Amalgamation and small-scale gold mining in the ancient Andes

Abstract

In 1532, the volume of gold provided by Atahualpa, the Inka king, as ransom for his release from the Spanish was hard evidence for the efficient small-scale gold mining that took place before European contact and the number of gold occurrences in the Andes. At Huancavelica, Peru, mercury occurs as a native metal and as cinnabar [HgS], which was used for pigments, funeral preparations, and retorted to obtain mercury. Using Inductively Coupled Plasma analysis (ICP), an average of 15 ppm (parts per million) mercury was found in the gold after the gold-mercury amalgam, with more than 300 000 ppm mercury, was burned to volatilize (rogado) the mercury. From 12,3 to 13,9 ppm mercury was found in worked gold foils from Huaca la Ventana, a Middle Sican (A. D. 900-1200) site at Lambayeque, Peru and low levels of mercury were found in pre-contact gold foils from Colombia (1-12 ppm). Similarly low levels of mercury in the analyses of modern refogado gold and pre-contact gold foils are consistent with a comparable, ancient small-scale mining technology that would have used mercury to amalgamate the fine-grained gold; and then, as now, burning the amalgam to volatilize the mercury and beautify and recover the gold.