Essay: Groundwater in contact with ore deposits

Abstract: Groundwater in contact with ore deposits may acquire a chemical composition that could be
used as a guide for exploration. Eight well-wa ter samples are collected from a known uranium-
mineralized area near Abu Zenima, west central Sinai to examine the applicability of using the
hydrogeochemical technique in the search for uran ium mineralization in si milar arid areas. The
analytical chemical data of the ground water is compared with ground radiometric measurements.
The obtained results indicate that groundwater a ffected by uranium mineralization has a specific
relativity of major anions expressed essentially as SO 4>Cl>HCO3 and to a lesser extent as
Cl>SO4>HCO3, associated as a rule with low magnesiu m content. This association constitutes a
signature of uranium mineralization on the compos ition of groundwater in west central Sinai and
could be used as an important exploration guide in the search for uranium depo sits in similar areas.
Anomalies in Ni, Fe, Zn and Cr and other pathfinder elements in groundwater can furnish
geochemical guides to uranium ores. The immobile trace element anomalies, including Zn, Ni and Fe
are strongly distributed near the orebody; whereas the relatively mobile trace elements, including Co,
U, V and Cr, constitute the dispersion haloes away from the orebody. A new hydrogeochemical
discrimination diagram is constructed to be used as a quick and cost effective exploration tool in the
search for uranium occurrences in environmentally similar arid areas. Based on the obtained results,
a new site for uranium occurrence, west of W. Baba, is delineated and recommended for future
detailed geological and geochemical surveying.
Key words: Hydrogeochemical exploration, Uranium ores, geospatial mapping, graphical exploration
tool, remote sensing, Sinai
1 Introduction
The geochemical detection of uranium deposits in
sedimentary rocks depends on the geochemical behaviour
of U and pathfinder elements. Uranium is extensively
dispersed under oxidizing conditions but is immobile
under reducing conditions. Groundwater in contact with
ore deposits may acquire a chemical composition that
could be used as a guide for exploration. Background
values for U in water are increased by evaporation and
transpiration in arid regions. Possible pathfinder elements
associated with U in sedimentary deposits include SO 4, V,
Cu, Cr, Zn, Ni, Co and other radioactive decay products
(Rose and Wright, 1980). The exploration approach must
take into account the channelling of dispersion and
possible concealment of deposits by bedding in
sedimentary rocks. Uranium and radium represent the
main radioelements characterizing some lithologies in the
west central Sinai sedimentary succession that is
considered to be one of the most arid parts of Egypt (El
Aassy et al., 2011). Sedimentary rocks of the upper
Paleozoic (lower Carboniferous) in the west central Sinai
arid region were subjected to several weathering and
alteration processes such as karstification (El Sharkawi et
al., 1989, El Sharkawi et al., 1990), lateritization (El
Aassy et al., 1999) and other pedogenic and hydrothermal
activities (Segev, 1984). This district has been known for
its polymetallic mineralization, especially copper deposits
and turquoise at Sarabit El-Khadim, since the Ancient
Egyptians (El-Rayes et al., 2001; Khalifa and Arnous,
2012). Furthermore, uranium mineralization in west
central Sinai occurs as secondary minerals formed by the
alteration of a pre-existing primary uranium mineral in
igneous rocks and subsequently hosted in Lower
Carboniferous rocks (Um Bogma Formation) (Dabbour
and Mahdy, 1988). Very little research has been carried
out into the water-rock system to locate uranium
mineralization in west central Sinai (Mahdy et al., 1998).
The geochemistry of natural waters traditionally has
provided important clues for the explorationist to locate
hidden deposits. The geochemical mobilities in natural
water are determined largely by three fundamental
processes: element speciation in solution, precipitation of
minerals, and surface sorptio n processes. In addition,
groundwater uranium contents can be so difficult to be
interpreting that it may be more useful to use the
relationship between the major element compositions of
groundwater in the search for uranium mineralization. The
obtained data are interpreted to assess the usage of some
pathfinder species as predictors of uranium mineralization
in other similar arid areas. The regional hydrogeochemical
prospecting and the verification of radioactive anomalies,
based on morpho-structural analysis, radiometric
measurements and other ancillary geological data, are very
important controlling factors to note the uranium ores in
arid areas (Gordanic et al., 2006; Verma et al., 2011).
The radiometric techniques are the most useful
exploration methods. In developing countries that are
interested in starting uranium exploration programmes,
there are other problems as well as those outlined above:
lack of, or difficulty in obtaining, the requisite number of
qualified personnel for field and laboratory activities (lack
of manpower); lack of administrative and technological
infrastructure needed to support an exploration effort (lack
of technology); and relatively small budgets for a multi-
year program (lack of money). Consequently, to determine
the major geochemical controls on ore deposits, regional
exploration geochemical modelling has been undertaken
using groundwater chemistry of wells draining a known
uranium deposit in the west central Sinai area. The current
study aims at a greater understanding of the spatial and
temporal variations in groundwater chemistry and
hydrogeochemical controls influenced by a uranium
orebody. Remote sensing, GIS and statistical tools were
applied to extract the lithological, structural and
geomorphological data, which were then integrated with
hydrogeochemical and radi ometric measurements to
design the hydrogeochemical exploration model for
uranium mineralization in west central Sinai, Egypt.
