4 R ESULTS
NPV is the primary measure to compare between the cases, while other impacts on pit inventories and cash flow are also documented. The key Prober® runs here for comparison are the ‘ Base Case Optimised Plan ’ and the ‘ ReCYN™ Optimised Plan .’ Prober® in each case was able to optimise the schedule to maximise NPV within the given mining and processing constraints for each scenario. This included mining fleet limits, individual site-by-site BCM limits and individual phase Vertical Rate of Advancement limits, Mill throughput constraints (measured in hours rather than tonnes given variety of hardness of throughput) and output constraints (e.g. gold room capacity). ‘ Base Case Optimised Plan ’ : A comparable run to the ReCYN™ runs using the base case WCPL pit designs, ABC costing and limits. This was fully optimised in all extents under theWhittle Consulting EO philosophy to maximise NPV of the current operations. The schedule outcomes from the ‘Base Case Optimised Plan’ result were then manually adjusted in a series of iterative ‘Static Analysis’ steps. These steps mimicked the outcome of a desktop exercise to examine ReCYN™, as well as to quantify the relative benefits of each aspect of inclusion on a fixed schedule. This was achieved iteratively via a four-stage manual adjustment to the schedule outcomes (i.e. no change to mining schedule, cutoff or destination), revaluing progressively on: o Intensifying Cyanide usage to increase Silver recovery given a portion is recoverable and detoxification issues are somewhat mitigated; and o The ReCYN™ ability to creating a new copper cathode product via electrowinning • ‘ReCYN™Optimised Plan ’ : Re-optimised in GEOVIAWhittle™ using a ReCYN™ outcome to produce new strategic shells, which then were optimised for schedule etc in Prober® also utilising a ReCYN™ outcome. The benefits modelled include those shown in the static adjustments above as well as the Base Case cyanide-soluble copper (CuCN) maximum blend limit at CIL being removed; The core run aims were as follows: • o Recovering Cyanide and re-using in CIL; o Reducing Detoxification costs;
The results of these runs are shown over the following two pages on Figure 8 and Table 4.
ReCYN™ Case Study – Martabe Operations
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