MAGNETIC PROPERTIES OF BURNED ROCKS OF THE KUZNETSK BASIN¹

Z. A. MYSHKO

(Presented at the scientific seminar of the Department of Geophysical Methods of Prospecting for Mineral Deposits)

In the search for and exploration of coals in Kuzbass, magnetic surveying is used, by means of which zones of burning-out of coal seams are detected and contoured. The identification of burn-out zones is necessary for the correct selection of areas for open-pit mining, for estimating reserves of hard coal, and for taking into account the hydrogeological conditions of a deposit.

When coal seams burn out, the enclosing rocks—chiefly the roof rocks—are baked; as a result, burned rocks are formed, possessing appreciable magnetic properties. Against the background of the quiet normal magnetic field corresponding to the sedimentary rocks of Kuzbass, the burned rocks create distinct magnetic anomalies. The strike of the anomalous zones coincides with the strike of the burned-out seams, while the zero isogam gives an idea of the contour of the burned-rock zone in plan. The dimensions of the anomalous zones vary from \(100 \times 20\ \text{m}\) to \(2000 \times 100\ \text{m}\). The depth of burning-out of steeply dipping seams sometimes reaches \(270\ \text{m}\), and of gently dipping seams, \(100\ \text{m}\). Magnetic anomalies of different sign are encountered, with intensities from \(\pm 200\gamma\) to \(\pm 9000\gamma\).

The burning-out of coal seams in Kuzbass was noted as early as 1733 by Gmelin’s expedition and later, in 1763, by Falck [2].

In 1932 Prof. V. I. Yavorsky [7], on the basis of the accumulated factual material, noted the burning-out of a large number of Lower Permian coal seams, which had occurred, in his opinion, at different times, no later than the Post-Pliocene, with the formation of thick zones of burned rocks. V. I. Yavorsky points to the considerable distribution of burned rocks in Kuzbass and gives a description of their properties. In the baked roof rocks of seam IV Vnutrennii at the Tayba II deposit he found samples of a peculiar iron ore composed of hematite and magnetite with an insignificant content of gangue minerals.

In 1933 B. P. Belikov [1] carried out detailed petrographic studies of the composition of the baked rocks of the Kemerovo district

of Kuzbass. At the outcrops of the burned rocks they noted the following zonality in the alteration of rocks:

1. Weakly altered rocks—reddening without change in texture and structure.
2. More altered rocks, retaining their original appearance but having new formations.
3. Strongly altered rocks, fused into a slag-like mass.

The study of thin sections by the immersion method enabled B. P. Belikov to establish, in rocks of type 3 and partly type 2, the presence of the following minerals: glass, quartz, mullite, tridymite, cordierite, green spinel, magnetite, and, in isolated cases, cristobalite, nepheline, and carnegieite. The article also gives data from chemical analysis of the burned rocks.

In 1943, at the Taiba II deposit, geophysical engineer I. S. Mikhelson first tested a magnetic survey with the aim of identifying burned-out coal seams. This survey gave positive results, and magnetic prospecting, mainly from 1947 onward, began to be used successfully in Kuzbass for the purpose of outlining zones of burning of coal seams.

In 1948 K. V. Gladkii, in his article [3], gives the results of determinations of the magnetic susceptibility of certain rock samples from the Siberginskoe deposit of Kuzbass, carried out in the laboratory of the Sverdlovsk Mining Institute: burned rocks showed \(\chi\) \(140—1140 \cdot 10^{-6}\) CGSM (5 samples); diabases \(\chi\) — \(20—63 \cdot 10^{-6}\) CGSM (3 samples); sandstones—\(0—60 \cdot 10^{-6}\) CGSM (4 samples); spherosiderite—\(170 \cdot 10^{-6}\) CGSM (1 sample). Magnetite and cristobalite were found in thin sections of the burned rock.

In 1953–1955, by the magnetic-prospecting party of the Kuzbass Geophysical Expedition under the author’s direction, along with magnetic surveying, the magnetic properties of burned rocks were studied on a large scale at the following deposits of the basin: Kiizak, Dalnie Goroda, Kar’ernyi Uklon, Kedrovskoe, Khorosheborskoe, Novobalakhonskoe, and Bachatskoe.

From mine workings about one thousand oriented samples of burned rock were selected, and with an M-2 magnetometer, with a scale division value of \(12 \gamma\), their magnetic susceptibility \(\chi\) and residual magnetization \(I_r\) were measured. The accuracy of the measurements, as shown by repeated determinations, was 15%.

