Petrographic Composition of the Coals of the Tataurovo Deposit, Chita Oblast

A. V. Aksarin, V. L. Kokunov

The Tataurovo deposit was discovered by the Garekapanskaya geological exploration party of the Western Expedition of the Chita Geological Administration in 1963 and was explored by the middle of 1966. The authors of the present work described the coal seams and the enclosing coal-bearing sequence from the cores of boreholes drilled by the Garekapanskaya geological exploration party. The coal core was subjected to petrographic study and spore-pollen analysis. The enclosing sandy rocks were studied by granulometric analysis, with calculation of coefficients according to the method of L. B. Rukhin (1947), and their mineralogical composition was studied under a microscope. Clayey rocks were studied by staining with methylene blue using an electron microscope. The coal core was studied in boreholes Nos. 353, 406, 402, 367, 405, 403, 366, 362, 404, 400, 240, 363, 401, 173, 232, 220; the enclosing rocks were studied in boreholes Nos. 401, 173, 240, 220, 232, 341, 347, and 375. The identification of plant impressions discovered during field work was carried out by Professor A. V. Aksarin.

The area of the Tataurovo deposit is composed of continental coal-bearing deposits which, according to the regional scheme of G. G. Martinson (1961), have a two-member division and consist of the following suites (from bottom to top): the Kharyulga (Bukachacha) and the Ulanganga. The Kharyulga suite of the regional scheme corresponds to the suite of basal conglomerates of V. P. Plotnikov and V. A. Kolicheva (1954) of the Chernovskoye deposit and to the conglomerate unit of V. F. Korolev (1965) of the Tataurovo deposit. The deposits of the Ulanganga suite, the upper beds of which were exposed by borehole No. 375, rest conformably on the deposits of the Kharyulga suite; according to the determination of the plant impressions collected by us, their age is Upper Jurassic. The deposits of the suite were divided by all investigators who studied it at the Chernovskoye and Tataurovo deposits into three parts according to the degree of coal-bearing character: the lower—coal-barren, the middle—carbonaceous-shale, or with frequent intercalation of rocks, and the upper—coal-bearing. It is proposed that the divisions of the Ulanganga suite be regarded as subsuites and that names be assigned to them according to the geographic principle on the basis of finds of fossil flora in them (see Table 1). It is proposed that the coal-barren unit be called the lower subsuite, the middle part of the Ulanganga suite—the Tataurovo subsuite, and the upper coal-bearing part—the Tormovo subsuite. The coal-bearing coefficient of the Tormovo subsuite is 21.5%. In all, in the section of the Tormovo subsuite there are up to 10 coal seams and interbeds-

Table 1

Comparison and age of the sections of the Tatarurovo and Black Sea troughs

Table 2

Microcomponent composition of the principal coal seams of the Tataurovo deposit

Table 3

Petrogenetic types of coals of seam III of the Tataurovo deposit

of which three seams have workable thickness. These are (from bottom upward) seams III, II, and I.

Seam III has a simple structure and a thickness of up to 16.6 m and is composed for 82.6% of microcomponents of the vitrinite group, for 5.2% of microcomponents of the semivitrinite group. The seam also contains about 7% fusinite and about 1.5% leiptinite (see Table 2). According to the alternation of petrographic types of coals composing seam III (see Table 3), it can be divided into 4 benches, each of which is apparently a distinct rhythm of coal accumulation, being composed in the lower half of coals of the clarain type, and in the upper half of coals of the duren type, or clarain-duren, or duren-clarain types.

A distinctive feature of the petrographic structure of seam II (Table 4), which, like seam III, has a simple structure, is the complete

Table 4

Petrogenetic types of coals of seam II of the Tatayurovo deposit

Table 5

Petrogenetic types of coals of seam I of the Tatayurovo deposit

absence of regularities in the superposition of petrographic layers, which indicates the extreme variability of the facies setting during the accumulation of this seam. Seam II contains 84.5% microcomponents of the vitrinite group, 6.7% microcomponents of the semivitrinite group, 4.5% fusinite, and an insignificant admixture of leiptinite (Table 2).

Seam I (Table 5), unlike those described above, has a complex structure, i.e., it contains rock interbeds. At the same time it also has strong variability in petrographic composition over the area of its distribution. The seam contains microcomponents of the vitrinite group—78%, semivitrinite—5.2%, fusinite—about 12%, and leiptinite—about 1%. This seam is the most enriched in fusinite (Table 1).

The process of coal accumulation at the Tatayurovo deposit must be assigned to the Chernovka type of coal accumulation, distinguished by Yu. A. Zhemchuzhnikov in 1941 when comparing the character of coal accumulation at the Bukachacha, Chelyabinsk, and Chernovka deposits.

The genesis of the coal is explained by a combination of favorable paleogeographic and tectonic prerequisites.

REFERENCES

1. Yu. A. Zhemchuzhnikov. Materials on the Genesis of the Chernovka and Bukachacha Coal Deposits. Gosgeolizdat, 1941.

2. G. G. Martinson et al. Jurassic and Cretaceous continental deposits. Geology of the USSR, vol. XXXVI, part 1, Gosgeoltekhizdat, 1961.

3. L. B. Rukhin. The Granulometric Method for Studying Sands. Leningrad State University Press, 1947.