Palladium-oxygenated compounds of the Gongo Soco mine, Quadrilatero Ferrifero, central Minas Gerais, Brazil

摘要

New data on the Gongo Soco palladium-oxygenated compounds are presented for the first time since the work of Johnson and Lampadius (1837). A variety of PdO species is documented, always in association with Cu, Fe and Mn, and includes Pd(OH)_2 or PdO.H_2O, and phases with metal excess in relation to oxygen, interpreted as metastable. Their remarkable occurrence in 'ouro preto' (black gold) and jacutinga (auriferous itabirite/iron ore) is the result of mertieite-II alteration. It involves leaching of Sb and As, limited removal of Pd, and incorporation of Cu, Mn and Hg into PdO species. The locus of Hg-bearing PdO species in microfractures parallel to the enclosing gold-mineralized shear band suggests at least one low-temperature hydrothermal generation. The presence of a halite crystal attached to gold testifies to the involvement of Cl-saturated hydrothermal fluids in the oxidizing environment of jacutinga formation.