Downhole data without delay

A new on-the-spot tool for analysing elements underground has saved a major mining company millions of dollars on drilling and assay costs. TIM TREADGOLD reports on how the industry can take advantage of this new development.

Time is money in any business and one reason why the mining industry has embraced a technology that eliminates the weeks, and sometimes months, it can take to receive assay results from exploration and mine development drilling.

Another reason is that fast assay results means that drilling can quickly sterilise areas that do not contain economic mineralisation, or accelerate the focus on potentially ore-rich targets.

Speed and accuracy are the keys to a technology developed by CSIRO with its French partner, Sodern, a nuclear-science arm of the aircraft manufacturer Airbus.

“FastGrade is a technology that hits all the right points for a mining company,” says Mining3 research program director from CSIRO, Stephen Fraser.

“After a hole is drilled, it saves time waiting for assays to be returned from a laboratory because the results with FastGrade are available immediately.”

The key to the technology is the way it pulses neutrons deeply into the rock surrounding a borehole. The data generated can be quickly analysed to provide a detailed picture of the elements in rock up to 50 centimetres from the hole.

French nuclear technology is amongst the most advanced in the world with a history that dates back to the mother of research on radioactivity, Marie Curie. The French have pioneered the use of neutrons in a process called pulsed fast and thermal neutron activation (PFTNA), which avoids the use of radioactive isotopes.

Earlier underground element analysis tools did use radioactive material, which made it difficult to handle in a field environment and required strict quality and safety control.

Sodern’s system is based on the use of an electrical source that poses no radiological risk for the environment if the tool is lost in a borehole – which has been known to happen.

CSIRO’s contribution to the ground-breaking technology behind FastGrade has been in designing and building the tool.  It’s inserted into a borehole as a piece of equipment measuring some three-and-a-half metres and consisting of three distinct parts.

“The probe lowered into a borehole contains an emissions module comprising Sodern’s Sodilog tube, which is a miniaturised particle accelerator in a ceramic body,” Mr Fraser says.

“Behind that sits a detection module that accommodates a scintillation crystal.  This is synchronised with the Sodilog unit to measure the gamma rays emitted from different elements after they’re hit with neutrons.

“At the top end of the tool, is the service module that’s designed as the communication and power interface for the logging tool and is connected to the surface via a 240-volt power link.”

As the nucleus of most elements gives off a unique gamma-ray signal, when activated by neutrons, the FastGrade tool can quickly measure the distribution of iron and other elements in rock surrounding the borehole.

In BHP Billiton’s case,  they’re looking for iron ore  around their  Newman mining centre, which  means the tool is calibrated to identify and  measure the  levels of iron ore  and  other elements important to mining iron ore,  including deleterious elements.

“Because neutrons and gamma rays used in PFTNA are energetic particles, they are able to penetrate the material surrounding the borehole by up to 50 centimetres. This is a far better sample area than simply assaying what comes out of the hole during drilling,” Mr Fraser says.

Sodern describes FastGrade as a major breakthrough in conventional core sampling, doing away with the costly extraction of cores as well as the transport and preparation of samples for assays – not to mention the time lost in waiting for assay results.

“Moreover, the analysis will be much more accurate and will be available in real time,” Sodern has stated.

Use of the FastGrade tool is expected to spread across the mining industry following a well-received technical paper presented by Sodern at a mining conference in Canada last March.

Sodern prefaced its paper by saying that: “in-situ borehole elemental analysis is a new driver of productivity for exploration”.

The tool itself has been designed to be lowered into 14 centimetre holes drilled by a low-cost reverse circulation rig as used in most mining areas around the world.

Because the data from FastGrade flows immediately to the surface, it can be quickly analysed in the field. Not only is an accurate assay recorded, but so too is the depth of what’s being analysed, enabling a quick assessment of an exploration or mine development target.

Mr Fraser says FastGrade is being recognised by industry as a tool that saves time, while also providing an accurate picture of underground elemental composition.

“It’s opening up opportunities to accelerate the flow of information and that means it will enhance the productivity of mining and exploration,” he says.

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Originally published in CSIRO’s resourceful magazine