Gold-Bearing Ores of the Ôe Ore Deposits in Hokkaido
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概要
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The Ôe mine in the southwestern part of Hokkaido is producing monthly 8, 500 tons of crude ores from which Au, Ag, Cu, Pb, Zn, Fe-S and Mn are extracted. The ore deposits are of epithermal fissure-filling vein type. The ores are mainly composed of rhodochrosite, chalcopyrite, galena, sphalerite and pyrite with minor amounts of native gold, argentite, pyrargyrite, etc.<BR>The Senzai vein, the largest one of this mine, is about 1, 500m long along the strike and extends to 500m along the dip with an average width of 5m. The gold contents are high at the upper and lower parts of the western ore shoot consisting of rhodochrosite and sulphide minerals. While at the upper parts of the vein, gold is associated with lead as shown by assays, at the lower parts and in the Manzai vein which runs parallel with the Senzai vein it is associated with copper. Originally, the native gold of this mine was discovered in lead concentrates about ten years ago.<BR>At the lower part, the native gold-bearing ores occur as aggragates of fine sulphide minerals. On the other hand, they occur in the banded ores consisting of rhodochrosite, quartz and sulphide minerals at the lower part of the Senzai vein and in the Manzai vein. These minerals were crystallized at the late middle stage of mineralization.<BR>Mineralogically, the native gold is closely associated with galena of 20μ average size at the upper part of the Senzai vein, while in the Manzai vein most native golds are associated with tetrahedrite of 15μ average size. By etching the polished surface of native gold with CrO<SUB>3</SUB>+HCI, a concentric banded texture was developed. Hence, it is confirmed that the gold grains which show this texture are composed of alternating concentric bands which are relatively rich or poor in silver. The heterogeneity of the grains could be also detected by electron probe X-ray micro-analysis and reflectivity using a microphotometer.
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