Tonnes of waste that must be moved for each tonne of ore — the number that quietly sets open-pit costs.
The ratio of waste rock that must be removed to extract one tonne of ore in open-pit mining. Lower stripping ratios indicate better economics. For example, a 3:1 stripping ratio means 3 tonnes of waste must be removed for every tonne of ore mined.
It is the most underappreciated figure in a pit study. A modest change to it moves operating cost per ounce more than a comparable change to grade, because waste haulage is the largest line item at most open-pit mines.
Check both the life-of-mine average and the profile by year. Ratios that climb steeply late in the plan mean the back end of the mine is worth far less than the headline reserve suggests.