Ore Value

Grade and tonnage are the two fundamental factors that determine the economic value of an ore deposit. Grade tells you how much metal is present, while tonnage tells you how much rock is available. Together, they define whether a deposit is profitable to mine and how it should be developed.

What Is Ore Value?

Ore value is the economic worth of a mineral deposit, based on:

• Grade — metal concentration
• Tonnage — total volume of ore
• Metal prices
• Mining and processing costs
• Recovery rates

A high‑grade deposit with low tonnage may be valuable, just as a low‑grade deposit with massive tonnage can also be profitable.

Why Grade and Tonnage Matter

1. Determines Economic Viability

A deposit must contain enough metal at a high enough grade to justify mining.

2. Guides Mine Design

Grade and tonnage influence:

• Open‑pit vs. underground mining
• Processing plant size
• Equipment selection
• Production rates

3. Supports Resource and Reserve Estimates

Geologists use grade and tonnage to classify deposits as:

• Inferred
• Indicated
• Measured
• Probable reserves
• Proven reserves

4. Influences Investment Decisions

Investors evaluate grade‑tonnage relationships to assess project potential.

Understanding Grade

What Is Grade?

Grade is the concentration of valuable metal in the ore.

Common units:

• g/t (grams per tonne) — gold, silver
• % (percent) — copper, lead, zinc, nickel
• ppm/ppb — trace elements

Examples of Typical Grades

• Gold: 1–5 g/t (open pit), 5–15 g/t (underground)
• Copper: 0.3–1.0% (porphyry deposits)
• Iron: 30–65% Fe
• Nickel: 0.5–2%

Higher grade generally means higher value — but not always.

Understanding Tonnage

What Is Tonnage?

Tonnage is the total amount of ore in a deposit, measured in tonnes.

How It’s Calculated

$$\text{Tonnage}=\text{Volume}\times \text{Density}$$

Large tonnage can compensate for low grade if mining costs are low.

The Grade–Tonnage Relationship

Grade and tonnage must be evaluated together.

High Grade + Low Tonnage

• Often mined underground
• High value per tonne
• Smaller operations

Low Grade + High Tonnage

• Typically open‑pit mines
• Large‑scale operations
• Lower value per tonne but massive output

High Grade + High Tonnage

• Extremely rare
• World‑class deposits

Low Grade + Low Tonnage

• Usually uneconomic

Cutoff Grade

What Is Cutoff Grade?

The minimum grade required for ore to be economically mineable.

Cutoff grade depends on:

• Metal prices
• Mining costs
• Processing costs
• Recovery rates

If prices rise, cutoff grade drops — and more ore becomes economic.

Metal Recovery and Ore Value

Not all metal in the ore is recovered.

Recovery depends on:

• Mineralogy
• Processing method
• Grain size
• Liberation characteristics

Effective recovery increases ore value.

Example: Calculating Ore Value

Step 1: Determine Metal Content

If a deposit has:

• 1.2% Cu
• 50 million tonnes

Metal content:

$$50,000,000\times 0.012=600,000\text{ tonnes of copper}$$

Step 2: Apply Recovery

If recovery is 90%:

$$600,000\times 0.90=540,000\text{ tonnes recovered}$$

Step 3: Apply Metal Price

Ore value depends on current copper prices.

This simplified example shows how grade and tonnage drive economics.

Conclusion

Ore value is determined by the balance between grade and tonnage. High grade increases value per tonne, while large tonnage increases total metal content. Together, they define whether a deposit is economically viable and how it should be mined. Understanding grade‑tonnage relationships is essential for exploration, resource estimation, and mine planning.