EXPERIENCE IN CONDUCTING HYDROGEOCHEMICAL STUDIES IN TRANSBAIKALIA

P. A. UDODOV

(Presented by the Department of Hydrogeology and Engineering Geology)

During the field seasons of 1957–1958, the Chita Geological Administration carried out prospecting for ore deposits by the hydrogeochemical method. Under conditions of perennial talik permafrost, this method had previously hardly been used. It was therefore necessary first of all to establish prospecting criteria for various heavy metals in the natural waters of this region.

The experience of the work carried out shows that the methodology of field hydrogeochemical studies varies somewhat depending on landscape zones. Unfortunately, the specific features of these studies remain insufficiently developed. The hydrogeochemical investigations being conducted had as their aim, simultaneously with the principal task—prospecting for ore deposits—to clarify certain questions concerning the methodology of field work.

Field hydrogeochemical investigations in the Krasnochikoysky district of Transbaikalia were initiated by the geologist A. D. Kanishchev. The entire complex of these works was carried out by students of the Tomsk Polytechnic Institute: Z. K. Moiseeva, N. A. Molchanov, A. N. Ivanenko, and others, under the direction of Associate Professor P. A. Udodov.

The hydrogeochemical conditions of any region are determined by a number of factors, which may be combined into the following two groups: 1) physiographic, 2) geological-hydrogeological.

In addition, they are determined by the geochemical properties of the elements and their compounds distributed in the region.

As is known, when studying the hydrogeochemistry of a region it is necessary first of all to examine the conditions and the character of the medium in which migration and deposition of elements take place. These factors are determined by the physiographic and geological-hydrogeological features of the region. In addition to the medium, the element itself also has an enormous influence on the migration of elements, namely: its ionic radius, valence, the capacity of chemical elements to form complex compounds, and to migrate in ionic and colloidal forms. Together with these data, it is necessary to take into account the solubility of compounds, the magnitude of the pH value of natural waters, the chemical activity of rocks, and their sorption capacity.

The content of heavy metals in natural waters is determined by the presence of zones of mineralization in the region and by the character of ore-bearingness of the rocks. Therefore, we shall first consider the content of ore ele-

...elements in various types of rocks. To characterize the ore-bearing capacity of the latter, we shall evaluate them according to I. I. Ginzburg [1]. Depending on the content of heavy metals in rocks, he distinguishes the following four gradations: “oreless” mineralization, “disseminated” mineralization, “enriched” mineralization, and “ore” mineralization.

The granite intrusions, sandstones, phyllites, and injection schists of the Baldzhikan and Chikoi suites of the area under study, according to metallometric sampling, show the presence in them of 17 elements—Pb, Cu, V, Ba, Sn, Co, As, Ag, Ni, Ti, Mn, Cr, Zn, Sb, Mo, Bi, Sr. The content and quantity of these elements in the granites are not the same for different sites. The granites distributed in the basin of the Kunalei River are characterized by the presence of 14 elements: W, Bi, As, Zn, Pb, Cu, Ba, Cr, Co, Sr, Ag, Ni, Sn, V. Rocks with so-called “oreless” mineralization are characterized by the presence of Pb at 13 points, Cu at 13 points, V at 15 points, Ba at 13 points, Cr at 11 points, Co at 2 points, Sr at 4 points, Ag at 1 point, Ni at 3 points, and Sn at 6 points.

“Disseminated” mineralization is noted for Pb at 2 points, Sr at 2 points, Ba at 1 point, Sn at 2 points, Zn at 1 point, W at 2 points, and As at 1 point. “Enriched mineralization” is observed for As at 1 point. “Ore” mineralization is established for W at 3 points and Bi at 2 points.

“Enriched” and “ore” mineralization in the rocks are confined to the area of the Kunalei tungsten mine.

