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Web Date: December 18, 2012

Where Did The Ancient Xiongnu Get Their Gold?

Cultural Heritage: Platinum levels suggest Xiongnu people of Mongolia produced their own gold jewelry
Department: Science & Technology
News Channels: Analytical SCENE, Materials SCENE
Keywords: Xiongnu, gold, Mongolia, XRF
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Precious Metal
The Xiongnu people, who lived in Mongolia in the second and third centuries B.C., valued gold in the form of decadent jewelry and crowns.
Credit: Gary Todd
Photo of xiongnu gold artifact
 
Precious Metal
The Xiongnu people, who lived in Mongolia in the second and third centuries B.C., valued gold in the form of decadent jewelry and crowns.
Credit: Gary Todd

Warrior nomads in Mongolia called the Xiongnu had a taste for the finer things in life, particularly gold jewelry, which they wore to their graves. Archeologists have wondered whether the gold objects found in second- and third-century B.C. Xiongnu burial sites originated from local deposits. Perhaps, researchers thought, the objects were gifts from the Chinese, who had a tumultuous relationship with their neighbors that alternated between warring and intermarrying.

Experiments using a synchrotron X-ray source now suggest that the Xiongnu gold originated from local panning in Mongolia instead of Chinese mines, says Martin Radtke, a physicist at Germany’s Federal Institute for Materials Research & Testing, in Berlin. Radtke’s team was invited to collaborate with researchers in Paris at the Center for Research & Restoration of Museums of France to pinpoint the likely geographical provenance of the Xiongnu gold (Anal. Chem., DOI: 10.1021/ac3025416).

Figuring out the gold’s provenance by a standard technique, such as studying the isotope composition of trace elements in the metal, was not possible, Radtke says. That’s because the method requires removing a small sample, which was not an option for the rare Xiongnu artifacts.

So the researchers turned to synchrotron radiation X-ray fluorescence (XRF), a noninvasive technique, and looked for the presence of platinum impurities in some 30 Xiongnu gold foils found in four tombs. They reasoned that if the Xiongnu had sourced the gold locally, they would have done so by panning, which leaves traces of platinum in the gold, Radtke says. Meanwhile if they found no platinum, the results would point toward a Chinese origin, since the mining techniques used by the Chinese during this point in history would have resulted in gold that was very low in platinum.

Unfortunately for the researchers, looking for trace platinum in gold using XRF is challenging because the signal for platinum is buried in the signal for gold. So the scientists employed a few experimental tricks to sidestep this problem.

First they adjusted the wavelength of the excitation energy to preferentially excite platinum signals. Next they measured or modeled the XRF spectra of all possible trace elements in the gold artifacts, such as tin, copper, and silver, and then subtracted these individual element spectra from the overall spectrum of the gold artifacts. The result was a spectrum that corresponded to that of platinum, suggesting that the origin of the artifacts was indeed the Xiongnu people themselves.

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Comments
Bill Cornelius (Mon Jan 14 14:44:21 EST 2013)
This sounds like the process for counting dinosaur livestock on Isla Sorna. Meaning what else is there that wasn't found, and could it have a combined pattern that looks like platinum?
Julien Biver (Tue Jan 15 04:57:06 EST 2013)
As an archaeologist, I've been working on metals as well as gold recently and I am a bit concerned about this study. Historicaly, of course, the chinese have mined the gold which tend to have lesser concentrations of platinium than the alluvial gold that had been panned. The problem with panning is that it is only leaves faint archaeological evidence : it could have been used in China at the time, in sources now extinguished and non retracable. My trail of thoughts here is more focused on the archaeological area than on the analysis altogether. That being said, I can only admire interdisciplinary studies such as this one !

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