Post on 02-Mar-2023
1 23
Arabian Journal of Geosciences ISSN 1866-7511 Arab J GeosciDOI 10.1007/s12517-011-0506-1
Geochemical characterization of zonedzircon from Wadi Abu Rusheid psammiticgneiss, south Eastern Desert, Egypt
Sayed A. Omar, Hassan A. A. Shahin &Masoud S. Masoud
1 23
Your article is protected by copyright and all
rights are held exclusively by Saudi Society
for Geosciences. This e-offprint is for personal
use only and shall not be self-archived in
electronic repositories. If you wish to self-
archive your work, please use the accepted
author’s version for posting to your own
website or your institution’s repository. You
may further deposit the accepted author’s
version on a funder’s repository at a funder’s
request, provided it is not made publicly
available until 12 months after publication.
ORIGINAL PAPER
Geochemical characterization of zoned zircon from WadiAbu Rusheid psammitic gneiss, south Eastern Desert, Egypt
Sayed A. Omar & Hassan A. A. Shahin &
Masoud S. Masoud
Received: 28 May 2011 /Accepted: 13 December 2011# Saudi Society for Geosciences 2011
Abstract A unique zircon was studied in the gneiss sam-ples collected from the Wadi Abu Rusheid psammitic gneissusing electron scanning microscope and electron probemicroanalyses. This zircon can be categorized into twotypes according to the texture and trace element content:(l) magmatic zircon slightly enriched in HfO2 with ordinaryzone. (2) Overgrowths of zircon occur as two species, thefirst species being highly enriched in HfO2 with irregularzoning. The second species is highly enriched in HfO2
forming a rim around the second species with a very sharpthinner boundary. The first type shows a distinct oscillatoryinternal zoning pattern without change in shape of this zoneand has conspicuous inclusion-free zircon overgrowths withdistinct poor concentrations in Y, Hf, Th, U, Nb, and Ta inboth rim and core. The second type shows two species, thefirst one displays distinct irregular interval zoning and irreg-ular overgrowth with abrupt change in composition of thesezones with distinct enrichment in Y, Hf, Th, U, Nb, and Tain the rim relative to the core. The second species is forminga rim around the first species also with distinct enrichmentin Y, Hf, Th, U, Nb, and Ta content. These indicate that twoevents (crystallization environment) have played an impor-tant role in the formation of this zircon and largely reflectdifferences in whole-rock trace element contents betweenthe successive generations of this zircon. The first event isbelieved to be of magmatic origin giving rise to normalcomposition of magmatic zircon. The second event showsan intense successive process of metasomatic activity during theformation of the Abu Rusheid radioactive gneiss. Electronmicroprobe analysis indicates that oscillatory zoned zircon
shows poor content of Y, Hf, Th, U, Nb, Ta, and rare earthelements (REE) in the rim and core, while overgrowths ofzircon are slightly enriched by these elements. Also, theseanalyses indicate that the Abu Rusheid psammitic gneiss hasbeen significantly enriched by the thoritemineral (Th content upto 54.72% ThO2) and columbite-bearing minerals (Nb contentup to 64.74%Nb2O5, Ta content up to 9.32% Ta2O5). The poorcontent of REE in overgrowths of zircon indicates mobilizationof REE during the metamorphism processes of gneiss.
Keywords Zoned zircon . Psammitic gneiss . Egypt
Introduction
Zircon is a chemically inert mineral that can survive theprocesses of weathering, transportation, diagenesis, metamor-phism, and even crustal melting (Luo et al. 2009). Magmaticzircon incorporates minor and trace amounts of geochemicallyimportant lithophile elements such as Sc, Y, Ti, Hf, Th, U, Nb,Ta, V, P, and the rare earth elements (REE) (Hinton and Upton1991). Zircon contains trace amounts of uranium and thorium(from 10 ppm up to 1 wt.%) and can be dated using severalmodern analytical techniques, e.g., isotopic and fission-trackgeochronology, and for geochemical tracer studies (Sawka1988; Bea 1996; O'Hara et al. 2001). Because of this, zirconcan contain a rich and varied record of geological processes.Hafnium (Hf) is a particularly important minor element inzircon, because its isotopic composition is a sensitive tracerof crustal and mantle processes (e.g., Taylor and McLennan1985; Vervoort and Blichert-Toft 1999).
