Prospecting for ore targetsGold's Journey from Exploration to Mining
Processing
Most of the ore from the mine is in fragments smaller than 300 mm. To make extraction of the gold possible the ore must be crushed and milled so that all particles are no more than 0.1 mm. This is done in several stages. Crushing is done in a dry condition and the milling is done wet. The energy costs of these steps are significant, and the process requires tight operational control.
The gold content of the ore is now for the most part physically exposed and ready for further processing. This is done through leaching with cyanide, which together with the oxygen in the atmosphere has the property of dissolving the precious metal in water. As the gold dissolves it is adsorbed onto activated carbon, which is added to the solution. This carbon, with its gold content, is then separated out for further processing.
The waste product (the ore stripped of gold and silver) is then pumped to a sand depot for disposal. During initial stages of the process a separation has been done so that the more environmentally hazardous elements, like sulphur and heavy metals, have been concentrated to a smaller part of the waste product. This part (around 10%) is disposed of in a very qualified way, while the non-toxic waste undergoes a more simple treatment.
The gold-laden active carbon is then leached with a concentrated cyanide solution at a high temperature. The carbon is then re-used. The gold-rich solution now undergoes electrolysis, at which point the gold along with silver is deposited on a cathode material consisting of steel wool.