Geological, Petrographic, and Geochemical Characterization of the Basement Complex Rocks in Madidi and Its Environs, Gusau Northwestern Nigeria

This study presents the geological, petrographic, and geochemical characterization of Madidi village and its environs, located in Bungudu Local Government Area, Zamfara State, Northwestern Nigeria. The area, covering approximately 30.4 km², forms part of the Precambrian North-Western Nigerian Basement Complex, specifically within the migmatite-gneiss-quartzite complex. Geological mapping at a scale of 1:25,000, supported by field observations, structural measurements, and sample collection, revealed that gneissic rocks dominate the lithology, with subordinate mica schist and minor quartz vein intrusions. The rocks exhibit NE-SW trending foliation and have undergone significant deformation, weathering, and metamorphism. Petrographic analysis under a polarizing microscope showed that gneiss samples are medium- to coarse-grained, phaneritic, and composed predominantly of quartz (~40%), biotite (~35%), plagioclase (~20%), with minor orthoclase, muscovite, and opaque minerals. Foliation and lineation are well-defined. Mica schist displays strong foliation, with muscovite as the dominant mineral (~65%), accompanied by quartz (~25%) and accessory chlorite and opaque phases. Geochemical data indicate high SiO₂ contents (74.42–78.12 wt%) in both rock types, confirming their felsic to intermediate character. Gneiss samples show low Fe₂O₃ and MgO, high K₂O relative to Na₂O, and calc-alkaline affinity, suggesting derivation from a K-feldspar-rich felsic protolith. Mica schist exhibits elevated Al₂O₃, reflecting aluminous clay-rich protolith, and evidence of K-metasomatism during metamorphism. Trace element concentrations, particularly high Ba and Rb, support a supracrustal, pelitic metasedimentary origin with detrital zircon influence. Tectonic discrimination diagrams indicate a calc-alkaline, likely continental arc or syn-collisional setting. The study provides new detailed lithological, structural, and geochemical data that fill gaps in existing regional geological maps and contribute to better understanding of the basement complex evolution in Northwestern Nigeria