A unique type of zircon occurs in the radioactive psam-mitic gneiss of the Wadi Abu Rusheid area which is locatedwithin the basin of Wadi Al Gemal in the south EasternDesert, at a distance of about 70 km southwest of Marsa
S. A. Omar :H. A. A. Shahin (*) :M. S. MasoudNuclear Materials Authority,P. O. Box 530, El-Maadi Cairo, Egypte-mail: hassanshahin03@Yahoo.com
Arab J GeosciDOI 10.1007/s12517-011-0506-1
Author's personal copy
Fig. 1 Location map and Google image for the Abu Rusheid area
Fig. 2 Geologic map for theWadi Abu Rusheid area, afterDawood (2010)
Arab J Geosci
Author's personal copy
Alam, along the Red Sea coast at latitude 24°35′ to 24°40′and longitude 34°40′ to 34°50′. (Fig. 1).
Geomorphologically, the area is characterized by rough,steep slopes and rugged mountains dissected by severalwadis including Wadi Nugrus, Wadi Abu Rusheid, andWadi Sikait. The area was studied geologically, minera-logically, and radiometrically by numerous authors (Ball1912; Akaad and El-Ramly 1960; Basta and Zaki 1961;Hassan 1964; El-Shazly and Hassan 1972; Hassan 1973;El-Gemmizi 1979; Hassan et al. 1983; Hassan and El-Gemmizi 1985; Hilmy et al. 1990; Mohamed and Hassanen1997; Raslan 2008; Assran 2009; Ibrahim et al. 2007, 2010a, b,and Dawood 2010).
This paper focuses on textures and trace element contentsof a unique zoned zircon from the Wadi Abu Rusheidpsammitic gneiss.
Geologic setting
The Abu Rusheid area is a part of the Arabian-NubianShield and can be considered a key domain in that shield,beside its very complex structures. This area lies in the WadiAl Gemal basin and hosts a wealth of sources of uraniumand other nuclear elements. In addition, this area is consid-ered as the southeastern extension of the Migif–Hafafitmetamorphic complex (El Ramly and Akaad 1960; Hassan1964; El-Shazly and Hassan 1972; Hassan and Hashad1990), which is highly tectonized and shows the featuresof the multiple types of mineralization and alteration pro-cesses in long time spans. The Migif–Hafafit metamorphiccomplex represents one of three major domal structures inthe Eastern Desert of Egypt (Fowler and Kalioubi 2002 andAbd El-Naby et al. 2008). The geology of the Hafafit area
Fig. 3 Photomicrograph showing zircon crystals surrounded by a regular rim. Under crossed polars
Arab J Geosci
Author's personal copy
Tab
le1
Microprob
eanalyses
(weigh
tpercent)of
zircon
sfrom
theWadiAbu
Rusheid
gneiss
S.No.
SiO
2Al 2O3
TiO
2MgO
CaO
P2O5
ThO
2UO2
ZrO
2PbO
Y2O3
La 2O3
Ce 2O3
Nd 2O3
Gd 2O3
Yb 2O3
HfO
2S
Ta 2O5
Nb 2O5
Pr 2O3
SmO
Total
114-6-1
31.077
00.01
20.00
80.01
30
00
68.452
0.08
10.09
40
00.18
0.16
20.114
0.86
10
00
0.00
40
101.05
7
114-6-3
30.437
00.12
20.00
20.09
20
00.07
167
.109
0.03
51.39
60
00.27
70.23
0.29
91.00
60
00
00.12
101.19
6
114-1-1
31.95
0.01
50.07
30
0.00
90
00.18
765
.768
00.16
70
00.10
60
0.01
61.37
90.00
60
00.03
40
99.709
GE7-9-3
28.503
0.08
50.02
60.03
0.119
00.011
0.46
463
.287
00.62
70
00
00.74
32.74
40.00
90
00.10
40
96.751
GE7-9-3
29.176
0.13
0.04
90
0.08
00
0.44
862
.834
00.32
20.00
90
00
0.59
52.50
90.05
10
00
0.08
296
.284
GE7-9-3
29.788
0.22
10.06
50.01
80.12
90
0.19
80.28
264
.245
00.51
30
00.18
80.02
40.75
32.40
20.03
10
00
