HYDROGEOLOGICAL CONDITIONS OF THE OSINNIKI COAL DEPOSIT IN KUZBASS

G. A. Plevako

(Presented by the scientific seminar of the Department of Hydrogeology and Engineering Geology)

The Osinniki deposit in the Kuznetsk Basin has large reserves of high-quality coking coals. It is located in the southeastern part of the basin, within the interfluve of the Tom and Kondoma rivers.

Geomorphologically, the area is a piedmont plateau, sharply dissected by the erosional activity of the river network. The relative elevations of positive landforms above river valleys reach 150–200 m.

The geological structure of the deposit includes continental coal-bearing sandy-clayey deposits of the Kolchugino series \((P_1—P_2)\) and conglomerate-sandy-clayey sediments of the conglomerate suite of Jurassic age \((J_{1—2})\). Jurassic and Paleozoic deposits are everywhere overlain by Quaternary sediments of insignificant thickness.

The productive deposits of the Ilyinka suite \((P_2)\), with a total thickness of 1300 m (Kostomanov, 1956), are represented by frequently alternating sandstones, siltstones, argillites, coals, and sometimes thin interbeds of siderites.

The deposits of the conglomerate suite, lying unconformably on the coal-bearing sediments of the Paleozoic, are composed of conglomerates (48–55%), sandstones (6–10%), siltstones, argillites (25–35%), and brown coals (3.9–4.3%). The established thickness of the suite is 550 m.

A characteristic feature of the Jurassic deposits is their facies variability. Relatively persistent both in section and along strike are beds of conglomerates with interbeds of sandstones (from top to bottom) between the coal seams Verkhnii and Moshchnyi, Moshchnyi and Srednii, Srednii and Nizhnii, Nizhnii and Novyi. The thickness of the beds in individual sections reaches 60–80 m. Siltstones and argillites usually make up the floor and roof of the brown-coal seams. Thus, in the section of the Jurassic deposits there is a fairly distinct alternation of coarse-grained and clayey varieties of rocks.

Tectonically, the productive deposits of the Ilyinka suite form the Shchelkan syncline of northeastern strike. The fold is sharply asymmetrical, with a steep (up to 70–85°) western limb and a gentle (10–30°) eastern limb. The steep western limb of the syncline, in places overturned to the east, is complicated throughout its length by a number of additional folds, which, together with widely manifested dislocations, give it a complex structure.

Jurassic sediments, apparently in the Late Kimmerian phase of folding, underwent weak plicative dislocations. The Podobass syncline, formed by Jurassic rocks, repeats the Paleozoic structure.

There is no unequivocal opinion regarding the presence of tectonic faults in the Jurassic sequence. In 1938, V. V. Stanov, on the basis of a rupture disturbance observed by him at the contact of the Jurassic with the Paleozoic in one of the adits, argued for the presence of disjunctive disturbances in deposits of Jurassic age. On the basis of exploration-drilling materials from recent years, G. M. Kostomanov (1956) came to the conclusion that they are absent from the Jurassic sequence.

The data we analyzed from the primary documentation of boreholes drilled in Jurassic deposits with core recovery made it possible to establish, in the Jurassic deposits, a large number of slickensides, planes of friction, and small zones of crushing and brecciation, which are mainly confined to areas with the most intense folding and rupture structures of the Paleozoic rocks of the western limb and the hinge part of the Shchelkan syncline. It was also established that, in the contact zone, Paleozoic and Jurassic rocks are intensely crushed: clayey varieties of rocks have been altered to the state of clays, and conglomerates are completely decemented. The thickness of the weakened rocks in the contact zone varies within the range of 2–22 m. A microfault of the type of a conformable reverse fault with an amplitude of 0.25 m was encountered in a coal seam of Jurassic age during the driving of drift No. 2 in the field of the Kapitalnaya-2 mine. Systems of tectonic cracks and microfaults in Jurassic sandstones were established on the Tarbagan area, which is the northern continuation of the Shchelkan syncline.

The factual material presented provides grounds for agreeing with V. V. Stanov’s opinion on the presence, in the Jurassic sequence, of small tectonic faults and intensely crushed zones, especially in the contact zone with Paleozoic deposits in areas where large disjunctives emerge beneath the Jurassic rock complex.

