Auriferous shear zones in the central Allaqi-Heiani belt: Orogenic gold in post-accretionary structures, SE Egypt

Abstract

The East-West Gondwana collision (0.75 – 0.5 Ga), by oblique convergence, was likely accompanied by high hydrothermal fluid flux and dispersed orogenic gold in the Arabian-Nubian Shield. Gold-bearing quartz veins along steep-dipping shear zones bordering or cutting through the ophiolitic and island arc rocks in the central Allaqi-Heiani belt in Wadi Defeit area deserved great interest of the ancient miners. Field and remote sensing data revealed the structural and lithological controls of gold-bearing quartz veins, providing means of exploration for new targets in the larger Wadi Allaqi environ. The auriferous shear zones are attributed to D3 (a non-coaxial continuation of early NE-SW compression regime), and D4 (slip reactivation by E-W compression and transcurrent deformation). Microscopic investigations of quartz veins reveal the association of gold blebs and specks with fissure-filling galena-spahlerite-tetrahedrite assemblage and Fe-As-sulfides (pyrite and arsenopyrite). As a gold-only province characterized by abundant, variably deformed and carbonated metabasic rocks, metamorphic devolatilization is suggested to explain the discrete gold mineralization by fluid focusing in complex shear intersections in this area. The available fluid inclusion data affirm the low salinity aqueous-carbonic composition of the ore fluids and mesothermal conditions of ore deposition, consistent with metamorphic devolatilization. Structures related to late ductile deformation in the post-accretionary stages of the evolution of the shield should be considered high priority zones for future exploration programs.

Full text

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Journal of African Earth Sciences xxx (2017) xxx-xxx
Contents lists available at ScienceDirect
Journal of African Earth Sciences
journal homepage: www.elsevier.com
Auriferous shear zones in the central Allaqi-Heiani belt: Orogenic gold in
post-accretionary structures, SE Egypt
Basem Zoheira, b, Ashraf Emamc, Maher El-Amawya, Tamer Abu-Alamd, ∗
aDepartment of Geology, Faculty of Science, Benha University, Benha 13518, Egypt
bInstitute of Geosciences, University of Kiel, Ludewig-Meyn Str. 10, 24118 Kiel, Germany
cDepartment of Geology, Faculty of Science, Aswan University, Aswan 81528, Egypt
dNorwegian Polar Institute, Tromsø, Norway
ARTICLE INFO
Article history:
Received 27 July 2017
Received in revised form 2 October 2017
Accepted 19 October 2017
Available online xxx
Keywords:
East-West Gondwana
Wadi Allaqi
South Eastern Desert
Egypt
Orogenic gold
Metamorphic devolatilization model
ABSTRACT
The East-West Gondwana collision (0.75–0.5 Ga), by oblique convergence, was likely accompanied by high
hydrothermal fluid flux and dispersed orogenic gold in the Arabian-Nubian Shield. Gold-bearing quartz veins
along steep-dipping shear zones bordering or cutting through the ophiolitic and island arc rocks in the central
Allaqi-Heiani belt in Wadi Defeit area deserved great interest of the ancient miners. Field and remote sensing
data revealed the structural and lithological controls of gold-bearing quartz veins, providing means of explo-
ration for new targets in the larger Wadi Allaqi environ. The auriferous shear zones are attributed to D3(a
non-coaxial continuation of early NE-SW compression regime), and D4(slip reactivation by E-W compres-
sion and transcurrent deformation). Microscopic investigations of quartz veins reveal the association of gold
blebs and specks with fissure-filling galena-spahlerite-tetrahedrite assemblage and Fe-As-sulfides (pyrite and
arsenopyrite). As a gold-only province characterized by abundant, variably deformed and carbonated metaba-
sic rocks, metamorphic devolatilization is suggested to explain the discrete gold mineralization by fluid fo-
cusing in complex shear intersections in this area. The available fluid inclusion data affirm the low salinity
aqueous-carbonic composition of the ore fluids and mesothermal conditions of ore deposition, consistent with
metamorphic devolatilization. Structures related to late ductile deformation in the post-accretionary stages of
the evolution of the shield should be considered high priority zones for future exploration programs.
© 2017.
1. Introduction
The Pan-African orogeny, which led to the assembly of the Gond-
wana supercontinent, was characterized by gold-forming events in
Arabian-Nubian Shield, Hoggar Shield, and Brasilia fold belt of West
Gondwana (Goldfarb et al., 2005). The Arabian-Nubian Shield, a large
exposure of mostly Neoproterozoic juvenile crust on both flanks of
the Red Sea, has long been known as a gold-base metal province with
hundreds of scattered small gold deposits and occurrences. In Eastern
Desert of Egypt, Sudan and Saudi Arabia, high-grade auriferous shear
zones and quartz ± carbonate veins commonly cut Pan-African gran-
ites or occur in their direct vicinity (e.g., Harraz, 2000; Klemm et al.,
2001).
Wadi Allaqi area in South Eastern Desert (SED) of Egypt (Fig. 1)
is known for rock and mineral resources exploited since the ancient
times, and still deserves careful consideration. Of these mineral re-
sources, 16 localities of Au-quartz veins in the region occur at con
∗Corresponding author.
Email address: tamer@npolar.no (T. Abu-Alam)
tacts between ophiolitic and island arc terranes, commonly periph-
eral to small granitoid intrusions. In almost every tributary of the ma-
jor Wadi Allaqi, there are remains of ancient gold mining activities.
Wadi Defeit is an E-W tributary with the conspicuous peaks of Ga-
bal Um El-Tuyor El-Foqani, Gabal El-Adrag, and Gabal Um El-Tuyor
El-Tahtani (Fig. 2). Gold mining in the Wadi Defeit area is expressed
in scattered heaps of dump, tailings and abundant remains of old min-
ers’ huts. Numerous 100s m-long trenches, shallow pits and shafts into
quartz veins point to significant activities in the past. The veins cut
mainly foliated ophiolitic mélange matrix, metasedimentary rocks and
less commonly granitic intrusions. Gold contents in the mineralized
veins from the Um El-Tuyor El-Foqani deposit show an average of
25 g/t Au (Zoheir, 2004, 2008a,b, and references therein).
This contribution attempts to reveal the setting of gold bearing
quartz veins and associated shear zones in relation to the structural
evolution of the Allaqi-Heiani belt, and to shed light on exploration
opportunities based on unambiguous geologic and structural setting.
Satellite imagery data along with new field studies are used to reveal
the geological and structural setting of gold mineralization in the cen-
tral Allaqi-Heiani belt for possible exploration along major structures
in SED and north Sudan.
https://doi.org/10.1016/j.jafrearsci.2017.10.017
1464-343/© 2017.

