How it is mined
Exploring and evaluating the viability of a copper deposit is an incredible endeavor. Potential areas where a copper deposit might occur are assessed based on basin modeling, structural geology, geochronology, petrology and a host of geophysical and geochemical comparisons. Scientists then draw parallels from successful exploration targets and ore settings to make predictions about the viability of a potential deposit as a mine. These predictions take into account not only the size and accessibility of a resource but factors like infrastructure, location, transportation, social stability, and global market conditions.
This is achieved by drilling boreholes hundreds to thousands of feet in depth to collect prospective lode and strata samples with the ultimate goal being to determine if there exists a resource density sufficient to warrant the cost of production. Resource estimation may require pattern drilling on a set grid and down-hole probing of drill holes to determine ore body continuity. The aim of resource evaluation is to assess and hopefully expand the known size and ore grade of a deposit. A scoping study is often carried out on the ore deposit at this phase of exploration to determine if there is enough ore at a sufficient grade to warrant the cost of extraction.
Resource estimation requires additional drilling on a set grid with boreholes spaced close together to demonstrate with certainty the ore body continuity. The drill sample results are used to construct geologic, geotechnical, geochemical, and long and short term mine models. Mine models include a feasibility resource evaluation based on the commodity value compared to the production cost.
The process from exploration site selection, through target generation, resource evaluation and ore deposit definition costs tens of millions of dollars, before the potential for a copper mine is confirmed, with that the path to production is still many years away. A mine developer then must go through a lengthy permitting process before extraction. The more uncertain the lead-time to acquire permits to mine, the riskier the investment which decreases the economic viability of the ore deposit.
Once confirmed as viable, the holes are filled with an explosive compound of fuel oil and ammonium nitrate, which is capable of blasting thousands of tons of ore in a single detonation. Once mined, copper ore is treated to remove copper-bearing material in one of two ways: either through concentrating or by a SX/EW (solution extraction-electrowinning) facility.
Some ore types can be treated by crushing, grinding and mixing ore with water to produce slurry. The copper-containing particles are then removed by a process called flotation. The product of this process is dry, gray powder called copper concentrate, which contains about 30 percent copper. The concentrated copper is sent by rail to a smelter where extreme heat is used to purify the copper. It then is refined to a high-quality copper product ready for market.
Other types of ore are treated by solution extraction-electrowinning, commonly referred to as SX/EW. The copper ore is placed in large “leach” stockpiles and the copper is leached from the rock by applying dilute acidic solutions to the stockpile. This copper-bearing solution is captured and sent to a SX/EW plant where the copper is concentrated in an electrolyte solution. It is then electroplated onto sheets of very pure copper, called copper cathodes. The cathodes are 99.99 percent pure and ready for market. No smelting is needed using this process.