Az Zabirah, Al Ba itha
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The Az Zabirah bauxite layer is distributed over an interval of 105 km, located approximately 500 km NW of Riyadh, 180 km NNW of Buraydah and around 50 km from the town of Qiba in central northern Saudi Arabia. 'Metallurgical' bauxite has been exploited at the Al-Ba'itha Mine to the SE, while 'industrial' bauxite and kaolin resources and reserves have been delineated at the Az Zabirah Mine site ~60 km to the NW.
(#Location - Al Ba'itha: 27° 40' 25"N, 43° 59' 12"E).
The Al-Ba'itha mine and associated crushing facility supplies bauxite to a refinery and smelter in Ras Al Khair 472 km to the east on the Persian Gulf coast, from where refined aluminium is passed to a primary aluminium production plant and a rolling mill, which includes an aluminium can recycling facility. Mining was initially restricted to Al-Ba'itha (Ma'aden Annual Report 2018).
Mineralisation is located on the Arabian Platform in shallowly north-east dipping Phanerozoic rocks towards the eastern margin of the underlying Proterozoic to Archaean Arabian Shield.
The Arabian Shield and Platform lie between the African Shield to the south-west and the more recent Alpine-Himalayan (Tethyan) Zagros mountains to the north-east. The 1500 x 500 km Arabian Shield, which forms the western half of Saudi Arabia, is the northeastern half of the Arabian-Nubian Shield, and is largely composed of the high grade metamorphic roots of a Neoproterozoic (1000 to 540 Ma) complex of continent margin magmatic arc volcanics (750 to 685 Ma), successor basin sediments (632 to 620 Ma) and post-orogenic intrusives (659 to 601 Ma). Older Paleoproterozoic to Mesoarchaean rocks are also known in the north. For detail of the Arabian-Nubian Shield see the separate Jebel Ohier record.
The unconformably overlying Phaerozoic rocks of the Arabian Platform comprise Palaeozoic, Mesozoic and Cenozoic shallow marine, lacustrine, fluvial and playa sequences up to 10 km thick that outcrop as relatively flat lying, gently east dipping beds of sandstone, siltstone, limestone, evaporites and subaerial volcanic rocks.
The Az Zabirah bauxite layer was formed at an early Cretaceous, ~112 Ma Aptian to Albian unconformity. This break reflects a hiatus in deposition and is interpreted to have coincided with a world-wide sea level low-stand followed by a gradually rising sea level that culminated in maximum flooding by the end of the Albian.
The immediately underlying succession, which rests on late Palaeozoic and early Mesozoic platformal sequences, was deposited in shallow-marine shelf and intra-shelf settings on the Arabian Plate passive margin with Neo-Tethys, influenced by the strong clastic sediment supply from a major delta to the west. These sediments comprise an extensive transgressive late Early Cretaceous Berriaian to Aptian sand-shale apron that form the Biyadh, Buwaib and Zubair formations.
Following the sea level low-stand, the initial sediments immediately above the unconformity were continental deposits of the Albian Kurnub Fm which incorporates the bauxite layer. The subsequent global coastal onlap resulted in overlying widespread shallow-marine platform carbonates and repetitive interbedding of limestones with silty shales and shales of the Wasia Formation reflected a reduced input of terrigenous clastics from the shield to the west. Generally, the succession became pure limestone toward the late Cenomanian. This sequence capped and preserved the bauxite accumulations.
The bauxite layer is exposed as shallowly dipping remnants towards the western margin of of the Arabian Platform, occurring in three discreet zones, the North, Central and the South Zones which cover a cumulative area of 250 sq. km. It is generally exposed over a width that averages 2.5 km and SE-NW trending strike length of 105 km, dipping at 0.5° NE.
The North Zone outcrops over a strike length of 35 km, while the Central Zone has a long axis of 25 km composed of 0.5 to 1 km long lenses of bauxite up to 5 m thick. The Central Zone has a high silica content, compensated by high alumina grades which in places exceed 60% Al2O3.
The South Zone crops out over a strike 30 km and contains the largest known bauxite accumulation over some 12 sq. km, but is seldom >2.5 m thick. It contains the largest reserve with similar grade to the ore in the central zone.
The bauxite occurs as a pisolitic profile that averages 8.5 m in thickness prior to erosion, overlying saprolitic clays for a total palaeo-weathing profile that averages 22 m in thickness. The clays of this regional profile represent one of the hosts to significant kaolin deposits in Saudi Arabia.
The South Zone has a mineral resource of 252 Mt @ 55.9% Al2O3, 10.05 % SiO2. The resource has alternatively been quoted as 126 Mt @ 57.5% alumina. The reserve of the initial mine within the South Zone is 90 Mt of bauxite at similar grades.
The bauxite is monohydrate type, similar to Weipa in Australia (see the Weipa record) and requires digestion under pressures at 245°C. Transformation testing using the Bayer process show that 2.38 t of wet bauxite are required to produce 1 t of alumina.
Current JORC compliant Ore Reserve and Mineral Resources (Ma'aden Annual Report 2018) were:
Az Zabirah Mine
Proved + Probable Ore Reserves 'industrial' bauxite - 7.3 Mt @ 53.6% Al2O3, 14.8% SiO2;
Total Mineral Resources 'industrial' bauxite - 30 Mt @ 51.6% Al2O3, 18.4% SiO2;
Total Mineral Resources 'metallurgical' bauxite - 40 Mt @ 47.1% Al2O3, 11.8% SiO2.
Az Zabirah Central
Total Mineral Resources 'industrial' bauxite - 29 Mt @ 49.7% Al2O3, 16.1% SiO2;
Total Mineral Resources 'metallurgical' bauxite - 37 Mt @ 47.2% Al2O3, 9.4% SiO2.
Az Zabirah North
Total Mineral Resources 'industrial' bauxite - 20 Mt @ 50.4% Al2O3, 16.8% SiO2;
Total Mineral Resources 'metallurgical' bauxite - 31 Mt @ 44.9% Al2O3, 9.3% SiO2;
TOTAL Az Zabirah Mineral Resources 'industrial' bauxite - 79 Mt @ 50.5% Al2O3, 17.1% SiO2;
TOTAL Az Zabirah Mineral Resources 'metallurgical' bauxite - 108 Mt @ 46.5% Al2O3, 10.3% SiO2.
Proved + Probable Ore Reserves 'metallurgical' bauxite - 192.2 Mt @ 48.2% Al2O3, 9.2% SiO2;
Total Mineral Resources 'metallurgical' bauxite - 242.7 Mt @ 44.8% Al2O3, 8.2% SiO2.
Mineral Resources are inclusine of Ore Reserves.
Production from the Al-Ba'itha mine in 2018 was 4.6 Mt of bauxite.
The most recent source geological information used to prepare this summary was dated: 2018.
Record last updated: 4/2/2020
This description is a summary from published sources, the chief of which are listed below.
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