Free Online Grade Tonnage Curve Calculator: Cutoff Analysis

Geology
All tools
Report
The grade-tonnage curve in table form: for each cutoff, the tonnes at or above it, their average grade, and the contained metal as grade times tonnes. Raising the cutoff always trades tonnage for grade; where the trade pays best depends on your costs, which is what the cutoff grade tool in this suite computes.

A deposit on one chart

The grade-tonnage curve is how a mineral deposit answers the only question that matters: what do you get if you insist on better rock? Paste your blocks as grade and tonnage pairs, set a list of cutoffs, and the tool above reports, for each cutoff, the tonnes at or above it, their average grade, and the contained metal. The highlight cutoff pulls one scenario into the stat cards, including what fraction of total tonnage survives. Every cutoff choice describes a different mine from the same rock.

Grade-tonnage curve chart with tonnage above cutoff falling and average grade rising as the cutoff grade increases, with a chosen cutoff marked
Raise the cutoff and tonnage falls while average grade climbs; the trade is the mine plan.

This is the centerpiece of the Mining and Resource Suite: composites from the assay tool feed it, and the cutoff grade tool tells you where on the curve your costs put you.

Reading the trade

  • Tonnage always falls and grade always rises with cutoff: the shape between those certainties is the deposit's personality, and skewed gold deposits bend very differently from disseminated copper.
  • Contained metal falls too, more slowly: metal in low-grade blocks is real metal, just metal that may not pay for its own processing.
  • The curve is only as selective as its blocks: curves built from big blocks flatter continuity, which is the support effect every resource geologist respects.
  • Reported resources are one point on this curve at a stated cutoff; the curve is what lets you ask what happens at any other.

What this tool is for

Scoping studies, comparing deposits on equal terms, checking sensitivity of a resource to its stated cutoff, and teaching the tonnage-grade trade that underlies every mine plan.

Related Calculators and Reference

Common Questions

What is a grade tonnage curve?

It is the curve showing, for every cutoff grade, how many tonnes of a deposit lie at or above that cutoff and what their average grade is. Raising the cutoff always trades tonnage for grade, and the curve maps that trade.

Why does average grade rise when tonnage falls?

Because raising the cutoff discards the lowest grade material first, the material that remains averages higher. The curve quantifies exactly how much tonnage each increment of grade costs.

What cutoff grades should I test?

Bracket your breakeven cutoff from costs and price, then step outward in even increments. The cutoff grade calculator in this suite computes the breakeven to center the list on.