The shut-off value for a panel cave mine determines when a draw point will be shut-off and mining will cease from that draw point. Using a shut-off value strategy for a panel cave mine is similar to using a cut-off value strategy for an open-pit mine.

In this new series we will discuss which parameters are important for determining the shut-off value and the strategies an engineer can use when deciding which shut-off value to use.

Introduction

A shut-off value strategy can only be applied if there is excess mining capacity within the panel cave mine. If the current design parameters cannot maintain the desired production rate then the shut-off value to use would be the mining and processing cost. Gains in value are only realized when there is an opportunity to choose whether to mine higher grade ore at the bottom versus lower grade ore at the top. Placement of the panel cave elevation would usually allow access to the high grade ore relatively quickly. However, there is dilution material with little to no grade which sits on top of the ore body and will dilute the ore at the top through mixing mechanisms.

A panel cave will advance horizontally, developing new draw points in the direction of the mining advance. As new draw points are opened, the older draw points will become depleted and eventually close. The shut-off value determines when these draw points will be closed. When there is excess mining capacity there is a choice of whether to mine the low grade material in the older draw points or close them before the break-even shut-off value and mine the high grade material from the new draw points. It is always better to choose the latter as it will have a higher value.

There is a certain point when the shut-off value will be too high and the older draw points will close faster than new ones can be opened. If this is the case then there will no longer be an excess production capacity and the higher shut-off value will lower the value of the project.

In this 4-part series

This series will discuss which parameters are important for determining the shut-off value and the strategies an engineer can use when deciding which shut-off value to use. A shut-off value can be applied during the planning process or for current operating mines as mining conditions change. Metal prices do not impact the actual shut-off value but it would change the corresponding height of draw (HOD) for that shut-off value. Increasing the metal prices would increase the height of draw and decreasing metal prices would lower the height of draw similar to revenue factors used to generate nested pit shells for open pit mines.

The break even shut-off value will always remain the same as long as the mining and processing cost are unchanged but the height of draw for that shut-off value can change with metal prices. The design parameters which would have the largest impact on the shut-off value would come from the production target, development rate of new draw points, and the average height of draw.

▶ In our next post, we will examine the production rate and the ideal case for any panel cave mine. Stay tuned!

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