Hinomaru-Nako Mine
Kiyo, Abu city, Abu county, Yamaguchi pref., japan
Occurrence
Acidic metasomatic rocks of Pyrophyllite zone
P-rich pyrophyllite deposit formed by hydrothermal alteration of rhyolitic tuff of the Late Cretaceous (87 Ma) Mitsugatake Rhyolites in the Fukuga Formation of the Abu Group. The Mitsugatake Rhyolites is considered as a member of the middle Cretaceous Caldera Complex, and associated with welded tuff, lacustrine sediments, and granite. The age of rhyolite was determined by Rb-Sr whole rock isochron age.
Outcrop of rhyolitictuff of the Fukuga Formation. The massive grayish-white outcrop is composed of andalusite-bearing pyrophyllite. Surface of the outcrop was covered with thin crust of brown limonite, the weathing product of pyrite. Andalusite crystals were grown in the open space of the massive pyrophyllite. Interstics of andalusite was filled with pyrite, and pyrite was dissolved in many cases by weathing.
Reported Minerals
- Pyrite
- Scorzalite
- Andalusite
- Augelite
- Trolleite
- Svanergite
- Florencite
- Diadochite
- Pyrophyllite
Mineral Assemblages
- Pyrophyllite - Quartz - Andalusite - Pyrite
- Pyrophyllite - Scorzalite - Augelite - Pyrite