Mineral resources come in three confidence levels. Inferred is the lowest: grade and tonnage estimated from limited drilling, geologically reasonable but not demonstrated. Indicated is drilled densely enough to support mine planning. Measured is the highest confidence, tightly drilled. The ladder is about how well the ground is known, not how much of it there is.
The distinction has teeth at the economic stage. A Preliminary Economic Assessment may include inferred material, which is why PEAs can show dazzling returns. But pre-feasibility and feasibility studies must exclude inferred resources entirely. A project whose economics lean heavily on inferred ounces can look very different once those ounces are barred from the mine plan — that is where optimistic PEAs deflate.
So the practical question on any resource is not just how many ounces or tonnes, but which category they sit in — and how much of the value depends on the least certain of the three.