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2 Journal of African Earth Sciences xxx (2017) xxx-xxx
Fig. 1. Geological map of Eastern Desert of Egypt and southern Sinai showing gold locations (white circles) – modified from Johnson et al. (2011).

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Journal of African Earth Sciences xxx (2017) xxx-xxx 3
Fig. 2. Structural map of the Wadi Defeit area and environs, in relation to Wadi Allaqi regional structures. Background image is a false-color composite ETM + band ratio image (5/
7, 5/1, 5/4*3/4). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
2. Geologic setting
The Allaqi-Heiani belt is considered as a key area for understand-
ing the evolution of the Arabian-Nubian Shield (e.g., Kröner et al.,
1987; Stern et al., 1989; Sultan et al., 1993; Taylor et al., 1993;
Greiling et al., 1994; Stern, 1994; Abdelsalam and Stern, 1996; Kusky
and Ramadan, 2002; Abdelsalam et al., 2003; Zoheir and Klemm,
2007). The major Allaqi-Heiani suture is associated with a curvi-
linear ophiolitic belt, and extends for more than 250 km in SED of
Egypt. It represents an arc-arc collision zone, formed when Gerf ter-
rane in the north overrode Gabgaba terrane in the south ca. 750-720
Ma (Kusky and Ramadan, 2002; Abdelsalam et al., 2003). The Pre-
cambrian basement rocks of the Allaqi-Heiani belt are classified into:
ophiolitic mélange, island arc metavolcanic/volcano-sedimentary/plu-
tonic assemblages, and late-to post-orogenic granitoids (e.g., Noweir
et al., 1996; El Amawy, 2001; Kusky and Ramadan, 2002;
Abdelsalam et al., 2003; El Amawy et al., 2004; Zoheir and Klemm,
2007; Abdeen and Abdelghaffar, 2011).
The Wadi Defeit area is underlain mainly by ophiolitic serpen-
tinite-metagabbro-metabasalt assemblages, island arc metasedimen-
tary-metavolcanoclastic successions and arc-related granitoid rocks
(Figs. 2 and 3). The area has a moderate to high relief topography of
extended rugged mountainous ridges and intensely weathered rocks
covering the slope of the elevated hills. The ophiolitic rocks are tec-
tonically embedded in a matrix of intermixed listvenized serpentinite,
graphite-bearing metasiltstone and metabasalt.
Successions of metasedimentary rocks include pelitic and
psammo-pelitic schists and less common marble bands. These rocks
are intruded by gabbro-diorite complex and granodiorite intrusions.
Metasedimentary rocks form roof pendants on the gabbroic rocks west
of Gabal Al-Adrag. Post-orogenic granitic bodies intruded the cores of
upright and anticlinal folds west of Gabal Um El-Tuyor Al-Tahtani.
Other dispersed bodies of post-orogenic granite forms subrounded in-
trusions along major fault zones, i.e., between Gabal Al-Adrag and
Gabal Um El-Tuyor El-Foqani. Mylonite zones cut the ophiolitic and
metasedimentary rocks and trend NNW parallel to the large scale folds
that are best traced in the metasedimentary rocks. Dacite dikes are
commonly associated with the mylonitized rocks along with quartz
veins.
The study area contains three gold occurrences, namely Um
El-Tuyor El-Foqani, Um El-Tuyor El-Tahtani, and Betam gold mines
(Fig. 3). Gold mineralization is generally related to Au-quartz veins
commonly associated with local sericite alteration and silicification.
The Um El-Tuyor El-Foqani deposit, abandoned around 1925, at-
tracted most attention and was subjected to many studies (Salem,

