Explained by Dennis P. Cox
On the choice of deposit models
Although no copper skarn deposits are known in southern Nevada, intrusion of plutons into the widespread carbonate rocks in this area represent permissive conditions for this deposit type.
On the delineation of permissive tracts
Copper skarn deposits can occur where plutons intrude carbonate rocks. Paleozoic sedimentary rocks are hidden by a thin veneer of sediment in many parts of the area. The permissive tract was defined as an area 10 km in radius around all plutons where they intrude Proterozoic and younger carbonate rocks. There are no known deposits or prospects in the tract.
On the numerical estimates made
Undiscovered copper skarn deposits might exist under cover of Cenozoic rocks and sedimentary deposits, but the likelihood is small because of the limited size of the permissive tract. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 0, 1, and 1 or more deposits consistent with the grade and tonnage model of Jones and Menzie (1986).
Jones, G.W., and Menzie, W.D., 1986, Grade-tonnage model of Cu skarns, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 86-89.