Mina do Andrade: redescoberta do potencial cuprífero no Escudo Sul-Rio-Grandense

Abstract

The study area, called “Mina do Andrade”, covers a territory of 220 ha, and it is located in Caçapava do Sul/RS. This occurrence of copper has been cited in the literature since the 19th century. The mineral research work, carried out before 1940, was recorded by the presence of an 18-meter-deep well, a 23-meter-long gallery and eighteen trenches of different sizes, opened on the western flank of Morro do Andrade. Since 2008, the history of Mina do Andrade, the main target of Projeto Primavera, began to change and this is what is discussed in this dissertation. The main objective was to carry out an analysis of the field results, as well as the geochemical, topographic, and geophysical results of Mina do Andrade. Thus, Mining Ventures Brasil, the company where the master’s student worked as an Exploration Manager, carried out a topographic survey; trench mapping and sampling; drilling; geochemical studies; aerial and terrestrial geophysics. Among the main results, we mention that the study in the trenches near off Mina do Andrade obtained an average content of 0.29% Cu and 3 ppm Ag, which stimulated the development of a drilling campaign. As host, ultramafic, basic, intermediate, and acidic volcanic rocks as well as pyroclastic. Copper mineralization is hosted in the metavolcanosedimentary rocks of the Passo Feio Metamorphic Complex, and it is concentrated along and at the intersection of regional structures, such as the Falha do Andrade, in the N-S direction, where hydrothermal and locally breached zones constitute the main mineralized zones. The paragenetic sequence consists of 5 phases: pyrite – chalcopyrite; chalcopyrite – bornite; bornite – digenite – chalcocite; chalcocite – covellite – tenorite – cuprite and finally malachite – chrysocolla. From aerial geophysics, the main regional fault zones were detected, such as the Falha do Andrade, confirmed by IP terrestrial geophysics. Surface geochemistry revealed several copper, silver and gold anomalies. After carrying out more than 7,000 meters of diamond drilling, a resource of 191.76Mt@0.26%Cueq or 66.6Mt@0.47%Cueq was estimated for of Mina do Andrade, which are interesting and positive values. Thus, we conclude that in economic geology a prospect should not be definitively discarded just because a large volume of ore has not been found, as new interpretations and new technologies used in these same areas can lead to important discoveries.