The document discusses Egyptian ore deposits, including occurrences of talc, asbestos, anthophyllite, vermiculite, corundum, and magnesite. Talc and asbestos are found associated with ultramafic intrusive rocks in the Eastern Desert. Anthophyllite and vermiculite are restricted to serpentinized ultramafic masses at Hafafit that are intruded by pegmatite veins. Corundum occurrences are also associated with pegmatites cutting ultramafic masses. Magnesite forms veins in serpentinized ultramafic rocks. Total magnesite production reached 800 tonnes in 1974.
2. Outline of Lecture 3:
• Occurrences of talc and asbestos are typically
associated with Precambrian ultramafic
intrusive rocks such as peridotite, serpentinite,
gabbro, and norite. Ultramafics of this type
host talc and asbestos deposits in the Eastern
Desert of Egypt.
2
4. 4
Fig. 1. a) Geological map of the crystalline basement of the Eastern Desert showing the threefold division of the Eastern
Desert, exposure of high-grade infrastructure gneisses and migmatites, and the location of Hafafit Metamorphic
Complex (HMC) (modified after Eliwa et al., 2010); b) Landsat RGB color composite image in PC5, PC3, and PC1 bands
for the HMC. Major and minor thrusts, and the antiforms are delinated after El-Ramly et al. (1993)
7. Two types of asbestos are known in Eastern Desert
namely:-
i) Chrysotite asbestos is known to occur as very small
veinlets (<2 m in width) and uneconomic, crossing
the serpentinitized parts of the ultramafic masses
almost wherever they crop out.
ii) Anthophyllite asbestos occurs in associations with
vermiculite in a number of occurrences spread over
an area of ~15 km2 between 24° 28/ to 24° 29/N
and 34° 27/ to 34° 47/E at Hafafit area. The main
occurrences are those of Wadi Shidani, El Duwaig,
Um Graf, Um Kuhl, Um Fahm, Um kisbash, Wadi El
Hisa, and North Bir Hafafit.
7
8. Anthophyllite and vermiculite are restricted to
serpentinized ultramafic mass (350 x 150 m at the North
of Bir Hafafit occurrence) embedded in the gneisses and
believed to represent blocks in a mélange zone.
The ore is developed only where these serpentinite
masses are intruded by pegmatite veins and veinlets.
Here, and at the periphery of the pegmatite veins,
vermiculite followed by actinolite, then anthophyllite
and lastly talc, are developed within the serpentinite
masses with the transformation of the pegmatite into a
quartz free, feldspar-mica rocks which may occasionally
bear corundum.
In the last-mentioned occurrences, anthophyllite of
been mined since 1944 with an average production of
500 tonnes per year, together smaller amounts of
vermiculite.
8
9. • The area of Hafafit in the Eastern Desert of
Egypt contains asbestos-vermiculite deposits
at several sites, occurs in the magnesium-
rich metapelitic schist-ultramafic complex.
9
Simplified geologic map of Gabal Hafafit
area, Eastern Desert, Egypt (after Greiling
and El Ramly, 1984)
10. • Extensive metasomatic zones of vermiculite-,
actinolite-, tremolite-, chlorite-, anthophyllite- and
talc-rich rocks have been developed at the contacts
of serpentinized ophiolites ultramafic bodies and
surrounding mica gneisses in the Hafafit area.
10
Cross sections in the vermiculite pits at Hafafit area (after El Shazly et al., 1975)
11. Table 1. Major Types and Subtypes of Vermiculite Occurrences in Serptntinites-
Metapelitic schists of the Migif-Hafafit Massif, southern Eastern Desert, Egypt.
For location of occurrences see Fig. 2
11
Characteristic mineral associations
Type 1. Vermiculite in leucogranitic pegmatite and pegmatite veins
a) V. in reaction zones of leucogranitic
pegmatite and pegmatites vein rocks
anthophyllite, clinoamphiboles,
chlorite (titanite; prehnite, fluorite,
corundum; tourmaline)
b) V. within leucogranitic pegmatite
and pegmatite vein rocks
chlorite (after clinoamphiboles)
Type 2. Verraiculite in fractures; primary, formed by hydrothermal fluids
a) V. in hydrothermal vein zones and
fracture systems
chlorites ± clinoamphiboles
b) V. dispersed in hydrothermally
altered serpentinite bodies
Chlorites, hydrobiotite, altered
minerals
14. Geologic setting
❖The mineralized area is occupied by granite gneiss with irregular masses of
serpentinite as well as pegmatite veins and lenticels. The serpentinite bodies
are usually not more than 300 m length and 150 m width and are generally of
flattened lenticular shape with a roughly avoid cross section. They show
certain conformity between their contacts and the direction of foliation of the
gneiss.
