The U of A's Dr. Alexander Wolfe, from the Department of Earth and Atmospheric Sciences, and Dr. Mark Abbott from the University of Pittsburgh, took samples from lake sediments deposited near the major silver deposit of Cerro Rico de Potosi, Bolivia. From concentrations of metals associated with smelting, such as lead, they inferred the history of smelting from the mountain's rich ores, proving than an active metallurgical industry existed well before even the Incas discovered the mountain--as far back as the 11th Century AD.
The research is published in the current edition of the prestigious international journal, Science.
"We began seeing high levels of lead which are heavy and not mobile in sediments and therefore making good markers for air pollution and for monitoring metallurgical activity," said Wolfe. "Also, Incas used a lead-containing flux to extract silver and to regulate the temperature of smelting, providing a good marker in the sediments."
The team was able to compare the sample with metals in the naturally occurring background from several thousand years ago and map out a chronology of when smelting took place. "We found a gross mismatch between the amount of silver apparently smelted from the mountain and the scant regional archaeological evidence in the form of silver artifacts that have survived," said Wolfe. "There has been no previous evidence for the intensity of metallurgy in the pre-Columbian times that we infer from the lake sediment record."
Although it is impossible to determine the precise amount of silver extracted from Cerro Rico, the research team's data implies that several thousand tons of silver were produced in pre-Incan times. There are two possibilities for the missing silver artifacts that would have been produced during the pre-Incan era: the silver exists somewhere but has not yet been located by archaeologists or more likely, subsequent cultures have looted the artifacts.
"Although major new archaeological discoveries in the Andes remain a distinct possibility, the likelihood seems equally probably that most of this silver was recycled and transported elsewhere in the Americas before conquest, or eventually exported overseas by the Spanish," write the authors in the paper.
The research also shows that early Andean cultures faced many challenges often associated with modern times. They were quite advanced technologically--so much so that they were capable of severely polluting the atmosphere as illustrated by the lead levels. This culture also apparently remained vulnerable to climate change, as evidenced by the decline of smelting (1200-1400 AD) during a known interval of drought.