Geochemistry and Petrogenesis of Gneisses Around Kafur-Yari Bori-Tsiga area within the Malumfashi Schist Belt, Northwestern Nigeria.

Abstract

The gneisses around Kafur-Yari Bori-Tsiga area consist of varieties such as banded gneiss, augen gneiss and granite gneiss. This area is underlain by both igneous and metamorphic rocks; the schist and migmatite-gneiss are intruded by the Pan-African granitoids. Minerals such as microcline, plagioclase, quartz, hornblende, biotite, orthoclase forms the major components in the gneisses while garnet, zircon and sphene are the accessories minerals. Foliation in the gneisses is defined by parallel alignment of mafic and felsic minerals (bands) having a major strike range of NE-SW to N-S and lesser of E-W directions. The geochemical study revealed major oxides such as SiO₂ in the range of 63.85-73.84 wt%, Al₂O₃ has content between 12.77-16.05 wt%, Fe₂O₃ is between 1.18-6.70 wt%, Na₂O is between 1.93-4.78 wt% and K₂O between 1.49-6.96 wt %. The concentrations of high field strength elements ( Hf, Th, U, Nb and Ta) is rather lower in the gneisses investigated and thus responsible for the small propotion of minerals like the zircon, sphene and apatite which all occurred as accessories minerals. The absence of minerals like sillimanite, kyanite, cordierite and staurolite which are typical of paragneiss confirmed an igneous protolith of the gneisses investigated.

Although, geochemical variations suggest igneous precursors for the gneisses of this area, it is obvious that they were not cogenetic but derived from differing sources and depths.

Keywords: “Basement Complex”, cogenetic, Malumfashi, “Older Granite”