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4 Journal of African Earth Sciences xxx (2017) xxx-xxx
Fig. 3. Geologic map of the Wadi Defeit area and environs. Notice the occurrence of gold deposits along km-scale shear zones, commonly showing sinistral shear features. AB
cross-section showing the main structural relations between different rock units (modified after Zoheir, 2004).
2003; Zoheir, 2004, 2008a, b). Salem (2003) mapped extensive alter-
ation zones (>1 km–long and 300 m-wide) in sheared metavolcanic
rocks, mostly confined to a NNW-SSE major sinistral shear zone
in the mine area. Gold-bearing quartz veins are mostly worked out.
Zoheir (2004) described the host rock of the Um El-Tuyor El-Fo-
qani deposit as ophiolitic mélange matrix associated with listvenite
blocks and graphite-bearing metasediments. Basic and acid dikes and
elongate granitic bodies cut the ophiolitic metabasalt and metasedi-
mentary rocks in and around the mine area. It is worth mentioning
that, the Um El-Tuyor El-Foqani mine area occurs at the intersection
between NNW-SSE and NE-SW fracture/fault directions at the clo-
sures of anticlinal folds in the ophiolitic metabasalt (Zoheir, 2008a).
The Um El-Tuyor El-Tahtani mine occurs along NW-SE sinistral
shear zone and at contact between a granitic intrusion and schis-
tose metavolcanics and metasedimentary rocks. At Betam mine, gold
mineralization is represented by fault-fill quartz veins and lensoidal
quartz bodies, commonly confined to deformed/sheared metasedi
mentary rocks, or at contacts between metasedimentary and metagab-
bro-diorite rocks (Zoheir, 2008b).
3. Hydrothermal alteration mapping by remote sensing
Recently, Enhanced Thematic Mapper (ETM+) and Advanced
Space-borne Thermal Emission and Reflection Radiometer (ASTER)
data are widely and successfully used for mapping lithology, struc-
tures and mineralized hydrothermal zones in the arid and semi-arid re-
gions (e.g., Rowan et al., 2005; Qiu et al., 2006; Gad and Kusky, 2007;
Qari et al., 2008; Aboelkhair et al., 2010; Amer et al., 2010; Madani
and Emam, 2011; Rajendran et al., 2012; Sadeghi et al., 2013; Zoheir
and Emam, 2014; Pour and Hashim, 2014; Emam et al., 2016). Sadek
et al. (2006, 2013) concluded that ETM + band ratio image (5/7, 5/1,
4) is effective in mapping of the different lithological units and detect-
ing gold-bearing alteration zones.

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Journal of African Earth Sciences xxx (2017) xxx-xxx 5
As image processing is highly scene dependent, the experimental
methodology in the study area is carried out using the ETM + scene
(Path 173/Row 45) acquired on March 09, 2005, and the ASTER
scene (Granule ID: ASTL1B 0403150819140808041013) acquired on
March 15, 2008. These satellite data are used for better lithological
and structural mapping of the area, and to reveal factors controlling
gold mineralization distribution. Processing and analysis were carried
out using the Envi 4.8 software (ENVI®software, from ITT Visual In-
formation Solutions).
Table 1
The PCA loading values for ETM+ of the study area.
Principal component analysis (PCA) - a multivariate statistical
technique - is used to remove redundancy in multi-spectral data and
provide significant image quality enhancement (Singh and Harrison,
1985). The PCA transformation is carried out for the 6
ETM + VNIR-SWIR bands and 9 ASTER VNIR-SWIR data of the
study area. The PCA loading values for ETM+ and ASTER data
(Tables 1 and 2) show the first PC of both ETM+ and ASTER data
with positive loadings for all bands. The difference between the vis-
ible and shortwave bands can be illustrated by ETM + PC2 that has
high positive (0.449) and negative (−0.503 and −0.606) loadings for
band 1, band 5 and band 7, respectively.
OH-bearing minerals have high reflectance on band 1
(0.441–0.514 μm) and high absorption on band 7 (2.064–2.345 μm).
Consequently, the mineralized alteration zones, Al-OH and Mg-OH
bearing rocks are delineated on ETM + PC2 image with bright pix-
els (Figs. 4 and 6a). On ETM + band 1 and band 3 (0.631–0.692 μm),
the iron oxides and Fe-bearing (e.g. mafic) rocks have high absorp-
tion and high reflectance features, respectively. Such rocks can be
clearly discriminated on ETM + PC3 gray-scale image with bright
pixels (Fig. 6b), where PC3 loadings are positive (0.716) and negative
Table 2
The PCA loading values for ASTER data of the study area.
Fig. 4. Gray-scale band ratio images of Wadi Defeit area; (a) ETM + band ratio (5/7) and (b) ASTER band ratio (4/7) show serpentinite and their related rocks with bright image
signature. (c) ETM + band ratio (5/4) and (d) ASTER band ratio (4/3) show Fe-bearing and basic rocks with bright pixels.

