Mapping of chromite occurrence in a meta-ultramafic complex by magnetometric prospecting, Sul-Riograndense Shield (Southern Brazil)

Abstract

This study presents the use of terrestrial magnetometry method in the characterization of a metamorphic and chromium-mineralized ultramafic body in the São Sepé region (RS). Several serpentinite exposures were recognized in the study area, characterized by a very evident schistosity marked by amphiboles and micas. The most preserved rocks are gray to dark green in color, silky to the touch and with folds and variable fracturing. The chromite present in serpentinites is associated with magnetite, and occurs in the form of small lenses. 1677 reading lines were made perpendicular to the main direction of the meta-ultramafic body, with 25m spacing between measurement points. The magnetometric maps revealed high-intensity anomalies related to meta-ultramafic rocks. 1677 reading lines were made perpendicular to the main direction of the meta-ultramafic body, with 25m spacing between measurement points. The magnetometric maps revealed high-intensity anomalies related to meta-ultramafic rocks. The results revealed the existence of highly magnetic individualized lenses orientated according to NE / SW, related to regional deformation events, with remobilization and mineral reconcentration. The direct relationship between high magnetization and chromite/ferro-chromite concentrations allows relatively detailed mapping of potentially mineralized areas, revealing dimensions more significant than the limits of the meta-ultramafic sequence defined in the geological map. The results indicate that the analytical signal amplitude map is a highly recommended product for planning sampling actions and reserve quantification, improving classical geological mapping.