Mark Abbott from the University of Pittsburgh and Alexander Wolfe from the University of Alberta detected traces of lead, antimony, bismuth, silver and tin in a sediment core from the bottom of the 11-meter-deep Laguna Lobato, which is located near the colonial mining center of Potosí. The researchers dated a 74.5-cm section in the core using measurements of radioactive elements and documented an increase in smelting-associated metals that began shortly after A. D. 1000.
The smelting process employed by the Inca people utilized a wind-drafted furnace called a huayra, and any technology employed by pre-Incan societies would probably bear some similarities. This process involved using wind to intensify charcoal-fueled fires that melted down a complex ore. The metal of interest--silver, in this case--could be isolated, but in the process various metals in the ore were volatilized. These evaporated particles eventually fell out of the air and were deposited stratigraphically in the lake sediment. Abbott says correlations between metal levels in his sample and the historically documented rise of colonial smelting as well as the large-scale tin production related to World War I demonstrate the reliability of his approach.
This earlier date for the start of smelting in the region suggests that the silver industry around Potosí may have been up and running despite the scarcity of extant pre-Incan silver artifacts. Abbott suggests that the Tiwanaku culture, which collapsed around A.D. 1100, may have been smelting silver on a large scale, but cautioned that previous archaeological work has not demonstrated this. So where did the pre-Incan silver go? "We figured by deduction that the only thing thats reasonable is that it has been recycled," Abbott remarks, "first by the Inca and then by the Spanish."