In 3 million years of mantle-driven activity, Piton des Neiges volcano (La Réunion) has built a large structure above sea level (>3000m). Its last activity (12 to 20 Ka) is characterized by silicic formations like trachytic lavas and a large syenite intrusive complex. Its hydrothermal system shows potential for geothermal exploitation with a thermal gradient measured at up to 18˚C/100m.
The hydrothermal activity is highlighted by numerous hot springs flowing out of old units with fracture-related permeability induced by volcanic intrusions. In such hydrogeological settings, a good understanding of thermal fluid circulations is needed to locate sufficient fluid flow for geothermal exploitation, which is the aim of my PhD research.
Prospection has led to the sampling of 71 hot springs, on which we performed analysis on major, trace elements and O, H, C, Cl, Li and Sr isotopes. We also monitored for a full hydrological year the conductivity and temperature of two springs, and aquired monthly data of O and H isotopes on two springs and two rain collectors. With this data, we are able to study the origin of waters and gas, reservoir connectivity and water-rock interaction. From these results, we are building a conceptual model for thermal fluid circulations that will assess the possibility of geothermal eploitation and address the issue of the precise location of the resource.