ANTIMONY IN GROUNDWATER OF SOME GOLD DEPOSITS OF THE KURAMA RANGE

V. B. Adilov, N. M. Shvartseva, D. Lyan

(Presented by Professor P. A. Udodov)

The need to determine antimony in hydrogeochemical prospecting was first indicated by P. A. Udodov, I. P. Onufrienko, and Yu. S. Parilov [4]. They discovered aqueous dispersion streams of this element within polymetallic, tungsten–tin, and copper–cobalt deposits. Subsequently, an elevated antimony content (up to 500 µg/l) was found by V. G. Ivanov (personal communication) in the Saralinsk gold-ore field (Kuznetsk Alatau), and by K. M. Davlittalieva and I. G. Diveev [1] within the sulfide deposits of the Maly Karatau (up to 90 µg/l). The highest antimony content (up to 3900 µg/l) is reported by D. S. Mukimova for the mine waters of the Kadamzhai antimony ore field (Central Asia), and by V. N. Makarov [2] for the antimony deposits of the Indigirka River basin, in whose mine waters the antimony content reaches 1.5–1.6·10^6 µg/l. However, to this day the nature of the distribution and the features of antimony migration in groundwater remain poorly studied. This is explained to a considerable extent by the absence, until recently, of reliable methods for analyzing groundwater. At the same time, proceeding from the general geochemical characteristics of antimony as an element, one may assume its high mobility in groundwater and the formation of broad aqueous dispersion streams [5]. Consideration of the behavior of antimony in waters from the standpoint of its use for prospecting purposes is undoubtedly of interest.

Hydrogeochemical investigations within the Kochbulak gold-ore deposit were carried out by V. B. Adilov in 1964, and at the Akturpak, Kurgashinkan, and Kalmakyr deposits by N. M. Shvartseva and D. Lyan in 1969. Analysis of antimony in the waters was performed by concentrating it with aluminum hydroxide, followed by spectral determination in the problem geological laboratory of TPI, and by an amalgam–polarographic method developed by E. M. Malkov in the Central Laboratory of the Ministry of Geology of the Uzbek SSR. The sensitivity of this method is 0.1 µg/l.

The deposits investigated are located within the exposed groundwater-pressure system of the Kurama Range. The strongly dissected relief promotes the penetration of infiltration waters to a considerable depth and the good flushing of rocks in the recharge and pressure-head formation area. Infiltration waters, rich in oxygen and carbon dioxide, possess a high dissolving capacity, which

favors the processes of leaching of rocks and the removal of chemical elements beyond the weathering profile. At the same time, the dry arid climate, the relatively small amount of precipitation, and its almost complete absence during the long summer period lead to the fact that present-day recharge of the groundwater of the deposits occurs only on the elevated exposed territory of the Kurama Range. This is confirmed at least by the fact that, according to observations in adits, the groundwater has an almost constant regime throughout the year. The total groundwater runoff within the Kochbulak deposit is estimated at approximately 5 l/sec, and at Akturpak—6 l/sec. Groundwater discharge takes place along river valleys and especially along zones of tectonic disturbances. Waters of zones of tectonic ruptures are usually opened by adits driven within the deposits.

The groundwater of the deposits is characterized by elevated total mineralization (up to 3.0 g/l), and by a sulfate and, more rarely, sulfate–hydrocarbonate sodium–calcium composition. The content of the sulfate ion in these waters is high and reaches 1377 mg/l. Acidic waters are encountered nowhere; pH varies from 6.9 to 7.8. A broad complex of elements has been found in the waters, with elevated contents of gold, arsenic, antimony, and also lead, copper, zinc, and molybdenum. Let us consider the behavior of antimony in the waters of each deposit separately.

The Kochbulak gold-ore deposit is located on the northern slope of the Kurama Range, in the interfluve of the Nishbash-say and Gush-say. Geologically, it is confined to tectonic faults and fractures filled with quartz, barite, calcite with sulfides, and gold. Among the ore-hosting rocks the most widespread are marbled and silicified limestones \((D_1—C_1)\), andesite and dacite porphyries \((C_2—C_3^{ak}, C_{2-3}^{ak1})\), basalt conglomerates and agglomeratic tuffs \((C_{2-3}^{ak1})\), etc.

