Tectonics of Mine Field No. 9/15 in the Anzhero-Sudzhensk District of Kuzbass

A. N. Leshcheva

Introduction

The mining of coal seams under complex tectonic conditions requires a rational direction for mine-development and cutting operations. Unexpectedly encountered tectonic faults greatly complicate the conduct of mining operations and disrupt the planned growth of coal output. Therefore the geological and mine-surveying service at a mine must provide the most effective assistance in studying the tectonics of the fields and the physicomechanical properties of the wall rocks of the seams being mined. However, present-day knowledge of the regularities in the manifestation of tectonic processes in coal-bearing strata still remains at a low level, and therefore the assistance of geologists in the exploitation of the mineral deposit does not meet the requirements imposed.

Using the example of mining coal seams in the Anzhero-Sudzhensk district, one can become convinced of the complexity of the tectonic structure of the district and of the importance of studying tectonics for the planning of more rational exploration and exploitation of deposits of this kind. Mine 9/15 has for many years been mining coal seams under the most complex tectonic conditions. During this time, an enormous amount of factual material has accumulated on seam mining and geological documentation. Unfortunately, in the past this material was not subjected to scientific processing and was used only periodically in recalculating coal reserves for the purpose of approval by the State Reserves Committee.

In 1954, on the initiative and under the direction of A. A. Belitsky, the generalization and scientific interpretation of the geological documentation was begun, with the carrying out of additional observations in mine workings. The present work is the first attempt to generalize the geological observations for Mine 9/15, with the aim of studying the regularities in the manifestation of tectonic processes and forecasting them for deep horizons.

Position of the Mine Field in the District, Its Exploration and Opening

Mine 9/15 of the Anzhero coal deposit is located in the central part of the city of Anzhero-Sudzhensk, Kemerovo Oblast. Structurally it occupies the hinge part of the Anzhero syncline, which from the northwest is cut off by a major fault—the Tomsk thrust.

The Mine 9/15 complex went into operation in 1907. By that time the first geological investigations, carried out by Zaitsev, Krasnopolsky, and later by mining engineer P. K. Yavorsky, were known. In 1917 Mine 9/15 was visited by M. A. Usov, who for the first time established a normal section of the group of seams being worked and gave a general picture of the structure of the district as a whole.

Systematic detailed exploration of the field of Mine 9/15 by core drilling was begun in 1929 and continues to the present, with the aim of further exploring the strongly disturbed seams.

More than 1,000 exploratory boreholes have been drilled over the entire field. A complete calculation of the coal reserves of all seams, taking account of the deep horizons, was carried out in 1956. In this calculation, reserves of the lower categories amount to 60%, which should be explained by the strong disturbance of the seams and the complex structure of the mine field.

The coal seams in the mine field were opened by the shallow shafts 9 and 10. Subsequently they were deepened to the +75 m level, which is the first working level. In 1917, in order to increase coal output, shafts 15 (skip shaft) and 15-bis (cage shaft) were sunk to the +75 m level and then deepened to the −13 and −124 m levels.

The +75 and −13 m levels have for the most part already been worked out, with the exception of individual strongly disturbed areas of the seams. At present the principal working level is −124 m. By means of inclined workings the −250 m level has also been opened. At the same time, work is being carried out to open coal reserves in the far western sector.

Geological Structure of the District and the Mine

Stratigraphy

The coal-bearing deposits of the Anzhero-Sudzhensk district belong to the Balakhon Series of Kuzbass. Lithologically, the sediments are characterized by sandy-clayey and carbonaceous rocks, as well as by coals.

In the present district, the Balakhon Series, essentially on the basis of differing workable coal content, is divided into three formations, from bottom to top: the Chilin Formation, 420 m thick; the Central Formation, 135 m thick; and the Alchedat Formation, 470 m thick. In accordance with the unified stratigraphic scheme of the coal-bearing deposits of Kuzbass adopted at the coordination conference in 1956 in Leningrad, the Chilin Formation is correlated with the Mazurovo Formation, the Central with the Alykaevo Formation, and the Alchedat with the Intermediate Formation of the Balakhon Series.

The Central Formation, being industrially the most valuable, has proved to be well studied; its coal content is 11%. Therefore all mines of the Anzherka deposit were laid out in the Central Formation. The thickness of the sediments of this formation is variable; it increases southward from 105 to 205 m. This formation includes from 5 to 8 workable seams, whose characteristics are presented in the table.

