Gold mining has changed substantially over the years. From Behind 25-Year High for Gold: Changes From Ground to Market:
As recently as the 1970s, 70% of the world’s gold was taken from South Africa’s deep underground mines. South Africa remains the world’s largest producer, but its output in tons now is one-third of what it was, and it represents 12% of the world’s expanded production. Australia and the U.S. follow with 10% each, China 9%, Peru 8% and Russia and Indonesia 7% each, according to London-based researcher GFMS Ltd.The gold mined in most parts of the world, including at Mr. Lenz’s Lone Tree Mine, differs significantly from the stuff that lured prospectors west 150 years ago. Visible sources of gold — gleaming mountainside veins or nuggets and powder lying in riverbeds — are becoming rarer. The Lone Tree Mine is an open pit two miles long and almost 1,000 feet deep, a monstrous gash that some day will be turned into a large lake. The gold Mr. Lenz removes from it consists of microscopic particles laced through earth and rock.
“I’ve been here for 14 years,” says Mark Evatz, who supervises Lone Tree Mine’s digging and transport, “and I have never seen an ounce of gold that I have mined.”
To find the gold, modern-day prospectors like Newmont’s Wayne Trudel pore over old drilling reports, set up computer models and theorize about which mineral formations are likely to contain fine gold particles. The process can take years, at a cost of $19 per ounce of discovery. The geologists drill out samples from various strata and examine them under microscopes. The results are plotted on three-dimensional computerized maps that outline twisting underground gold veins. As the price of gold rises, the areas on the maps considered worth mining expand.
At Lone Tree, each ounce of gold is sprinkled through 75 tons of rock and soil. Miners use Global Positioning System consoles to make sure they are digging in the right spot — since ore-rich rock looks little different from other rock. The gold is separated from rock and other metals through a variety of technologies that employ heat, pressure, cyanide and charcoal.
In all, Lone Tree produces about 600 ounces of gold a day, in the form of a damp, cake-like sludge that is 50% to 75% gold and also includes silver and other metals.
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The sludge is delivered to a Newmont plant in another mining town, Carlin, about an hour away. Technicians run an electrical current through the sludge, separating out more base metals. The gold is formed into 100-pound “buttons” shaped like Hershey’s kisses, now finally gold-colored but tinged with red, green or black (depending on how much copper, silver or nickel remains).About three times a week, when 2,000 ounces to 4,000 ounces have accumulated, workers melt the buttons into 55-pound to 60-pound bars. The bars, between 60% and 95% gold, are known as “doré,” a French word meaning “gilded” or “golden.”