Determining the directions of dangerous ecogeochemical impact of surface reservoirs of highly mineralized mine and open pit waters using a complex of geological and geophysical data

The issues of effective use of geological and geophysical methods for spatial assessment of dangerous ecogeochemical impact of storage ponds of highly mineralized mine and open pit waters are considered. An example of such an object is the Svystunovo gully (volume – 12 million m3), into which water is pumped out from all working open pits and mines of Southern and partially Central Kryvbas. To solve ecogeochemical problems associated with dangerous influence of such storage ponds, a well-known method for restoring Precambrian fault systems using a complex of geological, geophysical and geomorphological data was taken. At all research scales, based on the results of calculations of the significance of “weights” of fault signs, a clear trend was revealed for predominance of diagonal fault systems with strike azimuths: 35° - 305° and 45° - 315°. The spatial combination of tectonic information with results of detailed electrical exploration work made it possible to identify local directions of propagation of dangerous ecogeochemical influence of the studied storage pond of highly mineralized waters by anomalies of decrease / increase in geoelectric resistance in the emerging geochemical block of local system of integrated environmental monitoring of Southern Kryvbas.


Introduction
Mining has many environmental impacts.Significant amounts of polluting and toxic chemical elements enter the soil near mining enterprises: Cr, Ni, Pb, Cu, Zn, V, Mn, Ge, Be, Sn, Mq, Sr, Ba, Zn, Ga, Zr, Ti, Al, Ca, SB, As, W, Y, Au, etc.The ongoing changes in rock massifs and the underground part of the hydrosphere affect landscapes, surface waters, soils, aeration zone, atmosphere and through them (as well as directly) on the ecological systems of mining regions.The mining complex, and especially enterprises for the extraction and enrichment of iron ore, generate the largest masses of waste -~90% of the extracted raw materials turn into waste that accumulates and pollutes the environment.Among these wastes there are highly mineralized open pit and mine waters, which, in order to create safe conditions for the development of ore deposits, are constantly pumped to the day surface into storage ponds.These objects are sources of filtration of highly mineralized waters (including as a result of accidents), which leads to the transformation of soils and aeration zones, disruption of the regime and pollution of groundwater.Therefore, these objects should be one of the priorities in the developed system of integrated environmental monitoring.The latter is a complex scientific and applied problem, the solution of which requires the development of modern technologies for diagnosing both the state of ecosystems and the dynamics of anthropogenic impact on the environment.Research technologies that use a complex of geological and geophysical methods make it possible to quickly determine its state and functioning by a small number of parameters [1][2][3][4].Over many decades, these methods have evolved mainly under the influence of the requirements of the exploration process.The goal was to increase the efficiency of prospecting for mineral deposits at ever greater depths.Another goal was to transfer the accumulated "geological and geophysical" experience to the solution of geoecological problems "gravitating" to the day surface (where the main economic activity is concentrated).Therefore, in modern conditions, it is necessary to develop special procedures for geoecological interpretation of the data of these methods, for example, based on the tectonic factor [5].The purpose of our research is to determine the spatial distribution of the dangerous ecogeochemical impact of surface storages of highly mineralized open pit and mine waters.We used the data of geological and geophysical methods (including features of the tectonic structure) on the example of a storage pond of highly mineralized open pit and mine waters in the Svystunovo gully in Southern Kryvbas (figure 1).The maximum volume of this storage pond is up to 12.0 million m 3 , the area is up to 216 ha, the length of the dam is 7.125 km with a maximum height of 25.0 m.The pond is filled through a pressure pipeline with a diameter of 1200 mm (figure 2a).Discharge of water from the pond into the Inhulets River is carried out by one surface isolated outlet with a diameter of 1000 mm (figure 2b), near which, on the left bank of the river, there are areas of accumulated undiluted "brine" from the indicated storage pond (figure 2c).The latter is evidence of the dangerous ecogeochemical impact of the discharge of highly mineralized water from the storage pond in the Svystunovo ravine on the ecosystem of the Inhulets River.In the plane of the region, the Svystunovo gully is located on the border of two structural hydrogeological provinces -the Ukrainian Shield (USh) and the Black Sea artesian basin.This location causes the possibility of multidirectional movement of groundwater (in particular, the Sarmatian horizon) and, as a result, pollution of large areas during seepage losses and emergency emptying of the storage pond.At the same time, the negative impact of open pit and mine waters is enhanced by their chemical aggressiveness due to high mineralization.For most of its strike, this gully is a regional fault with clear signs of neotectonic activation.Such an object is an active geodynamic zone with a clear manifestation in the modern relief and is deciphered on aerial and space photographs.Here, intense tectonic fragmentation of rocks actively affects the dynamics of groundwater, changes in the filtration characteristics of water reservoirs, vertical filtration and transit overflow between different-level underground aquifers.As a result, highly mineralized waters in the storage pond (even with high-quality waterproofing of its bottom) can enter underground aquifers and contribute to the development of karst phenomena and salinization of the upper layers of the Earth's crust and soil.The difference in the rate of modern vertical and horizontal movements of adjacent blocks of the Earth's crust within the neotectonic zone causes deformations in the dam and impervious bottom screen.During the operation of the storage pond, several emergency complete devastations took place.As a result, the main ways of filtering highly mineralized waters from the storage pond were found on the impervious bottom screen.They are in the form of failed funnels (with a diameter of 1.5-15.0m and a depth of up to 3 m), contoured by a system of rupture cracks, as well as "open" cracks (up to 0.2-0.6 m wide, up to 2-2 m deep, 5 m and length up to 30-50 m).The formed sinkholes indicated the presence of a downward infiltration movement of water from the storage pond through the impervious screen and a powerful aeration zone.The presence of suffusion-unstable sands in contact with cavernous limestones contributes to the activation of the ancient buried karst while creating significant filtration gradients.Due to the indicated hydrogeological features of the bed, this storage pond still has the status of a "construction in progress".This requires constant complex geological and geophysical studies of the state of the earth's interior under this storage pond and in its immediate vicinity in order to predict and map possible pathways for the spread of pollution in zones of increased permeability.Therefore, in these complex geological and geophysical studies, special attention should be paid to the influence of the tectonic factor

