On the Geologic Structure, Volcanic Activity and Mineralization in the Kunitomi Mine Area

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Geologic history of the area, especially on the development of geologic structure, volcanic activity, sedimentary environment and metallic mineralization, is summarized here mainly based on drilling data with some geophysical measurements.<BR>Geology of the Kunitomi mine area consists of acid volcanic rocks of Miocene in age which are represented by tuff breccias, tuffs, lava domes, lava flows and dykes of dacitic in composition. The volcanic pile is covered by normal sediments of tuffaceous mudstone, sandstone and tuff with some dolerite lava flows.<BR>Geologic structure in this area is characterized by complicated pattern of sheared zones represented by two main systems of E-W and N-S directions. The pattern is thought to control the location of dacitic volcanic activities.<BR>Ore deposits of the mine are of so-called Kuroko type. The mineralization is classified into the following two types. The first shows very close genetical relation with eruption of dacite-A and is characterized by the development of bedded ore body with massive Kuroko ore on the top of dacitic lava dome, as No. 3, 4, 6 or 7 Ore Body. The other is dissiminated or stock-worked deposit mainly in the brecciated part of lava dome of dacite-B as No. 5 or Fuden Ore Body.
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