National mineral assessment tract SB18 (Polymetallic replacement + skarn Zn-Pb)

Tract SB18
Geographic region Southern Basin and Range
Tract area 11,500sq km
Deposit type Polymetallic replacement + skarn Zn-Pb
Deposit age Mesozoic - Tertiary

Deposit model

Model code 19a
Model type descriptive
Title Descriptive model of polymetallic replacement deposits
Authors Hal T. Morris
URL https://pubs.usgs.gov/bul/b1693/html/bull7q0k.htm
Source https://pubs.er.usgs.gov/publication/b1693
Model code 18c
Model type descriptive
Title Descriptive model of Zn-Pb skarn deposits
Authors Dennis P. Cox
URL https://pubs.usgs.gov/bul/b1693/html/bull4u7i.htm
Source https://pubs.er.usgs.gov/publication/b1693

Estimates

Confidence Number of
deposits
90% 0
50% 1
10% 2
5% 5
1% 7

Estimators: DCox, Albino, Church, Ashley, Diggles, Kleinkopf

Rationale

Explained by Dennis P. Cox
On the choice of deposit models
Plutons mainly of Cretaceous age intrude Paleozoic carbonate sedimentary rocks in the Ivanpah district and elsewhere in this tract. Intrusive contacts of such altered plutons with carbonate rocks are permissive environments for zinc-lead skarn and polymetallic replacement deposits. Because zinc-lead skarn deposits are possible in the same environment as polymetallic replacement deposits, a model that combines the zinc-lead skarn (Mosier, 1986) and polymetallic replacement (Mosier and others, 1986) was used to represent the undiscovered districts (Mark 3 no. 92).
On the delineation of permissive tracts
Skarn Zn-Pb and polymetallic replacement deposits can be present where plutons intrude carbonate rocks. The proximity of Mesozoic plutons and their inferred subsurface extents to areas underlain by Proterozoic and younger carbonate rocks defines the permissive tract. Small areas covered by basin fill more than 1 km deep are excluded.
Important examples of this type of deposit
The Shoshone district is the only significant example of this deposit type in the tract. Although galena-rich veins are numerous in the Ivanpah district, skarn and replacement ore bodies are unknown (Hewett, 1956, p.143).
On the numerical estimates made
Although few deposits of this type have been discovered in the past, large parts of the tract are covered by a thin veneer of sediment. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 1, 2, 5, and 7 or more districts consistent with the combined grade and tonnage model of zinc-lead skarn and polymetallic replacement districts of Singer (Mark3 index 92). This estimate was guided by estimates for the West Mojave Management Area (U.S. Geological Survey, 1992) and East Mojave National Scenic Area (Hodges and Ludington, 1991).
References
Cox, D.P., 1986, Descriptive 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.
Hewett, D.F., 1956, Geology and ore deposits of the Ivanpah quadrangle, Nevada: U.S. Geological Survey Professional Paper 275, 172 p.
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.
Morris, H.T., 1986, Descriptive model of polymetallic replacement deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 99-100.
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.
Mosier, D.L., Morris, H.T., and Singer, D.A., 1986, Grade and tonnage model of polymetallic replacement deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 101-104.
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.

Geographic coverage

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