Antimony in Groundwater of Some Ore Deposits of the Tien Shan

(Kuramin and Alai Ranges)

N. M. Shvartseva, D. Lyan

(Presented by Professor P. A. Udodov)

To date, the literature contains only isolated facts indicating the presence of antimony in the groundwater of gold-ore, antimony, polymetallic, and other deposits (Shvartseva, 1971). This element belongs to the group of hydrolyzing elements, i.e., already at pH less than 3 hydrolysis occurs with the formation of hydroxide. At the same time, our investigations have shown that antimony possesses fairly good migrational capacity in groundwater. Moreover, it reveals a clear tendency toward an increase in migrational capacity in the most alkaline and hydrogen-sulfide waters.

In order to clarify the general regularities of the behavior of antimony in the groundwater of ore deposits, we carried out hydrogeochemical investigations on the northern slope of the Kuramin Range in the area of the gold-ore deposits Kochbulak and Akturpak, the copper-molybdenum deposit Kalmakyr, and the polymetallic deposit Kurgashinkan. In parallel with these investigations, the ore waters of the antimony Kadamzhai deposit (northern spurs of the Alai Range) were specially studied. In all, 215 water samples were analyzed for antimony alone, not counting other determinations. The analyses were performed in the Central Laboratory of the Ministry of Geology of the Uzbek SSR and in the Problem Geological Laboratory of the Tomsk Polytechnic Institute.

The deposits investigated are situated within open aquifer systems of the Kuramin and Alai ranges and are characterized by the presence of common features in the formation of the chemical composition of groundwater. Thus, the strongly dissected relief promotes the penetration of aggressive infiltration waters to considerable depth and good flushing of the rocks in the recharge area, which favors the formation of background calcium-bicarbonate waters with mineralization of 0.1–0.4 g/l. Infiltration waters rich in oxygen and carbon dioxide possess great dissolving capacity, which is favorable for processes of leaching of rocks and removal of chemical elements beyond the weathering profile. At the same time, the dry arid climate, the relatively small amount of atmospheric precipitation, and its almost complete absence during the long summer period in the foothill part where the deposits described are located lead to the formation of sodium-sulfate waters with mineralization up to 11.2 g/l. An increase in concentration

in sulfate-ion waters, are often associated with processes of continental salinization.

A complex and heterochronous assemblage of sedimentary, effusive, and intrusive rocks participates in the geological structure of the region. A detailed description of the geological structure of the region can be found in the works of S. T. Badalov (1965), R. A. Musin (1970), E. Z. Meshchaninov (1969), N. A. Nikiforov (1969), and others; therefore we shall not dwell on this question.

As a result of the investigations it was established that antimony is widespread in the groundwater of this region. Its predominant contents were determined to be within the range of 0.01–2 μg/l, which corresponds to the background content. Elevated antimony values, in amounts of 5 μg/l, more often 10–20 μg/l, and sometimes from 42 to 5000 μg/l, are recorded only in the groundwaters of deposits.

In the area of the deposits, waters of all adits, springs, and waters of all exploratory adits were studied. Some results of these investigations are given in the table, from which it is evident that antimony is present in the groundwaters of gold-ore deposits in significant amounts (from 1.3 to 73 μg/l). At individual sampling points, the high antimony contents correspond to the maximum gold contents. However, in absolute terms the antimony contents exceed those of the latter by 5–50 times, and sometimes by 100 times.

Within all the deposits, neutral and slightly alkaline waters are widespread; nevertheless the concentration of antimony in them is everywhere high, especially when zones of unoxidized ores are exposed, the waters of which become enriched in antimony during intensive oxidation of the ore minerals exposed, for example, in the open pit of the Kurtashinkan deposit (points 1161–1164). A dependence of antimony contents on the character of groundwater recharge is also established. Thus, in the southern part of the Aktyurpak deposit, infiltration of fissure waters and waters of zones of tectonic disturbances by waters of alluvial deposits is observed. As a result, mixed hydrocarbonate-sulfate and sulfate-hydrocarbonate waters are formed here, with mineralization up to 1.0 g/l and an antimony content of only 2.2–3.8 μg/l. Farther along the direction of the groundwater flow, the hydrocarbonate-sulfate waters are replaced by sulfate waters with total mineralization up to 2 g/l. The antimony content in this case increases to 20 μg/l.

The results of the investigations carried out by us show that antimony in groundwaters forms dispersion flows of considerable size. Thus, for example, at the Kochbulak gold-ore deposit its dispersion flows are traced for a distance of up to 500 m.

The highest antimony concentrations, reaching 5000 μg/l, were found by us within the Kadamzhai antimony deposit, the waters of which are characterized by a pH reaction of 7.0–8.4, increased mineralization up to 11.2 g/l, and the presence of hydrogen sulfide (table). The fact that high concentrations of antimony are present in these waters indicates the existence of water-soluble complex compounds that hinder its hydrolysis. It is most probable that under such conditions the complex ion $\mathrm{SbS_3^{3-}}$ is formed, which, according to V. V. Shcherbina (1962), promotes the migration of antimony in a slightly alkaline and reducing environment. The high antimony contents found by us in the neutral and slightly alkaline waters of the Kadamzhai deposit testify to intense solubility, under certain conditions, of antimonite, possibly under the influence of autotrophic organisms recently discovered within this deposit by N. N. Lyalkova (1967), which contributes to a considerable removal of antimony beyond the limits of the deposit with the formation

Table

Antimony and gold content in groundwater of some deposits of the Tien Shan

* — hydrogen sulfide is present.

dispersion water flows up to 1.5 km long. Anomalous antimony contents (more than 1000 µg/l) are observed only in the groundwaters of the working adits and of the well-developed oxidation zone of the Kadaimdzhai deposit. In the waters of gold-ore deposits, similar processes may also occur, though on a smaller scale; the presence of antimony in their waters likewise indicates its migration in the form of complex compounds.

It follows from all this that antimony migrates well in the groundwaters of both antimony and gold-ore deposits. It is capable of forming distinct aqueous dispersion flows with a length of 500 or more meters. All this makes it possible to recommend antimony as a prospecting criterion for the indicated types of deposits in searches for deeply buried ore bodies.

REFERENCES

1. S. T. Badalov. Useful Minerals of the Almalyk Ore District. Uzbek SSR, “Nauka,” 1965.

2. N. I. Lyalikova. Oxidation of antimonite by a new culture of thionic bacteria. Doklady AN, vol. 176, no. 6, 1967.

3. E. Z. Meshchaninov. Geology of the Almalyk ore field. In: Ore Formations and Principal Features of the Metallogeny of Gold in Uzbekistan. Uzbek SSR, Publishing House of the Academy of Sciences, 1969.

4. M. A. Nikiforov. Mercury-Antimony Deposits of the Southern Tien Shan. Frunze, “Ilim,” 1969.

5. N. M. Shvartseva. Distribution of antimony in groundwaters. Izvestiya TPI, vol. 217, Tomsk, 1971.