Annals Geol. Surv. Egypt. XL (2024). pp. 1-18
Manuscript id: ASGE-2309-1004
Mineralogy and Geochemistry of Hydrothermally Altered Rocks and
Gold Mineralization, at Makhrag El-Ebl area, North Eastern Desert,
Egypt.
BY
Ibrahim A. Salem1, Abdelsalam M. Abo El Ela1, Sayed Ahmed Abu Elabn2 and Abdou M.
Zeina2
1.Geology Department, Faculty of Science, Tanta University, Egypt.
2.Egyptian Mineral Resources Authority, Egypt.
Abstract
Makhrag El-Ebl area is located in the north Eastern Desert of Egypt. The study area is
covered by Pan-African basement rocks which include granodiorites, Dokhan volcanics
(dacite), syenogranites and alkali granites. Auriferous quartz veins cut through the granitic
and dacitic rocks with development of alteration zones. The quartz veins display two main
trends, NW-SE. and NE-SW. They vary in length from few meters to more than 100 m and
in thickness from very thin veinlets to more than 20 cm. The quartz veins are massive, white
and occasionally stained by iron and copper minerals. They consist mainly of quartz which
carries variable amounts of gold, pyrite, native silver, hematite, goethite and barite. The
altered granitic and dacitic rocks in the study area were examined using microscopic
investigations, XRD, SEM-EDX analyses and whole chemical analyses of major and trace
elements. The mineralogical studies accompanied by geochemical analyses for the different
alteration zones revealed the existence of eight main facies include: silicification,
ferrugination, chloritization, sericitization, argellic, propylitic, carbonatization and
muscovite alteration.
Keywords: Hydrothermal alteration, mineralogy, petrography, geochemistry, Makhrag El-
Ebl area, North Eastern Desert, Egypt
1. INTRODUCTION
Makhrag El-Ebl area is located in the north Eastern Desert of Egypt between Latitudes 27°
49' 20'' - 27° 48' N and longitudes 33° 03' - 33° 05' 30" E (Fig. 1). The study area is a part of
the Egyptian Nubian shield rocks which in turn a part of the Arabo-Nubian Shield (ANS).
More than 95 gold occurrences are widely distributed in the Eastern Desert of Egypt and
are mostly confined to Precambrian basement rocks (El-Ramly et al, 1970). At the beginning of
the Twentieth century, the majorities of the gold deposits were reopened and exploited for gold
extraction by many international mining companies. Auriferous quartz veins and stockworkes
of quartz veinlets cut both granodiorite and dacite rocks have been excavated for gold since
ancient times. A zone of alteration usually develops along the contacts between the quartz veins
and the wall rocks. The alteration may cause a change in colour, textural, mineralogical and
chemical changes. The wall rock alterations are governed by i- the nature of the host rock, ii-
the character of the hydrothermal solutions and iii- the temperature and pressure at which the
reactions take place.
1
, Mineralogy and Geochemistry of Hydrothermally Altered Rocks and Gold Mineralization, at
Makhrag El-Ebl area, North Eastern Desert, Egypt
The present study deals with the detailed petrography and geochemical characteristics of the
unaltered granodiorite and dacite rocks as well as the auriferous quartz veins and alteration zones.
The study involves a detailed petrographic description of the hydrothermal alteration assemblages
and their chemical analyses in order to elucidate the possible reactions that occurred between the
original rocks and the hydrothermal fluid. The studies also determine the ore mineralogy, gold
content in both quartz veins and altered rocks
2. Geologic Setting
Makhrag El-Ebl area is covered by Pan-African basement rocks. It is dominated by
granodiorites,Dokhan volcanics, syenogranites, alkali granites, dykes and quartz veins.
Granodiorite rocks intrude the Dokhan volcanics with clear contact. Some enclaves from Dokhan
volcanic rocks occur within the granodiorite. In some places, they show boulder appearance and
exfoliated due to being highly weathered
Many old working as trenches and shafts are present in the granodiorite (Fig. 2A). The Dokhan
volcanics occupy the northern and north western part of the mapped area. They form moderate to
high relief and dacitic in composition. The Dokhan volcanics are intruded by younger granites with
sharp contact. These volcanics are sheared in NE-SW and NW-SE-directions. Hydrothermal
alterations are recorded along these shear zones.
The younger granites are represented by syenogranites and alkali granites. The syenogranites
occupy the southwestern and eastern parts of the mapped area. They are massive, equigranular
and form moderate to high relief. The alkali granites occur as small bodies in the northern and
western parts of the mapped area. They are of reddish colour, coarse grained and stained with
malachite along fractures.
Auriferous quartz veins and stockworks of quartz veinlets are recorded in these rocks. Quartz
veins cutting the granodiorite and alkali granite rocks (Figures, 2B and 2C). The majority of these
veins are white and some of them are stained by iron and copper minerals along fractured quartz
veins. These auriferous veins trend in two main directions namely NW-SE and NE-SW. These
veins are ranging in length from few meters to more than l00 m. and in thickness from very thin
veinlets to more than 20 cm.