❖Anthophyllite and vermiculate occur only where the serpentinite masses are
cut by leucogranite (pegmatitic leucogranites). The amount and concentration
of each of these two minerals vary from one site to another; some of them
are big enough to mine. The field study of a number of the mineralized sites
showed that they have the same mode of occurrence. They exhibit similar
rock types, structural relations and disposition within the same geological
framework. The main differences that could be observed between one site
and another are related to the total amount and the relative abundance of
the anthophyllite and vermiculate within the mineralized ultramafic mass.
❖The mineralized serpentinite mass ~200 x 100 m and lies in the northern
closure of the domal structure. The pegmatite cut across the serpentinite
mass in the form of dense stockwork of veinlets, the smaller veinlets net to
form bigger one following the contact between the serpentinite mass and the
enclosing gneiss. Generally, the pegmatites are composed essentially white
feldspar, glassy quartz, few red garnet crystals and black mica pockets, streaks
and sheaths, specially concentrated on the borders of the pegmatites. Within
the gneiss, these pegmatites are relatively rich in quartz and contain fair
amounts of garnets, where they cut across the serpentinite; they become
quartz-free plagioclasite pegmatites with rare garnet and with abundant black
mica.
❖Passing from the core of the serpentinite outwards towards the pegmatites, a
sort of zoning due to variable mineral composition is usually recognizable and
is roughly parallel to the pegmatite-serpentinite contact.
14
15. Origin
❖The formation of anthophyllite-vermiculite at Hafafit to
bimetasomatic reactions between pegmatitic material
and the ultramafic rocks, where alkalis and silica
supplied by the pegmatites infiltrated the ultramafic
mass, producing successive, almost monomineralic
zones of vermiculite, actinolite, anthophyllite and talc
away from the pegmatite intrusion (El-Shazly et al.,
1975).
❖The relative abundance of silica determines the degree
to which each of the anthophyllite or vermiculite zones
are developed. Moreover, a process of bimetasomatism
in situ, between the pegmatites and serpentinites,
resulted in the formation of asbestiform anthophyllite
on the expense of the ultramafic mass.
❖Pockets and streaks of black mica and vermiculite are
usually developed in the border zone of the emplacing
pegmatites and form an integral part of them.
15
16. Occurrences
❖Corundum occurrences are known in Egypt only at Hafafit area.
The main occurrences are at Abu Nimr, Abu Merikhat, Um Karaba,
Wadi El Hema, and Abu Fahm.
Geologic Setting
❖In all of these, corundum is restricted to plagioclasite pegmatite
cutting through the ultramafic masses enclosed within the Hafafit
gneisses.
❖At Abu Nimr a serpentinite mass is in contact with hornblende
gneiss. The contact is followed by pegmatite veins (80 m long and
80 cm wide) bears corundum, with the complete absence of
quartz. Away from serpentinite mass, similar pegmatite veins are
quite rich in quartz. The ultramafic rock is altered into actinolite and
vermiculite. Corundum constitutes between 5-60% of the vein, and
form eithers colourless crystals or crystals with pale-pink or blue
tints.
Origin
❖The plagioclasite-pegmatite and its associated corundum were
formed through a process involving the progressive metasomatism
between the upraises pegmatitic material and the ultramafic mass.
❖The removal of silica and alkalis from the pegmatitic material
during its ascent is the reason for the development of corundum.
16
17. 17
Occurrences
❖Ophiolite related magnesite is known to occur at
Semna, Khor Urn El Abas, Sagia, Bir Mineih, Um
Salatit, Gabal El Mayiet, Ambaout, Zargat Naam, and
Wadi Eikwan.
❖It forms thin veinlets, stockworks and pockets in the
serpentinized ultramafic masses (a few meters in
length and a few centimeters in width).
❖Magnesite was formed during the process of
serpentinization to accommodate the excess Mg
released during that process.
❖Total production reached a maximum of 800 tonnes
in 1974, the dropped to almost nil at present due to
the exhaustion of reserves.
18. • In The Central and Southern Portions of the Eastern Desert, Ophiolite
related magnesite is known to occur at Semna, Khor Um El Abas, Sagia, Bir
Mineih, Um Salatit, Gabal El Mayiet, Ambaout, Zargat Naam, and Wadi
Eikwan.
