Magmatic Evolution and Rare Metal Mineralization in Mount El-Sibai Peralkaline Granites, Central Eastern Desert, Egypt: Insights from Whole-Rock Geochemistry and Mineral Chemistry Data

Abstract

The Ediacaran peralkaline granites, which were emplaced during the post-collisional tectonic extensional stage, have a limited occurrence in the northern tip of the Nubian Shield. In this contribution, we present new mineralogical and geochemical data of Mount El-Sibai granites from the Central Eastern Desert of Egypt. The aim is to discuss their crystallization condition, tectonic setting, and petrogenesis as well as the magmatic evolution of their associated mineralization. Mount El-Sibai consists of alkali-feldspar granites (AFGs) as a main rock unit with scattered and small occurrences of alkali-amphibole granites (AAGs) at the periphery. The AAG contain columbite, nioboaeschynite, zircon and thorite as important rare metal-bearing minerals. Geochemically, both of AFG and AAG exhibit a highly evolved nature with a typical peralkaline composition (A/CNK = 0.82–0.97) and formed in within-plate anorogenic setting associated with crustal extension and/or rifting. They are enriched in some LILEs (Rb, K, and Th) and HFSEs (Ta, Pb, Zr, and Y), but strongly depleted in Ba, Sr, P and Ti with pronounced negative Eu anomalies (Eu/Eu* = 0.07–0.34), consistent with an A-type granite geochemical signature. The calculated TZrn (774–878 °C) temperatures indicate that the magma was significantly hot, promoting the saturation of zircon. The texture and chemistry of minerals suggest that they were crystallized directly from a granitic magma and were later subject to late- to post-magmatic fluids. Both granitic types were most likely generated through partial melting of a juvenile crustal source followed by magmatic fractionation. The lithospheric delamination is the main mechanism which causes uplifting of the asthenospheric melts and hence provides enough heat for crustal melting. The produced parent magma was subjected to prolonged fractional crystallization to produce the different types of Mount El-Sibai granites at different shallow crustal levels. During magma fractionation, the post-magmatic fluids (especially fluorine) contribute significantly to the formation of rare metal mineralization within Mount El-Sibai granites.

Geochemical characteristics, hazards impact assessment and radiogenic heat production of the alkaline rocks

“…It is important to mention that the high REEs, U and Th concentrations were recorded in some Egyptian natural resources including highly fractionated rare metal granites and pegmatites 17 . The content of U and Th increased with increasing the SiO 2 from quartz syenite to granite (Fig.…”

“…The radioactive elements and rare earth elements (REEs) are mainly sourced from resources such as phosphorites 2 ; ironstone 14 ; black shale 15 , rare metal granites 8 ; pegmatites 16 , carbonatites and alkaline-rich rocks 17 among others. Notable areas for REEs include China (Bayan Obo deposit) 18 , Australia (Mount Weld deposit) 19 , and Brazil (Catalão deposit) 20 .…”

Chemical and Textural Peculiarities of Zircon from Peralkaline Granites and Quartz-Bearing Syenites

“…In order to reflect the widest variety of chemical compositions of zircon from peralkaline granitoids, published zircon data from the REE-Nb-Zr-enriched alkaline plutons of Thor Lake and Strange Lake (both Canada) [33,35] and from the Sn, Nb-enriched Al-Sibai stock (Egypt) [55] are shown for comparison in the diagrams. With the intention of placing the studied zircon samples in the broadest possible context, chemical compositions of zircon from typical strongly peraluminous S-type and sub-to mildly peraluminous A-type granites are also shown in some diagrams for comparison.…”

Petrogenesis and Geodynamic Evolution of A-Type Granite Bearing Rare Metals Mineralization in Egypt: Insights from Geochemistry and Mineral Chemistry

“…Rare metals mineralization has a markedly wide distribution in granite and associated pegmatite, mylonite, and rhyolite flow tuffs, as well as in lamprophyre and felsite dikes and quartz veins, which could have originated from magmatic and/or metasomatic processes [8][9][10][11][12][13][14]. Rare metal granite is widely distributed in the Eastern Desert (Figure 1b).…”

“…These rocks are subdivided into metaluminous granite (Nb, Zr, and Y rich), peraluminous granite (Ta is the most predominant one, followed by Nb, Sn, W, Be, and Li), and metasomatized granite (Nb is the most abundant, followed by Ta, Sn, Zr, Y, U, Be, and W) [15][16][17][18]. Rare metals mineralization has a markedly wide distribution in granite and associated pegmatite, mylonite, and rhyolite flow tuffs, as well as in lamprophyre and felsite dikes and quartz veins, which could have originated from magmatic and/or metasomatic processes [8][9][10][11][12][13][14]. Rare metal granite is widely distributed in the Eastern Desert (Figure 1b).…”