Copper minerals and ores are found in both igneous and sedimentary rocks. Mining of copper ores is carried out using one of two methods.
- Underground mining is achieved by sinking shafts to the appropriate levels and then driving horizontal tunnels, called adits, to reach the ore. Underground mining is, however, relatively expensive and is generally limited to rich ores. El Teniente, in Chile, is the world’s largest underground copper mine.
- Open pit mining is employed when the orebodies are extensive, low in grade, and relatively near the surface, where they can be quarried after removal of overburden. Chile also boasts the world’s largest (in terms of output) open-pit copper mine, Escondida. The largest copper mine in North America (and the world’s largest man-made excavation) is the Bingham Canyon Mine near Salt Lake City, Utah. A $1.5 billion modernization program completed in 1998 turned Bingham Canyon into North America’s lowest-cost copper producer, a model of operational efficiency and environmental compliance.