Fluid Gas Composition during Hydrothermal Alteration of Komatiites in the Kostomuksha Greenstone Structure (Western Karelia, Russia)

This study reports data on the gas composition of the mineralizing fluid, which is associated with hydrothermal alteration of Mesoarchean komatiites in the Kostomuksha greenstone structure (Western Karelia, Russia) and responsible for the formation of the soapstone Ozerki deposit and the Pentinsuo occurrence. Gas chromatographic analysis identifies H2O (60.85‒94.49 mol %) and CO2 (3.11‒33.38 mol %) as the dominant fluid components. Soapstone (carbonate‒chlorite‒talc rocks) formed via interaction with oxidized fluids (CO2/(CO2 + CO + H2 + CH4) = 0.64‒0.96), with a significant CO2 molar fraction ( X_CO_2 = 0.082–0.334). Along with the high carbon dioxide content in the fluid, the primary factors controlling soapstone localization were the high magnesium content of the ultramafics and their tectonic deformation.