Of all the seams listed, only five are worked: the Tenth, Andreevsky, Petrovsky, Tonky, and Kozhovy. Under the conditions of the Anzherka deposit, where seam dislocations are frequent and it is necessary to solve the problem of finding the displaced limb, the ability to recognize coal seams in mine workings by the lithological composition of their floor and roof is of great importance and determines the success of the work of the mine geologist. Therefore the enclosing rocks and the structure of the seams are studied in detail both along the strike and along the dip. It should be noted, however, that the coal seams of the Central Formation throughout the entire extent of the mine—

...of the mine field basically retain their properties: the structure and lithological composition of the floor and roof. A change in the lithological composition of the roof is observed only in two seams: the Tenth and the Coke seams; however, the normal distance between seams is not constant, especially for the closely spaced seams Above-Tenth and Tenth, Petrovsky and Thin.

Table

The two remaining series—the Alchedatskaya and Chelinskaya—have been opened by boreholes and partly by mine workings. Because of their doubtful industrial value, they are not currently being worked, although the reserves of 9 seams of the Alchedatskaya series are listed on the mine’s balance sheet.

In the northern part of the district, beneath a thick cover of loose Tertiary formations, Jurassic sediments with 3 seams of brown coal up to 8 m thick were encountered. Lithologically, the Jurassic sediments are represented by weakly cemented aleurolites, sandstones, and conglomerates.

Tectonics

The Anzhero-Sudzhensk coal district is the northern margin of the Kuznetsk Basin. It is separated from the main area of Kuzbass by an anticlinal uplift. Structurally, the coal-bearing deposits constitute a complex synclinal fold elongated in a northwestern direction. Owing to bending of the fold axes, the latter split into three brachysynclines: Anzherskaya, Andreevskaya, and Kozlinskaya. The Anzherskaya brachysyncline is the largest tectonic structure of the district. In form it is a symmetrical fold plunging in a northwestern direction. The northwestern and western parts of the fold are cut off by a major rupture—the Tomsk overthrust. On the eastern limb of the fold lies the field of mine 5/7; in the crest part, the field of mine 9/15 (Fig. 1).

The plicative structures of the district are complicated by tectonic ruptures, among which the Tomsk overthrust is the largest. The amplitude of this overthrust is determined at several kilometers. Its strike and dip are variable—in the north of the district this rupture follows the strike of the series, i.e., meridionally, with a dip to the west at an angle of 45°. In the area of the field of mine 9/15 its strike changes sharply to northwestern, then to southwestern, and assumes a cross-cutting character with respect to the seam suite. The Tomsk over-

was studied during the exploration of the seams of the far western section of mine 9/15, where the dip angle of the fault plane was established as 25°.

Along the Tomsk thrust, Devonian sediments were thrust over rocks of the Balakhon series; in the process, a zone of rock crushing up to 150 meters wide was formed. As a result of this, the Devonian deposits came into contact

Fig. 1. Tectonic structure of the field of mine 9/15 at horizon −124.

with rocks of the productive sequence and of the Lower Carboniferous. Along with this, a number of large tectonic ruptures arose in the productive sequence, some of which have a meridional, or nearly meridional, longitudinal direction, while others have a latitudinal, or transverse, direction.

In general, the tectonics of the Anzhero-Sudzhensk district is a consequence of the thrusting of the mountain masses of the Kolyvan–Tomsk folded region onto the coal-bearing deposits of Kuzbass. As a result, the northwestern and northern boundaries of Kuzbass form an arc concave toward the interior of the basin. Situated on the northeastern flank of this arc, the coal-bearing deposits of the district were compressed between two rigid systems—the Kuznetsk Alatau and the advancing rocks of the Kolyvan–Tomsk folded region—and therefore were strongly deformed.

a) Principal plicative elements of the mine field

Structurally, the field of mine 9/15 is a synclinal fold plunging in a northwestern direction. The hinge of this fold is located in the southern part of the field, while its limbs occupy the eastern and western extremities (Fig. 1).

The limbs of the fold are strongly deformed. Thus, on the eastern limb there is a series of additional folds, one of which, of sharply asymmetric structure—the central syncline—was formerly taken to be the main Anzher syncline. Mining operations of recent years and

...by prospecting of the deep horizons it has been established that the closure of the main Anzherka syncline is very complex.

