Written and maintained by CASRAI Editorial Board
Last updated
A mineral resource is a concentration or occurrence of material of economic interest in or on the Earth’s crust, in such form, grade or quality and quantity that there are reasonable prospects for economic extraction. Resources are split into Inferred, Indicated and Measured categories by increasing geological confidence, and only the Indicated and Measured parts can be converted into a mineral reserve.
This page is written for researchers, lab staff and administrators who read mining company statements or technical reports and need to know what each term commits the author to. It follows the CRIRSCO International Reporting Template (June 2024 version, clause numbers cited below) and the U.S. SEC’s mining disclosure guidance.
Definition and scope
CRIRSCO clause 7.1 gives the definition quoted above. Three points in the surrounding guidance matter more than the definition itself:
- The test applies to every category. Clause 7.2 requires that all reported resources, whatever their classification, meet the “reasonable prospects for economic extraction” test, meaning more likely than not. Clause 7.3 adds that non-economic mineralisation does not qualify as either a resource or a reserve.
- A resource is not everything that was drilled. The template states that a mineral resource is not an inventory of all mineralisation drilled or sampled, regardless of cut-off grade, likely mining dimensions, location or continuity; it is a realistic inventory. Producing one implies a preliminary judgement by the Competent Person about the modifying factors.
- Dumps and tailings can count. The term covers material such as dumps and tailings, not only undisturbed rock.
Material assumptions behind an estimate should be stated and justified in the public report, and any grade cutting or factoring adjustments must be described.
How classification works: Inferred, Indicated and Measured
Classification reflects the confidence in the geology, not the size or value of the deposit. The table below sets out what the template says for each category.
| Category | Evidence standard (CRIRSCO) | Clause | Can become a reserve? |
|---|---|---|---|
| Inferred | Quantity and grade estimated on limited geological evidence and sampling; evidence is sufficient to infer but not demonstrate continuity; lower confidence than Indicated. It is reasonably expected that the majority could be upgraded to Indicated with continued exploration. | 7.4 | No. It must not be converted to a mineral reserve. |
| Indicated | Estimated with enough confidence to apply the modifying factors in sufficient detail to support mine planning and evaluation of economic viability; evidence is sufficient to demonstrate continuity between points of observation. | 7.8 | Only to a Probable Mineral Reserve. |
| Measured | Confidence sufficient for detailed mine planning and final evaluation of economic viability; evidence is sufficient to confirm continuity. | 7.10 | To a Proved or a Probable Mineral Reserve. |
Clause 7.5 adds that where a resource statement is predominantly Inferred, the supporting information must let the reader assess the risk.
Mineral resource versus mineral reserve
A mineral reserve (clause 8.1) is the economically mineable part of a Measured and/or Indicated mineral resource. It includes diluting materials and allowances for losses, and it is defined by a Pre-Feasibility or Feasibility Study that applies the modifying factors. Under clauses 8.10 and 8.12, a Probable Reserve comes from Indicated resources (and in some circumstances Measured), while a Proved Reserve comes from Measured resources only. The SEC’s guide uses the same structure: a reserve is an estimate of tonnage and grade of indicated and measured resources that can be economically mined, including dilution and losses.
The practical consequence is that a resource figure is a statement about geology with a preliminary economic screen, while a reserve figure rests on a completed study. Adding the two together, or reading a resource tonnage as “what will be mined”, misreads both.
Who signs off: Competent Person and Qualified Person
CRIRSCO-aligned codes name the author of a public report the Competent Person. In the United States, the SEC’s rules use the term Qualified Person: a mineral industry professional with at least five years of relevant experience who is a member or licensee in good standing of a recognised professional organisation. The SEC requires a technical report summary, dated and signed by the Qualified Person, to be filed as an exhibit when resources or reserves are disclosed for the first time or change materially. An initial assessment’s cash flow may include Inferred resources only with cautionary statements.
A checklist for reading a resource statement
These questions are derived from the clauses above; each can be answered from the report itself.
- Is the estimate split by category? Inferred, Indicated and Measured should be distinguishable (clauses 7.4, 7.8, 7.10).
- How much is Inferred? If the statement is predominantly Inferred, the report must give you enough to assess risk (clause 7.5).
- Are the assumptions stated? Look for the material assumptions, the reasoning for “reasonable prospects for economic extraction”, and any grade cutting or factoring.
- Is it a resource or a reserve? Reserves need a Pre-Feasibility or Feasibility Study; a figure with no such study is not a reserve.
- Who signed it? Identify the Competent Person or Qualified Person and the date.
- Could the material be non-qualifying? Inventory or government exploration reports may disclose material that does not meet the definition; such material is not a resource.
Where it matters for labs
This section is editorial interpretation rather than a CRIRSCO provision. Resource categories rest on points of observation (drill intervals, samples) and on how continuous the evidence is between them. The analytical data behind those points comes from sample preparation and laboratory analysis, so a lab’s data quality feeds directly into how much confidence a Competent Person can place in an estimate. Readers who work with such data may find these CASRAI guides useful background: ICP spectroscopy, atomic absorption spectrometry, handheld XRF analysers and XRD diffraction. For the policy side of mineral supply, see the EU Critical Raw Materials Act.
Common misunderstandings
- “Resource means it can be mined profitably.” It means there are reasonable prospects for economic extraction, a preliminary judgement, not a completed feasibility study.
- “Inferred resources will eventually become reserves.” Inferred material must not be converted directly to a reserve. It is expected that most could be upgraded to Indicated with more exploration, but that is an expectation, not a guarantee.
- “Resource is all the mineralisation found.” The template says it is not an inventory of everything drilled or sampled.
- “Qualified Person and Competent Person are the same label everywhere.” The role is similar but the term and the entry requirements depend on the reporting code, as the sign-off section above shows.
FAQ
What is a mineral resource in simple terms?
It is an estimate of a concentration of economically interesting material in the Earth’s crust, with enough grade, quality and quantity that extracting it could reasonably be economic.
What is the difference between a mineral resource and a mineral reserve?
A reserve is the economically mineable part of a Measured and/or Indicated resource, defined by a Pre-Feasibility or Feasibility Study. A resource carries only a preliminary economic screen.
Can an Inferred resource be reported as a reserve?
No. CRIRSCO clause 7.4 states that Inferred material must not be converted to a mineral reserve.
Who is responsible for a resource estimate?
A Competent Person under CRIRSCO-aligned codes, or a Qualified Person under SEC rules, who needs at least five years of relevant experience and good standing in a recognised professional organisation.
Sources
- CRIRSCO, International Reporting Template, June 2024 update (clauses 7.1-7.10, 8.1, 8.10, 8.12), percstandard.org, read 2026-11-08.
- U.S. SEC, small-entity compliance guide for Modernization of Property Disclosures for Mining Registrants (Subpart 1300), sec.gov, read 2026-11-08.
