PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au–Pd–Pt DEPOSIT, CARAJÁS MINERAL PROVINCE, NORTHERN BRAZIL

The Serra Pelada garimpo (1980–1984) was the site of the most spectacular gold rush in recent history, but the mineralogy of the bonanza-style mineralization has not so far been documented in detail. Rediscovery of an early drill-core, recovered in 1982 from the near-surface lateritic portion of the garimpo area, has provided coarse-grained gold aggregates for this study. The centimeter-long aggregates of gold occur in powdery, earthy material. They exhibit a delicate arborescent fabric and are coated by goethite. Four compositional types of gold are recognized: palladian gold with an atomic ratio Au:Pd of 7:1 (“Au7Pd”), Hg-bearing palladian gold (Au–Pd–Hg), Pd-bearing gold with up to 3 wt. % Pd (Pd-poor gold) and pure gold. A number of platinum-group minerals (PGM) are included in, or attached to the surface of, palladian gold: “guanglinite”, Sb-bearing “guanglinite”, atheneite and isomertieite, including the noteworthy presence of Se-bearing PGM (Pd–Pt–Se, Pd–Se, Pd–Hg–Se and Pd–Bi–Se phases, and sudovikovite and palladseite). They define an As–Sb–Hg–Se mineral assemblage typical of hydrothermal vein-type deposits formed at relatively low temperatures. Native palladium, characteristically situated in the goethite coating, is intimately associated with a Pd–O phase. The remarkable occurrence of native platinum associated with Pd-bearing gold, PGM (compositionally close to mertieite-II and isomertieite) and berzelianite from a nearby prospect (Elefante prospect) is also recorded