Density of the Network for Detailed Exploration and Sampling of Coal Deposits in Kuzbass

E. M. Pakh and E. M. Senderzon

General Information on the Geology of the Kuznetsk Basin

The coal-bearing deposits of the Kuznetsk Basin are represented by a series of sedimentary rocks from the Lower Carboniferous to the Middle Jurassic. At the base of the coal-bearing formation there everywhere lies the marine Lower Carboniferous. The productive complex is divided into suites, of which the lowest—the Balakhon suite—is the most coal-saturated and is developed more intensively than the others by mines and open pits. This suite contains 35 workable coal seams with thicknesses from 1–3 to 10–25 m. The thickest and most persistent seams are confined to the upper horizons of the suite.

The next coal-bearing Kolchugino suite upward is separated from the Balakhon suite by the Kuznetsk suite, in which workable coal seams are absent. The Kolchugino suite contains up to 60 workable seams, chiefly of small and medium thickness—0.70–2.0 m, more rarely 3–5 m. Individual seams in its upper parts reach thicknesses of 8–12 m.

The third coal-bearing suite—the conglomerate suite of Jurassic age—contains up to 12 workable seams of brown coal and is not being developed at the present time.

The sequence of deposits of the listed suites and their ages are shown in Table 1.

In terms of the conditions of occurrence, the basin is an enormous trough, the long axis of which has a NNW–SSE direction. In cross section the Kuzbass trough has an asymmetric structure owing to its steep southwestern limb and relatively gentler northeastern limb. The former limb is characterized chiefly by complex tectonic structures with narrow, linear-type folds. In this part of the basin the most complex disjunctive tectonics is developed, with faults having amplitudes up to 1000–1500 m.

In the central part of the basin the folds acquire gentle isometric outlines; the number and extent of fault disturbances are noticeably reduced. The northeastern limb of Kuzbass is characterized predominantly by monoclinal occurrence with gentle angles of dip of the rocks toward the center of the basin.

The basin is characterized by very poor exposure. Bedrock is exposed only in natural outcrops along the Tom River—the main drainage system of the basin—and its largest tributaries. All the remaining area is covered by an almost continuous mantle of loose—

Table 1

Stratigraphic scheme of Kuzbass, 1954, refined in 1956

Note. More detailed subdivisions are not shown.

…of post-Tertiary and, in places, more ancient deposits of varying thickness, sometimes reaching 60–100 m.

The coals of the Kuznetsk Basin are characterized by great qualitative diversity. The principal factors determining these qualitative changes are the degree of coal metamorphism and its petrographic composition.

The coals of the Balakhon suite are characterized by an especially great diversity of petrographic composition; among them 4 petrographic groups are distinguished. The Kolchugino coals fall into 2 groups. The currently accepted grouping of Kuzbass coals by petrographic composition is given in Table 2.

Table 2

The degree of metamorphism of coals, as a rule, obeys Hilt’s law and increases with the stratigraphic depth of occurrence of the coal seams, as well as from the periphery of the basin toward its center.

The classification of all Kuzbass coals according to GOST 8162-56, with the addition of petrographic groups, is given in Table 3.

Factors determining the exploration methodology

Detailed exploration of a deposit is the natural result of the favorable outcomes of the preliminary-exploration stage.

When proceeding to refine the geological structure of a mine field and the technological properties of the mineral, the geologist, on the basis of the preliminary-exploration materials, knows the structural type of the deposit, the degree of cover, the thickness class and degree of stability of the coal seams, and the rank composition of the coals in the principal seams.

Table 4

Industrial-genetic types of deposits in Kuzbass

All these factors are decisive in constructing a methodology for exploration and sampling of deposits. At the same time, the choice of exploration methodology and determination of the density of the network of exploratory workings depend on the exploration horizon and on the nature of the future mining operation—underground mining or open-pit work.

Table 3

*) When \(V\) is less than 6 mm and the nonvolatile residue is sintered, the coals are assigned respectively to groups G6, KZh6 and to grades GZh, K₂ and OS.

1. Tectonic structure or type of deposit.

All known deposits of Kuzbass, according to tectonic features, are clearly divided into three types: I—gentle monoclines, II—simple folded structures, III—complex folded structures. Owing to the specific features of Kuzbass deposits, both in tectonic structure and in other characteristics typical for this type of deposit, subtypes are distinguished within each of these three types.

The characteristics of the distinguished types of deposits and the features on which their distinction is based are given in Table 4, and the principal forms of tectonics of each type are clearly illustrated in Figures 1, 2, 3, 4.

Type I, gentle monoclines

Subtype “a,” Biryulinsky

Subtype “b,” Usinsky

Fig. 1

2. Stability of coal seams

The degree of stability of coal seams is assessed with reference to their thickness classes. For thick seams, fluctuations in thickness when assessing the degree of stability are allowed within greater limits than for thin seams and seams of medium thickness.

