Where does Copper Come From?

     Copper is a very abundant resource.  Worldwide resources are estimated at 5.8 trillion pounds, of which only 0.7 trillion has been mined (4). Chile is by far the largest copper producer in the world, estimated at 4,603,000 tons per year.  Next is the United States, averaging 1,473,000 tons per year.  Indonesia produces 1,006,000 tons, Australia 820,000 tons, Canada 634,000 tons, China 589,000 tons, Peru 554,000 tons, Russia 510,000 tons, Poland 463,000 tons, and Kazakhstan with 433,000 tons. (1) As expected, the Americas have the largest production rate of the continents averaging a whopping 7,789,300 tons.  All together the world production is 14.6 million tonnes per year (6).  This does not meet the world demand which is currently more than 15.2 million tonnes (5).

     Copper comes from many different kinds of deposits.  Hydrothermal deposits of copper are the most important worldwide, although magmatic and supergene deposits are most important in the UK.  

Porphyry deposits- Porphyry deposits are the world's largest source of copper, accounting for up to 60% of the world's production.  These deposits are created by subduction related felsic igneous intrustions.  They happen in plate boundary collision areas like the Andes, around the Pacific Basin in the Philippines, Indonesia, and the Canadian Cordillera.  These may contain hundreds of millions of tons of ore.  

Sediment-hosted deposits - Sediment hosted deposits are the world's second largest copper resource, making up approximately 20% of output.  These deposits are made up of disseminations of small sulphides in continental sedimentary rocks like sandstone and limestone.  One of the largest is in Lubin in Poland which contains 2,600 million tons of copper with a concentration of over 2%.

      There are also volcanogenic massive sulphide deposits, magmatic sulphide deposits, sedimentary exhalative deposits, epithermal deposits, skam deposits, vein deposits, and supergene deposits.  These are usually not economic because of their small size.        “British Mineral Survey”

     There are a few different ways in which copper is extracted from the ground.  The large size of porphyry copper deposits in conjunction with their often low-grade and fractured host rock make them an excellent candidate for opencast mining.  Epithermal deposits are best mined by the use of bulk open pit mining also.  Open pit mining is used near the surface, usually less than 100 meters down.  Open pit mining is very destructive, as it is done by large area digging and blasting with explosive.  Ore is then put onto trucks and taken to stockpiles.    One of the largest man made excavations in the world is the Bingham Canyon Copper Mine in Utah.  It is over 800 m deep and 4 km wide, and has been in operation for over 100 years.  It has produced more than any other mine in history.  Bingham Canyon is the largest copper mine in the world.  The oldest rocks at Bingham Canyon were deposited as sediment by seas that covered in the Paleozoic Era.  Between 60 and 135 million years ago there was a lot of folding and faulting.  30 to 40 million years ago giant igneous intrusions started mineralization in the area.  Pressure forced high temperature, mineral-rich solutions into the fractured intrusive and adjacent sedimentary rock.  This deposited giant amounts of metals in what is now known as the Bingham Stock.  All high-grade oxidized ores were exhausted by the 1890's.  A great amount remained but they were deep, unoxidized sulfides, and low in grade.  (7)

     Underground mining is a bit less common because it cost more than open pit and has many more safety issues.  This method is used to extract higher grade, small, or deep ore deposits.  This may include block carving, and room and pillar cutting.  The most rare type is in-situ leaching.  This is done by injecting weak sulphuric acid leach solution down into injection wells.  This dissolves the copper.  It is then pumped out to recovery wells in order to prevent the solution from escaping.  The deposit needs to be permeable and the surrounding rock impervious.  Finally, fresh water is pumped around the system to clean it, and the wells are cemented. (2)    

     At least 90% of copper production comes from disseminated copper sulphide deposits.  Chalcopyrite is responsible for almost half of all sulphide deposits.  Chalcopyrite crystals have unevenly faced tetrahedrons that are striated in different directions.  These crystals usually tarnish to iridescence or deep blues, purples, or blacks. (7)

     A recent mineral industry survey conducted by the U.S. Geological Survey showed a decrease in copper production.  Large companies attributed this to lower ore grades and reduced recoveries.  (8)  The top copper producing companies are Codelco, Xstrata, BHP Billiton, Rio Tinto, Phelps Dodge, Anglo American, Grupo Mexico, Freeport McMoran, Antofagasta, and Teck Cominco.  Their top producing mines are Escondida, Chuquicamata, Grasberg, Collahuasi, El Teniente, Morenci, Zhezkazgan, Mt. Isa, Antamina, and Los Pelambres. (9)

Figure 2.1 Bingham Canyon Copper Mine
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Figure 2.2 Copper ore being trucked out of an open pit at Bingham Canyon Copper Mine.
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