GEOLOGY, GEOCHEMISTERY AND RADIOACTIVITY OF POST COLLISION GRANITE AT WADI MURRA AREA, SOUTH EASTERN DESERT, EGYPT

Wadi Murra area lies between Lat. 22º 24' and 22º 30' N and Long. 33º 43' and 33º 52' E. The
studied younger granites in Wadi Murra area are represented by monzogranite, syenogranite and alkali
feldspar granite. Wadi Murra granites have a semi rounded-NS oval shape (11x8 km) comprising monzo
and syenogranite in the middle grading to alkali-feldspar granite at the peripheries. Alkali feldspar granite
intrudes the surrounding island arc metavolcanics as well as monzogranite of Gabal Umm Ara.
Monzo and syenogranite consist mainly of potash feldspar, plagioclase, quartz and mafic minerals
with noticeable amount of opaque minerals. The main characteristic texture is equigranular with
medium to coarse grain size. Porphyritic texture is also present. Alkali-feldspar granite is medium grained
and characterized by hypidiomorphic granular texture and composed mainly of alkali-feldspar (orthoclase
and minor microcline), quartz and subordinate plagioclase. The main mafic minerals are either amphibole
or biotite. Accessories are represented by zircon, sphene, apatite and iron oxides.
Geochemically, the studied granites are calc-alkaline in nature, emplaced in post collision granite
environment and have A2 character. The radiometric data for monzogranite show a wide variation in eU
and eTh contents. The eU content ranges from 6 to 12 ppm with an average of 8.5 ppm and the eTh
content ranges from 5 to 16 ppm with an average of 10.12 ppm. The potassium content ranges between
3.08 % and 7.67 % with an average of 4.49 % . The eU content in syenogranite ranges from 2.4 to 6 ppm
with an average of 3.78 ppm and the eTh content ranges from 7 to 9 ppm with an average of 8 ppm. The
potassium content is ranging between 4.08 % and 4.69 % with an average of 4.53 % . The eU content in
alkali feldspar granite ranges from 5 to 9.8 ppm with an average of 6.86 ppm and the eTh content ranges
from 8 to 16 ppm with an average of 13.25 ppm. The potassium content is ranging between 4.9 % and
4.95 % with an average of 4.70 %.
The picked minerals from the anomalous samples are identified confirmed by environmental Scan
Electron Microscope (ESEM) and XRD techniques at Laboratories of Nuclear Materials Authority
(NMA). The identified minerals are classified to: 1) Secondary uranium minerals (uranophane, autunite
and metautunite), 2) Thorium minerals (uranothorie), 3) Niobium-tantalum minerals (columbite), 4) Base
metals minerals (pyrite) and 5) Accessory minerals bearing U, Th and REEs (zircon, fluorite, monazite,
xenotime, sphene, allanite, apatite and iron oxides).