IRON ORE DEPOSITS IN EGYPT
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Transcript of IRON ORE DEPOSITS IN EGYPT
Outline of Lecture 9:EGYPTIAN IRON ORE DEPOSITS
Iron ore deposit of sedimentary nature
Sinai: Gabal Halal iron ore deposit
Western Desert:
Aswan iron Ore Deposits
Bahariya iron Ore Deposits
• The Banded Iron ore deposits (BIFs)• Geologic Setting
• General Characteristics of the Egyptian Banded Iron Ores
• Are the Egyptian Banded Iron Ores Unique? Genesis of Egyptian Banded Iron Formation
We will explore all of the above in Topic 9.
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Figure 1: Distribution of iron deposits in Egypt .
This figure shows the distribution of iron ores and iron oxide traces all over Egypt. Most of the
locations are inter-related in origin to each other. The trend of the iron oxides in Western Desert points
out to a common source of the iron deposits in this area.
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EGYPTIAN IRON ORE DEPOSITSIn Egypt economic iron ore deposits occur in two natures (or forms):
i) Iron ore deposit of sedimentary nature (Ironstone)
(Sedimentary iron ore deposit is a very limited occurrence, being found only in the 2 localities in the Western Desert and one locality in Sinai):- Sinai: Gabal Halal iron ore depositWestern Desert:
Aswan iron Ore Deposits
Bahariya iron Ore Deposits
and
ii) The Banded Iron ore deposits (BIFs) (BIFs have being found only in the 13 localities in the central Eastern
Desert)
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I) Iron ore deposit of sedimentary natureSedimentary iron ore deposit is a very limited occurrence, being found only in the:-
One locality in Sinai : Gabal Halal iron ore depositTwo localities in the Western Desert
Aswan iron Ore Deposits
Bahariya iron Ore Deposits
Sinai: Gabal Halal iron ore deposit
It is located ~4 km NW Sir Hadhira, Sinai (El-Far, 1965).
This area contain oolitic iron ores of lower Cretaceous age that
extending ~8 km.
The iron ore were found in two beds separated by 14 m sandstones:
The lower bed (~2.65 m in thickness) is a yellowish-brown
and compact bed mainly oolitic.
The upper bed (~5 m in thickness) is a typical oolitic iron ore.
Main ore minerals: goethite and hematite.
Gangue minerals: clay minerals, quartz, calcite-dolomite, and sulphate
minerals.
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I) Iron ore deposit of sedimentary nature
Gabal Halal iron ore deposit
It is located ~4 km NW Sir Hadhira, Sinai (El-Far, 1965).
This area contain oolitic iron ores of lower Cretaceous age that extending ~8
km.
The iron ore were found in two beds separated by 14 m sandstones:
The lower bed (~2.65 m in thickness) is a yellowish-brown and
compact bed mainly oolitic.
The upper bed (~5 m in thickness) is a typical oolitic iron ore.
Main ore minerals: goethite and hematite.
Gangue minerals: clay minerals, quartz, calcite-dolomite, and sulphate minerals.
Sinai:
Iron associated with manganese east of Abu Zenima has economic significance as a by-product of manganese extraction, potentially accounting for the difference between profit and loss.
Passing references occur in some reports to ferruginous horizons with oolitichematite in Cretaceous Nubian sandstones of the Plateau Province.
Micaceous hematite is known to occur in quartz veins in eastern Sinai, in granite at Gebel Abu Mesud.
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Iron ore deposit in Western DesertEconomic iron ore deposit of sedimentary nature, being found in the 2 localities in the Western Desert.
Sedimentary iron ore types only occur in
Upper Cretaceous (Senonian) sediments East of Aswan
Middle Eocene sediments north of the Bahariya oases
Note:
Senonian The final Cretaceous epoch which is dated at 88.5–
65 Ma ( Harland et al., 1989) and comprises the Coniacian,
Santonian, Campanian, and Maastrichtian Ages.
Some authors do not include the Maastrichtian Age within the
Senonian.
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Egyptian Ore Deposits
Items Bahariya Oasis mine Aswan mine
Age Middle Eocene Senonian (Upper Cretaceous)
Ore Type Hard-massive, Banded-cavernous,
Friable, and Oolitic- pisolitic
Oolitic hematite (dark red with a bluish
metallic tinge in place)
Ore Minerals • Mainly of hematite, goethite, and
hydrogoethite, with occasional
pockets of softly ochre and
lepidocordite, chamosite,
magnetite, psilomelane, and
pyrolusite.
• Pyrite and chalcopyrite occur as
rare minute single grains.
Mainly hematite with minor goethite
Gangue minerals Barite, kaolinite, glauconite, alunite,
chert, gypsum, calcite, chlorite, and
Tripoli
Quartz, gypsum, halite, glauconite and
clay minerals
Average iron content (%) 53.4 43
Average silica content (%) 6.1 18
Average phosphorous content (%) 0.21 1.1
Specific gravity (gm/cc) 3.45-4.35
Mineable Geological Reserve
(m.t.)
140
(126.7?)
El-Gedida 14
136
(142.6?)
Ghorabi
Nasser
El-Harra
Average thickness of iron bed (m) 13 0.7
Stripping ratio 0.185 2.5
Mine area (km2) 6 600
Ultimate Annual production (m.t.) 3.3 (2.5) 0.5
Distance from mine to plant at Helwan
(km)
330 850
Production cost of one ton
(Egyptian pound)
18.020
On 2004
8.865
On 1975
Number of labourers 503
on 2004
1400
On 1975
Compared between Aswan and Bahariya iron ore Deposits
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Western Deserti) Aswan iron Ore Deposits
Economic iron has been produced from East Aswan regions since Pharaonic times (1580 to 1380 B.C.) until 1973.
In recent years it was the main supply of iron ores for the Egyptian iron and steel industry till 1973 when it was replaced by Bahariya iron ore.
The main occurrence located East of Aswan(Kom-Ombo, Lake Naser), while small deposits are also encountered in the variegated shales along the Nile Valley to the south at Kalabsha, Garf Hussein, Kurusko, and Abu Simbil.
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Fig. 2. (A) Geological map of East Aswan shows the location of study samples from Wadi Abu Sobera and Wadi Abu Agag areas. (B) Geological map of the Um Hibal area showing the locality of the iron-bearing formation. (A: after Mucke (2000); B: after Ghazaly et al. (2015)). 12
Fig. 3. General stratigraphic column of the late Cretaceous sedimentary cover in Aswan area. (After El Sharkawi et al., 1996).
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Figure 1. Location map of the study area (up left), its main geologic topographic and iron ore localities illustrated on Landsat 8 false
color bands 7,4,2.
