The study by the University of Alberta's Colin Cooke and colleagues also determined that a tax imposed on local people by ancient Inca rulers might have forced a switch from production of copper to silver.
The researchers said prior evidence of metal smelting was limited mainly to the existence of metal artifacts dating to about 1,000 A.D. and the Wari Empire that preceded the Incas. The new evidence emerged from a study of metallurgical air pollutants released from ancient furnaces during the smelting process and deposited in lake sediments.
By analyzing metals in the sediments, the researchers recreated a 1,000-year history of metal smelting in the area, predating Francisco Pizarro and his Spanish conquistadors by 600 years.
The findings suggest smelters in the Morococha region of Peru switched from producing copper to silver about the time Inca rulers imposed a tax, payable in silver, on local populations.
The study is scheduled for the May 15 issue of the American Chemical Society's semi-monthly journal Environmental Science & Technology.