chalcopyrite - teaching student specimens from a mineralized vein - Unit of 10 smaller specimens

chalcopyrite   CuFeS₂

Mibladen Mining District, Morocco

Chalcopyrite is the primary sulfide ore of copper. The brassy yellow color, hardness 3.5-4 and greenish gray streak distinguish it from pyrite, hardness 6-6.5, which is paler, cannot be scratched by a nail and which has a brownish black streak.

This chalcopyrite comes from the old galena/fluorite mining district at Aouli, Midelt Province, Morocco. French companies operated mines in the Aouli vein-type lead-zinc deposit from 1923 to 1960, part of a larger lead ore mining area about 16 miles northeast of Midelt in the Middle Atlas Mountains. This area was actively mined until 1975, though local residents occasionally resume small  operations.

These specimens are from a mineralized vein and are associated with quartz, some malachite and occasional azurite. As chalcopyrite weathers, it becomes a dull gray-green. If treated with acid it tarnishes to an iridescent blue and purple, making it look like bornite. We prefer that students see chalcopyrite as it comes from the mine. The chalcopyrite that's treated with acid is sold as "peacock ore," confusing, since "peacock ore" has long been used to describe bornite, Cu₅FeS₄. 

Both minerals are found in oxidized hydrothermal veins, but bornite occurs in an enriched zone just below the water table, while chalcopyrite is a massive sulfide of the original vein.

Pyrite is common in these deposits. As it oxidizes, it changes from iron sulfate to iron oxide and takes in water to become limonite, forming a yellow-brown "iron hat" or gossan over the vein.

As pyrite chemically changes, it releases sulfur which forms sulfuric acid. This dissolves other minerals in the original ore, allowing them to be washed downward by rainwater. The resulting washed out or leached zone is easy to mine. The leached out minerals are carried down to the water table by the descending rainwater, forming a zone of mineral enrichment that is valuable but difficult to mine because of the water, which must be removed from the workings.

The Mibladen Mining District, in the Middle Atlas Mountains, is famous for the minerals it has produced, vanadinite, galena, sphalerite and barite, among others.

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