The middle confidence category — enough drilling to support mine planning, short of the certainty of measured.
A mineral resource for which quantity, grade, densities, shape, and physical characteristics are estimated with sufficient confidence to allow the appropriate application of technical and economic parameters. Indicated resources have a higher level of confidence than inferred resources but lower than measured resources.
Indicated is the threshold that matters commercially, because indicated resources can be converted to probable reserves and can carry an economic study. A company moving material from inferred to indicated is doing the work that turns a prospect into a project.
Drill spacing is the practical driver. Watch for infill drilling programmes described as resource conversion — that is a company spending money specifically to move a category boundary.
Assuming conversion is a formality. Some deposits never tighten up, because the mineralisation is genuinely erratic rather than under-drilled.
108 terms have their own page: the definition, why it matters to an investor, where it shows up in practice, and the mistake people make with it.