Grade, Tonnage & Scale
How Much Metal, in How Much Rock?
Why a little metal over a lot of rock can still add up to a real mine.
- Grade measures concentration; tonnage measures the amount of material. You need both.
- A large, lower-grade deposit can contain more metal than a small, higher-grade one.
- Contained metal is not the same as recoverable metal, revenue or profit.
- Mining costs, processing recovery and the deposit’s shape decide whether scale is useful.
- Compare deposits using consistent units, cut-off assumptions and resource categories.
Concentration and Quantity
Grade tells you how much metal is present in a given amount of rock. Tonnage tells you how much rock has been estimated. Together, they help describe a deposit’s metal content.
Picture two bowls of soup. One is small and packed with vegetables; the other is much larger but less concentrated. Concentration alone cannot tell you which bowl contains more vegetables. Mining has the same distinction between grade and scale.
A Simple Gold Example
These calculations describe metal content only. They say nothing about whether either deposit can become a profitable mine.
The Metal You Can Actually Recover
Some material may never enter the mine plan. Some metal is lost during mining and processing. Metallurgical recovery is the share recovered by the proposed processing method; it depends on the mineralogy and test work.
In a deliberately simplified example, processing material containing 100 ounces at 90% recovery would recover 90 ounces. That still leaves operating costs, capital spending and other charges before any profit reaches shareholders.
Multiplying every contained ounce by today’s metal price does not produce a company valuation.
It ignores the work, time, money and losses involved in extraction.
Why Low Grade Can Sometimes Work
A broad deposit near the surface may suit large equipment and high processing volumes. A narrow deposit deep underground may need more selective and expensive mining. This is why the same grade can be attractive in one setting and insufficient in another.
Scale can spread certain fixed costs across more tonnes, but it can also require a larger plant, more power, more water and a bigger construction budget. Bigger is helpful only when the plan can turn that size into worthwhile margins.
Questions to Ask Before Comparing
A lower cut-off can bring more material into an estimate while reducing average grade. An increase in reported tonnes therefore needs explanation. Look for an improved economic picture, not just a larger headline number.
Next in the Mining 101 Series
Mineral Resources vs. Reserves
The difference between "it's there" and "we can actually mine it."
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