economic recovery curves defeat chasing gold 13.1.14 Conclusions and Recommendations
The 2017 metallurgical program covered flotation optimization, variability testing, testing of simulated annual blends, comminution testing, concentrate and tailings characterization, oxidation and environmental testing and mineralogy. Four trade-off studies were completed to provide guidance on concentrate marketing, gold recovery from pyrite, arsenic reduction in the complex copper concentrate and concentrate transportation.
For much of the recent metallurgical program, it was planned to develop and optimize the flowsheet selected in the 2016 PEA, which produced two copper concentrates, a low arsenic and a complex concentrate. However, during variability testing, it was realized that a significant proportion of the orebody did not respond well to this flowsheet. Testing, and analysis of a flowsheet producing a single bulk concentrate was then carried out, and in conjunction with the project’s marketing consultants, a decision was made to base the PFS (PFS, 2018) on a simplified, more robust flowsheet that yields a single bulk concentrate.
Page 411: An interesting tidbit on the connection between the upper and lower zone... 24.3 Timok Lower Zone Opportunity
Prior to this study and the drilling program that was completed in February 2018, it was uncertain whether the Lower Zone could be considered as satisfying the criteria of having a reasonable prospect of eventual economic extraction. Now that the Upper Zone has been proven to be economic, it is likely that at least some of the infrastructure could be re-purposed for the Lower Zone, such that there is now a reasonable prospect of economic extraction for at least part of the Lower Zone. As such, Nevsun has completed an initial mineral resource for the porphyry copper portion of the Lower Zone. On the basis of this resource, future work will focus on determining how much of this resource is potentially minable by conducting preliminary scoping and PEA studies.
Page 414: 25.3 Mineral Processing and Metallurgical Test Work
The 2017 metallurgical program covered flotation optimization, variability testing, testing of simulated annual blends, comminution testing, concentrate and tailings characterization, oxidation and environmental testing and mineralogy. Four trade-off studies were completed to provide guidance on concentrate marketing, gold recovery from pyrite, arsenic reduction in the complex copper concentrate and concentrate transportation.
For much of the recent metallurgical program, it was planned to develop and optimize the flowsheet selected in the 2016 PEA, which produced two copper concentrates, a low arsenic and a complex concentrate. However, during variability testing, it was realized that a significant proportion of the orebody did not respond well to this flowsheet. Testing, and analysis of a flowsheet producing a single bulk concentrate was then carried out, and in conjunction with the project’s marketing consultants, a decision was made to base this PEA study on a simplified, more robust flowsheet that yields a single bulk concentrate.
Significant test work and engineering efforts were undertaken to establish an economic route for gold recovery from pyrite. However the low gold content of the pyrite in all but the initial years of production, the up-front capital required to produce a pyrite concentrate and store it separately for later reclaim, and the revenue deferral from this element of the Timok project rendered it uneconomic. It is not proposed to include pyrite recovery and separate storage in the flowsheet for Rakita. Pyrite in the copper tailings will report to the tailings storage facility.
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