Mineralogical Studies of the Underlying Rocks around Jiko Abandoned Mine Site, North-Central Nigeria

Abstract

The mineralogical characterisation of crystalline basement rocks is fundamental to constraining protolith affinity and geological and geochemical processes in mining-impacted terrains. This study presents the first integrated X-ray diffraction (XRD) and transmitted-light petrographic investigation of basement rocks underlying the Jiko abandoned mine site, North-Central Nigeria, within the Kusheriki schist belt of the Nigerian Basement Complex. The aim is to establish a mineralogical framework for interpreting rock evolution and its implications for geochemical behaviour. Six representative rock samples, ranging from fresh to moderately altered, were systematically collected and analysed using powder XRD (Cu-Kα radiation; 5–75° 2θ) for phase identification and optical petrography for textural and paragenetic relationships. XRD results indicate a dominant primary mineral assemblage of quartz, phlogopite, and albite, with accessory ilmenite occurring in Ti–Fe-enriched samples and secondary goethite and haematite preferentially developed in altered rocks. Petrographic analysis reveals two principal domains: (i) a schistose domain characterised by aligned mica laths, quartz ribbons, undulose extinction, and incipient feldspar sericitisation; and (ii) a gneissic to altered domain defined by compositional banding, granoblastic textures, fractured and oxidised micas, feldspar turbidity, and pervasive Fe-oxide precipitation along fractures and grain boundaries. These mineralogical and textural relationships indicate that the Jiko basement rocks represent low- to medium-grade metamorphic lithologies, consistent with phlogopite-quartz-albite schists and associated gneisses derived from predominantly pelitic to semi-pelitic protoliths, with local Fe-Ti enrichment. A progressive weathering sequence is established, transitioning from primary quartz-phlogopite ± albite ± ilmenite assemblages through early-stage mica degradation and feldspar alteration to advanced formation of goethite and haematite along structurally controlled fluid pathways. This evolution highlights the critical role of deformation fabric and fracture networks in facilitating fluid ingress and mineral transformation. The study demonstrates that basement mineralogy, coupled with microstructural controls, governs secondary mineral development and provides a robust framework for interpreting trace-element mobilisation and environmental risk in mining-affected basement terrains. It is recommended that future work integrates mineralogical data with in-situ microanalysis (e.g., SEM-EDS, EPMA) and isotopic tracing to better resolve mineral-geochemical linkages and element provenance. These findings are transferable to comparable Pan-African basement settings and contribute to a process-based understanding of mineralogical evolution in tropical weathering environments.