Experimental constraints on metal transport in fumarolic gases

Abstract

Metals are efficiently transported in a gas phase and the gas composition strongly affects transport rates of these metals in the gas phase. Here we present a new approach to systematically investigate metal transport and deposition from volcanic gases of different compositions: We test the effect of sulfur and chlorine on the volatilization of 30 metal oxides and the phases deposited along a temperature gradient of 1250–300 °C in evacuated silica glass tubes in water-free systems. In total, we observe 30 different deposited phases, including oxides, sulfides and chlorides. The experimental results are compared with closed system and open system thermochemical equilibrium calculations. The closed system calculations provide insights into the metal speciation in the gas phase, and the open system calculations provide thermodynamic predictions of the temperature ranges over which metals deposited from the gas phase. Both approaches only partially reproduce the experimental observations of the deposited phases in the silica glass tubes. However, when we compare our experimental results with records from fumaroles on three different volcanoes (Kudriavy volcano, Russia, La Fossa crater on Vulcano, Italy, and Momotombo, Nicaragua), we find that our experiments agree very well with natural observations. We suggest that similar experimental investigations are powerful tools in the study of metal transport in ore forming systems involving gas phases, and results may be applied to various processes in terrestrial and planetary environments.