THERMODYNAMIC MODELLING CONSTRAINTS ON LITHIUM ENRICHMENT IN FELSIC PEGMATITES. DOES ENRICHMENT OCCUR AT THE FINAL STAGES OF FRACTIONAL CRYSTALLISATION OR DURING THE EARLY STAGES OF ANATEXIS?

Lithium is a critical metal required for future clean energy technologies. Emerging clean energy technologies in particular require a significant amount of new resources that have to be mined at least until enough resources are present in the recycle chain to reduce the need for virgin material inputs. Currently most lithium is mined from low concentration spatially extensive brine deposits however small-scale high concentration granitic pegmatites provide a potential alternative that is globally distributed providing strategic advantages with less susceptibility to supply chain disruptions.

Critical metal enriched LCT pegmatites are customarily considered to be the products of extreme differentiation through fractional crystallization from a peraluminous granitic parental magma of S-type affinity where incompatible lithium is concentrated in the final liquids left after fractional crystallisation. This model has been recently challenged based on field and geochemical observations as it implies the occurrence of a temporal and spatial association between granites and their pegmatites as well as a simple geometric relationship between them. that is rarely documented. In an alternative anatectic pegmatite model, low grade partial melting of metapelites produces highly peraluminous, incompatible element-rich melts that are chemically similar to the highly evolved terminal products of magmatic differentiation of S-type granites.

Recent advances in phase equilibria modelling that allows open system models to be considered and new plugins that enable trace element partitioning in the modelling tool Rcrust (www.tinyurl.com/rcrust) provide insights into the pressure and temperature conditions during pegmatite formation and lithium enrichment. Careful studies of trace element chemistries and modelled partitioning elucidates key information on the processes of enrichment which informs future exploration studies of the conditions required to form mineralised pegmatites. This study provides a compelling case for the use of advanced petrological techniques to inform resource exploration.