July 2012

Getting ahead with pushbacks

With the latest release of MineSight Economic Planner (MSEP), we have added a new tool and additional functions that will enhance the toolbox for Mining Engineers to design pushbacks in MineSight. With the new tool AUTOP, the engineer can specify a limited mining arc for pushbacks and a preferred direction of advance, allowing the creation of pushbacks that more realistically conform to operating constraints. In addition, the pushback design process has become faster with the automatic creation of starter pits directly within MULTP and AUTOP.

MULTP and AUTOP – Automatic Generation of Starting Pit

One of the first steps in the pushback design process is to choose a starting pit. Traditionally, the starting pit is identified through the use of a price sensitivity study. The idea is to design a pit that reaches ore as quickly as possible, satisfying these requirements:

Be of a reasonable size for mining. It cannot be too narrow or too irregular.

This pit will contain the preproduction stripping so the amount of waste should be enough to expose ore while not mining waste before it is necessary.

The ore tonnage should be sufficient to provide ore to the plant for a period of time sufficient for the next pushback to expose more ore.

With the latest release of MSEP, both the MULTP and AUTOP pushback design utilities will automatically generate a starting pit if one is not defined. Within the tool, you have the option to constrain several factors (e.g., pit size, pit width) to ensure that a realistic starting pit is generated. If desired, you still have the option to create this pit manually and define it within MSEP.

Figure 1: MULTP and AUTOP pushback design options will now automatically generate a starting pit if you do not choose to specify one.

AUTOP – Directionally Controlled Pushback Design Tool

AUTOP is a new pushback design tool within MSEP. Using AUTOP, you can apply several directional constraints to guide mining progression. This is advantageous, as it allows you to control the sweep of the mining face around the pit – typically, you will not mine a concentric pushback sweeping 360 degrees around the pit, though MULTP logic will occasionally create such pushbacks. It also allows for the application of a preferred mining direction, which can be advantageous for satisfying operational restrictions. In addition, functionality has been added that makes design of laterally advancing pushbacks much easier.

Note: Like MULTP, AUTOP will select the best pushbacks based upon economics, with pushback size examined by increasing the value until a pushback of adequate size is found. In this way, pushbacks follow the best available material.

A Mining Arc can be entered in degrees to control the sweep of pushbacks around the outside of the pit. AUTOP will examine blocks in all directions, in incremental widths meeting the supplied Mining Arc criteria. As the mining arc is not limited when running MULTP, running this tool with a mining arc of 360 degrees would be analogous to what MULTP does.

A Mining Direction Azimuth can also be specified to indicate the preferred direction of advance. The block values for blocks in the indicated Mining Direction Azimuth will be weighted based on the Direction Factor. Block values for this favored zone will be multiplied by (1+Direction Factor), making it more favorable for pushbacks to advance in this direction.

Figure 2: Plan view of pushbacks designed using the Mining Arc and Mining Direction Azimuth features in the new AUTOP pushback design utility

Several functions within AUTOP allow for the creation of pushbacks that primarily advance laterally. This can be especially useful in the case of some flat-lying deposits. In the example below, we consider flat-lying coal deposit where laterally advancing pushbacks are desirable. The starter pit was placed by examining the results of a price sensitivity study, with the shell itself produced through the use of restriction codes in MSEP. The pushbacks were produced through the use of the following three options in AUTOP:

Limit blocks to vertical outcrop of previous pit: When using this option, AUTOP will only consider blocks existing directly below the previous shell as ore. This is beneficial when designing lateral pushbacks, as it will prevent the program from considering ore that will produce wide, flat pushbacks. This option can be used in conjunction with the pushback width to easily control where pushbacks are placed.

Pushback Width/Pushback Depth: In AUTOP, both pushback width and depth can be specified. If several benches are specified, this is used as the pushback depth; if a pushback width in meters is entered, this is used as a width. Depending on the deposit, you may obtain more reasonable pushbacks with one methodology than with the other. Try both methods to examine which is most favorable for your deposit.

Follow the limiting pit: When using this option, AUTOP is forced to mine small remnants of blocks left on the floor of the limiting pit. This will prevent blocks from being left behind at the pit floor as pushbacks advance laterally across the limiting pit.

Figure 3: Laterally advancing pushbacks for a flat-lying coal deposit, generated using the new AUTOP option in MSEP.

Note: When no further pushbacks meeting the minimum size can be found, all constraints are removed and the maximum pit is found. For this reason, the last pushback created by AUTOP may have a 360-degree mining face.

Conclusion

With the latest enhancements to MineSight Economic Planner, pushback design in MineSight is easier than ever. The introduction of automatic starter pit creation allows for the creation of reasonable mining pushbacks, without previously creating a starter pit. The introduction of the AUTOP option allows for the creation of pushbacks that more reasonably reflect operating restrictions. For more information about the new pushback design options in MSEP, contact your local technical support branch.