Nord – Pas de Calais.
(Nord et Pas de Calais), Valenciennes coal basin, is a coal basin in France that combines two areas of Carboniferous coal deposits, Hop and Pas de Calais, separated by an ancient uplift. The basin stretches as a narrow strip about 120 km. long and 10 to 20 km. wide, continuing on B. under the name. It stretches as far as the Liège Basin. Total reserves of the basin are 4.59 billion tons of coal. Coal production began in the 1st half. In the early 1960s, annual production was about 30 million tons and the basin accounted for 60% of the country’s total coal production. Reduction of production to 2.5 million tons in 1984 led to the basin’s share of 14%. The Carboniferous sediments of the Carboniferous basin are part of the Hercynian marginal trough. The total thickness of the deposits reaches 3500 m. The most coal-rich are the sediments of the Westphalian Stage, represented by continental sandstones with rare interlayers of marine formations and tonsteins. On the territory of the synclinorium the deposition of sediments is complicated by numerous faults and local thrusts, in addition, on the south wing the Silurian and Devonian sediments are thrust over the Carboniferous Carboniferous. The basin is distinguished by high coal saturation, large quantity of coal seams (70-80), more than 1 / 2 of which have thickness not less than 0.6 m (in cp. 1.1 m). The coals are represented by a wide range of grades – from lean to long-flame, including sintered fat coals, used to obtain first-grade coke, their sulfur content is 0.5-2.0%, the heat value is 33.5-35.6 MJ/kg. They are mined in several mines of cp. The gas is released at depths of 800-1000 m., the abundance of water in the mines is not high. The thickness of the mined layers is 1.35 m. They use massive and pillar mining systems. The length of the faces is not more than 100 m. The total collapse of the roof is a method of rock pressure control. The prevalent is plow extraction. Mechanical roof supports are used. By 1988 the mining in the basin is planned to be stopped.
Literature: Matveev A. K., Coal basins and deposits of foreign countries. M., 1979.
A. K. Matveev, A. Yu.
Mining Encyclopedia. – M.: Sovetskaya Encyclopedia. Edited by E. A. Kozlovsky . 1984-1991 .
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Valenciennes coal basin (Nord and Pas de Calais)
The Valenciennes basin, the most significant in France in terms of productivity, reserves and exploration, is located in northern France. Its area is up to 1000 km2. It represents the western part of the large Franco-Belgian basin (Fig. 11).
The basin stretches in a narrow strip over 100 km long and 10-15 km wide; in the east it continues into Belgium under the name of the Liège basin, in the west it stretches as far as the Channel, with a considerable break from Flechinel to the small Boulogne basin on the banks of the Channel, which connects the Franco-Belgian basin with the English basins.
By the uplift of ancient rocks the Valenciennes Basin is divided into two parts: the western, or Pas de Calais Basin, and the eastern, Nor Basin.
Stratigraphy. The geological structure of the basin involves Cambro-Silurian, Devonian, Carboniferous and Cretaceous deposits.
The ancient massifs in the Ardennes are the southern boundary of the Franco-Belgian Basin. They are composed of metamorphosed Cambrian and Silurian shales, which are the ancient basement of the basin; the Devonian sandstones lie unconformably on them. The Carboniferous is deposited on the Devonian sandstones.
The Carboniferous of the Valenciennes Basin is represented by two divisions – the Lower Maritime (Dinant) and Upper Carboniferous; the latter is divided into the Lower Namurian Low Carboniferous Stage and the Upper Westphalian Carboniferous Stage.
The Stefanian Stage is absent, and the Cretaceous sediments, represented by chalk, marls and dolomites, unconformably overlie the Westphalian.
The Namurian Stage is composed of sandstones and shales, partly of marine origin. The Namurian Stage is composed of sandstones and shales, some of them of marine origin.
The upper Westphalian carboniferous Westphalian Stage is composed of sandy-clay continental sediments with numerous subordinate coal seams; the marine strata are very limitedly developed. The horizon is divided into three formations: the Vicuan (Westphalian A), which is weakly coal-bearing; the Anzen (Westphalian B) and Brue (Westphalian C), the main formations with commercial coal-bearing capacity For the Valenciennes Basin, the marine Rember and Poissonière formations are the main markers. A distinct and stable marker horizon is the conglomerate (pudding) in the upper part of the Bruyé formation above the Edouard coal seam.
According to the marine layers of the Rembert and Poissonière horizons and the conglomerate of the Edouard formation, the coal formation is divided into major formations and horizons.
To parallel the individual coal seams of the main industrial Brué Formation, the characteristic interlayers of tonstones – homogeneous clay shales with a shell fracture from 2 to 20 cm in thickness, macroscopically not always identifiable. Under the microscope, the tonstones have a dark brown matrix with a large amount of the mineral leverierite. In the Nor Basin, up to nine stable tonstein horizons were identified in the Brueh Formation over an area of 50 km, of which four to six horizons remain stable over the entire basin area.
Tectonics. The Valenciennes Basin is a large syncline, or synclinorium, which is part of the marginal trough of the Hercynian folded zone and is complicated by numerous major faults and minor folds.
The northern flank of the basin is more gentle and calm, and here the coal-bearing Westphalian deposits underlie the Namurian, Dinantian and Devonian sediments. The latter are unconformably deposited on the underlying Cambro-Silurian sediments of the Brabant anticlinal massif.
