Tungsten West
Using Energy Dispersive Spectroscopy to identify variations in ore minerals
About Tungsten West
Based in South Devon, UK, Tungsten West plc is restarting the Hemerdon mine tungsten-tin deposit - the world's 2nd largest tungsten resource.
We worked with Tungsten West as part of our ERDF & University of Plymouth funded Plymouth Materials Characterisation Project, using Scanning Electron Microscopy and Energy Dispersive Spectroscopy to explore the ore mineral textures and geochemistry of their tungsten and tin minerals. This will optimise tungsten and tin concentrate recovery through their Mineral Processing Facility when they go into production.
Our Aim
The aim of this project was to identify variations within the ore minerals that may affect its recovery through the mineral processing facility at Tungsten West, and assess the rocks by their mineral properties, expanding upon geochemical assay assessment of the ore deposit. To do this, we prepared and carried out SEM-EDS on multiple areas of interest selected through rock cores using our JEOL IT800 FEG-SEM.
The Geology and Metallurgy departments at Tungsten West plan to use mineralogy to assess in-situ rocks as well as on-stream assessment of the various products and staged products they produce in order to understand how the minerals and geology vary, furthering their understanding of the orebody and metal recoveries.
Initial Investigations
For each sample, we started our investigations using the backscattered electron (BSE) detector. This detector allows us to visualise where elements with a larger atomic density occur across the sample by heavier elements appearing brighter and lighter elements appearing darker in a greyscale image (see on the right).
For this project, the minerals of interest were atomically heavy, such as wolframite (tungsten-rich), so these BSE images meant we could easily pick out where the minerals of interest occurred across the sample.
Compositional analysis
Once areas of interest had been identified using BSE, we could take the analysis a step further and start analysing the composition of the mineral phases. Using Energy Dispersive Spectroscopy we produced X-ray element maps (left) of the sample, where the detector would identify where each element is occurring across a sample site and assign each element a colour, so you can easily visualise where these elements are. The benefit of EDS is that this technique also quanitifies how much of each element is present in each site which means we can work out which mineral each phase is based on their composition.
For these samples, we were able to identify minerals such as arsenopyrite, wolframite and bismuth.
Large Area Mapping
This was also carried out at a much larger scale using the Large Area Mapping function on our JEOL IT800 FEG-SEM. This meant we were able to produce whole sample X-ray element maps, allowing us to identify where each element occurred across the entire sample and combine these maps together to then work out the distribution of each mineral across the sample. We were able to use these maps to work out which elements were often associated with each other, which could then be quantified in future analyses using Automated Mineralogy.
On the left is an example of these layered element maps, where yellow is wolframite, green is Fe-rich wolframite, dark green is quartz and pink is tourmaline.
