Oxidation of the arsenic-rich concentrate at the Přebuz abandoned mine (Erzgebirge Mts., CZ): mineralogical evolution

Abstract

Ore concentrate with up to 65 wt.% of arsenic (by-product of cassiterite extraction) exposed to climatic conditions was studied from the mineralogical point of view. Detailed sampling, X-ray diffraction analyses, energy-dispersive microanalysis (EDAX) and especially scanning electron microscopy (SEM) were applied to study the arsenopyrite–löllingite-concentrate weathering. The studied concentrate contains very small proportion (<5 vol.%) of gangue minerals such as quartz and feldspars; the oxidation of arsenopyrite and löllingite (and accessory pyrite) is thus practically not complicated by interference with additional minerals and elements. Arsenolite, scorodite, kaatialaite and native sulphur were found to be the main secondary phases originating by dissolution of arsenopyrite and löllingite. New secondary phases precipitate on the surface of the ore-concentrate body but also form cement among the grains of finely milled material. The following succession of secondary minerals was determined: arsenolite, scorodite+native sulphur and kaatialaite. Significant arsenic migration into the proximal environment was revealed: 2580 and 13 622 mg kg −1 were the highest arsenic concentrations in two sections excavated at distances of 0.5 and 1.5 m from the concentrate body.