Geological and geophysical studies of regional and local features of the tectonic structure of Kryvbas
The natural features of the tectonic structure directly or indirectly determine the natural conditions of the territory (landscape features, geological and hydrological structure, hydrographic network, types of soils and vegetation).The formation of the hydrodynamic regime and the hydrochemical appearance of groundwater of the first aquifer from the surface, as well as soil-forming processes, are completely determined by the features of landscape zones and the geological history of the formation of the upper layers of the Earth's crust, which in turn are predetermined by the features of the tectonic structure.Therefore, tectonic faults are an important factor in the issues of geoecological mapping and ecomonitoring of technogenically loaded territories.These complex three-dimensional geological bodies determine the paths of increased migration of gases, surface and groundwater.These conditions determine the transportation of various soluble substances and their pollution of the environment, as well as the acceleration of modern dangerous exogenous geological processes, in particular suffusionkarst ones.
As a tectonic basis for solving ecogeochemical problems associated with the dangerous geoecological influence of storage ponds of highly mineralized waters, the well-known method of restoring Precambrian fault systems using a complex of geological, geophysical and geomorphological data is taken.The technique is based on the concept of the planetary causes of structure formation in the earth's crust, and, consequently, on the uniform planetary patterns of the placement of tectonic structures [6].The application of this technique made it possible to establish that the earth's crust is broken by a system of subvertical faults with a complex hierarchy, starting with planetary faults and ending with faults separating blocks up to tens of kilometers or less.According to the chosen concept, in certain tectonic epochs, under the influence of the planetary stress field, the previously formed systems of faults in the earth's crust are activated.Each such system consists of hierarchically subordinate faults in two mutually orthogonal directions.(Within the USh, six fault systems are quite clearly identified, characterized by the following strike azimuths: 0° and 270°, 17° and 287°, 35° and 305°, 45° and 315°, 62° and 332°, 77° and 347 ° [7].) Regionally, the study area is located within the zone, which is characterized by an increased thickness of the lithosphere and an anomalous uplift of the layer surface at a reduced rate in the upper mantle (figure 3a).This large regional zone is also reflected in the data on modern vertical movements of the earth's crust.Within Ukraine it corresponds to the zone of relative subsidence of the Earth's crust at a rate of 1-2 mm/year, which separates large zones of uplifts: the Estonian-Carpathian (from the coast of the Gulf of Finland of the Baltic Sea to Moldova) and Central Russian (covering the upland of the same names, as well as partly the Donetsk Ridge and the Azov massif).
The integrity and importance of this zone is also evidenced by the results of calculations of the significance of the "weights" of fault systems.The essence of the applied spatial processing of information on the geological, geophysical and geomorphological features (indicators) of the systems of faults in the earth's crust is given in [8].For this purpose, the Catalog of indicated indicators of the systems of faults in the earth's crust for the entire territory of the USh [6] was used as the initial data.The results of the calculations revealed a clear trend in the predominance of diagonal fault systems with a maximum corresponding to a system with strike azimuths of 35 o and 305 o (figure 3b).This is a clear reflection of the zone indicated above with an increased thickness of the lithosphere and an anomalous uplift of the layer surface with a reduced velocity in the upper mantle.Moreover, this picture is more clearly manifested in the "ancient" geological and geophysical signs of faults (figure 3c) and somewhat less clearly -in the "young" geomorphological signs (figure 3d).At the same time, it should be noted that the use of exclusively gravimagnetic information in the study of the zone under consideration is ineffective.Figure 4 clearly shows that the predominant regional directions of strike of the steps of the indicated field are north-north-western and submeridional.This is a reflection of the predominant influence of near-surface conditions on the gravimagnetic data (which, in particular, is confirmed by hydrographic data -the strike of large fragments of the Dniester and Southern Bug rivers).The revealed clear regional trend of the prevalence of diagonal fault systems with a maximum corresponding to a system with strike azimuths of 35 o and 305 o can also be traced when the research scale is enlarged within Kryvbas.Despite the fact that the most important fault of this territory is the transregional Kryvyi Rih-Kremenchuk deep fault with a strike azimuth of 17 o (figure 5 and table 2).However, from the results of small-scale studies (figure 3c,d) within the Kryvbas, the indicated fault system with strike azimuths of 35 o and 305 o is less clearly manifested in geological and geophysical features (figure 5b) than in geomorphological features (figure 5c).In the geomorphological features themselves, the "contrast" of the manifestation of a system of faults with strike azimuths of 35 o and 305 o increases from south to north of Kryvbas (figure 5c).The revealed pattern in the transition to individual directions in fault systems is generally better preserved for the strike azimuth of 35 o and somewhat worse for the orthogonal direction of 305 o (figure 6).

