Growth in the use of heap leaching technology since 1980. Source IntelligenceMine.
Heap leaching technology is a low impact form of gold mining typically utilized in areas of volcanic mineralization, where ore is shallow depth, soft volcanic soil and can be extracted through excavation rather than the more destructive and expensive shaft mining. The ore is leached of minerals through continuous irrigation on a "football pitch" sized pad. The process is self contained and has a low environmental impact, especially important in ecologically sensitive rainforest areas. Refer Figure 1.
More information on the heap leaching process can be found at MINING.com .