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Arlit (Arlette), Akouta, Imouraren - Grand Artois, Artois, Ariege, Arlette, Argus, Tamou, Tabelle, Takriza, Arthe, Taza Nord, Taza Sud and Tamgak, Akola, Akouta Nord, Akouta Sud, Ebba Nord, Ebba Sud and Ebene, Imatra, Imfout, Omola, Azelik, Abokorum |
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Niger |
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U
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
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Sandstone hosted uranium deposits are known and mined in two main districts in north-western Niger, located 150 to 200 km north to NNW of Agadez. These are at Arlit (Arlette) in the north, including from NNE to SSW over a 13 km interval the individual, mainly open pit deposits of Grand Artois, Artois, Ariége, Arlette, Argus, Tamou, Tabelle, Takriza, Arthé, Taza Nord, Taza Sud and Tamgak. Separated by a gap of ~3 km to the south is the Akouta line of occurrences, that were mainly exploited from underground, and included, from north to south the individual deposits of Akola, Akouta Nord, Akouta Sud, Ebba Nord, Ebba Sud and Ebene. Some 75 km to the south again is the Imouraren District, which includes the Imatra, Imfout and Omola deposits, forming a 7 x 1 to 2 km mineralised interval. Other deposits distal from this corridor include Azelik, Abokorum and Madaouela.
The deposits of the three main districts parallel and follow the major Arlit-In Azoua Fault, forming a 1 to 3 km wide corridor ~50 km west of the exposed margin of the crystalline Aïr Cambrian to Precambrian basement. This basement is overlain by a south-tapering wedge of Ordovician volcanic rocks to the north, then by overlapping, predominantly grey Devonian to Carboniferous, fluvial to estuarine to marine continental sedimentary rocks, followed, in turn, by mainly red facies Permian to Late Cretaceous fluvial to lacustrine sedimentary rocks with significant intervals of volcanic derived sediments and tuffaceous rocks (analcimilites). Economic mineralisation is found at multiple levels within this stratigraphic pile, from the late Carboniferous to Early Cretaceous.
The original deposits were discovered in the 1950s. Total production to the end of 2002 was 87 859 t U (33 433 t from open pit mining; 48 641 t from underground mining; and 5785 t from heap leaching).
In 2019, 2982 tonnes of uranium were produced by the two mining operations, SOMAïR (Société des Mines de l'Aïr) and COMINAK (Compagnie Miniére d'Akouta) in the Arlit and Akouta districts respectively. Each included a number of the deposits listed above within the Tim Mersoi sub-basin (see below). The average grade at the former in 2019 was 1.9 kg/t of uranium. Following the depletion of its resources, the COMINAK underground mining operatrion ceased production on March 31, 2021. SOMAÏR is an open pit mine complex that has produced a cumulative 70 189 tonnes of uranium to 2017 at a rate of 1800 to 2250 tonnes per annum. COMINAK had produced 77 228 t of uranium during 47 years of mining from the Akouta, Akola and Ebba deposits. Future production is planned from the Imouraren operation, which was found in 1966, and is located 80 km south of Arlit and 160 km north of Agadez. Imouraren has reserves estimated at >158 000 tonnes of uranium after recovery (Orana website, viewed June, 2025).
These deposits are developed in cover rocks deposited over the Aïr Massif, the south-eastern segment of the Taureg Shield. The Taureg Shield is composed of three main physical massifs, the Aïr massif, the main Hoggar Mountains to the north and the Adrar des Iforas to the south-west.
The Taureg Shield, with the Benin-Nigeria Shield to the south are exposed parts of the Trans-Saharan (or Central Africa) Mobile Belt which was deformed during the Pan African (600 Ma) orogeny. This mobile belt is developed along the eastern margin of the West African Craton and is up to 1000 km wide and extends for 3000 km from the Mediterranean coast to the north to the southern West African coast in Nigeria to the south. The boundary between the West African Craton and the mobile belt is marked by a zone of gravity highs which has been interpreted to reflect an eastward dipping zone of un-rooted, dense mafic and ultramafic bodies, representing the Pan-African collision between the passive western margin of the West African Craton and the cordilleran-type margin that was the Trans-Saharan Mobile Belt of the Archaean to Paleoproterozoic eastern continent. The Taureg and Benin-Nigeria shields have subsequently been reworked during the Pan-African tectono-thermal events. Much of the mobile belt is concealed below a major, shallow, Mesozoic-Cenozoic downwarp, the Iullemmeden Basin which separates the The Taureg and Benin-Nigeria shields.
