Proceedings
of the Tomsk Order of the Red Banner of Labor Polytechnic
Institute named after S. M. Kirov

Volume 165　　　　　　　　　　　　　　　　　　　　　　　　　1969

On Modern Mineral Neoformations in Quartz-Sulfide Veins of the Tsentralnoye Deposit (Kuznetsk Alatau)

A. D. Mikov

(Presented at the scientific seminar of the cluster of departments of mineralogy and crystallography, petrography, geology, and exploration of mineral deposits)

The article gives a characterization of original modern mineral neoformations encountered in the summer of 1962 on the upper levels of the Tsentralnaya, Kazanskaya, Shkolnaya, and Lotereinaya veins of the Tsentralny mine.

These mineral neoformations are jelly-like, water-saturated masses, colored reddish-brown and white. The reddish-brown neoformations, sometimes with grayish, brownish, or yellowish shades, are very widespread at a depth of 50–150 m in adits along the Tsentralnaya and Kazanskaya veins and, to a lesser extent, along the Shkolnaya and Lotereinaya veins. As a rule, they are located on the walls, roofs, or supports of mine workings and usually have the form of incrustations up to 4–5 cm thick. More rarely, they are small stalactites reaching 2–3 cm in diameter and 8–10 cm in length. Sometimes these formations, in the form of a loose silt-like sediment, are deposited in drainage ditches.

Study of the dried neoformations showed that they consist of various kinds of limonitic material, chiefly ocherous, yellowish-brown, easily rubbed between the fingers into a dry-to-the-touch powder. In places such deposits are covered by very dense, thin, less than 0.2–0.3 mm, reddish-brown crusts of the same material. Under the microscope, the dense variety has medium reflectivity; brown reflections are visible in the powder. In the loose mass the reflectivity is considerably lower; reddish-brown reflections are well expressed. These varieties form a typical metacolloidal structure. In one of the polished sections there was found a fine dissemination (on the order of thousandths of a mm), more rarely small worm-like, white with a light-yellow tint, segregations of an ore mineral with high reflectivity, probably silver, whose arrangement repeats the structural pattern formed by the limonitic material. The mineral is isotropic. The diagnostic etching performed showed positive effects: with \(HNO_3\) it etches easily, turns gray, and with increasing etching time turns black. In addition, it is etched by aqua regia and \(FeCl_3\). The latter causes noticeable tarnishing, which disappears after wiping; no iridescent precipitate is observed. \(HCl\) gives a negative effect. The diagnostic etching performed agrees overall with the data for etching of silver. In such small se-

in the intergrowths, the iridescent precipitate characteristic of silver from the action of FeCl₃ may simply not be noticeable.

The reddish-brown neoformations described dissolve readily in acids. When dissolved in hydrochloric acid, gelatinous silica is released in an amount of 3–5%.

Spectral analysis showed a constant and, in a number of cases, high content of Fe, As, Si, Al, Mg, Ca, Mn, Zn, Cu in the reddish-brown varieties (Fig. 1). In addition, Pb, Ag, and Ni are present in a number of samples.

To determine the content of noble metals in the veins of Tsentralnaya and Kazanskaya, six samples of the material under study were taken. The results of assay analysis of these samples are given in Table 1.

The analytical data show that gold is present in all samples of the reddish-brown neoformations; its content ranges from 0.3 to 0.8 g/t. The silver content was determined in three samples and amounted to 7.6, 15.4, and 49.8 g/t.

In order to detect possible very fine particles of native gold, we undertook a study of the heavy fraction of the reddish-brown neoformations under an electron microscope. The heavy fraction was obtained by removing iron hydroxides with hydrochloric acid, followed by centrifugation of the resulting fraction in heavy liquid. The study showed the presence of extremely fine spherical particles. The general appearance of these particles is highly reminiscent of those described by M. N. Al’bov [1] from the heavy fraction of neoformations in mines of the Urals, which he took to be segregations of native gold.

White mineral neoformations, sometimes with a bluish and more rarely with an emerald-green tint, have an extremely limited distribution. They were encountered in the Tsentralnaya, Shkol’naya, and Lotereinaya veins. The forms of their segregations are analogous to those described above for the reddish-brown neoformations. Their mineral composition was not determined because of the absence of a sufficient quantity of material. Spectral analysis of the white neoformations showed elevated contents of Ca, Al, Zn, Pb, Cu (Fig. 1). One sample of white material was subjected to assay analysis (Table 1). The analysis recorded only traces of gold.

In the adits along the Tsentralnaya vein at the 87 m level and along the Lotereinaya vein at −64 m, the joint occurrence of the neoformations described can be observed. They occur as small incrustations, in which the reddish-brown material is overlain by white. Such a sequence indicates that predominantly reddish-brown, essentially ferruginous formations were deposited first, and then white ones with elevated contents of Ca, Al, Zn, Pb, Cu.

