Geochemical and isotopic analyses are well known tools for old metal provenance studies and ancient trade networks reconstitution. For relevant archaeological interpretation, the metallurgical processes
have to be taken into account and analyses must be performed on ores, slags and produced metal. Classically, trace elements analyses are used for ferrous metals provenancing (Coustures
et al., 2003), whereas lead isotopic analyses are used for non-ferrous metals (Stos-Gale
et al., 1997; Durali-Mueller
et al., 2007). However, these two techniques show limitations. Indeed, trace elements analyses of ferrous artefacts are performed on slag inclusions which induces significant deterioration of archaeological pieces. Moreover, a very pure metal does not contain any slag inclusions. Concerning lead isotopes analyses, distinct mining districts may have a homogeneous isotopic composition while ores from the same mine can show a heterogeneous isotopic composition. This may induce some questionings for provenance issues (Baron
et al., 2014). These limitations underline the need to develop new tracers as a complement to the existing ones.
For the first time, iron isotopes are used for old metals characterization and provenancing. To develop our method, we analyzed material from reduction experiments and metallic artefacts clearly constrained by archeology and by multi-elemental analyses. The isotopic ratios 57Fe /54Fe and 56Fe/54Fe were quantified using a Multi Collector Inductively Coupled Plasma Mass Spectrometer after sample dissolution and Fe purification.
Our first results show that iron isotope compositions of ores, slags and metal are homogeneous for each iron ore reduction experiments. Moreover, iron isotopes allow to distinguish iron ores from different sources which were undistinguishable using lead isotopes. It demonstrates here that whereas iron isotopes remain unaffected by the ferrous metallurgical process, they can become a powerful tool for provenance studies.
