The Incas, who once ruled a domain as large as the Roman Empire, are known for their extensive silver mining. But they weren't the earliest silver miners in South America, according to new evidence from lake sediments in Bolivia. Someone else was smelting silver hundreds of years before the Incas arrived.
Legend has it that a 15th century Incan ruler discovered the vast silver deposits at Cerro Rico de Potosi in southern Bolivia. The mines fueled a silver industry that thrived from the early 1400s through the Spanish invasion and well beyond. The Incas used clay-lined furnaces called huayras designed to harness wind as a natural bellows, stoking the fires needed to melt ore. During smelting, some metals become volatilized into the air and eventually the metal-laden soot settles as fallout onto soils, plants, and lakes.
While conducting a paleoclimate study, geologists Mark Abbott and Alexander Wolfe of the University of Pittsburgh sampled sediments from Laguna Lobato, a lake just 6 kilometers from the famed Cerro Rico mine. The Lobato lake cores capture a 12,000-year span of the region's history. Intrigued by Incan metallurgical lore, the team saw an opportunity to study the area's mining activity.
Surprisingly, they found silver, lead, tin, and other metals in sediments dating to 1000 to 1200 A.D., long before the Incas arrived. The levels correlated with production of several thousand metric tons of silver. In the 26 September issue of Science, the team suggests that the industrious miners could be the Tiwanaku people, despite evidence that empire was in severe decline at that point in time.
"There's little doubt about the timing, because lake sediments faithfully record the state of the environment,” says paleolimnologist Mark Brenner of the University of Florida in Gainesville. Heather Lechtman, an anthropologist and metallurgist at the Massachusetts Institute of Technology, agrees it's a fine technique, but she thinks the interpretation is all wrong. “Clearly someone was mining silver, but it wasn't the Tiwanaku,” she says. “We know the Tiwanaku were gone from that area, possibly as early as 900 A.D. The question is who mined the silver, where did it go, and who was it for?”