In terms of structural-lithological, facies, and hydrogeological features, the water-bearing rocks in the district are subdivided into three aquifer complexes, characterized by specific conditions of occurrence, movement, and formation of groundwater.

The first aquifer complex includes the coal-bearing continental sandy-clayey deposits of the Kolchugino series ($P_1$—$P_2$), with the development of fissure and fissure–bed waters. Within the deposit, the complex fully includes the productive deposits of the Ilyinka suite ($P_2$). The deposits of the Ilyinka suite as a whole are characterized by uneven and low water content.

The fissure waters of the productive formations have been studied in 80 boreholes, 100 springs and wells, and in the mine workings of four mines. Groundwaters actively migrating in the rocks and determining inflows into mines are concentrated mainly in the upper part of the section, where the water-bearing rocks have been affected by weathering and have open fracturing.

The zone of intensive water exchange, confined to the upper part of the section, has an average thickness of 100–120 m. Within this zone, the specific yields of boreholes vary from 0.002 to 5 l/sec; the average values are 0.1–0.15 l/sec.

In the productive deposits of the Ilyinka suite, three groups of coal seams are distinguished: the Polkashino, Kandalep, and Elban. The rocks enclosing the Polkashino coals are characterized by increased water content. Here sandstone beds 30–40 m thick predominate, interbedded with clayey rock packets enclosing the coal seams. Fissure–bed waters in the Polkashino sandstones—

have heads of more than 100 m, especially in the valleys of the Kandaleps and Talzhina rivers. The specific yields of wells are 0.15–0.25 l/s. In the zone of influence of the mines the waters are nonartesian, and in individual areas they have been drained to the level of the lower horizons.

The rocks of the Kandaleps and Elban groups of coal seams are somewhat less water-bearing, especially over a considerable area where they are covered at the surface by a Jurassic complex of deposits of considerable thickness, more than 50–60 m.

In general, the productive deposits are characterized by increased water abundance in river valleys and chiefly at the mouths of the Chernaya, Talzhina, and Kandaleps rivers and in the valley of the Tom River. In the northwestern part of the Kapitnalnaya-III mine field, in the area of exploration lines XVII–XX, wells (1163, 1198, etc.) encountered pressurized, self-discharging waters in sandstones of the Polkash tinskii and partly Kandaleps sequences. The specific yields of the wells exceeded 5–6 l/s, and in the area of the reinforced-concrete products plant at the Talzhina railway station the specific yield of a hydrogeological well was 31.8 l/s.

In the area noted, the Paleozoic rocks are overlain by a thin layer (up to 20–30 m) of Jurassic weathered and water-bearing conglomerates and sandstones. In the valley of the Tom River, the productive and Jurassic deposits are overlain by alluvial sandy-pebbly formations, which have high water abundance. Wells 106, 58, 115, 120 had specific yields of 5–7 l/s. The waters of the alluvial deposits have an excellent hydraulic connection with the groundwaters of the productive and Jurassic formations. Therefore, mining of the Polkash tinskii and Kandaleps coal seams in the northwest of the Kapitnalnaya-III mine field will take place under especially complex hydrogeological conditions.

Observations of the water abundance of rocks in mine workings indicate that the groundwaters are associated with open fractures. Water inflows into mines are formed in places where mine workings intersect zones of disturbance and regional-type fractures connected with the ground surface, especially beneath the valleys of rivers and ravines. During mining of the Polkash tinskii seams on the eastern limb of the Malaya Kandaleps syncline beneath the alluvial deposits of the B. Kandaleps River, water inflows into the dip heading of mine 4 reached 50 l/s, which exceeded the usual rates in other workings by 8–10 times. Similar conditions were observed during coal mining beneath the valleys of the Talzhina, Bukanai, and Polkash ta rivers. Water inflows are often sudden, when static reserves of groundwater are discharged along disturbance zones emerging beneath water-bearing Jurassic deposits or alluvial formations in river valleys.

