Canadian mining operations have long been key contributors to economic vitality. This has resulted in Canada standing at the forefront of implementing best practices that relate to mine closure projects. In the case of closing historical mines this can be a particularly challenging task as often the level of information available is much less than active mines preparing to close. Closing historical mines provides an opportunity to apply new, and innovative methods to collect the data required to design and execute a successful mine closure plan.
The site discussed in this study is in northern Canada and used interconnecting open pit and underground mining methods while in operation but has been closed for over half a century. Historical documents indicate that the mine was closed after a failure occurred at depth and some backfill material was lost. A pond currently exists where the open pit was located. This study is focused on rock mechanics and discusses the methods used to assess the geometry and stability of the historical mine workings. The need for innovation stemmed from the limited historical plans and documentation that existed. Empirical methods suggested that the crown pillar at the site was unstable and should have failed, which did not align with on-site observations.
Therefore, an alternative method of assessing the stability was required which involved undertaking bathymetric and 3D sonar surveys to gain a better spatial understanding of the open pit and underground environment.
These surveys improved the spatial understanding of the geometry of the mine workings, the quality of the rock mass, potential geologic structures exposed, the excavation conditions, and the stability of the excavation.
The quality of the data allowed the identification of joint sets and potential failure planes in the rock. Additionally, visualisation of the bottom of the mine workings allowed observations to be made that reflected the stability of the excavations. A lack of failed material suggested that minimal failures had occurred in the excavation walls and the crown pillar. This information made a positive contribution in assessing the future stability of the site.
