Irkutsk Coal Basin

located in the southern part of Irkutsk Oblast, RSFSR.

The basin extends for 500 km along the northeastern slope of the Vostochnyi Saian from the town of Nizhneudinsk to Lake Baikal. Its average width is 80 km, and its area is 42,700 sq km. The total geological coal reserves consist of 76.3 billion tons (1969), including balance reserves of 20.5 billion tons. In the vicinity of Irkutsk the basin is divided into two branches: the northeastern Baikal region and the southeastern Saian region. The Saian region is the most populated and economically most developed territory in Irkutsk Oblast.

The presence of coal in the Irkutsk Coal Basin was established in 1869 by A. L. Chekanovskii. In 1891, V. A. Obruchev estimated the Cheremkhovo deposit; it began to be worked in 1896.

The industrial exploitation of the Irkutsk Coal Basin proceeded with particular intensity during the Great Patriotic War and the postwar years. Coal production in the basin increased as follows (in tons): 69,000 in 1900, 498,000 in 1920, 1, 015,000 in 1930, 4, 968,000 in 1940, 8, 223,000 in 1950, 16, 171,000 in 1960, and 21, 550,000 in 1970. The basin is the largest energy base in Eastern Siberia, providing fuel to railroad transport, electric power plants, and public and industrial enterprises. The principal deposits are Cheremkhovo, Azeika, Mugun, Novo-Metel-kino, and Karantsai. The coal-bearing strata of the Irkutsk Coal Basin are composed of Lower and Middle Jurassic sediments of the continental type, underlain by Precambrian and Lower Paleozoic metamorphic, igneous, and sedimentary rocks. In the Saian section the coal-bearing deposits (sandstones, argillites, siltstones, lenses of conglomerates, and coal seams) have a total thickness of about 300 m. To the east—in the Baikal section— these deposits grade into the strata of the “Baikal” conglomerates with a total thickness of 600–700 m and with thin lenses of sandstone. In places in the central part of the basin small sections of the Jurassic sediments are overlain by Neogene remnants, represented by friable sandstones, sands, and clays with lenses of lignites 1–7 m thick. The Irkutsk Coal Basin is of the platform type, which is linked with tectonic basins; in the central part of the basin the Jurassic deposits occur almost horizontally.

There are as many as 65 seams and bands of coal, distributed unevenly throughout the section. (Of these no more than 25 have a thickness greater than 1 m.) Thick seams from 9 m to 18 m are located in the Cheremkhovo, Karantsai, and Azeika deposits. Although the coal seams are variable, they retain their workable thickness over areas ranging from dozens to 250 sq km and more. By genetic criteria, 87 percent of the coal reserves belong to the humic group; the remainder belong to the humite-saprope-litic and sapropelic groups; the sapropelic coal in the northwestern part of the basin may have an independent significance (Khakharei deposit).

The coals are of the medium-ash type, with an ash content ranging from 7 to 15 percent (rarely as much as 23 percent), and the light-ash type, but in certain deposits they have a high sulfur content (averaging 5–6 percent). The western part of the Irkutsk Coal Basin has brown coals, which are replaced by hard coals to the east, with a consequent increase in this direction in the degree of their metamorphism. (Hard, weakly caking varieties are found in the central part, and gaseous, moderately caking types are in the southeastern part of the basin.) An analogous increase in the degree of metamorphism of the coals has also been established as one proceeds in the direction of the Vostochnyi Saian. Besides variations as to area, a vertical variation in the quality of the coals has also been observed. As the depth of the occurrence of the coal seams increases, the moisture of the coal and the emission of volatile substances decrease, while the carbon content increases; at the same time there is also an improvement in the caking capacity of the coals. Mining in the Irkutsk Coal Basin is carried out primarily in open pits (87 percent); in the southeastern part of the basin mining operations are conducted by means of mines and partially by adits.

Besides coal the area of the basin is well known for its deposits of rock salt (Usol’e-Sibirskoe deposit), gypsum (the Zalari deposit), refractory kaolin clays, and sands used for making glass and molds.