The project lies within the IN-BOUKATT Mining Permit area, which is held by a Niger corporation, Societe Miniere de DASA SA (SOMIDA). The shares of SOMIDA are owned 80% by GAFC and 20% by the Republic of Niger.
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Summary:
The Dasa Project is located in north-eastern Niger inside the Tim Mersoï sedimentary basin. The basin covers an area of some 114,000 km2 and is part of the much larger Iullemeden Basin (Palaeozoic-Tertiary) that stretches into Mali, Algeria, Benin and Nigeria.
All known uranium occurrences and deposits in Niger are all classified to belong to the sedimentary tabular, paleo channel and roll-front or sandstone types.
In the Dasa deposit, characteristics more consistent with the paleo channel tabular type seem to prevail.
Uranium Mineralization
The uranium in many of the deposits of the Tim Mersoï Basin is oxidized. Among the primary tetravalent minerals, coffinite is dominant and accompanied by pitchblende and silico titanates of uranium. Uranium hexavalent minerals such as uranophane and meta-tyuyamunite are present in the Imouraren and TGT-Geleli deposits.
The gangue is composed of quartz, feldspar, analcime and often illite, kaolinite and chlorite; with accessories such as some zircon, ilmenite, magnetite, tourmaline, garnet, anatase and leucoxene.
The uranium minerals are frequently associated with copper minerals (native copper, chalcocite, chalcopyrite, malachite, chrysocolla) and also with iron minerals such as pyrite, hematite and goethite. Organic plant materials are generally plentiful in un-oxidized facies of greyish-greenish colour.
The Dasa deposit site corresponds to a major structural intersection of the Adrar-Emoles flexure and the Azouza fault which resulted in the doming and creation of the Azouza Graben (Siebenthal, 2013). These are features that characterize other major uranium deposits in the Tim Mersoï Basin.
The geometry and the distribution of the uranium mineralization as seen in the Dasa drill core is to a large extent comparable with what has been reported from the uranium mines in the Arlit and Imouraren areas outside the Project:
- There is a strong control by stratigraphy and lithology – with mineralization mainly hosted within the Tchirezrine 2 sandstones, particularly in the coarser-grained micro-conglomeratic facies of greyishgreenish colour containing frequent sulphides and organic matter such as plant remains.
- The mineralized lenses are contained within northeast-southwest trending channels. The thickness of the mineralization may vary considerably between drillholes most likely an indication that channel stacking of favourable lithologies has increased the normal thickness of the sediment pile.
- There are strong indications that the mineralization is influenced by a tectonic control along late northeast and southwest faults where some leaching has been observed.
- Uranium mineralization is controlled by zones of oxidation – from surface (ground oxidation) and local/regional horizons at depth.
Groundwater circulation has created overtime discontinuities in the mineralisation as a result of tectonic movements.
Thin section work and petrographic studies by Activation Lab (2007) on Dasa samples has revealed that the uranium host rocks are sandstone and wacke which are variably oxidized. The main component is angular quartz, some plagioclase and lesser orthoclase. They are cemented by goethite, amorphous iron-hydroxides, and various secondary uranium-rich minerals.
The original cement between the grains of quartz and feldspar consisted of sericite and carbonate which were replaced during later stages by goethite and the amorphous iron-hydroxides. The quartz and the feldspar contain micro fractures partly filled with uranium-rich oxide. The latter also rim some of the silicates. Uranophane in form of radiating aggregates forms cement between the silicates and partly replaces them.
Global Atomic Corporation initiated a mineralogical study of the uranium mineralization on its property (Molebale, 2012) with five drill samples and five residue samples submitted for analysis. The samples were from drillholes ASDH 351, 353, 354(1), 354(2) and one DADH sample. The samples were split into representative portions and polished sections were prepared. Subsamples were pulverized for x-ray diffraction (XRD).
Five uranium-bearing minerals have been identified in Dasa samples (Molebale, 2012):
• Carnotite K2(UO2)2(VO4)2 x 3H2O;
• Uranophane Ca(UO2)2SiO3(OH)2 x 5H2O;
• U-rich titanite (U,Ca,Ce)(Ti,Fe)2O6;
• Coffinite U(SiO4)1-x(OH)4x;
• Torbernite Cu(UO2)2(PO4)2 x 11H2O;
• Autunite Ca(UO2)2(PO4)2 x 12H2O.
Majority of the mineralization is comprised of carnotite, uranophane and uranium-rich titanite and contribute to most of the uranium in the ASDH samples in terms of mass %, while torbernite is dominant in the DADH sample. The average grain size for the observed uranium-bearing minerals is -38 µm.
The source of the uranium is very likely leaching of the frequent volcanic tuff and ash blankets and intercalations now altered to analcimolite within the Wagadi and Dabla sediment packages. This has occurred over time in the geological history of the area and probably began as pre-uranium concentrations during the early sedimentation in favourable reducing environments such as organic matter-rich lower flow regimes and in favourable lithologies. The first stratiform mineralized bodies would have been formed during the early digenesis. Later, structural deformation and ground water movement within coarser grained organic-rich sediments aided by fluid movements and influenced by faults and tectonic activity, initiated roll front like redistribution of the uranium thus giving the mineralized bodies their present shape.