Lake-sediment geochemistry reveals 1400 years of evolving extractive metallurgy at Cerro de Pasco, Peruvian Andes

The geochemical record preserved in lake sediments is a potentially powerful tool in archaeometallurgy. Here, sediments from Llamacocha, a small lake in the central Peruvian Andes, are used to reconstruct a 1400 year legacy of metal extraction from Cerro de Pasco, once the largest silver mine in the world. The earliest evidence for anthropogenic lead (Pb) enrichment occurs ca. A. D. 600 and is confirmed by Pb stable isotope ratios that match those of Cerro de Pasco ores. Early Pb pollution is attributed to precolonial smelting for silver production, which relied on galena-based fluxes. Following colonial control of the mine ca. A. D. 1600, the switch to mercury (Hg) amalgamation for winning silver resulted in atmospheric Hg emissions, as registered in Llamacocha sediments. Both Pb and Hg deposition increased through the twentieth century, attaining peak values in A. D. 1968 and 1942, respectively. Principal components analysis (PCA) identifies a gradient that differentiates anthropogenic from natural metals within the record, confirming that early smelting led to the volatilization of trace metals associated with local ore mineralogy. These results represent the first evidence for a major precolonial mining industry at Cerro de Pasco, provide a chronological framework for evolving extractive technologies, and are the first to document widespread Hg pollution associated with colonial Hg amalgamation.