In order to prepare this projection is important to consider the gold recovery as variable parameter in order to favors the initial extraction of zones with higher processing rates. In this way, the cut-off per phase and period may be adapted in order to maintain an average gold feed value without much variation and also to maximize the net present value of the project. The inventory of mineable resources has to be designed so that the production rate can be used as key reference. Obviously, there are phases with more resources than others and this parameter must be studied on each ore type. The operational cut-off of each period is different and has an impact on the mineable resources. Next figure shows the variability and average cut-off grades for a fifteen year gold project.
Variability in Cut-Off Grade