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Matsunaga Mine

Hongo, Tokigawa city, Hiki county, Saitama pref., Japan


Greenschist facies serpentinite

Talc schist and Tremolite schist in the Late Jurassic (150 Ma) to Early Cretaceous (130 Ma) accretionary complex subjected to Greenschist facies metamorphism as a part of the high-P Sambagawa metamorphic belt in the Late Cretaceous (70 Ma). The Sambagawa metamorphic rocks is considered that it has been near the ground surface since early Paleocene (65 Ma). Formation of talc can be explained by the reaction of serpentinite with quartz in surrounding sedimentary rocks. The origin of this serpentinite block is considered as sedimentary serpentinite mélange from serpentinite seamounts at the fore-arc slope. Metamorphic age was determined by K-Ar radiometric dating of muscovite.

Matsunaga Mine

Outcrop of tremolite schist of Sambagawa Metamorphic Rocks. Talc and tremolite were mined. This outcrop is mainly composed of dark gray to dark brown pelitic schist. The white bed at the left end is white tremolite-rich schist. The scale coin is at the boundary between tremolite schist and pelitic schist. Formation process of carbonate-absent talc schist can be explained by the reaction of serpentinite with quartz as follows:

Mg3Si2O5(OH)4 (Serpentine) + 4SiO2 >> Mg3Si4O10(OH)2 (Talc) + H2O

Reported Minerals

  • Tremolite
  • Talc
  • Chlorite
  • Stilpnomelane

Mineral Assemblages

  • Quartz(Host) - Stilpnomelane
  • Tremolite
  • Talc
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