Explained by Douglas B. Stoeser
On the choice of deposit models
Tertiary felsic to intermediate intrusive rocks emplaced into predominantly Paleozoic carbonate rocks have produced some zinc-lead skarn deposits in western Utah.
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. Because of the extensive occurrence of carbonate sedimentary rocks in western Utah, and the genetic association with porphyry copper-type deposits, we used the same geographic areas as for porphyry copper deposits. The tract consists of three east-trending belts in western Utah. The southernmost of the three is less deeply eroded than the other two, and any undiscovered skarn deposits would most likely be concealed by the volcanic and alluvial cover. Aeromagnetic surveys were employed to define areas of high magnetics that might indicate a buried intrusive body adjacent to which might be concealed skarn deposits.
Important examples of this type of deposit
Although a relatively rare deposit worldwide, western Utah has two deposits of this type, Ophir and Crypto (Fish Springs District). Of interest is that Crypto was a blind orebody. There are no known prospects. Other minor prospects and deposits are listed in Reid, 1991.
On the numerical estimates made
In making our estimates, the team considered the broad permissive terrane, coupled with the presence of two examples of this relatively rare deposit type. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 2, 3, 4, and 7 districts consistent with the grade and tonnage model for skarn Zn-Pb deposits (Mosier, 1986).
Mosier, D.L., 1986, Grade and tonnage model of Zn-Pb skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 90-93.
Reid, J.E., 1991, Skarn occurrences in Utah and the potential for associated gold mineralization: Utah Geological Survey Contract Report 91-13, 49 p.