Geology and Mineral Resources of West Africa, 1985

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 it may help the work of international organizations who already have an understanding of basic geologi­ cal principles. It is increasingly important that such as AGID, CIFEG and UNESCO to encourage the growing trend towards geological co-operation geologists working in this region should see it as made up of geological 'provinces' which transcend and correlation between different countries in West national boundaries. Africa.

1 The geological settingl.- 1.1 The African continent.- 1.2 The major subdivisions of geological time.- 1.3 The structural framework of Africa.- 1.4 The global context.- 1.5 Age provinces and mineral deposits.- 1.6 The geological framework of West Africa.- 1.7 Problems of regional treatment and correlation.- I The Precambrian of West Africa.- 2 Crustal development in West Africa.- 2.1 The concept of crustal reactivation.- 2.2 Orogeny and thermotectonic events.- 2.3 Regional patterns in the Precambrian of West Africa.- 2.3.1 Basement rocks.- 2.3.2 Supracrustal rocks.- 2.3.3 Granitic intrusions.- 2.4 Patterns of crustal reactivation.- 2.4.1 Older supracrustal relics.- 2.5 Summary of Precambrian events in West Africa.- 3 The Archaean of West Africa.- 3.1 Introduction.- 3.2 The basement complex.- 3.3 The supracrustal belts.- 3.3.1 The Marampa and Kasila belts.- 3.4 Granites.- 3.5 Fractures, faults and mylonites.- 3.6 Correlation and geochronology.- 3.7 Plate tectonics and the Liberian event.- 3.8 Repeating patterns of crustal reactivation - a reminder.- 3.9 Economic potential in the Archaean rocks of West Africa.- 3.9.1 Gold.- 3.9.2 Iron ores.- 3.9.3 Bauxite.- 3.9.4 Rutile.- 3.9.5 Other minerals.- 4 The Proterozoic of West Africa.- 4.1 Introduction.- 4.2 Basement.- 4.3 Supracrustals : the Birimian and Tarkwaian.- 4.3.1 The Birimian in Ghana.- 4.3.2 The Tarkwaian in Ghana.- 4.3.3 The Birimian and Tarkwaian in Ivory Coast and Upper Volta.- 4.3.4 A possible compromise.- 4.4 Granitic rocks.- 4.5 Correlation and geochronology.- 4.6 Plate tectonics and the Eburnian event.- 4.7 Economic potential in the Lower Proterozoic rocks of West Africa.- 4.7.1 Gold.- 4.7.2 Manganese.- 4.7.3 Diamonds.- 4.7.4 Bauxite.- 4.7.5 Iron ores.- 4.7.6 Other minerals.- 5 The Pan African of West Africa — the western domain.- 5.1 Introduction.- 5.2 The Rokelide-Mauritanide belt.- 5.2.1 Geochronology in the Rokelide-Mauritanide belt.- 5.2.2 Plate tectonics and the Rokelide-Mauritanide belt.- 5.3 Economie potential of the western Pan African domain.- 6 The Pan African of West Africa — the eastern domain.- 6.1 Introduction.- 6.2 The Togo belt.- 6.3 The eastern domain.- 6.3.1 The basement complex.- 6.3.2 The supracrustals.- 6.3.3 Granites.- 6.3.4 Fractures, faults and mylonites.- 6.3.5 Correlation and geochronology.- 6.3.6 Correlation with the Hoggar.- 6.4 Pan African plate tectonics east of the craton.- 6.5 Economic potential of the eastern Pan African domain.- 7 The Precambrian of West Africa — synthesis and review.- 7.1 The geological picture.- 7.2 The tectonic patterns.- 7.3 The mineral deposits.