ANALYSIS OF THE METHODOLOGY FOR EXPLORATION OF MINE FIELDS IN THE PROKOPYEVSK–KISELEVSK DISTRICT OF KUZBASS

V. Ya. Koudelnyi

(Presented by Professor, Doctor A. A. Belitskii)

Introduction

A considerable increase in the volume of geological exploration work requires a fundamental improvement in exploration methodology. In the periodical press the question of revising the methodology for exploring mineral deposits has been raised more than once (V. G. Solov'ev, 1952; A. I. Iolin, 1952; I. P. Sharapov, 1952; I. I. Molchanov, 1953). This applies fully also to coal deposits.

At the present time there is a large number of well-explored and partially or completely mined-out mine fields. This opens the way to an analysis of exploration and to a comparison of its results with operating data, which in the final analysis should lead to the solution of many problems of exploration methodology. Unfortunately, such works, generalizing a large body of factual material on exploration methodology, are almost unknown in the literature. True, recently more attention has begun to be paid to these questions (V. S. Popov, 1953; V. S. Ogarkov, 1954; E. M. Senderzon, 1956). Of definite interest in this respect is also the “Instruction on the Application of the Classification of Reserves to Coal Deposits,” approved in 1954. However, these works, being based on the statistical method, cannot fully solve a number of important exploration questions. Thus, because of insufficient consideration of the specific conditions of particular deposits, the instruction proves to be too general. For example, it practically does not resolve the question of distances between boreholes on exploration lines, and the ratio of balance coal reserves of categories A₂, B, and C₁, necessary for developing projects and allocating capital investments for the construction of mining enterprises, in some cases proves to be irrational.

The work of the All-Union Conference on methodology, economics, and quality of geological exploration work for coal within the geological exploration service of the Ministry of the Coal Industry of the USSR, held in June 1956 in Moscow, was of great importance in resolving questions of methodology for exploration of coal deposits. This conference developed a whole series of measures to improve exploration methodology and economic indicators. One such measure is the compilation of manuals on exploration methodology as applied to basins and large deposits, and this work was to be completed by 1958. The compilation of such manuals should be carried out on the basis of—

new generalizations of all the material accumulated on exploration methodology; at the same time, an important place should also be occupied by the method of comparing exploration results with data from mining operations. The almost complete absence in print of works on the analysis of exploration of mine fields and individual coal-bearing districts on the basis of comparing exploration results with operating data prompted us to attempt to carry out such work using the example of the mine fields of the Prokopyevsk–Kiselevsk district of Kuzbass.

General Part

Within this district, the productive deposits are those of the Balakhonka suite, which here, according to the local stratigraphic subdivision, has a fourfold division—zero, lower, middle, and upper strata, differing both in coal content and in lithological composition. Of greatest interest are the deposits of the last two strata, which contain more persistent coal seams and have a higher workable coal content.

The middle stratum, 170–260 m thick, consists of the rock complex usual for this suite: sandstones, aleurolites, argillites, carbonaceous argillites, and coals, but with sandstones predominating over all other varieties. The stratum contains up to 13 coal seams; of these, 5 occur very rarely, while the remaining 8 seams have workable significance in almost all mine fields. Two of these seams—Gorely and Moshchny—are distinguished by their considerable thickness (up to 20 m), as a result of which the workable coal content of the stratum proves to be high, in places reaching 20%.

The upper stratum, 150–250 m thick, is represented by aleurolites and argillites, although in individual areas sandstones are predominantly developed. The stratum contains 9 coal seams, of which 5 within the district almost do not lose their workable significance. The remaining seams occur only in individual mine fields. The workable coal content of the stratum reaches 13%.

The coal-bearing deposits of the district form a complex brachysynclinal fold, the limbs of which are gathered into relatively narrow, compressed folds complicated by longitudinal faults. The latter create an imbricate structure. In the western part of the district only synclines have been preserved. As for the anticlines, along major tectonic faults they have proved to be uplifted and denuded. In the eastern part, anticlinal folds have largely been preserved.

The limbs of the folds have steep dip angles, in individual areas changing from 30–40° to vertical and even overturned. Often, especially on the limbs of the main folds that have a western dip, additional folds and flexure-like bends of the seams are encountered.

