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Geology and Mineral Resources of West Africa PDF

193 Pages·1986·7.5 MB·English
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GEOLOGY AND MINERAL RESOURCES OF WEST AFRICA TITLES OF RELATED INTEREST Rutley's elements of mineralogy, 26th edn The poetry ofg eology H. H. Read R. M. Hazen (ed.) Physical processes of sedimentation Komatiites J. R. L. Allen N. T. Arndt & E. G. Nisbet (eds) Petrology of the igneous rocks, 13th edn Sedimentary structures F. H. Hatch, A. K. Wells & M. K. Wells J. D. Collinson & D. B. Thompson Metamorphism and metamorphic belts Geomorphological field manual A. Miyashiro V. Gardiner & R. V. Dackombe Petrology of the metamorphic rocks Gravity R. Mason C. Tsuboi The formation of soil material Metamorphic processes T. R. Paton R. H. Vernon Petrology of the sedimentary rocks Geology and man J. T. Greensmith Janet Watson The interpretation of igneous rocks Field mapping for geology students K. G. Cox, J. D. Bell & R. J. Pankhurst F. Ahmed & D. C. Almond Geology for civil engineers Geological howlers (boners/bloomers) c. A. C. McLean & D. Gribble I. Rolfe (ed.) Invertebrate palaeontology and evolution Statistical methods in geology E. N. K. Clarkson R. F. Cheeney Microfossils Echinoid palaeobiology M. D. Brasier A. Smith The inaccessible Earth Geomorphology in arid regions G. C. Brown & A. E. Mussett D. O. Doehring (ed.) Tectonic processes Petroleum geology D. Weyman F. K. North Terrain analysis and remote sensing Environmental change and tropical geomorphology J. R. G. Townshend (ed.) I. Douglas & T. Spencer (eds) Geomorphological techniques A practical introduction to optical mineralogy A. S. Goudie (ed.) C. D. Gribble & A. J. Hall Soils and landforms Introducing groundwater A. J. Gerrard M. Price Introduction to small-scale geological structures Principles ofp hysical sedimentology G. Wilson J. R. L. Allen Sedimentology: process and product Tectonic geomorphology M. R. Leeder J. T. Hack & M. Morisawa Metamorphic geology C. Gillen GEOLOGY AND MINERAL RESOURCES OF WEST AFRICA lB.WRIGHT editor and principal author Department of Earth Sciences, The Open University with contributions from D.A.Hastings WB.Jones H.RWilliams London GEORGE ALLEN & UNWIN Boston Sydney © J. B. Wright, D. A. Hastings, W. B. Jones & H. R. Williams, 1985. This book is copyright under the Berne Convention. No reproduction without permission. All rights reserved. Softcover reprint of the hardcover I st edition 1985 George Allen & Unwin (Publishers) Ltd, 40 Museum Street, London WCIA lLU, UK George Allen & Unwin (Publishers) Ltd, Park Lane, Heme! Hempstead, Herts HP2 4TE, UK Allen & Unwin Inc., 8 Winchester Place, Winchester, Mass. 01890, USA George Allen & Unwin Australia Pty Ltd, 8 Napier Street, North Sydney, NSW 2060, Australia First published in 1985 British Library Cataloguing in Publication Data Geology and mineral resources of West Africa 1. Geology - Africa, West I. Wright, J. B. 556.6 QE339.W4 ISBN 978-94-015-3934-0 ISBN 978-94-015-3932-6 (eBook) DOI 10.1007/978-94-015-3932-6 Library of Congress Cataloging in Publication Data Wright, J. B. Geology and mineral resources of West Africa. Includes bibliographies and index. I. Geology - Africa , West. 2. Mines and mineral resources - Africa, West. I. Title. QE339.W46W751985 556.6 84-28253 Set in 10 on II point Plantin by Paston Press, Norwich and Preface In this text, attention is focused mainly on those literature is accessible, however, it is to be expected countries in western Africa lying south of the Sahara, that teachers and lecturers will know of it and will be that is, between about SON and 15°N, and westward able to acquaint their students with it, where neces of about 15°E. Parts of the region as far north as sary. about 200N are considered from time to time, for A glossary of terms