Supervision by: Dr. Ahmed M. ZayedSupervision by: Dr. Ahmed M. Zayed
Edited by : Mostafa Abdel Azim MasoudEdited by : Mostafa Abdel Azim Masoud
Beni-Suef University- EgyptBeni-Suef University- Egypt
4. They are deposits of Precambrian age characterized by
being thin to medium bedded interlaminations of iron
oxide, iron carbonate, or iron silicate materials (layer
rich in iron ≥15% Fe ) with chert, quartz, carbonate, or
jasper (layer poor in iron).
Due to the extreme age of these formations, almost all
BIF have undergone some faulting, fracturing, folding,
compaction, veining, intrusions and metamorphism.
Although all BIF formations are probably
metamorphosed to some degree, but their general
character is still sedimentary.
N.B. BIFs are known as “taconite” in North America.
7. Oxide facies: Magnetite and hematite (taconite(.
Silicate facies: Cummingtonite, grunerite, greenalite, minnesotaite,
stilpnomelane, Fe chlorites, and Fe amphiboles.
Carbonate facies: Ankerite and siderite.
Sulphide facies: pyrite.
The classic facies zonation
from shallow to deeper
water deposition is:
oxide to carbonate to
8. Classification of BIFs according to
Three main types of banded iron formations are recorded allover
the world :
9. Algoma type (Archean age; 3500-3000 Ga)
→Formed by turbidity currents near island
arc trenches and typically sub marine
Island arc depositional environment.
The iron bands alternate with
metavolcanics and poyroclastics.
Lake- superior type (Early Proterozoic age; 2500-2000 Ga)
→ Shelf sediments precipitated in stable shelf or marginal basin (foreland or back-arc
basins), continental margin depositional environment.
The iron band alternate with metasediments.
Rapitan type ( 1000-500 Ga )
→Non volcanic type which formed in non volcanic rift zone at continental margin
1.BIF has been considered to be ferruginous sedimentary rock, which resulted from
the weathering, transportation, and precipitation of iron derived from landmasses
by erosion, with rhythmic deposition of iron as oxides, hydroxides, and hydrous
oxide-silicate minerals in the sedimentary systems.
2.Iron formations were deposited as end members, or final products, of carbonate
3.Depositions of iron formations resulted after buildup of iron concentration in the
sea, depending on pH and Eh conditions, the gradual buildup of oxygen and the
depletion of CO2 in the atmosphere lead to the precipitation of iron in seawater as
magnetite, hematite, and siderite.
4.Iron formation resulted from the upwelling of cold, deep seawater onto a warm
The cold water would be saturated in CO3, Ca2+ , and Fe2+.
Fe2+ would precipitate as ferric oxides, hydroxides, or silicates with increased
temperature, oxidation, and CO2 loss. The same waters would supersaturated in
amorphous silica and would precipitate chert.
11. Volcanic origin:
1.Silica and iron associated with volcanism were poured out on the sea floor from
springs of magmatic origin.
2.Iron formation beds were originally deposited as more thickly bedded fine-grained
ferruginous tuffs and other iron-rich sediments that were diagenetically oxidized and
silicified under the influence of solutions that were partly volcanic in origin.
12. The banded iron layers were formed in sea water as the result of
oxygen released by photosynthetic cyanobacteria (blue green algae),
combining with dissolved iron in Earth's oceans to form insoluble iron
oxides, which precipitated out, forming a thin layer on the substrate,
which may have been anoxic mud (forming shale and chert).
13. Occurrences in Egypt:
The Egyptian Precambrian
iron formations (BIF) and
the host metavolvanics or
widespread and easily
recognizable sequences at
134 localities distributed in
the Central Eastern Desert
(CED) between latitudes 25˚
12` and 26˚ 31`N.
Among them : ( Umm Nar,
G.El Hadid, Umm Khamis El
Zarga, W.Kareem, and W.
14. Two main genetic models have been postulated for the Precambrian Egyptian BIFs
including the Umm Nar occurrence:
1.A purely sedimentary origin during the accumulation of the Precambrian geosynclinal
2.A volcanogenic origin related to submarine magmatism and hydrothermal activity of
pan African island arc assemblages.
The original sediments of the BIF host rocks were most probably sandy and calcareous
shales or mudstones, sandstones, and limestones which are now metamorphosed under
greenschist and low amphibolite facies conditions.
Evidence of sedimentary origin of these
1.The geochemical characters of these rocks.
2.The bedded nature of these rocks and their
characteristic mm to cm rhythmic intercalations.
3.The absence of relics of igneous textures or
The lithofacies association of the metasediments
and BIF and their syn-sedimentary structures
(rhythmic bedding and laminations, cross
lamination and flaser structure) suggest deposition
in shelf environment.
15. (B) according to the present conclusions, the Egyptian
Precambrian BIFs can be preliminary reclassified into
two main genetic types of different ages:
1. Early Proterozoic BIF of pre pan-African shelf
environment, represented by the studied Umm Nar
2. Late Proterozioc BIF of Pan-African island arc
environment, represented by some other occurrences.
e.g. G. El Hadid, W. Karim and El Dabah
16. Two main genetic models have been postulated for the
Precambrian Egyptian BIFs including the Umm Nar
(1)A purely sedimentary origin during the accumulation of
the Precambrian geosynclinal sediments, and
(2)A volcanogenic origin related to submarine magmatism
and hydrothermal activity of pan African island arc
→ A detailed geologic, structural, and petrographic studies
of Umm Nar BIFs are included in the publication of El Aref,
Abdel Wahed, El Duogdoug and El Manawi (1993).and
they concluded the followings:
(a) The original sediments of the BIF host rocks were most
probably sandy and calc. shales or mudstones, sandstones,
and limestones now metamorphosed under greenschist and
low amphibolite conditions.
