The geology of the Tsuchihata mining area consists of formations as follows:
Tertiary Pliocene-Hanayama formation
Miocene Kurosawa formation
Kotsunagi formation
Kawajiri formation
Oishi formation
Oarasawa
Basement rocks
Various volcanics of Miocene age, chiefly rhyolite, are widely distributed in this district, and alternate with the formations above mentioned.
Most of the ore deposits of the Tsuchihata mine are so-called "network ore deposits", which are intermediate between "vein deposits" and "black-ore deposits", consequently they turn into either the vein type or the black-ore type according to their environments.
At the Washinosu deposits particularly, we can observe the transition from the network-type to one of the other types, as well as the connection between ore-deposits of each type and their proper environments.