Moreover, a novel hydrogeochemical discrimination
diagram for uranium-mineralized groundwater in west
central Sinai is proposed to be used in the search for
uranium ores in similar areas. Using the proposed
discrimination diagram will reduce the costs and time
needed for any exploration program in environmentally
similar arid regions around the world.
2 Geology and Mineralization of the Study
Area
The investigated area is located to the east of Abu
Zeneima Town on the east coast of the Gulf of Suez, west
central part of Sinai, Egypt. This environment is bounded
between Latitudes 29”00”29”05’N and Longitudes 33”
20”33”25’E and covers an area of about 71 km2 (Fig. 1). It
is covered by a sedimentary succession of Cambro-
Ordovician, Lower Carboniferous, Cretaceous and
Quaternary ages overlying the Proterozoic granitic rocks
that have an age of 591”6 Ma (Be’eri-Shlevin et al., 2009;
Eyal et al., 2010) and comprising the northern part of the
Arabo-Nubian crystalline massif. The Southern Sinai lies
between the eastern and western flanks of the Red Sea
Gulf rifts ( Fig. 2) and it has been subjected to intensive
faulting during the rift activities. There are two main fault
structures, the first one runs along the contact between the
sedimentary section and the basement complex, while the
second one runs along the Gulf of Suez coast to the west.
These two main faults are comparatively dissected by
minor transversal faults and sometimes they branch into a
series of small and roughly parallel step faults (Abdallah
and Abu Khadra, 1976). The Red Sea Basin Province
originated as an Oligocene continental rift impacted by
left-lateral wrenching. Rift location and borders are
defined by crustal weaknesses created more than 500 Ma,
including the late Proterozoic to early Paleozoic
cratonization of the Arabian-Nubian shield, its suturing to
the African continent, and subsequent supercontinent
breakup. Those events resulted in the juxtaposition of
structurally and compositionally different basement
terranes. Said (1962), and El-Gezery and Marzouk (1974),
showed that the depth of the basement increases
northwards towards the Mediterranean Sea. The Paleozoic
rocks are characterized by continental clastic deposits. The
marine episodes are minor in space and time.
The west central Sinai area forms topographically
moderate mountain peaks such as Gabal (G.) Um Rinna,
G. Hazbar and G. Nasib and is dissected by numerous
valleys (wadis) such as W. Baba, W. El-Seih, W. Allouga ,
W. Nasieb, and W. Hamata. The major one (Wadi Baba)
that forms the western boundary of the study area,
originated through the joining of Wadi Nasieb with Wadi
Seih at the north eastern part of the mapped area (Fig. 1).
These wadis are mainly structurally controlled by the NW
and NE fault trends ( Fig. 3). The study area is dominated
by an arid climate of desertic conditions. It has low
precipitation, high evaporation and temperature with a
long hot summer and a short mild winter. In addition, it
occasionally receives heavy rain storms every two or four
years (El-Shamy, 1983), producing heavy flash floods.
Many geological, structural, geochemical and
geophysical studies have been carried out on the study
area such as El Kassas (1967) , Soliman (1975), Moustafa
(1987), El Shahat and Kora (1988), El Rakaiby and El
Aassy (1989), El Sharkawi et al. (1990a), Mansour (1994),
Bishay (1994), Morsy et al. (1995), Botros (1995),
Ashami (1995 and 2003), Aita (1996), El-Agami (1996),
Amer (1997), Abd EL-Monem et al. (1997), Ammar et al.
(1999), Afifi (2001), Abdelaziz (2000), El Aassy et al.,
(2003) Shata (2006), El Aassy et al., (2011) Khalifa and
Arnous (2012). Hussein et al. (1971) stated that some of
the felsite and microgranites of the basement rocks of G.
Nasib have a radioactivity reaching three times the
background level. This may indicate that the Proterozoic
basement rocks constitute the ultimate source of uranium
mineralization in the overlying Paleozoic succession.
Moreover; the Paleozoic rocks are cut by numerous faults
in various blocks with vertical displacement reaching up to
100 m, sometimes forming horst and graben structures.
The major faults usually control the location of deep wadis
as well as the landscape (Ashami, 2003). Botros (1995)
suggested that the Carboniferous sedimentary rocks in the
Um Bogma area, west central Sinai have been subjected to
young rift tectonics during the Late Cenozoic producing
faults parallel to the Suez rift. There are two stages of
deformations; the first stage is the initial opening of the
Fig. 2. Major tectonic boundaries of Sinai subplate (after
Diabat, 2011).
Fig. 1. Physiographic and key location map of west centeral
Sinai, Egypt.
Fig. 3. Geological map of west central Sinai.