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6 Journal of African Earth Sciences xxx (2017) xxx-xxx
Fig. 5. False color composite ratio images: (a) FCC ETM + ratio image (5/7, 4/5, 3/1), (b) FCC ASTER ratio image (4/7, 3/4, 2/1), (c) FCC ETM + ratio image (5/7, 5/1, 5/4*3/4),
(d) FCC ASTER ratio image (4/7, 4/1, 4/3*2/3), (e) FCC ETM + ratio image (5/7, 5/1, 4), (f) FCC ASTER ratio image (4/7, 4/1, 3). (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
(−0.401) for band 1 and band 3, respectively. The alteration zones con-
taining clay and carbonate minerals have high reflectance and absorp-
tion features on band 5 and band 7, respectively.
ETM + PC4 loadings are positive (0.735) and negative (−0.672) on
band 5 and band 7, respectively. So, the ETM + PC4 image is best
to differentiate the alteration zones containing talc-carbonates, quartz
carbonates and listvenite with bright pixels (Fig. 6c). False color RGB
combination (Fig. 5) is created from the ETM + PC4 in red, the PC3
in green and the PC2 in blue. It is clear that all hydrothermal al-
teration zones have rose and orange image signature (Fig. 6d). The
PCs of ASTER VNIR-SWIR data show that the PC2 has high pos-
itive (0.647) and negative (−0.265) loadings for band 1 and band 5,
respectively. Granites and other siliceous rocks have black tone on
PC2 gray-scale image (Fig. 7a). The PC3 shows high positive (0.491)
and negative (−0.515) loadings for band 8 and band 4, respectively.
Fe-bearing and basic rocks (metagabbros, amphibolites) show bright
tone on the PC3 image (Fig. 7b). Moreover, PC5 has high positive
(0.638) and negative (−0.458) loadings for band 4 and band 6, re-
spectively. The alteration zones (talc-carbonates, quartz carbonates
and listvenite) appear with black tone on the PC5 image (Fig. 8c).
RGB combination is created from the ASTER PC6 in red, the PC5 in
green and the PC3 in blue (Fig. 7d). It is obvious that all hydrothermal
alteration zones are clearly delineated in pink and rose.
4. Structural observations
S2foliation is the most common meso-to microscopic fabric in the
study area. This foliation strikes consistently NW-SE and dips steeply
to SW, roughly conformable with the primary layering (S1) of the host
metasedimentary rocks. Locally, The S2foliation is disrupted by the
development of centimeter-scale crenulations (NNW-SSE moderately
dipping to W) and S3related pervasive cleavages. Alignment of chlo-
rite, muscovite, sericite and quartz ribbons defines an elongation lin-
eation on the S3planes. Mineral lineation on the cleavage planes (S3)
are attributed to a cleavage-parallel shearing. The S3foliation is as-
sociated with mm-to m-scale intrafolial folds, commonly in mica-rich
domains. These folds are clearly seen where alternating quartz-rich
and mica-rich bands occur, where slip on basal planes of mica along
NNW-SSE direction seems to accommodate shearing in the mi

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Journal of African Earth Sciences xxx (2017) xxx-xxx 7
Fig. 6. Gray-scale and FCC ETM + PC images: (a) gray-scale PC2 image shows Al-OH and Mg-OH bearing rocks with bright pixels, (b) gray-scale PC3 image shows iron oxides
and Fe-bearing rocks with bright pixels, (c) gray-scale PC4 image shows the alteration zones with bright pixels, (d) FCC PC image (PC4, PC3, PC2) delineates the hydrothermal
alteration zones with rose and orange image signatures. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Gray-scale and FCC ASTER PC images: (a) gray-scale PC2 image shows siliceous rocks with black image signature, (b) gray-scale PC3 image shows the metagabbros and
amphibolites with bright pixels, (c) gray-scale PC4 image shows the alteration zones with black pixels, (d) FCC PC image (PC6, PC5, PC3) delineates the hydrothermal alteration
zones with pink and rose image signatures. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
caceous bands. N-trending S4foliation planes overprint all the early
developed structures.
Four phases of map-scale folds (i.e. F1,F2,F3and rarely F4folds)
are traced by the non-to the penetrative foliations (S1,S2,S3and S4)
(Figs. 2 and 8). The map-scale folds are recorded in the dismem-
bered ophiolites, metasediments, arc volcanic rocks and the gneisses.
The F1is upright and overturned folds with axial traces parallel to
the WNW-ESE to NW-SE directions. Well-developed minor folds are