Salem, S.A. and E.A. El Gammal, E.A. (2015): Iron ore prospection East Aswan, Egypt, using remote sensing techniques. The
Egyptian Journal of Remote Sensing and Space Science, Volume 18, Issue 2,, 195–206. http://dx.doi.org/10.1016/j.ejrs.2015.04.003
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Types of iron-ore tThe ore is a bedded oolitic type of Senonian age in the form of three bands
interbedded with Ferruginous sandstone and clay/Ferruginous concretioncapping Precambrian rocks.
Three ypes of iron-ore have been distinguished in the provided areas (Salem and ElGammal, 2015) :
(1) Ferruginous sandstone iron-ore (up to 70.46% Fe2O3 content),
(2) Oolitic iron-ore (attains 54.24% Fe2O3 content); and
(3) Ferruginous concretion iron-ore(up to 63.2% Fe2O3 content).
The Oolitic iron-ore shows P2O5 and S contents exist in relatively higher proportionsthan in the ferruginous sandstone and ferruginous concretions. This is due to theparticular bioactivity in the marine environment of formation of the Oolitic ore.Its low manganese content may be attributed to the low pH exhibited by theleaching solutions, which dissolved the slightly basic iron with small amounts ofstrongly acidic manganese.
In spite of the less contents of Fe2O3 = 54.24 and Fe = 37.94 in the Ooloitic iron orerelative to the other ore types, it is considered as an important type due to itsdominance and distribution in the east of Aswan district, as well as thedeficiency in silica and MnO add a promise potential to the Ooloitic iron ore.
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Figure 7. Ferruginous sandstone iron ore illustrations (Salem and El Gammal, 2015). (a) Ferruginous sandstone thin beds in
Wadi Timsah hill. (b) Paleosole surface rich in iron oxides in the Nubian sandstone beds, Wadi Anid. (c) Ferruginous
sandstone cracked beds hand specimen (hs). (d) Ferruginous sandstone hs. (e) Limonite rich ferruginous sandstone hs. (f)
Ferruginous sandstone with calcite and Gibbsite.
Iron ore prospection East Aswan,
1) Ferruginous sandstone occurred and
was distributed in the lower parts of Timsah
Fm which was composed of fluviatile near-
shore marine and locally eolian fine-to
medium-grained sandstone with interbedded
channel and soil deposits.
Iron ore was found as inliers and caps and
in the paleosole surfaces of the Nubian
sandstone beds, forming hematite and
goethite strata having thickness varying from
50 cm to 4 m occuring at Gabal Timsah, Wadi
Timsah and Wadi Anid (Fig. 7a and b).
The iron ore is syn-genetic bedded of
Senomanian age, formed under lacustrine
environment. The gangue minerals
associated with the iron ore deposits include
quartz, gypsum, glauconite, and clay
minerals.
The hand specimens exhibit fine bedding
and plugs in red and brown to black colors
including limonite patches in yellow color (Fig.
7c–f).
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Figure 8. The Oolitic iron-ore illustrations (Salem and El Gammal, 2015). (a) General view, Gabal Abu
Hashim. (b) Spherical Oolitic grains hs. (c) Oolitic hematitic glauconitic coarse grains hs. (d) Hematitic
rich Oolites hs.
Iron ore prospection East Aswan,
2) Oolitic iron-ore is the more
dominant, most important and
valuable iron ore type in the study
district in spite of its low content of the
Fe2O3 relative to the other types.
It is found as compact beds vary in
thicknesses from 1–3 m. distributed
and alternated through the upper parts
of the Temsah Fm in Gabal Abu
Hashim, Gabal Nugur and Gabal
Naag areas of dark-red, Oolitic
hematite (Fig. 8a).
The oolites are cemented by pure
amorphous hematitic material and
ferruginous silica; therefore the iron-
content of the matrix is less than that
of oolites.
In the hand specimens, the Oolitic
hematitic grains are easily seen by the
naked eye varying in sizes in different
specimens and even in the same
specimen (Fig. 8b–d).
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Figure 9. The Ferruginous concretion iron-ore illustrations (Salem and El Gammal, 2015). (a) Ferric-duricrust surfaces of
ferruginous concretion and substratum in Wadi Quffa. (b) Hard compact masses of ferruginous concretion beds. (c) Fine
intersected beds in Ferruginous concretion in Wadi Timsah. (d) Hematite-goethite coarse grained in Ferruginous concretion hs.
(e) Blocky Ferruginous concretion hs. (f) Gebsite, and clay minerals in Ferruginous concretion hs.
Iron ore prospection East Aswan,
3) Ferruginous concretion iron-ore The Ferruginous concretion iron-ore form hard
compact masses of concretion beds and substratumrich in iron-ore, found as ferric-duricrust surfacesbetween isolated Nubia sandstone hills andmountains through Wadis Timsah, Quffa, Anid,Umm Udi and Abu Aggag (Fig. 9a,b).
The ferric-duricrust beds formed fromfragments accumulation of ferruginous sandstone,Oolitic iron-ore and ferruginous concretions whichwas already formed due to the action of surfacewater on the valleys floor (in wadi fill).
The thicknesses of the glauconitic coarse grainshs. (Fig. 9d) Hematitic rich Oolites hs. ferric-duricrustbeds vary from 10 to 60 cm, showing fantasticoutlines formed by precipitations from aqueoussolution in porous sedimentary rocks.
Due to the denudation of the sandstonecontaining hematite concretions and owing to theirresistance to weathering, they were often seenaccumulating in great quantities in places on theground surface giving it black and red colors. In thehand specimens, the concretions show hematite-goethite rich grain aggregations cemented in coarsegrained matrix of black and brown color s (Fig. 9c–f).
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Over hanging layer of oolitic
Iron, Wadi Abu Aggag Aswan
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The thickness of the bands varies from 20 up to 350 m.
Iron ore deposits occur in Senonian (upper Cretaceous) sediments ~7,000,000 tonnes were produced between 1956 and 1973.
The estimated reserves are 121 to 135 million tonnes with 20 million tonnes proved reserves with average content of 46.8% Fe (Attia. 1955).
Ore
The ore is oolitic hematite, dark red with a bluish metallic tinge in place, compact and dense (Sp.gr. 3.45-4.35 gm/cc).
Ore minerals: are mainly hematite with minor goethite. The hematite is occur in oolitic form range from 1-1.5 mm in diameter and is cemented by a compact hematitic matrix.
Gangue minerals: include quartz, gypsum, halite, glauconiteand clay minerals.
Fe31.2 - 62.3 %
(average 46.8%)
SiO2
5 - 31%
(average 14.1%)
Mn up to 1.3%
S up to 0.3%
P 0.4 - 3.5%
The oolites themselves contain 60% of Fe
while matrix contains 40% of the iron.
