TrekGEO > Mineral Trail > Kanto region > Ibaraki pref. > Ishibaiyama

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Motodo, Kasama city, Ibaraki pref., Japan


Dolomite skarn

Dolomite skarn deposit formed in the dolomite-limestone block of the Late Jurassic (150 Ma) Kasama Unit of an accretionary complex, the Yamizo Group. The dolomite-limestone block has been subjected to contact metamorphism by the early Paleocene (65 Ma) Inada Granite. The Kasama Unit corresponds to the Yabuhara Unit of the Tamba-Mino-Ashio accretionary complex. The Inada Granite is S-type (Ilmenite-series). Approximately 1 km apart from the Inada Granite, the heat source. There are minerals formed by the low temperature hydrothermal activity at the late stage of skarnization. Ages of sedimentary rocks were determined by radiolarians, and granite by K-Ar radiometric dating.


Outcrop of dolomite skarn in the Kasama Unit. The gray basement is recrystallized dolomite. White crusts on the surface is sepiolite. The surface of this outcrop is along the sepiolite vein. Sepiolite veins were formed by low temperature hydrothermal activity along fissures at the late stage of skarn formation.

Reported Minerals

  • Calcite
  • Dolomite
  • Wollastonite
  • Diopside
  • Tremolite
  • Forsterite
  • Serpentine
  • Sepiolite
  • Phlogopite
  • Spinel
  • Clinohumite
  • Dravite

Mineral Assemblages

  • Calcite - Dolomite - Sepiolite
  • Calcite - Wollastonite - Quartz
  • Dolomite - Diopside - Tremolite
  • Dolomite - Forsterite - Serpentine - Clinohumite
  • Hornfels(Host) - Dravite
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