Oashi Mine
Kusagyu, Kanuma city, Tochigi pref., Japan
Occurrence
Hornblende-hornfels facies bedded manganese deposit
Chert-hosted bedded manganese deposit in the Late Triassic (220 Ma) to Early Jurassic (175 Ma) chert block of the Late Jurassic (145 Ma) Kurohone-Kiryu Unit. The deposit has been subjected to Hornblende-hornfels facies contact metamorphism by the Kanoiri granodiorite in the Late Cretaceous (83 Ma). Slate near this deposit was metamorphosed to Cordierite-bearing hornfels. The Kurohone-Kiryu Unit corresponds to the Kanayama Unit of the Tamba-Mino-Ashio accretionary complex. The Kanoiri granodiorite is S-type (Ilmenite-series). Approximately 2 km apart from the Kanoiri granodiorite, the heat source. Ages of sedimentary rocks were determined by radiolarians, and granodiorite by K-Ar radiometric dating of biotite.
Reported Minerals
- Spessartine
- Helvine
- Rhodonite
- Manganocummingtonite
Mineral Assemblages
- Rhodonite - Manganocummingtonite - Spessartine
- Rhodonite - Quartz - Helvite
Localities
- Oashi Mine (Helvite)
- Hagidaira Mine (W, Bi, Te)
- Takanosu Mine (Axinite-(Mn))
- Higashizawa Mine (Axinite-(Mn))
Related Occurrences
- Bedded Mn (Diagenesis)
- Bedded Mn (Low-T zeolite facies)
- Bedded Mn (High-T zeolite facies)
- Bedded Mn (Prehnite-Pumpellyite facies)
- Bedded Mn (Pumpellyite-Actinolite facies)
- Bedded Mn (Greenschist facies)
- Bedded Mn (Epidote-Amphibolite facies)
- Bedded Mn (Amphibolite facies)
- Bedded Mn (Albite-Epidote-hornfels facies)
- Bedded Mn (Hornblende-hornfels facies)
- Bedded Mn (Pyroxene-hornfels facies)
- Ocean-floor Mn Nodule
- Ocean-floor Mn Crust
- Bedded Mn (Meteoric supergene)
- Bedded Mn (Marine supergene)