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 unit ........

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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