Hg Mineral Forms in Argillisites of the South Kamchatka Thermal Fields, Russia

This work considers the occurrence of Hg in a clay strata and pore fluids and conditions of Hg incorporation in sulfides and clay minerals abundant in thermal fields of the Koshelev, Kambalny, and Pauzhetka hydrothermal systems. It is shown that, under physicochemical conditions typical of the studied thermal fields, Hg is mostly incorporated in sulfides (pyrite, marcasite, cinnabar) and clay minerals (kaolinite and montmorillonite) as a result of sorption. Under the conditions of a thermal field, cinnabar is the most stable Hg form, because Fe sulfides are unstable during oxidation. The optimal pH value for Hg sorption by clay minerals (in the absence of chlorides and sulfites) is 3.15. In the presence of Hg-bonding chlorides, sulfites, and other anions, the optimal Hg sorption on layered silicates starts from a pH value of >5. The Hg sorption by clay minerals strongly depends on the local highly dynamic geochemical conditions.