2
, Ibrahim A. Salem, Abdelsalam M. Abo El Ela, Sayed Ahmed Abu Elabn and Abdou M. Zeina
3. Methodology
About 58 samples from fresh country rocks, alteration zones and quartz vein samples in
Wadi Makhrag El Ebl area were petrographically examined to determine their mineral
assemblages, textures and microstructures. Back-scattered imaging and energy Dispersive X-
ray (EDX) analyses were carried out using Scanning Electron Microscope (SEM), Model
Quanta 250 FEG at the Central Laboratories of the Egyptian Mineral Resources Authority
(EMRA). SEM has accelerating voltage of 30 keV, magnification range (14x-1000000x) and
resolution 1 nm. SEM was used on carefully selected spots to confirm the existence of ore and
gangue minerals. Twenty country rock samples were chemically analyzed for the major oxides
and trace elements. The whole-rock chemical analyses were made using Philips X-ray
fluorescence (XRF) spectrometer Model PW/2404 equipped with Rh radiation tube and eight
analyzing crystals. Powder pellets for trace elements and fused beads for major oxides were
prepared and measured at Central Laboratories of EMRA. Eight samples from both quartz veins
and the different alteration types were analyzed for gold content, using the fire assay method.
X-ray diffraction analyses (XRD) of six samples were used to distinguish between the different
mineral found within the different alteration zones. This technique was done at Central
Laboratories of EMRA.
Fig.2 A: Panoramic view of old working in granodiorites. B: Field photograph showing network of quartz
veinlets cutting across granodiorite. C: Field photograph showing quartz veinlets cutting across alkali
granites.
a. Petrography of the country rocks
Granodiorites are massive, medium to coarse grained of grey to pinkish grey colour.
Microscopically, granodiorites (Fig. 3A) showing equigranular, hypidiomorphic, perthitic,
graphic and poikilitic textures. They are composed mainly of plagioclase, microcline, quartz
associated with minor biotite and hornblende. Iron oxides and sphene are the main accessory
minerals. Secondary minerals are represented by sericite (Fig. 3B) carbonates, chlorite and
epidote.
Dacite rocks are fine to medium grained, unequigranular displaying amygdaloidal and
porphyritic textures. Microscopically dacites (Fig. 3C) are composed mainly of phenocrysts of
plagioclase and quartz embedded in groundmass composed of fine-grained aggregates of
plagioclase, quartz, alkali feldspar, biotite and muscovite. Secondary minerals are represented
3
Manuscript id: ASGE-2309-1004
Mineralogy and Geochemistry of Hydrothermally Altered Rocks and
Gold Mineralization, at Makhrag El-Ebl area, North Eastern Desert,
Egypt.
BY
Ibrahim A. Salem1, Abdelsalam M. Abo El Ela1, Sayed Ahmed Abu Elabn2 and Abdou M.
Zeina2
1.Geology Department, Faculty of Science, Tanta University, Egypt.
2.Egyptian Mineral Resources Authority, Egypt.
Abstract
Makhrag El-Ebl area is located in the north Eastern Desert of Egypt. The study area is
covered by Pan-African basement rocks which include granodiorites, Dokhan volcanics
(dacite), syenogranites and alkali granites. Auriferous quartz veins cut through the granitic
and dacitic rocks with development of alteration zones. The quartz veins display two main
trends, NW-SE. and NE-SW. They vary in length from few meters to more than 100 m and
in thickness from very thin veinlets to more than 20 cm. The quartz veins are massive, white
and occasionally stained by iron and copper minerals. They consist mainly of quartz which
carries variable amounts of gold, pyrite, native silver, hematite, goethite and barite. The
altered granitic and dacitic rocks in the study area were examined using microscopic
investigations, XRD, SEM-EDX analyses and whole chemical analyses of major and trace
elements. The mineralogical studies accompanied by geochemical analyses for the different
alteration zones revealed the existence of eight main facies include: silicification,
ferrugination, chloritization, sericitization, argellic, propylitic, carbonatization and
muscovite alteration.
Keywords: Hydrothermal alteration, mineralogy, petrography, geochemistry, Makhrag El-
Ebl area, North Eastern Desert, Egypt
1. INTRODUCTION
Makhrag El-Ebl area is located in the north Eastern Desert of Egypt between Latitudes 27°
49' 20'' - 27° 48' N and longitudes 33° 03' - 33° 05' 30" E (Fig. 1). The study area is a part of
the Egyptian Nubian shield rocks which in turn a part of the Arabo-Nubian Shield (ANS).
More than 95 gold occurrences are widely distributed in the Eastern Desert of Egypt and
are mostly confined to Precambrian basement rocks (El-Ramly et al, 1970). At the beginning of
the Twentieth century, the majorities of the gold deposits were reopened and exploited for gold
extraction by many international mining companies. Auriferous quartz veins and stockworkes
of quartz veinlets cut both granodiorite and dacite rocks have been excavated for gold since
ancient times. A zone of alteration usually develops along the contacts between the quartz veins
and the wall rocks. The alteration may cause a change in colour, textural, mineralogical and
chemical changes. The wall rock alterations are governed by i- the nature of the host rock, ii-
the character of the hydrothermal solutions and iii- the temperature and pressure at which the
reactions take place.
