Geoscience Reference
In-Depth Information
Fig. 7.10
Grade-Tonnage curves of the high secondary enrichment units of the Escondida Norte Porphyry Cu deposit
where
i
v
(
u
;
z
c
)
represents an indicator of perfect selection
for the SMU
v
and
z
c
is the cutoff grade. If the value of the
SMU
z
v
is higher than the cutoff, then the SMU is recovered
Consider, for example, a
z
c
= 2.0
cutoff; there are four pos-
sible outcomes:
a. The SMU is estimated to be ore and is recovered as such; in
this case, no error (or misclassification) is made (Quadrant I).
b. The SMU is estimated to be waste, and is recovered as
such; as before, no error (or misclassification) is made
(Quadrant IV).
c. The SMU is estimated to be ore, and is in fact waste; in
this case, dilution is sent to the processing plant (Quad-
rant II).
d. The SMU is estimated to be waste, and is in fact ore
(Quadrant III); in this case, ore loss occurs as economic
material is being discarded.
The imperfect selection described is a major component of
the information effect. The economic performance of any
operating mine is impacted by this unavoidable selection
error. Commonly, little attention is paid to optimizing that
selection, relative to its economic impact.
The simple scenario shown in Fig.
7.11
becomes more
complicated if there are several destinations for the ore, such
as crushed ore to the mill, crushed ore to the leach pad, and
Run-of-Mine ore to a different leach pad. In this case, there
are four possible destinations including waste. Optimal pro-
cedures for ore/waste selection are discussed in Chap. 13.
. The total tonnage, quantity of metal, and
grade thus recovered for any panel or region
V
is
i
v
(
u
;
z
c
)
=
1
t
v
(
z
c
)
=
N
i
v
(
u
j
;
z
c
),
v
∈
[1,
N
]; x
j
∈
V
(7.11)
j
=
1
q
v
(
z
c
)
=
N
i
v
(
u
j
;
z
c
)
·
z
v
(
u
),
v
∈
[1,
N
];
u
j
∈
V
(7.12)
j
=
1
m
v
(
z
c
)
=
q
v
(
z
c
)
t
v
(
z
c
)
(7.13)
For simplicity, the density (tonnage factor) in the above equa-
tions is assumed to be 1.0. Equations 7.11-7.13 assume perfect
selection, that is, knowledge of the true SMU value. However,
in reality, only an estimate of that true value is available.
Graphically, the ore/waste selection problem can be
represented by a scatter plot of the unknown true SMU
values vs. the estimated SMU values shown in Fig.
7.11
.
