Ore deposit type: Magmatic-hydrothermal, high-sulphidation (HS) epithermal
Provenance: Chelopech Mine, Bulgaria
Description: “Vuggy silica” alteration, made of highly porous microcrystalline silica (gray), in which part of the vugs are filled by white clay (probably kaolinite). The sample is cut by fine pyrite veinlets. “Vuggy silica” alteration is typical of high-sulphidation epithermal Au deposits and is the result of reactions with very acidic fluids of dominantly magmatic origin.