Sierra Madre / Encampment District
The Encampment mining district in the Sierra Madre mainly produced copper after its discovery in 1874. However, gold and silver were significant byproducts of copper mining (Hausel, 1986, 1989, 1997). The Encampment (also known as the Grand Encampment) district includes the entire Sierra Madre in south-central Wyoming and extends into Colorado. The district is bisected by the east-trending Mullen Creek-Nash Fork shear zone, which is more than one-half mile wide in places. This shear zone forms part of the Cheyenne belt suture that separates the Archean Wyoming Province to the north from cratonized Proterozoic basement of the Colorado Province to the south.
Thick successions of Late Proterozoic miogeoclinal metasediments that overlie the Archean basement characterize the northern part of the district, where mineralization is typified by copper-bearing quartzites, pegmatites, quartz veins, and unaniferous metaconglomerate. Middle Proterozoic calc-alkaline metavolcanics intruded by granitic plutons characterize the southern part of the district, where the eugeoclinal rocks host stratiform volcanogenic sulfides and related mineralization. Fracture-controlled, copper-dominated base metal deposits typify mineralization within the shear zone (Hausel, 1986, 1997).
The Ferris-Haggarty mine in the central Sierra Madre was one of the world’s more important copper deposits during the early 1900s. This significant deposit with accessory gold and some silver was developed in a sheared metaconglomerate. The mine produced an estimated 21 million pounds of copper with some byproduct gold and silver. A 1988 estimate of unmined ore included 928,500 tons of 6.5% copper containing 116,800 ounces of gold (Hausel, 1997). Current high metals prices have sparked re-evaluation and exploration of the Ferris-Haggarty and adjacent areas.
Although gold was always secondary to copper in the Encampment district, amateur prospectors still search the Sierra Madre for gold.
Recommended WSGS publications and maps related to gold in the Encampment district include:
WSGS Report of Investigations 37, Mineral deposits of the Encampment mining district, Sierra Madre, Wyoming-Colorado, by W. Dan Hausel (1986), 31 p.
WSGS Open File Report 04-10, Preliminary geologic map of the Saratoga 30′ x 60′ Quadrangle (Link to Geologic Mapping page), by Wayne M. Sutherland, and W. Dan Hausel, (2004), scale 1:100,000, 35 p.