On the Question of Ancient Valleys and Buried Trough Gold Placers in the Basin of the Kiya River

(Kuznetsk Alatau)

B. V. RYZHOV, L. Ya. LANINA, I. A. POPOVA (TsNIGRI)

Most geologists who have studied the relief and the loose cover of the Mariinsk taiga (Mirchink, 1947; Zimoglyadov et al., 1968) have formed the idea that, on the watershed saddles of the basin of the Kiya River, in its mountainous part, there exist remnants of alluvium of an ancient river network at the level of the upper terraces. Since in a number of cases gold placers are associated with the alluvium of these terraces, researchers draw conclusions about significant prospects for finding placers also on the watershed saddles. In contrast to this, S. F. Dubinkin (1968) considers the saddles taken to be fragments of ancient valleys to be pediment passages. The correct resolution of this question is generally of practical importance, but it becomes especially acute for the Mariinsk taiga, where gold placers within the outlines of modern valleys have to a considerable extent been worked out.

The territory under consideration is confined to the northwestern slope of the Kuznetsk Alatau uplift and is an erosionally dissected middle- and low-mountain country, within which the surface of the watersheds descends from elevations on the order of 1200–1400 to 400–450 m. Many features of the relief clearly reflect the characteristics of the geological structure. On unstable rocks, a smoothed relief with broad valleys develops. Areas where resistant rocks occur occupy elevated parts of the watersheds and are characterized by valley narrowings and more steeply sloping relief. Valleys, or separate segments of them, are often laid along zones of tectonic disturbances. On the watersheds such zones are recorded as lowered and broad saddles, which may suggest the existence of ancient valleys.

In the river valleys, terraces with an alluvial cover of varying degrees of preservation can be traced. Our investigations as a whole confirmed A. S. Kirillov’s scheme of valley structure, supplementing it by subdividing the IV above-floodplain terrace into two independent terraces. Taking this into account, in the valley of the Kiya River, along the segment from the settlement of Makarak to the mouth of the Kundat River, the following terraces are distinguished, combined into two complexes: the lower—floodplain, and the I, II, and III above-floodplain terraces with heights of 3–4 m, 6–8 m, 10–15 m, and 20–30 m; and the upper—the IV, V, and VI above-floodplain terraces.

with heights of 125–130 m, 140–150 m, and 170–180 m. Upstream, the relative heights of the terraces decrease, and in the headwaters of the tributaries of the Kiya River their levels often almost merge with the modern valley floors. Besides the floodplain, which is absent only in rare constrictions of the valley of the Kiya River, the terraces of the upper complex are widespread. These terraces, together with the slopes resting upon them, form a clearly expressed tier of relief that can be traced almost everywhere. Upstream, the terraces regularly increase their absolute elevations and, within the middle mountains, nowhere extend beyond the outlines of the valleys expressed in the modern relief; this gives grounds for speaking of the absence of reorganization of the erosion network of the Mariinskaya taiga, beginning with the epoch of formation of the alluvium of the upper terrace complex.*

Above the level of the sixth terrace, 10–40 m higher, along the sides of large valleys, even, almost horizontal platforms are encountered in places, forming two steps which apparently represent remnants of valley floors, presumably of Paleogene–Neogene age. In addition to these relief elements, confined to modern valleys, an even higher planation surface is distinguished, not always connected with the outlines of the modern hydrographic network, which, as will be shown below, can also be regarded as a remnant of an ancient drainage network.

As an example of a remnant of an ancient valley at the level of the upper terraces, reference is usually made to the Kedrovka saddle (the watershed of the Voskresenka River and the Levo-Troitskaya River). It is believed that, during the formation of the alluvium of the upper terraces, the Talanovka River flowed through this saddle. In support of such an idea the following evidence is cited: a) in the lower stretch of its course, where the Talanovka River makes a sharp turn to the right, its valley narrows abruptly and the upper terraces disappear; b) on the direct continuation of the middle course of the Talanovka River there is a morphologically expressed meridional depression, to which the broad valley of the Levo-Troitskaya River is confined, as well as lowered watersheds and saddles situated farther north (the Kedrovka saddle, Maiskoe field); c) on the site of one of these saddles lies the buried Kedrovka placer, the gold-bearing bed of which, according to I. Korovin, is confined to “ancient alluvium.”

