Facies analysis and depositional environments of the Vazante Group in the region of Morro Agudo mine, Paracatu, northwest of Minas Gerais state, Brazil

Abstract

Vazante Group rocks outcrop in the northwest of Minas Gerais state, in a continuous belt of approximately 250 km, from the region of Vazante city, in the south, to Unaí city, in the north. In this region is the zinc and lead mine of Morro Agudo, which together with the deposits of Vazante, Ambrósia and Fagundes, all housed in the Vazante Group, make up the main zinc province of the country. Twelve sedimentary facies and four facies associations (AFs) were described in six drill holes and outcrops, that indicate deposition in a carbonate-siliciclastic mixed passive margin setting. The most basal association is AF01, composed by carbonaceous mudstone and silt-sand rhythmic, representing sedimentation in a deep platform of low slope angle, in a regime of marine transgression. After the maximum flood surface, in the highstand systems tract, AF02 was deposited in a reef setting with a barrier at the platform edge. It is composed of laminated dolomites with stromatolites, dolarenites and dolarenite breccia, and carbonate carbonaceous mudstones with interleaved diamictite facies. The fall in relative sea level led to a forced regression and the deposition of AF03 in a forced regressive system’s tract. It is composed, at the base, by carbonaceous diamictite with AF02 fragments, passing to mudstone and silt-sand rhythmithes. The return of the rise of the relative sea level provided the deposition of AF04 and AF03 rocks in a more distal position. AF04 is composed by laminated and massive argillaceous dololutite, and intraclastic dolarenite, deposited in carbonate marine platform. The observed stacking pattern suggests that the deposition of all units occurred progressively, in process of rising relative sea level