O sistema cárstico de Vazante - carste em profundidade em metadolomitos do Grupo Vazante – MG

Abstract

The advanced state of karstification in the metadolomites of the Neoproterozoic Vazante Group cause several geotechnical and hydrogeological problems in the underground zinc mine located in the city of Vazante, Minas Gerais State. The continuity of karstification at depths below the regional base level and vadose zone, indicates the application of hypogenic espeleogenetic models, that consider the migration of fluids from below, driven by hydrostatic pressure or other sources of energy. In this work different kinds of tools were used to understand the karstification in the area. The existence of hydrothermal fluids was first investigated and its influence on the karstification, then the morphology of the conducts was studied to understand the fluid direction that caused the dissolutions. The conclusion that comes out from the data is that the geological and geomorphological history of the region makes possible the separation of at least four karstification phases. The first phase corresponds to a paleokarst formed by the migration of saline fluids with high temperature through the Vazante Fault, dissolving the metadolomites and forming veins and breccias with dolomite cement. The second stage is related to the exposure of these rocks and karstification by hypogenic and epigenic processes. The third phase corresponds to the subjacent-karst, which was completely buried by colluviums and alluviums, filling the caves opened in the previous phases. The last stage corresponds to the actual days, when the karstified rocks are exposed again, undergoing a subsidence process evidenced by the erosion of rivers banks, a period defined as exhumed-karst, subjected again to hypogenic and epigenic processes.