Residual grade is the average grade of the material remaining in a drill interval once the high-grade section has been stripped out.
Mining companies frequently report a wide intersection alongside a narrower 'including' interval. The headline width looks impressive, but the residual grade tells you whether the surrounding rock has any economic value on its own.
This matters because of a practice known as grade smearing. A narrow, high-grade hit can artificially inflate the apparent grade of a much wider, lower-grade interval. Grade smearing makes intersections look better than they are. The residual grade calculation cuts through it.
| Interval | Metres(m) | Grade 1 (% or g/t) | Grade 2 (% or g/t) | Grade 3 (% or g/t) |
|---|---|---|---|---|
| Length | ||||
| Including | ||||
| Including | ||||
| Including | ||||
| Including | ||||
| Including | ||||
| Residual Grade | - | - | - | - |
Enter the Data
Input the overall interval (metres and grade) and any high-grade 'including' sections.
Calculate
The calculator returns the average grade of the interval with the high-grade section excluded.
Interpret
Compare the residual grade against the cut-off grade for the commodity. If residual grade is below cut-off, the wider intersection is unlikely to be economic on its own.
Every tonne of rock moved in mining has a cost. Material that grades above the cut-off grade is ore — it is worth processing. Material below cut-off is waste — it costs money to move and adds no revenue.
If the residual grade is below cut-off, the broader intersection depends entirely on the high-grade core for its economics. That is a materially different situation to a uniformly high-grade intersection. Use the residual grade alongside our commodities grade guide to benchmark what constitutes ore across different commodities and geological settings.
Working with a multi-metal intersection? Use the Metal Equivalent Calculator to express the full value as a single equivalent grade before running the residual grade check.
Residual grade is the average grade of a drill interval after the high-grade 'including' section has been removed. It shows whether the wider intersection has economic merit beyond the headline hit.
Grade smearing (also called high-grading) occurs when a narrow high-grade interval inflates the apparent grade of a much wider, lower-grade intersection. The residual grade calculation exposes this. It is not necessarily deliberate — but investors should always check.
Enter the overall intersection in metres and grade, then add any high-grade 'including' intervals. The calculator returns the residual grade of the material that remains.
It means the material outside the high-grade interval is unlikely to be profitable at current commodity prices. The intersection may still have value if the high-grade core is wide enough to stand alone.
Yes. The Residual Grade Calculator is free to use on Discovery Alert. No account required.
