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Quantitative mineralogy plays a vital role in exploration geology by defining mineral assemblages, identifying metal-bearing phases, and providing clues to optimize ore processing. In peraluminous rare-metal granites such as those at Beauvoir (France), mineral quantification is challenging, especially in altered facies where partial replacement complicates the estimation of muscovite and feldspars. The present study applies micro-X-ray fluorescence (micro-XRF) to quantify mineral assemblages of the Beauvoir granite. Modal abundances were compared with normative proportions derived from whole-rock geochemistry. In fresh facies with Li contents between 4000 and 6000 ppm, albite and quartz dominate (~40% and 25%), respectively, while lepidolite averages 20%–25%. During alteration to greisen, feldspars and lepidolite are partly replaced by muscovite, reducing lepidolite by up to threefold and increasing muscovite to ~30%. The obtained results demonstrate that micro-XRF provides a fast and reliable method for quantifying mineral distributions in rare-metal granites. Combined with complementary microscale techniques, quantitative mineralogy offers a powerful approach to characterize Li-bearing granites, assess alteration intensity, and improve predictions of ore quality and processability.
Kahou et al. (Fri,) studied this question.