Petrographic Analysis of Medium-Grained Granite of Madagali Area, Northeastern Nigeria

Abstract

The Madagali area of northeastern Nigeria lies within the Precambrian Basement Complex and is characterized by diverse lithological assemblages comprising granites, migmatite–gneiss complexes, and schists that have undergone multiple tectonothermal events. This study focuses on the petrographic characterization of the medium-grained granite to determine its mineralogical composition, texture, and formation history. A total of six representative samples were collected and processed into twelve thin sections, which were examined under plane-polarized light (PPL) and cross-polarized light (XPL) using a polarizing microscope. The results revealed that the medium-grained granite consists predominantly of quartz, orthoclase, plagioclase feldspar, microcline, and biotite as essential minerals, with minor muscovite, and iron oxide as accessory constituents. The quartz grains exhibit undulose extinction and irregular boundaries, while feldspars display Carlsbad and tartan twinning, indicating slow cooling and magmatic crystallization within a plutonic environment. Myrmekitic intergrowths observed between quartz and feldspar suggest late-stage magmatic differentiation. Comparisons with previous studies in the Gulani and Kaltungo areas highlight mineralogical similarities, especially in the dominance of quartz and feldspar, though variations such as the absence of hornblende and sphene in the Madagali granite reflect local geochemical differences. The textural and mineralogical attributes indicate that the Madagali medium-grained granite is of igneous origin, likely emplaced during the Pan-African orogenic episode. The study contributes valuable petrographic data toward understanding the geological evolution of the Mandara Hills region and provides a foundation for future geochemical and geotechnical investigations.

Introduction

The Madagali area, part of the Precambrian Basement Complex, consists of diverse metamorphic and igneous rocks, including medium- to coarse-grained granites, migmatite-gneisses, schists, and quartzites. These rocks have undergone multiple metamorphic and deformational events. The granitoids are mainly calc-alkaline, ranging from granodiorite to monzogranite, while migmatites indicate partial melting. Schists and gneisses reflect medium- to high-grade metamorphism linked to regional tectonothermal activity.

Structurally, the region experienced significant deformation during the Pan-African orogeny, producing folding, faulting, and shearing, with dominant N-S to NE-SW trends and subsidiary NW-SE shear zones. Both brittle and ductile deformations are evident.

Economically, the area has potential mineral resources, including gold, tin, columbite, rare-earth elements, and pegmatite-hosted minerals. The Mandara Hills, featuring rugged highlands and low-lying granitoid outcrops, dominate the landscape and influence geological mapping.

Regional Geology

• Basement Complex: Composed of migmatites, gneisses, marbles, quartzites, and Older Granites (granite, granodiorite, diorite, syenite). These rocks show evidence of metamorphism, deformation, and metasomatism, with economic mineralization.

• Migmatite-Gneiss Complex: The oldest Precambrian rocks, formed during the Pan-African Orogeny (~600 Ma), include high-grade metamorphic rocks intruded by Pan-African granites and pegmatites, hosting economically significant minerals.

• Older Granite Suites: Pan-African granitoids emplaced along shear zones, exhibiting calc-alkaline geochemistry, hosting metallic and rare-earth mineralization, and reflecting crustal anatexis with mantle contributions.

• Mandara Hills: Comprised of migmatite-gneisses, quartzites, schists, amphibolites, and granites, structurally similar to other parts of the Nigerian Basement Complex.

Structural Trends
Multiple deformation phases created prominent structural orientations: N-S, NE-SW, and NW-SE, with older E-W fractures also present. These structures are linked to the Pan-African orogeny and regional shear zones, including connections to the Benue Trough and Chad Basin rift system.

Mineralization
The region hosts diverse economic minerals: metallic (gold, tin, columbite, uranium), non-metallic (gypsum, magnesite, limestone), and gemstones. Mineralization is structurally controlled, often concentrated along shear zones and pegmatites.

Methodology
The study employed geological mapping, systematic sample collection, thin-section preparation, and petrographic analysis to examine the mineralogical composition and textures of medium- to coarse-grained granites in the Madagali area.

Conclusion

The petrographic study of the medium-grained granite from Madagali in northeastern Nigeria revealed that the area is largely underlain by granitic and gneissic rocks of Pan-African origin. Microscopic examination of twelve thin sections prepared from six samples showed that quartz, orthoclase, plagioclase, microcline, and biotite are the essential minerals, while muscovite, iron oxide, and myrmekitic intergrowths occur as accessory minerals. The mineral composition and textures, such as undulose extinction in quartz, perthitic and tartan twinning in feldspars, and a hypidiomorphic granular structure, suggest slow crystallization within a deep-seated plutonic environment. When compared with other granites in the region, the Madagali samples display similar mineralogical features, confirming their igneous origin and emplacement during the Pan-African tectonothermal episode. Overall, this study provides valuable insight into the petrogenesis and structural development of the Madagali Basement Complex.

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Copyright © 2025 Abdullahi Banjaba Lawan, Saidu Baba, Hamman Ishaku Kamale, Najib Murtala Abulfathi, Abdulsalam Muhammad, Adam Ahmad Lawan, Asmau Usman Hardo. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.