Copper and How it Occurs
What is Copper and how does it occur?Copper is a metallic element, number 29 on the Periodic Table and known for its incredible electrical conductivity. Copper is brownish in color and is available in many forms including bars, foil, sheet, granules, plates, powder, shot, turnings, wire, insulated wire, mesh, "evaporation slugs", and rods.
Copper is primarily found in minerals associated with sulfur or in the oxidized products of these minerals. Copper easily combines with a number of other elements and ions to form a wide variety of copper minerals and ore deposits. Copper ore deposits typically contain less than 1% copper in the form of sulphide minerals. Approximately 85 % of the world's copper mining supply comes in the form of sulphide mineral ores and the remaining 15% comes in the form of oxide mineral ores. The following table shows the most common copper mineral ores:
| Mineral | Composition | Wt % Copper | Colour |
| Native copper | Cu | 100.0 | Copper Red |
| Cuprite | Cu2O | 88.8 | Red |
| Chalcocite | Cu2S | 79.9 | Dark grey |
| Covellite | CuS | 66.4 | Indigo blue |
| Bornite | Cu5FeS4 | 63.3 | Golden brown to copper red |
| Malachite | CuCO3Cu(OH)4 | 57.5 | Bright Green |
| Azurite | 2CuCO3Cu(OH)2 | 55.3 | Blue |
| Antlerite | Cu3SO4(OH)4 | 53.7 | Green |
| Chrysocolla | CuSiO32H2O | 36.2 | Bluish green, sky blue, turquoise |
| Chalcopyrite | CuFeS2 | 34.6 | Golden Yellow |
While commercially exploited deposits of copper ores are found in many parts of the world, the most concentrated copper deposits are located in the western cordillera of the Americas, mainly in Canada, the United States, Peru and Chile. In Africa, large deposits are found in Zambia and the Democratic Republic of the Congo and in Southeast Asia, large deposits are found in the Philippines, Papua New Guinea and Indonesia.
Copper deposits comprise both copper mineral "ore" and 'gangue' or host rock that has to be separated from the ore. Sulphide copper ores originate from sulphur-bearing magmas, which have separated into metal sulphides and siliceous melts. The most common geological formations related to copper deposit are as follows:
Porphyry deposits: Porphyry deposits are the world's most important source of copper, accounting for about 50% to 60% of world copper production. These deposits are associated with intrusive rocks that are uplifting from the earth's crust and the copper bearing sulphides usually occur as disseminations along hairline fractures as well as within larger veins, which often form stockworks.
Sediment hosted stratiform deposits ("SSC"): SSC copper deposits are a large, diverse class of deposits that include some of the richest and largest copper deposits in the world. They are found primarily in the African Copperbelt . These deposits formed during a time when sediments deposited in arid areas. A variety of processes were involved in different districts but metals were characteristically deposited at re- oxidation boundaries where oxic, evaporite-derived brines containing metals extracted from iron rich aquifers encountered reducing conditions.
Iron Oxide Copper gold deposits ("IOCG"): IOCG deposits have significant amounts of copper, gold and uranium and a few large deposits have been discovered in Australia. IOCG deposits are spectrum of sulphide-deficient low ore bodies of hydrothermal origin with polymetallic ( copper and gold) enrichments resulting from proximity to continental fault zones. The deposits are characterized by more than 20% iron oxides.
Skarn deposits: Skarns occur in the proximity of porphyry copper deposits where there has been a secondary geologic event associated with temperature and pressure. A Skarn is a fine grained metamorphic rock that is usually variably in colour and is usually polymetallic often containing zinc, gold or iron but is particularly important as a host of tin, molybdenum or copper. It usually forms by thermal metamorphism and metasomatism in the contact zone of magmatic intrusions like granites with carbonate-rich rocks such as limestone or dolostone.
Volcanogenic Massive Sulpide deposits (VMS"): VMS deposits are concentrations of base metal (copper, zinc, lead) and sometimes precious metal (gold, silver) sulphide minerals that occur in both ancient and modern submarine volcanic and volcanic-associated sedimentary environments. They are generally formed by the exhalation of hot, metal rich fluids onto the seafloor and have strong connections with the modern day "black smoker" deposits formed at spreading underwater ridges and often form in blocks. They are usually smaller in size and are common throughout the world.