Characterisation and rare-metal potential of the Winneba-Mankoadze pegmatites, Southern Ghana: Evidence of two pegmatite fields
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Date
2023
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of African Earth Sciences
Abstract
In southern Ghana, the region along the coast between Accra and Cape Coast hosts a large number of pegmatites
mineralized in lithium, niobium-tantalum and tin. The pegmatites occur in many distinct groups, each extending
over several kilometers. They intrude metasedimentary units of the Birimian Supergroup, and are associated with
early to late orogenic granite intrusions which are metaluminous, sterile, and too old to be potential parental
granites for the pegmatites. In this study, we characterized the Winneba-Mankoadze group of geographically
coeval pegmatites, using field description, petrography, rare-metal mineralogy and accessory mineral
geochemistry on micas, garnet and Nb–Ta–Sn minerals, in order to determine its rare-metal potential and to
investigate its origin. The results indicate that the pegmatites are part of the albite-spodumene type of the
Lithium–Cesium–Tantalum (LCT) family. The rare metal mineral assemblages are particularly complex and
display relevant oxide species such as columbite- and wodginite-group minerals, tapiolite, microlite, cassiterite
and rutile, which are evidences of an extremely evolved magmatic system. Based on mineral assemblages, whole rock geochemistry, and mineral geochemistry on garnet, micas and the CGM, two pegmatite fields are distin guished in the Winneba-Mankoadze group, and an anatectic origin is proposed. For the first time in West Africa,
we fully describe a highly fractionated LCT-family pegmatite field comparable to the most evolved pegmatite
bodies in the world.
Description
Research Article
Keywords
Rare-element pegmatites, Spodumene, Columbite-group minerals, Extreme fractionation