It is a worldwide phenomenon that, as copper mines are getting deeper, more sulfidic ore is encountered. Furthermore, the average grade of reserves and unexploited deposits is dropping. Acid heap leaching has been widely used to extract copper from oxide ores, and heap bioleaching (with forced air injection) is used for the treatment of low-grade secondary sulfide copper ores. The deeper primary hypogene copper ores account for the larger proportion of known resources that remain in the ground, but these are of relatively low copper grade. In addition, chalcopyrite is well known to be refractory to leaching, and a lot of research effort has therefore been spent on tailoring the heap leaching process to treating chalcopyrite ore.