Lead isotope analysis (LIA) can be applied to tin provenance studies when both the U–Th–Pb characteristics of cassiterite and potential Pb contamination are taken into account. As cassiterite (SnO2) contains higher concentrations of U than Pb and negligible Th, radioactive decay increases 206Pb/204Pb and 207Pb/204Pb ratios in cassiterite over time. However, 208Pb/204Pb ratio retains its primary value and can be correlated with LIA databases. A majority of documented Bronze Age tin ingots from Europe have Pb in excess of the 5 ppm maximum that can be derived from Cenozoic to Late Paleozoic cassiterite. A minute mass of galena (PbS) in the ore concentrate is sufficient to mask the cassiterite-derived lead, as would the addition of any lead contaminant introduced in the smelting/casting process. If the galena is cogenetic with the cassiterite, then LIA will be unaffected. The inclusion of uranium-rich minerals in the tin ore concentrate is another potential source of excess lead. In this case, the additional Pb is uranogenic, and so 206Pb/204Pb and 207Pb/204Pb will reflect the age of the uranium minerals, but 208Pb/204Pb will retain its primary value. If the U-minerals are cogenetic or coeval with tin mineralization, then a Pb isochron age will indicate the age of the ore. Between 1984 and 1994, at least 117 ingots, or roughly one tonne, of tin was raised from the Late Bronze Age Uluburun shipwreck (ca. 1320 B.C.). Over half of the analyzed ingots from this wreck site have high Pb concentrations (>100 ppm), indicative of contamination from non-radiogenic lead associated with lead metal or galena. LIA indicates that the Pb originated from the Pb–Ag-rich Bolkardağ region of the south-central Taurus Mountains. A second group of approximately 28 tin ingots with lower Pb content (<100 ppm) contain additional uranogenic Pb but retain 208Pb/204Pb compositions that overlap with the ca. 300 Ma tin regions of Western Europe and Central Asia, with the most likely source being the Tienshan Mountains in Kyrgyzstan, Tajikistan, and Uzbekistan. By compensating for previous uncertainty around the use of Pb isotopes for sourcing tin objects, it is now possible to contextualize the Uluburun tin ingots more securely within the metallurgical systems of the Central Taurus-Cilicia-Amanus axis. Recent scholarship has shown that tin production in the South-Central Taurus region had taken place at a scale not previously anticipated. Two parallel production systems appear to have been in place serving elite and common consumption networks via markedly different technologies. The South-Central Taurus and Cilician cities served as important components of maritime and terrestrial metal distribution around the eastern Mediterranean, providing a range of metals from a single geographical region.
Bibliographical noteFunding Information:
We dedicate this article to George F. Bass (9 December 1932?2 March 2021), a pioneering archeologist and visionary, who played a pivotal role in the creation and development of nautical archaeology as a scientific discipline. He founded the Institute of Nautical Archaeology (INA) in 1972, which has become one of the leading research institutes for the study of shipwrecks and founded one of the first academic underwater archaeology programs in 1976 at Texas A&M University where George Bass became a distinguished professor. In 1960, while still a graduate student, Bass excavated a 3200-year-old shipwreck at Cape Gelidonya in southern Turkey. This was the first shipwreck mapped and scientifically excavated in its entirety on the seafloor by diving archaeologists. The ship's primary cargo was one ton of copper and some poorly preserved tin ingots from which only a small sample of the tin could be collected. It was analyzed in an industrial laboratory in Turkey and verified as tin, establishing it as the first archaeological evidence for the occurrence of Bronze Age tin ingots; its provenance remains an enigma. In part, it was the quest for this ship-transported tin that led INA to launch extensive surveys along the southern Turkish coast searching for other Bronze Age shipwrecks. These efforts were rewarded in 1982 with the discovery of the 14th-century B.C. Uluburun shipwreck with its cargo of 10 tons of copper and one ton of tin ingots. George and his colleagues collaborated with scientists to determine the provenience of the tin, and also with archaeologists and metallurgists searching for tin in south-central Taurus Mountains of Turkey. Samples of Uluburun shipwreck tin were analyzed in laboratories in United Kingdom and USA and some of their LIA results were consistent with those of the Taurus region, offering the very first clue that at least a part of the ship's tin cargo originated in that area. He was most eager to learn about the results of our research. It is with incredible sadness, therefore, that we will not be able to share with him the findings presented here as we approach a more accurate method for sourcing much of the Uluburun tin ingots. The project was funded in-part by PSC- CUNY Grant 62609?00 50. The Uluburun shipwreck project was fully supported by the Institute of Nautical Archaeology (INA) since the inception of the excavation in 1984. Funding for the project was also provided by the Institute for Aegean Prehistory (INSTAP) for three decades. INSTAP also supported the research at Bolkarda?, Kestel, and Tell Atchana (Alalakh) for more than a quarter of a century. INSTAP funded the initial investigations into the lead isotope compositions of the Uluburun copper and tin ingots. This study would not have been possible without this history of continued support. Similarly, we are indebted to Zofia Stos-Gale and the late Noel H. Gale (1932?2014), the former directors of the Isotrace Laboratory at the University of Oxford for their pioneering work on LIA of the Uluburun ingots, and for permitting the use of their data over the years. In addition, we acknowledge the assistance of Thilo Rehren and Jeff Verfort for providing constructive pre-review commentary. Finally, we thank Vanessa Alfonso and Amanda Schreiner-Andri? for their assistance in sample preparation.
The project was funded in-part by PSC- CUNY Grant 62609–00 50 . The Uluburun shipwreck project was fully supported by the Institute of Nautical Archaeology ( INA ) since the inception of the excavation in 1984. Funding for the project was also provided by the Institute for Aegean Prehistory (INSTAP) for three decades. INSTAP also supported the research at Bolkardağ, Kestel, and Tell Atchana (Alalakh) for more than a quarter of a century. INSTAP funded the initial investigations into the lead isotope compositions of the Uluburun copper and tin ingots. This study would not have been possible without this history of continued support.
© 2021 Elsevier Ltd
- Bronze age
- Lead isotopes
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