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Secondary copper sulphide minerals such as bornite, chalcosite and covellite are the main culprits in this context, he explained, with Anglo Asian having included a SART (sulphidization-acidification-cyanide recycling-thickening) plant into its circuit to recover copper and silver from the pregnant solution as sulphides.
The mineral resource estimate shows that the hypogene mineral resource remains open to depth and along strike in most areas, and the higher grade supergene enriched mineralization, dominated by chalcocite and local covellite, is also open for expansion.
Transitional (underlying the above) - a variably developed, secondary, supergene pyrite (after pyrrhotite) -chalcocite - covellite - quartz dominant zone.
These shallow sub-economic occurrences contain manganese oxides, covellite, chalcopyrite, malachite, azurite, copper, and silver (Rose and Johnson 1990; Merlini 1998).
Primary copper mineralisation consists of chalcocite, bornite and chalcopyrite, with secondary mineralisation (chalcocite, chrysocolla, covellite, cuprite, azurite and wad) occurring along structures.
This last institution's case contained my candidate for most-downright-amazing specimen from Colorado: an extraordinary 20 X 20-cm mass of covellite crystals from Summitville, the sharp, hexagonal, dull blue-black crystals measuring uniformly about 2.
Examination of thin sections confirms the presence of widespread pentlandite together with millerite and lesser covellite.
The upper three blankets primarily contain oxide mineralization; below them is an intermediate horizon with secondary species mixed with primary sulfides; the two deepest blankets contain chiefly chalcocite and minor covellite.
There is a wide geologic variation present, from classic Cu/Au porphyry (sub-ore grade) to variable-thickness breccia pipes, higher-grade covellite with zones in pipes exceeding 100 m and grading >1% Cu.
Recognition of the presence of significant quantities of the enriched copper sulphides chalcocite and covellite allowed consideration of higher concentrate grades, particularly in early years.