Gold Assay QA/QC: How Investors Can Test Confidence in Reported Grades

A gold grade is only as dependable as the sampling, preparation, laboratory work, and data controls behind it. Assay quality assurance and quality control—usually shortened to QA/QC—helps technical teams identify contamination, analytical bias, poor repeatability, sample mix-ups, and other problems before results are used in a mineral-resource estimate or investment presentation.

What the main controls are designed to detect

Blanks are samples expected to contain little or no target metal. They help reveal contamination during crushing, pulverizing, handling, or analysis. A blank reporting unexpected gold does not automatically invalidate an entire program, but it should trigger a documented investigation into where contamination may have occurred.

Certified reference materials, often called standards, contain independently established concentrations. Comparing the laboratory result with the certified value helps detect analytical bias or drift. Standards should cover grade ranges relevant to the deposit; a low-grade standard alone may provide limited evidence about high-grade performance.

Duplicates test precision. Field, coarse-reject, and pulp duplicates examine different stages of the sampling and preparation process. Natural gold can be distributed unevenly, so duplicate variability may reflect geology as well as laboratory performance. Investors should ask whether the project explains the cause instead of treating every variance as a laboratory failure.

Check assays send selected material to a second laboratory. Independent checks can identify systematic differences between laboratories, but their value depends on sample selection, chain of custody, analytical method, and whether discrepancies are investigated.

Good QA/QC begins before the laboratory

Even precise analytical equipment cannot correct a nonrepresentative sample. Core recovery, sample intervals, cutting procedures, bag labels, security seals, storage, transport, crushing size, pulverization, and retained material all matter. A reliable program maintains traceable sample identifiers and records custody from the drill site through final reporting.

The CIM Mineral Exploration Best Practice Guidelines recommend external blanks, certified reference materials, duplicates, and regular third-party check sampling. They also recommend disclosure of QA/QC results for early, discovery, and delineation-stage exploration programs.

What current technical reports show

Real programs use different insertion rates based on project stage, deposit style, and risk. A 2026 SEC-filed Cascar technical report describes blanks and reference materials at approximately one per 20 samples, reverse-circulation duplicates at one per 25, and interlaboratory checks at one per 10. A 2025 CK Gold Project technical report also describes inserted commercial blanks and reference materials. These are external examples, not universal minimums and not GBDS projects.

The most useful disclosure goes beyond listing control samples. It reports failure limits, charts results over time, explains corrective action, identifies excluded batches, and states whether the qualified person considers the database suitable for its intended use.

A hypothetical insertion example

Hypothetical example: an exploration program submits 1,000 primary samples and adds 50 blanks, 50 standards, and 50 duplicates. The laboratory therefore receives 1,150 samples, of which 150—or about 13%—are controls. If three blanks exceed the project’s failure threshold, the key questions are where they appeared in the sequence, what samples preceded them, whether affected batches were reanalyzed, and whether the root cause was documented. The percentage alone does not determine data quality.

Investor questions and warning signs

Ask which laboratory and analytical method were used; whether the laboratory is independent and appropriately accredited; who selected and inserted controls; how high-grade or over-limit results were handled; and whether historical data were validated. Warning signs include missing chain-of-custody records, unexplained control failures, changing procedures without reconciliation, selective disclosure of successes, or resource estimates that rely heavily on unverified legacy assays.

The investor takeaway

QA/QC does not guarantee that a deposit will become an economic mine. It provides evidence about whether reported grades are accurate and precise enough for the decisions being made. Investors should evaluate the full control system, the failure response, and the qualified person’s conclusions—not merely the presence of blanks, standards, and duplicates.

This article is for educational purposes only and is not investment, legal, geological, or technical advice. Mining investments involve exploration, estimation, commodity-price, financing, environmental, and jurisdictional risks. Conduct independent due diligence and consult qualified professionals.