The entire thickness of the coal-bearing deposits is broken by a dense network of tectonic faults of various types. Almost all major longitudinal faults dip westward at an angle of 65–85° and have displacement amplitudes of hundreds and even thousands of meters. Usually, on the sides of these faults there is observed a dense network of smaller faults, oriented in various ways, with displacement amplitudes from units to several tens of meters. In general, the tectonic structure of the fields is heterogeneous. Along with areas of simple structure, the district contains areas of exceptionally complex structure, caused by the complexity of plicative structures and by the enormous number of tectonic faults differing in form and amplitude. This circumstance has led to the fact that tectonic

the complexity of the area became one of the main factors determining the exploration methodology in this district.

Studying the tectonic structure of the mine fields of the district and analyzing the methodology of their exploration, we came to the conclusion that it is necessary to distinguish at least three types of areas: the first and third types correspond

Table 1

to groups II and III distinguished by the Instruction (1954), while the second is intermediate between them. The characteristics of the established types are given in Table 1. The distinction of types is based on taking into account the complexity and nature of the manifestation of plicative formations, as well as the complexity, dimensions, and number of fault disturbances.

The second factor determining the exploration methodology within this district is the variability of the thickness and structure of the coal seams. For analysis, such fields were taken where deposits of the middle and upper series are developed. The overwhelming majority of seams of these series, according to the classification given in the Instruction (1954), should be assigned to relatively persistent seams.

In addition to these factors, other factors also exert a noticeable influence on the exploration methodology, for example, relief conditions, the depth of occurrence of the seams, the thickness and water saturation of the cover deposits, and the degree to which the district has been studied—

it and the use of materials from the exploitation of the upper horizons. The influence of these factors will be shown when considering the methodology for exploration of mine fields of various types.

As the principal method of analysis we have adopted the method of comparing the results of explorations of different stages and, where possible, comparing them with data from exploitation work. In doing so, both the geological and the economic effectiveness of the exploration carried out are compared (tectonic structure, consistency of coal seams in thickness, increase in reserves of high categories, consumption of core-drilling footage per 1 ton of explored coal). In carrying out such an analysis, special attention must be paid to the degree of preparedness of the field for exploitation and to the economy of exploration. At present, the indicator adopted as a measure of the degree of preparedness of a mine field for exploitation is the “degree of exploration,” which is the ratio, expressed as a percentage, of reserves of categories A₂ + B to all reserves of the mine field. It is convenient to analyze the economy of exploration by comparing expenditures, in particular the footage of core boreholes required per 1000 tons of explored coal reserves of high categories (A₂ + B). For convenience this ratio is called the indicator “P.”

When approving reserves in the GKZ, the latter usually requires that the mine fields of the Prokopyevsk–Kiselevsk district be assigned to groups “b” and “v” of the approved ratios of balance reserves of minerals of categories A₂, B, and C₁ for the development of designs and allocation of capital investments for the construction of mining enterprises (1954). From these ratios it is evident that the degree of exploration of mine fields for the indicated purposes should not be less than 50%. This figure is the basis for choosing the density of the exploration grid and, consequently, must determine the effectiveness and economy of exploration of a mine field. Let us consider the advisability of such provisions under the conditions of the Prokopyevsk–Kiselevsk district.

Analysis of the Methodology for Exploration of Mine Fields of the District

Exploration of Type I Mine Fields

The methodology for exploring the simplest fields in the Prokopyevsk–Kiselevsk district may be considered using the example of the Abinskoye-Severnoye mine field. Within this field the seams of the upper, middle, and partly lower strata are developed.

The tectonic structure of the field is characterized by considerable simplicity. The principal plicative structures developed here are the II Tyrgan anticline and the western limb of the Intermediate anticline (Fig. 1). The II Tyrgan anticline is a relatively broad, almost symmetrical fold, with a somewhat steeper western limb. The dip angles of the limbs do not remain constant, but change quite regularly—on the western limb from 55° in the south to 25° in the north, and on the eastern limb from 50° in the south to 15–20° in the north. The axis of the anticline in the southern part is almost horizontal (with a northward inclination at an angle of 1–2°), but northward the plunge increases to 15°, as a result of which the closure of all seams is recorded beneath the overburden. In addition to such bending of the axis, exploration work has established a more minor undulation of it.

The western limb of the Intermediate anticline has a steeper dip, in places reaching 90°. It is the more complex part of the field and should be assigned to Type II.

The western limb of the II Tyrgan anticline is cut by the tectonic fault L—L. This is a conformable reverse fault dipping westward at an angle of 75–80°, with a displacement amplitude along it of about 300 m. According to

Along the western limb of the Intermediate anticline there passes the second major fault of the R—R area, likewise of the type of a conformable reverse fault, with the plane of the displacer dipping westward at an angle of 80–85° and with a displacement amplitude in the plane of the displacer averaging 800–900 m. Exploration work has established a number of second-order faults affecting the axial part and the western limb of the Intermediate anticline.

