The Mining Process
Mining the gold from rock deposits
Miners and their equipment are transported underground by a strong steel cage which goes down a vertical shaft, sometimes to depths of 4km. This is only if the mine is an underground one. Otherwise, for an open-pit gold mine, gold is excavated on the ground’s surface to extract the ore.
In order to extract the valuable gold ore from the rock deposits, samples are taken and assayed. Assay results are used to demarcate which areas have higher concentrations of ore versus simple rock. In most instances in underground mines, the rock must first be blasted in a series of tunnels called stopes. This loosens the rock enough for more specialised tools like drills to be used. Underground-to-surface conveyors then transport the rock to the ore stockpiles, where mining trucks will take them to the primary crushers.
Crushing and Refinement
The primary crushers break the larger rocks down to a size suitable for transport on the conveyor belt which leads them to. From there, a conveyor belt made of tough materials to withstand weather changes, transports the rocks which have been crushed to the mill for further refinement. The ore is ground down to fine sand-like particles, combined with water to form a slurry, and then specific chemicals are added to it such as cyanide and carbon. This helps the gold to dissolve and facilitates better extraction. The gold particles attach themselves to the carbon. When done successfully, the process removes 93% of the gold which was in the slurry.
The carbon and gold now form what is referred to as “loaded carbon”. The loaded carbon is directed into an elution column where the bullion is washed off. Elution is the process of extracting a single material from another by washing it with a solvent. This removes the gold from the carbon. The carbon is now called “barren” and is recycled. The wash-solution is then passed through stainless steel cathodes where the gold bonds to the steel.
The cathodes are rinsed to yield a gold-bearing sludge which is dried, mixed with fluxes and put into the furnace. After several hours the molten material is poured into moulds producing bars of doré bullion. This is a semi-pure alloy of gold and silver, which is refined further, at a later stage. Once this is done the gold produced is 24 karat, pure gold.