The discovery date refers to when the deposit was recognised as having significant value. This is usually set as the date of the first economic drill intersection.

It should be noted that a review of the discovery history of the deposit may show that there were small-scale workings on the site.  For purposes of this study, if there is a order-of-magnitude step change in the known endowment of the deposit (i.e. from 100 kt to >1 Mt Cu, the date of the upgrade is viewed as the discovery date for the main deposit.  A separate record will be made of the earlier discovery – with the mine name usually having the suffix “(OLD WORKINGS)”.  An example of this would be Cadia – where small scale copper mine existed back in the 1880s.