干旱区生态环境知识资源中心

The present study investigates the use of ASTER and geochemical data in the exploration of new gold occurrences in altered granodiorite rocks at Samut area in the South Eastern Desert of Egypt. The mapping approach developed and applied in this study integrates image ASTER and field data sets to produce a map showing the alteration zones within granitoid rocks in the Samut area. Due to the differences in hydrothermal mineral components as well as their intensities and influences on the surrounding rocks, various alteration processes have been occurred within the host granodioritic rocks. Such alteration processes include sericitization, chloritization, silicification, and ferrugination, resulted from the chemical interaction between the host rock minerals and mineral bearing ascending solutions. Each alteration process is characterized by significant minerals. The sericite and altered plagioclase characterize the sericitization process, whereas biotite, muscovite, chlorite, and hornblende minerals are associated with chloritization. However, silicification process is manifested by the quartz veins and fractured quartz grains. The ferrugination process is characterized by the transformation of magnetite to hematite and goethite. The chemical analyses of the unaltered granodiorites yielded Au content between 0.01 and 1.61ppm, while in the altered granodiorite; Au content is around 0.02 to 14.79ppm. The presence of gold in the unaltered and altered granodiorite even in a low percentage, but in huge tonnages gives an importance and makes the study area worthy of gold exploration and possible exploitation and hence international propagation. The Samut district is made up of intermediate to acidic metavolcanics intruded by a hornblende granodioritic pluton and cut by acidic dykes and quartz veins and veinlets. The associated hydrothermal activity with the plutonic intrusion led to the occurrence of promising alteration zones for gold in the granodiorite.