Mineralizing events of the world-class Volta Grande gold deposit, southeastern Amazonian Craton, Brazil

The southeast region of the Amazonian Craton has been the target of several metallogenetic surveys, which recently led to the identification of the world-class Volta Grande gold deposit with gold reserves of ~ 3.8 Moz at 1.02 g/t. This deposit is located ~60 km southeast of Altamira city, Pará state, and is hosted in the Três Palmeiras intrusive-greenstone belt, itself located in the northern Bacajá Tectonic Domain (2.24 – 2.0 Ga). A mylonitized, high-level intrusive suite hosts the mineralization. Local kinematic indicators point to dip-slip movement with the greenstone moving up relative to the intrusive rocks. Native gold mostly occurs as isolated grains in centimetric quartz veins and veinlets associated with pervasive carbonatic alteration that was synchronous to dynamic metamorphism. Part of gold is also associated to sulfide disseminations in this generally low-sulfide mineralization. These relationships are compatible with orogenic lode-type gold systems elsewhere. New petrographic studies from core samples along the stratigraphic profile reveal the presence of lava flows and dykes of rhyodacite, rhyolite, and subordinated microgranite crosscutting earlier style of mineralization. These rocks are characterized by potassic, propylitic, sericitic, and/or carbonatic hydrothermal alteration in selective, pervasive, or fracture-controlled styles. Within the hydrothermally altered rocks, gold occurs as disseminated isolated grains or replacing sulfides. Both native gold and sulfides are also hosted in centimetric quartz veinlets. Such features of the deposit are similar to those of the porphyry-type and low- to intermediate-sulfidation epithermal systems already identified in the Amazonian Craton. These data indicate a second mineralizing event, a common fact in large-tonnage gold deposits, and is now proposed for the Volta Grande deposit that can represent a new exploration guide.