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Mount Tanakami

Tanakami-Mori village, Otsu city, Shiga pref., Japan


REE Miarolitic pegmatite

NYF family pagmatite in the Late Cretaceous (70 Ma) Tanakami Granite intruded in the Early Cretaceous (130 Ma) Kanayama Unit, a member of the Tamba-Mino-Ashio accretionary complex. The Tanakami Granite is S-type and Ilmenite-series. The Tanakami Granite is considered as the southern member of the Biwako Caldera, a huge ring complex measuring 50 km in diameter. Ages of sedimentary rocks were determined by radiolarians, and granite by K-Ar radiometric dating of biotite and Rb-Sr whole rock isochron age.

Mount Tanakami

A huge pocket in the pegmatite of the Tanakami Granite. The white outcrop in this photograph is weathered granite. This pocket, "Nakazawa pocket", is one of the most famous pegmatite pockets in Japan. Nakazawa pocket was named after Mr. Kazuo Nakazawa who found this pocket first in 1974. The size of this pocket is 160x70x650 cm.

Reported Minerals

Mineral Assemblages

  • Quartz - Feldspar - Zinnwaldite - Masutomilite
  • Quartz - Feldspar - Topaz - Zinnwaldite
  • Quartz - Feldspar - Dravite
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