A mineral reserve is that portion of a mineral resource that is economically mineable, based on assessments and other information. The mineral reserve classification can be broken down further into the following three classifications:
Proven reserves. Reserves where the size, shape, depth and mineral content of reserves are well-established.
Probable reserves. Similar to proven reserves, but the sites for inspection, sampling, and measurement are farther apart or are otherwise less adequately spaced.
Possible reserves. Those unproven reserves which an analysis of the data suggests are less likely to be recoverable than probable reserves.
The development phase of a mine is considered to have begun when management concludes that commercially recoverable mineral reserves exist, and has decided to develop the mine.