растворов Паужетской гидротермальной...