highsulfidation

High-sulfidation refers to a style of epithermal hydrothermal ore deposits formed by hot, acidic sulfate-rich fluids of magmatic origin at shallow crustal levels, usually associated with volcanic arcs. The term distinguishes these systems from low-sulfidation epithermal deposits, which form from less acidic fluids at similar depths.

The hallmark of high-sulfidation systems is pervasive acid-sulfate alteration, typically of advanced argillic character. Alteration minerals include alunite, natroalunite, jarosite, kaolinite, dickite, and pyrophyllite, often arranged in an overprinting sequence with silica-rich zones. The sulfide mineralization commonly comprises enargite, tennantite, pyrite, chalcopyrite, and bornite, with gold frequently associated with copper sulfides or appearing as native gold or electrum in distal halos. The alteration and mineralization together create a characteristic mineralogical halo that may include a silica cap and an outer, argillic alteration zone.

Geologically, high-sulfidation deposits form in volcanic or post-volcanic settings where magmatic intrusions drive vapor-dominated systems. Fluids ascend, boil, and oxidize, producing acidic sulfate solutions that alter rocks and deposit sulfides near the hydrothermal conduit. The ore body is usually near the surface, often within a few hundred meters to about two kilometers depth, and may be overlain by a supergene oxidation zone.

Economically, high-sulfidation deposits can host substantial gold and copper resources, typically as disseminated sulfides and stockwork networks. Exploration emphasizes recognizing alteration halos (notably alunite and jarosite), vuggy silica zones, and characteristic sulfide assemblages, with global distribution concentrated in tectonically active volcanic arc regions.