The Taureg Shield is divided into three main segments by a series of north-south oriented major, broad shear zones, the western Pharusian, the central Hoggar-Aïr and eastern Hoggar-Tenéré domains.
The 200 x 400 km crystalline Aïr Massif is the southern half of the Hoggar-Aïr domain and is composed of a core of Pan African granitoids intruding pre-Pan African crystalline rocks comprising probable Paleoproterozoic schists, gneiss and leptynites which were metamorphosed to amphibolites or upper greenschist facies. The crystalline core is separated from only mildly metamorphosed rocks of the flat lying, latest Neoproterozoic to Ordovician Proche Tenure molasse by overthrusts at Tafadek to the west and Aouzegeur to the east.
Caledonian uplift formed the Aïr Massif, a major horst block, leading to the erosion of the basal Palaeozoic sediments to expose the crystalline basement, where they are transgressively overlain by Lower Devonian sediments. The Aïr Massif is also an anticlinorium with kilometre width isoclinal folds, all dipping to the east. It is also characterised by north-south Pan-African thrusts which dip inwardly, related to the collision of the West African Craton and the Tran-Sahara Mobile Belt.
Over a dozen Palaeozoic - Ordovician to Devonian - (gabbro)-syenite-granite ring dyke complexes intrude the Paleoproterozoic basement, in central and southern Niger and northern Nigeria. This activity commenced with an acid volcanic phase, followed by gabbros, anorthosites, syenites and alkaline to peralkaline granites, all the result of the differentiation of basic magmas. It is suggested that these ring dyke complexes represent the eroded roots of volcanic edifices that were removed and deposited as part of the late Palaeozoic to Mesozoic basins that host the uranium mineralisation.
The Iullemmeden Basin is a large (0.36 million sq. km) structural depression covering much of western Niger, southern Algeria, Mali, Benin and Nigeria. It is filled by a poorly deformed, flat lying, 1500 to 2000 m thick, early Palaeozoic to Pleistocene succession of alternating marine and continental sediments. Tertiary volcanism is represented by more than 30 trachyte and phonolite plugs and associated basaltic lavas.
Along the western margin of the Aïr Massif, the Iullemmeden Basin commences with Devonian sediments which rest unconformably on crystalline basement and are overlain by Carboniferous, Permian and Mesozoic sequences to the late Cretaceous. The earliest Palaeozoic facies were epicontinental marine sediments which became lagoonal, deltaic and eventually continental in the lower Carboniferous. This change in sedimentation corresponded with major uplift along the Aïr axis.
Deeper in the basin, the Palaeozoic succession commenced with Cambro-Ordovician coarse siliciclastics, followed by Silurian graptolitic shales
Throughout the Permian and Mesozoic, the uplifted Aïr Massif was subjected to erosion by intermittent streams and rivers to form continental arkosic sandstones, siltstones, shales, and conglomerates known as the 'continental intercalaire' in the Iullemmeden Basin.
The Palaeozoic sediments in the Iullemmeden Basin, on the western margin of the Aïr Massif, are organised as a succession of wedges which each thin from north to south, controlled by north-south block faulting, possibly related to Hercynian tectonics. During the late Cretaceous, marine conditions were returned to the southern Sahara.
The Upper Cretaceous and Lower Tertiary sequences are marine, and comprise argillites, marls and fossiliferous limestones with lesser silty, sandy and gritty beds.
The sedimentary deposits adjacent to the western edge of the Aïr Massif, in the Tim Mersoi sub-basin (at Arlit) and in the more southerly In Gall basin (at Agades) are the most important host to uranium mineralisation.
Uranium occurrences hosted by Upper Carboniferous units, are found especially in sandstones, and also coal beds. Similarly, sandstone beds within the Jurassic and Cretaceous of the 'continental intercalaire' host uranium, copper and saline units which are mineable for salt. Much of the uranium in these units is hosted within sandstone and conglomerate units between layers of siltstone and shale which are rich in organic material and pyrite, lapping onto an erosional surface. The host units young to the south and west. Whilst the Arlit and Akouta deposits are hosted by Carboniferous units, the Abokorum and Azelik further to the west, occur within Lower Cretaceous. Mineralisation is found at depths of 10 to 75 m.