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8 Journal of African Earth Sciences xxx (2017) xxx-xxx
Fig. 8. Structural control of gold-bearing quartz veins in the Wadi Defeit area. Notice the development of shear zones at borders of S3folds in metasedimentary rocks.
parallel to the F1-fold axes and are more concentrated throughout the
limbs and hinges of the major folds. The axial planes of F1-folds are
parallel to WNW-ESE, E-W thrust planes. F2map-scale folds are the
most common in the area. The F2is NW-SE asymmetrical folds. In
Wadi Allaqi, one of these F2folds – thereafter Allaqi fold - is rec-
ognized in the gneisses, where its axis extends for 15 km. This Al-
laqi fold plunges NW and is sinistrally displaced by Wadi Allaqi
strike slip fault and both are lately dislocated along relatively mi-
nor NNE-SSW dextral strike-slip fault. Along and within the NE-SW
sinistral strike-slip fault zones in southeast of G. Um El Tuyor El Fo-
qani and southwest of G. Al Adrag, the S1and S2foliation planes are
overprinted by NE-trending F3minor folds which are developed on
the limbs and, occasionally, hinges of the NW-trending F2folds. A
map-scale N-S to NNW-SSE F3fold is observed at G. Al Adrag.
To the north of the Allaqi fold, the fold is bounded by a moder-
ate N-dipping thrust that delimits the metavolcanics and associated
ultramafic slices in the hanging-wall from the gneisses. To the west,
the trace of this thrust is extensively dislocated, in a sense of sinis-
tral movement, along a major NE-SW strike-slip fault. About 6 km
to the north from the displaced thrust segment, a subparallel thrust
fault is located and defines the contact between the ophiolites and
sheared metagabbro and amphibolite forming with this segment a se-
quence of N- to NNE-dipping duplex thrust along Wadi Allaqi (El
Amawy et al., 2004). To the east in Wadi Defeit, a similar N- to
NNE-dipping thrust fault outlines the contact between the ophiolites
to the north against metavolcanics and volcaniclastic metasediments.
An E-W to WNW-ESE striking thrust fault controls the eastern part
of Wadi Defeit and delimits the contact between the ophiolites and
underlying metavolcanics and volcaniclastic metasediments. To the
west, this thrust is cross cut by NE-SW sinistral strike-slip fault, which
extends for about 21 km and thrusts the dismembered ophiolites of G.
Um El Tuyor El Foqani over the metavolcanics and associated vol-
caniclastic metasediments in a style of oblique wrenching or transpres-
sion. This sense of oblique shear is previously recorded at the central
part of the first NE-SW sinistral strike-slip fault by El Amawy et al.
(2004), who assume the development via a sequence of NE-SW du-
plex strike-slip regime (i.e. transformation from pure shear to simple
shear duplex structures). The last structural element which is observed
in the study area is NE-trending faults that cut the early developed
structures.
5. Deformation phases
The crosscutting interrelationship between the NE-SW sinistral
and N-S to NNE-SSW dextral strike-slip faults and their dislocation
across the E-W to WNW-ESE Wadi Allaqi and Wadi Defeit thrust
faults indicate consistent deformation style of sinistral shear (Fig. 2).
This explains two successive phases of deformation (Table 3) started
during D1with development of WNW- to NW- trending F1folds and
E-W to WNW-ESE striking thrust faults but enhanced during D2with
extensive Riedel shear along the NE-SW sinistral strike-slip faults,
less common conjugate Riedel shear along the N-S to NNE-SSW dex-
tral strike-slip faults and spectacular features of NW-trending minor
and major F2folds (Fig. 2). These features express a principal stress
(σ 1) along N-S to NNE-SSW (strain model a; Fig. 2).
The presence of NE-trending F3minor folds which were devel-
oped on the limbs and the hinges of the NW-trending F2folds at in
southeast of G. Um El Tuyor El Foqani and southwest of G. Al Adrag
may indicate that the D3deformation is restricted only in these parts
of the study area. However, segmentation of Wadi Defeit (the west-
ern part, in particular) into an array of WNW-ESE to NW-SE sinis-
tral Riedel shear and another of ENE-WSW to NE-SW dextral conju-
gate Riedel shear, the formation of N-S to NNW-SSE major F3fold
at G. Al Adrag, sinistral offset of G. Um El Tuyor El Tahtani from G.
Al Adrag along NW-SE sinistral segment of Wadi Defeit and sinistral
dragging of F2major fold west of G. Al Adrag (Figs. 2 and 3) indi-
cate that the D3event was a major tectonic event that affects the entire
study area. Fig. (2 – model b) explains the deformation mechanism
during the D3, where the principal stress (σ 1) was acting from the ESE
direction and sense of movement along ENE-WSW to NE-SW fault
trends was continued with sinistral shear. The last event recorded in
the study area (i.e. D4) is E-W compression and transcurrent deforma-
tion which formed the NE-trending faults and resulting largely in slip
reactivation of the pre-existing NNW-trending shear zones.
6. Metamorphism
Three phases of regional metamorphism followed by a fourth
phase of contact metamorphism are recognized in the study area
(Zoheir, 2004). The first phase of metamorphism (M1) is recorded
as metamorphic mineral inclusion (e.g. chlorite, biotite and quartz)
within garnet porphyroblasts in the metasedimentary rocks or as acti-
nolite-chlorite-epidote-albite assemblage in the metavolcanics. The
M1event is observed in the ophiolitic rocks as some serpentinites
were transformed to talc carbonate rocks. Zoheir (2004) suggests
that the first metamorphic event occurred under condition of about
380 ± 50 °C.
The second metamorphic event occurred syn-D2. Hornblende, gar-
net, staurolite and sillimanite formed during this event, reflecting
metamorphic conditions of 534°- 561 °C and 5.26–6.20 kbar. Post-M2

