The ore-bearing veins of the Butte District are visualized as products of hydrothermal activity which was simultaneously altering the quartz monzonite host wall rock. The ratio of sulphur to sulphide-forming metals in the hydrothermal solution is postulated to exert a major determinative influence on copper-iron-sulphur series mineralogy at various zonal depths in the ore deposit. The distribution of the minerals representative of the system Cu-Fe-S as well as some of the textural relationships between them may therefore be correlated to intensity of wall rock alteration, especially to pyritization of the iron indigenous to the quartz monzonite by sulphur supplied by the hydrothermal fluid.

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