Exploration of the Abinsky Northern field was begun in 1930 by the sinking of test pits and by zigzag drilling, which established the presence of coal seams here. In 1932 preliminary exploration was undertaken; it consisted in laying out two exploration lines (VII and VIII), located 1650 m apart, on which 11 core-drilling boreholes were drilled, with a total footage of 2952 m (Fig. 1). This exploration established the development, in the given field, of the upper part of the deposits of the Balakhonka suite and a rather simple tectonic structure.

Later, in 1941–1942, detailed exploration work was carried out on the mine field; two more exploration lines were drilled (VIII—IX and VII—VIII), and additional boreholes were also drilled along the previously laid-out lines (Fig. 1). The distances between exploration lines during detailed exploration were reduced to 625–850 m. It must be noted that none of the boreholes drilled by that time went below the +100 m horizon. The boreholes along the exploration lines were arranged in such a way that, along individual lines, a continuous section was obtained (for example, along exploration line VII, Fig. 2, B), whereas along other lines not all seams on the limb of the anticline were intersected by boreholes (exploration line VII—VIII, Fig. 2, A). On those seams where there is a double intersection by boreholes, the distance between the points of intersection down the dip is within 160–200 m.

The results of the detailed exploration of 1941–1943 are shown in Table 2. From this table it is evident that the degree of exploration of the western limb of the II Tyrgan anticline (51.5) proved sufficient for transfer to exploitation, but for the other limbs of the folds of the field it is low (about 39%), as a result of which the overall degree of exploration reached only 42.4%.

On the western limb of the II Tyrgan anticline, the three upper horizons have a degree of exploration greater than 50%. Reserves of high categories are also present on the fourth horizon (10.4%). Thus, this limb, with the density of the exploration grid as of 1943, proved to be quite sufficiently explored. In this case, 2883 linear m of core boreholes were expended on exploration of the coal seams of the limb, and the value of the indicator “p” proved equal to 0.069.

The eastern limb of the II Tyrgan anticline has, on two horizons, a degree of exploration greater than 50%, but, owing to the weak exploration of the lower horizons, the overall degree of exploration proved low (39.6%). The seams of the western limb of the Intermediate anticline are explored even more weakly. Thus, a uniform density of the exploration grid in a field having varying complexity of tectonic structure produced a different degree of exploration. Hence it follows that, even within the limits of a single field, it is necessary to differentiate areas according to the complexity of their tectonic structure and, for each of them, to specify the corresponding density of the exploration grid.

In connection with the weak exploration of the lower horizons of this field, the Ministry of the Coal Industry of the USSR proposed carrying out additional exploration of it. This additional exploration was carried out in 1955 (Fig. 1). It must be noted that it did not solve the problems of mine-opening exploration, since there is still no mine design for working the seams of the field. In planning the additional exploration, the premise was that

Fig. 1. Map of coal-seam outcrops beneath the overburden (after G. N. Voronkova). 1—seam outcrops beneath the overburden (a—traced, b—inferred); 2—tectonic faults; 3—worked-out part of coal seams; 4—burned-out part of coal seams; 5—exploratory core-drilling boreholes: a—preliminary exploration, b—detailed exploration, c—additional exploration, d—exploration for open-pit mining of the Moshchnyi seam.

that, by tectonic characteristics, the field should be assigned to Group II with relatively stable seams (1954).

Table 2

Taking into account the degree of exploration of the limbs of the folds achieved in 1943 (Table 2), the main attention should have been devoted to further exploration of the lower horizons of the eastern limb of the II Tyrgan anticline and the western limb of the Intermediate anticline, since precisely these had not been sufficiently explored. In fact, further exploration was carried out on all three limbs, although on the western limb of the II Tyrgan anticline a degree of exploration of 51.5% had already been achieved.

According to the further-exploration data, the following results were obtained (Table 3).

Table 3

Fig. 2A. Geological section along exploration line VII—VIII.

Fig. 2B. Geological section along exploration line VII.
1 — coal seams (a — established, b — inferred, c — burned out); 2 — tectonic faults; 3 — exploratory core-drilling boreholes.

