Transport and reaction of light elements in pegmatitic systems at thermal disequilibrium – first insights from an experimental approach

The transition from fossil towards green energy sources is one of the major challenges for our society. In order to accomplish this, large amounts of lithium are necessary as a component in Li-ion batteries. Such resources can be obtained from pegmatites. These magmatic rocks are often associated with highly fractionated granites and are therefore abundant all over the globe. Rare-element pegmatites, a sub-group of pegmatites, are often strongly enriched in Li and B and a variety of strategic elements (e.g. Ta, Nb, Be, Sb, W). There are many models for the formation of such pegmatites, however, the mechanisms leading to strong metal enrichment are yet poorly constrained.

With our experimental study we want to address, whether Li and B isotopes can be used as tracers for magmatic and hydrothermal processes in pegmatites. For this purpose, we investigate the isotope fractionation of Li and B during the interaction between a pegmatitic melt and a fluid phase in a closed system. We have developed an experimental setup, where melt and fluid coexist. Diffusive transport is directed from the pegmatitic melt through an aqueous fluid into a sink (e.g. aluminosilicate melt or muscovite). To mimic natural conditions, temperature gradients ≤ 10 K/cm along the sample can be adjusted. First results of associated diffusion couple experiments show that Li diffusion is 1) several orders of magnitude faster than B and 2) insensitive to melt composition. B diffusion, on the other hand, strongly depends on melt composition and is mainly controlled by melt viscosity.