Among the additional folds on the eastern limb the following are clearly distinguished: the central syncline and anticline, as well as the eastern syncline and anticline.

The central synclinal fold is traceable along the entire strike of the eastern limb of the Anzherka syncline. It has a sharply expressed asymmetric character, with the limbs dipping eastward up to 90° and westward from 10 to 50°. The steep western limb of this fold proved to be disturbed by a gentle fault Q, along which the hanging wall was displaced along the fault from west to east. The strike of the limbs is meridional and parallel to one another, except for its closure, where it changes to latitudinal. The configuration of the fold and of its closure in section changes sharply along the strike (Fig. 2).

Tracing the central syncline from south to north, we note that within exploration lines IX and V the western limb lies vertically, the eastern—almost horizontally. Farther north, in the plane of exploration line III, plunging of the axis of the syncline is observed; at the same time the fold proved to be in the footwall of fault Q; on the western limb two small recumbent folds are formed. Along the line of the main crosscut the synclinal fold descends still lower and becomes narrower. Still farther north, at exploration lines XII and IV, it gradually dies out and flattens, with the formation of gentle flexures.

The central anticlinal fold in the southern part is denuded, and, owing to the plunge of its axis, it is clearly traceable only from the line of the main crosscut of horizon −124. Here its closure is displaced along fault Q by 140 m, with the formation on its steep eastern limb of a knee-shaped bend, which was established during the driving of mine workings (incline No. 2 and No. 3 of the Tenth seam).

North of the main crosscut, at exploration line XII, fault Q acquires a steeper attitude and cuts the seams near the closure of the anticline, the vertical limb of which becomes considerably smaller in size.

At exploration line 4 the central anticline flattens out, with the formation of gentle wave-like folds. The axes of the described folds have an almost meridional strike, with an initial plunge northward at an angle of 20°, then 10 and 0°, while at exploration line XII their rise of up to 5–8° is observed.

Thus, the central syncline and anticline have their maximum development in the area of the main crosscut, with gradual dying out and branching into smaller folds in the northern direction. It should be noted here that the maximum dimensions of the fold coincide with the maximum amplitude of fault Q.

The eastern synclinal and anticlinal folds are well traced by mine workings. In form these are symmetrical folds situated east of the central syncline. Their strike is close ...

IX–IX exploration line

V–V exploration line

(III–III) exploration line

Along the line of the main crosscut (b)

XII–XII exploration line

4–4 exploration line

Scale: 100 0 100 200 300 m

Fig. 2. Change in the character of the additional folding on the eastern limb of the Anzherka syncline within Mine 9/15.

toward meridional. The axes of these folds have an undulating, almost horizontal attitude. The configuration and dimensions of the folds vary along strike.

In the south of the mine field the folds are weakly developed, with the limbs dipping at angles of 12–20°; farther north the limbs of the folds steepen to 40°. In the section along the main crosscut the size of the folds reaches a maximum, while their limbs steepen to 65°. In the area of exploration lines XII and 4 the folds gradually die out and are smoothed.

The western limb of the main Anzherka syncline differs sharply in structural character from the eastern limb (Fig. 1). The strike of the entire sequence of the western limb is western and northwestern, with dips to the north and northeast at angles of 10–45°. There are no large folds here, but undulation in the attitude of the seams is observed, as a result of which the strike changes every 100–300 meters from western and northwestern to northern; this is confirmed by the driving of the main drifts.

As the large fault A is approached, the undulation develops and passes into second-order folding. Two such folds have been well traced by mine workings along the Tenth and Andreevsky seams (longwalls 75 and 80). The axial lines are inclined to the southwest and west at angles of 10–20° to 60° and coincide with faults that cut the folds in the hinges.

When mine workings approach the hinges of folds, strong lateral pressure with sudden collapses is usually observed, which is caused by considerable deformation of the rocks at the places where the coal-bearing sequence bends.

b) Fault structure of the field of mine 9/15

The folds described above were later broken by tectonic fractures, which considerably complicated their configuration and gave the mine field an exceptionally complex structure. The entire variety of tectonic faults may be reduced to the following types:

1. Large longitudinal faults of the conformable reverse-fault type.
2. Steep transverse faults of the strike-slip type.
3. A dense network of small faults of the reverse strike-slip, normal strike-slip, and thrust strike-slip types.
4. Tectonic pinches and swellings.