From a comparison of Tables 2 and 3 it is evident that the total reserves of the western limb of the II Tyrgan anticline changed hardly at all (decreased by 3%). The degree of exploration of the limb’s seams increased by 8.3%, but this was achieved by an increase in the footage of core boreholes of 1,930 linear meters, and the indicator “p” increased from 0.069 to 0.145. If the increase in the footage of core boreholes is related to the increase in reserves of high categories, the result is a very high figure (0.734), five times greater than for the eastern limb of this anticline.

The high percentage of reserves of category A₂ also attracts attention. According to the first calculation they amounted to 17%, and after supplementary exploration they increased to 33.6%, i.e., exceeded the required amount by more than 1.5 times.

The distances between the points at which seams were cut by boreholes along exploration lines were reduced to 90–100 m (section along exploration line VII–VIII (Fig. 3)), but the supplementary exploration did not introduce any substantial changes into the conception of the nature of the structure of this limb. It should be noted that, in the area, by 1943 the outcrops of coal seams beneath the overburden had been traced quite insufficiently. As a result, the places where seams closed on the outcrop map compiled in 1943 do not coincide with the 1956 map. Thus the Moshchnyi seam (Figs. 2, A and 3) was drawn on the 1943 map 350 m farther north than it actually is, as a consequence of which the reserves for the seam after supplementary exploration decreased by 10%. In general, the supplementary exploration led to re-exploration of the coal seams of this limb, while expenditures per 1,000 tons of reserves of high categories increased considerably.

A similar picture was obtained for the eastern limb of the II Tyrgan anticline. The presence here, after supplementary exploration, of a degree of exploration of 65.2%, with 36.9% of category A₂ reserves, likewise indicates over-exploration. The indicator “p” for this limb increased from 0.090 to 0.116. It must be taken into account, however, that the supplementary exploration did not resolve questions of development exploration; therefore, when opening the field, a considerable additional amount of borehole footage will be required.

In connection with consideration of the results of the supplementary exploration of this field, the question arises of exploration of the lower horizons. The over-exploration of the limbs of the II Tyrgan anticline was caused, first of all, by the desire to explore the coal seams in equally great detail on all horizons. It is unlikely that there is any need, at the ±0 m horizon, to have a degree of exploration of 30%, obtained at considerable exploration cost.

Finally, supplementary exploration of the western limb of the Promezhutochnaya anticline led to a considerable increase in the total amount of reserves, but the degree of exploration of the seams decreased from 38.9% to 35.3%. This limb has a more complicated structure; nevertheless, both during detailed exploration and during supplementary exploration the density of the exploration grid was the same as on the simpler limbs of the II Tyrgan anticline. As a result, the seams of the western limb of the Promezhutochnaya anticline proved to be underexplored.

From the analysis of exploration of the Abinsk North field and of fields analogous to it (Abinsk South, Ziminka 5, and others), the following conclusions follow.

1. In mine fields of type I, a degree of exploration of 50% of the required reliability is achieved with relatively small exploration expenditures.

2. Within one and the same mine field there may be areas of different types, which requires a differentiated approach when selecting the density of the exploration grid.

3. The distances between exploration lines, in order to achieve a degree of exploration of 50%, should be within the range of 500–800 m, and the dist—

Fig. 3. Geological section along exploration line VII–VIII according to supplementary exploration data.

distances between the points where the seam is intersected by boreholes on the exploration line are within 150–200 m.

1. Obtaining reserves of high categories on the lower horizons entails a considerable increase in exploration costs, whereas the exploitation of the upper horizons leads to an increase in the degree of exploration of the lower horizons. Proceeding from this, one should not strive for a high degree of exploration of seams on the lower horizons. Given the same amount of total reserves on different horizons in fields of type I, a degree of exploration of 50% can be obtained at lower cost if it is distributed over the horizons within the following limits: on horizon I—80–85%, on II—70–75%, on III—40–45%, and on IV—5–10%.

Exploration of Type II Mine Fields

The exploration of type II mine fields may be considered using the example of the exploration of the Krasnogorskaya mine field.

The productive deposits of the field of this mine, as in the preceding case, are represented by the upper and middle members of the Balakhonka series. This field is situated within the Krasnogorskaya anticline—a rather narrow brachyfold with an additional undulation of the axis in the vertical plane. In transverse vertical section the anticline has an asymmetrical form. The dip angles of the seams on the western limb are usually somewhat gentler and vary on average from 50 to 65°, whereas on the eastern limb they vary within 60–80°.

As a whole, the field is not complex with respect to disjunctive tectonics, although it is undoubtedly more complex than the structure of the II Tyrganskaya anticline in the Abinskoye Northern field. Exploration and mining-exploitation work revealed a major tectonic fault R—R and about a dozen smaller ones (Fig. 4).