The geological structure of the southern wing of the basin and its central part is much more complicated. Here, as a result of strong tangential pressure to the north and a major fault that limited the industrial part of the basin, the Silurian and Devonian deposits of the Dinant basin overlapped and partially overlapped the coal-bearing deposits of the basin. The coal-bearing sequence was folded and broken by numerous thrusts and faults of predominantly latitudinal strike, as well as diagonal in relation to them faults into separate sections and blocks displaced in the north direction, which created the typical Franco-Belgian scale structure and block structure of the entire basin. The southern part of the basin (especially in the Belgian part) consists of charred scales (covers) of Carboniferous sediments displaced from the south for considerable distances.
The main tectonic element of the entire Franco-Belgian basin is the major South thrust in the French part of the basin, and the Eifel, or Condros, in the Belgian part (see Fig. 11). This disturbance is also found in the German part of the Aachen Basin. The southern thrust dips gently southward in the near-surface part and more steeply at depth, with an offset amplitude of thousands of meters.
In the eastern part of the basin (Nor), there is a major thrust or Barrois Chariage parallel to the South thrust.
The faults dip southward at gentle angles of 15-25°; the main of them apparently join the South thrust at depth, being its apophyses.
The massifs enclosed between the faults are characterized by intense folding, dominated by sharp, often north-turned folds; the upper parts of anticlines and bottom parts of synclines are cut in places by large Barrois and Pruvo faults.
The western part of the basin (Pas de Calais) is characterized by similarly complex tectonics; some of the Nor district faults extend into the Pas de Calais (Pruveau thrust), some of them join the South thrust (Barrois fault), and new faults arise.
The main areas of the Valenciennes Basin are already mined by a large number of mines. Only the coal-bearing areas beneath the South thrust are not developed by the coal industry to depths well in excess of 1000 m. They will be developed by industry after the exhaustion of the reserves of existing coal companies, already conducting mining works at a depth of 800-1000 m.
Coal content. The basin is characterized by a fairly high coal content and contains in the thickness of 2000-2200 m up to 70-80 coal seams, of which about 50 have a working thickness of at least 0.6 m and a total thickness of 35-40 m.
The average thickness of the seams in the basin is about 1 m, the average thickness of the developed seams is 1.1 m.
In terms of coal saturation, the Valencienno basin is significantly inferior to the Lower Rhine-Westphalia and Upper Silesian basins and is close to the Donetsk basin.
The greatest number of coal seams is in the upper most powerful Brueh Formation, comprising up to 22-32 working seams with a total thickness of 16-25 m. According to the presence in the section of the coal-bearing strata noted above characteristic and stable stratigraphic benchmarks – marine layers and puddings – it identified four packages of coal seams traceable over significant areas; 1) Si Siion, 2) Ernestina, 3) Dizuiche and 4) Edouard. Each of these packages contains up to 8-10 coal seams.
The number of working seams in this suite varies somewhat at individual mined concessions.
The underlying (less thick) Anzen Formation has 8-10 beds with a total thickness of 5-6 m.
The weakly coal-saturated lower Vicuan Formation contains no more than 4-6 strata with a total thickness of 2-4 m, and only in the eastern part of the basin the number of strata in it increases to 10-12.
Due to the tectonic complexity, it is very difficult, and in most cases impossible, to accurately parallel coal seams. Therefore, the latter on individual concessions have a variety of names – numbered or proper names.
Seams are characterized by relative stability, preserving the working thickness in a number of exploited areas, and some seams – in the whole area of the basin, but their structure is subject to significant changes.
According to the petrographic composition, the coals are humus, striped shiny and semi-shiny, of varying and mostly high degree of carbonization. The coal seams are a frequent alternation of coarse claret bands and vitreous lenses; semi-matte and matte duren varieties are of subordinate importance; fusen is usually found in insignificant admixtures.
Coal beds are of autochthonous origin, and their soil is usually non-laminated sandy-clayey rock with the remains of plant rhizomes (analogous to the “kucheyavchik” of the Donetsk Basin); in the roof are laminated sandy-clayey rocks.
In the basin, coals of all grades from lean to flame dry (gas and long-flame), including a group of sintered fatty coals of various degrees of metamorphism, used for coking (Fig. 12) are distributed.
The coals of Valenciennes basin are characterized by low sulfur content within 0.5-2%, low humidity not exceeding 2-2.5% for the working fuel, and high heat of combustion of working fuel up to 8000-8500 kcal/kg; the amount of volatile matter per combustible mass varies from 10-12% (lean coals) to 40% (fat coals).
Sintering coals prevail, comprising up to 60-65% of all reserves, half of which is used for coking. The reserves of lean coals amount to 15-20%.
Changes in the qualitative characteristics of coals within the basin are very significant – the same coal seams change their quality both along the strike and down dip. With a clearly expressed pattern of Hilt – a decrease in the amount of volatiles with stratigraphic depth – for a number of mined areas are observed deviations associated with complex fault tectonics and in connection with it – the block structure of deposits, which resulted in coming into contact with areas with different coal quality.
In the basin area, coals with high volatile content are localized in the western part of the southern wing of the basin, while lean and stripped fat coals are distributed along the entire stretch of its northern wing; coking (fat) coals occupy an intermediate position.
Coal seams, mined at great depths – up to 800-1000 m, are characterized by high gas abundance, and by analogy with the Donetsk basin, most of the mines can be referred to the 2nd and 3rd category of gas. The watercut of the mines is not high and decreases with depth.
The reserves of the basin (actual and probable) to a depth of 1200 m from the surface are 1.62 billion tons, to a depth of 1800 m (with prospects) – 4.59 billion tons. Coal production in 1960 was 26.9 million tons.