In accordance with the “Instructions for the Application of the Classification of Reserves to Coal Deposits,” the coal seams of Kuzbass are divided into stable, relatively stable, and unstable (lenticular) seams.

Because, under the conditions of Kuzbass, coal quality is most often maintained within the limits of a single exploration area and does not affect the density of the exploration network, only the thickness and structure of the coal seam are taken as the indicator of stability.

To assign seams to one or another stability group, the following fluctuations between the extreme values of their thickness are allowed, depending on the class of the latter.

Table 5

Indicators of stability of coal seams

The mandatory condition in assessing the degree of stability, in addition to the fluctuations given above, must be the following: stable seams preserve

Type II. Simple folded structures

Subtype “v”: Baidaevsky

Visible seam labels in the section: seam 34; seam 32; seam 29; seam [[unclear]]; seam 25; seam 24; seam 22–[[unclear]]; seam 18; seam 17; seam 15; seam 12; seam 11; seam 9; seam 7; seam 6; seam 4–5; seam 1.

Subtype “g”: Leninsky

Visible labels in the section: Severnaya; [[unclear]]; Baikaimsky; Gramoteinsky; Guryevsky; [[unclear]]; Prokopyevsky; Zhurinsky fault; [[unclear]]; Severopechersky; Berëzovsky.

Fig. 2.

Type III. Complex folded structures

Subtype “d”: Prokopyevsky

Visible labels in the section: seam 3; Kalinin Mine; Mine No. 9; [[unclear]]; seam 5; Chernaya Gora Mine; shaft 3–3 bis; Severnaya Maganak Mine; seam 1; seam 2; seam 4; seam 5; [[unclear seam names]].

Fig. 3.

Type III. Complex folded structures

Subtype “E,” Anzherian

Visible seam and annotation labels: Tenth; Andreevsky; Double; coking; [[unclear: seam name]]; Andreevsky; Fourth; coking; Tenth.

Subtype “Zh,” Bachatsky

Visible seam and annotation labels: [[unclear: seam name]]; Prokopyevsky; Udarny; Moshchny; Bezymyanny; Polysaevsky; Gorely; Magistralny; [[unclear: seam name]]; Fourth; Third; Moshchny; Prokopyevsky; Tonky; Bezymyanny; Boldyrevsky; Osinovsky.

Fig. 4.

working significance and structure everywhere (in all reliable intersections) within the area. Relatively persistent seams, apart from the stated permissible fluctuations, with a more or less regularly varying thickness, may at isolated points (over small areas) lose their working significance. Unstable seams are characterized by irregular changes in thickness and by a lens-like structure, up to the complete disappearance of the seam.

3. Degree of cover of a deposit

The depth at which coal-seam outcrops occur from the surface is an essential factor in constructing a methodology for exploring the upper horizons—the horizons to be developed first in mining. The overwhelming majority of Kuzbass deposits are overlain by loose Quaternary cover of varying thickness. In addition, a number of Paleozoic deposits are located beneath Jurassic, Cretaceous, or Tertiary deposits of great thickness. Therefore all deposits of the basin (exploration areas) are divided into open, semi-covered, and covered. Of course, the concept “open” is introduced conventionally for deposits where uncovering the seam outcrops is possible by trenches or other shallow prospecting workings. A characterization of deposits by degree of cover is given in Table 6.

Table 6

Characterization of the degree of cover of deposits

4. Character of the object being explored

Depending on the mining-geological conditions of the area being explored, the degree to which it has been developed by mining, and the possible methods of extraction, one and the same type of deposit may be explored by a different network of workings. In the general case, when designing the density and the character of the arrangement of exploration workings, it must be borne in mind that, when exploring a new area not yet developed by mining, the main attention should be concentrated on detailing the first horizon from the surface, where the maximum ratio of high categories must be achieved. As for objects suitable for open-pit development, their exploration cannot be considered completed if the seam outcrops have not been traced. Moreover, taking into account the considerable step-like character of horizons that are small in height, the density of the network of workings in fields being prepared for open-pit exploration must be twice as great.

The lower horizons, lying beneath developed or worked-out areas of mine fields, may be considered explored in detail with a network of workings substantially more widely spaced than that for the upper horizons.

Exploration methodology and density of the network of workings

The principal means of determining the geological structure of a deposit at the stage of detailed exploration is core drilling. To expose seam outcrops and trace them at the surface, shallow exploratory workings are also used.

As a result of exploration, exhaustive data must be obtained for constructing the tectonic structure of the area and the elements of occurrence of the strata, on the basis of a completely covered and reliably correlated section in steep and inclined occurrence of the seams. For gently dipping or horizontally lying seams, the results of exploration must ensure the construction of hypsometry. In all cases, the reliability of the thickness and correlation of the coal seams must be ensured.

The overwhelming majority of Kuzbass deposits are explored by lines of boreholes. Deposits of the “Anzher” subtype, as well as gently dipping seams of some deposits of the Erunakovo suite, Itatka, Bogotol, and other similar deposits, are more appropriately explored by means of a square network of workings.

