Kazymchin Lead-Zinc Ore Occurrence

A. R. Levertov, A. M. Kuzmin

In the area of the Kuznetsk Alatau, up to the present time only three very small lead-zinc deposits are known (Yuliya, Igr-Gol, Karasuk), along with a number of insignificant ore occurrences [1, 2].

In this connection, the discovery on the eastern slope of the Kuznetsk Alatau of the new Kazymchin polymetallic ore occurrence is of great interest. The latter is located in the headwaters of the Kazymchi River, a left tributary of the Tom River. It was found in 1962, and from 1963 onward it was studied by means of mining and drilling operations, which showed that the ore formations are represented by one relatively large and several small lens-shaped accumulations of oxidized, predominantly zinc ores, confined to a major tectonic zone of sublatitudinal strike and spatially gravitating toward the contact of Upper Proterozoic sedimentary rocks with intrusive rocks of Cambrian–Ordovician age.

The enclosing sedimentary sequence is composed of white, dark-gray, and pinkish-gray dolomitized limestones with interbeds of oncolitic shales, gravelites, and siliceous shales of small thickness. In the immediate vicinity of the intrusive rocks, dolomites are developed; in the contact zone they are recrystallized and transformed into white, saccharoidal dolomitic marbles. In areas of intense crushing, the degree of alteration of the rock increases considerably. Throughout the entire mass of sedimentary rocks, pyrite, later subjected to limonitization, is disseminated as fine impregnations; somewhat more rarely, disseminated apatite occurs in the form of the finest rounded grains (Fig. 1).

The bedding of the sedimentary rocks is monoclinal, with dip at an azimuth of 25–340° and angles of 25–45°.

The described sedimentary-metamorphic formations are intruded by intrusive rocks of the Tygyrtysh (Cm₃–O) intrusive complex. Directly in the southern part of the ore field, a small stock-like intrusive body is exposed at the surface, composed of granodiorites, biotite granites, biotite-plagioclase diorites, and quartz diorites, with a predominance of granodiorites.

granodiorites, which consist of approximately 45% plagioclase and 25% biotite, with 5% accessory minerals (magnetite, leucoxene, apatite). Calcite and epidote-zoisite are present as secondary minerals; limonite is developed in cavities and fissures. The rock texture is transitional from hypidiomorphic-granular to micropegmatitic. In the near-contact parts of the intrusive body, albitites are sometimes encountered.

In the central part of the ore field, a blind intrusive body of alaskite granites has been exposed by core drilling (Fig. 2); these apparently constitute a small fissure intrusion. The strike of the intrusion coincides with the strike of the tectonic zone of northeastern trend; the dip of the contacts is steep. The composition of the alaskite granites is fairly simple and is represented by acid plagioclase, K-feldspar, and quartz. Among the secondary minerals, sericite and a small amount of pelite are present; among the accessory minerals, ilmenite and leucoxene occur. In altered alaskite granites, in close association with smithsonite and ankerite, rutile is present; it forms radial-radiate reniform aggregates and is often replaced by leucoxene. The rock texture is granitic, locally pegmatitic.

Dikes of diorite porphyrites and granite-porphyries are fairly widely developed in the ore field. The thicknesses of the dikes vary widely, from tens of cm to several meters; their strike is sublatitudinal, coinciding with the strike of the ore zone, and their dip is vertical, with slight deviations to the south and north.

In composition the diorite porphyrites are close to hornblende spessartites and consist of 55% plagioclase, 35% hornblende, 5% biotite, and 5% accessories represented by magnetite and apatite. The rock consists 95% of a holocrystalline groundmass and 5% of rare large porphyritic phenocrysts of plagioclase and completely decomposed hornblende or, possibly, pyroxene. The rock texture is typical porphyritic.

The granite-porphyries consist of a holocrystalline groundmass and porphyritic phenocrysts of feldspar, decomposed biotite, and quartz. The groundmass is composed of small grains of feldspar, quartz, flakes of colorless mica, and an insignificant amount of magnetite, leucoxene, and apatite.

The dikes cut all sedimentary and intrusive rocks within the ore-field area. The greatest saturation with dikes occurs in the zone of contact between the white saccharoidal dolomites and the alaskite granites, or, in other words, in the areas where mineralization is localized.

