Target Parameters
The following parameters can be used in the Parameters column of the Target parameters data grid:
- SWITCH
- REHANLDE
- ADDITIVE_LOAD_SIZE
- ADDITIVE_ONLY_AS_BUFFER
- STOCKPILE_BLENDING_SAMPLE_SIZE
- VARIABLE_THROUGHPUT
- MAX_DRAW
- MIN_DRAW
- STANDARD_STOCKPILE
- SCOPE_LEVELS
- SCOPE_LEVELSHORIZONTAL
- SCOPE_LEVELS_VERTICAL
SWITCH
The target scheduling algorithm, called MineBlend, consists of two sub-algorithms, called Extrema and Optima. The two sub-algorithms are used in sequence, the Extrema algorithm is used first in each scheduling period and Optima is used second within each scheduling period.
You use the SWITCH parameter to specify how far through the scheduling period the algorithm that is used changes from Extrema to Optima. The value for the SWITCH parameter can be any number between zero and one. A value of zero means the Extrema algorithm is used for the entire period. A value of one means the Optima algorithm used for the entire period. The default value is 0.75, which means the Extrema algorithm is used for the first three quarters of the period and the Optima algorithm is used for the last quarter of the period. The default value produces reasonable results in most cases.
The SWITCH parameter is applied to all locations. You cannot set SWITCH to different values for different locations. You can use different SWITCH values in different scheduling periods.
You can experiment with the switch point. The best time for switching algorithms is based on a number of factors including period length relative to the time taken to mine a single block, the number of targets, and the variance of block values within the deposit. Usually, the more targets you have, the earlier you should make the SWITCH setting.
Note: If you choose to change the SWITCH value, it is recommended that you experiment with changes no greater than 0.1 for each schedule run. For example, start with 0.75, then experiment with 0.65, then 0.55, and follow this pattern until you find the value that returns the best results.
The Extrema algorithm, which is used first in the scheduling period, processes very quickly, and mines the value extremities of the available blocks. Early in the period it mines blocks that are extremely above or below the target value, balancing the blocks so that the average remains close to the target. Mining the blocks with extreme values early in the period allows sufficient time over the rest of the period to meet the targets. If the extreme blocks were mined late in the period, it is more likely the period totals would be different from the targets. When you use the default setting of 0.75, the Extrema algorithm is used for the first three quarters of the scheduling period.
The Optima algorithm, used second in the scheduling period, is a true optimisation algorithm which chooses the best available block to mine to achieve the target. The Optima algorithm takes significantly longer to process than the Extrema algorithm. When you use the default setting of 0.75, the Optima algorithm is used for the last quarter of the scheduling period.
If you choose a SWITCH value of 1, only the Extrema algorithm is used. For some scenarios, this setting can produce excellent target results with faster processing speed and more regularity in the blocks selected.
If you choose a SWITCH value of 0, only the Optima algorithm is used. This setting results in a slower processing speed, and a mining sequence in which the best blocks are selected first, and blocks furthermost from the targets are mined at the end of each scheduling period. However, for some scenarios, especially those where you want to achieve multiple quality targets, it could return the best results.
REHANDLE
You use the REHANDLE parameter to define whether material from mining locations can be rehandled with material from stockpiles to achieve the target thresholds set for processes.
By default REHANDLE is set to yes. To turn REHANDLE off, type no for the Value.
When REHANDLE is set to no, the process always processes material directly from the mining locations before material from stockpiles. If more material is mined than the process can handle, as is defined by the value for the process throughput, the material that is furthermost from the quality targets is sent to the stockpiles. If less material is mined than the process can handle, material that best meets the quality targets is sent from the stockpiles to the process.
When REHANDLE is set to yes, the process throughput is still met with a combination of material from the mining locations and material from the stockpiles. Material from the mining locations is used in preference to material from the stockpiles unless the quality target thresholds cannot be met. If the quality target thresholds cannot be met, and using material from the stockpiles will provide the process material that is closer to the thresholds, mined material is replaced by stockpile material. MineSched calculates rehandling using a method which minimises the amount of material that is rehandled. The mined material that has the biggest effect on not meeting the process targets is placed on the stockpiles, and the stockpile material that has the biggest effect on meeting the process targets is processed.
When REHANDLE is set to yes, if the process target thresholds cannot be met by rehandling material from the standard stockpiles, and using material from the additive stockpiles will provide the process material that is closer to the thresholds, material is rehandled from the additive stockpiles. Rehanding with material from additive stockpiles means that less material is pulled from the mining location and stockpiles. Mining material is not exchanged for additive stockpile material.
Note: Additive stockpiles are stockpiles that are not fed material by a mining location or another stockpile.
ADDITIVE_LOAD_SIZE
You use the ADDITIVE_LOAD_SIZE parameter to set the amount of material that can be added at each increment from the additive stockpiles.
Additive stockpiles are stockpiles that contain material that can be pulled into the process, but to which material is not added from other stockpiles or mining locations. Material is only taken from the additive stockpiles when the process target thresholds cannot be met by the material from the mining locations and the standard stockpiles.
The ADDITIVE_LOAD_SIZE is not the total amount of material that can be added to the process for the scheduling period, but the amount that is added before each recalculation to see if the process target threshold is met. The total amount of material pulled to the process from the additive stockpiles is a multiple of the ADITIVE_LOAD_SIZE.
The ADDITIVE_LOAD_SIZE parameter is applied to all stockpiles, it cannot be set to different values for different stockpiles. You can use different ADDITIVE_LOAD_SIZE values in different scheduling periods.
