Surface subsidence analysis associated with caving at La Encantada Silver Mine

Abstract

This study describes a multi-year effort to calibrate a numerical model to mapped surface subsidence and other damage indicators in a historic silver mine that is now being exploited via caving. In 2017, the subsidence extent along with the general condition and character of the rock mass both underground and in the vicinity of the craters was evaluated during a site visit. Surface cracks were mapped in the vicinity of the existing crater to provide a more accurate representation of the 2017 fracture limit that needed to be captured by the numerical model before any forward prediction was made. A numerical model was developed to back analyse the 2017 conditions following from the historic mining that had taken place, resulting in close agreement with observations made on site. A forward surface subsidence prediction was then obtained based on the target draw schedule to exploit the remaining orebody via caving. In 2020, the actual draw schedule followed until that point was updated in the model to evaluate the validity of the results of the numerical model as well as future predictions. As new extraction points with updated production tonnages were added to the mining plan, the calibrated model was used to provide updated estimates of cave growth, surface subsidence, and building/infrastructure potential damage through the life-of-mine.