Development of the mine field began in 1931, when, during geological surveying, the closure of an anticlinal fold formed by Seam VI Internal was discovered. In 1933, for prospecting purposes in the middle part of the field, exploration line VIII was drilled (Fig. 4); at the same time, at shallow depth the closure of the Krasnogorskaya anticline was exposed, composed of coal-bearing deposits with the Internal seams. In the course of preliminary exploration, exploration lines I and XVI were drilled, located at a distance of 1800–2000 m from exploration line VIII; thereby the main features of the structure of the field were established and an idea of its industrial significance was obtained. After these lines had been drilled, they proceeded to reduce the spacing between them to 1 km. For this purpose, exploration lines IV and XIII were drilled. The complexity of the structure of the northern part of the field also required the laying out of exploration line II. In all, at this stage of exploration, 28 core boreholes were drilled, with a total footage of 6663 linear m.

As a result of this exploration, reserves were calculated down to the ±0 m horizon (Table 4).

Table 4

Fig. 4. Map of coal-seam outcrops beneath the overburden in the field of the Krasnogorskaya mine. 1—prospecting-exploration boreholes; 2—preliminary-exploration boreholes; 3—detailed-exploration boreholes; 4—production-exploration boreholes; 5—boreholes for exploration of deep horizons.

After approval of the reserves based on preliminary exploration data, a working design was prepared for the Krasnogorskaya mine, but the expert review and the VKZ noted that the field had not been explored sufficiently and proposed that it be further explored. As early as 1939, detailed exploration began; in the course of it, an additional 17 core boreholes were drilled, with a total footage of 3503 linear m. These boreholes drilled exploration lines VI and X and supplemented the lines laid out earlier (Fig. 4). The distances between exploration lines proved to be within the range of 350–525 m.

According to the detailed exploration data, the following reserves were established (Table 5).

Table 5

From a comparison of Tables 4 and 5 it is evident that there were no substantial changes in the total quantity of reserves, but after detailed exploration their categories changed considerably. The degree of exploration increased to 49%.

According to the data of this exploration, in 1945 the Krasnogorskaya mine was laid out on the field; however, extraction work at the +200 m horizon encountered certain difficulties. It was necessary to clarify the position of the closure along seam IV Inner and to determine the position of a number of tectonic faults. Thus, it became necessary to increase the degree of reliability of the reserves of industrial categories on the operating horizon. To solve these tasks, additional exploration was carried out, which was at the same time development exploration. For this purpose, new lines were laid between the existing exploration lines, and the distances between them became 200–500 m. Further, owing to insufficient exploration of the ±0 m horizon, and also taking into account the limited coal reserves on the upper horizons, exploration of the deep horizons was begun. As a result of these works, another 38 boreholes were drilled, including 10 deep ones, with a total footage of 11080 linear m. Recalculation of the reserves after carrying out the indicated exploration work and opening the +200 m horizon by mine workings gave the following results (Table 6).

Table 6

Comparing the results of the calculation of total reserves, it should be noted that the greatest discrepancies were obtained at the ±0 m horizon. Previously, at the ±0 m horizon, the outcrop of the Kharakternyi seam was assumed to average—

...with a thickness of 1.4 m, which was included in the reserve calculation. Deep boreholes established that the Kharakternyi seam in this field has been eroded, and its place in the stratigraphic section is occupied by the Gorelyi seam, 10 m thick.

Further, the slight change in the degree of exploration of the field is noteworthy: it increased by only 4.3%, despite the fact that during follow-up exploration 11,080 linear m of core boreholes were drilled, and the +200 m horizon by that time had in fact been exposed by mine workings.

It would seem that by 1954 the +200 m horizon should have had the highest degree of exploration. In fact, it decreased to 39.6% as against the previously established 88%; that is, the reliability of the reserve categories established by detailed exploration with distances between exploration lines of 500 m was not confirmed on this horizon, although the total quantity of reserves on the horizon remained practically the same.

This decrease in the degree of exploration on the given horizon is connected with the fact that, in addition to the plunge of the anticline axis to the north and south from the central part of the field, a waviness of the second-order axis with an amplitude of up to 50 m was established along the seams. In order to avoid major errors in establishing reserves of high categories in the hinge part, a belt was distinguished for each seam, the reserves of which were assigned to category C₁. In addition, many additional faults were encountered by mine workings and boreholes. These faults broke up some of the large blocks whose reserves had previously been assigned to high categories into smaller ones, and therefore the reserves in some of them were transferred to lower categories. The establishment of fault 1—1 (Fig. 4), extending almost across the entire field, led to a significant decrease in the degree of exploration. In the blocks adjoining this fault, the reserve categories were also lowered. Further, refinement of the structure of the hinge part of the fold in some cases also led to the lowering of reserve categories.

