Bornite

BORNITE, peacock ore, variegated copper ore (has been named after the Austrian mineralogist Ignaz von Born * EN: bornite, peacock ore, purple copper ore, horseflesh ore; DE: Bornit, Buntkupfeckies, Buntkupfererz; FR: bornite; ES: bornita; RU: борнит) is mineral, the complex sulphide of copper and iron, Cu5FeS4. In association with the defectiveness of structure, there are observed wide variations of chemical composition (%): Cu is 52-65, Fe is 8-18, S is 20-27. It crystallizes into the cubic crystal systems. There are known tetragonal, trigonal, and rhombic polymorphic modifications. The structure is of the spinel type. It may be most often found in the form of continuous masses or grains of irregular shape; crystals are extremely rare. There are known twins along the (111) plane. The colour on the fresh fracture is dark copper-red, and within the air, there emerges the variegated (mostly blue) iridescence. The lustre is semimetallic. The cleavage is practically absent, the fracture is fine-conchoidal, uneven. The hardness is 3-4. The density is 4900-5300 kilograms per cubic metre. It is brittle and opaque. It is paramagnetic. The resistivity is 10^-3 - 10^-4 ohm-metres, and substantially changes during heating.

The genesis is diverse: the hypogene bornite (usually from the hydrothermal deposits) is typical for the pyrite ores; the supergene bornite is typical for the zone of secondary sulfidic enrichment, and for the sedimentary rocks. Within the hydrothermal deposits, bornite associates itself with chalcopyrite, pyrite, sphalerite, fahlore. Within the zone of oxidation, at the expense of bornite, there form themselves malachite, azurite, cuprite, and other supergene minerals.

Bornite is the important mineral of the copper ores. The major method for beneficiation is flotation. It is extracted together with other copper sulphides, with the usage as collectors, of xanthates (pH is approximately 12), and of dithiophosphates (pH is 7-8), with the usage as regulators for environment, of CaO, N2SO3, H2SO4, and with the usage as depressors, of Na2S, NaCN, ferrocyanides, and ferricyanides.