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19 March 2018 3 min read

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Understanding rock types deep underground without drilling

By combining geological data from several different sources in an innovative way, CSIRO researchers have been able to provide a junior exploration company with a detailed 3D map of the rock types up to 800 metres underground. Previous approaches could only "see" about 100 metres below the surface.

Marindi Metals inherited a tenement in the McArthur Basin in the Northern Territory from a merger with Brumby Resources. The collaboration with CSIRO has now provided the company with data on the block, which looks like yielding a better targeted drilling program for a fraction of the time and resources it would normally cost.

"We provided some geophysical data and CSIRO provided us with the expertise to interpret it in new ways," Marindi managing director, Joe Treacy says.

"The net result was that it changed our thinking on that particular block. It's been a great help to us. It showed us the target horizon was not as deep as people thought, which makes it more prospective.

"In the past, we would have had to drill to find that out – that's expensive and a real problem for a small company."

We worked with Marindi Metals in the Northern Territory's McArhur Basin to map rock types 800 metres underground. ©  Nick Rains

Exploring and testing new models through collaboration

At the same time, the six-month project has allowed researchers from CSIRO to explore and test new models and ways of combining airborne electromagnetic data with ground-based gravity data and geochemistry from drillcores.

The collaboration came together under the Australian Government's Innovation Connections program. Innovation Connections provides grants of up to $50,000 to small-to-medium enterprises (SMEs), enabling the placement of a researcher in their business to work collaboratively on a project "to develop and implement a new idea with commercial potential".

Projects funded through Innovation Connections last for up to a year and companies are generally required to match the government money on a dollar-for-dollar basis. In this case, CSIRO also contributed funds to drive the project because of its strategic alignment.

The story actually began in another place at another time. CSIRO project leader, Sam Spinks, a geochemist, had earlier been working in the Capricorn region of Western Australian on the southern edges of the Pilbara, where Marindi also have interests.

Dr Spinks worked on how to use geochemical indicators to point to the location of potentially exploitable mineral deposits. His work in the Capricorn provided Marindi with useful information as to where deposits of zinc and even gold might lie in their area.

Linking research opportunities with commercial outcomes

Dr Spinks had also worked in the McArthur Basin. Given his previous links with Marindi and how they valued engaging with research and development, it occurred to him that their intention to explore in that area was the perfect opportunity to look at employing a combination of different types of survey data on a local scale.

Marindi already had airborne electromagnetic data across their block, and Dr Spinks was able to get hold of cores previously drilled in the area and lodged with the

Northern Territory Geological Survey (NTGS) in Darwin. The collaborative team then commissioned a commercial survey company to take ground-based gravity readings across the block.

Dr Spinks' geochemical interpretation gave CSIRO geophysicists a better understanding of the likely mineral make-up of the area. It allowed them to calibrate and better interpret the picture derived from the electromagnetic and gravity data, producing a much more refined 3D model of the rocks beneath.

"The geophysical datasets are absolutely complimentary, and using both in combination with geochemistry improves our understanding of the subsurface geology in 3D," Dr Spinks says.

The project has not only provided useful and practical information to the two collaboration partners, but has also given the NTGS important feedback on what data it can gather to expand the local useability of its information, and where it should be taking a closer look.

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