ABSTRACT
Dilution is defined as the low-grade material (waste or fill) that is mined and processed together with the ore stream, thus reducing its value. Ore loss refers to any unrecoverable economic ore left inside a designed stope boundary. This ore may be broken, in place as pillars, or not properly blasted. Any valuable ore not recovered by the mineral processing system also constitutes ore loss. Dilution and ore loss are always defined and quantified with respect to an idealized (planned) stope boundary. However, dilution is not always defined in an identical fashion. The two most widely used equations to quantify dilution are (Pakalnis et al., 1995):
Dilution 1 Waste tonnes mined
Ore tonnes mined = (9.1)
Dilution 2 Waste tonnes mined
Ore tonnes mined Waste tonnes mined =
+ (9.2)
Equation 9.1 is more sensitive to stope wall slough. In addition, a number of other definitions have been provided by Pakalnis et al. (1995):
Dilution 3 Undiluted in situ grade from drillholes
Sampled assay g =
rade at drawpoint (9.3)
Dilution 4 Undiluted in situ grade reserves
Mill headgrades from s =
ame tonnage (9.4)
Dilution 5 Tonnage mucked Tonnage blasted
Tonnage blasted =
− (9.5)
Dilution 6 Footwall slough (m) Hangingwall slough (m)
Orebody wi =
+
dth (m) (9.6)
Dilution 7 Fill (Tonnage actually placed Calculated to fil= − l void) (9.7)
In order to quantify dilution, an orebody must be properly delineated and the extracted volumes must be effectively measured. Waste rock that is left inside a stope (selective mucking) is often not considered as dilution. In addition, high dilution may not necessarily mean a low mining recovery. However, when dilution decreases, there is a higher risk of leaving ore behind (Figure 9.1). In some cases where dilution decreases, an increase in ore loss is also experienced as shown in Figure 9.2.
