Dilution

The concept of dilution is introduced here. There are four different types of dilution in mining: planned, unplanned, external and internal dilution.

During development of a mining project various factors and difficulties affect the plant design and economics  of an operation. One of the main contributors is dilution – which  is waste material mixed in with the ore during the mining phase and fed to the processing plant. The discrimination between ore and sub-economic dilution material is the site – and process specific cut-off grade.

Planned dilution refers to the rock with a lower mineralization content than the cut-off grade within stope limits. Unplanned dilution refers to the rock with a lower mineralization content than the cut-off grade that originates from outside the planned stope limits, for example by poor rock control, see schematics below which illustrates planned and unplanned dilutions.

Internal and external dilutions can be better understood in relation to the ore body. External dilution is the waste outside of the ore body that is mined during the mining process. Internal dilution occurs inside the ore body. This is the waste that cannot be avoided by any means by selective mining and is therefore always mined together with the ore.

Selection and separation of minerals can be carried out at different scales, starting from the selection of suitable deposits to individual minerals in final concentration stages. Dilution is therefore always relative to a particular reference scale. Dilution is the quantitative measure of the amount of waste particles in an ore stream. Waste is generally considered to contain zero or net-negative financial value and the reference is the cut-off-grade, which is case dependent. Dilution (δ) is calculated as

Conventional physical separation is usually performed at small particle sizes where liberation has been increased by comminution, e.g. by changing physical properties. Therefore, little effort has been made to describe liberation and dilution in coarse run-of-mine streams. However, available literature indicates that there are coarse wastes liberated in a wide variety of ore types.

Ores are often much more heterogeneous than we thought they were!

Integration of blasting, waste ejection and grinding has significant potential to increase overall productivity. Sequential milli-second blasting technology can be used to liberate coarse particle size waste for early stage ejection with sensor-based ore sorting.