Tectonic Structure of the Field of Mine 5/7 in the Anzhero-Sudzhensk Coal District of Kuzbass

R. G. Kolomin

Introduction

The Anzhero-Sudzhensk coal district of Kuzbass is characterized by a complex tectonic structure. The coal-bearing deposits of the district are gathered into folds complicated by tectonic ruptures of various types and amplitudes. The formation of these structural elements was accompanied by intra- and interstratal movements, which led to sharp changes in the thickness and structure of the coal seams.

Our principal attention was devoted to the study of the so-called “small” structural forms, which include additional folding and plication, pinching and swelling of seams, comparatively small faults with displacement amplitudes of up to tens of meters, jointing, bedding-plane displacements, and others. Because of their insignificant size, “small” structural forms are not always detected during geological exploration work and therefore, as a rule, are established in the course of exploitation of the deposit. At the same time, they hamper coal extraction, lead to significant losses of coal reserves, and, when strongly developed, partially or completely render sections of coal seams unsuitable for exploitation.

It is entirely obvious that clarifying the character of the manifestation of “small” structural forms and their dependence on the main structural elements of the district is of great theoretical and practical importance. As a result of studying these structural forms, it is possible to establish the regularities of their manifestation and interrelations, to outline the history of formation of the tectonic structure of the district, and, on this basis, to attempt to develop a method for predicting the disturbed character of mine fields.

Brief Geological Outline of the Anzhero-Sudzhensk District of Kuzbass

At the base of the coal-bearing sequence of the district lie Lower Carboniferous deposits, represented by sandy-clayey shales and limestones. On the eroded marine sediments of the Lower Carboniferous lie deposits of the Ostrog Formation, at the base of which there is a basal conglomerate. Above the latter lie yellow-gray and dirty-green, medium-grained sandstones that do not contain coal seams. The age of these deposits is conventionally assigned to the Lower Carboniferous.

The Ostrog Formation is overlain by deposits of the Balakhonka Series. Lithologically, this series is characterized by sandy-clayey-

…with sandy rocks, carbonaceous argillites, and coals. In the Anzhero-Sudzhensk district the coal-bearing deposits of the Balakhon series are represented by its lower horizons, which belong to the Lower Balakhon suite \((C_2—C_3)\). The latter, in this district, are conventionally divided into three members from top to bottom: the Alchedat, Central, and Chelin members.

The Central member is of the greatest industrial importance; coal mining in the Anzhero-Sudzhensk district is based on its coals. This member contains 7 principal workable coal seams:

The coal seams listed are well persistent along strike and therefore are classed as stable seams.

The Chelin and Alchedat members are characterized by comparatively low coal content and by rather abrupt changes in the thickness and structure of the coal seams. Their industrial significance has not yet been sufficiently clarified.

The tectonics of the Anzhero-Sudzhensk district is connected with the overthrusting of the rock masses of the Kolyvan–Tomsk folded region onto the coal-bearing deposits of Kuzbass. Situated on the northeastern flank of the indicated folded region, the Anzhero-Sudzhensk district proved to be, as it were, clamped between two rigid systems—the spurs of the Kuznetsk Alatau and the advancing rocks of the Kolyvan–Tomsk folded region. As a result, the rocks of the district underwent considerable deformation.

Fig. 1. Diagram of the tectonic structure of the Anzhero-Sudzhensk district of Kuzbass.

Structurally, the coal-bearing deposits of the Anzhero-Sudzhensk district constitute a complex synclinal fold elongated in a northwestern direction. Owing to the bending of the fold axes, the latter was divided into three brachysynclines: the Anzher, Andreevka, and Kozly synclines (Fig. 1). The Anzher syncline, in form, is an irregular asymmetric fold which, in its northern, northwestern, and western parts, was cut off by the Tomsk overthrust. Along this major tectonic rupture the Middle Devonian rocks were thrust onto the deposits of the Balakhon series.

The other two brachysynclines—the Andreevka and the adjacent Kozly—are located in the southeastern part of the district; they are separated from the Anzher syncline by an anticlinal uplift. The indicated brachy-

the synclines are separated from one another by the rather large Terent’ev reverse fault.

