Copper was intentionally alloyed with tin as bronze about 3500 BC, and this harder metal was so universal in early history that one period is known as the Bronze Age. Copper is easily worked and is remarkably ductile. Hence it is an ideal metal for making wire. The oxidized ores, such as cuprite and tenorite , can be reduced directly to metallic copper by heating with carbon in a furnace. The sulfide ores, such as chalcopyrite and chalcocite , require a more complex treatment in which low-grade ores must be enriched before smelting begins.
Sulfide ores are more important commercially.
Half of the world's copper deposits are in the form of chalcopyrite ore. Ores are removed either by open-pit or by underground mining. For many years, Chile has been the world's largest producer of copper, with the United States a close second. Other major producers include Canada, Zambia, Russia, Poland, China, Mexico, Kazakhstan, and Indonesia. After Arizona, the leading copper-producing states in the U.S. are New Mexico, Montana and Utah.