干旱区生态环境知识资源中心

Um Safi area is located in the southern part of the Central Eastern Desert of Egypt. The total count airborne radiometric survey data of this area have been treated qualitatively and quantitatively and correlated with the geological map of the study area. The total count image of this area shows some radiometric anomalies related to the younger granites and are structurally controlled by the dominating faults trending in NW-SE, NE-SW, and E-W directions. The map also shows some anomalies associated with the rhyolite flow tuffs. This survey indicates that the study area possesses gamma radiation ranging between 0.5 and 14 Ur as a total count. Field investigations reveal that the basement rock units of Um Safi area are extruded by rhyolite stocks and trachyte plugs and these rocks show high potentiality of radiometric elements. Detailed ground geological and geophysical studies are made over the rhyolite zone of Um Safi area by the authors; these surveys of detailed ground survey have been conducted along 16 parallel profiles oriented at N-S direction with profile separation of 40 m and with stations every 20 m along the profiles. The location of each station was determined using GPS. The analysis of the gamma-ray spectrometric readings for the rhyolite zone of Um Safi area by using the Geosoft programs indicates that there is an increase in the eTh content from 18 to 397 ppm eTh at the rhyolitic volcanic rocks. Moreover, the eU content shows an increase from 2 to 95 ppm eU at these rocks. The main trend of their eU and eTh anomalies is the NW-SE direction. The VLF method was used and the data were interpreted qualitatively to determine the location of subsurface structures. The highly conductive zones, that are consistent with rhyolite rocks trending in the NW-SE and NE-SW direction, are due to mineralization and they are interpreted as fractured mineralized zones. The integration of the results of the ground gamma-ray and VLF-EM interpretation reveal that all the radiometric anomalies lie over the rhyolite rocks and are associated with elongated positive conductivity anomalies having NW-SE and NE-SW direction. The NW-SE direction is considered as the main trend which plays an effective role in the distribution of the radioactive elements in the rhyolite zone of Um Safi area.