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Nigerian rare‐metal pegmatites and their lithological framework
Author(s) -
Matheis G.
Publication year - 1987
Publication title -
geological journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.721
H-Index - 54
eISSN - 1099-1034
pISSN - 0072-1050
DOI - 10.1002/gj.3350220620
Subject(s) - pegmatite , geology , geochemistry , proterozoic , cassiterite , orogeny , mineralization (soil science) , columbite , tin , tectonics , paleontology , chemistry , organic chemistry , phase (matter) , soil water , soil science
Most of Africa's rare‐metal potential is linked to Proterozoic pegmatite fields except for the Jurassic tin‐bearing ring complees of the Jos Plateau Nigeria. In order to establish the position of the Nigerian tin province in terms of economic rare‐metal mineralization, occurrences of mineralized pegmatitic phases of the Nigerian basement complex, including the so‐called ‘Older Tin‐Fields’, have been investigated. Rb/Sr geochronology confirms the end Pan‐African ages for the pegmatites in the range 580‐530 Ma. Although emplaced within the same time span, the mineralogy, geochemistry, and mineralization of these pegmatites differ according to the lithology of their host‐rock. Pegmatite occurrences from southwest Nigeria, which are emplaced into Proterozoic meta‐sedimentary‐metavolcanic sequences, are enriched in tantalum relative to niobium. These geochemical characteristics are also displayed by the composition of eluvial heavy‐mineral concentrates as well as by the trace‐element distribution in cassiterites. Although Pan‐African granites with an age range of 700‐520 Ma are dispersed throughout Nigeria, associated rare‐metal mineralized pegmatites are known almost exclusively along a southwest‐northeast striking belt about 400 km long, which intersects the Jos Plateau tin‐fields. A direct genetic link between the rare‐metal bearing pegmatites and proximal granite occurrences was never observed. It is suggested that reactivation of old tectonic lineaments during the Pan‐African orogeny provided excess heat and fluid to concentrate rare‐metal pegmatites by partial melting with selective leaching from the country rocks, i.e. their lithological framework.