Yashio Mine
Onishi, Fujioka city, Gunma pref., Japan
Occurrence
Greenschist facies serpentinite
Cr deposit associated with serpentinite in the Late Jurassic (150 Ma) to Early Cretaceous (130 Ma) accretionary complex subjected to Greenschist facies metamorphism as a part of the high-P Sambagawa metamorphic belt in the Late Cretaceous (70 Ma). The Sambagawa metamorphic rocks are considered that it has been near the ground surface since early Paleocene (65 Ma). The origin of this serpentinite block is considered as sedimentary serpentinite mélange from serpentinite seamounts at the fore-arc slope. Metamorphic age was determined by K-Ar radiometric dating of muscovite.
Reported Minerals
- Aragonite
- Hydromagnesite
- Chromite
- Kämmererite
- Coalingite?
- Albite
Mineral Assemblages
- Serpentine - Chromite - Kämmererite
- Serpentine - Coalingite
- Serpentine - Hydromagnesite - Aragonite
Localities
- Orihara (Talc, High-P)
- Matsunaga Mine (Talc, High-P)
- Shiraki (Pectolite, High-P)
- Arai (Diopside, High-P)
- Osaka (Ophicalcite, High-P)
- Miyazawa (Dolomite, High-P)
- Onara (Fe-Ni, High-P)
- Yashio mine (Fe-Cr, High-P)