De Beers is currently developing closure plans for two open pit mines. At first glance they appear quite similar; both are relatively remote, have operated for 10 years, have similar pit dimensions (250-300 m deep and 1.5 km wide) and have Palaeozoic sedimentary host lithologies with weak upper units overlying more competent lower materials. However, Victor Mine in the sub-Arctic Canada, is one of De Beers wettest mines (dewatering volume of 75,000 m 3 /d) and is hosted predominantly in good quality limestone with excellent final wall performance. While Voorspoed Mine, in semi-arid Southern Africa required virtually no dewatering, has poor wall performance associated many with mudstone and country rock breccia instabilities. Victor Mine is expected to achieve stable pit lake in less than 10 years (and less than 2 years with supplementation from a nearby river), while Voorspoed will take over 100 years to reach ultimate pit lake level (due to low groundwater inflows, high evaporation and limited opportunity for flow supplementation). This paper describes a process to determine closure stability design acceptance criteria (DAC) and characterise the zone of long-term surface disturbance surrounding the pit (i.e.: potentially unstable pit edge zone to define the closure exclusion zone). This involved: 1) Pit break back-analysis using i) industry guidelines; ii) an empirical approach based on historical slope instabilities; and iii) stability analysis using predicted post-closure phreatic surfaces. 2) Estimates of erosion potential. These results along with the well documented historical slope performance provided the basis for detailed Geotechnical Risk Assessments which addressed two periods. • Active closure with personnel undertaking rehabilitation activities in and surrounding the pits, and • Long-term closure, personnel and equipment not permitted within the long-term break back zone. Risk-based monitoring plans were developed along with Trigger Action Response Plans (TARPs) to ensure that closure of the pit proceeds safely and efficiently while satisfying the regulatory requirements.

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Rio Tinto Iron Ore's (RTIO) Western Australian mine operations comprises 14 mines with a centralised 'Mission Control' Operations Centre (OC) in Perth, and currently delivers 237 Mt/a ore from over 120 individual open pits. Operational challenges in terms of implementation of effective slope monitoring systems with appropriate visibility of system health and alarm notifications needed to be addressed. The geotechnical, management and support teams are site and Perth based, and all require access to geoscience monitoring data.Historically, each site had an independent monitoring and alarming systems. Transparency of monitoring data, health checks and alarming capabilities were limited. The lack of a system to display temporal geotechnical (slope performance), and hydrogeological monitoring data, with 24/7 alarm and system health status had been identified as a 'gap' following a previous slope instability incident at one of the Pilbara Operations.At project inception, the need for a visualisation and management tool which had a multidisciplinary focus and integrating georeferenced geoscience monitoring data with physical models in near real time, was identified. Consequently the Geoscience Monitoring Data System (GMDS) was developed to address three main requirements: Provide a consolidated overview of all geoscience monitoring data and physical models.  Show monitoring system and device health, and alarm status at a high level. Be integrated with existing slope performance and hazard management systems. This tool is in alignment with Rio Tinto's Mine of the Future and RTIO's Operations Centre vision by using technology to reduce costs, increase efficiency and improve health, safety and environmental performance. It provides the functionality to manage diverse instrumentation data in a consistent, standardised approach to support RTIO's geographically spread expansion plans.

A planar failure of approximately 600 kT occurred on the north wall of Centre Pit North (CEPN) at West Angelas Mine site in February 2010. The failure impacted a substantial resource of high grade iron ore and left a number of significant geotechnical hazards on and adjacent to the failure surface. These presented a series of challenges which had to be overcome in order to remediate the failure and reclaim the bulk of the buried ore. A number of recovery options were investigated and presented to management. This paper outlines the plan which was adopted, the challenges encountered during its implementation and the risk management and mining procedures used to bring the remediation and recovery to a successful conclusion. A significant fall of ground occurred on the north wall of CEPN at the West Angelas Mine site on the evening of the 3 February 2010. The failure occurred in the Mount Newman Member of the Marra Mamba Iron Formation, which is comprised predominantly of banded iron formation (BIF) with interbedded shale. Bedding dip was roughly parallel to the overall slope angle, except where it flattened towards the pit, on the lower benches. The failure was due to planar sliding on the NS2 shale, which was daylighted in places, towards the toe of the slope. The resultant failure surface is approximately 112 m high, dipping at an average of 42°. The failed rill heap of approximately 600 kT, covered a significant resource of high grade iron ore.

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