This was explained by the inaccurate isometricity of the samples and by the heterogeneity of the magnetite inclusions. All samples that created a magnetic field of less than 6 gammas (0.5 scale division), i.e., approximately with \(I_r < 200 \cdot 10^{-6}\) CGSM and \(\chi < 330 \cdot 10^{-6}\) CGSM, were classified as practically nonmagnetic. No correction for the shape of the sample was introduced, since the values of \(\chi\) for the most part did not exceed \(10000 \cdot 10^{-6}\) CGSM.

For each mine working we constructed variation curves of magnetic susceptibility, residual magnetization, its azimuth and angle of inclination, and also calculated the mean values of these quantities.

We shall consider the results of the investigations for each deposit separately.

Kiizak deposit. It is located in the Tom’-Usinsk district and is composed of rocks of the Usyat sequence of the Balakhon suite of Lower Permian age: sandstones, siltstones, argillites, and coal seams. This sequence includes three coal seams of working thickness. The objects of our investigations were the burned rocks of the roofs of coal seams III and IV–V, locally burned out to a depth of 30–60 m. Seam III has a thickness of 7.5 m and is characterized by simple

structure, but in individual sections it is divided into two benches. Seam IV—V most often consists of 2—3 benches with a total thickness of 10.4 m, dipping at an angle of 8—25° toward NW.

The collection of baked rocks was carried out from the roof of the burned-out seams: seam III—150 specimens and seam IV—V—24 specimens. Depending on the degree of burning of the rocks, the values of the magnetic properties change noticeably. Weakly baked rocks have low values of $\chi$. The mean and predominant values of $I_r$ do not exceed $1400 \cdot 10^{-6}$ CGSM.

Strongly baked rocks have a value of $\chi$ greater than $1000 \cdot 10^{-6}$ CGSM, and $I_r = 5000—7000 \cdot 10^{-6}$ CGSM. An increase in magnetic properties is observed in the area where the burned-out seam emerges beneath the cover deposits.

The position of the vector $I_r$ in oriented specimens, characterized by the azimuth $\alpha$ and the angle of inclination $i$, does not depend on the degree of burning; only a small difference is observed in the values of $\alpha$ and $i$ for baked rocks of different seams. For the baked rocks of seam III, $\alpha = 210—240^\circ$ and $i = -35—0^\circ$, while for the baked rocks of seam IV—V, $\alpha = 260^\circ$ and $i = -43^\circ$; moreover, the character of the anomalies of the $Z$-component over the two seams is somewhat different. Over seam III the field is complex, with frequent alternation of low positive and negative values against a general negative background, whereas for seam IV—V there is a clearly expressed negative anomaly of the $Z$-component with $Z_{\min} = -400\gamma$ (Fig. 1).

Fig. 1. Curves $\Delta Z$, $\Delta H$ and $I_r$ over the burned-out coal seam IV—V: 1 — cover deposits, 2 — baked rocks, 3 — coal, 4 — dudki.

The Kar’ernyi uklon deposit is located in the Prokop’evsk-Kiselevsk district. The productive deposits are represented by rocks of the middle part of the Upper Balakhon subformation, including 8 workable coal seams (from top to bottom): Kharakternyi, Gorelyi, Lutuginskii I, Lutuginskii II, Prokop’evskii, Moshchnyi, Bezymyannyi I, Bezymyannyi II. The object of our investigations was the baked rocks of the roof of the Moshchnyi seam, which had burned out here over a considerable extent to depths of 10—18 m. The structure of the seam is most often simple; in places it splits into benches. The thickness of the seam varies from 11 to 23 m. The seam dips to the WSW at an angle of 35—45°. Magnetic surveying revealed 2 negative anomalies (Northern and Southern) of considerable extent. The length of the northern anomalous zone exceeds 425 m along the strike (to the north it has not been traced). The width of the anomaly is [[unclear: continues on next page]]

is 20 m in the south and increases to 60 m toward the north, where burning-out of several coal seams occurs. The values of \(Z_{\max}\) fluctuate within the range of 400–1600 \(\gamma\). The positive fields outlining the negative zone rarely reach 1200 \(\gamma\).

