SOME FEATURES OF THE TECTONICS OF THE FIELD OF THE “TSENTRALNAYA” MINE IN THE KEMEROVO DISTRICT OF KUZBASS

Yu. N. Popov

(Presented by the Department of Geology and Exploration of Mineral Deposits)

The “Tsentralnaya” mine is one of the oldest in the Kemerovo district of Kuzbass. The beginning of production work in its field dates to 1908–1910. A number of major researchers—M. A. Usov [5], V. I. Skok [4], and S. S. Rumyantsev [3]—studied the tectonics of this field, but about 30 years have passed since the publication of their works. During this time the mine workings have descended to deeper levels (260–300 m). The accumulated materials of mine geology and geological-exploration work, as well as the results of special structural observations, make it possible to examine the tectonics of the field of the “Tsentralnaya” mine on a more modern basis.

The productive deposits of the Kemerovo subseries worked by the mine may, by lithological composition, be divided into two units of approximately equal thickness: the upper, including the main workable seams of the field, Kemerovsky and Volkovsky, is composed essentially of sandstones; the lower, containing the group of Lutuginsky seams, is represented predominantly by rocks of clayey varieties. The boundary between these lithological stages passes along the Vladimirovsky seam.

The Kemerovo district is situated between the consolidated folded structure of the Kuznetsk Alatau in the east, which played to some extent the role of a buttress, and the younger structures of the Tomsk–Kolyvan arc in the northwest, from whose side the stress was directed. This accounts for the marked asymmetry of the district’s tectonics, with a gradual complication of structures in the western and southwestern directions. In connection with this, A. A. Belitsky and E. M. Pakh [2] distinguished three tectonic subzones in the area described:

a) the near-Kuznetsk-Alatau subzone;

b) the subzone of relatively gentle folds, which inherited the extension of the folds of the Kuznetsk Alatau;

c) the subzone of intense linear folding and faults.

Being located in the middle part of the explored western limb of the Kemerovo syncline, the field of the “Tsentralnaya” mine belongs to subzone “c.”

The formation of the structure of the mine field under consideration, as of the entire Kemerovo district, took place under conditions of a complex three-dimensional stress state.

The main structural element of the field is the western limb of the Kemerovo syncline, dipping to the southeast at an angle of 40–60°, complicated by additional folding and by disjunctive disturbances of various orders (Fig. 1).

The largest second-order structure, which chiefly determines the structure of the mine field, is a complete fold, traceable through almost the entire field and, along its whole extent, considerably complicated by fold-fault B (Fig. 2). The axes of its syncline and anticline are, in general, parallel; they plunge to the southwest at an angle of 5–12°, and here, as throughout the western limb of the Kemerovo syncline, the direction of the axes of second-order folds approaches the submeridional direction, which corresponds to the direction of the axis of the main Kemerovo syncline. Their axial planes are vertical or dip steeply to the west. In the northern part of the mine field, on the hanging-wall side of fault B, the complete fold is, in general, symmetrical, with limb dip angles of 30–45°. On the footwall side of the dislocation, in the immediate vicinity of the fault plane, a sharp torsion of the fold limbs is observed, where their dip angles reach 70°, and in places overturned bedding is recorded. The general character of the fold becomes simpler southward: the dip angles of the limbs decrease, the hinges become gently inclined and cylindrical, and finally, in the southern part of the mine field, the fold dies out completely.

Fig. 1. Combination of structural forms of different orders. Structural map of the Kemerovo seam.
1 — floor contours of the seam; 2 — footwall and 3 — hanging-wall cutoffs of the seam in the walls of the disjunctive disturbance; 4 — small disjunctive disturbances; 5 — fold axes; 6 — lower boundaries of seam extraction.

