Mineral chemistry, ASTER hydrothermal alteration mapping, and geotechnical characterization of granitic rocks of the Arabian-Nubian Shield; A case study from Wadi El-Hima, South Eastern Desert, Egypt

In this study of Wadi El-Hima granites, we present the results of petrographic, whole-rock chemistry, and mineral chemistry (microprobe) characterization; hydrothermal alteration mapping using ASTER data; and physico-mechanical (geotechnical) characterization, including suitability of using these granites for dimension and decorative stone. Our geological and petrographical results indicate that Wadi El-Hima contains four types of granitoids, divided into approximately coeval suites: an older granodiorite and trondhjemite suite, and a younger syenogranite and alkali feldspar two-mica granite suite. Despite the difference in relative ages, all phases exhibit high-K calc-alkaline to weakly peraluminous signatures except for alkali feldspar granite that ranges in affinity from metaluminous to peralkaline. Trondhjemite is an unusual HREE-enriched peraluminous granitoid placing it into a novel category comprising <3 % of global granitoids. The tectonic origin of the older granodiorite-trondhjemite suite most closely resembles volcanic arc granite, in particular, I-S-type granite, whereas the younger syenogranite-alkali feldspar two-mica granite suite trends toward within-plate granite and A-type granite. Remote sensing mapping of hydrothermal alteration using ASTER relative band depth, band ratio, and mineral indices indicate that epidote, chlorite, carbonate, and sericite comprise the predominant alteration phases, whereas kaolinite and iron oxides comprise minor phases. Physico-mechanical test results show that bulk density ranges from 2.56 g/cm³ (syenogranite) to 2.72 g/cm³ (granodiorite). Water absorption ranges from 0.15 % (trondhjemite) to 0.22 % (alkali feldspar granite). Uniaxial Compressive Strength ranges from 50.9 (granodiorite) to 141 MPa (trondhjemite). The modulus of rupture and flexural strength of all the granites have similar ranges of 3.8–10.8 MPa and 3.2–8.9 MPa, respectively. All four rock types passed the minimum physical requirements (bulk density, water absorption, apparent porosity) of ASTM C20 and 97 tests, but, owing to mechanical flaws, failed the minimum mechanical requirements (Uniaxial Compressive Strength, Modulus of Rupture, and Flexural Strength) of ASTM C170, 99, 880, and 615 tests. Accordingly, Wadi El-Hima granitic rocks have low suitability for load-bearing construction applications but moderate to high suitability for non-load-bearing decorative applications, such as countertops and wash basins. This paper reflects global efforts to characterize the suitability of granites for use as dimension and decorative stone and to link such findings to petrochemical and remote sensing results.