1. 39
OCCURRENCE OF URANIUM BEARING MINERALS IN UM SAFI
PYROCLASTICS, CENTRAL EASTERN DESERT, EGYPT.
Ibrahim, M. E.*
, Attawiya, M. Y.*
, Osman, A. M.**
and Ibrahim, I. H.*
*
Nuclear Materials Authority, Cairo, Egypt.
**
Ain Shams University, Cairo, Egypt.
ABSTRACT:
Um Safi rhyolite (USR) and associated pyroclastic rocks form relatively moderate to high relief (615m) extruded
volcanoclastic and volcano-sedimentary association, serpentinites and ortho-amphibolites with Knife sharp
contact, forming small oblate body striking NW-SE, covering about 0.3 km2
. These rocks show different degrees
of subsoildus autometasomatic processes; argillization, greisenization, silicification, hematitization and
fluoritization. USR is originated by a combination of fractional crystallization of lithospheric source and crustal
contamination, whereas the magma was extruded at active continental margin environment
Um Safi pyroclastics (USP) comprise agglomerates and laminated tuffs. The coarsers (agglomerates) show
fragmental structure at the base of rhyolite extrusion whereas the finer laminated tuffs show contorted bands
(0.5-1 cm) of differing shades and occur upward direction. The pyroclastics were erupted with explosive
violence as a turbulent mixture of hot, expanding gases and gas-emitting lava fragments at relatively low
pressures. The pyroclastics could be considered as a good trap for secondary uranium and U-bearing minerals.
The base metal minerals (pyrite, arsenopyrite and corondite) are formed in the deeper part of the epithermal
zone. In the next zone to the top where ascending solutions rise further towards the surface and mingled with the
descending meteoric water, precipitation of secondary uranium mineral (kasolite) and U-bearing minerals
(plumbobetafite, columbite and betafite) occur as a function of oxidation and failing temperature.
Keywords: Um Safi – uranium bearing minerals - pyroclastics.
1. INTRODUCTION
Um Safi volcanic rocks were mapped previously as
felsite by several workers (Akaad and El Ramly,
1963; El Ghawaby, 1966; Akaad et al., 1996;
Abdalla, 2001). Radioactive mineralization of
columbite, uranothorite and zircon were recorded as
fracture filling in the sheared parts of the felsite
rocks at Um Safi (El Ghawaby, 1966). Abdalla
(2001) considered Um Safi as subvolcanic
equivalent for the metaluminous alkali rare metal
granites and is belonging to the post-collision and
orogenically related A2-type granites with only
zircon and uranothorite as radioactive minerals. Um
Safi granitoids (southern part of the studied area)
are composed of a succession of metaluminous
calc-alkaline (older granitoids) and metaluminous
to peraluminous sub-alkaline sub-leucogranites
(younger granites) emplaced during three
successive tectonic events (Ibrahim et al., 2001).
The shear zone (N-S) in muscovite sub-
leucogranites (1.5 km south USR) is considered as
a good trap for uranium mineralizations (zippeite
and beta-uranophane). This work is a contribution
to the understanding of geology, geochemistry and
genesis of secondary uranium and uranium-bearing
mineralization in USP.
2. GEOLOGIC SETTING AND
PETROGRAPHY
USR form relatively moderate to high relief (615m)
extruded the volcano-sedimentary association
(slate, phyllite, Banded Iron Formation and schist),
serpentinites and ortho-amphibolites with Knife
sharp contact, forming small oblated body striking
NW-SE, covering about 0.3 km2
(Fig. 1). The
volcanic rocks of Um Safi are successive sheets of
lavas and pyroclastics, the former being dominant.
The bulk composition of lavas is mainly rhyolitic.
The USR are fine-grained, massive and varies in
colours from buff, yellow or even grey and pink
with dark buff in colour. They show locally
porphyritic and fracturing particularly along the
marginal parts of the extrusion. These rocks show
different degrees of alteration, hematitization,
kaolinitization and silicification so that the colour
sometimes is reddish brown or dark brown due to
the presence of considerable iron oxides and other
opaque minerals. Fluorite veinlets (1 –3 cm thick,
and up to 2 m long) are common through
pyroclastics and made up of violet, green and black
fluorite, quartz and calcite. Quartzification is
clarified by development of many quartz vein,
veinlets and pods in decreasing order. They
crosscut the USR body at its northern part. Some
Egyptian Journal of Geology, v. 46/1, 2002, pp. 39-54

2. 40
quartz veins contain pyrite and arsenopyrite.
