The Application of Sr isotopes to decipher the source of Nabataean bronze coins collected in Israel

This study presents the analyses of the strontium (Sr) isotope ratio of 40 copper-based coins, belonging to the Nabataean Kingdom and hailing from the Israel Antiquities Authority at the Israel Museum (Jerusalem). The Nabataean Kingdom was a powerful political entity, that flourished in modern-day Jordan, Israel, and Syria between the 4th century B.C.-106 A.D. The Nabataeans were a nomadic tribe, expert in trades, and able to control vast trading networks. The elements concentration in the coin-solutions was analyzed using ICP-AES at the Geological Survey of Israel. Sr isotopic compositions were determined by TIMS and MCICP-MS-“Nu Plasma” at IGAG-CNR laboratories at La Sapienza - University of Rome and at the Geological Survey of Israel. Additional samples, including a prill and an ore material from the Timna area, the most important local source of copper, were employed to detect the provenance of the samples under study. Lead isotope ratios, commonly used to trace metal provenance sources, are powerful geochemical tracers but could not be sufficient to identify the original ore deposits due to some coinage processes such as mixing and re-melting. The use of Sr isotope ratio as a geochemical tool (fingerprints) could overcome this obstacle, even if his application is not yet been explored due to the low Sr concentrations in metals. The results show that Sr isotope ratio can effectively trace the metal provenance. So, the Nabataean copper archaeometallurgy was investigated thanks to the ubiquitous geological database of the Sr isotope ratio, identifying in the Arabah Valley the local source of Nabataean copper coins.