• Accumulations of snow-white, cryptocrystalline (amorphous) magnesite
have been deposited as fracture-filling material in the altered ultramafic
part of this complex.
• Dunites and harzburgites, which are serpentinized to different degrees,
are the hosts to the magnesite veins.
• It forms thin veinlets, stockworks and pockets in the serpentinized
ultramafic masses (a few meters in length and a few centimeters in width).
Magnesite was formed during the process of serpentinization to
accommodate the excess Mg released during that process.
• Total production reached a maximum of 800 tonnes in 1974, the dropped
to almost nil at present due to the exhaustion of reserves.
18
20. • Talc forms as a product of metamorphism on hydrothermal
alteration of Mg-rich rocks, especially ultramafics, dolomites,
basic volcanics, and tuffs.
• In Egypt, talc deposits are known to occur in two petrological
assemblages:
i) in the mafic-ultramafic assemblages of ophiolite
sequence. The talc is always found in association with
serpentine minerals, carbonates, silica and tremolite in
the carbonatized serpentinite formed after the
ultramafic members of the ophiolitic suite.(Barramiya-
Um Satatite area, Atalla, Gabal El Rabshi, Wadi
Ghadir area, Al Allaqi, Abu Dahr), and
ii) in the basic volcanic rocks (e.g., Um Samuki , Atshan,
Darhib, Abu Gurdi, Um Selimat, and Egat ). Most of talc
product in Egypt comes from the intensively altered basic
volcanics and tuff rocks.
• Production of talc in Egypt amounts to 12,200 tons/year
(1983-1984), most of it is used as a filler in local industries,
though ~1500 tons were exported in the same year
(Geological Survey Egypt, 1984).
20
22. • The rock is of a buff to light creamy in color, with a reddish tint. It is fine-
grained, spongy, very soft and talcose, weathering into cavities 30 cm
across, giving the rock a cavernous appearance. The cavernous
appearance of these rocks is due to the leaching of carbonates by
weathering. The rocks consist of talc, carbonate, and hematite, with or
without small amounts of antigorite and aggregates of limonite and
arsenopyrite. The talc is found in fine-flaked, rarely radial talc. Platy
crystals of talc ranging from 0.01 to 0.48 mm in diameter are sometimes
seen replacing the antigorite. The carbonate is present by dolomite in
big quantities as irregular crystals (0.03-0.15 mm) sometimes it occurs
in euhedral rhombs that are scattered amongst the talc; every gradation
is seen between the serpentinite and these talc-carbonate rocks.
• This mode of occurrence can be described as that the CO2 has been
released from the calcareous schist series (i.e. calcareous
metasediments) during their metamorphism and their dedolomitisation.
This metasomatic replacement is due to the simple addition of CO2
without the addition of any other constituent is clear from that the
unaltered serpentinite relics (10-50 cm in dimensions) are embedded in
talc-carbonate rocks are devoid of any zones of other minerals.
22
23. • Talc (including steatite, soapstone and
phyrophyllite) is known in some 35 sites in the
Eastern Desert and Sinai,
• The most important occurrences are those
associated with the belt of island arcs hosting the
Zn-Cu-Pb volcanogenic massive sulfide deposits of
Um Samuki talc mines.
• The main talc producers in Egypt are the Darhib talc
mine and a number of surface and underground
workings around Atshan, near Hamata.
23
25. Atshan Talc Mine
The Atshan talc mine (latitude 24° 15', longitude 35° 13'), is one of several talc deposits in the
Hamata area of the Eastern Desert, 18 km west of the Red Sea, is the largest talc deposit in
Egypt.
At Atshan the host rocks are volcanic and volcaniclastic rocks of basaltic to rhyolitic
composition.
The Atshan deposit occurs within a thick sequence of arc-related volcanic rocks intercalated
with some sediments (cf. Abdel-Rahman 1995, Fasfous, 1992) and are intruded by granitic to
dioritic rocks, whereas the other three talc deposits occur in tectonized Alpine-type settings
within thick carbonate beds and clastic sediments.
The talc deposits of the Hamata area occur within the Hamamid Group of the Shadli
metavolcanic rocks. A sequence of mafic flows, andesites, dacites and pyroclastic rocks
intercalated with some sediments (Fasfous, 1992).
The volcanic rocks were deposited within an island arc setting and were later subjected to
conditions of greenschist-facies metamorphism (Searle et al.,1976).
The Atshan mine, just as the other talc occurrences in the area, is associated with small
lenses of sulfide (Hussein, 1990), consisting of pyrite, sphalerite, chalcopyrite and galena.
