Secrets beneath the Great Artesian Basin uncovered

18 October 2018

A five-year project spanning approximately 135,000 square kilometres across New South Wales and Queensland has delved beneath the Great Artesian Basin to learn more about the geological development of eastern Australia.

The findings of the Southern Thomson Project are on show today at the inaugural Australian Geoscience Council Convention in Adelaide.

Dr Ian Roach said Geoscience Australia collaborated with the Geological Survey of New South Wales and the Geological Survey of Queensland to learn more about one of Australia's most underexplored regions.

Due to the complexity of this image no alternative description has been provided. Please email Geoscience Australia at clientservices@ga.gov.au for an alternate description.

Mud rotary drill chip samples.

"You know the Australian saying 'at the back of Burke'? Our actual starting point was Burke and then we kept going," Dr Roach said.

"We wanted to learn more about part of a geological province that underlies northwestern New South Wales and much of central Queensland.

"It was a piece of Australia that we didn't know much about. The one thing we did know is that age-dating the rocks in the southern region of the Thomson Orogen had the potential to give us a much better picture about how eastern Australia formed. Way back when that part of Gondwana was being put together.

"Geologically, on the surface, there's not much out there, lots of dust and sand dunes, salt lakes and claypans.

"Only around one per cent of the project area was exposed rock or what is called an outcrop."

Dr Roach said the rest of the project area was buried by the sedimentary cover of the Great Artesian Basin. The project conducted airborne electromagnetic surveys to map the thickness of the cover.

"We could actually see where basement rocks rose up to form little islands, which would have been in the Cretaceous sea with dinosaurs swimming amongst them around a hundred million years ago.

"Unlike now, it would have been cold and where the Great Artesian Basin is, there would have been icebergs.

"Probably the best current day example of what it would have looked like is the Norwegian archipelago Svalbard in the Arctic Ocean."

Dr Roach said in addition to airborne electromagnetic data, gravity and seismic data were used to conceptually map out what is happening deep underground.

"Using this new data, we built up a solid geology map, a picture of what we thought was going on underground.

"The final step was to drill some holes through the sedimentary cover to test our ideas about the age of the rocks and the potential mineral endowment of the region.

"In total, we successful and safely drilled 12 bore holes that gave us a really good understanding of how old the metamorphic rocks in the southern region of the Thomson Orogen are.

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Mud rotary drill chip samples being collected.

"They are a similar age to rocks in the Lachlan Orogen, which is connected to the south of the Thomson Orogen and has a known mineral endowment including copper, gold and base metals.

"It had been suggested previously that the Lachlan and Thomson orogens were very different things. It looks like now they are similar. In fact, it's possible they may be one and the same.

"We already knew from outcropping rock in the Thomson Orogen there was potential for minerals such gold, tungsten, tin, copper and molybdenum.

"We were able to show the mineral potential in areas with outcropping rock extended much further undercover."

Dr Roach said academics, geological surveys and the exploration industry sector will continue to analyse the data collected during the five year project to learn more about the region.

"I used to call it the big black hole in our understanding, now it's a grey area. Although we now know a lot more about the geology of the southern Thomson Orogen, we still have many questions.

"Thanks to the collaborative efforts of Geoscience Australia, the Geological Survey of New South Wales and the Geological Survey of Queensland, we're now closer than ever before to getting some answers."