The western limb of the Kemerovo syncline is affected by a series of fairly large tectonic faults, among which reverse faults predominate; their characteristic feature is their close connection with folding. The mechanism of formation of reverse faults, rarely encountered in other areas of Kuzbass but very characteristic of the Kemerovo area, deserves attention. The formation of reverse faults has been explained differently by various researchers (M. A. Usov, A. S. Zabrodin, and others). We are inclined to believe that the process by which these faults arose is distinguished by great complexity and peculiarity, determined by the tectonic setting of the Kemerovo area. In explaining the formation of reverse faults, it is necessary to take into account a number of their characteristic features: 1. Reverse faults in the Kemerovo area are known only on the limbs of folds whose dip coincides with the direction of pressure; on the opposite limbs, concordant—

Fig. 2. Character of second-order structures. Sections along exploration lines:

• III exp. line
  Labels: NW; SE; Kemerovo seam; Volkov seam; Vladimir seam; “b”; elevations/points: 330, 334, 325, 2403; \(+0\).

• V exp. line
  Labels: NW; SE; K-4; Kemerovo seam; Volkov seam; Vladimir seam; Luthugin seam; “b”; elevations/points: 318, 338, 729, 2334; \(+0\).
  Scale: 100 — 0 — 100 — 200 — 300 m.

• IX exp. line
  Labels: NW; SE; K-3; Kemerovo seam; Volkov seam; Vladimir seam; Luthugin seam; “b”; elevations/points: 2335, 206, 2401; \(+0\).

reverse faults, but correlating them according to M. A. Usov’s scheme [5], because of the small amplitudes of the faults and the large sweep of the fold limbs, will not always be correct, although classical forms are sometimes encountered. 2. The angles formed by the planes of the displacer and of the seams remain approximately the same in all fields of the district. 3. Where the seams are gathered into folds of the second order, straight thrusts, as a rule, also have a folded character—plicatogenic according to V. I. Skok [4]. 4. The displacement amplitude along these faults rarely exceeds 100 m. 5. Being almost conformable and having small displacement amplitudes, straight thrusts not associated with folds almost lack rotations of the seams at the displacer and zones of small tectonic ruptures.

All these features indicate that the overwhelming majority of straight thrusts were initiated at early stages of folding, in a rather simple tectonic setting, and subsequently some of them underwent considerable complication. In their initiation, the principal role was apparently played by the bedding and fracturing of the rocks, as well as by the physicomechanical conditions in the deformed strata.

The complexity of the formation of these ruptures was reflected especially clearly in folded straight thrusts, a typical representative of which is fault Б in the field of the Tsentralnaya mine. The displacer Б, like the coal-bearing deposits ruptured by it, forms an anticlinal and a synclinal fold, parallel to the folds of the coal seams (Fig. 2). As a result, complex relationships arise between the displaced parts of the seams, and the fault changes its form from an oblique reverse fault to a straight thrust. The multiphase character of the formation of the disjunctive was reflected in a considerable complication of the structure of the coal-bearing strata on its flanks, which led to an increase in the intensity of the folds, the appearance of a group of small faults, and the formation of a fairly thick zone of crushed rocks under the discordant bedding of the displacer and the limbs. In the southern part of the mine field, where the second-order fold dies out, fault Б assumes the form of a straight thrust, and here all the complications described above disappear.

In addition to disjunctive Б, two rather large tectonic faults of the type of conformable reverse faults have also been noted within the mine field: А is located in the northern part, and Ж in the southern part of the mine field; both affect the lower group of seams.

The formation of a complex second-order structure in the field of the Tsentralnaya mine could not but lead to the occurrence of a large number of small additional folds and faults. Of particular interest is the concentration of these structural forms along the upper group of seams in the northern part of the mine field, between exploration lines III and IV, complicating the crest and limbs of an additional anticline (Fig. 3). Such a picture apparently arose as a consequence of the dying out in this sector of faults А and Б, similar to what was established by A. A. Belitskii in the example of the Kalinin mine in the Prokopyevsk-Kiselevsk district, where a complication of the tectonic structure in places where large faults die out was shown, associated with the formation of a series of small disjunctives and additional folds [1]. In the area described, the crest of the anticlinal fold and its limbs proved to be literally shattered by a whole series of small faults, among which conformable reverse faults predominate; discordant reverse faults are encountered more rarely, and the form of one and the same fault may change along different seams. Mining workings have confirmed the plicatogenic character of some small faults; however, this phenomenon cannot be considered so characteristic as to attach to it such great significance as S. S. Rumyantsev did [3]. In our opinion, faults

