What is Ore Grade?

Ore grade is the concentration of a valuable mineral or metal within the rock that a mine processes. It is the single most important geological variable in determining whether a deposit is economically viable and how profitable mining it will be. Higher grades mean more metal per tonne of rock processed, which translates directly into lower costs per unit of output.

Grade is expressed differently depending on the commodity. Gold grades are measured in grams per tonne (g/t), meaning how many grams of gold are contained in each tonne of ore. Copper and nickel grades are expressed as a percentage, representing the fraction of the rock that is the target metal. Iron ore grades are also percentages, typically ranging from 56 to 67 percent Fe content for commercial ores.

Grade drives costs more than almost any other variable. Consider two gold mines processing the same amount of ore. Mine A has a grade of 4.0 g/t, producing 4 grams of gold per tonne. Mine B has a grade of 2.0 g/t, producing 2 grams per tonne. If both mines have similar processing costs per tonne of ore, Mine B will have roughly double the cost per ounce of gold produced, because it processes twice as much rock to get the same amount of gold.

This relationship between grade and cost is roughly inverse and roughly linear for most operations. A 20 percent decline in grade, all else being equal, leads to approximately a 20 percent increase in cost per unit of production. In practice, the relationship is not perfectly linear because some costs scale with ore tonnes while others scale with metal produced, but grade remains the dominant variable.

Mining companies sometimes report both head grade, the grade of ore fed into the processing plant, and reserve grade, the average grade of the remaining ore body. The gap between these two numbers can tell you whether a company is high-grading, meaning selectively mining the richest parts of the deposit to boost short-term production at the expense of future mine life.

One of the defining trends in the mining industry over the past two decades is the steady decline in average ore grades globally. The richest, most accessible deposits were mined first, and new discoveries tend to be lower grade, deeper, or in more remote locations.

In gold mining, average head grades for the major producers have fallen from roughly 3 to 4 g/t in the early 2000s to around 1.0 to 1.5 g/t today. In copper, new projects often have grades below 0.5 percent, compared to historical grades of 1 to 2 percent for older operations.

This grade decline is a structural headwind for the industry. It means that even with technological improvements in processing and mining methods, the industry has to move more rock to produce the same amount of metal. It drives capital intensity higher, increases energy consumption per unit of output, and puts upward pressure on costs over time.

Tracking grade trends at the company level reveals which operations are managing grade decline well and which are facing accelerating challenges. A company that maintains stable production with gradually declining grade is likely offsetting the grade decline with throughput increases or processing improvements. A company where both grade and production are falling is in a more difficult position.

Grade and recovery rate are closely linked. Recovery rate is the percentage of the valuable mineral that is successfully extracted from the ore during processing. Higher-grade ores often achieve higher recovery rates because the mineral particles are larger and more accessible to the extraction process.

As grades decline, achieving high recovery rates becomes more technically challenging. Lower-grade ores often have finer mineral particles that are harder to separate from the waste rock. This can require more energy-intensive grinding, more reagents, and more sophisticated processing circuits.

The product of grade and recovery gives the actual yield per tonne of ore. A mine with 2.0 g/t grade and 95 percent recovery produces 1.90 grams per tonne. A mine with 3.0 g/t grade but only 80 percent recovery produces 2.40 grams per tonne. Both numbers matter.

ProveMines tracks head grade as a commodity-specific metric: grade_au for gold (in g/t), grade_cu for copper (in percent), and so on. By tracking grade alongside production and cost data, users can see the relationship between grade changes and cost changes at the company level.

A company where AISC is rising and grade is falling is experiencing cost pressure from geological factors. A company where AISC is rising despite stable grades is likely facing operational or input cost issues. This distinction matters for understanding whether the cost trend is structural or reversible.