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Mount Nesugata

Shimoda city, Shizuoka pref., Japan


Mount Manzo


Moderate-T hydrothermal deposit

Moderate temperature hydrothermal deposit in rhyolite of the middle Miocene (13 Ma) Yugashima Group. The ryolite was intruded in the middle Miocene (15 Ma) Shirahama Group. This ryolite contains 50-70% K-feldspar, and was mined as the K ore of 6-8% K2O. Ages were determined by microfossils.

Mount Nesugata

Outcrop of rhyolite of the Yugashima Group associated with hydrothermal veins of manganese dioxide. The host is purple rhyolite. The rhyolite looks purple as it includes fine hematite crystals. The dark gray veins are mainly composed of ramsdellite. The thin black bed at the boundary between the host rhyolite and the ramsdelite vein is pyrolusite. It seems that ramsdellite filled the open spaces of rhyolite breccia.

Reported Minerals

Mineral Assemblages

  • Ramsdellite - Pyrolusite
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