Homret Ghannam Post-collisional Granites in the Eastern Desert of Egypt: Petrogenesis, Geodynamic Evolution, and Rare-metal Significance

Abstract

Homret Ghannam alkali feldspar granite (HGAFG) in the central Eastern Desert (CED) of Egypt represents a distinctive example of late Neoproterozoic magmatism in the Arabian-Nubian Shield (ANS). This study integrates field observations, petrography, mineral chemistry (EMPA), and whole-rock geochemistry to investigate its petrogenesis, geodynamic evolution, and rare-metal potential. HGAFG comprises two cogenetic varieties, alkali feldspar granite and riebeckite-bearing granite, hosting rare-metal minerals such as zircon, fluorite, columbite and apatite. HGAFG exhibits diagnostic A-type geochemical characteristics, including high SiO₂ contents (73.81–77.86 wt%), metaluminous to mildly peralkaline composition (ASI: 0.92–1.03), enrichment in HFSE (Zr ≈ 791.80 ppm, Nb ≈ 68.12 ppm, Y ≈ 90.81 ppm) and ΣREE (103.40–475.57 ppm), and pronounced negative Eu anomalies (Eu/Eu^* = 0.07–0.20). Zircon saturation thermometry yields high crystallization temperatures (T_Zr ≈ 908.87°C) and low emplacement pressures (1.46 kbar) under reducing conditions (ƒO₂ ≈ –11.5). The mineralogical and geochemical results reveal that HGAFG originated from a hybrid, fluorine-rich magma generated by anatexis of lower crust, followed by extensive fractional crystallization, during late post-collisional extension associated with lithospheric delamination. The reduced nature and fluorine enrichment of HGAFG magma promoted the mineralization of Nb–Ta–REE phases, highlighting its significance as a fertile, high-temperature product of the terminal magmatic stage in ANS evolution.

Keywords

alkaline granites / riebeckite / arfvedsonite / columbite / petrogenesis / Homret Ghannam

RIGHTS & PERMISSIONS

2026 Geological Society of China