The characteristic occurrence of these neoformations on the walls, roof, and supports of mine workings, in the form of incrustations or stalactites, indicates that they are precipitates from mine waters. This is also confirmed by comparison of the composition of trace elements in the neoformations and in the mine waters (Fig. 2). It should be noted that the assemblage of elements in a given vein—both in the mine water and in the neoformations—correlates well with the ore mineralization of the vein. Reddish-brown precipitates are confined to sections of veins enriched in pyrite, whereas white ones are characteristic of sections more enriched in sphalerite, galena, and chalcopyrite. All sections in which neoformations are present in significant quantities are confined, within the veins, to ore shoots. This confinement indicates that no significant transport of the described precipitates by mine waters took place.

Thus, the material presented above makes it possible to establish

Fig. 1. Trace elements in modern mineral neoformations of the Tsentralnoye deposit

Neoformations:
Veins: reddish-brown; white.
Sample no.: 4, 5, 6, 7, 30, 31, 35, 37, 38, 39, 40, 41, 42, 44, 8, 9, 64, 33, 34, 62, 33, 33, 34, 45, 13, 14, 35, 35, 60, 61.

Vein groups shown:
- Reddish-brown — Central vein
- Kazan vein
- Potresinnaya vein
- White — Central vein
- Shtholnya vein
- Potresinnaya vein

Elements plotted: Pb, Cu, Zn, Cr, Ni, Co, Mn, Ba, Sr, Ca, Mg, Al, Si, Fe, Ti.

Legend:
- < 0.0001%
- 0.0001–0.001%
- 0.001–0.01%
- 0.01–0.1%
- 0.1–1.0%
- 1.0–10%
- > 10%

the fact of the transport of gold by mine waters at the Tsentralnoye deposit. As for the possible forms of gold transport, it is difficult to say anything definite in this respect. All views existing in the modern literature on this question may be reduced to three principal hypotheses:

Table 1

Gold and silver contents in mineral neoformations of the Tsentralnoye deposit

1. Transport of gold in the form of true solutions—the chloride and sulfide hypotheses, which are recognized by many geologists: S. S. Smirnov [3], V. M. Kreiter [2], M. N. Al’bov [1], and others.

2. Transport of gold in the colloidal state. The wide development in sulfide minerals of a mechanical admixture of finely dispersed gold leads S. S. Smirnov [3], F. V. Chukhrov [5], M. N. Al’bov [1], and others to recognize this type of migration.

Fig. 2. Content of microelements in the mine waters of the Tsentralnoye deposit. Symbols as in Fig. 1.

1. Transport of gold in the form of a suspension. The possibility of such transport has been recognized by many geologists. M. N. Al’bov [1] considers this form of migration the most probable for quartz-sulfide veins.

The data of chemical analysis of the mine waters of the deposit described indicate a comparatively low content in them of chloride and sulfate ions. According to 7 analyses, their contents range, respectively, from 3.5 to 35.0 mg/l and from 2.5 to 125.5 mg/l. With such

with the low content of chloride ion and sulfate ion in the mine waters, their effect on the dissolution of gold probably cannot be of substantial significance.

We do not have definite evidence for a significant role of colloidal migration of gold. F. V. Chukhrov [4] described modern mineral neoformations from certain deposits of Kazakhstan that are similar to ours. He indicates that they are deposits of ferric hydroxide gels. In sulfide minerals the presence of gold in the form of a fine mechanical admixture is characteristic. In the lower part of the oxidation zone of the deposit described here, an increased content of gold and ferric oxide hydrates is observed. It is known [1] that ferric oxide hydrates are protective colloids for gold gels. Taking the foregoing into account, we consider it quite possible to explain the migration of gold at the deposit by its transport in colloidal form.

At the Tsentralnoye deposit no grain-size analysis of native gold from the quartz-sulfide veins was carried out. By analogy with the quartz-sulfide veins of other deposits, it may be assumed that a significant part of the gold belongs to the class of suspensions (0.1–100 microns). Transport of such gold by mine waters downward along the dip of the veins under the conditions of the deposit described is quite probable.

The material set forth above allows us to draw the following conclusions:

1. The neoformations described are very young. Their age does not exceed 30–40 years.

2. Their precipitation from solution occurred by coagulation.

3. The dehydration products of the reddish-brown neoformations are, in external appearance, typical iron ochres.

4. The process of coagulation of gels and their subsequent dehydration is one of the paths of ochre formation in the oxidation zone of sulfide deposits.

5. The presence of gold in the reddish-brown neoformations indicates that its migration is closely connected with the transport of ferric hydroxide gels.

References

1. M. N. Al’bov. Secondary Zoning of Gold-Ore Deposits of the Urals. Gosgeoltekhizdat, 1960.

2. V. M. Kreiter et al. The Behavior of Gold in the Oxidation Zone of Gold-Sulfide Deposits. Gosgeoltekhizdat, 1958.

3. S. S. Smirnov. The Oxidation Zone of Sulfide Deposits. ONTI, 1936.

4. F. V. Chukhrov. Modern mineral neoformations from certain deposits of Kazakhstan. Transactions of the All-Union Mineralogical Society, 74, No. 3, 1945.

5. F. V. Chukhrov. On the migration of gold in the oxidation zone. Proceedings of the Academy of Sciences of the USSR, geological series, No. 4, 1947.