ESTIMATING THE UNDISCOVERED COPPER RESOURCES OF THE CENTRAL AFRICAN COPPERBELT: RESULTS OF THE USGS GLOBAL MINERAL RESOURCE ASSESSMENT PROJECT (GMRAP)

The majority of copper (Cu) produced from Africa comes from the Neoproterozoic Katanga sedimentary basin of the southern Democratic Republic of Congo, eastern Angola, and northern Zambia; collectively called the Central African Copperbelt (CACB). In collaboration with geologists from academia and industry, the USGS delineated permissive areas for undiscovered sediment-hosted copper deposits at a scale of 1:1,000,000 and to a depth of 2 kilometers below the surface to provide probabilistic estimates of the number of undiscovered deposits within those permissive areas. These estimates together with grade and tonnage models of CACB deposits types are used in computer simulations to provide a probabilistic estimate of the amount of undiscovered Cu. This assessment is part of the larger GMRAP study.

The assessment is based on: 1) new deposit models (descriptive and grade and tonnage) and newly compiled databases and GIS files of point locations of >500 deposits and prospects, projected surface extents of selected ore bodies, and areal extents of open pits (Taylor and others, 2012), 2) existing databases and maps of the location, size, and geologic type of known mineral deposits and occurrences, 3) maps and explanations of regional geology, metallogeny, petroleum geology, tectonics, geochemistry, and geophysics, 4) and mineral exploration history. Eleven tracts permissive for the following subtypes of sediment-hosted copper deposits were delineated: stratabound shale-, sandstone- and carbonate écaille-hosted deposits of the Roan Group; structurally controlled replacement and vein deposits; and areas that may host undiscovered deposits of all subtypes.

Tracts were created based upon their position relative to the External Fold and Thrust belt (EFTB) of the Lufilian arc. These include tracts in the foreland, in allochthonous strata within the structural margins of the EFTB , on the inner side of the EFTB in areas of autochthonous or para-autochthonous strata ( the Iron Belt and the Domes, Synclinorial, and the Katanga High regions), and near the Kafue anticline in Zambia. The probabilistic assessment of these tracts followed by computer simulations of contained metal suggests that more than 180 undiscovered deposits containing more than 300 million tonnes of Cu may be present.