Applying Pb-Sr isotopic analysis to the provenance study of Bronze coinage from Elea/Velia in ancient metallurgical networks: common and noble approaches

This study focuses on a collection of one-hundred bronze coins from Elea/Velia, an ancient Greek colony, which dates from the late 5th century to the early 1st century BC. The study combines archaeological preservation with cutting-edge archaeometric techniques, made possible through collaboration among La Sapienza University of Rome, the IGAG-CNR laboratories, Laboratori Nazionali del Gran Sasso (LNGS- INFN), and the Università degli Studi di Salerno (DiSPaC). The alloy compositions (Cu-Sn-Pb) and select trace metals were analyzed using ICP- MS on a small fraction of the sample, specifically drilled from the polished edges of the coins. Variations in the percentages of Cu, Sn, and Pb were noted throughout the development of the coinage. Spider diagrams of trace elements (Fe, Co, Ni, Zn, As, Ag, Sb, Au, and Sr), complemented by principal component analysis, revealing a clustering of samples from the same mineralization source. Lead (Pb) and strontium (Sr) isotopic ratios were measured using the same solution as the trace elements and analyzed through the TIMS (Thermal Ionization Mass Spectrometry). These isotopes serve as valuable geochemical tools for deducing the ore deposit provenance of archaeological materials, shedding light on ancient mining and metallurgical practices as well as trade networks. Lead isotopes are commonly employed in archaeometry, to establish provenances, however, their effectiveness can be hampered by factors such as ore mixing and smelting processes. In contrast, strontium isotopes hold considerable promise, thanks to the wealth of geological data available in the literature. However, they are often overlooked in analyses, likely due to their lower concentrations in artifacts. Our findings indicate that lead isotopes effectively trace the provenance of 82 coins, primarily sourced from Greece and Spain, with minor contributions from Italy. In addition, Pb isotopes reveal that most metals in earlier coinages (Heracles, Athena, and Zeus/Owl coins from the 4th–2nd century BC) likely originated from Aegean Greece, particularly the Cyclades, while later coinages (Athena/Tripod coins from the 1st century BC) exhibit metals from Spanish deposits near Cartagena-Mazarrón and Almería. Some alloys trace back to Italian sources in Sardinia and Tuscany. On the contrary 18 coins cannot be associated with any known source, suggesting the possibility of extensive metal recycling. The analysis of the strontium isotopic ratios (87Sr/86Sr) in 99 samples indicates a potential geological connection to the provenance locality, as suggested by the lead isotope findings. The absence of comprehensive mineral data from various mineralization types currently limits the application of Sr isotopes in assessing the provenance of ancient coins. However, our findings demonstrate the promising application of Sr isotopes in the study of metal artifacts and highlight the need for robust isotopic databases on ores to aid in provenance attribution. In conclusions, this work introduces a pioneering Pb-Sr isotopic database for the coinage of Velia, contributing to advancements in provenance methodologies and enhancing our understanding of ancient Mediterranean metallurgical and economic networks.