Ore Grade and Contained Metal Calculator

Ore Grade

Ore grade is the concentration of a valuable metal or mineral in ore.
For precious metals (gold, silver): expressed in grams per tonne (g/t) or oz/ton.
For base metals (copper, zinc, lead): expressed in percent (%) by weight.
For rare earth/specialty metals: expressed in ppm (parts per million).
1 ppm = 1 g/t = 0.0001% by weight.

Contained Metal Calculation

Contained metal = Ore tonnage × Grade
For gold: Gold (grams) = Ore (tonnes) × Grade (g/t)
Gold (troy oz) = Gold (grams) / 31.1035

Recovery and Payable Metal

Metallurgical recovery: not all contained metal is recovered during processing.
Gold heap leach: 60–80% recovery | CIL/CIP milling: 88–95% recovery
Copper flotation: 85–92% | Zinc flotation: 85–93%
Payable metal = Contained × Recovery rate

Cut-Off Grade

The cut-off grade (COG) is the minimum grade that justifies mining.
Below COG = waste; above COG = ore.
COG depends on: metal price, mining costs, processing costs, royalties.
Gold example: underground mines usually cut off somewhere around 2–5 g/t and open pits at 0.3–0.8 g/t. Both fall when the gold price rises, which is why a deposit’s reported resource can grow without a single new drill hole.

Unit Conversions

1 troy oz = 31.1035 g | 1 short ton = 907.18 kg | 1 long ton = 1016 kg
1 metric tonne = 1000 kg = 2204.6 lb
g/t × 0.02917 = troy oz / short ton
1% = 10 kg/t = 10,000 ppm = 10,000 g/t. Base metals are quoted in %, not g/t.