Pb isotopes as a reliable marker of early mining and smelting in the Northern Harz province (Lower Saxony, Germany)

Overbank sediments from the River Weser provide a record of geochemical anomalies which vary distinctively from the regional background as far back as 3500 years BP. The use of Pb isotopes, measured by inductively coupled plasma mass spectrometry (ICP-MS), in combination with the determination of heavy metal concentrations has identified the mining and smelting activities that took place early in the Hart Mountains. as the source of contamination. The regional background was defined from sediments deposited prior to 3500 years BP with Pb and Zn concentrations of about 23 +/- 7 and 109 +/- 38 mu g g(-1), Pb-206/Pb-207 ratios of 1.215 +/- 0.002 and Pb-208/Pb-306 ratios of 2.044 +/- 0.002. The isotopic characteristics of the Pb in the sediments can be easily explained by a simple two-component mixing model involving: (i) the background component; and (ii) Pb derived from the Harz Mountain ore bodies characterised by Pb-206/Pb-207 ratios of 1.167-1.187 and Pb-208/Pb-206 ratios of 2.075-2.096. The rapid determination of isotopic ratios by ICP-MS has advantages over Thermal Ionisation Mass Spectrometry. It enables large-scale investigations in prospecting archaeology or more-recent history. (C) 2000 Elsevier Science B.V. All rights reserved.