GEOLOGY AND RADIOACTIVITY OF PERALUMINOUS GRANITE AND ASSOCIATED PEGMATITE HOSTING MAGNETITE MINERALIZATION AT UM REGEBA AREA, SOUTHEASTERN DESERT, EGYPT

The study area represents the southeastern part of Wadi El-Gemal-Hafafit culmination in the south
Eastern Desert of Egypt. Magnetite mineralization occurs in Wadi El-Gemal area in many localities, Um
Regeba area is the case study.
Petrographically, the studied peraluminous granites (PG) are medium- to coarse-grained and mainly
composed of plagioclase (An5-10), K-feldspar, quartz, biotite and muscovite. Sericite and chlorite are
secondary minerals, while allanite and zircon are the common accessories. The peraluminous pegmatites
(PP) are coarse-grained and composed essentially of K-feldspar, quartz, plagioclase (An6-10), muscovite and
biotite. Titanite, allanite, zircon and magnetite are common accessories.
Geochemically, the studied peraluminous granites and peraluminous pegmatites are monzogranite and
syeno- to alkali feldspar granite respectively. They have peraluminous character, calc alkaline and alkaline
affinities respectively, emplaced in within plate setting, crystallized under water–vapor pressure (2-3 Kb),
temperature from 760o to 800o C, pertaining to the I-type granite originated by highly differentiated magma
generated from upper mantle contaminated with some crustal materials.
Magnetite usually occurs as small lumps, concentrated by to accumulation in magmatic segregations
that developed in response to fractional crystallization. Magnetite showed lamellar intergrowth with
ilmenite. The latter can be seen with a hand lens in most magnetite samples. The magnetite of Um Regeba
area represents a late stage magmatic product. From the microprobe results, magnetite is characterized by
high content of SiO2, Al2O3, CoO and Cr2O3, whereas ilmenite is characterized by high content of MnO
and ZnO. The average eU content in the peraluminous granites is 1.96 ppm, while it reaches 5.65 ppm for
eTh. The average eU content in the peraluminous pegmatites is 9.12 ppm, while the average eTh content
is 21.76 ppm.