Decoding water-rock interaction and volatile input at La Soufriere volcano (Guadeloupe) using time-series major and trace element analyses in gas condensates

The geochemical behavior of major and trace elements in fumarolic gas condensate samples collected between April 2017 and January 2021 was investigated at La Soufriere hydrothermal volcano. Samples collected from Cratère Sud and Napoleon Nord fumaroles (temperature varying from 93.9 to 108.4 °C) offer a unique opportunity to reveal the physicochemical processes that affect the deeper magmatic and shallow hydrothermal systems feeding fumaroles. Gas condensate samples exhibit abundant solid particles that suggest strong water-rock interaction and erosive processes in fumarolic conduits at La Soufriere. These particles were incorporated during sampling, except for rare Si-rich spherules that appeared to have precipitated during storage time. Gas condensate samples displayed abundant concentrations of S, halogens (Cl, Br, I), metals/metalloids (B, Ni, Cu, Zn, As, Mo, Ag, Cd, Sb, Pb, and Bi), as well as enhanced concentrations of rock-related lithophile and siderophile elements. The relative abundance of major and trace elements in gas condensates suggests the permanent contribution of volatile-rich magmatic fluids and strong water-rock interaction processes. Based on elemental correlations and the physical properties of chemical elements, it is postulated that most of them are discharged in the aerosol phase, except for the halogens and S, which can be found in the gaseous phase in low-temperature fumarolic emissions. Metals and metalloids (Sb, Bi, Zn, Mo, Ni, Ag, Cd, As, and Pb) enriched in gas condensates were transported within tiny aqueous droplets, while rock-related elements (including REEs) were transported in the aerosol phase. Trace element enrichments in La Soufriere's condensates are comparable with those found in worldwide magmatic-hydrothermal systems such as Kawaj Ijen (Indonesia), Lastarria (Chile), and White Island (New Zealand) volcanoes. The size of the hydrothermal system and the degree of water-rock interaction are thought to be important parameters in controlling the abundance of major and trace elements in low-temperature fumarolic discharge.