National mineral assessment tract SB22 (Polymetallic replacement)

Tract SB22
Geographic region Southern Basin and Range
Tract area 20,900sq km
Deposit type Polymetallic replacement
Deposit age Middle 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

Estimates

Confidence Number of
deposits
90% 3
50% 7
10% 12
5% 14
1% 18

Estimators: Bartsch-Winkler, McLemore, Ludington, Wallace, Nash, Berger, Spanski

Rationale

Explained by Alan R. Wallace, Steve Ludington, and Virginia McLemore
On the choice of deposit models
Southwestern New Mexico contains several known middle Tertiary polymetallic replacement prospects, characterized by the replacement of carbonate rocks by base-metal sulfides, precious metals, and related gangue minerals.
On the delineation of permissive tracts
Polymetallic replacement deposits form where intermediate to felsic intrusive rocks, which are the principal sources of the metals, are emplaced into carbonate rocks. The general rule for delineation of the permissive tract was to exclude all areas that show no evidence of middle Tertiary plutonism. In addition, areas where erosion has left Precambrian igneous and metamorphic rocks exposed at the surface were excluded, as were areas inferred to be covered by surficial deposits thicker than 1 km.
Important examples of this type of deposit
There are no districts with known production large enough to qualify as significant for the purposes of this study, although several are close. We identified 11 areas—Granite Gap, McGhee Peak, Victorio, Cookes Peak, Lake Valley west, Apache, Carpenter, North Cookes Range, Rincon, Tres Hermanos, and Tierra Blanca—where rock mineralized in this style is known, but where recorded production is unknown, incomplete, or small.
On the numerical estimates made
This area contains a remarkable concentration of poorly-known prospects. We believe that the known prospects are not fully explored and that further exploration could result in several of them advancing to the status of districts consistent with the grade and tonnage model for polymetallic replacement deposits of Mosier and others (1986). The team evaluated each of the known prospects and extrapolated the judgments to the entire tract, including a large covered area that is at least as large as the exposed area. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 3, 7, 12, 14, and 18 or more deposits consistent with the grade and tonnage model for polymetallic replacement deposits of Mosier, Morris, and Singer (1986).
References
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.

Geographic coverage

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