Faster and cheaper than diamond drilling. Non-valuable materials associated with the ore minerals. Usually lower than reserve grade because of dilution by non-ore grade materials. The metal-laden solution is then collected for metal recovery. The broken rock is extracted and the resulting open chamber is not filled with supporting material.
Oxidation tends to make the ore more porous which facilitates flow of solutions into the rock.
This effect is particularly important for oxidized gold ore as it permits more complete permeation of cyanide solutions so that minute particles of gold in the interior of the mineral grains can be readily dissolved. Reclamation activity includes the removal of buildings, equipment, machinery and other physical remnants of mining, closure of tailings impoundments, leach pads and other mine features, and contouring, covering and revegetation of waste rock piles and other disturbed areas. It is generally stated as a percentage of the material recovered compared to the total material present. The refractory nature can be either silica or sulfide encapsulation of the gold or the presence of naturally occurring carbons that reduce gold recovery. Reserves are customarily stated in terms of ore when dealing with metallic minerals.