GEOPHYSICAL STUDIES USING GAMMA-RAY SPECTROMETRIC AND SELF-POTENIAL TECHNIQUES OF MAKHRAG EL-EBEL AREA, SOUTH GABAL MONQUL, NORTH EASTERN DESERT, EGYPT

Gamma-ray spectrometric and self-potential (SP) surveys were carried out to determine the radioactive anomalous zones and to follow their extensions at Makhrag El-Ebel area, south Gabal Monqul, Northeastern Desert. The study area and its surroundings is built up of igneous and metamorphic rocks of late Precambrian age. The basement rocks of Makhrag El Ebel area are part of the Pan African belt. They comprise Dokhan volcanics which are distinguished into basic and acidic volcanic, younger granite, dolerite dykes, quartz and barite veins. These rocks are traversed by dry wadies.
The ground gamma-ray spectrometric data have been analyzed qualitatively and quantitatively by applying specific interpretation techniques. These data revealed that, the study area shows relatively wide range of concentrations, oscillating from 3.25 to 67.3 Ur, 1.72 to 52.8 ppm, 2.04 to 64.2 ppm and from 0.83 to 6.3 %, for the total count (T.C.), equivalent uranium (eU), equivalent thorium (eTh) and potassium (K), respectively. The uranium composite image showed that, the highly radioactive parts are mainly associated with the younger granite rocks. Also, the interpreted radiometric lithologic unit map reflects a distinct content of radioelements for each of the interpreted radiometric lithologic (IRL) units, and probably, common features that could be found in the lithologic composition for each unit.
The SP data of the surveyed area exhibit moderate to very high anomalies, with amplitudes vary from -147.2 to +123.2 mV. The very high anomalies (relatively high negative amplitudes -44.2 to -147.2) are associated with strong surface mineralization or shallow ore bodies, these anomalies zones associated with younger granite which has fracture fillings with copper (Cu) and barite mineralization and a basic dyke which is located in the centeral southern part of the selected area as confirmed from the field observations. The moderate anomalies (relatively moderate negative amplitudes -8.4 to -44 mV), which located in the northern part of mapped area, can be related to ground water and wadi sediments, as confirmed from the field observations. The parameters of the source causative bodies, such as the locations, depth, polarization angle and electric dipole momentum were estimated for six SP anomaly lines (profiles), representing six anomalies. A fair agreement was found among the radiometric and SP anomalies at some places of the study area. This may indicate that the surface radiometric mineralization continued to deeper
depths at these parts.