The Mackay sulphate of potash project is located in Western Australia, approximately 785km south of Wyndham Port. Image courtesy of Agrimin.
The project will extract sulphate of potash minerals dissolved in the brine within Lake Mackay. Image courtesy of Agrimin.
The definitive feasibility study will be completed by June 2020. Image courtesy of Agrimin.

The Mackay sulphate of potash (SOP) project is a world-class project focused on the extraction of SOP dissolved within Lake Mackay, Western Australia.

Owned and operated by Agrimin, the pre-feasibility study (PFS) for the Mackay SOP project was completed in May 2018. The definitive feasibility study (DFS) is scheduled to be completed in June 2020 while the environmental impact assessment (EIA) is currently underway.

The project was accorded Major Project Status by the Australian Government in May 2020, allowing it to receive additional support. The life of the mine is estimated to be 20 years.

The project will generate approximately 300 jobs during construction and 200 jobs during operations. It is also expected to support more than 600 jobs in the supply chain.

Mackay sulphate of potash project location

The Mackay SOP project area consists of 12 tenements occupying a total area of 4,370km². The mine is situated 785km from the Port of Wyndham in Western Australia.

The nearest town is Kiwirrkurra, which is located 60km southwest of the project site.

Geology and mineralisation

Lake Mackay is overlaid by the Palaeoproterozoic Arunta complex and Neoproterozoic Amadeus Basin basal sequence apart from the Ngalia basin. These sequences are underlain by members of the Neoproterozoic Redcliff Pound Group, which comprises chert, calcareous, siltstone, quartz arenite, conglomerate, and dolomite.

The lake surface includes a thin layer of evaporite mineral deposits, particularly halite, which is underlain by a variable lakebed sequence. The sequence consists of reworked gypsiferous sand deposits, including silty to clayey sands; lacustrine deposits, including green clays to sandy clays; gypsum layers; and hard calcrete and silcrete layers.

The salt lake contains hypersaline brine with potassium and other elements dissolved within the brine. The lake is a single aquifer unit with the brine starting at only 40cm below the surface and extending beyond the deepest drilling of 30m.

Mackay sulphate of potash project reserves

The Mackay SOP project is estimated to contain a combined mineral resource of 123.4Mt of SOP comprising 3.9Mt of measured resources and 19.5Mt of indicated resources.

Mining at Mackay sulphate of potash project

The Mackay SOP project will use on-lake trench system to extract the Potassium-rich brine. A network of shallow trenches will be used to extract brine from the top 3m of the lake.

The brine will flow through the trenches and will be pumped into a system of solar evaporation ponds. The ponds will be designed to initially cover an area of 34km² and up to 52km² during the tenth year of operation.

The evaporation in the ponds will cause SOP-bearing salts containing high-quality SOP to precipitate. The main SOP-bearing salt being targeted at the project is kainite, which will be wet harvested and transported to the process plant.

The project is designed to have an average annual brine extraction rate of 66.3mm³ with an average SOP grade of 8kg/m³ over a 20-year mine life.

Processing details

The process plant will be located west of the evaporation ponds and as near as possible to the west shore of the lake. The kainite salts will be crushed to a size 850 microns and pumped into a floatation circuit to separate halite and other waste salts.

The kainite is then decomposed to schoenite and treated with heated water to dissolve magnesium sulphate and precipitate the SOP. The SOP is then washed, dried, compressed, and shaped to meet the necessary customer specifications. The finished product will be exported through an integrated logistics chain through the Port of Wyndham.

The process plant is expected to produce 426,000tpa of SOP fertiliser as a dry granular product. The average potassium recovery is estimated to be 80% during the production process.

Infrastructure facilities

Infrastructure at the site will include a reverse osmosis plant and wastewater treatment facilities, power plant, access roads, transmission lines, and an accommodation camp with 200 beds. The project site will also include medical services, laboratory, administration, firefighting facilities, an airstrip, and vehicle and maintenance workshops.

The raw water used in the process plant will be abstracted from the site’s borefield located approximately 38km southeast.

A reciprocating gas-engine powered power station will supply power for the project site. A gas-fired water heating system will also be part of the process plant. The gas for the power plant will be supplied through a new pipeline from the Amadeus gas pipeline under a build-own-operate (BOO) contract.

Contractors involved

The main contractors involved in the PFS include Advisian, Knight Piesold, Global Potash Solutions, Saskatchewan Research Council, Hydrominex Geoscience & H&S Consultants, 360 Environmental & Strategen Environmental, and Qube Bulk.

Agrimin contracted Primero for conducting the DFS and awarded the engineering design contract for the process plant in July 2019.

Agrimin formed a joint venture (JV) called Newhaul Bulk with Craig Mitchell, a trucking specialist, to deliver haulage services for the project. The JV will give Agrimin control over the logistics chain while delivering cost reduction and minimising risk.