1988 Volume 38 Issue 207 Pages 1-13
The Hidaka Supergroup exposed in the Nupun-Tomuraushi area, central part of the Hidaka Belt, shows repeating cycles of black shale, meta-basalt, red shale, green shale and gray shale in ascending order. Fine-grained sandstone and siliceous gray shale are intercalated with the black shale which is broadly distributed in the studied area. The black shale contains higher amount of clastic grains of quartz, feldspar and opaque minerals than the other shales do. The meta-basalt consists of pillow lava, massive lava and hyaloclastite, and is regarded to have extruded on a deep seafloor of black mud.
The green and red shales are richer in Mn, Fe, Mg, Ba, Co, Zn, Cu and Pb, and poorer in Ti, Al, V and Cr than the black shale. The gray shale has an intermediate average composition between the black shale and the red and green shales. Assuming that the black shale represents terrigenous material, it is inferred that heavy metal elements such as Mn, Fe and Co supplied by hydrothermal activity were added to the material to have produced the green and red shales. On the basis of the geology and chemistry of the rocks, we conclude that the submarine volcanism generated the hydrothermal system and played an important role in the formation of red and green shales, and of associated ore deposits such as bedded hematite and bedded manganese.
