Fluorine and PGE-Au elevated signature of alkaline magmas from the Yilgarn Craton: insights into mantle fertility

Our current understanding of the nature of the mantle, under the Archean Yilgarn Craton, Western Australia is predominantly based on the image provided by a number of geophysical datasets and on the radiogenic isotope (e.g., Lu-Hf, Sm-Nd) composition of granitoid and ultramafic rocks. The PGE-Au signature of deeply sourced alkaline magmas may provide key insights into the metallogenic fertility of the mantle underlying the Yilgarn Craton. The Yilgarn Craton contains various types of alkaline rocks, including calc-alkaline lamprophyres (CAL), ultramafic lamprophyres (UML), carbonatites, orangeites and kimberlites. The PGE patterns of the CAL exhibit elevated (Pd/Ir)_N ratios, whereas the other rock types are characterised by less fractionated PGE patterns, with lower (Pd/Ir)(N) ratios. In general, most alkaline magmas from the Yilgarn Craton appear to be anomalously enriched in Au. Furthermore, their key constituent magmatic minerals, such as amphibole, mica and apatite are anomalously enriched in F, and S. These volatiles may play a crucial role in the transport and concentration of precious metals from the mantle into the crust, contributing to explaining its exceptional metal endowment.