Explained by Dennis P. Cox
On the choice of deposit models
Although no distal disseminated Ag-Au deposits are known, intrusion of plutons into the widespread carbonate rocks in this area represent permissive conditions for this deposit type.
On the delineation of permissive tracts
Distal disseminated Ag-Au deposits can be present where plutons intrude sedimentary 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 except where the plutons intrude Precambrian igneous and metamorphic rocks.
Important examples of this type of deposit
There are no known deposits or prospects in the tract.
On the numerical estimates made
An undiscovered distal disseminated Ag-Au deposits might exist under cover of Cenozoic rocks and sedimentary deposits, but the likelihood is small because of the limited size of the permissive area. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 1, 1, and 2 or more deposits consistent with the grade and tonnage model of Cox and Singer (1992).
Cox, D.P., and Singer, D.A., 1992, Descriptive and grade and tonnage model of distal-disseminated Ag-Au, in Bliss, J.D., ed., Developments in deposit modeling: U.S. Geological Survey Bulletin 2004, p. 20-22.