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The paper presents data on two cores from the dispersion train of gold-bearing sulfide tailings in the Novo-Ursk deposit (Kemerovo region, Russia), where organic-bearing mud and natural organic matter are interbedded with cyanide tailings and acid mine drainage (AMD). The study focuses on speciation of Au, Ag and potentially toxic elements (PTE), including Fe, Cu, Zn, As, Se and Pb according to selective sequential extractions. Since large contents of elements are found in water solution and bound to Fe(III) compounds, sulfides and/or organic matter in both cores, the organic material behaves as a natural biogeochemical barrier for potentially toxic elements and precious metals released from AMD. The interaction with organic matter results in biogeochemical sorption and immobilization of elements and is favourable for secondary enrichment in gold and silver. It leads to immobilization of elements that further form new mineral phases or become partitioned between existing phases. On the other hand, very high concentrations of water-soluble and oxidizable species of PTE and Au, which are unstable in surface conditions and may become remobilized when the environment changes, make the organic material less workable and even potentially hazardous. Thus, both positive (secondary enrichment) and negative (pollution) effects should be taken into account in the planning and design of systems for purification, disposal of cyanide tailings and recovery of useful components from tailings using natural organic matter as a geochemical barrier.

We study the contents of elements and group composition in natural organic matter (NOM) that interacts with acid mine drainage (АMD) and high-sulfide tailings at the Ursk site (southwestern Siberia, Russia). AMD causes biomass changes in NOM, related changes in the composition of fractions, and hydrolysis of hydrolyzable compounds; it increases the water-soluble fraction and maintains depolymerization of humic acids to fulvic acids, but exerts no effect on substances soluble in organics (bitumen) or on poorly hydrolyzable compounds. Accumulation of inorganic elements and precipitation of minerals obscure the true fraction composition of NOM: the superposed mineral component contributes significantly to the water-soluble, humic acid, hydrolyzable and non-hydrolyzable fractions, and may reach 26.4% per total of all fractions. Rock-forming and potentially toxic elements partition among NOM fractions and predominate in the water-soluble fraction. The contents of Au and Ag are the highest in the fractions of humic acids and hydrolyzable compounds but are lower in the non-hydrolyzable residue. The obtained data have implications for possible migration of potentially toxic elements and noble metals and thus for remediation of polluted areas. The observed fractionation of Ag and Au in NOM helps us to understand the mechanisms of their distribution in organic-bearing environments, such as peatlands or coal basins.

The recovery of gold from ores containing arsenopyrite releases significant amounts of arsenic into the environment. Arsenic releases primarily result from the processing and oxidation of stored mine tailings. This investigation examines: (1) the distribution of arsenic, iron, manganese and their chemical species in sediment cores extracted from a tailings impoundment in the Kemerovo region of southwestern Siberia; and (2) the weathering of arsenic minerals collected from its tailings dam. The data demonstrate that during storage of the sediments within the impoundment, arsenic is predominantly present as residual arsenopyrite and, to a lesser degree, as substances co-precipitated with iron hydroxide. The arsenic released from the sediment results from an oxidative dissolution of arsenopyrite and reductive dissolution of Fe oxides.