On the +100 m horizon, the degree of exploration also decreased for the same reasons, although it should have increased, since this was promoted by the mine workings on the +200 m horizon and by the increased number of seam intersections by boreholes. It cannot but be noted that the decrease in the degree of exploration of the +200 m and +100 m horizons gives grounds for questioning the reliability of the reserve categories on the lower horizons. Thus, the increase in borehole footage led to refinement of individual elements of the structure (Fig. 5) and to a significant decrease in the degree of exploration on the upper, most thoroughly explored horizons, although overall for the field the degree of exploration increased somewhat. It is clear that in this case the increment in the degree of exploration lagged behind the increment in borehole footage. Thus, the index “p,” according to preliminary-exploration data, at a degree of exploration of 25.4%, proved to be 0.398, while according to detailed-exploration data, at a degree of exploration of 49%, it decreased to 0.306. Consequently, in the second case the relative increase in reserves of high categories was greater than the relative increase in core-borehole footage. A further increase in the degree of exploration to 53.3% was already accompanied by an increase in the index “p” to 0.392.

It should be noted that the practically complete coincidence of the quantity of reserves for the different calculation periods indicates a high degree of reliability of the category C₁ reserves.

From the analysis of exploration of the Krasnogorskaya mine field and other fields, a number of conclusions follow.

Fig. 5. Geological section along exploration line VIII:
a — according to preliminary exploration data;
b — according to detailed exploration data;
c — according to operational exploration data.

1. The reliability of the calculated reserves of the higher categories, established by detailed exploration, proves to be comparatively low. This is confirmed by the decrease in the degree of exploration of the working horizons as the exploration grid is tightened and as they are opened by underground mine workings. A striking proof of this is also the comparison of the degree of exploration of seams on working horizons and on the horizons adjacent to them. Paradoxical as it may seem, the degree of exploration of a working horizon well studied by underground workings is usually lower than that of the underlying horizon, although the latter has been studied incomparably worse. Of course, in individual cases a reduction in reserves of the higher categories on a working horizon may occur as a result of the mining out, first of all, of the most persistent undisturbed seams, and therefore the proportion of strongly disturbed and less explored seams may increase. However, with respect to the field of the Krasnogorskaya mine and to some other mine fields of this type in the given district, where mining of the seams of the working horizon is only beginning, these considerations cannot alter our principal conclusion.

2. If the degree of exploration of the working horizon is taken as the basis, since it is the best studied not only by boreholes but also by a large number of underground mine workings, then, probably, one cannot count on obtaining, as a result of detailed exploration, 50% of reserves of the higher categories of sufficient reliability over the entire mine field as a whole.

Proceeding from this, a 50% degree of exploration of sufficient reliability for mine fields of type II can be obtained only in the course of operational exploration. It would hardly be rational to set such a task for detailed exploration, since this would involve enormous expenditures.

Exploration of Type III Mine Fields

Let us consider the methodology of exploration of type III mine fields using the exploration of the field of the Kalinin Mine as an example.

The principal plicative structures of this field are the western limb of the III syncline and the eastern limb of the II syncline. The first has a persistent strike with dip angles of 70—75°. In the north the limb is complicated by an additional fold, cut off to the south by a large fault. The seams of the eastern limb of the II syncline have dip angles of 65—75°. In the central part of the field, a sharp anticlinal fold has been identified on the limb, also cut off in the north and in the south by large tectonic faults. These generally simple plicative structures are complicated by large longitudinal faults B—B, D—D, C—C, M—M, A—A and by a large number of small tectonic faults of various forms and amplitudes, as a result of which the field of the Kalinin Mine proved to be the most complex in the Prokopyevsk-Kiselevsk district (Fig. 6).

