Here is the latest instalment of the Proactive magnum opus on copper...
Each of these deposits brings with it a suite of ores, the raw materials of the copper trade. Chalcopyrite, bornite, and chalcocite are the marquee names here, the blue-chip stocks of the copper ore world. Chalcopyrite, with its brassy yellow colour, is particularly abundant. It's the main attraction in porphyry deposits and a reliable source of copper, though its entourage of sulfur and iron can make it a challenging commodity to process.
In Awe of Ore
Bornite (see below), with its peacock hues, is a showstopper, fetching the nickname 'peacock ore' for its vibrant array of colours. And chalcocite, the dark horse, is rich with copper content, often found lurking in the deeper, more sultry parts of the deposit.
Above are the riffs and variations. However, it is worth remembering that ores are broadly classified into two main types: sulfide and oxide, each with distinct characteristics and processing methods.
Sulfide: The Deep Vein Treasures
Sulfide ores are typically found deep underground and are the primary source of copper. They contain copper in the form of copper sulfide minerals, such as chalcopyrite (CuFeS2), chalcocite (Cu2S), and bornite (Cu5FeS4). These minerals are often associated with other sulfide minerals and metallic ores, such as pyrite (FeS2), molybdenite (MoS2), and silver (Ag).
The processing of sulfide ores involves crushing and grinding, followed by flotation, a process that separates the copper minerals from the waste rock. The resulting copper concentrate contains about 25-35% copper along with various sulfides of copper and iron, plus smaller concentrations of gold, silver, and other materials.
The next step is smelting, which involves heating and melting the concentrate in a furnace to produce copper matte, which is a mixture of copper sulfide and iron sulfide. The matte is then converted into blister copper, which is typically about 98% pure copper, through a process of oxidation and reduction.
Oxide: The Surface Bounty
Oxide ores are typically found near the surface and are less abundant than sulfide ores. They contain copper in the form of copper carbonate, sulfate, phosphate, and silicate minerals. Examples include malachite (Cu2CO3(OH)2), azurite (Cu3(CO3)2(OH)2), and cuprite (Cu2O).
These ores are processed differently from sulfide ores due to their different chemical compositions. The most common method is heap leaching, which involves piling the ore into large heaps, then irrigating the heaps with a weak sulfuric acid solution, which dissolves the copper content. The resulting solution, known as a pregnant leach solution (PLS), contains dissolved copper ions that are then recovered through solvent extraction and electrowinning (SX-EW) processes.
The SX-EW process involves extracting the copper from the PLS into an organic solvent, then stripping the copper into an electrolyte solution. The final step is electrowinning, where the copper is plated onto cathodes by applying an electrical current, producing nearly pure copper.
Mixed: Blending the Two
Some deposits contain a mix of both sulfide and oxide ores. These mixed ores pose a unique challenge for miners and processors, as they require a combination of processing methods to extract the copper. Typically, the oxide layers are processed first, as they are easier to access and treat, while the deeper sulfide layers are processed later