Why Deposit Type Matters to Copper Users
Almost all refined copper in world trade starts as ore from a small number of geological deposit types, and the type of deposit determines the ore grade, the impurity profile and the by-products that reach the smelter. Those factors in turn influence the cost and the consistency of the copper and copper alloy products that leave a mill, from a plain copper tube to a lead brass rod or a cast graphite sleeve. Understanding the deposit mix behind world supply is therefore useful to any buyer who needs to judge why copper prices move and why concentrate quality varies between regions.
The Six Main Copper Deposit Types and Their Resource Share
World copper resources are dominated by six deposit classes. The shares below are the proportions of total world resource reserves commonly quoted for each type, and together they account for 97.7 per cent of the total.
| Deposit type | Share of world copper resources | Typical setting |
|---|---|---|
| Porphyry type | 69.0% | Volcanic arc intrusive complexes |
| Sedimentary rock hosted stratiform type | 11.8% | Red bed basins and copperbelt sequences |
| Magmatic sulfide type | 5.1% | Mafic and ultramafic intrusions |
| Volcanic massive sulfide type | 4.9% | Ancient sea floor volcanic centres |
| Iron oxide copper gold type | 4.7% | Hydrothermal breccia and hematite systems |
| Skarn type | 2.2% | Intrusive contact with carbonate rock |
Porphyry Copper Deposits: the Backbone of World Supply
Porphyry copper deposits are the single most important source of copper in the world, and the gold, molybdenum or zinc that occurs with them is itself of major economic value. The very large deposits, generally those above five million tonnes of contained copper, are concentrated in a small number of metallogenic domains: the Pacific Rim domain covering Chile, Peru, the United States, Panama, Indonesia, the Philippines and Papua New Guinea; the Tethys Himalayan domain including China and Pakistan; and the ancient Asian domain covering Mongolia and Kazakhstan. The Pacific Rim occurrences are themselves concentrated further in the South American Andes belt, which is why a handful of Andean mines can move the world concentrate balance.
Sedimentary Rock Hosted Stratiform Copper
Stratiform copper deposits are mined mainly in the Central African copperbelt of the Democratic Republic of Congo and Zambia. They carry very significant economic value and are also the world's principal source of cobalt, which is recovered as a by-product. Deposits of the same class also occur in Poland, Kazakhstan, Chile and Australia. Because these ores are generally low in arsenic and antimony compared with some porphyry concentrates, they are valued for the quality of the metal they produce.
Volcanic Massive Sulfide and Iron Oxide Copper Gold Deposits
Volcanic massive sulfide deposits formed at ancient sea floor hydrothermal vents and are typically rich in zinc as well as copper; the Neves Corvo zinc copper deposit in Portugal is a well known example, and the class is the source of much of the world's zinc and a useful share of its copper. Iron oxide copper gold deposits are a separate class in which copper, gold, uranium and rare earth elements are hosted by hematite rich hydrothermal systems; the Olympic Dam deposit in Australia is the classic example and is notable both for its size and for the unusual breadth of its by-product suite.
Skarn Type Copper Deposits
Skarn deposits form where a hot intrusive body intrudes carbonate rock and the resulting chemical exchange concentrates copper, and often iron, tungsten or molybdenum, in the altered contact zone. They are relatively small in total resource share but can be rich and are often found close to existing mining infrastructure. Examples include skarn copper occurrences in the United States and the Dongguashan copper mine at Tongling in Anhui province, China.
From Ore to Copper Tube and Copper Alloy Product
The deposit mix explains several practical facts about the copper products that reach an engineering workshop. Porphyry ore, which supplies about 69 per cent of resources, is low grade and produces large volumes of concentrate with variable amounts of arsenic and other impurities, so smelters blend feed carefully to keep cathode quality within the limits of standards such as the LME grade A specification for refined copper. Cobalt rich stratiform ore ties a share of copper supply to electric vehicle battery demand. By-product credits from gold, molybdenum, nickel or zinc determine whether a marginal mine keeps running, which is one reason copper availability does not always track the copper price alone. For the buyer of copper tube, lead brass rod or a cast bearing sleeve, the practical consequence is that consistent chemistry depends on a smelter with disciplined blending rather than on the ore type of any single mine.
Frequently Asked Questions
Q: Which copper deposit type is the most important in the world?
Porphyry copper deposits, which account for about 69.0 per cent of world copper resource reserves. Their associated gold, molybdenum and zinc credits give them additional economic value, and the largest examples cluster in the Pacific Rim, Tethys Himalayan and ancient Asian metallogenic domains.
Q: How much of world copper comes from the six main deposit types together?
The six classes of porphyry, sedimentary stratiform, magmatic sulfide, volcanic massive sulfide, iron oxide copper gold and skarn account for 97.7 per cent of world copper resource reserves in total, leaving only a small fraction in minor deposit styles.
Q: Why does deposit type affect the price of a finished copper product?
Because it fixes ore grade, impurity content and by-product credits. Higher impurity concentrate needs more blending and refining, and by-product revenue from gold, cobalt, nickel or zinc changes the cost at which a mine can keep operating, both of which feed through to refined copper and alloy prices.
Q: Are skarn copper deposits commercially significant?
They represent about 2.2 per cent of world resources, the smallest share of the six main types, but individual skarn deposits can be rich and are often close to existing infrastructure, which makes them economic despite their modest global total.