Among the large number of faults of different sizes and different orientations, the leading ones are the large longitudinal faults of the conformable reverse-fault type and the transverse faults of the strike-slip type that cut them. On the flanks of these faults are concentrated small faults of various orientations, forming zones of increased disturbance of the coal seams. At the intersections of longitudinal and transverse faults these zones reach maximum development (Fig. 3).

Large longitudinal faults

Large longitudinal faults of the conformable reverse-fault type are widely distributed on the eastern limb of the Anzherka syncline (Fig. 1). Within this limb, seven such faults have been established by mine and exploration workings: I, II, IIю, III, IV, V, VI. Within the −124 m level only the last four faults are recorded.

The strike of these faults is close to meridional. Both in plan and in vertical sections they cut the seams at acute angles. Their displacers dip to the west at angles of 20–50–60°, depending on the change in the dip angle of the coal-bearing sequence, to which the faults are confined. The displacement amplitude along the displacer for large faults ranges from 10 to 100 m and more. As a result of the manifesta-

... of these faults the coal seams are successively thrust over one another from west to east, forming a shingled structure characteristic of this district.

Our investigations have shown that the longitudinal faults probably formed at the end of fold formation, since the faults cut the axial planes at an acute angle and displace them. The bends of the dislocators that we observe in the vertical and horizontal planes are a consequence of the adjustment of the faults to the bedding, as to the direction of least resistance.

Along with the formation of faults, plastic deformation of the rocks continues; as a result, the folds are twisted and, in the sides of the dislocators, underturns and even drag folds are formed. However, in the concluding period of folding these phenomena play a subordinate role. The leading significance at this stage of deformation of the rocks belongs to the formation of tectonic faults.

Study of the surface of the dislocators of longitudinal faults of the type of concordant reverse faults, both large and small, shows that the angle formed by the direction of striation and the strike of the dislocator is close to 90°. This indicates that the faults in question are situated approximately perpendicular to the principal force flow that created the present tectonic structure of the coal-bearing deposits of the Anzhero-Sudzhensk district. The degree of expression of the striation varies depending on the lithological composition of the rocks exposed in the plane of the dislocator. In sandstones the striation is less noticeable; in rocks of the argillite and siltstone type it is seen more distinctly.

It is also necessary to dwell on one more longitudinal, but peculiar, fault, \(Q\), of the thrust type, confined to the central synclinal and anticlinal folds. This fault cuts all the seams of the coal-bearing series. It begins to develop from exploration line III and farther north. Its strike is northeastern, with a bend to latitudinal at exploration line III; the dip is western, from 5 to 45°.

The flattening of the fault is confined to the overturned western limb. The maximum overturning of the seams coincides with the maximum amplitude of the fault, reaching 140 m (Fig. 2—section along the main crosscut). North of the main crosscut, fault \(Q\) gradually diminishes, with simultaneous decrease and flattening of the fold.

It must be assumed that fault \(Q\) was formed as a result of extension of the overturned limb of the central fold.

Major transverse faults of strike-slip type

Along with longitudinal faults of the type of concordant reverse faults, transverse faults of strike-slip type occupy an important place in the field of mine 9/15. It is impossible to detect these faults by prospecting boreholes, since the exploration lines are situated parallel to these faults. Only by means of systematic observations in underground workings has it been possible to reconstruct the scheme of their location and the sequence of their formation.

Until recently, one such fault, \(P\), located in the southern part of the mine field, was noted on the mine-workings plans. As studies of recent years have shown, in the mine field not one but a series of similar faults is established, with a definite regular spatial arrangement.

According to the state of mine workings at the present time, five transverse faults of strike-slip type are established in the mine field: \(P\), \(P_1\), \(P_2\), \(P_3\), \(P^a\) (Fig. 1). Fault \(P—P\), established in the southern part of the field near exploration line V, cuts in a latitudinal direction all folds, as well as...

