AS Australia’s greenfield outcropping and sub-cropping deposits become increasingly scarce, miners are digging deeper than ever before, exploring new options on green and brownfields tenements.
To do this, they must be able to look further underground to map the subterranean deposits before expensive exploratory drilling programs can take place.
Geophysical technology allows explorers to do just that – giving explorers high resolution 3D models of up to 3km below the surface.
According to Independence Group (IGO) chief geophysicist, Andrew Fitzpatrick, “the new frontier is exploring undercover”.
Mr Fitzpatrick spoke with the Australian Mining Review about the way IGO has been using geophysical methods and technologies on the company’s Nova deposit, and its satellite Albany Fraser copper-nickel project in WA.
The Nova deposit was discovered in 2012 and during the initial exploration, a host of potential satellite deposits were discovered, one of them being the Albany Fraser copper-nickel project.
The geology of the tenement is magmatic nickel-copper, and is hosted within the lower granulite facies mafic rocks of the Fraser Zone of the Albany-Fraser Orogen.
To map the deposit, IGO used a variety of geophysical methods such as electromagnetic (EM), magnetics, gravity, and seismic modelling.
Mr Fitzpatrick said that for the exploration of nickel, IGO focused mostly on the use of EM and seismic techniques, as they can be used to directly detect mineralisation.
“We use airborne EM to provide a rapid reconnaissance of the belt, and follow-up with ground EM over potential targets prior to drilling,” he said.
“We just completed one of the largest high-resolution airborne EM surveys in Australia using the Spectrem system collecting over 46,000-line km.
“Additionally in 2018, we completed a large 3D seismic survey over the Nova Mining lease to assist in our brownfields exploration program.”
The 3D seismic survey has been, according to Mr Fitzpatrick, the real game-changer to brownfields exploration.
“From my perspective, hard rock seismic is gaining momentum, where our other geophysical methods lack the resolution and depth of investigation to adequately define geology at depth.”
“At Nova, we now have a seismic cube that is high resolution at depths over 3km.”
Whereas traditionally, the electromagnetic (EM) techniques were limited to depths between 500 and 1000m, “the seismic technique is comparable to MRI technology in the medical industry, and we’re only starting to realise its benefits,” he said.
The self-organising map algorithms are able to interrogate a number of geophysical models and simultaneously help map geology in 3D to show any anomalous areas.
Although it is not new, the technology helped IGO to solidify its geological understanding in most areas, and to identify areas that were less understood.
IGO has also been looking at a number of new ideas to get the most out of its 3D seismic techniques, such as machine learning and more advanced model algorithms.
At Nova, the program has proved successful and Mr Fitzpatrick said that even after the first initial holes were drilled, the geological interpretation of the seismic models were robust and gave the company confidence to test new targets at depth.
“This year we also saw our own in-house geophysics crews deploy SQUID sensors in our EM surveying,” he said.
“These SQUID sensors are cryogenically cooled, and their increased sensitivity translates to seeing deeper.”
The geophysical datasets, gathered by the increasingly sensitive technology, do not just support the understanding of the area’s geology, they allow IGO to objectively identify and drill targets and reduce the risk involved in exploration programs.
This means that the advancement of the understanding and the increased knowledge of data-rich seismic data from Nova is not confined to one mine lease – the geological insights gained by these advanced methods can be applied and extended to greenfield programs too.
“We like to think of Nova as our laboratory where we can test and trial new ideas.”
While miners are always on the lookout for new, game changing technology, Mr Fitzpatrick said that although there is room for improvement, geophysical technology primarily works off incremental improvements across all technology.
“Everyone is looking for the new silver bullet, and if I knew of a game changer, I’d probably keep that within IGO,” he said.
“From a nickel perspective, I’d like to see the sensitivity of downhole EM systems be improved.
“Increasing the search radius from 100m to 300m or so would be a game-changer, particularly when we drill beyond the depths of surface EM detection.”
