The Chemical and Isotope Composition (H–O–C–S) of Hydrothermal Solutions and Gases in the Koshelevsky Volcanic Massif, Kamchatka, Russia

This paper presents results of 2025 sampling of steam vents and thermal waters in the Nizhne-Koshelevsky and Verkhne-Koshelevsky thermal fields. We considered macrocomponent composition of water (рН, SO4, Cl, NH4, and H3BO3) and the chemical composition of gases, including hydrocarbons up to C6. We are the first to report data on the isotope composition of water, carbon in CО2 and CН4, sulfur in H2S, and dissolved sulfate. We discuss possible factors that have affected the differences in the chemical and isotope compositions of fluids in the thermal fields of the Koshelevsky volcanic massif.