Reclaim Policy

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MiningMath's standard stock reclaim policy

Stockpiles are managed as a post-processing phase of the optimization algorithm (learn more). The decision-making process for reclaiming stockpiled blocks is driven by their economic value, with the algorithm aiming to maximize NPV. Consequently, blocks with the highest value are reclaimed first, regardless of when they were mined and added to the stockpile.

Diverse operational needs

Various mining software packages may use different conventions for stock reclaim policies, typically aligned with the specific goals of each application or module. Some of the possibilities may include:

FIFO: First In, First Out.
FILO: First In, Last Out.
Reclaiming an average grade for the entire stockpile.
Reclaiming the highest-value blocks first (MiningMath uses this method).

Pros and Cons

Each one of these other possibilities is an approximation of reality, with its pros and cons.

FIFO and FILO are quite logic but represent a level of selectivity that is not practical. The angle of repose and the positioning of each block are likely the most intuitive examples of reasons for lower selectivity in practice.
An average grade for the entire stockpile is naturally an approximation, considering the amount of material that should be blended to make it close to the reality.
Reclaiming the high-value blocks first also assumes a selectivity level that is not possible in reality. However, it is quite aligned with the mathematical goal of maximizing the project's NPV for strategic evaluation.

Ultimately, none of these approaches are fully operational. The final decision still relies on the expertise of the professional overseeing the strategy optimization, who uses their preferences, experience, and skills to introduce additional levels of control.

Guiding the Reclaim Policy

This section aims to bring a few ideas on how the user might guide the algorithm in order to follow one’s preferred reclaim strategy. For this article, the user should have prior knowledge in the following concepts.

How to use pre-define destinations.
How to create multiple economic assumptions, and how to handle fake destinations.
How to handle different output files (mainly MinedBlocks.csv and AllBlocks.csv).

Baseline Scenario

The general idea is to set up and run a baseline scenario to find what is optimal for the long-term value. The solution obtained in this step will guide further executions.

Output Format

For this manipulation you will need to switch the output format to export the entire block model along with the optimization results, which is saved in the AllBlocks.csv file. This is essential for any iteration requiring re-optimization of a previous solution. By default, MiningMath exports only the MinedBlocks.csv file.

The results will indicate which blocks should be mined, when they should be mined, and whether they were immediately processed, stockpiled and later processed, or discarded.

Iterating over multiple scenarios

The goal is to utilize previous outputs to generate new columns of economic values by introducing fictitious destinations. This involves creating multiple processing streams that do not coexist but effectively represent a single plant. These fictitious destinations, combined with predefined economic values, enable the user to impose their preferred level of control.

Additionally, based on prior results, the user must adjust the new economic values by specifying the final destination for each block.

Hands-on Approach

Example: FIFO Approach

For the FIFO approach, a block stocked during the second period on the first run, should be sent to the stockpile of Process 1 to be reclaimed first. Hence, this block must have a very negative value for all other destinations.

Define a criteria for stocked blocks (Period Mined different from Period Processed) that should be reclaimed early or later. This criteria must be based on the previous results from the AllBlocks.csv (depicted below), and on the columns Mined Block, Period Mined, Period Processed, and Destination.
Block model file. The value -99 indicates unassigned values, meaning the block was not mined, processed, or assigned a destination.
Add a pre-defined destinations column based on the criteria adopted.
Set up your scenario considering the pre-defined destinations will not coexist.
Notice that: 1) Process 1 and its stockpile will be used from Period 1 to Period 5; 2) Process 2 and its stockpile will be used from Period 6 to Period 10; and 3) Process 3 and its stockpile will be used from Period 11 to .
Optimize the new scenario to have a better approximation for the final NPV, considering the strategy of your preference.

MiningMath

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