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Akatani Mine

Higashi-Akatani, Shibata city, Niigata pref., Japan


Metasomatic skarn deposit

Skarn formed by the middle Paleocene (60 Ma) granodiorite intruded in the Tamba-Mino-Ashio accretionary complex. The moderate temperature hydrothermal deposit in the skarn was formed by dacite dikes of the early Miocene (21 Ma) Mikawa Formation, and subjected to oxidative metasomatism by the dikes. The oxidative metasomatism formed hematite deposit and replaced hedenbergite to actinolite. The protolith of the skarn is considered as the Permian (270 Ma) limestone of the Early Jurassic (180 Ma) Funafuseyama Unit from the lithology. The granodiorite, heat source of the skarn is S-type (Ilmenite-series), and is less than 1 km apart from the deposit. The sulfide deposits are in contact with the dacite dikes. The Mikawa Formation is composed of continental andesite-rhyolite lava and pyroclastic rocks, and unconformably overlies the granodiorite. Ages of sedimentary rocks were determined by microfossils.

Reported Minerals

Mineral Assemblages

  • Hematite - Calcite
  • Hedenbergite - Sphalerite - Pyrite
  • Hedenbergite - Actinolite
  • Hedenbergite - Andradite - Calcite
  • Hematite - Green Quartz


  • 1780's: The deposit was discovered.
  • 1898: Started to mine.
  • 1998: Closed.
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