37 The results indicated that ILR was preferentially suited to the upper zone of the deposit, where higher grade material and more favourable access conditions supported underground upgrading. This suggested that ILR was not applied uniformly across the orebody, but was chosen where the combination of grade, access, material characteristics and processing constraints made early upgrading economically attractive. The introduction of in-place mining in the plan also significantly increased the production compared with the conventional base case with a positive impact on project economics. Under conventional mining, only stopes that satisfied the economic and processing requirements of the surface route were selected. When ILR and IMR were introduced, additional stopes became economically accessible because material could either be upgraded before processing or recovered through in-mine leaching. This expanded the recoverable portion of the orebody and created a more diversified production profile. Figure 7 summarises the economic impact of the IPM scenarios. The conventional mining base case at 5 Mtpa remained below the zero-NPV line, indicating that the project would be marginal under the reference conventional mining configuration. Introducing ILR moved the project into positive value by rejecting waste before surface processing which reduced OPEX from lower material transport requirements and reduced outlay for tailings disposal, while improving the grade fed to the concentrator plant thereby improving recovery potential. Adding IMR created an additional step-change in value because copper could be recovered without requiring all material to follow the conventional haulage and milling pathway. Leaching of tailings and waste used to backfill empty stopes allowed the operation to recover copper long after mining was completed. Figure 7 – Impact of ILR and IMR on case study economics One of the main benefits of deploying ore sorting ahead of the processing plant was to reduce the amount of material feeding the plant. Even though the addition of ore sorting by itself turned the project economics from negative NPV to slightly positive, the full potential could only be reached if the mining rate could be increased to take advantage of the processing capacity created by leaving some of the low grade waste underground. When bottlenecks were
RkJQdWJsaXNoZXIy MTM0Mzk2