New Gold's New Afton mine is a six million tonne per year operating mine located 8 km southwest of Kamloops, British Columbia, Canada. The current mining lift is approximately 600 m below ground, partially beneath the historical Afton pit. The subsidence zone at New Afton has developed asymmetrically and has deviated from the initial feasibility study modelling estimates. The growth of the subsidence zone extents is now being monitored in consideration of the mine's surface infrastructure. The subsidence monitoring system at New Afton has been developed in phases in response to project needs. Initially, monitoring was setup to track the predicted cave growth and surface deformation near the crater. The monitoring network was expanded to areas away from the crater using additional instruments of various types. An automated data collection and retrieval system was implemented, with existing electrical instruments retrofitted to collect and transmit data automatically to the mine's database. Drilling completed to install these instruments allowed collection of new subsurface information used to refine the geological model, thus improving the mine's understanding of subsidence progression. In addition to providing information necessary for day-to-day mine operations, data collected from this monitoring system allow for refinement of predictions of future subsidence. The different data types each come with limitations and interpretation challenges. This paper discusses the development of the monitoring network, along with instrument selection criteria and performance information for New Afton.

During deep tunnelling or mining infrastructure development, the assumed stress state has significant implications on geomechanical design. Remote measurement of the three-dimensional stress state at depth has proven to be a significant challenge and is often assumed from historic tests or the regional tectonic setting. To date, borehole breakout analysis has only provided some assistance for orientation of the principal stresses in the plane perpendicular to the borehole axis. This paper presents a stress estimation methodology using numerical modelling, which allows for the back analysis of breakout profiles from a shaft pilot hole at KGHM's Victoria project in Sudbury, Canada. By iteratively changing the horizontal principal stress ratio and maximum tangential wall stress, a set of generalised curves relating breakout characteristics (breakout depth and opening angle) and borehole strength along the 2 km borehole were made. By recording the change in breakout geometry along the length of the hole, the curves can be used to gain an understanding of changes in stress state as a function of depth and lithology. Given the foliated nature of the units intersected throughout the borehole, the effects of systematically oriented structure on breakout was assessed. This provides a relative understanding of how such structure may cause an overestimation of stress from the back analysis of breakout. With the choice of an appropriate constitutive model, characterisation of the full stress tensor through back analysis of borehole scale failure was made with a greater degree of confidence.

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Operating open pits are exposed to geotechnical stability risks throughout the life of mine. These risks can be considered part of normal operating conditions and are managed by mining teams. Following the completion of mining, weak rock slopes can exhibit progressive failure mechanisms due to severe erosion or deterioration and are negatively influenced by the post-mining hydrogeological and hydrology conditions. In this context, these failure mechanisms can impact existing or planned mine infrastructure (e.g., water treatment, diversion channels, closure landforms) that is needed to achieve mine closure objectives. This paper describes key geotechnical and hydrogeological aspects that need consideration in developing a work plan for rigorous mine closure open pit stability assessment in weak rocks. The paper is supported by a case study of a pit stability assessment at the Faro Mine Complex, a former lead-zinc open pit located in YukonTerritory, Canada. For this case study, the importance of the stability assessment work to the positioning of a new permanent non-contact water diversion channel is described, including locating the alignment outside of the predicted long-term pit slope break-back.