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Toi Mine

Toi, Izu city, Shizuoka pref., Japan


Toi Gold Mine, Izu Silver Mine


Hydrothermal Au-Ag deposit

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.

Toi Mine

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


  • 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.
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