ORIGINAL PAPER Natural radioactivity in basement rocks and stream sediments, Sharm El Sheikh Area, South Sinai, Egypt: radiometric levels and their significant contributions M. Th. S. Heikal & B. T. El-Dosuky & M. F. Ghoneim & M. I. Sherif Received: 21 December 2011 / Accepted: 27 June 2012 # Saudi Society for Geosciences 2012 Abstract The present study examines the natural radioac- tivity in basements rocks including granites and associated dikes besides stream sediments in Sharm El Sheikh area. Two main rock units are concerned; granites pertaining to Younger Granites of Precambrian age and clastic sedimen- tary rocks related to Miocene and Pliocene ages. This area is traversed by two shear zones that were delineated as the master fractures trending NW and NNE and controlling uranium and thorium enrichment in granites and dikes. The field and laboratory radiometric measurements revealed radiometric anomalies, in particular, along shear zones. The results of radiometric analyses including concentrations of equivalent uranium (eU), equivalent thorium (eTh), Ra, and K radionuclides as well as the calculated ratios eTh/eU and eU/Ra for representative samples belonging to all rock va- rieties, revealed that the felsic dikes have the highest values of the average radionuclides potential followed by the alkali feldspar granites, while the mafic dikes display the lowest radioactivity potential. On the other hand, the trends defined in the variation of uranium and thorium reflects the amount of remobilization of uranium that has occurred within the plutons. The eTh and eU/eTh ratios shows a negative cor- relation, suggesting that distribution of uranium and thorium was at least controlled by magmatic differentiation, while, the positive correlation between eU and eU/eTh ratios indi- cates enrichment of uranium through post magmatic pro- cesses. Some precautions and recommendations are proposed to avoid any possible environmental impacts from shear zone areas with high intensity of natural radiation sources. Keywords Natural radioactivity . Radiometric levels and environmental impacts . Origin of radioactive of U and Th . Sharm El Sheikh area . Egypt Introduction The Sharm El-Sheikh area (∼600 km 2 ) is located in the southern end of Sinai massif (∼28,450 km 2 ). This area is occupied by granites (∼580 km 2 ) of Precambrian age and Miocene and Pliocene clastic sedimentary rocks (∼20 km2; Fig. 1). The Precambrian rocks including granites and asso- ciated dikes are of great importance because they contribute significantly to the radiation doses received by humans. The area under consideration has been studied by few workers (Nasr et al. 2006; El-Bialy and El-Omla 2007). They focalized indicators of radioactive potential within some granite exposures. The main goals of the present study were to measure the radiometric aspects on granites, dykes, and stream sediments using field and laboratory equipments to de- termine the distribution of the main radionuclides; U, Th, Ra, and K in these rocks as well as to determine the anomalous spots of uranium and thorium in the investigated area. Geology The granitic rocks of the mapped area (after Sherif 2011) embrace four plutons: Att ElSharqi Monzogranites and Sye- nogranites (∼200 km 2 ), Madsus Syenogranites and Alkali Feldspar Granites (∼120 km 2 ), Sharm Alkali Feldspar Gran- ites (∼80 km 2 ), and Umm Adwi Reibekite-Bearing Granites (∼180 km 2 ). These plutons are intruded by mafic, felsic, and alkaline dykes trending NNE and NE. M. T. S. Heikal (*) : B. T. El-Dosuky : M. F. Ghoneim : M. I. Sherif Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt e-mail: mtheikal@yahoo.com Arab J Geosci DOI 10.1007/s12517-012-0622-6