Geochemistry and Petrogenetic Relationships Between Pegmatites and Host Rocks in the Keffi Area, North Central, Nigeria

Abstract

Keffi pegmatites area which contains numerous mineralised and non-mineralised pegmatites lie between the Wamba pegmatite field to the NE and Nasarawa pegmatite field to the SW on the North Central Pegmatite belt of Nigeria. In Keffi area exploitation of deposits is currently being done by small scale miners, whose activities are haphazard and uncoordinated, because of that information on the geology and petrology that will enable a systematic study of the pegmatites in the area is scanty. Systematic geochemical investigations of the pegmatites and surrounding host rocks aimed at establishing petrogenetic relationships amongst the various rock types in the area were conducted. Major, trace and REE investigations of the pegmatites and associated granitoids have indicated petrogenetic relationships amongst the pegmatites and between the pegmatites and surrounding granitoids of Keffi area. Also, the variation diagram of major, trace and REE in whole rocks and K-feldspar samples show patterns which categorised the pegmatites of Keffi area into; (1) Non-mineralised, (2) intermediate and (3) mineralised pegmatites. It was also deduced from the geochemical characteristics (variation diagrams in major and trace element, REE geochemistry and tectonic environment classification) that a genetic model based on the evolution of melt by partial melting of metasedimentary protolith during ultrametamorphic and deformational activities (anatexis) is proposed for the granite-pegmatite system of Keffi area. This information will be useful as guide for fruitful exploration of the pegmatites and serves as model for the exploitation of pegmatite veins in similar geologic settings.