Hematitization is manifested by change of USR
colour into red to brown especially along fractures
due to the presence of impregnation of iron oxide.
The USR are invaded by N-S sub-vertically
greisenized microgranite, which shows exfoliated
and cavernous.
The USP consist of detrital materials expelled from
rhyolite volcanics, transported aerially and
deposited upon land surface in lakes or in marine
waters (Heinrich, 1956). They comprise
agglomerates and laminated tuffs. The coarse-
grained agglomerates show fragmental structure at
the base of rhyolite extrusion (0.5-2 m above Wadi
level) whereas the finer-grained laminated tuffs
exhibit contorted bands of differing shades and
occur upward direction (1.5 – 3 m). The
pyroclastics and greisen rocks gain importance due
to their high intensities of radioactivity (114-280
ppm eU and 167-1133 ppm eTh respectively) (Fig.
2). Visible non-radioactive minerals are observed
such as pyrite, arsenopyrite and manganese oxides
or dendrites, as well as, violet fluorite and metallic
black veinlets (N-S trend).
A- Rhyolite is extrusive holocrystalline to
hypocrystalline with aphanitic matrix. The rock is
hard, massive and light coloured. They are often
banded with flow structures, which may appear as
coloured bands strips or lines of spherulites and
spherulitic textures. Breccias, tuffs and welded tuffs
are often associated. They are composed of quartz
and alkali potash feldspars (sanidine) embedded in
cryptocrystalline groundmass and consist of quartz,
sanidine and secondary muscovite. The common
accessories are opaques, apatite and zircon.
Quartz occurs as phenocrysts (0.7×1.2 mm) and
fine-grained groundmass in the matrix. The matrix
quartz is either fine-grained, or intergrown with
alkali feldspar in a complex pattern. Some quartz
forms aggregate of tiny plates and spherulites,
which composed of radiating fibres of feldspar and
cristobalite (Moorhouse, 1959).
Potash feldspar occurs either as subhedral to
anhedral phenocrysts (0.5×0.8 mm) or as fine-
grained groundmass in matrix. Phenocrysts
(sanidine and microperthite) are usually clear and
may be untwinned or twinned according to the
Carlsbad low, sometimes exhibit corrosion effects
due to corrosion by the matrix. Also radial
spherulitic texture appears from central elongated
microperthite phenocrysts. The common alteration
products are kaolinite, sericite and calcite.
Muscovite occurs either as anhedral fine-grained
crystals in groundmass due to alteration products of
potash feldspars, or as veinlets crosscut the other
constituents.
Opaques occur as anhedral crystals or small
veinlets associated with fluorite. Epidote occurs as
small aggregates associated with opaques and
fluorite. Fluorite varies in colours from colourless
to pale violet through deep violet or black. It
usually occurs as small veinlets associated with
opaque minerals. Apatite, allanite and zircon are
present as individual euhedral crystals enclosed
within quartz and feldspar.
B- Pyroclastics are well banded, reddish grey in
colour and composed mainly of crystals and rock
fragments in fine-grained groundmass. The coarser
agglomerates are not well represented for thin
section studies, except forming fine-grained matrix
they may possess. According to Schmid (1981) the
pyroclastics can be classified into fine crystal tuffs
and crystal lithic tuffs.
i. Fine crystal tuffs are fine-grained, laminated or
banded and composed of more than 50% crystal
fragments of quartz, feldspars and epidote set in a
fine-grained matrix of quartz and potash feldspars.
ii. Crystal lithic tuffs are composed of lithic
fragment of rhyolite and quartzite, as well as, sub-
angular to subrounded crystal fragments of quartz
and perthite embedded in fine-grained groundmass
of the same mineral composition. Quartz crystals
are strongly fractured, probably owing to
compaction and cooling of the glass matrix
(Williams and Mc Birnery, 1979). Perthite crystals
sometimes show one side with a crystal face and
elsewhere show irregular or fractured edges. Other
perthite crystals are rounded or irregularly embayed
indicating a high temperature of the environment of
deposition. Ferromagnesian minerals are altered
and commonly bent.
3. GEOCHEMISTRY
3.1. Methodology
Seven samples from fresh volcanics and five
samples from altered rock, as well as, two samples
from greisen were analyzed in the laboratories of
the Nuclear Materials Authority for major elements
by the wet chemical and atomic absorption (with <
1 % error). Some trace elements are determined
using the X-ray fluorescence technique (with 1-5 %
error). The data of chemical analyses and CIPW
normative values are given in Tables 1 and 2. Two
samples from pyroclastic and greisenized rocks
were crushed and their heavy minerals were
separated using Frantz isodynamic separator and
bromoform. XRD and EDAX-SEM techniques
were used for mineral separation by hand picking
under the binocular microscope.
