_..._ Natural Environment Research Council -2 Institute of Geological Sciences - -- Mineral Reconnaissance Programme Report c- - _.a - A report prepared for the Department of Industry BRITISH GEOLOGICAL SURVEY Natural Environment Research Council 1 1 Mineral Reconnaissance Programme I Report No. 70 Regional geochemical and geophysical surveys in the Berwyn Dome and 1 adjacent areas, North Wales Geochemistry D. C. Cooper, BSc, PhD I Geophysics K. Rollin, BSc I J. D. Cornwell, MSc, PhD with contributions on geology by 3 M. F. Howells, BSc, PhD and mineralogy by D. J. Morgan, BSc, PhD 1 I 0 Crown copyright 7984 London 1984 A report prepared for the Department of Trade and fno’ustry This report relates to work carried out by the British Geological Survey on behalf of the Department of Trade and Industry. The information contained herein must not be published without reference to the Director, British Geological Survey. D. Ostle Programme Manager British Geological Survey Keyworth Nottingham NG12 5GG No. 70 Regional geochemical and geophysical surveys in the Berwyn Dome and adjacent areas, North Wales . Mineral Reconnaissance Programme Reports 58 Investigation of small intrusions in southern Scotland 31 Geophysical investigations in the 59 Stratabound arsenic and vein antimony Closehouse-Lunedale area mineralisation in Silurian greywackes at Glendinning, south Scotland 32 Investigations at Polyphant, near Launceston, Cornwall 60 Mineral investigations at Carrock Fell, Cumbria. Part 2 - Geochemical investigations 33 Mineral investigations at Carrock Fell, Cumbria. Part 1 -Geophysical survey 61 Mineral reconnaissance at the Highland Boundary with special reference to the Loch Lomond and 34 Results of a gravity survey of the south-west Aberfoyle areas margin of Dartmoor, Devon 62 Mineral reconnaissance in the Northumberland 35 Geophysical investigation of chromite-bearing Trough ultrabasic rocks in the Baltasound-Hagdale area, Unst, Shetland Islands 63 Exploration for volcanogenic sulphide mineralisation at Benglog, North Wales 36 An appraisal of the VLF ground resistivity technique as an aid to mineral exploration 64 A mineral reconnaissance of the Dent-lngleton area of the Askrigg Block, northern England 37 Compilation of stratabound mineralisation in the Scottish Caledonides 65 Geophysical investigations in Swaledale, North Yorkshire 38 Geophysical evidence for a concealed eastern extension of the Tanygrisiau microgranite and its 66 Mineral reconnaissance surveys in the Craven Basin possible relationship, to mineralisation 67 Baryte and copper mineralisation in the 39 Copper-bearing intrusive rocks at Cairngarroch Bay, Renfrewshire Hills, central Scotland south-west Scotland 68 Polymetallic mineralisation in Carboniferous rocks 40 Stratabound barium-zinc mineralisation in Dalradian at Hilderston, near Bathgate, central Scotland schist near Aberfeldy, Scotland; Final report 69 Base metal mineralisation associated with 41 Metalliferous mineralisation near Lutton, Ivybridge, Ordovician shales in south-west Scotland Devon 70 Regional geochemical and geophysical surveys in 42 Mineral exploration in the area around Culvennan the Berwyn Dome and adjacent areas, North Wales Fell, Kirkcowan, south-western Scotland 71 A regional geochemical soil investigation of the 43 Disseminated copper-molybdenum mineralisation Carboniferous Limestone areas south of Kendal near Ballachulish, Highland Region (south Cumbria and north Lancashire) 44 Reconnaissance geochemical maps of parts of 72 A geochemical drainage survey of the Preseli Hills, south Devon and Cornwall south-west Dyfed, Wales 45 Mineral investigations near Bodmin, Cornwall. Part 2-New uranium, tin and copper occurrence in the Tremayne area of St Columb Major 46 Gold mineralisation at the southern margin of the Loch Doon granitoid complex, south-west Scotland 47 An airborne geophysical survey of the Whin Sill between Haltwhistle and Scats’ Gap, south Northumberland On 1 January 1984 the Institute of Geological Sciences 48 Mineral investigations near Bodmin, Cornwall. was renamed the British Geological Survey. It continues Part 3-The Mulberry and Wheal Prosper area to carry out the geological survey of Great Britain and Northern Ireland (the latter as an agency service for the 49 Seismic and gravity surveys over the concealed government of Northern Ireland), and of the surrounding granite ridge at Bosworgy, Cornwall continental shelf, as well as its basic research projects; it 50 Geochemical drainage survey of central Argyll, also undertakes programmes of British technical aid in Scotland geology in developing countries as arranged by the Overseas Development Administration. 