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| Titel |
Pan-African shear zone-hosted gold mineralization in the Arabian-Nubian shield |
| VerfasserIn |
Tamer Abu-Alam, Eugene Grosch, Mohamed Abd El Monsef |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080963
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| Zusammenfassung |
| A new tectonic model of the exhumation mechanism of the Arabian-Nubian Shield will be
presented at the EGU2013 by Abu-Alam and Stüwe (2013). According to this new tectonic
model, the shear zones of the Arabian-Nubian Shield can be classified into two types;
deep-seated and relatively shallow shear zones. The deep-seated shear zones are accompanied
with deep sub-horizontal crustal channel flows which are response to the exhumation of the
metamorphic complexes from the peak condition depth to a shallower crustal level
(ductile-brittle transition). An example of these deep-seated shear zones is the Najd
Fault System – the largest shear zone on the Earth. At the ductile-brittle transition
crustal level, the deep-seated shear zones were overprinted by a greenschist facies
condition or the Ïă2 and Ïă3 of the principle stresses may be flipped with each other. This
flipping can produce other conjugate shallow shear zones in a greenschist facies
conditions.
The Egyptian gold deposits can be classified into three main types (Botros, 2004), These
are stratabound deposits, non-stratabound deposits and placer gold deposits. The
non-stratabound deposits are the most common (ex: Sukari, Wadi Allaqi, Abu Marawat,
Atalla, El-Sid and Atud gold mines). They are found in form of vein type mineralization or as
disseminated mineralization hosted in volcanics and volcaniclastic rocks (volcanogenic
massive sulphides). Spatial and temporal relationships between gold veins and structures in
the Arabian-Nubian Shield suggest a genetic relationship between mineralization and major
tectonic events.
At Sukari, Wadi Allaqi and Abu Marawat areas, the gold is hosted in quartz veins parallel
to a deep-seated NW-SE to NNW-SSE shear zones. For Atud, El-Sid and Atalla area, the gold
is hosted in NE-SW veins parallel to a shallow shear zone but at the conjugate point with a
deep-seated NW-SE shear zone.
According to the new tectonic model, we propose the following model for gold formation
(non-stratabound). They were deposited from hydrothermal solutions which were
produced in a deeper crustal level due to metamorphic or magmatic processes or
combination between both. These solutions transfer through the deep-seated shear zones
which cutting the all rock unites of the shield. The hydrothermal solutions can
leach the gold out from a source rock (e.g. ophiolitic or gabbroic rocks). Once the
solutions enter the ductile-brittle transition crustal level, the quartz veins and the hosted
gold begin to precipitate parallel to the regional foliation of the deep-seated shear
zones.
Abu-Alam T.S. and Stüwe K. (2013) Sub-horizontal channel flow: an exhumation
mechanism during the Gondwana collision. EGU2013-9778
Botros N. (2004) A new classification of the gold deposits of Egypt, Ore Geology
Reviews 25, 1 –37 |
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