1980 Volume 30 Issue 161 Pages 153-167
Re-examination of the volcanostratigraphy of the Fukazawa-Ezuri area, central Hokuroku basin, has clarified the paleo-volcanic structures related to the formation of the kuroko and vein-type deposits. Circular distribution of post-kuroko volcanics (intrusives and lava flows) representing eruptive centers and a crystalline stock within the circle seem to be suggestive of a latent "resurgent cauldron" in this area, as predicted by KounA and KOIDE (1978). However, any evidence of subsidence and up-doming implied by their model has not been recognized in this investigation.
It is suggested that block movement of the basement rocks is more important in having formed structural shear zones that have acted as a leading pass of acid magma, kuroko solution and post-kuroko basalt flows. Spatially, the Fukazawa orebodies have close relationship to pre-mineralization rhyolite lava domes and phreatic explosion breccias at the near surface of these domes.
Vein-type deposits were formed in a stage later than the kuroko deposits, probably during the early Funakawa stage (about 9 m.y. B.P.). Most of them are distributed along the margin of the crystalline stock and some in a local crater cauldron in the Takarakura area. Reconstructed paleo-volcanic structure of this area suggests that the vein-type deposits were formed at depth of 300 to 600 meters under very shallow submarine or terrestrial environment.
