# Current State of the Gold Mining Waste from the Ores of the Ursk Deposit (Western Siberia, Russia)
## 4 Discussion  
The vertical electrical sounding, performed in the Ursk mine tailings area, revealed conductive zones which are connected with watering due to seepage of atmospheric waters and spreading of drainage waters in the relief depression, as well as with mechanical drifting of the solid matter (Figure 6). In addition, it is likely that groundwater recharging the lake to the northeast of the site flows in a north-southeast direction (noted at depths of up to 15.5 m). A conductive zone up to 20 m deep to the southwest of the dumps coincides with a fracture formed due to erosion by drainage water. Infiltration of drainage water into the natural fault zone in the southeastern direction from the dumps was described earlier in the work of [25] and confirmed by us within the framework of this study. The color of the deposits (light in the northern part and dark in the southern part, Figure 1) is related to the concentration of ferromagnetic in their composition and, consequently, to their increased (in the northern part) and decreased (in the southern part) magnetic susceptibility (Figure 8). The digital elevation model allows us to trace individual features of the relief, i.e., watercourses and embankments. The main water catchment occurs in the northwestern part of the site with formation of watercourses, merging into the creek in the southern part. The main embankment is subjected to intensive erosion on the southwestern slope, and erosion gullies are formed here. Material from this slope enters the channel of the central watercourse and partially forms a deluvial plume to the south of the embankment, probably preventing the flow of the watercourse that wraps around the embankment from the east, which leads to waterlogging in the southeastern part of the area (Figures 9 and 10). The resulting model of thermal imaging (Figure 11) illustrates a number of temperature anomalies:  
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The high concentrations of Fe in the drainage solution are caused by its leaching from sulfide minerals (pyrite and pyrrhotite) in the supergene zone [31]. \[2\text{FeS}_{2}+7\text{O}_{2}+2\text{H}_{2}\text{O}\to 2\text{FeSO}_{4}+2 \text{H}_{2}\text{SO}_{4}.\]  
\[2\text{FeSO}_{4}+4\text{H}_{2}\text{SO}_{4}+2\text{O}_{2}\to 2\text{Fe}_{2}( \text{SO}_{4})3+4\text{H}_{2}\text{O}.\]  
\[\text{CaCO}_{3}+\text{H}_{2}\text{SO}_{4}\rightarrow\text{Ca}^{2+}+\text{SO}_{4 }{}^{2-}+\text{H}_{2}\text{O}+\text{CO}_{2}.\]  
\[\text{MgCO}_{3}+\text{H}_{2}\text{SO}_{4}\rightarrow\text{Mg}^{2+}+\text{SO}_{4 }{}^{2-}+\text{H}_{2}\text{O}+\text{CO}_{2}.\]  
In spite of the oxidative conditions (Eh 0.6 V), the low pH values (3.61) favor the formation of the Fe\({}^{2+}\) compounds [32], characterized by high solubility and mobility. The sulfate class of drainage water and Ca-Mg type of mineralization are related to the oxidation of sulfides in the tailings, dissolution of calcite and dolomite, and leaching of the Ca and Mg. The dissolution of chalcopyrite, sphalerite, galena, and arsenopyrite leads to extremely high concentrations of Cu (3000 ug/L), Pb (1200 ug/L), As (1300 ug/L), and Hg (34 ug/L) in the Ursk drainage, significantly exceeding [PERSON]'s and maximum allowable concentrations (Table 3) [29; 30]. According to research data from previous years, it has been shown that active gas release occurs in this zone, including gases of biotic origin (C\({}_{2}\)H\({}_{6}\)S) due to methylation of sulfide-containing compounds by bacteria _Bacillus mycoides_. Interestingly, we found a local heating up to +5 \({}^{\circ}\)C in this zone under the snow cap during the studies of the dump in February at ambient temperature \(-\)20 \({}^{\circ}\)C [6]. A sharp decrease in the electrical conductivity of the drainage flow and the concentrations of chemical elements at a distance of 200 m from the dump are primarily attributed to sorption on natural sorbents the drainage stream flows through. For example, sorption of divalent metal ions and arsenic on peat is quite effective [32; 33].