MINERALOGICAL- GEOCHEMICAL STUDY OF LANDI KOTAL SLATE, PAKISTAN

Abstract

The Landi Kotal formation of the Khyber region, northern Pakistan, hosts fine-grained argillaceous/pelitic rocks that have undergone low-grade regional metamorphism to slate. In this study, a representative slate sample from the Landi Kotal formation was characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF) spectrometry, and Fourier-transform infrared (FTIR) spectroscopy to establish its mineralogical composition, bulk geochemistry, and molecular-level structural signatures. XRD analysis reveals a mineral assemblage dominated by quartz, with subordinate illite/muscovite (mica group, ~10 Å basal spacing) and chlorite (~7.1 Å basal spacing), accompanied by minor feldspar. Bulk-oxide XRF data show the sample is dominated by SiO2 (67.0 wt.%) and Al2O3 (22.2 wt.%), with Fe2O3 (5.7 wt.%), K2O (3.8 wt.%), TiO2 (0.77 wt.%), CaO (0.28 wt.%) and MnO (0.09 wt.%) as minor to trace constituents, together with trace V, Zn, Zr, Cu, Cr, Rb, Sr and Y. The low CaO and negligible detectable Na2O, combined with a Chemical Index of Alteration (CIA) of ~83, indicate an intensely weathered, illite-rich clastic precursor. FTIR spectra corroborate the XRD mineralogy, displaying the diagnostic quartz doublet near 779 and 797 cm⁻¹, strong Si–O stretching between 1163 and 999 cm⁻¹, Al–O–Si bending near 521 cm⁻¹, and an intense Si–O–Si bending mode at 462 cm⁻¹, with only a negligible O–H stretching feature near 3620 cm⁻¹. The convergence of the three techniques confirms a quartz–illite/muscovite–chlorite mineral paragenesis typical of low-grade (sub-greenschist to lower greenschist facies) pelitic slates, consistent with the regional tectono-metamorphic history of the Khyber region. These results provide baseline mineralogical–geochemical data for the Landi Kotal Formation with implications for provenance interpretation, metamorphic grade assessment, and potential industrial (dimension stone / aggregate) applications.