Trace metals dispersion from 1000 years of mining activity in the northern French Alps

Abstract This paper investigates the long-term dispersal of trace metals and their impact on the environment long after mine closure in the French Alps. Three statistical methods derived from modern mining (Exploratory Data Analysis, fractals and Sediment Quality Index) were applied to geochemical analyses of streambed sediments to produce mineral prospectivity maps. About 5% of the samples have a poor or marginal quality and may have an effect on biota. Positive anomalies are either related to the geological background (lithology, major tectonic contacts) or to ancient mining sites. The local impact of former mining was investigated on a medieval Pb–Ag district (Brandes; Pbmax ~8 000 mg kg−1), a small district mined during the 17th–19th c. (Peisey-Nancroix; Pbmax = 583 mg kg−1), and a major modern Pb–Ag mine (Macot-La Plagne; Pbmax ~ 3 200 mg kg−1).The mining heritage is still traceable in the northern French Alps. The anomalies observed at local scale are related to the volume of extracted ore rather than to the timing and duration of mining, suggesting that old mining sites still release trace metals over centuries and up to a thousand years. The statistical methods used provide a strong tool for archaeological prospection and environmental studies.