Subscribe to resourceful magazine
These days many would argue that understanding ore at the micro scale is as important as the mine process itself. New technologies are transforming the small scale world with profound implications.
The extractive potential of a given deposit is about knowing its chemistry, mineralogy and texture, and how these impact processing. It's also about knowing what the ore might be mixed with, as well as its petrophysical properties – such as density and hardness.
All these things can be deciphered before a mine is even considered and it's why improvements in the science of geometallurgy are changing the landscape of mineral extraction.
"Geometallurgy can now reliably inform economic models around a mine that can help you to decide on its viability" CSIRO's research director for minerals processing, Chris Vernon, says.
Predictive geometallurgy to determine process options
Dr Vernon gives the very simple example of two similar copper deposits of roughly the same size and grade: are they of equal value and of equal interest to a mining company? Not necessarily.
"If one is tied up in chalcopyrite, which is a copper iron sulphide, and the other is an oxidised copper that is easily dissolved in acid, the geometallurgy will tell you to ignore the one that is harder to process and go for the one which is much easier," Dr Vernon says.
He offers another example: determining the viability of aluminium extraction from bauxite mines. The ore extracted from two potential sites might show similar elemental analysis, but this may not be enough information on which to base a decision to extract.
"Some alumina phases are quite refractory and need very high temperatures to extract the aluminium," Dr Vernon explains.
For example, at bauxite reserves in the Darling Range in Western Australia, aluminium can be extracted at low temperatures, making it a highly economic process.
One of the reasons that these bauxites were ignored when first discovered was a belief that the high silica level would make extraction too expensive.
"The geometallurgy work eventually found that the silica component was largely quartz, which can't be digested at low temperatures, whereas the alumina phases can," Dr Vernon says.
"This understanding meant that what looked like the world's worst bauxite was actually some of the best."
Next level resource characterisation facilities and techniques
At the cutting edge of geometallurgy, are the instruments and methods that do all the close-up detection work. These instruments offer chemical, textural and spectroscopic analysis.
Dr Louise Fisher, who leads CSIRO's minerals characterisation research program, says they are now in the process of developing a geoscience drill core laboratory that will take scanning technology to yet another level.
The work is challenging and Dr Fisher says that getting an elemental and contextual understanding of rock formation at a smaller scale often changes the assumptions made about how rocks are formed or what processes have occurred.
"The laboratory is allowing us to connect the understanding of domains recognised at mine-scale to wet chemical analysis results or detailed imaging data from scanning electron microscopes," Dr Fisher says.
"We will be seeking to understand what the metal of interest is doing in the drill core and what minerals it is associated with at a range of scales."
Imaging technology at the cutting edge
Among the specific new developments is the CSIRO-developed, one-of-kind Maia Mapper technology that can produce a detailed picture of a drill core of up to 50 centimetres with a pixel size of 30 microns (less than the breadth of a human hair), looking at the sample's texture and chemical composition using an intense, focused x-ray beam.
"It's a chemical mapping approach that has previously been deployed at a synchrotron. We have brought that into a laboratory setting, to create an instrument that allows us to chemically image drill cores with unprecedented scale (length) and with very high resolution."
Dr Fisher says it allows a full understanding of the variability of the sample, guiding subsequent sampling and investigation. One unique application of the technology is the ability to locate rare, minuscule particles of platinum and gold in-situ within the drill core and understand where they sit within the mineral assemblage.
"We can see what minerals these particles are in contact with and that information allows geometallurgists to assess processing options and determine whether the commodity is viable."
The importance of capturing reliable data
One might argue that the "art" behind the science of geometallurgy is having the foresight to collect all of the required data, and in ways where the datasets are connected enough that there is easy overlay between different properties.
There are still challenges to be overcome, says Dr Fisher, and most of these reside in receiving reliable data. There is plenty of legacy data that's not easily accessible.
For scientists to have "the full picture" it's important to have information from a number of different sources, processes and characterisation tools, over multiple scales, she says.
"We need these to be made available in ways that are acceptable to any potential user," Dr Fisher says.
"We need interoperability of data and we need to make sure we can get it on an ongoing basis."