Although most of these sulfide occurrences are uneconomic, the Umm Samiuki deposit,
located ~100 km southeast of El Atshan, is currently mined for Zn and Cu.
25
30. Ore body
Talc orebodies at the Atshan mine were impure dolomitic limestones locally intercalated
with clastic sediments.
Talc occurs, in the footwall rocks to the sulfide bodies, in association with tremolite,
epidote, quartz, dolomite and magnesite, in an alteration zone 30 m wide that extends for
some 500 m in an E-W direction.
They enclose a number of small lenses of the massive sulfides, exposed as gossans
on the surface and inducing a greenish tint to white colours in their vicinity.
The deposit is composed of several lensoid orebodies located along two distinct faults and
within two shear zones (Fig. 1).
The roughly N-S-trending shear zone is about 1300 m long and 200 m wide, whereas the
E-W-trending shear is ca.700 m long and 200 m wide.
The largest orebody (No. 1) occurs within the E-W shear, and the second largest orebody
(No. 5) occurs within the N-S shear zone.
A large intrusive body, the Reiidi grey granite (composed of quartz diorite: Fasfous 1992)
intrudes the volcanic rocks south of the mine, and localized stocks of the same occur
within the mineralized zones.
Small lenses containing massive sulfides and disseminated sulfides (pyrite, pyrrhotite,
sphalerite, lesser chalcopyrite and minor galena) occur in the two shear zones, and they
are enclosed by the talc orebodies.
The sulfide lenses are parallel to the shear zones, as well as to the banding in the host
metavolcanic rocks (Zidan,1989). Although a rite, hematite and limonite-rich gossans
outcrop at the surface, indicating supergene enrichment above the water table, most
sulfides occur at depth.
Reserve
The Atshan mine was in operation intermittently from 1962 to 1992, and has an estimated
reserve of about 60,000 tonnes of talc.
30
34. The sulfide-talc association
The association of Mg-rich minerals such as talc and tremolite with sulfides at the Atshan
talc mine and at other talc deposits in the Hamata area is enigmatic. Various
hypotheses have been discussed in connection with the origin of sulfides at the Atshan
mine and at similar talc deposits in the area.
❖ Early investigators suggested that the sulfides are undeformed, suggesting an
epigenetic origin, and that they were introduced along faults and shear zones by
hydrothermal fluids (Hume 1937, El Shazly & Afia 1958, Kovacik 1961, Mansour et al.
1962).
❖ More recently, investigators proposed that the sulfides in the talc-rich rocks represent
VMS-type mineralization associated with Mg-metasomatism of the host rocks during
felsic submarine volcanism (Rasmy et al., 1983).
However, no evidence for VMS type mineralization were found (Schandl et al., 1999).
The absence of superimposed potassic and Al-rich alteration zones, and the high
concentrations of Mg in rocks of non-igneous origin, would favor a sediment-hosted
rather than a volcanogenic origin for the sulfides.
The presence of fractured, fragmented pyrite and pyrrhotite in the clastic sediments
suggests that these sulfides were present prior to the high-temperature contact
metamorphism. However, the development of pyrite and chalcopyrite rims on hercynite,
and of chalcopyrite stringers along cleavages in tremolite, suggests remobilization of
some sulfides during the lower temperature event.
Finally, although contact and regional metamorphism destroyed most primary minerals at
the mine, the low and variable concentrations of trace elements, including the REE, imply
that the protoliths of the Mg-rich rocks were most likely impure carbonate beds
containing fragments of clastic sediments. We suggest that the high-temperature
assemblages formed at the time of emplacement of the Reiidi grey granite (a quartz
diorite body), whereas the subsequent lower-temperature assemblages (including talc)
formed during regional metamorphism associated with faulting and shearing. This event
would result in enhanced permeability of the rocks, thus, the development of channel
ways for the fluids. The abundance of relict serpentine at the mine suggests that the
fluids had a relatively high H2O:CO2 ratio. Mg was derived from the breakdown of
dolomite and possibly magnesite.
34
35. Origin
The origin of talc was related to a process of hydrothermal alteration acting upon lenses and bodies of
ultramafic rocks enclosed within the volcanic pile (El Shazly, 1957; Nessim et al. 1954).
The very low Ni, Cr and Co contents of these ultramafic rocks preclude such an ultramafic origin (Gad
et al., 1978).
It is believed that talc and the associated minerals (serpentine, tremolite, chlorite, magnesite) were
formed through a process of intensive Mg-metasomatism of pre-existing volcanic rocks. Deposition
of sulfide and talc in the area occurred during two separate (unrelated) fluid-circulation events.
