Accumulation and provenance of pollutant metals into a remote shallow peat bog from the Massif Central mountains (France)

We examine the accumulation and provenance of non-ferrous metals in a shallow peat sequence (60 cm) collected in the Valley of Chassezac (Narcettes, Cevennes) in the French Massif Central (FMC), one of the oldest mining districts in Europe. The core is dated between the Modern period (<250 years old) and the 5th millennium BCE ( 14 C and pollens). Trace metal (Pb, As, Sb, Cu, Ni, Zn) enrichments generally increase from mid-core at 31 cm [70 CE–180 BCE] to the top, with maxima during the Modern period (0–18 cm, <250 yr). Statistical analyses (Principal Component Analysis and a source apportionment MixSIAR Bayesian model) applied to trace metals and stable Pb isotopes enable to discriminate the excess Pb imprint and its geographic provenance from Pb–Ag mining in France and surrounding countries within the first 31 cm. The most striking findings are the almost non-existent imprint from the numerous Spanish mines and the overwhelming French and Italian source imprints. Few Greek mines also contribute Pb enrichment, most particularly at depth, during the Roman period and late Iron Age. As expected from its proximity to the Narcettes core, the FMC (northern area and the mont Lozère) and mines from the Alps dominate the French contribution. The significant input from the mont Lozère extends its well-known medieval Ag–Pb exploitation into the Roman, and possibly, Gallic periods. Finally, a specific enrichment centered at 47–51 cm [3.2–4.1 ky BCE] is clearly discerned for Zn, Cu and Ni that may be associated with indigenous Cu smelting from nearby Cu mining districts in the Languedoc region (Cabrières and Roquemengarde). This finding would signify one of the oldest atmospheric metal contamination at a remote French site.