Lead isotope data for metal artefacts, marls and shales

Lead isotope compositions for metal samples 1 to 30 and 32 (31 was excluded) and samples 33–36 (marls, shales) were submitted as small chips. The samples were analysed by multicollector-inductively coupled plasma mass spectrometry (MC-ICP-MS) at the University of Melbourne, Australia. Samples (1–241 mg) were weighed into Savillex PFA beakers and reacted with 7M HNO3 (2 mL, 120°C, 15 h). Cu-rich samples formed blue solutions with minor residue while marl/ shale samples produced abundant residue. After drying, the samples were re-dissolved in 0.6M HBr, followed by Pb extraction on small (15 × 0.4 mm) beds of AG1-X8 (100–200 mesh) anion resin, using the HBr-HCl technique. Pb isotope ratios were measured on a Nu Plasma MC-ICP-MS with sample introduction via a low-uptake PFA nebuliser and Aridus desolvator. Data were collected using total Pb signal of 10–12 V, and instrumental mass bias was corrected using thallium doping (Woodhead, 2002). The thallium doping technique is expected to yield iPb/204Pb results with an external precision of 0.04%–0.08% (2std dev). This is confirmed by the results for the SRM 981 Pb standard, analysed as unknowns in the same sessions. Seven analyses of Pb extracted from the BCR-2 reference basalt show greater variability, but the average agrees with the GeoREMpreferred composition (http://georem.mpch-mainz.gwdg.de) and is consistent with the long-term laboratory average and with TIMS reference data.