Bauchi is part of sheet 149NE which falls within the Northern Basement Complex of Nigeria. In this study, the area was mapped on a scale of 1:25,000. Samples were collected at the flanks of the outcrops, railway cuts, road cuts as well as blasting sites within the area. At each sampling point, two or more samples were collected based on morphological variations. The first and second order morphological classifications of migmatites as being metatexite or diatexite; banded orthogneiss, stromatic, schlieren or nebulite were used as the guiding principle. This technique was repeated for the rest of the sampling points in the area covering about fifteen (15) different locations. A total of 10 representative samples were studied geochemically. Together with the field relationship and morphological features, it was observed that the area has five (5) different lithologic units as metasediment (quartzite), melanocratic diatexite (schlieren), nebulites (Bauchite, quartz-diorite and granulitic granite) in a sequence of prograde metamorphism. The SiO2 content for the samples is between 64.2 and 77.8 wt %. Save for CaO, K2O and Sr, all the major oxides and minor elements show negative correlation with the silica. Zr and Hf show no clear correlation with the SiO2. Negative Nb, Ta, Ce and Y anomalies are characteristics of volcanic and plutonic rocks formed above subduction zones. It further signifies the contribution of mantle materials to the melt. All the samples are ferroan, which probably reflects derivation from reduced basaltic rock either by fractional crystallization or partial melting; and peraluminous which implies high development of K-Feldspar that is necessary for the formation of the nebulites. The rise in alumina and a corresponding decline in silica indicate fractionation which is yet against normal granitization process (magmatism).
Key words: Quartzite, Shlieren, Nebulite, Prograde Metamorphism, Ferroan, Peraluminous
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