The principal ore-controlling structure of the deposit is a rather thick tectonic zone of sublatitudinal strike, embracing sedimentary-metamorphic and intrusive rocks. The formation of this tectonic zone, in all probability, was rather prolonged in time, and the intrusion of the alaskite granites, the dike complex of rocks, and the primary ore formation are associated with its establishment and development. Secondary redeposition of ores in the upper parts of the deposit takes place within the same zone.

In connection with the existence of this tectonic zone, dislocation metamorphism is exceptionally strongly developed in the Kazymchin ore field. All rocks participating in the structure of the ore field are cataclased, and individual areas are mylonitized. The near-contact parts of the granodiorite intrusion are especially intensely crushed and kneaded to the state of mylonites. Breccias of limestones and dolomites are widely distributed in the rocks of the carbonate sequence.

The host rocks of the ore manifestation have undergone intensive hydrothermal alteration. Thus, the granodiorites, granite-porphyries, and other intrusive formations are kaolinized and sericitized.

and carbonatized. The limestones are intensely dolomitized and calcitized, while the immediately ore-hosting band is silicified and ankeritized. Sulfidization of the rocks is very widely developed in the ore field. Skarn rocks are absent at the deposit.

The bulk of the ores of the Kazymchin ore field tends toward the contact of aplite granites with white, saccharoidal dolomites, which form in the apical part of the granites themselves a kind of “cap,” descending along the contacts of this intrusive body to a depth of not less than 250 m from the surface (Fig. 2).

The main ore body has been traced by mine workings and core-drilling holes along strike for 600 m (Figs. 1 and 2). In form, the ore body at the surface is an ac-

Fig. 1. Schematic geological map of the Kazymchin polymetallic deposit: 1—dark-gray, pinkish-gray dolomitized limestones with interbeds of siliceous shales, gravelites, and flints; 2—dolomites, white saccharoidal dolomitic marbles; 3—granodiorites, biotite granites, biotite-plagioclase diorites, quartz diorites; 4—Alaskan granites; 5—dikes: a) diorite porphyrites, b) granite porphyries; 6—ore bodies

molite-shaped lens with a characteristic splitting on the flanks. In the near-surface part, approximately to a depth of 50–60 m, owing to oxidation and secondary redeposition, the total thickness of the lens is sharply increased and amounts to 100–140 m. At greater depths the thicknesses of the ore body are fairly constant, varying within the range of 25–40 m.

From the north and south the main ore body is, as it were, fringed by a series of ore bodies of small thickness (1–7 m). In individual cases these bodies are traced at the surface for distances of up to 300–500 m.

The material composition of the ores of the Kazymchin deposit differs significantly from the ores of deposits known in the Kuznetsk Alatau. Whereas the ores of Karasuk, Yuliya, and Igr-Gol are predominantly lead ores, at Kazymchin the lead ores, in comparison with the zinc ores, amount to approximately 15–20%.

![Fig. 2. Schematic geological section of the Kazymchin polymetallic deposit. For legend, see Fig. 1.]

Fig. 2. Schematic geological section of the Kazymchin polymetallic deposit. For legend, see Fig. 1.

Oxidation processes are very intensely manifested at the deposit; these gradually diminish with depth. However, from a number of boreholes it has been established that even at depths of 200–250 m, zones of oxidized and semi-oxidized ores occur. Therefore, at the present time the Kazymchin ore occurrence is regarded as substantially oxidized.

The principal useful component of the deposit is smithsonite, observed in dense fine- and very fine-grained aggregates, in banded colomorphic kidney-shaped forms, as cellular and earthy-porous masses, and also as small druses of idiomorphic crystals filling fractures, fissures, and pores. Of sharply subordinate importance among the oxidized zinc ores is calamine, occurring as isolated sporadic patches against the background of the predominant mass of smithsonite ores. Very rarely, in isolated cases, hydrozincite is detected by a phase microchemical reaction using the imprint method. With depth, the amount of sphalerite in the ores increases sharply; it is represented mainly by its purest variety—cleiophane. Sphalerite is present in strongly crushed, fractured rocks; its fine-grained aggregates fill fractures and cavities, and also form fine disseminations in the rock.

