During the mining boom years, the focus was on producing as much as possible from the resource to take advantage of higher prices. OEMs did very well selling the addition machinery required to achieve the extra production. So now that commodity prices are low and capacity is already installed, the main game of late has been to drive economies of scale by pushing production even higher. This approach carries a penalty that might not immediately be obvious.
In a truck shovel operation, all we ever talk about is the excavator. We schedule the excavator, measure it’s productivity, compare various models and make judgements about which ones perform best. But In fact, the excavator doesn’t put any material in the dump or stockpile, its the trucks that do all the work and incur most of the cost of moving the material. So we should really be looking at which is the best truck to use. Assuming that the truck and excavator size are appropriately matched (between 3 and 5 bucket passes to fill a truck), the performance of the excavator only comes into the equation during loading which is perhaps 2 minutes out of a total truck cycle time of 20 minutes. So if the excavator hits some hard dig and takes 3 minutes to load a truck, the excavator productivity will fall by 50% but the truck productivity will only fall by 5% which hardly affects the unit cost of the operation.