Bauxites and associated terrestrial sediments in Nigeria and their position in the Bauxite belts of Africa

Abstract

The African surface, Lower Tertiary in age, its special ferralitic weathering mantle and reworking products (LDF) are discussed. Dominant facts are: 1. 1. Not only bauxitisation but also supergene ore formation of manganese, iron, nickel, gold, gossan mineralisation and supergene phosphatisation characterize that Lower Tertiary ⪡surface⪢. 2. 2. From the paleocoast to the inland, high-grade bauxites change laterally into low-grade ferralites or ferricretes. 3. 3. The African planation surface on high plateaus in Nigeria represent the beginning of a morphogenetic sequence. It is expressed by an interaction of in-situ weathering, induration to ferricretes, alucretes, silcretes and their reworking and resedimentation as laterite-derived facies (LDF) on a topographically and morphologically low relief in a short time span during Paleogene. One to several sequences of ⪡composed profiles⪢ or only one ⪡ in-situ paleosol covered by LDF⪢ act as forming factors of that ⪡first-order⪢ paleosurface. 4. 4. Contemporaneous or later block tectonics led to a displacement and tilting of surfaces and activation of erosion, progressively creating a relictic inselberg landscape. 5. 5. Refilling of older erosion channels and depressions by younger volcanic flows and sediments gives the image of a uniform land surface which - in reality - is composed of surfaces and connected weathering profiles of different age forming a ⪡Schachtelrelief⪢. 6. 6. Younger polyphase soil alteration results in polygenetic soils. 7. 7. New supergene geochemical provinces develop in the ferralitic weathering crust with increasing tendence to mono-element concentration.