New Occurrence of Gold Mineralization at the Eastern Part of Wadi El Gemal, South Eastern Desert, Egypt

The basement rock units of the study area are represented by metasediments-metavolcanics association, diorite rocks, granodiorites and syenogranites. The whole sequence is cut by basic dykes, pegmatites and different quartz (jasper) veins. Metasediments-metavolcanics association is represented by hornblende schist and metadacite respectively. There is visible sulfides mineralization in hornblende schist, metadacite and diorite rocks at their contacts at the wadi level. So, polished sections were prepared to study opaque minerals under the ore microscope, which reveals the presence of gold, pyrite and goethite. The radioactivity of this area is weak, where the average eU contents in metasediments-metavolcanics association, diorites, granodiorites, syenogranites, pegmatites and jasper veins are 2.8 ppm, 1.9 ppm, 3.26 ppm, 4.91 ppm, 4.32 ppm and 6.7 ppm respectively. The intrusion of granodiorite rocks may act as a source for hydrothermal solutions ascending along fractures of all older rocks. During this stage, a chemical reaction of hydrothermal fluids with metasediments-metavolcanics association and diorite rocks lead to forming sericite and enrichment of silica content. The enrichment of silica content led to the formation of quartz-diorite. Also, iron derived from the host rocks and sulfur from the hydrothermal fluids could have formed pyrite while the gold was precipitated at the contact between metasediments-metavolcanics association and diorite rocks.

Petrology, REE Geochemistry and Tetrad Effect of Some Muscovite Granites at Wadi El Gemal Area, South Eastern Desert, Egypt

The muscovite granites at the study area are being emplaced into biotite granites and ophiolitic mélange settings. They occur in four exposures namely;Umm Seleimat, Sikait, Umm El Kheran and Umm Addebaa exposure. The presence of garnet and muscovite flakes may reflect the peraluminous nature of the studied muscovite granites. Petrographically, the studied granites are mostly subsolvus and consist of plagioclase, K-feldspars, quartz, muscovite and biotite. Garnet, zircon, allanite and opaques are accessories. The textural features of these granites are expressed by bent plagioclase lamellae, distorted microcline twinning, deformed mica flakes and development of myrmekite and recrystallization of feldspars into fine-grained aggregates. Umm Seleimat and Sikait exposures are more differentiated due to the presence of high content of K-feldspar and LREEs. The REE budget decreased from Umm Seleimat-Sikait exposures to Umm El Kheran-Umm Addebaa exposures as (514.5 - 495.6) to (195.9 - 197.7), respectively. Umm Seleimat-Sikait exposures have lower HREE/LREE (0.12 - 0.67), relative to Umm El Kheran-Umm Addebaa exposures (0.99 - 2.06). The studied granites revealed that the chondrite normalized REE patterns are the normal M-type of tetrad effect, where TE1,3 tetrad effect is higher than 1 in all samples which implies that there was an interaction between melt and water-haloid-rich fluid when these granites are crystallized from magma. Spectrometric values of Umm Seleimat and Umm Addebaa indicate that U content is more than Th content. Applying the U mobilization equation proved that the studied granites have been originated from a late magmatic phase of magma very rich in radioelements, also the majority of measurements lie above the zero line indicating that the studied granites affected with hydrothermal solutions rich in uranium than thorium which indicates uranium addition.

Flash Floods and Groundwater Recharge Potentials in Arid Land Alluvial Basins, Southern Red Sea Coast, Egypt

Flash flooding is one of the periodic geohazards in the southern Red Sea Coast. However, their freshwaters are the main source of recharging alluvial and fractured aquifers. This paper presents hydrological and geomorphologic classification of Wadi El-Gemal, Wadi Umm El-Abas, Wadi Abu Ghuson and Wadi Lahmi, along the southeastern Red Sea Coast in Egypt. The main goal is to find a relationship of flash floods and groundwater recharge potentials. Satellite imageries and topographic data were analysed via remote sensing and GIS techniques. The main four valleys’ orders range from six to seven. Wadi El-Gemal was the main focus of this study;it is characterized by high stream frequency, low stream density and coarse texture, reflecting influence of highly fractured Precambrian rocks. Most of the wadis have umbrella-shaped catchment areas, due to the influence of NW-SE Najd Fault System and late E-W strike-slip faults. The main wadis were divided into 45 sub-basins. 14 of the studied sub-basins flow into Wadi El-Gemal, 7 flow into Wadi Umm El-Abas, 10 are in Abu Ghuson, and rest of the basins flow into WadiLahmi. A conceptual model was used in this study, showing that most of the sub-basins have high flash flooding and low groundwater recharge potentials. However, only two sub-basins have low potential of flooding and high potential of groundwater recharge, whereas few sub-basins have moderate potential of groundwater recharge as well as flooding. For flash floods beneficiation and mitigation, construction of multifunctional embankment dams is imminent.