Fig. 3. Interrelation of major and minor tectonic faults, as well as fracturing, in mine field 9/15.
a—tracing from the mine-workings plan of the Petrovsky seam (longwalls No. 7 and No. 8); b—circular diagram of the orientation of minor tectonic faults; c—circular diagram of the orientation of fracturing.
1—longwall face lines at the time of mapping and their number; 2—contours of the seam floor; 3—minor reverse faults; 4—steps; 5—thrust faults; 6—line of truncation of the hanging wall of longitudinal fault N; 7—line of truncation of the footwall of longitudinal fault N; 8—strike-slip faults; 9—places where fracturing was observed; 10—poles of obliquely cutting fractures; 11—poles of normally cutting fractures; 12—mine workings; contours on the circular diagrams indicate the conventional boundaries of the distribution of fracture and fault systems.

same longitudinal faults with displacement from west to east along a steep displacer of 5 to 20 m.

Fault P₁, located 600 m north of fault P, has been traced by mine workings for a distance of 1.8 km through all seams of the central unit. Fault P₂, located 500–600 m north of fault P₁, is encountered in the Tenth and Andreevsky seams and has been traced for 1.2 km. Fault P₃ has been recorded near exploration line XII. So far it has been encountered in the main entries along the Tenth and Andreevsky seams of the −124 horizon. Fault P₀, established on the −13 horizon 700 m south of fault P, has been studied in the Petrovsky seam for a distance of 300 m.

On the plans of workings from previous years this fault is not shown, but it must be assumed that it was present, since all areas unprofitable for extraction and written off earlier are situated along the strike of this fault.

The structure of a fault of type P has been well studied by us in mine workings. Usually it is a steeply dipping plane, with a dip of about 60–85°, the surface of which is covered with softened and crushed plates of sandstone or argillite, depending on the lithological composition of the rocks adjoining the fault, with slickenside traces in the form of impressed and smoothed horizontal grooves.

Coal in contact with the displacer is strongly crumpled and is represented by an earthy, structureless mass, tightly pressed against the plane of the displacer. Usually such crumpled coal is traced for 1.5–2.0 m, after which a second crack is found, serving as a distinct boundary between the crumpled coal and the hard coal with normal structure, but with well-pronounced jointing. In this interval the roof of the seam is disturbed; separate fragments of it are pressed into the coal. Deposits of calcite and pyrite are observed (Fig. 4).

Fig. 4. Structure of fracture P.

Thus, the characteristic features of transverse faults of the strike-slip type are: latitudinal strike of the faults, their steep attitude at an angle of 60–85° with dip to the north, horizontal and, more rarely, diagonal striation on the plane of the displacer, and an inconstant displacement amplitude—from 25 to 2 m.

On the flanks of the displacers, smaller faults of various orientations are usually observed, represented by reverse strike-slip faults, thrust strike-slip faults, upthrow strike-slip faults, and reverse upthrow strike-slip faults¹). The small faults, grouping along the main displacers, form a zone 100–200 m wide. The distance between the zones is determined to be about 700–500 m.

As is evident from observations, transverse faults of the strike-slip type are later formations, since they cut and displace all longitudinal faults. Nevertheless, there is every reason to believe that the longitudinal and transverse faults arose in connection with one and the same western direction of the force flow, which is confirmed by observations of striation on the planes of displacers: in longitudinal faults it is vertical, in transverse faults horizontal, and also by the identical eastward direction of displacement of the shifted limbs.

¹) The names of the faults are given according to the classification of A. A. Belitsky.

Minor Faults

Minor faults in mine field 9/15 are very widespread. As noted above, they are usually concentrated along the flanks of major faults of the type of concordant reverse faults and strike-slip faults (Figs. 3, 5, 6).

Fig. 5. Geological sketches of longwall No. 7 of the Petrovsky seam in mine field 9/15.
The numbers in circles indicate the numbers of the longwall sketches shown in Fig. 3.

In form, minor faults are varied. Among them there occur upthrow–strike-slip faults, concordant and, more rarely, discordant reverse–strike-slip faults, thrust–strike-slip faults, and strike-slip faults. Of one thousand such faults, taken by us over the entire mine field, upthrow–strike-slip faults constitute 73%, reverse–strike-slip faults 26%, and thrust–strike-slip faults 2%.

The spatial orientation of minor faults is different, but most often—

most often longitudinal or diagonal, and more rarely transverse. A good example characterizing small faults and their interrelation with large faults is provided by our observations in the stoping workings in the Petrovsky seam, in longwalls No. 7 and No. 8 (Figs. 3, 5, 6).

