SOME ISSUES IN THE METHODOLOGY OF EXPLORING MINE FIELDS IN THE ANZHERO-SUDZHENSK DISTRICT

V. Ya. Koudelny

A substantial increase in the volume of geological exploration work for coal requires improvement in the methodology and quality of exploration. There is a real need to analyze and generalize the enormous body of material on the exploration and exploitation of coal deposits.

Over the course of several years we have analyzed the methodology of exploring mine fields in the Prokopyevsk–Kiselevsk district of Kuzbass. On the basis of this analysis, certain regularities were established that appear when exploration work is carried out in complexly dislocated mine fields. Some of the results of these studies have by now been published [1; 2]. The importance of the conclusions obtained prompted us to continue the work in other districts of Kuzbass as well. In the present article we intend to set out some results of the work carried out in the Anzhero-Sudzhensk district.

Within the Anzhero-Sudzhensk district, the productive deposits are those of the Balakhon series, divided according to the principle of workable coal content into three sequences—the Chelin, Central, and Alchedat sequences. Of greatest industrial interest are the deposits of the Central sequence, which has more persistent coal seams and a higher workable coal content. The latter, within the boundaries from the floor of the Koksovy seam to the roof of the Naddesyaty seam, has a thickness of 115 to 190 m and consists of a rock complex typical for this suite: sandstones, siltstones, argillites, and coals, but with the former predominating over all other varieties, especially in the southern part of the district. The sequence contains 8 coal seams; of these, the upper one—the Naddesyaty seam—has no workable significance, while the Dvoinoi and Sluchainyi seams acquire workable significance only in the northern part of the district. In connection with the variability of the thicknesses of the coal seams and the deposits of the sequence, its workable coal content does not remain constant. The greatest coal content of the Central sequence is observed in the north of the district, where it reaches 7%. Toward the south, the coal content of the sequence decreases, and within the Kozlinsk syncline it does not exceed 4%.

Because of its considerable variability, the Alchedat sequence long remained unstudied, and only in the most recent period has serious attention been paid to it, which is to a significant degree connected with the presence in this sequence of coals suitable for coking. The lower boundary of the sequence is drawn along the roof of the Naddesyaty seam, while the upper boundary has not been reliably established. Its maximum thickness (up to 360 m) has been established in the northern—

of the part of the district. Here it contains up to 12–15 coal seams, of which 8–10 locally acquire workable significance.

The coal-bearing deposits of the district form a complex brachysynclinal fold, subsequently broken up into three synclines: the Anzher, Andreevka, and Kozly synclines. The northernmost—the Anzher syncline—plunges northward. In its deep part, in the northwest, it is cut by the Tomsk or Devonian thrust, along the plane of which the coal-bearing deposits have been brought into contact with Middle Devonian rocks. The same thrust has, to a considerable extent, cut off the western limb of the syncline. As a whole, the Anzher syncline has an asymmetric structure, with highly variable dip angles of the limbs, complicated by additional folds of higher orders and by a dense network of tectonic dislocations varying in character and amplitude.

To the south, separated from the Anzher syncline by an anticlinal uplift, lies another large brachysyncline of the district—the Andreevka. This brachysyncline also has an asymmetric structure, due to its steep western (40–80°) and gentle eastern (10–30°) limbs. It is characterized by uneven plunging of the axes, accompanied by additional bends in the vertical plane. The strike of the axes is characterized by considerable changes in azimuth; moreover, their branching is often observed. The coal-bearing deposits within this brachysyncline are also broken by a considerable number of tectonic dislocations.

Still farther south lies the third large fold of the district—the Kozly syncline, elongated almost in a meridional direction. It is separated from the Andreevka brachysyncline by tectonic dislocation BB. The eastern limb of the syncline, dipping westward at an angle of up to 25°, is most developed. The western limb of the syncline has been almost completely cut off by tectonic dislocation BB. As in the preceding folds, additional folding and gentle waviness have been identified here.