The valley of the Talanovka River does indeed narrow sharply in its lower stretch, but here too slope breaks are usually noted at the level of the terraces of the upper complex, and near the mouth, at a height of about 50–60 m above the river—that is, at the level of the IV floodplain terrace—an alluvial pebble bed with weakly weathered pebbles has been encountered. The narrowing of the valley is connected not with a young capture, but with the fact that the river, leaving an area of easily eroded Cambrian carbonate rocks, cuts into resistant Devonian volcanogenic rocks. Upstream along the Levo-Troitskaya River, i.e., in the direction of the supposed flow of the ancient Talanovka, the absolute elevations of the upper terraces increase (Fig. 1), as is observed in normal valleys, and there is no basis for assuming that the alluvium of these terraces was formed by the watercourse of the proto-Talanovka.

Consequently, analysis of the geomorphological structure does not allow the valley of the Talanovka River at the level of the upper terraces to be “extended” through the valley of the Levo-Troitskaya River and the Kedrovka saddle.

This conclusion is also confirmed by the study of the unconsolidated deposits lying on the Kedrovka saddle. Here (Fig. 2) a thick sequence of sediments is exposed, subdivided into three horizons: 1) loams and sandy loams, predominantly brownish-gray, with durable gruss of shales and porphyrites, about 1 m thick; 2) clays and loams, brown—

* The territory meant is that which encompasses the basin of the Kiya River above the mouth of the Bol. Kozhukh River, as well as the right bank of the latter.

Longitudinal profile along the valleys of the Talanovka and Levo-Troitskaya rivers and Kedrovskii Log

Fig. 1. Longitudinal profile along the valleys of the Talanovka and Levo-Troitskaya rivers and Kedrovskii Log.

1 — terrace surfaces with alluvium of varying degrees of preservation; 2 — above the river’s edge; 3 — IV above-floodplain; 4 — V above-floodplain; 5 — VI above-floodplain; 6–8 — upper remnants of ancient valleys, lacking an alluvial cover; 6 — predominantly of Paleogene–Neogene low-mountain levels; 7 — predominantly of Paleogene–Neogene high-level surfaces; 8 — of presumed age; 9–12 — elevations of modern terraces and planation surfaces (probable remnants of the floors of ancient valleys) above the river’s edge according to data from: 9 — maps; 10 — the party of A. S. Kirillov; 11 — the Mariinsk expedition of the WSGU; 12 — the Mariinsk party of TsNIGRI; 13 — terrace surfaces with observed pebble alluvium.

Fig. 2. Geological section across the Kedrovka saddle

1 — deluvial deposits: gray and brown sandy loams and loams with rubble; 2 — deluvial–alluvial deposits: brownish-brown clays and loams with weathered rubble; 3 — deluvial–alluvial deposits: red-brown and ocher-yellow clays and loams with weathered rubble and concretions of iron and manganese hydroxides; 4 — loose weathering products; 5 — Devonian volcanogenic rocks; 6 — limestones; 7 — gold-bearing shales; 8 — barren; 9 — traces—100 mg/m³; 10 — 100–500 mg/m³; 11 — more than 500 mg/m³.

reddish-brown and ocher-yellow, with fragments of schists and porphyrites in varying degrees of weathering; thickness up to 25 m; 3) red-brown, brownish, and ocher-yellow clays and loams with the same kind of rubble as in horizon 2, thickness up to 20 m. The entire sequence is characterized by considerable clay content, poor roundness of the fragments, and uniformity of their composition. The composition of the clastic material in the loose sequence is determined by the composition of the local bedrock. It is precisely this that explains both the uniformity of their composition as a whole and the differences observed in the composition of the fragments along the western and eastern sides of the saddle. On the western side, where schists are developed, the fragments consist mainly of schists and quartz; whereas on the eastern side, adjoining a slope composed of porphyrites, fragments of porphyrites predominate in the loose sequence and fragments of quartz are absent. Thus, the general character and features of these deposits, and the conditions of their occurrence (they form broad aprons), distinguish them markedly from the pebble alluvium of the upper terraces of the Talanovka River and indicate their deluvial nature.

