The mode of occurrence of pisolitic pyrite ores and the internal heterogeneities revealed by chemical etching of pyrite crystals consisting of the pisolite as well as of iron sulphide ores from the Abuta mine were studied.
The pisolitic ore is generally composed of a small number of relatively large pyrite crystals and a large number of minute crystals of more or less uniform size. This indicates the conditions under which numerous nuclei of pyrite were formed but not enough growth took place. Such conditions may be realized when pyrite ore is formed from the solution with steep temperature gradient. Under low pressure, hot water lake such as Oyunuma of Noboribetsu spa may be presumed. In contrast, the internal structures of pyrite crystals consisting of ordinary ores occurring at some distance from the pisolitic ore are conjectured to have formed under higher pressure and higher temperature conditions than the pisolitic ores.
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