Sr-Nd ISOTOPE FINGHERPRINTING AS A TOOL FOR BRONZE COINS PROVENANCE: THE CASE STUDY OF NABATAEAN KINGDOM

This innovative study was developed by means of combined use of Strontium (Sr) and Neodymium (Nd) isotope ratios and chemical elemental analysis carried out on 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 political entity, composed of a nomadic tribe, expert in trades, which flourished in modern-day Jordan, Israel and Syria between the 4th century B.C.-106 A.D. Sr-Nd isotope ratios are measured to detect the metal provenance source of the coin, prill and ore samples from Timna area, the most important local copper source in Levant zone. The elements concentration in the coin-solutions was analyzed using ICP-AES at the Geological Survey of Israel while the isotopic compositions of Sr and Nd were measured with both TIMS and MC-ICP-MS-“Nu Plasma” at IGAG-CNR laboratories at La Sapienza and at the Geological Survey of Israel. Lead isotopes, commonly used to trace metal provenance source, are valid geochemical tracers but sometimes could not be sufficient to identify the original ore deposits due to mixing/re-melting processes. The use of Sr and Nd isotope ratios as geochemical tools could overcome this obstacle, but they have not yet been explored probably for the low elements' concentrations in metals. The results show that Sr and Nd isotope ratios can trace the metal provenance and combined with those of Pb allow obtaining more complete information. The ubiquitous geological database of the Sr isotope ratio and the resistance to the weathering of the Nd allowed to investigate the Nabataean copper archaeometallurgy, identifying the Arabah Valley as the local source of Nabataean copper coins.