Ryushima Mine
Azumi, Matsumoto city, Nagano pref., Japan
Occurrence
Moderate-T hydrothermal deposit
Mn-dominant moderate temperature hydrothermal deposit formed by the Late Cretaceous (69 Ma) Nagawa Granite in the Early Cretaceous (140 Ma) Shimashima Unit. The Shimashima Unit corresponds to the Kanayama Unit of the Tamba-Mino-Ashio accretionary complex. The Nagawa Granite is S-type (Ilmenite-series). Approximately 2.5 km apart from the Nagawa Granite, the heat source. Ages of sedimentary rocks were determined by radiolarians, and granite by K-Ar radiometric dating.
Outcrop of a kutnahorite vein network in slate of the Shimashima Unit. The pale pink network is veins of massive kutnahorite, and euhedral crystals are in open spaces of the vein. Black host is silicified slate. Brownish-black crusts on the outcrop surface at the upper left and the upper right are pyrolusite formed by weathering of kutnahorite.
Reported Minerals
- Kutnohorite
- Pyrolusite
- Pyrite
- Sphalerite
- Galena
Mineral Assemblages
- Kutnohorite - Pyrolusite
- Kutnohorite - Sphalerite - Galena - Pyrite
History
- 1899: Mr. Fukazawa, a local person, found the deposit.
- 1921: Mr. Amano from Osaka started to mine manganese ore.
- 1927: Restarted to mine 10-50 t/month ore.
Localities
- Kisan-mori Mine (Cu-Pb-Zn)
- Mikawa Mine (Cu-Pb-Zn, Siderite)
- Takami Mine (Cu-Pb-Zn)
- Yunosawa Mine (Pb-Zn)
- Okuto Mine (Pb-Zn)
- Arakawa Mine (Cu-Zn)
- Osarizawa Mine (Cu-Zn)
- Sayama Mine (Cu-Zn)
- Washinosu Mine (Cu-Zn)
- Yashu Mine (Cu)
- Takaneyama Mine (Cu-Zn-Mn)
- Kawazu Mine (Zn-Au-Te-Mn)
- Manju Mine (Zn)
- Mount Nesugata (Mn oxide)
- Ryushima Mine (Mn carbonate)