Gold, iron and manganese in central Amapá, Brazil

Wilson Scarpelli,Élio Hiromi Horikava

doi:10.1590/2317-4889201720170114

Abstract

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.

Highlights

The objective of the authors is to divulge geological knowledge acquired throughout the years in exploration activities for deposits of iron, gold and manganese in the State of Amapá, Brazil, on behalf of Indústria e Comércio de Minérios S.A. (ICOMI), Unigeo Geologia e Mineração, Minorco Brasil, Anglo American do Brasil, AngloGold Ashanti, Min
It is expected that this note will help to understand the geology and mineral potential of the area and be useful in forthcoming mineral exploration there and elsewhere
The described deposits occur in the Brazilian part of the Precambrian Guiana Shield (Fig. 1), which is constituted by four laterally collated tectonic provinces (Cordani & Teixeira 2007, Cordani et al 2016), all of them containing Archean rocks metamorphosed into granitoids, presenting intrusive, volcanic, metamorphic and sedimentary units of variable ages

Summary

INTRODUCTION

The objective of the authors is to divulge geological knowledge acquired throughout the years in exploration activities for deposits of iron, gold and manganese in the State of Amapá, Brazil, on behalf of Indústria e Comércio de Minérios S.A. (ICOMI), Unigeo Geologia e Mineração, Minorco Brasil, Anglo American do Brasil, AngloGold Ashanti, Min. Next to the coast, the Maroni-Itacaiunas (MI) Province is mostly made of Archean and Paleoproterozoic granitoids, presenting belts of greenstone and associated intrusives, granulites, archean nuclei (Rosa-Costa et al 2006), blocks of high metamorphic-grade rocks and granulites. The province was subject to several phases of tectonism and metamorphism, being tectonically stabilized at 2.26 to 2.01 Ga. From Venezuela to the Amazon Valley, the greenstones are remarkable for their mineral deposits of gold, iron and manganese, plus tantalum and tin in pegmatites. The Central Amazonian Province, stabilized at 2.03 to 1.88 Ga., contains several nuclei of Archean ages surrounded by Paleoproterozoic rocks and in the Middle Proterozoic received a large load of acid intrusives and extrusives in the south and of clastic sediments in the north.

33 Fe Ipitinga

Findings

CONCLUSIONS