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International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
An Open Access, Online International Journal Available at http://www.cibtech.org/jgee.htm
2017 Vol. 7 (1) January-April, pp. 65-80/Raslan et al.
Research Article
Centre for Info Bio Technology (CIBTech) 65
MINERALOGY OF MINERALIZED PEGMATITE OF RAS MOHAMED
GRANITE, SOUTHERN SINAI, EGYPT
Mohamed F. Raslan, ٭Mona M. Fawzy and Hanaa A. Abu-Khoziem Nuclear Materials Authority, Cairo, Egypt
Author for Correspondence٭
ABSTRACT
An economically important rare-metal mineralization is recorded in the mineralized pegmatite injected in
alkali-feldspar microgranite of Gabal Samma at North Ras Mohammed granitic pluton, Southern Sinai,
Egypt. The studied mineralization was found as distinguishable megascopic crystals scattered within the
pegmatitic bodies of Gabal Samma granite and reach up to tens of centimeters. The mineralogy and
geochemistry of the studied rare metal mineralization were determined using microscopic examination
and X-ray Diffraction (XRD) as well as scanning electron microscope (SEM). These minerals include a
unique occurrence of colored ishikawaite (uranium- rich samarskite) together with fergusonite-Y, allanite,
titanite, zircon-thorite association, uranothorite and fluorite. The obtained SEM data for the studied
minerals are showing the compositional limits of these minerals as specified in the literature. The
occurrence of colored ishikawaite varieties (light brown, reddish dark brown and dark greenish brown)
was recorded for first time in Egypt. The analytical data indicate that the increased color intensity of
ishikawaite mineral is most probably due to increase of uranium content. Accordingly, Nb, Ta, Y, U, and
REE together with Zr and Th mineralization of the Ras Mohamed pegmatite can be considered as a
promising target ore for its rare-metals.
Keywords: Mineralized Pegmatite, Ishikawaite, Fergusonite-Y, Allanite, Titanite, Zircon-Thorite
Association, Uranothorite, Southern Sinai
INTRODUCTION
Several rare metal mineralization occurrences have been recorded in different localities of the Eastern
Desert and South Sinai of Egypt.
However, these mineralizations are mainly restricted to the granite pegmatite bodies associated with the
younger granite that are widely distributed in the Eastern Desert (Ibrahim et al., 1996; Abdalla et al.,
1998; Ibrahim, 1999; Ammar, 2001; Abdalla and El Afandy, 2003; Ali et al ., 2005; Abd El Wahed et al.,
2005; Raslan, 2005; Abdel Warith et al., 2007; Raslan et al., 2010 a & b; Raslan and Ali, 2011; Raslan,
2015) and South Sinai (El Aassy et al., 1986; El Reedy et al., 1988; Abdel Monem et al., 1997; Saleh,
2006; Bisher, 2007; Abu Khoziem, 2012).
Several studies worldwide have revealed the presence of granite-pegmatite-hosted rare-metal
mineralizations including Nb-Ta oxides and zircon (e.g., Matsubara et al., 1995; Erict, 2005; William et
al., 2006 and Pal et al., 2007). Rare-metal mineralization can be attributed either to magmatic or post-
magmatic metasomatic processes (Schwartz, 1992; Abdalla et al., 1998).
The study area is located in the Southern most part of Sinai Peninsula at North Ras Mohamed area
between latitudes 27° 47` – 28° 9`N and longitudes 33° 55` – 34° 24`E (Figure 1). The area is traversed
by regional road between El-Tour City on the Gulf of Suez and Sharm El-Sheikh City and several desert
roads.
Topographically, the study area is distinguished from the Northern part by its rugged terrain and relief,
and characterized by low, moderate to high topographic features. It includes Gabal (G) Khashabi, G.
Attsharqi, G. Sahara, G. Samma, G. Umm-Adawi and G. Mezriya. The general elevation decreases gently
from the east to the west. The main Wadis (streams) dissecting the area are Wadi (W) Lathi, W. Umm-
Adawi, W. Mander, W. Ngeibat, W. Khashabi, W. Sahiya and W. Att El Gharbi. Some of these wadis
drain ultimately into the Gulf of Aqaba and others into the Gulf of Suez.
