BEHAVIOR OF GOLD AND ITS ASSOCIATED ELEMENTS IN THE FIELDS OF GOLD DEPOSITS IN THE NORTHERN PART OF THE KUZNETSK ALATAU

B. A. Vorotnikov, L. M. Popova, N. A. Roslyakov, N. V. Roslyakova,
V. G. Tsimbalist (IGiG, Siberian Branch, USSR Academy of Sciences)

At the present time, geochemical methods of prospecting for sulfide deposits have become firmly established in production practice. There are successful variants of the application of geochemical investigations for identifying gold mineralization [2, 3, 4, etc.]. However, these works have not yet passed beyond the experimental stage. The main difficulty in using geochemical methods in the search for gold mineralization has consisted in the fact that, in investigations, only the elements associated with gold were analyzed (copper, arsenic, lead, zinc, etc.). Because of the low sensitivity of analytical methods, determination of gold in geochemical prospecting was carried out extremely rarely. Therefore, the distribution of gold in ore outcrops, in the loose deposits overlying them, in bottom sediments, and in waters of gold-ore fields remains unclear. Nor have regularities been found in the relationships of gold with other elements during oxidation of primary ores.

With the aid of radioactivation (analyst L. K. Pavlova) and spectrochemical (analyst V. G. Tsimbalist) methods (sensitivities respectively \(1 \cdot 10^{-9}\%\) and \(1 \cdot 10^{-7}\%\)), we were able to study the distribution of gold in various formations of the hypogene and hypergene zones of the fields of gold-ore deposits of the Mariinsk taiga and to reveal its geochemical relationships with other elements of the primary ores. Geochemical investigations were carried out at the Berikul, Komsomolsk, Tsentralny, Natalyevsk, and Kundat deposits.

The geological structure of these deposits is generally known. It should only be emphasized that the Berikul, Komsomolsk, and Tsentralny deposits belong to the vein type, Natalyevsk to the skarn type, and the Kundat group of deposits to the stockwork type. The enclosing rocks at Berikul and Kundat are porphyrites and, to a lesser degree, limestones; at the Tsentralny and Komsomolsk deposits, granodiorites and gabbro-diorites; at Natalyevsk, limestones and granodiorites. The mineral composition of the primary ores of these deposits is given in Table 1 (in order of abundance).

The background content of gold and its associated elements, characterizing the content of elements in the rocks outside the ore fields, is given in Table 2.

It is evident from Table 2 that the background value of gold (regional background) in porphyrites is \((4—9) \cdot 10^{-7}\%\), in gabbro-diorites \(6.2 \cdot 10^{-7}\%\), in granodiorites \(1.3 \cdot 10^{-6}\%\), and in limestones about \(1 \cdot 10^{-7}\%\). These conten-

Table 1

Mineral composition of the primary ores of the Berikulskoye, Komsomolskoye, Tsentralnoye, Natalyevskoye, and Kydatskaya group deposits
(compiled from data of N. V. Roslyakova, using published and archival materials)

... values are very close to the Clarke values, according to A. P. Vinogradov [1], which, despite the small number of samples analyzed by us, may attest to the high reliability of the numerical material presented in Table 2.

In the rocks of ore fields, the same elements have been established as outside them, but their contents here are significantly higher (local background). Thus, for example, within ore fields the concentrations of gold in all rocks are an order of magnitude higher than the regional background. In these cases gold has a high positive correlation (correlation coefficient \(r \gg 0.5\)) with copper, lead, barium, sometimes silver, manganese, titanium, and zirconium. All this may serve as a good geochemical indicator in small- and medium-scale prospecting. Gold contents in rocks above \(2 \cdot 10^{-6}\%\), and its geochemical association with a definite complex of elements, make it possible to identify promising areas already at the initial stage of geochemical investigations.

Near ore bodies the content of gold and its associated elements increases sharply. The gold content in these halos is \(n \cdot 10^{-5}\%\) and higher. The width of the halos depends on many causes and, first of all, on the composition of the enclosing rocks, their fracturing, and the intensity of near-ore alteration. In massive porphyrites that have practically not undergone hydrothermal metamorphism, the dispersion halos of gold reach 5 m, whereas in beresitized granodiorites they reach 20 m. Primary dispersion halos of gold and its associated elements usually have a complex structure (Fig. 1).

Fig. 1. Distribution of gold, lead, copper, zinc, nickel, and manganese in primary dispersion halos of the Berikul deposit.

