Namibia constitutes a uraniferous province with known uranium enrichment occurring in basement granite gneiss, in Damaran metasedimentary rocks and intrusives, in Karoo sediments and carnotiterich calcrete and in siliciclastic hosted surficial deposits which developed in the Tertiary.

Granites in the Rössing Uranium Mine SJ area are dominated by sheeted leucogranites that intruded into weak zones such as faults and shear zones and preferentially at the Khan/Rössing Formation contact. At Valencia the main mineralised body is formed by a series of coalesced leucogranite sheets intruded into a local disharmonic kink fold to the east of a major anticlinorium. Around the Ida Dome, uranium-bearing sheeted leucogranites have intruded preferentially along the east and southeast sides of the Dome approximately at the Khan-Rössing Formation contact although thinner sheets also intrude the Rossing marbles.

Uranium in the Rössing, Valencia, Ida and Goanikontes areas, is hosted in primary uraninite and betafite (a pyrochlore-group) within late stage leucogranites. Secondary uranium minerals such as uranophane and uranophane occur as replacements of the primary minerals in the granites, or as films and coatings along fractures in both the granites and country rocks although metatorbernite, metahaweeite, carnotite, thorogummite and gummite have been noted.

The mine site encompasses a licence area of about 180 km2, of which 25 km2 is used for mining, waste disposal and processing. Mining is done by blasting, loading and hauling from the main open pit, referred to as the SJ Pit, before the uranium-bearing rock is processed to produce uranium oxide.

Ore is delivered to the primary crushers by haul truck and then by conveyor to the coarse ore stockpile. It passes through a further series of crushers and screens until the particles are smaller than 19 mm. After weighing, the fine ore is stored on another stockpile.

Wet grinding of the crushed ore by means of steel rods reduces it further to slurry with the consistency of mud. The four rod mills, which are 4.3 m in diameter, are utilised as required by production levels and operate in parallel.

A combined leaching and oxidation process takes place in large mechanically agitated tanks. The uranium content of the pulped ore is oxidised by ferric sulphate and dissolved in a sulphuric acid solution.

The product of leaching is a pulp containing suspended sand and slime. Cyclones separate these components and, after washing in Rotoscoops to remove traces of uranium-bearing solution, the sand is transported via a sand conveyor to a tailings disposal area.

Counter-current decantation thickeners wash the slimes from previous stages. A clear uraniumbearing solution (‘pregnant’ solution) overflows from the thickeners, while the washed slime is mixed with the sands and pumped to the tailings area.

The clear pregnant solution now comes into contact with beads of specially formulated resin. Uranium ions are adsorbed onto the resin and are preferentially extracted from the solution. Beads are removed periodically to elution columns where an acid wash removes the uranium from the beads. The resulting eluate is a purified and more concentrated uranium solution.

The acidic eluate from the ion exchange plant is mixed with an organic solvent which takes up the uranium-bearing component. In a second stage, the organic solution is mixed with a neutral aqueous ammonium sulphate solution which takes up the uranium-rich ‘OK liquor’. The acidic ‘barren aqueous’ solution is returned to the elution columns.
The addition of gaseous ammonia to the ‘OK liquor’ raises the solution pH, resulting in precipitation of ammonium diuranate, which is then thickened to a yellow slurry.

The ammonium diuranate is recovered on rotating drum filters as yellow paste - known as ‘yellow cake’.

Final roasting drives off the ammonia, leaving uranium oxide. The product is then packed into metal drums. Neither ammonium diuranate nor uranium oxide are explosive substances.

The drums of uranium oxide are loaded and exported to overseas converters for further processing.