In the zone of slow water exchange at depths greater than 100–120 m, open fracturing of the rocks dies out and the water abundance of the productive deposits decreases sharply. In the mine workings of the Osinniki Mine Administration at the +40 and −60 horizons the rocks are practically dry, and coal mining is carried out with forced spraying of the faces. With a total inflow of groundwater into the Kapitnalnaya-I mine of 350 m³/h, 60–90 m³/h is accounted for by workings on the −60 horizon. In this case the water enters mainly from Jurassic rocks during their underworking, and also along mined-out seams from the upper horizons.

During construction of the Kapitnalnaya-III mine (1956–1958), despite the abundance of small disturbances at the +100 horizon (depth 150–200 m), the total inflow into the mine was 8–15 m³/h; many workings were completely dry. Water inflows began to increase only after roof collapse of the lavas and the development of subsidence zones in the Jurassic water-bearing deposits.

In studying the water abundance of coal-bearing deposits in the mine field-

of the Kapitalnaya-III mine under the Jurassic rocks established that, in the interval of 160–250 m, they proved to be practically waterless. The specific yield was 0.004 l/s; from the overlying Jurassic formations, pumping showed a specific yield of 0.96 l/s and an almost complete absence of hydraulic connection with the waters of the underlying Paleozoic rocks. Consequently, the coal-bearing formations at the deposit are weakly watered, except in river valleys, where complications may arise during mining.

The second aquifer complex is associated with the Jurassic formations, which unconformably overlie the productive rocks. Their greatest thickness is observed in the central part of the Shalkan syncline, formed by the coal-bearing sediments of the Ilyinka suite.

At present all mines of the Osinniki mine field work coal seams mainly beneath the Jurassic complex of rocks. The Jurassic formations are watered everywhere, but the water abundance of the water-bearing rocks is uneven. As with the rocks of the first aquifer complex, the Jurassic deposits have increased water content in the zone of intensive water exchange, the thickness of which exceeds 170–180 m. In the upper part of the section, down to 80–100 m, sandstones and conglomerates are often strongly weathered and have high water saturation through pores and open fractures. In the valleys of ravines and small rivers, the specific yields of wells, as a rule, do not fall below 0.8–1.5 l/s and often amount to 2–5 l/s. This has been established from numerous wells and mine workings. In the valley of the Kalandas and Kandaleps rivers, groundwater is used for the water supply of the mine complex and the town of Osinniki. The productivity of individual wells reaches 50 l/s at drawdowns of 3–4 m. However, very often the specific yields of wells, even in valleys, vary from hundredths to tenths of a liter per second, which demonstrates the uneven watering of the rocks due to their facies variability and heterogeneous weathering in the upper part of the section.

The waters are often artesian, especially in the lower reaches of small rivers and in the valley of the Tom River. The magnitude of the heads varies from 8.0 to 172 m (Sukhopolsky, 1964) and depends on the degree of permeability of the confining interbeds of argillites and siltstones. In wells that have encountered water in valleys, self-flow is most often observed.

During the sinking of shaft No. 2 at the Kapitalnaya-III mine in 1958, the water inflow from conglomerates at a depth of 50–70 m reached 70 m³/h, and into shaft No. 4 in 1968 it was 200–250 m³/h. Thus, in the upper part of the section, Jurassic conglomerates and sandstones often have high water content within intervals of intense rock weathering. In areas with development of silicified conglomerates and strong sandstones, the water content is low and not infrequently amounts to fractions of a liter per second.

In the deep parts of the section, in the zone of retarded water exchange, the conglomerates and sandstones have a dense structure and mainly a closed type of fractures, while the clayey formations with brown coals that separate them may be regarded as practically impermeable.

In 1965, in different parts of the Osinniki deposit, we drilled groups of wells for interval-by-interval testing of the water abundance of the conglomerates and sandstones of the Jurassic deposits down to their contact with the productive deposits (12 groups of three wells). It turned out that the middle and lower beds of conglomerates and sandstones are exceptionally weakly watered, although the waters have a high head (more than 150–200 m). At depths from 140–150 to 200–270 m, the specific yields of wells varied from 0.037 to 0.01 l/s at drawdowns of 30–60 m. The filtration coefficients in the tested intervals, as a rule, are below 0.1 m/day.

In the intervals from 210–290 to 300–450 m, in the presumed lower

in the aquifer of the Jurassic deposits, the specific yields in wells varied from 0.002 to 0.0008 l/sec, and the filtration coefficients were of the same orders. The hydraulic connection between the aquifers in the section is very weak.

