Chile is host to some of the most extensive natural resources in the world. However, these resources also pose some key challenges: the complex geology present - faults, rock heterogeneities and discontinuities. The aim of the GeoSafe project is to twofold: to develop a new collaboration between the Rock Mechanics Laboratory (RML), University of Portsmouth (UoP) and the School of Mining Engineering and Structural & Geotechnical Engineering, Pontificia Universidad Católica de Chile (PUC), and to measure and link underpinning rock-physics parameters to the development of fracture damage and heterogeneity in mines. New data is needed in order to understand and manage physical safety (e.g. bench collapse or rock-bursts) and environmental safety (e.g. mapping and simulating likely fluid/contaminant flow) in stressed rock masses.
Here we present data from two mining districts. The Tiltil artisanal mine, and the El Teniente large scale facility in the O'Higgins region, ~2 hours South-East from Santiago. Both are dominated by complex series of mineralized bodies hosting porphyry-copper type deposits within successions of volcanic and plutonic rocks. The Tiltil district also hosts porphyry coppers as strata bound deposits. As with many areas of the Andes, both districts are heavily faulted with abundant mineralization and alteration which combine to generate significantly different rock mechanical properties even within the same rock unit. Over the course of 18 months the team conducted 4 bilateral rock collection visits to generate an extensive database on these units, and conducted field surveys of the rock masses insitu (within tunnels).
Rock Physics data shows that the inherent anisotropy has a huge effect in both areas, with Unconfined Compressive Strength (UCS) ranging from 70 to 114 MPa for a dacite lithology and 90 to 140 MPa for an andesite (designated CMET) unit. Tensile strength reveals tensile strength between 6.2 and 10.9 MPa (dacite) and 10.7 and 13.2 MPa (CMET). Triaxial experiments also show significant variability with strength ranging from approximately 50MPa at 5MPa confining pressure to approximately 175MPa at 25MPa confining pressure, and with complex strain paths. We interpret this to be as a result of the orientated veining in the rock mass (and thus samples) which controls the deformation and influences the eventual strength at failure. This is supported by cyclical experiments using Acoustic Emission (both USC and triaxial) suggesting that damage preferentially accumulates along the veining. Future work will include these data into new COMSOL-based models of the larger rock mass.
