Shima Mine
Shima, Nakanojo city, Agatsuma county, Gunma pref., Japan
Occurrence
Acidic metasomatic rocks of Pyrophyllite zone
Pyrophyllite deposit formed in andesitic-rhyolitic radial dikes and quartz diorite by hydrothermal alteration of the late Miocene (8 Ma) Shima Quartz Diorite. The radial dikes and quartz diorite were intruded in the middle Miocene (13 Ma) Daido Formation. The radial dikes, quartz diorite, and the Shima Quartz Diorite are probably members of the late Miocene (8 Ma) caldera complex associated with the dacitic Kirigakubo welded tuff. The Daido Formation unconformably overlies the middle Miocene (13 Ma) Akaya Formation, and unconformably underlies the late Miocene (8 Ma) Takadayama Formation. The Takadayama Foramtion is composed of andesite lava and pyroclastics deposited in a continental environment. The Shima Quartz Diorite is I-type (Magnetite-series). Approximately 1 km apart from the Shima Quartz Diorite, the heat source. The age of sedimentary rocks were determined by bivalvia fossils.
Outcrop of pyrophyllite deposit formed by hydrothermal alteration of quartz porphyry, a part of radial dikes. The white parts are pyrophyllite with residue quartz grains of quartz porphyry. Black parts are dirt on the surface.
Reported Minerals
- Pyrophyllite
- Rutile
- Titanite
- Pyrite
- Hematite
- Dumortierite
Mineral Assemblage
- Pyrophyllite - Quartz - Rutile - Titanite
- Hematite
- Pyrophyllite - Dumortierite
History
- around 1953: Mined in an adit.
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)