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THE TECTONIC STRATIGRAPHIC FRAMEWORK OF THE CAETÉ REGION, QUADRILÁTERO FERRÍFERO, MINAS GERAIS, BRAZIL

Texto do resumo

The complex tectonic and stratigraphic structure of the Caeté region has been a subject of discussion since the beginnings of gold mining in the region that is the birthplace of the large mines still in production in the Quadrilátero Ferrífero (QF). In this region, geological maps show a regional scale fold where the Morro Vermelho Formation (MVF), base of the Nova Lima Group (NLG), is at the center of the structure, representing what would be an anticline. However, the geometry of the structure is a synform where the axis of the fold dips to the opposite side of its closure (E-SE). Thus, the Caeté Fold is characterized as an anticlinal synform, that is, a complex fold interference structure, which generates different interpretations and models among the scientific community. The present work seeks to elucidate and simplify the tectonic and stratigraphic relationships in the region using unpublished data from exploratory research by the company Jaguar Mining Inc. The geological structural mapping, description of drilling cores and multi-element geochemical data in the Carrancas and Rocinha target region showed a stratigraphic sequence containing laminated schist between sericite and quartz interspersed with layers of metatuffs, BIF's/metacherts and late mafic dikes. These rock occurrences do not represent the Morro Vermelho Formation described for the region on regional geological maps. Other evidence raised that helps with differentiation is the absence of characteristic metamafic rocks and carbonaceous shales, the reduced amount of BIFs/metacherts, the physiographic difference and styles of outcrops. Based on the differences found between regional and local geology, we suggest the creation of a new geological formation, younger in the NLG stratigraphy, named Rocinha-Carrancas Formation for this work. With this new knowledge it is possible to simplify the structural understanding of the region, giving the Caeté Fold the classification of an inverted syncline, isoclinal, axis with a gentle dip (10º-15º) to the SE and the two flanks with a gentle dip (20º-25º) to the S -SE, ruling out the complex fold interference model. This proposed geometry, supported by structural data collected in the region, leads to the interpretation of the formation of the Caeté Fold in a single Archean deformational event where the strain was significantly high, in a constrictive deformation regime, forming L-tectonites, tight intrafolial folds and sheath folds (A-axis folds) which explains the parallelism between the axis and intersection lineations with the stretching lineations and mineral lineations, which is observed throughout the area. This way we can separate this region of Caeté into 3 different tectonic domains. The central domain, strictly Archean, is represented by the inverted Caeté Fold syncline, delimited to the S-SE by the Ribeirão da Prata fault, which represents a Paleoproterozoic tectonic sliver, with vergence from SE to NW, and which transports the NLG base over the top sequences. The third domain is to the E, is limited by the Caeté fault, which represents a Brasilian tectonic sliver, with vergence from E to W, and transports the NLG base and the Caeté dome over the Caeté Fold.

Palavras Chave

Quadrilátero Ferrífero; caeté fold; jaguar mining