National mineral assessment tract NR50 (Homestake stratiform Au)

Tract NR50
Geographic region Northern Rocky Mountains
Tract area 152sq km
Deposit type Homestake stratiform Au
Deposit age Archean

Deposit model

Model code ofr94250
Model type descriptive
Title Descriptive and grade-tonnage models of Archean low-sulfide Au-quartz veins and a revised grade-tonnage model of Homestake Au
Authors Klein, T.L., and Day, W.C.
URL https://pubs.usgs.gov/of/1994/ofr-94-0250/
Source https://pubs.er.usgs.gov/publication/ofr94250

Estimates

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

P(none): 0.98

Estimators: Day, Ludington, Hausel

Rationale

Explained by Warren Day
On the choice of deposit models
These deposits are stratiform and are found within predominantly carbonate- and silicate-facies iron formation that is the product of submarine hot-spring activity related to volcanism. Metamorphism and deformation may have caused minor to significant remobilization of metals, sulfides, and gangue. Precambrian rocks of this composition are present locally in several mountain ranges in Wyoming.
On the delineation of permissive tracts
Carbonate- and silicate-facies iron formations are exposed in two small areas in southern Wyoming. These areas are the Hartville uplift, north of Ft. Laramie, and in the Medicine Bow Mountains, west of Laramie. The delineated tracts are larger than the area of the iron formations, which are only tens of meters thick.
Important examples of this type of deposit
No deposits of this type are known in the permissive tracts.
On the numerical estimates made
The primary (and perhaps only) rationale for considering this model type for this area is the presence of favorable lithologies. The areas are small and no deposits or prospects are known. For the 90th, 50th, 10th, 5th, and 1st percentiles, the team estimated 0, 0, 0, 0, and 1 or more deposits consistent with the grade and tonnage model for Homestake stratiform gold deposits of Klein and Day (1994).
References
Klein, T.L., and Day, W.C., 1994, Descriptive and grade-tonnage models of Archean low-sulfide Au-quartz and a revised grade-tonnage model of Homestake Au: U.S. Geological Survey Open-File Report 94-250.

Geographic coverage

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