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

Abstract

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 (Ni 5 As 2 ) and breithauptite (NiSb) and other new phases that cluster around the following stoichiometries: (Ni,Cu) 7 (Sb,As) 3 , (Ni,Cu) 2 (Sb,As), (Ni,Cu) 11 (Sb,As) 8 , Ni 3 As, Ni 5 (As,Sb) 2 and Ni 7 (As,Sb) 3 . As orcelite is a non-stoichiometric mineral, (Ni,Cu) 7 (Sb,As) 3 , Ni 5 (As,Sb) 2 and Ni 7 (As,Sb) 3 may correspond to Cu and/or Sb-rich terms of this phase. A mineral phase corresponding to (Ni,Cu) 2 (Sb,As) was first described in the Tulameen complex of Canada. A phase with stoichiometry Ni 3 As was found in the Bon Accord oxide body of South Africa. The (Ni,Cu) 11 (Sb,As) 8 probably represents a Cu-rich Sb analogue of the mineral maucherite (Ni 11 As 8 ). Such 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 in contact with the Gomati ophiolite.