Lake Macdonnell, South Australia


Lake Macdonnell, marine seepage sump, Great Australian Bight

Lake Macdonnell, near the head of the Great Australia Bight in South Australia, is a smaller marine seepage salina compared to Lake Macleod, but with a similar Quaternary coastal carbonate dune-hosted marine seepage hydrology. It has an area of 451 km2, a 10 m-thick fill of Holocene bedded gypsum and is located in a milder BSk setting, compared to Lake Macleod.

Even so, annually, the Lake Macdonnell operation is quarrying more than 1.4 Mt of Holocene coarsely-crystalline near-pure gypsum and producing more than 35,000 t of salt via by pan evaporation of lake brines. It is the largest gypsum mine in Australia. Gypsum is quarried by first pumping down the water level then using bulldozers and excavation equipment. The gypsum product is stockpiled for several years to allow halite to leach, driven by low levels of natural rainfall. It is then loaded onto trains using front-end loaders and taken to the port.

Like Lake Macleod, Lake Macdonnell is currently evaporating seawater via a seepage-fed drawdown hydrology. Yet, it has not had a hydrographic connection to the ocean for more than 4,000 years (see Warren 2016, Chapter 4 for more detail).

Interestingly, when the climatic settings of Holocene coastal salinas of southern and western Australia are compared, all of which show similar interdunal depression seepage hydrologies, it is clear that gypsum forms from marine brines in Koeppen BSk and lower precipitation regions Csb, settings. Halite dominates the marine-fed fills in BWh coastal settings, while Coorong-style meteoric-fed carbonates dominate in similar interdunal coastal seepage depressions in the more the humid Csb settings of the Coorong region

Lake Macdonnell. Colour contrast in adjacent evaporation pans indicative of differrent halotolerant biotal response to salinity variation.
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