The operating water intakes testify to the extremely impeded hydraulic connection between the highly water-bearing aquifers in the upper parts of the section and the low-water-bearing ones in its middle part and lower parts. In the valleys of the Maly and Bolshoy Kandalep rivers and the Talzhina River, since 1952 there have been 9 water-intake wells in operation, continuously using groundwater from conglomerates and sandstones of the upper aquifer with an average discharge of 200–250 m³/hour. These water intakes have been undermined by the Kapitalnaya I, Kapitalnaya II, and Mine 9 mines at various depths. The smallest undermining depth is 150 m under well 398 in the field of Mine 9. Despite the drainage of the lower aquifers into the mine workings, the upper and middle ones remain “suspended,” and their waters are used for a permanent water supply.

In the field of the Kapitalnaya I mine there is a large number of wells obtaining water from the first aquifer. The lower horizons, however, have been drained by the mines. At the experimental hydrogeological cluster, well 1416a exposed an aquifer in conglomerates in the interval 223–285 m before the contact with the productive deposits. Before pumping, the well had been undermined by longwall 261, and the conglomerates were drained for a week without noticeable water inflows into the longwall. Wells 1415 and 1416 exposed the first and second aquifers, which showed almost no response to the drainage of groundwater from the lower member.

Despite the low water content of the Jurassic rocks in the middle and lower parts of the section (at depths from 200 to 500 m), sudden breakthroughs of groundwater into mine workings are observed from the area of contact with the Jurassic deposits. It has been established that Jurassic conglomerates and sandstones in depressions of the Paleozoic relief and in areas of major and minor faults affecting the productive rocks at the contact with the Jurassic are often crushed and recemented to the state of talc and sand. Such collectors have repeatedly been exposed by wells and mine workings, with confined waters found in them. Isolated collectors contain certain static reserves of groundwater, which are rapidly discharged into longwalls when zones of caving and subsidence spread into the Jurassic rock complex. The severity of a sudden breakthrough will depend on the capacity of the isolated local collector.

From 1957 to 1968, 12 sudden breakthroughs of groundwater from Jurassic deposits occurred: two at the Kapitalnaya-I mine, six at the Kapitalnaya-II mine, and four at the Kapitalnaya-III mine. Water inflows during sudden breakthroughs into longwalls amounted to 100–250 and only into longwall 271 of the Kapitalnaya-I mine—500 m³/hour. The breakthroughs are, as a rule, short-lived. The greatest inflows persist for 1–2 days, and in some cases for several hours. Then their discharges gradually decrease and stabilize.

Thus, the waters of the Jurassic deposits are dangerous when they are undermined by mines not only within the upper, highly water-bearing horizons, but also at the contact with the Jurassic formations at depths of 200–500 m. Mining operations are especially complicated on the northern limb of the Kapitalnaya-III mine at the main horizon +100, where there is a constant threat of water breakthrough from the Jurassic deposits composing the upper part of the section.

The third aquifer complex is associated with deposits of Quaternary age. The widespread eluvial-deluvial formations, having a clayey composition, have low water content and are of no practical interest. High water content within the composition

the complex are alluvial deposits in the valleys of the Tom and Kondoma rivers. Their average thickness is 8–9 m; filtration coefficients reach 100 m/day. In the sandy–gravel deposits of the terraces, powerful groundwater flows have been established; these are used for water supply and will create substantial complications during the development of mining operations beneath these valleys.

The main direction of groundwater movement in the upper part of the section is from the watersheds toward the river valleys and into depressions. Hydroisohypses and piezoisohypses repeat the relief of the terrain to some extent. This indicates that the groundwater within the deposit area is recharged by atmospheric precipitation. The role of remote recharge areas is exceptionally small.

For the successful extraction of coal seams beneath river valleys and water-saturated Jurassic rocks, it is necessary continuously to determine the hydrogeological conditions in the rock complexes being undermined and to take appropriate measures depending on the circumstances.

REFERENCES

1. G. M. Kostomanov. New data on the stratigraphy and tectonics of the Osinniki district of Kuzbass. Problems of the Geology of Kuzbass, vol. 1, 1956.