Akira Soeda

Regional and local variations in the composition of the wolframite series from SW Japan and possible factors controlling compositional variations

The regional and local variations in the composition of the wolframite series associated with the ilmeniteseries and magnetite-series granitoids in the Inner Zone of SW Japan were investigated using X-ray diffraction and microprobe analyses. It is concluded that the variation in Mn/Fe ratios in the source materials (granitic magmas in most cases) is the dominant factor controlling the regional variation in the wolframite compositions, while, as exemplified by the Kaneuchi mine, Kyoto Prefecture, the wallrock chemistry and pH of ore fluids are responsible for the local variation within a single vein system. Within a fresh euhedral crystal from the mine, only slight compositional variation of less than 3 mole% MnWO4 is found in the form of oscillatory zoning. This study, combined with the fluid inclusion research, indicates that the wolframite compositions (Mn/Fe ratios) cannot be used as a geothermometer.