Cratons and orogenic belts of the Brazilian Shield and their contained gold deposits

Abstract

The Brazilian Shield extends over much of South America to the east of the Andean Chain, and is partly covered by Phanerozoic sedimentary rocks. The three major tectonic units (older than 900 Ma) of the shield are the Amazon, Sao Francisco, and Rio de la Plata Cratons, whereas rocks of the Neoproterozoic (900–550 Ma) Brasiliano Cycle belts surround the cratons in the eastern half of Brazil. Paleoarchean rocks occur as small cratonic nuclei in northeastern Brazil, but the cratons contain voluminous 3.0–2.6-Ga granitic and greenstone belts and a large volume of Paleoproterozoic rocks. Late Mesoproterozoic belts (~1.2 Ga) occur in the western and northwestern Amazon Craton and possibly in northeastern Brazil. There are voluminous Paleoproterozoic and Mesoproterozoic intrusive and volcanic rocks in the Amazon Craton. Belts of reworked crust are common, but the Amazon Craton grew to the north and west mainly during accretionary orogens. The Neoproterozoic Brasiliano Cycle belts contain 5% of juvenile crust in central and southern Brazil, but are dominantly derived from reworking of older crust. It is possible that the cratons were continuous in a super-continent during the Mesoproterozoic prior to the Brasiliano Cycle. Gold deposits are concentrated in the Archean and Paleoproterozoic terranes, including the Carajas and Quadrilatero Ferrifero gold provinces of the Amazon and Sao Francisco Cratons, respectively, but some also occur in younger terranes. Recent alluvial gold deposits and supergene deposits in the weathering zone are widespread in Brazil.