A new algorithm for using Pb isotopes to determine the provenance of bullion in ancient Greek coinage

A new algorithm is proposed that uses Pb isotopes to help identify the ore deposits utilized as sources of silver in Antiquity. The algorithm takes natural and analytical isotope fractionation into account. It proposes a statistical measure of the distances between the Pb isotope compositions of ores and artifacts. This measure is amenable to statistical tests at any confidence level. The new algorithm is applied to the Pb isotope compositions of the end -members derived from 368 new Pb isotope data on silver coinage minted between the late 6th to late 2nd centuries BCE and presented in Albarede et al. (2024). The algorithm identifies the local sources expected for the mints associated with major silver ores found in the territories of Athens, Thasos, and Thrace, while demonstrating that Thrace, Northern Macedonia, and Chalkidiki supplied notable amounts of bullion to Aegina and Ptolemaic Egypt. Minor proportions of what we are designating an old Sardinian 'mix' created by long-distance trade was used by archaic Athens, Corinthia (Corinth and surrounding city-states), and Aegina. Various islands in the Cyclades (Siphnos, Keos, Seriphos) also appear to be early contributors to archaic Corinthian and Macedonian silver. The present study clearly demonstrates that recycled and mixed bullion formed a substantial part of the silver stocks of mints. The new algorithm warrants more detailed Pb isotopic studies of well -dated coinage to document the changing nature of silver fluxes over time.