Sadly, many open pit mines fail to achieve their production targets and disappoint their shareholders.

This article touches on one aspect of planning that affects most metalliferous mines, namely bridging the gap between long-term planning and short-term forecasts.

Common practice is to construct a resource model, apply modifying factors to produce a reserve or mining model and then use this model for planning over various timeframes.

However, the often wide-spaced and limited data informing the resource estimate means it may only be reliable at deposit-scale or, at best, an estimate of what might be recoverable over the course of a year or two.

Mines that rely on resource models for short-term schedules and production estimates commonly experience significant unexpected fluctuations in run-of-mine tonnage and grade.

Without the buffer of large ore stockpiles, these mines can slip into a continuous cycle of reactiveness, such as changing short-term mine plans, additional equipment moves and tinkering with cut-off grades.

This reactive operating mode increases costs, prohibits development of a stable, efficient operation and ultimately leads to lower profit.

Having well-informed production schedules and mining plans can greatly reduce this reactiveness but that means more information is needed in advance of the planning cycle.

Figure 1 shows a resource definition and mine scheduling program developed and implemented recently for a metalliferous mine. In this instance, the site uses reverse circulation methods to collect samples well in advance of the current production benches.

The grade control drilling is aligned with and uses the infill drilling pattern (Figure 2).

Each year the drilling programs replace the previous 12 months of resource depletion.

The strategy means that the operation has a managed program of data collection at the increments needed for medium and short-term mine planning.

Life-of-mine plans (at annual increments) use predominantly wide-spaced exploration data.

Budget or five-year mining cycle plans use predominantly infill drilling data to provide precision down to monthly periods and short-term schedules are derived from accurate grade control drilling to support weekly planning increments.

At first glance, the cost and logistics of providing the forward information may appear prohibitive.

Budget and access to real estate for drilling may require the mine to phase in the approach over two or three years but, once established, annual drilling costs to maintain a forward inventory remain much the same as grade control drilling on current production benches.

This approach delivers several benefits including:

• Mine plans being more stable, reducing unscheduled equipment moves and allowing better managed access to working faces in the pit and reducing operating costs
• Reserve definition in the short to medium-term (one year) being greatly improved by closer spaced samples providing greater confidence in production targets.

Better knowledge of the orebody is the key to miners consistently delivering the mine plan, allowing the operation to develop into a steady state and giving staff the time to focus on optimisation and improving efficiency.

Sites that seek expert advice and adopt this approach are truly planning for success.

*For more information contact Andrew Weeks, principal mining geologist, Golder Associates on +61 8 9213 7629 or aweeks@golder.com.au.