3.2. Fresh Samples

3. 41
The average chemical composition of the studied
fresh volcanic rocks is compared with the average
corresponding published Egyptian and World
rhyolite rocks (Table 3). Generally the values of
major oxide compositions of USR fall between the
corresponding values of the Egyptian and World
rhyolites. It contains nearly similar values of SiO2,
Al2O3, MgO, K2O, CaO and P2O5 with less Fe2O3
and Na2O contents compared with the Egyptian
rhyolite that given by Aly and Moustafa (1984).
Cox et al., (1979) used the total alkalis versus silica
diagram (Fig. 3) for the geochemical classification
of the volcanic rocks. The data points of the studied
fresh volcanic rocks fall in the rhyolite field.
Miyashiro and Shido (1975) proposed the Cr-
FeOt
/MgO and Ni- FeOt
/MgO discrimination
diagrams to identify island arc volcanic rocks
through the behavior of Cr and Ni with advancing
fractional crystallization of basaltic magma. The
plots of the examined rhyolite on these diagrams
(Figs. 4&5) show that, they fall mostly within the
island arc and continental margin tectonic setting.
The normalized values of the studied rhyolite rocks
relative to MORB (Hofmann, 1988) are given in
(Fig. 6a). It shows a strong enrichment in all
compatible elements except Sr due to the effects of
assimilation of either crustal materials or oceanic
matter. In comparison with normalized values
related to the bulk continental crust (Hofmann,
1988), the plot in (Fig. 6b) shows that rhyolite is
enriched in Rb, Ba, Zr and Y and depleted in Sr and
Nb, suggesting a significant role of crustal
contamination.
3.3. Altered Samples
According to the normative Q-Ab-Or compositions, the
altered samples could be classified as sodic,
potassic, silicic and greisen as shown in Fig. (7)
after Stemprok (1979). Two altered samples lie
below the granitic eutectic temperature and exhibit
a trend corresponding to crystallization in high PH2O
range (the range is from 0.5 to 3 k bar after Winker
et al., 1975 and closely parallel to the sodic trend).
The other altered samples lie in silicic trend. The
greisenized samples fall close to the greisen trend.
The Na-K variations diagram after (Cuney et al.,
1989) shows five alteration types; Na-
metasomatism, K-metasomatism, silicification,
desilicification and argillization. On figure (8)
argillization and silicification are the main
alteration processes affected the investigated
samples.
Figures (9 a&b) shows that the major oxides of the
altered samples suffered enrichment in MgO, MnO,
CaO, Fe2O3, P2O5, and SiO2 and depletion in K2O,
Na2O, FeO, Al2O3 and, TiO2, than fresh rhyolite
samples, while the trace elements of the altered
samples display enrichment in Th, U, Nb and Zn
and also show depletion in Rb, Ba, Ni, Pb and V
than fresh rhyolite samples.
3.4. Distribution of eU and eTh
The eU-content in fresh rhyolite ranges from 17 to
34 ppm with an average 26 ppm, and the eTh-
content ranges from 32 to 75 ppm with an average
50 ppm, while the eTh/eU ratio is equal 1.9 (Table
4). The eU and eTh values of USR are greater than
values of acidic effusive rocks of Adams et al.,
(1956) while their eTh/eU ratios are lower than
those reported, indicate to uranium enrichment
rather than thorium.
The field radiometric measurements localized three
radioactive anomalies, two within pyroclastics
(includes one tunnel and eleven trenches were
dugged by nuclear materials authority since 1964)
and one within greisenized microgranite.
a- The first one is represented by only one tunnel
(about 1.5 m in width and 6 m in length), which
considered as one of the highst radioactive zones.
The mineralized joint sets in the tunnel strike ENE-
WSW and NE-SW. Kaolinitized, sericitized and
argillized products of USP contain the higher
radioactive values with violet fluorite. The eU-
content ranges from 53 to 563 ppm with an average
of 285 ppm, whereas the eTh-content ranges from
236 to 2229 ppm with an average of 1133 ppm. The
eTh/eU ratio ranges from 2.8 to 4.71 with an
average of 3.9 (Table 4).
b- The second anomaly is represented by trenches.
