Mineralogy and origin of aerosol from an arc basaltic eruption: case study of Tolbachik volcano, Kamchatka

Intense emission of volcanic aerosol accompanied the 2012-13 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 made more than 95% of the solid fraction of the condensation aerosol. The remaining 5% were represented by native elements (Au, Ag-Pt alloy, Pt); sulfides of Fe, Cu, Ag and Re; oxides and hydroxides of Al, Fe, Cu, Zn, Mo, W, Te, Ta and Zr; halides of Al, Mg, Na, K, Ca, Cd, Pb, Ag and Tl; 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 aerosols, such as magnetite spherules or phosphate-carbonate-fluorite association, likely had a nonvolcanic origin (country rocks, wood fly ash). Physical and chemical properties of minerals from the volcanic aerosols have an effect on the geochemical and environmental behavior of the trace elements emitted by volcanoes.