As a whole, the tectonic structure of all three synclines is heterogeneous. The structure of the Anzher syncline is, undoubtedly, more complex than that of the Andreevka and Kozly synclines, although the latter are also complicated to a considerable degree. This circumstance has led to tectonic complexity of the fields becoming one of the principal factors determining the exploration methodology in this district. In this connection, it will be convenient to consider the methodology for exploring the mine fields of this district separately for individual groups of fields and areas characterized by similar features of tectonic structure. For this purpose, all the mine fields and areas of the district may be divided into two groups. The first may include fields located within the Andreevka and Kozly synclines. They are characterized by the development of large folds, usually with small dip angles of the limbs, which are complicated by additional folds, waviness, and a certain number of tectonic dislocations, which determines a rather complex hypsometry of the coal seams.

The second group may include mine fields located within the Anzher syncline. Here, too, large folds are developed, with dips of their limbs from 5–30° in the south to 90°, and in places even overturned bedding is encountered in the north, complicated by additional folds of higher orders, as well as by numerous tectonic dislocations. This syncline is characterized by an enormous number of small dislocations of various forms, which are localized chiefly along the flanks of large longitudinal dislocations. The latter, in combination with plicative formations varied in form, ...

...with disturbances account for the exceptional complexity of such fields (the field of mine 9/15, Western section).

The exploration methodology for fields of group 1 may be considered through the example of exploration of the fields of the mines “Fizkulturnik,” “Andreevskaya-2,” and “Andreevskaya-3.” All the listed mine fields are situated within the limits of the Andreevka brachysyncline, the main structural features of which were indicated above.

Exploration work within the limits of the Andreevka brachysyncline began in 1915, when two exploratory adits were driven and 75 percussion-drilled boreholes were drilled, with an average depth of about 21 m. Later, beginning in 1929, core drilling was begun at the deposit. By 1939, when the first calculation of reserves was made, 40 core-drilled boreholes had been drilled in the field of the “Fizkulturnik” mine, located on 5 exploration lines spaced from one another at distances of up to 700 m. In addition to these lines, by that time 3 lines of percussion-drilled boreholes had been drilled in the field of the “Fizkulturnik” mine and 11 shafts had been sunk.

The indicated works enabled A. M. Zhuravlev not only to establish correctly the position of the coal seams exposed within the limits of this syncline in the general stratigraphic section of the district, but also to calculate reserves. In all, down to the +80 m horizon, reserves were approved in category B—6200 thousand tons, in category C₁—15062 thousand tons, and in category C₂—3754 thousand tons.

In the period from 1939 to 1941, exploration work within the limits of this mine field continued, and by 1942, 10 lines of core-drilled boreholes had already been drilled (Fig. 1). As is evident from the figure, the boreholes proved—

Fig. 1. Seam map of the +80 horizon of the fields of the “Fizkulturnik” and “Andreevskaya-2” mines as of 1941.

1 — coal seams, a — established, b — inferred; 2 — tectonic faults; 3 — core-drilled boreholes; 4 — shaft of the “Fizkulturnik” mine.

were located almost along mutually perpendicular lines, the distances between which were on average 400–600 m. On the basis of these exploration data, the reserves shown in Table 1 were calculated. It is evident from the table that the percentage of reserves of categories \(A_2+B\) on the two horizons proved to be very high (89.2), reaching a maximum for the Eleventh and Tenth seams.

In 1943 the “Fizkulturnik” mine went into operation. The workings of this mine showed that the structure of the mine field was in reality more complicated than had previously been assumed, as a result of which it became necessary to carry out supplementary exploration of the field in order to refine the tectonic structure of individual areas and to increase the reliability of the coal reserves for certain seams. Thus, by 1952 the question arose of writing off 433.8 thousand tons of reserves of the Eleventh seam, previously calculated as category \(A_2\), because the seam proved to be broken by a series of small tectonic faults and over a considerable area had lost its workable thickness.

Mine workings on the \(+80\) m horizon and supplementary-exploration boreholes for certain seams substantially changed the understanding of the structure of the mine field (Fig. 2), which was also reflected in the reserve categories (Table 2). From a comparison of Tables 1 and 2 it is evident that, for all seams on both horizons, after they had been opened by mine workings and supplementary exploration had been carried out, there was some decrease in the share of reserves of categories \(A_2+B\) in the total reserves of the seams, although on the whole it remained high. As for the total quantity of reserves, taking into account the change in the southern boundary of the field and some extraction of the seams by the mine, in all three calculations they proved to be practically identical.

