Mapeamento geológico-geotécnico: mina de Barro Alto - GO, Anglo American

Abstract

The Barro Alto Mafic-Ultramafic Complex is part of the Goiás Massif, which is inserted in the geological context of the Tocantins Province. The deformations associated to the amalgamation of Gondwana generated in the study area a series of structures and deformation stages. A schistose (S1) subparallel to the compositional banding (S0) is characterized. Boomerang-like refolding patterns associated with flexural slip mechanisms are also observed. Conjunctively, a NE-SW and NW-SE fracture system compatible with idealized fracturing models associated with cylindrical flexural folding are observed. The Barro Alto supergene nickel deposit is composed of lithological units derived from ultrabasic rocks - dunite-serpentinized, dunite boulder, base ore, acid ore, ferruginous ore, internal waste rock, soft chalcedony, hard chalcedony and laterite soil. Nickel extraction in Barro Alto is characterized by open pit mining, which consists of excavation of the soil or soft rock and consequent modification of the topography. These modifications must be technically planned, in order to optimize resources and increase safety levels. Saprolitized heterogeneous massifs are composed of reliquary structural features, rock blocks immersed in the weathered profile (bedrock), and irregular zones with contrasting weathering. These heterogeneities usually control the failure mechanisms and locations, as well as the factor of safety. For this work, in addition to good internal practices, the geological-geotechnical characterization was carried out based on the recommendations suggested by the ISRM and the criteria established by the RMR rock mass classification system (Bieniawski, 1989). The geological-geotechnical characterization indicated a rather heterogeneous and anisotropic massif. Furthermore, the simple kinematic analysis performed as a preliminary study obtained indices higher than 0.1 (10%) for planar and wedge type ruptures.