Explained by Dennis P. Cox
On the choice of deposit models
Tertiary andesite that is intruded by high-level plutons and accompanied by areas of widespread alunite alteration is a favorable scenario for porphyry copper deposits (Wallace, 1979; Hudson, 1983). Alunite alteration occurs in the Alunite district (Longwell and others, 1965) near Boulder City and may represent the uppermost extent of a porphyry system. Polymetallic veins of the Searchlight district are weakly suggestive of the presence of a porphyry system.
On the delineation of permissive tracts
Tertiary volcanic rocks and plutons and their inferred subsurface extent define the permissive tract. Small areas covered by basin fill more than 1 km in depth are excluded.
On the numerical estimates made
Because of the rarity of porphyry mineralization of Tertiary age in southern Nevada and bordering States, our estimate is low. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 0, 1, and 2 or more deposits consistent with the grade and tonnage model of Singer and others (1986).
Hudson, D.M., 1983, Alteration and geochemical characteristics of the upper parts of selected porphyry systems, Western Nevada: Reno, University of Nevada, unpub. Ph.D. dissertation, 229 p.
Wallace, A.B., 1979, Possible signatures of buried porphyry copper deposits in middle to late Tertiary volcanic rocks of Western Nevada, in Ridge, J.D., ed., Proceedings of the Fifth Quadrennial IAGOD Symposium: Reno, University of Nevada, Mackay School of Mines, v. 2, p. 69-76.
Singer, D.A., Mosier, D.L., and Cox, D.P., 1986, Grade-tonnage model of porphyry copper, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 77-81.