A similar situation is also observed in the field of the “Andreevskaya-3” mine. Here, supplementary exploration in 1952–1956 also produced some change in ideas about the structure of the field through the establishment of a number of tectonic faults and gentle waves, but the total quantity of reserves and the ratio of the individual categories remained the same. Detailed exploration in this field was likewise carried out by core-drilling boreholes arranged along mutually perpendicular lines. It should be noted that in this case the distances between exploration lines and between boreholes did not remain constant, since they were determined in each case by the specific geological setting. Such an arrangement of boreholes, combining the advantages of exploration along exploration lines and on a geometric grid, and taking into account the structural features of the Andreevskaya and Kozlinskaya brachysynclines, proved very successful, since it ensured the interpretation of additional folds, differently oriented waves, and bedding-parallel and cross-cutting tectonic faults.

On the whole, for the four areas distinguished within the Andreevskaya brachysyncline, the density of the exploration network is the same, although the share of reserves of categories \(A_2+B\) in the total reserves of the areas and the exploration expenditures per 1000 tons of coal proved to be different (Table 3).

It should be noted, however, that the increased value of the indicator “p” for the Andreevsky Western and Eastern areas, with a smaller ratio of high-category reserves to total reserves, is explained by the position of these areas in the central part of the brachysyncline, where the maximum subsidence of the seams is observed.

Thus, in the simplest mine fields of the Anzhero-Sudzhensk district, as well as in the mine fields of the first group of the Prokopyevsk-Kiselevsk district [2], 50% of high-category reserves can be obtained with comparatively small exploration expenditures. It should also be noted that, whereas in the Prokopyevsk-Kiselevsk district this is achieved at distances between exploration lines recommended by the instruc-

Fig. 2. Seam map of the +80 horizon of the fields of the “Fizkulturnik” and “Andreevskaya—2” mines as of 1952 (after Altyn-Bash).
1 — coal seams; 2 — portions of coal seams exposed by mine workings; 3 — tectonic faults; 4 — core-drilling boreholes; 5 — mine workings; 6 — mine shafts.

Table 1

Table 2

…[3], then in the Anzhero-Sudzhensk district, owing to the specific structure of such fields, the picture is somewhat different. While belonging, in geological structure, to Group II as distinguished in the instructions, such fields at the same time require, in order to obtain reserves of high categories, a denser exploration grid than is recommended by the instructions.

Table 3

Practice shows that, for the exploration of these fields, a mutually perpendicular arrangement of exploration lines, with a distance between them of 250–300 m, is more acceptable. The indicated distances may vary in one direction or the other depending on the complexity of the area being explored.

The exploration of mine fields of Group II may be considered using the example of the field of mine 9/15, as well as the Western area. The field of mine 9/15 is situated in the closure part of the Anzherka syncline, truncated in the northwest by the largest tectonic rupture in Kuzbass—the Tomsk overthrust. A detailed description of the structure of this field is given in the article by A. N. Leshcheva, published in the present collection. As is known, the field of this mine, located on the footwall side of the Tomsk overthrust, is characterized by exceptional complexity; it is therefore understandable that it has been assigned to Group III of the instructions [3]. It was no accident that it was here that M. A. Usov carried out his classical studies; here his classification of tectonic ruptures was created and a new field of geology—mine tectonics—arose.

Exploration of the field of mine 9/15, as well as exploration of the Andreevskaya brachysyncline, was begun by drilling percussion boreholes and sinking pits; from 1929 onward, core drilling began to be used. As in many mine fields of the Prokopyevsk-Kiselevsk district, exploration in this field was closely connected with the servicing of mining operations. As a result, by 1949, 363 boreholes had been drilled in the mine field, located on 34 exploration lines. The distances between exploration lines and boreholes can be seen in Fig. 3. By that time, mining operations had been concentrated on the +75 m and −13 m levels, and preparatory work was being carried out on the −124 m level. On the basis of these data, in 1949 reserves were calculated and approved; they are given in Table 4.

In considering this table, what first stands out is the significant percentage of high-category reserves on all levels, including…

and at the —124 m horizon, which, for reserve estimation, had been explored by a sparse network of boreholes and had only begun to be opened up by preparatory mine workings (Fig. 3). The subsequent working of the seams at the +75 m and —13 m horizons, and later also at the —124 m horizon, constantly required additional exploration work. Right up to 1955, exploration of the deep horizons continued in the mine field. For this purpose, in the period from 1949 to 1956, another 28 boreholes were drilled. At this time, drilling of core holes from underground mine workings became widely used here; these were employed both for solving questions of geological servicing of operating workings and for exploration of deep horizons.

