酸化マンガン鉱物の生成場 鉱物学から地球化学へ

Abstract

The manganese oxide phases are often metastable, intimately intergrown with other materials, and so poorly crystalline that attempts to identify them by conventional X-ray diffraction techniques are brought with difficulties. The fundamental structure unit in manganese (IV) oxides is the [MnO6] octahedron which are linked by corner-sharing and edge-sharing to give a variety of chain, tunnel and layer structures. Initial data on the hydrogen isotopic composition in hydrous manganese minerals from various occurrences fall in a wide range from -298 to -84‰ relative to SMOW. Hydrogen isotope fractionation factors between manganite and water were experimentally determined to be 0.7894, 0.7958 and 0.8078 at 150, 200 and 250°C, respectively. This experimental results indicate that if manganite were formed at temperatures below 250°C, under isotopic equilibrium conditions, most of the manganite mineralization in the Tertiary manganese deposits must have precipitated from meteoric hydrothermal solutions. The manganese ores in the Cretaceous formation of northeastern Hokkaido are characterized by low Fe/Mn ratios. The trace element concentrations and REE patterns are similar to those of the submarine hydrothermal manganese deposits. Distribution patterns of trace elements (Co Ni Cu and Zn) and REE in the manganese oxide ores of this area are of two types: (1) hydrogenous deposits which have relatively high concentrations and (2) submarine hydrothermal deposits which have low concentrations.