Hot Spring Deposit

Index Minerals

Opal

Required Geological Setting

Island arc volcanoes

Associated metasomatic zones

Halloysite zone, Cristobalite zone, Smectite zone

Occurrence

Deposit formed near the ground surface by hydrothermal fluid less than 50 degree originated from volcanoes associated with magmatic activities of volcanic island arc. Origin of hydrothermal fluid is magmatic water from magma, meteoric water, and/or seawater. Meteoric water and seawter are circulated by heat of magma. This type of deposits is formed at very shallow circumstances such as ground surface or seafloor whereas Hydrothermal deposit along fault is formed at deep circumstances along undergroud faults by the same hydrothermal fluid less than 50 degree. Typical elements concentrated are Si, Ca, and/or Mn. Minerals deposited depend on characteristics of each hydrothermal fluid such as magmatic water, meteoric water, and/or seawater, and also on geological settings mixturing these fluids. Host of deposits are volcanic products or basements of volcanoes. The deposit may shift to Hydrothermal Au-Ag deposit in the shallower level.

Mineral Assemblages

Opal, Quartz, Calcite