Okura Mine
Okura, Minami-Uonuma city, Niigata pref., Japan
Occurrence
Hydrothermally altered magmatic deposit formed by granite intruded in a serpentinite block associated with Mizunashigawa Metamorphic Rocks of Joetsu Belt. The deposit is approximately 1 km apart from the granite body. The protolish of Mizunashigawa Metamorphic Rocks is the accretionary complex probably older than Permian. Mizunashigawa Metamorphic Rocks have been subjected to Greenshist facies metamorphism. Mizunashigawa Metamorphic Rocks corresponds to Renge Metamorphic Rocks.
Outcrop of oxidation zone of the pyrrhotite-bearing serpentinite associated with Mizunashigawa Metamorphic Rocks. The brown cliff of this photograph is composed of limonite only. There are also Pb-Zn moderate-T hydrothermal deposits. Pyrrhotite and gersdorffite may be formed by combining S in hydrothermal fluid with Fe and Ni released from peridotite during serpentinization process.
Reported Minerals
- Pyrrhotite
- Sphalerite
- Pyrite
- Gersdorffite
- Limonite
- Goethite
- Hematite
- Epidote
- Phlogopite
- Talc
- Serpentine
- Orthopyroxene(Bastite)
- Hornblende
Mineral Assemblages
- Serpentine - Orthopyroxene(Bastite) - Pyrrhotite
- Serpentine - Gersdorffite
- Goethite - Hematite - Quartz
- Quartz - Talc - Pyrrhotite
- Quartz - Sphalerite - Galena
- Amphibolite(Host) - hornblende
History
- 1920's: There is a record that this deposit was mined.
- 1943: Mining limonite was started.
- 1945-1951: Mining was most active.
Localities
- Okura Mine (Serpentinite, Limonite)
- Yokokawa river (Serpentinite, Pyrrhotite)