In the southern part of the Northern anomaly two shallow pits were sunk in the zone of weakly burned rocks of the roof of the Moshchnyi seam. The magnetic properties of 99 selected samples proved to be low: \(\chi = 0\text{–}400 \cdot 10^{-6}\) CGSM, \(I_r = 1000\text{–}1400 \cdot 10^{-6}\) CGSM, \(\alpha = 215^\circ\), \(i = -40^\circ\) (Fig. 2, a).

Fig. 2. Variation curves \(\chi, I_r, \alpha, i\).

The Dal’niye Gory deposit is located in the same area as the Kar’ernyi Slope. The geological structure of the deposit includes rocks of the middle and upper members of the Upper Balakhon subseries, represented mainly by siltstones, argillites, and sandstones. The upper member includes 8 workable coal seams, called the Inner seams. The middle member includes 5 workable coal seams (from top to bottom): Gorelyi, II-Prokop’evskii, I-Prokop’evskii, Moshchnyi, and Bezymyannyi. All seams of the deposit have undergone burning-out to one degree or another. Broad and deep zones of burning-out, according to drilling data, have been established, for example, for the thick seams: IV-Inner, Gorelyi, and Moshchnyi, burned out for 1.5–2 km along strike and to depths locally reaching 270 m. The strike of the rocks is NW, the dip is to the SW at an angle of 80–90°.

Above the burning-out zone of all steeply dipping seams there is observed a complex, unstable negative field with fluctuations of \(Z\) from 1200 \(\gamma\) to 2570 \(\gamma\). The positive fields bounding the negative zone reach 400 \(\gamma\). The length of the anomaly is more than 1 km (the northern and southern boundaries have not been traced), and the width of the anomaly varies within 75–220 m owing to the uneven burning-out of the coal seams. The values

a significant part of the shafts exposed rocks of weak firing with low values of \(\chi\), \(I_r = 1000 \cdot 10^{-6}\) CGSM. Two shafts exposed rocks of substantial firing with \(\chi = 1000 \cdot 10^{-6}\) CGSM and \(I_r = 2000\)—\(5000 \cdot 10^{-6}\) CGSM. The magnetic azimuth and angle of inclination of the vector are well maintained in samples of burnt rocks from different mine workings and are \(a = 210\)—\(220^\circ\) and \(i = -40^\circ\).

The Kedrovskoye deposit is located in the Kemerovo district and is composed of rocks of the Kemerovo suite of the Upper Balakhon subseries. Five coal seams of workable thickness are subordinate here to this suite (from top to bottom): Kemerovsky, Volkovsky, Viktorovsky, Vladimirsky, and Lutuginsky; of these, the first two seams have burned out to a depth of 10—60 m. The object of our investigations was the baked rocks of the roof of the Volkovsky seam. The thickness of the seam varies from 6 to 23 m. Its structure is complex, in the form of 2—3 benches. The strike of the rocks is NNW, the dip SW at an angle of 12—40°. Magnetic surveying revealed 5 negative magnetic anomalies at the deposit with values of \(Z_{\min} = 400\)—\(2400\gamma\). The areas of negative values are outlined by positive fields of 100—1200 \(\gamma\).

At the deposit, in the area of the closure of a small anticlinal fold of the burned-out Volkovsky seam, rocks of weak firing with low \(\chi\) and \(I_r = 1000 \cdot 10^{-6}\) CGSM, with \(a = 215^\circ\) and \(i = -34^\circ\), were exposed by two shafts.

The Khorosheborskoye deposit lies east of Kedrovskoye. The dominant strike of the productive measures is latitudinal, with the beds dipping north at an angle of 12—30°. At the deposit, burnout of the Volkovsky seam occurs in 5 areas in the zone of synclinal and anticlinal bends. The depth of burnout varies within 20—60 m.

Magnetic surveying over the Volkovsky seam outlined 3 negative and 2 positive anomalies. The burnt rocks selected in the area of a positive anomaly are characterized by comparatively high values of \(\chi = 1000 \cdot 10^{-6}\) CGSM and \(I_r = 3000 \cdot 10^{-6}\) CGSM, with \(a = 30^\circ\) and \(i = 40^\circ\).

In the area of a negative anomaly, the majority of burnt rocks are characterized by weak magnetic properties with \(\alpha = 210^\circ\) and \(i = -25^\circ\). The burnt rocks here are distinguished by weak firing.

The Novobalakhonskoye deposit is a direct continuation of the Kedrovskoye deposit to the north. Here, as a result of the splitting of the Volkovsky seam, two benches separated and formed the independent Podvolkovsky seam, 4—19 m thick. The seams dip SW at an angle of 30—60°.

