A scoping study, or Preliminary Economic Assessment (PEA), is a report for the preliminary evaluation of a mining project. The only question that a scoping study report really has to answer is whether it is worth spending more money on the project. It is not valid for project financial evaluation or reserve reporting. The level of accuracy for capital and operating costs is typically +/-40-50% and the principal factors are mostly assumed and/or factored.
Flow sheet development is often based on limited data and metallurgical testwork, if available at all, and it is common to use benchmarked data from similar projects with appropriate assumptions.
A pre-feasibility study (PFS) is the critical step in evaluating the technical and economic viability of a mining project. Although the total engineering content is normally <10%, the accuracy levels are typically +/-25%. However, during the PFS process, trade-off studies will be conducted as appropriate, and following the requisite metallurgical testwork, to enable selection of the optimum flowsheet to take forwards to feasibility study.
Significant metallurgical testwork will therefore be conducted on representative samples of ore, taking into account all the different ore types and lithologies present, and including blends as necessary to represent the expected life of mine schedule. Pilot plant testing can also be included as required. Flowsheet modelling is often conducted, particularly for the comminution circuit.
Capital and operating cost estimations will use vendor quotations for major equipment, but other construction costs are typically factored.
A feasibility study (FS), represents the final step in the process of evaluating a mining project and a decision to proceed or not, with a full and detailed evaluation of the technical and economic viability of the project. It is a natural follow-on from the PFS, whereby the optimum process flowsheet or flowsheets has already been determined. Therefore, the capital and operating cost accuracy is higher than the PFS at typically +/-15%, although the overall engineering content is still relatively low.
Detailed test work will have been completed to allow the requisite level of process engineering design and cost accuracy, including flowsheet development, metallurgical mass and water balances, process design criteria, process flowsheet description, equipment selection and sizing, power consumption, reagents & consumables (primarily based on testwork), process flow diagrams, piping and instrumentation diagrams, general arrangement drawings and capital and operating cost estimates (derived from take-offs and full vendor quotations).
The amount of process engineering required varies for the three levels of study and whether the study is to international standards (normally required for project financing) or local national standards.
However, once metallurgical testwork is complete, it will variously include some or all of the following components:
- International benchmarking of similar projects
- Selection of optimum processing flow sheet
- Metallurgical mass and water balances
- Basis of design
- Process design criteria
- Flowsheet description
- Equipment sizing and selection
- Plant layout
- Plant services
- Tailings disposal
- Capital & operating cost estimates