Deposition of trace elements from high temperature gases of Satsuma-Iwojima volcano

The Satsuma-Iwojima volcano has been emitting continuously high temperature (600degrees to 900degreesC) gases for at least 800 years. We identified the minerals that form in response to closed-system cooling of these gases and from air-mixing reactions. Major differences compared with the sublimates observed at other volcanoes are the occurrence of wulfenite (PbMoO4) and several mixed chlorides. This is the first report of wulfenite in fumarolic deposits. Thermochemical modeling shows that wulfenite precipitates between 540degrees and 490degreesC from a gas with lower sulfur content and/or higher fO(2), and a higher Mo content (log fSO(2) = -2.1, log f H2S = -5, = - 18.6, log fH(2)MoO(4) = -4.5, T = 500degreesC) than the previously reported gas composition. The occurrence of abundant K, Pb, Fe, Zn, Rb and Cs mixed chlorides may be promoted by the low S/Cl of the Satsuma-Iwojima high temperature gases. Natural sublimates of metallic elements (molybdenite, wulfenite, anglesite, Tl-Pb and Tl-Bi sulfides, Mo oxydes and Pb oxides) are deposited along the fumarolic conduit and on the ground under conditions of variable temperatures and f O-2. The increase in fO(2) due to the mixing of the gases with the atmosphere reduces the volatility of several elements (As, Sn, Na, K and Pb) by promoting their condensation at higher temperatures. As air mixes with volcanic gas in the fumarolic plume, we can expect to find these metals as aerosols.