In numerous deposits of the Copiapó mining district of northern Chile copper and copper-iron sulfides persist as early products of post-Miocene oxidation of hypogene and supergene sulfides, the latter formed during a preceding enrichment episode. The sulfides of oxidation origin have been subsequently partially altered, predominantly to malachite and goethite. In the oxidation zones of this area, hypogene chalcopvrite has been converted to normal covellite; hvpogene bornite to “anomalous bornite”, idaite, chalcopvrite, and normal covellite; supergene djurleite and hvpogene chalcocite to digenite (or anilite), and to blaubleibender and normal covellite; and supergene digenite to blaubleibender and normal covellite.
Electron probe microanalysis of blaubleibender covellite revealed a wide compositional range, probably extending from stoichiometric CuS to at least Cu1.4S, the composition of blaubleibender covellite synthesized by Frenzel (1961). Idaite is shown to have a composition closely approaching Cu3FeS4, and is considered to be quite distinct from synthetic Cu5.5xFexS6.5x. “Anomalous bornite’7 in these ores possesses at least 2 weight percent less copper and 2 percent more sulfur than optically-normal, hypogene bornite. These analytical data necessitate the revision of present concepts of the low temperature phase equilibria in this region of the system Cu-Fe-S.