The Lake Carnegie Potash Deposit is a brine, containing the target potassium and sulphate ions that could form a potassium sulphate salt. It has potential for potash mineralisation with a wide range of exploration targets from shallow brine within the lake sediments to deeper brine horizons in the palaeochannel basal sand aquifer. Advisian name five different prospective exploration targets for obtaining brine supplies associated with the Lake Carnegie project, which include:
• Evaporite sand layers in the lake sediments;
• A minor aquifer associated with alluvial and colluvial deposits;
• A sandy horizon at top of palaeochannel stratigraphy;
• Basal palaeochannel sand; and
• Fractured-rock aquifers at the southern and northern edges of the lake.

Lake Carnegie is part of an extensive palaeodrainage system that was active in the area until the middle Miocene. The palaeodrainages are infilled with a basal palaeochannel sand that is overlain by dense plasticine clay, and a variable thickness of alluvium and colluvium. Numerous tributaries incising the Earaheedy Group and draining towards Lakes Carnegie and Wells were once connected to this system and are now represented by calcrete-rich valley floors, and isolated areas of playas and associated material.

There are also a wide range of weathering profiles and weathering products derived from the basement lithologies, as well as associated with the deposition of the lake systems. Vall ........

There are two principal methods applicable to extract the brine from the surrounding sediments:

• pumping from wells in the basal sands (lower aquifer) plus leakage from potential brine bearing segments within the clays;

• pumping from trenches inside the alluvial sediments (upper aquifer).

It is likely that both methods will be used because of the properties of the different aquifers. The design of the bore field will be based on the brine demand and aquifer conditions.

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Given the arid nature of the environments that brine deposits occur in Australia it is naturally difficult to identify a large scale fresh water source. At this early stage of the project it is important that potential fresh water supply sources are located and de-risked.

The WIN database search identified pastoral bores located to the north of the lake overlying the Kulele Limestone with salinities in the range of 700 to 1 500 mg/L TDS. This would suggest that the Kulele Limestone has fresh to brackish groundwater potential and is a potential zone of recharge at outcrop. These locations are subject to some ground-based mapping to identify future exploration targets.

There are also a large number of pastoral wells on the southern and western side of the catchment that have no water quality data. It is recommended that these bores be surveyed, sampled and hydraulically tested to obtain a full understanding of regional water quality, water levels and basic aquifer parameters.

Large areas of calcrete are mapped in the 1:250,000 GSWA map series between Lake Wells and Lake Carnegie as well as the tributaries to the west of the lake. These areas are also highly prospective but may be subject to abstraction restrictions due to potential stygofauna impacts.

To determine the most prospective water supply search areas a pastoral bore survey should be completed in conjunction with geological mapping in the vicinity of prospective targets identified.