Magnetic prospecting at the deposit outlined 4 large burnout zones within the Volkovsky and Podvolkovsky coal seams. All anomalies are positive, with values of \(Z_{\max} = 300\)—\(9000\gamma\); the bounding negative fields sometimes reach \(1200\gamma\).

Samples of burnt rocks taken at the outcrop of the burned-out Volkovsky seam beneath the overburden are distinguished by a high intensity of firing: these are blackened fused rocks, whose thin sections are characterized by a predominant content of glassy mass. The magnetic properties of these burnt rocks are distinguished by high values: \(\chi = 3000 \cdot 10^{-6}\) CGSM and \(I_r = 8000 \cdot 10^{-6}\) CGSM. The ratio \(I_r : I_i\) is 4—8. The vector \(I_r\) is directed downward at an angle of 45° to the horizon with a predominant magnetic azimuth of 45° (Fig. 2,6).

The Bachatskoye deposit is located in the Guryevsk district of Kemerovo Oblast and is composed of rocks of the middle suite of the Upper Balakhon subseries. The objects of magnetic investigations were zones

of burning-out of the Moshchnyi and II-Prokop’evskii seams. The Moshchnyi seam has a persistent NW strike and a thickness from 10 to 42 m. The structure of the seam is simple. The roof and floor are represented by sandstone. The II-Prokop’evskii seam varies in thickness from 0 to 11.7 m, averaging 5.2 m. The dip of the seams is NW at an angle of 30–60°. According to drilling data, the Moshchnyi seam has burned out over a distance of 0.7 km to a depth of 30–60 m, and the II-Prokop’evskii seam over a distance of 200 m to a depth of 28 m.

Magnetic surveying at the deposit has contoured two positive anomalies. The first is over the burned-out Moshchnyi seam. Its length is 700 m, width 60–260 m, and the intensity \(Z\) varies within the limits of 200–1300 \(\gamma\). The second anomaly is located over the burned-out II-Prokop’evskii seam. Its length is 220 m, width 25 m. The field intensities are fairly persistent along the strike and vary within 1200–1300 \(\gamma\). Negative fields along the margins do not exceed 600 \(\gamma\).

The magnetic properties of the burnt rocks of the Bachatskoe deposit were studied in three directions: across the strike of the burned-out Moshchnyi seam, vertically, and along the strike. Investigation of clinker rocks selected across the strike of the zone of burnt rocks showed a sharp increase in magnetic properties toward the area where the Moshchnyi seam comes out beneath the overburden (Fig. 3). The ratio \(I_r : I_i\) varies within 4–18, while the prevailing angle of inclination of the vector \(I_r\) is fairly persistent and is 40°. The prevailing magnetic azimuth \(\alpha\) varies within 350–50° for the clinker rocks of the Moshchnyi seam and 300–338° for the clinker rocks of the II-Prokop’evskii seam.

Fig. 3. Curves of \(\Delta Z\), \(\chi\), and \(I_r\) above the burned-out part of the Moshchnyi seam.

In the northern open pit, samples of clinker rocks were taken vertically from 5 depths (Fig. 4). The ratio \(I_r : I_i\) in the open pit varies from 5 to 16. The vector \(I_r\) of most samples is directed downward at an angle of 40°. The prevailing magnetic azimuth varies within 350–50°.

The variation curves reflect changes in the mean and prevailing values of \(\alpha\) and \(I_r\) vertically and clearly record an increase in magnetic properties in the roof of the seam, in the depth interval 13–18 m, where \(\chi = 1800 \cdot 10^{-6}\) CGSM and \(I_r = 8200 \cdot 10^{-6}\) CGSM. The place of the upper burned-out part of the seam is occupied by a layer of intensely fired rocks with the highest magnetic properties.

Along the strike of the burnt-out Moshchnyi seam, three zones of intensely burned rocks were sampled. It has been established that \(\chi\) of the clinker along the strike varies within the limits \(1000—2000 \cdot 10^{-6}\) CGSM, while \(I_r\) changes appreciably. In the northern quarry the predominant value of \(I_r = 8200 \cdot 10^{-6}\) CGSM; in the central part, \(10000 \cdot 10^{-6}\) CGSM; and in the southern quarry, \(2000 \cdot 10^{-6}\) CGSM, which may have been caused by prolonged washing-out of the clinker by water during the mining of the Moshchnyi coal seam.