here arose both at the early stages of formation of the additional fold and in the process of its subsequent development, in close genetic connection with fault B, especially in the closures of small folds. In the mine field there is also a group of folds of higher orders, associated with the dying out of the main additional fold of the field. In the middle part of the mine field a series of small folds and associated minor faults is recorded, complicating the plicative structure of the second order in the footwall of fault B.

In addition to the structural forms described, small isolated folds and faults occur, usually affecting one seam and not exerting

Fig. 3. Complicated second-order anticline in the hanging wall of fault B. Section along incline 18.

any substantial influence on the overall structure of the mine field and its working.

Since the structure was formed under conditions of tangential compression, and most of the additional faults have a longitudinal character, they all lead to a reduction of dimensions in the direction of pressure, which is achieved by doubling of the fault limbs regardless of its form. This greatly facilitates the search for the displaced limb.

For predicting the tectonic structure, both the spatial and the genetic confinement of zones of enhanced development of minor additional folding and faults to structures of the second order is especially important. The more complex the structure of the second order, the more frequent and more diverse is the manifestation of small tectonic forms.

In the field of the Tsentralnaya mine, the internal structure of coal seams is of interest; it is characterized by fracturing, slaty cleavage, intra- and interbed displacements leading to the formation of pinches and swellings. The presence of two lithological horizons within the mine field caused the formation of two structural levels. Deformation of the more competent rocks of the upper level occurred under different physico-mechanical conditions than in the more plastic rocks of the lower one, where stress relief could take place substantially by means of intra- and interbed displacements.

Our observations of fracturing in the field of the Tsentralnaya mine were carried out mainly in the Kemerovsky seam in the area of exploration lines VI and VII, in the footwall of fault B, on the limbs and in the closure of the additional anticline. A number of observations in the Volkovsky seam showed the identical orientation of the fracture systems of these two seams. It should be noted that the principal seams of the mine field are cut by a fairly dense network of differently oriented fractures (Fig. 4). The study of fracturing under different structural conditions showed—

that the normal-cutting jointing was most distinctly manifested; it is represented here by four systems: longitudinal, transverse, and two diagonal ones. The oblique-cutting jointing is somewhat less pronounced. The gently dipping diagonal strike-concordant system with a dip azimuth of 60–80° is represented best of all. Such a system with a dip azimuth of 140–160° is manifested considerably more weakly. Systems of gently dipping longitudinal joints, both strike-concordant and strike-discordant, are often encountered; systems of steeply dipping longitudinal joints are noted much more rarely. Among the systems of transverse oblique-cutting jointing, one should note a gently dipping system with northerly dip azimuths, which occurs more often than a similar system dipping

329 measurements; 0.5–1.0–2.0–3.0–4.0%

Fig. 4. Character of coal jointing. Diagram of the attitude elements of joints measured in longwall No. 2 of the second section on the southeastern limb of the anticline on the footwall side of fault B.

to the south. Oblique-cutting joints are characterized by the intensive development of striations and even grooving, as well as by a comparatively lower frequency relative to the normal-cutting joints.

It has been noted that the frequency of these or other systems of joints in a coal band is directly dependent on the content in it of coals of bright varieties.

The intensive development of jointing in the strong coals of the Kemerovo and Volkov seams creates favorable conditions during their mining, forming weakened planes that facilitate coal breakage. Thus, in section No. 4, with a dip azimuth of the Kemerovo seam of 275° and a dip angle of 10°, the face of longwall No. 1 is a ribbed surface formed by the intersection of two oblique-cutting systems of joints with dip azimuths of 355° and 170° and dip angles, respectively, of 65° and 70°. The ribs bear intensive striations extending

along the working face; the angles of junction are smoothed. The spacing of these surfaces is 30–50 cm; the coal splits readily along them. When the direction of the working face coincides with the strike of the ribs, coal extraction is considerably facilitated.

