Unpacking the dynamics of mine production

By Motive Mungoni

Mining is a multi-faceted procedure that comprises of many different components of an operation. A good example of such an interwoven operation is mine production, one of the three pillars of a mining project. The other two pillars are costs and safety. Optimisation of mine production is not only concerned with the delineation of the economic boundaries of an orebody but the efficient design and scheduling of the extraction process. Although mine production is an iterative, daily routine, it needs planning which should be backed up by good geological data which should be continuously reviewed. Thus mine production is a cycle of activities which are done after a geological evaluation of a mineral resource and include marking of holes, charging, drilling, blasting, loading and hauling. These activities of mine production are all integrated into a single system that ensures availability of ore at the plant for processing. Depending on the design and planning of the mine, these activities can happen concurrently. All activities of mine production rely on each other’s performance and any lack of efficiency or productivity will carry across the entire shift(s). It is the responsibility of the mine manager to make sure all components at the mine operate in harmony at their peak productivity. Below is a discussion of the key components of mine production which should be considered prior to and during production for a mine to be a successful business.

Mine strategic planning and minerals

Every mine should have a strategic plan for the mineral(s) it is extracting and processing. Where possible, beneficiation and value addition of the mineral commodity is critical dependent on the needs of the market and/or client. Mine strategic planning is mostly concerned with the long term goal of the mines and its specific objectives, vis a vis, where it wants to go, and how it expects to get there. The planning and scheduling is mostly concerned with the development of an optimum mining sequence for ore and waste required to sustain production.  It is under the tutorage of top management and is principally concerned with the economic, financial, and technical aspects of the business and/or operating environment of the mine, with particular attention given to the future of the enterprise. Shareholders, stoke holders or owners of the mine often influence this plan because of the amount of capital injection, perceived pay-back period, profitability, risks not-withstanding the cyclic nature of mineral commodity prices.

On strategic minerals, how rich the ore body is, which is considered a depleting asset, and how strategic it is are critical issues that should be looked at. An example of a strategic mineral in recent times is lithium which is mined in Bikita as spodumene used as a form of clean, renewable and environmentally friendly energy source. Regardless of how important lithium has become in our world today, only a particular grade can be mined which ensures a mine breaks even and that becomes the cut-off grade.

Operational Planning and grade control

This form of planning is involved with short-term aspects of the mine and closely linked to the production cycle, and unfortunately, it often consumes most if not practically all of management’s planning attention. It is concerned with maximization of return and problems of budgeting, scheduling, monitoring, and controlling the daily or short-term (one to three years) activities of the firm. A good example is grade control which refers to a decision-making process in which the classification of a block as ore or waste is revised on a day-to-day basis. This is done by ore graders and mine geologists through blast hole data processing, visual observation of faces, and operational considerations. The rationale by the mine geologist is to push through the desired ore grade to the processing plant with ore of uniform quality to ensure it operates optimally. 

Differentiating strategic from operational planning is not an easy task and classification is further complicated by the use of additional terms and definitions. Tactical (means and goals for attaining objectives), year-to-date (budgetary or shorter-term), and administrative (combination of staff and operational) planning are terms that further define and circumscribe the types of planning.

Drilling and blasting

This is basically the rock breakage system of reducing the size of ore so that it can easily be handled and transported either vertically or horizontally for processing at the plant. This is a critical stage of the mine production cycle which can determine whether the production target for that day is met not. It is an engineering science that is determined by the type and properties of the rock being mined, drilling pattern, type and amount explosives used and then blasting. If it is not managed well, it has a number of repercussions which include increase in costs due to under-fragmentation or over-fragmentation, misfires, falls of ground or fly rock, ore dilution and many other challenges.

Ground control

The competence of the ground especially after blasting is important for both surface and underground mining systems. In surface mining, it can determine the stability of the slope and prevent slope failure and in underground mining, falls of ground. It is because rock masses for both soft and hard rocks are heterogeneous and thus have faults, joints, fractures and other discontinuities which form planes of weakness. In order to design an effective ground control or support system key rock properties are measured and these are strength properties of rocks, Mohr ‘s rock hardness and rock mass rating (RMR) after Bleniawski in 1989 just to mention a few. Empirically, underground mining systems are more dangerous and prone to hazards linked to ground movement compared to surface mining systems and as such have seen design of complex and ICT linked ground control programs to reduce rock bursts and other hazards.

Loading and hauling

Loading and hauling is an important part of mine production which involves mucking and horizontal transportation of both waste and ore material especially for surface mining systems. It is the second highest operating cost after processing. Selection and matching of equipment for such an important link of activities can never be underestimated. The success and sustainability of a mining operation is heavily dependent on the overall efficiency, availability, utilisation of the fleet of machinery a mine is using. In order for the loading and hauling system to sustainably work, it has to be cost effective and cost drivers such as inefficient fuel usage, poor care & maintenance system, wear and tear, tyres replacement.    It is the responsibility of the designers and planners to make sure the loading and hauling operation meets the production requirements and goals safely, economically, and effectively. It is then the responsibility of the managers and operators to perform the tasks according to the designs and implement all the required steps in order to meet the production goals. The hauling and loading system or equipment is integrated into all other units of operation, as well as the design of various components of the mine. Therefore, the system must be compatible with all other units of operation in the mine.

Motive Mungoni is a geotechnical engineer/earth scientist with over 12 years experience as a consultant/lecturer/researcher in the extractives and energy sector. Email: motivemungoni@gmail.com  

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