Geochemical study of a Neolithic metallurgical site, Le Planet (France): Detection of paleopollution recorded in archaeological soils

Abstract

A geochemical study was carried out at the metallurgical site of Le Planet (Fayet, Aveyron), situated in the south of France. The site dates from the 3rd millennium BC, and is one the oldest copper smelting metallurgical sites known in France. The site reveals numerous phases of occupation, all dated from the Late Neolithic. The geochemical study of the site aimed at identifying the signature of the metallurgical activities in the archaeological soils and their spatial distribution. The analyses were carried out by X-ray fluorescence (p-XRF). Two main sampling methods were used. The first, grid-based method, allowed the sampling of the totality of the archaeological excavation surface. The second sampling method aimed to study the vertical distribution of the trace elements in the stratigraphic sequence. Four vertical profiles, positioned throughout the site, allowed a high-resolution sampling of the totality of the stratigraphy, which permitted to identify the stratigraphic distribution of polluted archaeological horizons. The geochemical analyses reveal the importance of the pollution due to the prehistoric metallurgical activities, mainly of lead, copper and arsenic. For instance, the measured values of lead vary between 26 and 9831 ppm. These values for copper are between 53 and 1154 ppm, whereas for arsenic they vary between 35 and 258 ppm. The metallurgical furnaces seem to constitute the main hotspots for the spatial distribution of the pollution. The geochemical study of the profiles identifies two main polluted archaeological horizons, and thus allows having a better understanding of the stratigraphic extension of horizons containing geochemical traces of metallurgical activities.