At Snowden our Mine Planning group thrives on solving complex problems quickly. Because each project is unique, we often develop our own tools to get the best bottom-line outcome for our clients. We do this by leveraging our diverse range of skills, experiences and perspectives as mining engineers, mathematicians and software developers. This series of articles provide some examples of where we have developed innovative solutions to problems; solutions that could also help add value to your project or operation.
In the mid-2000s, Snowden recognised the lack of suitable tools to help optimise the strategy for underground mines to develop robust solutions in a rapid and robust way (similar to tools like Whittle 4X that are routinely used for open pit modelling). Many mining projects have suboptimal plans due to a lack of understanding of the project value drivers, and the need to optimise a project globally for NPV. Potentially, many hundreds of millions of dollars of value can be left on the table.
With this in mind, we developed a tool to do this for us and this led to the inception of Evaluator. Given an underground mining inventory at a range of cut-off grades (usually defined using our Stopesizor software), the key development assumptions, some economic parameters and sequencing constraints, Evaluator will produce a range of outcomes to assist you in determining the optimal production rate and cut-off grade of the resource.
This initial version of Evaluator was successfully used on a number of complex underground projects. However, underground mines were often associated with open pit mines and they needed to be scheduled together to get an optimal outcome for the whole business. To resolve this issue, Snowden modified Evaluator to also optimise a combination of open pits and underground inventories, and purely open pit operations.
The Evaluator tool used over the last few years is a global scheduling and cut-off grade NPV optimiser, based on a Mixed Integer Programming method. The software considers the structure of the mining business, intuitively modelling the flows of material through the system.
The user applies economic parameters, sequencing rules, and system constraints (like tonnage moved or processed, product railed, product specifications. or plant/truck hours) are applied and the resultant Evaluator solution will indicate to you when each parcel of material should be mined, and where it should go, to maximise the NPV of the project. The global optimisation considers all factors and periods simultaneously and allows you to make the most informed decisions on waste stripping, stockpiling, cut-off grade, capital allocation, and blending; issues that cannot be resolved optimally with rules-based schedulers.
Over the years, based on the needs of mining projects, Snowden has added features such as:
Schedule smoothing: Some linear programming based tools will produce impractical schedules. Snowden has implemented the ability to smooth production to produce realistic mining schedules.
Backfill: If it is economically attractive Evaluator can mine out pits, opening them up for backfilling.
Capital optimisation: Evaluator has the ability to optimise the allocation of capital. For example, how many trucks should you buy and when? When should you expand your plant?
Grade penalties: Some mining projects pay penalties when their product is outside a set product specification. However, sometimes it is economically worth the penalty to sustain production. Evaluator helps to quantify these trade-offs for your project.
Variable advance rates: Not every bench, or underground level, is the same. Evaluator enables variable durations for each mining activity to provide a more realistic schedule.
Snowden has used Evaluator to help give mining projects the edge they need to present the best possible business case for financing. The improvements are often more than 20% on NPV when compared to a traditional mine plan.
Some examples are shown below.