Document Type : Original Article
Authors
1
Petrological Studies, Research Division, Nuclear Materials Authority.
2
Ground exploration Department, Exploration Division, Nuclear Materials Authority.
3
Geochemical Exploration, Research Division, Nuclear Materials Authority.
Abstract
El Sela area is mainly covered by ophiolitic mélange (Sul Hamed), biotite granite, two-mica granite
(El Sela), muscovite granites (Qash Amer), and cross cut by microgranite dolerite and bostonite dikes as
well as quartz and japser veins. These granitic rocks are hydrothermally altered, especially around El Sela
ENE-WSW shear zone, that causing hydrothermal alterations accompanied by radioactive mineralization.
These rocks are mainly composed of alkali feldspar, quartz, muscovite, and biotite with zircon, fluorite,
apatite and iron oxides as an accessory minerals. The radioactive minerals are represented by uranophane,
autunite, meta-autunite and phurcalite which are restricted in the highly sheared microgranite, dolerite
dikes as well as jasper veins. Uranium contents (eU) range from 10.1 to 17.7 ppm at Qash Amer with their
thorium contents (eTh) vary from 5.8 to 22.7 ppm. El Sela granites have uranium contents (eU) range from
6.4 to 19.7 ppm with equivalent thorium content (eTh) range between 14.0 and 44.9 ppm. The eU-eTh, (eU/
eTh)-eU and eU-[eU+(eTh X 3.5)] diagrams show depletion of uranium for both the Qash Amer and El Sela
granitic samples, suggesting that uranium may be leached out of the original rock towards the ENE-WSW
and NNW-SSE shear zones. The migrated uranium (Um) amount was calculated and indicated as either
migration out or migration in at Qash Amer and El Sela granites, mostly to the shear zone cutting through
the area. Absorbed Dose Rate (D), annual effective dose equivalent (AEDE), radium equivalent activity
(Raeq), external (Hex) and internal (Hin) hazard index, in addition to activity gamma index (Iγ) caused by
gamma emitter natural radionuclide were determined from the obtained values of 238U, 232Th and 40K. Most
of the studied samples have radiological parameters values higher than the international recommended
values suggesting that El Sela and Qash Amer granitic rocks are hazardous and not recommended for use
as ornamental stones with respect to workers and human beings.
Keywords
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