Supervolcano of Gawler Ranges 1.6 billion years ago leaves the legacy of South Australia's ore riches at Olympic Dam
Thick lava layers from the Gawler Ranges supervolcano cooled to form hexagonal "organ pipe" columns.
Image courtesy Stacey McAvaney
The remnants of a supervolcano found in the Gawler Ranges of South Australia drawfs the Yellowstone Caldera, the largest active supervolcano today on Earth. Gawler Ranges, comprising stoney hills to the north of Eyre Peninsula, were formed by the supervolcano nearly 1.6 billion years ago.
The supervolcano spread a lava field 500 kilometres in diameter and up to 300 metres thick. The total lava volume was as high as 500,000 cubic kilometres – enough to fill Sydney Harbour a million times over. The lava reached temperatures above 1,000 degrees Celsius and erupted from the volcano almost instantaneously — most likely from large fissures bursting open in the crust.
A consequence of this geological phenomenon was the world's largest hydrothermal deposit: a spectacular ore system filled with huge reserves of copper, uranium, silver and gold. Olympic Dam mine area, with about nine billion tonnes of ore, and OZ Minerals’ Carrapateena were extracting the bounty of the hugely enriched ore-forming fluids associated with the Gawler Ranges volcanic system in the 21st Century.
Bornhardts – dome-shaped steep bald rock outcrops – dominated the landscape of the Gawler Ranges, traditional home of Gugada Aboriginal people. The ranges were given their European name by Edward John Eyre in honour of South Australia’s second governor Geogre Gawler in 1839. This was on one of Eyre's earlier expeditions before his famous crossing of the Nullabor Plain further west. On this expedition, Eyre made the first recorded sighting of South Australia's floral emblem: the Sturt desert pea.
Stephen Hack explored the range in 1856 and in 1857 the first pastoral lease was taken up in the area and more sheep station were soon started. Good seasons in 1857 and 1858 had pastoralists reporting permanent freshwater lakes on their runs. Stations were required to stock 50 sheep per square mile (19 per square kilometre) but soon properties such as Nonning were shearing flocks of 90,000.
The Coralbignie (Houlderoo) Rocks, at the southern end of Nonning, were a feature of 100-metre-wide sloping granite rock. They were listed of the South Australian heritage register.
