Designing or excavating an open pit mine requires a detailed understanding of major structures that have the potential to create large failures in pit walls. Evaluating large scale structures geometrically and kinematically enables an operator to mitigate the associated structural risk in developing an open pit.
Using accurate three-dimensional modeling, SRK combines detailed mapping and kinematic analysis of large scale structures in real time, taking into account mining induced stress fields and neotectonic seismic activity.
Recently, SRK conducted structural geological investigations of the Antamina Mine for Compania Minera Antamina Inc. and the Magistral project for Inca Pacific Resources Inc. Both deposits are located high in the Peruvian Andes. As part of the broader geotechnical characterisation of the deposits, the studies were principally focused on the construction of 3D structural models by integrating all available data (drillholes, surface maps and structural studies of drillholes), with the aim of delineating the geometry of major structures (faults, dykes and stratigraphic contacts) that might present possible zones of pit slope failure.
For both deposits, the major structures were constructed in three dimensions using a combination of Gemcom, AutoCAD, and Leapfrog software. The structures modeled included different generations of faulting and their kinematics, dykes, and lithological contacts. All model entities were ground-truthed and geotechnically characterised in the field, to provide a more robust correlation between surface geological observations and drillhole geological observations. The drillhole databases for both deposits contain a large number of fault intersections, which, in the absence of oriented data, is easy to misinterpret. As a result, the field mapping constraints proved extremely important in guiding the interpretation of the major faults. The fault intersections and offsets were also checked against field evidence to produce a realistic representation of the major structures within the pit area.
For the Magistral deposit, a total of ten structures were modeled and evaluated for their potential for pit slope failure. This resulted in the slight modification of the design of the planned open pit geometry. For the Antamina deposit, a total of sixty structures were modeled and evaluated for their potential for pit slope failure. No major geotechnical issues affecting current pit stability were identified at Antamina, though further investigations are warranted into possible intersections of structures with the ultimate pit.
