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Yunishi River

Yunishigawa, Nikko city, Tochigi pref., Japan


Meteoric oxidation zone of moderate-T hydrothermal deposit

Oxidation zone of the moderate temperature hydrothermal deposit associated with rhyolitic tuff of the middle Miocene (12 Ma) Yunishigawa Rhyolites. The Yunishigawa Rhyolites unconformably overlies Kuriyama Formation and Tadamigawa Granites. The Yunishigawa Rhyolites are considered as caldera fill of the Miocene Yunishigawa Caldera. There are opinions that Kuriyama Formation is a part of Kurohone-Kiryu Complex of Ashio Belt.

Yunishi River

Outcrop of oxidation zon of Cu lode. The massive pale brown host is rhyolitic tuff of the Yunishigawa Rhyolites. The black vein from the upper righ to the lower left is the lode with quartz gangue. Cuprite and pyrite are in the quartz vein.

Reported Minerals

  • Malacite
  • Cuprite
  • Langite
  • Pyrite

Mineral Assemblages

  • Quartz - Cuprite - Pyrite
  • Cuprite - Malacite - Langite
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