098
.858
GE7-9-3
29.61
0.08
60.06
20.00
40.07
90
00.20
564
.868
0.10
60.19
90
00.05
20
0.43
32.94
70.03
40
00
098
.686
GE7-9-4
15.138
0.29
0.06
10.01
71.19
21.78
150
.393
4.60
46.48
20.02
95.73
10
00
0.14
51.55
0.16
30.03
60
0.29
80
0.09
88
GE7-9-5
16.251
00.05
10.04
81.17
12.02
251
.443
4.72
66.35
0.15
56.18
90
00.07
01.45
10.06
10.05
90
0.59
70.05
30
90.697
GE7-9-6
14.245
0.17
20.03
10.03
60.94
1.57
443
.69
3.411
4.28
60.19
34.61
70
00
00.77
10.24
30.07
30
0.59
90
0.01
474
.896
GE7-9-7
16.43
0.23
10.10
90.04
1.20
51.94
153
.622
3.66
15.01
70.02
15.09
90
00
01.30
10.03
50.05
90
0.55
30.04
20.24
689
.613
GE7-9-8
15.417
0.23
50.10
30.05
71.19
31.82
154
.663
4.03
44.75
60.35
25.15
90
00.08
80.10
41.22
30.34
30.08
40
0.61
20.05
20.12
990
.425
GE7-9-9
12.099
0.08
50.01
0.05
50.9
1.34
448
.495
2.93
43.58
70.20
63.87
60
00.12
10
1.47
0.13
60.04
60
0.45
20.08
40
75.9
GE7-9-10
16.973
0.24
50.00
90.03
61.211
1.84
853
.154
2.78
5.26
70.18
66.37
0.05
00
0.48
41.54
40
0.06
40
0.27
20.04
10.03
290
.566
GE7-9-11
16.984
0.22
40.07
50.03
61.16
81.99
652
.151
3.85
56.17
30
5.88
30
00.07
20.12
91.60
30.27
80.05
70
0.89
30.09
70
91.674
GE7-9-12
15.891
0.17
30.07
70.05
21.18
81.95
254
.721
4.00
36.41
90.22
35.85
50.00
90
0.09
80.31
91.06
70.38
0.04
90
0.39
20
0.08
492
.953
GE7-9-13
27.838
0.28
90.03
30
0.27
80
0.01
40.45
261
.713
0.08
1.03
40
00.20
30
1.27
52.49
50.00
40
00.05
095
.758
GE7-9-14
29.721
00.01
20
00
0.04
90
57.397
0.02
60.06
70
00.08
70
0.90
910
.992
0.03
40
00
0.06
199
.356
GE7-11-9
30.522
0.06
30.03
60.01
70.06
40
00.17
163
.006
0.09
0.112
00
00
0.29
85.45
60.01
70
00
0.14
399
.994
GE7-11-
1029
.691
0.08
80.00
70.00
30.115
00.111
0.23
362
.578
0.07
40.62
90
00.10
20.03
70.66
43.44
10.03
70
0.13
20
097
.94
GE7-13
-125
.914
0.57
30.04
70.05
0.43
20
0.15
50.65
357
.198
0.03
33.04
70
00
0.29
51.58
32.17
20.04
70
0.00
20
092
.201
GE7-13
-229
.282
0.41
50.00
20.01
50.37
90
0.02
10.33
861
.28
01.37
90.01
00
00.84
52.33
50
00
0.08
10.05
796
.437
GE7-13
-330
.469
0.03
0.04
10.00
90.07
30
0.13
30.33
464
.734
00.38
60
00
0.07
90.69
42.96
30.02
50
00.07
20
100.04
2
GE7-12
-130
.193
0.07
60.00
80.00
70.04
30
0.07
20.10
563
.412
0.14
0.10
40
00.05
50
0.30
24.64
60
00
00.00
499
.165
GE7-12
-130
.14
0.14
70.00
50
0.09
50
0.111
0.12
63.135
0.14
0.411
00
0.04
50.02
0.51
95.18
90.04
60
00.00
90.04
410
0.17
5
GE7-12
-131
.098
0.02
50.02
60
0.03
90
0.05
40.08
463
.723
00
00
0.08
60.10
30
5.56
80.03
70
00
0.05
110
0.89
2
GE7-12
-128
.769
0.17
40.08
50.02
40.25
70
00.22
763
.055
0.02
80.92
60
00.06
50.01
80.92
62.18
40.00
50
0.06
40.00
20.14
796
.957
GE7-12
-130
.083
00.07
30
0.111
00.07
30.40
563
.819
00.42
20
00.06
80
0.54
2.14
30.02
80
0.13
90.01
80.01
797
.938
GE7-12
-129
.838
00
0.02
40.15
50
0.04
90.39
63.175
0.04
70.46
30
00.12
40.23
10.95
2.71
50
00
0.00
20
98.161
GE7-12
-130
.614
0.02
80.04
30.01
20
00.01
80.14
261
.103
00
00
00.16
0.50
68.26
40.02
80
00.07
20
100.99
1
GE7-12
-230
.721
00
0.00
60.01
20
00.16
163
.989
00
00
00.11
0.29
35.35
40
00
0.07
70.04
910
0.77
3
Arab J Geosci
Author's personal copy
has been described as the Hafafit and Nugrus unitsseparated by Nugrus Thrust and undeformed leucogranites(Abd El-Naby and Frisch 2006).
