Explained by Steve Ludington, Dennis P. Cox, and Michael F. Diggles
On the choice of deposit models
Skarn deposits form where intermediate to felsic intrusive rocks, which are the principal sources of the metals, are emplaced into carbonate rocks. In the Mojave Desert, the deposits are mainly Mesozoic in age.
On the delineation of permissive tracts
The plutons of the southern Basin and Range include Jurassic or Cretaceous felsic rocks that, in places, intrude carbonate rocks, mostly of Paleozoic age. The tract is defined to be those parts of the area underlain by carbonate rocks of any age that are in close proximity to Mesozoic plutons. Some skarns in the New York Mountains may be Proterozoic in age. The Clark Mountains have prominent skarns along their west flank, including Copper World.
Important examples of this type of deposit
There are 26 known skarn Cu deposits, prospects, and occurrences in the eastern Mojave Desert, most of which are quite small, and none were included as significant deposits in this study. An example is the Copper World deposit from which more than 2,400 metric tons of copper was produced, along with additional Pb, Ag, Au, and Zn.
On the numerical estimates made
Although no significant deposits of this type are known for the Mojave, the region is permissive in terms of the overall geological environment. Only a few of the known deposits have sizes similar to those that belong to the grade and tonnage models of Jones and Menzie (1986). For the 90th, 50th, and 10th, percentiles, the team estimated 1, 2, and 4 or more skarn Cu deposits consistent with the grade and tonnage model of Jones and Menzie (1986).
Cox, D.P., and Theodore, T.G., 1986, Descriptive model of Cu skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 86.
Hodges, C.A., and Ludington, Steve, 1991, Quantitative assessment of undiscovered metallic mineral resources in the East Mojave National Scenic Area, southern California: U.S. Geological Survey Open-File Report 91-0551, 18 p.
Jones, G.M., and Menzie, W.D., 1986, Grade and tonnage model of Cu skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 86-89.
U.S. Geological Survey, 1991, Evaluation of metallic mineral resources and their geologic controls in the East Mojave National Scenic Area, San Bernardino County, California: U.S. Geological Survey Open-File Report 91-0427, 278 p., 6 plates.