Medicine Bow Mountains and Sierra Madre
The Medicine Bow Mountains and Sierra Madre are Precambrian-cored Laramide uplifts that straddle the margin of the Wyoming Craton.
The Wyoming craton was established more than approximately 2.7 billion years ago (2.7 Ga, or Giga-annum), but was later affected by a
regional metamorphic event 1.9 – 1.7 Ga. The south boundary of the Wyoming Craton in the Medicine Bow Mountains and Sierra Madre
terminates against the Mullen Creek-Nash Fork shear zone. This shear zone, which forms part of the Cheyenne belt suture, represents a
continental-arc collision zone separating the Wyoming Province to the north from cratonized (1.7 Ga) Proterozoic basement of the Colorado
Province to the south.
Within the Colorado Province south of the Cheyenne belt, metavolcanic and metasedimentary rocks provide excellent hosts for magmatic
massive sulfide mineralization (copper, zinc, lead, silver, gold) and some shear zone copper, gold, and associated gold placers. Layered
mafic-ultramafic intrusives, ultramafic massifs, and fragments with platinum, palladium, gold, silver, copper, titanium, chromium, and
vanadium anomalies occur within the Proterozoic terrain – most notable are the Mullen Creek, Lake Owen, and Puzzler Hill complexes. The
New Rambler mine is located along the northeastern edge of the Mullen Creek mafic-ultramafic complex in the Medicine Bow Mountains and is
Wyoming’s only mine known to have historically produced platinum and palladium. The mineralization, occurring in hydrothermally altered mafic shear-zone
cataclastics, may have been remobilized from the layered complex. Because of their high potential for platinum-palladium mineralization,
Mullen Creek, Lake Owen to the east, and Puzzler Hill in the Sierra Madre continue to be platinum exploration targets.
North of the Cheyenne belt in the Medicine Bows and Sierra Madre, the Wyoming Province includes amphibolite-grade schists and gneisses
overlain by younger Archean and Proterozoic metasedimentary and metaigneous rocks. Metaconglomerates found in several of the Precambrian
units are considered potential sources for uranium, thorium, and REE. Similarities between these rocks and the gold-rich
quartz-pebble metaconglomerates of the Witwatersrand, South Africa, suggest that they also have potential to host significant
During the late 1800s and early 1900s, intense prospecting left numerous remnants of mines and prospects concentrated in the broad region
underlain by sheared rocks of the Cheyenne belt, although scattered mineralization occurs throughout both mountain ranges. There is no
evidence that any of the significant historical mines, with the exception of the Centennial mine, were ever mined out. Mine operations
usually ceased due to factors that included declining metal prices, lack of technological developments, ore complexity below the zone of oxidation, outbreak of war, and other
political or human-related factors. The Centennial mine ceased operations because the mineralized lode was offset by faulting – the
extension of the ore deposit was never found.
Centennial Ridge District
Placer gold, discovered in gravels along the Middle Fork of the Little Laramie River, led to the organization of the Centennial
Ridge mining district in the east-central Medicine Bow Mountains in 1876. Placer activity was followed by several lode discoveries
including the Centennial mine. A new wave of prospecting and development followed the 1901 discovery of platinum associated with copper
ores at the New Rambler mine 5 miles to the southwest. Structural fabric within the district is generally northeast-trending and parallel
to the Cheyenne belt. Lode mineralization includes foliation/schistosity parallel gold-bearing quartz veins in biotite and hornblende
gneisses and schists, and gold-platinum fracture-filling and replacement veins in shear zones and faults cutting the gneisses and schists.
Sulfides and arsenides accompany gold-platinum in the fracture fillings. Sulfide-rich zones, dominated by pyrite and occurring in mafic host
rocks, usually accompany the richest ores in the district. Actual production from the Centennial Ridge district is unknown. However, the
Centennial mine produced an estimated 4,500 ounces of gold.
Douglas Creek District
The Douglas Creek district in the central Medicine Bow Mountains includes all placer deposits along Douglas Creek and its tributaries, from Rob Roy Reservoir southward for 6
miles to below Lake Creek. Gold was discovered in Moore’s Gulch, a tributary of Douglas Creek, by Iram Moore in 1868. Lode gold discoveries in both the New Rambler and
Keystone districts resulted from placer gold being traced upstream to its primary sources. Heavy placer activity along the creek included elaborate hydraulic ditches in use by
1876. Resurgent placer activities during the 1930s, 1940s, and 1950s used gasoline-powered draglines and floating washing plants. Gold recovered from gravels up to 20 feet thick
varied from 890 to 960 fine, with some silver and traces of platinum. Currey (1965) estimated total gold production from the Douglas Creek placers at about 4,000 ounces. The
Douglas Creek district remains a popular area for amateur placer mining.
New Rambler District
The New Rambler district, just west of Douglas Creek, is located near the south edge of the
Cheyenne belt along the Rambler shear zone, an east-trending branch of the Mullen Creek-Nash
Fork shear zone. The Rambler shear zone, numerous local northeast-trending shears, and a few
northwest-trending faults cut foliated granodiorite, the younger Rambler Granite, and the distorted
northeast extremities of the Mullen Creek mafic-ultramafic complex.
