Basin evolution and tectonics of the Leicestershire coalfield.

The Leicestershire coalfield constitutes a NW-SE orientated area of approximately 125 km2, centred on the town of Coalville in the East Midlands. The area is underlain by Carboniferous, coal-bearing strata of Westphalian A and B age. In the south the Carboniferous rocks are concealed below Permo-Triassic sediments. The investigation was restricted to the parts of the Leicestershire coalfield worked by British Coal deep mines. A synoptic view of the entire coalfield was taken, using exploration borehole data and underground quality control samples (where available). The study describes aspects of these data as they relate to the geology and depositional setting of the Leicestershire coalfield. The observed geometry and distribution of the coal seams and interseam sediments are related to the causative depositional processes. Computer modelling of the data examined the lateral and vertical lithological relationships within the Westphalian A and B succession of the Leicestershire coalfield in three representative parts of the stratigraphic interval, namely the middle section of the Westphalian A, the Westphalian A-B contact, and the mid Westphalian B. The lateral and vertical lithological relationships were defined using isopach and structural contour maps as well as correlation (scatter) diagrams. This study shows that there is probably not one single control on sedimentation, but a complex interaction of factors that have led to the deposition of the coal and coal-bearing strata in the Westphalian of the Leicestershire coalfield. The most important factor appears to be base level change, and resultant changes in water table level. Base level changes in turn may be controlled by tectonics, eustacy or doming of the peat during growth. There is a significant change in sedimentary style between the mid Westphalian A and the mid Westphalian B. Controls on sedimentation changed during the Westphalian, from predominantly structural factors in the mid Westphalian A to factors inherent in the depositional system in Westphalian B. Subsidence in the Westphalian A was in response to regional crustal extension and took place along the faults bounding the block and basin topography of the basement. Subsidence was rapid and basin fill sequences were thick, but coal seams were thin. With relaxation of extensional tectonics isostatic readjustment and thermally induced subsidence took place in the Westphalian B, with sedimentation keeping pace with the subsidence so that deposition occurred in shallow water which meant that the sediment and coal accumulated as a result of compactional, topographical and depositional factors

Geological controls on the mineralogy and geochemistry of the Beypazari lignite, central Anatolia, Turkey

17 páginas, 8 figuras, 2 tablas.The raw coal from the Çayirhan mine, Beypazari basin, Turkey contains an average of 28.5% mineral matter, consisting up to 80% zeolites. The coal seam is split by a 1-m-thick tuffaceous siltstone into the upper, first (Tv) and lower, second (Tb) seams, which contain essentially different zeolites. The first seam contains Ca-rich zeolites (clinoptilolite/heulandite) whilst the second seam contains Na-rich zeolites (analcime). Experimental work has shown that a Na-rich activation solution will produce Na-rich zeolites when the original volcanic glass is Na-rich, but will produce Ca-rich zeolites when the volcanic material is Ca-rich. It is thought that a Na-rich activation solution, derived from contemporaneous volcanics in the Beypazari basin, reacted with volcanic tuffs of different chemical composition to produce the vertical variability in the mineral matter of the two seams. Trace element analyses of the raw coal showed that they are enriched in As, B, Cr, Ni and Zr when compared to world-wide averages of coal. They are also enriched in the major elements Na and K. These elements are probably also derived from a volcanic source. Barium and Sr show a clear affinity for analcime, whilst Li, Cr, Ni, Cu, Zn, Co and Ga show a clear affinity for clinoptilolite/heulandite. Trace elements showing a positive correlation with the organic matter are Mn, B, Be, Ge, Y, Zr, Nb, Hf, W and U. Manganese, U, Th, Sc, Ge and HREE (heavy rare earth elements) show correlations with phosphate. Trace elements showing correlation with both Fe and S contents are Co, Mo, Ta, Pb and IREE (intermediate rare earth elements). Arsenic and V seem to have mixed affinities with sulphides and zeolites, and organic matter and zeolites, respectively. Although a proportion of the As, B and S are retained in the ash during coal combustion, due to the sorption mechanism of CaO derived from the clinoptilolite/heulandite decomposition, significant emissions of these elements may arise from the Çayirhan thermal power station due to the anomalously high concentrations of these elements in the Beypazari coal. The high total alkali metal content of these coals exceeds the recommended maximum for steam coal, but it is believed that sodium occurring in a mineralogical form such as analcime is not as likely to contribute to boiler fouling as organically-associated sodium.This study was facilitated by financial support given by the British Council (grant number 1199) and the Spanish Ministry of Education and Science (grant number AI-HB94-208) in a joint British/Spanish collaborative research programme.Peer reviewe

Zeolites in Tertiary coal from the Çayirhan mine, Beypazari, Turkey

10 páginas.The study focuses on the mineralogy of the upper coal seam accumulated at the top of the Çoraklar Formation (Miocene), Beypazari, Turkey. This coal seam is laterally extensive and averages 3.0 m thick, varying from 1.0 to 4.9 m. Analcime and clinoptiolite comprise up to 80% of the mineral matter (which also includes feldspars, quartz and pyrite and traces of dolomite, clay minerals and apatite) in the coal from the Cayirhan mine. Zeolites were formed when sodium-rich solutions altered aluminosilicate epiclastic material derived from contemporaneous volcanic activity. The allocthonous organic matter accumulated as a result of detrital plant and epiclastic material from an adjacent fresh-water environment being washed into a saline lake in sufficient quantities to form peat with a high mineral matter content (29.7% mean mineral matter content in raw coal). Subsequent syngenetic alteration of the volcanic glass incorporated into the peat resulted in zeolite formation. Alteration of sodium-rich epiclastic material by sodium-rich solutions resulted in the formation of analcime, whilst alteration of calcium-rich epiclastic material by sodium-rich solutions resulted in the formation of clinoptilolite.Peer reviewe