Acta Musei Moraviae

Arsenic supergene mineralisations and arsenic behaviour in waste dumps of base-metal deposit Dlouhá Ves near Havlíčkův Brod (Českomoravská vrchovina Highlands)

Arsenic-bearing mineralisation, represented by primary arsenopyrite-pyrite assemblage is typical for basemetal deposit at Českomoravská vrchovina Highlands. Waste rock piles from historical mines located at Dlouhá Ves near Havlíčkův Brod have been investigated in two profiles using powder X-ray diffraction, electron microprobe analysis, bulk composition analysis and Mössbauer spectroscopy. The mobility of arsenic and other contaminants was evaluated by leaching experiments. The dumps have initial high sulfide and low carbonate content. The primary source of the arsenic was arsenopyrite, which was significantly oxidized. Where arsenopyrite predominates, it is coated by scorodite and other Fe–As phases, which limit their further oxidation. The major supergenne As-phases in the profile (a) studied at Dlouhá Ves are goethite and Fe³⁺-oxohydroxides with As portion (2.70–7.37 hm. % As₂O₅), including a variety of nonstoichiometric phases adsorbing As, and minerals of the jarosite group (0.04–0.90 wt. % As₂O₅). At profile (b), minerals of the jarosite–beudantite group (0.51–13.48 wt. % As₂O₅), scorodite and kaňkite were found. The paste pH was lower at profile (a) – minimum about 1.9, than at the outcrop profile (b) – minimum of about 2.8 in Dlouhá Ves. Processes weathering in the piles are also affected by the pyrite/arsenopyrite ratio, where high pyrite content increases the S/As ratio and results in the formation of jarosite group minerals and low pH conditions. Arsenic concentrations released during the leaching experiments were generally low; maximum amounts were released from horizons with jarosite and arsenopyrite. In contrast, minimum amounts of arsenic were released from horizons with beudantite and scorodite. It seems that beudantite and scorodite represent a long-term option for immobilization of arsenic, but arsenic stored in jarosite can be mobilized relatively easily.