The Hafafit unit (western unit) consists of Hafafitdomes which include from core to rim granite gneiss oftonalitic and trondhjemitic composition, banded am-phibolite which is overthrusted by ultramafic rocks,alternating bands of biotite and hornblende gneiss,and the psammitic gneisses at the rim of the domalstructure. The Nugrus unit (eastern unit) is composedmainly of low-grade mica schists and metavolcanicsand related volcaniclastics. The Hafafit and Nugrus unitshave been intruded by undeformed leucogranites, especiallyalong thrust zones.
The main rock units encountered in the Abu Rusheid areaare represented by metasediments, ophiolitic melange,amphibolites, metagabbros, hornblende gneisses, psammiticgneisses, undeformed leucogranites, and pink granites(Fig. 2). This area is located between two major thrusts tothe NE. The metasediments are represented mainly by NE–SW elongated separated masses of pale gray highly foliatedmica schist locally thrusted over the psammitic gneisses.The ophiolitic melange comprises a metamorphosed sed-imentary matrix enclosing amphibolite sheets, serpentin-ite and gabbroic masses, as well as quartzitic bands.Amphibolites and metagabbros are probably related tothe calc-alkaline metagabbros associated with Hafafit gneisses(El Ramly et al. 1993). The hornblende gneisses are formed ofNW elongated mass, gray–green in color, coarse to mediumgrained, and highly foliated.
Abu Rusheid gneisses were studied by many authors.They identify it as psammitic gneisses (Hassan 1973; AbdEl-Monem and Hurley 1979; Hilmy et al. 1990; Abd El-Naby and Frisch 2006 and Dawood 2010). Some authorsdescribed these rocks as gneissic granites (Ibrahim et al.2000; Raslan 2008) and cataclastic granites (Ibrahim et al.2007). The effects of the hydrothermal solutions on the AbuRusheid gneisses were reported by El-Shazly and Hassan(1972), Hassan (1973), Abd El-Monem and Hurley(1979), and Ibrahim et al. (2000). The gneisses exhibitextensive alteration, including silicification, sericitization,kaolinitization, chloritization, hematitization, and limonitiza-tion (Abd El-Naby et al. 2008). These alterations are closelyassociated with the shear zones indicating that some ofthese fractures have worked as channel ways for meta-somatizing fluids.
Leucogranites are pink granites and minor intrusions offelsite and aplite. The younger granites are locally devel-oped along thrust faults and contain numerous enclavesfrom older rocks particularly mica schist. Generally, theleucogranites are medium to course grained, composedmainly of quartz, K-feldspar, plagioclase, garnet, biotite,and muscovite. T
able
2Microprob
eanalyses
(weigh
tpercent)of
Nb-Tafrom
theWadiAbu
Rusheid
gneiss
S.No.
SiO
2Al 2O3
TiO
2MgO
CaO
P2O5
ThO
2UO2
ZrO
2PbO
Y2O3
La 2O3
Ce 2O3
Nd 2O3
Gd 2O3
Yb 2O3
HfO
2S
Ta 2O5
Nb 2O5
Pr 2O3
SmO
Total
GE7-10
-10
00.42
40.02
70.011
00.00
80
00.07
90.12
40.05
40
00
00
0.03
47.25
969
.344
00.119
77.482
GE7-10
-10
00.54
80
0.03
50
00
00.114
0.18
50.01
20
0.03
00.27
70.19
20.011
8.33
968
.885
00.09
78.717
GE7-10
-113
.106
0.24
93.75
20.12
82.16
0.09
81.32
642
.082
0.00
80.59
90
00
00.05
90.16
60
0.00
70
12.503
00.03
976
.28
GE7-10
-10.21
0.04
90.52
50
0.05
90.01
80.05
40.01
20
0.04
90.19
30
00
0.13
10.06
10.03
90.01
35.61
662
.719
00
69.748
GE7-10
-10
00.53
90.00
60.03
90.00
30
00
0.46
10.18
90
00
00.117
00.01
37.28
671
.383
00.23
880
.274
GE7-10
-20
00.43
00.011
0.011
00
00.35
60.16
20
00
0.11
0.115
0.17
30.00
27.19
271
.104
00.07
879
.744
GE7-11-1
00
0.41
30
0.00
50
0.00
70
00.21
30.04
50
00.03
60
0.31
90.17
30.00
17.02
371
.676
0.01
40.00
179
.927
GE7-11-2
0.04
60.02
30.46
40
00.01
60.04
90.05
20
0.49
50.19
10
00
00.02
70
0.01
36.88
170
.608
00
78.866
GE7-11-3
00.011
0.45
80
0.03
50.00
10
0.07
10
0.21
20.20
60
00.12
50
0.02
60.115
0.05