It is clear that the common mineralized joints,
striking ENE-WSW and NE-SW. The alteration
product; ferrugenation, Mn-dendrites and oxidized
with oxidized sulphide crystals support the
hydrothermal effect. The eU-content (ranges from
132 to 335 ppm with an average of 236 ppm), is
less than the eTh-content (ranges from 157 to 1188
ppm with an average of 905 ppm). The eTh/eU
ratio ranges from 0.5 to 5.8 with an average of 4.1
(Table 4), which is related to mobilization and
redistribution of uranium.
c- The third anomaly is close to greisenized
microgranite, which trend N-S to N20ºE-S20ºW
directions. It is characterized by brownish to
reddish colour (due to ferrugenation) ranging from
4 to 5 m thick and rich by vugs due to oxidized
cubic sulphide crystals. The eU- content (ranges
from 101 to 125 ppm with an average of 114 ppm)
is less than eTh-content (ranges from 161 to 172
ppm with an average of 167 ppm). The eTh/eU
ratio ranges from 1.33 to 1.61 with an average of
1.48 (Table 4).

4. 42
4. MINERALIZATIONS
The mineralizations in Um Safi pyroclastics can be
classified into five categories; 1) U-bearing
minerals (columbite, plumbobetafite and betafite),
2) secondary U-mineral (kasolite), 3) thorium-
bearing minerals (uranothorite and yttrialite), 4)
base-metal minerals (pyrite, arsenopyrite,
cassiterite and corondite) and 5) accessory minerals
(zircon, allanite and fluorite).
i) Columbite [(Fe,Mn)(Nb,Ta,U)2O6] is
isomorphous with tantalite, black in colour and is
an ore of niobium as well as a source of tantalum
(Nb/Ta ratio 4.9). The columbite of Um Safi (Fig.
10a) is radioactive due to presence of moderate
UO2 and ThO2 contents (16.7% and 13.3%
respectively).
ii) Plumbobetafite [(Pb,Ca,U)(Nb,Ti)2O6(OH,F)]
confirmed by EDAX (Fig. 10b). The mineral is
composed mainly of TiO2 (41.3%) and Nb2O5
(20.1%) while UO2 and ThO2 are not common
(1.7% and 2.1% respectively).
iii) Yttrialite [(Y,Th)2Si2O7] is olive-green mineral.
Semi-quantitative analyses (Fig. 10c) indicate that,
it has ThO2 (41.1%) more than Y2O3 (14.3%) and
SiO2 (26.0%).
iv) Uranothorite [(Th,U)O2] is confirmed by
EDAX (Fig. 11a) and contains 40.65% ThO2,
14.0% UO2, 12.0% Y2O3 and 16.0 % SiO2.
v) Arsenopyrite (FeAsS) occurs as silver-white to
steel-grey colour. it is isomorphous with loellingite
mineral and constituting the principle ore of
arsenite. Semi-quantitative analyses of picked
grains were using the EDAX-SEM technique
(Fig.11b ) gives 37.3% As, 35.1% Fe and 25.0% S.
vi) Coronadite (PbMn6O14) is black mineral
associated with iron oxides in ferruginated
pyroclastics (trenches). Semi-quantitative analyses
of picked grains were obtained using the EDAX-
SEM technique (Fig.11c). It contains 67.8% MnO
and 21.5% PbO2 with Pb/Mn ratio equal to 3.2.
vii) Betafite [(Ca,Na,U)2(Ti,Nb,Ta)2O6.(OH)]
occurs as radiated black mineral associated with
quartzo-feldspathic groundmass in pyroclastics
(Fig. 12a).
viii) Kasolite [Pb(UO2)SiO4.H2O] shows dark
yellowish brown colour with radiated or fan likes
shape under Crossed Nicol and considered as
secondary uranium minerals (Fig.12b).
ix) Zircon (ZrSiO4) occurs as euhedral six-sided or
eight-sided form with clusters of opaque inclusions.
It is mainly colourless to pale yellow and associated
with iron oxides and fluorite. Average zirconium
contents is higher in fresh samples (1030 ppm) than
in altered samples (936 ppm). Rankama and
Sahama (1955) stated that thorite is isomorphic
with zircon and it is evident that a large part of
thorium is incorporated in the zircon structure. The
ionic size of zirconium and thorium are not too
unlike and therefore thorium is able to enter the
zircon structure in which it replaces. Two thin
section from greisen were tested for their
radiometrically using SSNDTD type Kodak CN-85
films. The test reveals that zircon in greisen is
radioactivity carrier and show high concentrations
of alpha tracks (Figs. 12c&d).
x) Fluorite (CaF2) minerals possess vitreous luster
and white streak. It is mainly recorded filling
cavities and micro-fractures, which reflect their
secondary origin as resulting from hydrothermal
alteration of rhyolite and/or associated greisen.
