FORMATION OF COMPOSITION OF THE ABSORBED CATIONIC COMPLEX OF MONTMORILLONITE OF sOUTH-KAMBALNY GEOTHERMAL SYSTEM (KAMCHATKA)
A.V. Sergeeva1, S.N. Rychagov1, O.V. Kravchenko1, A.G. Vakhromeev2, E.V. Kartasheva1, A.A. Kuzmina1, M.A. Nazarova1, D.O. Martynenko1
1Institute of Volcanology and Seismology FEB RAS, Petropavlovsk-Kamchatsky, Russia
2Institute of the Earth'S Crust SB RAS, Irkutsk, Russia
Keywords: Kambalny volcanic ridge, geothermal systems, hydrothermal clays, argillizita, montmorillonite, ionic exchange
Abstract
The composition and conditions of formation of the absorbed cation complex (ACC) of montmorillonite, which was formed on the thermal field of the modern geothermal system of the Kambal Volcanic Range, located in the south of Kamchatka, are considered. The 9-m-thick layer of hydrothermal clays is composed mainly of montmorillonite and has a vertical zonation due to the upward flow of alkaline metal-bearing thermal waters and the influence of meteoric waters. Vertical zonation is also observed in the composition of PCC, which is caused by both the form of the metals in the pore solutions and the presence of an evaporative barrier. Montmorillonite absorbs a wide range of elements from the pore solutions, and Al, Fe, Zn, Cu, Rb, Cs, Li, and other elements are fixed in the composition of ACC. The absorption of these elements by montmorillonite through cation exchange is due to their form in the solution. In the carbonate leaching zone, aluminum was not absorbed by montmorillonite because it was in the form of an anionic complex, but as it moved towards the sulfuric acid leaching zone and transitioned to a cationic hydrated form, aluminum began to be absorbed by montmorillonite. The iron content in the ACC for the carbon dioxide leaching zone is about 30-100 g/t, but when it comes to the sulfuric acid leaching zone, the iron content increases by almost an order of magnitude, reaching values over 1300 g/t. Both aluminum and iron clearly mark the vertical zoning in the composition of the ACC montmorillonite. The calcium content is increased in the carbon dioxide leaching zone, where carbonate mineralization is developed, and the anion composition is dominated by the hydrocarbonate ion. Ore elements, such as zinc and copper, are present in the carbon dioxide leaching zone at levels of up to 1 g/t, but their content in the sulfuric acid leaching zone increases to 76 and 20 g/t, respectively. The group of alkali metals, which are poor complexing agents, is concentrated mainly in the upper part of the section, closer to the surface, and in the evaporative barrier. The lithium content in the lower part of the clay layer is 0.3 g/t, while it reaches 1 g/t in the upper part of the section. Rubidium and cesium are also concentrated in the upper part of the clay layer, where their contents reach 1.3 g/t and 17 g/t, respectively. In the lower part of the section, the content of rubidium and caesium generally varies slightly, averaging 0.5 and 3 g/t, respectively. As the acidity increases, more metals are converted to cationic forms and absorbed by montmorillonite, while rare alkaline elements are concentrated within the evaporative barrier.
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