Results and discussion
The results of detailed geoelectrical studies of the upper part of the geological section in the area of the storage pond of highly mineralized open pit and mine waters have been analyzed.In the area of the storage ponds of highly mineralized open pit and mine waters in the Svystunovo gully, since 2008, electrical exploration work has been carried out in the modification of vertical electrical sounding (VES) with small separations in order to study in detail the upper part of the Earth's crust -the aeration zone.In particular, to identify rock layers with different electrical resistance, which are considered to be water or water-resistant horizons and to determine the degree of their moisture and to place zones of increased permeability in them by electrical resistance indicators, [9].VES repeated after several years (at the same observation points) make it possible to determine changes in the geoelectric parameters of the geological section associated with natural and technogenic changes in hydrogeological conditions.
According to the results of the analysis and interpretation of the available gravimetric, magnetic and electrometric observations within the area, numerous discontinuous tectonic faults of different directions and geological nature were revealed [10].Tectonic faults are most clearly manifested in the transition zone from purely granitoid strata to granitized metabasites, in the gravitational field.Above which numerous zones of elevated horizontal gradients are well fixed, often coinciding with anomalous and gradient zones of the geoelectric field.According to the data of repeated VES in the study area, a spatiotemporal change in the electrical resistance of rocks in the upper part of the geological section is recorded.The combination of the mapscheme of discontinuous tectonics [9,10] constructed according to the interpretation of the local component of the gravitational field with the spatial change in geoelectric resistance (for example, for the period from 2008 to 2012) shows their fairly good compatibility (figure 7).These schematic maps clearly record anomalies in the decrease in geoelectric resistance caused by the filtration of the water flow along the northwestern fault system from the upper reaches of the Svystunovo gully to the Inhulets River.This is also supported by the presence here of a trough-like trough in the same direction of strike of the aquiclude surface, the Glin Kyiv Formation.At the same time, in the south-western direction downstream of the Svystunovo gully (below the enclosing dam of the reservoir of highly mineralized open pit and mine waters), there is no filtration of the water flow.This is evidenced by the presence here of "blocking" anomalies of increasing geoelectric resistance.From the standpoint of the New Rotational Hypothesis of Structure Formation [6], this can be explained by the local geodynamic features of the modern activation of diagonal fault systems (with strike azimuths of 35 o -305 o and 45 o -315 o ) compression ("closed cracks") for orthogonal faults of southwest strike.Local directions of distribution (and non-proliferation) of the dangerous ecogeochemical influence of the storage pond of highly mineralized mine and open pit waters are identified by a complex of geological, geophysical and tectonic data.They will be used to refine the spatial position of the VES profiles in the emerging geophysical block of the local system of integrated environmental monitoring of Southern Kryvbas.

