It's estimated that there are more than 10 million metres of drillcore samples in vast warehouses around Australia, crammed with invaluable information for government, industry and researchers. The National Virtual Core Library is a fast-growing, globally-unique, open-access online resource of Australia's mineralogy. JANE NICHOLLS reports

One of the tremendous challenges in exploration is the expense spent merely identifying sites likely to hold the resource for which you are prospecting. Once you have some confidence you are close, it’s time to start sampling material for further analysis.

Drilling as deep as two kilometres beneath the surface, coffee‑cup-diameter tubes of core are extracted for geologists to study. Each drillhole costs around $200 to $300 per metre of core.

"In a good year, the Australian exploration industry can spend in the order of half a billion dollars per annum drilling holes," CSIRO honorary fellow, Jon Huntington, says.

How to turn 10 million metres of core into a virtual library

To make better use of the wealth of information stored in these drillcores, Dr Huntington co-developed a game‑changing automated drillcore analysis system that is integral to AuScope's National Virtual Core Library (NVCL).

Drilled rock core samples in metal trays.

Drill cores to be analysed with a hylogger to determine what minerals are present from their unique spectral signatures.  ©CSIRO, Damien Smith Photography

Known as the HyLogger, it uses hyperspectral scanning to split the wavelengths of visible and infrared light into multiple slices – usually more than 800 continuous slices – to reveal the mineral makeup of the drillcore.

The team combined this system with The Spectral Geologist (TSG) interpretation software, also CSIRO‑developed, to produce automated 'logs' or reports that geologists have traditionally created manually. HyLogging brings the rock-solid consistency of objective, algorithm‑based analysis, in much more detail and at a fraction of the time and cost.

The Hylogger instruments are now licensed to Perth-based METS company Corescan, which is developing the next generation of the equipment (the Hylogger-4), while CSIRO continues to refine its TSG interpretation software.

The HyLogger machine looks like a cross between a giant photocopier and a sun‑bed, awaiting trays of core in neat rows placed on a robotic table for scanning. The platform moves while the infrared spectrometers above are static, sensing each row of rock as it moves in a neat pattern beneath it.

The Hylogger scans trays of core in four minutes

"The core is illuminated with very bright white light," Dr Huntington explains.

"This light interacts with selected molecules in the minerals making up the rocks, setting up vibrations within them and allowing us to measure patterns of differential reflection and absorption from different minerals – it's molecular‑scale sensing of minerals."

Decades of ingenuity from many engineers – electronic, mechanical, software and database – and of physicists, chemists, mathematicians and geologists have built the HyLogging systems.

The HyLogger scanning and analysis of all this drillcore is building a virtual library, core tray by core tray. Each tray takes only about four minutes to scan. But the manual task of bringing them in on pallets for scanning at the geological surveys is considerable, involving conveyer belts and other core-library staff to lift the trays onto the HyLogger's platform.

"The vision of the National Virtual Core Library is to characterise the top one-to-two kilometres of the Australian continent," mineral exploration geologist, Belinda Smith, says.

Ms Smith has been the Northern Territory Geological Survey's (NTGS) HyLogging geologist since 2010 and also works with private industry. She has been scanning existing drillcore and freshly extracted material since then, as have many other colleagues at the other geological surveys around Australia.

Scanning new and old cores reveals new information for explorers

The NVCL is using the HyLogging system to scan and analyse the more than 10 million metres of drillcore archived in warehouses administered by the geological surveys in every state and territory, as well as new and old core from the private sector. Revisiting old cores reveals so much more because the NVCL is representative of exploration misses and near-misses, as well as successes.

Digitising the national core samples won't shut down physical core collections, but it is incentivising companies to share their drillcore samples with the geological surveys for HyLogging.

"Companies benefit in the short term when they get the results from the scans, and the industry at large will benefit in the long term," Dr Huntington says.

The enormous geographic coverage of the NVCL will make it easier for researchers and companies to access analyses about specific areas of interest. It will also steadily add to the body of knowledge about what lies beneath Australia’s deeply weathered cover.

"HyLogging helps exploration and mining companies to identify the minerals in the rock, which can then help them map between drillholes," Ms Smith explains.

"Normally, a geologist will look at a rock and identify what's in it, then there'll be another drillhole nearby and they'll log what's there and interpret the relationship between the two drillholes."

In some types of rock, it's hard to correlate that geological information. The consistency and richness of the HyLogging data is transforming that process.

Enabling a mineral systems approach

A core tray as seen by the National Virtual Core Library

"HyLogging gives us the mineralogy and the textures of the area, and helps us to understand the correlations or the relationships between adjacent drillholes," Dr Huntington says.

"In the past, exploration was often quite commodity – and spatially – focused; a nickel miner would look intensively for nickel in conventional nickel terrains but not consider other commodities.

"The modern concept in exploration is the examination of an entire mineral system, which has multiple spatial and geological age dimensions possibly containing multiple commodities.

"Traditionally, if you found a vein of gold, you focused on that. Today you would be interested in the five to ten kilometres around that vein and even other commodities – a mineral system is a much bigger target than an orebody."

Dr Huntington adds that the exploration search space has greatly increased with the realisation that the mineral system might indicate that 'good country' for a particular resource extends for kilometres away from the known orebody.

The NVCL provides the data to characterise larger swathes of country.

"With the NVCL, we can go back to the old drillcores and ask, 'What are the near miss indicators?' I can now interpret the non-economic, alteration minerals in a drillcore that suggest I am in a good place – whether it's 100 metres, a kilometre or even five kilometres away."

Accessing the National Virtual Core Library

The NVCL is an open-access resource for anyone in the world.

"You can sit in Helsinki – anywhere on the face of the Earth that has the internet – and look at drillcores, and their contained mineralogy, sourced from all over Australia," Dr Huntington says.

"You no longer have to fly to Kalgoorlie or Darwin or Perth, and you don't need your own HyLogger."

Its potential is already being realised by progressive exploration companies and it will continue to build on global geological science, furthering our understanding of orebodies and the complex mineral systems around them.

The NVCL is positioned to be a powerful tool for future under cover exploration initiatives.

"Fashions change because of available technology and commodity value – lithium and cobalt are highly prized now, whereas they weren't so much 50 years ago," Dr Huntington says.

"Geological concepts change and our knowledge has improved. The easy resources at the surface have mostly been found, so we need to go deeper under cover and drilling is the ultimate tool.

"Given the cost of drilling, the need for the NVCL's value‑adding technologies will become more and more important."

Workshops for the exploration industry

In the workshops he and CSIRO colleagues run for industry and Australia's Geological Surveys, Dr Huntington says they urge people to think beyond the target alteration and ore minerals.

"We need to think about the geological processes that put them there, and what that might say about the mineral system and where to look further.

"It's a detective game for geological processes that span millions of years, and the mineral system is the whole box and dice."

The NVCL databases are already packed with clues; while new drillcores continue to arrive in the geological surveys and the HyLogger's scanning reveals further descriptive evidence.

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