TITLE:
Mineral Chemistry of Two-Mica Granite Rare Metals: Impact of Geophysics on the Distribution of Uranium Mineralization at El Sela Shear Zone, Egypt
AUTHORS:
Ibrahim Gaafar, Michel Cuney, Ahmed Abdel Gawad
KEYWORDS:
Boreholes, Shear Zone, Radon, Spectrometric, Magnetic, Conductivity
JOURNAL NAME:
Open Journal of Geology,
Vol.4 No.4,
April
21,
2014
ABSTRACT:
The present work aims at
identifying Nb-Ta-, Zr-Hf-, REE-, Th-U-bearing two-mica granite from
geological, geophysical cross-sections and mineral chemistry studies from three
boreholes at G. El Sela shear zone. Microscopically, the three boreholes are
composed mainly of two-mica granite. They are composed of K-feldspar,
plagioclase, quartz, biotite and muscovite. Accessories are pyrite, zircon,
fluorite, rutile, monazite with Th-U-mineralization identified by scanning
electron microscope (SEM) and electron probe-microanalyses (EPMA). Chlorite,
muscovite, sericite, kaolinite are secondary minerals. Geochemically, two-mica
granite boreholes are A-type granites and peraluminous characteristics. They
are enriched in large ion lithophile elements (LILE; Ba, Rb and Sr), high field
strength elements (Y, Zr and Nb), and LREE but depleted in HREE with negative
Eu anomaly. U-enrichment associated with chloritization, muscovitization,
albitization, sericitization, kaolinization and argillization results from
convective hydrothermal circulation of fluids through brittle structures along
the ENE-WSW main shear zone. The ratios Nb/Ta (7.7 - 17.7) and Zr/Hf (16.9 -
26.4) are relatively enriched in the lighter isovalents Ta and Hf. The
accessory minerals observed in the two-mica granites are represented by
metallic sulfides (pyrite, arsenopyrite, chalcopyrite, galena and sphalerite),
Nb-rutile, Hf-zircon, fluorite, monazite, columbite, betafite, thorite,
phosphothorite, uranothorite, brannerite, uraninite, coffinite and pitchblende
at G. El Sela shear zone. Uraninite with a low Th content indicates a
hydrothermal origin of U-mineralization, Thorite, uranothorite, monazite and
zircon is the main uranium bearing minerals of magmatic origin within the
enclosing granite. The primary U-mineralization has been observed in two
boreholes. In order to illustrate the geophysical signature of El Sela
U-mineralization, the radiometric, magnetic, and VLF-EM data as well as radon
concentration are included. The magnetic, electrical conductivity and
radiometric profiles were produced from detailed ground surveys. The shear zone
is characterized by relatively weak levels for both K and eTh, but very high eU
anomalies (