Previous S isotope works suggested that the Mount Keith and Cliffs komatiite hosted Ni deposits in the Yilgarn Craton of Western Australia formed in different volcanic environments. The Mount Keith deposit was interpreted to have formed near the komatiite vent and a VMS style S source in the felsic volcanic substrate, whereas the Cliffs deposit formed at a distal position on a basaltic substrate. It was inferred that the felsic stratigraphic substrate at Mount Keith was more prospective than the mafic substrate at Cliffs. However, recent modelling of metal upgrading during transport of assimilated crustal sulfides in komatiites indicates a positive relationship between the travel distance and the resulting metal tenors of the deposited sulfides (Yao and Mungall, 2021). This relationship has not been observed between the Mount Keith and Cliffs deposits. New S isotope data from the Cliffs Ni deposit confirm the presence of a VMS style source in the immediate footwall to the deposit. We suggest that the Cliffs Ni deposit also formed in a rift environment, proximal to its crustal S source. This implies that rift environments where bimodal magmatism occurs, mafic-hosted systems may be as prospective as felsic-hosted ones, significantly increasing the search space for high-tenor mineralisation associated with komatiites. The proximity of the Ni deposits to their crustal S sources for both mount Keith and Cliffs emphasises the importance of complex flow dynamics and multistage entrapment and re-entrainment of assimilated and transported sulfide droplets over extensive lateral flow and distal deposition of sulfide mineralisation. 

Reference(s)

Yao Z-s, Mungall JE (2021) Kinetic controls on the sulfide mineralization of komatiite-associated Ni-Cu-(PGE) deposits. Geochimica et Cosmochimica Acta 305:185-211. doi: https://doi.org/10.1016/j.gca.2021.05.009