The Anzhero-Sudzhensk district is separated from the main part of the Kuznetsk Basin by an anticlinal uplift known in the literature as the Nevsky.

Tectonic structure of the field of Mine 5/7

The field of Mine 5/7 is located on the eastern limb of the Anzher syncline, the western limb of which, within the limits of the mine field, is cut off by the Tomsk thrust. In plan, the eastern limb, elongated in the meridional direction, has the form of an arc convex toward the east.

All coal seams within the mine field have a westerly dip, which varies from 10–15° in the central areas to 80°; overturned bedding is even observed near the northern boundary. The limb described is complicated by additional folding.

In addition to folding, the coal-bearing deposits are affected by a series of large longitudinal faults of the concordant reverse-fault type. Along these reverse faults the coal seams have undergone repeated doubling, which has led to an increase in coal reserves.

Besides the large longitudinal reverse faults, the coal seams are affected by a large number of small ruptures, variously oriented in space, with displacement amplitudes ranging from several centimeters to tens of meters. Along with this, jointing, intra- and interseam movements, pinchings, swellings, and other disturbances are well expressed in the coal seams. Such numerous and diverse tectonic disturbances have determined the complexity of the tectonic structure of the mine field.

Additional folding

Within the field of Mine 5/7, the character of the manifestation of additional folds is not the same in its different areas. In the northern part of the mine field, where the coal seams occur at steep angles and are cut by closely spaced large longitudinal reverse faults whose displacers have a steep dip, the additional folding has an intense character (Fig. 2). In form, the folds here resemble corrugation: they are characterized by small dimensions and steeply dipping limbs, as a result of which their hinges have a sharp profile. In each section one can distinguish a series of such folds.

Moving southward, as the seams flatten, the intensity of the additional folds decreases—they gradually die out and disappear completely within the limits of line IX.

In the central areas of the mine field, additional folds appear again, but already possess a different character. Here the folds are manifested as large waves whose hinges have smooth outlines. The axial planes of these folds dip to the west, as a result of which they have an asymmetrical structure (Fig. 3). In the southern part of the field there is only one, but rather large, fold with a smooth bending of the seams in the hinge part and a symmetrical structure.

It should be noted that, although the axial planes of the additional folds have different structures in different areas, their axial lines are almost always horizontal and, on the whole, repeat the strike of the strata. Additional folding within the mine field is most clearly manifested on the upper horizons of the coal-bearing deposits and probably dies out with depth.

Fig. 2. Character of the additional folding in the northern part of the field of Mine 5/7.
1 — mined-out portions of coal seams; 2 — coal seams not yet exposed by mine workings; 3 — tectonic faults; 4 — underground mine workings.

Major Longitudinal Thrust Faults

The eastern limb of the Anzhera syncline is broken by a series of parallel longitudinal concordant thrust faults, with displacement amplitudes of 100–300 m. Within the limits of the mine field, nine such thrust faults have been identified; they determine the fault-block structure of the mine field. As a result of the manifestation of these thrust faults, the coal-bearing deposits have been divided into relatively large slices, which are successively thrust over one another in a west-to-east direction. Owing to this, the coal seams have been duplicated, and in some places even a threefold overlapping of coal seams is observed.

In plan and in sections, concordant thrust faults cut the coal-bearing deposits at acute angles, following the strike and dip of the seams. Therefore tectonic ruptures quite often rather clearly repeat the bends of the seams, and only in those areas where additional folding is developed do the angles between the planes of the displacers of the major thrust faults and the bedding increase, in places reaching even 90° (Figs. 2, 3).

Fig. 3. Character of additional folding in the central part of the field of Mine 5/7
(legend as in Fig. 2).

It should be noted that the major longitudinal thrust faults do not exert a substantial influence on the conduct of mining operations, since the lines of outcrop of the coal seams broken by them are situated almost horizontally, and therefore boundary workings are driven along them, limiting the mining sections. It is also important to note that in the course of exploration work the position of these ruptures is established without particular difficulty.

