NATURAL RADIOACTIVITY OF THE KOLCHUGINSKAYA SERIES OF DEPOSITS IN THE LENINSKY GEOLOGICAL-ECONOMIC DISTRICT OF KUZBASS

L. I. IVANCHURA, V. Yu. TOREEV

(Presented by the scientific seminar of the Department of Geophysical Methods of Exploration)

The determination of natural radioactivity was carried out on 1435 samples selected from boreholes during drilling. The samples are represented by fine- and coarse-grained dark-gray siltstones and fine-grained sandstones belonging to the Upper Permian deposits of the Kolchuginskaya series.

The measurements were performed on a DP-100 decade-counting unit. Radiation was recorded by the relative method, using a potassium standard. The potassium standard was made from a crystal of potassium chloride grown in a chemically pure solution. The activity of the samples was determined as the percentage content of potassium according to known relationships [1].

In processing the data, a statistical method was applied, the essence of which was as follows: for lithological varieties, point diagrams and variation curves of the distribution of the percentage content of potassium were constructed (Fig. 1). To construct the variation curves, the grouping interval was calculated by Sturges’ formula; it amounted to 0.5% potassium. From the grouped data, arithmetic means, variances, and standard deviations were determined. The arithmetic mean values for fine- and coarse-grained siltstone and fine-grained sandstone are, respectively: 2.75% K; 2.48% K; 2.27% K, which indicates a regular decrease in natural radioactivity from siltstones to sandstone.

In terms of the magnitude of the variance and standard deviation, the lithological varieties also differ, although only slightly. For fine- and coarse-grained siltstone and fine-grained sandstone these values are, respectively: 0.51; 0.50; 0.47; and 0.71; 0.70; 0.69, which also indicates a decrease in variance (as well as in standard deviation) from siltstones to sandstone.

Figure 2 shows a graph of the dependence of the arithmetic mean value on the grain size composing the rocks under consideration.

Along with the mass determination of the natural radioactivity of siltstones and sandstones, individual measurements of this parameter were carried out for coals of grades D, G, and Zh. The investigations showed that the natural radioactivity of the coals is close to zero.

On the basis of the results obtained, the following conclusions may be drawn:

1. There exists a definite difference in natural radioactivity—

Fig. 1. Variation curves of the distribution of the percentage potassium content.
1. Fine-grained siltstone. 2. Coarse-grained siltstone. 3. Fine-grained sandstone. 4. Coal.

Fig. 2. Graph of the dependence of the arithmetic mean value on the size of the grains composing the rock.

…between the principal lithological varieties of rocks composing the Kolchuginskaya series of deposits in the Leninsky geological-economic district of Kuzbass.

1. In terms of natural radioactivity, coal differs sharply from the enclosing rocks.

2. The natural radioactivity of the rocks decreases regularly from siltstones to sandstones and to coals.

Thus, the results of laboratory determinations provide a basis for carrying out radioactive methods in geophysical investigations in boreholes. Such methods are currently being used in the Leninsky district of Kuzbass, in combination with other methods, to identify coal seams. According to logging data, coal seams are traced with sufficient reliability. The results obtained provide additional material for subdividing the deposits enclosing the coals.

LITERATURE

1. V. N. Kobranova. Physical Properties of Rocks. Gostoptekhizdat, 1962.