Mastering the tricky art of responsible waste planning

Mines are under increasing pressure to reduce their environmental footprints. Tougher government regulations and increased public scrutiny have elevated responsible reclamation to be a higher priority across the industry. It’s especially relevant in the South Pacific islands of New Caledonia, where mines operate under the added oversight of UNESCO (United Nations Educational, Scientific and Cultural Organization).

In 2008, UNESCO added the Lagoons of New Caledonia to the World Heritage Site list, meaning mines are subject to rigorous environmental standards and regulations. One example of these standards is in the restriction of disturbance limits. The disturbance area is restricted to the ultimate pit limits, and all mining activity must stay in this confined area. This imposes a series of limitations and challenges, including a limitation on the space available for waste dumps.

This means the mines must manage material efficiently and backfill the pit with previously mined waste material. However, opening the space on the pit floor to accommodate the waste can be tricky. In the process of opening the pit floor for backfill, the management and availability of the multiple ore types materials needs to be considered.

This poses a significant challenge in the mine planning process; the excavation requires a very precise schedule to remove the different material types to maintain the grade balance at the mill, while minimizing re-handling.

Nickel in New Caledonia

A significant amount of the world’s nickel production comes from New Caledonia, one of the top five nickel producers in the world. Many of these nickel mines have started producing cobalt with the recent upsurge in renewable energy. The nickel/cobalt mines in New Caledonia (mostly open pit operations) consist of very large nickel laterite deposits, that are typically located close to the surface.

The deposition sequence includes iron oxides (laterites) near the surface, and magnesium silicates (saprolites) beneath. Knowing the geology of the deposit is key, and the first step in the long and difficult process of preparing a strategic mine plan.

 

Meeting grade constraints

The restrictions for magnesium and manganese percentages to the mill are rigid and must be met in order to maintain the plant’s recovery. Unfortunately, the high-grade nickel and cobalt ore typically come with high amounts of magnesium and manganese as well.

Using MinePlan’s Schedule Optimizer (MPSO), the grade constraints can be applied and altered on a multi-period basis to maximize the mills processing abilities. This means that the mine plan will try to honor the magnesium and manganese restrictions. If there was a time that the grade balance could not be kept, the schedule would seek other routes, or fail to find an excavation strategy.

This kind of long-range planning tool helps the site verify that they can achieve their mining objectives and provides a schedule for the life-of mine. The long-term plan allows the site engineers to simulate different mining scenarios when considering commodity prices and inflation by the input of economic information. Using all the tools at their disposal, the engineering group can optimize the schedule and evaluate many of the possibilities the mine may see.

Grade constraint set up in MPSO.

Optimal dump planning

With the stringent mill constraints and the minimal working area, engineers fight an up-hill battle with no summit in sight. All the material must stay within the working area which only consist of the ultimate pit limits. This means that the first waste dumps will be placed on the future ore zones, requiring the material to be moved at a later date. Using MinePlan 3D software (MP3D) the engineers can create the dump designs with a specific amount of volume or tonnage in mind. This allows the engineers to design waste dumps to be re-handled at a specific time and they can strategically schedule the start of the final waste dump areas.

In-pit dump placement for the first-workings waste.

Cut planning

Timing the sequencing of all these moving parts requires the expertise of an experienced user and the right tool for the job. MPSO was not only able to manage the need to re-handle waste material, but also strategically schedule the mining cuts. MPSO optimized the sequencing of mining of cuts to maximize net present value while trying to honor all the quality, quantity and blending constraints. The sequence and constraints are performed through multiple iterations of the plan to get the best results.

Plans can be made solely on nickel recovery, or factor in the extraction of cobalt, which will dramatically change the order in which the pit is opened up. The ability to create multiple plans to account for different scenarios the mine may face is one of MPSO’s strongest qualities. The long/medium range plans prepared with MPSO are then used as a guideline for short-term plans, which are prepared with MinePlan Activity Scheduler.

Re-handling the waste material and creating the first waste dump.

Mining increasingly depends on digital solutions and relies more on accurate planning to both improve the recovery of minerals and reduce the disturbance on the environment. The environment and local ecosystems must be protected by using an adequate plan which ensures the mine is meeting or exceeding all regulations set by the local government and company polices.

Strategic re-handling of waste material allows the mine to stay profitable, while adhering to all restrictions in place. MinePlan 3D is the leading software for creating of life-of-mine plans and allowing mine sites to optimize every aspect of the mine planning process.

 

Summarized from ‘An environmentally friendly approach to dump planning optimization’ by Corbin Goldsmith and Principal Mine Planning Specialist, Ernesto Vivas.

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