SOME FEATURES OF THE FORMATION OF THE CHEMICAL COMPOSITION OF WATERS IN ZONES OF TECTONIC DISTURBANCES

(USING THE TOM–YAYA INTERFLUVE AS AN EXAMPLE)

P. A. UDODOV, V. M. MATUSEVICH

(Presented by the Department of Hydrogeology and Engineering Geology)

For folded mountain structures and hydrogeological massifs, the principal pathways of groundwater circulation below the weathering zone are tectonic disturbances. They constitute very complex and diverse water-bearing systems, as noted in the works of A. M. Ovchinnikov [6].

A characteristic feature of this type of water is a somewhat elevated total mineralization and a more complex composition of macro- and microcomponents, which reflects the complex conditions of their recharge and circulation. In the process of discharge they mix with waters of various horizons, sometimes differing considerably in chemical composition. In addition, these water-saturated zones may occur under different geochemical conditions.

The distinctive character of the chemical type of waters in zones of tectonic disturbances is especially clearly manifested in the composition and content of microcomponents. As is known, most zones of tectonic disturbances are characterized by the presence of one or another mineralization, which is a source of enrichment of waters with microcomponents. In the process of their enrichment, gases dissolved in the waters play a significant role \((O_2, CO_2,\) etc.).

The study of the waters described is of great importance for solving the following problems of hydrogeology:

1. Formation of the chemical composition of groundwaters, especially for areas overlain by a thick sequence of loose deposits [6].
2. Prospecting for deposits of useful minerals (the hydrogeochemical method).
3. Prospecting for groundwaters for purposes of water supply and mineral waters.

In what follows we shall briefly dwell on the consideration of these questions using the example of one of the areas of the Tom–Kolyvan folded zone, where for several years the authors have been studying the chemical composition of waters in zones of tectonic disturbances in the course of hydrogeochemical surveying.

The study area is confined to the junction of three geological structures: the Tom–Kolyvan folded zone, the Kuznetsk Alatau, and the Kuznetsk—

basin in the area of their junction with the southeastern margin of the West Siberian Lowland. The geological structures of the area have a two-tier structure. The lower structural tier is represented by strongly dislocated deposits of Paleozoic age (effusive-sedimentary sequence); the upper tier is composed of sandy-clayey unconsolidated deposits and covers the basement rocks as a mantle. Outcrops of bedrock at the surface are observed in some river valleys. The thickness of the unconsolidated formations averages 50–60 m and increases markedly toward the West Siberian Lowland, as well as in areas of ancient erosional-tectonic depressions.

In the area of the Tom–Kolyvan folded zone, the Devonian and Carboniferous sandy-shale sequence is cut by numerous dikes of diabase, doleritic diabase, diabase porphyrite, and others of various ages, with the youngest tentatively assigned to the Triassic or Jurassic [5]. The dikes fill tectonic faults predominantly of northwestern trend, i.e., transverse to the main geological structure. In addition, tectonic dislocations of northeastern strike are noted in the area.

Weak disseminated and veinlet sulfide mineralization (pyrite, chalcopyrite, marcasite, sphalerite, stibnite, etc.) is associated with zones of tectonic disturbances of various orientations.

The geological structure of the study area is also reflected in the hydrogeological conditions. Here two aquifer complexes may be distinguished: 1) the aquifer complex of the sandy-clayey deposits of the cover and 2) the aquifer complex of the regional fracturing of the weathering crust of Paleozoic rocks and zones of tectonic disturbances. The substantiation of these complexes and their brief characterization, with identification of water types, are given in the authors’ work [9].

It should only be noted that each of the distinguished complexes may be associated with different hydrodynamic zones and settings. Thus, for example, stratal-pore waters of the upper structural tier in areas of erosional-tectonic depressions occur in a zone of slow water exchange, whereas fissure waters of the second aquifer complex (lower structural tier) in areas of uplifts and drainage by river valleys are characterized by active circulation.

On the whole, according to N. K. Ignatovich [4], the study area belongs to a semi-exposed, flushed hydrogeological structure.

