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Iwaisawa Mine

Kitagawa, Hanno city, Saitama pref., Japan


Pumpellyite-Actinolite facies bedded manganese deposit

Chert-hosted bedded manganese deposit in a chert block of the Early Cretaceous (130 Ma) Kashiwagi unit, a member of the Northern Chichibu accretionary complex. The kashiwagi unit has been subjected to Pumpellyite-Actinolite facies metamorphism as a low grade part of the Sambagawa metamorphic belt in the Late Cretaceous (100 Ma). The age of chert is Permian Guadalupian (270 Ma) or Late Jurassic (145 Ma). One of type localitis of Taneyamalite. Ages of sedimentary rocks were determined by radiolarians, and metamorphic age by K-Ar or Ar-Ar radiometric dating of muscovite.

Iwaisawa Mine

Outcrop at the entrance of an adit. The adit is opened on the outcrop of brown bedded chert of the Kashiwagi Unit. Its surface turns black by oxidation of manganese in the deposit, which is the typical feature of the manganese deposit.

Reported Minerals

Mineral Assemblages

  • Braunite - Quartz - Hematite - Piemontite
  • Quartz - Hematite - Caryopilite - Rhodochrosite - Pyrite
  • Quartz - Caryopilite - Cinnabar
  • Caryopilite - Quartz - Rhodochrosite - Taneyamalite
  • Caryopilite - Quartz - Rhodochrosite - Bannisterite
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