Provenance and selective quarrying of New Kingdom Nubian sandstones on Sai Island, Sudan: Insights from ilmenite alterations and matrix compositions

• All Nubian sandstones from Sai Island show highly similar petrography. • Ilmenite alteration series and similar matrix compositions are present in all samples. • Fe-Ti-oxide assemblages indicate a common late-stage magmatic provenance. • Temple sandstones are finer-grained, lighter, and more homogeneous than quarry samples. • Sandstones were likely intentionally selected for Temple A. This study examines the mineralogical composition and alteration products of ilmenite and the matrix in Nubian sandstones from Temple A and ancient quarries on Sai Island (northern Sudan) for insights into their provenance. We characterized the grains and their diagenetic alteration products via polarized light microscopy, scanning electron microscopy (SEM), and Raman spectroscopy. All samples, deriving from Late Bronze Age contexts (c. 15th–14th cent. BCE), are dominated by quartz (>90 %), minor feldspar (<10 %), and rare lithoclasts (<5%). Depending on the amount of matrix (5–50 %), the sandstones are classified as quartz arenites or quartz wackes. Generally, temple sandstones are moderately sorted, smaller-grained (250 μm to 310 μm), and lighter colored, compared to quarry samples, which are (very) poorly sorted, larger-grained (190 μm to 750 μm), and darker. All sandstone samples bear ilmenite alteration products (pseudorutile, rutile, anatase, hematite, Fe-hydroxides) and have matrices composed of kaolinite and illite, indicating similar weathering, diagenetic, and burial histories. The grains derive from a pluton and the Fe-Ti-oxide assemblage before alteration was consistently ilmenite with minor rutile and hematite, which suggests a late-stage magmatic source with comparable temperature and oxygen fugacity conditions for all samples. The results indicate that all investigated samples likely originate from the same or closely related stratigraphic units. The mineralogical homogeneity precludes precise attribution of temple blocks to specific quarries, however, the difference between moderately sorted temple and (very) poorly sorted quarry sandstones could be explained by selective quarrying by ancient builders to ensure aesthetic and material consistency in construction.