Resource-to-Reserve Conversion

Resource-to-reserve conversion determines which parts of a Mineral Resource support economically justified extraction at the reporting date. Canada's CIM Definition Standards (2014) distinguish the resource's reasonable prospects for eventual economic extraction from the reserve's supporting demonstration, including mining dilution and losses.^[1]

The engineering task is to connect geological confidence, a practicable development plan and evidence for its assumptions. A favorable grade estimate cannot demonstrate that access, processing, infrastructure and approvals are achievable together. Equally, an attractive project cash flow does not improve the geological knowledge supporting the material included in it. Conversion is a conclusion about a supported plan, rather than a percentage applied to the resource total.

Geological Confidence and Conversion Eligibility

CIM 2014 establishes these conversion possibilities, subject to the other reserve requirements:^[1]

Measured material can support a Probable Reserve when confidence in the Modifying Factors does not justify Proven classification. That outcome does not necessarily reduce its geological classification.^[1]

Review geological confidence, extraction feasibility and the resulting category separately. Greater confidence in ore grade does not demonstrate water-supply availability; proven processing equipment does not establish mineralized continuity. Further investigation should address the governing evidence gap.

Supporting Studies and Reporting Context

The June 2024 CRIRSCO International Reporting Template is advisory; applicable national or regional codes take precedence. Its provisions provide a useful common reference, but they do not constitute one worldwide reporting law. The framework and edition governing a particular estimate must therefore be identified.^[2]

Within that template, a scoping study cannot establish Mineral Reserves. At least a pre-feasibility study is needed to demonstrate a technically achievable, economically viable plan with material Modifying Factors assessed. A pre-feasibility study identifies preferred extraction and beneficiation methods and supports financial analysis with reasonable, demonstrated assumptions. A feasibility study develops the selected option to higher confidence; a full feasibility study is not universally required for conversion under this template.^[2]

A study label is consequently a claim about its evidential content, not a substitute for examining that content. Reviewers should be able to follow the chain from data to assumptions, design, schedule and economic results. A detailed cost estimate for one facility does not remedy a poorly supported recovery assumption elsewhere. Where an operating mine supplies measured performance, establish which parts of the future plan those observations represent: results from existing workings do not automatically validate different ground conditions or a proposed expansion.

Demonstrate a Coherent Extraction Case

Modifying Factors connect the resource estimate to the proposed operation and external conditions. The South African SAMREC Code, 2016 edition, organizes supporting evidence in Table 1: mining design, representative metallurgical testwork, infrastructure, environmental and social matters, markets, costs, risk and economic analysis. It distinguishes surface considerations such as slopes and stripping from underground mining and ventilation considerations.^[3]

For engineering review, the key interfaces can be expressed as questions:

These questions synthesize the dependencies in SAMREC's technical-study provisions; they are not additional reporting categories.^[3]

Checking interfaces can reveal contradictions that separate discipline reports conceal. A mine schedule may assume a production rate that the infrastructure schedule cannot support. A processing model may use an average feed response while the mine plan delivers distinct material types in different periods. In each case, the review should resolve which assumption governs and propagate that choice through the affected calculations. Combining individually plausible inputs is insufficient when those inputs describe different projects.

Evaluate Constraints in Their Actual Setting

The evidence needed for a Modifying Factor depends on the project. Rupprecht's 2020 study of South African tailings reclamation discusses metallurgical testwork, slurry-transfer routes and associated surface rights, water and power availability, processing infrastructure, and rehabilitation. It illustrates why accessible mineralized material can still require substantial work to demonstrate an integrated extraction case. These observations concern the tailings operations studied and are not universal design parameters for other mines.^[4]

As an engineering thought experiment, suppose a proposed reclamation project has adequate sampling and favorable processing tests, but its assumed pipeline corridor becomes unavailable. Recheck the alternative route, pumping arrangement, construction schedule, capital and operating costs, and implications for affected land. The geological estimate might remain unchanged while the proposed development case becomes unsupported or requires redesign. This inference follows the dependency on transfer infrastructure described in the study; additional drilling alone would not resolve the corridor problem.^[4]

SAMREC 2016 calls for disclosure of permit status and a reasonable basis for expecting outstanding permits to be obtained.^[3] A reserve statement is consequently distinct from a permit, financing commitment or decision to construct. The supporting record should make outstanding conditions visible rather than allow the reserve label to obscure them.

Make the Conversion Traceable

CIM 2014 also requires the reserve reference point to be stated. A mill-feed estimate precedes plant-recovery deductions; a saleable-product estimate includes the applicable yield. Mixing these bases misstates the quantities being compared.^[1]

Maintain a documented connection between the resource model used, selected extraction areas, design assumptions and reported reserve estimate. An effective review record can identify the model and study versions, responsible disciplines, evidence supporting material assumptions, unresolved conditions, and reasons for excluding particular areas. This proposed review structure makes it possible to reproduce the decision rather than merely reproduce the final arithmetic.

For example, a change register can distinguish material excluded because geological confidence is insufficient from material excluded because access is uneconomic. The first may call for better geological evidence; the second may call for a different development configuration or remain excluded. Recording both simply as a lower conversion percentage removes the information needed to decide what work could change the outcome.

Any comparison of successive estimates also needs a common basis. A percentage change in reported tonnes can be misleading if the underlying model, extraction boundary, dilution treatment or reference point changed simultaneously. Explain those changes separately before attributing the difference to improved mineability. The conversion record should preserve the reason for each material decision, including decisions to retain uncertainty rather than conceal it behind a single aggregate factor.

Review, Challenge and Revise

Conversion includes professional judgment, so review should challenge both assumptions and their use. Peattie, Chamberlain and Flitton describe AngloGold Ashanti's governance arrangements in their 2017 paper, including documented reporting guidelines, defined technical responsibilities, internal peer review and external review. Their reported peer-review process included attempts to reproduce parts of the work independently. This is a documented organizational example, not a prescribed structure for every company.^[5]

Applying that principle, a review can test whether a change in one discipline actually reaches the schedule and evaluation used for classification. It can also check whether a mitigation measure has been costed and incorporated into the design, or merely mentioned in a risk register. Assigning responsibility for resolving an assumption is different from demonstrating that the assumption is justified.

Revision should respond to changed evidence and conditions. Preserve the previous estimate, identify what changed, and reconsider the affected development case and classification. Improvements can support conversion where an earlier constraint prevented it; adverse information can remove previously supported material. Neither outcome follows automatically from a change in commodity price, drilling density or study title. The defensible result is the estimate whose geological basis, engineering assumptions and economic case remain consistent at the reporting date.