The deposits of the Arlit and Akouta districts are hosted in Carboniferous units and carry reduced uranium mineralisation (predominantly the U4+ minerals - uraninite/pitchblende and coffinite). In contrast, the Imouraren deposit, which occurs within a Jurassic formation, is characterised by oxidised uranium mineralisation predominantly U6+ vanadate (metatyuyamunite) and silicate (uranophane) minerals with some relics of
reduced mineralisation (Mamane, et al., 2022).
The Akouta uranium deposits occur within the basal Upper Carbonifeous Visean Guezouman Formation, composed of reduced fluvio-deltaic sandstones, particularly organic-rich channel formations (Forbes, 1989). Mineralisation is dominantly represented by uraninite ±coffinite associated with trace U-Ti oxides and minor galena, chalcopyrite, molybdenum-vanadium oxide and iriginite. The uraninite occurs within the intergranular porosity of the sandstones or associated with plant material. The Akouta uranium ore has an average grade of 0.413% U3O8 and is mined in an underground mines at a depth of ~250 m below surface. (Mamane, et al., 2022).
The Arlit deposits are hosted by the late Upper Carbonifeous Namurian Tarat Formation, which contains reduced fluvial sandstones and organic-rich clays and silts (Sempéré, 1981; Elhamet, 1983; De Rouvre, 1985). Uranium mineralisation is substantially in the form of variably 'coffinitised' (i.e., alteration of uraninite to coffinite with the increase of Si content) uraninite associated with pyrite and minor amounts of U-Mo or U-Ti-(V) oxides within the sandstone porosity (Cavellec, 2006). The Arlit uranium ore, which has an average grade of 0.2.8 % U3O8, is mined by open-pit at an average depth of 60 m below surface (Mamane, et al., 2022).
Two facies are defined at both Arlit and Akouta: i). reduced facies sandstones composed of grey sandstone rich in reduced organic matter,
pyrite, chlorite and blackish ore (uraninite), and trace to absent oxidation; and ii). a mixed reduced-oxidised facies composed of reduced grey
sandstone with blackish ore following the laminae and moderate oxidising alteration including hematite and minor yellow products resulting from meteoric alteration (Mamane, et al., 2022).
The Imouraren uranium deposit is hosted by the Upper Jurassic oxidized continental arkoses and analcime-rich sandstones of the Tchirezrine II Formation (Pacquet, 1969; Valsardieu, 1971; Vallance, 2007). Uranium is found in secondary minerals with some relicts of primary U-minerals (Mamane, et al., 2019). This relict primary uranium mineralisation is mainly represented by uraninite, accompanied by U-Ti-(V) oxides and Cu- sulphides, predominantly
chalcopyrite, which was subsequently altered or replaced later by chalcocite. The secondary U-minerals developed by in situ oxidation and alteration of earlier uraninite. Both the uraninite and secondary U-minerals are found in several textures and styles of fill, specifically: i). in interstitial space, filling the intergranular porosity of the sandstones; ii). replacing the cores of analcime spheroids, as well as between the analcime-rich layers; iii). as pseudomorphic replacement of analcime rims; and iv). in the albitised cleavages of potassic feldspars (Mamane, et al., 2022).
At Imouraren, three facies have been distinguished: i). minor reduced grey sandstone rich in sulphides, chlorite and blackish ore (uraninite ±U-Ti oxides) with trace to weak oxidation; ii). predominantly orange to red oxidised sandstone containing oxy-hydroxides and
yellow uranium ore (secondary uranium minerals) exclusively; and iii). an intermediate facies composed of both the reduced grey sandstone and
the oxidised sandstone (Mamane, et al., 2022).
