Silver isotope and volatile trace element systematics in galena samples from the Iberian Peninsula and the quest for silver sources of Roman coinage

Silver played a key role in the progressive monetization of early Mediterranean civilizations. We combine Pb and Ag isotopes with volatile trace elements (Bi, Sb, and As) to assess whether, during the Roman occupation of Iberia, galena constituted a significant source of silver. We find that the Pb and Ag isotopic compositions of 47 samples of galena from eight different Iberian mining provinces, many of them exploited during Roman times, are uncorrelated. This indicates that their respective isotopic variabilities depend on different petrogenetic processes. Moreover, the range of Ag isotopic abundances is approximately six times wider than that displayed worldwide by silver coins in general and Roman silver coins in particular. Although galena from the Betics provides the best fit for Pb isotopes with Roman coins, their fit with Ag isotopic compositions is at best sporadic. We suggest that, together with Sb, Bi, and As, silver is primarily derived from fluids boiled off from differentiated mantle-derived magmas. These fluids, in turn, reacted with preexisting galena and functioned as a silver trap. Lead sulfides with ε109Ag of ~0 and unusually rich in Ag, Sb, Bi, and As were the most probable sources of ancient silver, whereas samples with ε109Ag departing significantly from ~0 reflect low-temperature isotopic fractionation processes in the upper crust.

Supplemental Material: Silver isotope and volatile trace element systematics in galena samples from the Iberian Peninsula and the quest for silver sources of Roman coinage

Method of elemental analyses, a description of the Iberian galena deposits, and Figure S1 (Pb ratios of coins and Iberian galena samples from the various mining provinces).<br>

Supplemental Material: Silver isotope and volatile trace element systematics in galena samples from the Iberian Peninsula and the quest for silver sources of Roman coinage

Method of elemental analyses, a description of the Iberian galena deposits, and Figure S1 (Pb ratios of coins and Iberian galena samples from the various mining provinces).<br>

Revealing ancient gold parting with silver and copper isotopes: implications from cementation experiments and for the analysis of gold artefacts

Gold parting enabled the production of very pure gold for various purposes from the sixth century BC onwards, but analytical proof of this pyrotechnical process is difficult. We describe a new analytical approach for the identification of purified gold combining silver and copper isotopic with trace element analyses. Parting experiments were performed with gold-silver-copper alloys using the classical salt cementation process to investigate potential silver and copper isotope fractionation and changes in trace element concentrations. In addition, we provide the first comprehensive dataset of silver isotope ratios of archaeological gold objects from the Mediterranean and Central Europe to test whether or not gold refining can be identified on the basis of isotope systematics. The results show that very heavy silver and copper isotopic compositions are clear evidence for parted gold, but that the application of copper isotopes might be limited.