Randal Birkey was commissioned by a Denver, Colorado graphic design firm in the 1980’s to prepare a series of illustrations on “How Gold is Made for Kids”. The illustration series was to be used by their client, Santa Fe Pacific, (now Newmont Gold), in printed corporate communication brochures, posters and other tools. The series was modified several times over the years to reflect changes in company ownership and name, as well as changes and enhancements to the gold mining process.
1. EXPLORATION: The gold mining process begins with geologists discovering a deposit.
2. DRILLING: After finding indications of gold, drill rigs are used to obtain samples from below the surface. These samples are analyzed for their gold content. If there is enough gold in the deposit to make mining economically feasible, and after permitting, design and construction, a mine is developed.
3. MINING: The ore is mined in four steps: drilling, blasting, loading and hauling. In the case of a surface mine, a pattern of holes is drilled in the pit and filled with explosives.
4. BLASTING: The explosives are detonated in order to break up the ground so it can be loaded by large shovels or front end loaders into haul trucks.
5. SHAFT MINING: Some orebodies are more economically mined using underground methods. In this case a tunnel called an adit, or a shaft, is dug into the earth. Short tunnels leading from the adit or shaft, called stopes, are dug to access the ore. The surface containing the ore, called a face, is drilled and loaded with explosives. Following blasting, the broken ore is loaded into trucks and taken to the surface. Once mining is completed in a particular stope, it is backfilled with a cement compound.
6. HAULING: The haul trucks transport the ore either to heap leach pads for heap leaching or directly to the mill to recover the gold from the ore.
7. PROCESSING: Heap leaching – The ore is crushed or placed directly on lined leach pads where a weak cyanide solution is applied to the surface of the heap. The solution percolates down through the ore, where it leaches the gold and flows to a central collection location. All of the solution is recovered in this closed system, preventing any infiltration into the ground below.
8. MILLING: The ore is fed into a series of grinding mills where steel balls grind the ore to a fine slurry or powder.
9. AUTOCLAVE: Some types of ore require further processing before gold is recovered. In this case, the slurry is pressure-oxidized in an autoclave (shown above) before going to the leaching tanks or a dry powder is fed through a roaster.
10. ROASTER: A dry powder from the autoclave is fed through a roaster, in which it is oxidized using heat before being sent to the leaching tanks as a slurry.
11. LEACHING TANKS: The slurry is thickened and run through a series of leaching tanks. The gold in the slurry adheres to carbon in the tanks.
12. STRIPPING: The carbon is then moved into a stripping vessel where the gold is removed from the carbon by pumping a hot caustic solution through the carbon. The carbon is later recycled.
13. Electro-Winning: The gold-bearing solution is pumped through electro-winning cells or through a zinc precipitation circuit where the gold is recovered from the solution.
14. POURING: The gold is then melted in a furnace at about 2,100 degrees F and poured into molds, creating Dore bars.
15. DORE BARS: Dore bars are unrefined gold bullion bars containing anywhere from 60% to 95% gold.
16. REFINERY: The bars are sent to a refinery for further processing into pure gold.
17. RECLAMATION: To restore the landscape for future uses such as ranching, recreation or wildlife habitat protection, reclamation, including revegetation, is implemented concurrently during mining.