In a prospect pit near the saddle, in the lower part of the loose deposits, I. Korovin in 1948 noted “strongly clayey pebble beds and sands, accompanied by clastic material of igneous and sedimentary rocks and quartz of varying degrees of roundness,” which he regarded as ancient alluvium. Study of the core from boreholes drilled by the Martaiga expedition of the WSGU in 1966 near the prospect pit showed that, in fact, deluvial clays and loams are developed here, saturated at the very base with weakly rounded rubble of schists, porphyrites, and angular fragments of quartz, and evidently representing hollow formations. It may therefore be assumed that the deposits exposed by the above-mentioned prospect pit were also of the hollow type. North of the saddle, i.e., down the Kedrovsky log, the character of the deposits changes slightly: the fine-earth component becomes coarser and more sandy; the clastic material is sometimes concentrated into separate, clearly distinct layers; the degree of roundness of the fragments increases somewhat. Here the deluvial deposits begin to alternate with deluvial-alluvial (hollow) deposits. Yet even here their general features are preserved, features characteristic of the loose deposits of the saddle (weak roundness of the fragments, uniformity of their composition, its dependence on the rocks of the nearby slopes, and the generally considerable clay content of the deposits).

Similar deposits are also developed on the southern slope of the Kedrovsky saddle, in the hollow of the Levo-Tronitskaya River basin.

Thus, the deposits considered are characterized by features inherent in deluvial and deluvial-alluvial (hollow) sediments. Very rarely do well-rounded pebbles, gravel, and quartz grains with a shiny, polished surface occur in them, which sharply distinguishes them from the main mass of pebbles and grains contained in Quaternary deposits. These “polished” pebbles and grains have been redeposited from more ancient sediments, now eroded, and therefore the presence of such formations cannot serve as a basis for assigning the enclosing deposits to alluvium.

As for the Kedrovsky placer, as can be seen from the plan (Fig. 3), it is confined to the narrow bottom of a buried log, the contours of which as a whole are repeated by the modern log. The productive part of the placer is surrounded by a halo of weak gold content, and it is widest along the left side, where there is a zone of intensely silicified rocks with which the “Zolotaya Gorka” ore occurrence is associated. Assay data from boreholes drilled here by the Martaiga—

PLAN OF THE AURIFEROUS PLACERS
OF THE KEDROVSKY AREA

Conventional symbols

• Porphyrites
• Limestones
• Shales
• Zone of intense [[unclear: alteration/impregnation]]
• Gorda gold ore occurrence
• Auriferous placers:
• a — alluvial
• b — terrace
• c — ravine
• Outline of areas of non-industrial gold content
• Contours of the present-day surface (contour interval 25 m)
• Contours of the bedrock-relief surface (contour interval 5 m)
• Exploration workings
• Line numbers

Fig. 3.

by the expedition of the WSGU, show quite clearly that the removal of gold occurred precisely from this side. On the saddle itself no commercial placer has been found; only weak gold content is noted there. A new enrichment of gold up to commercial grade is observed in the right headwaters of the Levo-Troitskaya River near the settlement of Pervomaiskii, situated within the same zone of quartz-veined rocks.

Thus, here the connection of the placer with the logs is clearly observed, as is the dependence of their distribution on the position of the primary sources.

The close spatial connection of the placer of Kedrovskii Log with the local primary sources is also confirmed by the character of the gold itself. The gold in the placer of Kedrovskii Log, according to I. P. Beresnevich (1912) and I. Korovin, is predominantly coarse, unrounded, and often intergrown with quartz. According to an oral communication by M. S. Budylin, it resembles the gold from the “Zolotaya Gorka” ore occurrence. Laboratory study of the gold by S. V. Yablokova confirmed its similarity to the gold of the indicated ore occurrence, and also showed that the gold had undergone almost no secondary transformation and had preserved its primary structure; consequently, it cannot be considered ancient. “Ancient” gold transported from afar has not been found, which indicates either its complete absence or that its role in the formation of the placer was negligible.

Observations carried out by us on other saddles, which were also regarded as remnants of ancient valleys (Zimoglyadov et al., 1968), showed the absence of alluvium on them. We were able to judge the nature of the loose formations on these saddles from dumps of old shafts, working cuts, and drill cores (the divide of the right tributary of the Talanovka River with Topki Creek, belonging to the basin of the Bayanzas River), and from excavations for the railway roadbed (a saddle in the upper reaches of Novyi Creek). In all these cases, the Quaternary deposits on the saddles are represented by deluvial brown loams with unrounded or weakly rounded fragments of local rocks, which toward the watercourses pass into deluvial-alluvial (trough) deposits differing little lithologically from the deluvial ones. The thickness of these loams usually does not exceed 2–4 m. Beneath the Quaternary loams, in places, a weathering crust of bedrock was exposed, in some cases (the saddle of the Talanovka River and Topki Creek) apparently brecciated in the zone of tectonic disturbances or in karst sinkholes.

