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Captivating Coompana

Geological riches ignite greenfield space.

Stunning new technical insights from one of Australia’s least known geological provinces – Coompana – has reinforced the value of collecting precompetitive data to inspire industry investment in a new greenfield search space.

That endorsement was shared by Mithril Exploration Managing Director, David Hutton, during the Coompana Drilling and Geochemistry Workshop held at the South Australia Drill Core Reference Library in early August.

Clive Foss from CSIRO. (Photo 416703)
Clive Foss from CSIRO spoke on ‘Highlights of the Coompana gravity and magnetic modelling and inversion study’ – one of the world’s most whopping examples of remnant magnetism. (Photo 416703)

Before a captivated audience of industry geologists and peers, geologists from the Geological Survey of South Australia (GSSA) and their collaborators presented hard-won knowledge collected over a five-year geoscientific effort at Coompana in South Australia’s remote west that will be key to opening up this frontier.

An immediate highlight for industry from the far-ranging Coompana program is the identification of areas with the right geological conditions that make it prospective for economic minerals: copper, nickel and platinum group minerals; zones prospective for copper–gold; and hot spots prospective for lucrative specialist metals niobium and tantalum, along with rare earths. The depth to basement is not as deep as previously thought, putting it well within the economic search space.

Opening the workshop Alex Blood, Executive Director of Mineral Resources, championed the Coompana Geoscience program as a once in a generation effort to open up a new area to explorers and scientists for the future benefit of all South Australians.

The Coompana Province is an approximately 200,000 km2 region underlying the Nullarbor Plain and the effort to better understand its geology and prospectivity involved a direct cash investment of $8 million, with a contribution of $7 million from the state government, and $1 million from the federal government’s Exploring for the Future program. Just as valuable was the in-kind combined expertise of the GSSA, joining with collaborative partners Geoscience Australia, CSIRO, University of Adelaide, University of South Australia, Curtin University, Australian National University and AuScope. As the project gathered momentum, a number of partners and postgraduate students clambered aboard.

Creaming prospects

Drawing together key insights the workshop presenters recapped highlights of seismic surveys, magnetic and radiometric surveys and a gravity survey, and shared latest findings of magnetotellurics modelling, geochemical studies and drill core analysis from a public geoscience drilling program.

Geoscience Australia’s Richard Blewett reinforced the ‘first-mover advantage’ for industry in going to greenfield search spaces. Presenting illustrations of creaming curves, a concept well-known in petroleum circles, he showed the most worthwhile discoveries in a new region are typically made early in its exploration history – proven to add most value to the cumulative total of resources discovered.

‘From the public precompetitive releases encapsulated today, now it’s up to industry to come up with targets that are the opportunity to make new tier 1 discoveries.’

For geoscientists, the journey can be as important as the destination.

GSSA’s Carmen Krapf and CSIRO’s Ignacio Gonzalez-Alvarez read the qualities of the land surface to see what lies beneath. In the process, they catalogued the subtleties of 15 regolith landform units. While sniffing at the surface did not directly show geochemical signatures of the bedrock beneath, landform features are controlled by deep-seated basement structures, suggesting these features may be the best place to focus on to potentially see into the bedrock below. For the first time a detailed regolith map has been compiled for an area on the Nullarbor Plain.

Ryan Noble of CSIRO provided an excellent demonstration of surface geochemistry sampling methods, and veracity of mobile field analysis as standing up well alongside traditional analysis. Not only had the geochemistry program provided a valuable baseline of information for future exploration, it had also shown opportunities to streamline sample collection without comprising data, holding applications for other field exploration programs across the country.

From a scientific point of curiosity CSIRO’s Clive Foss pulled no punches by describing the enigmatic Coompana magnetic anomaly as one of the ‘world’s most whopping examples of remnant magnetism to be found on the planet’. ‘To find another’, he said, ‘you would probably have to look at Mars’. After studying the anomaly and a number of smaller associated intrusions, he has formed the view that the magnetism has the hallmarks of being acquired over a considerable period of time – 300 million years. The strong magnetic signal has been confirmed to be due to gabbro, a coarse-grained mafic intrusive igneous rock that can mobilise metals from the mantle. ‘With potentially multiple magmatic events in the area, it’s more likely to develop a mineral system, so that’s good news for exploration.’

Mark Pawley from the GSSA (centre left). (Photo 416704)
Mark Pawley from the GSSA (centre left) showed points of interest during the two-hour break allocated for geoscientists to study a selection of Coompana drill core on display in the viewing hall of the South Australia Drill Core Reference Library. (Photo 416704)

It was possible to hear a pin drop when the GSSA’s Mark Pawley presented the story of the Coompana drill core, pointing to areas of prospectivity. In the mix of ingredients found in a selection of core from the targeted eight-hole drilling program were basaltic and granitic intrusives, and a number of new surprises that point to significant hydrothermal alteration and migrating melts. Later in walking through the crustal architecture and recapping the initial seismic survey and shear zones, Mark shared how each of the various Coompana domains serve up their own points of interest.

Mike Ravella, representing Boart Longyear’s involvement in the drilling program, said new technologies deployed reinforced their approach of tearing down the hurdles in frontier mining exploration. Amidst the challenge of remoteness, dust storms and spiked tyres, he lauded the professionalism of working with the GSSA and Geoscience Australia to deliver useful results.

The GSSA’s magnetotelluric specialist, Stephan Thiel, presented new resistivity models of the lithosphere revealing zones of conductivity in the upper mantle and lower crust with structurally controlled conductors correlating with shear zones coming to the surface.

GSSA’s Coompana project leader, Rian Dutch, enthralled with confirmation of rock suite units analogous to known prospective areas, while also describing eight new rock units amidst descriptions of deep mantle shoshonitic melts, crustal melts, and melting, assimilation, storage and homogenisation (MASH) zones, flagging areas with potential to host rare metals.

GSSA’s Tom Wise closed formalities, tying the story of Coompana’s evolution from four key geological events over a billion years that will rewrite a new basement map.

Of industry significance, the Coompana program has confirmed four new areas prospective for metals, being:

  • Giles Complex equivalent intrusive rocks that can be prospective for copper, nickel and platinum group elements
  • arc-related magmatism and shoshonites with raised copper–gold potential
  • long-lived structures which have localised hydrothermal fluids leading to significant alteration
  • new drill core showing acidic fluorine-rich magmatic fluid with the capacity to mobilise specialist lucrative metals niobium and tantalum.

Download Coompana workshop extended abstracts (PDF 35.1 MB)

Link to Coompana workshop presentations

– Grace Taylor, August 2018

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