428
waste blocks from the ore blocks which carry a recoverable value once processed. Any ore
block that has a grade less than 0.05 oz/t will be treated at the leach pads or sent to the waste
dump once it is mined. Moreover, an ore block with a grade greater than or equal to 0.08 oz/t
will be processed at the mill or sent to the waste dump.
If the grade of a mined ore block is between 0.05 oz/t and 0.08 oz/t, it will be either processed at the mill, treated at the leach pads or sent to the waste dump. The ore blocks in these
grade intervals are categorized as “undecided blocks” which means that the process destination is not designated based on a cutoff grade; instead the optimum destination will be determined based on the state of the system. Table 2 presents the cutoff grade intervals adopted for
this particular example. Furthermore, the proportions of the blocks in the process stream that
belong to different risk categories such as inferred, indicated and measured will be controlled
by enforcing risk constraints which are in a form of blending constraints. The deposit characteristics are illustrated in Table 3. It is clear that out of 1.9 million blocks in the block model,
only 87 thousand blocks are qualified to be ore blocks with an average grade of 0.061 oz/t.
Among the ore blocks, almost half the blocks are leach blocks with an average grade of
Table 1. Economic parameters.
Parameters
Value
AU
1250 $/oz
MILL COST
12 $/t
LEACH COST
6 $/t
MILL RECOVERY
90%
LEACH RECOVERY
70%
DISCOUNT VALUE
12.5%
Figure 1. McLaughlin mine process flow.
Table 2. Summary of the cutoff grade intervals.
Cutoff
Grades
BREAKEVEN
> = 0.03 oz/t
LEACH
< 0.05 oz/t
UNDECIDED
> =0.05 oz/t AND < 0.08 oz/t
MILL
> = 0.08 oz/t
Table 3. McLaughlin deposit characteristics.
Material Type
Blocks
Tonnage
AVG Grade
TOTAL
1,922,749
961,374,500
–
WASTE
1,835,583
917,791,500
–
ORE
87,166
43,583,000
0.061 oz/t
MILL
18,144
9,072,000
0.133 oz/t
LEACH
44,634
22,317,000
0.034 oz/t
UNDECIDED
24,388
12,194,000
0.057 oz/t
waste blocks from the ore blocks which carry a recoverable value once processed. Any ore
block that has a grade less than 0.05 oz/t will be treated at the leach pads or sent to the waste
dump once it is mined. Moreover, an ore block with a grade greater than or equal to 0.08 oz/t
will be processed at the mill or sent to the waste dump.
If the grade of a mined ore block is between 0.05 oz/t and 0.08 oz/t, it will be either processed at the mill, treated at the leach pads or sent to the waste dump. The ore blocks in these
grade intervals are categorized as “undecided blocks” which means that the process destination is not designated based on a cutoff grade; instead the optimum destination will be determined based on the state of the system. Table 2 presents the cutoff grade intervals adopted for
this particular example. Furthermore, the proportions of the blocks in the process stream that
belong to different risk categories such as inferred, indicated and measured will be controlled
by enforcing risk constraints which are in a form of blending constraints. The deposit characteristics are illustrated in Table 3. It is clear that out of 1.9 million blocks in the block model,
only 87 thousand blocks are qualified to be ore blocks with an average grade of 0.061 oz/t.
Among the ore blocks, almost half the blocks are leach blocks with an average grade of
Table 1. Economic parameters.
Parameters
Value
AU
1250 $/oz
MILL COST
12 $/t
LEACH COST
6 $/t
MILL RECOVERY
90%
LEACH RECOVERY
70%
DISCOUNT VALUE
12.5%
Figure 1. McLaughlin mine process flow.
Table 2. Summary of the cutoff grade intervals.
Cutoff
Grades
BREAKEVEN
> = 0.03 oz/t
LEACH
< 0.05 oz/t
UNDECIDED
> =0.05 oz/t AND < 0.08 oz/t
MILL
> = 0.08 oz/t
Table 3. McLaughlin deposit characteristics.
Material Type
Blocks
Tonnage
AVG Grade
TOTAL
1,922,749
961,374,500
–
WASTE
1,835,583
917,791,500
–
ORE
87,166
43,583,000
0.061 oz/t
MILL
18,144
9,072,000
0.133 oz/t
LEACH
44,634
22,317,000
0.034 oz/t
UNDECIDED
24,388
12,194,000
0.057 oz/t