51 A reconnaissance geochemical survey of Anglesey 52 Miscellaneous investigations on mineralisation in The British Geological Survey is a component body of the sedimentary rocks Natural Environment Research Council. 53 Investigation of polymetallic mineralisation in Lower Devonian volcanics near Alva, central Scotland 54 Copper mineralisation near Middleton Tyas, North Bibliographic reference Yorkshire Cooper, D. C., and others. 1984. Regional geochemical 55 Mineral exploration in the area of the Fore Burn and geophysical surveys in the Berwyn Dome and igneous complex, south-western Scotland ’ adjacent areas, North Wales. Mineral Reconnaissance Programme Rep. Br. Geol. Surv., No. 70 56 Geophysical and geochemical investigations over the Long Rake, Haddon Fields, Derbyshire 57 Mineral exploration in the Ravenstonedale area, Printed for the British Geological Survey by Four Point Cumbria Printing Ii CONTENTS 21 Summary of anomalous results for elements not plotted in figures 14-20 In pocket Summary 1 22 Anomalous results in panned concentrates from the Afon Trystion 17 Introduction 1 23 Summary of highly significant inter-element corre- Geology and Mineralisation 4 lation for panned concentrates from the Afon Sedimentary and volcanic rocks 4 Trystion 18 Intrusions 7 24 Anomalous results in drainage samples from Cwm Structure 7 Rhiwarth 20 Mineralisation 7 25 Anomalous results in drainage samples from around Pennant Melange11 2 1 Geophysical Surveys 10 26 Contoured greyscale plot of copper in stream Gravity survey 10 sediment 23 Fieldwork and data reduction 13 27 Contoured greyscale plot of lead in stream The Bouguer gravity anomaly field 13 sediment 24 The aeromagnetic anomaly field 13 28 Contoured greyscale plot of zinc in stream General interpretation 19 sediment 26 Mineralisation and Bouguer anomalies 19 29 Contoured greyscale plot of barium in stream Stream Sediment Survey 19 sediment 27 Sampling and analysis 19 30 Contoured greyscale plot of iron in stream Interpretation of results 22 sediment 29 Distribution analysis 22 31 Contoured greyscale plot of manganese in stream Major causes of element variation 25 sediment 30 Definition of anomalies 34 32 Contoured greyscale plot of nickel in stream Description of anomalies 34 sediment 32 33 Contoured greyscale plot of vanadium in stream Conclusions and Recommendations 56 sediment 33 Acknowledgements 57 34 Contoured greyscale plot of zirconium in stream References 5 7 sediment 35 35 Contoured greyscale plot of chronium in stream Appendix 1 Metal mines and trials in the Berwyn sediment 36 Dome and its environs 59 36 Contoured greyscale plot of molybdenum in stream Appendix 2 Phosphate workings in the Berwyn sediment 38 Dome 59 37 Contoured greyscale plot of zinc in stream water 39 Regional geochemical trends related to Appendix 3 38 Contoured greyscale plot of copper in panned lithostratigraphy 60 concentrate 41 Appendix 4 Analytical results for 399 streams 39 Contoured greyscale plot of of lead in panned sediments, panned concentrate and water sample; concentrate 42 (fiche) 40 Contoured greyscale plot of zinc in panned concentrate 44 41 Contoured greyscale plot of barium in panned FIGURES concentrate 45 1 Location of the survey area 2 42 Contoured greyscale plot of of iron in panned 2 Simplified geological map of the Berwyn Dome and concentrate 48 adjacent areas In pocket 43 Contoured greyscale plot of manganese in panned Bouguer anomaly survey area 3 concentrate 49 Bouguer anomaly map and outline geology. In pocket 44 ‘Contoured greyscale plot of nickel in panned Regional Bouguer anomaly map 5 concentrate 5 1 Residual Bouguer anomaly map 6 Contoured greyscale plot of titanium in panned Aeromagnetic map 8 45 concentrate 52 Main geological and geophysical features of the 46 Contoured greyscale plot of arsenic in panned Berwyn Dome 9 concentrate 54 9 Diagrammetric geological section across the Berwyn 47 Contoured greyscale plot of tin in panned Dome 11 concentrate 55 10 Summary of positive inter-element associations 12 11 Diagrammatic interpretation of the positive inter- element associations 12 TABLES 12 Distribution of cobalt in stream sediment with Generalised geological succession in the Berwvn respect to acid upland soils 14 Hills 4 13 Distribution of cerium in panned concentrate with Densities of some North Wales Rock 13 respect to acid upland soils 15 Summary of analytical results in ppm for 399 stream 14 Plot of anomalous copper results 1n pocket sediments, water and panned concentrate 15 Plot of anomalous lead results In pocket samples 25 16 Plot of anomalous zinc results In pocket Summary of highly significant inter-element corre- 17 Plot of anomalous barium results In pocket lations 28 18 Plot of anomalous arsenic results In pocket Threshold levels and class intervals for anomalous 19 Plot of anomalous iron results In pocket results 37 20 Plot of tin results