A mineral resource is not an objective fact about the ground; it is everything above a chosen cut-off grade — the minimum grade a company assumes is worth including. Set a low cut-off and you sweep in more tonnes at a lower average grade; set a high one and you report fewer, higher-grade tonnes. Both can be defensible, and both can be gamed.
The trick to watch is a cut-off that does not match the mining method or the metal price. A low cut-off justified by an optimistic long-term price can inflate a resource that would shrink dramatically at a conservative price. An open-pit cut-off applied to material that would have to be mined underground does the same. The headline tonnage means little without the assumption behind it.
When you read a resource, find the cut-off and the price deck before the tonnes. Then ask what happens to both if the cut-off rises by a quarter of a gram. A resource that collapses under a small change was flattered; one that holds is real.