3-billion year old craton gives up its mineral secrets in area the size of California


The world’s miners are being invited to South Australia, lured by just-completed geological surveys of the richly mineralised zone known as the Gawler Craton.

Stretching from the northern reaches of South Australia, right down to the tips of the peninsulas, this ancient body of rock is the oldest and largest part of the state’s geology.

And it could be a gold mine – literally. Or possibly a nickel, or uranium, or rare earth element mine – there are plenty of options.

The area is already home to several of South Australia’s richest mines, including the Olympic Dam mine near Roxby Downs (copper, gold, silver and uranium), and Prominent Hill (gold and copper).

The craton is about 440,000km2. The youngest rocks are nearly 1.5 billion years old, while the oldest are more than 3 billion years. Over that time, the ground has weathered, stretched, and changed, bringing a host of different minerals to the surface.

The Gawler Craton – the coloured section at the centre of the map. Credit: Department for Energy and Mining, the Government of South Australia, Solid geology map of the Gawler Craton, sourced on 11/12/2023, https://www.energymining.sa.gov.au/industry/geological-survey/geology/gawler-craton

The Gawler Craton – and specifically its western end, a remote patch with little to no road access – has been an area of interest to the Geological Survey of South Australia (GSSA) for the last few years. The government organisation has been collecting as much information as they can to map the mineral potential in their Gawler Phase 2 project, culminating in a huge data drop.

The GSSA went through their trove of data in a workshop held at the end of November.

So, what do they want people to do with the data? Find a mine, according to Dr Bronwyn Camac, Director of the GSSA.

“We’re here to deliver back to the people of South Australia. Mining creates jobs; opportunities for the local communities; improves quality of life and generates income for the state through the royalties,” Camac told Cosmos at the conference.

According to the state budget, royalties from all sources generated roughly $385 million in state revenue in 2022-23. According to the federal government’s Jobs and Skills Atlas, 1.5% of the state’s jobs come from the mining industry.

“Hopefully companies are excited with the new data, and they’ll take up leases, we’ll have more drilling, and ultimately find mineral deposits,” says Dr Claire Wade, a senior geologist at the GSSA.

Wade says that the exciting part of the project for her, from a research perspective, has been figuring out how the region formed.

“We’ve got the final product that’s been mashed up and split apart and moved around. We’ve got to try and deconstruct that, and then figure out what it looked like two and a half billion years ago.”

The geological history is crucial to learning where mines might best be placed. Learning about the craton has required a huge number of techniques, both in the field and back in Adelaide.

This includes identifying elements in rock samples from the state’s drill core library, electromagnetic surveys of the region done via airplane, devices that find rock density by tracking the slightest changes in gravity – and new machine learning programs stitching datasets together.

“Different data sets can throw crazy ideas out there,” says Dr Mark Pawley, a senior geologist at the GSSA.

“You’ve got to think: well, what’s that mean? What’s that telling us?”

For Pawley, the most exciting part is mapping the different geological features of the region.

“I’m a bit old fashioned: I like making maps. When you make a map, you see how things fit. You see where things are spatially, and you develop a story on how that part of the world formed and evolved.”

A large part of the $2.5 million project has been working with the Traditional Owners of the land under investigation.

“It was underestimated how long that would take to get access to the land and build those positive relationships on country which can stand the test of time,” says Camac.

Camac says the team was “choosing to go through the right channels” in negotiating this access.

“It does takes time, but it is important to us and for our community that we work positively and respectfully together on these state-wide projects.”

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