Magmatic Controls on the Genesis of Ni-Cu±(PGE) Sulphide Mineralisation on Mars

The Martian crust is dominated by igneous rocks, some of which showing striking mineralogical, petrographical and chemical similarities with terrestrial komatiites and ferropicrites. Given the fact that these terrestrial magmatic systems are usually the host of Ni-Cu +/-(PGE) sulphide mineralisation, this study aims at unravelling the potential for similar mineralisation to have formed on Mars. Focus is laid on the crucial magmatic factors that dictate mineralising events: a) the precious metal and sulphur fertility of mantle sources and derived partial melts, and b) the capacity of magmatic systems to reach sulphide supersaturation and sulphide liquid segregation. Martian mantle melts are calculated to reach sulphide saturation likely within 30 wt% crystal fractionation; a value comparable to that calculated for the mineralised ferropicrites at Pechenga, Russia. The majority of mineralised komatiites and ferropicrites formed due to the assimilation of crustal sulphur, thus promoting the segregation of precious metal-rich sulphide liquids at early stages of melt evolution. The Martian crust is strongly enriched in sulphur. Sulphur-rich lithologies range from sulphide-bearing magmatic rocks to sulphate-rich regoliths and sedimentary deposits. It is proposed that channelled lava flows, which potentially assimilated sulphur-rich substrate, may have led to the formation of Ni-Cu +/-(PGE) sulphide mineralisation on Mars.