In the area of the Asakan River basin, in the granite massif, in addition to those elements that were encountered in the Kunalei River basin, with the exception of W and As, a number of new metals are noted. The granites in the area of the Asakan River basin are characterized by the presence of 15 elements. All elements that are encountered only in the area of the Asakan River basin are highly specific to mineralization zones. The content of the most characteristic elements varies within the following limits: “oreless” mineralization is characterized by the presence of Cu at 32 points, Pb at 23 points, Zn at 7 points, Ba at 17 points, Ag at 7 points, Ni at 31 points, Co at 5 points, Sn at 18 points, Mo at 5 points, Ti at 22 points, Mn at 26 points, Sr at 17 points, Cr at 16 points, and Bi at 2 points.

“Disseminated” mineralization: Cu at 1 point, Pb at 16 points, Zn at 16 points, Ba at 9 points, Co at 2 points, Sn at 3 points, Ti at 4 points, Mn at 11 points, Sr at 6 points, and Cr at 13 points.

“Enriched” mineralization: Ba at 4 points, Ti at 3 points, Zn at 1 point, Pb at one point. “Ore” mineralization: Sn at 1 point, Ba at 1 point.

It should be noted that points chiefly of “enriched” and “ore” mineralization are characterized simultaneously by an elevated content not of one, but of several elements. Thus, point 226, in addition to ore mineralization of tin, is characterized by “enriched” mineralization of lead. Point 220 has “ore” mineralization of Ba and “disseminated” mineralization for Pb, Zn, V, and Sr.

The rocks of the Baldzhikan suite in the upper reaches of the Antsnoyka River, in the middle course of the Asakan River, and in the upper reaches of the Gornachikha River, represented by gray quartz-like graywacke and arkosic sandstones interbedded with black argillites, are characterized by the following features.

The rocks of the Baldzhikan suite, according to spectral-analysis data, are characterized by the presence of “oreless” mineralization for heavy metals: Pb at 24 points, Zn at 7 points, Ba at 14 points, Sr at 14 points, Cu at 28 points, Ni at 23 points, Co at 12 points, Sn at 11 points, Mn at 14 points, Ti at 13 points, Cr at 11 points, V—

Fig. 1. Schematic map of hydrogeochemical zoning.

The geology of the basin of the Kunaley River is given according to data from a group of geologists of the Chita Geological Administration. 1—leucocratic porphyritic granites (Mesozoic); 2—medium-grained, uneven-grained porphyritic biotite granites (Mesozoic); 3—intercalation of conglomerates, sandstones, quartz porphyries; 4—hornfelsed sandstones and shales, quartzitic sandstones, crystalline schists and gneisses, intercalation of sandstones with phyllite-like shales; 5—greenish-gray sandstones with interbeds of phyllites.

The geology of the basin of the Asakan River was compiled by A. D. Kanishchev. Variscan and Mesozoic intrusions. 6—medium- and fine-grained biotite and leucocratic granites; 7—small intrusions of granite-porphyries and biotite granites; 8—sharply porphyritic and coarse-grained biotite granites; 9—biotite-hornblende granodiorites; 10—the Chikoy Formation, intercalation of calcareous sandstones and phyllite-like shales, acidic effusives; 11—the Chikokon Formation, black aleurolites, sandstones, with subordinate conglomerates and acidic effusives; 12—the Baldzhikanskaya Formation, sandstones, phyllites, carbonate shales; 13—presumed geological boundaries; 14—presumed zones of tectonic disturbances.

Areas containing various complexes of heavy metals in natural waters. 15—areas with the presence, in most cases, of the complete complex of specific elements in natural waters (for dispersion flows of mineralization zones) and elevated contents of some of them; 16—areas with the presence of an incomplete complex of specific elements in natural waters (for dispersion flows of mineralization zones); 17—areas with the presence of individual heavy metals in natural waters (background metal content).

