National Geographic : 1968 May
Rotating grinder reduces crushed ore to sand. Agitator tank concocts a soup of finely ground ore and powerful cyanide solution used to dissolve gold. D EVOURING 2,500 TONS of earth's crust a day, the mill works around the clock, digesting every morsel for gold. Each parti cle goes through days of grinding, soaking, filtering, and smelting in the boulder-to-bullion process shown here. The first plant to extract invis ible gold on so vast a scale, Carlin dissolves fine grains with cyanide, a method developed in Scotland in 1887. The mine also utilizes Atomic Age technology: gamma rays to measure the consistency of mud in the thickener tanks and an atomic assaying process to run frequent checks on the ore. Automated me tering controls the solutions. The entire operation stresses efficien cy, for though production costs can rise, the price of gold remains fixed by the Federal Government to help stabilize the dollar and other free-world currencies. WASTE CLARIFIER FILTER CLARIFIEDSOLUTIO SURGETANK DEAERATOR S POWDERED ZINC Thickener tanks settle out waste while gold-bearing cyanide, called pregnant solution, flows off the top. PRECIPITATEFILTER ANDPRESS GL MELTING GOLDBUTTONM URNACE lowing furnace smelts a gold "button," about 95 pounds. Clear solution (above), mixed with zinc dust, flows into filter presses (below). Zinc-gold compound emerges (above right).