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Abstract

The aim of this work is to establish an overview of the tin isotope ratios of cassiterite and stannite from various mineralized regions in Europe, the Mediterranean and Central Asia in order to assess the possibility to geochemically discriminate tin ore deposits, which could have been exploited in ancient times. The motivation for this study was to eventually relate the tin found in ancient bronze objects to specific tin ore deposits and thus to clarify the origin and distribution of the tin bronze technology in the Bronze Age of the so-called Old World. For this purpose, we determined 413 primary and secondary cassiterite and stannite samples from the major tin provinces in SW England and Ireland, the Saxonian-Bohemian province, the Iberian Peninsula, France, Italy, Serbia, Egypt and Central Asia. The tin isotope compositions were analysed in solution with a multi-collector inductive-coupled plasma mass spectrometer (MC-ICP-MS) in the Curt-Engelhorn-Zentrum Archäometrie in Mannheim. The samples mainly derive from granitic pegmatites and hydrothermal vein mineralizations of tin ore deposits associated with granite complexes in the Variscan and Asian fold belts. Overall, the isotope ratios in primary and secondary cassiterites are highly variable and range from δ124Sn/120Sn -0.82 to 0.85 ‰. This variation is observed in the tin ore samples from SW England which have an average δ124Sn/120Sn of 0.10 ± 0.59 ‰ (2SD). Among the tin provinces of the Variscan fold belt in Europe those of SW England and the Saxonian-Bohemian province (δ124Sn/120Sn = 0.12 ‰ ± 0.37) show the largest variations but the ranges of isotope ratios in both regions overlap to a large extent. Despite the large overlap, cassiterite from Spain (δ124Sn/120Sn = -0.07 ‰ ± 0.35) and France (δ124Sn/120Sn = -0.005 ‰ ± 0.31) tend to have on average lighter isotopic compositions than SW England, the Saxonian-Bohemian province or Portugal (δ124Sn/120Sn = 0.07 ‰ ± 0.40). However, the stannite samples from SW England and the Saxonian-Bohemian province have significantly lighter isotope ratios than the associated cassiterites. The tin ores from Central Asia exhibit the largest total variation of 1.94 ‰ ranging from -1.27 to 0.67 ‰ for δ124Sn/120Sn. This extent of fractionation is observed in cassiterites from Afghanistan and Uzbekistan. Afghanistan with its pegmatitic cassiterite has the lightest isotopic composition of all investigated areas with -0.38 ± 0.84 ‰ for δ124Sn/120Sn and, therefore, stands out as an identifiable source. Similar to the European stannites, the Asian stannites also have significantly lighter isotope compositions. Because of the large overlap and the highly variable isotope composition of cassiterites from all tin provinces a clearcut discrimination based on tin isotope ratios is difficult. But on a more detailed scale within each tin province it is possible to distinguish several mining or granite areas by their Sn isotope composition. However, it is also difficult to distinguish between different mineralization types.