Abstract
The Wadi Sikait area lies at about 95 km southwest of Marsa Alam City along the Red Sea Coast, Eastern Desert, Egypt. It is occupied by Precambrian rocks of ophiolitic mélange, metamorphosed sandstones (MSS), gabbros and monzogranites which were later intruded by lamprophyre dykes and quartz veins.
The lamprophyre dykes were extruded in NW-SE and NE-SW trends cutting monzogranites and metamorphosed sandstones. The lamprophyres are porphyritic and composed of clinopyroxene, olivine and amphibole phenocrysts enclosed in a fine-grained groundmass of clinopyroxene, amphibole, opaque and lithium mica. The alteration products are represented by amphibole (tremolite-actinolite and hornblende), carbonate, epidote, chlorite, iddingsite, clay minerals, limonite and serpentine.
The Sikait lamprophyre dykes can be classified as alkaline lamprophyres characterized by silica contents ranging from 41.65 wt% to 50.88 wt% and Na2O>K2O. They are enriched in LILE, LREE and HFSE, but strongly depleted in compatible elements such as Cr and Ni relative to the primitive mantle. Sikait lamprophyres have moderate Zr/Hf (35.6–52.8) and Nb/Ta (20.5–22.5) ratios. Most of these features are attributed to the origin of these dykes from the metasomatized mantle affected by subduction-related fluid. These lamprophyres are compositionally similar to Salu lamprophyres in eastern China.
The Sikait lamprophyre samples have high LREE (320×10−6–419×10−6) relative to HREE (20×10−6–33×10−6) with ratios (LREE/HREE=11.6–18.7) and no negative Eu anomaly (Eu/Eu*=0.9–1.04). The relative presence of positive Ce anomaly (Ce/Ce*=1.04) in lamprophyre samples suggests the oxidizing condition under which the REEs were precipitated due to the common occurrence of fluorite and apatite.
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El-Ahmadi, I.M., Ahmed, R.A. Geochemistry of lamprophyre dykes, Wadi Sikait area, South Eastern Desert, Egypt. Chin. J. Geochem. 30, 323–331 (2011). https://doi.org/10.1007/s11631-011-0516-4
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DOI: https://doi.org/10.1007/s11631-011-0516-4