It is evident from Fig. 1 that in direct contact with the veins the contents of gold, lead, zinc, manganese, and nickel are sharply lowered. Copper shows the opposite tendency. Then, with increasing distance from the veins, the contents of gold and its associated elements first increase and then gradually pass into the local background values.

In ores and primary halos, gold is concentrated in native form, as well as in the form of a finely dispersed admixture in ore and vein minerals (see the report by N. V. Roslyakova). In ores and halos of deposits of the vein type, gold has a high positive correlation coefficient (\(r \gg 0.5\)) with arsenic, lead, and copper, more rarely with manganese, titanium, zirconium, and barium; and in deposits of the skarn type, with bismuth, cobalt, and molybdenum. The revealed regularity can be used...

used for an approximate assessment of the type of gold-ore mineralization from the results of large-scale geochemical prospecting. The sampling interval in large-scale surveys of primary dispersion halos should be determined on the basis of the geological structure of the area being studied: the more acidic and coarse-grained the enclosing rocks, the greater, other conditions being equal, the distance between sampling points.

In oxidation zones, the secondary dispersion halos of gold and its associated elements are broader and less contrasting than the primary ones. The maximum concentrations of gold are also localized directly in the ore body, but near the selvages of the veins the areas with sharply reduced gold contents become more diffuse, especially at the lower contact down the slope. Then, as in the primary halos, the gold content in the secondary halos first increases, and with distance from the outcrop passes into the local background (Fig. 2).

Fig. 2. Distribution of gold, antimony, arsenic, copper, and lead in the near-surface part of the oxidation zone of the Central deposit. The left scale shows the gold content in weight percent; the right scale shows the content of antimony, arsenic, copper, and lead. 1, 2, 3... 8—sampling sites; filled in black—the outcrop of the Tonyshevsky vein.

Thus, in the near-surface part of the oxidation zone, a gold-ore outcrop may be expressed by two or three areas with anomalous concentrations of gold. In this connection, certain difficulties may arise when outlining a gold-ore outcrop by gold peaks. The elements associated with gold can be of great assistance here. In ore anomalies, together with gold, elevated contents of almost all elements of the primary ores are present, especially antimony, copper, lead, and arsenic. In barren anomalies, gold is accompanied chiefly by zinc and bismuth. This is confirmed graphically (Fig. 2) and mutu—

Table 2

Contents of indicator impurity elements in rocks of the studied areas, wt. %

Note. An empty cell means that the element was not detected by the analysis.

correlation-statistical (in the oxidation zone gold has a direct high correlation—\(r>0.7\)—with antimony, arsenic, and lead, and a lower one—with zinc and bismuth—\(0.7>r\geq 0.5\)).

The enrichment or depletion of oxidation zones in ore elements observed at the present time depends in many respects on the degree of erosion of the modern relief, which in general increases from the deposits of the northern part of the region described (Komsomol’skoe) to the more southerly ones (Tsentral’noe). Thus, for example, in the oxidation zone of the Komsomol’skoe deposit, characterized by intense chemical alteration and depth (35–80 m), the elements, according to the enrichment coefficient (the ratio of the average content of the element in the oxidation zone to its average content in the zone of primary ores), are arranged in the following series (the series was constructed from materials of L. K. Pavlova):

\[ \begin{array}{ccc} \mathrm{Ag}<\mathrm{Au}<\mathrm{Zn} & <\mathrm{Ga}<\mathrm{Sb}<\mathrm{Mn} & <\mathrm{Pb}<\mathrm{Cu} \\ K_{\text{enr.}}\leq 0.2 & 2.1>K_{\text{enr.}}>1.0 & K_{\text{enr.}}>7.5 \end{array} \]

Under conditions close in geological structure, at the Tsentral’noe deposit, but with a more eroded oxidation zone, this series has the following form:

\[ \begin{array}{ccc} \mathrm{Sr}<\mathrm{Cr}<\mathrm{Mo} & <\mathrm{As}<\mathrm{Mn} & <\mathrm{Co}<\mathrm{Ga}< \\ K_{\text{enr.}}\leq 0.5 & 0.9>K_{\text{enr.}}>0.5 & 1.2\geq K_{\text{enr.}}>0.9 \end{array} \]

\[ \begin{array}{cc} <\mathrm{Zr}<\mathrm{Ti}<\mathrm{Zn}<\mathrm{V}<\mathrm{Bi}<\mathrm{Cu}<\mathrm{Ni}<\mathrm{Au}<\mathrm{Ag} & <\mathrm{Ba}<\mathrm{Pb}. \\ 1.5\geq K_{\text{enr.}}>1.2 & K_{\text{enr.}}\ 1.5 \end{array} \]

It should be emphasized that ore elements are significantly leached only from the surface part of the oxidation zones of all deposits. This is caused by modern weathering processes superimposed on ancient oxidation zones. Since the prospector is concerned first of all with the surface, this phenomenon must be taken into account in practical work. In geochemical prospecting by secondary dispersion halos in the oxidation zone, the sample should include material less affected by modern leaching processes (from a depth on the order of 1 m).