Fig. 4. Curves of mean and predominant values of \(\chi\) and \(I_r\) by quarry: 1—clinker gravel, 2—coarse-fragment clinker, 3—bedrock clinker, 4—coal, 5—curves of mean values, 6—curves of predominant values.

On the basis of an analysis of the graphical material, partly illustrated here, we have compiled the summary Table 1 of the magnetic properties of the burnt rocks for individual deposits of the basin, presented below.

Unburned sedimentary rocks proved to be practically nonmagnetic. Mineralogical analysis in polished sections of sandstones and argillites revealed fine inclusions of nonmagnetic minerals: pyrite, limonite, hematite, and siderite.

The appearance of magnetic properties in sedimentary rocks after firing is explained by petrographic and chemical analyses. In 1932 [1] and in 1948 [2], magnetite was found in burned rocks. In 1954, at the Department of Mineral Deposits of the Tomsk Polytechnic Institute, in polished sections of burned sandstones of the roof of the Volkovskii seam, fine inclusions of magnetite with grain sizes of \(0.10—0.02\) mm were also established, concentrated in the form of rims around cavities.

Chemical analysis of the burned rocks of the roof of the Volkovskii seam showed a significant content of ferrous and ferric iron (Table 2).

A comparison of the results of chemical analysis of the clinkers of the roof of the Moshchnyi seam (Bachat deposit) with magnetometric

Table 1

Note. a and b are weakly baked rocks; b) strongly baked rocks.

the data show that with an increase in the percentage content of iron oxide, $\chi$ and $I_r$ of the burned rocks increase noticeably (Table 3).

The wide range of variation in the magnetic properties of the clinker, taken from the same sampling depth from the same pit, is evidently due, judging from Table 3, to different magnetite contents.

Table 2

In the coal-chemistry laboratory of the Tomsk Polytechnic Institute the author carried out several experiments on the transformation of nonmagnetic sedimentary rocks and ferruginous components (limonite, hematite, and siderite) into substances with appreciable magnetic properties. Sedimentary rocks and ferruginous components in powder form were calcined in the presence of oxygen for 2–4 hours at temperatures of 200, 400, 600, 800, and 1000°C. After cooling, only siderite, beginning at temperatures of 800° and higher, acquired noticeable magnetic properties, turning into a black substance with a sharp metallic luster.

Table 3

When powders were calcined with hard coal, i.e., in a reducing medium, all samples, beginning at temperatures of 500° and higher, after cooling acquired a dark color and noticeable magnetic properties. In the course of the experiments it was observed that the number of magnetic particles in the powders increased with increasing calcination temperature. The magnetic field in the electric furnace during cooling of the samples was close to the terrestrial field.

Chemical analysis of the powders before firing and after firing (500–600°C) gave the following results (see Table 4).

Mineralogical analysis of a polished section of artificially burned sandstone revealed fine inclusions of pyrrhotite; the presence of magnetite could not be established because of the dust-like character of the ore grains. In the same polished section before firing, a small amount of fine hematite and pyrite inclusions had been noted; during firing, the latter apparently passed into pyrrhotite:

$\mathrm{Fe_2O_3 + 2FeS_2 + 3C = 4FeS + 3CO}$.

Sedimentary rocks acquire residual magnetization, as well as increased magnetic susceptibility, as a result of firing.

The increase in the magnetic properties of burned rocks toward the fire seat, noted in our investigations, is due to unequal temperature action: with distance from the fire seat the temperature decreased, and different portions of the sedimentary rock sequence were fired under different temperature regimes. Experimental studies by T. N. Roze in 1949 proved the dependence of the magnitude of residual magnetization on the heating temperature, and it was noted that weakly ferromagnetic rocks acquire the highest thermoremanent magnetization \(I_{rt}\) when cooled in the geomagnetic field from temperatures above or close to the Curie point; moreover, the magnitude of \(I_{rt}\) far exceeds the value of \(I_r\) corresponding to the given field [5].

Table 4

The causes of the reverse polarity of burned rocks, which occurs in many deposits of Kuzbass, have not yet been established. A joint study of geological and magnetic-prospecting materials gives the author grounds to note the following.

1. Negative and positive magnetic anomalies occur over burned-out seams of various extent, both with gentle and with steep dips in all directions, both in the area of development of numerous disjunctive disturbances and in an area with comparatively calm tectonics.

