Chromium, iron, gold and manganese in Amapá and northern Pará, Brazil

Wilson Scarpelli,Elio Hiromi Horikava

doi:10.1590/2317-4889201820180026

Abstract

Information is presented on the geology and mineral deposits in greenstone belts and mafic-ultramafic complexes in Amapa and northern Para, 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 Para, 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.

Highlights

Following our description of the geology of the Amapari Greenstone Belt near Serra do Navio, Amapá, and its deposits of manganese, iron and gold (Scarpelli & Horikava 2017), we expand laterally the limits of our area of observation and describe other areas of the Paleoproterozoic MaroniItacaiúnas Tectonic Province (MIP) presenting similar geology and mineralization
The area object of the present note covers the MIP from the coast of Amapá, at east, to the headwaters of the Ipitinga River, in the north of the Pará State, at west. As it happened with the first article, the details disclosed come from direct field observations made by the authors, with data from published and unpublished reports of several geologists and mining companies which the authors worked for or visited, amongst them Indústria e Comércio de Minérios S.A. (ICOMI), Unigeo Geologia e Mineração, Minorco Exploração, MMX Mineração, Extrativa Mineração, El Dorado Gold and others mentioned in the text
The work done by the mining companies indicates that the greenstone sequence and their remnants always present at base a unit of orthoamphibolite derived from basalts (Scarpelli & Horikava 2017), indicating an extensive episode of extrusion of basalt (Jornal Formation) over the shield, covering areas with granites and granitoids of Archean and Paleoproterozoic ages

Summary

INTRODUCTION

Following our description of the geology of the Amapari Greenstone Belt near Serra do Navio, Amapá, and its deposits of manganese, iron and gold (Scarpelli & Horikava 2017), we expand laterally the limits of our area of observation and describe other areas of the Paleoproterozoic MaroniItacaiúnas Tectonic Province (MIP) presenting similar geology and mineralization. The area object of the present note covers the MIP from the coast of Amapá, at east, to the headwaters of the Ipitinga River, in the north of the Pará State, at west As it happened with the first article, the details disclosed come from direct field observations made by the authors, with data from published and unpublished reports of several geologists and mining companies which the authors worked for or visited, amongst them Indústria e Comércio de Minérios S.A. (ICOMI), Unigeo Geologia e Mineração, Minorco Exploração, MMX Mineração, Extrativa Mineração, El Dorado Gold and others mentioned in the text Over this larger area, the MIP is similar to what was described in the previous article, but with regional variation in the ages of the younger granitic intrusives, variations in the stratigraphy of the greenstone belts, locally distinct metamorphic phase, alkaline intrusives at west, and, quite important, a layered mafic-ultramafic intrusive, with magmatic seams of chromite. Paleoproterozoic ages were obtained from the syntectonic granitic intrusions associated with the greenstone belts, for the layered mafic-ultramafic intrusions, and for a granulitization event observed in the eastern portion of the Amapa Block (João et al 1978),

21 Grande Formation

Findings

CONCLUSIONS AND SUGGESTIONS FOR