Talc mineralization can be attributed to "Pyrometasomatism" and to the interaction of CO2-rich fluids
with volcanic rocks during the emplacement of igneous intrusions (Fasfous, 1992).
Schandl et al.(1999) did not find evidence for VMS type mineralization (and contemporaneous Mg-
metasomatism) at the Atshan talc deposit.
➢ Thus, the small bodies of sulfide possibly represent segregations within the original beds of
carbonate-dominant sediment.
➢ The presence of late veinlets of chalcopyrite in fragmented, fractured pyrrhotite, sphalerite
and pyrite suggests the remobilization (and redistribution) of the metals during the various
metamorphic events.
➢ The extremely low concentrations of trace elements, including the REE, and the low and
variable Al concentrations in these rocks are inconsistent with igneous protoliths. The
magnesium needed to form the talc orebodies was derived from the breakdown of pre-
existing carbonates.
❖ Rocks at the Atshan mine have been subjected to at least two episodes of metamotphism, contact
and regional.
The serpentine + talc + tremolite + chlorite assemblage replaced the carbonates during regional
metamorphism and associated faulting and shearing. Serpentine and tremolite at the Atshan deposit
could have formed during prograde reactions, and talc, during retrograde reactions.
Small lenses of massive and disseminated sulfide (pyrite, pyrrhotite, sphalerite, chalcopyrite) within the
talc orebodies may represent sulfide segregation in the original sediments prior to metamorphism.
Some of the pyrite and pyrrhotite grains are fragmented and rimmed by talc, suggesting that they were
present prior to talc mineralization. Chalcopyrite was probably remobilized, and it occurs along tremolite
cleavages and fractures.
35
38. Darhib Talc Mine
• The Darhib talc mine, located in the Southern Eastern
Desert (N24.00.680, E035.00.134, Height 593 m), is
one of the largest talc deposits in Egypt together
with the El Atshan and Atshan mines.
• The rocks of such an area were probably subjected to
metamorphisms so that serpentine, talc, tremolite
and chlorite replaced the carbonates.
• Small lenses of sulphide consisting of pyrite,
sphalerite, chalcopyrite, pyrrhotite and galena within
the talc ore bodies may represent sulphide
segregation in the original sediments before the
metamorphism.
• Moreover, not far from the Darhib mine, at about
100 km, there is the Umm Samiuki deposit which is
Zn- and Cu-rich, so that the sulphide may be enriched
with such elements.
38
45. References
AbdeL Kader, Z, & Shalaby, I.M. (1982): Post-ore alteration at the Atshan talc mine, Hamata, Eastern Desert, Egypt,
Annals Geol. Surv. Egypt 12, 163-175.
Abdel-Rahman, A.F.M. (1995): Tectonic-magmatic stages of shield evolution: the Pan African belt in northeastern Egypt.
Tectonophys. 242, 223-240.
Eliwa, H., Breitkreuz, C., Khalaf, I., El Gameel, K., (2010). Depositional styles of Early Ediacaran terrestrial
volcanosedimentary succession in the Gebel El Urf area, North Eastern Desert, Egypt. Journal of African Earth
Sciences 57, 328–344.
El-Ramly, M.F., Greiling, R., Rashwan, A.A., Rasmy, A. (1993). Explanatory note to accompany the geological and
structural map of Wadi Hafafit area, Eastern Desert of Egypt. Egyptian Geological Survey and Mining Authority.
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El Shazly, E. M. (1957). Classification of Egyptian Mineral Deposits. Egyptian Journal of Geology 1 ( No. 1) pp. 1-20.
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Engel, AE.J., Dixon, T.H. & Stern, R.J. (1980): Late Precambrian evolution of Afro-Arabian crust from ocean arc to craton.
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associated mineralization in Hamata talc mine, Eastern Desert, Egypt. J. Afr. Earth Sci. 7, 195-199.
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Hussein, A.A.A., 1990. Mineral deposits. In: Said, R. (Ed.), The geology of Egypt. 1990. A.A. Balkema,
Rotterdam/Brookfield, pp. 511-566.
Rasmy, A.H., Takla, M.A. & Gad, M.A. (1983): Alteration associated with ore formation at Umm Samiuki, South Eastern
Desert, Egypt. Annals Geol. Surv. Egypt 13, 1-21.
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Desert, Egypt: A geochemical and mineralogical study. The Canadian Mineralogist 37, 1211-1227
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