Photogeological and geophysical studies on the Basement rocks in Wadi El Miyah, Eastern Desert of Egypt

Abstract

Wadi El Miyah area is located in the central part of the Eastern Desert of Egypt. It is covered mainly by Basement rocks of Precambrian age, overlain on its western side by Nubian sandstones. The basement rocks comprise igneous and metamorphic rocks. The different types of rocks were studied photogeologically and checked in the field radiometrically and magnetically from the air to differentiate between these rock types and to delineate the contacts between them. All the information and results obtained were used to improve and correct the geological map previously constructed for the same area. It was found that the different structural features interpreted photogeologically could be correlated with the aeroradiometric results. Besides the centers of high structural intensities in the structural contour map were found to be comparable with the centers of high radioactivity on the aeroradiometric map.

Photogeological interpretation indicated that each type of rocks has its characteristics and the contacts between the main rock types are clear using the criteria of topographic expression, photographic tone, surface texture and drainage density.

Radioactivity of the rock exposures was found to vary with the different rock types and each group of the same rock type has nearly the same background aeroradioactivity. The serpentinites and the geosynclinical volcanics have the lowest radioactivity level, (0.83–6.00 Ur) the geosynclinal sediments have moderate radioactivity level (3.33–5.00 Ur), the synorogenic plutonites have high radioactivity level (2.5–12.67 Ur) and the late orogenic plutonites have very high level of radioactivity (4.17–25.00 Ur). The aeroradiometric contacts were quite clear when there is marked difference in the radiometric level between the studied rock exposures and the surrounding rocks.

The aeromagnetic survey showed that the NE-SW and WNW-ESE tectonic trends are the prominent structural trends in the studied area. They represent faults and dykes. There are other trends namely the NNE-SSW, N-S, NW-SE which affect nearly all types of rocks in the Basement complex.