It’s a bonus Product Tips & Trick post today, courtesy our GEOVIA MineSched™ Project Manager, Jeremy Hanrahan.
A common mistake when using maximum & minimum thresholds in MineSched’s Quality Targets data grid is not having material flow correctly setup, which can prevent it from working correctly—here’s why…
Background on Target Scheduling
In target scheduling, the software automatically allocates resources to locations and chooses the blocks to mine within a location in order to best meet user defined quality and material ratio targets. Target scheduling in MineSched is based on the proprietary MineBlend algorithm, which is a collection of sub-algorithms that have proved very effective in meeting multiple targets efficiently while producing practical schedules.
Incorrect set up
When trying to achieve a certain Quality Target, it is important to minimise the amount of material being rehandled from stockpiles because of the associated costs. Frequently, setups have upper and lower threshold values included for Rehandle, but the incorrect material flow renders their effectiveness obsolete.
An incorrect setup example:
In the above example shown here, the minimum and maximum thresholds are not being used by MineSched’s MineBlend algorithm because there is no option for direct tip (i.e. there is no material movement path setup to connect directly from either of the pit stages to the mill) or for stockpile rehandling (i.e. material taken from the stockpile to the mill). This means that in this example, there is only blending from stockpiles and therefore the upper and lower thresholds are not required and not used.
When to use Thresholds
In the MineSched MineBlend automatic target-scheduling engine, ‘Target Thresholds’ are only used under the following circumstances:
- you are setting a target on a process (eg: a Mill)
- your process can be fed directly from mining locations as well as from stockpiles
- the target parameter REHANDLE is set to yes (This is the default value for this parameter)
Note: When your target is set on a stockpile or when the process is not fed directly from mining locations target thresholds are not used.
In this scenario, below, a material movement path has been added to allow ‘direct tip’, meaning material can now travel from pit locations directly to the mill.
The parameter REHANDLE has also been explicitly set to “yes”
Now, with REHANDLE enabled by default, the MineBlend algorithm will select material to be directly tipped at the mill if the grade of the mined parcel helps meet the threshold range and lies between the minimum and maximum threshold values set for this process target.
However, this may not always be the case. For example, if a parcel mined falls between the minimum and maximum thresholds but through adding material from the stockpile helps achieve the desired Quality Target, then the material mined may still be swapped out or rehandled.
Understanding the Impact of Thresholds
Like targets, target thresholds can change with time. As targets are calculated on a period-by-period basis, it is only logical to change target thresholds at the start of a scheduling period as the change takes effect at the start of the next scheduling period.
As mentioned, the size of the thresholds set will increase or reduce the amount of material determined to be rehandled. A very small threshold range typically means the amount of material able to satisfy the blending requirements by direct feed will diminish and therefore the amount of rehandle will increase. By contrast a very large threshold range will reduce the amount of rehandle required. This is because you are effectively not as tightly constrained by grade and can allow a larger grade variance over the use of more rehandle. If the process target thresholds still are not reached by rehandling mined material, direct tip is utilised as it is more often cheaper; or alternatively additive stockpiles will be used if they exist.
Be sure to check back for more Product Tips & Tricks.
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