Petrografia e mineralogia das alterações hidrotermais associadas ao bloco Sul do depósito aurífero Volta Grande do Xingu, Domínio Bacajá (PA), Cráton Amazônico

Abstract

The world-class Volta Grande gold deposit, at the Bacajá Domain, contains measured reserves of approximately 6.0 Moz at 1.02 g/t, divided into the north and south exploratory blocks. Historically, this mineralization has been classified as orogenic (lode-type) and is found within a set of mylonitized granitoids in the amphibolite facies of medium to high metamorphic degree attributed to the Três Palmeiras Group (2.41 Ga) and the Oca Granodiorite (2.16 Ga). However, recent research on the rocks of the northern block has established a late volcanic sequence with significant gold mineralization. Aiming to contribute to its metallogenetic modeling, this Master’s Dissertation focused on the southern block, involving macroscopic and microscopic petrographic descriptions and the application of VNIR–SWIR reflectance spectroscopy in core samples from the Pequi, Grande, and Itatá targets. First, the results include the petrography of metamorphic rocks, represented by amphibolite and mylonitic granodiorite, and an associated isotropic volcanic and plutonic suite. The data compilation revealed mineral paragenesis related to metamorphic and magmatic-hydrothermal processes. The metamorphic paragenesis reveals regional and dynamic-thermal metamorphisms and moderate overprinting of hydrothermal alterations typical of epithermal systems, associated with the emplacement of the isotropic rocks package. Second, in the isotropic rocks, there is an overprint of hydrothermal alterations and gold mineralization conceivably of intermediate- and high-sulfidation epithermal-type genetically linked to magmatic-hydrothermal systems, with carbonate alteration in a boiling zone and advanced argillic alteration. In conclusion, data integration from the southern block shows, similarly to the northern block, at least two genetically distinct gold mineralizing events that enhanced the grade and tonnage of the Volta Grande deposit, thus representing a new prospective model for the Bacajá Domain.