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Waga-Sennin Mine

Sennin, Waga village, Kitakami city, Iwate pref., Japan


Tohira-Natsuhata Mine


Metasomatic skarn deposit

Skarn formed by the Late Cretaceous (99 Ma) Oarasawa granodiorite intruded in the Sennin metamorphic rocks. The skarn has been subjected to oxidative metasomatism by the dacite-rhyolite dikes associated with the middle Miocene (15 Ma) Oishi Formation. The oxidative metasomatism formed hematite deposit and replaced hedenbergite to actinolite. The Sennin metamorphic rocks consist of biotite gneiss, biotite schist, limestone, and biotite hornfels, and the protolith is probably the Permian (270 Ma) sediments. The Oarasawa granodiorite, heat source of the skarn is S-type (Ilmenite-series), and is less than 1 km apart from the deposit. The Oishi Formation is composed of neritic to bathyal andesite lava and pyroclastics, and unconformably overlies the granodiorite. Ages of sedimentary rocks were determined by microfossils.

Reported Minerals

Mineral Assemblages

  • Pyrite
  • Calcite - Hematite
  • Hedenbergite - Andradite - Tremolite - Calcite
  • Hedenbergite - Actinolite
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