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Figure 16.2 demonstrates the relationship between the mineralized material (yellow
bar) contained within the pit shell and the PV for each of the nested pit shells. The
blue line in this figure represents the cumulative PV of the pit shell for a best case
scenario. The best case scenario consists of a schedule that mines out Pit Shell 1
(the smallest pit), and then mines out each subsequent pit shell from top down,
before starting the next pit shell. In other words, there are as many intermediate
mining pushbacks as there are pit outlines within the one that is being mined. This
schedule is seldom feasible because the pushbacks are usually much too narrow; its
usefulness lies in setting an upper limit to the PV.
The red line represents the worst case scenario in which the schedule consists of
mining each bench completely before starting on the next bench. This schedule, or
one that is very close to it, is usually feasible and also serves to set a lower limit to
the PV.
The green line represents specified case that is a more realistic approach to mine a
deposit.
The value curve is quite flat after Pit Shell 10 for both best case and specified cases.
Since there is no significant difference between different pit shells, the base case pit
shell was chosen as the final pit for production scheduling and financial analysis.
Figure 16.2 Present Value of the Pits for Different Optimum Pits
The tabulated results of the nested pit shells are presented in Table 16.4. The base
case pit (Pit Shell 26) is highlighted.
Prophecy Platinum Corp. 16-5 1193460500-REP-R0001-02
Wellgreen Project Preliminary Economic Assessment,
Yukon, Canada