How Mineralogy and Geochemistry Can Improve the Significance of Pb Isotopes in Metal Provenance Studies (original) (raw)
Related papers
Lead isotopes combined with trace element data represent a powerful tool for non-ferrous metal provenance studies. Nevertheless, unconsidered geological factors and archaeological data, as well as ignored analytical procedures, may substantially modify the interpretation of the isotopic and trace element signature obtained as a potential ore candidate. Three archaeological examples, accompanied by high-resolution lead isotopic measurements (MC-ICP-MS), are presented here to discuss the above-mentioned criticisms and to propose some solutions. The first example deals with prehistoric/historical gold/silver-mining activity from Romania (the Baia Borşa and Roşia Montanȃ ore deposits). The second one regards the lead/silver metallurgical activity from the Mont-Lozère massif (France) during medieval times. The third example focuses on the comparison between two batches of lead isotope data gathered on Roman lead ingots from Saintes-Maries- using different SRM 981 Pb values. geochronology: more details are reported elsewhere . We only recall that three stable Pb isotopes out of four, 206 Pb, 207 Pb and 208 Pb, are radiogenic (time dependent) and that they are produced by the radioactive decay of 238 U, 235 U and 232 Th, respectively. The 204 Pb isotope is stable (time independent) and its abundance has been constant since the Earth's formation. The abundances of the four lead isotopes are approximately 52.4%, 22.1%, 24.1% and 1.4% for 208 Pb, 207 Pb, 206 Pb and 204 Pb respectively. Since the introduction of multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) in the mid-1990s, it has been possible to measure several isotopes simultaneously, with a high mass resolution (Rehkämper and Halliday 1998). These new spectrometers permit notable advances in geochemistry, and more recently in archaeology too. The presentday precise and accurate measurements improve the tracing by increasing the analytical precision by a factor of 10 over that obtainable with routine thermal ionization mass spectrometry (TIMS), and comparable to the precision of TIMS with double or triple spiking. MC-ICP-MS also allows the measurements of new isotopic tracers such as Cu, Fe, Sn and so on (called 'non-traditional isotopes') . The isotopic data measured nowadays by MC-ICP-MS are more significant and relevant, and they can be more accurately interpreted.
Lead isotopes combined with trace element data represent a powerful tool for non-ferrous metal provenance studies. Nevertheless, unconsidered geological factors and archaeological data, as well as ignored analytical procedures, may substantially modify the interpretation of the isotopic and trace element signature obtained as a potential ore candidate. Three archaeological examples, accompanied by high-resolution lead isotopic measurements (MC-ICP-MS), are presented here to discuss the above-mentioned criticisms and to propose some solutions. The first example deals with prehistoric/historical gold/silver-mining activity from Romania (the Baia Borşa and Roşia Montanȃ ore deposits). The second one regards the lead/silver metallurgical activity from the Mont-Lozère massif (France) during medieval times. The third example focuses on the comparison between two batches of lead isotope data gathered on Roman lead ingots from Saintes-Maries- using different SRM 981 Pb values. geochronology: more details are reported elsewhere . We only recall that three stable Pb isotopes out of four, 206 Pb, 207 Pb and 208 Pb, are radiogenic (time dependent) and that they are produced by the radioactive decay of 238 U, 235 U and 232 Th, respectively. The 204 Pb isotope is stable (time independent) and its abundance has been constant since the Earth's formation. The abundances of the four lead isotopes are approximately 52.4%, 22.1%, 24.1% and 1.4% for 208 Pb, 207 Pb, 206 Pb and 204 Pb respectively. Since the introduction of multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) in the mid-1990s, it has been possible to measure several isotopes simultaneously, with a high mass resolution (Rehkämper and Halliday 1998). These new spectrometers permit notable advances in geochemistry, and more recently in archaeology too. The presentday precise and accurate measurements improve the tracing by increasing the analytical precision by a factor of 10 over that obtainable with routine thermal ionization mass spectrometry (TIMS), and comparable to the precision of TIMS with double or triple spiking. MC-ICP-MS also allows the measurements of new isotopic tracers such as Cu, Fe, Sn and so on (called 'non-traditional isotopes') . The isotopic data measured nowadays by MC-ICP-MS are more significant and relevant, and they can be more accurately interpreted.
Geological constraints on the use of lead isotopes for provenance in archaeometallurgy
Archaeometry, 2020
The first half of this article is a brief critical history of the use of lead isotopes for inferring the geological provenance of archaeological materials, with emphasis on non-ferrous metals. The second half examines variation in the lead isotopic ratios of oxide and sulphide ore minerals in selected regions of the world, and relates these to the geological histories of ore formation in each region. This exercise shows that in regions where most ore deposits are of similar geological age-as in the Andes, Europe, and the circum-Mediterranean-provenance analysis with lead isotopes is inherently difficult because geographically distant sources often exhibit similar isotopic ratios. Conversely, regions with many periods of ore formation-like southern Africa-appear to be very promising regions for future studies of provenance with lead isotopes. The wider implication of our exploratory survey is that archaeologists should consider carefully the range and clustering of geological lead isotopic ratios in their regions of interest before investing large sums of money in lead isotopic analysis of artefacts.
BSGF - Earth Sciences Bulletin
The identification of mineral supply sources and trade routes are at the heart of the archaeological issues. The tracing of sources of metal production via lead isotopy has been used since the 1980s to identify the deposits from which the metal constituting the archaeological objects came. Such studies are based on mineral signature repositories and archaeologists have thus built up databases containing thousands of ore deposit analyses. The databases, however, only very rarely include geological information and are limited to geographic information. But considering only geographical data leads to many limitations of studies, including the overlapping of signatures between remote regions. This problem could nevertheless be circumvented by taking into account precise ore deposit data that enables to think in terms of restricted mineralized subsets. We illustrate this through the example of data collected in the Alps by Marcoux (1986) and Nimis et al. (2012). Taking into account geolo...
Lead isotopic measurements in archeological objects
Archaeological and Anthropological Sciences, 2009
Pb isotopic analyses on metal artifacts help constrain their provenance. Useful and reliable data require analytical protocols that ensure accuracy and monitor precision. The interpretation can sometimes be ambiguous because natural ore deposits frequently have overlapping Pb isotopic compositions. In most cases, however, provenances can be reliably narrowed down. For the Alpine region, a pattern of small, strongly localized mine exploitations in pre-Roman times, supplemented by some longdistance trading, is taking shape.
Medieval lead making on Mont-Lozère Massif (Cévennes-France): Tracing ore sources using Pb isotopes
Applied Geochemistry, 2006
This study aims to document the origin of metallurgical activities on the Mont-Lozère Massif (Cévennes Mountains, South of Massif Central, France), which is the largest medieval site of Pb-Ag metallurgical activities in France. These activities are characterised by more than 70 sites comprising numerous dispersed slags. Related charcoal samples dated by 14 C have yielded a medieval, ca. XI-XII th. C. age. Numerous ore deposits, now mostly old mine tailings, surround the granitic massif and are possible candidates for suppliers of the old smelting activities. In Western Europe, Pb-Ag mines were of primordial importance for the medieval monetary system. Mines were intensively coveted by Lords, Bishops and Kings, and their exploitation was strictly regulated by each owner. The scarcity of ancient manuscripts makes it impossible to use a historical approach to determine the ore source regions related to a given metallurgical activity.