Hydrogeochemical studies in the area and experimental work at individual sites connected with the study of mineral waters (the Zavarzino radon waters) showed that in most cases there is a hydraulic connection between fissure waters of the weathering crust and waters of zones of tectonic disturbances, and between the latter and waters of the upper structural tier. This connection is expressed, first, in the fact that very often we observe in groundwater the presence of a suite of elements characteristic of waters of disturbance zones (lead, zinc, antimony, arsenic, barium, etc.). In addition, this connection is indicated by the comparatively constant regime of some surface watercourses during the low-water period.

However, as a result of hydrogeochemical surveying, discharges of springs were also noted that are associated mainly with waters of zones of tectonic disturbances. They have a more constant discharge rate (0.5–1.0 l/sec), temperature (5–6°C), composition, and content of macrocomponents. The formation of carbonate travertines (calcareous tuffs) in the form of cones, bowls, covers, etc., is usually associated with the discharge of these springs. Their thickness reaches two or more meters (the Ushayka and Basandaika rivers,

Kirgizka, and others). They sometimes contain a significant amount of iron and manganese, which accounts for their varying coloration (from white to dark brown and black). Spectral analysis of travertines shows the presence in them of a significant complex of microcomponents (zinc, lead, silver, barium, copper, nickel, cobalt, etc.). Some of these were found both in groundwaters and in rocks of tectonic-disturbance zones. Thus, along one of the disturbance zones (the Shcherbak zone of crumpling), rocks with disseminated sphalerite mineralization were penetrated by a borehole. Other zones are associated with an antimonite ore occurrence, etc. The content in the waters of tectonic-disturbance zones of certain complexes of heavy metals, depending on the type of mineralization, makes it possible to use them as prospecting criteria in conducting hydrogeochemical investigations. Experience has shown that even when the mineralization zone occurs at a depth of about 200 m, it is recorded at the surface during hydrogeochemical sampling of springs connected with this zone (the Shcherbak zone of crumpling).

The complexes and contents of heavy metals in waters serve as the principal criterion in detecting and tracing zones of tectonic disturbances overlain by a thickness of unconsolidated deposits.

Hydrogeochemical investigations carried out by the authors in the territory of the Tom–Yaya interfluve showed that carbonate travertines, like the waters of tectonic-disturbance zones, are characterized by a complex assemblage of microcomponents. Below we give the results of chemical and spectral analyses of the waters and travertines described. As can be seen from Table 1, the waters of tectonic-disturbance zones have a very complex and varied chemical composition. Here hydrocarbonate, sometimes hydrocarbonate-chloride waters occur, with the presence of the sulfate ion (up to 20 mg/l). A somewhat elevated total mineralization (on average 600 mg/l) is noteworthy; for other types of waters in the area it rarely exceeds 200–250 mg/l. The presence in the water of such components as divalent iron, as well as an increased content of carbon dioxide and chlorine, indicates a considerable depth of circulation of these waters. In any case, the presence of certain elements characteristic of a reducing environment in the water is evident, since the ratio

\[ \frac{\mathrm{Fe}^{2+}}{\mathrm{Fe}^{3+}} \]

is sometimes greater than ten.

As for microcomponents, it should be noted that their content is elevated in the waters of tectonic-disturbance zones. Such specific elements as mercury, cadmium, silver, antimony, arsenic, and others are present here, which indicates the presence of a mineralization zone. The elevated temperature of the water in some boreholes is also noteworthy. Two of them are given in Table 1. The nature of this phenomenon has not yet been clarified; however, the factual material permits the assumption that one of the sources of the elevated temperature may be the process of oxidation of sulfides under conditions of somewhat impeded discharge of groundwater. The latter circumstance occurs in the area because of the presence of a considerable thickness of unconsolidated deposits of essentially clayey composition. In this case, evidently, artificial intensification of water discharge (for example, self-flowing boreholes) should, on the one hand, lead to a decrease in the temperature of the water and, on the other, to a decrease in the content in the water of the sulfate ion and heavy metals. Indeed, in two sectors of the area where the authors were able to compare the results, this fact is observed. Thus, in the sector of the Malka River, near the village of Semiluzhki, during hydrogeochemical sampling an elevated water temperature (11°C) was recorded. The content of the sulfate ion is 8 mg/l, and the sum of chalcophile ...

