Mineralogy of sulfides from certain Hawaiian basalts

Polymineralic sulfide grains, composed principally of Fe sulfide and Fe-Cu sulfide, with magnetite, have been studied mineragraphically and by electron probe, and interpreted in terms of experimental data for the system Fe-Ni-Cu-S. The three main phases are monosulfide solid solution, a Cu-Fe sulfide (solid solution) with composition near cubanite, and Ti-free magnetite. The grains are believed to represent phases unmixed from an immiscible liquid phase in the basalt magma. Compositions of the two main sulfide phases suggest quenching below 700 degrees C. Most of the Ni has been retained in the monosulfide solid solution by rapid quenching.