Inventories |
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Inventories |
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Inventories |
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Inventories |
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An inventory is defined as material that has been released for scheduling due to the removal of other material. Inventories will most commonly apply to laminar deposits, such as coal, where waste material is being removed to access the ore underneath it.
For the purpose of calculating inventories, XPAC monitors the following quantities for each activity during scheduling.
| • | Mined quantity - this is the amount actually scheduled in the output paths. |
| • | Released quantity - this is the amount that is exposed or released by the preceding activity. |
| • | Inventory quantity - this is the amount available to be mined at any point in time. |
The three quantities are related to one another as follows. To determine the closing inventory for an activity, take the opening inventory, add the quantity that has been released through mining of the activity above, and subtract the quantity of the current activity that has been mined. This is illustrated in the diagram below.
To calculate the inventory for each activity, XPAC must have a starting point. This is called the opening inventory. At the start of the schedule, before the mined out quantities or preschedule tables are run, the opening inventory for all activities is assumed to be zero. The only exception to this rule is Activity 1.
For the uppermost activity (activity 1), XPAC assumes that 100% of the activity is available for mining at the start of the schedule, so the opening inventory is 100%. For a two dimensional deposit this assumption is quite valid as activity 1 will always be accessible. In a deposit where the database records are physically located one on top of the other, this assumption may not be valid. In this situation, the inventory quantities reported for activity 1 will not be correct, however the inventory quantities will still be valid for all other activities.
The closing inventory for one time period is the same as the opening inventory for the following time period. This applies to the total schedule as well as to the individual records that make up the schedule. Therefore:
| • | The inventory at the start of the schedule is equal to the opening inventory for the Mined Out Quantities. |
| • | The closing inventory for the Mined Out Quantities is equal to the opening inventory for the Preschedule. |
| • | The closing inventory for the Preschedule is equal to the opening inventory for the first Time Period. |
| • | The opening inventory for period n is equal to the closing inventory for period n-1. |
In some schedules you may want to control your inventory so that it does not include material that is released but is not readily accessible. This situation may arise if a haul road traverses a block of material, if a large item of equipment is positioned on top of the material or if water must be pumped out prior to mining a block of material. In such cases, the percentage of the activity that is released should be reduced to more accurately represent the situation.
If x% of activity n is mined, then it will normally release x% of activity n+1. If you want it to release less than x% of activity n+1, then you can change it. This can be done in the Mined Out Quantities, the Preschedule Table and/or any Input Path.