Table 1

Content of macro- and microcomponents in the waters of tectonic fault zones, by springs and wells of the Tom–Yaya interfluve

elements exceeds 500 μg/l. In the well located 50 m from the one indicated above (the latter yields self-flowing water with a discharge of 0.1 l/sec), the temperature dropped to 7.5°C, the sulfate ion is absent, and the content of the same group of elements decreased by more than 30 times. A similar picture is observed in hand-drilled wells in the area of the Kirgizka River, where, with a decrease in water temperature, the content of sulfate ion decreases by more than 16 times, and the sum of elements by more than 20 times (Table 1).

In the facts described, some doubt is raised by the considerable amplitude in the change of water temperature, equal to 5°C, with a comparatively low sulfate-ion content. In this connection, we note that in some wells along the Urbei zone of folding, at a water temperature of 8–9°, the sulfate-ion content reached 60 mg/l, and the sum of elements exceeded 1000 μg/l. Unfortunately, in these areas it was not possible to compare the indicated data with self-flowing wells, since the area is confined to a watershed. However, in springs, as a rule, a reduced content of microcomponents is observed, and the sulfate-ion content rarely exceeds 4 mg/l.

The elevated temperature of water in wells in zones of tectonic disturbances may also be the result of thermometamorphic phenomena. This is quite consistent with signs of deep circulation of the waters. The absence of elevated water temperature in springs is evidently connected with the fact that, in the overwhelming majority of cases, ascending waters, before reaching the ground surface, mix with waters of the upper horizons, which have a lower temperature. In addition, the temperature of water in springs associated with zones of disturbances, changing only insignificantly in winter, is 5–6°C, which considerably exceeds the mean annual temperature of the region.

In the formation of the chemical composition of waters, an enormous role belongs to the gases dissolved in them, especially oxygen and carbon dioxide. Tectonic disturbances, as is known, ensure the greatest depth of penetration of oxygen dissolved in water, as a result of which oxidation processes of sulfides may occur even at considerable depths. As the results of testing of mapping wells show, at a depth of 150 m from the surface, oxygen and sulfate ion are recorded in the waters, although the oxygen content decreases with depth. Free carbon dioxide in this region exerts a considerable influence on the formation of the chemical composition of waters. The significance of carbonate travertines as prospecting criteria in identifying and tracing zones of tectonic disturbances has already been noted above. Their formation is connected with the action on carbonate rocks of waters enriched in CO₂ at some depth under thermodynamic conditions differing from atmospheric ones, according to the well-known reaction

$$ \mathrm{CaCO_3 + H_2O + CO_2 \rightleftarrows Ca(HCO_3)_2}. $$

When the waters emerge onto the ground surface, as a result of the removal of carbon dioxide into the atmosphere, carbonate equilibrium is disturbed and deposition of carbonate travertines occurs

$$ \mathrm{Ca(HCO_3)_2 \rightleftarrows H_2O + CO_2 + CaCO_3}. $$

Attention was drawn to these formations as early as 1925 by M. P. Orlova [7] in evaluating the groundwaters of the environs of Tomsk with respect to their use in balneology. Chemical analyses of water from some travertine springs, cited in her work, show an elevated content in them of CO₂ (up to 219 mg/l), calcium (up to 156 mg/l), HCO₃ — up to 600 mg/l. M. P. Orlova associates the “lime waters” with tectonic zones and diabase dikes.

The data presented by the authors in Table 1 also indicate a very high content of calcium, bicarbonate ion, and free carbon dioxide in the waters. At present, the question of the origin of carbon dioxide in waters in such quantities that carbonate travertines (calcareous tuffs) could form at the surface remains debatable. Without dwelling on the consideration of different points of view, we note that the main source of \(CO_2\) in the waters of zones of tectonic disturbances is thermometamorphic processes, discussed in detail in the works of A. G. Betekhtin [1], A. M. Ovchinnikov [6], and other researchers. Recently S. A. Durov [2] has paid considerable attention in this question to the processes of sulfide oxidation, to which Academician S. S. Smirnov [8] drew attention. The free sulfuric acid that forms interacts with carbonate rocks:

\[ H_2SO_4 + CaCO_3 = CaSO_4 + H_2O + CO_2. \]

In the area under consideration, neither of the two indicated methods of formation of free carbon dioxide can be ignored, since this fully corresponds, on the one hand, to the deep circulation of the waters and, on the other, to their characteristic low sulfate content, despite the significant development of pyritization along zones of disturbances and the high content of microcomponents in the waters. In any case, these processes do not exclude one another, but complement one another both in the formation of carbonic waters and in increasing the temperature of the latter.

