ABSTRACT:Greenstone belts with deposits of gold, iron and manganese are common in the Paleoproterozoic Maroni-Itacaiunas Tectonic Province of the Guiana Shield. In Brazil, in the State of Amapá and northwest of Pará, they are represented by the Vila Nova Group, constituted by a basal unit of metabasalts, covered by metasediments of clastic and chemical origin. The basal metasediments, the Serra do Navio Formation, are made of a cyclothem with lenses of manganese marbles at the top of each cycle. Under the intense weathering of the Amazon, these lenses were oxidized to large deposits of high-grade manganese oxides. The exploitation of these oxides left behind the manganese carbonates and low-grade oxides. The overlaying Serra da Canga Formation presents a calcium and magnesium domain grading to an iron domain with banded silicate and oxide iron formations, mined for iron ores. Overlapping structures and superposed metamorphic crystallizations indicate two phases of dynamothermal metamorphism, the first one with axis to north-northeast and the second one to northwest, with an intermediate phase of thermal metamorphism related to syntectonic granitic intrusions. Shears oriented north-south, possibly formed during the first dynamothermal metamorphism and reactivated in the second, are ideal sites for hydrothermalism and gold mineralization, which is greater when occurs in iron formation and carbonate-bearing rocks, as it happened at the Tucano mine. Layered mafic-ultramafic intrusions in the greenstones represent a potential for chromite and platinum group elements. Pegmatites are source of cassiterite and tantalite exploited from alluvial deposits. KEYWORDS:Group Vila Nova greenstones; Manganesiferous Precambrian cyclothem; Precambrian iron formation; Precambrian mafic-ultramafic complexes; Superposed metamorphic cycles. RESUMO: A Província Tectônica Paleoproterozoica Maroni-Itacaiunas estende-se ao longo de toda a área costeira do Escudo das

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Information is presented on the geology and mineral deposits in greenstone belts and mafic-ultramafic complexes in Amapá and northern Pará, with the emphasis in iron, gold, manganese, and chromium. At Santa Maria, the Vila Nova Group presents deposits of iron and gold, the latter in carbonatic metasediments crossed by a north-south shear. The group is intruded by the Bacuri Mafic-Ultramafic Complex, with mineable deposits of chromite and magnetite. The overlaying 21 Grande Formation presents minor gold mineralization. At Serra das Coambas there is a significant show of iron formation, and, at its flank, the 21 Grande Formation presents extensive areas exploited by gold miners for gold. Serra do Ipitinga, in Pará, contains the greatest units of iron formation of the area, accompanied by frequent shows of alluvial and primary gold mineralization. The distribution of manganesiferous metasediments identified by mining companies indicate that they were deposited in an about 90 km long narrow basin oriented to northwest, with Serra do Navio near its center. The exposures of iron formation indicate that they were deposited on a belt greater than 350 km long and 100 km wide, oriented and still open to northeast, covering areas of different ages of metamorphism and tectonical stabilization.

Article InformationPublication type: Review article

Article InformationPublication type: Historical Review