Análise e modelagem estrutural do depósito de cobre do Andrade, Caçapava do Sul - RS

Abstract

The Andrade’s copper deposit is inserted in the Passo Feio Metamorphic Complex metavolcanosedimentary rocks, composing part of the Sul-riograndense Shield, in the central area of the Rio Grande do Sul state. The genesis of this deposit is associated with the magmatic fluid percolation from the Caçapava do Sul Granitic Complex intrusions, which leached the base metals from the enveloped rock bodies and relocating these metals in later fractures. Therefore, an essential structural control for this copper mineralization is admitted. The copper mineral is a commodity which is in economic growth in the world market, and also a mineral of interest in the city of Caçapava do Sul and the regions around. The present research aimed for a structural-geologic 3D modeling of the west face of the Cerro do Andrade, where the Andrade deposit is located. The structural model was elaborated by 252 mapping point’s data obtained in the fieldwork and a virtual outcrop model generated by Structure from Motion–Multi-View Stereo methods. The model shows seven structural sections, made by the kink-band method, which is one of the operating tools of the software MOVE™. In this method, the software was able to generate a model for the highest amplitude folds found in the deposit and to analyze its structural aspect. Along with the geological profile, four thin sections were made for microstructural analyses. Kinematic indicators of shadow pressure, S-C pairs and mica-fish occur and are counter-clockwise kinematic. In the field, it was analyzed that the mesoscale folds have a vergence asymmetry mainly into SW direction with interlimb angle tending from gentle to close. The structural profile analysis proved similar characteristics with the structures seen in the field, showing folding with vergence to SW. With all the given information, it is proposed that the relocated mineralization on the upper portion of the deposit was produced not only by an intense brittle control but also by ductile deformation.