7.69
369
.727
00
78.73
GE7-11-4
00
0.40
30
0.01
90
00
00.09
80.10
20
00
00.05
0.13
50.00
17.04
969
.541
00
77.399
GE7-11-5
00
0.41
70.01
90.02
30.02
30
0.01
40
0.41
70.09
80
00.06
40
0.01
30.14
40
7.62
270
.812
00.115
79.781
GE7-11-6
00
0.51
50
0.02
70
00
00.40
40.03
40
00.02
60
00.115
08.24
968
.922
00
78.292
GE7-11-7
00
0.52
0.00
30
00.07
40
00.27
30.14
30.01
40
0.14
40.04
70
0.04
80.01
28.20
770
.185
00
79.67
GE7-11-8
00.00
10.76
10
0.03
30.02
10
0.22
90
0.24
0.21
40
00
0.10
20
00
6.51
669
.509
00.01
777
.645
GE7-11-9
00.011
0.39
30
0.02
60
0.04
0.00
60
0.28
20.13
00
00
0.35
50.29
70
7.02
970
.064
0.03
20
78.665
Arab J Geosci
Author's personal copy
Zircon occurrence
The topmost 50 m of the psammitic gneiss is radioactive andhosts a great number of economic minerals of uranium, suchas Th, Nb, Ta, Zr, and Hf (Hassan 1973; Bugrov et al. 1973;
Krs et al. 1973; Hassan et al. 1983; and El-Gemmizi 1984).Among these minerals, a unique type of zircon with abnor-mally high content of hafnium was recorded which may beused as a fingerprint of geological history and a good source ofhafnium in this area. El-Gemmizi (1984) called it mud zircon.
(b)
(a)
1O
2O
1O Beam No.
Fig. 4 a Back-scattered electron image showing traverse section in magmatic zircon. b Bar diagram showing the electron microprobe analyses forthe same crystal
1O
1O Beam No.
2O
3O
4O
5O
6O
7O
(a)
(b)
Fig. 5 a BSE image showing traverse section in overgrowths of zircon without rim. b Bar diagram showing the electron microprobe analyses forthe same crystal
Arab J Geosci
Author's personal copy
Zircon textural features
Two types of zircon were distinguished from the studiedsamples, magmatic zircon and overgrowths of zircon. Thesezircons are prismatic grains with bipyramidal terminationsintergrown, mostly are subhedral to euhedral crystals asso-ciated with quartz, plagioclase, and biotite.
Magmatic zircon occurs as euhedral prismatic crystals upto 200 μm in size, mostly as subhedral to euhedral crystals.This zircon shows an oscillatory internal zoning patternwithout change in composition in these zones and has con-spicuously inclusion-free zircon overgrowths. Overgrowthsof zircon occur as pale yellow to pale brown prismaticgrains with bipyramidal terminations intergrown, mostly
(b)
(a)
6O
1O
2O1
O Beam No.
3O
4O
5O
7O
8O
9O
Fig. 6 a BSE image showing traverse section in overgrowths of zircon with rim. b Bar diagram showing the electron microprobe analyses for thesame crystal
1O 2
O
1OPeam No.
3O
(a)
(b)
Fig. 7 a BSE image showing traverse section in overgrowths of zircon with rim. b Bar diagram showing the electron microprobe analyses for thesame crystal
Arab J Geosci
Author's personal copy
subhedral to euhedral crystals reaching up >400 μm in thelongest dimension. The crystals are composed of a core,which is forming themain body of the crystal, and a rim whichforms an outside cover of the core. The core is irregularlyzoned, with irregular and gradation boundaries between colorsof blue, red, and brown. The rim is much thinner than thezoned core and surrounds it with a very sharp contact; its coloris very light blue to deeper blue resembling the intensity of thedeep blue of the core. Most of the crystals of this zircon arecomplex, forming more than two twins; others are irregular inshape and have an irregular boundary and contain many
inclusions of the co-existing minerals (Fig. 3). From theseobservations, we conclude that the core and the rim wereformed during two phases of metasomatism, probably withdifferent intensity, duration, and chemical reactions.
Zircon chemistry
The zircon from the Abu Rusheid area was analyzed using aCAMECA SX-100 electron-probe microanalyzer methodwith four wavelength-dispersive spectrometers at the Centre
(a)
(b)
9O
1O
2O
3O
4O
5O
6O
1O Beam No.
