Deep thinking

Materials World magazine
,
3 Sep 2015

With miners having to drill deeper to find new mineral resources, Guy Richards reports on how one research group is developing technology to make that process quicker, safer and cheaper.

One of the key issues facing the mining industry these days is the declining rate of discovery of new mineral resources, especially in well-explored regions and where mining is a mature industry. Not only are new discoveries of a lower grade than in the past, but miners are having to look harder – and deeper – for them now that most of the easily accessible deposits have been found, which, of course, is pushing up costs.

This presents companies with a choice. On the one hand, they can search for deposits in developing countries, where there’s a greater chance of finding fresh ‘low-hanging fruit’ but where the local jurisdictions are often unstable, or they can search in the traditionally more stable and developed regions, and face the greater technical challenges and risks of finding resources that are becoming evermore elusive. And despite technical advances in other areas of mining, trying to find those resources – which are now under cover – still comes down to using diamond drills and recovering core samples.

What is needed, then, is a method of drilling holes and analysing samples quickly and cheaply, in stable jurisdictions and, in acknowledgement of this, a few years ago the Deep Exploration Technologies Cooperative Research Centre (DET CRC) was established in Australia. Part of the Australian Government’s broader CRC programme, DET CRC is funded partly by the government, partly by industry partners such as Anglo American and BHP Billiton and partly by research providers such as the CSIRO and the University of Adelaide. Its head office is in the Asia Pacific headquarters of drilling services firm Boart Longyear, another of its partners, in Adelaide. 

DET CRC’s research is divided into three programmes – drilling, logging and sensing, and targeting. In the first is its flagship project, the development of a coiled tubing (CT) drilling rig, where a continuous coil of drill string is wound from a spool during drilling and then wound back as the string is brought back out of the hole, unlike the traditional approach where drill rods have to be connected and disconnected repeatedly during drilling.

Drilling

By removing the need to use separate drill rods, a CT rig makes drilling more cost-effective and safer and, since it allows a smaller drill pad and fewer vehicles to be used, its environmental impact is lower. DET CRC’s target is to develop a rig that weighs less than 10 tonnes and is capable of drilling 500-metre holes at a cost of about US$50 a metre – less than half that of conventional diamond drilling.

The technology that underpins it is already proven, having been used in the oil industry for more than 20 years, but it has to be modified for use in the harder rocks it will encounter in mineral exploration. To this end, DET CRC is experimenting with tubing made from carbon- and glass-fibre composites, among other materials but, as David Giles, a programme leader at the centre, explains, ‘We are keeping our options open for as long as we can, as there is unlikely to be a one-size-fits-all solution. Different materials have properties that might mean they are useful for specific tasks.’

Logging and sensing

In the logging and sensing programme, the centre is developing a suite of downhole sensors and a pair of platforms on which to mount them – what it calls the AutoSonde and the Autonomous Shuttle. Giles says, ‘Ultimately, we would like to see a broad range of primarily geophysical sensors that could be mounted on the AutoSonde or the Shuttle. Our most mature sensor is a gamma radiation counter. We are also working on an electromagnetic sensor and a sensor to determine seismic properties.

‘With these sensors we hope to be able to measure several things – total gamma radiation, concentration of radioactive elements, density, magnetic susceptibility, seismic wave speeds and seismic impedance. All of these are key properties with which to reconcile downhole data with regional- to prospect-scale geophysical data.’

As for the platforms, he adds, ‘The AutoSonde is deployed inside the drill rods at the completion of drilling, the sensors protrude through the drill bit and logging takes place while the rods are removed from the drill hole. By contrast, the Shuttle sits behind the core barrel and logs while drilling. Each platform has its strengths and weaknesses, but the key advantage is that logging is part of the drilling process rather than requiring a separate deployment.’

Targeting

In the third programme, one of the main objectives is to design and build a sampling and analysis platform called Lab-at-Rig, which will use drill cuttings returned to the surface to produce on-site and near real-time geochemical and mineralogical data about the rock mass being drilled. As Giles explains, ‘There are many advantages in dealing with a physical sample at the surface for geochemistry and mineralogy. The main one is pushing the precision and accuracy of the analyses as far as we can. Another is the ability to archive a sample for future reference.

‘On the other hand, geophysical logging is easier to do downhole – compared to chemistry and mineralogy – and there is an advantage in sensing a volume of material around the drill hole, rather than a small sub-sample. There may also be circumstances in which the geophysical sensors provide enough information to drive decision-making, and we don’t need to do anything with the physical sample.

‘Our aim with the Lab-at-Rig is to provide rapid results that can drive decision-making during the drilling deployment. Obviously we are striving to get the best quality analytical results possible, but there will be circumstances where the accuracy and precision of lab assays will also be required. A scenario that is very easy to imagine is that the Lab-at-Rig results are used to identify a subset of samples that require further work. However, whatever we do, the material we displace from the hole will have to come to the surface – it’s just a matter of what we choose to do with it.’ 

In whatever way the data is generated, the full system will then be able to transmit analysis results to a decision-maker anywhere in the world, so long as communications are available. Which comms to use will depend on the circumstances – for many remote operations it is likely to be by satellite, but closer to home the mobile network should be sufficient for most of the data. Power will come from a diesel generator, as standard in the industry. 

Full real-world deployments of all these technologies are still a couple of years off, although in February 2015 DET CRC signed its first commercialisation agreement with Boart Longyear, for the AutoSonde technology. At the announcement, Kent Hoots, Senior Vice President of Boart Longyear’s products division, said, ‘The primary focus for the introduction of this technology will be initially for diamond coring, but there will be additional opportunities for its introduction in reverse circulation and mud rotary drilling. It is anticipated that the tool will be commercially available in late 2015.’

In a parallel strand of development, in June 2015, a collaboration between DET CRC and a group of mineral explorers and research institutes was announced that will see them undertake a drilling programme in the eastern Gawler Craton Olympic Copper-Gold Province, in the northern Eyre Peninsula – an area regarded by many as one of South Australia’s key emerging mineral provinces. It will see technologies including the AutoSonde and Lab-at Rig being rolled out in a real-world setting to explore for base and precious metals.

The work of the DET CRC is a cross-stakeholder response to a pressing – and growing – need, and in an industry that’s historically cautious and conservative in its approach to embracing new technologies, the fact that these emerging systems are based at least in part on proven equipment, and developed ‘in-house’, should make them a new and attractive option for mineral exploration.