Fig. 6. Geological sketches of longwall No. 8 of the Petrovsky seam, mine field 9/15.

Longwalls No. 7 and No. 8 of the Petrovsky seam are located in the southern part of the field, in the area of exploration line V, at the −124 m level. This area represents the eastern limb of the central syncline, situated on the footwall side of a large disturbance Q of the thrust-fault type (Fig. 3). The strike of the seam here is northeastern, with dip to the northwest at an angle from 10 to 40°. The seam thickness is 1.6 m.

Within this field there are three transverse faults—P′, P, P″—of the strike-slip type, with a displacement amplitude from 22 to 1.5 m, and one longitudinal disturbance N of the concordant reverse-fault type, 500 m in length, with an ampli-

of the fault along the displacer is up to 30 m. The transverse fault P divides the extraction field along the strike into two parts, in one of which longwall No. 7 is located, and in the other longwall No. 8. The longitudinal disturbance N, in turn, also divides the extraction field along the dip into two parts—the lower and the upper. Observations were carried out by means of geological sketches of the longwall faces as the stoping operations advanced. In this process, the attitude elements of small faults in the seam were recorded, slickensides on the displacer planes were studied, and the attitude elements of coal jointing were measured.

In longwall No. 7 (Figs. 3, 5), over a distance of 350 m along the strike, 18 sketches of the longwall faces were made. Coal jointing was studied at five locations. As is evident from the geological sketches, a concentration of small faults is observed in the area where the larger fault P′ is located, represented by two fractures diverging from a single point at the end of counter-drift No. 7. These fractures have the following attitude elements: dip azimuth 20°, dip angle 72°, and dip azimuth 40°, dip angle 50°. The throw of the fault is from 0.5 to 1.5 m. The small faults near fault P′ are represented by conformable reverse strike-slip faults, and by conformable and nonconformable normal strike-slip faults, mainly of meridional strike. Then, following the strike of the seam (Fig. 3) from north to south in longwall 7, we note that from sketch 6 to sketch 13, over a distance of 170 m, the seam occurrence is persistent and only isolated faults are encountered. Farther on, 100 m from the next fault P, the number of small faults again increases; this is recorded in the upper part of longwall No. 7 and along reserve drift 07 (Fig. 3). Here the longitudinal fault N of the conformable reverse-fault type also begins to develop.

In the lower part of this longwall, a transverse fault of the strike-slip type and smaller fractures were encountered. Measurements of jointing in the zone of small faults show the presence of seven systems of oblique fractures oriented almost in accordance with the small faults (Figs. 3 b and c).

In longwall No. 8, over a distance of 260 m, 16 sketches of longwall faces were made, and at 10 locations measurements of coal jointing were carried out. Beginning with the first and ending with the last sketch (Figs. 6 and 3), we observe a dense network of small faults concentrated near the longitudinal disturbance N and the transverse disturbance P₂. The small faults are varied in form and orientation, but among them faults of the type of conformable reverse faults and upthrusts stand out, as if feathering the longitudinal fault N.

Along the line of sketch 14 (Fig. 3) there is a transverse disturbance P₂ of the strike-slip type, with attitude elements: dip azimuth 160°, dip angle 82°. On the displacer plane, gentle slickensides are observed at an angle of 30° to the strike of the displacer.

Along the line of sketch 15 we observe the place where fault P″ intersects the seam truncation by fault N (Fig. 7). Fault P₂ cuts and displaces the longitudinal fault N by a distance of 1.40 m. At the point of intersection of the two faults, the Petrovsky seam is broken up to a great degree by small fractures; the coal is crushed and crumpled over a distance of 5–8 m along the strike of the seam.

Fault P″ cuts and displaces not only the larger longitudinal fault N, but also small longitudinal faults, which we observe in the upper part of longwall No. 8, where fault P″ cuts and displaces a fault of the conformable reverse-fault type (Fig. 3).

Measurements of jointing in longwall No. 8 establish seven systems of oblique fractures. Evidently, this corresponds to the diversity of orientation of the small faults that we observe in longwall No. 8 (Figs. 3 b, c).

Thus, our observations in longwalls No. 7 and No. 8 in the Petrovsky seam show that the orientation of small faults coincides