There is an increasing realisation that mining and mineral processing should be considered as linked activities, rather than as separate and unrelated activities. As art example of the new trend, the increasing dominance of autogenous and semi-autogenous grinding circuits in new operations is helping to focus attention on the linkage between fragmentation in mining and grinding circuit performance. The general mining rule is that coarse fragmentation is preferred within the constraint of limiting the amount of boulder size muck. Comminution circuits using fine crushing and rod and/or ball milling are largely insensitive to the size of muck produced in mining. However, AG/SAG grinding circuits are quite sensitive to the mix of fine and coarse material in the mill feed. This paper explores the relation between fragmentation size and grinding circuit tonnage by using simulation methods.