7O
8O
12O 10
O
11O
Fig. 8 a EDX and BSE image showing the semi-quantitative chemical composition of thorite. b Bar diagram showing the electron microprobeanalyses for the same crystal
Arab J Geosci
Author's personal copy
de Recherches Petrographiques et Geochimiques, Nancy,France. Analyses were performed using an acceleratingpotential of 15 to 20 kv and a beam current of 10 nA(Tables 1 and 2). From all zircons studied using scan-ning electron microscope (SEM) with a back-scattered elec-tron (BSE) imaging and electron probe microanalyses
(EPMA), two patterns were detectable: (l) zircon withdistinct poor concentrations in Hf, Th, U, Nb, and Ta inboth rim and core and (2) zircon with abrupt change incomposition of these zones and distinct enrichment inHf, Th, U, Nb, and Ta in the rim relative to the core(Figs. 4, 5, 6, 7, and 8).
(a)
(b)
1O
2O
3O
4O
5O
6O
1O Beam No.
Fig. 9 a EDX and BSE image showing the semi-quantitative chemical composition of columbite. b Bar diagram showing the electron microprobeanalyses for the same mineral
Arab J Geosci
Author's personal copy
Niobium and tantalum multiple-oxide minerals such ascolumbite associated with zircon in the uppermost divisionof psammitic gneiss. Columbite (Fe, Mn)Nb2O5 occurs inminute crystals disseminated in this gneiss particularly inthe parts that were affected by the metasomatism process.Columbite was studied using SEM with a BSE imaging andEPMA (Fig. 9a and b). Metamict zircon and columbitecould be also considered as additional sources for uranium(Finch and Murakami 1999; El-Kammar et al. 2001).
Conclusion
Textural and geochemical characteristics of zircon hosted atthe Wadi Abu Rusheid gneiss indicate two types according tothe texture and trace element content: (l) magmatic zirconslightly enriched in HfO2 with ordinary zoning and (2) over-growths of zircon that show two species, the first one beinghighly enriched in HfO2 with irregular zoning. The secondspecies is highly enriched also in HfO2 forming a thinner rimaround the second species with a very sharp boundary. Theprevious two types indicate two events reflecting largely theenvironments in which they were formed.
The first type seems to be ordinary zircon which occurswidely as an accessory mineral in many igneous rocks andhas suffered transportation and deposition and a detritus insedimentary rocks, which was later metamorphosed to givethe psammitic gneiss of Haffafit metamorphic succession.This zircon is characterized by distinct oscillatory internalzoning without change in composition of these zones andhas conspicuously inclusion-free zircon overgrowths withdistinct poor concentrations in Y, Ti, Hf, Th, U, Nb, and Tain both rim and core. This zircon is believed to be of magmaticorigin giving rise to normal composition of magmatic zircon.
The second type is the most abundant and forms the maincomponent of this zircon and indicates a long, intense, andvariable stage of metasomatic activity during the formationof the mineralization in the Abu Rusheid radioactive gneiss.This activity is probably associated with the Pan Africanevent with a high degree of Zr development in a hydrothermalenvironment with distinct enriched zircon in Y, Ti, Hf, Th, U,Nb, and Ta. The metasomatic effect during this event isbelieved to be prevailing during most of the Pan Africanorogeny (Hassan 1973; Hassan and Hashad 1990). This meta-somatic activity is giving rise to development overgrowthzircon which occurs as two species.
The large difference in Hf content between the magmaticzircon of the first type on the one hand and the overgrowthsof zircon of the second type on the other hand may alsosupport the previous two events which reflect different fluidsources for each. The previous two events are also compat-ible with the isochron age of the Wadi Abu Rusheid gneiss,where Abd el-Monem and Hurley (1979) determined an age
of 1,770±40 Ma for the detrital zircon from the psammiticgneiss of Wadi Abu Rusheid and Wadi Sikait. This agerepresents the age of old sediments deposited before thepsammitic gneiss formed and reflects that this zircon is olderin age than the psammitic gneiss and may be derived fromthe weathering of peri-existing felsic rocks. Therefore, thisage is believed to be corresponding to the first event (mag-matic zircon). Hashad et al. (1972) obtained an Rb–Sr age of590±20 Ma for mica separated from the white granite, andHashad et al. (1981) obtained an Rb–Sr age of 600 Ma formica separated from the psammitic gneiss. These two agesof Hashad et al. (1972, 1981) are representing successiveevents of strong metamorphism processes that took place onthe psammitic gneiss of the Abu Rusheid area, where thewhite granite intruded the psammitic gneiss causing strongmetasomatism. This metasomatism enriched the psammiticgneiss by radioactive rare earth elements and radioactiveminerals. Therefore, these ages are believed to becorresponding to the second event (overgrowths of zircon)in the Abu Rusheid psammitic gneiss. These overgrowths ofzircons of the Abu Rusheid psammitic gneiss are also com-patible with Gulson and Krogh (1975) who determined thatzircon overgrowths are related to post-tectonic intrusions inigneous and high-grade metamorphic rocks.
