Baltic Shale Basin

a shale basin located primarily in the northern part of the Estonian SSR, the southwestern part of Leningrad Oblast (along the southern coast of the Gulf of Finland from the city of Haapsalu in the west to Gatchina and Budogoshch’ station in the east), and Pskov and Novgorod oblasts. The area of explored continuous industrial shale (with a shale layer of more than 0.7 m) is roughly 5,500 sq km. Total geological reserves of combustible shales in the basin to a depth of 300 m are estimated at 16.6 billion tons (1968). The Baltic shale basin is divided by the Narva River into the Estonian deposit in the west, whose processing center is the city of Kohtla-Jarve, and into the Leningrad (Gdov) deposit in the east, whose processing center is the city of Slantsy. The Veimarn and Chudo-vo-Babino deposits, which are of limited industrial importance, lie to the southeast.

Baltic shales were first discovered in the 18th century. In the 19th and early 20th centuries a geological study was conducted in the area, and small-scale exploratory work and production testing of the raw material were carried out. Test extraction of shales was conducted in 1916 in the Kohtla-Jarve region and from 1918 to 1923 at the Veimarn deposits.

Industrial development of the Estonian deposit was begun in 1921 and continued, primarily through private entrepreneurs, until 1940. The Leningrad deposit was identified in 1927, and industrial development began in 1930. After the Great Patriotic War (1941-45), thorough study of the raw material established the importance of the Baltic shale basin as a major center of solid fuel and domestic gas for the Estonian and Latvian SSR’s and for Leningrad, Pskov, and Novgorod oblasts.

The Baltic shale basin, part of the southern slope of the Baltic shield, is a sedimentary complex of Lower and Middle Paleozoic rocks (from the Cambrian to the Devonian, inclusively) 150–300 m thick in the north to 700 m thick in the south and southeast. It occurs on a gentle slope of a crystalline foundation and submerges in the south. The gentle monoclinal bedding of the rocks is broken by a few zones of stepped faults and flexures with submeridianal and northeasterly strikes and by karst processes that are particularly extensive in the tectonic breakup zones.

The industrial shale is related to the Kuckruse horizon of the Middle Ordovician, which is composed in varying degrees of argillaceous and dolomitized limestones that include as many as 30 interlayers of kuckersites. The thickness of the horizon increases from 5-8 m in the west (near Tallinn) to 10-35 m in the east (near the city of Chudovo). In the Estonian and Leningrad deposits, four to six close interlayers of kuckersite form the industrial layer, that is, the layer that is mined. The thicknesses of the shale interlayers and the limestones separating them in this stratum vary from a few centimeters to 0.9 m. The maximum general thickness of the industrial layer in the central part of the Estonian deposit reaches 3.2 m; the total thickness of the kuckersite interlayers is 1.8 m and decreases regularly eastward and westward. The depth of the shales varies from 20 m in the north to 100–150 m in the south.

The shales extracted contain 40-60 percent ash and 1.1–1.8 percent sulfur. The heat of combustion is 10.5-14.6 megajoules per kg (2,500–3,500 kilocalories per kg). The resin yield is 18–40 percent. Shale extraction has grown from 1.8 million tons in 1940 to 4.7 million tons in 1950, 12.3 million tons in 1960, 21 million tons in 1970, and 28 million tons in 1973. Mining involves large shafts and pits. The capacity of the largest pit, Sirgala, has reached 4.7 million tons a year; the largest shaft mine, Viru, produces 2.1 million tons annually. The projected annual capacity of the Estonia shaft mine is 3.4 million tons. As of Jan. 1, 1974, the explored reserves to a depth of 100 m were 4.8 billion tons in categories A, B, and C and 3.1 billion tons in category C₂. The shales are used primarily as fuel for state regional power plants, heat and electric power plants, and various kinds of boilers. The shale is also processed to obtain household gas and various kinds of chemicals.