Considering Pb Mixing in Lead Isotope Analysis (LIA) of Tin Artifacts

Summary

This is an abstract from the "Geological and Technological Contributions to the Interpretation of Radiogenic Isotope Data" session, at the 89th annual meeting of the Society for American Archaeology.

LIA of tin metal must consider the U-Th-Pb characteristics of cassiterite ore. The initial Pb content of cassiterite is <1 ppm and Th is <0.005 ppm. However, it contains as much as 50 ppm U. Therefore, 206 Pb and 207 Pb accumulate over time, potentially allowing the definition of an isochron. However, given the age of most Eurasian tin ores (300–30 Ma) and the relatively low U concentration, little radiogenic Pb is produced. Unusually, U-enriched 300 Ma cassiterite (50 ppm) would generate only 2.5 ppm of Pb, which mixes with the ~0.5 ppm of initial Pb. Thus, every tin LIA is a mixed value. Only one of the 140 LBA European tin ingots contains less than the 3 ppm U limit expected in Variscan ore. Therefore, most tin objects contain an additional Pb source: inclusion of galena or zircon in the ore concentrate; contamination by residual Pb metal in the smelting/casting ceramics; and recycling of tin metal into a new composite object. Accordingly, conducting a detailed mixing analysis is essential to correctly interpret the results of LIA of tin ingots and other artifacts. Here, we present the results of such an analysis on the European ingot assemblage.

This Resource is Part of the Following Collections

• Geological and Technological Contributions to the Interpretation of Radiogenic Isotope Data   •
• Society for American Archaeology 89th Annual Meeting, New Orleans, LA (2024)

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Record Identifiers

Abstract Id(s): 40145.0