Chemical composition of weathering products in neutral and acidic mine tailings from stibnite exploitation in Slovakia

Here we describe the chemical composition of the weathering products at two abandoned stibnite deposits, Dúbrava and Popro in Slovakia. The tailings at Dúbrava are circumneutral (pH 7-8), richer in Sb than As and rich in carbonates. The tailings at Popro 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 (FeS2), less frequently stibnite (Sb2S3) and arsenopyrite (FeAsS); minor berthierite (FeSb2S4) was found only at Popro . 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 Popro , 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.