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Shibusawa Mine

Shibusawa, Hadano city, Kanagawa pref., Japan


Intermediate acidic metasomatic rocks of low-T silicified zone

Smectitization deposit formed by hydrothermal alteration of tuff in the middle Miocene (15 Ma) Oyama Subgroup, the Tanzawa Group. The Oyama Subgroup is mainly composed of basaltic to andesitc lava and pyroclastics. The Tanzawa Group is considered as the accreted Izu island arc. Gypsum and pyrite was formed in the alteration zone. Ages of sedimentary rocks were determined by microfossiles.

Shibusawa Mine

Outcrop of tuff of the Oyama Subgroup, Tanzawa Group subjected to smectitization alteration. The grayish-green block is altered tuff, and is hard as it was silicified. White soft parts around them are clay rich zones. Fine yellow pyrite crystals are included everywhere in this outcrop. Reddish parts are abundant in fine crystals of rutile.

Reported Minerals

  • Gypsum
  • Pyrite
  • Rutile
  • Beta quartz

Mineral Assemblages

  • Gypsum - Pyrite
  • Quartz - Rutile


  • 1935: Began to mine gypsum and pyrite.
  • 1948: The mine was closed.


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