Given the scale of operations involved, any changes to mine plans in response to changes in external factors – such as the price of gold or inputs like oil – take time. These factors may affect which areas of an ore body are profitable (economic) to mine. In times of higher prices, mining low-grade ore (“low-grading”) will become profitable as the higher gold price will offset the increased cost of extracting and milling a greater volume of ore. When the price is lower, it might only prove profitable to might areas of higher-grade ore (“high grading”).