Exploring the rhenium-osmium isotopic system and metal trace-elements analysis for iron provenance

Although programs focusing on the provenance of ancient iron are becoming more common in archaeometallurgical research, no standardised approach currently exists. Recent studies have shown the potential of osmium (¹⁸⁷Os/¹⁸⁸Os) isotope analysis as a robust and effective method. It was also shown that trace element composition analysis, of the metal phase, provides a complementary fingerprint to refine hypotheses about the origins of archaeological iron, and to overcome the overlapping of isotopic signatures. This study further explores the potential of the rhenium-osmium isotope system and the ¹⁸⁷Re/¹⁸⁸Os isotope ratio as an additional parameter for distinguishing ore sources. By analysing metallurgical products smelted experimentally, this research utilises the residual solutions from Os and Re isotope analysis (conducted via Carius tube digestion) to directly determine the concentrations of 12 trace elements within the metal phase (Cr, V, Co, Ni, Mo, Cu, As, Sb, Sn, Zn, W, Pb) using solution inductively coupled plasma mass spectrometry (ICP-MS). The study also qualitatively compares the efficiency of this method against results obtained by laser ablation ICP-MS analyses of polished blocks. Findings demonstrate that the new method offers better comparability with Os and Re concentrations. Moreover, the study identifies two siderophile (Co, Ni) and four chalcophile elements (Mo, Cu, As, Sb) that exhibit near-complete reduction from ore to metal in the bloomery process while also highlighting the potential of the ¹⁸⁷Re/¹⁸⁸Os isotope ratio for distinguishing ore sources. Thus, the study enhances the potential for large-scale diachronic and synchronic investigations of ancient iron artifacts, providing critical insights into metallurgical practices and their socio-economic and political contexts.