PROSPECTS FOR THE GOLD-BEARING POTENTIAL OF DEPOSITS OF ANCIENT VALLEYS IN THE MARIINSK TAIGA OF THE KUZNETSK ALATAU

B. N. ZIMOGLYADOV, L. N. POPOVA, E. D. SHPAIKHER (SNIIGGiMS)

To strengthen the raw-material base of the gold-mining enterprises of the Mariinsk taiga in the coming years, it is proposed to significantly intensify geological work aimed at identifying placer gold deposits. Their development has a number of advantages in comparison with the exploitation of ore deposits, namely: the time required for their exploration and commissioning is considerably shorter, the capital investments required for this are substantially smaller, and the cost of the metal obtained is lower. Thus, at present the need has become urgent to intensify research on the prospective evaluation of placer gold potential in the Mariinsk taiga.

However, in carrying out such work it should be taken into account that, over the nearly 150-year history of gold mining, the placers of the modern hydrographic network have for the most part been explored and those deserving attention have been worked out by artisanal and hydraulic methods, while those suitable for dredging have mostly been explored (the rivers Kiya-Shaltyr, Bol. Tulu-yul, Kundustuyul) or are at the exploration stage (the rivers Kiya, Shaltyr-Kozhukh).

On the territory of the Mariinsk taiga, deposits of valleys of the ancient hydrographic network of pre-Quaternary age are rather widely distributed, but their gold-bearing potential has been quite insufficiently assessed, although in many cases they were objects of mining, and insufficient research has been carried out to clarify questions of their preservation and their position in the modern relief.

Since the district is gold-bearing, questions of the formation and evolution of placers must be connected with the study of the modern relief and the history of its development.

In the Mariinsk taiga, gently rolling and generally level interfluves are developed, along with deeply incised, narrow, often canyon-like modern valleys. Mountain summits stand out sharply above the residual planation surface of an ancient continental land, which was peneplained in the Tertiary or in the Upper Cretaceous epoch and later dissected by prolonged and complex processes of denudation (V. K. Monich [2], A. S. Kirillov, 1952). On the basis of an analysis of the available factual material, the following course of relief development appears to us.

At the end of the Mesozoic and the beginning of the Tertiary period, the peneplained surface of the region, with a thick (up to 50 m) crust of chemical weathering—

... lateritic-type deposits was subjected to dissection. The relief of that time was a comparatively leveled surface, dissected by broad and gentle valleys, named by A. R. Burachek-Elansky (1943). These valleys are filled with redeposited products of the weathering crust, represented by thick sequences of ancient, strongly weathered alluvium with a characteristic yellow-ochre coloration and a high content of polished pebbles. The ancient alluvial deposits lie with a sharp erosional boundary either on the weathering crust or on deposits of ancient deluvium (hydraulic sections of the ancient valley of the Talanova River). The development of the crust of deep chemical weathering created favorable conditions for the liberation of gold from the enclosing rocks, and its subsequent redeposition contributed to an increase in the concentration of gold in the alluvium of the ancient valleys. The uplift of the region that occurred in the Quaternary period led to its dissection. The deep incision of rivers caused by these tectonic movements was the principal factor characterizing the modern relief. The canyon-like character of the valleys indicates a high rate of dissection of the peneplain, which continues at the present time. Neotectonic movements were expressed in vertical displacements of individual blocks, which caused the stepped character of the relief surface and a certain rearrangement of the plan of the river network. The major river arteries—the Kiya, Kozhukh, Kiysky Shaltyr, Kundat, and Tuluul rivers—combine features of ancient and young valleys; the latter are incised as much as 120–130 m into the broad terraces of the Elan level. The upper tier, represented by deposits of valleys of the Elan level, has two terrace steps: the upper terrace is traced in fragments and is separated from the lower one by a weakly expressed scarp or a gentle slope. In most cases the alluvial deposits of the terrace have not been preserved. The lower terrace of the Elan level is widely developed and is composed of alluvial material. Below is given a section of its deposits on the Kiysko-Tatar divide.

0.0–0.8 — vegetal layer.

