Precious Metal [+]Enlarge 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.

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.

Sign up for C&EN's must-read weekly newsletter Email Address * Subscribe » Contact us to opt out anytime

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.