Estelle Camizuli à l’HIMAT (Photo F. Cattin)
L’étude “Ancient mining near the Bibracte oppidum and its nowadays impact on ecosystems: a multidisciplinary approach” par E. Camizuli, F. Monna, I. Jouffroy-Bapicot, F. Cattin, R. Scheifler, C. Gourault, J.-P. Guillaumet, C. Petit, G. Hamm, R. Losno, J. Labanowski, F. van Oort, et Paul Alibert a été présentée à l’HIMAT 2012, Innsbruck [la présentation]
ABSTRACT: The Morvan Massif (Burgundy, France), nowadays a pristine-like protected area, was a major economic center during the Iron Age, as attested by the Bibracte oppidum, the largest settlement of the Aeduan Celtic tribe (ca. 180 BC–25 AD). Study of several peat archives enhanced computing of anthropogenic metal fluxes, generated by local mining and metallurgical activities. All activities led to broad forest clearances for energy. Such indirect indications suggest that metallurgy started as early as the Middle Bronze Age (ca. 1650 cal BC) and continued irregularly until the 20th century AD. Recently, an excavation near the oppidum provided direct clues of Iron Age mining activities.
Locating the mines is capital, but systematic pedestrian survey in the Morvan forest landscape is difficult. Areas where mineral substances are abundant must be targeted. Geochemical anomalies can be delineated from the background, using Exploratory Data Analysis and fractal models. A 900 km² pilot area was first selected, where 2543 stream sediment samples were previously analyzed. The model efficiency was demonstrated using 119 past and modern, already listed, mining sites. Final results suggest hundreds of potential mining sites in the Morvan.
Considerable amounts of metals generated by ore-processing and metal-working were likely incorporated in soils over centuries. Three 1-km² zones, variously affected by historical mining, were studied for spatial metal distributions, using 210 topsoils and 11 streambed sediments. In the first zone, a Pb-Ag mine exploited mainly during the 15th-16th centuries, soils are highly contaminated, Pb contents reaching up to 5000 mg kg-1 and Cd contents to 50 mg kg-1. The second site, mined during the 19th-20th centuries for iron, included slags dating from 133 AD-335 AD. Here, Pb and Cd contents in soils were intermediate: 40–4500 mg kg-1 and 0.5–3.2 mg kg-1, respectively. The third site was free of mining activity and the soil concentrations in Pb (50 mg kg-1) and Cd (0.5 mg kg-1) represent local geochemical background.
Contamination hot spots, as those found in the first two areas, likely have deleterious effects on local biota. To assess their impacts on aquatic and terrestrial ecosystems, brown trout (Salmo trutta) and wood mice (Apodemus sylvaticus) were used as biomonitors. A total of 72 fish livers and 91 rodent kidneys were analyzed for elemental concentrations by ICP-AES. For the aquatic ecosystem, relations between biotic and abiotic parameters were not clear, probably to the poorly constrained trout habitat. For the terrestrial ecosystem, wood mouse kidneys Pb and Cd concentrations match the observed soil metal patterns, illustrating mine–soil–rodents pathways.