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
An Open Access, Online International Journal Available at http://www.cibtech.org/jgee.htm
2017 Vol. 7 (1) January-April, pp. 65-80/Raslan et al.
Research Article
Centre for Info Bio Technology (CIBTech) 66
The aim of the present paper is to identify mineralogical and chemical characteristics of radioactive as
well as economic heavy minerals of pegmatites associating alkali-feldspar microgranite of the G. Samma
from N.W. Mander.
Geologic Setting
Based on the field observations and relationships, the rock units can be arranged chronologically,
beginning with the youngest, as following (Figure 2): sedimentary cover, post Cambrian dykes, post
Cambrian granites, Cambro-Ordovician Araba Formation, post-granitic dykes (precambrian dykes),
pegmatites and aplites, Younger granites (alkali-feldspar microgranite, alkali-feldspar granite,
syenogranite, monzogranite), dokhan volcanic, older granites and metamorphic rocks (the oldest), Abu
Khoziem (2012).
Pegmatites are considered as the most abundant rocks bearing anomalous radioactive signature. The
pegmatites and aplites are disseminated among all granitic types. The pegmatites occur as simple or
complex aggregate pockets and dykes. According to radioactivity magnitude, more interesting pegmatites
are the following: 1-Alkali-feldspar microgranite of G. Samma occurs as pod-like bodies with an oval
shape extending for about 100 m. 2-Monzogranite of W. Um Adawi occurring as pockets varying in size
from 0.5 to 30 m and dykes with thickness of about 25 cm and extent of about 15 m. 3- The contact
between the monzogranite and the alkali-feldspar granite at the upstream side of W. Lathi. Pegmatites
occur as dykes with thickness of about 50 cm and extent of about 20 m. 4-Monzogranite at the
downstream side of W. Umm Malaq, where pegmatites occur as dykes with thickness of about 50 cm and
extent of only about 75 cm. 5-Akali-feldspare granite in the Eastern side of G. Att El Sharqi, where
pegmatites occur as small pockets varying in size from 0.25 to 0.75 m.
The Nb-Ta mineralization associated with pegmatites can be distinguished even by naked eye especially
in W. Lathi, W. Um Adawi and N.W. Mander (Figure 3). On the other hand, non-radioactive pegmatites
are widely distributed in the studied area within all granitic types. They are recorded both as zoned and
unzoned pockets that vary in size from 0.5 to 50 m.
Figure 1: Location Map of the Study Area
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
An Open Access, Online International Journal Available at http://www.cibtech.org/jgee.htm
2017 Vol. 7 (1) January-April, pp. 65-80/Raslan et al.
Research Article
Centre for Info Bio Technology (CIBTech) 67
Figure 2: Geological Map of the Studied Area North Ras Mohamed, South Sinai, Egypt (After
Saleh, 2006)
Figure 3: Close-up Photographs Showing A- Rare Metal Mineralization Associated to Pegmatite
Present as Large Black and Brown Grains; B- Vugs Filled with Nb-Ta Oxide Minerals
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
An Open Access, Online International Journal Available at http://www.cibtech.org/jgee.htm
2017 Vol. 7 (1) January-April, pp. 65-80/Raslan et al.
Research Article
Centre for Info Bio Technology (CIBTech) 68
Sampling and Analytical Techniques A large bulk composite sample representing different mineralized zones of pegmatite bodies associating
the alkali-feldspar microgranite of G. Samma from N.W. Mander and weighing approximately 70 kg was
collected for mineralogical investigation. The sample was crushed, ground, and sieved before subjecting
the liberated size fractions to heavy-mineral separation, using bromoform (specific gravity = 2.85 g/cm3).
