Natural variations detected in the isotopic composition of copper: possible applications to archaeology and geochemistry

Abstract Copper isotopic compositions have been measured both in natural copper minerals from supergene/oxidation zones and in some ancient metal artefacts using two different instruments. Measurements were first made using a low temperature thermal ionisation technique with a thermal ionisation mass spectrometer (TIMS); independent data was obtained using a commercial inductively coupled plasma (ICP) magnetic sector multiple collector mass spectrometer. Significant variations of isotopic composition were found in both types of material, suggesting that there may be considerable potential for copper isotope analyses in metal provenance studies, at the least as a supplement to lead isotope studies. For minerals, δ values ranging from −1.63 to +7.71 were obtained, whilst archaeological artefacts had δ values from +0.22 to +4.32. This study also made a preliminary examination which suggests that fractionation of the isotopic composition of copper does not occur during smelting and fire refining processes thought to have been used in ancient times.

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