This indicates that the reverse polarity of burned rocks is not connected with the tectonics or with the orientation of coal seams.

1. One and the same burned-out coal seam creates both negative and positive anomalies (the Volkovsky, Moshchny, and III coal seams).

2. In the area of positive magnetic anomalies the structure of the seam is more often simple and rarely complex (Fig. 3).

3. In the area of negative magnetic anomalies there is always a complex structure of the coal seams burned out in the upper horizons, or a sharp decrease in the distance between two burned-out seams (Fig. 1).

In the composition of the sedimentary rocks of the roof of 1 and 2 seams (or benches), there may have been various magnetic components with different Curie points and different values of coercive force [4, 8], which during firing could have led to the reverse polarity of the burned rocks.

Conclusions

1. The magnetic properties of burned rocks vary within very wide limits, from values close to zero to values of \(10000 \cdot 10^{-6}\) CGSM for \(\chi\) and \(76000 \cdot 10^{-6}\) CGSM for \(I_c\). At the same time, a gradu-

a gradual increase in the magnetic properties of the burnt rocks toward the area where the burnt-out seam passes under sediments, and vertically—toward the roof of the seam; moreover, the place of the burnt-out coal seam is occupied by a layer of the most intensely baked rocks with the highest magnetic properties. The ratio \(I_r:I_i\) varies from 2 to 18. The direction of the vector \(I_r\) is distinguished by great diversity even within one and the same mine working. However, statistical analysis by deposits gives grounds to note that the vector \(I_r\) in samples taken in the area of negative anomalies has a predominant upward direction at an angle of 50° to the vertical and is located in the SW sector with a predominant azimuth of 220°; for positive anomalies the vector \(I_r\) is directed downward and deviates from the vertical by an angle of 50°, and in azimuth toward NW or NE—within 30–50°.

1. The magnetic properties of burnt rocks, according to petrographic analyses, are due to the presence in them of magnetite and pyrrhotite. Limonite, hematite, siderite, and pyrite, which are constituents of sedimentary rocks and occur as inclusions in coal seams, during baking pass into magnetite, and pyrite—into pyrrhotite (according to experiments), and the sedimentary rocks become ferromagnetic. Upon cooling in the Earth’s magnetic field, the burnt rocks acquire a noticeable thermoremanent magnetization.

2. The reverse polarity of the burnt rocks of the Kuzbass does not depend on the tectonics and age of the rocks, and, apparently, is connected with the structure of the burnt-out seams and the distance between burnt-out seams. As a rule, negative magnetic anomalies are confined to burnt-out seams of complex structure, consisting of 2–3 benches, or to two closely spaced burnt-out seams.

The vector of the reversely magnetized burnt rocks is almost directly opposite to the vector of the burnt rocks with direct magnetization. This fact argues for the existence in the burnt rocks of two magnetic components, which should be verified by studying the Curie points and coercive forces of reversely magnetized burnt rocks.

1. In determining the depth of burning-out of coal seams, it is necessary to take into account the possibility of inclined magnetization, since in burnt rocks \(I_r>I_i\).

REFERENCES

1. Belikov B. P. On the composition of some burnt rocks of the Kuzbass. Proceedings of the Petrographic Institute of the Academy of Sciences of the USSR, issue 4, 1933.

2. Geology of the USSR, vol. XXI, Kuznetsk Basin, ed. by V. I. Yavorsky.

3. Gladkii K. V. Experience in applying magnetic prospecting to identify and delineate zones of burning-out of coal seams. Journal “Exploration of Mineral Resources”, No. 5, 1949.

4. Grabovskii M. A., Petrova G. N., Isakova L. I. On the origin of thermoremanent magnetization of rocks, Publishing House of the Academy of Sciences of the USSR, Geophysical Series, No. 1, 1956.

5. Logachev A. A. Course in Magnetic Prospecting. Gosgeolizdat, 1951.

6. Roze T. N. Magnetic properties of some rocks at different temperatures. Scientific Notes of Leningrad State University, Physical Series, issue 9, 1949.

7. Yavorsky V. I., Radugina L. K. Coal fires in the Kuznetsk Basin and phenomena associated with them. Mining Journal, No. 10, 1932.

8. Nagata I. Reverse thermoremanent magnetism, Nature, 169, 704, 1952.

1. The materials for this article were reported by the author in a paper at the scientific and technical conference on methods and results of studying the physical properties of rocks of Siberia, in May 1958, in Novosibirsk. ↩