Heap leaching has become the preferred method of recovering minerals from low-grade ore from open pit mines. Copper, gold, silver and other metals are most common. The metal deposits are dissolved by chemicals applied to the top of the heap of ore, which eventually leach to the bottom of the pile. Here a geomembrane liner captures the solution preventing it from migrating into the ground, before directing the solution by gravity to a collection system. The solution is sent to a refinery where the metal can be precipitated out and the solution sent back to the heap to be used again to dissolve more metal.