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DiscussionThe east of Aswan area is a suitable environment for iron ore occurrences due
to the following reasons:
(1) Presence of huge Nubia sandstone rocks which formed from the compilations and accumulation of old rock fragments and deposits including iron.
(2) The aquatic marine environment present in the study area is suitable for leaching, precipitating and deposition of iron oxides from the iron rich solutions in the sandstone terrain as hematite and limonite.
(3) Varied topography between the basement and sedimentary rocks traced by intermountain substratum and basins are suitable for collection and catchment of different debris, rock fragments, slags, and wadi deposits with iron constituents. These factors motivated us to study the surface geology of this area exploring and locating the iron ore deposits through the exposed rocks and landforms.
The marine encroachments in the Cretaceous part of the east of Aswan area attained N–S to SE directions forming depositional basins (Issawi, 1981). Iron ore in the east of Aswan is considered by (Hussein, 1990) to have been formed under lacustrine conditions, during the deposition of Senomanian sediments. The sedimentary iron deposits are invariably confined to the middle series of the Nubian sandstone formations which lie unconformably on the basement rocks. The iron oxide bands are often associated to ferruginous sandstones and clays. Transitions from ferruginous sandstone to Oolitic iron deposits are often encountered (Adelsberger and Smith, 2009).
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Gneiss
Ore is considered to have formed undersedimentary lacustrine to fluviomarineconditions during the deposition of UpperCretaceous (Senonian) sediments of Aswanembraces all the non-marine to marginaland shallow marine siliciclastics exposed inthe Nubia area.
The iron is mostly dissolved from bottomsediments and mobilized in so-called"carbon-dioxide zone" as ferrousbicarbonate, then precipitated in anoxidizing environment as ferric hydroxide.
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II) Western Desert:Bahariya iron Ore Deposits
• The Bahariya oasis is located in central plateau of Western Desert between 27° 48/ -28° 30/ N and 28° 55/ - 29° 10/ E.
• Its northern edge is located along the contact between the stable and unstable shelves.
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Gebel El-MaghrafaGebel El- Dist
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Geologic map of the Bahariya area
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Geologic map of the northern Bahariya area (after Said and Issawi, 1964)
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The iron ore of El Harra belongs to El Harra member of El HaffufFormation; whereas El Gedida iron ore belongs to Naqb Formation.
The area is covered by Bahariya Formation (unfossiliferous varicoloredsandstone of Cenomanian age) followed by El Heiz Formation(brownish limestone and sandy clay beds), and El Haffuf Formation ofsandstone, sandy clay, and ferruginous beds, which are partly taken bythe iron ore deposit, Khuman Formation (chalky limestone), and NaqbFormation of thick limestone beds with few marl and clay associations.The iron content in the ironstone deposits ranges from 30% to 58% Fe,and the manganese content ranges from 0.7% to 7.66% Mn .
The stratigraphic position of Naqb Formation is partly taken by iron oredeposits at El Gedida, El Harra, and Ghorabi; where El Gedida iron oremember belongs to iron deposits of Lower Middle Eocene (NaqbFormation) and the upper Eocene (Abu Maharik Formation. The ore islocalized in the crest of anticline.
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Fig. 6. A. Panoramic view of the Naqb Formation showing ironstone beds and clay
intercalations (white arrows) arranged in two sequences. B. Outcrop view of the
ironstone succession exposed at the central part of El Gedida mine (X is the location of
the collected fossil sample). (after Afify et al., 2016)
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A composite section (not at scale) of the main Eocene lithostratigraphic and chronostrigraphic units and shallow benthic foraminiferal zones (SBZs) after Serra-Kiel et al. (1998). The shallow benthic zones written in red color are re-interpreted after previous dating by Boukhary et al. (2011) and Said and Issawi (1964). The violet shaded rectangle is the relative timing proposed for the iron mineralization. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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The other areas: Ghorabi, Nasser, El Heiz, and El Harra are of low grade ores and of high manganese content. In addition, these areas have relatively thick overburden.
These occurrences are called El Gedida, Ghorabi, Nasser and El Harra,extending over 11.7 km2; and the ore thickness varies from 2 to 25 m(averaging 9 m).
The deposits are under laid unconformably by the Bahariya formationsandstones and overlaid by the Redwan formation.
The iron ore deposits are generally irregular in outline. They form asuccession of beds which are concordant with local dips (~4°).
The ore is thought to be localized in the crests of two major anticlinestrending in a NE-direction. El Gedida and El Harra ore deposits are localizedon the eastern anticline, while Ghorabi and Nasser are on the westernanticline.
The high-grade ores exist in the crests and that low-grade ores arelocalized in the limbs of the anticlinal structures.
Major faults disturb the peripheries of the ore bodies, forming the majorwadis which surround the area of the iron ore deposits. Many small faultsaffect the iron beds in the four areas. These structure natures of the foldsapparent to be generated by faulting affiliated with the Pelsuium mega-shear, along which the Bahariya oasis are located (Neev et al., 1982).
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1.1.1. Forms, Shapes and Textures
Several forms characterize the constituents of the ore deposits such as massive crystalline, crystal aggregates, granular, botryoidal-shape, kidney-shaped, oolitic, pisolitic, pseudoolites (spheroids), subspherulitic, and sponges.
Therefore, several textures are recognized in the ore deposits such as banded, disseminated, cavity filling, cavernous, andreplacing.
1.1.2. Mineralogy
Main ore minerals: hematite, goethite, Limonite, and hydrogoethite, with occasional pockets of softly ochre and lepidocordite, chamosite, magnetite, psilomelane, and pyrolusite.
Pyrite and chalcopyrite occur as rare minute single grains.
