National mineral assessment tract CR01 (Skarn Cu)

Tract CR01
Geographic region Central and Southern Rocky Mountains
Tract area 4,450sq km
Deposit type Skarn Cu
Deposit age Laramide

Deposit model

Model code 18b
Model type descriptive
Title Descriptive model of Cu skarn deposits
Authors Dennis P. Cox and Ted G. Theodore
URL https://pubs.usgs.gov/bul/b1693/html/bull7nxq.htm
Source https://pubs.er.usgs.gov/publication/b1693

Estimates

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

P(none): 0.99

Estimators: Ludington, Wallace, Nash, Berger, Spanski

Rationale

Explained by Steve Ludington
On the choice of deposit models
In Colorado, many Laramide felsic to intermediate intrusive rocks are emplaced into carbonate rocks, the chief requirement for copper skarn formation.
On the delineation of permissive tracts
Skarn deposits may form where intermediate to felsic intrusive rocks, which are the principal sources of the metals, are emplaced into carbonate rocks, which, in Colorado, are principally of Paleozoic age. Therefore, the permissive tract for Laramide copper skarn deposits is that broad area where Laramide intrusive rocks are coincident with Paleozoic carbonate units, as defined by the State map (Tweto, 1979). This tract generally consists of the part of the northeast-trending Colorado mineral belt that contains carbonate rocks.
Important examples of this type of deposit
There are no known deposits or prospects.
On the numerical estimates made
Perhaps due to relatively deep erosion and a small area of carbonate rock outcrop, mineralized skarns appear uncommon in Colorado, and there are no known deposits. Nevertheless, there are a few Laramide intrusions near carbonate rock outcrops, and, for the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 0, 0, and 1 or more deposits consistent with the copper skarn model of Jones and Menzie (1986).
References
Tweto, Ogden, 1979, Geologic map of Colorado: U.S. Geological Survey Map, scale 1:500,000.
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.

Geographic coverage

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