Geologia, geofísica aérea e geoquímica de solo do depósito aurífero Pereira Velho, Coité do Nóia (AL), Brasil

Abstract

Orogenic Deposits are responsible for a large part of the world's gold reserves, which attracts a lot of attention and investment in mineral research in these types of deposits. In the central portion of Alagoas, inserted in the municipalities of Coité do Nóia, Limoeiro de Anadia and Taquarana, there is the Pereira Velho Gold Deposit, which is being researched by Pereira Velho Exploração S.A. and served as the subject of this work. In geological terms, gold mineralization occurs in the Arapiraca Complex, belonging to the Rio Coruripe Domain (Borborema Province). The geology of the region is marked by rocks of high metamorphic grade from the Archean to the Proterozoic, represented by gneisses and paraderived migmatites, banded iron formations, metamafic-metaultramafic rocks, syenogranitic intrusions, in addition to auriferous quartz coming from hydrothermal quartzite rocks that make up the gold mineralization in the area. This work focuses on the investigation of the gold mineralization of the Pereira Velho deposit based on the integration and interpretation of data from geology, aerial geophysics (magnetometry and gamma-spectrometry) and soil geochemistry, with the aim of helping to elucidate whether this deposit represents a deposit Gold Orogenic. The methodology comprised geological mapping combined with petrography of representative samples, in addition to the processing and interpretation of airmagnetometry, airgammaspectrometry and soil geochemistry data. It was verified that the gold mineralization occurs in quartz veins, with pyrite content <5%, hosted in mylonitic quartzites, controlled by shear zones with preferential NW-SE direction. In addition, the reservoir is enveloped by sericitic alteration, with localized silicification and distal propylitic alteration. All these characteristics corroborate a typical genesis of orogenic gold deposits, however, in the petrographic study of the ore gangue, the presence of fluorite was verified, which is not compatible with this model and suggests the participation of fluids from granitic sources, which opens up the possibility for other models, such as gold deposits related to reduced intrusion systems and gold-rich porphyries.