PhD thesis: Aplicação de Processamento e Inversão Geofísica 3D de Dados de Aerogradiometria da Gravidade na Estimação da Estrutura do Minério de Ferro no Sinclinal Gandarela - Quadrilátero Ferrífero - Minas Gerais

(2013) Dionísio Uendro Carlos


The Quadrilátero Ferrífero in southeastern Brazil hosts one of the largest concentrations of lateritic iron ore deposits in the world. Our study area is over the southern flank of the Gandarela syncline which is one of the regional synclines of the Quadrilátero Ferrífero. The Gandarela syncline is considered the Brazilian megastructure with the highest perspectives for iron ore exploration. Most of the iron ore deposits from the Quadrilátero Ferrífero are non-outcropping bodies hosted in the oxidized, metamorphosed and heterogeneously deformed banded iron formations. Therefore, the assessment of the 3D geometry of the iron body is of the utmost importance for estimating reserves and production development planning. We inverted the airborne gravity-gradient data from the study area by using two inversion methods to estimate the 3D density-contrast distribution which retrieves the shape of the iron ore mineralization. The highest values of the estimated density contrast agree reasonably well with the information provided from the lithologic logging data of drill holes and retrieve a northeast-elongated iron formation in agreement with the previous geologic mapping of the study area. The volume of the estimated iron body varies along its strike showing a southwestward increase. The presence of a large volume of iron ore in the southwest portion of the study area may be due to the hinge zone of the Gandarela syncline, which is the zone of maximum compression. The estimated iron ore mass discloses variable dip directions. In the southernmost, central and northernmost portions of the study area, the estimated iron body dips, respectively, inwards, vertically and outwards with respect to the syncline axis. Because one of the inversion methods estimates a 3D compact iron ore body with density contrast of 0.75 g/cm3 , then it allows estimating the volume of this body in 965 million m3. By considering that this estimated