The zinc content in the Kazymchin ores varies within fairly wide limits, from tenths of a percent to 40%. A fairly clear dependence is established: the lead content decreases as the zinc content in the ores increases, and vice versa. Cadmium is isomorphically associated with sphalerite; its contents in substantially zinc ores are fairly high—from 0.03–0.05% to 0.10–0.12%. Spectral analyses indicate the presence of gallium and indium.

A special position at Kazymcha is occupied by the lead ores, which are represented chiefly by small, low-thickness ore bodies of limited strike extent, gravitating toward the contacts of dikes and spatially located in the central part of the main ore field. According to the available data, the extension of the lead bodies to depth is very limited, and only in one drill hole, at a depth of 200 m from the surface, was a three-meter interval of lead ores intersected. The strike of the lead-ore bodies is concordant with the general strike of the ore zone, and at the surface their presence is marked by thick eluvial debris.

The predominant constituent of the lead ores is galena, forming solid granular masses that undergo intense oxidation with replacement by anglesite and pyromorphite, and then by cerussite. Anglesite is observed in the form of fine-grained or colloform formations around galena, often with a rather dense xenomorphic dissemination of relict galena. Sometimes anglesite contains intergrowths of secondary galena and is closely intergrown with pyromorphite-mimetesite. The latter are poorly distinguished from anglesite and are reliably identified only by a phase microchemical reaction. In crushed material, pyromorphite is more often distinguished. In addition to the minerals indicated, by the imprint method in oxidized lead ores the presence of plumbojarosite is established in isolated cases.

The lead content in the Kazymcha ores varies within wide limits (from tenths of a percent to 15–20%, sometimes reaching 50–60%).

In galena, after etching, at a magnification of 900, argentite, pale ore, and other complex silver carriers are noticeable in the form of emulsion inclusions, as well as isolated extremely fine inclusions of native silver. The content of the latter in the ores of the occurrence is 8–10 g/t.

Of the iron minerals, pyrite is the most widespread at the occurrence; it is present in all ores and rocks, most often in the form of disseminations. Pyrite is often completely or peripherally pseudomorphically replaced by iron hydroxides (hydrohematite, goethite, hydrogoethite, and hydrolepidocrocite), which in the ores and rocks form loose colloform crusts. In the oxidized part of the occurrence, ankerite is widely distributed, together with which hematite is sometimes encountered. In insignificant quantities, jarosite occurs together with plumbojarosite and iron hydroxides in the oxidized lead ores.

The history of the geological formation of the Kazymcha ore occurrence may be schematically represented as follows. The carbonate sequence of the upper Proterozoic—lower Cambrian was intruded during the Salair phase of folding by an intrusion of granodiorites. In connection with a later fault dislocation, a large tectonic zone of sublatitudinal strike arose at the contact of this intrusion with the enclosing sedimentary-metamorphic sequence. Along this zone, the emplacement of a small intrusion of alaskite granites took place, accompanied by a considerable number of dikes of diorite porphyrites and granite porphyries. The weakened zones at the contacts of the alaskite-granite intrusion proved to be the most favorable channels for the penetration of the dikes; these same sectors proved the most suitable for ore deposition. The outcrops of the Kazymcha ores at the surface and beneath the alluvium indicate that the upper part of the ore concentrations of the ore field was denuded.

In conclusion, it should be said that the prospects of the district are not limited to the Kazymcha ore occurrence described itself. Three km west of the latter, in the Vodorazdelny area, a zone of oxidized lead-zinc-

… ores 25–50 m thick, having the same material composition as in the Kazymchin mineralization described above.

All this once again emphasizes that in the Kuznetsk Alatau the discovery of industrially valuable deposits of polymetallic ores is possible.

REFERENCES

1. A. A. Amiraslanov. Basic Types of Lead and Zinc Deposits. Gosgeoltekhizdat. Moscow, 1957.

2. A. Ya. Bulynnikov. On the distinctive polymetallic “essentially lead” mineralization of the Kuznetsk Alatau and the Eastern Sayan. In: Basic Ideas of Academician M. A. Usov in Geology, Alma-Ata, 1960.