The Zacarias Au-(Ag-barite) deposit, Neoproterozoic Goiás Magmatic Arc, Brasília Orogen, Central Brazil: Constraints on the metallogenesis of a gold-rich quartz-barite exhalite-related to VMS mineralization

The Zacarias deposit is a gold-rich volcanogenic mineralization (0.65 Mt @ 4.36 g/t Au, 48.86 g/t Ag, and 10.67% barite) hosted within Neoproterozoic rocks of the Mara Rosa metavolcano-sedimentary sequence in the Goiás Magmatic Arc. To determine the genesis of the deposit and the role of barite, we investigated its geological and geochemical characteristics. The mineralized zone consists of barite-muscovite-quartz-pyrite lenses hosted in mafic and felsic metavolcanic and chemical metasedimentary rocks, all affected by amphibolite facies metamorphism. Aluminous schist (muscovite-phlogopite-quartz, gahnite-phlogopite-quartz) assemblages are interpreted as metamorphosed hydrothermal alterations, reflecting phyllic, chloritic, or argillic alteration precursors generated by volcanic-exhalative processes. In this context, the host rocks of the mineralization are interpreted as gold-rich barite-quartz-muscovite meta-exhalite. We present a comprehensive dataset of mica chemistry, which reveals significant barium concentrations in muscovite (5.75-6.96 wt.% BaO) and phlogopite (2.20-3.36 wt.% BaO). Gahnite is common, with high Cr 2 O 3 content (12.42 wt%). We explore evidence for the sulfur isotope signatures of pyrite (δ 34 S: +2.81 to +7.24‰), which can indicate a mix of sulfur from thermo-chemical sulfate reduction (TSR), with possible contributions from magmatic and/or biogenic sources. LA-ICP-MS zircon U-Pb dating of felsic metavolcanic rocks yields a crystallization age of 908.3 ± 7.4 Ma, indicating that the deposit likely formed by volcanic-exhalative processes during the early stages of the Goiás Magmatic Arc, as part of the tectonic evolution of the Mara Rosa Segment.