Gangue minerals: barite, kaolinite, glauconite, alunite, chert, gypsum, calcite, chlorite, and Tripoli
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Glauconite and Fe-rich chlorite
Rich Ore
Wadi area
(Western)
Barite Zone
Sands and Sandy clays
(Overburden)
Quartzite sandstone and
conglomerate (Radwan
Formation)
Unconformity
Intercalations
Footwall
(Bahariya Formation)
Barite patches
Saliferous Ore
High Central Area
Intercalations of clays, sand,
chert concretions and alunites
Mn rich
Wadi area
(Eastern)
East
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Detrital Barite
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Detrital Barite
الباريت المتفتت فى منطقة الهضبة بمنجم الحديد بالجديدة، الواحات البحرية•
Bahariya)بالجزء العلوى للحجر الرملى التابع لتكوين البحريةيوجد أسفل طبقة الخام• Formation)
عند منطقة التالمس بين الخام وتكوين البحرية ومتداخال مع الجزء السفلى لطبقة الخام•
سم وفى بعض الحاالت إلى مترين50سم إلى 5يتراوح السمك من •
ورة غير يوجد على هيئة جيوب او تجمعات وليس على هيئة طبقات متصلة، وهذه التجمعات منتشرة بص•ملىمنتظمة ومتفاوتة فى السمك واألبعاد ويفصلها مساحات خالية من الباريت تكون من الحجر الر
ب إلى يكون الباريت مختلط بالرمال وبنسب متفاوتة من خام الحديد وتتفاوت درجة تماسكه من سائ•متماسك في حالة اختالطه بالحجر الرملى وشديد التماسك فى حالة اختالطه بخام الحديد
•
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Detrital Barite
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1.1.3. Ore TypesGenerally, four types of ore are distinguished based on texture, constituents and chemical composition namely:
Hard-massive ore type: This type is relatively massive hard crystalline and has a deep reddish-brown color. It consists mainly of hematite (>80%) with minor amounts of goethite and limonite. Micro- and macro-fossils which are replaced by hematite (and/or goethite) are common. Manganese minerals (mainly psilomelane) are rare in this ore type.
Banded-cavernous ore type: It has a brown or yellowish color, generally banded and cavernous. The cavities being filled with red or yellow ochre or manganiferous powder. It consists mainly of an intergrowth of goethite and hematite together with a little amorphous limonite and minor amounts of manganese minerals. The pyrite and chalcopyrite are present as minute grains within limonite or in the core of subspherulitic goethite bodies. This banded texture is attributed to pre-existing laminations in the original limestone.
Friable-ore type: Generally, bright yellow, soft, friable and has an earthy luster. The ore minerals consist mainly of goethite and limonite together with minor amounts of hematite. Glauconite is the most common gangue mineral and result in the appreciable increase Al2O3 content of these ore type.
Oolitic-pisolitic ore type: Low to moderate grade ore (49-45 % Fe) has a yellow to yellowish-brown color and oolitic to pisolitic texture. It is mainly formed of goethite, Iimonite and quartz, minor amounts of hematite, glauconite and Fe-rich chlorite.
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Reserves
• Economic iron ores confined to the lower part of the middle Eocene limestone (El Naqbformation) in four major occurrences north of Bahariya oasis.
Today, the left minable reserves are estimated by only 63 Mt, which are just enough for about15-20 years at the present mining rate of 3 to 3.5 Mt/y.
Bahariya iron ores have 53% Fe that is suitable for the iron high ovens in Helwan Cityfactories, now, iron ores excavated from El-Gedida mine with an annual rate 3.3Million Tons then carried about 300 km away to Helwan City factories by a specialtrain.
It is necessary to blend the various types to obtain:
Fe 53%, SiO2 7.5%, Cl 0.7%, and MnO 1.98%,
for use in the metallurgical plants at Helwan Iron and Steel Co., Cairo.
How Geologist do this mixture???
Area Reserves Fe SiO2 Mn S P Cl
(M.Tonnes) %
El Gedida 126.7 53.6 8.9 2.3 0.9 0.2 0.6
Ghorabi 57.0 48.0 9.0 3.0 0.7 0.9 0.8
Nasser 29.0 44.7 6.7 3.9 0.6 0.1 1.3
El Harra 56.6 44.0 12.5 2.9 1.0 0.1 0.8
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They classified ore blocks according to Fe-content into three categories as following:
Poor ore (17-35% Fe): Low-grade iron ore, highly ferruginous sandstones and hydrogoethite ore.
Normal ore (35-45% Fe): Oolitic and pisolitic hydrogoethite ore, banded hydrogoethite, and hydrohematite ore
Rich ore (>45% Fe): Colloform hydrogoethite ore and massive hydrogoethite-hematite ore.
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Genetic Ore TypesThe largest and richest of these occurrences in that of El Gedida (~127 million tonnesproven ore). At El Gedida mine, distinguishing three genetic, types:I) Iron ore of a massive nature and a hydrothermal-metasomatic type (Type I): Represented by the high central area in El Gedida mine. The ore is high-grade, with high Fe and NaCl contents, and low Si, and high traces of Zn
and Cu. The mineralized middle Eocene limestone (El Naqb formation) is brecciated and
metasomatically replaced by hydrothermal solutions ascending along NE-SW trending fractures.
II) Iron ore is cavernous, ochreous or massive type (Type II): Following the emergence and faulting of the mineralized middle Eocene block, the
generated depressions received reworked rocks including high-grade ore from the high central area.
Fresh water lakes occupied the depressions where remobilization of Fe and Mn and their redeposition were effected, possibly through biogenic interference.
Tripoli earth and kaolinite were authigenetically deposited with the debris. Detrital barite is a common associated. Abrupt change in grade characterizes the iron ore of this genetic type
III) Iron ore is oolitic or pisolitic type (Type III): This follows type II in age and is tied to post-middle Eocene glauconitic succession
which caps the reworked iron ore of type II Enrichment of the marine depositional basin in Fe and K promoted the formation of
glauconitic. Cyclic deposition of glauconitic clays and sands was interrupted by intermittent
emergence followed by lateritic weathering of glauconite sediments Profound changes in the mineralogy of these sediments took place resulting in the
deposition of low-grade Fe ore characteristically poor in Mn and Ba.
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1.1.4. OriginAmbiguity arises regarding the genesis of the iron ores in the Bahariya oases
area.Attia (1955) favored a shallow water lacustrine origin during Oligocene time.
Deposition of leached iron under lagoonal environment and subsequent replacement of the underlying middle Eocene and Cenomanian beds. Evidence of replacement is apparent where most of the calcareous fossils, especially the diagnostic nummulites of the middle Eocene, are almost completely replaced by iron oxides.
El Shazly and Hassan (1962) assumed that the Ghorabi iron ore was derived from the chemical weathering of older rocks.
Contrary of these opinions, Tosson and Saad (1974) suggested that the ores were formed by metasomatic replacement associated with impregnations and cavity filling from ascending solutions affiliated with volcanic activity. The oolitic and pisolitic iron ore outcropping in the Ghorabi area to be syngenetic, the iron being supplied by weathering processes and the high grade ores exist in the crests and that low-grade ores are localized in the limbs of the anticlinal structures.
On the other hand, El Aref and Lotfy (1985) suggested that the iron deposits were formed through lateritization processes during the senile stage of post Eocene karst event. Karst depressions and excavated unconformity acted as traps where iron oxides are accumulated. Iron deposits together with soil products also form surfacialcrust (duricrust), capping and cementing highly subdued and altered carbonate rocks. The evolution of megascopic and microscopic ore fabrics, the oxidation of iron bearing minerals, and their relation to the gangue and weathering products reflect the changes in the moisture regimes and the physicochemical conditions involved during the pedogenesis.