Exploration of this field began in 1929. During 1929—1930 a sparse network of core exploratory boreholes and pits was driven, located along exploration lines II, V, XI and XIII, with distances between them of 1000—1300 m (Fig. 6). On the basis of this exploration a mine was laid out in 1932. From 1934, exploration work on the mine field was resumed, and by 1938 the distances between exploration lines had been reduced by half (lines I, III, VII, X and XII were drilled). The initiation of exploration work was caused by the need to establish the actual structure of the field, since underground mine workings had revealed a more complex geological structure of the mine field than had been assumed at the time the mine was laid out. After the conducting

Fig. 6. Map of seam subcrops beneath the overburden in the field of the Kalinin Mine (after A. N. Mankevich).
1—core-drilling boreholes drilled in the mine field by the time the mine was laid out; 2—boreholes drilled in 1938; 3—boreholes drilled in 1941; 4—boreholes drilled in 1947; 5—boreholes drilled before 1952; 6—supplementary-exploration boreholes of 1953–1954.

On the basis of this exploration, in 1938 K. S. Kuryshev compiled a map of the outcrops of seams beneath the overburden and seam maps of the horizons (Fig. 7).

On the seams of the eastern limb of syncline II, a large number of tectonic faults were shown. On the whole, despite the considerable volume of exploratory drilling (87 core holes with a total footage of 17,370 linear m) and the presence of mine workings, by this time there was no clear conception of the structure of the field, which necessitated continuation of the exploration work. By 1941, when geologist A. A. Kostlivtsev had compiled a new map, differing substantially from the previous one (Fig. 8), another 30 boreholes had been drilled, with a total footage of 2,800 linear m. On the basis of the materials from these exploration and mining operations, a calculation of reserves down to the \(+0\) m horizon was made; it identified 167,287 thousand t of coal at a degree of exploration of 25.9%, of which 36,263 thousand t, at a degree of exploration of 53.4%, was established on the \(+220\) m horizon.

The low degree of exploration of the seams of the upper horizon (\(+220\) m) attracts attention, although by that time a significant part of them at this horizon had been exposed by mine workings. Thus, the seams of the western limb of syncline III had been almost completely exposed by mine workings (Fig. 8). A large number of mine workings had also been driven on the eastern limb of syncline II. At the same time, a considerable part of the reserves exposed by underground mine workings had not been worked out, since by the time of the recalculation only 14% of the coal reserves on the horizon had been mined and lost. The indicator “p,” according to exploration data up to 1941, proved to be 0.464; moreover, it is necessary to take into account the significant increase in the degree of exploration due to mine workings.

After 1941, exploration work in the mine field continued, and by 1947 another 71 boreholes had been drilled, with a total footage of 7,600 linear m, which resulted in an exploration-grid density of 125–300 m (Fig. 6). On the basis of these data, geologist A. S. Zabrodin reviewed all materials relating to the tectonic structure of the mine field. The map compiled by A. S. Zabrodin (Fig. 9) differs substantially from the preceding maps in its greater detail and in its new interpretation of the structure of a number of areas of the field.

On the basis of the compiled materials, a reserve calculation was made in 1947. We have at our disposal only the results of the calculation for the western limb of syncline III, where the degree of exploration of the seams of the limb down to the \(+0\) m horizon proved to be 16.3%; on the \(+220\) m horizon, 51.9%; on the \(+140\) m horizon, 41.4%; and on the \(+0\) m horizon, 0%. Once again, the low degree of exploration attracts attention, both for the limb as a whole and for individual horizons, especially the horizon of mine workings (\(+220\) m) and the adjacent one (\(+140\) m). In fact, by this time all coal seams on the 220 m horizon had been exposed by mine workings (Fig. 9), and nevertheless the degree of exploration barely reaches 50%. This example quite definitely indicates that, in mine fields of this type, it is impossible to obtain 50% of reserves in the reliable categories \(A_2 + B\) by drilling operations.

Despite the dense grid of exploratory boreholes and the presence of a large number of mine workings, the complex geological structure of the mine field required production exploration to be carried out on a broad scale; as a result, by 1952 another 16 boreholes had been drilled. Finally, in 1953 exploration of the lower horizons of the field was begun, and in 1954 it was completed. In all, during this period 38 boreholes were drilled, with a total footage of 12,750 linear m. On the basis of the materials of this exploration, taking into account all pre-

Fig. 7. Seam map of the \(+220\) horizon of the field of the Kalinin Mine as of 1938 (after K. S. Kuryshev).
1—coal seams (a—established, b—presumed); 2—tectonic faults; 3—mine workings; 4—core-drilling boreholes.

Fig. 8. Seam map of the +220 horizon of the field of the Kalinin Mine as of 1941 (after A. A. Kostlivtsev).

previous work, new graphic materials were compiled and the reserves were recalculated.

