Native sulfur deposits on fumarolic fields at Ebeko volcano (Northern Kuriles, Russia) are enriched in chalcophile elements (As-Sb-Se-Te-Hg-Cu) and contain rare heavy metal sulfides (Ag₂S, HgS, and CuS), native metal alloys (Au₂Pd), and some other low-solubility minerals (CaWO₄, BaSO₄). Sulfur incrustations are impregnated with numerous particles of fresh and altered andesite groundmass and phenocrysts (pyroxene, magnetite) as well as secondary minerals, such as opal, alunite, and abundant octahedral pyrite crystals. The comparison of elemental abundances in sulfur and unaltered rocks (andesite) demonstrated that rock-forming elements (Ca, K, Fe, Mn, and Ti) and other lithophile and chalcophile elements are mainly transported by fumarolic gas as aerosol particles, whereas semimetals (As, Sb, Se, and Te), halogens (Br and I), and Hg are likely transported as volatile species, even at temperatures slightly above 100°C. The presence of rare sulfides (Ag₂S, CuS, and HgS) together with abundant FeS₂ in low-temperature fumarolic environments can be explained by the hydrochloric leaching of rock particles followed by the precipitation of low-solubility sulfides induced by the reaction of acid solutions with H₂S at ambient temperatures. The elemental composition of native sulfur can be used to qualitatively estimate elemental abundances in low-temperature fumarolic gases.

High concentrations of primary sulfuric acid (H₂SO₄) in fumarolic gases and high emission rate of sulfuric acid aerosol in the plume were measured at Bezymianny volcano, an active dome-growing andesitic volcano in central Kamchatka. Using direct sampling, filter pack sampling, and differential optical absorption spectroscopy measurements, we estimated an average emission of H₂SO₄ at 243 ± 75 t/d in addition to an average SO₂ emission of 212 ± 65 t/d. The fumarolic gases of Bezymianny correspond to arc gases released by several magma bodies at different stages of degassing and contain 25–92% of entrained air. H₂SO₄ accounts for 6–87 mol% of the total sulfur content, 42.8 mol% on average, and SO₂ is the rest. The high H₂SO₄ in Bezymianny fumaroles can be explained by catalytic oxidation of SO₂ inside the volcanic dome. Because sulfate aerosol is impossible to measure remotely, the total sulfur content in a plume containing significant H₂SO₄ may be seriously underestimated.

Sulfur contents in 98.5% of melt inclusions (MI) from calc-alkaline subduction basalts do not exceed 4000 ppm, whereas experimentally established limits of sulfur solubility in basaltic melts with high fO₂ (characteristic of subduction zones, e.g., QFM + 2) surpass 14,000 ppm. Here we show that primitive (Mg# 62-64) subduction melts may contain high sulfur, approaching the experimental limit of sulfur solubility. Up to 11,700 ppm S was measured in olivine-hosted MI from primitive arc basalt from the 1941 eruption of the Tolbachik volcano, Kamchatka. These MI often contain magmatic sulfide globules (occasionally enriched in Cu, Ni, and platinum-group elements) and anhydrite enclosed within a brown, oxidized glass. We conclude that the ubiquitous low sulfur contents in MI may originate either from insufficient availability of sulfur in the magma generation zone or early magma degassing prior to inclusion entrapment. Our findings extend the measured range of sulfur concentrations in primitive calc-alkaline basaltic melts and demonstrate that no fundamental limit of 4000 ppm S exists for relatively oxidized subduction basalts, where the maximum sulfur content may approach the solubility limit determined by crystallization of magmatic anhydrite.

Intense emission of volcanic aerosol accompanied the 2012–2013 basaltic effusive eruption of Tolbachik volcano, Kamchatka. The aerosols sampled contain sulfuric acid droplets, glassy particles, and 70 mineral phases. All aerosol particles may be classified by their origin. The fragmentation aerosol includes magma fragments: silicate glass clasts, silicate microspheres, and small phenocrysts (olivine, pyroxene, and magnetite). The alteration aerosol comprises particles of quenched silicate melt covered with secondary minerals (fluorides, sulfates, and oxides/hydroxides of rock‐forming elements) and fragments of altered rocks composed solely of secondary minerals. The condensation aerosol dominated the mass during the later stages of the eruption when the explosive activity had ceased, and was characterized by the greatest variety of particle compositions. Na‐K sulfate and Fe (III) oxide comprised more than 95% of the solid fraction of the condensation aerosol. The remaining 5% was represented by native elements (Au, Ag‐Pt alloy, and Pt); sulfides of Fe, Cu, Ag, and Re; oxides and hydroxides of Al, Fe, Cu, Zn, Mo, W, Ta, and Zr; halides of Al, Mg, Na, K, Ca, Cd, Pb, Ag, and Tl; and sulfates of Na, K, Pb, Ca, and Ba; the only silicate was As‐bearing orthoclase. Droplets of H₂SO₄ formed the liquid phase of the condensation aerosol. Some of the aerosol components, such as magnetite spherules or phosphate‐carbonate‐fluorite association, likely had a nonvolcanic origin (country rocks and wood fly ash). The volcanic aerosols and their contained minerals, discharged at Tolbachik and elsewhere, result in a physical and chemical effect on the environment in the region of such volcanoes.