Features of trace elements in the groundwater of the Bakchar iron ore deposit (Tomsk Oblast)

The article investigates the spatial distribution, geological and hydrogeological conditions, chemical composition of ferriferous groundwater of the Middle Ob basin. From the depths of 10-30 m, and even of 2-5 m in the bogs, the groundwater is enriched with iron everywhere. Its content quite often reaches 30-40 mg/l. Major factors and regularities of such a distribution of iron in the water are known; it is more complicated to deal with the sources and mechanisms of accumulation of this element in the water. To identify these problems, since 2008, the authors have studied the specific conditions for the formation of iron-containing water using thermo-dynamic calculations of processes in the system "water - rock" in the territory of the Middle Ob basin (Tomsk Oblast). The most interesting is the area of Bakchar where one of the largest iron ore deposit in the world, the Bakchar iron ore deposit, is located. The groundwaters of the Quaternary and Paleogene deposits are fresh, neutral and weakly alkaline, hydrocarbonate calcium and calcium-magnesium. This water is enriched not only with Fe but also with Mn, their concentration reaches 10 mg/l and 0.5 mg/l. The waters of the Upper Cretaceous sediments have greater salinity. There is a change in the composition of water from calcium bicarbonate to sodium bicarbonate (soda), which explains the large variations in the stiffness. Relatively higher-lying waters are characterized by high alkalinity. The content of Fe and Mn in the water is reduced. All this confirms the high washed-out character of the geological structures in the region. Practically all the groundwater circulating above the ore deposit, contains high concentrations of Fe ions. Below the ore deposit at a depth of 390 m the concentration of Fe in the water decreases by 6 times from the average, but only by the data of one well. Trace elements of the groundwater in the territory of the Bakchar iron ore deposit is investigated in detail. From the 64 studied elements Ca, Fe, Sr, Mn, P and rare cases of Na, As, B, Li, Ni, La have a high content in the water. Zn, Ti, Ni, Cr, Mo, Pb, Y, V, Cu, Ge, Ga, Zr, Cs, Sb have lower values. Nb, Cd, Sn, Ce, Pr, Sm, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Tl, Bi are below detection limits. In deeper waters there is an increase in the content of Na, K, Li, B, V, Cr, As, Sr, Mo, Sb and a decrease in the concentration of Ca, Fe, Si, Mn, Zn. The sources of chemical elements are aluminosilicate rocks which developed in the territory: sands and clays of the marine genesis. Depending on the features of the geochemical environment (pH, Eh, organic matter and others), there is an accumulation of some elements. Part of elements, on the contrary, leaves the water to become secondary sediments. Elements are redistributed between rock and water. In ores, for example, such elements as V, Ti, Zn, Mo, Cr, Sb, Cu, Pb, Ni, Sc, Ge, Be, Zr, Y, U, Th, Au are concentrated, their content in the water is low or average. Ca, Na, Sr, B, Li are concentrated in the water, and their content in the rock is sharply low. Fe, Mn, P,As are well concentrated in water and in ores. This work was supported by the RSF grant no. 15-17-10009.

Keywords

Authors

References