is provided at the end of the purposes of correlation and cQntinuity. The map on volume, and there is a summary at the beginning of p. xiii indicates the approximate extent of the cover each chapter. age. This book is dedicated to the many colleagues and The principal aim is to provide a broad view of students with whom we have worked in West Africa West African geology as a whole, for undergraduates and who have stimulated and encouraged our teach who are studying for honours degrees in geology and ing and research in various ways. We hope also that who already have an understanding of basic geologi it may help the work of international organizations cal principles. It is increasingly important that such as AGID, CIFEG and UNESCO to encourage geologists working in this region should see it as the growing trend towards geological co-operation made up of geological 'provinces' which transcend and correlation between different countries in West national boundaries. Africa. As economic geology is of central importance to Responsibility for the text and illustrations rests many developing countries, the relationship of chiefly with the principal author. The contributing economic mineral deposits to the different geological authors have supplied written material and ad 'provinces' is stressed, and some attempt has been ditional information, based on their extensive made to account for the occurrences. experience of teaching and research in West Africa. The bibliography at the end of each chapter con They have also provided much valuable editorial tains references to published source materials and advice during the various stages of preparation, but selected items can be used as a further reading list. they are not responsible for errors, omissions, or The bibliographies will, in general, not contain other inadequacies. references to the publications of national geological surveys. These are normally too detailed for the The authors regret that there was insufficient time general reader, but they are readily available to those to incorporate into the text the renaming of Upper seeking further information in the countries con Volta as Burkina Faso. There is no political implica cerned. As different authorities place geological tion in this omission, and we trust that no reader will boundaries in different places, maps from different be offended. sources do not always agree in detail. It was decided not to cite references specifically in J. B. Wright the text, for two main reasons. First, it often inter D. A. Hastings rupts the narrative flow, particularly for the student W. B. Jones reader. Secondly, students in West Africa often find H. R. Williams it very difficult to get access to the original literature, chiefly because of the straitened financial cir cumstances of so many universities. Where such Reader survey Please help us to improve future editions of this book by completing the brief ques tionnaire at the back of the book. Vll Acknowledgements Figure 2.3 reprinted from B. F. Windley 1977. The from Nature 292, 123-8. Copyright© 1981 Macmil Evolving Continents. London: Wiley. © 1977 lan Journals Limited; R. Black (6.3); W. S. Pitcher B. F. Windley, by permission of the author and (7.1); K. S. Burke (10.3); P. Lehner, P. A. C. de John Wiley & Sons, Ltd; H. R. Williams (2.4a); Reuter and the American Association of Petroleum Figures 3.1, 3.2 and 3.5 reprinted by permission Geologists (11.7); J. E. Ejedawe and the American from Nature 272, 440-2. Copyright © 1978 Macmil Association of Petroleum Geologists (12.1); R. Black lan Journals Limited; Figures 3.4a&b reprinted by and M. Girod (13.1a&b); Figure 16.2 reproduced permission from Nature 282,606-9. Copyright © by permission from Nature 277, 152-3. Copyright 1979 Macmillan Journals Limited; Elsevier Science © 1979 Macmillan Journals Limited. Publisher (5.1); Figure 5.2 reprinted by permission Vlll Contents Preface page vii 3.7 Plate tectonics and the Liberian event 31 Acknowledgements Vlll 3.8 Repeating patterns of crustal List of tables xii reactivation - a reminder 32 3.9 Economic potential in the Archaean Contributors xii rocks of West Africa 33 General study guide X111 3.9.1 Gold 33 3.9.2 Iron ores 33 3.9.3 Bauxite 35 1 The geological setting 1 3.9.4 Rutile 35 1.1 The African continent 1 3.9.5 Other minerals 36 1.2 The major subdivisions of Bibliography 36 geological time 3 1.3 The structural framework of Africa 4 4 The Proterozoic of West Africa 38 1.4 The global context 5 4.1 Introduction 38 1.5 Age provinces and mineral deposits 6 4.2 Basement 40 1.6 The geological framework of 4.3 Supracrustals: the Birimian West Africa 6 and Tarkwaian 40 1.7 Problems of regional treatment 4.3.1 The Birimian in Ghana 40 and correlation 8 4.3.2 The Tarkwaian in Ghana 41 Bibliography 8 4.3.3 The Birimian and Tarkwaian in Ivory Coast and Upper Volta 41 Part I THE PRECAMBRIAN OF WEST AFRICA 4.3.4 A possible compromise 42 4.4 Granitic rocks 42 2 Crustal development in West Africa 13 4.5 Correlation and geochronology 43 2.1 The concept of crustal reactivation 13 4.6 Plate tectonics and the Eburnian 2.2 Orogeny and thermotectonic events 15 event 44 2.3 Regional patterns in the Precambrian 4.7 Economic potential in the Lower of West Africa 15 Proterozoic rocks of West Africa 45 2.3.1 Basement rocks 16 4.7.1 Gold 45 2.3.2 Supracrustal rocks 18 4.7.2 Manganese 47 2.3.3 Granitic intrusions 19 4.7.3 Diamonds 48 2.4 Patterns of crustal reactivation 20 4.7.4 Bauxite 48 2.4.1 Older supracrustal relics 22 4.7.s- Iron ores 49 2.5 Summary of Precambrian events in 4.7.6 Other minerals 49 West Africa 22 Bibliography 50 Bibliography 23 5 The Pan African of West Africa 3 The Archaean of West Africa 25 - the western domain 51 3.1 Introduction 25 5.1 Introduction 51 3.2 The basement complex 25 5.2 The Rokelide-Mauritanide belt 51 3.3 The supracrustal belts 27 5.2.1 Geochronology in the 3.3.1 The Marampa and Rokelide-Mauritanide Kasila belts 29 belt 54 3.4 Granites 29 5.2.2 Plate tectonics and the 3.5 Fractures, faults and mylonites 29 Rokelide-Mauritanide 3.6 Correlation and geochronology 30 belt 54 ix CONTENTS 5.3 Economic potential of the western 9.3 The Taoudeni Basin 82 Pan African domain 55 9.3.1 Geochronology and Bibliography 55 development of the Taoudeni Basin 84 6 The Pan African ofW est Africa 9.3.2 The Bove Basin 84 - the eastern domain 56 9.3.3 The Iullmedden Basin 85 6.1 Introduction 56 9.4 The glaciation events 85 6.2 The Togo belt 56 9.5 Palaeozoic sediments in coastal 6.3 The eastern domain 59 basins 86 6.3.1 The basement complex 59 9.6 Economic potential of the older 6.3.2 The supracrustals 60 basins 87 6.3.3 Granites 62 Bibliography 88 6.3.4 Fractures, faults and mylonites 62 10 Mesozoic to Tertiary basins - inland basins 89 6.3.5 Correlation and geochronology 63 10.1 Interregnum: Upper Palaeozoic 6.3.6 Correlation with the to Mesozoic 89 Hoggar 63 10.2 The Iullmedden Basin 90 6.4 Pan African plate tectonics east of 10.2.1 The Sokoto sector 93 the craton 65 10.2.2 The Continental Terminal 93 6.5 Economic potential of the eastern 10:3 The Chad Basin 94 Pan African domain 65 10.3.1 Cretaceous of the Chad Bibliography 68 Basin 95 10.3.2 Quaternary of the Chad 7 The Precambrian of West Africa Basin· 95 - synthesis and review 70 10.3.3 Basin subsidence 96 7.1 The geological picture 70 Bibliography 96 7.2 The tectonic patterns 71 11 The Benue Trough and coastal basins 98 7.3 The mineral deposits 72 Bibliography 72 11.1 The Benue Trough 98 11.1.1 Albian-Cenomanian 99 11.1.2 Turonian-Maastrichtian 102 Part II SEDIMENTARY BASINS IN WEST AFRICA 11.1.3 The Bida Basin 104 11.1.4 Folding in the Benue 8 Introduction to sedimentary basins 75 Trough 105 8.1 