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Stones Forum >> Pre-Columbian Societies Knew a Thing About Extracting Gold
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Pre-Columbian Societies Knew a Thing About Extracting Gold |
bat400
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from South Central Indiana, US
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|  Posted 20-11-2009 at 04:23
Submitted by coldrum ---
When Spanish conquistadors seized the Inka emperor Atawalpa in 1532, they demanded an enormous ransom of silver and gold. Such an enormous stash suggests that the Andean people knew sophisticated metallurgy, but there has been little evidence to support this. Now a team of geologists and archaeologists have found clues that these indigenous people refined gold with mercury amalgamation, an important metallurgical technique today.
To extract precious metals from ore, workers mix liquid mercury with finely ground gold or silver ore, creating an amalgam or alloy. They then separate out the heavier amalgam and heat it to boil away the mercury, arriving at almost-pure silver or gold. The Romans knew of mercury amalgamation in the 1st century, but it was not widespread in Europe until the 12th century. Polish engineer-archaeologist Arthur Posnansky insisted as far back as 1945 that amalgamation was used near the famed Incan site of Machu Picchu, but archaeologists have always vigorously disputed these claims, noting that much of Posnansky's work was overly credulous. Instead, experts believed that the process was nonexistent in the Americas until colonist Bartolomé de Medina developed a variant in Mexico in 1557.
But William Brooks, a geologist based in Reston, Virginia, couldn't believe that societies, which produced large quantities of gold, lacked techniques to recover it from placer gold, the minute gold flakes in stream beds found along coastal Peru. So Brooks and colleagues in Peru and Colombia analyzed residual mercury levels in seven samples of pre-European-contact gold foil--three from the Sicān culture (750 C.E. - 1375 C.E.) in Peru, and four from Colombia. The team found signs of amalgamation similar to those seen in contemporary gold foil in southeastern Peru, it reports today at the Geological Society of America's annual meeting in Portland, Oregon. "We think this technique was used throughout the Andes, probably centuries before it was commonly used in Europe," Brooks says.
The researchers' work has not escaped criticism, however. Almost all known Sicān gold artifacts were looted from elite burial sites. Izumi Shimada of Southern Illinois University in Carbondale, director of the Sicān Archaeological Project says, both artifacts and bodies in the tombs were often "painted from head to foot in cinnabar," a brilliant vermillion pigment made from a mercury-sulfur compound, which could have contaminated the scientists' measurements.
Brooks agrees that contamination is a potential issue. If there were still cinnabar contamination, however, Brooks says he would have expected random variations between samples instead of the consistent measurements his team observed. Also, amalgamation, he says, just makes sense: "They had to have some way to produce all that gold, and an obvious candidate is the metallurgical technique used everywhere else in the world."
For more, see http://sciencenow.sciencemag.org/cgi/content/full/2009/1020/2.
[ This message was edited by: bat400 on 2009-11-20 04:24 ]
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