Scoping, Pre-Feasibility and Feasibility Studies: What Changes Between Each Stage?

Scoping, Pre-Feasibility and Feasibility Studies are often described as successive levels of detail. While that is true, it misses the more important point: each stage supports a different mining project decision and determines the confidence available for Resource-to-Reserve conversion.

A common misconception is that a Scoping Study produces a mine plan which is then simply refined through Pre-Feasibility and Feasibility. In reality, the purpose of each stage changes as confidence increases. Early studies explore options and identify the most promising development pathway. Later studies test whether that pathway can be demonstrated to be technically achievable and economically viable.

Understanding these distinctions is important for mine planners, investors and Competent Persons. As a mining consultancy in Perth, Go Engineering applies practical mining-engineering experience to project evaluation, mine planning and JORC Resource-to-Reserve conversion, helping clients determine when an Ore Reserve can be reported.

The study progression

Scoping Study: testing the project concept

A Scoping Study is typically the first formal economic assessment of a project.

At this stage, the objective is not to optimise a mine plan. The objective is to determine whether further study can be justified and which development concept appears most likely to succeed.

For a small underground gold project, the study team may assess several mining approaches, such as:

• Longhole stoping with paste fill

• Longhole stoping with rib pillars

• Avoca stoping

• Cut-and-fill mining

The purpose is not necessarily to produce a detailed design for every option. Rather, sufficient engineering is completed to compare the alternatives and identify the preferred pathway.

For example:

The outcome may be a recommendation that longhole stoping appears to offer the best balance of productivity, recovery and economics.

At this stage, the design remains conceptual. Production schedules, equipment fleets, capital costs and operating costs are generally based on high-level engineering assumptions and benchmarking.

Importantly, a Scoping Study cannot support the declaration of an Ore Reserve.

Pre-Feasibility Study: proving the preferred option

Once a preferred development approach has been identified, the project moves into Pre-Feasibility.

The question changes from:

"What mining method should we use?"

to:

"Can the preferred mining method be demonstrated to work?"

This is where option selection gives way to option refinement.

Using the underground gold example, a Scoping Study may conclude that longhole stoping with paste fill is preferred. The Pre-Feasibility Study then develops that concept substantially further.

Typical areas of investigation include:

• Stope dimensions

• Mining sequence

• Level spacing

• Fill strategy

• Infrastructure requirements

• Ventilation requirements

• Production rate

• Equipment fleet requirements

• Economic cut-off grade

• Ore Reserve conversion assumptions

Rather than comparing completely different mining methods, a PFS often tests different versions of the preferred option.

For example, the study may evaluate:

The objective is to understand impacts on:

• Net Present Value (NPV)

• Internal Rate of Return (IRR)

• Capital intensity

• Fleet requirements

• Development requirements

• Project risk

The preferred production rate may remain 450 ktpa, but the conclusion is now supported by engineering analysis rather than preliminary assumptions.

A Pre-Feasibility Study also begins to provide a basis for Ore Reserve declaration.

Feasibility Study: preparing for implementation

A Feasibility Study focuses on the selected development option.

The question at this stage becomes:

"Are we ready to commit capital and proceed with development?"

By now, the preferred mining method, processing route and overall mine strategy are usually established.

The focus shifts to detailed engineering, implementation planning and increased confidence in the Modifying Factors.

Typical work includes:

• Detailed mine design

• Detailed production schedules

• Procurement strategies

• Vendor quotations

• Construction planning

• Detailed infrastructure design

• Ventilation engineering

• Paste fill system design

• Project execution planning

The development approach has typically been established by this stage, although optimisation and refinement continue.

The resulting level of confidence is generally suitable to support investment and financing decisions.

When can an Ore Reserve be declared?

This is one of the most misunderstood aspects of the study process.

Under the JORC framework, a Scoping Study cannot support an Ore Reserve declaration.

Ore Reserves require studies completed at least at Pre-Feasibility or Feasibility level, together with consideration of the relevant Modifying Factors.

Importantly, JORC does not require a Feasibility Study before an Ore Reserve can be declared. A sufficiently rigorous Pre-Feasibility Study may be sufficient.

Resource classifications and study stages

Resource classification and study stage are related, but they are not the same thing.

A common misconception is that Scoping Studies use Inferred Resources, Pre-Feasibility Studies use Indicated Resources and Feasibility Studies use Measured Resources. In practice, the relationship is not that rigid.

A more realistic representation is:

The key restriction is that Inferred Resources cannot be converted directly into Ore Reserves.

The relationship between Resources and Reserves is:

Even a Measured Resource does not automatically become a Proved Ore Reserve. The final classification depends on confidence in the relevant

Modifying Factors, including mining, processing, economics, approvals and other project-specific considerations.

What are Modifying Factors?

Modifying Factors are the considerations used to determine whether a Mineral Resource can be economically mined.

They commonly include:

• Mining

• Processing

• Metallurgical

• Infrastructure

• Economic

• Marketing

• Legal

• Environmental

• Social

• Governmental factors

As a project advances through the study stages, these factors are progressively tested, refined and de-risked.

For example, a Scoping Study may assume paste fill is achievable. A Pre-Feasibility Study may evaluate fill strengths, binder requirements and operating costs. A Feasibility Study may include detailed paste plant design, infrastructure layouts and implementation planning.

Confidence in these factors is ultimately what underpins an Ore Reserve.

The key takeaway

The difference between Scoping, Pre-Feasibility and Feasibility Studies is not simply the amount of detail.

Each study answers a different question.

• Scoping Study:What mine should we build?

• Pre-Feasibility Study:Can this mine work?

• Feasibility Study:Are we ready to build it?

A Scoping Study identifies the most promising development pathway. A Pre-Feasibility Study tests whether that pathway can be demonstrated to be technically achievable and economically viable. A Feasibility Study develops the preferred option to a level of confidence suitable for investment and project execution.

Understanding where a project sits on that journey is fundamental to understanding both its risk and its value.

About Go Engineering

Go Engineering is a Perth-based mining consultancy providing mine planning, mining studies, Ore Reserve estimation, technical due diligence and operational support across Western Australia and internationally.

Our mining consultants support projects from Scoping and Pre-Feasibility through to Feasibility, mine optimisation and JORC-compliant Ore Reserve reporting.

Need an independent study review, an Ore Reserve Competent Person or support progressing a project from Resource to Reserve? Go Engineering can help.

Sources

• JORC Code 2012, particularly Clauses 29-40 covering Ore Reserves, Scoping Studies, Pre-Feasibility Studies and Feasibility Studies.

• ASX Listing Rules Chapter 5.

• ASX Guidance Note 31: Reporting on Mining Activities.

• AusIMMStudy Processes Handbook(Monograph 35), Chapters 4, 8, 9 and 10.