Egyptian Hammamat molasse basins and their relations to arc collision stages: Implications for radioactive elements mineralization potential

Our understanding of the formation style and tectonic setting of Hammamat molasse sedimentary rocks (HMSR) as well as their chronological situation in the legend of the geologic maps is as yet deficient. The purpose of the work is to decipher the misinterpretation of the HMSR genesis. As such, we present a new classification for HMSR that provides answers about its significant field relationships with the mature island arc volcanics that obviously explains the changes in the depositional environments of HMSR, tectonic setting in addition to the shape and type of their constituents. In the light of our suggested thematic evolution model, the HMSR have been deposited in 3 different tectonic settings: (a) fore-arc, intra-arc, and back-arc basins during pre-collision stage; (b) fore-arc basins and low land basins in accretionary prism during syn-collision stage; and (c) low land and intramontane basins during late-collision stage. The characteristics of HMSR in each stage differ according to the shape and type of basin and the source of sediments supplying. Thus, they show different types and sizes of clasts, mineralization, and radioactivity. The low radioactive potentiality of HMSR is entirely related to their composition, nature, and source of sediments. Generally, any radioactive anomalies are not related to HMSR themselves, but to the surrounding U-rich rocks and/or the hydrothermal and super-heated solutions. Siltstones of HMSR with their recognizable low permeability could be a good barrier for solutions carrying uranium and probably form visible uranium mineralization. Spots of visible uranium mineralization are scattered at the contact between HMSR and late-collision granites within the southern periphery of Um Tawat Basin and at the contact between trachytes and HMSR within Wadi El Kareim Basin; the extension of this mineralization does not exceed more than few centimetres away from the contact.