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Qatrani Formation At El Gedida Mine. You can see here a
burrowing of ants then filled with iron.
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• In the Eastern and Western Wadi areas, the ore successions are truncated unconformably by late Lutetian-Bartonian glauconitic sediments with lateritic ironstone interbeds of the HamraFormation.The iron ore and the overlying glauconitic sediments are folded and undulated. The iron ore sequence attains its maximum thickness, up to 35 m, in the Western and Eastern Wadi areas, reduced into 11 m in the high central area. This iron ore sequence consists of a pisolitic oolitic iron stone unit followed by highly karstified bedded ferruginous dolostones and mudstones. Ore conglomerates mixed with silicified limestone and chert overly the karst ore. The genesis of the ores has been a matter of a scientific discussion for a long time.
@ Hassan Harraz 2017 49
Glauconitic green sand at Gabal El Dist(Bahariya Formation)
Upper Eocene Hamra Formation (Glauconite and Iron beds)
@ Hassan Harraz 2017 50
Charcoal at Gabal El Dist
@ Hassan Harraz 2017 51
ii) EGYPTIAN BANDED IRON FORMATION
(BIFs)
@ Hassan Harraz 2017 52
ii) EGYPTIAN BANDED IRON FORMATION (BIFs)
The banded iron ore deposit is a very limited occurrence, being found only in the 13 localities in the central Eastern Desert, approximately between Latitude 25° 15/ - 26° 40/ N and Longitude 33° 22/ - 34° 20/ E.
These iron ore type is concentrated in five main localities: Abu Marawat, Wadi Kareim, Wadi El Dabbah, Wadi Um GhamisEl Zarqa, Gabal El Hadid, and Um Nar.
The bands are variable in thickness and extension from one locality to another and within the same occurrence.
Their extension usually vanes from some meters up to more than 2 km along the strike, and vary in thickness from a few cmsto 18 m (normally ranging between 0.5 and 3 m).
In the most cases, the ore is present in the form of bands and lenses of magnetite, martite and hematite with a gangue dominantly of quartz.
The reserves for BIF ore type in Egypt amounts to 47.6 million tonnes (Akaad and Dardir 1983) as estimated for the whole of Quseirarea.
@ Hassan Harraz 2017 53
Localities Latitude Longitude
Abu Marawat 26° 31/ N 33° 22/ E
Wadi Kareim 25o 56/ 40// N 34° 03/ E
Wadi El Dabbah 25° 48/ N 34° 09/ E
Wadi Abu Rakab 25° 48/ 30// N 34° 11/ E
Wadi El Hindusi 25° 47/ 30// N 34° 11/ E
Gabal Um Shaddad 25° 39/ 20// N 34o 20/ E
Wadi Um Ghamis El Zarqa 25° 33/ N 34° 17/ E
Wadi Sitra 25° 32/ N 34° 14/ 30// E
Wadi Siwiqat Um Lassaf 25° 21/ N 34° 08/ E
Gabal El Hadid 25° 20/ N 34° 10/ E
Um Mar 25° 18/ N 34° 15/ E
Wadi Um Hagalig 25° 15/ 30// N 34° 16/ 30// E
Map showing major iron deposits in central Eastern Desert, Egypt.
Geographic co-ordination of the Banded Iron Ore deposits in the central Eastern Desert of Egypt
Fig. 1: Thematic Landsat image of Egypt showing the location of eleven of the most important banded iron-ores (blue circles). Inset is a simplified geological map of the area outlined in the white rectangle (from Egyptian Geological Survey, 1981) .
1) Hadrabia
2) Abu Marawat,
3) Gabal Semna
4) Diwan
5) Wadi Kareim,
6) Wadi El Dabbah,
7) Gabal Um Shaddad
8) Wadi Um Ghamis El Zarqa,
9) Gabal El Hadid,
10)El Emra
11)Um Nar
12)Wadi Hammama
13)Um Anab
Wadi Abu Rakab
Wadi El Hindusi
Wadi Sitra
Wadi Siwiqat Um Lassaf
Wadi Um Hagalig
54
Table 1: Tectonostratigraphic basement units of the Egyptian Eastern Desert
Sources: Egyptian Geological Survey (1981); El-Gaby et al. (1990); Hassan and El-Hashad (1990); Stern et al. (2006); Avigad et al. (2007); Moussa et al. (2008).
Eon/
Era
Tectonic
Stage
Age
Ma
Rock Types/ Associations Granitoid intrusion
Ph
aner
o
zoic Po
st-
Oro
gen
i
c
< 5
70
. Younger Granites (post-tectonic, alkalic): Granite, granodiorite,
monzonite
Gattarian (570 – 475
Ma)
Neo
pro
tero
zoic
Pan
Afr
ican
Acc
reti
on
/
Co
llisi
o
n6
50
-
57
0
Dokhan metavolcanics (andesite, rhyolite, rhyodacite,
pyroclastics) intercalated with Hammamat metasediments
(breccias, conglomerates, greywackes, arenites, and siltstones)
Sub
du
ctio
n
75
0 -
65
0
Isla
nd
Arc
Shadhli Metavolcanics (rhyolite, dacite, tuff);
Volcaniclastic metasediments; Diamictites (Strutian: 680
– 715 Ma).
Banded Iron Ores
Meatiq (710 – 610)
Hafafit (760 – 710)
Spre
adi
ng
85
0 -
75
0
Op
hio
li
tes
Tholeiitic basalt, sheeted dykes, gabbros, serpentinites,
all weakly metamorphosed
Shaitian Granite
(850 – 800 Ma)
Arc
hea
n?/
Pale
op
rote
ro
zoic
Pre
-Pan
-
Afr
ican
<1.8
Ga
Metasedimentary schists and gneisses (Hb-, Bt-, and Chl-
schists), metagreywackes, slates, phyllites, and
metaconglomerates Some BIF? Umm Nar?Migiff – Hafafit gneiss (Hb and Bt gneiss) and migmatite
@ Hassan Harraz 2017 55
Geologic Setting Central Eastern Desert (CED) is a part of the Arabian Nubian
Shield (ANS) which constitute the northeastern sector of the Pan-African (650-550 Ma., Clifford 1970) tectonic belt. The EgyptianBanded iron formation (BIF) and the host geosynclinalmetavolcanics and/or metasediments constitute widespread andeasily recognizable sequences at 13 localities distributed in theCED.
The iron formations occur as sporadic deposits in layered thevolcanogenic rocks of Neoproterozoic age. The Neoproterozoicbasement complex of the CED consists largely of a crudely layeredsequence of volcanic rocks and derivative sedimentary rocks,mainly of greenschist facies metamorphism. The terrene has manylithologic similarities to the Archean greenstone terrenes.
