It’s Tip Tuesday! Today’s post comes from Truong Bui, Mining Industry Process Consultant.
Using the constraints option in the production scheduler allows GEOVIA PCBC™ users to apply operational constraints to a production schedule to make it comply with tonnage or grade constraints. The amount of tonnes that can go through an ore pass or crusher is limited by the capacity of the ore pass or crusher. Draw points can be grouped based on the ore pass or crusher and a constraint can be assigned to this grouping of draw points. A grade constraint can also be applied to achieve a specific mill head grade or to limit the amount of an unwanted grade element.
To set up the production schedule for use of constraints, a string bucket needs to be created to identify the grouping of draw points to be used. This is most easily done based on the draw points sector, group or production block. To do so, follow these steps:
1. Add the CONSTRAINTS keyword to the input sheet in the prodtons.xlsx file.
2. Use one of the constraint methods listed below in the Table sheet.
- QSURF – Follows a given height surface (using LOADSURF keyword)
- QREMAIN – Similar to EVEN and COMBO method in concept. Most appropriate in a block cave situation
- QSMOOTH – Similar to SMOOTH method in concept. Most appropriate in a panel cave situation.
- QVALUE – Similar to QREMAIN but with “value” enhancement. Can be used to improve grades in earlier years at the expense of later years. Best for use in a block cave situation.
- LP – Optimizes remaining column value using LP. The objective is maximum NPV (vertically discounted). This does not yet support grade type constraints.
3. Create a new Constraints sheet in the prodtons.xlsx file.
4. Set up the Constraints sheet like the example, below, for a tonnes constraint.
Be sure to note the following about this constraint:
- Cell A1 specifies how many constraints are being used.
- Cell B1 (Weight) is not currently used and does not need to be changed.
- Cell A2 is the name of the string buckets being used for the constraint.
- Cell B2 (100%) is not currently used and does not need to be changed.
- Cell C2 determines whether a constraint is a tonnage or grade constraint. Use 0 for a tonnage constraint. If using a grade constraint, enter the grade element number of the grade element to be constrained. For example, if the grade elements are Cu, Au, Ag, Diln, and you want to constrain Diln, the value in column C would be 4.
- Cell D2 is either LE (less than or equal) or GE (greater than or equal to).
- Cell A6 denotes how many groupings of draw points are being constrained
- The columns WEST and EAST refer to the constraint bucket ZONES. The constraint type for this bucket is “tonnes” based on the value of 0 in cell C2. The equality is LE so the tonnes will be kept below 25,000,000.
- If there is more than one string bucket, the position for the actual constraints (row 4 above) moves down accordingly with one blank line between constraints buckets and the subsequent constraints groupings.
Here are the before and after results of applying a tonnes constraint on a production schedule.
It should be noted that tonnes and grade constraints can be used together. A total of ten constraints can be used at once. However, if there are too many constraints, the system may not find a possible solution. If this is the case, remove or relax some of the constraints.
Looking for more PCBC tips? Check out Truong’s earlier post on Understanding Tactical Shut-Off Value Strategies for Cave Mines.
Be sure to check back next Tuesday for more Product Tips & Tricks.
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