Geochemistry of the Miocene Sandstone and Shale at Um Greifat Area, Central Eastern Desert, Egypt: Implications to Provenance, Tectonic Setting and Rare Earth Elements Potentiality

Abstract

The studied Miocene sandstone and shale rocks are belonging to El-Ranga Formation. Petrographically, the sampled sandstone is classified as sublitharenite with evidence on variable transportation distances and derivation from sedimentary, igneous and/or metamorphic rocks. The iron oxides appear as the dominant cementation while quartz is the main matrix material in this sandstone. On the other hand, the shale appears as silty-to sandy shale consisting of fine to very fine, subangular to angular and moderate to poor sorted grains. Mutual bands of the black manganese oxides and brownish-yellow iron oxides are sometimes observed with indication of silica-rich solutions post-dated the formation of these bands.Geochemically, the studied rocks were confirmed as sublitharenite and shale rich in iron. The active continental margin and island arc appeared the probable tectonic settings for Um-Greifat sandstone and shale, respectively. The quartzose sedimentary provenance and the mafic igneous provenance are expected as the primary provenances for the sandstone and shale respectively. The total REE content in the sandstone samples ranged between 0.49% and 0.83% while in the shale samples it ranged from 288 to 526 ppm and the accessory minerals are the main factor controlling the REE concentration and distribution particularly in Um-Greifat sandstone.