Unlikely lead-bearing phases in river and estuary sediments near an ancient mine (Huelgoat, Brittany, France)

Abstract

Anthropocene mineral diversity is the result of the purification of metals naturally combined with other chemical elements in natural environment. Moreover, the advent of human mining and manufacturing mineral-like compounds has experienced a punctuation event in diversity and distribution owing to the pervasive impact of human activities. In this context, the wastes of an abandoned historical mine, Huelgoat mine (Brittany, France), famous during the eighteenth and the nineteenth century contain significant amounts of chemical elements potentially dangerous to the environment. Lead concentration and Pb-bearing phases were quantified in 7 sediments samples located from mine upstream to the Aulne estuary (100km downstream to the mine). Results show very high concentrations of lead in the stations located upstream and downstream of the Huelgoat mine, using X-ray fluorescence spectroscopy, ranging from 7000mg/kg downstream of the mine to a natural concentration of about 80mg/kg upstream. At the same time, Pb-bearing phases were identified depending on the particle sizes, fine (< 50μm) and coarse (> 50μm), using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), total organic carbon (TOC), and pH analyses. For the first time, evidence of anthropogenic mineral "iodoplumbate" formation has been described in a natural environment.