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

2002; Mineralogical Association of Canada; Volume: 40; Issue: 5 Linguagem: Inglês

10.2113/gscanmin.40.5.1451

1499-1276

Alexandre Raphael Cabral, Bernd Lehmann, Rogerio Kwitko-Ribeiro, C. H. C. Costa,

Geochemistry and Elemental Analysis

The Serra Pelada garimpo (1980)(1981)(1982)(1983)(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 ("Au 7 Pd"), Hgbearing palladian gold (Au-Pd-Hg), Pd-bearing gold with up to 3 wt.%Pd (Pd-poor gold) and pure gold.A number of platinumgroup 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.