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Was silver coinage minted from fresh metal newly extracted from the mine or was it from recycled silver deriving from older coins, silverware, or cult objects? The answer helps understand the provenance of coins and their circulation. Using Pb isotopes, the present work proposes a method to disentangle the sources of 368 silver-alloy coins from Athens, Corinth, Aegina, Thasos, Thrace, Macedonia, and Ptolemaic Egypt. We outline a new mixing model based on Principal Component Analysis and allowing for multiple steps of bullion recycling. The first component accounts for 94–99% (typically 97–99%) of the total variance, which indicates that the data form a well-defined alignment indicative of a nearly binary mixture between two source ores referred to as 'end-members'. Isotopic evidence establishes the subordinate but pervasive practice of remelting. The strong skewness of the first principal component distribution shows that lead is dominated by the binary mixing of end-members. The geologically young end-member has high 206Pb/204Pb and is best exemplified by Laurion ore used in Athenian coinage. With the possible exception of Ptolemaic samples, the second end-member attests to the persistence of a low-206Pb/204Pb, geologically much older, end-member. In most cases, the distributions of a further two principal components are nearly symmetric and can be considered normal. If they represent ore sources, their very small contribution to the total variance qualifies them as 'noise' (caused by random isotopic fluctuations in the ores and analytical issues). We find that the Pb isotope ratios in the coinage issued by each minting authority are distributed as a power law. The slope of this distribution varies from one mint to another, with the steepest slopes (Corinth and Ptolemaic Egypt) indicating the predominance of freshly mined silver. The shallow slope of Macedonia demands a larger proportion of geologically old Pb. Silver supplied to the mint of Athens shifted from a mixture of high- and low-206Pb/204Pb in the late 6th c. BCE to a predominance of unmixed high-206Pb/204Pb ore from the mines of Laurion thereafter and fell back to a mixture with intermediate Pb isotope compositions in the second half of the 4th c. BCE. The limitation of the present study resides in the relatively small number of Pb isotope data for each mint, which, in most cases, prevents a statistically significant analysis of these data by periods. Nevertheless, the quasi-binary nature of most silver mixes stands out as a new and strong first-order, albeit somewhat counterintuitive, inference from the present data. • The present work addresses the issue of silver mixing in antique Greek coinage. • New Pb isotopic compositions have been determined on 368 ancient silver coins. • PCA of Pb isotopic data shows the prevalence of quasi-binary mixing. • The two end-members consist of minor geologically old and predominant young ores. • The Pb isotope ratios issued by each minting authority follows a power law. [ABSTRACT FROM AUTHOR]

Variations of 109Ag/107Ag in silver coins and ores are particularly useful in assessing the provenance of silver bullion. Silver isotope variability results from the temperature-dependent thermodynamic fractionation of Ag isotopes among the solutions and minerals participating in ore formation. They differ from lead isotopic variations which result from the decay of uranium and thorium and reflect the geochemical properties and the tectonic age of the possible ore sources. A remarkable property of Ag isotopes is the very narrow range of isotopic variations in silver bullion used for coinage (±1×10−4) with respect to the range of ores (±1×10−3). To test the practical usefulness of the technique, we analyzed the Ag isotopic abundances of 29 ore samples from ancient mining districts in the Aegean with major and minor Ag-bearing mineralizations, and of 34 ancient Greek coins minted from the sixth to late fourth centuries BC. We distinguished two groups among the coins: a dominant population (93% of the samples) with 109Ag/107Ag consistent with literature data (ε109Ag = −1 to +1) and an isotopically lighter population (ε109Ag = −2 to −1) which we show originated from Ag-bearing mineralizations in Lavrion (Attica). We further found that sulfur (also analyzed in this study) and silver isotope compositions in Aegean ores do not correlate, a finding that we confirmed on a selection of Iberian galena samples. This shows that the genetic ore type (whether hypo, meso, or epithermal) and silver productivity are not related. Finally, we undertook chemical analysis of the Aegean ore samples and confirmed that Ag-rich ores are also Sb-rich in both Greece and Iberia. A remarkable outcome of the present Ag isotope studies of galena ores from Iberia and Greece is that silver isotope compositions can exclude, with a high degree of reliability, the majority of mines identified by lead isotope analysis as sources from which coinage silver could plausibly have been extracted and thus significantly narrow down the actual source(s). Silver isotope data on galena ores are thus a useful tool for deciding which Pb isotope data included in ore databases should be included in provenance assessment studies. Contrary to some earlier assessments, subtle silver isotope variations can occasionally help determine ore provenance within a single mining district such as Lavrion. [ABSTRACT FROM AUTHOR]