When a model of an ore reserve is created using a geological modelling tool, the objective is to create an accurate representation of the deposit's location, size and quality. However, when the reserve must be scheduled, this representation is usually inadequate and an alternative approach is required.

Instead of modelling the entire deposit based on its geological characteristics, the reserve is normally subdivided into a number of discrete reserve units. The design of these reserve units is based on the intended mining method and the subdivision is normally performed hierarchically.

In an underground metalliferous deposit, for example, the reserve may be split into levels, with each level split into drives and each drive split into rings. A section through such a deposit is shown below, including a representation of development requirements.

In an open cut mine, the deposit is again subdivided into a number of discrete reserve units, but this time the reserve may be divided into push-backs, with each push-back subdivided into benches, each bench subdivided into rows and each row subdivided into columns. A section through a particular column of such an open pit is shown below.

Subdivision of the reserve is usually performed with a geological modelling tool, which calculates the quantity and quality of the materials within each reserve unit. XPAC does not store any sampling data and is not used to perform this function. However once the data has been generated from the geological model, an XPAC reserve database required for scheduling can be created using the XPAC Import/Export wizard.

Data is only generated for the reserve units themselves and not for the higher level subdivisions of the deposit. For example, in the open pit shown above, data would only be generated for each of the smallest reserve units, the rows, and not for the columns, benches or push-backs. These are merely summaries of the reserve units and not reserve units themselves.

When deposits are subdivided into reserve units, it is not always feasible to split every portion of the reserve to the same level of detail. Consider an operating open pit mine with a number of indicated satellite deposits. It would be inappropriate to break the satellite deposits down to the same level of detail as the main pit, and reserve units that represent complete benches, strips or even each entire pit may be used.