Hydrotermal

Hydrotermal, often spelled hydrothermal, describes processes driven by hot water circulating through rocks or other materials. In geology, hydrotermal systems involve fluids that are heated by the surrounding rock or magma, dissolved minerals as they move, and changes in temperature, pressure, or chemistry that cause minerals to precipitate. These fluids can transport metals and other elements over varying distances, contributing to the formation of mineral deposits.

In geological contexts, hydrotermal activity is responsible for a wide range of ore bodies. Epithermal deposits form near the surface and commonly host gold and silver; mesothermal deposits occur at greater depths; porphyry copper systems are large, low-grade, long-lived sources of copper; and skarn deposits arise where hydrotermal fluids interact with carbonate rocks. The mineral assemblages typically include quartz, sulfides (such as pyrite, chalcopyrite, galena), and gangue minerals like calcite or fluorite. Temperature, pressure, and fluid chemistry control where and when minerals crystallize.

Oceanic hydrothermal systems occur on the seafloor at mid-ocean ridges and other tectonic settings. Seawater percolates into the crust, becomes superheated by underlying magma, and re-emerges as mineral-rich fluids that precipitate metal sulfides, forming hydrothermal vents and chimneys. These environments host unique chemosynthetic communities independent of sunlight.

In materials science, hydrothermal synthesis uses aqueous solutions at elevated temperatures and pressures in sealed vessels to crystallize minerals and nanomaterials. Conditions typically range from about 100 to 350°C under autogenous pressure, enabling growth of zeolites, oxides, and other crystalline phases with controlled morphologies.