Toi Mine
Toi, Izu city, Shizuoka pref., Japan
Synonym
Toi Gold Mine, Izu Silver Mine
Occurrence
Low temperature hydrothermal Au-Ag deposit in andesitic and basaltic pyroclastic rocks of the late Miocene (7.5 Ma) Yugashima Group. The pyroclastic rocks, the host of the deposit, is calc-alkaline to tholeiitic, and have been subjected to strong propylitization alteration. The Yugashima Group unconformably underlies the Shirahama Group. Ages of volcanic rocks were determined by K-Ar radiometric dating and fission track dating of zircon.
Outcrop of oxidation zone of the Au deposit in andesitic tuff breccia of the Yugashima Group. The reddish-brown crust on the surface is limonite formed by oxidation of pyrite in the deposit. This is called as "Gossan", and is a good trace to find deposits. The white parts are quartz, gangue of the deposit. The light brown basement is propylitized andesitic tuff breccia.
Reported Minerals
- Gold
- Pyrite
- Truscottite
Mineral Assemblages
- Quartz (Gangue) - Gold
History
- 750's: Gold nuggets were mined as the placer deposit.
- 1577: The deposit was discovered and started to mine under the name of Tensho mine.
- 1625: Tensho mine was closed.
- 1685: Started to mine for a few years.
- 1854: The mine was buried by the Ansei-Tokai Earthquake.
- 1903: Started to mine the deposit.
- 1906: Keijiro Hasegawa renamed to Toi mine and started to mine.
- 1945: The mine was closed.
- 1949: Started to mine the northern parts of the deposit.
- 1965: The mine was closed.
- 1972: Opened as an industrial heritage.
Localities
- Shobusawa (Izu Peninsula)
- Seikoshi Mine (Izu Peninsula)
- Toi Mine (Izu Peninsula)
- Tensho Mine (Izu Peninsula)
- Takatama Mine (Gold/Silver deposit)
- Nishizawa Mine (silver sulfides)
- Nebasawa Mine (Gold/Silver deposit)
- Hishikari Mine (Kyusyu Island)