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Karasawa Mine

Itaga, Kanuma city, Tochigi pref., Japan


Pneumatolytic deposit

W-Bi pneumatolytic deposit associated with the early Paleocene (63 Ma) Karasawa Granodiorite intruded in the Late Jurassic (145 Ma) Kurohone-Kiryu Unit. The Karasawa granodiorite is S-type (Ilmenite-series). The Kurohone-Kiryu Unit corresponds to the Kanayama Unit of the Tamba-Mino-Ashio accretionary complex. Ages of sedimentary rocks were determined by radiolarians, and granodiorite by K-Ar radiometric dating of muscovite and biotite.

Karasawa Mine

Outcrop of the Karasawa Granodiorite, the host of a W-Bi pneumatolytic deposit. The silver-white muscovite was formed in the granodiorite by strong alteration. The brown part at the upper right is the ilmonite crust formed by weathering of sulfide minerals.

Reported Minerals

  • Bismuth
  • Joséite(Joseite)
  • Ferberite
  • Bismutite
  • Bismuthinite
  • Muscovite
  • Schorl

Mineral Assemblages

  • Quartz - Bismuth - Bismutite
  • Quartz - Joséite(Joseite)
  • Quartz - Ferberite
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