Rio Tinto subsidiary Dampier Salt operates the Lake MacLeod project, 54 kilometres north-west of Carnarvon. The mine holds expansion opportunities for the company; Rio Tinto planned to increase the site’s current operating area from 764 hectares to 1000 hectares by 2012 on a lease of about 220,000 hectares.
Lake MacLeod’s current production capacity is 2.9 million tonnes per year. The average ship loading rate is between 2500 and 3000 tonnes per hour, with a peak ship loading rate of 3300 tonnes per hour.
The saturated brine contained in Lake MacLeod is about 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). The average fresh water evaporation rate for the site is 3250 millimetres per year, with 270mm of salt deposited in the crystallisers per year.
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 an 8.5km transport channel that leads to a common collection point, before being pumped into the crystallisers.
A total of 1650 hectares of evaporators have been constructed on Lake MacLeod. There are 33 crystallisers averaging 23 hectares each that are used for salt production. The excess area is used to store residual brine containing other dissolved salts.
Harvesting of salt is carried out using a laser controlled salt cutter with an average capacity of 1000t/hr discharging directly into three 60t trailers, which are hauled by a prime mover.
Dry salt is hauled 24km, by road trains of up to 240t capacity, to a 200,000t stockpile at Cape Cuvier for shipment.
In 1997, Dampier Salt commissioned a gypsum project next to the Lake MacLeod solar salt fields. The product was exported to the wallboard and cement industries in Japan and other parts of Asia, Africa and Australia. Gypsum is no longer mined at lake MacLeod.
Operating with opportunity for expansion. Rio Tinto reported in the December 2009 quarter there was no production at Lake Macleod during October 2009 due to planned maintenance on a radial stacker.