Suez rift in the Late Oligocene and the second stage is due
to late Cenozoic rifting. El-Agami (1996) concluded that
faulting plays a major role in the tectonics of the Um
Bogma area. The NNW and NW trending faults are most
abundant, while the N-S, NNE, NE and ENE trending
faults are subordinate. He added that folding plays a
secondary role in the structural evolution of the study area.
The Paleozoic succession in west central Sinai forms
the most important sedimentary basin that contains
uranium mineralization in Egypt. This succession belongs
to seven formations of the Paleozoic era ( Fig. 4), which
are grouped, from older to younger, into two main
associations, the Cambrian Lower Clastics and the Early
Carboniferous Upper Clastics. The former comprises the
Sarabit El-Khadim, Abu Hamata and Adedia Formations.
The latter is made up of the Um Bogma, El-Hashash,
Magharet El-Maiah and Abu Zarab Formations (Soliman
and Abu El-Fetouh, 1969). Not all of these formations are
exposed in the study area. The present study is restricted
to the Um Bogma carbonate Formation which hosts highly
uraniferous levels (800-5000 ppm U) (Hussein et al.,
1992), and the base of the disconformably overlying El
Hashash Formation. The Um Bogma Formation is
subdivided into three members described below:
(1) Lower Shaly-Ore Member comprises black shales
with thin sandy dolomite bands and manganese-iron ore
(Weissbrod, 1969) (Fig. 5a). Its thickness ranges from 2 to
14.5m. El Sharkawi et al. (1989) suggested a karstification
process in this member and the formation of karstified
dolostone rocks with intrakarstic product housing
manganese ores and caliche nodules. El Aassy et al.
(1999) introduced the lateritic profile section and the
formation of gibbsite-bearing shale. This rock unit is
highly radioactive when it is karstified and lateritized. The
Fig. 4. Compiled lithostratigraphic section of Precambrian and Paleozoic rocks,
south-western Sinai, Egypt (modified from El Agami, 1996).
lateritization process leads to the migration of uranium,
but the produced laterites of either grey (Al) or brown (Fe)
soils are good adsorbents for uranium and other heavy
metals. The karstification process leads to the formation of
caves which are filled by either allochtonous or
autochtonous soils. These karst soils host uranium and rare
earth elements (El Aassy et al., 2006).
(2) Middle Marly Dolostone-Siltstone Member is also
karstified and lateritized and consists of marl with
siltstone and gibbsite-bearing siltstone (Fig. 5a). Its
thickness is 6’9 m and it is moderately radioactive.
(3) Upper Dolostone Member unconformably overlies
the karstified and lateritized middle member and consists
of bedded dolostone with thin shale interbeds (Fig. 5b).
The dolostone beds are present as step-like forms and in
some parts are not deposited and laterally vary to grey
claystone. The dark grey claystone as noticed in the
Allouga, Abu Zarab and Abu Hamata localities is enriched
in elemental sulphur as an oxidation product of pyrite and
chalcopyrite. Its thickness is 3’4 m and the dolostone has
low radioactivity, while the dark grey claystone is
moderately radioactive. Visible secondary uranium
mineralizations are observed associated with the Um
Bogma Formation in siltstone, shale, clay, and gravel.
The El Hashash Formation disconformably overlies the
Um Bogma Formation and consists of sandstone with thin
siltstone at the base. The contact with the unit below
shows siltstone with alunite which indicates severe
alteration at the base of this formation. It is 10’20 m thick,
and has low radioactivity, except at the base where it is
enriched in alunite.
El Aassy et al. (1986) recorded some radioactive
anomalies in various localities of the investigated area at
Abu Thor, Allouga, Ramlet Homaier, W. Um Hamd and
Ras Rahia. The mineralization occurs mainly as secondary
uranium minerals, including liebigite, K-zippeite,
carnotite, Rb-carnotite, meta-autunite, hydrogen-autunite,
metatorbernite, meta-zeunerite and meta-tyuyamunite; and
detrital radioactive minerals, including xenotime, sphene,
apatite, zircon, monazite, euxenite, fergusonite and allanite
(Dabbour and Mahdy, 1988; Hussein et al., 1992; Shata,
2012). Uranyl minerals of the middle carbonate rock units
(Um Bogma Formation) are represented mainly by
zippeite, uranophane, carnotite, meta-autunite and meta-
torbernite (Hussein et al., 1971; El-Reedy et al., 1988;
Afifi, 1991; Hussein et al., 1992; El-Agami, 1996; Abdel
Monem et al., 1997 and El Galy et al., 2008).
Geochemical studies indicate that uranium was
deposited from alkaline water at pH 7.5 to 8.5 and
concentrated by evaporation under oxidizing conditions
(El-Reedy at al., 1988). Hussein et al. (1992) suggested
that the uranium mineralization in the Paleozoic rocks of
the study area is of surficial type uranium deposits.
Hussein et al. (1971) stated that some of the felsite and
microgranites of the basement rocks of G. Nasib have a
radioactivity reaching three ti mes the background level.