The heavy mineral grains were manually picked from each of the obtained heavy fractions under
binocular microscope. Some of these selectively picked grains were analyzed by X-ray diffraction
technique (XRD) after heat treatment using Philips X-ray generator model PW 3710/31 a diffractometer
with automatic sample changer model PW1775 (21 position). The X-ray radiation used is Cu-target tube
and Ni filter at 40 kV and 30 mA. This instrument is connected to a computer system using X-40
diffraction program and ASTM cards for mineral identification. The metamict state is characterized by
structure disorder (amorphous to X-rays) while the crystal habit is frequently well developed. The
essential features of this state were discussed by Pabst (1952). The metamictic state can be changed by
appropriate heating of such mineral at temperatures higher than 400 °C leading to their recrystallization.
Some of the separated grains were examined by Scanning Electron Microscope (SEM). This instrument
includes a Philips XL 30 energy-dispersive spectrometer (EDS) unit. The applied analytical conditions
were an accelerating voltage of 30 kV with a beam diameter of 1μm for a counting time of 60-120 s and a
minimum detectable weight concentration ranging from 0.1 wt % to 1wt %. All these analyses were
carried out at the laboratories of the Egyptian Nuclear Materials Authority (NMA).
RESULTS AND DISCUSSION The systematic and detailed mineralogical examination of the heavy minerals obtained from the bulk
composite sample of Ras Mohamed pegmatite revealed the presence of several economic minerals. Thus,
in addition to the Nb-Ta oxide minerals (ishikawaite and fergusonite), a Th-U mineral (thorite or
uranothorite) was discovered in close association with zircon. Microscopic examination of the heavy
fractions of the four size classes (− 0.800+ 0.600 mm), (− 0.600 + 0.400 mm), (− 0.400 + 0.200 mm), and
(− 0.200 + 0.063 mm) revealed that the content of the accessory minerals in the bulk composite sample of
the studied Ras Mohamed pegmatite amounts to approximately 2.5 wt %. The contents of heavy and
accessory minerals have been determined using the counting technique. These data indicate that
ishikawaite (uranium-rich samarskite) is the predominant mineral followed by zircon-thorite association
and allanite in all size fractions (− 0.800-0.063 mm). In addition to those minerals, fergusonite, titanite,
and fluorite occur in much lower amounts.
Niobium-Tantalum Oxide Minerals
A. Ishikawaite (Uranium-Rich Samarskite): (Fe, U, Y) (Nb, Ta) O4
Under the binocular microscope, the examined ishikawaite crystals were found to be distributed in almost
all size fractions between 0.800 mm and 0.063 mm. The defined ishikawaite (uranium-rich samarskite)
crystals are generally massive grains of anhedral to subhedral and granular form and having a
characteristic vitreous or resinous luster.
Also, the investigated mineral crystals are generally translucent, compact, metamict and hard. It is
interesting in this regard to mention that ishikawaite in the studied samples exhibits a wide range of
colors.
Some of the grains are yellowish brown, while others are reddish dark brown and dark greenish brown
with different gradations. It is worth to mention that nearly all ishikawaite grains cited in the previous
literature in Egypt are black in color (Raslan, 2008). Therefore, the presence of colored varieties of
ishikawaite in the studied samples was recorded for the first time in Egypt. Scanning Electron Microscope
(SEM) data of the studied ishikawaite grains show that the mineral is enriched in niobium, uranium and
thorium. The obtained data of the investigated ishikawaite of yellowish brown color (Figure 4A and B),
dark reddish brown ishikawaite (Figures 4C and D) and dark greenish brown color (Figsure 4E & F) are
shown in Table 1.
