Mapeamento geológico 1:20.000 da Região Norte do depósito de cobre do município de Bom Jardim de Goiás - GO

Abstract

The Bom Jardim de Goiás (BJG) region is part of the geological context of the Arenópolis Magmatic Arc, located in the far west of Goiás. It became the object of research in the 1970s, after the Geological Survey of Brazil (CPRM) identified radiometric anomalies on the edge of the Serra Negra Granite, which led to the development of extensive research projects. Despite this, the geological complexity of the region and the typology of the deposit are still not fully understood. The Bom Jardim de Goiás Metavolcanosedimentary Sequence features a diversity of volcanic rocks, ranging from metabasalts and metandesites to rhyolites, while the sedimentary portion includes metaconglomerates, phyllites and quartzites. The intermediate tuffs contain a small deposit of copper sulphides, initially associated with volcano-exhalative processes. The general objective of the work was to carry out detailed geological mapping of the northern region of the Bom Jardim de Goiás copper deposit, with the aim of improving understanding of the deposit model by integrating data from aerial images, geophysics, field studies and laboratory analyses. Specifically, the aim was to draw up a 1:20,000 scale geological map with geological profiles, correlate maps of magnetometric and gammaspectrometric domains and homologous zones, carry out detailed petrographic descriptions and reinterpret the structural geology of the area. The study covered an area of 24 km², with semidetailed geological mapping integrated with the interpretation of aerogeophysical data, photointerpreted satellite images and petrographic descriptions. Based on this data, a reinterpretation of the structural geology was proposed and, based on historical information, comparisons were made with the geological model of the deposit. In the pre-field phase, a bibliographic survey and compilation of historical data were carried out. During the field phase, geological mapping was carried out, hand samples were taken and structural data was obtained. In the post-field phase, the geological map and data were prepared in a GIS environment, petrographic description, structural interpretation with stereograms and rosette diagrams, and the information was consolidated in a report. The work involved geological-structural mapping of an area made up of basic and metavolcanosedimentary rocks from the Paleoproterozoic, with the aim of detailing their lithological and structural characteristics. During the study, it was possible to individualize the Metabasalt Lithofacies in the Córrego da Furna Formation, based on magnetometric responses, in addition to identifying new, previously unknown occurrences of sulphides. This data made it possible to propose a different deposit model from the existing ones, contributing to understanding the geological evolution of the area. The analysis also indicated the possible continuity, to the north, of the copper deposit previously identified by CPRM, broadening the region's exploration prospects. In structural geology, four structural domains were defined and at least three phases of deformation recorded in the lithologies were recognized. Domain 1, associated with the Cuiabá Group rocks, has a N-S structural trend and isoclinal folds related to the D1 deformation. Domain 2 covers the Morro do Urubu, Aldeinho and Morro Selado Formations of the BJG Sequence, with a N-S trend and dips to the E and W. Domain 3, associated with the Córrego da Furna and Córrego da Aldeia Formations, where the copper deposit to the south is located, showed the main S1 foliation subdivided into two pole patterns: one in the NE-SE quadrants and the other in the NW-SW quadrants. This garland pattern suggests a second phase of deformation and was the only one to differ from the bibliography. Finally, Domain 4, related to the Serra Negra Granite Unit, showed structures oriented predominantly to the east. These results highlight the tectonic complexity of the area and provide new information on its structural evolution.