Palladseite and its oxidation: evidence from Au-Pd vein-type mineralization (jacutinga), Caue iron-ore mine, Quadrilatero Ferrifero, Minas Gerais, Brazil

Palladseite (palladium selenide) and palladian gold occur as euhedral inclusions infill of microstructures and interstices in magnetite aggregates (host rock fragments) within specularite- auriferous veins (jacutinga) Palladseite has minor amounts of Pt (0.6-3.5 wt.%), Hg (0.9 1,9 % wt.%), and Ag (0.3-0.5 wt.%). The palladian gold contains up to 6 wt.% Pd. and minor Cu and Ag. Isomertieite (Pd11Sb2As2) and sudovikovite (PtSe2) are also recorded. The veins cross-cut the main tectonic Coliation of the wallrock (itabirite). The feature of fracture infill and the Sc-Sb-As-Hg-Cu-Ag geochemical mineralogical signature of the Au-Pd mineralization point to it post-ductile deformatation and possibly low-ternperature (epithermal) origin of the jacutinga mineralization style. Palladseite is replaced locally by a Pd-rich oxidation phase. Electron microprobe analysis of alteration halos around palladseite yields 76-80 wt.% Pd. Oxygen calculated by stoichiometry accords with a monoxide compound of the type PdO. However, the measured oxygen content is lower than expected fior the PdO stoichiometry suggesting loss of volatile species. and a more 'hydrated' compound, such as an oxyhydroxide.