magmatichydrothermal

Magmatic-hydrothermal systems are geological processes in which fluids released from cooling magmas move through surrounding rocks to transport and deposit metals, producing a wide range of hydrothermal ore deposits. As shallow-level intrusions crystallize, volatiles such as water, chlorine, sulfur, and carbon dioxide exsolve into a high-temperature, saline fluid. This fluid ascends via fractures and conduits in the crust. When pressure drops or the fluid mixes with cooler or meteoric waters, boiling and phase separation promote mineral precipitation and extensive alteration of the host rocks.

Fluid composition and metal transport: Magmatic fluids are rich in H2O, Cl, S, and CO2, with salinities often high enough to stabilize metal complexes. Metals such as copper, molybdenum, gold, silver, tin, and tungsten are transported in chloride- and sulfide-bearing complexes. The hottest portions occur near the intrusion, while cooler circulating fluids can deposit ore minerals at greater depths or shallower levels as they evolve chemically.

Alteration and deposit types: The interaction of fluids with host rocks causes characteristic alteration halos, such as potassic, phyllic (sericitic), and argillic zones around intrusions. Ore deposition occurs where fluids cool, decompress, or mix with meteoric waters, leading to sulfide precipitation. Principal magmatic-hydrothermal deposits include porphyry copper systems (large disseminated Cu sulfides with extensive alteration) and epithermal gold-silver deposits near the surface, often accompanied by skarns or tungsten-tin mineralization in certain settings.

Significance and exploration: Magmatic-hydrothermal processes underpin many world-class ore deposits, especially copper and gold. Exploration targets include intrusive bodies and their alteration halos, veined stockworks, fluid inclusions that record high temperatures and salinities, and geophysical signatures associated with high-discharge, high-temperature hydrothermal systems.