Table 4

Underground mine workings and core-drilling boreholes made it possible to detail the structure of the mine field. The latter proved to be considerably more complex than had been assumed earlier (Figs. 3, 4).

Fig. 3. Seam map of the —124 m horizon of the field of mine 9/15 as of 1949 (after Burykh).
1 — coal seams; 2 — tectonic faults; 3 — fold axes; 4 — core-drilling boreholes intersecting seams above the —124 m horizon; 5 — boreholes drilled below the —124 m horizon.

Fig. 4. Seam map of the −124 m horizon of mine field 9/15 as of 1956
(after N. N. Elisafenko).
1 — portions of coal seams exposed by mine workings; 2 — underground core-drilling boreholes.

As became clear as a result of mining operations and supplementary drilling, the complexity of the field structure is caused by the extensive development of so-called small structural forms—minor additional folds, flexures, and tectonic ruptures of various shapes, established mainly by underground mine workings. It is understandable that the broad development of such disturbances cannot substantially change the total amount of coal reserves in a mine field, but it greatly complicates the driving of mine workings and, in some cases, may completely preclude the possibility of working seams in individual areas.

Table 5 presents the results of the reserve calculation for the field of mine 9/15 as of the state of our knowledge on January 1, 1956. From a comparison of Tables 4 and 5 it is evident that down to the −124 m horizon the total amount of coal reserves, taking into account extraction and losses (10 million tons), changed very little. The discrepancies in the reserve calculation amount to only 10 percent.

If the total amount of reserves changed hardly at all, their categories changed substantially. In the latest reserve calculation, the reserve categories on the three upper horizons were considerably lowered (Tables 4, 5).

Table 5

The same situation also occurs in many complex fields of the Prokopyevsk–Kiselevsk district. This reduction in the share of high-category reserves in the total reserves of a field as the exploration grid is tightened and seams are opened by mine workings is usually explained by various reasons. In some cases such a reduction is explained by different approaches to evaluating reserve categories at different times; in others, by the fact that more stable and less disturbed seams are worked first, as a result of which the share of reserves in less stable and more disturbed seams increases.

Without denying the influence of these reasons, on the basis of a comparison of the results of different periods of exploration with the operating data for highly dislocated fields, we arrived at a different conclusion. The main reason for the reduction in the share of high-category reserves as the degree of exploration of a field increases is the low degree of reliability of the identified high-category reserves. To be convinced of this, let us turn to the factual material. The principles for identifying high-category reserves when calculating reserves for the field of mine 9/15 in 1949 and 1956 essentially remained unchanged. Meanwhile, on the −124 m horizon the share of high-category reserves decreased from 64.0% to 37.4%, although on this horizon, in the interval

Fig. 5. Calculation plan of the Desyatyi seam.
A — as of 1949; B — as of 1956.
1 — seam structure contours; 2 — tectonic faults; 3 — fold axes; 4 — mined-out areas of seams; 5 — mine workings; 6 — boundaries of pillars; 7 — core-drilling boreholes; 8 — block boundaries; 9 — blocks, their categories and dip angles.

during the interval between reserve calculations, a large number of boreholes had been drilled and, moreover, this horizon had to a considerable extent been opened by mine workings (Figs. 3, 4). On the other hand, if this decrease in the share of reserves of the high categories had been caused by the extraction of reserves of categories \(A_2+B\), then the absolute quantity of reserves of category \(C_1\) would have remained the same. In reality, for all seams on this horizon there was an increase in reserves of category \(C_1\), with the total amount of reserves of the horizon remaining practically the same.

Such a picture could have arisen only in the case where part of the reserves of categories \(A_2+B\) had been transferred to category \(C_1\). A comparison of the structural cards on which reserves were calculated in 1949 and 1956 confirms this conclusion. Figure 5 shows the blocks and categories established in the reserve calculations of 1949 and 1956 in one of the areas of the Tenth seam. From a comparison of the blocks it is evident that an area of the seam previously calculated in the high categories was subsequently, because of strong disturbance, calculated in category \(C_1\) and even partly written off.

