Located on western Eyre Peninsula and southwest of the Poochera Kaolin Project are coastal salinas Lake Purdilla and Lake Toorna which contain abundant gypsum (CaSO4). The mineral gypsum is hydrated calcium sulphate (CaSO4 2H2O) and principal uses are in the manufacture of plaster products including wall and ceiling boards, mouldings, and blocks for construction use, as well as sculpturing plasters, medical and dental uses, and pottery. Another major use of gypsum is in the cement industry, where it is added to cement clinker prior to final grinding to retard the setting rate of concrete.
Gypsum at Lake Purdilla occurs as both coarsely crystalline selenite (crystals >2 mm), sand-sized gypsarenite (crystal size 1-2 mm) and finer gypsite (flour gypsum), which formed during the Holocene by inflow of groundwater and seawater during winter and subsequent evaporation and precipitation of salt and gypsum during summer.
Figure 1: Lake Purdilla block model showing lake gypsum blocks at -1 to -2mRL (orange blocks >80% gypsum, red blocks >90% gypsum) relative to drillhole collars and satellite imagery.
Figure 3: Gypsum sand (gypsarenite) formed by wind blown breakdown of crystalline gypsum (selenite).
Lake Purdilla and Lake Toorna, covering 35km2, contain a JORC 2012 resource of 87 million Tonnes of 91% purity gypsum mineral.