What is an hydrothermalism in geology ?

Hydrothermalism : definition

Hydrothermalism refers to the circulation of hot water in the earth's crust, in connection with volcanic and plutonic systems, and with metamorphic events. Hydrothermal fluids are usually hot (from 50°C to over 350°C), salty, corrosive, and loaded with dissolved substances acquired in magma or during percolation through rocks. They transport, concentrate and redeposit these dissolved salts in the form of minerals in certain particular sites : hydrothermal deposits (veins, sulfidic masses, skarns, etc...). Hot springs, geysers, fumaroles, acid lakes... are current manifestations of hydrothermalism.

These hydrothermal deposits frequently constitute ore deposits (Pb, Zn, F, Ba, Au, Ag, etc...), widely exploited on the planet. The minerals formed by deposits of substances dissolved in these fluids are called hydrothermal agents (barite, fluorite, numerous sulphides, native sulphur, etc...).

Beyond the critical temperature of water (374°C), one passes from the hydrothermal domain to the pneumatolytic domain.