Fluorite in USR and greisen samples exhibits a
wide range of colours. Some of them are colourless,
while others are pale rose, pale violet, deep violet
and very deep to blackish violet to black. Some
fluorite grains have various gradations of colours
was separated by hand picking under the
microscope to be tested for their radiometically by
using the Solid State Nuclear Track Detectores
(SSNDTD) type Kodak CN-85 films. This test
reveals that violet and black fluorite grains are
radioactivity carrier and show high concentrations
of alpha tracks (Figs. 12 e&f). Serra (1947) and
Allen (1952) stated that fluorite colour is attributed
to the action of their rare earth elements during the
differentiation of magma or due to the presence of
manganese. Derr et al., (1962) indicated that the
presence of trace and/or rare earth may cause the
different colouration of fluorite. Abdalla (2001)
recorded that Um Safi fluorite is characterized by
considerable enrichment in REE (av. Σ REE = 4179
ppm).
xi) Allanite [(Ce,Ca,La,Y)(Al,Fe)3(SiO4)3.OH] is
brown in colour and pleochroic from pale brown to
dark brown (Fig.12g ). In most cases the allanite
mineral is uranium and thorium carrier but altered
and inverted to an amorphous substance product by
break down of the space lattice by radioactive
emanation (Kerr, 1977).
xii) Cassiterite (SnO2) is a brown or black
tetragonal mineral. It is the principal ore of tin.
They occur in prismatic crystals, massive and form
compact concentric structure (Fig. 12h). Swart and
Moore (1982) suggested that the presence of
coloured zones in the cassiterite crystals is due to
variation in U concentration that range from 0-6
ppm in darker bands.
xiii) Pyrite (FeS2) occurs as well developed cubic
crystals, with pale brass-yellow colour and metallic
luster, often with yellowish brown tarnish

5. 43
associated with goethite. Pyrite occurs either
disseminated in smoky quartz veins or associated
with USP.
xiv) Thorite (ThSiO4) is strongly radioactive
mineral, brown to black tetragonal mineral like
zircon and dimorph with huttonite. It is
isostructural with thorogummite [Th (SiO4)1-X
(OH)4X] and may contains as much as 10%
uranium.
5. SUMMARY AND CONCLUSIONS
The average of eTh/eU ratios are increased from
1.5 in the greisenized microgranite through 1.9 in
the fresh rhyolite to about 4.0 in the pyroclastic
samples (kaolinized and argillite). The lowering of
the eTh/eU ratio indicates redistribution and
localization of secondary uranium mineral
(kasolite). The enrichment of U and Th in
pyroclastics (425-520 ppm eU and 1700-2000 ppm
eTh) may indicate the stabilization of them in late-
to post-magmatic fluids. In the pyroclastics
samples, U and Th are largely incorporated in
uranium bearing-minerals e.g. columbite, yttrialite,
betafite, plumbobetafite and uranothorite. The
higher mobility of U could be retained by Fe- and
Mn-rich solutions and adsorbed by lately deposited
amorphous Fe-oxides and explained its lower Th/U
ratio (Table 2).
The greisen (pneumatolytically altered granitic
rocks) is composed mainly of quartz and mica
(muscovite and sericite) as well as fluorite,
cassiterite, kasolite, allanite, zircon and
arsenopyrite in decreasing order. The lower eTh/eU
ratio (1.6) of greisen rather than tunnel (average
eTh/eU= 3.9) and trenches (average eTh/eU= 4.1)
indicates that the greisen is affected by
hydrothermal-bearing uraniferous solution. The
normal Th/U in the crust is equal to 3.5. So, the
lower ratio may be attributed to the magmatic
activity through the N-S shear zone in muscovite
subleucogranite where their Th/U ratio around 0.2
(Ibrahim et al., 2001).
