An Assessment of Osmium Isotope Ratios as a New Tool to Determine the Provenance of Gold with Platinum‐Group Metal Inclusions*

Abstract

The sudden increase in the amount of Celtic gold coins circulating in central Europe during the second century BC coincides with the appearance of platinum-group mineral (PGM) inclusions in the Celtic gold. It has been proposed that large amounts of gold were introduced from the eastern Mediterranean by mercenaries following the conquest by Alexander the Great, but another hypothesis might be the discovery of entirely new gold sources in central Europe during this time. The presence of PGM inclusions in gold objects is usually taken as an indication for an origin from placer deposits (Hartmann 1970; Park 1986). Initially, it was hoped that those inclusions could be characteristic for a certain deposit, but Meeks and Tite (1980) have shown that the compositional variation within a single gold object can be as large as the total variation observed in all investigated gold artefacts. Therefore, the elemental composition of the PGMs in gold artefacts does not provide any reliable information on the provenance of the gold.An alternative to chemical analysis of the inclusions is the determination of their osmium isotope ratios. Similarly to lead, osmium exhibits a variable isotopic composition due to the radioactive decay of 187 Re and 190 Pt. In order to investigate the potential of this new geochemical tool to determine the provenance of ancient gold, a quasi-non-destructive method for the determination of Os isotope ratios with LA-MC-ICP-MS has been developed.The results show that different types of deposits can be distinguished by Os isotope patterns and their distributions when applying a simple descriptive statistical method. In contrast to lead isotope ratios, the variations of Os isotope abundances are rather large in many ore deposits. But, also contrary to lead, the heterogeneity of the Os isotope ratios of the deposits is preserved in the artefacts, because the analysed PGMs are not dissolved during melting of the gold. Therefore, it is feasible to distinguish between different types of gold sources and to define specific deposits provided that the artefact contains several PGMs. The application of this new technique to Celtic gold coins from southern Germany and coins from western Anatolia has been demonstrated in this study.

Role of laser ablation–inductively coupled plasma–mass spectrometry in cultural heritage research: A review

“…In [99,108], the authors proposed the investigation of the osmium isotope ratios 187 Os/ 188 Os and 187 Os/ 186 Os in the platinum group metal inclusions for the study of the provenance of Celtic gold coins. In [108] the authors gave an exhaustive vision of both geological and historical aspects of such issue. In [99] applications and limits of LA and MC-ICP-MS in osmium isotopic ratio measurements were discussed.…”

“…This was a very powerful conclusion for provenance studies, since alloying and minting did not disturb the isotopic patterns. Results coming from this work aimed Junk and Pernicka (see [108]) to apply this new technique to the study of Celtic coins from Southern Germany and coins from western Anatolia and to the characterization of several geological samples (geological details in [108]). The results showed that different types of deposits can be distinguished by Os isotope patterns applying a quite simple statistical descriptive method such as the probability plot.…”

“…NIST 610 glass standard was utilized for standardization and correction of instrumental drift. Correlation mode PCA was the most efficient chemometric method to distinguish ochres coming from different areas, being 45 Sc, 82 Se, 85 Rb, 108 Pd, 178 Hf, 232 Th and 238 U the discriminating elements. Arnold et al compared INAA and LA-ICP-MS techniques in the investigation of the so-called Maya blue, through the analysis of one of the two components, i.e.…”

An overview on the ancient goldsmith's skill and the circulation of gold in the past: the role of x‐ray based techniques

“…For lower precision, laser ablation removal of a sample is possible in the case of MC-ICP-MS, 22 otherwise dissolution is necessary. 23,24 However, we must note that only the isotopic ratios of lead (element commonly present at very low contents in objects produced with native gold) or of osmium (found only in particular geo-chemical formations, 25 ) are useful for fingerprinting gold. For these reasons, elemental analysis, which can be totally nondestructive, is preferred.…”

Wands in the hand! Or Potter’s powers

“…However, there is still a need to characterise natural gold, despite the work that has been undertaken, particularly in Ireland, where the study of gold has traditionally been a topic of 'national interest' (Chapman et al, 2006). Other recent research has centred on the analysis of osmium isotope ratios for those samples of gold that display metal inclusions belonging to the platinum group (Junk and Pernicka, 2003); lead isotope signatures have been used for Au-Ag-Cu alloys with a gold content of more than 70% (Bendall et al, 2009). Both systems have been used to study coins.…”