Tin isotope fractionation during experimental cassiterite smelting and its implication for tracing the tin sources of prehistoric metal artefacts

Although tin recovery on smelting in the field was low (20-30%) due to tin losses to fuming and slag formation, the results indicate that the tin isotope composition is less affected than anticipated from theoretical considerations (Rayleigh fractionation). If cassiterite is completely reduced during the smelting reaction the tin metal becomes enriched in heavy tin isotopes with a fractionation of Δ124Sn = 0.09-0.18‰ (0.02-0.05‰ u−1) relative to the original cassiterite. An estimate of the provenance of the original cassiterite and the potential ore source would still be possible because the variability of tin isotope ratios in tin ore provinces is much larger. If the cassiterite becomes incompletely reduced, however, then fractionation increases significantly up to Δ124Sn = 0.88‰ (0.22‰ u−1) and conclusions on tin sources are limited. Similarly, condensed tin vapours (Δ124Sn = 1.13‰ (0.28‰ u−1)) and slags (Δ124Sn = 0.42-1.32‰ (0.11-0.33‰ u−1)) that are by-products of the smelting process show large fractionation with respect to the original tin ore as well, which makes them unsuitable for provenance studies.