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This contribution deals with new geology, petrography, and bulk-rock/mineral chemistry of the poorly studied ultramafics of Wadi Ibib–Wadi Shani (WI–WS) district, South Eastern Desert, Egypt. These ultramafics are dismembered ophiolitic rocks that can be subdivided into serpentinites and serpentinized peridotites. Primary minerals such as olivine and pyroxene are absent in serpentinites, but relics of them occur in serpentinized peridotites. Pseudomorph after olivine is indicated by common hourglass textures with less mesh, whilst schistose bastites reflect a pyroxene pseudomorph. Chromite can be subdivided into Cr-spinel and Al-spinel. Cr-spinel ranges from chromite to magnesochromite in composition, whereas Al-spinel belongs to the spinel field. Cr-spinel includes YCr (Cr/(Cr+Al+Fe+3), YAl (Al/(Al+Cr+Fe+3), and YFe+3 (Fe+3/(Fe+3+Al+Cr), similar to forearc peridotite, whilst Al-spinel is more similar to abyssal peridotite, and may be formed during inanition of subduction processes in proto forearc environments. The main secondary minerals are tremolite, talc, and chlorite—which is subdivided into pycnochlorite and diabantite—and their temperature ranges from 174 to 224 °C. The examined rocks had undergone high partial melting degrees (>25%), as indicated by the Cr# of their unaltered cores (Cr-spinel, >0.6), whole rocks (Al2O3, SiO2, CaO, and MgO), trace and REEs, depleted Na2O, Al2O3, and Cr2O3 of clinopyroxene, and high forsterite content ((Fo = 100 Mg/Mg + Fe), av. 95.23 mol%), consistent with forearc settings.

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Lithologically, the rock types of G. El Fereyid-W. Rahaba area are dominantly granites associated with pegmatites. The granitic rocks comprise tonalite and monzogranite with (minor acidic dykes), quartz and pegmatites occur as a vein type (granitic and perthitic pegmatites) hosted within the monzogranite. Structural analysis shows the presence of a prominent set of folds with axes striking WNW to NW and a less prominent set with pronounced ENE and NNW trends. Petrochemical studies and tectonic discrimination diagrams for the monzogranite reveal that it is classified as post orogenic granites (POG). Geochemically, monzogranite shows enrichment (peaks) of large ion lithophile elements (LILE; Pb, Rb, Ba, Sr) and high field strength elements (HFSE; Y, Zr, Nd,) and depletion (troughs) of K, P and Ti. Pegmatite shows enrichment (peaks) of large ion lithophile elements (LILE; Pb, Rb, Sr) and high field strength elements (HFSE; Y, Zr, Th, U, Nb) and depletion (troughs) of K, P and Ti. They exhibit high K-calc alkaline magma and peraluminous characteristics and considered as post orogenic granites (POG). The monzogranite reveal small to moderate negative Eu anomaly, while the pegmatites reveal moderate to large negative Eu anomaly. The pegmatite displays clear W-type tetrad effect of the REE while, the studied monzogranite do not show tetrad effect.

A net of pegmatite veins crosscut gneiss and dismembered ophiolitic ultramafic rocks are abundant in the Migif-Hafafit culmination area, South Eastern Desert, Egypt. Some of these pegmatites are corundum-bearing. Corundum-bearing pegmatites are studied in eight localities around the Migif-Hafafit complex. The present study aims to integrate field investigation, whole rock and corundum chemistry, remote sensing studies, and the conventional methods to detect the corundum-bearing pegmatites, which led to finding out the genesis of the corundum mineralization. In addition, the tectonic regime has been detected using bulk rock geochemistry. False-color composite (FCCs), band ratio (BR), principal component analysis (PCA), minimum noise fraction (MNF), decorrelation stretch (DS), and the constrained energy minimization (CEM) image processing algorithms were proposed and applied on Landsat-8 OLI, and Sentinel-2A data to discriminate the exposed lithological units and to detect the corundum-bearing pegmatites in the study area. These detected pegmatites are structurally controlled following the NW-SE direction. The ultramafic rocks are the host of six areas and the gneisses are the host rocks of the two others. Gneisses and pegmatites are characterized by a steep slope of LREEs relative to HREEs with week Eu negative anomaly. The studied pegmatites have both plumasite and marundite. On the other hand, the studied corundum has Al2O3 content up to 99.72 wt% in pegmatite-gneiss and up to 100 wt.% in pegmatite-ultramafics. Corundum is ascribed to metamorphic/metasomatic type according to its chromosphere. Desilication in pegmatites led to the excess of alumina content in the residual melt producing corundum mineralization.

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