Areas of dispersion flows in natural waters by type of mineralization. 18—tungsten mineralization; 19—tin mineralization; 20—complex mineralization; 21—170-b—numbers of hydrogeochemical sampling points; the direction and length of the vector correspond to the content of a definite element in natural waters. Content of specific elements in water in mg/l. 22—0.0001; 23—0.0002; 24—0.0003; 25—0.0005; 26—0.0008; 27—0.002; 28—0.004; 29—projected boundaries of areas of dispersion flows of mineralization zones.

Note. At the points plotted on the map, only the contents in natural waters of the specific elements characteristic of the given area are shown.

in 25 points. However, in the field of the Baldzhikan suite there is a considerable number of points of disseminated mineralization. Thus, Pb was encountered in 3 points, Zn in 16 points, Cu in 1 point, Sn in 1 point, Ba in 8 points, Co in 4 points, Sr in 1 point, and Cr in 14 points.

The Chikokon suite, occurring north of the Baldzhikan suite, has a small thickness; it is represented by black shaly siltstones interbedded with gray psammitic sandstones, and is characterized by the presence in it of 13 heavy metals (Pb, Zn, Cu, Ba, Sn, Ni, Co, Mo, Mn, Ti, Sr, Cr, V). “Disseminated” mineralization is observed at one point for Sn, at one point for Sr, at six points for Cr, and at four points for Zn. “Enriched” mineralization has been recorded only for Ba at two points. Consideration of these data shows that the Chikokon suite is apparently less promising with respect to “ore” mineralization of the rocks. In the rocks of the Chikokon suite such specific elements as As, Bi, and others have not been encountered.

The Chikoi suite is represented by interbedded green and steel-gray shales with brown and greenish-gray calcareous sandstones and sandy limestones, among which a horizon of tuff lavas, quartz porphyries, and tuffites is distinguished. The metallogeny of this suite is characterized by “barren” and “disseminated” mineralization. Thirteen elements are typical of it; of these, Pb, As, Cu, Ni, Ti, and Mn have the character only of “barren” mineralization. For Co, Zn, Sn, Ba, Sr, Cr, and V, in addition to “barren” mineralization, “disseminated” mineralization is also observed at individual points. “Enriched” and “ore” mineralization have not been encountered in the rocks of the Chikoi suite.

Consideration of the metallometric data for the bedrock of the study area makes it possible to conclude that the greatest number of samples with “enriched” and “ore” mineralization is observed only in the granites and rocks of the Baldzhikan suite. However, it must be noted that the very limited number of rock samples for spectral analysis makes it difficult to give a more complete assessment of their metallogeny.

In studying the content of ore minerals in rocks, special attention should be given to areas of primary dispersion halos of mineralization zones, since they serve as the main sources of enrichment of natural waters with ore elements and, especially, with specific elements.

The assessment given above of the rocks of the district with respect to their degree of mineralization is necessary in hydrogeochemical investigations for understanding the sources of mineralization of natural waters. In addition, it is also very important for studying the process of migration of heavy metals.

As a result of field investigations, 145 samples of various rocks were collected to determine their chemical activity. These determinations were carried out in the problem-oriented geological laboratory of the Tomsk Polytechnic Institute. The results of the determinations showed that most of the rocks of the district belong to the group of weakly active rocks [3]. These include phyllitized shales and quartzitic sandstones. Carbonatized sandstones and hornfels developed around small intrusions have increased activity. The activity of hornfels increases due to calcite veinlets (secondary chemical activity of rocks). Chemically inactive or very weakly active rocks are the massive crystalline rocks of the district: granite, aplite, and others.

The study of the chemical activity of rocks is also very important for identifying and substantiating zones of mineralization.

Depending on the chemical activity of rocks, the pH of natural waters also changes. Thus, for example, the waters of inactive granites are acidic; the waters of crystalline schists are slightly acidic and neutral; the waters of active sandstones and hornfels are slightly alkaline and even alkaline.

The pH value of natural waters alone, for the area described, cannot serve as a prospecting criterion for zones of mineralization, since in a number of cases it is caused by acidic bog waters. If, in addition to a low pH value in natural waters, an elevated sulfate-ion content is observed in them, then such points indicate the presence of zones of mineralization.

