Xenothermal Deposit

Required Geological Setting

Caldera complexes

Occurrence

Combined vein-type deposit formed by overlapping three types of hydrothermal deposits: Low-T hydrothermal deposit by 100-250 degree hydrothermal fluid, Moderate-T hydrothermal deposit by 200-300 hydrothermal fluid, and High-T hydrothermal deposit by 300-500 hydrothermal fluid. These three types of hydrothermal fluid are originated from Acidic (Rhyolite) to Neutral (Dacite, Andesite) magmatic activities by volcanoes such as caldera complexes in volcanic island arc. High-T hydrothermal deposit is usually formed at the early stage, and it is followed by Moderate-T hydrothermal deposit and Low-T hydrothermal deposit along with cooling of the heat source. Rare minerals such as Sn-bearing sulfosalt minerals may be formed at the Moderate-T hydrothermal deposit and Low-T hydrothermal deposit formation stage as Moderate-T and low-T hydrothermal fluid reacts with minerals of High-T hydrothermal deposit. It is considered that xenothermal deposits are formed under large geothermal gradient such a circumstance as a high temperature heat source at shallow level.

Mineral Assemblages (Characteristic minerals)

Stannoidite, Franckeite, Ikunolite, Mawsonite