Minor Faults

The coal-bearing deposits forming the eastern limb of the Anzhera syncline are affected by a large number of comparatively small tectonic—

tectonic faults with a displacement amplitude from several centimeters to tens of meters. In contrast to large faults, which are longitudinal, small faults usually have various strikes—longitudinal, diagonal, and transverse with respect to the strike of the coal-bearing deposits. Longitudinal faults dip to the southwest and northeast at angles of 60–70°. Diagonal faults dip to the northwest and southeast at the same angles. Transverse faults dip to the southwest and to the northeast at angles of 50–80°. Usually these faults can be traced along one, more rarely along two or three coal seams, and they die out rather quickly along strike and down dip.

In form, small faults are also distinguished by great variety—among them there occur conformable and nonconformable upthrows, overthrusts, strike-slip faults, and reverse faults¹.

It should be noted that whereas large faults do not cause particular difficulties in the conduct of mining operations and are comparatively easily detected during exploration work, small faults behave differently in this respect. As a rule, they are not detected during geological exploration; however, they exert a great influence on the conduct of mining operations, since their large number in individual areas often complicates the extraction of coal seams.

Therefore it is quite obvious that determining the spatial position and the character of manifestation of small faults, as well as establishing regularities in their manifestation, is of great importance. A. A. Belitskii studied this question at a number of Kuzbass deposits. As a result of his investigations he came to the conclusion that all small faults usually develop on the flanks of large faults and are directly connected with their formation.

This conclusion is of great practical importance, since it makes it possible to predict the presence of small faults, their spatial position, and the character of their manifestation in those areas that have not yet been opened by mine workings.

Analysis of the small fault disturbances within the mine field 5/7 fully confirms these conclusions. In all, we processed about 700 small faults. Of these, the greatest number are conformable upthrows and reverse faults. Strike-slip faults and overthrusts are encountered very rarely.

According to the character of manifestation of small faults, the coal seams of the central sequence are clearly divided into two bands, which differ from one another.

The first band includes the Tenth and Andreevskii seams, occurring in the upper part of the central sequence. Here 335 small faults were studied, of which conformable and nonconformable upthrows account for 72%, reverse faults for 25%, overthrusts for 2%, and strike-slip faults for 1%. Small faults in the seams of this band can be observed mainly only in the northern areas (Fig. 4). In plan they are well traced from the “Northern Boundary” line to line III. Farther south, owing to the disappearance of large longitudinal faults, small faults in this band are not observed.

In analyzing the small faults, the following feature is established in their spatial distribution. Although the small faults have different spatial orientations, a predominant number of faults of one strike is observed in individual, comparatively small areas. Thus, in the area situated within the limits of the “Northern Boundary” and XIV lines, the most frequently manifested are lon—

Fig. 4. Interrelationship of large and small faults, as well as fracturing, along the Tenth seam of Mine 5/7.

a—structural chart of the Tenth seam, field of Mine 5/7; б—circular diagram of the orientation of small tectonic faults; в—circular diagram of the orientation of fracturing; г—section along exploration line 21 of the crest; д—section along exploration line VII.
1—small faults; 2—truncations of seams by longitudinal faults; 3—presumed zone of development of small faults on the lower horizons (horizon 400 m); 4—belt of fracturing and faults; 5—horizons exposed by mine workings (solid line) and not exposed by mine workings (dashed line).

Fig. 5. Relationship of major and minor faults, as well as jointing, in the Dvoynoy seam of Mine 5/7.

a — structural map of the Dvoynoy seam of Mine 5/7; б — circular diagram of the orientation of minor tectonic faults; в — circular diagram of the orientation of jointing; г — section along exploration line X; д — section along exploration line XI (symbols are the same as in Fig. 4).

longitudinal faults. Diagonal and transverse faults in this area occur only in isolated cases. South of line XIV to line VI, diagonal faults begin to predominate. Longitudinal faults do occur, but comparatively rarely. Transverse faults in this area are isolated. South of line VI, transverse faults are encountered most often. Diagonal and longitudinal faults are found here comparatively rarely.