This may indicate that the basement rocks constitute the
ultimate source of uranium mineralization in the overlying
Paleozoic succession. The surficial uranium deposits in
sedimentary environments of arid regions are formed by
the interaction of surface or groundwater upon the
geomorphic surfaces in favourable geological terrains and
climates. Uranium dissolution and transportation mostly
occurs under oxidizing conditions. The formation of
surficial uranium mineral deposits in the study area
includes at least three geochemical processes leading to
their deposition (Hussein et al., 1992), namely:
(1) Leaching of pre-existing uranium minerals
present in the source Basement complex by circulating
meteoric water at high Eh. The dissolved uranium is
complexed by the formation of uranyl dicarbonate and
Fig. 5. a-Lower (L), middle (M) and upper (U) member of
Um Bogma Formation at Wadi Abu Hamata locality. b- Un-
conformity surface between lower siltstone (Ls) and middle
marl (Mm) of Um Bogma Formation at Abu Thora locality.
tricarbonate (UDC and UTC) complexes (Gamble, 1984).
After precipitation of calcite and/or dolomite from water,
the bicarbonate concentration decreases leading to the
dissociation of the UDC and UTC complexes. The
released uranium ions then combine with the dominant
potassium and the small amounts of vanadium to form
potassium uranyl vanadate (carnotite).
(2) Trapping of the uraniferous solutions within
suitable structural and lithological controls that are
represented in the study area by clays, shales and dolomite
associations. Clay minerals may represent an important
parameter in uranium concentration. This was confirmed
by Gauthier’s (1961) experimental work on adsorption or
co-precipitation of uranium by different types of clays.
(3) Evaporation and re-deposition processes by the
action of percolating waters under arid climatic conditions
which are characterized by low average rainfall, high
average temperatures and low average humidity.
3 Materials and Methods
3.1 Remote sensing and GIS
Remote sensing and GIS tools play important roles in
the spatial integration of various data sets including
geological maps, Landsat ETM+7 image, ASTER GDEM,
airborne radiometric data and hydrogeochemical data was
applied to show the distribution and intensities of
radioactive mineralization relative to the lithological units
and structural elements of the study area by using ERDAS
Imagine and ARC GIS software.
Landsat Enhanced Thematic Mapper plus (ETM+7)
data of the study area was processed for geological and
structural mapping. A single Landsat ETM+ scene (Path
175, Row 40, date 2005) with eight bands of Landsat-7,
about 185”185 km covering the investigated area, was
geometrically and radiometri cally corrected. The ETM+7
was then represented in UTM projection with an output
pixel size of 30 meters. The panchromatic band of the
ETM+7 is digitally processed and merged with an output
pixel size 15 meters using topographic maps of scales
1:50,000, 1:100,000 and the geological map of CONOCO
(EGPC/CONOCO, 1987) as reference maps. False colour
composite (FCC) images (7, 4, 2 in RGB), principal
component (PC) images (4, 2, 1 in RGB), ratio images
(bands 5/7, 5/4, 3/1 and 5/7, 4/5, 3/1) in RGB and
brightness inversion techniques are used for detecting the
regional tectonic structures, lithological discrimination,
drainage network as well as for revealing the
radiometrically anomalous zones in the study area (Fig. 6).
Toward this end, spatial analyses and digital mapping of
the geographical database by GIS tools were used to
analyse the lithological, st ructural, geomorphological,
radiometric, hydrogeological and hydrogeochemical data
of the study area.
3.2 Radiometric ground survey
Radiometry, that is the measurement of radioactivity, is
considered as one of the most important remote sensing
techniques applied in uranium exploration, mostly
depending on detecting gamma radiation using a
scintillation counter. However, although uranium is easy
to detect at or near the surface, it is less so when it is
concealed under a thick soil cover. To overcome this,
some uranium prospecting techniques utilize the daughter
element radon as a pathfinder (Said and Assran, 2005). In
the present work, the anomaly location map of the
radiometrically active sites is extracted from the airborne
radiometric data map by using GIS tools ( Fig. 7).
Moreover, a detailed ground radiometric survey using
gamma ray spectrometer model GS-512 was conducted
along six profiles crossing the mineralized zone, and used
to correlate the hydrogeochemical data with the ground
radiometric anomalies (Fig. 8).
The GS-512 is a Gamma Ray Spectrometer designed for
field gamma ray spectrometry, especially for
determination of K, U, Th contents and total gamma ray
activity. Immediately after th e end of measurement, the
contents of K (%), U, Th (ppm) or the number of count
rates in the surveyed area can be displayed. The
instrument is adjusted and Calibrated at the Nuclear
Material Authority facility, Cairo, while the short term
stability and consistency of th e instrument are carried out
in the field camp. The instrument has a stabilisation
sensitivity of 0.5 %.
