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Boron, Metasomatism, PdPt, Gold–palladium belt, Minas Gerais, Brazil
Abstract:
The platiniferous gold–palladium belt of Minas Gerais, Brazil, forms an approximately 240-km-long, roughly north–south trending domain that includes numerous auriferous lodes and platiniferous alluvium. The belt transects two Precambrian terranes, the Quadrilátero Ferrífero in the southern part, and the southern Serra do Espinhaço in the northern part. Both terranes were overprinted by regional fluid flow that led to tourmalinisation, with or without hematitisation, and precious-metal mineralisation. Here, we report the occurrence of coarse-grained gold–tourmaline aggregates and integrate recently obtained ages and tourmaline boron-isotope values published elsewhere. One type of aggregate is unique because it has patches that are close to stoichiometric PdPt, in which gold content varies from 2.5 to 33.5 at.%. The gold–tourmaline aggregates seem to be the ultimate expression of the boron metasomatism.