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
An Open Access, Online International Journal Available at http://www.cibtech.org/jgee.htm
2017 Vol. 7 (1) January-April, pp. 65-80/Raslan et al.
Research Article
Centre for Info Bio Technology (CIBTech) 69
Table 1: SEM Chemical Analyses of Different Colors of Ishikawaite
Dark Greenish Brown Reddish Dark Brown Yellowish Brown Element Oxide
35.7 48.7 58.1 Nb2O5
1.0 2.6 2.6 Ta2O5
1.1 1.3 2.1 TiO2
29.6 19.3 9.9 UO2
5.2 4.7 9.8 ThO2
3.5 4.1 2.7 FeO
8.7 5.0 - Y2O5
3.3 4.2 3.9 CaO
- - 5.6 PbO2
- - 0.5 Ce2O3
- - 0.6 Nd2O3
2.0 2.1 - Al2O3
0.6 0.6 - MnO
8.4 5.7 4.2 SiO2
1.0 1.7 - Sc2O3
100 100 100 Total
Samarskite is a group of the Nb-Ta mineral varieties occurring in pegmatite granites and having the
general formula Am Bn O2 (m+n) where A represents Fe2+
, Ca, REE, Y, U and Th while B represents Nb,
Ta and Ti. According to Hanson et al., (1999), the complete metamict state, alteration and the broad
variation of cations in A-site of these mineral varieties render their crystal structure a problematic case.
Therefore, these authors have proposed a nomenclature for the samarskite group of minerals based on
their classification into three species.
Thus, if the REE + Y are the dominant, the name samarskite-(REE + Y) should be used with the dominant
of these cations as a suffix. If U + Th are the dominant, the mineral is properly named ishikawaite
whereas if Ca is the dominant cation, the mineral should be named calciosamarskite. Hanson et al., (1999)
have also reported that ishikawaite and calciosamarskite are depleted in the light rare-earth elements
(LREE) and enriched in the heavy rare-earth elements (HREE) together with Y. Recently, samarskite-
(Yb) has been identified as a new species of the samarskite group (William et al., 2006). It is interesting
to mention that ishikawaite with an average assay of about 50 % Nb2O5 and 26 % UO2 has been identified
for the first time in Egypt in the mineralized Abu Rushied gneissose granite (Raslan, 2008). From the
obtained data, it is quite clear that the studied Nb-Ta mineral variety of Ras Mohamed pegmatite reflects
the chemical composition of U and Th-rich samarskite species. The lines of evidence of the latter
(ishikawaite) can be summarized as follows:
1. The obtained SEM data revealed that Nb2O5 is dominant in the investigated mineral where it attains
content of 58.14 wt % in the yellowish brown variety. The sum of average content of Ta2O5 and TiO2
attains 4.76 wt %, which is much lower than content of Nb2O5. Also, Nb2O5 is dominant in the reddish
dark brown variety (48.68 wt %) and the sum of average content of Ta2O5 and TiO2 attains 3.90 wt %,
which is much lower than content of Nb2O5. The Nb2O5also is dominant in the dark greenish brown
variety (35.72 wt %) and the sum of average content of Ta2O5 and TiO2 attains 2.13 wt %, which is much
lower than content of Nb2O5. The samarskite group comprises only those species in which the Nb content
in B-site is higher than that of Ta and Ti (Hanson et al., 1999).
2. The studied mineral actually falls within the compositional limits of both samarskite-Y and ishikawaite.
Both samarskite-Y and ishikawaite have a dominant Nb in the B-site and the distinction between the two
varieties must be based on the content of A-site occupancy.
3. Samarskite-Y has been described as a mineral with Y + REE dominant at the A-site (Nickel and
Mandarino, 1987).
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
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2017 Vol. 7 (1) January-April, pp. 65-80/Raslan et al.
Research Article
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4. The investigated mineral is actually rich in both uranium and thorium, where the yellowish brown
variety contain (9.88 %) and (9.80 %) respectively. The dark brown variety contains U (19.29 %) and Th
(4.73), whereas the dark oily or dark greenish brown variety contains 29.57 % and 5.21 % for uranium
and thorium respectively.
5. The investigated samarskite variety separated from the Ras Mohamed pegmatite is characterized by
dominant U + Th, Nb> Ta + Ti and relatively rich in Y.
6. In summary, the studied mineral most probably falls within the compositional limits of other
ishikawaite cited in the previous literature.
