Guide · 6 min read
How to read a mining drill result
What '12.5 m @ 4.2 g/t Au' actually tells you — and what it leaves out. A practical decoder for the headline numbers in a junior miner's exploration press release.
The anatomy of an intercept
A drill intercept is reported as 'length @ grade' — for example '12.5 m @ 4.2 g/t Au'. Length is how much of the drill core returned mineralization above the cut-off grade; grade is the commodity concentration in that core. Together they give you a sense of how rich the intercept is and how wide the mineralized body might be.
But neither number is what you should compare across projects. The geologically meaningful figure is grade × length — sometimes called gram-metres for gold or percent-metres for base metals. A 5 m @ 10 g/t intercept (50 gm) is more impressive than a 50 m @ 1 g/t intercept (50 gm) only because high-grade structures suggest different ore-genesis economics, even though the gram-metre product is the same.
True width vs downhole length
A drill hole rarely intersects a mineralized vein at exactly 90°. When it crosses at a shallow angle, the downhole length of the intercept over-states the actual thickness of the vein. The geologically meaningful number is the true width — the perpendicular thickness.
Issuers are required by NI 43-101 (Canada) and JORC (Australia) to state whether reported lengths are true width or downhole. If only downhole is reported, treat the intercept as apparent-width-only and discount your mental width estimate by 30–50% pending follow-up drilling.
Cut-off grade and the headline number
Every intercept is reported at a cut-off grade — the minimum grade at which material is included. Higher cut-off → narrower, richer-looking intercept. Lower cut-off → wider, lower-grade intercept. Some issuers report multiple cut-offs ('including high-grade subsections') to highlight the best parts of the intercept.
When comparing intercepts from different companies, check the cut-off. A 30 m intercept at 1 g/t cut-off is not the same as a 30 m intercept at 0.3 g/t cut-off — the second one would be much shorter at the first cut-off.
Bonanza grades and what they mean
A 'bonanza grade' is an intercept dramatically above the deposit's typical grade — for gold, usually >30 g/t. Bonanza intercepts can move share prices because they suggest high-grade structures that materially raise project economics.
They also need careful follow-up. A single bonanza hole can be a one-off pocket rather than continuous mineralization. Watch for the next round of drilling to test step-out holes around the bonanza — if grades stay high, the structure is real; if they drop off sharply, the bonanza was a fluke.
What a press release leaves out
A drill-result release will almost never include the full assay table, all unmineralized intervals, or the QA/QC data. Those go into the eventual Technical Report. The headline release is curated to put the best results forward — that's a fact, not a criticism, but it means you can't judge a project from one release.
What you can do is track the trend across releases. Is each round of drilling extending the strike length? Increasing the grade? Tightening the resource? Or are step-out holes returning weaker grades, suggesting the deposit has limits? OreStocks Terminal aggregates every drill result per project so this trend is visible at a glance.
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