Distribution of the basins 75 11.1.5 Trans-Saharan seaways 106 8.2 Older basins 76 11.2 The Niger Delta Basin 107 8.3 Younger basins 76 11.3 Other coastal basins 108 11.3.1 The Senegal Basin 111 8.4 Crustal lineaments and basin Bibliography 112 development 77 Bibliography 78 12 Economic potential of the younger sedimentary basins 114 9 Infracambrian to Lower Palaeozoic 12.1 Energy resources 114 basins 79 12.1.1 Petroleum 114 9.1 Introduction 79 12.1.2 Coal 116 9.2 The Volta Basin 79 12.1.3 Uranium 117 9.2.1 Geochronology of the 12.2 Metals and non-metals 117 Volta Basin 82 12.2.1 Phosphate 117 12.2.2 Other minerals 118 Bibliography 120 x CONTENTS Part III MESOZOIC TO CENOZOIC IGNEOUS 16.2 Cenozoic volcanism 140 ACTIVITY IN WEST AFRICA 16.2.1 Hoggar and southern Air 140 16.2.2 The Gulf of Guinea 13 Introduction to anorogenic magmatism 123 province 141 13.1 The distribution of anorogenic 16.2.3 Cenozoic volcanism west magmatism 123 of the craton 143 Bibliography 125 16.3 Controls of Cenozoic magmatism 143 16.4 Diamond fields in West Africa 144 14 The Permo-Triassic dolerites and 16.5 Economic; potential of Cenozoic carbonatites 126 volcanics 145 Bibliography 146 14.1 The dolerites 126 14.1.1 Petrology and age 126 14.1.2 The Freetown complex 127 Part IV THE QUATERNARY OF WEST AFRICA 14.1.3 The tectonic setting 127 14.2 The undersaturated complexes 127 17 Introduction: earthquakes, volcanoes 14.3 Economic potential of the and meteorites 151 Permo-Triassic intrusions 128 Bibliography 128 17.1 Introduction 151 17.2 Earthquakes and volcanism 151 IS The Younger Granites 129 17.3 Lake Bosumtwi 152 17.3.1 The evidence for an 15.1 Introduction 129 impact origin 152 15.2 Evolution of the complexes 130 17.3.2 Ivory Coast tektites 152 15.2.1 Eruption of early rhyolites 130 17.3.3 Lake sediments 152 15.2.2 Eruption of later rhyolites 130 Bibliography 153 15.2.3 Marginal ring dykes 131 15.2.4 Internal ring intrusions 132 18 Geomorphology, Quaternary deposits 15.2.5 External dykes 133 and water resources 154 15.3 Regional distribution and setting 133 15.4 Petrogenesis 134 18.1 Geomorphology 154 15.4.1 Younger Granites and 18.1.1 Drainage 155 mantle plumes 135 18.1.2 Erosion surfaces 155 15.5 Economic potential of the 18.2 Laterites 156 Younger Granites 135 18.3 Other deposits 158 Bibliography 136 18.4 Some economic aspects 158 18.4.1 Water resources 159 16 Cretaceous and Cenozoic magmatism 138 Bibliography 161 16.1 Igneous activity in the Cretaceous 138 Glossary 163 16.1.1 Kimberlites and related rocks 138 Index of place names 173 16.1.2 Cretaceous magmatism Subject index 175 ofthe Benue Trough 139 Xl List of tables 2.1 Principal rock sequences and events 10.1 Correlation of Mesozoic-Tertiary strata in the Precambrian crustal evolution of in the Iullmedden Basin 92 West Mrica page 23 11.1 Correlation of Cretaceous-Palaeocene 3.1 Correlation for the Archaean of strata in the Benue Trough 100 West Africa 30 11.2 Palaeocene and younger sediments 9.1 Generalised sequence and correlation mapped at the surface in the Niger Delta within and between Taoudeni and Basin 107 Volta Basins 81 Contributors D. A. HASTINGS Adjunct Principal Geophysicist, Ghana Geological Survey now at EROS Data Center, Sioux Falls, South Dakota, USA. W. B.JONES Phillips Petroleum Company Europe-Africa, The Adelphi, John Adams Street, London H. R. WILLIAMS Department of Geological Sciences, Brock Univer sity, St. Catharines, Ontario, Canada. xu

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In this text, attention is focused mainly on those literature is accessible, however, it is to be expected countries in western Africa lying south of the Sahara, that teachers and lecturers will know of it and will be that is, between about SON and 15°N, and westward able to acquaint their students
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