How to Read Exploration Results and Drill Intercepts

Drill intercepts are the raw data reported when a mining company bores into the ground to sample subsurface rock. Understanding how to read those results — including assay grades, intercept widths, depth, grade continuity, cut-off grades, and quality-control protocols — helps investors evaluate what a disclosure actually says, and what it does not.

What a Drill-Result Announcement Contains

When an exploration company releases drill results, the announcement typically lists one or more intercepts in a table format. Each row describes a single drill hole or a highlighted interval within that hole. The core data points are:

• Hole identifier (e.g., DDH-24-001) — a unique label linking back to collar-location data.
• From / To depths — the downhole interval sampled, measured in metres along the drill rod.
• Intercept length — calculated as the difference between “from” and “to.”
• Assay grade — the concentration of the target metal in the sampled rock.

Grade units vary by commodity. Gold and silver are conventionally expressed in grams per tonne (g/t). Platinum-group elements may be quoted in g/t or occasionally in parts per million (ppm, numerically equivalent). Base metals such as copper, zinc, lead, and nickel are expressed as a percentage (%) by weight. Uranium is reported as a percentage or in parts per million U₃O₈. Readers should verify that the unit used is consistent throughout the announcement; switching units mid-table is a recognised source of confusion.

These disclosures are subject to NI 43-101, the Canadian Securities Administrators’ standard that governs technical disclosure for mineral projects. Under NI 43-101 and its companion CIM Definition Standards, any written disclosure of exploration results — including news releases — must be approved or supervised by a Qualified Person (QP).

Downhole Length vs. True Width: A Critical Distinction

The single most common misreading of drill results is treating the reported intercept length as the actual thickness of the mineralised zone. It is not, in most cases.

Drill holes are not necessarily perpendicular to the plane of the ore body. A hole drilled at an oblique angle through a steeply dipping vein will intersect a longer core interval than the vein’s actual thickness. That longer measurement is the downhole length (also called apparent width). The true width is the perpendicular thickness of the mineralised structure.

The geometric relationship is: True Width = Downhole Length × sin(α), where α is the angle between the drill-hole axis and the plane of the mineralised zone. When a drill hole is nearly parallel to a vein, α is small, sin(α) approaches zero, and a very long downhole intercept can correspond to a very thin mineralised body.

NI 43-101 Section 3.4 requires that a technical report disclose whether reported widths are true or apparent. News releases issued under the continuous disclosure framework should also state this. Readers should look for language such as “true widths are estimated to be approximately X% of reported lengths” or an explicit statement that true widths have not yet been determined. The absence of any such statement in a headline intercept is a reason for caution, not celebration.

For junior mining companies at early drill stages, true-width calculations may genuinely be unavailable — determining vein orientation requires multiple holes in different orientations. That is a legitimate technical limitation. The disclosure should say so.

Assay Grades, Cut-Off Grades, and Grade Continuity

A reported intercept is never simply the raw average of every sample in a drill hole. Companies select intervals using a cut-off grade: a minimum metal concentration below which material is excluded from the reported intercept. The choice of cut-off grade is not neutral — it determines which samples enter the calculation and therefore what the headline grade appears to be.

Most announcements report a single cut-off grade applied consistently. However, some use internal dilution rules (allowing a fixed length of sub-cut-off material within an intercept) or composite multiple narrow high-grade zones to produce a single long headline number. The method should be stated explicitly. When it is not, the reader cannot verify the arithmetic.

Grade continuity is the spatial persistence of mineralisation along strike and down dip. A single high-grade drill hole has no proven continuity. Continuity only becomes demonstrable as additional holes confirm that grade and width persist over meaningful distances. CIM Definition Standards distinguish between an inferred resource (limited drill spacing, low geological confidence) and measured/indicated resources (tighter drilling, higher confidence). Isolated drill intercepts sit below even the inferred category — they are exploration results, not resource estimates.

Note: These ranges are approximate educational references derived from published literature. They vary widely depending on deposit type, metallurgy, location, and prevailing metal prices. They are not cut-off grades, valuations, or investment signals.

QA/QC: The Chain That Makes Assays Trustworthy

Assay results are only as reliable as the procedures used to collect, handle, and analyse the samples. Quality assurance and quality control (QA/QC) is the suite of protocols that allows a reader — and a QP — to assess whether the analytical data are reproducible and free from contamination.

Four tools form the backbone of any credible QA/QC program:

• Certified reference materials (CRMs / standards) — rock pulps of known metal content, prepared and certified by an independent provider, inserted at regular intervals (typically every 20th sample) into the sample stream. Results outside acceptable limits flag a problem with the assay run.
• Blanks — crushed barren rock with no detectable metal content, inserted to detect contamination between samples during sample preparation. An elevated blank reading suggests cross-contamination in the preparation equipment.
• Field duplicates and pulp duplicates — split samples re-submitted to check the reproducibility of the sampling and assaying process. High variability in duplicates can indicate a nugget effect (coarse, unevenly distributed metal grains) or inconsistent splitting procedures.
• Accredited laboratories — independent laboratories holding ISO/IEC 17025 accreditation for the specific analytical methods used. Accreditation requires participation in inter-laboratory proficiency testing and regular audits.