Acknowledgments Thanks are due to the Centre de RecherchesPetrographiques et Geochimiques, Nancy, France, for use of theirelectron microprobe. Many thanks go to Prof. Dr. Mamdouh Hassan,Nuclear Materials Authority (NMA), Egypt, for revising the manuscriptand his constructive remarks.
References
Abd El-Monem AA and Hurley PM (1979) U-Pb dating of zircon frompsammitic gneisses, wadi Abu Rusheid-wadi Sikait area, Egypt.Proceeding of the Symposium on the Evolution and Mineralizationof the Arabian-Nubian Sheild 2:70–165
Abd El-Naby H, Frisch W (2006) Geochemical constraints from theHafafit Metamorphic Complex (HMC): evidence of Neoproterozoicback-arc basin development in the central Eastern Desert of Egypt. JAfr Earth Sci 45:173–186
Abd El-Naby H, Frisch W, Siebel W (2008) Tectono-metamorphicevolution of the Wadi Hafafit Culmination (central eastern desert,Egypt). Implication for Neoproterozoic core complex exhumationin NE Africa. Geol Acta 6(4):293–312
Akaad MK, El-Ramly MF (1960) Geological history and classificationof the basement rocks of the central Eastern Desert of Egypt. GeolSurv Egypt 9:24
Assran ASM, Omran MA, Ibrahim ME, Hassan MA, Mansour GR(2009) Horizontal loop electromagnetic and self-potential signaturesof mineralized structures: a case study from Abu Rusheid Area,Southeastern Desert, Egypt. Earth Sci 20(2):27–43
Ball J (1912) The geography and geology of south Eastern Egypt.Survey Dept, Cairo, p 121
Basta EZ, Zaki M (1961) Geology and mineralization of wadi Sikaitarea, south Eastern Desert. J Geol UAR 5(1):1–38
Arab J Geosci
Author's personal copy
Bea F (1996) Residence of REE, Y, Th and U in granites and crustalprotoliths; implications for the chemistry of crustal melts. J Petrol37:521–552
Bugrov VA, Abu El Gadeal A, Soliman MM (1973) Rare-metallicalbite as a new type of ore mineralization in Egypt. Annals GeolSurv Egypt VIII:185–206
Dawood YH (2010) Mineral chemistry and genesis of uranyl mineralsassociated with psammitic gneisses, Abu Rusheid Area, SouthEastern Desert of Egypt. Earth Sci 21(1):137–169
El Ramly MF and Akaad MK (1960) The basement complex in theCentral-Eastern Desert of Egypt between latitudes 24° 30′ and 25°40′. N Geol Surv Egypt 8–35
El Ramly MF, Greiling RO, Rashwan AA and Rasmy AH (1993)Explanatory note to accompany the geological and structuralmaps of Wadi Hafafit area, Eastern Desert of Egypt. GeologicalSurvey of Egypt, Paper No. 68
El-Gemmizi MA (1979) The mineralogy and concentration of heavyminerals from the psammitic gneiss of Wadi Nugrus-Wadi Sikaitarea, Eastern Desert, Egypt. Ph D. thesis, Faculty of Science,Cairo University
El-GemmiziMA (1984)On the occurrence and genesis ofmud zircon in theradioactive psammitic gneiss of wadi Nugrus, Eastern Desert, Egypt
El-Kammar AM, Salman AE, Shalaby MH, Mahdy AI (2001) Geo-chemical and genetical constraints on rare metals mineralization atthe central Eastern Desert of Egypt. Geochem J 35(2):117–135
El-Shazly EM, Hassan MA (1972) Geology and radioactive minerali-zation at Wadi Sikait-Wadi El-Gemal area, south Eastern Desert.Egypt J Geol 16(2):201
Finch RJ and Murakami T (1999) Systematics and paragenesis ofuranium minerals. In: PC Burns and R Finch (eds) Uranium:mineralogy, geochemistry and the environment, 38, p. 91–180.Reviews in Mineralogy and Geochemistry, Mineralogical Societyof America, Chantilly, Virginia
Fowler A, El Kalioubi B (2002) The Migif-Hafafit gneissic complex ofthe Egyptian Eastern Desert: fold interference patterns involvingmultiply deformed sheath folds. Tectonophysics 346:247–275
Gulson BL, Krogh TE (1975) Evidence of multiple intrusion, possibleresetting of U-Pb ages, and new crystallization of zircons in thepost-tectonicin trusions (“rapakivi granites”) and gneissefsr omSouth Greenland. Geochim Cosmochim Acta 39:65–82
