Ag and Pb isotope systematics in galena ores from southern Sardinia and southern France flag potential silver sources in antiquity

While lead isotopes serve to determine potential ore provenance, silver isotopes help evaluate if a specific ore flagged by Pb isotopes has actually been exploited as a silver source of bullion in antiquity. The combination of Ag and Pb isotopes thus constitutes a powerful tool to address provenance and identify potential ore sources. It has recently been observed that the vast majority of silver isotopic abundances in hundreds of silver coins from different historical periods (pre-Roman and Roman, Middle Ages, early modern times) and different localities (Persia, Greece, Rome, Western Europe, England, Spanish Americas) falls in a remarkably narrow interval (± 0.1 permil, or ± 1 on the epsilon scale used by geochemists to enhance the visibility of small isotopic differences, group 1). Five Greek coins and some pieces from Levantine hacksilber hoards dated to the Late Bronze and Early Iron Ages have isotopic abundances somewhat below the range of group 1 (–0.2 to –0.1 permil, or -2 to -1 on the epsilon scale, group 2).

The coverage of Ag isotopes in ores from the western Mediterranean, with the exception of Iberia, is inexistant. Here the above-mentioned approach is illustrated with new Pb and Ag isotopic analyses of samples from southern Sardinia and southern France. The majority of Ag isotope compositions of galena samples from Sardinia belongs to group 2 and none to group 1. While scholarly works imply that Sardinia may have provided silver to the Levant during the Iron Age, the exact location of the Sardinian ores that contributed to classical and archaic Greek coins is still unknown. Galena samples from southern France (the Pyrenees, Montagne Noire, Cévennes) are characterized by Ag isotope compositions from both groups 1 and 2, indicating that silver-bearing ore deposits in Gaul could be considered a potential source for silver bullion, both before and during the Roman era.