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Copper mining and processing
Copper extraction and processing involves obtaining copper from ores through a multi-stage process. Depending on the site and the project, copper mining is performed on the surface or underground. This article provides the 101 on copper mining, including presenting the two main applications of copper mining – open-pit and underground mining – as well as the various processing techniques used when mining for copper.
What is copper mining?
Copper mining includes the extraction and processing of copper ores. Copper is obtained from its ores through a multi-stage extraction process, which is done through open-pit mining and underground mining. The usage of these techniques depend on the location and depth of the copper deposits, which influence the choice of drilling techniques, like directional core drilling.
Mining for copper ores
When humans first discovered they could use copper for tools and weapons, they mostly used native copper, which was copper that could be found in free form in nature and only needed to be hammered into shape. With the discovery of metallurgy and smelting, not only could native copper be smelted into large ingots, but also ore could be smelted, to separate copper. In modern times, native copper mining is rare, so most of the copper mining is focused on copper ore.
Two types of copper ore
- Sulfides
- Oxides
Types of sulfides
Among sulfides, the most common ones are Chalcopyrite (CuFeS₂), Bornite (Cu₅FeS₄), and Chalcocite (Cu₂S), while the most sought-after oxides are Malachite (Cu₂CO₃(OH)₂), Azurite (Cu₃(CO₃)₂(OH)₂), Cuprite (Cu₂O), Tenorite (CuO).
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Copper extraction
Copper deposits that are large enough to be economically viable for mining need to be first identified through exploration. Once the deposit is mapped and the resources have been estimated, the process of extraction can begin. The depth at which the ore has mineralized will determine how it will be mined. Largely, it can be done in two ways; open-pit mining and underground mining.
Extraction method: Open-pit mining
Through a surface mining technique, which is known as open-pit mining, successive layers of rock are removed. It starts with peeling of the surface layer. This method involves creating a large, terrace pit that expands outward and downward as ore and waste rock are excavated.
Common use areas
It is commonly used for mining copper, gold, iron, and other bulk commodities.
Benefits and challenges
Open-pit mining is cost-effective for large, low-grade deposits and allows for high productivity with the use of heavy machinery such as haul trucks, drills, and shovels. However, it has significant environmental impacts, including habitat destruction, dust generation, and long-term land alteration, which require careful management and reclamation efforts.
Extraction method: Underground mining
For deeper deposits, underground mining is used, when the ore body is too deep or too narrow for open-pit mining. It involves constructing tunnels, shafts, and chambers to access and remove the ore, using methods like room-and-pillar, cut-and-fill, or block caving depending on the geology and ore type.
Common use areas
This technique is often used for high-grade deposits of copper, gold, silver, and other metals.
Benefits and challenges
While more expensive and labor-intensive than surface mining, underground mining minimizes surface disturbance and is more suitable for environmentally sensitive areas. However, it poses higher safety risks, including rockfalls, ventilation challenges, and potential subsidence.
Copper mining processing
After the copper ore has been extracted, it needs to be processed into ingots. In older times, purely smelting the ore was enough, and particularly the smelting of sulfide ore was the only way of processing copper until the 20th century. Even today, almost 80% of copper ore is still only processed through smelting. Since Aziwell is a proud Trønder company, we have to mention here as an example the copper works from Røros. It operated well into the 20th century, processed local copper ore through smelting, and at times was one of the most important copper producers in Scandinavia.
Nowadays, processing techniques have gotten more complex, allowing the separation of copper out of a wider range of sulfides and oxides, with the type of deposit determining the way it should be processed.
Processing in sulfide ore mining
- Processing technique: Smelting (heat)
- Type of extraction: Underground or open-pit mining
- Risks: Acid mine drainage (AMD), heavy metal contamination, and wetland destruction
In sulfide ore mining, the ore is crushed and ground, then processed using froth flotation to concentrate the copper minerals. The concentrate is then smelted and refined via pyrometallurgical techniques, producing blister copper (~98–99% pure), which is further purified through electrorefining to produce high-purity cathode copper.
Processing in oxide ore mining
- Processing technique: Leaching (chemical solutions)
- Type of extraction: Open-pit mining
- Risks: Soil contamination and environmental damages, health risks for workers, and safety hazards
For oxide ores, hydrometallurgical methods such as heap leaching, solvent extraction, and electrowinning (SX-EW) are employed, allowing copper to be extracted from low-grade ores near the surface without intensive crushing or high-temperature treatment. Once the minerals have been extracted, they can be further refined through electrolysis, before being smelted into ingots and sold as raw materials for manufacturing.
Copper ore deposits
There are a number of ways copper ore mineralizes in the Earth’s crust to form deposits, of which three types will be summarized below, as they are the most commercially important on a global scale.
