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Gara Djebilet, Mechri Abdelaziz |
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Algeria |
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Fe
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The Gara Djebilet and Mechri Abdelaziz iron deposits are 250 km apart and located approximately 130 km to the southeast and 400 km east of Tindouf respectively in far western Algeria. Gara Djebilet is 300 km directly from the Atlantic Ocean (via Mauritania or Morrocco) and 1600 km south of the Mediterranean coast of Algeria (#Location: Gara Djebilet - 26° 52' 56"N, 7° 0' 1"W).
These deposits are hosted within the Early Devonian sediments of the Tindouf Basin in the Algerian Sahara of North Africa and is an important occurrence of the 'North African Palaeozoic Ironstone Belt' extending from the Zemmour to Libya, and also includes ironstones of Ordovician, Silurian and Devonian age. These sediments are on the northern margin of the Reguibat Shield which hosts the Archaean BIF deposits of Mauritania (see the Tiris record) some 600 km to the southwest. The Tindouf Basin, which contains a sequence of Cambo-Ordovician sandstones, overlain by Silurian to Carboniferous siltstone, shales, limestones and minor sandstones, occurs as a large WSW-ENE elongated synformal structure bounded to the north by the Anti-Atlas orogen. The Gara Djebilet and Mechri Abdelaziz deposits are located on the southern limb of this structure where it overlies the Reguibat Shield.
Minette type oolitic iron ore occurs within the Upper Djebilet Formation of Pragian (Lower Devonian) age. At Gara Djebile, three large lenses form three individual deposits, extending east-west for about 60 km, namely Gara West (14 x 4 km and 0 to 30 m thick), Gara Centre (20 x 5 km and 0 to 30 m thick) and Gara East (7 x 1 km and 0 to 9 m thick). The deposits are preserved as mesas of flat lying (1.5 to 2° north dipping) oolitic ironstone lenses interbedded with predominantly argillaceous and sandy sediments.
The oolitic mineralisation can be related to a barrier island palaeo-environment, where the oolitic sediments were trapped by Palaeozoic shoals, bordered by an inner lagoon or shallow embayment and an epicontinental sea. The oolitic sediments have a mineralogy characterised by magnetite, hematite, goethite, maghemite, chamosite (bavalite), siderite, apatite and quartz.
In the Gara Djebilet district, three paragenetic associations present a vertical distribution with a:
i). Lower non-magnetite ore (Fe=54.6%; 3 to 10 m thick), composed of 20 to 50 cm beds of tabular-planar and crossbedded quartz-rich hematitic chamosite - containing chamosite, siderite, hematite, goethite, apatite and quartz;
ii). Middle magnetite ore (Fe=57.8%; 6 to 10 m thick), which represents the main economic ore, is composed of tabular-planar and crossbedded magnetic-chamosite ore with 1 to 20 mm diameter sideritic inclusions - containing magnetite, maghemite, chamosite, siderite, hematite and apatite. It has a chemical composition averaging SiO2=4.9%, Al2O3=4.2%, Fe2O3=61.43%, FeO=19.2%, and P2O5=1.8%. and
iii). Upper non-magnetite ore (Fe=53%; 4 to 12 m thick), comprising 0.5 to 1 m thick parallel laminated beds of hematitic-chamositic ooids, with iron crusts at different levels, and containing ooids, siderite, apatite and pyrite - containing goethite, chamosite, hematite, siderite and apatite.
Three petrographical facies types have also been defined:
i). a cemented facies (FOC), comprising cemented, jointed ooids and pore-filling structures;
ii). a detrital facies (FOD) with scattered ooids in a quartz-rich groundmass; and a
iii). non-detrital facies (FOND) occurring as scattered ooids in a quartz-poor groundmass.
At a 57% Fe cut-off the Gara Djebilet deposit has a quoted resource of 985 Mt @ 57.8% Fe, predominantly within the magnetite ore zone (Guerrak,1988).
Marelle (1970) quoted a resource at Gara Djebilet of 1.48 Gt @ 49 to 54% Fe, 4.9% SiO2, 0.8% P.
The Ministry of Energy and Mining of Algeria (2005) quotes a resource at Gara Djebilet of 750 Mt @ 58% Fe, and at Mechri Abdelaziz of 1.35 Gt @ 50% Fe. The ores contain 4 to 5% Al2O3, 0.8 % P and 0.03 % As.
The most recent source geological information used to prepare this decription was dated: 1990.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Gara Djebilet
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Selected References:
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Guerrak S, 1988 - Geology of the Early Devonian oolitic iron ore of the Gara Djebilet Field, Saharan Platform, Algeria : in Ore Geology Reviews v3 pp 333-358
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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