The indirect hydrogeochemical criteria considered (pH, SO″₄) can give a correct assessment of an area with respect to its metallogeny only under certain geological-hydrogeological and physiographic conditions.

Experience from field investigations has shown that direct hydrogeochemical criteria are the most precise. These include the presence of specific elements in natural waters and, in general, an elevated content of some metal. Under field conditions we determined, directly at the observation points, the total content of metals in natural waters with dithizone. This determination gives only a certain idea of the comparative evaluation of individual points. The determination of heavy metals was carried out by concentrating them by the coprecipitation method (the TPI procedure), which makes it possible to determine the qualitative and semiquantitative content of individual metals in waters.

The applicability of the hydrochemical method for prospecting ore deposits in Transbaikalia is confirmed by testing it in previously known zones of mineralization. Thus, at the Kunalei tungsten mine, spectral analysis of rocks and minerals showed the presence of 16 heavy metals: Pb, Cu, Ni, Co, As, Ag, Zn, V, Sr, Ba, Bi, Cr, Ti, W, Mn, Sb. Comparing the results of these analyses with the assemblage of heavy metals established in natural waters by coprecipitation, we have almost complete agreement. The content of heavy metals in natural waters of the mineralization zone of the Kunalei mine shows the presence of the following 16 heavy metals: Pb, Cu, Mo, Ni, Co, As, Zn, Sb, Ba, Bi, Cr, Ti, Be, W, V, Cr.

In addition, comparing spectral analyses of rocks outside the mineralization zone (Pb, Co, Ni, V, Ba, Cr, Ti, Cu) with the content of metals in the natural waters of the background of the area (Pb, Cu, V, Zn, Ni, Ti, Mn), we also establish some correspondence in quantitative terms.

In the natural waters of the Kunalei River basin, 18 heavy metals were established, namely: W, Sn, Mo, Pb, Zn, Ba, As, Ni, Co, Ag, Bi, Cr, Ti, Sr, Mn, Sb, V, Cu.

Exactly the same assemblage of elements was also established in the natural waters of the Asakan River basin. It is interesting to note that, in quantitative terms, the frequency of occurrence of some elements in the waters is different. For example, silver in the Kunalei River basin was encountered in only one sample, whereas in the Asakan River basin it was encountered in 87 samples. Certain characteristic microcomponents are recorded in water samples for the Asakan River basin almost five times more often than in the Kunalei River basin. The number of occurrences of Zn, Sn, Cu, Cr, Ti, Mn in samples of natural waters of the Asakan River basin is twice as great as for the Kunalei River.

Such elements as Bi, Co, Mo, W, As, Sb occur very rarely. They are observed mainly in natural waters of mineralization zones.

mineralization zones. Therefore, we assign this group of elements to the specific indicators of various mineralization zones. Thus, in the waters of the Kunalei mine almost the entire group of specific elements has been encountered, but the conditions of their migration have not yet been sufficiently studied. Any element may serve as an indicator of mineralization zones if its content exceeds the background by no less than five times. We have developed a classification scheme for the natural waters of mineralization zones of the mountain massifs of Western Siberia, which was published in the work of I. I. Ginzburg [1]. According to this classification, a mineralization zone is distinguished on the basis of a series of hydrogeochemical criteria, of which the principal one is the content in the waters of one, two, or three leading elements characteristic of the given type of zone. On the basis of this classification, various areas of mineralization zones have been distinguished on the schematic map of hydrogeochemical regionalization.

The background content of metals in waters for the region as a whole is determined as from 0.0025 to 0.0030 mg/l. In individual areas, apparently because of permafrost, the background of the region decreases (the Kunalei mine); at the same time the background content of elements varies depending on the geological structure. Thus, for example, the waters of granites have an elevated background value (0.0030–0.0035 mg/l). For waters of the sandy-shale sequence the background is somewhat lower (0.0020–0.0025 mg/l).

