ENIGMA OF ALLUVIAL GOLD MINING IN PRE-CONTACT PERU-THE PRESENT IS KEY TO THE PAST

The Inca king Atahualpa’s gold ransom is hard evidence of the exceptional indigenous gold mining technology in the ancient Andes. Peru has produced metals for more than 3000 years and is the leading gold producer in Latin America today; however, the gold mining technology used in pre-contact Peru has thus far not been described. Therefore, an understanding of present-day gold mining methods is key to gold mining in the past. For example, in 2018, Peru’s large-scale open-pit gold mines produced 123,767 kg of gold using cyanide and 18,875 kg of gold were produced from small-scale alluvial gold mines that used gravity separation and mercury. Industrial amounts of gold are produced in only two ways: 1) gravity separation/mercury, and 2) cyanide. Since cyanide was not used until the 1880s, mercury amalgamation must be critiqued as the mining technology that produced industrial amounts of gold from alluvial sources in pre-contact Peru. Gravity separation is the oldest method and utilizes the high specific gravity of the gold (~19 sg), first in water to provide a gold-bearing, heavy-mineral concentrate 'arena negra', and then mercury 'azogue' is added. Sparse nuggets found in streams could easily be removed by hand; however, the visible gold flakes 'chispitas' which are mm-sized and smaller, can only be selectively recovered from the heavy-mineral separate by using the centuries-old method of mercury amalgamation.