Sulfide-olivine Fe-Ni exchange and the origin of anomalously Ni-rich magmatic sulfides

摘要

Equilibration between sulfide liquid and olivine is expressed in terms of the exchange coefficient for Fe and Ni,KD = (XFeS/XNiS)sulfide_liquid / (XFeO/XNiO)olivine.The positive dependence of KD on Ni+Cu content of sulfide liquid has been demonstrated experimentally,and gives rise to a critical non-linearity in the relationship between sulfide and olivine-saturated silicate liquid compositions.This effect has been modelled quantitatively,using an empirical best fit to available experimental data as a parameterisation of the KD variability.It is shown that it is a key factor in giving rise to extremely Ni-rich sulfides as exemplified by disseminated magmatic sulfide ores at Betheno (Western Australia) and Mirabela (Brazil).