The background content of metals in natural waters is also influenced by the water regime.

The complex of elements characteristic of the region (both for rocks and for natural waters) generally corresponds to the tin–tungsten belt of mineralization distinguished by S. S. Smirnov [2]. Within this belt, mineralization zones of the cassiterite–quartz and cassiterite–sulfide formations are widespread.

The results of hydrogeochemical investigations and geochemical study of the described regions of Transbaikalia make it possible to outline for them certain additional regularities in the distribution of heavy metals. The schematic map of hydrogeochemical regionalization (Fig. 1) shows that specific elements with elevated contents in natural waters are confined to individual areas, the waters of which are usually characterized by the presence of a definite complex of elements, representing natural associations of mineralization zones. The identification and substantiation of them from the geological-hydrogeological standpoint constitutes the principal task of hydrogeochemical surveying.

Mineralization zones are most often traced along the contacts of intrusions and sedimentary rocks. In addition, zones of major tectonic disturbances deserve special attention. In most cases, zones of various mineralization are associated with them. This is also confirmed by the results of studying the metalliferousness of natural waters. Thus, according to the data of hydrogeochemical investigations of 1952–1953, in the Kuznetsk Alatau, along the tectonic zone from Bryusnichnyi Ples to Krutoy Spring (over a distance of ~32 km), a mineralization zone has been traced in individual sections.

Consequently, when interpreting the results of hydrogeochemical investigations it is necessary to link them with the tectonics of the region. In areas with development of a cover of loose deposits, the results of hydrogeochemical investigations can sometimes be used for tracing zones of tectonic disturbances.

Data from hydrogeochemical investigations on the content and quantity of specific elements in natural waters make it possible to distinguish in the region described three sharply different areas (Fig. 1). One of them in most cases is characterized by the presence of a complete complex

specific elements encountered in the dispersion halos of mineralization zones. The area with an incomplete complex of specific elements in the waters has been distinguished separately. In addition, an area has been distinguished that is characterized mainly only by the presence of individual heavy metals, among which no specific elements were found.

In the first area, depending on the diversity of associations of heavy metals in the waters, dispersion halos with tungsten, tin, and beryllium mineralization have been distinguished. In all, seven dispersion halos are indicated in this area: one with an elevated tungsten content, two with an elevated tin content, and four with an elevated beryllium content.

The revealed dispersion halos of mineralization zones require further, more detailed study.

Dispersion halos with elevated tin content are located in the upper reaches of the B. Lobachi River (the basin of the Fedoshkin Klyuch stream) and in the middle reaches of the Uvalistaya and Sobashnikova rivers.

Within the dispersion halo of the B. Lobachi River, over an area of approximately 30 km², 34 concentrates were taken. Tin was found in nine of them (Fig. 1), and in three an elevated content of it was recorded. The clarke content of tin in waters is 0.00008 mg/l, while at point 89 spectral analysis of the concentrate showed the presence of tin at 0.002 mg/l.

An elevated Sn content is observed not only in concentrates of granite waters, but also in rock samples. “Ore” mineralization in the granites is characteristic of tin and its associates W and Bi. In addition, “enriched” mineralization for arsenic is also noted in the granites.

Thus, the dispersion halos in the waters of the granites are also confirmed by the mineralization of the rocks.

In the natural waters of the area under consideration, among the indicator elements of mineralization zones, Bi should be noted.

Heavy-mineral-concentrate surveying carried out in this area shows an elevated tungsten content.

The dispersion halo over the area of the Shumilovka ore cluster, located on the watershed of the Kunalei and Chikokon rivers, is characterized according to determinations of metals in samples of natural waters taken by employees of the Shumilovka mine. On the schematic map of hydrogeochemical zoning it is distinguished by a sharply elevated content of metals in the natural waters. This may be explained by the presence here of a number of tin and tin–tungsten deposits of the greisen type, as well as placer tin deposits.

