Multistage mineralizing episodes of the Proterozoic world-class Volta Grande gold deposit, Amazonian Craton, northern Brazil: Implications for the Bacajá Domain metallogenesis

Abstract

The easternmost region of the Amazonian Craton in northern Brazil has been the focus of several mining exploration surveys, which led to the identification of the world-class Volta Grande gold deposit (∼6.0 Moz@1.02 g/t). The deposit is inserted in the Bacajá Domain (2.24–2.0 Ga), and part of the mineralization occurs in Proterozoic mylonite, gneiss, and associated metamafic rocks that underwent greenschist to amphibolite-facies metamorphism. Electrum (Au–Ag) occurs as grains in cm-sized quartz high-grade veins and veinlets (up to 34.1 g/t in some rock intervals) that follow the mylonitic foliation and are associated with pervasive carbonate alteration, synchronous with the dynamic metamorphism. Disseminated electrum grains, pyrite, chalcopyrite, arsenopyrite, tellurides, and galena occur associated with potassic, argillic, propylitic, and silicic alteration types mainly in fracture-controlled or pervasive styles. These geological features as a whole suggest an orogenic high-tonnage orogenic gold system. Isotropic core samples along a stratigraphic profile reveal late andesite, dacite, rhyodacite, and rhyolite lava flows and dikes and plutonic rocks such as quartz monzonite, granodiorite, monzodiorite, and subordinate microgranite crosscutting the older metamorphic rocks. These rocks reveal potassic, propylitic, argillic, silicic, and sericitic alteration types. Electrum grains, possibly related to boiling deposition, occur along cm-sized quartz, calcite, and adularia high-grade veins (up to 29.5 g/t in some rock intervals) with chalcopyrite, pyrite, arsenopyrite, tetradymite, and tellurobismuthite. Such mineralogy is compatible with a low-sulfidation epithermal system. Data integration points to at least two distinct mineralizing events leading to the Volta Grande gold deposit – orogenic gold and low-sulfidation epithermal – which explains such large-tonnage and high-grade ore accumulation. It configures a new exploration guide for the Bacajá Domain of the Amazonian Craton, attested by other worldwide regions with similar metamorphic, magmatic, and hydrothermal alteration characteristics.