Geophysical Prospecting Over a Meta-Ultramafic Sequence with Indicators of Gold Mineralization in Rio Grande do Sul State, Southernmost Brazil

Abstract

This work investigates the occurrence of gold on meta-ultramafic rocks at Funcho Farm, Sao Sepe, Rio Grande do Sul state, southernmost Brazil. The presence of base metals in meta-ultramafic rocks whose origin is related to volcanic massive sulfide (VMS) deposits has only rarely been explored in the scientific literature. The gold was identified in geochemical prospecting of current sediments in previous works, and suggested that the host rock of the mineralization is the serpentinite of Funcho Farm. The methodology used to achieve the study objectives included geological field surveys, surveys of structural measurements and acquisition of geophysical data utilizing electrical resistivity (DC) and induced polarization (IP) methods, using electrical tomography, with the execution of dipole–dipole arrays. In this study, nine electrical tomography lines, each 400 m, were acquired. The data were processed in 2D electrical inversion and then interpolated for 3D visualization. The information acquired for interpretations during field studies revealed that the probable mineralization is hosted in structures such as fractures and hinges and is also associated with milky quartz veins. The data analysis allowed the 3D delimitation of possible deep sulfide mineralizations from hydrothermal fluids, probably from the intrusion of the Sao Sepe granite. The results presented in this work are very useful, because they can serve as an appropriate analogy of geological reality associated with a reliable deposit architecture, helping to outline a strategy for a future drilling campaign directed to the targets found.