The mining industry recognises that “underground mines are getting deeper and the available commodity grades are reducing”. Although a generic statement, new high‑grade deposits are less common, and it is easily accepted that underground mines face greater challenges. Increasing health and safety demands and environmental requirements rightly increase the rigour of the mine planning and study process. The plans developed are required to enable mine operators to deliver expected financial returns to investors within environmental, social and governance (ESG) outcomes which meet stakeholder expectations.
That is why mining engineers seek to optimise their mine’s production plans using available planning tools and their experience to focus on possible scenarios and outcomes. Digitalisation of mine planning processes and the increased affordability of computer processing capacity has made computer planning tools more accessible and useable, which enables assessment of more scenarios and inputs in support of design choices selected by the engineer.
Mineable Stope Optimiser (MSO) is widely recognised as the industry-standard software tool for generating stope optimisation shapes. SRK has been an early adopter of MSO and successfully uses the software in a variety of projects across many commodities and alternative mining methods, for all development stages of mining projects. The software is currently distributed through Datamine, Deswik and Maptek mining software providers. Its origins however are in the Stope Shape Optimiser algorithm developed by Alford Mining Systems (AMS) who first commercialised the software in 2011. AMS describes MSO as “a strategic mine planning tool that automates the design of stope shapes for a range of stoping methods for underground mines. Using constraints detailing mining method and design parameters MSO provides the optimal stope shape design to maximise the value of an orebody.” MSO has made an impressive impact on the underground mine planning process by providing significant opportunities for improving project value, enabling profitability with marginal projects and identifying future mining areas to target for exploration and development.
Mineral resource block models are the main data source for using the MSO software; however, several other technical and economic parameters are required and these typically need preliminary work to ensure they are sufficiently reliable to use in the optimisation process. Key inputs relate to stope geometry arising from geotechnical characterisation and assessment, planned dilution and cut-off grades or values such as net smelter return (NSR). Preparation and assessment of these parameters will require some time and need close interaction with other technical disciplines, such as structural and resource geologists, geotechnical engineers, and with financial and other corporate teams to integrate cost and revenue information and strategic objectives for the mine into the optimisation process. We would argue that, although relatively easy to setup and produce quick results, the experience of mining engineers working with these planning tools has never been more important.
MSO outputs (stope wireframes, section strings and reports) can provide valuable information to the mining engineer to assist in understanding the optimal and economic stope shapes for individual deposits in less time and with more accuracy compared to manual approaches, if even comparable. Limitations of MSO outputs are usually found to be a result of input data quality and the selection of inappropriate design and constraining parameters. Particular attention should be given to the mineral resource block model parameters such as cell and sub-cell size, axis rotation (if any) and estimation methods. Block model cell and sub-cell dimensions should consider the variable orebody thickness, minimum mining width and orientation to provide adequate resolution of a practically mineable stope shape. This is balanced against usability and accuracy of the optimisation process: smaller cell and sub-cell sizes create very large block model files. More detail in larger block models may not necessarily provide a greater accuracy, and this can impact the level of confidence the study aims to achieve.
The 3D wireframes generated represent the mineable stope solids that meets all the input criteria and fundamentally, which are above a given cut-off grade or value; and by default through assessment of alternative scenarios can identify stoping areas at different cut-off grades and their economic viability. These stope shapes are used as a basis in all phases of mine planning, from the study level (Conceptual through to Feasibility) to operations such as detailed mine design and scheduling for strategic (long term) planning, to delivering short term production planning. Other regular uses that can benefit from analysis using MSO software include demonstrating a reasonable economic prospect for extraction as a criterion for mineral resource estimates, establishing grade control models, supporting due diligence and mining inventory verification, and assessing dilution impacts in open pit mining studies. In all cases, an “experienced eye” is required to review MSO outputs to ensure that practical and meaningful interpretations are provided that add value and accuracy to the planning and assessment processes.
MSO is demonstrably a valuable planning tool that can assist mining engineers to create optimised mine plans and contribute to the efficient progress of mining studies by rapidly defining mineable stope shapes. MSO can also be used to quickly assess potential impacts in production if assumptions change in any mine planning scenarios and test the sensitivity and robustness of an operation or a project.