Kaolinitization, ferrugenation, and argillation
represent the hydrothermal alterations associated
with the high radioactivity values in rhyolites and
greisen. The widespread sericitization through the
rhyolite rocks provides additional evidence of
large-scale movement of solutions through these
rocks. The hexavalent U is ready leached from
rhyolites by dilute acid solutions so some U may
have been transported as UO2(OH)+
and UO2
-
complex
The USP appears to have provided less-welded
layers and lenses. This is coincidence with the
similar observation (Smellie, 1982) described from
Duobblon rhyolitic ignimbrites. The leached U
from solutions percolating through fractures,
fissures and permeable bands were re-deposited and
sink. The pyroclastics were erupted with explosive
violence as a turbulent mixture of hot, expanding
gases and gas-emitting lava fragments at relatively
low pressures. The base metal minerals (pyrite,
arsenopyrite and corondite) are formed in the
deeper part in the epithermal zone. In the next zone
to the top where ascending solutions rise further
towards the surface and mingled with the
descending meteoric water, precipitation of
secondary uranium mineral (kasolite) and U-
bearing minerals (plumbobetafite, columbite,
yttrialite, betafite and uranothorite) occur as a
function of oxidation and failing temperature
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Swart, P.K. and Moore, F., 1982, The occurrence
of uranium in association with cassiterite,
wolframite and sulphide mineralization in
South-West England. Min. Magazine, v. 46, p.
211-215.
Williams, H. and Mc Birnery, A.R., 1979,
Volcanology: San Francisco, Freeman, Cooper
& Co.
Winkler, H.G.F., Boes, M. and Marcopoulos, T.,
1975, Low temperature granitic melts. N. Jb.
Min. Mn., v. 6, p. 245-268.

7. 45
U Nb
Nb
U
Ca
Si
TaFe
TiSc
(a)
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00
Ti
Nb
Nb
Fe
Ta Pb
Si
UCa
(b)
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00
Th
Si
Y
Fe Th
Al
Fe
2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00
(c)
Fig. (10): Semi-quantitative analyses using the EDAX –SEM.
a) Columbite, b) Plumbobetafite and c) Yttrialite.

8. 46
Th
U
Ca
Fe
Si
Y
Fe
Al
(a)
0.70 1.40 2.10 2.80 3.50 4.20 4.90 5.60 6.30
As
S Fe
As
(b)
1.70 2.70 3.70 4.70 5.70 6.70 7.70 8.70 9.70
(c)Mn
Ba
Pb
SiMn
2.00 4.00 6.00 8.00 10.00
Fig. (11): Semi-quantitative analyses using the EDAX –SEM.
a) Uranothorite, b) Arsenopyrite and c) Coronadite.

9. 47
285 236
114
1133
905
167
55 35 95
0
200
400
600
800
1000
1200
Tunnel
(n=12)
Trenches
(n=9)
Greisen
(n=4)
eU(ppm)
eTh(ppm)
Ra(ppm)
35 45 55 65 75
0
3
6
9
12
15
18
Nephelin
P-N
B+T
P-T
Phonolite
Benmorite
Mugearite
Hawaiite
Basalt
B-A Andesite
Dacite
Trachyandesite
Rhyolite
Trachyte
SiO2 (wt)
Na2O+K2O(wt)
Fig. (2): Bar-diagram showing the average
contents of eU, eTh and Ra (ppm) for the
anomalies sites of Um Safi area. (n= number
of samples)
Fig. (3): Na2O+K2O versus SiO2 diagram for
volcanic rocks, Um Safi area, after Cox et
al., (1979).
0 1 2 3 4 5 6
1
10
100
1000
FeOT
/MgO
Cr(ppm)
Abyssal tholeiites
Field volcanic rocks
of island arcs and continental
margins
0 1 2 3 4 5 6 7 8
1
10
100
400
FeOT
/MgO
Ni(ppm)
MORB
Island arcs
Fig. (4): Cr vs. FeOt
/MgO for rhyolite, Um Safi
area, after Miyashiro and Shido (1975).
Fig. (5): Ni vs. FeOt
/MgO for rhyolite, Um Safi
area, after Miyashiro and Shido (1975).
0.003
0.01
0.1
1
10
100
1000
Sr K Rb Ba Nb Zr Y
Rock/MORB
( a )
0.1
1
10
100
Sr K Rb Ba Nb Zr Y
Rock/C.C.
( b )
Fig. (6): Spider diagrams of normalized values of rhyolite, Um Safi area, after Hofmann (1988).
a) related to MORB b) related to bulk continental crust

10. 48
Ab Or
Q
Greisen
Silicic
Sodic Potassic
P H2O= 1kb
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
7
Na (%)
K(%)
D
esilicification
K- m
etasom
atism
Na - m
etasom
atism
Argillition
Silicification
Fig. (7): Normative Q-Ab-Or ternary diagram,
showing the alteration of volcanic rocks, Um
Safi area, after Stemprok (1979).
Fig. (8): Na% – K% variation diagram, showing
the alteration types for volcanic rocks, Um
Safi area, after Cuney et al. (1989).
