Document Type : Original Article
Authors
1
Department of Geology, Faculty of Science, Zagazig University
2
Nuclear Materials Authority of Egypt
3
Nuclear Material Authority, Research Sector, Post box 530, Al Maadi, Cairo
4
Geology Department, Faculty of Science, Zagazig University, Zagazig-4451, Egypt
Abstract
The Wadi El-Dob pegmatite body, located in the northern Eastern Desert, consists of three distinct zones: the border zone, intermediate zone, and core zone. It is hosted within alkali-feldspar granite and contains minerals such as plagioclase, quartz, muscovite, rare K-feldspar, fluorite, topaz, hematite, rutile, pyrite, cassiterite, columbite-tantalite, and xenotime, so they classified as NYF-type pegmatites. Fluid inclusion studies revealed the presence of three types of inclusions: two-phase aqueous, three-phase (H2O-CO2), and poly-phase inclusions. The first type (stage I) showed low salinity and homogenization temperature, while the second type (stage II) exhibited high salinity and temperature. The poly-phase inclusions formed during the hydrothermal stage. The wide temperature range of homogenization could be attributed to simple cooling. The estimated temperatures from isochors varied between a lower and upper range under a specific pressure. The fluids of both stages I and II likely originated from a magmatic source, possibly associated with the devolatilization of alkali-feldspar granites. The coexistence of different types of inclusions can be explained by the partial immiscibility of a homogeneous fluid (H2O-CO2-NaCl) due to the presence of H2O-rich and CO2-rich inclusions, their occurrence in the same region and samples, and the similar microthermometric results. Generally, pegmatites are commonly suggested to be derived from crystallizing granitic melt especially those pegmatites, which are hosted within the parental granite. Geochemically, the resemblance of magma type between alkali-feldspar granites and the associated pegmatite body suggests a common source magma. Both granite and pegmatite samples display a typical trend of magmatic differentiation, which is consistent with fractional crystallization. NYF, garnet-REE pegmatite containing ilmenite and Nb-Ta minerals may originate as the product of melt segregation within the granite during its crystallization. Furthermore, NYF pegmatites may have originated from mantle-sourced anorogenic magmas with a peralkaline signature. The border zone of the pegmatite experienced crystallization temperatures within a range (560 - 570 °C). The chemical composition of the intermediate zone (K-feldspar) from Wadi El-Dob and the physical tests conducted on ceramics made from pegmatite samples indicate their suitability for wall ceramic tiles according to standard values. Field radiometric measurements of the El Dob pegmatites revealed varying content of K-40, uranium, and thorium. These variations indicate the presence of hydrothermal and magmatic types, suggesting significant post-magmatic processes. Consequently, it is recommended to exclude measurement stations with high values from use in the ceramic industry.
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