Provenance of Tin in the Late Bronze Age Balkans: Preparation of Cassiterite for Sn Isotope Analysis and the Probabilistic and Spatial Analysis of Sn Isotopes

The sources of tin for the European Bronze Age (2200-1050 B.C.E.) have remained undetermined. Isotopic analysis has shown promise as a means of providing “fingerprints” of bronze artifacts that can be matched to their parental ore sources. This project has accomplished the following: (1) further tested and defined a method for the preparation of cassiterite for isotopic analysis, and (2), determined the provenance of tin used for metallurgy in the central Balkans during the later Bronze Age based on Sn isotopic compositions of bronze artifacts and local tin ores. Two distinct methods have been applied in recent isotopic studies of cassiterite: (1) reduction to tin metal with potassium cyanide (KCN) at high temperature (800 °C), with subsequent dissolution in HCl, and (2) reduction to a Sn solution with hydroiodic acid (HI) at low temperature (100 °C). The most robust method for preparing cassiterite is via the Haustein et al. (2010) method with a flux to sample ratio of between 4:1 and 6:1 for a duration of 40 minutes or more. The HI method proposed by Yamazaki et al. (2013) can produce unreliable results because Sn may fractionate as a volatile during the HI reduction process and this method is not recommended for the preparation of cassiterite for isotopic analysis. The laboratory induced fractionation observed here (up to 0.35‰ per mass unit) suggests that Sn isotope fractionation can span a range greater than previously recorded in the literature. We report the largest published dataset to date of Sn-isotopic compositions of Bronze Age artifacts (338) along with 150 cassiterite samples (75 new) from six potential tin ore sources from which the tin in these artifacts were thought to have originated. Artifacts enriched in heavy isotopes (δ124Sn \u3e 0.7‰) that cluster in west-central Serbia are likely associated with the ores from Mt. Cer in west Serbia. Mixed artifact assemblages (high and low δ124Sn) in this region are attributed to the use of cassiterite from the two Serbian sites (Mt. Cer and Mt. Bukulja). Moderate composition artifacts that occur north of the Middle Danube in Vojvodina, Transylvania, and Central Europe are likely associated primarily with ores from the West Pluton of the Erzgebirge. Compositionally light bronzes (δ124S