Cutoff grade is the minimum grade required in order for a
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
or
metal
A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
to be economically
mined (or processed). Material found to be above this grade is considered to be
ore
Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...
, while material below this grade is considered to be waste.
The cutoff grade can be determined through a variety of methods, each of varying complexity. Cutoff grades are selected to achieve a certain objective, such as resource utilization or economic benefit. Dividing these objectives even further gives way to specific goals such as the maximization of total profits, immediate profits, and present value. It is important to recognize that the cutoff grade is not simply calculated to a definitive answer. It is in fact a strategic variable that has major implications on mine design. The cutoff grade is adapted as the economic environment changes with regard to
metal prices and mining costs, and is therefore constantly changing. Metal value is not the only factor affecting the profitability of an ore block. The presence of unwanted material in an ore block may increase the processing cost. This is also considered when classifying waste rock and ore.
References
Mining engineering
Mineral economics
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