Estudo geológico comparativo entre as bentonitas de região de Melo (Uruguai) e da região de Vitória da Conquista (Bahia)

Abstract

The bentonite deposit in the Bañado de Medina region, located 18 km southwest of the town of Melo in Uruguay, is the first occurrence in the region with potential for commercial exploitation. The studied bentonite appears in the Serrinha Member, belonging to the Rio do Rasto Formation, which is part of the Upper Permian of the Paraná Basin. According to the texture, sedimentary structures and color, the bentonite layer was divided into four units. The determination of mineralogy by X-ray diffraction shows the predominance of dioctahedral calcium smectite followed by quartz, plagioclase and alkali feldspar appear in smaller amounts. The chemical results indicate a smectite with a low iron content (2.01% up to 3.94%), significant contents in Mg2 + and Al3 +, since the values are considered high of Mg2 + between 4.57% and 6.54% and Values of Al3 + appear with levels of 14.64% and 17.75%. The Pradoso bentonite deposit is located about 16 km west of Vitória da Conquista. In the deposit area, it is interpreted that the gneiss and basic intercalations occur on the edge of the Vitória da Conquista Plateau, in an altered state, with incipient signs of greenish smectite. The mineralogical analysis by X-ray diffraction indicates montmorillonite, kaolinite, vermiculite and quartz. The chemical analysis shows significant levels of aluminum, magnesium and iron. The type B bentonite of the Vitória da Conquista deposit is the one with the highest amounts of montmorillonite, reaching 95% of the total sample. It is important to emphasize that the two bentonites have quartz, but the bentonite of Bañado Medina has more significant amounts. This differentiated content of quartz is interpreted as reflecting the composition of the source rock, the volcanic ash composition of the river-dacitic (Calarge, 2001) in the bentonite of Bañado de Medina and a basic rock (amphibolite) in the Bahia deposit. The deposits compared in this work are located more than 2400 km away.