Distinguishing Between Legally and Illegally Produced Gold in South Africa

Abstract

The identification of gold-bearing material is essential for combating the theft of gold in South Africa. Material seized in police operations is generally a mixture of gold from different mines, and as such cannot be traced back to a single location. ICP-OES analysis of material dissolved by acid dissolution provided a database of gold compositions comprising gold from South African mines, illegal gold stolen from the mines, and commercial gold alloys and jewelery. Discrimination between legal and illegal gold was possible due to the presence of Pb, As, Sb, Sn, Se, and Te in the stolen material, elements which are not present in legally produced gold. The presence of these elements is a quick and simple way to distinguish between gold alloys based on refined gold, such as in commercially manufactured jewelery, and gold alloys containing a proportion of unrefined and therefore illegally obtained gold.Gold lost from mining operations due to theft in South Africa makes up for a large volume of the total production value [1,2]. Anything from the ore to the final metal product is stolen and the challenge is to develop techniques like elemental profiling to identify the original source of the gold, despite different beneficiation procedures applied by companies and criminal syndicates. The mineralogy of gold ores from the Witwatersrand mines is relatively consistent and the recovery of the gold is easily achieved with unsophisticated methods, such as panning, amalgamation, and cyanidation [3,4].The trace element profiles of substances such as paint [5,6], glass [7,8] and precious metals [9] have been used to prove a link between a sample of the material in question and samples from known provenance. There have been problems with the interpretation of the results of such profiling [10], and this has been extensively discussed and reviewed in the literature [11]. Using such a database, which is representative of the population(s), should enable the attribution of the type and source of such material on a scientific basis, without having to worry about the terms -unique‖ or -identification‖ [12], and should produce results which have more weight when presented in court [13,14]. It has been shown that samples from the same source show significant uniformity in trace element distribution, and significant variation between different sources, leading to good discrimination between sources [15,16].

Global developments in forensic geology

“…A major project of the Forensic Science Laboratory, has been the identification of elemental and isotopic source markers of gold, mainly to determine its origin within Africa. This expertise has been successful not only in South Africa (Roberts et al, 2016), but also in criminal cases in South America and elsewhere.…”

The role of forensic geology in the illicit precious metals trade

“…Fingerprinting has been practiced on gold (Watling et al, 1994) as well as the platinum group metals and also on precious stones, including diamonds (Coney et al, 2012). The investigation of the intermediate products of gold processing has been done by Nixon et al, 2011, to determine the origin of gold used to produce coins from debris in the moulds, and also Dixon 2014 and Roberts et al, 2016 in tracing the origin of illegally mined gold from the Witwatersrand Basin, South Africa.…”

“…Pieces of brass and copper, and Au-free jewellery (possibly Au-coated jewellery with a negligible Au content), are shown against the y axis. It can be seen that the suspect samples have much greater variation than the normal jewellery (Roberts et al, 2016). product from base metal operations (operations in Russia, Canada, and Botswana).…”

Data Evaluation for Cassiterite and Coltan Fingerprinting

“…Analytical tools that provide information on the origin of minerals or raw materials have been developed for different materials such as gem stones [9][10][11][12], gold [13,14], yellow cake [15] or base metals [16] amongst others. For several years, the German Federal Institute for Geosciences and Natural Resources (BGR) has developed a tool called the analytical fingerprint (AFP), which aims to check independently whether the declared origin of a coltan, cassiterite or wolframite shipment is credible or not [17][18][19][20][21][22].…”