Evaluating the Utility of Principal Component Analysis on EDS X-Ray Maps to Determine Bulk Mineralogy

Due to advances in EDS technology, electron microscopy techniques have become an important tool to determine the relative abundance of mineral phases. However, few studies have directly compared EDS X-ray mineralogy with traditional techniques for assessing bulk mineralogy and elemental composition. We show that analysing a limited area (similar to 0.5-3.2 mm(2)) of fine-grained metal extraction samples using EDS X-ray principal component analysis phase mapping yields results that agree within 10% with more traditional techniques for mineral phases present at greater than 5%m/m. Electron beam sensitive minerals, such as the carbonates, have poor correlations between EDS and X-ray Diffraction (XRD) and/or WD-XRF. Likewise, poor correlations between methods can be expected for particles that are smaller than the interaction volume of the electron beam (similar to 1.5 mu m); this strongly affected the phyllosilicates. One strength of EDS phase mapping is that it can identify phases present below the detection limit of powder XRD (< 1%). Our results demonstrate that EDS phase mapping is sufficient to estimate bulk sample mineralogy. If polished thin sections have been prepared, this approach may save time and/or money relative to the more traditional approaches of preparing separate subsamples for XRD and/or WD-XRF.