Yanahara mine, Okayama Prefecture, Chugoku Region, Honshu Island, Japan

Ref: Geology and Mineral Resources of Japan (Geological Survey of Japan, 1960)

In the late 1950s this was the largest pyrite mine in the world. Ore consisted overwhelmingly of massive compact pyrite, with minor localized chalcopyrite, pyrrhotite and magnetite at the intrusive contacts. Mined principally for the pyrite (for sulphuric acid production), with minor byproduct copper, cobalt, and a special iron oxide (for magnetic audio tape). (1958 production: 626,594 tons ore, yielding 278,036 tons sulphur and 282 tons Cu.) Had closed by 1970.

The pyrite formed an irregular massive deposit emplaced concordantly in late Paleozoic sandstone and clayslate, intruded by younger quartz dioritic and granitic porphyry. Some of the slate has been altered to an unusual cordierite-anthophyllite rock at contact with the orebody.