Application of lead isotope analysis to provenance studies in archaeology
Advances in mass spectrometry in the second half of this century allowed very accurate measurements of isotopic compositions of various elements. In turn it was discovered that due to the radiogenic origin of some of these isotopes their composition often reflects the geochemical history of minerals and rocks. Terrestrial lead is composed of four isotopes, of which three are radiogenic in origin as daughters of uranium and thorium. In geochronology the isotopic composition of minerals helps in dating the ore and rock formations. However, if there is enough diversity amongst the isotopic compositions of different deposits, then their lead isotope composition can be used as a simple and unique 'fingerprint', which can be scientifically measured. This feature can be used as a powerful tool in the identification of sources of ancient metals, because it passes unchanged through the smelting and refining processes. However, one of the most important requirements for such 'lead isotope provenance studies' is empirical investigation of the 'fingerprints' of ore deposits which are relevant to a given archaeological research. In this dissertation the scientific foundations of lead isotope provenance studies are described and examined in detail. All available evidence concerning the possibility of distinguishing isotopically between different European ore deposits is examined and methods of visual and numerical evaluation of the lead isotope data are suggested. Two examples of applications to specific archaeological problems are also given: the identification of sources of metals used for production of Bronze Age Cretan weapons and of non-ferrous metals in the Roman Period in Southern Poland. The interpretation of lead isotope data for archaeological objects is based on nearly 1500 isotopic analyses of ores.