Ore grade

Ore grade is the concentration of a valuable metal within mined rock, usually stated as a percentage or in grams per tonne, and it determines processing volume needed.

Ore grade tells a mining company how much valuable metal sits within a given amount of rock, usually stated as a percentage for base metals like copper or in grams per tonne for gold. A higher grade means less rock needs to be dug up, crushed, and processed to recover the same amount of metal, which directly affects a mine’s cost per unit of output.

Grades typically decline over a mine’s life as the richest, most accessible ore is extracted first, leaving lower-grade material for later years. A country or company’s mine production figures can rise even as average ore grade falls, if the mine compensates by processing a larger volume of lower-grade rock. Grade is confirmed through assay testing of drilled samples before a mine is developed and throughout its operation.