TrekGEO > Mineral Trail > Chugoku region > Yamaguchi pref. > Naganobori Mine, Eboshi Heading

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Naganobori Mine, Eboshi Heading

Naganobori, Mito village, Mine city, Yamaguchi pref., Japan


High-T hydrothermal skarn deposit

Skarn formed by the Late Cretaceous (85 Ma) granite porphyry intruded in the Permian Guadalupian (270 Ma) limestone of the Akiyoshi Limestone Group, a member of the Akiyoshi accretionary complex. Formation of the high temperature hydrothermal deposit associated with skarn may be related to the Late Cretaceous (88 Ma) Sasanami Caldera Complex approximately 5 km apart from this locality. The granite porphyry is S-type (Ilmenite-series). Approximately 1 km apart from the granite porphyry, heat source. The Akiyoshi Limestone Group is considered as the Carboniferous to Permian reef limetone, reef on the summit of the seamount in the Panthalassa (Panthalassic Ocean). Ages of limestone was determined by microfossils and coral fossils, Caldera Complex by Rb-Sr whole rock isochron age.

Reported Minerals

Mineral Assemblages

  • Hedenbergite - Grossular - Cobaltite - Erythrite
  • Hedenbergite - Quartz - Babingtonite
  • Hedenbergite - Bornite
  • Chrysocolla - Cuprite
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