Downloaded from http://jgs.lyellcollection.org/ by guest on September 28, 2021

Journal of the Geological Society, London, Vol. 146, 1989, pp. 351-352. Printed in Northern Ireland

Conference Report

Lignite and associated deposits of the Tertiary Lough Neagh Basin, Northern Ireland

J. PARNELL & I. G. MEIGHAN Department of Geology, Queen’s University, Belfast BT7 INN, UK

Report of a meeting of the British Sedimentological Research sediments have a provenance dominated by the basalts of Group of the Geological Society held atthe Queen’s theAntrim Lava Group, but also including Dalradian University of Belfast on 27-28 September 1988. The metasediments, the Ordovician Tyrone IgneousComplex, organizers were J. Parnell, I. G. Meighan and I. C. Legg. and the Tertiary MourneGranites. New techniques employing the traceelement chemistry of zircons and opaque minerals have allowed a high quality resolution of The existence of lignite in the Tertiary deposits of the the different sources. Lough Neagh Basin has been known since the eighteenth J. Quigg reportedthe results of explorationin the century. Recent drilling by the Geological Survey of Ballymoney region by Meekatharra(N.I.) Ltd. Boreholes NorthernIreland and several exploration companies has have intersecteda cumulative lignite thickness of up to shown that the lignite deposits occur on a substantial scale 140m, averaging 40mto 50m. The materialhas a high and,therefore, may providea major source of energy, calorific value compared to many other lignites. Correlation particularly as a fuel for electricity generation. The meeting of boreholes has been achieved by geophysical methods and was convened as a forum for the presentation of results by a by matching sideritic bands. C. T. Morley presented the multi-disciplinary group of geologists, chemists, civil geological results of drilling in the Lough Beg region (SSW engineers, chemical engineers and economistsconcerned of Crumlin). The exploration had not revealed prospects of with lignite deposits, its extraction and upgrading. Fourteen economic potential but had, interestingly, penetrated lignite pagerswere presented, followed by one-daya field below a layer of basalt, which was tentatively explained as excursion to North Antrim and the exploration office of BP representing peat deposition onan irregularundercut Coal Ltd. surface. Coarsesediment in boreholesadjacent to faults The geological background to the deposits was described suggests that alluvial fans developed off active fault scarps. by H. Cherry, who showed that the Oligocene Lough Neagh M. G. Dewison explained the methods used forthe basin developed on the irregular surface of the Palaeocene geochemical and mineralogical analysis of lignite. Trace Antrim Lava Group and explained the allocation of licenses element analysis can be undertaken by a recently developed for lignite exploration by the N.I. Department of Economic X-ray fluorescence ‘whole coal’ procedure which is quicker Development. I. C. Legg outlined the distribution of lignite andrequires less material than techniques which involve deposits within the basin, and gave details of particularly ashed samples. I. G. Meighan, M. G. Dewison & D. D. rich deposits in the regions of Crumlin, Co. Antrim; Coagh, Jamison described the inorganic geochemistry of the lignites Co. Tyrone;and Ballymoney,Counties Antrim and from the Lough Neagh Group. Theycontain higher Londonderry. Lignite deposits also occur tothe south of proportions of elements with a ‘basaltic’ signature (V, Cr, Lough Neagh in Co. Armaghbut not atworkablea Ni, Cu)than most lignites fromelsewhere in the world. thickness or depth. These and other elements show strong positive correlations J. Parnell & B. Shukla described the lithofacies and with ash contents, implying that the metals were introduced likely palaeoenvironment of the LoughNeagh Group principally in the (largely basalt-derived) inorganic fraction sediments. The sediments were deposited in a mid-Tertiary of the lignite. precursor tothe present Lough Neagh,although the J. G. Stuart & M. G. Gallagher described the deposits may have been more or less isolated in a series of mineralogy is comparable with that of other Oligocene clays sub-basins. The sub-basins may have developed in an at Bovey Tracey and Petrockstowe. S. McRandal reported extensional regime constrained by NNW-SSE faults normal over-consolidated, stiff fissured clays similar to the London to extension and strike-slip movement on NE-SW faults. Clay. The predominant clay mineral is kaolinite with much The lignite representsautochthonous lake-marginswamps lesser quantities of mica and illite andno smectite.This andparautochthonous openlake deposits. M. Boulter mineralogy is comparable with that of other Oligocene clays reportedthat the flora of the Lough Neagh Group at Bovey Tracey and Petrockstowe. S. McRandal reported representsa warm temperate climate,this luxuriant tests undertakento predict the behaviour of the clay vegetation contrastingsharply with plantsfrom theearly sedimentsduring opencast mining of lignite. A possible Tertiary interbasaltic beds of County Antrim which grew in opencastsite at Crumlin is immediatelyadjacent tothe an environment dominated by volcanicity which allowed the present Lough Neagh, which could flood the pit if a development of a much less diverse vegetation. The Lough hydraulic connection exists or the lignite is too permeable. Neagh Group spore assemblage is very similar to those of Water is present in the basalts below the Lough Neagh other Oligocenedeposits in westernBritain, including Group, such that when the upper sediments are removed by Bovey Tracey and Petrockstowe. B. Shukla described heavy mining the relaxation in pressure may allow water to heave mineral studies which showed that the Lough Neagh Group up the remaining sediment. 35 1 Downloaded from http://jgs.lyellcollection.org/ by guest on September 28, 2021 352 REPORT CONFERENCE

A. H. Fawcett & J. Grimshaw presented cross- of the lignite would be very important if EEC regulations polarization magic-angle spinning I3C spectra for the lignite, demand that coal-fired power stations incorporate sulphur- obtained by NMR spectroscopy. The data indicate that the scrubbers. In his concluding remarks, H. E. Wilson lignite has greater affinities with lignins/peat than with reminded the meeting thatthe economicpotential of the brown coal, which supports vitrinite reflectance determina- Lough Neagh Group sediments might also include the tions in showing that the material represents a very early exploitation of clays forceramic purposes, andthe large stage of lignite development. M. Brady, A. Galwey & M. quantities of siderite as a source of iron. Burnett reportedthat the water content of the lignite is During the field excursion, R. Lawman displayed cores about 50% andthat the kinetics of dehydration, an through the basalt below the Lough Neagh Group in the important process in upgrading the raw material, are Crumlin area, which exhibits a weathering profile up to 60 m geometrically controlled such that they follow the thick. The basalt is extensively weathered to kaolinite but is contracting cube function, and would be dependent on the recognizable through relict igneous textures including flow vapour pressure of water around the sample. tops, porphyritic textures and amygdales. Erosion of the C. Jefferson discussed the potential uses of the lignite, weathered basalt was the source of the thick clays in the particularly asa fuel ina minemouth power station.The Lough Neagh Group. local availability of lignite (but notcoal) would be an important factor in determining the means of fuelling future A review paper and abstracts will be published in the Irish power stations in Northern Ireland. The low sulphur content Journal of Earth Sciences.

Received 20 October 1988