Hashad AH, Sayyah TA, El-Kholy SB, Youeseff A (1972) Rb-Srisotopic age determination of some basement Egyptian granites.Egypt J Geol 16:269–281
Hashad AH, Sayah TA, El-Reedy MWM (1981) Geochronological andstrontium isotope study of the psammitic gneiss of Wadi nugrus,Eastern Desert, Egypt. J Geol 25:58–149
Hassan MA (1964) Geology and petrographical studies of the radioactiveminerals and rocks inWadi Sikait-Wadi El-Gemal area EasternDesert,U.A.R. M. Sc thesis, Faculty of Science, Cairo University. 165 p
Hassan MA (1973) Geology and geochemistry of radioactivecolumbite-bearing psammitic gneiss of wadi Abu Rusheid. SouthEastern Desert, Egypt. Annals Geol Surv Egypt VIII:207–225
Hassan MA, El-Gemmizi MA (1985) Zircon in the metamorphic rocksof Wadi Nugrus, Eastern Desert, Egypt and its bearing on theirorigin. Annal Geol Surv Egypt XV:137–1147
Hassan MA, Hashad AH (1990) Precambrian of Egypt. In: Said R (ed)The geology of Egypt. Balkema, Rotterdam, pp 201–245
Hassan MA, Aly MM, Eid AS (1983) Petrographical and geochemicalstudies on the radioactive psammatic gneiss of Wadi Abu Rusheid,Eastern Desert, Egypt. Annal Geol Surv Egypt V. XIII:143–155
Hilmy ME, El Bayoumi RM, Eid AS (1990) Geology, geochemistryand mineralization of the psammitic gneiss of Wadi Abu-Rusheid,Eastern Desert, Egypt. J Afr Earth Sci 2:197–205
Hinton RW, Upton BGJ (1991) The chemistry of zircon: variationswithin and between large crystals from syenite and alkali basaltxenoliths. Geochim Cosmochim Acta 55:3287–3302
Ibrahim ME, Assaf HS, Saleh GM (2000) Geochemical alteration andspectrometric analysis in Abu Rusheid altered uraniferous gneissosegranites, south Eastern Desert, Egypt. Chieme der Erde 60:173–188
Ibrahim ME, El-Tokhi MM, Saleh GM, Hassan MA, Rashed MA(2007) Geochemistry of lamprophyres associated with uraniummineralization, Southeastern Desert, Egypt. Chin J Geochem 26(4). doi:10.1007/s11631-007-0356-4
Ibrahim ME, Saleh GM, Dawood NA, Aly GM (2010a) Ocellar lamp-rophyre dyke bearing mineralization, Wadi Nugrus, Eastern Desert,Egypt: Geology, mineralogy and geochemical implications. J GeolMin Res 2(4):74–86
IbrahimME, SalehGM, IbrahimWS (2010b) Low grademetamorphosedsandstone-type uranium deposit, Wadi Sikait, South Eastern Desert,Egypt. J Geol Min Res 2(6):129–141
Krs M, Soliman AAH, Amin AH (1973) Geophysical phenomena overdeep-seated tectonic zones on southern part of Eastern Desert ofEgypt. Annals Geol Surv Egypt VIII:125–238
LuoY, YinQZ, Ayers JC, Ryerson F and Hutcheon I (2009) Experimentalmeasurements of zircon/melt trace element partitioncoefficients: keyissues and possible solutions with nano-sims
Mohamed FH, Hassanen MA (1997) Geochemistry and petrogenesisof Sikait leucogranite, Egypt: an example of S-type granite in ametapelitic sequence. Int J Earth Sci 86(1):81–92
O'Hara MJ, Fry N, Prichard HM (2001) Minor phases as carriers oftrace elements in non-modal crystal-liquid separation processes II:illustrations and bearing on behaviour of REE, U, Th and the PGEin igneous processes. J Petrol 42:1887–1910
Raslan M (2008) Occurrence of Ishikawaite (Uranium-Rich Samarskite)in the mineralized Abu Rushied Gneiss, Southeastern Desert, Egypt.Int Geol Rev 50(12):1132–1140
SawkaWN (1988) REE and trace element variation in accessory mineralsand hornblende from the strongly zonedMcMurryMeadows Pluton,California. Trans Roy Soc Edinburgh Earth Sci 79:157–168
Taylor SR, McLennan SM (1985) The continental crust: its compositionand evolution. Blackwell Scientific, Oxford, p 312
Vervoort JD, Blichert-Toft J (1999) Evolution of the depleted mantle:Hf isotope evidence from juvenile rocks through time. GeochimCosmochim Acta 63:533–556
Arab J Geosci
Author's personal copy