Kuroko ore. Ainai Mine, Akita Prefecture, Japan

Ainai Mine lies within the Furutobe Caldera which is part of the Miocene Hokuroku Basin. This basin is the most important Kuroko district of the Green Tuff region of Japan.

Major Minerals:

Pyrite, chalcopyrite, sphalerite, galena, tetrahedrite group minerals

Minor Minerals:


Trace Minerals:

Include stromeyerite, electrum, argentite, native silver, bournonite, boulangerite, djurleite, haematite, magnetite


The ores show soft sediment deformation, including flame textures and slumping in addition to undeformed graded bedding. Collomorphic textures are common between sulphides, as are recrystallization textures. There is extensive replacement of pyrite and sphalerite by chalcopyrite (chalcopyrite disease)


Ishikawa and Yanagisawa, 1974; Urabe and Sato, 1978