The precipitation of calcareous tuffs evidently plays a major role in the formation, in the Tomsk area, of alkaline waters (\(pH = 8.0\)--\(8.6\)), which is explained by the removal from the waters of calcium carbonate and free carbon dioxide and, in connection with this, by the sharp predominance in the water of sodium bicarbonate, which is more stable in solution than calcium. Therefore, in most cases surface watercourses in areas of tectonic disturbance zones (the Shcherbak, Berezovaya, Omutnaya rivers, etc.) are characterized by increased alkalinity, which can evidently be used, along with the presence of calcareous tuffs, as a prospecting criterion in identifying and tracing zones of tectonic disturbances covered by loose sediments.

The \(CO_2\) balance in the waters of tectonic disturbance zones in the area has a great influence on the migration of microcomponents. The latter are characterized by the greatest fluctuations in composition and content in comparison with macrocomponents. Table 2 gives the results of spectral

Table 2

Content of certain elements in the calcareous tuffs of the Tom--Yaya interfluve, in % (according to spectral analyses)

analyses of several samples of calcareous tuffs of the Tom--Yaya interfluve, showing the presence of a complex assemblage of elements in these formations. Here copper, nickel, cobalt, manganese,

zirconium, chromium, vanadium. It is quite obvious that travertines were enriched in these elements from groundwater. The precipitation of such elements as cobalt, nickel, copper, and vanadium leads to a sharp decrease in their content in natural waters, which somewhat complicates the assessment of the metallogeny of waters in zones of tectonic disturbances. The tuffs are especially enriched in manganese and cobalt, whose migration in the hypergene zone, as is known, ends with the precipitation of asbolanes and psilomelane-vads. These formations are very widely distributed in the area and create a certain variety of calcareous tuffs (manganese-bearing tuffs). They are usually black in color, more earthy and friable. Another variety is calcareous-ferruginous travertines, also distinguished by friability. These two varieties are characterized by the most complex suite of microcomponents, since in the process of hydrolysis of iron and manganese salts they capture many elements. It is interesting to note that those elements which are observed in calcareous tuffs show a deficiency in natural waters (copper, vanadium, cobalt, nickel), with the exception of manganese. Elements such as titanium, zinc, antimony, and arsenic, not found in the travertines, occur in higher contents in natural waters.

In assessing the metallogeny of waters in zones of tectonic disturbances, it is necessary to take into account the elements present in the travertines. For these purposes, from a travertine sample of a given spring a weighed portion of calcareous tuff is taken, corresponding to the average content of CaCO₃ in the waters (the sum, determined by analysis, of the Ca²⁺ ion and half of the HCO₃⁻ ion). A hydrochloric-acid extract is then prepared from this weighed portion. The filtrate is diluted with distilled water to one liter, from which a water concentrate is taken by the method of TPI coprecipitation. The obtained contents are summed with the contents determined in the water of the spring during the field period.

The precipitation of microcomponents with carbonate travertines partly explains their different content in waters at depths of 100–150 m (according to wells) and under surface conditions (travertine springs in these same sectors). Data for one such sector are given in Table 3. As can be seen from the table, in addition to changes in the content of microcomponents, a more complex suite of them is observed in the spring. This indicates a significant enrichment of the waters at the expense of the upper rock horizons, for which such elements as manganese, chromium, vanadium, etc. are characteristic. The entire complex suite of elements, as a rule, is characterized by elevated contents in sectors of zones of tectonic disturbances.

