Lake MacLeod has our greatest opportunity for expansion. Its current operating area is 764 hectares with plans in place to expand operations to 1000 hectares by 2016 on a lease of 220,000 hectares.
The saturated brine contained in Lake MacLeod is approximately 10 times saltier than normal seawater, eliminating the need for a series of concentration ponds normally required to evaporate water to reach "salting" point (sodium chloride saturation).
A collection ditch has been cut to the halite layer to recover brine from Lake MacLeod. The brine is pumped at an average rate of 55 cubic metres per minute from the collection ditch into 8.5 kilometres of transport channel to a common collection point before being pumped into the crystallisers.
A total of 1,650 hectares of evaporators have been constructed on Lake MacLeod. There are thirty three crystallisers averaging 23 hectares each are used for salt production. The excess area is used to store residual brine containing other dissolved salts.
The crystallisers for salt production have a 300 millimetre thick salt pavement to support the equipment used in the harvesting operation and to prevent contamination of the salt during harvesting. Deposition is stopped by draining the remaining brine when about three quarters of the sodium chloride has been deposited and before other dissolved salts come out of solution in significant quantities. The residual brine called bitterns contains high concentrations of potassium, magnesium and other salts and is a potential source of these minerals.
Harvesting of salt is carried out using a laser controlled salt cutter with an average capacity of 1,000 tonnes per hour discharging directly into three 60 tonne trailers hauled by a prime mover. Laser equipment enables accurate control, leaving an even surface for the next year's growth of crystals. After harvesting, the crystallisers are cleaned and refilled with brine.
To ensure high quality salt with a minimum of impurities, the harvested salt is washed with saturated brine at the wash plant. This removes the soluble impurities (magnesium, sulphate and chloride) and the insoluble solids (gypsum and soil).
The washed salt is drained on stainless steel mesh belts before being conveyed to the washed stockpile. The salt drains in this stockpile for approximately two months for the moisture content to decrease below 2.5 per cent. Dry salt is hauled by road trains of up to 240 tonne capacity, 24 kilometres to a 200,000 tonne stockpile at Cape Cuvier for shipment.
Reclaim for ship loading is by dozers which push the salt into a hopper, which feeds onto the shiploading conveyor.
Ships are held in position beneath the shiploader by mooring lines attached to six buoys and are positioned under the shiploader by the vessel's own winches.
In 1997, Dampier Salt commissioned a gypsum project next to the Lake MacLeod solar salt fields. The product was exported to the wall board and cement industries in Japan and other parts of Asia, Africa and Australia. Gypsum is no longer mined at lake MacLeod.
Salt field data
Current production capability
2.9 million tonnes/year
Average evaporation (fresh water)
Average shiploading rate
2,500 - 3,000 tonnes/hour
Total lease area
Peak ship loading rate
Berth depth at low water
Salt deposited in crystallisers