TITLE:
Geophysical Mapping, Geochemical Evidence and Mineralogy for Nuweibi Rare Metal Albite Granite, Eastern Desert, Egypt
AUTHORS:
Ibrahim Gaafar
KEYWORDS:
Albite, Spectrometric, Magnetic, Columbo-Tantalite, Ixiolite, Thorite
JOURNAL NAME:
Open Journal of Geology,
Vol.4 No.4,
April
21,
2014
ABSTRACT:
The present study aims to
shed light on the rare metals of Nuweibiareaalbite granite in the Eastern
Desert through the chemical analyses of the two types of fine-grained albite
granite (FAG) and medium-grained albite granite (MAG) in addition to
mineralogical studies as well as ground spectrometric survey and aeromagnetic
mapping. On the basis of ground spectrometric measurements K, eUand eTh
distribution maps were obtained. The concentration of K, U and Th content shows
maxima (4.5%, 13 ppm and 27 ppm on average, respectively) in the FAG, and
(4.5%, 10 ppm and 35 ppm on average) in the MAG. The eU/eTh ratio significantly
increases in FAG with higher magma differentiation than MAG reaching 0.63. This
paper uses magnetic geophysical methods to investigate geometry and sense of
motion across the Nuweibi area. The interpreted structures from the magnetic
maps are characterized by two main intersecting sets of NW-SE and NE-SW
trending faults in addition to other three minor faults that trend in N-S,
NNW-SSE and ENE-WSW directions. The NW-SE trending faults represent the recent
sets in the study area where they are dissected and displaced by the other old
faults. The Werner depth map shows the interface depths of the granite and
basement rocks that extend to great depths ranging from 10 to 380 m. FAG is
extended underneath most of the surrounding schist rocks because of their
attributed low magnetic intensity that confirmed also with drilling. Microscope
and Microprobe analyses indicated that the most important radioactive minerals
include uranothorite, thorite, zircon, and monazite. Columbite group minerals
represent the most common Nb-Ta host in Nuweibi-albite granites that contain
significant levels of Ta (up to 65.4 wt. % Ta2O5) and Nb
(up to 60 wt. % Nb2O5), with Ta/(Ta+Nb) ratio ranging
from 0.17 to 0.84. Columbite group minerals are represented mostly by columbite-(Mn)
and tantalite-(Mn), with Mn/(Mn+Fe) ratio ranging from 0.42 to 0.89. Ixiolite,
wodgnite and tapiolite-(Mn) were found only in the FAG indicating the final
stages of the evolution of parental granitic magma. The U-Th and U-K variation
diagrams suggested that magmatic processes controlled the distribution of these
elements. The Scanning Electron-microprobe analyses reveal variable
compositions and extents between the MAG and FAG in the Nb, Ta-Ti, Sn-Fe, Mn
triangular plot. It is worthy to be noted that because of the higher Ta/Nb
ratio in the tapiolite-Mn and ixiolite of FAG in comparison with the coexisting
Mn-columbite in the MAG, levels of HfO2 greater than 15% and even attaining
23%, characterized the hafnium zircon in the Nwueibialbite-enriched facies.
There is a close correlation between Hf/(Hf + Zr) and Ta/(Nb + Ta) which seems
mainly associated with the FAG.