PGE distribution in Fe-Ni-Cu sulfides from the Potosí mine (Eastern Cuban Ophiolites)

Abstract

Unusual sulfide-rich chromitites of the Potosí mine are hosted in the Moho Transition Zone (MTZ) of the Moa-Baracoa ophiolite. Bulk-rock compositions of samples of these sulfide-rich chromitites are characterized by flat chondrite-normalized PGE patterns due to enriched Pt and Pd. A positive correlation between PGE content and increasing abundance of sulfides (mainly Co-free pentlandite, pyrrhotite, cubanite and chalcopyrite) is observed. However, LA-ICP-MS analyses on different sulfides exhibit low PGE contents, which cannot explain the general PGE abundance in the sulfide-rich ore. All analyses of sulfides are strongly depleted in Pt. Interestingly, many pentlandite grains host visible nano- to micrometric crystals of sperrylite. Textural observations together with new analytical data reported in this contribution suggest that sperrylite has crystallized from a Pt–arsenide-saturated melt, prior or contemporaneous with the crystallization of the sulfide melt from which the base metal sulfides were crystallized.