Yoji Mine
Yoji, Sakuho city, Minami-Saku county, Nagano pref., japan
Closed to collecting
Occurrence
Acidic metasomatic rocks of Pyrophyllite zone
Pyrophyllite deposit formed in the late Miocene (11 Ma) by hydrothermal alteration by the middle Miocene (14 Ma) Moraisan Granodiorite of sediments of the early Miocene (17 Ma) Uchiyama Formation and the Early Jurassic (175 Ma) Northern Chichibu accretionary complex. The Uchiyama Foramtion unconformably overlies the Northern Chichibu accretionary complex. The sediments of the Northern Chichibu accretionary complex in this locality is probably the Sumaizuku Unit or the Kamiyoshida Unit. The Moraisan Granodiorite is I-type (Magnetite-series). Approximately 2 km apart from the Moraisan Granodiorite, the heat source. Ages of sedimentary rocks were determined by radiolarians and microfossils, granodiorite by K-Ar radiometric dating of biotite, and pyrophyllite deposit by K-Ar radiometric dating of whole rock.
Reported Minerals
- Rutile
- Topaz
- Zunyite
- Pyrophyllite
- Florencite
- Quartz
Mineral Assemblage
- Pyrophyllite - Zunyite
Localities
- Momura (B rich)
- Kyonosawa (B rich)
- Shima Mine (B rich)
- Hinomaru-Nako Mine (P rich)
- Yoji Mine (Al,F rich)
- Shin-yo Mine (Al,F rich)
- Mount Kawate (Zunyite)
- Mount Shoko (Al rich)
- Nekoyama (Al rich)
- Mitsuishi (Al rich)
- Isshiki Mine (Al rich)
- Toho Mine (Al rich)
- Hongo Mine (Sulfide deposit)
- Masutomi Mine (Sulfide deposit)
Related Occurrences
- Halloysite zone (Alunite zone, Argillized zone)
- Kaolinite zone (Alunite zone, Argillized zone)
- Minamiite-Alunite zone (Alunite zone)
- Pyrophyllite zone
- Smectite zone (Argillized zone)
- Interstratified mineral zone (Argillized zone)
- Illite-Chlorite zone (Propylite zone)
- Epidote-Actinolite zone
- Stilbite-Mordenite zone (Zeolite zone)
- Heulandite-Analcime zone (Zeolite zone)
- Laumontite-Albite zone (Zeolite z., Propylite z.)
- Wairakite-Albite zone (Zeolite zone)