3.3 Hydrogeochemical Methods
The most abundant dissolved constituents measured are
the major ions (Bartos and Ogle, 2002), which can be both
positively charged (cations) and negatively charged
(anions). The most abundant cations present in water are
calcium (Ca 2+), magnesium (Mg 2+), sodium (Na +), and
potassium (K +); while the most abundant anions are
bicarbonate (HCO3
-), chloride (Cl-), and sulphate (SO4
2-).
Eight well waters around the known uranium
mineralization of the study area were sampled using a
non-metallic thief-type sampler and chemically analysed
for major and some trace metal contents. The polyethylene
bottles were rinsed three times with the water to be
sampled. Two samples were taken from each well: a 500
ml unfiltered sample for major ion determinations, and a
100 ml sample which was filtered and acidified with
HNO3 to a pH value less than 2 and used for trace element
determinations. All samples were analyzed using the
standard methods described by APHA (1989).
Determination of the major constituents was performed by
using several determinative methods: HCO 3
-, Cl-, Ca2+ and
Mg2+ titrimetric, Na + and K + flame photometric and SO 4
2-
colorimetric.
Trace element analyses including Zn, Ni, Fe, Co, V and
Cr were performed with an atomic absorption
spectrophotometer (Perkin Elmer), while U was
fluorimetrically determined. Detection limits are 1.5 ”g/l
Zn, 6 ”g/l Ni, 5 ”g/l Fe, 9 ”g/l Co, 60 ”g/l V, 3 ”g/l Cr
and 50 ”g/l U. All detection limits are based on a 98%
confidence level.
The ionic composition of water is used to classify it into
ionic types based on the dominant dissolved cation and
anion, expressed in milliequivalents per litre (meq/l). A
milliequivalent (meq) is a measurement of the molar
concentration of the ion, normalized by its ionic charge.
Cation and anion concentrations (in meq/l) for each ground-
water sample were plotted on a Schoeller diagram
(Schoeller, 1935). Trace elements were represented as
element distribution contour maps using SURFER’
software.
3.4 Statistical analysis of the data
Statistical analyses were applied to the obtained
hydrogeochemical data of the study area using SPSS
software. The statistical anal yses associations include R-
mode and Q-mode cluster analysis based on the complete
linkage method, correlation coefficients and factor
analysis.
Cluster analysis is the name given to an assortment of
techniques designed to perform classification by assigning
observations to groups so each is more-or-less
homogeneous and distinct from other groups (Davis,
1986). As an exploratory technique with graphic output,
Fig. 6. Enhanced ETM satellite image of west central Sinai, Egypt.
cluster analysis does not require many of the assumptions
that other statistical methods do, except that the data is
heterogeneous. It provides an easily understood graphic
display (dendrogram), and is a method used frequently in
the geological sciences to help classify or group samples/
variables of a data set. It helps to identify natural
groupings for samples (Q-mode) or variables (R-mode),
and, in turn, reduces the size of the samples/variables into
smaller numbers of groups.
For the Q-mode analysis of the present geochemical
data, the Cosine Theta simila rity coefficient was used.
Cosine Theta expresses the similarity between samples by
regarding each as a vector defined in p-dimensional
variable space, and calculate s the cosine of the angle
between the two vectors. It is sensitive only to the relative
proportions of the variables, and not to their absolute
magnitudes. This makes it a very good method for this
data set, because it is the grouping of samples according to
variables that is of interest, not the relative chemical
distribution among the samples.
For the R-mode analysis, the Product-Moment
Correlation Coefficient was chosen in order to be
consistent with later R-mode factor analysis in which the
Correlation Coefficient is considered the standard method
in similarity matrix calculation. Before the similarity
coefficient matrix was calculated, percentage
transformation was done for each sample in order to avoid
the influence of the magnitude of a particular variable.
4 Hydrogeology
The Adedia Formation together with the underlying
Abu Hamata and Sarabit El-Khadim Formations (Lower
Sandstone unit) are the primary water-producing units in
the study area. It is equivalent to the Cambrio-Ordovician
aquifer that is regionally spread out all over central and
northern Sinai. The regional flow in this aquifer takes
place from the outcrop areas in the south towards the north
and northwest (Mills and Shata, 1989). On the local scale,
the lower sandstone (Adedia Formation) attains a
thickness of about 60m and is tapped by large-diameter
dug wells with depths varied between 6m and 15m. The
lower sandstone unit is hydraulically connected with the
overlying carbonate unit (Um Bogma Formation), so that
the downward percolation of groundwater from the
overlaying Um Bogma Formation moves freely to the
lower sandstone unit through the interconnected bedding
planes and open fractures ( Fig. 9). This is confirmed by
the absence of any perched water over the Um Bogma
Formation. The principal rechar ge occurs in the southern
high mountainous area of Sinai at El-Tih Plateau, where
this unit crops out and directly receives the rainwater, that
Fig. 7. Airborne radiometric anomaly location map of west
central Sinai (modified from AGS, 1966).
Fig. 8. Ground isoradiometric map of west central Sinai,
Egypt.
it has a maximum intensity of about 70mm/y (Shata,
1992). A possible secondary recharge might occur by
leakage from the adjacent base ment aquifer as subsurface
inflow through the joint system, especially at the lowland
areas and valley floors (Fig. 3).