In the covering unconsolidated deposits, the gold content is an order of magnitude lower than in the oxidation zone, while in soils it is 2–3 times higher than in loose soil-forming rocks. Maximum concentrations of gold are localized in two horizons: 1) directly above the oxidation zone in the lower part of the section of loose deposits, and 2) in the lower subhorizon of the soil-vegetation layer (subhorizon \(A_1\)).

A buried gold-ore outcrop can by no means always be contoured by anomalous gold contents either in loose deposits or in soils. They may be practically absent above the ore outcrop and form a secondary halo downslope from the outcrop. A buried oxidized outcrop can be established more distinctly by the companions of gold in primary ores—lead, antimony, and copper (Fig. 3). In this case it is sufficient to sample subhorizon \(A_1\).

In evaluating an ore outcrop from data of large-scale metallometric surveying, one should take into account the relative enrichment or depletion of ore elements during soil formation. In the soils of almost all deposits, copper and bismuth are strongly depleted, and sometimes lead; zinc and gold accumulate. The stability series of the elements has the following form (Tsentral’noe deposit):

\[ \begin{array}{ccc} \mathrm{Cu} & <\mathrm{Bi}<\mathrm{Cd}<\mathrm{Pb}<\mathrm{Sb}<\mathrm{Zn} & <\mathrm{Au} \\ K_{\text{enr.}}=0.8 & 1.2>K_{\text{enr.}}>0.8 & K_{\text{enr.}}=1.8. \end{array} \]

In loose deposits, gold loses its correlation with all the companion elements of the primary ores.

Waters in the district are low-mineralized (up to 400 mg/l), predominantly hydrocarbonate-calcium waters with a stable, low content of chloride and sulfate ions, as well as sodium and magnesium. Their chemical composition depends on the character of the water-bearing rocks. Thus, waters confined to carbonate rocks are characterized by high mineralization—about 250 mg/l, an alkaline reaction, a hydrocarbonate-calcium composition, and depletion in trace elements. The waters of the intrusive rock complex, in contrast to the preceding ones, are hydrocarbonate-calcium-sodium waters with a neutral environment and lower mineralization. Their trace-element content reflects the composition of impurity elements in the water-bearing rocks. Waters within the effusive-sedimentary sequence, in chemical composition, are intermediate between those described above. They are characterized by an elevated content of titanium, cobalt, and vanadium.

Fig. 3. Distribution of gold, arsenic, antimony, copper, and lead in the soil-vegetation layer above the vein of the Tonashevskoye Central deposit. Symbols are the same as in Fig. 2.

Within each district, background waters differ by the predominance of a distinctive complex of elements. The background waters of the Berikul deposit district are characterized by elevated contents of copper and sulfate; those of Komsomolskoye—aluminum and silver; those of Kundatskoye—lead and tin; those of Natalyevskoye—titanium, gallium, chromium, vanadium, nickel, zirconium, and iron.

The chemical composition of the waters of ore fields of the vein type, situated in the eluvial landscape of the foothills (Komsomolskoye), differs little overall from the background. Ore waters within the transeluvial …

of the low-mountain landscape (Berikul) are distinguished by elevated contents of arsenic, molybdenum, antimony, bismuth, sulfate ion, etc., while those of the eluvial mid-mountain landscape (Kundat) are distinguished by lead, molybdenum, chromium, nickel, barium, gallium, and tin. The ore waters of the skarn deposit (Natal'evskoe), despite their confinement to the eluvial low-mountain landscape, stand out clearly by high contents of most trace elements.

The gold content in waters was determined by the spectrochemical method in dry residues of waters, mostly naturally enriched. Of 66 analyzed samples, gold was found in 60%, and its content ranges from 0.001 to 8.3 γ/l (discharge into the river from the concentrating mill at the Komsomol'skoe deposit). Radiochemical analysis of 11 samples established the presence of gold in all samples within the range from 0.0006 to 0.076 γ/l (sample from the Komsomol'skaya mine). This material permits the following conclusions to be drawn regarding the distribution of gold in waters.

