The Kamagamine "Roseki" mine, located in the western part of the Shokozan district, produces about 2, 500 tons of "Roseki" monthly, as a raw material for refractories, paper-clay, tiles and crucibles.
Terrigenous volcanic rocks of the Cretaceous age, interposing fine grained tuff, tuffaceous shale and shale, are distributed extensively around this mine.
The stratigraphic sequence is as follows :
Upper
Lower
Dikes: Quartz porphyry and porphyrite.
Granitic rocks: Biotite granite, granite porphyry and quartz-diorite porphyry.
Rhyolitic tuffs: Rhyolitic crystal tuff, lapilli tuff and welded tuff.
Dacitic tuffs: Dacitic tuff breccia, lapilli tuff, welded tuff, fine tuff, shale, tuffaceous shale and volcanic conglomerate.
Andesites : Andesite lava, andesitic tuff and dacite lava.
The hydrothermally altered zone, which is mainly composed of pyrophyllitized, silicified and sericitized rocks, occurs in the dacitic lava and dacitic tuff beds. The "Roseki" deposit, consisting of pyrophyllitized and silicified rocks, is concordant with the bedding of the wall-rocks, at the near surface part, while, at the deeper part, it sometimes occurs in pipe-and vein-like shapes cutting the bedding of wall-rocks of host formations.
The "Roseki" deposits are believed to. have been formed immediately after the deposition of the dacitic tuffs.
The main constituent minerals of "Roseki" clay are pyrophyllite, quartz and sericite, and accesories are diaspore, boehmite and kaolinite. The mineral assemblages of pyropyllite-quartz and pyrophyllite-sericite-quartz predominate, while meager occurrences of pyrite and hematite are noted in the clay.
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