Archean and Early Proterozoic mineral deposits in Brazil

Abstract

In this paper is presented a rough review and an up-to-date compilation on the Archean and Early Proterozoic mineral deposits in Brazil and their metallogeny. The large Precambrian shields which cover about 2/3 of the Brazilian territory enclose a great number of ore mineralizations. Among these the most important and well investigated are those of iron, manganese, gold, base metals (Cu, Pb, Zn), nickel, asbestos, chromite, pegmatite minerals (tin, columbite-tantalite and gemstones), uranium, tale, magnesite and limestones. Their host rocks are represented by four main geologic environments: volcanic-sedimentary (iron formations and greenstone belt type structures), mafic and ultrumafic complexes, granulitic zones and granitic-gneissic belts. ln several cases only the protore is Archean and or Early Proterozoic in age and the ore enrichment is related to Cenozoic process as observed for some iron, manganese, nickel and placer mineral deposits. It is very difficult to establish the correct ages for many mineral deposits due to the complex geologic history, reactivation and superimposed geological process in the Precambrian terrain. For the presentation of this paper the following age subdivision is considered: Early Proterozoic - up to 1,800 Ma (Transamazonico Cycle); Late Archean - 3,000-2,600 Ma (Jequie Cycle); Early Archean - more than 3,000 Ma (pre Jequie-Guriense Cycle). The names, location, geologic environments, economic figures and other data on the mineral deposits mentioned here correspond to the 1:2,500.000 Gcological and Mineral Deposits Map of Brazil to be published by Departamento Nacional da Producao Mineral (DPNM).