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Momura

Momura, Nasu-Shiobara city, Tochigi pref., Japan

Synonym

Nasu-Roseki Mine, Kinomata River

Occurrence

Acidic metasomatic rocks of Pyrophyllite zone

B-rich pyrophyllite deposit formed by hydrothermal alteration of rhyolite and ryolitic tuff of the middle Miocene (15 Ma) Fukuwata Formation. The source of the hydrothermal fluid has not been specified but may have relation to Nasu Volcano, approximately 6 km apart from this locality. Ages of volcanic rocks were determined by stratigraphic works.

Momura

Outcrop of rhyolite or rhyolitic tuff of the Fukuwata Formation subjected to phyrophyllitization alteration. The white host is massive phyrophyllite. Bluish-gray spherules are radial aggregate of foitite and magnesiofoitite.

Momura

Outcrop of rhyolitic tuff of the Fukuwata Formation subjected to hematite-bearing hydrothermal alteration. The black parts are hematite associated with small amount of chlorite. The white host is altered ryolitic tuff, and its bedding planes are clear from the lower left to the lower right. Hematite beds are parallel to the bedding plane.

Reported Minerals

Mineral Assemblages

  • Pyrophyllite - Dumortierite
  • Pyrophyllite - Foitite - Magnesiofoitite - Quartz - Pyrite
  • Quartz - Hematite - Chlorite

Localities

Related Occurrences

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