The second group includes the Dvoinoi, Petrovskii, Tonkii, Sluchainyi, and Koksovyi seams. Here 328 small faults have been studied, of which conformable and nonconformable normal faults account for 46%, reverse faults for 51%, strike-slip faults for 2%, and thrusts for 1%. Almost all the small faults in this group, in contrast to the first, are located in the southern parts of the mine field (Fig. 5). This circumstance is due to the fact that in the southern part of the field the seams of the lower group are disrupted by large longitudinal normal faults, whereas in the northern part they are absent.

Analyzing the small faults in the second group, we also observe a nonuniform manifestation of the various fault systems in different areas. Thus, in the area situated between exploration lines II and III, transverse faults with displacement planes dipping to the south–southwest are mainly manifested. Diagonal and longitudinal faults occur more rarely. South of line III, as far as line VII, longitudinal faults are most developed; transverse faults are developed to a lesser degree, and diagonal faults occur only in isolated cases. In the area located between lines VII and XIII, diagonal and transverse faults are mainly developed; longitudinal faults have comparatively slight development. North of line II, large longitudinal faults disappear, and therefore the intensity of manifestation of small faults within the working horizons decreases sharply.

Fracturing

We also studied fracturing in the coals and enclosing rocks. Observations of fracturing were carried out at 95 points, distributed more or less uniformly over the entire area of the mine field within the 200 and 400 m horizons.

In the enclosing rocks, observations of fracturing were made mainly along crosscuts and field drifts; in the coals, chiefly along longwalls, and also along furnaces, ventilation, and conveyor drifts. We sought to ensure that observations at each point were made under identical structural conditions, i.e., that in this area the seam did not change its elements of occurrence, thickness, or structure. The observation points themselves were arranged so that, as far as possible, they would characterize fracturing in areas with different tectonic structures.

At each observation point, the elements of occurrence of all manifested fractures were measured; in doing so, normal-cutting and oblique-cutting systems were distinguished. The former included those systems which, being almost perpendicular to one another, at the same time were arranged perpendicular to the bedding. Usually these comprise two systems: a longitudinal one, whose strike coincides with the strike of the seams, and a transverse one, cutting the seams across their strike. Being tied to the elements of occurrence of the seams, the normal-cutting fracture systems change their position in space depending on changes in the elements of occurrence of the seams. A characteristic feature of these fracture systems is the absence of traces of movement on their surfaces, which indicates their formation as a result of tensile stresses.

Particular attention was paid by us to the study of obliquely cutting fracturing, which, as a rule, is manifested most clearly in the coals, rather than in the enclosing rocks. Unlike normally cutting fractures, obliquely cutting fracturing intersects both itself and the bedding at arbitrary angles. The surfaces of these fractures bear traces of movement—slickensides and slip striations. In its appearance, obliquely cutting fracturing must be assigned to shear fractures.

As a result of the study of fracturing, it has been established that at each observation point one can detect a large number of fracture systems, with considerable variation in the elements of their attitude. If the attitude elements of all fractures measured at one point (longwall, face, drift) are plotted on a stereographic net (Fig. 6), the poles of the fractures fill almost the entire circle. However, isolines of equal numbers of points usually reveal 8 fracture systems, which may be classified as follows (see table).

Table

Despite the fact that obliquely cutting fracturing is most clearly manifested in coals as compared with the enclosing rocks, in the latter we observe the very same fracture systems.

It is important to note that the identified systems of obliquely cutting fractures can be found at any place in the mine field, despite the fact that the observation points are situated under different structural conditions. If we compare the fracturing diagrams constructed from measurements made in different parts of the mine field, we shall see that there is no substantial difference between them (Fig. 6).

The nature of the manifestation of obliquely cutting fracturing at each observation site depends on many causes. At mine 5/7 it has been established that, with a westerly dip of the seams, the longitudinal systems dipping west and the diagonal systems dipping southwest and northwest are best revealed. The transverse systems, situated unfavorably with respect to the direction of the general movement of the rock masses, are naturally manifested more weakly. Near tectonic ruptures, those systems are best manifested which are parallel to the rupture itself.

The dimensions of the mine working, the area of exposure, the orientation of the face, and the rate of extraction of the coal seam also exert a considerable influence on the manifestation of fracturing at each observation site. Thus, for example, the larger the area of exposure and the slower the advance of the face, the more distinctly all fracture systems are manifested.