All concentrates from the area are characterized by an elevated tin content, which in some of them is determined as 0.007 mg/l. In addition to tin, specific elements are encountered. Over the entire area of the Shumilovka ore cluster, a very elevated Zn content is noted in the water.

For a final assessment of the metallogeny of the mineralization zone under consideration, it is necessary to conduct a hydrogeochemical survey.

Hydrogeochemical studies showed an uneven development of specific elements in the natural waters of the described region of Transbaikalia. Thus, in the basin of the Kunalei River only 11% of the concentrates showed the presence of these elements. Meanwhile, in the basin of the Asakan River they were found in 46% of the concentrates. Such a sharp difference in their distribution in the waters is due to the distinctive geological structure of the areas. In the south of the region, intrusions of granites and pegmatites, with which they are usually associated, are more widely developed.

As a result of the hydrogeochemical studies, we distinguish four dispersion halos of complex mineralization of specific

elements. One of them is in the middle course of the Gornachikha River (the Kunalei River basin), and three are in the Asakan River basin. All the dispersion streams of this mineralization, identified by the metal content in natural waters, are of interest for their further hydrogeochemical study. We shall therefore give a fuller description of them.

The mineralization in the middle course of the Gornachikha River is apparently associated with an acidic Mesozoic intrusion. Scheelite was found in panned concentrates from the Gornachikha River; spectral analysis of the rocks shows the presence of Sn, Co, and others.

The dispersion stream over the area of the Baranchikha River basin and the middle and upper courses of the B. Podgolechnaya River (Asakan River basin) is also associated with a granitic Mesozoic intrusion. The content of specific elements in almost all concentrates is comparatively high (thousandths of mg/l). Such a content makes it possible to regard this stream as the most promising of all those selected for the organization of further geological prospecting work. Sn, Ag, Ba, and others occur in the concentrates. In the area described, weakly acidic waters are equally widespread. Their pH is 6.4–6.8. Spectral analysis of the country rocks shows the presence in them of Sn, Co, Ba, and other elements. Scheelite, cassiterite, and other minerals have been found in panned concentrates.

Complex mineralization in natural waters is noted in the basin of the Antonovka River (Asakan River basin). Here an acidic intrusion has been established, with which this mineralization is apparently associated. The total content of metals in each concentrate is thousandths of mg/l. No points with a sharply elevated content of metals in natural waters were encountered. As, Sn, Ag, Ba, and others were detected in the waters. In the country rocks, according to spectral-analysis data, the presence of Co and other specific elements has been established. Scheelite, rutile, and other minerals have been found in panned concentrates.

For the waters of the Antonovka River basin, the pH is 6.9–7.1 (neutral water type).

On Asakan Golets and in the upper course of the Nizhnyaya Podgolechnaya River, a dispersion stream with complex mineralization is also distinguished (Asakan River basin). On the slope of the golets, blocks of fine-grained pegmatite with crystals of ore minerals were found, as well as a vein of it in the bedrock outcrop. The vein outcrop is observed in the walls of a cliff (cirque). At its base there is a small lake (about 200 m in diameter), in the waters of which complex mineralization has also been detected.

The data presented from the hydrogeochemical survey make it possible to consider that it clarifies and develops certain questions of the geology, geochemistry, and hydrogeology of the region. We therefore believe that hydrogeochemical surveying will gain wide recognition within the complex of geological investigations.

REFERENCES

1. Ginzburg I. I. Experience in developing the theoretical foundations of geochemical prospecting methods. Gosgeolizdat, 1957.

2. Smirnov S. S. An outline of the metallogeny of Eastern Transbaikalia. Gosgeolizdat, 1944.

3. Udodov P. A., Onufrienok I. P., Kristalev P. V. Chemical activity of rocks and minerals with respect to hydrogen ions. Experience in developing hydrochemical methods for prospecting ore deposits. ONTI, Gosgeoltekhizdat, 1959.