The Yeelirrie uranium deposit is the largest known uranium deposit in Western Australia. It occurs in calcrete hosted material in the central drainage channel of a wide, flat and long valley which is flanked by granitic breakaways of low topographic relief with elevations between 490 m AHD and 610 m AHD.

The mineralisation extends from the surface to an approximate depth of 10 m, with the main concentration centred about 4 m below the surface, with a thickness ranging from 1 to 7 m. The surface extent of the identified resource is 9 km long and an average of 1 km wide, with a maximum width of about 1.5 km. The resource is sufficient to provide approximately 15 years of ore to the metallurgical processing plant at a nominal processing rate of 2.4 Mtpa.

Lithological and mineralogical studies conducted in the Yeelirrie valley (WMC 1975, and studies conducted for this PER) show that there are four principal lithological units at the proposed development site:

1. Overburden: consisting of a combination of sandy loam, siliceous and ferruginous cemented hard- pan and carbonated loam, which is probably a weathered calcrete.
2. Calcrete: a calcite and/or dolomite replacement of the clay-quartz, although relics of partially replaced clay-quartz are common throughout the calcrete. The upper portion of the calcrete comprises friable ‘earthy calcrete’, a continuous layer grading upwards into the overlying soils. Nodular porcellanous calcrete represents the lower layer of the calcrete and consists of up to 70% carbonate (McKay and Miezitis 2001).
3. Clay-quartz: a kaolinitic clay-quartz alluvial fill material. Bands of quartz grit and arkose are randomly scattered through the clay-quartz as horizontal beds. Upper clays are predominantly montmerillonite, with kaolinite becoming more abundant at depth.
4. Archaean granitic basement complex: generally seen in drill holes at depths of around 30 m below the surface near the ore body.

Uranium mineralisation occurs as carnotite, a potassium uranyl vanadate (K2(UO2)2(VO4)2.3H20), which is found in the overburden and clay quartz unit. However, mineralisation is richest within the calcrete and transitional calcrete material. It typically fills fractures and voids, occurring as a coating on surfaces and as a very fine-grained dispersion through the mineralised units. Although found throughout the ‘earthy calcrete’ and the nodular porcellanous calcrete, approximately 90% of the ore is in the clay-rich carbonated rocks of the transition zone at the base of the calcrete unit.

Uranium mineralisation in the (mainly) calcrete is related to groundwater levels and chemistry. Key processes involved in the precipitation of uranium mineralisation can be summarised as:

• oxidation of mildly reducing uranium, potassium and vanadium-bearing waters, either by direct contact with air, or by mixing with more oxidised surface water; and
• evaporation concentration of water during drier climate cycles or along the flow path towards salt lakes. The majority of the uranium mineralisation occurs beneath the water table due to the leaching of uranium by carbon dioxide in rainfall infiltrating from the surface.

The majority of the uranium mineralisation occurs beneath the water table due to the leaching of uranium by carbon dioxide in rainfall infiltrating from the surface.

Mining of the pit would use standard surface mining equipment, such as excavators and front-end-loaders in conjunction with haul trucks and scrapers, to remove the ore and overburden. Due to the typically high friability of the ore and overburden material, minimal drilling and blasting would be required, although this technique may be needed in areas of the open pit if hard rock was encountered. For the purpose of the impact assessment presented in this document, a realistic worst-case scenario has been adopted, whereby 16 blasts are undertaken each year, using a total of about 70 tonnes of explosives and emulsion product.

Given the shallow nature and relatively small footprint of the area being mined at any time, the total mining fleet would consist of 3 to 6 excavators, or similar surface mining equipment, feeding about 12 haul trucks. Standard surface mining support fleet would include water trucks, graders, drill rigs and bulldozers. From the open pit, ore will be trucked to various stockpile areas based on grade and other geochemical characteristics.

A metallurgical plant would be established to treat ore extracted from the open pit at a nominal rate of 2.4 Mtpa and producing up to 6,500 tpa of UOC, and over the 15 year ore processing period averagind approximately 3,850 tonnes of UOC, depending on the uranium grade of the ore.

Uranium would be extracted from the ore in a series of agitated and heated alkali leaching tanks. To optimise uranium extraction, the feed material from the grinding mill feed (or blending) stockpiles would be ground to reduce the particle size before leaching. The leach residue would be separated from the uranium solution (termed pregnant leach solution, PLS) and washed in a counter- current decantation (CCD) circuit. Uranium would be precipitated from the PLS as an impure sodium diuranate (SDU), and subsequently dissolved and purified before being precipitated a second time as uranium peroxide (UO4.2H2O). This would then be dewatered, dried and packed as UOC.