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Komoto Mine

Kanaya, Niimi city, Okayama pref., Japan


Moderate-T hydrothermal skarn deposit

Skarn formed in the Permian Guadalupian (270 Ma) Northern Formation of the Atetsu Limestone Group in the Akiyoshi belt by contact metamorphism of the early Paleocene (62 Ma) Tottori Granite. The moderate temperature hydrothermal deposit associated with the skarn was formed by the early Paleocene (62 Ma) quartz porphyry dike. The Atetsu Limestone is composed of massive limestone, and considered as the marginal part of the reef on the seamount. The Tottori Granite and the quartz porphyry dike are I-type (Magnetite-series). The Tottori Granite and the quartz porphyry dike are considered as the center pluton and the dikes of the Paleocene Niimi Caldera Complex, respectively. The Tottori Granite and the quartz porphyry dike are in contacts with the Atetsu Limestone in this outcrop. The age of limestone was determined by coral fossils, granitic rocks by K-Ar and Rb-Sr radiometric dating.

Komoto Mine

Outcrop of a magnetite lode associated with skarn in the Northern Formation, Atetsu Limestone Group. The black vein from the upper left to the lower right is the magnetite lode. The white part at the lower left is weathered granite of the Tottori Granite, and the gray part at the upper right is marble, contact metamorphosed limestone. The width of magnetite lode is a few cm to tens cm. Various Cu secondary minerals were recovered in the open spaces of the magnetite bed. No variation in marble and granite was observed near the boundary of them.

Reported Minerals

  • Magnetite
  • Brochantite
  • Malachite
  • Aurichalcite
  • Tyrolite

Mineral Assemblages

  • Magnetite - Brochantite - Aurichalcite
  • Magnetite - Tyrolite
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