National mineral assessment tract SB15 (Porphyry Cu)

Tract SB15
Geographic region Southern Basin and Range
Tract area 23,100sq km
Deposit type Porphyry Cu
Deposit age Laramide

Deposit model

Model code 17
Model type descriptive
Title Descriptive model of porphyry Cu
Authors Dennis P. Cox
URL https://pubs.usgs.gov/bul/b1693/html/bull9ik5.htm
Source https://pubs.er.usgs.gov/publication/b1693

Estimates

Confidence Number of
deposits
90% 2
50% 3
10% 4
5% 6
1% 9

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

Rationale

Explained by Steve Ludington and Virginia McLemore
On the choice of deposit models
Southwestern New Mexico contains numerous Laramide calc-alkaline plutons, part of a cluster of intrusions of this age that lies mostly in neighboring Arizona. In addition, there are known deposits that are type examples of porphyry copper deposits in North America. Some of these intrusive rocks also exhibit a halo of polymetallic veins that might reflect a concealed porphyry copper deposit associated with the intrusive bodies.
On the delineation of permissive tracts
The permissive tract in southwestern New Mexico is contiguous with a large permissive area in Arizona that contains numerous Laramide porphyry copper deposits. Geologic constraints on the occurrence of porphyry copper deposits in this area are discussed in detail in the descriptions of the Arizona tracts. In southwestern New Mexico, the amount of covered area is approximately equal to that exposed. The general rule for delineation was to exclude all areas that show no evidence for Laramide plutonism. In addition, areas of plutonism that are overwhelmingly gabbroic or granitic, or strongly alkaline, were excluded. Manifestation of plutonism may include exposed plutonic terranes, known polymetallic vein, skarn, and/(or) replacement deposits, unexposed plutons, inferred to exist by geophysical or other means, and any other inferred magmatic trends.
Important examples of this type of deposit
Southwestern New Mexico contains two producing Laramide porphyry copper deposits, Santa Rita (Chino) and Tyrone, and one explored but inactive deposit, Copper Flat (Hillsboro). In addition, there are at least seven known porphyry copper prospects in the area.
On the numerical estimates made
The team evaluated the seven known prospects individually. Then, considering the extent of exploration and the amount of area covered by thin surficial deposits, we extrapolated those judgments to the entire permissive tract. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 2, 3, 4, 6, and 9 or more deposits consistent with the worldwide porphyry copper grade and tonnage model (Singer and others, 1986).
References
Singer, D.A., Mosier, D.L., and Cox, D.P., 1986, Grade and tonnage model of porphyry Cu, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 77-81.

Geographic coverage

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