The gold mining life cycle
Step 1 (Surface)
Prior to mining, exploration takes place to find gold-bearing ore in commercially viable concentrations. Geochemical and geophysical techniques are used to identify the presence of a buried ore deposit. Geologists drill to check mineral quality in identified locations. The South African government regulates the mining licence processes for exploration, mining, environmental authorisations and water use.
Step 2 (Surface)
The mine site must be prepared for development. The headgear over the mine shaft needs to be built and the shaft sunk deep into the ground to transport people and materials in and out of the mine. Other required infrastructure includes structures for mining, milling and processing; and various workshops.
Step 3 (Underground)
Miners, mining materials and equipment are transported deep underground via the mine cage in the vertical shaft, which can go to depths of up to 3.5km below the surface. Open-pit gold mining also takes place in South Africa. This is a mining technique which excavates at the surface to extract ore. The mine is open to the surface for the duration of its life.
Step 4 (Underground)
Mine planning and on-reef development involves establishing tunnels – haulages and cross-cuts – to open up the earth and the stope face so that the gold-bearing reef can be accessed.
Step 5 (Underground)
Once the stope face has been established and the gold-bearing reef exposed, drilling begins in preparation for blasting of the reef.
Step 6 (Underground)
BLASTING AND HAULING
After the stope has been blasted, the rock broken in the blast (the gold-bearing ore) is collected – this is called vamping and sweeping – and transported to the shaft, via conveyors and underground locos, to be hoisted to surface.
Step 7 (Surface)
The ore is hoisted to surface in the materialshandling shaft from where it is conveyed, either by overland conveyor, surface rail or truck to the crushing and milling circuits where the process to extract the pure gold from the rock begins.
Step 8 (Surface)/h5>
The large pieces of ore (broken rock) are fed into a series of crushers and grinding mills to break down the ore into much smaller sized rock so that the gold can be more easily extracted. At this stage of the process, the ore is ground down to fine sand-like particles.
Step 9 (Surface)
These sand-like particles are combined with water to form a slurry to which additional chemicals – cyanide and carbon – are added to facilitate dissolving the gold and help with its extraction. The gold particles, extracted in this process, attach themselves to the carbon. The next step in the process involves stripping the carbon from the gold. Most companies retreat their slurry or 'tailings' for any remaining gold, uranium and sulphides.
Step 10 (Surface)
The gold obtained once the carbon has been stripped away is then smelted ie heated at extreme temperatures so that it liquefies, and is poured to form doré bars.
Step 11 (Surface)
The doré bars are sent to precious metal refineries for further processing and refining to a purity of at least 99.5% to meet the good delivery quality standards set by the London Bullion Market Association.
Step 12 (Surface)
CLOSURE AND REHABILITATION
Once the gold reserve at a mine has been exhausted, the owner must close and rehabilitate the site before a closure is permitted. Underground tunnels are stabilised and entrances are sealed off. Rehabilitation means the process of returning mined land to its pre-existing condition or to another agreed use.
Note: Environmental management and rehabilitation take place at each stage of the mining process.