Table 3

Comparative table of the content of heavy metals in waters from one of the sectors of a tectonic-disturbance zone, by spring and well

Thus, when tracing zones, elements of the nonsulfide group may also be used as prospecting criteria. Inte-

It is interesting to note that in travertines and in waters of zones of tectonic disturbances an elevated content of zirconium is observed. This can be explained, as Shtrok and Drexler [3] indicate, by the migration of zirconium in the form of a complex bicarbonate–zirconium ion under conditions of enrichment of waters with carbon dioxide. Apparently, not only zirconium is transported in this form, but also certain other elements.

Elements of the sulfide group are of enormous importance in tracing zones of disturbances, as was mentioned above. The most characteristic among them are zinc, antimony, silver, arsenic, cobalt, and barium. Using all the criteria indicated above, the authors have identified aqueous dispersion streams of mineralization zones, many of which were confirmed by the presence, at considerable depths, of disseminated and veinlet sulfide mineralization. At present, on the basis of hydrogeochemical investigations in the Tom–Yaya interfluve area, large tectonic zones have been traced—the Semiluzhinskaya, Urbeiskaya, Shcherbakskaya, and zones of sublatitudinal trend, filled by diabase dikes.

Recently, new data have been obtained on tracing a major fault zone in the area southeast of the villages of Turuntaevo and Podlomsk, which was established by the work of the Tomsk Integrated Expedition. This zone, unlike the others, is characterized by the presence in its waters of a low-temperature complex of elements—zinc, antimony, and mercury. At some points cadmium, a companion of zinc deposits, has been found in the waters. The mercury content in the waters reaches up to 100 μg/l.

The presence of mercury argues in favor of young tectonic movements in the area, and also in favor of a thermometamorphic origin of CO₂ in the waters. It is no accident that the outlets of travertine springs are confined to faults, which in most cases are filled by dike bodies of Early Mesozoic (?) age. The presence in individual sections of dikes of considerable fracturing, partially healed by calcite, is evidence of possible tectonic movements and hydrothermal activity at later stages. The most recent echoes of these processes are apparently the deposition of carbonate travertines by waters of zones of tectonic disturbances. Possessing considerable water abundance, an elevated content of calcium bicarbonates, the presence of certain specific trace components, and possibly an elevated temperature at depth, these waters are of great importance in solving water-supply problems and may be used in balneology. It should be noted that the waters of zones of tectonic disturbances have been studied very poorly because all the wells present in the area penetrate only the upper part of the zone of active circulation (well depths 100–200 m). For the same reason, questions of the stratigraphy, tectonics, and mineral resources of the area also remain poorly studied.

Meanwhile, as was noted earlier, the study of aqueous dispersion streams of heavy metals confined to zones of tectonic disturbances shows that sources of mineralization exist in the area, apparently located at considerable depths.

Solving these questions is impossible without drilling wells 300–500 m deep.

LITERATURE

1. A. G. Betekhtin. Hydrothermal solutions, their nature and the processes of ore formation. Basic Problems in the Study of Magmatogenic Ore Deposits. Publishing House of the Academy of Sciences of the USSR, 1953.

2. S. A. Durov. Synthesis in Hydrogeochemistry. Rostov Book Publishing House, 1961.

1. H. Degenhardt. On the geochemical distribution of zirconium in the lithosphere. In: Geochemistry of Rare Elements, Izd-vo IL, 1959.

2. N. K. Ignatovich. Zoning, formation, and activity of groundwater in connection with the development of the geostructure. Questions of Hydrogeology and Engineering Geology, No. 13, 1950.

3. K. V. Ivanov, M. I. Yudin. Report, Funds of NTGU, 1956.

4. A. M. Ovchinnikov. Mineral Waters. Gosgeoltekhizdat, 1947.

5. M. P. Orlova. Certain calcareous and radioactive springs in the vicinity of Tomsk. Proceedings of Tomsk State University, vol. 76, Tomsk, 1925.

6. S. S. Smirnov. The Oxidation Zone of Sulfide Deposits. Academy of Sciences of the USSR, 1955.

7. P. A. Udodov, V. M. Matusevich. The role of microcomponents in the formation of the chemical composition of groundwater. Proceedings of the First Interdepartmental Conference on Hydrogeochemical Prospecting for Ore Deposits, Tomsk State University Press, 1962.

NOTED MISPRINTS