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Journal of African Earth Sciences xxx (2017) xxx-xxx 9
Table 3
Summary of deformation phases shaped the geology and structure of the Wadi Defeit
area.
Deformation Structure elements Metamorphic events/foliation trend
D1-Moderately NW-dipping
thrusts separate the ophi-
olitic blocks (top) apart
from the underlying is-
land arc rocks.
-F1upright and overturned
folds with axial traces
parallel to the thrust
planes (WNW-ESE).
-M1(380 ± 50 °C)
D2-S2fabrics in the island arc
metasedimentary and
metavolcanic rocks.
-Asymmetric small scale
and regional NW-SE F2-
folds.
-L2lineation plunges
mostly to N grown on the
F2axial planes.
-Related extensional shear
fractures are subsidiary
and mainly confined to
the hinge zones of the F2
folds.
-Orientation of the major
D2structures at high-an-
gles to the major fold-
and-thrust structures of
D1reflects a change in di-
rection of the compres-
sional regime during D2
(e.g. Zoheir, 2004).
-M2(534°- 561 °C and
5.26–6.20 kbar)
D3-Open F3folds and crenu-
lations overprint the D2
structures
-Formation of NNW-SSE
strike slip faults extended
parallel or subparallel to
the axial planes of F3
folds.
-The D3led to general up-
lift of the central part of
the study area.
-The D3is interpreted as
a manifestation of a NE-
SW non-coaxial com-
pressional stress regime.
-M3
-Main structural controls on gold
mineralization
Table 3 (Continued)
Deformation Structure elements Metamorphic events/foliation trend
D4-N-trending S4and NE-
trending faults cut the
early developed struc-
tures.
-The D4records an
episode of E-W compres-
sion and transcurrent de-
formation resulting
largely in slip reactiva-
tion of the pre-existing
NNW-trending shear
zones, of which, many
are gold-bearing.
-M4due to intrusion of post-tectonic
granites
minerals, e.g. chlorite and biotite traversing staurolite and garnet por-
phyroblasts in the examined metapelites, and replacement of horn-
blende by epidote and iron oxides in the metavolcanic rocks suggest a
third metamorphic event in the study area. Zoheir and Klemm (2007)
suggest that the third metamorphic event was a result of non-coaxial
deformation associated with D3.
Intrusion of late-orogenic granites in the area was associated with
a contact metamorphic cycle and activation of fluid-rock interaction
processes along the pre-existing structures (sensu Abu-Alam et al.,
2010). The fourth metamorphic event is observed as disrupted foli-
ations and reactivations along previous discontinuities accompanied
by widespread alteration and quartz veining. This event is interpreted
as contact metamorphism related to the emplacement of the post-oro-
genic granite (Zoheir, 2004).
7. The auriferous shear zones
In the study area, some tens to several hundreds of meters long
gold-bearing quartz veins are hosted by NNW-trending brittle-duc-
tile shear zones (dip generally to SW) bounding the hinge zone of
NNW-folds in the metasedimentary rocks. Occurrence of small bod-
ies of granitic rocks are a common feature in the three gold deposits.
Gold bearing quartz veins at the um El-Tuyor El-Foqani mine occur
where the NNW shear zone cuts the E-W contact between the ophi-
olitic mélange and the pelitic metasedimentary rocks close to Wadi
Defeit (Fig. 9a, b and c). At Betam mine, gold-bearing quartz veins are
confined to conjugate shear zones (NNW- and ESE-trending), partic-
ularly at contacts between gabbro-diorite and altered metasedimentary
rocks (Fig. 9d and e). The high grade ore bodies are those confined to
shear zones marginal to small-scale (10s m-wide) elongate bodies of
late-orogenic granite. Gold-bearing quartz veins in the Um El Tuyor
El-Tahtani deposit are confined to milky quartz and quartz-carbonate
veins, striking more or less conformable with NW-SE to N-S folia-
tions of the country metasedimentary rocks (Fig. 9f and g).
Deformation is manifested by morphological features of the
gold-quartz veins, ranging from pinch-and-swell structure,
ridge-in-groove lineation and undulating geometries both down-dip
and along the strike. At the microscopic scale, recrystallization, defor-
mation lamellae and brecciation characterize domains in which fine
specks of gold are dispersed in the quartz veins (Fig. 10a, b, c and d).
The large quartz crystals show sinistral offseted segments (Fig. 10e, f
and g). Abundant gold blebs and inclusions are reported in thin quartz
veins (a few cm-wide), particularly where wall-rock selvage is abun-
dant.
Evidence for wall-rock alteration is commonly limited to a 1–10 m
wide halo of bleached rocks and disseminated arsenopyrite,

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10 Journal of African Earth Sciences xxx (2017) xxx-xxx
Fig. 9. Mining and geologic features. a) Mining ruins, including, heap dump, tailing, cement building, crusher and electricity generator room, b) Deflection of the main NW-SE
foliation into shear planes and abundant quartz lenses at the wall of an inclined shaft in the mine area (Looking N), c) Intensively kaolinitized, silicified and ferruginated shear
zone between granite body (right side and the ophiolitic mélange matrix (i.e. metasiltstone to the left) (Looking SE), (d) Old mining activities confined to kaolinitized, silicified
metagabbroic rocks and metasedimentary rocks, (e) Silicification zone enveloping the mineralized quartz veins at the contact between the metasedimentary and metagabbro rocks, f)
Upheaved strongly foliated quartz-sericite schist with carbonate bands form roof pendent on late-orogenic granite at the Um El-Tuyor El-Tahtani mine area (Looking to N), and g)
Quartz veins and silicified granite with disseminated pyrite.
pyrite and carbonate aggregates and veinlets. The alteration zones
around the investigated quartz veins are parallel to the foliation, but
indented where veins are oblique, suggesting that fluid percolation
was controlled by the host rock foliation anisotropy. Alteration as-
semblages, more or less directly attributable to vein-forming fluids,
comprise local silicification, extensive pervasive illitic assemblage,
propylitic alteration and albitization. Silicification is confined to zones
adjacent to quartz veins, covering some few meters-wide zones. The
alteration envelop correlates positively with the thickness of the silici-
fication zone and quartz lodes.

