The deposit is a brine containing potassium and sulphate ions that can form a potassium sulphate salt. The brine is contained within saturated sediments below the lake surface and in sediments adjacent to the lake. The lakes sit within a broader palaeovalley system that extends over hundreds of kilometres, this system has been eroded into the North-West Officer Basin sediments.

The lake bed alluvial sediments form the upper surficial aquifer and host the first brine horizon. The second brine horizon is hydraulically connected to the upper aquifer and comprises the lacustrine clay. The basal sand of the palaeochannel and the fractured bedrock form the third and fourth brine horizons and are considered to be hydraulically disconnected from the shallow aquifer.

The Project area is located within the Collier, Salvation, Scorpion, and North-West Officer Basins. The Marymia Dome is located on the northeast fringe of the Yilgarn Craton (southeast magin of the Basins) and comprises Archaean greenstone belts intruded by granites, and
notably monzogranitic rocks, which outcrops to the south of the Project.

Monzogranites are characterised as potassium rich and composed mostly of quartz and potassium feldspar (alkali-feldspar); their proximity to the BSOPP area, along with other granitic inliers, makes them a suspected source of the potassium enrichment in the region’s sub-surface brine deposits.

Hydrogeology
Two regional aquifer units have been identified within the Cenozoic sediments, the palaeochannel sand aquifer of Eocene age that is located at the base of the palaeo-drainage system, and the shallow surficial aquifer comprising Pliocene and Quaternary evaporites, calcrete and silt of the lake surface and alluvium. These aquifers are considered to be hydrogeologically separated from one another by a thick sequence of stiff lacustrine clays that form an aquitard.

The regional bedrock is considered to be on the whole of low aquifer potential; however deep weathering profiles in sandstones of the Jilyili Formation and vesicular basaltic sills in the vicinity of the palaeovalley have proven to be highly prospective aquifer targets from the 2018 drilling program. In addition, regional structural features described above and specifically the unconformity between the Willy Willy Formation and the Backdoor Formation enhance aquifer transmissivity as linear
features.

Groundwater within the surficial aquifer is generally between 0.2 m and 11 m below ground level, with depth to the ground water table determined by location within the catchment and local topographic changes. Groundwater flow within the surficial aquifer is generally driven by rainfall and episodic creek flow recharge to the aquifer system. The groundwater flow direction generally follows the surface topography, with recharge and groundwater mounding dominant in the ephemeral creek systems and discharge via evaporation occurring in the playa lakes through evaporation.

Off lake the surficial aquifer generally comprises of low transmissivity silt and soft clay unless calcrete is encountered. Calcrete is characterised by secondary porosity with very high transmissivity, but moderate to low storage.

The palaeochannel sand aquifer is a confined porous system, laterally bounded by the edges of the palaeovalley system and the poddy nature of the sand sequences. The aquifer can be characterised as behaving as a strip aquifer system where multiple reduced hydraulic conductivity boundaries

There are two principal methods applicable to extract the brine:

• Pumping from production bores in the basal sands (lower aquifer) plus leakage from brine bearing segments within the palaeovalley clay and fractured/weathered bedrock; and

• Pumping from trenches inside the alluvial sediments (upper aquifer) in trenches up to 10 m depth.

Both methods will be used because of the properties of the different aquifers. The design of the bore field and trenches will be based on the brine demand and aquifer conditions.

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The general mineral processing concept is comprised of the following areas, which are explained in further detail below:

• Brine concentration and crystallization of solid raw materials for the processing plant;
• Purification plant;

The brine concentration and crystallization process begins with brine entering the evaporation ponds whereby water is removed by solar evaporation. This causes gypsum, halite and astrakainite to crystallise sequentially in the first two sets of ponds. Unless determined economical to process, the calcium and sodium salts are left within the ponds to be harvested once full. The remaining brine crystallises producing KTMS comprising leonitic, schoenitic and carnallitic mixed salts in the next set of ponds. These salts are harvested and stored separately prior to mixing, pre-crushing and transferral to the SOP plant. The resultant bittern from the solar evaporation process may be transferred to a magnesium treatment plant.