RECOGNITION OF FAVORABLE ZONES FOR URANIUM AND THORIUM ACCUMULATION, AT UM ARA-UM SHILMAN GRANITIC PLUTON, SOUTH EASTERN DESERT, EGYPT, USING AIRBORNE SPECTROMETRIC AND MAGNETIC DATA

The objective is aimed at identifying significant U and Th anomalies, the amount of re-mobilization of U and Th, the structural framework of the granite pluton and the distribution of spectrometric anomalies. T he study revealed that the granite pluton could be represented as a si ngle radio-lithologic unit excluding abnormal measurements exceeding ( X) over bar+2S. It also revealed the existence of eight strong spectro metric anomalies. Observed values of eU correlate well with eTh, r=0.7 2, while the correlation between eU/eTh and eU is lacking, r=0.190. Me anwhile, there is a negative correlation between eU/eTh and eTh, r=-0. 335. This deficiency in correlation suggests a limited or zero remobil ization of uranium, which was partly governed by magmatic processes. A n interpretative basement structural map of the study-area showed some striking features: four NW-trending faults of first-order magnitude ( probably shear zones); three NE-trending faults of second-order magnit ude; a series of third-order magnitude faults trending in different di rections and, questionably, strike-slip faults as well as some basic a nd acidic dykes. Most of the radioactive anomalies were found within o r near the major contact faults which may act as channels for minerali zed fluids from the subsurface. These fluids possess increased concent rations of U and/or Th which could exist in appropriate chemical and/o r structural traps. The U and Th anomalies were found to be associated with the northern and southern parts of the granite pluton respective ly. The difference between the northern and southern parts of the gran ite pluton may be attributed to differences in radioelement content, t he effect of partial and/or complete digestion of older rocks, or to d ifferent levels of erosion.