It should be noted that at ruptures of the thrust-fault type the hanging walls of the disrupted [[unclear: continuation cut off]] are most intensely affected by fracturing.

Fig. 6. Circular diagrams of fracturing of the Double seam.
a — longwall No. 45 in the northern part of the field near major longitudinal faults; b — longwall No. 28 in the southern, undisturbed part of the field; dots indicate the belt of obliquely cutting fracturing, crosses the belt of normally cutting fracturing; solid lines with an arrow indicate the elements of occurrence of the seam. The isolines were constructed without taking into account the normally cutting fracturing.

of the seam, in the lying walls the fracturing is manifested more weakly (Fig. 7). In faults of the upthrow type, on the contrary, it is manifested most distinctly

Fig. 7. Tectonic fault of the upthrow type. Fracturing is more clearly manifested in the hanging wall than in the lying wall.
1 — coal; 2 — sandstone; 3 — argillite; 4 — fracturing in coal; 5 — fracturing in rocks.

fracturing in the lying limbs of the ruptured seams (Fig. 8). In faults, fracturing is manifested more or less uniformly in both limbs of the ruptured seam.

Fig. 8. Tectonic rupture of the upthrust type. Fracturing is more clearly manifested in the lying limb than in the hanging limb (the symbols are the same as in Fig. 7).

If the circular diagrams of minor ruptures are compared with the circular diagrams of fracturing, it is clearly evident that, in their general features, they repeat one another (Figs. 4, 5). This fact, as well as direct observations, makes it possible to conclude that fracturing and minor ruptures have a definite genetic relationship. A similar connection between minor ruptures and fracturing was established by A. A. Belitskii for other districts of Kuzbass as well.

The established connection between the manifestation of fracturing and minor and major longitudinal ruptures is of great practical importance, since it makes it possible to forecast the degree of disturbance on unworked horizons of mine fields. Thus, for example, it was noted above that within the 200 and 300 m horizons of the mine field, in the seams of the lower suite, all minor ruptures are concentrated in the southern areas, on the flanks of the corresponding major longitudinal ruptures of the concordant reverse-fault type. Analysis of the tectonic structure of the projected 400 and 500 m horizons requires substantial corrections to be made in the distribution of minor ruptures on these horizons. Using the established regular relationship between major and minor ruptures, it may be asserted that on the 400 and 500 m horizons the minor ruptures will be most intensely manifested in the seams of the lower suite in the northern areas of the mine field, whereas on the upper horizons they occurred chiefly in the southern areas of the field.

Intra-seam movements

In the field of Mine 5/7, bedding-plane movements are also widely developed; these are most clearly manifested in the coal seams. They include displacements along planes that usually coincide with, or are close to, the bedding-

ruptures. Where there are no major ruptures, minor ruptures are practically absent.

1. Minor ruptures are oriented in space in various ways, but they can be reduced to eight systems, corresponding to the eight maxima of point concentration on the circular diagram.

2. Within the mine field, jointing is clearly developed; it likewise has eight systems, whose elements of occurrence generally correspond to the elements of occurrence of the minor ruptures.

3. A close genetic relationship has been established between the manifestation of major upthrusts, minor ruptures, and jointing. The minor ruptures are connected with the major longitudinal ruptures and develop along the jointing, as along the direction of least resistance. This relationship may be used to develop a method for predicting the disturbance of mine fields in areas not yet opened by mine workings.

4. Pinches and swells are widely developed in the coal seams, being the result of movements along the bedding and along the jointing.

REFERENCES

1. Belitskii A. A. Classification of tectonic ruptures and geometric methods for studying them. Gosgeolizdat. 1953.

2. Belitskii A. A. On the question of the mechanism of formation of cleavage fractures. Proceedings of the Mining-Geological Institute of the West Siberian Branch of the USSR Academy of Sciences, issue 6. 1949.

Tomsk Polytechnic Institute
named after S. M. Kirov.

1. The names of faults are given according to the classification of A. A. Belitskii [1]. ↩