Decoding complex gold mineralization in the Pitangui Greenstone Belt, Brazil: Overprinting systems revealed by pyrite trace elements and sulfur isotopes

Abstract

Tracing the sources of metals and sulfur in orogenic gold deposits remains debated due to the diversity of these systems. This study constrains the origin and evolution of mineralizing fluids through trace element and sulfur isotope (δ³⁴S) analyses of pyrite from the Papagaios gold deposit, located in the Pitangui Greenstone Belt (PGB), Brazil. The results reveal a multistage metallogenic history linked to the tectonic evolution of the PGB. Pre-foliation (pre-Sn) mineralization represents an ancient seafloor hydrothermal system, similar to VHMS-like deposits, with pyrite I enriched in metals derived from oceanic crust leaching (Ni, Co, Cu, Pb, Zn, and Au) caused by seawater convection. δ³⁴S values indicate contributions from both thermochemical (TSR) and biological sulfate reduction (BSR). Syn-Sn mineralization corresponds to the orogenic overprinting of this earlier system, forming pyrite II, which largely preserves the geochemical signature of the pre-Sn event and indicates recycling of metals and sulfur during deformation and metamorphism. Pyrite III records further recycling from pre-existing mineralization, with a subordinate contribution from an intrusion-related system, as indicated by enrichments in Bi, Ag, Sn, As, and Se. Its δ³⁴S values suggest isotope fractionation associated with sulfate disproportionation during magmatic degassing. These results identify a previously unrecognized oceanic-floor hydrothermal system in the southern São Francisco Craton as the primary metal source for the Papagaios deposit. They also highlight the role of metamorphism and late-stage magmatism in overprinting earlier mineralization and enhancing gold enrichment, positioning the deposit as an analogue for overprinted gold systems worldwide.