The BIF geologic sequences are considered to be geneticallyrelated to Pan-African weakly metamorphosed island arcassemblages ( island arc volcanics and volcanoclastics ofNeoproterozoic age) which are often associated with ophioliticmélange rocks
@ Hassan Harraz 2017 56
Fig. 2: Location of Wadi Kareim (K) and El Dabbagh (D) study areas. Location of Meatiq dome (M) is also shown. Dark green area between Kareim and Dabbagh is a Hammamat basin. From Google Earth.
@ Hassan Harraz 2017 57
Figure 23: Geologic map of Wadi Kareim area (left) and Wadi El Dabbagharea (right; note north arrow (Stern and Dixon, unpublished)
@ Hassan Harraz 2017 58
Geological map of Wadi El Dabbah iron ore deposit ( after Akaad and Dardir, 1983)
@ Hassan Harraz 2017 59
• Fig. 2: Geological maps of (a) Wadi Kareim area (AFTER El-Habaak and Mahmoud, 1994) and (b) Umm Nar (after El-Aref et al., 1993). Ellipse in (a) shows location of banded iron ore. 60
@ Hassan Harraz 2017 61
General Characteristics of the Egyptian Banded Iron formation
The general characteristics of the iron formation in the central Eastern Desert are as follows:
1)The BIF occurs as sharply defined stratigraphic units within layered volcanic-volcaniclastic sequences of calc-alkaline nature and andesitic composition.
2)Some deposits (e.g. Wadi Kareim) are reportedly associated with diamictites (e.g. Stern et al., 2006) suggesting some relation to glaciations and possibly “Snowball Earth” conditions.
3)Individual bands range from a few centimeters to more than 10 m in thickness and are frequently faulted and folded with steeply limbs.
4)Frequent contemporaneous folding, faulting, brecciation and slump structures are found.
5)Microbanding occurs on a scale of centimeter or less, where iron-rich bands alternate with bands of jasper or, sometimes, of carbonates or silicates.
6)In a given area, the zone containing layers of iron-formation typically has a stratigraphic thickness of 100 to 200 m, in which the aggregate thickness of BIF is on the order of 10 to 20 m.
7)The lateral extents and thicknesses of individual ore bodies are relatively small, typically on the order of tens of meters (Fig. 2).
8)The entire sequence (iron ore + host rocks) is strongly deformed by a series of folds and thrusts, and was regionally metamorphosed under at least greenschist facies conditions.
9)Deformation evident on the regional, outcrop, and hand specimen scales (Figs. 2).
10)Rhythmic banding is either streaky (Umm Ghamis) or continuous (Hadrabia) where layers of magnetite and hematite alternate with quartz – rich layers on macro-, meso- or micro-scales.
@ Hassan Harraz 2017 62
General Characteristics of the Egyptian Banded Iron Ores
11) Hadrabia is the only deposit with oolitic and pisolitic textures. None of the other deposits have oolites, pisolites, pellets, or granules . Other wave generated primary structures are also lacking.
12) Oxide and silicate facies ubiquitous; carbonate facies usually represented by calcite is common in several deposits (e.g. Wadi Kareim, Wadi Dabbah, and Hadrabia). Sulfide facies is generally lacking.
13) Magnetite is dominant, except in a few deposits (e.g. Hadrabia) where hematite -magnetite. Most crystals of magnetite have undergone some grain coarsening attributed to metamorphism in several areas (e.g. Wadi Kareim).
14) Magnetite commonly altered to martite, specularite, or goethite due to post-metamorphic oxidation.
15) Most of the iron is present as magnetite (altered in places to martite) concentrated in steel-back bands alternating with reddish jasper or with iron-poor grey or greenish bands; hematite is less frequent. The gangue minerals present are mainly quartz, chlorite, biotite and clay minerals.
16) Silicate facies characterized by the minerals: chlorite, epidote, garnet, hornblende, and stilpnomelane.
17) Some deposits are also strongly altered, often developing a porous texture
18) Many of the iron ore deposits (e.g. Gebel Semna, Gebel Hadrabia and Abu Merwat) are characterized by high Fe and low Si contents in comparison with Algoma, Superior, or Rapitan BIF types (Fig. 7, Table 2), whereas others (e.g. Gebel El Hadid and Wadi El Dabbah) are characterized by Fe/Si ratios somewhat comparable to Rapitan BIF. Altered samples with a porous texture are typically characterized by some of the highest Fe/Si ratios (Table 2).
19) Greenschist facies metamorphism, with the development of chlorite, sericite and the iron silicate stilpnomelane and possibly minnesotaite occur. On the contact with intrusives, local metamorphism may reach amphibolite facies with the recrystallization of the iron minerals and silica and development of epidote and garnet.
@ Hassan Harraz 2017 63
Table 5: Mineralogical compositions and mode of occurrence the BIF, Central Eastern Desert, EgyptWadi Kareim Wadi El Dabbah Umm Ghamis El Zarqa Gabal El Hadid Umm Nar
Country rocks
Metavolcaniclastics,
metavolcanics,
granodiorites, Hammamt
sediments, trachytes
tetavolcanics, serpentinites,
Older Granites, Hammamat
sediments, Younger
Granites
Metasediments, metavolcanics,
serpentinites, metagabbros,
diorites, granodiorites, granites
Metasediments,
metavocanics, serpentinites,
metagabbros, granites
Shaitian granites, metasediments,
serpentinites, metagabbros, younger
gabbros, granites
Host rocks
Metavolcanic rocks
intercalated with
volcaniclastic rocks
(andesite-dacite tuffs,
metagreywackes &
metamudstones)
Tuffaceous metasediments Calcareous metamudstones
intercalated with
metagreywackes
Metasediments-
metapyroclastics (consists of
metagreywackes,
metamudstones,
metasiltstones,
metaconglomerates,
metatuffs)
Mica-schists, amphibole schists,
marbles and quartzites.
