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Moderate-T Hydrothermal Deposit

Chemical Process (Liquid-phase Growth) - Open system under ground

Synonym

Mesothermal deposit, Moderate-T hydrothermal vein deposit, Moderate-T hydrothermal ore deposit

Index Minerals

Chalcopyrite, Galena, Sphalerite, Pyrite

Required Geological Setting

Caldera complexes

Associated metasomatic zones

Minamiite-Alunite zone, High-T silicified zone, Illite-Chlorite zone

Occurrence

Vein-type deposit formed by 200-300 degree hydrothermal fluid originated from Acidic (Rhyolite) to Neutral (Dacite, Andesite) magmatic activities by volcanoes such as caldera complexes in 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. Typical elements concentrated are Cu, Pb, Zn, and/or As. 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 high-T hydrothermal deposit in the deeper level, and to Low-T hydrothermal deposit or Hydrothermal Au-Ag deposit in the shallower level.

Moderate-T Hydrothermal Deposit

Distribution of Moderate-T Hydrothermal Deposits described in this site. Green dots are As-free deposits and red dots are As-bearing deposits. Yellow lines are volcanic fronts.

Mineral Assemblages (Ore)

Chalcopyrite, Pyrite, Galena, Sphalerite, Arsenopyrite

Mineral Assemblages (Gangue)

Quartz, Rhodochrosite, Calcite, Dolomite, Siderite, Barite, Kaolinite

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