Chain of custody documentation records sample handling from the drill core tray through splitting, packaging, transport, and receipt at the laboratory. A break in chain of custody — samples left unattended, improper labelling, incomplete paperwork — undermines the evidentiary value of the assays regardless of how accurate the laboratory analysis might be.

NI 43-101 Form 43-101F1, Item 11, requires that a technical report describe the nature and quality of the sampling, the sample preparation and analysis procedures, and the QA/QC measures employed. News releases are not required to include full QA/QC tables, but reputable companies provide them or reference their availability.

What to Check Before Accepting a Headline Intercept

Reading a drill-result release critically requires cross-referencing several elements that are sometimes buried in technical footnotes rather than the headline paragraph.

• Is the width described as true or apparent? If apparent, is a conversion factor given or promised in a forthcoming report?
• What cut-off grade was used? A change in cut-off relative to previous releases can make an intercept look better or worse without any change in the actual rock.
• Is internal dilution allowed? If so, by how much, and is that consistent with prior releases?
• How does this hole relate to previous holes? An isolated result with no adjacent holes cannot demonstrate continuity.
• Is a Qualified Person named and affiliated? Under NI 43-101, the QP must be named, must have relevant experience for the commodity and type of deposit, and must have either personally reviewed the data or supervised the work. The QP’s relationship to the company (employee, consultant) should be disclosed.
• What QA/QC summary is provided? At minimum, the release should acknowledge that standards, blanks, and duplicates were inserted and that results met acceptable tolerances.
• Has the company selectively reported only the best holes? NI 43-101 requires that exploration results not be selectively disclosed to give a misleading impression. If a company has drilled ten holes but reports only two, the other eight should be acknowledged even if assays are pending.

Full technical reports and historical drill data for Canadian issuers are available through SEDAR+ filings, where 43-101 technical reports, annual information forms, and news releases are archived. Comparing a new release against prior technical reports filed on SEDAR+ allows a reader to assess whether methodology has changed and whether the current disclosure is consistent with the property’s documented geology.

This article is educational. Disclosure standards and technical figures appearing in exploration announcements are not investment signals, valuations, or recommendations of any kind.

The Qualified Person Requirement Under NI 43-101

The Qualified Person concept is the cornerstone of NI 43-101’s credibility framework. A QP is defined in the instrument as an engineer or geoscientist with at least five years of relevant experience in mineral exploration, mine development, or production, who is a member in good standing of a recognised professional association, and who has relevant experience in the type and style of mineralisation being disclosed.

The QP must review and take responsibility for the technical information in a news release before it is issued. This does not guarantee accuracy — no regulatory framework can eliminate all error or misrepresentation — but it creates professional accountability. A QP who signs off on misleading disclosure is subject to discipline by their professional association in addition to securities regulatory consequences.

If a news release carries no QP certificate or contains boilerplate language that cannot be traced to a named, credentialed individual, that is a procedural red flag under the standard. CSA Staff Notice 43-307 and related guidance documents discuss expectations for how QP sign-offs should be presented in news releases.

FAQ

Sources

Canadian Securities Administrators, National Instrument 43-101 Standards of Disclosure for Mineral Projects, including Form 43-101F1 and Companion Policy 43-101CP, consolidated version (CSA, 2011, as amended); Canadian Institute of Mining, Metallurgy and Petroleum, CIM Definition Standards for Mineral Resources and Mineral Reserves (CIM, 2014); Canadian Institute of Mining, Metallurgy and Petroleum, CIM Estimation of Mineral Resources and Mineral Reserves Best Practice Guidelines (CIM, 2019); Canadian Securities Administrators, CSA Staff Notice 43-307 Mining Technical Reports — Preliminary Economic Assessments (CSA, 2012); Canadian Securities Administrators, CSA Staff Notice 43-309 Review of Website Investor Presentations by Mining Issuers (CSA, 2015); SEDAR+ (System for Electronic Document Analysis and Retrieval Plus), Canadian Securities Administrators, sedarplus.ca; Ontario Securities Commission, OSC Policy 43-601 — Disclosure Standards for Mineral Projects guidance materials, osc.ca; International Organization for Standardization / International Electrotechnical Commission, ISO/IEC 17025:2017 General Requirements for the Competence of Testing and Calibration Laboratories (ISO, 2017). Accessed 2026-06-10.

By Boersenpost · reviewed by Carsten Schmider, financial analyst — last updated 10 June 2026. Educational content, not investment advice.