Principal iron mineralMagnetite, hematite Hematite and/or magnetite Magnetite with or without
hematite
Magnetite, hematite Magnetite, hematite, stilpnomelane
Subsidiary iron minerals
(rarer minerals in
parenthesis)
Goethite, siderite,
greenalite, ninnosotaite,
stilpnomelane, pyrite,
(pyrrhotite, chalcopyrite,
sphalerite)
Goethite, martite (pyrite) Martite, goethite Goethite, siderite, (pyrite,
chalcopyrite)
Martite, goethite
Gangue minerals
Quartz, jasper, calcite,
ankerite, dolosite, garnet,
epidote, chlorite, actinolite,
talc
Quartz, jasper, calcite,
garnet, epidote, chlorite,
actinolite
Quartz, jasper, chalcedony,
calcite, epidote, chlorite, garnet,
hornblende, feldspar
Quartz, jasper, chert, calcite,
dolomite. ankerite, chlorite,
epidote, muscovite, biotite,
feldspar, apatite
Quartz, calcite, plagioclase, muscovite,
biotite, hornblende, graphite, epidote,
garnet
Iron formation faciesOxide, carbonate, silicate,
sulfide
Oxide, oxide-silicate Oxide, oxide-silicate Oxide, carbonate (rarely
sulfide)
Oxide, oxide-silicate
Ore types
Banded siliceous Massive
magnetite
Magnetite-rich (black)
Hematite-rich (red-violet)
Magnetite-jasper-(hematite) Jasper-hematite Magnetite)
Nodular chert-magnetite-
(hematite) Siderite-magnetite)
Quartz-magnetite, Hematite-
magnetite-quartz-garnet
Fe% surface
Fe% subsurface
Reserve (m.t.)
44.6
43.0
17.8
38.2
34.9
6.0
44.6
42.1
5.6
45.7
45.0
3.6
45.8
41.8
13.7
Texture
Bedding, banding,
lamination, lensoidal, slump,
pelitic, psamo-pelitic, relics
of oolitic, granular, massive
Bedding, banding,
lamination, lensoidal,
Massive
Banding, bedding, lamination,
lenses, slump, crenulation
Banded, bedded, lensoidal,
deformation, massive,
colloform, rim veins, relict
replacement
Bedding, banding, lamination, cross-
lamination, flaser structure,
granoblastic, lense, slump, lensoidal
Band thickness 0.4 to 12 m Few cm to 10 m 10 cm to 5m Few cm to 3.8 m Few cm to 3 m@ Hassan Harraz 2017 64
BIF with japer laminations (Wadi El Kariem)
d) Meso- and (e) micro-scale banding (lamination) between alternating jasper (red) and Fe-ore in unaltered samples from Wadi Kareim.
@ Hassan Harraz 2017 65
Fig. 4: Photomicrographs showing selected textural relations. (a) through (e) taken under polarized reflected light, oil immersion; (f) - (h) under plane polarized transmitted light. (a) Magnetite coarsened by metamorphism, Wadi Kareim; (b) relicts of primary? magnetite (Mgt) replaced by hematite, Wadi Kareim; (c) coarse grained porphyroblasts of strongly martitizedmagnetite, Wadi Kareim; (d) relict magnetite strongly martitized, and transformed into platy specular hematite (Hm) Wadi Kareim; (e) primary magnetite (arrow) and quartz embedded in a matrix of secondary goethite, Gebel Semna; (f) oriented platy hematite, oxide facies, strongly altered porous sample from Gebel Semna; (g) fibrous stilpnomelane (Stp) in silicate facies; Wadi Kareim; (h) epidote (Ep; arrow) coexisting with magnetite, silicate facies; Wadi Kareim; (i) chlorite coexisting with sericite and quartz, silicate facies; Gebel Semna; cross polarized transmitted light.
@ Hassan Harraz 2017 66
Reserves
Abu
Marawat
Wadi
Kareim
Wadi
El Dabbah
Umm
Ghamis El
Zarqa
Gabal
El Hadid
Umm
NarTotal (m.t.)
Reserves* (m.t.) 6.5 17.7 6.0 5.6 3.6 13.7 53.1
Fe% surface 44.4 44.6 38.2 44.6 45.7 45.8 43.7
Fe% subsurface - 43.0 34.9 42.1 45.0 41.8 -
Fe% in concentrate - 56.4 53.5 59.7 69.0 61.0 55.3
Expected
concentrates
- 10.0 3.2 3.6 2.6 7.0 27.4
@ Hassan Harraz 2017 67
Are the Egyptian Banded Iron formations Unique? The size and general characteristics of the Egyptian BIF led to the suggestion that they are “Algoma type” deposits (e.g.
Sims and James, 1984; Table 2). However, several points suggest that the Egyptian BIFs may be unique, namely:
Algoma and Superior type deposits are Late Archean or Paleoproterozoic in age (e.g. Klein, 2005), whereas the Egyptian BIF’s are Neoproterozoic (Fig. 5). Only Umm Nar is suspected to be Paleoproterozoic (El-Aref et al., 1993).
The Neoproterozoic Rapitan/ Urucum type deposits are typically jaspilites associated with glacial deposits. Among the Egyptian iron ores, only Hadrabia is characterized by Hm >Mgt? (Essawy et al., 1997). Diamictites have only been reported from Wadi Kareim (Stern et al., 2006).
Egyptian BIFs are intercalated with calcalkalic metavolcanic and metapyroclastic rocks of island arc affinity rather than the tholeiites typical of Algoma type deposits.
Sulfide facies is lacking, carbonates minor, usually predominated by calcite (or ankerite) rather than siderite; well developed silicate facies with stilpnomelane, chlorite, epidote, and garnet; oxide facies predominated by magnetite.
Garnet in many Egyptian BIFs is grossular rich (and in some cases free of almandine; Khalil, 2001; Takla et al., 1999) unlike garnets from Algoma or Superior BIFs which are typically almandine – spessartine solid solutions (e.g. Klein and Beukes, 1993).
Amphibole in many Egyptian BIFs is a magnesiohornblende (e.g. Takla et al., 1999; Khalil, 2001) rather than cummingtonite – grunerite.
Chlorite in all Egyptian BIFs is a clinochlore – ripidolite with significantly higher Mg/(Fe + Mg) ratios (0.5 – 0.7) compared to Algoma and Superior type BIFs (Fig. 6).
All Egyptian BIFs characterized by an unusually high Fe/Si ratio (Fig. 7), as well as higher Fe3+/Fe2+ ratios compared to Algoma and Superior types (Fig. 8). Fe/Si is considerably higher for BIFs affected by alteration (hydrothermal or weathering?).
Egyptian BIFs characterized by bulk chemistries that vary considerably from one deposit to another. However, many deposits are characterized by high Al and low Cr and Ni compared to Algoma type BIFs (Table 2).
REE patterns for Egyptian BIFs vary from one deposit to another, and do not resemble those patterns characteristic of Algoma, Superior, or Rapitan BIFs. “Fresh” Umm Ghamis and Umm Shaddad have prominent negative Sm and positive Ndand Eu anomalies, and slight HREE enrichment . Hadrabia deposit (“altered”) is characterized by a positive Eu anomaly. Strongly oxidized samples from Hadrabia show LREE enrichment relative to North American Shale Composite (NASC) .
