Sensoriamento remoto e mapeamento geológico-estrutural para a caracterização de estruturas rúpteis associadas a mineralizações de cobre na Bacia do Camaquã – RS

Abstract

The Sul-rio-grandense Shield (SrgS) is composed of a diversity of petrotectonic assemblies formed between the Paleoproterozoic and Neoproterozoic, with rocks that host different types of mineralizations. Despite the greater variety of research that addresses ductile shield tectonics, works that address brittle structural geology at a detailed scale are still scarce. Considering the importance of copper as a commodity mainly used in the basic, energy, telecommunications and technology industries, the discovery of new mineral reserves is extremely important for the country's economic development. In this context, the present work proposes a study of the brittle structural geology and the relationship of these structures with copper mineralizations in a portion of the Serra de Santa Bárbara, Caçapava do Sul -RS municipality, where there are rocks from the Santa Bárbara Group and Acampamento Velho Formations, characterized by a succession of volcanic-sedimentary rocks. For this, remote sensing techniques will be used to characterize the geomorphological lineaments at scales of 1:200,000, 1:100,000, 1:50,000 and 1:25,000. Subsequently, field work was carried out to collect geological and structural data that served to characterize the rupestrian structures of the region. From the remote sensing data, it was possible to verify the predominance of geomorphological lineaments of NE-SW direction, followed by lineaments of NW-SE and N-S direction. It is noticeable that with the detailing of the work scale, the more discontinuous the geomorphological lineaments end up becoming. In the field, it was possible to identify a zone with subvertical normal faults that affects the basic and acid volcanic rocks of the Acampamento Velho Formation, which may be secondary and parallel to the Cerro dos Cabritos Fault Zone. This fault zone shows clear evidence of hydrothermalism, also giving rise to cataclasis zones and volcanic breccias. The analysis of fracture density in some outcrops of the study area showed that the sedimentary rocks have a very low fracture density, and the further away from the fault zone, the lower the fracturing of these rocks. The highest values of fracture density are associated with the acid volcanic rocks, which presented a multidirectional fracture pattern, with the predominance of N-S direction, followed by E-W direction fractures. These fractures were characterized as extensional fractures and are possibly related to the last ESrg deformation event in this region. From the lineament density analysis, it was possible to identify that the Crespos mineral occurrence is in a high-density zone cut by multidirectional lineaments. The integration of the remote sensing data allowed us to identify that the multidirectional and multitemporal fracturing pattern of the volcanic rocks was fundamental for ore deposition, with N-S extensional fractures being the most important. The percolation of the fluids occurred in a restricted way to the contact between the acidic and basic volcanic rocks of the Acampamento Velho Formation, being the acid terms the most fractured creating a greater porosity and permeability for the deposition of the copper ore.