Geochemical, radiological, and heat-production characteristics of the ElGara granitoids (Southwestern Desert)

This study provides an integrated geochemical, petrographic, and radiological assessment of the El Gara El Hamra and El Gara El Soda granitoids in Egypt's Southwestern Desert. Whole-rock major, trace, and REE geochemistry, combined with tectonic discrimination diagrams, reveals that the granitoids belong to ferroan A-type suites and comprise both peraluminous and peralkaline varieties. These contrasting chemistries reflect heterogenous crustal sources and within-plate magmatic processes associated with late Neoproterozoic post-collisional extension. Elemental ratios (e.g., Nb/Yb, Ga/Al) and HFSE enrichments support an anhydrous, oxidized, high-temperature melt regime consistent with the regional evolution of the Arabian-Nubian Shield. High-resolution gamma spectrometry was used to quantify primordial radionuclides (²³⁸U, ²³²Th, ⁴⁰K). Thorium and potassium show pronounced enrichment in the peralkaline samples, whereas uranium displays moderate variability across the granitoid suites. Calculated radiological parameters-including absorbed dose rate (D_γ), annual effective dose (E_annual), radium equivalent activity (Ra_eq), and hazard indices-exceed global crustal averages but remain within ranges typical of A-type granites worldwide. Radiogenic heat production (RHP) varies significantly between the peraluminous and peralkaline groups, reaching up to 9.99 µW/m³, indicating favorable potential for shallow-crust geothermal exploration. Organ-specific dose modeling (ICRP-based) identifies the bone marrow and lungs as the most impacted tissues under hypothetical prolonged exposure scenarios. Although some samples exceed recommended limits for unrestricted building use, actual public exposure would depend on rock utilization and exposure geometry rather than intrinsic radionuclide concentrations alone. Overall, the El Gara granitoids represent a compositionally diverse A-type system with elevated heat-producing elements and moderate radiological significance. These findings highlight the need for site-specific radiological evaluation before large-scale quarrying or use as construction materials, and underscore their potential relevance for geothermal energy assessments.