@ Hassan Harraz 2017 68
Table 2: BIF from the Eastern Desert of Egypt compared to the main types of BIF
O = oxide, Si = silicate, C = carbonate, Sf = sulfide, Mgt = magnetite, Hm = hematite.
Algoma Superior RapitanEgyptian BIF
Fresh Altered
Age(Ga) >2.5 2.5 - 1.9 0.8 - 0.6 0.85? - 0.65 0.75-0.6
Size small large small small small
Thickness (m) <50 >100 75 - 270 Very thin 5 -30
Deformation Very strong Undeformed Deformed Strong Strong
Facies O, Si, SfC O, Si, C O, Si,C
Oolites rare always common none none
Ore Minerals Mt>HmMt>Hm
Higher HmHm Mt>Hm MtHm
Rock
Associations
Tho to CA
vol,tuffs,
wackes/shales
Carbonaceous DiamictitesCA volcanic, tuffd, shales,
wackes; Diamictites?
ChemistryHigh, Cr, Mn,
Ni, Cu, As
Low Cr, Co, Ni,
Cu, Zn
High P, Fe,
Low Cr, Co,
Ni
Low Cr, Co, Ni, Cu,
Variable Al
REE/NASC
+Eu, -Ce, slight
HREE-
Enrichment
+Eu , strong
HREE-
Enrichment
Weak +Eu,
Very strong
HREE
Enrichment
-Sm, Ce?,
+Nd and Eu,
HREE- rich?
+Eu, -Yb,
LREE-rich
Fe/Si <1.36 <1.36 1.3 - 1.6 1.4 -2.75 3 -4.7
Fe2O3/FeO 1.9 2.76 46- 100 5.5 - 8 7 -57
@ Hassan Harraz 2017 69
Fig. 5: Schematic diagram showing age and abundance of the three main types of BIF relative to Hamersley Group as a maximum (from Klein, 2005). Note Egyptian BIF age.
@ Hassan Harraz 2017 70
Fig. 6: Compositional range for chlorites from the silicate facies of the Egyptian BIF relative to the fields of Sheikhikhou(1992).
@ Hassan Harraz 2017 71
Fig. 7: Bulk rock compositions of “Fresh” and “Altered” BIFs from Egypt relative to Algoma, Superior, and Rapitan average compositions from Gross & McLeon (1980).
@ Hassan Harraz 2017 72
Fig. 8: Bulk rock major oxide components of Wadi Kareim iron formation (solid circels) compared to overall averages for Algoma and Superior type BIFs (shaded green) from Klein (2005). All analyses recalculated on an anhydrous, CO2 – free basis.
@ Hassan Harraz 2017 73
Fig. 9: REE patterns normalized relative to North American Shale Composite (NASC) for (a) “fresh” BIF from Taklaet al. (1999); El-Habaak & Soliman, (1999); (b) “altered” BIF from Hadrabia (Essawy et al.,1997), and Kareim (El-Habaak and Soliman (1999) compared to patterns typical of Algoma (c), Superior (d), and Rapitan (e). (c) – (e) from Klein (2005).
@ Hassan Harraz 2017 74
GENESIS OF EGYPTIAN BANDED IRON FORMATION
The Egyptian banded iron formation (BIF) and the host metavolcanics or metasediments constitute widespread and easily recognizable sequences at 13 localities distributed in the Central Eastern Desert (CED) between latitudes 25° 12/ and 26° 31/ N. These BIF sequences are considered, in the recent literatures, to be genetically related to Pan-African weakly metamorphosed island arc volcanic and volcaniclastic assemblages (Late Proterozoic) which are often associated with ophiolitic mélange rocks.
However, the understanding of the environment of deposition and geologic setting of each BIF-bearing sequence is very important to unravel the origin of the related BIF facies as well as its genetic relationship with the complex history of the Pan-African rock assemblages.
Two main genetic models have been postulated for the banded Egyptian BIFs:1) a purely sedimentary origin during the accumulation of the Precambrian
geosynclinal sediments (i.e. chemical marine sediments in geosynclinalbasin; Shukari et al., 1959, and Rasmy, 1968), and
2) a volcanogenic origin related to submarine magmatism and hydrothermal activity of Pan-African island arc assemblage (i.e., subaqueous volcanogenic deposits in an island arc environment: (Sims and James, 1984; El-Gaby etal., 1988).
@ Hassan Harraz 2017 75
It is generally agreed that the BIFs are chemical precipitates from water, but there is no general agreement as to the source of the iron and silica in them or to the physical environment in which they were deposited.
The BIF and base metal sulfides of the Egyptian Eastern Desert seem to be occurring exclusively in the island arc assemblage which consists of weakly metamorphosed volcanogenic sequences, where the iron oxides represent an aerated near-shore environment to the north and the sulfides represent deeper euxinic environment to the south.
On the other hand, the two southernmost iron occurrences at Gabal El Hadid and Umm Nar contain pyrite, chalcopyrite and siderite beside iron oxide minerals (Sabet et al., 1976; El-Dougdoug et al., 1985); these occurrences may represent transitional conditions shallow or near shore facies (i.e. iron oxide).
El Aref et al. (1993) preliminary reclassified the Egyptian BIFs into two main genetic types of different ages;1) Early (?) Proterozoic BIF of pre-Pan-African shelf environment,
represented by the Umm Nar occurrence., and2) Late Proterozoic BIF of Pan-African island arc environment,
represented by Gabal El Hadid, Wadi Kareim, and Gabal El Dabbah.
@ Hassan Harraz 2017 76
Table 3: Paragenetic sequence of mineral formation of the central Eastern Desert BIFs in relation to the metamorphic history
Sedimentation and
Diagenesis
Metamorphism Hydrothermal
process
Weathering process
Regional Contact
Mineralogical
Composition
Colloidal materials of
ferruginous/
calcareous sediments,
muds, shale, silica
gel and detritus materials ?
Magnetite
(fine euhedral
crystals)
Hematite (fine
prismatic and
flaky crystals)
Stilpnomelane
Minnosotaite
Quartz
Chlorite
Muscovite
Dolomite
Ankerite
Biotite
Epidote
Hornblende
Actinolite
Talc
Garnet
Apatite
Magnetite
(large euhedral
crystals)
Magnetite
(after chlorite)
Chlorite
Epidote
Garnet
Graphite
Magnetite (veinlets)
Goethite (veinlets)
Pyrite
Chalcopyrite
Pyrrhotite
Sphalerite
Quartz (veinlets)
Calcite (veinlets)
Hematite (martite)
Goethite
Kaolinite
Sericite
Chlorite
Textures
Banded
Massive
Colloform
Pelitic and psmao-pelitic
Relics of oolitic
Nodular
Granular
Banded
Lensoidal
Massive
Granoblastic
Vein replacemet Replacenent
Colloform
77
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