Pit Optimization Settings: Sequencing

To access this screen:

Optimization control bar >> Ultimate Pit >> Settings and select the Sequencing tab.

Sequencing options are different for NPV optimization than for blending.

For a more detailed explanation of the overall processes involved, see Pit Optimization.

Also see Ultimate Pit Optimal Extraction Sequence.

Optimize NPV

LG phases can be obtained by varying net profits (block values), product prices or mining costs.

Consider the following notes

Suppose you have chosen Use price factors, set the Up to Factor % to 120 and set the Increment % to 5%: the program will attempt to calculate 24 phases, the largest one corresponding to all reference prices multiplied by 1.2, the second largest corresponding to all reference prices multiplied by 1.15, and so on until the smallest phase corresponding to all reference prices multiplied by 0.05. The actual number of phases generated by the program may be less than 24 as pits corresponding to different prices may be identical.

The modifying factors are applied slightly differently for each parameterization option. The profit factors are applied to blocks having positive values (ore blocks) leaving the values of waste blocks unchanged. The price factors are applied to blocks with positive gross revenue and if the modified revenue is less than the block's processing cost, the block value is set to its mining cost (the block is treated as waste). The mining cost factors are applied to all blocks, ore and waste alike.
Every economic model has a maximum number of phases that can be generated for the model, and this maximum number can never be exceeded regardless of the values of the two factors.
For both profit and price options, the maximum number of phases that the program will attempt to generate equals the Up to Factor % divided by the specified Increment %. For mining cost factors, the maximum number of phases is set to 100.
You can vary the pattern of increments within the range. See Pit Optimization Settings: Variable Factors Example.
If using multiple variable ranges, they must be in the correct order; in other words, the Up to Factor % values must increase down the table records.
In many cases, but not always, greater numbers of phases tend to lead to an extraction sequence with a higher NPV.

To produce nested shells showing the impact of PROFIT or PRICE factor changes within a value range:

Note: variable profit factors are useful if your primary goal is to obtain high NPV. Price factors may be interesting if your primary goal is to obtain high NPV and you are interested in “price sensitivity” analysis.

Select Use profit factors or Use price factors.
Enter an Increment % and an Up to Factor % for each pattern of value ranges you want to see.

For example, you could choose an ultimate pit with a 10 % incremental factor between 1 to 50 % of revenue factor, 5 % of incremental factor between 50 to 90 % of revenue factor and 1 % of incremental factor between 90 to 100 % of revenue factor. See what this looks like.
Choose how the Optimal Extraction Sequence search is performed. You do this using OES search based on options:
- Proximity Values—the value for block B is a combination of its intrinsic value and its proximity to the current block A.
- Lookahead Values—the value for block B is a discounted sum of profits to be had from B and a set of blocks contained in a downward looking cone with a vertex at B. Use the slider to determine the extent of the lookahead 'cone' as described by number of benches.

To produce nested shells showing the impact of MINING COST factor changes within a value range:

Note: mining cost factor assessment can be useful if you are interested in “mining cost sensitivity” analysis.

Select Use mining cost factors.
Enter a Min cost factor. This is a parameter defining the largest LG phase (ultimate pit). Cost factors less than 100% usually result in ultimate pits larger than the pit corresponding to the reference prices and costs. This is convenient for sensitivity analysis. If your goal is just to obtain NPV optimal extraction sequence, set the factor to 100%. Note that setting a cost factor to more than 100% may result in an ultimate pit smaller than the one corresponding to the reference prices and costs.
Enter an Incremental Factor. This is a parameter defining a percentage reduction in revenues or costs between two consecutive phases. A small reduction, say 1%, will usually result in a greater number of phases than a larger reduction, say 5%.

Optimize Blending

Blending optimization is performed by creating a blended extract sequence from blocks that are available on the current surface.

To specify blending targets:

Select Optimize blending.
Click Add to display the Define Target screen.
Define your target (see Define Target) and click OK.
Click Edit to modify the selected target, again using the Define Target screen.
Delete targets that are no longer required.
In the Enter 0 for quick search or set search depth in the 1-10 range field, enter a value from 0 to 10, where higher numbers involve successively 'deeper' searches for a solution, at the cost of performance.

Note: the extraction sequence obtained with the parameter values between 1 and 10 is never worse than the extraction sequence obtained by the quick search (the parameter set to '0'), but a smaller positive parameter, say '1', may produce a better solution than a greater parameter, say '10'.