Explained by Dennis P. Cox

On the choice of deposit models

Plutons, mainly of Mesozoic age, intrude Precambrian metamorphic and Paleozoic sedimentary rocks in many localities in southeastern California. Porphyry-style alteration and mineralization occurs at the Crescent Peak prospect 7 km to the east of the tract in Nevada and in the northern Ivanpah Mountains (T.G. Theodore, written commun., 1994). A porphyry copper prospect, Red Hill, is known in the Ord Mountains. It contains 3.6 million metric tons of rock that average 0.305 percent copper and 0.155 percent molybdenum in two shear zones cutting granitic rock (U.S. Geological Survey, 1992). Large alteration zones in the Mojave mining district may indicate a buried porphyry copper system.

On the delineation of permissive tracts

The permissive tract is a nearly continuous area marked by small plutons that intrude Precambrian metamorphic and Paleozoic sedimentary rocks. Small areas covered by basin fill more than 1 km in depth are excluded.

On the numerical estimates made

For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 0, 2, and 3 or more porphyry copper deposits consistent with the grade and tonnage model of Singer and others (1986) (Mark3 index 4). This estimate was guided by the combination of estimates for the West Mojave Management Area (U.S. Geological Survey, 1992) and East Mojave National Scenic Area (Hodges and Ludington, 1991).

References

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.

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.

U.S. Geological Survey, 1992, Evaluation of selected metallic and nonmetallic mineral resources, West Mojave Management Area, southern California: U.S. Geological Survey Open-File Report 92-595, 89 p.