of tonnages and grades to estimate possible tonnages and grades of undiscovered deposits. The second part develops mineral resource maps that answer the question, does an area's geology permit the existence of one or more types of mineral deposits? The product of this part of the assessment is identification of so-called permissive tracts of land and is based on mapped geology in the region and descriptive models. For those areas that are permissive for a deposit type, the third part of the assessment develops estimates of the possible number of undiscovered deposits of each type based on deposit density models or expert judgment. These estimated undiscovered deposits are consistent with the grade and tonnage models of the first part and with documented deposit densities. This so-called three-part form of quantitative mineral resource assessments has been widely used. Among the places where they have been applied are the United States, Venezuela, parts of Canada, South America, Australia, Finland, and the Urals as part of a global assessment [10]. See also Uncertainty Mineral resource classification Ore References Mineral exploration