The depth of exploration is determined by the conditions necessary to ensure the normal service life of the mining enterprise and, before the start of geological exploration work, is agreed upon with the design organization. In the absence of natural boundaries of the detailed exploration area along the strike, these boundaries (economic boundaries) are determined by the design organization.

In accordance with existing regulations, for all Kuzbass deposits, upon completion of detailed exploration, the ratio of reserves in high categories to the total must be not less than 50%; at the same time, the maximum quantity of reserves in categories \(A_2 + B\) must be located on the horizon of priority development by the mining enterprise.

To ensure the necessary degree of exploredness, the following density of exploratory workings is recommended for each type of deposit of Kuzbass and the Chulym-Yenisei Basin (Table 7).

Table 7

Density of the network of exploratory boreholes for detailed exploration of Kuzbass deposits

Deposits of type 1 — gently dipping monoclines

Continuation of Table 7

Deposits of Type II—simple folded structures

Deposits of Type III—complex folded structures

Notes. 1. For areas of open workings, the grid on one working horizon is made twice as dense.

1. When determining the density of the borehole grid from the conditions of seam stability, the group prevailing in the section is taken into account.

2. In open deposits, in order to obtain the designated categories on one working horizon, small mining-exploration workings must be driven between the borehole lines.

3. For the Anzherka and Bachatsk subtypes, within the limits of reserve and deep horizons, category $A_2$ is not distinguished, regardless of the grid density.

4. For deposits of the Anzherka subtype, boreholes are to be arranged on a square grid, not along lines.

5. The Itatskoye, Bogotolskoye, and other analogous deposits of the Chulym-Yenisei basin are assigned, by borehole-grid density, to Type I deposits of Kuzbass.

6. If unstable seams predominate in the section (the Alchedatskaya, Ilyinskaya, and other formations), the grid is made twice as dense as for the group of relatively stable seams of the corresponding type of deposit.

Method of Coal Sampling during Detailed Exploration of a Site

The initial premises for the method of coal sampling during detailed exploration of a site are the results of its preliminary exploration. In the course of preliminary exploration, sampling of coal seams is carried out from all geological-exploration workings. In addition, in order to obtain samples of the greatest representativeness, one or two special sampling boreholes or heavy-type mining-exploration workings are driven into the typical seams of each grade, depending on the degree to which the seams of the same name have been studied in the adjoining area, on mining-engineering conditions, and on the grade composition of the coals.

Table 8

Density of the sampling network for coal seams during detailed exploration of blocks

Note. The coal oxidation zone is studied specially.

When evaluating coal quality from preliminary-exploration data, it must be taken into account that such average indicators as the yield of volatile matter and the thickness of the plastic layer, as determined from core samples from exploration boreholes, are usually somewhat understated because of losses of fragile caking components during the disintegration of coal seams. Depending on the stage of metamorphism and the petrographic composition, the yield of volatile matter in core samples is reduced by 1–2%, and the thickness of the plastic layer by 2–4 mm.

The choice of the sampling-network density during detailed exploration of a site is made depending on the degree of variability of the principal quality indicators, as well as on the thickness and structure of the coal seams over the area of the site, as established by preliminary exploration or from data for adjacent areas previously explored or being worked. The principal quality indicators of coal seams are ash content, yield of volatile matter, and caking capacity.

According to the degree of variability of these quality indicators, all seams are divided into two groups—stable and unstable. To assign seams to the indicated groups of stability with respect to quality, the following characterization should be used.

1. Seams stable in quality. The yield of volatile matter and caking capacity make it possible to assign the seam, within the site or within a large independent structure, to one definite grade or group according to the existing GOST standards. In thickness and structure the seam is stable or relatively stable (see Table 5). Fluctuations in the ash content of the seam, or of its individual benches, according to representative samples, are no more than 25%. The average ash content does not exceed 25%.

2. Seams unstable in quality. The yield of volatile matter and caking capacity do not make it possible to assign the seam to one definite grade or group. In thickness and structure the seam is unstable. The extreme values of the ash content of the seam and of its individual benches, according to representative samples, differ by more than 25%; the average ash content is more than 25%.

The density of the seam-sampling network on a site, depending on their stability, is given in Table 8.

Samples, in all possible cases, are taken by benches (differential samples). The size of the samples and the methods of their taking and processing must conform to the existing standards. The types of investigations and analyses are determined depending on the intended industrial use of the coal, in accordance with the existing GOST standards and technical specifications.

From heavy-type mine workings, sampling of seams is carried out for all necessary kinds of analyses and investigations. From core-drilling boreholes, samples may be taken only for determining the principal indicators, chiefly those which are subject to substantial changes, are specified by the conditions, or are important for coal grading (ash content, caking capacity, yield of volatile matter, sulfur and phosphorus content, etc.).

Trust “Kuzbassuglegeologiya”