0.8–4.0 — gray clay, without fragments.

0.4–7.0 — gray clay, with an admixture of sand and coarse pebbles; quartz pebbles occur.

7.0–24.0 — red clay, with an admixture of sand and well-rounded pebbles, including quartz. In the intervals 9.0–15.0 and 18.8–20.0, the presence of boulders 15 to 20 cm in diameter is noted.

24.0–24.5 — yellow clay, with an admixture of sand and well-rounded pebbles. Most of the pebbles are strongly weathered and crumble into grus.

The age of the deposits of the terraces of the Elan level is determined as Upper Pliocene–Middle Pleistocene (A. S. Kirillov, 1950).

We have distinguished three types of ancient valleys.

I. Valleys that, in their present state, lack a watercourse.

II. Sections of ancient valleys that partly coincide with modern valleys.

III. Sections of ancient valleys that occupy watershed depressions in the modern relief.

Let us dwell on a brief characterization of the distinguished types of ancient valleys.

A significant reorganization of the hydrographic network occurred in the transitional zone from the mountains to the plain; along the facade of the Kuznetsk Alatau, the work of S. G. Mirchink and A. R. Burachek (1943) revealed the extensive valley of the Bol. Elan River.

In recent years, within the limits of the indicated valley, comprehensive geological-geomorphological and geophysical work has been carried out to assess...

... its gold content (E. D. Shpaikher, L. N. Popova, 1965; Bekbulatov, 1965).

The valley of the Bolshaya Elan extends in a latitudinal direction for 35 km from Lake Bol. Berchikul to the right bank of the Kiya River; it is asymmetrical throughout, with a steep southern side. The width of the valley floor is variable, amounting to 1.0–1.5 km. In the headwaters of the Kalba River the valley has lake-like widenings up to 5–6 km. In individual sectors (the Kashtak River near Mount Karamyshka) the valley narrows to 0.3–0.5 km. The valley has no watercourse; modern rivers cross the Bol. Elan, the leveled areas of whose floor serve as watersheds for the present hydrographic network. From the western bank of Lake Bol. Berchikul, a trough-shaped depression about 1 km wide has been traced, extending in a latitudinal direction as far as the Tisulka River. Farther west, toward the Komsomolskoye gold-ore deposit, it has been traced along the Aleksandrovka River, in whose upper reaches it changes its direction to meridional and, along the Lamaevsky Creek (a right tributary of the Voskresenka), crosses the valley of the latter at the level of its third terrace and opens, as a broad trough-like depression, into the valley of the B. Elan, thus being its large “tributary.” Along the sides of the valley, terrace-like inclined surfaces are observed. On the southern side of the valley these surfaces pass into a peneplainized watershed, while on the northern side they merge with an alluvial plain. This is the second terrace of the Elan level, which formed simultaneously with the fifth terrace of the Kiya River in its mountainous part. Below is a section characteristic of the unconsolidated deposits filling the bed of the ancient valley:

0.1–0.0 m — soil-vegetation layer with shrub roots, gravel, small pebbles, sand.

0.1–0.4 m — pebble bed, size \(2 \times 5\) cm — 15%; gravel with sand — 80%; boulders up to 12 cm in diameter — 3%; yellow-gray clay — 2%.

0.4–7.8 m — well-rounded pebbles, size 2–5 cm — 20%; diameter 5–10 cm — 15%. Gravel and vari-grained sand — 45%; boulders up to 15 cm in diameter — 10%; blocks and boulders, size 15–25 cm — 5–7%; clayey admixture of yellow-gray color — 5%. The orientation of the material is horizontal. Composition: predominantly quartzite, rarely quartz pebbles, as well as granodiorites, porphyrites, diorites, gabbro, shales, very rarely syenites, granites, and silicified limestones. The pebbles are strongly weathered.

7.8–8.0 m — bedrock — eluvium of porphyritic diorites.

