Ibrahim Hassan Ibrahim
Nuclear Materials Authority, Egypt
Title: Origin and mode of occurrence of Abu Rusheid-Sikait Mylonite Rocks, South Eastern Desert, Egypt
Biography
Biography: Ibrahim Hassan Ibrahim
Abstract
Abu Rusheid-Sikait area forms part of the Arabo-Nubian basement exposures that is situated at the northern peripheral contact between the Central and the South Eastern Desert. Abu Rusheid mylonites are a ductile deformed fault rocks originated from the parent granitic rocks that were formed as sheet like body injected along major antiform and affected later by ductile shearing. Four deformation phases are recognized in Abu Rusheid-Sikait area during the late Pan-African event. The first two compressional phases (D1 & D2) and the second two deformations are mainly extensional phases (D3 & D4). The D3 is mainly development of sub-horizontal mylonite rocks with a bout maximum thickness of 50 m along ductile shearing. Shear sense indicators give a consistent regional transport direction to the SSE. Abu Rusheid-Sikait mylonites have two stages of mineralization; the first one is mainly magmatic stage related to the parent granitic rocks during which monazite, thorite, uranothorite, allanite, columbite, xenotime, fluorite and zircon minerals were formed. The second stage is secondary minerals due to precipitation of uranium-bearing hematite, uranophane, torbernite, kasolite and epidote minerals in micro-fractures. In situ gamma-ray spectrometry measurements support these two stages of mineralization. The av. eTh/eU ratio varies from 3.2 to 13.3 in mylonites and pegmatitic pockets within mylonites indicate thorium is enriched rather than uranium supporting the magmatic origin (first stage), while the fractured mylonites are enriched in eU over than eTh (eTh/eU ratio from 0.1 to 1.1) indicates U-remobilization and give the second stage of mineralization.