The noted lowering of reserve categories in complexly dislocated fields is caused by the fact that subsequent mining and exploration work reveals a much more complex picture of the field structure than had been assumed in the preceding reserve calculation. The same is true for the field of mine 9/15, as is clearly seen from a comparison of Figures 3 and 4. In such fields it is not uncommon for reserves directly adjoining development or stoping operations and assigned to high categories subsequently to prove to have been written off because of strong tectonic disturbance that precludes the possibility of their extraction. It is understandable that reserves of high categories delineated in areas of similar mine fields and explored by a less dense network of exploratory boreholes, and also in the absence of mine workings, will possess a very low degree of reliability.

In this connection there arises the question of the method for delineating reserves of high categories on deep horizons. From Table 5 it is evident that, on the 375 m horizon of the field of mine 9/15, intersected by only 18 boreholes, reserves of high categories amount to 49.2%, i.e., considerably more than on any upper horizon explored not only by a larger number of boreholes but also opened by underground mine workings. It follows that, within one and the same field, the reserves of the upper and lower horizons possess different degrees of reliability. If the total amount of reserves changes comparatively little, then in reality the structure of the seams most often proves to be considerably more complex, and therefore the extraction of such seams is associated with great difficulties and, in places, becomes completely impossible.

All this makes it possible to raise the question of the lack of justification for delineating reserves of high categories on the deep horizons of complexly dislocated mine fields that have been explored by a more widely spaced exploration grid than is accepted for the upper horizons. Meanwhile, exploration by such a sparse grid for lower horizons may be recognized as rational, since it makes it possible, at low cost, to establish the position of the principal structural elements of the field. As for the reserves of the lower horizons in such mine fields, it is advisable to calculate them in category \(C_1\).

On the other hand, the exceptional complexity of the structure of such fields, and especially the wide development of small structural forms, require a more cautious assignment of reserves to high categories even on the upper horizons, since exploration by drilling, even with a very dense grid, cannot ensure the detection of the actual disturbance of the sea—

seams. In this respect, the decision of the VKZ in approving the reserves for the Western sector deserves attention. For this sector, owing to the extreme complexity of its geological structure and to the conditional correlation of the coal seams, it was decided not to distinguish reserves of category \(A_2\), considering it permissible to plan the mine on the basis of a certain quantity of category \(B\) reserves.

It has been noted more than once above that the total reserves of fields calculated in different periods, both in the Anzhero-Sudzhensk and in the Prokopyevsk-Kiselevsk districts, changed comparatively little. From this one may conclude that category \(C_1\) reserves possess a sufficiently high reliability. In this connection it is necessary to dwell on the calculation of the industrial coal reserves of mines.

At present, according to the directive order of the Ministry of the Coal Industry of March 19, 1954, No. D-64, industrial reserves are to be calculated from the sum of balance reserves \(A_2 + B + 50\%\,C_1\), subtracting from it 15% for losses. If there are 50% reserves of categories \(A_2 + B\), only 60% of the coal reserves of the mine field will enter the mine’s industrial reserves; and with a smaller share of reserves of the higher categories, which is almost always the case in complexly dislocated fields, still less. Meanwhile, even in the worst case, an error not exceeding \(\pm 15\%\) may be made in calculating reserves, but even then the mine’s industrial reserves will amount to 70% of all the field’s reserves. Since category \(C_1\) reserves possess a high degree of reliability, it is necessary to take them fully into account, subtracting from the total reserves of the field \((A_2 + B + C_1)\) the losses and, possibly, to establish a correction coefficient for the accuracy of reserve calculation, taking into account the complexity of the field structure and the stability of the seams. Such a method, first, will make it possible, when establishing industrial reserves, to approach mine fields differentially, taking into account their tectonic complexity and the stability of the seams; and second, to take more fully into account the identified reserves, which will make it possible correctly to establish the amortization period and productivity of future mines.

LITERATURE

1. Koudelny V. Ya. Exploration in the Prokopyevsk-Kiselevsk district of Kuzbass. Collection of articles “Experience in the Exploration of Coal Deposits,” Ugletekhizdat, 1957.

2. Koudelny V. Ya. On the question of the methodology of exploration of coal deposits. “Exploration and Protection of Mineral Resources,” No. 5, 1957.

3. Instructions for applying the classification of reserves to coal deposits, Gosgeoltekhizdat, 1954.

Tomsk Polytechnic Institute
named after S. M. Kirov