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 mining of placer and hard-rock gold deposits that took place before European contact. Thus far, however, there has been no research into gold mining technology in the ancient Andes. Mercury is used for contemporary small-scale gold mining and was also used in the ancient world. Mercury was available in Huancavelica, Perú, as a native metal and as cinnabar [HgS], which was powdered and used for funeral preparations, pigments, and retorted to obtain mercury. Small-scale placer gold mining requires initial gravity concentration, or panning, and then mercury is used to amalgamate and recover the fine-grained gold. In modern and in ancient Perú, vein or rock containing fine-grained gold would be crushed using a quimbalete and water, and then mercury would be added to amalgamate the gold. Using Inductively Coupled Plasma (ICP) analysis, an average of 15 ppm mercury was found in end-product gold produced by present-day small-scale gold mining in Perú after the gold–mercury amalgam was burned. Similar concentrations were found in end-product, hammered gold foils from Huaca la Ventana, a Middle Sicán site at Lambayeque, Perú, and low levels of mercury were found in precontact gold foils from Colombia. The similarly low levels of mercury in the analyses of present-day gold and precontact hammered gold foils are consistent with a comparable, ancient small-scale gold mining technology using mercury to amalgamate the gold and then burning the amalgam to volatilize the mercury, beautify, and recover the gold.