Field Geological description of Pegmatites Occurrence inIdah Sheet 267, Nigeria

Abstract

Field Geological description of Pegmatites Occurrence in Idah Sheet 267, Nigeria was carried out. The pegmatites in the Sheet occurs and are distributed around two main locations in the Sheet, that is around Ogodo (Ajaokuta) and Itobe areas respectively. The pegmatites in the Ogodo (Ajaokuta) occur as swarms of discrete dykes and ridges to form large N-S trending bodies whereas, those around the Itobe area occur mainly as dykes and trends in similar manner with the Ogodo (Ajaokuta) pegmatites. The main strike directions of the pegmatite dykes is N-S (80-89). The pegmatites intrudes into the basement granites and schist in both the Ogodo (Ajaokuta) and the Itobe areas respectively. The Mineralogy of pegmatites around the Ogodo (Ajaokuta) area consist of simple to complex mineralogy. The simple pegmatites (barren) comprise of Quartz, Feldspar (largely pinky K feldspar) and Mica (Muscovite) .The complex mineralogy besides Quartz, Feldspar and Mica also contain well developed crystals of Tourmaline and disseminated Tourmaline. Whereas, the pegmatites in the Itobe area is complex and more diverse in terms of assemblages of gemstones than the pegmatites in Ogodo (Ajaokuta) area. The pegmatites around the Itobe area consist of three distinct mineralogical zones viz: (1) Qaurtz, Feldspar (plagioclase), Mica (Muscovite) and Beryl zone, (2) Quartz, Feldspar (plagioclase), Mica (Muscovite), Beryl and Tourmaline zone and (3) Quartz, Feldspar (plagioclase), Mica (Muscovite), Beryl and suspected Lepidolite /tin bearing zone. The style of zonation of mineralogical assemblages across the Ogodo (Ajaokuta) and Itobe pegmatites field from simple to complex type pegmatites may suggest that the pegmatites evolve by fractional crystallizations of the residual melt generally of granitic composition.Field geologic descriptionsprovide a preliminary insight into the evolution, class and mineralization potential of the pegmatites in the study area.