Bismuth minerals from cupriferous pyrrhotite ores at Okura mine are intimately associated with pyrrhotite, chalcopyrite, sphalerite, chromite and galena. Bismuth minerals are bismuthinite, native-bismuth and unknown minerals, probably wittichenite. Wittichenite occurs as reaction rims along the boundaries between chalcopyrite and native-bismuth.
Pyrrhotite is a relatively high temperature mineral and occurs in association with other high ordinary minerals. The writer studied the properties of pyrrhotites in Japan with special reference to the relation between α-pyrrhotite and β-pyrrhotite with the change of chemical composition. The main results obtained are as follows: (1) Pyrrhotite can be classified into the following three types according to the physico-chemical properties: (a) α-pyrrhotite (b) β-pyrrhotite (c) α+β-pyrrhotite (2) α-pyrrhotite is peak type at the magnetism and β-pyrrhotite is Weiss type. (3) α+β type pyrrhotite is a mechanical mixture of α-pyrrhotite and β-pyrrhotite and may be appear to be lamellae textures Zerknitterungs Lamelle (4) Zerknitterungs Lamelle texture is often observed in the Kieslager type deposits, but it is not so common in the vein and replacement deposits. (5) The writer, as well as many other investigators believes that nonhomogenity of pyrrhotite caused by the variation of Fe: S ratio and Zerknitterungs Lamelle texture are interpreted as the result of exsolution of solid solution or thermal metamorphic differentiation.
Pyrrhotites of Japan have been studied with special reference to their magnetic properties. The important conclusions are as follows: (1) The curie point of pyrrhotite is 305°to 320°C. (2) The magnetic susceptibility of pyrrhotite increases with their atomic ratio of sulphur, and can be divided into the following three growps, 1, 000_??_11, 000×10-6, 11, 000_??_20, 000×l0-6 and >20, 000×10>-6. (3) From the magnetization-temperature curve, pyrrhotites can be classified into following three groups by their temperature dependency of magnetism: (a) Peak type: α-pyrrhotite with weak magnetism, (b) Weiss type: β-pyrrhotite with strong magnetism which shows no peak on a I-T curve, (c) Peak+Weiss type: mixture of α- and β-pyrrhotites. (4) Peak type pyrrhotite is converted from weak magnetic to strong magnetic by heating and converted mineral becomes to Weiss type pyrrhotite above the curie point. (5) Peak type pyrrhotite occurs abundantly in the hydrothermal veins, while weiss type is very frequent in the Kieslager type deposits. This indicates that the peak type pyrrhotites formed primarilly in the hydrothermal veins are transformed secondarily to Weiss type by the later metamorphism.
