Selection of mining method

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Selection of mining method

Context: The selection of a mining method for a given orebody can be a challenging assignment and may need to address personal bias for or against a particular method. The selection of the mining method may also need to occur prior to the completion of desired geotechnical or ore value determinations. The Mining professional will need to continually debate if the information picture is complete enough for the design. In some cases the picture will only be more complete when mining has commenced. A clear understanding of the risks in mine design and their mitigation is also essential.

The chapter will need to describe the selection process in enough detail that a new professional to the industry could follow the process, while balancing the desire to encourage senior or retired professionals to contribute to this chapter based upon their experiences. The various business and technical considerations influencing choice of mining method should be discussed, and linkages with topics described in other chapters should be made to emphasize value creation through consideration of the entire mining system as opposed to single components of the design.

The understanding of value creation and where value is lost in our mine design and subsequent execution needs to be explained in mining method selection.

Purpose: clarify the process of selecting a mining method for an orebody.

Quantity: one chapter with multiple sub-sections

Quality: the following topics would be covered in this chapter

• How the data gathered in the previous chapter links with the method selection

• What additional data is required for method selection

• How to use operational data and what to watch out for in the data.

• Can the selection process be shown in a flow chart

• What criteria is used at each selection steps and how to determine how a method will perform

• How specific site characteristics or requirements may affect choice of mining method

• How to address bias for or against a particular mining method

• How to factor in new or novel approaches in mining which may affect the method selected

• Risk assessment and mitigation in mine design

• What can be learned from past mining method selections

Review of the main mining methods

Review for the purpose of differentiating as a function of the geological and geotechnical characteristics discussed in the previous chapter. Dilution factors, mine recoveries and operating costs ranges are also discussed. Sources of information on costing are discussed.

Room and pillar

Shrinkage

Sub-level stoping

Longitudinal long-hole retreat

Cut & fill

Underhand cut & fill

Sublevel caving

Panel caving

Preliminary selection of mining method

This section would be used in conceptual and scoping studies for trade-off analysis. Applicable mining methods are chosen based on geometrical and geomechanical criteria, and for each option, a quick economic analysis is done to establish, the required cut-off grade, the available resources, and the potential production rate. The process must recognize that more than one mining method can be used in the mine.

Cut-off-grade selection

Selection of mining methods, sizing of stopes

The first selection will be based mostly on the shape and the geotechnical characteristics of the orebody. Review of the main points in reference to the previously discussed mining methods

Estimation of the resources and reserves for each

Each mining method have associated dilution factors and operating costs, and it is possible to get a quick estimate of the amount of resources and reserves available for each.

Grade and tonnage distribution

Dilution and ore recovery

Dilution and ore recovery

Presence of mineral domains and blending requirements

Preliminary estimation of mining cost per tonne

Estimation of the potential production rate

Each estimated resource has the potential for a certain production rate. Discussion of the techniques for estimating such rates, as well as the operating constraints limiting the productivity.

Rough estimate of revenues, operating costs, and margins

Combining all the previous points, get a rough estimate of operating margins, both on a unit basis and in total for the orebody.

Selection of the most promising options

Discussion on how to use all this information to determine the most promising mining methods.

Refined selection of mining method

In this section, more details are added to determine rough estimates of capital costs for development, transport infrastructures, and ventilation, the technical risks are analysed and mitigated to eventually choose the mining method for detailed design work.

Rough layout and costing of the ore, waste, backfill, materials, labour transport development

Rough layout and costing of ventilation infrastructure

Risk assessment matrix

Risk mitigation profile

Selection of mining method(s) for detailed design

Value addition

Discussion of the sensitivity of the design and the effects on production and value. Show how some deposits may have much more flexibility than others.

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