5 Radiometric Survey
The area under investigation is included in the airborne
radiometric survey conducted by the airborne geophysical
section of the Egyptian Atomic Energy Authority program
(AGS, 1966), covering a large segment of western Sinai,
Egypt. The extracted airborne radiometric map of the
study area exhibits 18 radiometrically active sites
reflecting the high radioactive ore potentiality of the study
area (Fig. 7).
To confirm the obtained results of the airborne
radiometric data, six profiles of ground radiometric survey
crossing the uraniferous zone were measured using
gamma ray spectrometer model GS-512. They crossed the
Basement rocks, Adedia, Um Bogma and El-Hashash
Formations. The obtained ground measurements are
converted into the equivalent mg/l uranium (eU ppm)
(Table 1) and used to construct the ground isoradiometric
map of the surveyed area to define the distribution of
radiometric anomalies and correlate them with the
locations of water wells (Fig. 8). The resultant radiometric
map shows two main anomalies. The first one is very
strong and located along the western flank of Wadi Naseib
with a long axis extending E-W. This anomaly is very
close to well numbers N-1, N-2, and N-3 of Wadi Naseib.
Fig. 9. 3-D water table ma p of west central Sinai, showing the regional and local groundwater flow direc-
tions.
Table 1 Ground radiometric measurements along the U-
mineralized zone of west central Sinai, Egypt
Station No. Formation Lithology eU (ppm)
1-1
1-2
1-3
1-4
1-5
1-6
1-7
Um Bogma
Um Bogma
Um Bogma
Um Bogma
Um Bogma
Adedia
Basement
Marl
Dolostone
Dolostone
Marl
Dolostone
Sandstone
Granodiorites
56
6
4
38
5
6
3
2-1
2-2
2-3
2-4
2-5
Um Bogma
El-Hashash
Um Bogma
Adedia
Basement
Dolostone
Sandstone
Dolostone
Sandstone
Granodiorites
4
6
5
5
2
3-1
3-2
3-3
3-4
3-5
Um Bogma
Um Bogma
Um Bogma
Um Bogma
Basement
Marl
Shale+gibbsite
Marl
Marl
Granodiorites
14
286
44
31
3
4-1
4-2
4-3
4-4
4-5
Um Bogma
Um Bogma
Um Bogma
Um Bogma
Um Bogma
Shale
Shale+gibbsite
Marl
Dolostone
Shale
664
845
23
6
264
The second anomaly, which is weaker than the first one, is
located to the west of the mapped area at the eastern flank
of Wadi Baba. Well number H-5 drains the area of this
anomaly.
6 Hydrogeochemical Exploration
Because groundwater uranium contents can be so
difficult to interpret, it may be more useful to use the
relationship between the major element compositions of
groundwater in the search for uranium mineralization.
Eight groundwater samples were collected from the
Cambrio-Ordovician aquifer of the study area. All the
samples were obtained from large-diameter, shallow dug
wells of a depth less than 15m. Groundwater samples were
chemically analysed for majo r and some minor and trace
constituents. The compositional data including total
dissolved salts (TDS), Ca 2+, Mg2+, Na+, K+, HCO3
? , SO4
2 ?
and Cl ? with their relative proportions are listed in table 2.
Minor and trace elements content including Fe, Zn, Ni,
Co, U, V and Cr are listed in table 3. The obtained data
was interpreted to assess the usage of some pathfinder
species as predictors of uranium mineralization in the west
central Sinai area.
6.1 Statistical analyses and data grouping
Previous hydrogeochemical studies have tried to group
wells using graphical methods (Kimmelmann et al., 1989,
Szikszay et al., 1981 and Teissedre and Barner, 1981). The
present study has identified two main groups of
groundwater in the study area (Table 2), SO4
2? -type and Cl-
-type. Although the separation of these two waters is clear
based on the dominant anion, the absence of any
predominant cation in the groundwater system of the study
area makes it difficult to discern changes in water
chemistry. In trying to get a better separation of the
groundwater geochemical data, we used graphical methods
of cluster analysis, which gave more useful results.
6.1.1 Q-mode cluster analysis
Relying on the major ion data set, the output of the Q-
mode cluster analysis (Fig. 10) recognizes two clusters of
wells according to the level of clustering. By plotting the
wells on the location map, the two groups (A and B) can
be seen to be separated physiographically.
To recognize the mineralized wells (wells nearby and
affected by the uranium orebody), Q-mode cluster analysis
is performed based on major ions and the trace element
data set. The output of the Q-mode cluster analysis
recognizes two clusters of wells designated as mineralized
group (C) and non-mineralized group (D) ( Fig. 11). The
mineralized group contains four wells (N-2, N-3, H-3, H-2
and H-5) which are located along the flow path of ground
waters draining the orebody zone, whereas the non-
mineralized group contains wells (H-4, H-1 and N-1)
which are located relatively far away from the orebody
zone (Fig. 8).
