Ice-Core Evidence of Earliest Extensive Copper Metallurgy in the Andes 2700 Years ago

Abstract

The importance of metallurgy for social and economic development is indisputable. Although copper (Cu) was essential for the wealth of pre-and post-colonial societies in the Andes, the onset of extensive Cu metallurgy in South America is still debated. Comprehensive archaeological findings point to first sophisticated Cu metallurgy during the Moche culture ~200-800 AD, whereas peat-bog records from southern South America suggest earliest pollution potentially from Cu smelting as far back as ~2000 BC. Here we present a 6500-years Cu emission history for the Andean Altiplano, based on ice-core records from Illimani glacier in Bolivia, providing the first complete history of large-scale Cu smelting activities in South America. We find earliest anthropogenic Cu pollution during the Early Horizon period ~700-50 BC, and attribute the onset of intensified Cu smelting in South America to the activities of the central Andean Chiripa and Chavin cultures ~2700 years ago. This study provides for the first time substantial evidence for extensive Cu metallurgy already during these early cultures. Andean cultures developed one of the great metallurgical traditions of the ancient world, but they have been far less investigated and understood than the ones in the Middle East and Europe, or Asia. For Andean metallurgy copper (Cu) in particular was an important resource and still plays a central economic role in many South American countries today. All ancient Andean alloys, except the naturally occurring gold-silver (Au-Ag) alloy, contained Cu. This metal is therefore often referred to as the "backbone of Andean metallurgy-the mother of all Andean metals" 1. Despite of this importance the onset of extensive Cu metallurgy in South America is still debated. Most direct evidence is provided by archaeological artefacts. Earliest Cu artefacts in the central Andes found at Mina Perdida in Peru date back to ~1410 to 1090 BC 2. They consist of native Cu and Au hammered into thin foils, documenting that working of native Cu preceded the production of smelted Cu objects 2. A first hint of the use of molten Cu is a Cu-Ag bead from the Peruvian site of Malpaso dated to ~1000 BC 3,4. Thus, temperatures of about 1000 °C were achievable at that time and it is very likely that South American Cu production by smelting started soon after 1000 BC. The verification of this hypothesis is challenging since very few extant artefacts are known from that early period and ancient metallurgical sites are difficult to find because of the lack of substantive remains, particularly smelting installations. Prehistoric smelting furnaces tended to be small or smelting was performed on open fires and thus left little permanent remains 5. The scarceness of Cu artefacts holds true also for the following ~1000 years. Among the archaeological findings attributed to the Chavin culture in Peru (~900-200 BC) most were produced from native Au or Au-Cu-Ag alloys and only very few from pure Cu 6-9. Further south, Cu slag was found at Wankarani on the Bolivian Altiplano and p...