Gold found for the first time at Timbopeba, an iron-ore mine in the Quadrilátero Ferrífero of Minas Gerais, is characterised as "ouro preto", or black palladiferous gold. The gold comes from haematite-bearing veins which truncate the host iron formation, i.e. itabirite.
Its black colour originates from a dark coating consisting of iron oxides, haematite and goethite, and Pd-O phase(s). The Pd-O component of the dark coating occurs on palladium minerals located on the surface of palladiferous gold. The Pd-O coating has desiccation cracks, which represent the
early stage of a deoxygenation-dehydration process from a Pd-O-H phase towards native palladium. The discovery of "ouro preto" provides argument for a systematic prospecting for gold not only at Timbopeba, but also in other iron-ore deposits of the Quadrilátero Ferrífero.
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