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

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 t hree 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 Neoproter ozoic (900-550 Ma) Brasiliano Cycle belts surround the cratons in the easte rn half of Brazil. Paleoarchean rocks occur as small cratonic nuclei in nor theastern Brazil, but the cratons contain voluminous 3.0-2.6-Ga granitic an d greenstone belts and a large volume of Paleoproterozoic rocks. Late Mesop roterozoic belts (similar to1.2 Ga) occur in the western and northwestern A mazon Craton and possibly in northeastern Brazil. There are voluminous Pale oproterozoic 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 B rasiliano Cycle belts contain 5% of juvenile crust in central and southern Brazil, but are dominantly derived from reworking of older crust. It is pos sible that the cratons were continuous in a supercontinent during the Mesop roterozoic prior to the Brasiliano Cycle. Gold deposits are concentrated in the Archean and Paleoproterozoic terranes, including the Carajas and Quadr ilatero Ferrifero gold provinces of the Amazon and Sao Francisco Cratons, r espectively, but some also occur in younger terranes. Recent alluvial gold deposits and supergene deposits in the weathering zone are widespread in Br azil.