Dendritic palladian gold from Serra Pelada, Brazil (SEM image)


The formation of Pt-Pd nuggets is not well understood.Córrego Bom Sucesso in the the Serro mining district of Minas Gerais, Brazil, is famous for historical Pt-Pd nuggets, as well as for gold and diamond which all occur in the same alluvia. The alluvial Pd-Pt-Au mineralization occurs as botryoidal Pd-Pt nuggets and delicate palladiferous gold aggregates in clastic and organic-rich valley infill on quartzite and hematitic  rocks  of  the  Paleo-  to  Mesoproterozoic  Espinhaço  Supergroup. We studied this area geologically and mineralogically, and delineate an approximately 240-km-long, north-trending Au-Pd-Pt belt, which hosts hydrothermal Pd-Pt−bearing gold mineralization in its southern part (Quadrilátero Ferrífero and Itabira district) and alluvial Pd-Pt-Au mineralization in its northern part (southern Serra do Espinhaço). The hydrothermal  Pd-Pt−bearing  gold  mineralization,  locally  known  as  jacutinga,  occurs  as  late-orogenic  quartz-hematite-(talc-kaolinite) veins, which truncate the Brasiliano regional tectonic foliation of the itabiritic host rocks of the Paleoproterozoic Itabira Iron Formation. The  Au-Pd-Pt  belt  follows  the  regional trend of major thrust faults related to the ~0.6 Ga Brasiliano orogeny, and the hydrothermal jacutinga mineralization  could  be  regarded  as  an  oxidized  variant  of  the  orogenic  gold  deposit  spectrum.  Secondary botryoidal and arborescent Pt-Pd aggegates and primary (detrital) Au-Pd grains are peculiar to the alluvial platiniferous deposits of the northern part of the belt in the Serra do Espinhaço. We suggest that their source was jacutinga-style vein mineralization, as deduced from abundant detrital hematite and rutile, and the discovery of detrital hongshiite, a Pt-Cu alloy that forms bonanza pockets within jacutinga at Itabira. We suggest that the botryoidal Pt-Pd aggregates grew in situ by electrochemical metal accretion from dilute solutions carrying Pt and Pd from the dissolution of detrital Pt-Pd minerals from jacutinga. The  connection  between  jacutinga  and  platiniferous  alluvia  indicates  that  there  is  a  prospective  trend  of about 240 km for Pd-Pt−bearing gold mineralization reaching from Ouro Preto to Diamantina. The very high oxidation state required for efficient low-temperature aqueous mobilization of Pt, Pd, and Au was apparently controlled by the quartzitic and hematitic rocks in the Serra do Espinhaço, but not in the southern belt where greenstone rocks buffered fluids to moderate pH and lower oxidation states.

(DFG project LE 578/29-1)


Cabral AR, Lehmann B, Tupinambá M, Schlosser S, Kwitko-Ribeiro R, de Abreu F (2009) The platiniferous Au-Pd belt of Minas Gearis, Brazil, and genesis of its botryoidal Pt-Pd aggregates.

Economic Geology 104: 1265-1276



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