ISOTOPICALLY PROVENANCING TIN IN BRONZE ARTIFACTS, CENTRAL BALKANS

Tin is a rare metal that is essential for bronze production. In contrast to those of western Europe, tin sources in the Balkan region are small and poorly documented. Therefore, the tin ore sources for the Balkan-Aegean region during the European Bronze Age (2200-1050 B.C.E) remain undetermined. Tin isotopic analysis may allow for the identification of tin deposits exploited in prehistory. Bronze artifacts produced from a single tin deposit will share a common isotopic signature with the source cassiterite. Accordingly, those signatures can be used for provenance analysis of ancient tin. Analysis of an initial set of 60 bronzes obtained from museums across Serbia and Romania indicate two geographically distinct tin isotopic signatures in late Bronze Age artifacts. This suggests that there were at least two distinct sources of tin that were exploited in Western Romania and Northern Serbia, but the specific ore sources have yet to be identified conclusively. Whereas, the methodology of analysis of tin isotopes in bronze is well-established and verified, the preparation method of cassiterite for isotopic analysis remains problematic. Proposed cassiterite preparation methods have included: (1) Graphite reduction at approximately 1200C, (2) Potassium cyanide reduction at approximately 800C, and (3) dissolution using hydroiodic acid at 100C. Due to poor instrumental precision at the time at which reduction-based studies were undertaken, it is uncertain whether high-temperature reductions result in tin evaporation and associated isotopic fractionation. Studies that have applied HI dissolution methods lack documentation of Sn recovery and speciation, and indicate that some fractionation occurs in the preparation process. Thus, there is no consensus on the appropriate method of cassiterite digestion for isotopic analysis. We are currently conducting comparative tests of the three previously proposed preparation methods in order to determine the most accurate cassiterite preparation method for Sn isotopic analysis. Results of this comparative methodological study will allow for provenancing of bronze artifacts in the Balkans and elsewhere.