Experimental constraints on the sources of lithium-rich granites and pegmatites

Abstract Rare-metal granites and pegmatites are enriched in critical metals, such as lithium (>5000 ppm), relative to conventional granites in the crust (<100 ppm). The petrogenesis of lithium-bearing pegmatites has been historically associated with the high-degree fractional crystallisation of parental granites. However, the extent of lithium enrichment during this process remains debated due to uncertainties concerning the partitioning behaviour of lithium between minerals and felsic melts. Alternatively, lithium enrichment in granitic pegmatites may reflect the composition of their crustal source. To test the anatectic origin of rare-metal granites and pegmatites, partial melting experiments were performed on variably enriched metasedimentary rocks (100–800 ppm lithium). The experiments produced felsic melts with a lithium content of 180–2200 ppm and constrained mineral-melt partition coefficients for granitic systems. Trace element modelling demonstrates that high-grade granite-related deposits (>5000 ppm lithium) are sourced from the anatexis of enriched crustal rocks (>300 ppm lithium), followed by the moderate fractional crystallisation of the partial melts.