Contribution of Precambrian ore deposits to the production of base metals is very low in South America, as compared with those in other shield areas of the world. The situation might be considerably changed in future with increasing mineral potentials of the Brazilian shield, as exemplified by recent success in exploration for base-metal sulphide deposits in Central Brazil, the geotectonic setting of which is the primary concern of this paper.
Precambrian rocks in Brazil were formed and metamorphosed in five major, orogenic cycles; the Archean Guriense and Jequié, and the Proterozoic Transamazonian, Uruaçuan (Espinhaço), and Brazilian Cycles. The last one corresponds to the period of Pan-African tectonothermal events in Africa. Geologic setting of Archean and Early Proterozoic ore deposits of special metallogenic importance is briefly referred in relation to each tectonic province; e.g., the banded iron formation and copper deposits in the.Carajás Range, Caraíba copper deposits in granulitic pyroxenite, Boquira lead-zinc deposits in greenstone belt, the itabiritic iron formation and Morro Velho gold deposits in the Quadrilátero Ferrífero (Iron Quadrangle), and Late Proterozoic stratiform lead-copper, deposits at Perau mine.
In the Goiás Plateau of Central Brazil, the geotectonic evolution of Earlier Precambrian terrains has advancingly been elucidated by recent research and exploration activities to an extent that metallogenic consideration enables comparative study with other regions, and can benefit for future exploration. The Chapada copper-pyrite deposit has been discovered in Archean greenstone belt, and komatiitic peridotite and metavolcanic sequence of neighbouring greenstone belts are potential areas for nickel-copper and gold ores. Residual nickel deposits derived from Archean ultramafic granulitic terrain have been developed in the Niquelândia and Barro Alto complexes. The Americano do Brasil nickel-copper deposits of massive and disseminated ores occur in the layered intrusive of possible Early Proterozoic age. Stratiform copper-zinc deposits have been, explored at Palmerirópolis in the isoclinally folded volcano-sedimentary sequence of probable, Early Proterozoic age. Galena and sphalerite disseminations have been found in the Castelão area, yet unsuccessful, in the epicontinental carbonate formation of the Middle Proterozoic, which are quite similar in nature to lead-zinc deposits of the Mississippi Valley type in the Late Proterozoic Bambuí Group, that underlies the Vazante-Paracatú-Morro Agudo area and extends further east to cover the São Francisco craton.
Paleomagnetic reconstruction gives still uncertain configuration of the Proterozoic Gondwanaland. There are conflicting opinions on the existence of proto-South Atlantic ocean and possible operation, of the Wilson cycle between Brazilian and African continental segments during the periodd of Late Proterozoic.