Finally, the analytical data indicate that increasing color intensity of ishikawaite mineral is most probably
due to increasing of uranium content; the uranium content increase gradually from 9.88 % in the lighter
colored variety to 19.29 % in the reddish darker brown, and to 29.57 % in the very deep colored variety.
B. Fergusonite-Y: (Y, REE>Ca, U, Th) (Nb, Ta) O4
Under the binocular microscope, the defined fergusonite grains are generally massive grains of anhedral
to subhedral and granular form and having a characteristic vitreous or resinous luster. Also, the
investigated mineral crystals are generally translucent, compact, metamict and hard. The fergusonite
crystals are mainly velvet-yellow brown to honey yellow in color.
The SEM data of the studied fergusonite crystals (Figures 4G and H) show that the mineral is enriched in
niobium, yttrium and REE elements. The obtained SEM analyses of the investigated fergusonite of
velvet-yellow brown to honey yellow color (Figures 4G and H) have resulted in Table 2.
Table 2: SEM Chemical Analyses of Fergusonite-Y
Wt. (%) Element Oxide
41.0 Nb2O5
3.6 Ta2O5
14.1 Y2O5
27.3 ΣREE
3.2 UO2
5.5 ThO2
0.7 CaO
3.4 Al2O3
1.0 MgO
100 Total
The fergusonite group consists of REE-bearing Nb and Ta oxides, many of which are metamict and
therefore, commonly poorly characterized. The structure of fergusonite group is comparable to that of
samarskite group but with large A-sites. Most of these minerals are monoclinic, although orthorhombic
and tetragonal unit cells arise from cation ordering. Similar to other (Y, REE, U, Th)-(Nb, Ta, Ti) oxides,
fergusonite (ideal formula: YNbO4), occurs typically as an accessory component in granites (Poitrasson et
al., 1998) and granitic pegmatites (Ercit, 2005). Accordingly, the obtained data reflect the chemical
composition of fergusonite-Y and show that the mineral is enriched in niobium (41.03 wt %) in B-site,
yttrium (14.14 wt %) and total REE elements (27.33 wt %) in A-site.
Pure monomineralic sample from ishikawaite grains of various colors and fergusonite were prepared by
hand picking and subjected to XRD analyses. The obtained XRD data for ishikawaite and fergusonite
after annealing (heat treatment) are presented in (Figure 5A & B). The data conforms to the ASTM cards
index No. 10-398 and 4-0617 for samarskite and No. 9-443 for fergusonite-Y.
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
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Research Article
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Figure 4: A- Ishikawaite Crystals with Yellowish Brown Color; B- EDX and BSE Image of
Yellowish Brown Ishikawaite; C- Ishikawaite Crystals of Reddish Dark Brown Color; D- EDX and
BSE Image of Reddish Dark Brown Ishikawaite; E- Ishikawaite Crystals with Dark Greenish
Brown Color; F- EDX and BSE Image of Dark Greenish Brown Ishikawaite; G- Fergusonite
Crystals with Velvet-Yellow Brown to Honey Yellow in Color; H- EDX and BSE Image of
Fergusonite Crystals
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
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2017 Vol. 7 (1) January-April, pp. 65-80/Raslan et al.
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Figure 5: A-XRD Diffractograme of Various Colors Ishikawaite; B- XRD Diffractograme of
Fergusonite-Y
Zircon-Thorite Association
Under a binocular microscope, zircon occurs as dark brown massive compact grains that are generally
translucent to opaque (Figure 6A). The surface of the zircon grains is generally ill-defined, rough, and
dull. It possesses a zonal structure with almost translucent to isotropic zones. Morphologically, some
crystals are typically short to equidimensional, with a length/width ratio of 1:1, and they tend to exhibit
square to trapezoid, rhombic or hexagonal cross sections (Figures 6 B & C). Other zircon grains occur as
bright yellow massive compact crystals (Figure 6D). Scanning electron microphotographs confirm that
A
B
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
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almost all the investigated zircon crystals characteristically contain several black inclusions of thorite
(Figures 6 B, C & E).
