Tailings deposits generated from mining activities represent a potential risk for the aquatic environment through the release of potentially toxic metals and metalloids occurring in a variety of minerals present in the tailings. Physicochemical and mineralogical characteristics of tailings such as total concentrations of chemical elements, pH, ratio of acid-producing to acid-neutralizing minerals, and primary and secondary mineral phases are very important factors that control the actual release of potentially toxic metals and metalloids from the tailings to the environment. The aims of this study are the determination of geochemical and mineralogical characteristics of tailings deposited in voluminous impoundment situated near the village of Markušovce (eastern Slovakia) and identification of the processes controlling the mobility of selected toxic metals (Cu, Hg) and metalloids (As, Sb). The studied tailings have unique features in comparison with the other tailings investigated previously because of the specific mineral assemblage primarily consisting of barite, siderite, quartz, and minor sulfides. To meet the aims, samples of the tailings were collected from 3 boreholes and 15 excavated pits and subjected to bulk geochemical analyses (i.e., determination of chemical composition, pH, Eh, acid generation, and neutralization potentials) combined with detailed mineralogical characterization using optical microscopy, X-ray diffraction (XRD), electron microprobe analysis (EMPA), and micro-X-ray diffraction (μ-XRD). Additionally, the geochemical and mineralogical factors controlling the transfer of potentially toxic elements from tailings to waters were also determined using short-term batch test (European norm EN 12457), sampling of drainage waters and speciation-equilibrium calculations performed with PHREEQC. The tailings mineral assemblage consists of siderite, barite, quartz, and dolomite. Sulfide minerals constitute only a minor proportion of the tailings mineral assemblage and their occurrence follows the order: chalcopyrite > pyrite > tetrahedrite>arsenopyrite. The mineralogical composition of the tailings corresponds well to the primary mineralization mined. The neutralization capacity of the tailings is high, as confirmed by the values of neutralization potential to acid generation potential ratio, ranging from 6.7 to 63.9, and neutral to slightly alkaline pH of the tailings (paste pH 7.16-8.12) and the waters (pH 7.00-8.52). This is explained by abundant occurrence of carbonate minerals in the tailings, which readily neutralize the acidity generated by sulfide oxidation. The total solid-phase concentrations of metal(loid)s decrease as Cu>Sb>Hg>As and reflect the proportions of sulfides present in the tailings. Sulfide oxidation generally extends to a depth of 2 m. μ-XRD and EMPA were used to study secondary products developed on the surface of sulfide minerals and within the tailings. The main secondary minerals identified are goethite and X-ray amorphous Fe oxyhydroxides and their occurrence decreases w...

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This work presents the results of investigation of the primary minerals and their weathering products of two tailing ponds near the villages of Rudňany and Slovinky in eastern Slovakia. The tailings are near-neutral or slightly alkaline (pH = 7.2-8.8) because the acidity generated by the decomposition of the sulfides is efficiently neutralized by the abundant carbonate minerals. The most frequent primary gangue minerals are siderite, quartz, barite, and muscovite. The primary sulfide minerals in both tailing ponds are pyrite and chalcopyrite; less common are tetrahedrite and arsenopyrite. The most frequent secondary and tertiary (i.e., formed in the tailings, not in the oxidation zone of the deposits) minerals at both localities are iron oxides, either goethite or poorly crystalline hydrous ferric oxide. Other minerals (cuprite, malachite, delafossite; identified by X-ray microdiffraction or Raman spectroscopy) are minor or rare and occur only in Slovinky. The iron oxide minerals are enriched in a suite of elements, including Cu, Si, Ca, Zn, As, Mg, and Mn. The transformations of the poorly crystalline hydrous ferric oxide to goethite and maturation of goethite is controlled by both highvalence tetrahedral cations (Si, As, P) and lower-valence octahedral cations (Cu), as shown by the measurements of the size of coherently diffracting domains in goethite and the chemical composition of goethite. The iron oxide minerals, by virtue of their adsorption capacity, prevent separate minerals of many metals and metalloids (Cu, Ca, As, Sb) from nucleating and growing, and therefore control the entire neutral mine drainage (NMD) system. Geochemical modeling of the discharged waters shows that all common Cu and ferric arsenate minerals are strongly undersaturated, confirming the central role of iron oxide phases in the NMD system.

Here we describe the chemical composition of the weathering products at two abandoned stibnite deposits, Dúbrava and Poproč in Slovakia. The tailings at Dúbrava are circumneutral (pH 7-8), richer in Sb than As and rich in carbonates. The tailings at Poproč are acidic (pH 3-5), the Sb/As ratio is usually close to 1, carbonates are missing, and the tailings have elevated Pb contents. The most common sulphide at both sites was pyrite (FeS 2 ), less frequently stibnite (Sb 2 S 3 ) and arsenopyrite (FeAsS); minor berthierite (FeSb 2 S 4 ) was found only at Poproč. At both sites, sandy layers of the tailings contain the weathering products; the clayey portions are sterile. The most frequent secondary phases in the Dúbrava impoundments are oxidation rims on pyrite and arsenopyrite, with relics of the primary sulphides commonly preserved. At Poproč, the primary sulphides were completely oxidized and decomposed. A common feature of the oxidation rims on all primary sulphides is their enrichment with respect to elements rather rare in the primary phase, an effect which is most apparent in the outermost portions of the rims. Rims around arsenopyrite may be enriched in Sb, around pyrite in As and Sb, and around stibnite in Pb. Antimony is usually incorporated into Sb-Fe, Fe-Sb, Sb, or Sb-Ca oxides, with the Sb/(Sb + Fe) ratio varying from 0 to 1. Arsenic behaves differently in comparison with Sb in that the highest As/(As + Fe) ratio on a wt. % basis is 0.41, as observed in weathering rims on arsenopyrite, the only primary sulphide with a substantial As content. Our results show that the nature of the weathering products is controlled by the primary mineralogy and the ability of the aqueous solutions to transport As, Sb, Ca, Fe, and Pb. There is no indication that the final products would be chemically or mineralogically different if weathering reached the terminal stages at the two studied sites.

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