HYDROGEOTHERMAL CONDITIONSIN EIREbyC.R. Aldwell* and D.J. Burdon**An orig<strong>in</strong>al paper prepared for section 14.2Fossil fuels, <strong>of</strong> the XXVI International<strong>Geological</strong> Congress, Paris, 1980.Ref. No. 14.0068.SUMMARY<strong>Hydrogeothermal</strong> conditions <strong>in</strong> Eire have not yet been substantially<strong>in</strong>vestigated, but a project entitled "Geothermal Energy Potential <strong>of</strong> <strong>Ireland</strong>"is planned to commence <strong>in</strong> mid-1980, with.EEC assistance. The data presentedhere, ma<strong>in</strong>ly on warm spr<strong>in</strong>gs, forms part <strong>of</strong> the preparation for this project.The 17 known warm spr<strong>in</strong>gs are listed <strong>in</strong> Table 1, and shown on Figs. 1and 2. Temperatures <strong>of</strong> the Le<strong>in</strong>ster Group <strong>of</strong> warm spr<strong>in</strong>gs have beencollected s<strong>in</strong>ce 1971, and most were chemically analysed at end-1979, Tables 3and 4. From a study <strong>of</strong> the location, geological and geophysical sett<strong>in</strong>g andhydrological, thermal and hydrochemical characteristics, a number <strong>of</strong><strong>in</strong>ferences have been reached. These may be summarised here: (i) Severalwarm spr<strong>in</strong>gs occur on higher ground than might be expected; (ii) Some havebeen made functional only by man's activities; (iii) The Le<strong>in</strong>ster warmspr<strong>in</strong>gs appear to be distributed at 8 krn distances apart; (iv) All the warmspr<strong>in</strong>gs issue from D<strong>in</strong>antian limestones, ma<strong>in</strong>ly from the Visean; (v) Somesmall Tertiary <strong>in</strong>trusives have been reported from their vic<strong>in</strong>ity;(vi) The occurrences can <strong>of</strong>ten be related to fold structures, as along asyncl<strong>in</strong>e; (vii) Certa<strong>in</strong> gravity lows may have some connection with thesewarm spr<strong>in</strong>gs; (viii) Discharges <strong>in</strong>crease <strong>in</strong> spr<strong>in</strong>g and fall <strong>in</strong> autumn,<strong>in</strong>dicat<strong>in</strong>g groundwater flow controlled by the normal hydrological cycle;(ix) Temperatures peak <strong>in</strong> spr<strong>in</strong>g and decl<strong>in</strong>e <strong>in</strong> autumn, but are irregular;(x) Most <strong>of</strong> the warm spr<strong>in</strong>gs show no abnormal hydrochemical characteristics;·(xi) High Cl and TDS are found <strong>in</strong> three spr<strong>in</strong>gs occurr<strong>in</strong>g along a syncl<strong>in</strong>alstructure, but two other spr<strong>in</strong>gs located there have as yet not been analysed;(xii) There are fa<strong>in</strong>t <strong>in</strong>dications that Si and I <strong>in</strong>crease with <strong>in</strong>creas<strong>in</strong>gtemperature.Of the Munster warm spr<strong>in</strong>gs, those <strong>in</strong> Cos. Clare and Limerick appearto be similar to those <strong>of</strong> Le<strong>in</strong>ster. However, the Mallow Spa spr<strong>in</strong>g, thebest-known <strong>in</strong> <strong>Ireland</strong>, issues where the D<strong>in</strong>antian limestones are highlycompressed, downfolded and thrust. Boreholes <strong>in</strong> the Mallow area adjacentto the spr<strong>in</strong>g have located warm water.While the m<strong>in</strong>eralization <strong>of</strong> the Lower Carboniferous <strong>in</strong> <strong>Ireland</strong> has beenattributed to hydrothermal concentration and precipitation <strong>of</strong> base metals,present-day geothermal circulation bears no relationship to such ancientactivity. However, the groundwater circulation is considered as due to theeffects <strong>of</strong> heat, on cirCUlation cells <strong>of</strong> the order <strong>of</strong> 50 km 2 , with conduction-* <strong>Geological</strong> <strong>Survey</strong> <strong>of</strong> <strong>Ireland</strong>, 14 Hume Street, Dubl<strong>in</strong> 2.** Consultant, <strong>Geological</strong> <strong>Survey</strong> <strong>of</strong> <strong>Ireland</strong>; and Director, M<strong>in</strong>erex Ltd.
convection upris<strong>in</strong>g <strong>of</strong> warm water <strong>in</strong> the centre <strong>of</strong> each cell, and rechargeand downflow at the edges, as <strong>in</strong> Fig. 7. Depths <strong>of</strong> circulation may be<strong>of</strong> the order <strong>of</strong> 700 metres. As yet, the source <strong>of</strong> the heat has not beenidentified, while the problem <strong>of</strong> heat conservation by impermeable strata orcover is under consideration. In brief, the problem has been but stated;<strong>in</strong>tensive <strong>in</strong>vestigation under the "Geothermal Energy Potential <strong>of</strong> <strong>Ireland</strong>"project will be required to solve the mechanisms and lead to the properutilisation and management <strong>of</strong> this natural energy resource <strong>of</strong> the country.
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