Along with the intensive development of fracturing, within the mine field there is widespread development of intraformational displacements, complicating the internal structure of the coal seams. First of all, it is necessary to note here the phenomenon of boudinage of a sandstone parting in the Kemerovo seam, recorded throughout the entire mine field and undoubtedly connected with elongation of the seam (Fig. 6). This could have occurred through bending during formation of the structure, or through flattening due to the normal component of tangential pressure.

On the steep limbs of folds, on approaching fault B, there appears a series of intraseam ruptures of the type of conformable and nonconformable reverse and thrust faults, formed along obliquely cutting fractures; this considerably weakens the stability of the seam and leads to the fall of large blocks of coal into the face area.

Along the second longwall of sector No. 2, a significant swelling of the seam was recorded, associated with a steep fold broken along its hinge by a conformable reverse fault (Fig. 5). We were able to observe this phenomenon even during the approach. The swelling itself, as a result of the low stability of the coal and roof rocks, proved unsuitable for extraction. As a result of the piling up of the coal mass at the site of the swelling, intense platy structure formed,

Fig. 5. Internal structure of the Kemerovo seam. Sketch of swelling of the Kemerovo seam in longwall No. 2 of the second sector.
1 — fractured coal; 2 — sandstone parting; 3 — siltstone parting.

into which rock partings of sandstone and siltstone are involved, affected by a series of small intraseam ruptures. The floor of the seam bears intensive traces of sliding.

A characteristic change in the internal structure of the Kemerovo seam occurs in the lying wall of disjunctive fault B (Fig. 6). As the seam approaches the displacer, a sharp increase is observed in the frequency of longitudinal normal-cutting fractures, which form a vertical jointing resembling slaty cleavage. In addition, planes of gently dipping fractures are noted, bearing clearly expressed striation. Closer to the rupture, the dip of the seam is sharply twisted, and within it there appears intense platy structure formed by oblique folds with almost horizontal

axial planes, along which zones of crushed coal are formed. In places, movements have occurred along them; this is, as it were, the incipient development of small ruptures from folds.

The internal structure of the seams of the lower level is distinguished by the intensive development of bedding-plane displacements, which have disrupted the original structure of the coal seams and transformed the coal into a loose mass; this is one of the reasons for the sudden outbursts of coal and gas that often occur here.

From consideration of the internal structure of the coal seams it follows that complication of the latter is usually accompanied by tectonic forms of larger dimensions. Therefore, a change in the character of fracturing and in the internal structure of a coal seam should be regarded as a signal of the appearance of more substantial dislocations.

Fig. 6. Change in the internal structure of the Kemerovo seam when approaching displacer B. Section and sketch along dip 63-bis; 1 — fractured coal, 2 — sandstone parting.

Thus, from the example of examining the tectonics of the field of the “Tsentralnaya” mine, it is evident how small folds and ruptures, as well as complication of the internal structure of coal seams, are closely connected and mutually conditioned by additional structures of the second order, which is an important factor in forecasting the tectonic structure of areas to be mined.

REFERENCES

1. Belitskii A. A. On the development of a method for predicting the disturbed character of mine fields in Kuzbass. Izv. TPI, vol. 99, Tomsk, 1958.

2. Belitskii A. A., Pakh E. M. Regularities of the geological structure of the Kuznetsk Basin. Academy of Sciences of the Kazakh SSR, Alma-Ata, 1960.

3. Rumyantsev S. S. Tectonic disturbances observed on the northwestern margin of Kuzbass and their explanation. Gornyi zhurnal, Nos. 10 and 11, 1928.

4. Skok V. I. Kemerovo district. Mineral Resources of the West Siberian Territory, vol. III, Novosibirsk, 1935.

5. Usov M. A. Forms of disjunctive dislocations in the mines of Kuzbass. Collection on the Geology of Siberia. Publ. of the West Siberian Geological Prospecting Trust.