Explained by D.P. Cox, Steve Ludington, B.R. Berger, M.G. Sherlock, and D.A. Singer, (USGS); and J.V. Tingley (Nevada Bureau of Mines and Geology)
On the delineation of permissive tracts
The permissive tract is based on the distribution of rocks of the Ordovician Roberts Mountains assemblage, which include seafloor basalts, and represent a deep-water assemblage.
On the numerical estimates made
Because of uncertainties about the classification of Rio Tinto, and the geologic controls of this deposit type, we made a low estimate of the number of undiscovered deposits. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 1, 2, 2, and 3 or more deposits in the delineated area that are comparable in grade and tonnage to the Besshi massive sulfide model of Singer (1986).
Coats, R.R., and Stephens, E.C., 1968, Mountain City Copper Mine, Elko County, Nevada, in Ridge, J.D., ed., Ore deposits of the United States, 1933-1967 (Graton Sales Volume): New York, American Institute of Mining, Metallurgical, and Petroleum Engineers, v. 2, p. 1074-1101.
Fox, J.S., 1984, Besshi-type volcanogenic sulphide deposits—a review: Canadian Mining and Metallurgical Bulletin, v. 77, p. 57-68.
Singer, D.A., 1986, Grade-tonnage model of Besshi massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 136.