Whilst the Carboniferous units in the North were not exposed to palaeo-weathering, the Jurassic formations at Imouraren to the south underwent intense continental weathering in western Africa from early Cenozoic to very recent times (Beauvais et al., 2008). Reactivation of regional structures, such as the Arlit Fault, took place during the collision between the African and Eurasian plates during the Late Cretaceous, at around 80 Ma (Forbes, 1989). This is envisaged as having led to a significant progressive uplift of the Imouraren series, in particular the host Tchirezrine II and underlying Abinky formations, to as shallow as 150 m below surface. Supergene alteration favoured the formation of a significant quantity of secondary uranium minerals, as well as hematite and goethite, in the host Jurassic formations at Imouraren. The iron source is probably the oxidation of chlorite from the Tchirezrine II Formation and detrital Fe-Ti ±V oxides from the underlying Abinky formation. The Imouraren deposit hosts a large uranium tonnage at a low-grade ore (0.06 % U3O8) and lies at a
depth of 130–150 m below surface (Mamane, et al., 2022).
The main deposits known in 2005 were within the Tim Mersoi sub-basin, the mainly continental part of the Iullemmeden Basin. These included the Ariege, Artois, Arlette, Taza, Takriza, Tamou and Akouta.
The source of the uranium appears uncertain. Some authors suggest that it is derived from Pan African granites of the Aïr Massif, while others attribute it to eroded volcanic piles that were deposited above the Palaeozoic ring dyke complexes mapped within the massif. Remnant beds of Palaeozoic ignimbrites on the massif associated with ring-dyke centres contain uranium concentrated in the matrix and on secondary iron-oxide coatings surrounding lithic and crystal fragments. Based on variable Th/U ratios and degree of oxidation, it has been concluded that the original ignimbrite field was enriched in uranium, but that a considerable proportion was leached during the weathering of the volcanic pile.
U-Pb SIMS data from the deposits of the Arlit and Akouta and Imouraren districts suggest there are two main stages of uranium deposition and ore metallogenesis (Mamane, et al., 2022):
i). between145 and 90 Ma in the Lower Cretaceous mineralisation, related to a significant tectonothermal event, synchronous with the Atlantic rifting that induced deformation and brine migration from Triassic formations. Primary uraninite and chalcocite were formed by fluid mixing in a reduced environment at a depth of ≤1 km, at temperatures of 115 to 150°C, hotter than that of the reservoir.
ii). during later Cenozoic exhumation of the basin, when a series of remobilisation events of primary uranium mineralisation resulted in the formation of much younger uraninites under reduced conditions. This occurred at Arlit-Akouta at ~50 Ma. At Imouraren, younger uraninites formed between 34 and 8
Ma under locally reduced conditions, and were followed by secondary U-minerals from 21 Ma up to 3 to 1.6 Ma during supergene events. These ages are close to, or were superimposed upon the main oxidation stages, affecting West Africa during the Cenozoic, and attest to water table oscillations.
Grades of ore reserves in the underground mines average 5 kg/tonne U, while the open pit deposits average 5 kg/tonne U. The Imouraren oxide deposit averages 1.1 kg/tonne U
Total reserve and resource figures for the Niger deposits in 2002 include:
Reserve at <USD 40/kg - 89 800 t U
Reserve at <USD 80/kg - 102 227 t U
Resource at <USD 40/kg - 125 337 t U
Total production to 2002 was 87 859 t U (for more details see above)
The Tim Mersoï Basin hosts the highest-grade and tonnage uranium ores in Africa, totaling 439 400 t U, i.e., reasonably assured + inferred resource categories, recoverable at <USD 260/kg U (OECD/NEA, 2020).
The most recent source geological information used to prepare this description was dated: 2022.
Record last updated: 24/06/2025
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.
Arlit
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Mamadou, M.M., Cathelineau, M., Deloule, E., Schmitt, R. and Brouand, M., 2020 - Cenozoic oxidation episodes in West Africa at the origin of the in situ supergene mineral redistribution of the primary uranium orebodies (Imouraren deposit, Tim Mersoi Basin, Northern Niger): in Mineralium Deposita v.55, pp. 1333-1352.
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Mamane, M.M., M. Cathealineau., Deloule, E., Reisberg, L., Cardon, O., Vallance, J. and Brouand, M., 2022 - The Tim Mersoi Basin uranium deposits (Northern Niger): Geochronology and genetic model: in Ore Geology Reviews v.145, 23p. doi.org/10.1016/j.oregeorev.2022.104905.
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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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