Tensile stress and related Th-U-REE mineralizations in the granite of Wadi Ras Abda, North Eastern Desert, Egypt

Abstract

The main rock types exposed at Wadi Ras Abda area are subduction-related older granite intruded by fine-grained alkali feldspar granite (microgranite intrusions). These rock types are dissected by acidic dykes (rhyolite) and basic dykes (basalt and dolerite) with their associated pegmatites and quartz veins. Ras Abda microgranite is highly radioactive and this radioactivity is structurally related. The thorium, uranium, and rare metal mineralization are distinguished within the microgranite intrusions along fault zones that are trending N40° E with high dipping angle reaching to 86°. It shows radioactive measurements ranging from 500 to 9500 ppm and showing visible secondary uranium and thorium minerals in addition to the deposition of black rare metal minerals. Uranothorite, thorite, and secondary uranium minerals (uranophane) are the main radioactive minerals at Wadi Ras Abda area, in addition to the rare earth–bearing mineral (REE) fergusonite. Six events are affected in W. Ras Abda area. Each event begins with compression (CP) and then extensional (EXT) phase of deformation. These events were arranged chronologically basing on field relations from the oldest to the youngest as following: WNW-ESE (CP), NNE-SSW (EXT), E-W (CP), N-S (EXT), NE-SW (CP), NW-SE (EXT), NNE-SSW to N-S (CP), WNW-ESE to E-W (EXT), NW-SE to NNW-SSE (CP), ENE-WSW to NE-SW (EXT) and ENE-WSW (CP), and NNW-SSE (EXT). The WNW-ESE to E-W–directed tensile stress reactivated faults and induced new faults along which the mineralized fluids flow. It is recognized that the low-stress regions in the vicinity of faults and their associated tension joints, along contacts between microgranite and older granite, are favorable locations for alterations and Th-U and REE mineralization.