- Porphyry copper deposits
- Polymetallic replacement deposits
- Iron oxide-copper-gold deposits
Porphyry copper deposits
They are large, disseminated mineral systems formed in continental arc settings, typically associated with subduction-related magmatic activity. They are characterized by low to medium copper grades (commonly 0.3–1% Cu), but their immense size makes them economically significant.
The geological architecture of a porphyry copper deposit typically exhibits a vertically zoned system: a central core of potassic alteration with high-grade copper and molybdenite mineralization, surrounded by zones of phyllic, argillic, and propylitic alteration. These deposits often occur at depths of 1–2 km and are commonly linked with surface expressions like alteration halos or epithermal veins.
How are they formed?
These deposits form when hydrothermal fluids, released from cooling, silica-rich magmas, deposit metals such as copper, molybdenum, and gold into the surrounding host rock – usually a porphyritic intrusive (hence the name). The mineralization occurs in a network of veins, fractures, and disseminations, often centered around a porphyritic intrusion.
Examples of porphyry deposits include
Notable examples include the Chuquicamata and Escondida mines in Chile and Grasberg in Indonesia. Porphyry copper systems are the world’s primary source of copper and molybdenum and a major source of gold, making them vital to the global mining industry.
Polymetallic replacement deposits
Also known as carbonate-replacement deposits or CRDs, polymetallic copper deposits are a type of hydrothermal ore deposit that forms when metal-rich fluids replace carbonate host rocks such as limestone or dolomite. This replacement occurs through metasomatism – a chemical exchange between the rock and the fluid – resulting in the selective removal and deposition of metals like lead (Pb), zinc (Zn), copper (Cu), silver (Ag), and sometimes gold (Au).
These deposits are typically irregular in shape (mantos, chimneys, or pods) and are often found near or beneath porphyry or skarn systems, reflecting their genetic linkage to magmatic intrusions.
How are they formed?
Geologically, polymetallic replacement deposits display strong structural and lithological control, forming along faults, fractures, and bedding planes that act as conduits for fluid movement. They are often zoned, with copper and gold occurring closer to the intrusion and silver, lead, and zinc more distal. These deposits are known for their high metal grades and can be economically significant, especially for silver and zinc.
Examples of polymetallic deposits include
Classic examples include the Santa Eulalia district in Mexico and the Leadville district in Colorado, USA. CRDs are crucial to understanding regional metallogeny, as they often occur in conjunction with other deposit types within broader mineralized belts.
Iron oxide-copper-gold deposits
Iron oxide-copper gold (IOCG) deposits are a distinctive type of mineral deposit characterized by the association of significant copper and gold mineralization with large accumulations of iron oxides, typically hematite or magnetite. These deposits form from hydrothermal fluids that are rich in iron, often derived from deep crustal or mantle sources, and are emplaced in a variety of host rocks, including granites, volcanic rocks, and sediments.
Unlike porphyry systems, IOCG deposits are not necessarily associated with porphyritic intrusions and tend to have lower sulfide content but higher concentrations of iron oxides. They often feature broad zones of brecciation, alteration, and mineralization that can extend over several kilometers.
How are they formed?
IOCG deposits are highly variable in size and grade, with some of the world's largest mineral systems falling into this category. They are economically important for their copper and gold content but can also yield significant quantities of uranium, rare earth elements (REEs), silver, and cobalt. The mineralization style and alteration zoning in IOCG systems differ from traditional copper deposits, often including sodic (albite) and potassic alteration assemblages.
Examples of IOCG deposits include
Major examples include the Olympic Dam in South Australia – one of the largest known IOCG systems – and Candelaria in Chile. Their complex genesis and polymetallic nature make IOCG deposits a key target for exploration globally
Copper throughout the history
Humans began experimenting with copper, which could be hammered into tools, weapons, and ornaments, as far back as 9500 years ago. Although that was initially native copper, they soon learned how to smelt copper ore. Once that was achieved, the Copper Age, also known as the Chalcolithic Age began, roughly dating from 5000 to 3000 BCE.
It marks a significant advancement in technology and social organization: Settlements became more permanent, trade networks expanded (especially for valuable materials like copper and obsidian), and early forms of societal hierarchy began to emerge.
Once humans discovered the harder and more durable bronze by alloying copper with tin, the Bronze Age started, and entire civilizations were built on the copper and bronze trade. Since then, copper became a sought-after commodity, maintaining a role in human society, even after the smelting of iron became available.
Indeed, after the beginning of the Iron Age, copper was much less used, but it was nevertheless still extracted, since bronze was significantly more affordable than iron. Especially for tools, cookware, and even jewelry, those from the poorer layers of society would’ve had easier access to bronze.
Later on, during the Age of Discovery (15th to 17th century) bronze was commonly used in shipbuilding, and as a common alloy for building cannons. However, copper once more became a valuable commodity once it was discovered that it is a highly conductive material. As such, nowadays it is the main metal used in electrical wiring and components.
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