19. Ironstone is a fine-grained, heavy and compact
Its main components are the carbonate or oxide of
iron, clay and/or sand. It can be thought of as a
concretionary form of siderite.
Ironstone also contains clay, and sometimes calcite
21. Bog iron ores:
Formed in peat bogs, marshes, swamps and lakes in regions of
Pleistocene glaciations and in volcanic lakes.
1.Lake ores are formed as oolitic goethite in agitated waters along lake
2.Volcanic lake ores are made up of purely limonitic material with up to
50% Fe and owe their origin to iron bearing thermal springs.
Clinton type iron ore:
is characterized by :
1.The absence of chert.
2.Presence of hematite and chamosite oolites.
3. Herring bone cross statifications implying intertidal deposition.
Black band & sideritic iron ores:
These are fresh water deposits as thin beds, discontinuous lenses or
nodules associated with coal.
Source of Iron:
1.From weathering processes upon land, especially in the tropical climate and the subsequent
introduction of iron by rivers into seas and oceans, mostly in the adsorbed form or as colloidal
suspensions. (sedimentary origin)
2.Iron formations are attributable to submarine exhalations of fluids and the ooidal ironstones
especially attributed to hypersaline fluids which have risen to marine bottom along deep faults
(Kimberly, 1989). (volcanic origin)
3.The microbial and the other digenetic processes affecting the clayey sediments, rich in organic
matter and deposited in deltas, lagoons, and stagnant anoxic basins, lead to mobilization of iron
(fe3+→fe2+). According to this hypothesis, the anoxic sediments could have acted as very
important source and temporary storage of huge quantities of iron. (biogenic origin)
Origin of Ooids:
1.By metasomatic ferruginization of ooidal limestones.
2.Ooides growing in the state of suspension, in an agitated, high energy aqueous environment.
24. SUGGESTED ENVIRONMENTAL SETTINGS
OF THE OOLITIC IRONSTONES
Continental Environments Marine Environments
Low Energy Env. High Energy Env.
Shallow / Deep Shelf
26. 2 5
2 5 3 0
M ED ITER R A N EA N SEA
K H A R G A
O A S I S
D A K H L A
O A S I S
FA R A F R A
O A S I S
E L B A H A R I Y A
O A S I S
S IW A
O A S I S
FA IY U M
O A S IS
C A I R O
S a lu m
A l ex a n d r ia
A S W A N
S I N A I
1= Jurrasic ooltic ironstone, G abal E l M aghara
2= Low er C retaceous oolitic ironstone, G abal E l H alal
3-7= U pper C retaceous oolitic ironstones, w estC entral Sinai (3), north Wadi Q ena (4),
A sw an region (5,6,7)
8-10= M iddle E ocene oolitic ironstones (E l B ahariya region
O C C U R R E N C E S O F T H E E G Y PT IA N P H A N E R O Z O IC
O O L IT IC IR O N ST O N E S
29. Types of iron deposits and genesis:
According to El Sharkawi et al., (1987), the Bahariya iron ore can be classified into threeAccording to El Sharkawi et al., (1987), the Bahariya iron ore can be classified into three
Genetic type (I):Genetic type (I):
OOolitic-pisolitic iron ore of limonitic composition.
The host rock is limestone of the Naqb Fm.
Mainly shoal and lagoonal depositional environment.
Genetic type (II): (Karst ore)Genetic type (II): (Karst ore)
Stratabound supergene ore formed due karstification of Qazzun Fm. (Nummulitic
It is barite-bearing, hematite, goethite iron ore (Karst ore).
Karst textures are dominant.
Genetic type (III):Genetic type (III):
Statabound supergene ore formed of green sand followed by lateritic weathering of
glauconite in the Upper Eocene HamraFm.
The ore is mainly composed of glauconite and hematite.
Notes de l'éditeur
#Differences between BIFs and Ironstones:
Age: BIFs are Precambrian and ironstones are Phanerozoic
N.B. Phanerozoic BIFs are recorded, but Phanerozoic is not the age of their formation, it is the age of the tectonic events that led to their exposure like the Alpine, Caledonian orogenies.
2. Textures: BIFs (banding), Ironstones (ooids, peloids, onchoids, etc..)
3. BIFs are affected more by tectonism and metamorphism
#Banded: because BIF is banded and takes all the scales of banding (thick banding-thin banding-laminae-varves).
#Formation: not the stratigraphic term, but the same as its English meaning.
#BIFs are affected by different sedimentary structures:
Primary or synsedimentary deformational textures: BIFs are affected by syndeformational tectonism (like slumping, cross-lamination and folding (as it appears here in the photo))
The folding in this photo is restricted to a definite zone and is not found above or below it, that’s why we say that it is synsedimentary.
2. Secondary or postsedimentary structures (like folding and faulting and veining)
#The dark band is Jasper, and the light band is the Fe-rich band
The black to gray to silver colored iron oxide layers contrast with the iron rich chert, jasper and shales which are generally red in color.
#Jasper: a form of chalcedony (cryptocrystalline Qz), it is opaque impure variety of silica, Jasper is basically chert which owes its red color to iron III inclusions
#Jaspilite is a BIF rock that often has distinctive bands of jasper.
≥15% Fe in the Iron-rich layer only not in the bulk BIF sample with its different bands, where when we make chemical analysis for BIFs, we analyze each band alone.
Rolling over the sustrate at the interface between seawater and the deposited sediments on a core