Prosecutors in South Africa hope to use a technique that produces a chemical “gold fingerprint” to trace where a stolen haul of the precious metal originated.
By analysing chemical impurities, scientists hope to show that the gold, which was purportedly being sold as jewellers’ offcuts, was stolen from South African mines.
This is the first time the combination of tests that make up a gold fingerprint has been used in court.
“It is possible to clearly discriminate between gold from within various parts of the Witwatersrand Basin [a gold producing region of South Africa] and gold from other Southern African and world-wide sources,” Henriette Ueckermann, of the University of East Anglia in Norwich, told the annual meeting of the American Academy of Forensic Sciences in San Antonio, Texas. “Furthermore, there is a clear discrimination between bullion, manufactured gold alloys and illegally produced gold.”
The illegal gold market is big business. The South African mining industry estimates that between 21 and 42 tonnes of gold, worth around R1,034-billion, is stolen in the country annually — around 0,8% and 1,6% of global annual production. “It’s a huge amount of gold,” said Ueckermann, who is collaborating with the South African police service’s forensic crime laboratory in Pretoria.
The thieves range from opportunistic mine workers to organised gangs who steal large amounts. It is then “laundered” by organised criminals. They typically claim it is jewellery offcuts or smuggle it out of the country before re-importing it, claiming it was mined in another African country. “It is directly and indirectly used to sponsor organised crime syndicates and various illegal activities, both nationally and internationally,” Ueckermann added.
Currently, only around 2% of South Africa’s stolen gold is recovered.
Differences in the way the gold ore is formed geologically leads to subtle differences in its chemical composition, which can be used by scientists to work out its origins.
The fingerprinting works by using a battery of analytical techniques to look at the relative amounts of 30 different impurities, including platinum, palladium, lead, thallium and bismuth.
For certain elements such as lead, the researchers also look at the ratio between the metal’s different isotopes — forms of the same element which have a different number of neutrons in the nucleus. No single element analysis will pinpoint the gold’s original location on its own, but the results from a combination of tests can give a reasonably precise geographical location.
When the team receives a sample of suspected illegal gold they compare its chemical fingerprint with a database of previously collected samples of known origin. This database, which has been built up since 2000, includes gold from around South Africa and other countries.
Ueckermann said the technique could be adapted to test the provenance of other precious metals or commodities such as food. – Guardian Unlimited Â