BASIC PRINCIPLES AND A PILOT SCHEME FOR DETAILED GEOLOGICAL-FORMALISTIC GROUPING OF SOLID MINERAL DEPOSITS FOR UNIFIED EXPLORATION METHODS

L. M. PETROVSKII

(Presented by the scientific seminar of the Department of Geology and Exploration of Mineral Deposits)

The main criteria for grouping deposits according to the new classification of reserves of solid mineral deposits and the instructions for its application to deposits of various kinds of minerals are: the degree of tectonic disturbance of areas, the variability of the thickness and structure of the principal workable seams and of the quality of their coals for coal deposits; the dimensions of the mineral body, the variability of its morphology (thickness), and the character of the distribution of mineralization for all other deposits. For each of the groups distinguished—chiefly for ore deposits of useful minerals—together with the general geological-industrial characterization of exploration objects, numerical limits are established for the degree of variability of one or another grouping criterion [4, 5, 6, 7]. Nevertheless, when choosing the required density of the exploration grid at the detailed stage of exploration, it often proves difficult to decide objectively whether each given part of a deposit should be assigned to one of the adjacent groups distinguished in the instructions for applying the reserve classification. Below a pilot scheme is proposed for detailed geological-formalistic grouping of indigenous ore (Table 1) and coal deposits (Table 2), making it possible to assess more objectively the complexity of objects according to their exploration conditions.

As is evident from the tables, the proposed schemes for detailed geological-formalistic grouping of mineral deposits (areas) are based on the principle of a formalized numerical assessment of each principal grouping criterion and on a comparative integrated consideration of possible natural combinations of criteria for different degrees of their assessment, on the basis of calculating the value of the so-called formalistic coefficient \(F\). In this case, the dimensions of ore bodies and coal seams, as well as of the areas themselves, are expressed in areal quantities. Accordingly, in the latter case, the areal discontinuity of mineralization and the areal coal-bearing capacity of the principal workable seams in the area are also taken into account. The degree of persistence of the principal workable coal seams is expressed through the nonuniformity index NP [2], and the degree of tectonic disturbance, according to the experience of the Karaganda specialists, through the dislocation index [3].

An entirely new criterion for grouping deposit areas according to their exploration conditions is the so-called conditional co-

Grouping of bedrock ore deposits

Table 1

* The numerical limits of the degree of variability of thicknesses are adopted according to [4].

Table 2

Grouping of coal deposits

regression coefficient \(R\). Its physical meaning follows from the important concept of regression of reserve categories [1]. According to the latter, an increase in the detail of a study occurs not only in proportion to the required increase in the accuracy of the assessment of reserves as a whole, but also in connection with the transition to a smaller study area. A conventional expression of the degree of regression of reserve categories may be the conditional regression coefficient \(R\), calculated as the ratio of the total area of the deposit \(S\) to the area of the preliminarily explored part of the deposit \(S_1\), or, for the conditions of detailed exploration, as the ratio of the area of the preliminarily explored part of the deposit \(S_1\) (before the start of detailed exploration) to the area of the site being explored in detail \(S_{\mathrm{st}}\). It is obvious that the smaller the part represented by the site being explored in detail relative to the preliminarily explored area, or the latter relative to the total area of the deposit, the greater the degree of regression of reserve categories will be, and the greater in magnitude the conditional regression coefficient \(R\) will be. As a rule, the largest conditional regression coefficients are characteristic of large deposits, and, among deposits equal in size, of tectonically disturbed ones. The smallest conditional regression coefficient, equal to 1, is characteristic of small deposits that are fully involved in the preliminary and detailed stages of exploration.

According to the various combinations of features of deposits that characterize different conditions of their exploration, it is necessary to distinguish 4 groups of ore (Table 1) and 3 groups of coal (Table 2) deposits (sites). Each of the distinguished groups is characterized by a certain limiting value of the formalistic coefficient \(F\). For the first group of ore deposits the limiting value of coefficient \(F\) is 0.32 (ore bodies of medium size, continuous in mineralization and with consistent thickness, with a uniform distribution of the useful component); for the second group this value is 2.3 (ore bodies of medium size, weakly discontinuous in mineralization and with inconsistent thickness, with an uneven distribution of the useful component); for the third group it is 7.5 (ore bodies of medium size, discontinuous in mineralization and with highly inconsistent thickness, with a highly uneven distribution of the useful component); and for the fourth group the limiting value of coefficient \(F\) is more than 7.5 (small or medium ore bodies, but with an extremely uneven distribution of the useful component). In this case, ore bodies of the first, second, and third groups characterized by continuous mineralization may be normally explored at the detailed stage by drilling exploration systems (Ia, IIa), while ore bodies of these same groups characterized by weakly discontinuous mineralization may be explored by mining-and-drilling systems with a predominance of drilling (Ib, IIb, IIIb). Finally, ore bodies of the second and third groups characterized by discontinuous mineralization must be explored by mining-and-drilling systems with a predominance of mining workings (IIc, IIIc). In addition, in deposits of groups IIIc and IV (for medium ore bodies) ore bodies with a thickness of up to 2 m should be distinguished, in the exploration of which the layout of production blocks is possible, and ore bodies with a thickness of more than 2 m, when the layout of production blocks in the process of exploration is excluded.

As applied to coal deposits, the limiting values of the formalistic coefficient \(F\) are: for the first group, 0.007; for the second, 0.02. Deposits (sites) with continuous areal coal-bearing capacity of the main workable coal seams can be normally explored (with the exception of technological testing) at the detailed stage exclusively by drilling exploration systems-

exploration (Ia, IIa); deposits (areas) with weakly discontinuous and discontinuous coal-bearing character of the principal workable seams, including coal seams complicated by nest-like rock inclusions, can be properly explored at the detailed stage only on condition of trial driving, to one extent or another, of underground mine workings (Ib, IIb, IIIb).

Thus, the proposed methodology makes it possible, first, to carry out a sufficiently objective quantitative assessment of the relative complexity of exploration targets and, second, to express the dependence of the relative complexity of exploration both on the dimensions of a deposit (area) and on the degree to which the preliminarily explored area is covered by the area of detailed exploration.

REFERENCES

1. V. I. Biryukov. Regression of reserve categories. Izvestiya vuzov, “Geology and Exploration,” No. 4, 1965.

2. V. V. Bogatsky. Mathematical Analysis of the Exploration Network. Gosgeoltekhizdat, 1963.

3. N. A. Ko, D. A. Dymov. Methodology for exploration of individual districts of the Karaganda Basin. Geological evaluation and practical methods for calculating reserves of solid combustible minerals. Abstracts of reports. Novosibirsk, 1969.

4. V. M. Kreiter. Prospecting and Exploration of Mineral Resources. Gosgeolizdat, 1940.

5. V. M. Kreiter. Prospecting and Exploration of Mineral Deposits. Part 2. Gosgeoltekhizdat, 1961.

6. V. I. Smirnov. Geological Foundations of Prospecting and Exploration of Ore Deposits. Moscow State University Press, 1957.

7. V. I. Smirnov. On the density of the exploration network. Soviet Geology, Collection 58, 1957.