Life-of-mine ventilation planning at Diavik

Abstract

A framework for ventilation planning, with particular focus on planning to the end of mine life, was developed for use at the Diavik Diamond Mine. Diavik has been an underground operation since 2012 and has a mine life of only 13 years. With only eight years remaining the mine will go through some fundamental milestones before closure. These milestones include the closing of two orebodies, leaving a single orebody for the final three years of mine life. A significant change to the ventilation system will be required to support the transition to the final configuration. The framework achieved this result through the reconciliation of the production plan with the ventilation plan by creating design acceptability criteria, and using the value-ease analysis method to narrow down relatively quickly the ideas generated to two options for detailed assessment and economic analysis. For Diavik, the framework was successfully utilized by the mine engineers to select a cost effective ventilation plan based on twinning an exhaust raise and re-equipping an old drift to the pit as an exhaust path with a new fan chamber. Introduction The Diavik Diamond Mine has been an underground-only operation since 2012 and has a remaining mine life of eight years. In the first year of underground-only operations the production rate ramped up from 60 kt of ore per month to over 160 kt per month, and in the subsequent years this rate was pushed continuously as the operation went through various improvement initiatives. These increases are shown in Table 1; they demonstrate how early plans created before commercial production became detached from reality after a few years. By the end of 2016 Diavik was 1.2 Mt (+14.8%) ahead of the 2012 Mine Plan. Table 1. Plan vs Actual Ore Production at the Diavik Underground Mine 2012-16 (Harry Winston, 2012) (Yip and Pollock, 2017) Diavik UG 2012 2013 2014 2015 2016 Actual Underground Production 0.94 Mt 1.96 Mt 2.28 Mt 1.98 Mt 2.21 Mt 2012 Budget Plan 0.96 Mt 1.8 Mt 1.8 Mt 1.8 Mt 1.8 Mt During its remaining operational life, the mine will pass through several fundamental milestones. For ventilation, these milestones are the opening of C-block for sublevel stoping in the A154N orebody in 2018, the depletion of the A154S orebody in 2019, and the depletion of the A418 orebody while opening D-block in A154N in 2021, identified in Figures 1 and 2. This plan will leave a single orebody in operation for the final three years of mine life (Yip and Pollock, 2017). A significant change to the ventilation system was required to support these transitions to the final configuration. A framework for ventilation planning has been developed and was utilized to select a ventilation plan that will meet the requirements of the life-of-mine plan. Ventilation and Primary Fan Description Diavik’s primary surface “FAR” Fans, identified in Figure 1, move approximately 710 m3/s (1.5 Mcfm) with five Alphair 10150-AMF-5500 Full Blade 2.6m (101.5”) diameter fans operated in parallel, each powered by a 336 kW (450hp) motor. These fans push air into the underground through three fresh-airraises. Diesel heaters in front of the fans maintain a temperature underground that is above freezing. Fresh air is delivered to a mid-point in the mine known as the “Haulage Drift” which connects the southern A418 orebody with the northern A154 South and A154 North orebodies, also shown in Figure 1. Booster fan installations direct air to the bottom of the main ramps at either end of the mine, and other installations push or pull fresh air across the production levels (Robinson and Gherghel, 2013). There are no doors or other regulating controls in the main ramps; airflow is directed around the mine with the aforementioned booster fans. The mining method for the A418 and A154 South orebodies is sub-level retreat (SLR), which is similar to sub-level caving except without caving of the hanging wall. In A154 North orebody blast hole stoping (BHS), also known as sublevel or longhole stoping, is the mining method with a primary-secondary sequence and backfill (Yip and Pollock, 2017). Figure 1. Isometric view of the Diavik Underground Mine Framework for Ventilation Planning A framework for ventilation planning was built for use by Diavik but this framework could be used also by other operating mines to guide long range ventilation planning. The framework was designed to help then mine engineers select a ventilation plan after the mine plan had already been completed, rather than in tandem as would be expected for a feasibility study, and uses evaluation methods such as the “valueease principle” to advance rapidly from numerous ideas to a detailed options analysis. The framework can be summarized as follows. Prepare Inputs 1. Simplify the Mine Development and Production Plan 2. Determine Design Acceptability Criteria and Estimate Airflow Requirements 3. Prepare Calibrated Ventilation Model of Current Mine A418 Ore Body A154S Ore Body A154N Ore Body FAR Fans