Ian Mannix
Cosmos newsroom
A drilling program in far western New South Wales has reinforced theories about the ancient geology of the region, providing improved knowledge of the area’s mineral potential.
Under the Exploring for the Future program, Geoscience Australia is starting to deliver new data and geological insights from stratigraphic drilling on the mineral and groundwater potential in a vast area of southeast Australia, including western NSW, eastern South Australia, western Victoria and western Tasmania.
Drilling started late last year as part of the program’s Darling Curnamona Delamerian project, and analysis of the sampled rocks suggest there is potential for future exploration interest for copper, gold and critical minerals, according to Geoscience Australia’s Director of Regional Geology and Drilling, Chris Lewis.
One of the project’s aims was to understand the underexplored region between Broken Hill and Wentworth, NSW. The city of Broken Hill has been the centre of one of Australia’s biggest lead-zinc-silver mines for more than a century (and once had NSW’s largest gold mine) but the area to its south is underexplored.
“We asked ourselves, ‘What if the known prospective areas in western Victoria and to the north-east of Broken Hill, continue under the cover of the Murray Basin?’ We know that the rocks meet under cover between these areas, so that’s what we went to test,” Lewis told Cosmos.
’’“There is heavy mineral sand exploration in the Murray Basin, but very few people are looking for base and precious metals, like gold, copper, and nickel, which may also exist in the basement rocks underneath the Murray Basin.”
The rocks of interest to the project formed about 500 million years ago, says Lewis.
“It was at the point of time of the “Cambrian Explosion”, after the Earth had emerged from its “Snowball” stage, when life just exploded in the oceans—where we see trilobites, sponge and brachiopod-like animals, and molluscs starting to evolve.
“Around 500 million years ago the region in western NSW was the eastern edge of the Australian tectonic plate as part of the ancient Rodinia supercontinent” says Lewis.
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A subduction zone was established to the east, and oceanic crust was being pushed beneath, the then proto-Australian continent, ultimately creating a volcanic arc that ran all the way from Australia to Antarctica, which was joined to Australia 500 million year ago.
“This massive mountain building event is termed the ‘Delamerian-Ross Orogeny.’
“These dynamic geological regions are places where metals could be mobilised and pushed up from the depths of the Earth, and through to the upper crust, making them prospective for exploration activities and potentially future mining.
“The Paleo-Pacific Plate started to be pushed and pulled beneath the Australian continent in the Cambrian. When that happened, it started to melt the subducting slab, mantle wedge and overlaying continental crust. Consequently, this caused magmatic and hydrothermal activity, and led to the formation of a volcanic arc, producing lavas at the surface and large magma chambers at depth.”
The volcanic arc has what Lewis describes as “having all the right elements…”
“The elements creating the volcanic rocks are also associated with multiple types of magmatic-hydrothermal mineralisation. And so that’s where we start looking.”
Geologists knew from geophysical survey data (like magnetic and gravity) that the area might be a continuation of the volcanic arc.
“But,” says Lewis, “in the region between Broken Hill and Wentworth, very few people have undertaken such a systematic approach and regional drilling to assess these arc rocks and their potential for mineralisation.”
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Initial core samples show the region was indeed a place of magmatic activity in the Cambrian.
“We’ve dated some of these arc rocks, and they’re coming back with ages of about 500 million years. These ages are similar to the ages of the rocks in the mineral-endowed Stavely Zone of western Victoria.
“They might not be exactly the same rocks—we do have a little bit more work to do to assess and compare their geochemical characters—but based on their ages, we are more confident that this arc is in fact continuous.
“Our drilling didn’t hit what would be termed ‘economic mineralisation’. However, the geological systems identified could have the potential to generate economic mineral systems. And we do see evidence of some ‘sniffs’ of mineralisation in our drilled cores. We identified ‘smoke’, and where there’s smoke there can also be fire.
“In our drill cores we have seen sulphide minerals like pyrite, chalcopyrite and, to a lesser extent pyrrhotite. If you get these minerals in high enough concentrations, they could start to become mineral deposits, being good sources for copper and gold, that may be of interest for future exploration activities.
“So, we believe there is potential for similar mineral systems seen in Victoria to occur farther north, beneath the Murray Basin cover sequences.”
The final results and data will be released at the annual Exploring for the Future Showcase in August this year.
“We’ll provide the new precompetitive data of the fundamental geology in western New South Wales beneath the cover of the Murray Basin.”
The drilling campaign was a collaboration between Geoscience Australia; The mineral exploration CRC (MinEx CRC), which bills itself as the world’s largest mineral exploration collaboration, and the Geological Survey of New South Wales.
