Outback water: in search of underground oases
If you’ve ever flown over Australia’s heart, you will have witnessed the beauty of nature’s patterns rippling across the red landscape. On the ground, this mostly flat, ancient expanse of red sand, gibber stones and occasional outcrops hides its complex history – and geology – under those subtle contour lines.
The Musgrave Ranges in the remote far northwest of South Australia that straddle into West Australia and the Northern Territory, hint at the ancient landscape. The ranges lie between the Great Victoria Desert to the south and the Gibson Desert to the north. The range’s Mount Woodroffe is in fact South Australia’s highest peak at 1435 metres above sea level.
The Musgrave Province is about 60,000km² stretching across the Anangu Pitjantjatjara Yankunytjatjara Lands (APY Lands), country held under title by Traditional Owners. In recent years, fixed-wing aircraft and helicopters belonging to the minerals and energy industry have criss-crossed this landscape.[i] They’ve been gathering geophysical information on what lies in the subsurface, conducting what’s called Airborne Electromagnetic Surveys (AEM).
That is because, for the minerals and energy industries at least, the Musgrave Province is among the last unexplored frontiers in Australia; identified by the South Australian Government as “highly prospective for nickel, copper, chromium, platinum group elements and base metals”[ii]. Aerial surveys mapping the magnetic and electrical signature of the landscape, gathering information about the rock and sediment beneath the surface, are one of the most important tools in geology today[iii] – fast and cheap.
The drawback to mining out here is that this is arid country, with low and unreliable rainfall averaging about 230 mm/year[iv], in an area where relatively little is known about the groundwater. Finding reliable and sustainable water supplies is going to be critical for mining and energy companies to viably extract minerals held in the rock of the Musgrave Ranges.
Call in the experts
Dr Tim Munday a Research Group Leader with CSIRO Minerals Resources and Dr Mat Gilfedder from CSIRO Land and Water joined forces to lead the G-FLOWS project – Finding Long-term Outback Water Solutions – which is funded by the South Australian Government and partner organisations of the Goyder Institute for Water Research.
It’s predicted, Dr Munday says, that there will be a three-fold increase in water demand in South Australia from 43,000 mL in 2010 to about 130,000 mL in 2019, by the mining and energy sector. Mining’s a thirty beast and needs potable and non-potable sources in ore-processing, slurry transport and dust suppression, as well as for the people living and working on site.
“There was a recognition that remote parts of South Australia were targets for exploration and therefore had the potential for mine development, but there’s always been a paucity of information about the ground water system in these remote areas,” he says.
“If you’re going to create an industry around mining you have got to find out where the water comes from. It’s a non-starter without the water.”
The G-FLOWS project team set out to establish where groundwater might be found and how it is replenished.
A picture of water under the surface
Just as the AEMs paint a picture of the potentially valuable mineral resources below the surface, they can also be used to detect water conductivity.
The first stage of the G-FLOWS project did something uncommon in the mining industry – the team succeeded in getting mining companies to share their existing AEM data collected to identify possible mineral deposits, information they might usually guard with secrecy.
This kind of geophysical data has historically been undervalued in terms of the insight it might provide on groundwater, and the G-FLOWS work involving the interpretation of historical exploration of geophysical data sets is considered to be an international first.[v]
They then compared the existing geophysical data to topographical maps to create a 3D model of the landscape.
What their work revealed in more detail, was that under the surface in South Australia’s far northwest are ancient hidden drainage systems.
“What we can picture is that the ancient rocks were subject to a long period of weathering and erosion, particularly during the pre-Pliocene period – when valleys were carved out and then filled in with sediment. The transition happened between 50-20 million years ago,” Dr Munday says.
Over millennia, these buried valleys became today’s aquifers, containing precious groundwater. By building a local-scale 3D hydrogeological conceptual model, researchers have been able to “up-scale” a regional-scale water assessment, while also beginning to get a clearer picture of the variability of groundwater.
“What we now understand about this landscape is that we have a structurally controlled palaeovalley system. We can use this understanding to infer where aquifers might be present in areas away from the domains of the mineral explorers ” says Dr Munday.
Can the water be used sustainably?
The G-FLOWS team then looked at data they could gather on ground which might give them an idea of how old the water is and, therefore, how rapidly it is replenished.
Using water samples from existing bores, the project team visited remote bores on the APY Lands and analysed the age of groundwater samples. Using tracers, they have been able to estimate the age of the water at different bore sites. This gives an idea of how rapidly this underground water is replenished.
Dr Gilfedder says the team found that to the north of the Musgrave Province, up against the Pre-Cambrian ranges and rock, there is direct recharge into the aquifer from episodic rainfall events.
“This is young water, under 50 years old, and mostly tapped for the local communities,” says Dr Gilfedder.
“But the further away from the ranges you go, going south, the groundwater is significantly older and more saline. That shows that the rate of replenishment, through the ancient drainage patterns and on a very slight hydraulic gradient, is very slow.”
Dr Gilfedder says that by overlaying the bore water data on the 3D images of the palaeovalley aquifers the team has been able to get a better idea not only of where water is but how sustainable it might be.
“The research combines multiple techniques that extend our ability to target and manage our precious water resources. In a continent as dry as ours it’s important we use the best knowledge and technology for water management, to benefit community, industry and the environment,” he said.
G-FLOWS2, the second stage of the project, moved to Eyre Peninsula, and proved that they could extrapolate the mapping work done in the Musgraves.
CSIRO now enters G-FLOWS3 – a contract with the South Australian Government until March 2016 to fly more geophysics in the Musgraves and undertake more on-ground work to refine the existing information. It will be used in conjunction with additional work by minerals resources companies, as well as work being done by the state government on community water access.
Stage 3 is about refining the existing picture to identify particular areas where there might be a water source suitable for mining. Further work is also planned through the second term of the Goyder Institute for Water Research that has been funded by the South Australian Government.
“I think if you had a mine you could legitimately extract water without significant impact on other communities’ resources or without significant impact on the environment,” says Dr Munday.
“But you have to target those deeper valley systems and be quite careful about where you go. The biggest challenge of all is to test those aquifers to determine the actual water resource that sits in them. A lot of what we’ve come up with is conjecture, albeit with some insight into the resource. A lot of work needs to be done on how the aquifers are connected across the landscape and how they link to the landscape. There is still a lot we don’t know and follow-up ground investigations are still needed.”
[iv] Hydrogeological review of the Musgrave Province, South Australia. Author Sunil Varma. Goyder Institute for Water Research Technical Report Series No. 12/8
[v] Facilitating Long-term Outback Water Solutions (G-FLOWS Stage-1) Final Report. Authors: Gilfedder M, Munday T. Goyder Institute for Water Research Technical Report Series No. 13/13