Hydrothermal Au-Ag Deposit

Synonym

Telethermal Deposit, Low-T Hydrothermal Vein Deposit, Low-T Hydrothermal Ore Deposit

Index Minerals

Electrum, Silver

Required Geological Setting

Caldera complexes

Associated metasomatic zones

Halloysite zone, Cristobalite zone, Smectite zone, Stilbite-Mordenite zone

Occurrence

Vein-type deposit formed by 50-100 degree hydrothermal fluid originated from Acidic (Rhyolite), Neutral (Dacite, Andesite), or Alkaline (Basalt) magmatic activities by volcanoes such as caldera complexes in volcanic island arc. Origin of hydrothermal fluid is meteoric water and/or seawater, which are circulated by heat of magma. This type of deposits is formed at shallow circumstances whereas Hydrothermal Au-Bi-Te deposits are formed at deep circumstances by the same 50-100 degree hydrothermal fluid. Typical elements concentrated are Au, Ag, and/or Te. Host of deposits are volcanic products or basements of volcanoes. Mineral assemblages depends on geological settings of deposits; terrestrial volcano, sumarine volcano, and host rock types in which hydrothermal fluid circulated. The deposit may shift to Moderately low-T hydrothermal deposit or Moderate-T hydrothermal deposit in the deeper level, and to Hot spring deposit in the shallower level.

Mineral Assemblages (Ore)

Gold, Electrum, Silver, Acanthite, Pyrite

Mineral Assemblages (Gangue)

Quartz (Acidic-Neutral), Mordenite (Alkaline), Adularia, Calcite, Truscottite