6.1.2 R-mode cluster analysis
Based on the trace element data set, the R-mode
analysis is preformed to recognize the mobility of trace
element species. The dendrogram for the R-mode analysis
shows that there are two groups of trace elements in the
groundwater system of the study area, a Zn-Ni-Fe group
(E) and a U-Co-V-Cr group (F) ( Fig. 12). The group (E)
species is designated as immobile elements as they have
conspicuous anomalies close to the orebody zone, owing
to their relative immobility in this environment ( Fig. 13).
The group (F) species is designated as mobile elements as
they have significant concen trations as the distance
increases away from the orebody along the water flow
path (Fig. 14).
Table 2 Organized hydrochemical analytical data and the relative proportions of ions in groundwater from west central Sinai,
Egypt (Values in mg/l and meq/l*)
Hydrogeochemical
Group Sample No. TDS Ca Mg Na K HCO 3 SO 4 Cl Ion Relativity
N-1 700 84
4.19*
45.5
3.74*
61.6
2.68*
5.8
0.15*
99.6
1.63*
283
5.89*
120
3.39*
SO 4 >Cl>HCO 3
Ca>Mg>Na
H-5 958 116
5.79*
57
4.69*
123
5.35*
11
0.28*
104
1.71*
316
6.58*
231
6.52*
SO 4 >Cl>HCO 3
Ca>Na>Mg
N-3 655 61.7
3.08*
27.3
2.25*
105
4.57*
5.4
0.14*
115
1.89*
197
4.10*
144
4.06*
SO 4 >Cl>HCO 3
Na>Ca>Mg
N-2 718 72.5
3.62*
34.5
2.84*
98.6
4.29*
5.7
0.15*
99.6
1.63*
283
5.89*
125
3.53*
SO 4 >Cl>HCO 3
Na>Ca>Mg
H-3 927 90.3
4.51*
51.7
4.25*
105
4.57*
11
0.28*
114
1.87*
350
7.29*
204
5.75*
SO 4 >Cl>HCO 3
Na>Ca>Mg
A
H-4 1330 109
5.44*
71.5
5.88*
216
9.40*
11
0.28*
138
2.23*
490
10.20*
295
8.32*
SO
4 >Cl>HCO 3
Na>Mg>Ca
H-2 1181 152
7.59*
76
6.25*
129
5.61*
9.3
0.24*
108
1.77*
397
8.27*
309
8.72*
Cl>SO 4 >HCO 3
Ca>Mg>Na B
H-1 2822 252
12.58*
126
10.37*
586
25.50*
28
0.72*
78
1.29*
748
15.57*
998
28.15*
Cl>SO 4 >HCO 3
Na>Ca>Mg
Fig. 10. Q-mode cluster analysis of the major ion data set showing the chemical groups of
groundwater samples in west central Sinai area.
Fig. 11. Q-mode cluster analysis of the major ion and trace metal data set showing two groups of
groundwater in west central Sinai area.
Fig. 12. R-mode cluster analysis of the trace metal data set showing two groups of groundwater
in west central Sinai area.
Fig. 13. Immobile trace element distributions in the groundwater of west central Sinai, Egypt.
6.2 Major element hydrochemistry
Chebotarev (1955) concluded that groundwater tends to
evolve chemically toward the composition of sea water.
He observed that this evolution is normally accompanied
by changes in the dominant anion along the flow path
from HCO 3
– at the recharge zone (the start of the flow
Fig. 14. Mobile trace element distributions in the groundwater of west central Sinai, Egypt.
path), to SO4
2- at the intermediate zone and finally to Cl- at
the discharge zone (the end of the flow path). The
groundwater of the study area is highly enriched with
sodium and calcium relative to magnesium and potassium.
Sulphate contents are higher than chloride in the majority
of the samples, which also are depleted in bicarbonate.
This confirms that the st udy area is located at the
intermediate zone relative to the regional flow path of the
groundwater.
Schoeller plots (Schoeller, 1935), which illustrate the
Ca2+, Mg 2+, Na ++K+, Cl -, SO 4
2- and HCO 3
– contents in
meq/l, have been made for each water sample. The shape
of each plot is a ‘finger print’ for that water. Finger print
similarities have been used to identify waters that are
genetically related. On the basis of similarities in the
anionic part of each plot, samp les have been sorted into
two groups; ‘A’ and ‘B’ as illustrated in figure (15) and
table (2).
Group (A) consists of six samples (N-2, N-1, N-3, H-3,
H-5, H-4), having anion relativity arranged as
SO4>Cl>HCO3 (Fig. 15, group A).
Group (B) consists of two samples (H-2, H-1), with
Cl>SO4>HCO3 anion relativity patterns associated with
Na+ as a dominant cation (Sample No. H-1), reflects
groundwater of a longer flow path, and Ca as a dominant
cation (Sample No. H-2) that reflects mixing with water of
a shorter flow path (Fig. 15, group B). As groundwater
moves along its flow paths in the saturated zone, increases
of total dissolved salts (TDS) and most of the major ions
normally occur (Freeze and Cherry, 1979). The relatively
higher salinity level (high TDS) of the first water type (H-
1) and the lower salinity of the second water type (H-2)
confirm this hypothesis (Table 2).
