The Hübnerite/Ferberite ratio as an exploration tool for W-deposits

Abstract

is now possible to focus X-rays to a small spot size using a polycapillary lens, and accordingly a microX-ray fluorescence (XRF) system can be operated using similar parameters as an e-beam system and thus yield results compatible with traditional automated mineralogical analysis. Micro-XRF systems have distinct advantages over e-beam based systems in that the sample preparation is simpler (sample cut to have a surface plane parallel to chamber table and no carbon-coating required) and that larger samples can be analysed (33 × 17 × 12 cm in dimension, with the maximal analysis area being 20 × 16 cm). In addition, the X-ray source yields a spectral excitation with significantly lower limits of detection. However, e-beam based systems are able to obtain a smaller beam size. As with traditional automated mineralogical systems, there are fundamental parameters that impact on the mineralogical classification and analytical time; this includes (but is not limited too) X-ray beam excitation (kV and μA), detector active areas (mm), pixel spacing (μm) and dwell time (ms). Rare Earth Element (REE) bearing samples are important from a strategic and political perspective, and are on the European Union’s list of critical raw materials. To confirm the micro-XRF’s applicability, a variety of REE case studies are presented, including samples from an ion adsorption REE deposit and from a REE-bearing carbonatite. The samples were analysed using a Bruker M4 TORNADO system. Figure 1 is an example of the analysis of an REE-bearing protolith from an ion adsorption deposit. These samples are described in detail in Menzies et al. (2015). The sample is dominated by the silicates of quartz, plagioclase, garnet and biotite, and also contains the REE-bearing mineral allanite, as well as monzonite and xenotime, whose concentrations are minor (<0.5 mass%). Once identified, it is possible to do point analyses on these minerals and accurately quantify the various REE. This is especially important in understanding the ratio of light-to-heavy REEs, as the later are economically more desirable. The identification of these REE-bearing minerals is important in understanding the geological processes and potential REE enrichment in other parts of the deposit as well as providing key information for the mineral processing cycle.