Metal provenancing using isotopes and the Oxford archaeological lead isotope database (OXALID)

Zofia Anna Stos-Gale Nol H. Gale 0 ) Nuffield College , Oxford, UK This paper reviews the research into the methodology of lead isotope provenance studies carried out at the University of Oxford between 1975 and 2002, at first in the Department of Geology (Geological Age and Isotope Research Laboratory), later in the Isotrace Laboratory based in the Department of Nuclear Physics, and eventually part of the Research Laboratory of Archaeology and the History of Art. These 27 years of intensive work, funded initially by the Stiftung Volkswagenwerk, and later from numerous UK Government and Charitable funds and finally by the Institute of Aegean Prehistory laid the foundations of the lead isotope provenance methodology and resulted in a large database of analytical isotope and elemental results. In spite of the efforts of the authors, this database is still not comprehensively published or easily accessible in a digital format by all researchers interested in using this method for their projects. The possibilities of advancing this situation are discussed. The authors discuss in detail the basic restrictions and advantages of using the lead isotope compositions of ores in mineral deposits for finding the origin of the raw materials used for making ancient artefacts. Methods for the scientific interpretation of the data are discussed, including attempts to use statistical methods. The methodology of creating the Oxford lead isotope database (OXALID) is outlined and a summary is given of the lead isotope resource provided by OXALID. - From very early in the study of ancient metals, one important goal was to establish the geological origin of the metal used to make particular metal artefacts, thus, directly addressing issues of trade, trade relationships and movement of objects. Initially, the approach taken was through chemical analysis, beginning in 1934 (Noddack and Noddack 1934) and leading on to the large-scale chemical analytical programmes of Otto and Witter (1952) and the Stuttgart group (Junghans et al. 1960, 1968, 1974), conveniently reviewed by Hrke (1978). Valuable though these studies were for establishing the development of metallurgy through time, they did not contribute much to establishing the metal ore sources used. Chemical analyses by themselves fail to provenance metals due to chemical heterogeneities in ore deposits and variable fractionation of chemical elements between ores, slag and metal in primitive smelting procedures, as discussed by Gale and Stos-Gale (1982, 2000). With the widespread recognition that chemical analysis had failed as an approach to determining the geological origin of the metal used to make metal objects, two research groups independently suggested that this objective might be achieved instead by the comparative lead isotope analysis of artefacts and metal ores (Brill and Wampler 1965; Grgler et al. 1966). The Swiss group of Grgler et al. did not pursue this line of research further, while Brill and his colleagues continued to publish lead isotope analyses of glass, coins and other metal objects but did not advance the subject significantly because they failed to accompany their work on artefacts with the sufficiently extensive lead isotope analyses of metal ores that is also necessary. Systematic studies and applications of lead isotope provenancing began in the 1970s when a group at the Max-Planck-Institut fr Kernphysik in Heidelberg, comprising W. Gentner, G. A. Wagner and O. Mller, invited N. H. Gale at the University of Oxford to join them in collaborative work. This resulted in several years of close collaboration between Oxford and Heidelberg, financed by grants from the Stiftung Volkswagenwerk and focused on studies of the provenance of ancient Greek silver coins using both trace element and lead isotope analysis. A new and central feature of this collaboration was the emphasis, beyond the analytical work, on extensive fieldwork on leadsilver deposits in and around the Aegean, involving geological and mining archaeological field work, as well as mineralogical studies of ores and metallurgical remains. A paper summarising the early stages of the lead isotope side of the project was presented at the 16th International Symposium on Archaeometry in Edinburgh in 1976 (Chamberlain and Gale 1980) whilst further papers resulting from this collaboration were presented at the 18th International Symposium on Archaeometry in Bonn in 1978 (Gale 1979; Muller and Gentner 1979; Wagner and Weisgerber 1979). More detailed publications of this research were published between 1980 and 1988 (Gale et al. 1980; Wagner et al. 1980; Wagner and Weisgerber 1985, 1988). During the fieldwork in the Aegean for the Oxford/ Heidelberg project, both Wagner and Gale independently became interested in collecting obsidian from such sources as Melos and Antiparos to explore new methods for its provenancing (Wagner et al. 1976; Gale 1981). The geographical range of the Oxford obsidian collection was greatly extended by samples kindly provided by A.C. Renfrew from his then unrivalled collection in Southampton. Renfrew suggested that beyond the initial joint project on silver sources for the Greek Archaic/Classical city states, there was an untapped potential field of research for the Isotrace Laboratory at Oxford into the sources of metals for the Bronze Age peoples of the Aegean and wider Mediterranean. This began in Oxford with studies of the sources of lead and silver for the Bronze Age Aegean (e.g., Gale 1980; Gale and Stos-Gale 1981a, b; Gale et al. 1984). As Rehren and Pernicka (2008, 238) have written The breakthrough in provenancing by isotope ratios came with the extension of lead isotope analysis to copper and copperbased alloys (Gale and Stos-Gale 1982). By the combination of lead isotope ratios and trace element patterns it became possible, for the first time, to relate with high probability metal artefacts to specific ore deposits, something that had been aimed at for more than 100 years. The work culminated with major syntheses for the metal from Cyprus by Stos-Gale et al. (1997) and for the south-east European Chalcolithic by Pernicka et al. (1997) and one can add, by Gale et al. (2000). The Isotrace Laboratory was at first located at the University of Oxford in the Department of Earth Sciences, from 1989 in the Department of Nuclear Physics, and from 1994, it remained physically in Physics but was for administrative purposes part of the Research Laboratory of Archaeology. Since the mid-1970s, all of the projects on lead isotope provenance studies at Oxford and Heidelberg have been based on parallel geological and archaeo-metallurgical collection of samples for analysis and mapping the ore deposits, ancient mines and slag heaps relevant to Bronze Age archaeology. The main interest of both teams was in the beginnings of metallurgy in the Mediterranean, South East and South West Europe, Anatolia and the Near East and resulted in many publi (...truncated)