We are grateful to Davi Newton Pinheiro da Costa Gomes, Geologist Engineer – Rock Mechanic at AngloGold Ashanti, for producing this paper. The paper is provided in the original Portuguese as well as English  , and aims to show how the rockmass classification of the mine known as Orebody V was performed, as well as different ways of interpreting a 3D geotechnical model.

Pre-feasibility of open pit mining

The study serves as the initial step of the pre-feasibility of open pit mining. Due to the lack of fresh rocks, this classification was performed only on the basis of drill-cores. Most of the drill-holes analysed were drilled at the end of the 1990s, when Serra Grande Mine adopted the procedure to discard the most weathered drill-cores. Significant non-recovered intervals occur due to the existence of “cavities” developed in karst, as well as in saprolite. The structural data required for the development of the study comes from underground ore-drives.

The four classes of rock identified enabled two interpretations of different 3D models. The first interpretation considers the data in a qualitative way, with the direct association of the rock-mass classes and the Down-Dip of the main foliation. The second interpretation considers the data in a quantitative way, so the boundaries between the classes are delimited by a geostatistical method which influences the numerical data of the neighbouring intervals.

Due to the geological environment where the Orebody V mine is located, it can’t be considered certain that the geotechnical parameters have significant spatial continuity in a specific direction. For this reason, the model interpreted in a qualitative way, with correlated classes, was considered the best option.

Portuguese and English paper.