In addition, several zircon crystals were subjected to semi quantitative analyses using SEM. While the
SEM microphotograph (Figures 6B & C) reflect morphological features of the investigated zircon as well
as its uranothorite inclusions, the SEM analysis (Figures 6B & C) and Table 3 confirm the semi
quantitative chemical composition of zircon and the thorite inclusion, respectively.
However, the latter tends to be uranothorite species due to the presence of a remarkable amount of
uranium (11.43 %) together with Th (35.81 %) and Si (13.27 %). The uranothorite inclusions are present
in variable sizes ranging from 1 μm to 40 μm. They occur either as numerous minute inclusions in a zonal
distribution pattern, especially in the outer zone of the zircon grain (Figures 6B & 6C), or as randomly
distributed inclusions of varying sizes (Figures 6E).
Zircon incorporates uranium into its lattice and encloses the radioactive materials as minor inclusions.
The observed color changes of zircon have long been a matter of debate.
The documented high contents of U, Th and REE may enhance metamictization and color variation of
zircon. It is noteworthy that Ali et al., (2005); Abdel Warith et al., (2007); Raslan, (2009); Raslan et al.,
(2010b) reported the presence of thorite inclusions in rare-metal mineralization and accessory heavy
minerals (zircon, samarskite and spessartine garnet) that are separated from some Egyptian granitic rocks
and their associated pegmatites.
Table 3: SEM Chemical Analyses of Dark Brown and Yellowish Brown Zircon
Yellowish Brown Zircon Dark Brown Zircon Elements
57.5 68.3 Zr
14.7 2.0 Th
4.7 1.6 U
3.2 2.9 Hf
7.3 2.2 Fe
11.6 19.5 Si
1.1 2.1 Ca
- 1.6 Al
100 100 Total
Uranothorite: [ (Th,U) SiO4]
Uranothorite occurs as pale to dark yellow brown grains that are generally translucent to opaque. They are
found as massive grains of anhedral to subhedral and granular form, having a characteristic vitreous or
resinous luster (Figure 6F). Scanning Electron Microscope (SEM) data (Figure 6 G & H) and Table 4
reflects the morphological features and chemical composition of uranothorite. These results indicate that
the major elements in uranothorite are ThO2 (59.61 wt %), SiO2 (15.47 wt %) and UO2 (14.28 wt %).
Also, minor amounts of Fe2O3 (1.42 wt %) and CaO (1.48 wt %) were reported as substitution in
uranothorite.
Table 4: SEM Chemical Analyses of Uranothorite
Wt. (%) Element Oxide
15.5 SiO2
1.5 CaO
1.4 Fe2O3
59.6 ThO2
14.3 UO2
7.8 ZrO2
100 Total
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
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Figure 6: A- Zircon Crystals with Dark Brown Color; B- EDX and BSE Image of Zircon; C- EDX
and BSE Image Showing a Zonal Structure in Zircon and Uranothorite Inclusions; D- Zircon
Crystals with Light Brown Color; E- EDX and BSE Image of Zircon and Uranothorite Inclusions
together; F- Uranothorite Grains with Dark Brown Color; G- BSE Image of Uranothorite; H-
EDX of Uranothorite
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
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REE-Bearing Minerals
A. Allanite: [(Ca, REE, Th)2 (Fe2+
,Al)3 Si3O12 (OH)]
Allanite occurs as black massive translucent crystals of anhedral to subhedral form and has a
characteristic vitreous luster (Figure 7A). SEM data of the studied allanite crystals (Figure. 7B) show that
the mineral is enriched in silica, alumina, iron, calcium and REE elements. The obtained SEM analyses of
the investigated allanite have resulted in Table 5.
The accessory mineral allanite [(Ca, REE, Th)2 (Fe2+
,Al)3 Si3O12 (OH)] is a prime target for dating
geological processes because it plays a key role in the storage and mobility of geochemically important
trace elements including the rare earth elements (REE), strontium and thorium. Allanite occurs in a wide
range of rock types, but is most commonly reported as an accessory phase in metaluminous granites to
tonalites and pegmatites (Exley, 1980; Giere and Sorensen, 2004).
