Explained by Dennis P. Cox and Steve Ludington
On the choice of deposit models
Distal disseminated Ag-Au deposits (Cox and Singer, 1992) are commonly associated with polymetallic replacement deposits which are common in western Utah. Areas where Tertiary felsic to intermediate intrusive rocks were emplaced into predominantly Paleozoic carbonate rocks are permissive for this deposit type.
On the delineation of permissive tracts
The permissive tract for this deposit type is defined primarily by the distribution of intrusive rocks and suitable reactive host rocks, especially carbonate-bearing sedimentary rocks. It is made up of three east-trending belts in western Utah. The southernmost of the three is less deeply eroded than the other two, and any undiscovered replacement deposits in the south would most likely be concealed by the volcanic cover and alluvial cover. Aeromagnetic maps were employed to define areas of buried intrusive bodies.
Important examples of this type of deposit
The only deposit of this type is Tecoma, in northwest Utah near the Nevada border.
On the numerical estimates made
Because of the rarity of distal disseminated deposits in this tract the team estimated that the probability of an undiscovered deposit was less than 0.01
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.