1
, Mineralogy and Geochemistry of Hydrothermally Altered Rocks and Gold Mineralization, at
Makhrag El-Ebl area, North Eastern Desert, Egypt
The present study deals with the detailed petrography and geochemical characteristics of the
unaltered granodiorite and dacite rocks as well as the auriferous quartz veins and alteration zones.
The study involves a detailed petrographic description of the hydrothermal alteration assemblages
and their chemical analyses in order to elucidate the possible reactions that occurred between the
original rocks and the hydrothermal fluid. The studies also determine the ore mineralogy, gold
content in both quartz veins and altered rocks
2. Geologic Setting
Makhrag El-Ebl area is covered by Pan-African basement rocks. It is dominated by
granodiorites,Dokhan volcanics, syenogranites, alkali granites, dykes and quartz veins.
Granodiorite rocks intrude the Dokhan volcanics with clear contact. Some enclaves from Dokhan
volcanic rocks occur within the granodiorite. In some places, they show boulder appearance and
exfoliated due to being highly weathered
Many old working as trenches and shafts are present in the granodiorite (Fig. 2A). The Dokhan
volcanics occupy the northern and north western part of the mapped area. They form moderate to
high relief and dacitic in composition. The Dokhan volcanics are intruded by younger granites with
sharp contact. These volcanics are sheared in NE-SW and NW-SE-directions. Hydrothermal
alterations are recorded along these shear zones.
The younger granites are represented by syenogranites and alkali granites. The syenogranites
occupy the southwestern and eastern parts of the mapped area. They are massive, equigranular
and form moderate to high relief. The alkali granites occur as small bodies in the northern and
western parts of the mapped area. They are of reddish colour, coarse grained and stained with
malachite along fractures.
Auriferous quartz veins and stockworks of quartz veinlets are recorded in these rocks. Quartz
veins cutting the granodiorite and alkali granite rocks (Figures, 2B and 2C). The majority of these
veins are white and some of them are stained by iron and copper minerals along fractured quartz
veins. These auriferous veins trend in two main directions namely NW-SE and NE-SW. These
veins are ranging in length from few meters to more than l00 m. and in thickness from very thin
veinlets to more than 20 cm.
2
, Ibrahim A. Salem, Abdelsalam M. Abo El Ela, Sayed Ahmed Abu Elabn and Abdou M. Zeina
3. Methodology
About 58 samples from fresh country rocks, alteration zones and quartz vein samples in
Wadi Makhrag El Ebl area were petrographically examined to determine their mineral
assemblages, textures and microstructures. Back-scattered imaging and energy Dispersive X-
ray (EDX) analyses were carried out using Scanning Electron Microscope (SEM), Model
Quanta 250 FEG at the Central Laboratories of the Egyptian Mineral Resources Authority
(EMRA). SEM has accelerating voltage of 30 keV, magnification range (14x-1000000x) and
resolution 1 nm. SEM was used on carefully selected spots to confirm the existence of ore and
gangue minerals. Twenty country rock samples were chemically analyzed for the major oxides
and trace elements. The whole-rock chemical analyses were made using Philips X-ray
fluorescence (XRF) spectrometer Model PW/2404 equipped with Rh radiation tube and eight
analyzing crystals. Powder pellets for trace elements and fused beads for major oxides were
prepared and measured at Central Laboratories of EMRA. Eight samples from both quartz veins
and the different alteration types were analyzed for gold content, using the fire assay method.
X-ray diffraction analyses (XRD) of six samples were used to distinguish between the different
mineral found within the different alteration zones. This technique was done at Central
Laboratories of EMRA.
Fig.2 A: Panoramic view of old working in granodiorites. B: Field photograph showing network of quartz
veinlets cutting across granodiorite. C: Field photograph showing quartz veinlets cutting across alkali
granites.
a. Petrography of the country rocks
Granodiorites are massive, medium to coarse grained of grey to pinkish grey colour.
Microscopically, granodiorites (Fig. 3A) showing equigranular, hypidiomorphic, perthitic,
graphic and poikilitic textures. They are composed mainly of plagioclase, microcline, quartz
associated with minor biotite and hornblende. Iron oxides and sphene are the main accessory
minerals. Secondary minerals are represented by sericite (Fig. 3B) carbonates, chlorite and
epidote.
Dacite rocks are fine to medium grained, unequigranular displaying amygdaloidal and
porphyritic textures. Microscopically dacites (Fig. 3C) are composed mainly of phenocrysts of
plagioclase and quartz embedded in groundmass composed of fine-grained aggregates of
plagioclase, quartz, alkali feldspar, biotite and muscovite. Secondary minerals are represented
3
