広島県矢野勝光山パイロフィライト鉱床の生成環境 : 火山層序と熱水変質作用

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The Yano-Shokozan pyrophyllite deposits occur in acidic volcanic rocks of the late Cretaceous age. Dacitic to rhyolitic rocks are widely distributed in the Yano-Shokozan area, and those rocks are divided into by three units as Lower, Middle, and Upper units which can be correlated to the Takada rhyolitic rocks. The Lower unit mainly consists of acidic tuff with intercalated lithic lapilli, pumice and thinly bedded tuff in ascending order. The Middle unit is further divided into two layers as "a" and "b" ; the former is composed of acidic lava, vent lapilli tuff, acdic tuff, and spherulitic tuff, the latter is made up of medium bedded tuff, acidic tuff with intercalation of lapilli tuff and fine tuff, spherulitic lava and thinly bedded tuff. The Upper unit, consists of alternative shale and tuffaceous sandstone, and rhyolitic tuff. The Middle unit is about 270 meters thick and has undergone extensive hydrothermal alteration. Two horizons of pyrophyllite deposits were recognized in this Unit by volcano-stratigraphic study. The main orebodies of the Yano-Shokozan Mine are the Nishiyama, Nishiyama-higashi. Nishiyama-minami, Takinotani, Hagiwaraguchi, Sashikawa, and Nakayama orebodies. The first three occur in the pyroclastic rocks of the "a" layer of Middle unit, while the last four occur m lacustrine sediments of the "b" layer of the Middle unit. Pyrophyllite deposits which are intimately related to bedded tuff of lacustrine origin. They tend to occur as the layers just above the bedded tuff and as the layers intercalated between two bedded tuffs.
日本粘土学会の論文
1996-09-13

広島県矢野勝光山パイロフィライト鉱床の生成環境 : 火山層序と熱水変質作用

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