Magnetometria terrestre aplicada ao mapeamento de corpos magnéticos intrusivos no granito Santo Ferreira – Caçapava do Sul, RS

Abstract

The region where the Granito Santo Ferreira is exposed consists of a complex arrangement of metamorphic, igneous and sedimentary rocks. The metamorphic rocks make up the Passo Feio Metamorphic Complex, which is intruded by the Granite Suite Caçapava do Sul and the Granite Santo Ferreira. These, in turn, are intruded by generations of dikes containing magnetic minerals, targets of the present work. In the region, there are sedimentary and volcanic rocks of the Bom Jardim and Guaritas Groups. In this complex arrangement of rocks and tectonic structures, there is a series of mineral deposits bearing copper, gold, phosphates, marbles, etc. Understanding the relationship between dikes and nesting rocks is important in order to define the best geological model for the mineral exploration of the deposits that occur in the region, besides contributing to the understanding of regional geology. In this sense, the objective of this work was to determine the direction and thickness of the iron oxides associated with dikes that cut the Santo Ferreira Granite in subsurface, using aeromagnetic map provided by CPRM that shows the lineaments present in the region and correlating with data acquired by geophysical method of magnetometry, of terrestrial technique. Three profiles were made with a length of 60 m and a spacing of 0.5 m between measurements. The profiles were made with a distance of 14 m between them. The study area was imaged by aerial photographs, which were used for orthophotomosaic construction and digital elevation model; which were georeferenced using field control points whose coordinates were determined in the field with DGPS and Total Station. The results suggest that the magnetic anomalies related to the dikes are in the central portion of the study area with an approximate orientation in the NW-SE direction. In the S-SE portion of the area the total magnetic field tends to soften, indicating a thinning of the structures in this region.