Water with anion relativity arranged as Cl>SO 4>HCO3
associated with Ca2+ as the main cationic species reflects a
mixing of different types of waters. The increasing Ca
content gives an indication of the increased proportion of
water from the recharge area (rich in Ca 2+ content with
shorter flow path) in this mixture relative to the proportion
of water from the discharge area (rich in Cl- content with a
longer flow path).
Fig. 15. Schoeller plots of the major element composition of groundwater in west central Sinai, showing the ion rela-
tivities of each water group.
6.3 Trace element hydrochemistry
In groundwater, the majority of trace elements are
migrating as complex compou nds with the major ions.
Thus, the elements that are less capable of forming soluble
complex compounds are less mobile in water (Shvartsev et
al., 1975). Trace elements such as U, V, Co and Cr,
capable of forming negatively charged complex
compounds, are the most mobile in oxidation environments
(Perel’man 1963). A number of elements, including Zn, Fe
and Ni, form readily soluble compounds under this
condition, leading to increase their mobility. Spirov (1970)
notes that Zn, Ni and Co are concentrated mainly in the
precipitated carbonate and gypsum. This is consistent with
the association of uranium mineralization in west central
Sinai, where uranifereous Zn- and Co-rich jarosite [KFe 3+
3
(SO4)2(OH)6] and Cr-rich atacamite (Cu 2Cl(OH)3) are
strongly associated with evaporite minerals such as
gypsum, halite, calcite and barite. Ni-rich xenotime (YPO 4)
is mainly found as detrital U-bearing minerals in sandstone
beds of the study area (Hussein et al., 1992).
The uranyl core readily co mplexes with carbonate to
form charged soluble carbonate complexes that increase its
solubility, availability, and mobility with low affinities to
soil. The dissolved uranyl carbonate may precipitate due to
changes in pH, temperature, and saturation state along the
flow path. This is demonstrated in the study area by the
precipitation of the uranyl carbonate complex Ca[(UO 2)3
(CO3)2O2].6(H2O) along the drainage streams from water
migrating away from the orebody (Shata, 1997). Omer
(2011) concluded that uranophane [Ca(UO 2)2SiO3(OH)2.5
(H2O)], dolomite [CaMg(CO 3)2], chrysocolla [(Cu,Al)
2H2Si2O5(OH)4.n(H2O)], and malachite [Cu2(CO3)(OH)2] is
the principal mineral association identified in the middle
marly dolostone member of the Um Bogma Formation.
The hydrogeochemical survey of the present area
showed that there are conspicuous anomalies of Zn, Ni
and Fe distributed close to the locations of radiometric
anomalies of the uranium orebody (Figs. 8 and 13), owing
to their relative immobility in this environment. On the
other hand, the contents of relatively mobile elements in
water, including Co, U, V and Cr significantly increase as
the distance increases away from the orebody, forming
dispersion aureoles (Fig. 14). Vanadium is largely
immobile during metamorphism (Condie 1976). The
vanadium content of sedimentary rocks reflects primarily
the abundance of detrital Fe oxides, clay minerals, hydrous
oxides of Fe and Mn, and organic matter. The redox
regime is important, vanadium remaining mobile under
oxidising conditions but being subject to precipitation just
above the redox threshold within a pH range of 5.0’8.0
(Brookins 1988). The solubility of vanadium is strongly
controlled by its oxidation state. Its solubility is highest in
oxic environments, where vanadyl cations predominate.
Complexes with fluoride, sulphate and oxalate may also
act to increase vanadium solubility under oxidising
conditions (Wanty and Goldhaber 1992), although the
presence of uranium and phosphates can result in the
formation of highly insoluble V5+ complexes.
From the data given in table (3), it may be concluded
that there is a more significant contrast level in aqueous
dispersion aureoles of vanadium compared to the rest of
the analyzed trace elements. Th is may give an indication
to the possibility of using this element, in association with
uranium, chromium and cobalt (Figs. 14 and 8), as a good
indicator for the presence of uranium at the up-gradient
headwater.
Nickel exhibits a strongly positive anomaly located
close to the uranium orebody (Fig. 13). It is associated
with strongly positive anomalies of iron and zinc,
reflecting the good possibility of using this association as
an indicator for the presen ce of uranium mineralization
nearby their anomalous distribution. The nickel content of
groundwater from the uranium-mineralized zones varies
from 17 ”g/L to 105 ”g/L (72.6 ”g/L in average, Table 3).
This average value is clearly distinguished from the lower
average values of groundwater derived from barren sites
that has 25.6 ”g/L (Table 3). Because of this high contrast
level of nickel, it could be easily used as a good indicator
element for uranium occurrences.