Iwaisawa Mine
Kitagawa, Hanno city, Saitama pref., Japan
Occurrence
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.
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
- Cinnabar
- Pyrite
- Hematite
- Rhodochrosite
- Manganite
- Calcite
- Braunite
- Piemontite
- Caryopilite
- Bannisterite
- Taneyamalite
- Pyrolusite?
Mineral Assemblages
- Braunite - Quartz - Hematite - Piemontite
- Quartz - Hematite - Caryopilite - Rhodochrosite - Pyrite
- Quartz - Caryopilite - Cinnabar
- Caryopilite - Quartz - Rhodochrosite - Taneyamalite
- Caryopilite - Quartz - Rhodochrosite - Bannisterite
Localities
- Omiya Mine (Hausmannite)
- Iwaisawa Mine (Braunite)
- Hinozawa Mine (Rhodochrosite)
Related Occurrences
- Bedded Mn (Diagenesis)
- Bedded Mn (Low-T zeolite facies)
- Bedded Mn (High-T zeolite facies)
- Bedded Mn (Prehnite-Pumpellyite facies)
- Bedded Mn (Pumpellyite-Actinolite facies)
- Bedded Mn (Greenschist facies)
- Bedded Mn (Epidote-Amphibolite facies)
- Bedded Mn (Amphibolite facies)
- Bedded Mn (Albite-Epidote-hornfels facies)
- Bedded Mn (Hornblende-hornfels facies)
- Bedded Mn (Pyroxene-hornfels facies)