The alluvial deposits composing the ancient valley are distinguished by good rounding of the material, sorting, and persistent horizontal stratification. The most characteristic deposits are pebble beds and sands. The thickness of the unconsolidated deposits ranges from 1.0 to 20 m. Well-rounded pebble beds, the yellow-brown coloration of the enclosing rocks, and their occurrence in a broad ancient valley on brightly colored clays of the chemical weathering crust make it possible to correlate the deposits of the ancient valley of the Bol. Elan with the deposits of the Elan terraces in the mountainous part of the district.

A representative of valleys of the second type is the ancient valley of the Talanova River, located in the mountainous part of the district and having a meridional direction. Many watercourses of the modern hydrographic network coincide with it. In its northern part, the ancient valley of the Talanova River opens into the Kiya River at the level of the Elan terraces. In the south it has been traced by us as far as the Mal. Bayanzas River (the Tom River system). S. G. Mirchink [1] indicated a connection between the ancient valley of the Talanova River and the basin of the Tom River; however, we cannot agree with her conclusions that the ancient valley of the Talanova River had runoff in a southerly direction. We consid...

we believe that the direction of flow was northward and that the valley passed through the Talanovaya River, the Levo-Troitskaya, Kedrovskii Spring, the Annenka River, and joined the Kiya River. The basis for such an assertion, in addition to analysis of the development of the relief, is provided by the materials of the Martaiga expedition of WSGU (E. D. Shpaikher, 1963). In a detailed study of the chromites of this area it was established that those from ore occurrences in the area of Mount Zelenaya and from the alluvium of the Semenovka and other hydraulic cuts proved identical in chemical composition and accessory elements and could have been brought only from the south.

In addition, in the ancient alluvial deposits of the Talanovaya River below the mouth of the Kazanka River, gabbroids (the Taskyl massif), absent in the headwaters, are widely developed. The absence of alkaline rocks in the alluvium of the Elan terraces south of the valley of Izvestkovyi Brook testifies to the same thing.

The modern valley of this river partially coincides with the outlines of the ancient one, while the sharp change from a meridional direction to a latitudinal one below the mouth of the Levo-Troitskaya River is due to capture that occurred as a result of the cutting through of the watershed by a tributary of the larger valley of the Kiya River. North of the headwaters of the Levo-Troitskaya River, on the watershed with the Voskresenka River, a segment of the ancient valley is not controlled by modern watercourses. In the cross section of the ancient valley identified in the headwaters of the Talanovaya River, two complexes of deposits are distinguished: 1. A complex of deposits represented by alluvium of the floodplains and low terraces of the modern valley of the Talanovaya River; 2. A complex of deposits represented by ancient alluvium of terraces of the Elan level. Terraces of the Elan level have been traced as a continuous belt along both sides of the valley and have a width of 700 to 3000 m, with an elevation of 35–50 m above the water line of the Talanovaya River.

The generalized section of the Elan deposits along the valley of the Talanovaya River is as follows (from top to bottom).

1. Loams of gray, yellow, and brown color, loose, with rubble and rare inclusions of gravel and pebbles; thickness 1.0–5.0 m.

2. Ancient alluvial gravel-pebble deposits cemented by dark-brown, yellow-brown viscous clay. The percentage ratio of the clastic-material fractions is as follows: gravel 10–70%, pebbles 10–60%, sand 5–25%, clay 20–60%. The pebbles and gravel are represented by intensely weathered gabbro, diorites, and porphyrites. Well-rounded pebbles of quartz, quartzites, and hornstones covered with a black desert-varnish crust are often encountered. The thickness of these deposits ranges from 1.0 to 23.0 m. The stratum of ancient alluvium rests with a sharp erosional boundary either on the weathering crust or on the bedrock.

The Kedrovka placer has a distinctive structure; it is located within an area that experienced slight uplift and is overlain by modern alluvial deposits. It has a two-tiered structure: the upper tier, 4–8 m thick, is represented by Quaternary gray-colored, weakly auriferous alluvium; below it are developed ancient alluvial clayey pebble beds of variegated coloration. The pebbles are represented by porphyrites, diorites, and schists that have undergone deep chemical weathering. Rounded quartz pebbles are noted in significant quantities. The thickness of the ancient alluvial deposits reaches 30 m, with the lowest horizon, 5.5 m thick, containing gold in commercial concentrations. The bedrock of the placer consists of light-gray, intensely karstified limestones.