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Journal of African Earth Sciences xxx (2017) xxx-xxx 11

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12 Journal of African Earth Sciences xxx (2017) xxx-xxx
Fig. 10. Photomicrographs (XPL) of the auriferous quartz veins of the investigated deposits showing: a) Incipient recrystallization defined by small polygonal quartz grains and
sub-grains occupying intergrain planes, mainly parallel to the grain boundaries and vein margins, b) Quartz vein with shear planes filled with carbonate + clay minerals. Stretching
of individual quartz ribbons indicate top-to-the left sense of shear, c) Vein quartz crystals displaying undulate extinction and conjugate sets of dialation fractures within which later
hydrothermal quartz has been invaded, d) Curved, recrystallized muscovite flakes with irregular boundaries and variable intergrain bulging. Large muscovite is thought to have been
derived from abundant sericite dispersed in mineralized quartz veins during late deformation, and left-lateral slip deformation characterizing the mineralized quartz veins in (e) Um
El-Tuyor El-Foqani, (f) Um El-Tuyor El-Tahtani deposit, and (g) Betam deposit.
In the Um El-Tuyor El-Foqani deposit, hydrothermal mineral
phases include quartz-sericite ± graphite and chlorite-calcite-epidote
assemblages are observed. Gold occurs preferentially in the inner
sericite ± graphite alteration zone. The mineralized quartz veins cut
the host rock foliation, but some thin veins are buckled around the
rock foliation. Gold and base metal enrichment increases from the
outer alteration to the inner alteration zone. The latter presents the
highest gold grade (>20 g/t Au), especially where it is cut by thin grey-
ish quartz and quartz-carbonate veins.
At the Betam mine, an intensely altered wall-rocks zone mainly
kaolinitized metagabbro, occupies a conjugate trend to the NNW-SSE
fault/shear plane and cuts several NNW-trending quartz veins and
granitic bodies. This zone extends for more than 500 m and its width
is ∼50 m on average. Gold grade in the intensely silicified parts of this
zone vary from traces up to 2.2 g/t (Zoheir et al., 2013).
Microscopic investigations of the orebodies and mineralized
wall-rocks from the three investigated deposits reveal a common par-
agenesis of the ore minerals. Generally, the microscopic and SEM ob-
servations of the polished sections among representative vein sam-
ples and mineralized wall-rocks indicate simple mineralogy (Fig. 11).
An early assemblage of sulfide mineralization comprises fine-grained
(10s to a few 100s μm-across) arsenopyrite, pyrite, pyrrhotite, ±chal-
copyrite, ±gold/electrum. This assemblage occurs commonly inter-
granular in the quartz veins as disseminations or clustered with car-
bonate aggregates. A late assemblage of sphalerite, and galena re-
places the early pyrite and arsenopyrite crystals. These two sulfide
assemblages are also dispersed in the altered wall-rocks. Gold is ei-
ther free milling or mutually associated with pyrite, arsenopyrite and
chalcopyrite (Fig. 11). Gold and electrum form either inclusions in ar-
senopyrite; blebs (≤10 μm-long) at pyrite-arsenopyrite contacts; dis-
seminations (≤70 μm-long) in the carbonate-rich domains; and
stringers (≤5 μm-wide) and irregular grains in oxidized sulfide crystals
or along microfissures in the quartz veins. If occurs along microfrac-
tures in quartz veins, high fineness gold is associated with galena and
tetrahedrite (Fig. 11).
8. Gold ore formation
Observations from the study area and other areas from Ara-
bian-Nubian Shield indicate that the gold mineralization is structurally
controlled mainly by ∼NW-SE/NNW-SSE shear zones. Recent stud-
ies (e.g. Abu-Alam and Stüwe, 2009; Abu-Alam et al., 2010; Zoheir,
2011, 2012; Meyer et al., 2014; Hassan et al., 2016) have high-
lighted the tectonic implications of the NW-SE shear zones in the
Arabian-Nubian Shield. Based on several observations in the Eastern
Desert and Arabia, we assume that structures related to the D3are
the main structural controls on gold mineralization, and this system
had essential role in the fluid infiltration process and metamorphic de-
volatilization.
Criteria including anastomosing vein morphology, alteration min-
eral assemblages, spatial and genetic relationships with a brittle–duc-
tile shear zone indicate that the studied gold ore is typical for the
metamorphic/orogenic gold deposits (Groves et al., 1998; Goldfarb et
al., 2005). A metamorphic devolatilization process was suggested by
Phillips and Powell (2010) to explain the formation of the metamor-
phic/orogenic gold deposits. In the present study, a similar process
may apply as a model explaining the gold formation process of in the
central Allaqi-Heiani belt.
The metavolcano-sedimentry sequence and the ophiolites of the
Arabian-Nubian Shield are metamorphosed under greenschist-amphi-
bolite facies transition. The peak metamorphism occurred prior to the
compressive deformation phase D2(Abu-Alam and Stüwe, 2009) or
syn-D2. While the main exhumation phase is the D3(e.g., Abu-Alam
et al., 2014; Meyer et al., 2014; Abu El-Enen et al., 2016; Abu-Alam
and Stüwe, 2009). After the exhumation to a crustal level of about
14–17 km, post-tectonic plutonic rocks intruded the shield and a ma-
jor fluid circulation event occurred (e.g., Abu-Alam et al., 2010). The
D4event in Wadi Defeit area is suggested here to be related to the in-
trusion of post-orogenic granites and associated with fluid-rock inter-
action events.
In the metamorphic devolatilization model, the metavolcano-sed-
imentry sequence and the ophiolites are the source rock of the gold.
Considering that the ore fluids are mainly metamorphic water (fluid
inclusion studies: Zoheir, 2004, 2008a,b) and the spatial association
with locally small granite or dacite bodies, these may imply gold min-
eralization stage coeval to the peak metamorphism in the region. The
hydrated and carbonated source rocks were devolatilized primarily
across the greenschist–amphibolite facies boundary. Devolatilization
process extracted H2O, CO2, S, Au and low base metal. The process
occurred at a crustal level equivalent to about 4 kbar (e.g. peak meta-
morphic conditions of the source rocks; Abu-Alam and Farahat, un-
published data). Gold-bearing fluid migrated upward in the crust via
D3shear zones to a crustal level of about 0.5–1.5 kbar. Fluid inclusion
studies (e.g., Zoheir and Moritz, 2014) indicate that the quartz veins
associated with the D3were crystalized under conditions of about
0.6–1.3 kbar. The geometery of the D3structures allow the gold-bear-
ing fluid to be focused into small volumes enough to form economic
accumulation of the gold. Depositional of gold from the fluids needs
redox agents which can be found in carbon- and graphite-bearing
country rocks (i.e., in the study area: graphite-bearing metasiltstone
and carbonaceous schists). Gold deposition is accompanied by carbon-
ation and sulfidation process.
9. Conclusions
Gold mineralization in the Wadi Defeit area occurs as fault-fill
quartz veins in bedding-concordant and bedding-discordant fault seg-
ments, and in extension arrays throughout shear zone systems at-
tributed to the D3structures (a non-coaxial continuation of the early
NE-SW compressional stress regime), and D4(an episode of E-W
compression and transcurrent deformation resulting largely in slip re-
activation of the pre-existing NNW-trending shear zones). Structural
control on gold-quartz veins is evidenced from field, remote sens-
ing and microscope observations. Wroth noted, in the three investi-
gated gold deposits, gold-bearing quartz veins are similar in composi-
tion, predominantly of quartz, and minor calcite, chlorite, sericite and
sulfides. The gold-bearing quartz veins at the um El-Tuyor El-Tah-
tani mine are hosted by NNW-trending shear zones bounding the
hinge zone of ∼NNW- folds in the metasedimentary rocks. At the um
El-Tuyor El-Foqani mine, the mineralized veins are associated with
NNW-trending shear zone cutting the E-W contact between the ophi-
olitic mélange and pelitic metasedimentary rocks. At Betam mine,

