1990 Volume 40 Issue 221 Pages 159-173
Strata-bound manganese oxide and manganiferous iron deposits are distributed in the Tokoro Belt. The manganiferous iron deposits are found between the bedded chert and greenstone whereas the manganese oxide deposits usually occur within the radiolarian chert. These deposits are regarded to have been formed by submarine hydrothermal activities, as inferred from the mode of occurrence of the country rocks.
The manganese oxide ores are characterized by low Fe/Mn ratios which are similar to those of the submarine hydrothermal deposits. The average Fe/Mn ratios of manganese oxide and manganiferous iron deposits are 0.017 and 6.41, respectively. It is considered that the fractionation between Fe and Mn takes place during their formation. According to the distribution of the trace elements (Co, Ni, Cu, and Zn) in the manganese oxide ores, two types can be distinguished: one type has rather high chemical concentrations as hydrogenous deposits, the other has low concentrations as submarine hydrothermal deposits.
These compositional trends and geological evidences on the occurrence of manganese deposits suggest that they are syngenetic and have been formed by precipitation from submarine hydrothermal activities with limited hydrogenetic effects during early Cretaceous.