The terraced transverse profile of the ancient valley and the character of the alluvial deposits of its terraces are evidence of a large river, the existence of which was interrupted by neotectonic movements in Middle Quaternary time.

Fig. 1. Distribution scheme of ancient valleys in the Kiya River basin

1. Valleys with a modern complex of deposits.
2. Valleys with an ancient complex of deposits.
3. Leveled watershed surfaces.
4. Contour of valleys of the ancient hydrographic network.
5. Sections of ancient valleys worked for gold.
6. Sections of ancient valleys with established gold content.
7. Sections with a lateritic weathering crust.

Examples of reorganization of the ancient hydrographic network are also the numerous valley sections preserved in watershed depressions (Fig. 1).

The gold content of deposits of the ancient valleys of the Elan level has been reliably established over a broad territory of the Mariinsk taiga, and in many cases they were objects of gold mining, often with high grades (the Talanovaya River, Kedrovsky Spring, the Kiisko-Tatarsky ridge, etc.). In the Sarala district an ancient placer described by A. M. Khazagarov was worked [3].

For the deposits of the indicated ancient valleys, the characteristic feature is the presence of a gold-bearing bed represented by sorted, horizontally bedded pebble gravel cemented by dense, viscous, variegated clay (sometimes with an admixture of sand). Pebbles of various rocks are, as a rule, well rounded, sometimes polished, but strongly weathered and easily destroyed, with the exception of quartz and quartzites. The thickness of the gold-bearing bed ranges from 1.0 to 12.0 m (area of the Tatarka River).

The soil of ancient placers in most cases is a dense yellow-brown ocherous clay with fragments of various rocks (redeposited products of the chemical weathering crust), overlying bedrock; but sometimes it has been eroded and the gold-bearing bed rests directly on the bedrock floor.

The gold content in ancient alluvial deposits is distributed unevenly; the coarsest gold is concentrated in the lower part of the gold-bearing bed.

The gold of ancient valleys is usually coarser than in younger placers. This point is illustrated by Tables 1 and 2.

Table 1

Table 2

Thus, the gold of ancient placers is mainly larger than 1.0 mm and 1.0–0.5 mm; nuggets from 1 to 50 g are sometimes encountered, while larger nuggets are rare. The fineness of the gold is 800–900.

Usually the gold is yellow in color, well rounded, less often semi-rounded; intergrowths with other minerals are rare. Gold is often encountered in a “jacket” of black and dark-brown color.

In recent years, prospecting and exploration work using geophysical methods (VES and electrical profiling) has outlined the ancient valleys of the Bol. Elan and Talanovaya rivers, and then the gold content of the valley of the Bolshaya Elan was established over a distance of about 30 km, as well as that of the watershed part of the Kundustuyul and Troitskie Vershiny rivers (the northern continuation of the ancient valley of the Talanovaya River).

Thus, within the study area, a wide development of deposits of the Elan level and their gold content has been established.

For a prospective assessment of their gold content, it is necessary to carry out integrated geological-geomorphological investigations, including geophysical methods (electrical prospecting).

As priority targets, we recommend the following:

1. The ancient valley of the Talanova River.
2. The ancient valley of the upper reaches of the Kiiskii Shaltyr River.
3. The ancient valley of the Tatarka River.
4. The ancient valley of the Bogorodskii Brook.

REFERENCES

1. Mirchink S. G. Ancient valleys and the gold-bearing placers associated with them, exemplified by the Patom Upland, the Yenisei Ridge, and the Kuznetsk Alatau. Proceedings of the NIGRIzoloto Institute, issue 16, 1947.

2. Monich V. K. A geomorphological outline of the Kuznetsk Alatau. Proceedings of NIGRIzoloto, issue 6, 1947.

3. Khazagarov A. M. Mesozoic and Tertiary gold-bearing placers of the Eastern Sayan and the Kuznetsk Alatau. In: Geology of Placers. Nauka Publishing House, 1965.