Recently forming secondary copper minerals as indicators of geochemical conditions in an abandoned mine in Radzimowice (SW Poland)

Abstract

An occurrence of twelve recently formed secondary copper minerals (SCM) was observed in underground workings of an abandoned Cu-As-Au mine in Radzimowice. The minerals, mainly sulphate species, were identified using Powder X-Ray Diffraction (PXRD), scanning electron microscope with energy dispersive spectroscopy system (SEM-EDS) and electron microprobe analysis with wavelength-dispersive spectrometry system (EPMA-WDS) methods. The SCM of Radzimowice form the following assemblages: paragenesis I is characterized by langite, posnjakite, brochantite and devilline. These minerals crystallise directly from pH 6.0–7.0 mine waters. Paragenesis II also comprises hydrous copper sulphates (HCS), and in addition contains native copper, cuprite, ferrihydrite and gypsum. Secondary HCS mainly crystallise as products of reactions of sulphate-rich mine waters with native copper and cuprite. The pH of these waters varies from ~5.0 to 6.0. The III paragenesis is dominated by woodwardite, associated with variable amounts of chalcoalumite and amorphous Cu-Al sulphates. Accumulations of woodwardite occur in the zones where Al- and sulphate-rich acid mine waters (pH ~2.5–3.0) mix with neutral waters (pH 6.5–7.0). Paragenesis IV is rare, dominated by chrysocolla, coexisting with small amounts of mottramite and goethite. This assemblage formed as a result of mobilization of silica released during decomposition of rock-forming aluminosilicates attacked by acid mine waters