Reassessing the source controls of Ni sulfide mineral systems

The composition of magmatic sulfide deposits is controlled by the metal budget of the magma, which itself is controlled by the composition of the mantle source and degree of partial melting. Traditional models assume that high degrees of partial melting (>15%) are required to sufficiently liberate Cu and PGE from sulfide and Ni from olivine, assuming peridotitic mantle rocks. However, we show that hydrous pyroxenite in the mantle hosts Ni and other critical metals in minerals such as phlogopite and amphibole, which have significantly lower melting temperatures than olivine. We propose a classification of magmatic sulfide deposits that reflects (1) the source composition; and (2) the melting regime. We show that Ni-fertile magmas may be formed in a broader range of geotectonic settings than previously thought if sourced from metasomatised mantle, opening up exploration search spaces for critical battery metals.