Geology and Mineral Resources of West Africa

193 Pages·1986·7.5 MB·English

by  J. B. Wright (auth.)

GEOLOGY AND MINERAL
RESOURCES OF WEST AFRICA
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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