Ground gamma-ray spectrometric (GRS) and horizontal-loop electromagnetic (HLEM) surveys were carried out to determine the radioactive anomalous zones and to follow their lateral and vertical extensions in east Gabal (G.) El-Urf area, Northern Eastern Desert, Egypt. This area and its surroundings are mainly covered by basement rocks of Late Precambrian age, represented by quartz diorites and granite porphyry, which are intruded by pegmatites, quartz veins, and basic dykes. These rocks are traversed by dry wadis (dry valleys), which are filled by Quaternary sediments. The ground gamma-ray spectrometric data revealed that the study area possesses a wide range of radioelement concentrations, oscillating from 37 to 2164 μR/h, 0.9-170 ppm, 0.1-312 ppm, and 0.2%-7.8% for total count (TC), equivalent uranium (eU), equivalent thorium (eTh), and potassium (K), respectively. The eU composite image showed that high radioactive parts are mainly associated with the pegmatite rocks. Ground HLEM survey was performed at four frequencies (7040 Hz, 1760 Hz, 440 Hz, and 110 Hz) in the study area. The interpretation of the HLEM data indicated the presence of various conductive zones, mainly associated with pegmatite bodies. The parameters of source causative bodies, such as location, dip angle, width, and conductivity thickness were estimated for three conductive bodies. The calculated depths to the selected HLEM anomalies appear to be shallow, varying from 10 m to 22 m. All the anomalous bodies have dips ranging between 60° and 80° toward the south and west. The widths of the anomalous bodies range from medium conductors (13 m) to broad conductors (40 m or more). The conductivity thicknesses showed a wide range (1.14-72.7 Siemens), with the highest value associated with the highest eU anomaly.
Keywords: Eastern desert; Egypt; Gabal El-Urf; Gamma-ray spectrometry; Horizontal-loop electromagnetic.
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