1 313
SiO2
TiO2
Al2O3
Fe2O3
FeO
MnO
MgO
CaO
Na2O
k2O
P2O5
EnrichedDepleted
Fresh
Altered
1 10 3011030
Rb
Sr
Ba
Zr
Y
Nb
Zn
Pb
V
Cr
Ni
Co
Ga
U
Th
EnrichedDepleted
Fresh
Altered
Fig. (9): The enrichment and depletion of major oxides (a) and some trace elements (b) of the
altered relative to the fresh rhyolite samples, Um Safi area.
(a) (b)

11. 49
Table (1): Result of chemical analyses and CIPW normative minerals for
fresh volcanic rocks, Um Safi area.
Fresh volcanic rocksMajor
Oxides
1 2 3 4 5 6 7
SiO2 75.07 69.49 71.2 70.51 69.55 70.61 71.16
TiO2 0.13 0.12 0.11 0.12 0.11 0.13 0.11
Al3O3 12.5 14.09 13.85 14.12 14.62 14.29 13.09
Fe2O3 1.76 2.01 1.21 1.61 2.71 2.72 2.45
FeO 0.40 0.36 0.56 0.76 0.86 0.44 0.32
MnO 0.07 0.06 0.09 0.08 0.07 0.08 0.09
MgO 1.01 0.91 0.88 0.96 0.79 1.12 1.11
CaO 1.80 1.36 1.68 1.40 1.12 1.40 1.96
Na2O 3.93 4.63 3.80 3.90 3.75 3.64 4.10
K2O 3.36 4.43 4.55 4.24 4.58 3.79 3.46
P2O5 0.09 0.08 0.10 0.07 0.10 0.08 0.09
L.O.I 0.79 1.99 1.64 1.68 1.14 1.27 1.74
Total 99.91 99.53 99.67 99.54 99.41 99.57 99.68
Trace elements (in ppm)
Rb 298 308 239 259 223 215 54
Sr 12 12 19 11 12 13 13
Ba 494 249 440 466 283 430 350
Zr 876 921 883 1005 1205 1007 1307
Y 282 296 283 321 387 321 420
Nb 32 31 33 30 32 31 30
Zn 23 37 48 31 56 28 41
Pb 78 81 38 36 75 41 595
V 5 5 7 7 5 5 5
Cr 58 97 86 78 120 95 110
Ni 1 3 3 3 5 4 2
Co 4 3 3 3 3 4 4
Ga 52 56 33 38 46 52 39
U* 32 24 25 29 28 17 34
Th* 41 51 44 49 48 32 75
CIPW normative values
Q 34.61 22.49 27.69 27.98 27.38 31.01 29.54
Or 19.85 26.86 27.45 25.65 27.57 22.81 20.9
Ab 33.18 40.12 32.76 33.71 32.25 31.3 35.38
An 6.50 4.65 7.4 6.69 5.06 6.59 7.21
Di 1.47 1.39 0.40 - - - 1.7
Hy 1.84 1.69 2.08 2.47 2.01 2.85 2.05
C - - - 0.72 1.69 1.84 -
Mt 1.14 1.03 1.79 2.39 2.73 1.32 1.03
Hm 0.97 1.35 - - 0.88 1.85 1.79
Il 2.25 0.23 0.21 0.23 0.21 0.25 0.21
Ap 0.20 0.18 0.22 0.16 0.22 0.18 0.20
* = Radiometric analyses

12. 50
Table (2): Result of chemical analyses and CIPW normative minerals for altered volcanic
rocks and greisen, Um Safi area.