Table 5: SEM Chemical Analyses of Allanite
Wt. (%) Elements Oxide
33.3 SiO2
13.4 Al2O3
17.2 Fe2O3
9.5 CaO
11.1 Ce2O3
10.6 La2O3
0.9 Nd2O3
0.6 Pr2O3
2.0 MnO
1.4 ThO2
100 Total
B. Titanite: [CaTiSiO5]
Titanite occurs as brownish yellow massive translucent crystals of anhedral to subhedral form and having
a characteristic vitreous luster.
Generally, it is widespread as an accessory mineral occurring in igneous rocks. It is a calcium titanium
silicate mineral (CaTiSiO5) with sphenoid habit.
The brown color of titanite is attributed to presence of Fe2O3, whereas the yellow varieties are low in iron
content and brown or black titanite may carry 1%, or more, Fe2O3 (Deer et al., 1962). Some titanite
crystals have been found to be metamicted. The obtained SEM analyses of the investigated titanite
(Figure 7C) have resulted in Table 6.
Scanning electron microphotographs confirms that almost all the investigated titanite crystals
characteristically contain several bright inclusions enriched in Y2O3 (22.04 wt %) and P2O5 (7.85 wt %)
most probably due to xenotime substitution (Figure 7D).
Table 6: SEM Chemical Analyses of Titanite
Wt. (%) Element Oxide
15.0 Al2O3
36.7 SiO2
22.7 CaO
17.1 TiO2
0.8 Nd2O3
0.8 MnO
7.0 Fe2O3
100 Total
International Journal of Geology, Earth & Environmental Sciences ISSN: 2277-2081 (Online)
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Figure 7: A- Allanite Crystals; B- EDX and BSE Image of Allanite; C- EDX and BSE Image of
Titanite; D- EDX of Bright Inclusions in Titanite; E- Colorless, Rose and Pink Fluorite Crystals; F-
BSE Image and EDX Spectrum of Fluorite
C. Fluorite: CaF2
The fluorite occurs as colorless and colored transparent crystals. They are present as cubes and are
characterized by a vitreous luster. The majority of the fluorite crystals occur as multicolored or as rose,
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pink and blue to violet (Figure 7E). The obtained SEM analyses confirm the chemical composition of
fluorite (Table 7).
Table 7: SEM Chemical Analyses of Fluorite
Wt. (%) Element Oxide
30.7 F2O
1.4 Y2O3
67.9 CaO
El-Kammar et al., (1997) remarked that the change in the color in the fluorite is controlled by the Y
content, in particular, and the Y group, in general. Several workers attributed the color of the fluorite to
the effect of radioactivity (Deer et al., 1962; Mackenz and Green, 1971; Nassau and Prescott, 1977;
Raslan, 2000). The results of SEM analysis were confirmed by XRD analysis. Mono-mineralic sample
from allanite and titanite crystals were prepared by hand picking and analyzed using XRD technique. The
obtained data are presented in Figure 8. The diffraction lines are in accordance with the ASTM cards No.
(9-474) for allanite and No. (11-142) for titanite.
Figure 8: A- XRD Diffractograme of Allanite; B- XRD Diffractograme of Titanite
Conclusion
Microscopic investigation, SEM, and XRD analyses confirm the presence of ishikawaite mineral species
in the mineralized pegmatite injected in alkali-feldspar microgranite of Gabal Samma at North Ras
Mohammed granitic pluton, Southern Sinai, Egypt. The mineral is associated with fergusonite-Y, allanite,
titanite, zircon-thorite association, uranothorite and fluorite. The occurrence of colored ishikawaite
varieties (light brown, dark reddish brown and dark greenish brown) was recorded for the first time in
Egypt. The analytical data indicate that the increasing of color intensity of ishikawaite mineral is most
probably due to increasing uranium content. The studied pegmatite has high economic potentiality as a
source far as nuclear materials is concerned.
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