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Manju Mine

Shimo-Terashima, Shioya city, Shioya county, Tochigi pref., Japan


Keikoku Mine


Moderate-T hydrothermal deposit

Moderate temperature hydrothermal deposit associated with rhyolite dikes in the middle Miocene (15 Ma) Tamanyu welded tuff member of the Kazami-Yamada Formation. The Kazami-Yamada Formation uncomformably overlies the early Paleocene (65 Ma) Okunikko Rhyolites. The Tamanyu welded tuff member was formed under shallow marine environment, and uncomformably underlies the Oya Formation. Ages were determined by microfossils and fission track dating of zircon.

Manju Mine

Amethyst vein in welded tuff. The white host with purple patches is welded tuff of the Tamanyu Welded Tuff Member, Kazami-Yamada Formation. The pale purple vein is amethyst associated with pale yellow clay at the boundary between the amethyst vein and the host.

Reported Minerals

Mineral Assemblages

  • Amethyst(Gangue) - Mottramite - Palygorskite
  • Quartz(Gangue) - Sphalerite
  • Quartz(Gangue) - Adularia


  • around 1750: The deposit was discoverd and mined.
  • 1900's: The deposit was mined several times.
  • Genkichi Okdada mined SiO2 ore.
  • 1964: Began to mine gold again. The ore was smelted at Tamafune mine, which locates at the north of Manju mine.
  • 1965: Mined ore is 110 t/day.
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