Mineralogical studies and radioactivity of Wadi Steih stream sediments, south Sinai, Egypt

Wadi Steih stream sediments are generally produced from long term successive physical and/or chemical weathering and consequence erosion processes of the surrounding rock units such as younger granites, Iqna volcanics and gabbro. The representative diagrams of the plotting of the average trace element contents versus those of the surrounding rock units along with the Co/Th ratio indicate that the trace elements recorded in the Wadi Steih stream sediments are derived from the surrounding rock units. The radiometric surveying indicates the over dominance of thorium rather than uranium. The thorium content ranges from 4.4 ppm to 335 ppm with an average of 62.5 ppm. Uranium content ranges from 2 ppm to 15 ppm with an average 6.2 ppm. The high thorium contents of these stream sediments are generally ascribed to the presence of monazite, zircon and huttonite. These minerals are trapped by widespread basic dykes that act as physical barriers. The source of uranium present in the stream sediments is ascribed, in part, to its mobility from the surrounding uraniferous younger granites and its adsorption along the grain boundaries of the clay minerals which are originated from the weathering processes acting on the basic dykes where uranium is ultimately adsorbed along their boundaries. The other probable source of uranium is the presence of secondary lead uranyl hydroxide mineral spriggite. The distribution of the radioelements of Wadi Steih stream sediments is mainly controlled by the presence of both basic dykes which are acting as physical barrier and the prevailed NW-SE drainage patterns.