As noted earlier, within the study area the highest level is distinguished, not always connected with the plan of the modern hydrographic network. Remnants of this level are traced along the sides of the valleys of the Kiya River and its large tributaries, as well as on saddles and low watersheds outside the valley outlines. A. S. Kirillov and other researchers noted well-rounded quartz pebbles, and sometimes pieces of conglomerates with limonite cement, on leveled areas of the watersheds of the tributaries of the Berikul River and the Nikol’ka Moskovskaya River, apparently belonging to this level. The presence of well-rounded quartz pebbles permits them to be regarded as a remnant of the floor of an ancient valley. Limonite cement and pebbles mainly of resistant rocks are noted in the Cretaceous deposits of adjacent territories. This gives some basis for considering the level in question—on which pieces of conglomerates with limonite cement and quartz pebbles were found—to be Cretaceous. According to A. S. Kirillov, brightly colored clays, weathered pebble beds, and quartz sand exposed along the Talanovka River in the area of the settlement of Semenovka at a height of 130 m above the river presumably also belong to the Cretaceous.

The rounded pebbles and grains of quartz with a polished surface mentioned in the description of the Kedrovka saddle may, with a certain degree of conditionality, be attributed to rewashed remnants of Cretaceous (?) alluvium. Individual “polished” pebbles and grains of quartz were encountered not only in the area of the Kedrovka saddle, but also in the channel of the Levo-Troitskaya River and in the valley of the Talanovka River near Zakharevka, in deposits of the second floodplain terrace. They are especially abundant in slope and trough deposits on the left bank of the Talanovka, in the quarries of Sukhoi Log and Spornyi-I. Consequently, the localities where redeposited pebbles and quartz grains have been found lie within the contours of the depression of the so-called ancient valley of the Talanovka River, to which the meridional segment of the valley of this river and its continuation northward through the Levo-Troitskaya River and the Kedrovka saddle are confined. Therefore the indicated depression may be regarded as a remnant of an ancient (presumably Cretaceous) river valley associated with this high level.

While recognizing the presence of a partial reorganization of the drainage network in the earliest stages of relief development, we consider it necessary to emphasize that, with the exception of the single example in the Semenovka area, Cretaceous (?) deposits are nowhere observed in the mid-mountain part of the Mariinsk taiga. They are absent on the saddles considered above, and also on the leveled surface of the Mayskoe Field, through which a valley of presumably Cretaceous age may have passed. Here, boreholes of the Martaiga Expedition of the ZSGU penetrated a thin (no more than 1.5 m) cover of deluvial loams overlying limestones and the weathering crust of scattered porphyritoids.

Conclusions

1. There was no reorganization of the erosional network in the mountainous part of the Kiya River basin at the level of the upper terraces. A depression expressed in the relief, extending through the valleys of the Talanovka and Levo-Troitskaya rivers, and a number of lowered saddles are a relic of a more ancient (presumably Cretaceous) valley. Deposits associated with this valley have been almost entirely destroyed by subsequent denudation.

2. In the areas of the saddles, deluvial and deluvial-alluvial (trough) deposits are developed, with which, where primary sources are present, trough gold placers are associated.

3. Owing to the relatively small dimensions of the trough placers and the indicated limitations in the conditions of their formation, the prospects of such placers cannot be rated very highly.

4. The close connection of trough placers with local sources of supply makes it possible to localize the search for primary gold deposits.

Literature

1. Beresnevich I. P. Report on the statistical-economic and technical study of the gold industry of the Tomsk Mining District. SPb., 1912.

2. Dubinkin S. F. On pediments and gold-bearing placers associated with them. In: Problems of the Geology of Gold Deposits of Siberia, Proceedings of the Tomsk Polytechnic Institute, vol. 134, 1968.

3. Zimoglyadov B. N., Popova L. N., Shpaikher E. D. Prospects for the gold content of deposits of ancient valleys of the Mariinsk taiga of the Kuznetsk Alatau. In: Problems of the Geology of Gold Deposits of Siberia, Proceedings of the Tomsk Polytechnic Institute, vol. 134, 1968.

4. Mirchink S. G. Ancient valleys and gold-bearing placers associated with them, based on examples from the Patom Upland, the Yenisei Ridge, and the Kuznetsk Alatau. Transactions of the NIGRIzoloto Institute, issue 16, 1947.