The lower parts of the Tertiary sediments at Ou-Mountainland, Iwate Pref., are so-called green tuff formation, which are divided in the Oishi beds, the upper, and the Oarasawa beds, the lower, according to the lithological and stratigraphical characteristics.
All of the metallic ore deposits in the Oarasawa beds and in the lower part of the Oishi beds are vein type deposits, while almost all of the ore deposits in the upper part of the Oishi beds are network and impregnation deposits, accompanied by swall veinlets. And also, ore deposits in the uppermost part of the Oishi beds and the lowermost part of the overlying beds are body type deposits, which are called “black ore deposits.”
All of these metallic ore deposits contain quartz, chalcopyrite, and pyrite as general components and their origin is seemed to be related to the liparite (so-called plagiorhyolite) at the middle Miocene age.