Geology of the Ooe-Inakuraishi Mine
with Special Reference to the Vein System
1974 Volume 24 Issue 124 Pages 119-128
Details
1974 Volume 24 Issue 124 Pages 119-128
The Ooe-Inakuraishi mine, located in Shakotan Peninsula, southwestern part of Hokkaido Island has been known as a manganese producer.
The major geological units of this area are volcanic and pyroclastic formations of Miocene which are intercalated with thin beds of conglomerate, sandstone and shale. There are also intrusives of quartz diorite, basalt and dacite. The NW tectonic trend is predominant as shown by the folds and faults of the same direction.
The Ooe deposits consist of the veins which fill the several subparallel shear fractures of N50°-60°W trend as well as a great number of accompanied tension fractures with minor extension in N80°W direction. The wall rock is mostly quartz diorite, and the ore shoots are located near to the peripheral shell of the intrusive body.
The Inakuraishi deposits, the veins in the "propylitized" andesite, fill the shear fractures of N55°W trend, many tension fractures of small extension in N80°W direction and also fill the several fractures of N70°E trend of much greater extension. The occurrence of the shoots at the intersections of the two kinds of fractures are remarkable.
These two fracture systems may be interpreted as to depend upon the stress set up by the intrusion of the quartz diorite and to the horizontal stress which caused the folding too, respectively. The formation of the Ooe deposits are more closely related to the former stress, while the Inakuraishi deposits more closely to the latter.
