APPPLICATIONS OF GIS FOR A GLOBAL PORPHYRY COPPER ASSESSMENT

Mineral resource assessments provide information about where there are known deposits, and where the geology is permissive for the occurrence of undiscovered deposits. The U.S. Geological Survey (USGS) conducted a mineral assessment of world porphyry copper resources with the objective to identify potential for undiscovered porphyry copper resources within the upper kilometer of the earth’s surface. The assessment was done using the USGS form of mineral resource assessment based on mineral deposit models. In this form of assessment, mineral deposit models define the characteristics of a deposit type that are used to identify permissive areas (tracts). Data required for the global assessment include 1) geologic maps at a scale of 1:1,000,000 or larger; 2) mineral deposit and prospect maps and databases which show the distribution of mineral occurrences; 3) grade and tonnage models suitable for estimating the grades and tonnages of undiscovered deposits; 4) and if available, information that would allow interpretation of concealed tracts up to 1 kilometer (km) below the surface.

Geographic Information Systems (GIS) allows users to visualize, analyze, and interpret all forms of data. GIS was utilized to compile and integrate the data for this assessment. Geologic units were extracted from digital geologic maps and classified as permissive or non-permissive for association with porphyry copper mineralization. Permissive rocks were further classified by age and plotted with deposits and prospect databases to form the preliminary permissive tract. Preliminary tracts were modified by fault boundaries and areas where cover was known to be > 1 km thick were excluded to create final tracts. Once tract areas were derived and known resources were identified, probabilistic estimates of numbers of undiscovered porphyry copper deposits in the tracts are combined with appropriate grade and tonnage models to produce a probabilistic estimate of undiscovered resources.