A comparison of A. S. Zabrodin’s map (Fig. 9) with the 1954 map (Fig. 10) shows that, in tectonically complex areas, even an exploration-network density of 120–150 m, despite the presence of a large volume of mining workings, does not ensure correct deciphering of the structure. This can be seen in the example of the exploration of part of the eastern limb of syncline II, enclosed between exploration lines III and IV (Figs. 9, 10, 11a, 11b).

Table 7 gives the results of the 1954 reserve calculation. It is interesting to note that the discrepancies in determining the total amount of reserves according to the calculations of 1941 and 1954 are within 10–12%, i.e., here too the high reliability of the reserves of category $C_1$ is confirmed.

From Table 7 it is evident that at the lower horizons $+140$ and $+60$ m the degree of exploration is even somewhat greater than at the $+220$ m horizon, and this ensured a comparatively high degree of exploration of the mine field—51.2%. Meanwhile, taking into account the very complex structure of the field, one may assert that the high degree of exploration of the lower horizons has low reliability. We have already noted above that, owing to complex tectonics, the densification of the exploration network and the increase in the number of underground workings often led not to an increase, but to a decrease in the

Table 7

degree of exploration. This is characteristic not only of the Kalinin mine, but an analogous situation was observed at the Ziminka 3–4 mines, the Vakhrushev mine, and others. Therefore, the high percentage of industrial categories of reserves at the lower horizons, explored only by boreholes and, moreover, by a sparser network than the working horizon, which is also well explored by underground mine workings, is in no way justified. This indicates that the methodology for distinguishing industrial categories has been developed inadequately, and that production orga-

Fig. 9. Seam map of the \(+220\) horizon of the field of the Kalinin Mine, as of 1947 (after A. S. Zabrodin).

Fig. 11a. Geological section along exploration line III, as of 1947 (after A. S. Zaborodin).

Fig. 116. Geological cross-section along exploration line III as of 1954 (after A. N. Mankevich).

...organizations do little to analyze and generalize exploration materials; in particular, they poorly study and use, when calculating reserves, the regularities in the tectonics of mine fields.

Analysis of the exploration of mine fields of type III makes it possible to draw a number of important conclusions.

1. The low degree of exploration of fields of this type indicates that the density of the exploration grid adopted for their exploration, even with a large number of mine workings, does not ensure that 50% of reserves of high categories of the required reliability will be obtained. Further tightening of the grid in the course of detailed exploration is unlikely to be rational. Suffice it to say that, in order to obtain a degree of exploration of only 30%, in the presence of a significant number of mine workings on the upper horizon, it is necessary to drill 6–7 times more core boreholes than are needed to obtain the same degree of exploration in fields of type I.

2. When detailed exploration is carried out in fields of type III, the leading structural elements must be established (the principal and subsidiary folds, major tectonic faults, and their largest apophyses), and the principal regularities in their manifestation must be clarified. Of great importance here should be the prediction of the faulting of the field, based on study of the regularities of its tectonic structure. It is clear that such detailed exploration will make it possible to calculate reserves mainly in category $C_1$, and only a small part of them can be calculated in category B.

3. In order to provide a front for stoping operations in such fields, it is necessary to organize a more detailed study of the tectonic structure during the conduct of development and stoping operations. In this case, development workings, accompanied by directed production exploration, must be driven with a considerable lead time.

REFERENCES

1. Solov’ev V. G.—On the state of the development of questions of exploration methodology. Razvedka nedr, No. 3, 1952.

2. Iolin A. M.—On the question of developing the problem of exploration methodology. Razvedka nedr, No. 6, 1952.

3. Sharapov I. P.—Overcome the lag in exploration methodology. Razvedka nedr, No. 6, 1952.

4. Molchanov I. I.—Against formalism in exploration methodology. Razvedka nedr, No. 2, 1953.

5. Popov V. S.—On the question of exploration methodology and the geological evaluation of coal deposits of the Donets Basin. Ugol’, No. 9, 1953.

6. Ogarkov V. S.—Geological factors determining the methodology of prospecting and exploration of coal deposits of the Moscow Basin. Razvedka i okhrana nedr, No. 6, 1954.

7. Senderzon E. M.—On the stages of geological exploration work for coal under the conditions of Kuzbass. Razvedka i okhrana nedr, No. 9, 1956.

8. Instructions for applying the classification to coal deposits. Gosgeoltekhizdat, 1954.

Corrections and Noted Misprints

In S. A. Stroitelev’s article “Study of the Crystallization of Epsomite and Mirabilite,” for technical reasons braces have been replaced by square brackets, for example: [100] instead of {100}, etc.