TIN SOURCES ASSOCIATED WITH BRONZE AGE ARCHAEOLOGICAL SITES IN WEST SERBIA

The discovery of Bronze Age archaeological sites in West Serbia has led to a search of local tin-bearing minerals and their bedrock sources. A rare metal, tin is essential for making the alloy bronze (about 90% copper and 10% tin). To test the hypothesis that at least some of the tin used by Serbian Bronze Age settlements was mined locally from placer deposits, sand and gravel samples were collected every 50 meters from sand bar, bank and stream bottom deposits of the Milina and Ravnajica tributaries flowing south of Mt Cer. In the field, samples were washed, separated into sand and gravel fractions, dried, and analyzed for metal contents using a hand-held X-ray fluorescence apparatus with an approximate detection limit of 50-150ppm for Sn. Only two of 130 samples yielded Sn levels above detection limits. However, subsequent heavy -mineral separates produced by a float/sink process using sodium-polytungstate increased the Sn signal in reprocessed samples. For example, one sample that yielded a statistically invalid concentration of 21ppm in the total sand fraction, yielded a tin concentration of 24,398 ppm in the heavy mineral concentrate. SEM and EDS analysis of Sn-bearing heavy mineral concentrates indicate that tin is present in at least two optically and chemically distinct forms of cassiterite (black, low-Al; brown, high-Al), and that cassiterite-bearing sands also contain the Nb-Ta-bearing mineral columbite. Having documented the presence of tin ore in the region, sampling and analysis will expand in 2011 with field implementation of heavy mineral concentration by heavy liquids.