Altered volcanic Greisen
Kaolinized Argillite Silicified FerrugenatedMajor
Oxides 8 9 10 11 12 13 14
SiO2 70.57 71.11 72.05 76.7 81.5 80.06 69.07
TiO2 0.10 0.11 0.10 0.12 0.13 0.11 0.13
Al3O3 12.19 13.19 11.57 8.94 9.25 11.10 9.43
Fe2O3 3.03 2.18 4.39 3.39 0.81 2.42 10.2
FeO 0.52 0.20 0.28 0.56 0.36 0.80 1.64
MnO 0.14 0.18 0.08 0.08 0.11 0.04 0.18
MgO 2.00 2.80 1.20 0.80 0.80 0.80 0.60
CaO 2.80 1.68 2.24 1.98 1.68 1.12 1.96
Na2O 4.60 0.67 2.76 2.64 0.34 0.31 0.67
K2O 1.22 2.67 1.22 0.93 0.83 1.00 2.37
P2O5 0.10 0.13 0.10 0.10 0.10 0.12 0.15
L.O.I 2.70 3.56 3.94 3.70 3.55 2.08 2.47
Total 99.97 98.48 99.93 99.94 99.46 99.96 98.87
Trace elements (in ppm)
Rb 114 39 112 84 22 507 646
Sr 10 13 14 12 13 12 12
Ba 232 257 226 233 241 98 100
Zr 1193 862 1148 830 855 1133 529
Y 385 277 370 269 274 363 169
Nb 32 32 31 34 35 30 28
Zn 144 80 788 729 248 316 325
Pb 68 44 38 36 49 266 409
V 5 3 4 4 4 4 5
Cr 69 99 78 87 119 86 87
Ni 1 2 2 1 1 2 2
Co 3 4 4 4 3 3 3
Ga 43 34 53 43 30 55 52
U* 105 74 435 426 522 101 125
Th* 249 304 2007 1736 2006 161 172
CIPW normative values
Q 32.26 52.17 46.89 54.68 74.86 72.68 42.93
Or 7.42 16.64 7.52 5.72 5.12 6.04 14.54
Ab 39.97 5.97 24.3 23.18 3.00 2.68 5.87
An 9.24 7.98 10.97 9.6 8.08 4.96 9.18
Di 3.45 - - - - - -
Hy 3.54 7.37 3.13 2.08 2.09 2.04 1.56
C - 6.75 1.92 0.20 5.16 4.83 2.60
Mt 1.89 0.96 0.91 1.78 1.19 2.44 5.70
Hm 1.81 1.63 3.95 2.29 0.02 3.85 17.02
Il 0.20 0.22 0.20 0.24 0.26 0.21 0.26
Ap 0.22 0.30 0.23 0.23 0.23 0.27 0.34
* = Radiometric analyses

13. 51
Table (3): Average of chemical composition of the studied rhyolite in comparison with
some Egyptian and World related rocks.
RhyoliteMajor
Oxides 1 2 3 4 5 6
SiO2 71.08 73.22 75.31 75.83 69.7 72.8
TiO2 0.12 0.42 0.23 0.24 0.38 0.28
Al2O3 13.79 12.59 12.55 12.3 14.0 13.3
Fe2O3 2.07 1.60 0.77 1.71 2.26 1.50
FeO 0.53 0.10 0.54 0.59 1.50 1.10
MnO 0.08 n.d 0.04 0.03 0.07 0.06
MgO 0.97 0.81 0.14 0.17 0.99 0.39
CaO 1.53 0.97 0.35 0.56 1.60 1.14
Na2O 3.96 5.38 3.86 3.32 4.20 3.60
K2O 4.06 3.58 4.29 4.12 4.10 4.30
P2O5 0.09 n.d 0.03 0.02 0.09 0.07
n.d= not determined
1-Average of fresh rhyolite of the studied area.
2-Average of rhyolite of Wadi Natash, Eastern Desert (Sayyah and El Shatoury, 1973).
3-Average of rhyolite of Wadi Kid, Sinai (Shahien, 1996).
4-Average of rhyolite of Abu Swayel, South Eastern Desert (Shahien, 1996).
5-Average of Egyptian rhyolite (Aly and Moustafa, 1984).
6-Average of World rhyolite (Le Maitre, 1976).
Table (4): eU, eTh and Ra contents in ppm and K (%), eU/Ra, eU/eTh and eTh/eU ratios of rhyolite and
anomalies.
Radiometric measurements
Rock types
eU
(ppm)
eTh
(ppm)
Ra
(ppm)
K(%) eU/Ra eU/eTh eTh/eU
Min. 17 32 12 1.75 1.4 0.4 1.7
Max. 34 75 14 4.29 2.4 0.6 2.2
Rhyolite
(n=6)
Average 26 50 13 2.99 2 0.5 1.9
Min. 53 236 13 0.39 3.7 0.2 2.8
Max. 563 2229 115 3.44 6.9 0.4 4.7
Tunnel
(n=12)
Average 285 1133 55 1.71 5.2 0.3 3.9
Min. 132 157 21 0.19 3.9 0.2 0.5
Max. 335 1188 49 4.4 9.7 2.1 5.8
Trenches
(n=9)
Average 236 905 35 1.6 7.0 0.5 4.1
Min. 101 161 90 2.08 1.09 0.62 1.33
Max. 125 172 97 2.66 1.29 0.75 1.61
Anomalies
Greisen
(n=4)
Average 114 167 95 2.37 1.19 0.68 1.48

14. 52
.
*–*–***
*
**
)(
.–
..
.
.
)().(
.
)––(.
)(
).(