Rare and new compounds in the Ni-Cu-Sb-As system: first occurrence in the Gomati ophiolite, Greece

The Gomati ophiolite (Northern Greece) is located in the Serbo-Macedonian Massif, in the Hellenides orogenic belt. It consists of altered peridotites hosting scattered chromitite bodies. The ultramafics are enclosed in Silurian gneisses and schists, and are partially in contact with late Cenozoic granites. The present work focuses on accessory minerals in the Ni-Cu-Sb-As system, found in a chloritized clinopyroxenite in contact with chromitite. The electron microprobe analyses revealed the presence of known minerals such as orcelite (Ni5-xAs2) and breithauptite (NiSb) and new phases that cluster around the following compositions: Ni3As, Ni5(As,Sb)2, (Ni,Cu)5-x(Sb,As)2, (Ni,Cu)2(Sb,As), and (Ni,Cu)11(Sb,As)8. The compound (Ni,Cu)5-x(Sb,As)2 may correspond to a Cu-rich Sb dominant variant of this phase. A phase corresponding to (Ni,Cu)2(Sb,As) was first described in the Tulameen complex of Canada. A phase with stoichiometry Ni3As was formerly known as the mineral dienerite, later discredited by the IMA and only recently under revalidation. The compound (Ni,Cu)11(Sb,As)8 probably represents a Cu-rich Sbdominant analogue of the mineral maucherite (Ni11As8). The mineral assemblage in the Gomati ophiolite is puzzling. While ultramafic rocks contain Ni and As of magmatic origin, the presence of Sb, Ag, Au and Cu minerals could be indicative of a metasomatic enrichment, probably linked to the presence of fluids emanating from the granite body or a nearby porphyry copper mineralization.