Hypogenic versus supergenic

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Hypogenic copper sulfides are an economically important sources of copper.

Hypogenic deposits are formed by ascending solutions carrying high levels of metal ions at fairly high temperatures (up to 500° C.). As these solutions cool, metal sulfides are deposited as crystallized ore minerals as the solutions move up toward the Earth's surface. As a result, hypogenic deposits are characterized by metal sulfide bearing veins or irregular masses formed within fractures in the rock. Within these hypogenic deposits, a variety of hypogenic copper sulfides may be found depending on the chemical composition of the ascending solution. Some of hypogenic copper sulfides found in hypogenic deposits are chalcopyrite, bornite, enargite, tetrahedrite, and tennatite. Hypogenic copper sulfides are also sometimes referred to as primary enriched copper sulfide minerals. The ascending solutions may also eventually reach the surface and appear as hot springs. In these situations, the solutions generally become diluted with ground water and thus have lower metal ion levels. As a result, the metal ions in these hot springs typically precipitate out as metal sulfate salts over time. In addition, the copper sulfide minerals that are formed above the water table may become altered over time by oxidation to sulfates by the circulation of air, water and bacteria.

These soluble metal salts are subsequently carried away in a solution by downward moving ground water. As the ground water moves to the oxygen deficient lower levels, a secondary enrichment can take place. The copper-bearing solutions react with the existing chalcopyrite and other hypogenic sulfides such as bornite, enargite, tetrahedrite, and tennatite to form new copper sulfide minerals. The new minerals formed by the descending solutions are sometimes called supergenic or secondarily enriched copper sulfide minerals. The supergenic copper sulfides—or secondary enriched copper sulfides as they are sometimes referred to—are higher in copper and characterized by the minerals covellite and chalcocite. They are also more readily oxidizeable than the hypogenic copper sulfide minerals. Supergenic copper sulfide minerals are generally located below the oxidized zone and the water table and above the lower grade of primary sulfide ore.

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References

  1. http://www.freepatentsonline.com/20070125199.html?highlight=bioleach&stemming=on
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