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Journal of African Earth Sciences xxx (2017) xxx-xxx 13
Fig. 11. Backscattered electron images of ore minerals (a) Inter-relationships between arsenopyrite and pyrite-chalcopyrite of Um El-Tuyor El-Foqani gold deposit, reflecting co-ex-
istence with primary gold/electrum inclusions, (b) Gold specks, of Um El-Tuyor El-Foqani gold deposit, occur mostly where strong zoning due to variable as contents in zoned
arsenopyrite, (c) Electrum grain at the contact between zones with variable as content in compositionally zoned pyrite of Um El-Tuyor El-Tahtani gold deposit, (d) High fineness
gold, of Um El-Tuyor El-Tahtani gold deposit, associated with galena along microfracture in quartz vein, and (e) Backscattered electron image of Betam deposit showing intergrown
galena, tetrahedrite and gold along interstitial spaces in quartz veins.
gold-bearing quartz veins are confined to conjugate NNW- and
ENE-trending shear zones through the contacts between gabbro-dior-
ite and altered metasedimentary rocks (Zoheir et al., 2013). Exposures
of small bodies of granitoid rocks are common features in the three
gold deposits.
Variable deformation textures in the mineralized gold-quartz veins,
ranging from pinch-and-swell structure, ridge-in-groove lineation and
boudinaged lenses, suggesting syn-kinematic formation under an
oblique compressional regime. The field relations and internal de-
formation features of the mineralized quartz veins suggest forma-
tion during the different stages of shear development. In view of
the deformation history of the mine areas and surroundings, forma
tion of the shear zone is attributed to a late transpression event (D3)
postdating peak metamorphism (e.g., Zoheir, 2008a; b).
The processed ETM+ and ASTER data reveal that gold occurs
where the shear zone traverses the tectono-stratigraphic contact be-
tween ophiolitic and pelitic metasedimentary rocks, which suggests
rock rheology and composition likely imparted dilational sites for the
circulating ore fluids, where the pelitic metasedimentry rocks worked
as redox agent of the gold-bearing fluid. The abundance of granitic
bodies, dacite dykes in the mine areas and close to the ore zones sug-
gests a possible contribution of magmatic and/or metamorphic fluids.
Zoheir et al. (2013) used the REE patterns of hydrothermally altered
rocks adjacent to the mineralized quartz veins to deduce the source of
ore-fluids compared with the host metagabbro and metasedimentary

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14 Journal of African Earth Sciences xxx (2017) xxx-xxx
rocks. They concluded that the ore fluids have likely liberated from
dehydrated metasedimentary and metavolcanic rocks, with or without
contributions from magmatic waters.
The metamorphic devolatilization model of Phillips and Powell
(2010) is suggested therefore as formation model of the gold deposits.
In the western Allaqi-Heiani belt, Sm/Nd age for a garnet-bearing rock
(ca. 590 Ma) is interpreted as cooling age close to the metamorphic
peak (Abd El-Naby et al., 2000). This assumption is supported by de-
formation of late-orogenic granite abide to shear nature of D3struc-
tures in the region. Exploration targets in the central Allaqi-Heiani belt
and its surroundings are, therefore, structures of the D3the D4, espe-
cially where signs of percolation of metamorphic ± magmatic fluids
are observed.
Acknowledgements
Field work was supported by the STDF through grant No. 150. BZ
would like to acknowledge the support by Alexander von Humboldt
(AvH). Thanks should also go to Profs. Mamadouh Abdeen and Mo-
hammed El-Bialy for their constructive comments, helped in improv-
ing the early version of this manuscript.
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