MERCURY AND SMALL-SCALE GOLD MINING IN ANCIENT PERU

The volume of gold provided by Atahualpa, the Inka king, as ransom for his release from the Spanish in 1532 is hard evidence for the efficient small-scale gold mining that took place before European contact as well as the number of placer, vein, and porphyry gold occurrences in Peru. Mercury and cinnabar, the most common ore of mercury, were available at Huancavelica, Peru; mercury occurred as a native metal and cinnabar was used for pigments, funeral preparations, and retorted to obtain mercury. Small-scale gold mining is the oldest, ongoing use of mercury and dates to 8,000 years ago in Turkey.

Using Induced Coupled Plasma (ICP) analysis, 8 ppm mercury was found in gold after amalgam was burned (refogado) in the modern gold shops in Madre de Dios, Peru. From 12.3 to 13.9 ppm mercury was found in worked gold foils from Huaca la Ventana, a Middle Sicán (A.D. 900-1200) site at Lambayeque, Peru. Similarly low levels of mercury were found in pre-contact worked gold samples from Colombia and Ecuador. The presence of low levels of mercury in analyses of modern refogado gold and pre-contact worked gold is consistent with and indicates a comparable, ancient technology that used mercury to amalgamate the fine-grained placer and vein gold, and then, as now, burning the amalgam to volatilize the mercury, beautify, and recover the gold.