Mineralogical and Geochemical Studies on Granitic and Volcanic Rocks At Nusab El Balgum Area, South Western Desert, Egypt

Abstract

This work is concerned with studying the Permo-Triassic volcanic rocks, altered granitic rocks, post granitic dykes and veins exposed in Nusab El Balgum area, South Western Desert, Egypt. This included field observations, petrographic, mineralogical, geochemical and radiometric studies in order to determining the rare metals mineralization, tectonic settings and different types of alterations. Nusab El Balgum area covers about 40Km2, located at the south Western Desert of Egypt, about 600 km south west of Aswan City near Kurkur and Dungul Oases. It is occurred at the intersection of Lat. 23o15/ to 23o 20/ N and Long 29o 15/ to 29o20/ E. 1-Geologic setting and petrography Nusab El Balgum forms an elongated body trending in the NNE-SSW and composed of Permo-Triassic volcanic rocks and surrounded by the peneplained surface of older sandstones. Due to the strong effect of weathering and denudation, Nusab El Balgum is represented by a number of isolated low hillocks (showing blocky shape) separated by numerous fault planes in different directions that are covered by windblown sand . The area consists mainly of sandstone (Devonian), volcanic rocks (Permo-Triassic), altered granitic rocks, post granitic dykes and veins. I-Sandstone: It is the oldest rock unit in the study area (Paleozoic age) and form few isolated outcrops rise about 5 m above ground level occurring in the low-lying parts of the area. Chapter Six Summary and Conclusion 385 II-Conglomerate: It separates the extrusive rocks (volcanics) from the underlying sedimentary rocks (sandstone). The thickness of this unit ranges between 1m to 4m. The age of this unit is not clearly defined because there were no fossils collected from its lithology. The microscopic investigation revealed that the conglomerate is composed of quartz grains of size up to 7.0mm associating angular quartz grains of sand size (<2.0) hold by a matrix of amorphous silica. Zircon and monazite represent the accessory minerals. III-Volcanic and Volcaniclastic rocks: The volcanic rocks form abundant hills of different elevation. The prominent highest is that of Gabel Nusab El Balgum with an elevation of 366m (a.s.l) .The volcanic rocks are also present in the form of numerous plugs with dykes and veins. They dip gently to steeply towards the northwest and are surrounded by low land of altered granitic rocks from the south direction. These volcanic rocks together with their associated altered granitic rocks form triangular body (1.5 km in length and 650 m in width) with its apex looking NNE, while its base trend in the E-W direction. This body is about. Microscopic investigation for volcanic rocks revealed that, they range in composition from acidic to intermediate and could be classified petrographically, into rhyolite , dacite, in addition to tuffs that characterized by light weight and brittle appearance.