Abstract

Decarbonising our energy and transport systems is a major challenge for addressing the climate crisis. This will require a whole range of different raw materials including critical elements associated with LCT granites and pegmatites (Linnen et al., 2012). However, at the moment we are lacking a solid understanding of how and where LCT melts form which also means reliable geological exploration models don’t exist.

Geochemical characterisation of LCT granites and pegmatites shows (re-)melting of continental crust as the source (Černý et al., 2012). Which means metamorphism and partial melting are an essential process in the formation of LCT melts. The classical model assumed the onset of muscovite melting to be the key process. As micas are known hosts of critical elements (e.g., Li, Be, V, Rb, Cs, Sn, Ta, W) and would release their trace elements into a relatively small volume of melt, which creates enriched melts. These melts would be further enriched during fractional crystallisation finally creating element concentrations of economic interest. Contrary to that theory a study on whole rock compositions (Wolf et al., 2018) and of metamorphic micas from greenschist to granulite facies conditions (Kunz et al., 2022) have shown that biotite is the major host of elements associated with LCT melts. This raises the question if (1) biotite melting might be the essential process for producing LCT enrichment and (2) under which partial melting conditions this would create the highest critical element enrichment.

Over the last couple of years, a number of studies have started to address these questions ranging from natural observations to modelling and partial melting experiments. Some of the key questions and challenges at the moment are: (1) is an enriched sedimentary source needed?; (2) what is the importance of the melting conditions/reaction for enrichment?; (3) overcoming limitations of natural and experimental research approaches and (4) developing robust input parameters for partial melting modelling.