AAM's ore reserves were based on high-grading with smaller...

AAM's ore reserves were based on high-grading with smaller mining gear making for a tighter pit and lower strip ratio. However AAM have migrated to using much bigger equipment which requires wider ramps and working areas which has increased strip ratios thus increasing costs. Much more BCMs to shift but also the bigger equipment means higher dilution of these relatively narrow ore bodies. It is unlikely the original ore reserve could never be achieved. As well as this the new northern pit was only recent and therefore would not have been part the original ore reserve but provided necessary blending feed albeit at a lower grade.
The point is, it is misleading that AAMs published ore reserve figures have not been changed to reflect their new mining style. Surely they have these figures by now. Its been six months since the MD left.