Grade
The concentration or proportion of valuable mineral content in ore, expressed as percentage or grams per tonne.
Detailed Definition
Grade refers to the concentration of valuable mineral or metal content within ore. It is a critical factor in determining the economic viability of a mineral deposit.
- Percentage (%): Used for base metals, iron ore
- Grams per tonne (g/t): Used for precious metals
- Parts per million (ppm): Used for trace elements
- Ounces per ton (oz/t): Traditional measure for gold
Grade classifications
Cutoff Grade: Minimum grade required for profitable mining. Material below cutoff is classified as waste.
Average Grade: Mean concentration across a deposit or mining block.
Head Grade: Grade of ore fed to the processing plant.
Recovery Grade: Actual metal recovered after processing losses.
Grade control: - In-pit sampling and assaying - Blast hole sampling - Grade estimation models - Ore/waste boundary definition
Economic significance: Higher grades generally mean: - Greater revenue per tonne mined - Lower cost per unit of metal produced - Improved project economics - Extended mine life at given capacity
Related Terms
Mineral Reserve
The economically mineable portion of a measured or indicated mineral resource, classified as probable or proven.
Ore
Rock or material from which valuable minerals or metals can be profitably extracted.
Assay
A chemical test performed on ore or rock samples to determine the concentration of valuable minerals.