Mineralogically, the ores of the Kochbulak deposit are represented by accumulations of pyrite, fahlores, hematite, sphalerite, chalcopyrite, barite, quartz, and carbonates. The principal components of this deposit are gold, zinc, lead, copper, and antimony. Supergene minerals are represented by hydrohematite, pyrargyrite, bornite, and covellite, which form rim-like microtextures. Among the ore minerals, antimony-bearing minerals have been encountered: bournonite, jamesonite, plagionite, stibio-luzonite, etc. These minerals are considered to be of medium stability, and their oxidation products are sparingly soluble. Nevertheless, apparently, these minerals are the main source of enrichment of the groundwater with antimony.

In the area of the deposit, the waters of the nearby says Aktash, Uzuk, Akturpak, and Kochbulak and the waters of all adits were studied. In all, 68 samples were taken, in 44 of which antimony was detected with contents from 1.5 to 42 µg/l. Some results of these studies are presented in Table 1, from which it is evident that the groundwater of the adits is distinguished by elevated contents of antimony, arsenic, and gold. Its maximum values are characteristic of the groundwater of the adits. In the waters of surface watercourses not connected with the deposit, the antimony content reaches only 5 µg/l. The exception is the Aktash say, in whose waters antimony was found up to 27 µg/l. This is explained by the fact that, along its entire length, the river crosses longitudinal tectonic disturbances along which groundwater associated with the deposits is discharged. It is interesting to note that at individual sampling points, high antimony contents correspond to maximum contents—

Table 1

Content of antimony, gold, and arsenic in groundwater of the Bobotubak deposit

Fig. 1. Dispersion plume of antimony in the natural waters of the Kochbulak gold-sulfide deposit: 1 — dispersion plume of groundwater with an antimony content of more than 2 µg/L; 2 — sampling point: numerator — point number, denominator — element content; 3 — conventional contours; 4 — element content in groundwater of less than 1 µg/L.

of arsenic and gold. The nature of the aqueous dispersion train of antimony is shown in Fig. 1, from which it is evident that antimony is distributed throughout the area, and the aqueous trains form clear boundaries at a distance of more than 500 m from the ore body. The aqueous trains of antimony and arsenic at this deposit coincide in general outline, with the dimensions of the aqueous train for antimony being somewhat larger than for arsenic.

Thus, against a background of 2.6 μg/l, the maximum antimony content in the waters of the deposit reaches 42 μg/l, while contents of 15–20 μg/l occur everywhere, i.e., the contrast coefficient is, as a rule, greater than 5–10. The observed aqueous dispersion trains are contrasting in character and can be detected in the course of hydrogeochemical surveying.

The Aktyurpak gold-ore deposit is located in the valley of the Nakpai River and its right tributary, the Aktyurpaksai. Geologically, it is associated with quartz-pyrite veins occurring in Devonian limestones, granodiorite porphyries, syenite-diorites, and andesite-dacite porphyries. Chalcopyrite, galena, and sphalerite are of subordinate importance among the ore minerals. The leading role in the water supply of the deposit is played by waters of zones of tectonic disturbances, which receive recharge both as a result of regional groundwater runoff and from the overlying aquifer horizons.

In the course of hydrogeochemical surveying, a broad complex of elements was found in the waters, analogous to that in the waters of the Kochbulak deposit. Among the elements of gold-ore deposits observed in this case, the leading place belongs to antimony, silver, and molybdenum. Some results of hydrogeochemical sampling are presented in Table 2, from which it is evident that the groundwater of this deposit has a neutral and slightly alkaline medium, an oxidizing-reducing environment, and the sulfate-ion content, as a rule, exceeds 300 mg/l. The highest content of the SO₄ ion was found in the waters of zones of tectonic disturbances (up to 1155 mg/l).

