3D Modelling of a subsector of Casas Novas gold mineralization, Montemor-o-Novo, Portugal

The aim of this study is to build a 3D model of classes of gold grades in the high strain domain subsector of Boa Fé fault Zone, near Montemor-o-Novo - Évora, SW Iberian Massif. Data for this study were provided by Iberian Resources Company, and consists of boreholes and trenches log descriptions and grades of gold. The proposed model was developed in two consecutive stages: i) construction of a geological model; ii) stochastic simulation of classes of gold grades conditioned to the geological model. In the first stage log descriptions from boreholes and trenches were coded into a categorical variable named lithogroups, i.e. associations of "similar" lithologies. Among the 39 initial lithological descriptions 3 lithogroups were obtained. With this data, heuristic geological limits of these lithogroups were digitized in several parallel sections using the capabilities of gOcad. Finally, 3D closed surfaces were interpolated for the entire area leading to 3D vector geobodies of lithogroups. In the second stage, gold grades were previously classified into 3 classes (high, medium and low) and boreholes and trench data are regularized into supports of the same size. Gold grades were intersected with the geobodies of lithogroups enabling calculation of geobodies statistics in terms of gold grades. Finally, images of gold classes were generated with sequential indicator simulation (SIS), conditioned both to boreholes and trenches (hard data) and the local proportions of gold grades given by the geological model of lithogroups (soft data).