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Ore fluids of orogenic gold deposits of the Gurupi Belt, Brazil: a review of the physico-chemical properties, sources, and mechanisms of Au transport and deposition

2014; Geological Society of London; Volume: 402; Issue: 1 Linguagem: Inglês

10.1144/sp402.2

2041-4927

Evandro Luiz Klein,

Geochemistry and Elemental Analysis

Abstract The Neoproterozoic Gurupi Belt in northern Brazil developed at the southwestern margin of the Palaeoproterozoic São Luís-West Africa Craton. Orogenic gold deposits of this belt are hosted in Palaeoproterozoic (2160–2147 Ma) metavolcano-sedimentary and calc-alkaline granitoid rocks formed in arc and/or back-arc settings during a protracted Rhyacian orogeny (2240–2080 Ma). These host rock assemblages were tectonically and isotopically reworked during the Neoproterozoic and represent the reworked margin of the craton, that is, the external domain of the Neoproterozoic (Brasiliano-Pan African) orogen. The location of the gold deposits is controlled by the Tentugal shear zone, which represents the tectonic boundary between craton and the Gurupi Belt, and its subsidiary structures. Gold occurs in veins and in association with pyrite, and subordinately arsenopyrite and chalcopyrite, in strongly altered and variable deformed host rocks. Geological characteristics, petrographic, fluid inclusion, and isotopic evidence indicate near-neutral, reduced aqueous-carbonic metamorphic fluids, with local contributions from host rocks at the deposit site. Ore deposition occurred at about 300–370 °C and up to 3 kbars in response to fluid immiscibility and fluid-rock reactions (sulphidation, desulphidation, carbonatization, CO 2 removal) and local fluid mixing and oxidation.