Origin of the columbite mineralization in the radioactive psammitic gneiss of Wadi Abu Rusheid, Eastern Desert, Egypt

An assemblage of rare metal accessory minerals occurs in the radioactive part of the psammitic gneiss of Wadi Abu Rusheid, Wadi Nugrus and Wadi Sikait, Eastern Desert of Egypt. Columbite constitutes from 0.08% up to 0.18% of the whole rock, and forms 14.10% to 31.5% of the heavy fraction separated from that rock. Main radioactive minerals are zircon and thorite. The columbite content increases appreciably going upwards in the psammitic gneiss and maximum content is recorded in the pegmatoidal part at its upper contact with the overlying schists. This sort of mineralization was formed as a result of the metasomatic alteration that alteration that acted on the psammitic gneiss. This process resulted in the enrichment of columbite and other minerals in the upper 50m of the rock and depleted it from the lower non-radioactive part. It has been shown that the source of this metasomatised columbite was the old detrital mineral particles presented in the original sediments from which the host rock was derived by metamorphism and metasomatism