Lake MacDonnell Gypsum Mine, Ceduna, Eyre Peninsula, South Australia, Australiai

Regional Level Types
Lake MacDonnell Gypsum Mine	Mine
Ceduna	Town
Eyre Peninsula	Peninsula
South Australia	State
Australia	Country

Lake MacDonnell, Australia's largest gypsum mine, developed on deposits of gypsum and salt deposited within a 20km NW-trending depression in calcreted coastal dunes of the Pleistocene Bridgewater Formation. The gypsum and salt formed by natural solar evaporation of marine brines during Holocene times. In the deeper parts of the embayment selenite (rock gypsum) domes were initially deposited from gypsum-saturated brine. Domes pass upward to laminated selenite comprising vertically orientated crystals with layers of aragonite pelletoids. As the volume of brine decreased freshening by meteoric water resulted in cessation of laminated selenite deposition and formation of up to 1m of laminated gypsarenite (seed gypsum). Maximum total thickness of gypsum was 8m, average 3.9m. Main impurities are aragonite and salt, which must be reduced to ~1%. Indicated reserves in 1980 were 575 million tonne at an average grade of 91.3% CaSO4.2H2O in a bed averaging 3.87 m thick. Grade distribution was an upper ~1m zone of gypsarenite at 93% CaSO4, and an underlying zone of selenite at 94-96% CaSO4. Mining commenced in 1919. Workings extend over an area of ~10 x 8 km. Production from 1920-78 was 6,114,938 tonne gypsum. Production for the period 1978-2011 was ~40 million tonne. Annual production is in the order of several 100,000 tonne. After mining, crushing and screening, the salt content of stockpiled gypsum is reduced to acceptable levels by stockpiling on site for several years to allow the leaching action of rainwater. Solar salt has been extracted annually from the western end of the lake since 1968 with 936,608 tonne harvested. Operators are Gypsum Resources Australia (100%), formed in 1984 when CSR and Boral combined separate operations. The gypsum product is railed 64km to a 160,000 tonne stockpile at Thevanard. Gypsum from Lake MacDonnell is mainly used for the manufacture of plaster products for the building industry. It is shipped in bulk to production plants located near major Australian cities.

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