Asturian mineral coal basin

ASTURIAN MINERAL COAL BASIN (RU: Астурийский каменноугольный бассейн) is the largest coal basin within Spain. It is situated within the northern and central parts of the Oviedo province. The start of the industrial development belongs to the middle of the 19th century. The area of the basin, according to the outcrops of the coal-bearing depositions onto the surface, is approximately 3000 square kilometres; the reserves of the mineral coal amount to 1215 million tonnes (including anthracites amount to 53 million tonnes), the proven reserves are 442 million tonnes (of which anthracites amount to 35 million tonnes). The major deposits are: Central (is divided into the zones Caudal and Nalon), Teverga and Gijon. The major coal extracting enterprises are concentrated within the central part of the basin, where are located the easily coking coals; anthracites are being extracted at the relatively small Cangas del Narcea, Tineo, and Tormaleo deposits. The basin is confined to the northern zone of the Hesperian, or Iberian, epi-Paleozoic massif (miogeosynclinal sub-zone). The depositions of the coal-bearing Carboniferous (the thickness is more than 4000 metres) are embeded conformably onto the Devonian, and are represented by the paralic type of accumulation. The industrial coal-bearing capacity is confined to the Sama suite (formation), (middle and upper Westphal), with the total thickness of up to 2800 metres, which is represented by the alternation of the shales, conglomerates, sandstones, limestones, and marls with coal layers.

The Asturian mineral coal basin is the large Hercynian syncline, which is complicated by the folds of the higher order. The angles of dip of the rocks are up to 80 degrees, the entire coal-bearing stratum is broken by the numerous faults. The coal-bearing Westphal contains 70-75 layers of coal, of which 35-39 are the working layers with the thickness of 0.6-2.5 metres. There are being developed at the Central deposit the 50 layers with the total thickness of 30 metres. The thickness and structure of the layers are unstable along the strike. The coals are medium-ash and low-ash, the average ash content is 4-5%; there exist the layers with the ash content of more than 15%. The emission of the volatile substances within the coals of the southern part of the basin is 7%-17%, within the northern part is more than 40%. The heat of the combustion is 28.0-34.7 megajoules per kilogram. The coals are represented by all the marks, from anthracites within the southern part of the basin, to the lean and fat coals, which are suitable for coking, within its central part, to the slightly metamorphosed, similar to the brown ones, along its north-western periphery, where exists the layer of the coal with the thickness of 12 metres. The depth of the development is down to 400 metres, approximately 300 metres on average.

The mining-geological conditions are complicated, the majority of the layers, which are being developed, are prone to the sudden outbursts and spontaneous ignition. The system of the development of the deposits is determined by the steep bedding of the coal layers, by their small thickness and strong disturbance.

There is most common the overhead stoping development system. The length of the long wall stopes is often limited by the tectonic disturbances, and amounts to 20-60 metres. The excavation of the coal is usually performed by the jackhammers, sometimes they additionally use the hydromechanical excavation. For the working of the thin steep layers, there are used several tens of the combined cutter-loader machines. During the extraction of the strong coal, there are conducted the blasting works. Almost universally, they use the wooden roof supports. The underground transport is railway and conveyor. There performs the works within the basin the largest within the country "Empresa nacional huilera del Norte S. A." concern. The main share of participation within the concern belongs to the government, while all of the mines are unified into the 7 coal extracting centres. The extraction is approximately 3.5 million tonnes (1980). All coking coals, which are extracted, are shipped to the enterprise of the "Parkes" company for the preparation of the coal charge, which is supplying it into the steel plants within Spain. As the energetical raw material, the coal is also used by the industrial enterprises, electrical power plants, and rail roads.