- II Sedimentary Basins in West Africa.- 8 Introduction to sedimentary basins.- 8.1 Distribution of the basins.- 8.2 Older basins.- 8.3 Younger basins.- 8.4 Crustal lineaments and basin development.- 9 Infracambrian to Lower Palaeozoic basins.- 9.1 Introduction.- 9.2 The Volta Basin.- 9.2.1 Geochronology of the Volta Basin.- 9.3 The Taoudeni Basin.- 9.3.1 Geochronology and development of the Taoudeni Basin.- 9.3.2 The Bové Basin.- 9.3.3 The Iullmedden Basin.- 9.4 The glaciation events.- 9.5 Palaeozoic sediments in coastal basins.- 9.6 Economic potential of the older basins.- 10 Mesozoic to Tertiary basins — inland basins.- 10.1 Interregnum: Upper Palaeozoic to Mesozoic.- 10.2 The Iullmedden Basin.- 10.2.1 The Sokoto sector.- 10.2.2 The Continental Terminal.- 10.3 The Chad Basin.- 10.3.1 Cretaceous of the Chad Basin.- 10.3.2 Quaternary of the Chad Basin-.- 10.3.3 Basin subsidence.- 11 The Benue Trough and coastal basins.- 11.1 The Benue Trough.- 11.1.1 Albian-Cenomanian.- 11.1.2 Turonian-Maas trichtian.- 11.1.3 The Bida Basin.- 11.1.4 Folding in the Benue Trough.- 11.1.5 Trans-Saharan seaways.- 11.2 The Niger Delta Basin.- 11.3 Other coastal basins.- 11.3.1 The Senegal Basin.- 12 Economic potential of the younger sedimentary basins.- 12.1 Energy resources.- 12.1.1 Petroleum.- 12.1.2 Coal.- 12.1.3 Uranium.- 12.2 Metals and non-metals.- 12.2.1 Phosphate.- 12.2.2 Other minerals.- III Mesozoic to Cenozoic Igneous Activity in West Africa.- 13 Introduction to anorogenic magmatism.- 13.1 The distribution of anorogenic magmatism.- 14 The Permo-Triassic dolentes and carbonatites.- 14.1 Thedolerites.- 14.1.1 Petrology and age.- 14.1.2 The Freetown complex.- 14.1.3 The tectonic setting.- 14.2 The undersaturated complexes.- 14.3 Economic potential of the Permo-Triassic intrusions.- 15 The Younger Granites.- 15.1 Introduction.- 15.2 Evolution of the complexes.- 15.2.1 Eruption of early rhyolites.- 15.2.2 Eruption of later rhyolites.- 15.2.3 Marginal ring dykes.- 15.2.4 Internal ring intrusions.- 15.2.5 External dykes.- 15.3 Regional distribution and setting.- 15.4 Petrogenesis.- 15.4.1 Younger Granites and mantle plumes.- 15.5 Economic potential of the Younger Granites.- 16 Cretaceous and Cenozoic magmatism.- 16.1 Igneous activity in the Cretaceous.- 16.1.1 Kimberlites and related rocks.- 16.1.2 Cretaceous magmatism of the Benue Trough.- 16.2 Cenozoic volcanism.- 16.2.1 Hoggar and southern Aïr.- 16.2.2 The Gulf of Guinea province.- 16.2.3 Cenozoic volcanism west ofthecraton.- 16.3 Controls of Cenozoic magmatism.- 16.4 Diamond fields in West Africa.- 16.5 Economic potential of Cenozoic volcanics.- IV The Quaternary of West Africa.- 17 Introduction: earthquakes, volcanoes and meteorites.- 17.1 Introduction.- 17.2 Earthquakes and volcanism.- 17.3 Lake Bosumtwi.- 17.3.1 The evidence for an impact origin.- 17.3.2 Ivory Coast tektites.- 17.3.3 Lake sediments.- 18 Geomorphology, Quaternary deposits and water resources.- 18.1 Geomorphology.- 18.1.1 Drainage.- 18.1.2 Erosion surfaces.- 18.2 Laterites.- 18.3 Other deposits.- 18.4 Some economic aspects.- 18.4.1 Water resources.- Index of place names.