In general, a decrease in the gold content in waters is observed in the direction from the Komsomol'skoe deposit toward the Berikul'skoe, Natal'evskoe, and Kundat deposits, which generally corresponds to an increase in the prevalence of carbonate rocks, as well as to the dissected character of the relief in these areas.

No dependence of the gold content on the hydrodynamic types of waters has been established.

In waters associated with known gold-ore mineralization, including mine waters, no overall increase in gold content is evident; exceptions are individual samples of mine waters from the Komsomol'skoe, Berikul'skoe (vein-type), and especially Natal'evskoe (skarn-type) deposits, in which the gold content is at a maximum (0.2–0.9 γ/l).

Hydrogeochemical anomalies identified by elements accompanying gold mineralization are not distinguished by an elevated gold content in the waters (the anomaly along the Veselen'kii brook in the area of the Komsomol'skoe deposit is an exception).

In the waters of the ore fields of vein-type deposits, the macrocomposition (the content of sulfate ion, sodium, as well as total mineralization and the ratio of sulfate ion to chlorine) changes only weakly in comparison with the background. A more noticeable change is observed within the skarn deposit; the magnesium content in particular increases. In the waters of the ore fields, extensive dispersion streams of such elements as arsenic and molybdenum are noted. Zinc, chromium, and titanium occur less often and form less extensive dispersion streams. In the immediate vicinity of sulfide mineralization, bismuth, antimony, cobalt, and cadmium are recorded in the waters.

Compared with the waters of the ore fields, mine waters have the following characteristics. They are relatively enriched in sulfate ion and sodium, have elevated pH values and contents of such trace elements as lead, nickel, silver, and bismuth. At the same time, a change in chemical composition with depth is observed. In waters of the upper levels, a broad range of elements is found in elevated quantities: chromium, strontium, barium, manganese, mercury, etc.; in the lower levels, only the principal ore elements: arsenic, molybdenum, antimony, more rarely cobalt and tin.

Main conclusions

1. The regional background of gold in the rocks of the studied areas is \(n \cdot 10^{-7}\%\). In the rocks of the ore fields, the gold content is an order of magnitude or more higher than the regional background. In small- and medium-scale geochemical

surveys, promising areas may be delineated by a gold content in rocks of \(n \cdot 10^{-6}\%\) and higher.

1. The primary dispersion halos of gold have a complex form. Their dimensions in the direction of the thickness of the ore bodies decrease from granodiorites (20 m) to porphyrites (5 m).

2. Secondary dispersion halos of gold in the near-surface part of the oxidation zone are broader and less contrasting than the primary ones. Anomalous gold concentrations do not always correspond to the ore outcrop. In anomalies above an ore outcrop, elevated contents of antimony, copper, arsenic, and lead are present together with gold.

3. In loose deposits overlying a gold-ore outcrop, gold peaks by no means always correspond to the position of the buried outcrop. The latter may be indicated by anomalies of antimony, copper, and zinc.

4. A clearly expressed general increase in the gold content in waters of ore fields, as compared with background waters, is not observed. Some increase in the gold content is noted in waters of the oxidation zones of deposits, especially of the skarn type, and also in landscapes with well-developed loose deposits.

5. As indirect hydrogeochemical prospecting indicators for gold mineralization, the following may be used: arsenic, molybdenum, tin, chromium, titanium, bismuth, antimony, cobalt, and cadmium.

The authors are grateful to L. K. Pavlova for the materials provided on the oxidation zone and cover loose deposits of the Berikul, Komsomolsk, and Kundat deposits.

REFERENCES

1. Vinogradov A. P. Average content of individual chemical elements in the principal rock types. Geochemistry, 1962, No. 7.

2. Wolfson N. V., Chembarisov Sh. A., Chistyi B. I. Experience in the application of geochemical and geophysical methods in prospecting for gold-ore mineralization in Uzbekistan. Bull. NTI MG and ON USSR, No. 1 (35), 1962.

3. Grigoriev A. M. On the possibility of applying the biochemical method of prospecting for gold in Buryatia. Materials on the Geology and Mineral Resources of the Buryat ASSR, issue 8, 1962.

4. Fedorenko Ya. D. Geochemical methods of prospecting for gold-ore deposits in Transbaikalia. Bull. NTI MG and ON USSR, No. 1 (35), 1962.