Metal recycling tracked by mercury and helium isotopes in platinum–palladium nuggets from Córrego Bom Sucesso, Brazil

The enigmatic botryoidal nuggets of platinum (Pt) and palladium (Pd) from Córrego Bom Sucesso in the southern Serra do Espinhaço, Minas Gerais, Brazil, are considered to have formed during supergene alteration placer deposits. This requires hitherto unidentified precious-metal enrichment processes is inconsistent with Pt–Os age 180 Ma that entails formation at depth, as recently proposed. Here we report first mercury (Hg) helium (He) isotopic determinations Pt–Pd nuggets. Mercury compositions a mass-independent fractionation (MIF) signature an odd-mass deficit (Δ199Hg = − 0.22 ± 0.04; 1SD, n 15), which aqueous photochemical reduction Hg (II). Extremely low 3He/4He (<0.001 Ra) extremely high concentrations He (up 1.9 × 1017 at/g) indicative nugget He-enriched fluids within quartzite sequence Espinhaço basin, not meteoric surface water. data consistent nugget-forming setting deep biosphere, result groundwater interaction Pt–Pd–Hg minerals Pan-African-Brasiliano post-orogenic veins. We propose negative Hg-MIF was inherited vein originally acquired their Earth's intracratonic sedimentation Proterozoic basin.