Early atmospheric metal pollution provides evidence for Chalcolithic/Bronze Age mining and metallurgy in Southwestern Europe

Although archaeological research suggests that mining/metallurgy already started in the Chalcolithic (3rd millennium BC), the earliest atmospheric metal pollution in SW Europe has thus far been dated to ~ 3500–3200 cal. yr. BP in paleo-environmental archives. A low intensity, non-extensive mining/metallurgy and the lack of appropriately located archives may be responsible for this mismatch. We have analysed the older section (> 2100 cal. yr. BP) of a peat record from La Molina (Asturias, Spain), a mire located in the proximity (35–100 km) of mines which were exploited in the Chalcolithic/Bronze Age, with the aim of assessing evidence of this early mining/metallurgy. Analyses included the determination of C as a proxy for organic matter content, lithogenic elements (Si, Al, Ti) as markers of mineral matter, and trace metals (Cr, Cu, Zn, Pb) and stable Pb isotopes as tracers of atmospheric metal pollution. From ~ 8000 to ~ 4980 cal. yr. BP the Pb composition is similar to that of the underlying sediments (Pb 15 ± 4 μg g− 1; 206Pb/207Pb 1.204 ± 0.002). A sustained period of low 206Pb/207Pb ratios occurred from ~ 4980 to ~ 2470 cal. yr. BP, which can be divided into four phases: Chalcolithic (~ 4980–3700 cal. yr. BP), 206Pb/207Pb ratios decline to 1.175 and Pb/Al ratios increase; Early Bronze Age (~ 3700–3500 cal. yr. BP), 206Pb/207Pb increase to 1.192 and metal/Al ratios remain stable; Late Bronze Age (~ 3500–2800 cal. yr. BP), 206Pb/207Pb decline to their lowest values (1.167) while Pb/Al and Zn/Al increase; and Early Iron Age (~ 2800–2470 cal. yr. BP), 206Pb/207Pb increase to 1.186, most metal/Al ratios decrease but Zn/Al shows a peak. At the beginning of the Late Iron Age, 206Pb/207Pb ratios and metal enrichments show a rapid return to pre-anthropogenic values. These results provide evidence of regional/local atmospheric metal pollution triggered by the earliest phases of mining/metallurgy in the area, and reconcile paleo-environmental and archaeological records.This work was funded by the projects CGL2010-20672 and HAR2008-06477-C03-03/HIST (Plan Nacional I + D + i, Spanish Ministerio de Economía y Competitividad), 10PXIB200182PR (General Directorate of I + D, Xunta de Galicia), and CDS-TCP (CSD2007-00058, Programa Consolider-Ingenio 2010). José Antonio López-Sáez, Fernando Gil Sendino, Carmen Fernández Ochoa and Roberto Zapico for their collaboration and assistance during the fieldwork, to José Rodríguez Racedo for helping with the geochemical analyses, and to Suzanne Leroy for perceptive comments on an earlier draft