LATE CRETACEOUS BONANZA-STYLE METAL ENRICHMENT IN THE SERRA PELADA Au-Pd-Pt DEPOSIT, PARA, BRAZIL

A 40Ar/39Ar age of 75 +/- 6 Ma (2 sigma) was obtained for aggregates of Mn-Ba oxide intergrown with palladiferous gold and Pd-Pt minerals, representative of near-surface bonanza Au-Pd-Pt mineralization that triggered the gold rush to Serra Pelada in northern Brazil. The mineralization occurs in goethite-rich tectonic breccia and records recurrent fault displacement in the still active Cinzento strike-slip fault system. The goethite-rich tectonic breccia is truncated by the bonanza-style Au-Pd-Pt-Mn-Ba enrichment, with which tabular hematite is spatially associated on a micrometric scale. The tabular hematite is coarsely crystalline, >5 mu m in grain size, and lines cavity walls in the goethite-rich breccia. The presence of coarsely crystalline tabular hematite constrains the metalliferous overprint to temperatures in excess of about 100 degrees C. We suggest that the bonanza mineralization is a Late Cretaceous, epithermal-like, fault-breccia system that overprinted Paleoproterozoic intrusion-related Au-Pd-Pt mineralization preserved at depth.