The unit for ADDITIVE_LOAD_SIZE is the unit for the process rate, which, by default, is Mass. If you do not define a value, the ADDITIVE_LOAD_SIZE is 0.1 percent of the process throughput for the scheduling period.
ADDITIVE_ONLY_AS_BUFFER
You use the ADDITIVE_ONLY_AS_BUFFER parameter to specify that additive stockpiles can be used only if the amount of mined material available is less than the process throughput capacity.
By default, ADDITIVE_ONLY_AS_BUFFER is set to no, which means that, if REHANDLE is set to yes, additive stockpiles are used, when necessary, to meet the quality targets.
When ADDITIVE_ONLY_AS_BUFFER is set to yes, additive stockpiles are used only when they are required to meet the process throughput. The additive stockpiles are not used to help meet the quality target thresholds.
STOCKPILE_BLENDING_SAMPLE_SIZE
You use the STOCKPILE_BLENDING_SAMPLE_SIZE parameter to set the sample size used in the stockpile blending algorithm for user calculation targets.
If you do not define a value, the STOCKPILE_BLENDING_SAMPLE_SIZE is 0.2 percent of the process throughput for the scheduling period.
If you increase the STOCKPILE_BLENDING_SAMPLE_SIZE, the time taken to run the schedule decreases but the results might not be as close to the targets as they would be with a smaller value. If you decrease the STOCKPILE_BLENDING_SAMPLE_SIZE, the result might be closer to the targets but the time taken to run the schedule is likely to increase.
The unit for the STOCKPILE_BLENDING_SAMPLE_SIZE is the unit for the process rate, which, by default, is Mass.
VARIABLE_THROUGHPUT
You use the VARIABLE_THROUGHPUT parameter to specify whether achieving the process throughput or achieving a quality target value is prioritised.
By default, VARIABLE_THROUGHPUT is off and meeting the throughput quantity is prioritised, even if that means the quality target is not met.
To turn VARIABLE_THROUGHPUT on, type yes for the Value. When VARIABLE_THROUGHPUT is on, the quality target for the process is met exactly, even if that means processing less than the process throughput for the period.
Note: VARIABLE_THROUGHPUT is valid only for processes with a single quality target defined. If more than one quality target is defined for the process, an error message appears when you run the schedule.
MAX_DRAW
You use the MAX_DRAW parameter to set the maximum quantity of material that can be pulled from a stockpile to a process each day.
The unit for the quantity is determined by the unit set for the process rate.
Note: The MAX_DRAW setting can significantly affect whether quality targets can be met.
MIN_DRAW
You use the MIN_DRAW parameter to set the minimum quantity of material that must be pulled from a stockpile to a process each day.
The unit for the quantity is determined by the unit set for the process rate.
If there is less material remaining on a stockpile than the MIN_DRAW quantity, all of the remaining material is drawn by the process.
Note: The MIN_DRAW setting can significantly affect whether quality targets can be met.
STANDARD_STOCKPILE
You use the STANDARD_STOCKPILE parameter to specify that an additive stockpile is to be treated as a standard stockpile.
Additive stockpiles are stockpiles for which movements are defined only from the stockpile, not to the stockpile. Standard stockpiles are stockpiles which have movements defined to and from the stockpile. Material from additive stockpiles is used on the process only when process throughput or process targets cannot be achieved using material from the mining location and standard stockpiles that are feeding the process.
When you set STANDARD_STOCKPILE to yes for an additive stockpile, material on the stockpile is used for blending in the same way as for a standard stockpile.
SCOPE_LEVELS
You use the SCOPE_LEVELS parameter to specify the number of levels of blocks "ahead" that are considered by the Extrema sub-algorithm. This allows you to prioritise mining the blocks which expose blocks which help achieve the targets more quickly.
You can use any integer value for the scope levels. Usually the SCOPE_LEVELS value is between one and five. By default, the SCOPE_LEVEL value is one. When SCOPE_LEVELS is set to one, only the currently available blocks are considered by the Extrema sub-algorithm when choosing which blocks to mine. When the SCOPE_LEVEL is set to two, the block one row past and one bench below the currently available blocks are considered by the Extrema sub-algorithm. When the SCOPE_LEVEL is set to three, the blocks up to two rows past and two benches below the currently available blocks are considered by the Extrema sub-algorithm.
The higher the number of scope levels, the longer the processing time for the schedule. Beyond a particular SCOPE_LEVELS value, it is no longer usefule to at blocks farther "into" the model because these blocks will not be mined in the current period. The effect of the SCOPE_LEVELS parameter is dependent on many other schedule factors; as a result it is recommended that you experiment with values to determine which value gives the best results for your schedule.
SCOPE_LEVELS_HORIZONTAL
You use the SCOPE_LEVELS_HORIZONTAL parameter to specify the number of rows of blocks into the mining face, on the horizontal plane, that are considered by the Extrema algorithm. You use SCOPE_LEVELS_HORIZONTAL when you want to use a different value for the horizontal and vertical scope levels.
The default value for SCOPE_LEVELS_HORIZONTAL is the value set for SCOPE_LEVELS.
SCOPE_LEVELS_VERTICAL
You use the SCOPE_LEVELS_VERTICAL parameter to specify the number of benches down from the current block that are considered by the Extrema algorithm. You use SCOPE_LEVELS_VERTICAL when you want to use a different vale for the vertical and horizontal scope levels.
The default value for SCOPE_LEVELS_VERTICAL is the value set for SCOPE_LEVELS.