Assessing potential hazard of technogenic formations of natural and man-made complexes of some sulphide deposits of the Eastern Zabaykalye

The analysis of chemical composition of technosol and soil samples from Akatuyevsky and Blagodatsky polymetallic deposit mines of the Eastern Zabaykalye revealed that the main pollutant in the soil samples is As. Material excess of the Maximum allowable concentrations was registered for Pb, Zn, Cd and Mn. Calculation of potential hazard coefficients showed that the most hazardous for the environment are man-made formations of Akatuyevsky and Blagodatsky mines. Of all the chemical elements which are most commonly encountered at the Akatuyevsky and Blagodatsky mines technosol the most hazardous are As, Pb, Zn and Cu. It is noted that these chemical elements are part of sulphide ore minerals.

Mining territories of the Eastern Zabaykalye are potentially hazardous for the environment. Heavy metals which accumulate in the tailings facilities and in the soil affect physiological processes of plants and animals. The areas of Akatuyevsky and Blagodatsky polymetallic deposits located in the Nerchinsko-Zavodsky and Alexandrovo-Zavodsky districts of the Zabaykalsky krai are also potentially hazardous (figure 1).
Technosol and soils are characterized by high contents of As, Pb, Zn, Cd, Cu, Cr and Co (table 1). The main pollutant in the soil samples from Akatuyevsky and Blagodatsky mines is As (567 and 89.1 times in excess of the Maximum allowable concentrations). In addition, Akatuyevsky mine soil samples have significant excess of the Maximum allowable concentrations for Pb (35.4 times), Zn (33.5 times), and Cd (22.1 times), and Blagodatsky mine samples have excessive content of Zn (9.6 times), Mn (5.8 times), and Cd (3.5 times).
It is known that the component distribution series as pertains to the average content of leaching water in the technogenic water are the following: As>Zn>Mn>Fe>Sr>Cd>U>Pb>Sb>Mo>Cs>Se>Co water from Akatuyevsky mine tailings facilities, As>Pb>Sb>Zn>Cd>Mn>Mo>Al>La>Sr>Cu>Uwater from Blagodatsky mine tailings facilities [3]. Potential hazard of the deposit mines technosol will be assessed with the method developed by a group of authors from All-Russian Scientific-Research Institute of Mineral Resources named after N M Fedorovsky [1]. According to this method environmental hazard of a potentially "toxic ore deposit" is assessed on the basis of the "lithotoxicity" of chemical elements (Tl). "Potential toxicity of ore deposit" is calculated as (1): where GEopotential toxicity of the ore deposit; Tlelement lithotoxicity coefficient; В = X/Q, where Xelement concentration, Qelement contents in the environment. Calculation of "potential toxicity" of the technosol revealed that tailings facilities of the Blagodatsky (GEo = 74441) and Akatuyevsky (GEo = 61803) polymetallic deposits are characterized by high environmental hazard. "Potential toxicity" of the soil samples is substantially lower -Akatuyevsky deposit (GEo = 8987), Blagodatsky deposit (GEo = 1855). According to the method described above the calculated GEo values correspond to the coefficients of potential toxicity of the polymetallic deposits.
In order to assess sanitary and hygienic pollution of the soil at the area, immediately adjacent to the technogenic landscapes we should calculate Z c . It is calculated with the following formula (2): where K cconcentration coefficient of the i-th chemical element, nnumber equal to the number of elements included in the geochemical association. Concentration coefficient (K c ) is calculated as follows: К с = С i /С backgr , where C iactual contents of the element; С backgr .geochemical background.
According to the calculation, the soil of Akatuyevsky deposit mine is Z c = 68.9, whereas the calculations for the territory immediately adjacent to the tailings facility of Blagodatsky deposit showed Z c = 55. This value conforms to hazardous pollution of soil [2].
The calculations show high potential hazard of technogenic formations of Akatuyevsky and Blagodatsky mines. However, the methods used above do not take into account such properties of chemical elements as the rate of their dissemination in the environment under acidic and recovery conditions, and their aggregate content in potentially hazardous objects.
Therefore, in order to identify the degree of potential hazard of some chemical elements we will use the methods to calculate Pollution Load Index (PLI) and Geoaccumulation index (I geo ), which are widely used in international research [4,5].
The assessment of potential hazard of soil pollution with heavy metal compounds from the tailings facility in this method is done with the following equations (3) and (4):   where PI is the single factor pollution index of each metal PI < 1 is non polluted; 1 ≤ PI < 2 is slightly polluted; 2 ≤ PI < 3 is moderately polluted; PI ≥ 3 highly polluted; C soil and C background are the concentrations of metal in the soil sample and background respectively (mg/kg -1 ). PLI is pollution load index PLI < 2 is moderately to unpolluted; 2 ≤ PLI < 4 is moderately polluted; 4 ≤ PLI < 6 is highly polluted; PLI > 6 is very highly polluted; PI is the single factor pollution index of each metal, and n is the number of pollutants assessed (eight in the current study); PI is the single factor pollution index of each metal. The calculations show that based on the soil pollution load index the surroundings of Akatuyevsky and Blagodatsky mines can be referred to moderately polluted territories (2 ≤ PLI < 4). The highest PI values were accounted for As, Pb, Zn and Cu in the soil samples from Akatuyevsky mine. In the Blagodatsky mine soil samples high PI values are registered for As, Pb and Ba (table 2). According to the method suggested by Müller [5] geoaccumulation index (I geo ) in the soil can be calculated as follows (5): where C n is measured concentration of heavy metal compounds in the sample; BE n is average background concentration of the measured elements. This index reflects the level of exposure for such toxic compounds as arsenic, copper, antimony and lead within the boundaries of effect of tailings facilities of the studied abandoned mines. In the current study in order to insure the most accurate estimate of the potential hazard of the chemical elements we calculate the indices for As, Pb, Zn and Cu.
According to the calculations the highest accumulation index I geo is observed for As, followed by Zn and Pb, with the smallest index for Cu (table 3). It is noted that the index values for Akatuyevsky mine soil is generally higher than for samples taken from Blagodatsky mine; the only exception is 5.1 for As in the Blagodatsky mine soil samples. At the same time potential hazard of Blagodatsky tailings is generally higher than the same material from Akatuyevsky mine. Thus, the calculations show that of all the studied chemical elements the highest potential hazard comes from As, Pb, Zn -I and II hazard class chemical elements. This fact is explained by the mineral composition of flotation tailings of the initial lead-zinc ore of Akatuyevsky and Blagodatsky mines (figure 2).