Banjo
Banjo, Tokigawa city, Hiki county, Saitama pref., Japan
Occurrence
Greenschist facies metamorphic rocks
Tuff in the Late Jurassic (150 Ma) to Early Cretaceous (130 Ma) accretionary complex subjected to Blueschist facies to Greenschist facies metamorphism as a part of the high-P Sambagawa metamorphic belt in the Late Cretaceous (70 Ma). The Sambagawa metamorphic rocks is considered that it has been near the ground surface since early Paleocene (65 Ma). Metamorphic age was determined by K-Ar radiometric dating of muscovite.
Outcrop of blue glaucophane schist of Sambagawa Metamorphic Rocks. The blue parts are glaucophane-bearing schist and the brown parts are Fe3+ stilpnomelane-bearing schist. White veins are quartz. There are two occurences of stilpnomelane: Stilpnomelane surrounding quartz-rich beds parallel to the schistosity and stilpnomelane veins vertical to the schistosity.
Reported Minerals
- Riebeckite
- Fe3+ rich Stilpnomelane
- Hematite
- Actinolite
Mineral Assemblages
- Glaucophane - Fe3+ rich Stilpnomelane - Quartz - Magnetite
- Quartz(Gangue) - Hematite
Localities
- Kami-Nagatoro (Stilpnomelane, High-P)
- Banjo (Glaucophane, High-P)
- Yamabuki creek (Hematite, High-P)
- Yoshimi (Zeolite, High-P)
- Kami-Suwa (Chloritoid, Middle-P)
- Takarayama Mine (Quartz, Middle-P)
Related Occurrences
- Albite-Epidote-hornfels facies
- Hornblende-hornfels facies
- Pyroxene-hornfels facies
- Sanidinite-hornfels facies
- Pumpellyite-Actinolite facies
- Blueschist facies
- Epidote-Amphibolite facies
- Eclogite facies
- Ultrahigh-pressure faices