What is a mineral resource estimate, and what do Inferred, Indicated, and Measured mean?

A mineral resource estimate is a company's quantified statement of the tonnes and grade of mineralisation in a deposit, and therefore the contained metal. Under CIM/NI 43-101 (and the equivalent JORC categories), resources are classified by geological confidence:

• Inferred: lowest confidence; based on limited, widely-spaced drilling. Cannot carry economics beyond a PEA.
• Indicated: enough drilling to support mine planning and a feasibility study.
• Measured: highest confidence, closely-spaced data.

Resources are not reserves. A reserve (Probable or Proven) is the economically mineable part of a Measured/Indicated resource, demonstrated by at least a Pre-Feasibility Study. Inferred resources can never convert directly to reserves.

For investors, the split matters: a deposit that is 90% Inferred is far less de-risked than one that is mostly Indicated and Measured. Watch grade, contained metal, the cut-off grade used, and whether subsequent drilling is converting Inferred ounces to higher categories.