A deep palaeovalley (ranging between 150 and 170m in depth) extends along the length of the LSOP area, infilled with predominantly lacustrine clays and sand interbeds of Tertiary age. Seven hydrostratigraphic units have been identified comprising:

• An extensive surficial unit of mixed alluvial/lacustrine sediments comprising:

- Approximately 15m of sandy loam, including local laterite and evaporite deposits, overlying the entire lake area.

- An upper, low permeability, clay-rich unit with minor sand horizons extending across the entire lake area.

- Local areas of permeable calcrete and / or silcrete.

• An upper sand aquifer unit at the base of the surficial unit, occurring at depths ranging between 35 and 70m, with thicknesses varying between 1 and 12m and anticipated to be continuous both along the length and across the width of the palaeochannel.

• A lower clay aquitard comprising puggy lacustrine clay with minor sandy interbeds. Adopted permeability ranging between 0.07 and 0.8 m/d

• A mixed aquifer unit comprising interbedded sand and clay.

• A basal sand aquifer located along the length of the paleochannel and encountered in 25 drill holes. Although predominantly of Tertiary age, in places, there are thin remnants of Permian glacial deposits (conglomerates and diamictites) overlying the Archean basement, which have also been included in this hydrogeological unit.

The brine contained in this aquifer sequence is enriched in potassium; the aquifer sequence has a
weighted mean average potassium concentration of 3,345 mg/L and a maximum recorded concentration of 7,380 mg/L. Groundwater levels are essentially at ground surface.

Brine abstraction
The bore-field network will be developed into the palaeovalley hosted deposit containing the potassium rich brines. The bore-field network has been designed to meet the required production flow rate. Bores will be developed into the upper and lower (or basal) aquifer units, with leakage of overlying units recharging the abstracted brine.

The bore-field design is based upon an abstraction rate across the network of 540 litres per second (l/s) of brine for the life of mine, producing 100,000 tpa of SOP. Total annual brine abstraction volume into the evaporation pond network is 17 gigalitres per year.

DFS bore-field design includes 78 bores on a nominal spacing of 800 metres. A contingency of 8 bores has been included that will be held on stand-by to cover scheduled maintenance.

The Project will be developed as a solar salt operation, comprising brine abstraction, brine evaporation and salt processing.

Brine evaporation
The solar evaporation ponds are the first stage of processing the brine to produce SOP. Water is evaporated from the brine, precipitating potassium (K) bearing salts.

There are three types of ponds in the evaporation sequence: the buffer pond, where brine is stored and released to manage seasonal fluctuations in evaporation; the preconcentration ponds, where the playa brine is concentrated and sodium chloride (halite) deposits as a waste material; and, the harvest ponds, where the potassiumbearing salts are crystallised and harvested.

The pre-concentration ponds will be constructed on the lake and will be configured to take advantage of the natural clay layer and topography, minimising construction costs. Berm walls will consist of an impermeable core section keyed into the underlying playa clay. The harve ........