When people ask me what is the best way to make a major impact on a mine my answer is always start with the mine plan. If you know where to look you can identify options that will add value through prudent changes to the configuration, timing and matching of equipment to the mine plan whilst increasing its resilience and providing options.
Have a look at a few days work at a Central Queensland Open Cut Truck Excavator Mine. The target was $50m additional cash and with this plan (and the followup work and correct implementation) it was comfortably achieved.