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The investigated area in this study is a pyrite-bearing waste dump in the Gyöngyösoroszi-Mátraszentimre region, Mátra Mts., Hungary, exposed to environmental conditions for about 40 years. At the time of sample collection, secondary mineral formation was still active. The material consists of Miocene andesitic volcanic rocks hosting a medium temperature hydrothermal vein-type mineralization, with dominant sulfide minerals pyrite, sphalerite, galena, chalcopyrite, marcasite. Mining activity in this region produced numerous sites containing high concentrations of Pb, Zn As and Cu. The last mining activity ended in 1986. In 2006 a large-scale project was launched for the remediation of the mining region (more than 20 waste dumps, improperly sealed adits and shafts). The Bányabérc dump was removed from its original location, offering systematic sampling across full profiles (up to 5-10 m). Its total volume reaches 26 000 m3, its bulk pH is around 3.7. For proper estimation of the environmental hazard we carried out XRD, SEM+EDX measurements and Mössbauer (RT-MB, LN-MB), Raman and infrared spectroscopy of the mineral phases present in the altering waste dump material.
Minerals found in the system are: pyrite, gypsum, jarosite, hydronium jarosite, plumbojarosite, quartz, feldspars, goethite, hematite, pickeringite, alunogen, epsomite, smectite group, galena, sphalerite and, in traces, calcite, chalcopyrite. The jarosite-group phases form generally euhedral crystals in the 0.1-3 m size range and are the most common environmentally formed minerals in the current stage of the surface processes on the Bányabérc waste dump. They incorporate several environmentally hazardous elements (e.g. Pb, As). Goethite is found to be superparamagnetic, as shown by LN-MB. Acid release from mine wastes is still active. The sources are iron sulfide oxidation, dissolution of weakly soluble sulfate minerals like jarosite, and dissolution of water-soluble secondary sulfates. Sulfidic mine wastes develop a wide variety of highly soluble Mg and Al efflorescent salts in longer dry periods, by evaporative processes from the pore water. Alteration of sphalerite was not directly detected, but Zn was still found both in the weakly (jarosite-group) and highly (halotrichite-group) water soluble secondary sulfate phases. Arsenic is present both in connection with jarosite and iron-hydroxy-sulfates of higher Fe/S atomic ratios.
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