Antimony in the groundwater of the deposit is distributed throughout. It is mainly found at low values from 1.2 to 3.8 μg/l, and only individual points contain it above 15 μg/l. It was not possible to establish any dependence of the antimony content on pH, SO₄, and Eh. At the same time, a clear dependence is observed between the antimony content and the character of groundwater recharge. Thus, in the southern part of the Aktyurpak deposit, fissure-ground and fissure-vein waters are recharged by waters of the alluvial deposits of the Nakpai River valley. As a result of such mixing, mixed hydrocarbonate-sulfate or sulfate-hydrocarbonate waters with mineralization up to 1 g/l are formed here. In them, antimony was found in amounts from 1.3 to 3.5 μg/l, silver up to 0.3 μg/l, and molybdenum up to 4 μg/l. More mineralized sulfate waters are widespread in the northern part of the deposit. Most often these waters are associated with zones of tectonic disturbances and contain maximum amounts of antimony (15–26 μg/l) and silver (7.5–34 μg/l). At the same time, the waters of the Limonite and Northern faults, opened by an adit, contain no antimony. This is explained by the fact that these waters are recharged from the overlying aquifer horizons, not directly connected with the deposit. Antimony was also not found in springs located 1.5–2.2 km from the deposit. It was not possible to trace in detail the aqueous dispersion trains of antimony at this deposit; nevertheless, on the basis of the available data it may be assumed that their length does not exceed 1.5 km. Within the Aktyurpak deposit, antimony, silver, molybdenum, and gold are distributed in the waters in quantities significantly exceed-

Table 2

Contents of sulfate, gold, silver, and molybdenum in waters of the Zolotorudnoye occurrence, Akturpak

Table 3

Content of sulfur, molybdenum, and gold in groundwaters of the Kuraminka and Kalmakyr deposits

exceeding the background content. It was also noted that the presence of gold in water is always accompanied by the presence of antimony, and its content, as a rule, exceeds the amount of gold by 5–10 times or more. From all that has been said, it may be concluded that antimony forms fairly broad aqueous dispersion streams and can be used as an indicator element in prospecting for gold-ore deposits by the hydrogeochemical method.

In order to determine the presence of antimony in the waters of other types of deposits, we carried out investigations at the Kurgashinkan deposit (polymetallic with gold) and the Kalmakyr deposit (copper-molybdenum with gold). Some results of analyses of water samples are given in Table 3, from which it is evident that antimony, in amounts from 0.8 to 6 µg/l, is present in the waters of the oxidation zone, which have a slightly alkaline reaction and a sulfate–hydrocarbonate–sodium–calcium composition. In the zone of unoxidized ores, waters of mixed composition are widespread, the principal ones being sulfate–sodium–calcium and sulfate–chloride–magnesium–sodium waters. The antimony content in these waters is 5–10 times higher than in the waters of the oxidized zone.

Within the Kalmakyr deposit, waters sampled at various levels of the open pit were studied, and in all of them antimony was found in amounts from 0.5 to 9 µg/l, i.e., for the most part above background values. At the same time, the antimony content in the waters is often higher than that of molybdenum or gold.

From all that has been said, it follows that antimony is widely distributed in the groundwaters of the studied gold-ore, polymetallic, and copper-molybdenum-with-gold deposits. Under the conditions of the Kurama Range, it forms aqueous dispersion streams whose length varies from 0.5 to 1.5 km. All this permits the conclusion that it is expedient to use antimony as a criterion in prospecting for the indicated deposits by the hydrogeochemical method. In addition, it should be emphasized that the observed broad aqueous dispersion streams of antimony are formed under neutral and slightly alkaline conditions, which is a favorable factor for using this element in prospecting for deeply buried ore bodies within which no oxidation zone is formed.

REFERENCES

1. K. M. Davlitgalieva, I. G. Diveev. Hydrogeochemical prospecting indicators of useful minerals of Mugodzhar and the Lesser Karatau. In: Hydrochemistry and Hydrothermy of the Groundwaters of Kazakhstan. Alma-Ata, “Nauka,” 1969.

2. V. N. Makarov. Hydrochemistry of antimony deposits of the Indigirka River basin. In the abstracts: Geochemical Prospecting in the Regions of Cryogenesis. L., 1970.

3. S. S. Smirnov. The Oxidation Zone of Sulfide Deposits. Publishing House of the Academy of Sciences of the USSR, 1955.

4. P. A. Udodov, I. P. Onufrienok, Yu. S. Parilov. Experience in Hydrogeochemical Investigations in Siberia. M., “Vysshaya shkola,” 1962.

5. P. A. Udodov, S. L. Shvartsev. On certain regularities in the migration of microcomponents in groundwaters of hypergenesis. Proceedings of the Interdepartmental Conference on Hydrogeochemical and Paleohydrogeological Research Methods for the Purpose of Prospecting for Mineral Deposits. Tomsk State University Publishing House, 1969.