Conclusions
Mining has a variety of, incl.dangerous ecogeochemical impact on the environment.Highly mineralized open pit waters and mine occupy a special place among mining wastes.They are constantly pumped out to the surface into storage ponds in order to create safe conditions for the development of ore deposits.On the example of a storage pond in the Svystunovo gully, into which water is pumped out from working open pits and mines of the Southern and partially Central Kryvbas, the spatial distribution of the dangerous ecogeochemical impact of such surface reservoirs of highly mineralized mine and open pit waters was studied using the data of geological and geophysical methods.
The use of geological and geophysical methods, which have proven their effectiveness in the exploration process, to solve various geoecological problems, requires the development of special data interpretation procedures, in particular, based on the tectonic factor.To solve ecogeochemical problems associated with the dangerous influence of storage ponds of highly mineralized waters, a well-known method of restoring Precambrian fault systems using a complex of geological, geophysical and geomorphological data was taken.The technique is based on the concept of the planetary causes of structure formation in the earth's crust, and, consequently, on the uniform planetary patterns of the placement of tectonic structures.
In all scales of research (from small-scale to detailed), based on the results of calculations of the significance of the "weights" of geological, geophysical and geomorphological features of fault systems, a clear trend was revealed for the predominance of diagonal systems with strike azimuths of 35 o -305 o and 45 o -315 o .The spatial combination of tectonic information with the results of detailed electrical surveys in the modification of the VES in the area of the storage pond of highly mineralized mine and open pit waters in the Svystunovo gully made it possible to clearly record anomalies in the decrease in geoelectrical resistivity.The anomalies are caused by the filtration of the water flow along the northwestern fault system from the upper reaches of this gully to the Inhulets River.At the same time, in the south-west direction downstream of this gully (below the enclosing dam of the reservoir of highly mineralized open pit and mine waters), there is no filtration of the water flow.The identified local directions of distribution (and non-proliferation) of the dangerous ecogeochemical influence of the storage pond of highly mineralized mine and open pit waters will be used to clarify the spatial position of the VES profiles in the emerging geochemical block of the local system of integrated environmental monitoring of Southern Kryvbas.

Figure 1 .
Figure 1.Location of the storage pond for highly mineralized open pit and mine waters in the Svystunovo gully in Southern Kryvbas.
Svystunovo gully To prevent flooding of existing open pits and mines in the Southern and partly Central Kryvbas, constant pumping of highly mineralized groundwater began in 1975.It is carried out in the winter (non-growing season) in the Inhulets River.Data on the chemical composition of the waters of this reservoir are shown in table 1.

Figure 2 .
Figure 2. The place where the storage pond is filled with highly mineralized water in the upper reaches of the Svystunovo gully (a), the place where water is discharged from this storage pond into the Inhulets River (b) with the remainder (sediment) of the accumulated undiluted "brine" (c).

Figure 3 .
Figure 3. Structural diagram (a) of the upper mantle according to deep seismic sounding data (Sollogub V.B., 1985) (1isohypses of the asthenosphere surface, km; 2surface of the layer with reduced velocity in the upper mantle, km; 3mantle faults northeastern direction; 4 -mantle faults; 5 -local areas of research: 1 -the vicinity of the city of Yuzhnoukraіnsk, 2 -the south of Kryvbas, 3 -the vicinity of the city of Dnipro) and comparison of the "weights" of the fault systems as a whole (b) and separately geological and geophysical (c) and geomorphological, incl.diurnal and buried relief (d) indicators/signs in various parts of a regional uplift in the upper mantle under central Ukraine.

Figure 4 .
Figure 4. Expanded rose-diagram of the strike directions of the steps in the levels of the gravitational (1) and magnetic (2) fields of the south of the Ukrainian Shield.

Figure 5 .Figure 6 .
Figure 5.The normalized sum of the weight coefficients of fault systems in different parts of the Kryvyi Rih-Kremenchuk fault: a -the total sum of the "weights" of all features (indicators), b -separately the sum of the "weights" of geological and geophysical features, cseparately the sum of the "weights" of geomorphological signs (1southern Kryvbas, 2 -south of Kryvyi Rih, 3 -north of Kryvyi Rih, 4 -Zhovti vody, 5 -averaged over the entire Kryvbas).

Figure 7 .
Figure 7. Combination of the local tectonic map and the map of changes (from 2008 to 2012) of geoelectrical resistance, in Ohm•m: 1storage pond of highly mineralized open pit and mine waters in the Svystunovo gully, 2 -Inhulets River.

Table 1 .
Concentrations of pollutants (mg/l) in the waters of the storage pond in the Svystunovo gully (estimated according to the control analysis of water coming from the pressure pipeline (figure2a), 2017)

Table 2 .
Priority local areas of dangerous geoecological impact in different parts of the Kryvyi Rih-Kremenchuk fault.