Primary copper sulfides and gold occur in quartz veins, as fracture fillings, and in zones of brecciation.
Significant secondary mineralization, found only in the New Rambler mine, often
assayed more than 35 percent copper. The New Rambler mine first opened as a gold mine in 1870.
Copper was discovered in 1900 at a depth of 65 feet, and platinum within the covellite ore was
discovered in 1901. Estimated production from the New Rambler mine totaled 171.3 ounces of gold,
7,346 ounces of silver, 1,753,924 pounds of copper, 910 ounces of platinum, and 16,870 ounces of
palladium. The New Rambler area is considered an attractive target for platinum group metals
The Keystone district, about 3 miles southeast of the New Rambler district, hosts lode gold
mineralization concentrated along northwest-trending shears that cut quartz diorite, quartz-biotite
schist, and foliated granodiorite. These shears, subsidiary to the Mullen Creek-Nash Fork shear
zone, provide loci for quartz veins and veinlets and copper-gold mineralization with associated
epidotization of wallrock. Currey (1965) estimated the total lode gold production from the mines
in the Keystone district at about 8,500 ounces.
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. 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 generally 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 (see Principal Metal Districts Map above) that separates the Archean
Wyoming Province to the north from cratonized Proterozoic basement of the Colorado Province to
Thick successions of Late Proterozoic 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
rocks host stratiform volcanogenic sulfides and related mineralization. Fracture-controlled,
copper-dominated base metal deposits typify mineralization within the shear zone.
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 percent copper containing 116,800 ounces of gold. Current high metals prices
have sparked re-evaluation and exploration of the Ferris-Haggarty and adjacent areas.
Amateur prospectors still search the Sierra Madre for gold although it was always secondary to
copper in the Encampment district.
Selected References Related to Metals in Wyoming
Publications relating to metals in Wyoming can be downloaded or purchased from the WSGS Sales
and Downloads minerals – metals category of the online catalog and from the WSGS Sales
Geologic Mapping page.
Blackstone, D.L. Jr., 1988, Traveler’s guide to the geology of Wyoming: Wyoming State Geological
Survey Bulletin 67, 130 p.
Blackstone, D.L. Jr., and Hausel, W.D., 1982, Field guide to the Seminoe
Mountains: Wyoming State Geological Survey Reprint 48, 10 p.
Currey, Donald R., 1965, The Keystone gold-copper prospect area, Albany County,
Wyoming: Wyoming State Geological Survey Preliminary Report 3, 12 p., scale
Eggler, D.H., et.al., 1988, Tectonomagmatism of the Wyoming Province: Colorado
School of Mines Quarterly, p. 25-40.
Gersic, J., Peterson, E.K., and Schreiner, R.A., 1990, Appraisal of selected
mineral resources of the Black Hills National Forest, South Dakota and Wyoming:
U.S. Bureau of Mines Open File Report MLA 5-90, 225 p.
Graff, P.J., 1978, Geology of the lower part of the Early Proterozoic Snowy Range Supergroup,
Sierra Madre, Wyoming: Laramie, University of Wyoming, Ph.D. dissertation, 85 p.
Harris, R.E., Hausel, W.D., and Meyer, J.E., 1985, Metallic and industrial
minerals map of Wyoming: Wyoming State Geological Survey Map Series 14, scale
Hausel, W.D., 1982, General geologic setting and mineralization of the porphyry
copper deposits, Absaroka volcanic plateau, Wyoming: Wyoming State Geological
Survey Reprint 40, 17 p.
Hausel, W.D., 1982b, Ore deposits of Wyoming: Wyoming State Geological Survey
Preliminary Report 19, 39 p.
Hausel, W.D., 1984, Tour guide to the geology and mining history of the South
Pass gold mining district, Fremont County, Wyoming: Wyoming State Geological
Survey Public Information Circular 23, folded pamphlet, scale 1:24,000.
Hausel, W.D., 1986, Mineral deposits of the Encampment mining district, Sierra
Madre, Wyoming-Colorado: Wyoming State Geological Survey Report of
Investigations 37, 31 p.
Hausel, W.D., 1989, The geology of Wyoming’s precious metal lode and placer
deposits: Wyoming State Geological Survey Bulletin 68, 248 p.
Hausel, W.D., 1991, Economic geology of the South Pass granite-greenstone belt,
southern Wind River Range, western Wyoming: Wyoming State Geological Survey Report of Investigations
44, 129 p., scale 1:48,000.
Hausel, W.D., 1992, Form, distribution, and geology of gold, platinum,
palladium, and silver in Wyoming: Wyoming State Geological Survey Reprint 51, 18
Hausel, W.D., 1992, Mining history and geology of some of Wyoming’s metal and
gemstone districts and deposits: Wyoming State Geological Survey Reprint 56, 26
Hausel, W.D., 1993, Guide to the geology, mining districts and ghost towns of
the Medicine Bow Mountains and Snowy Range Scenic Byway: Wyoming State
Geological Survey Public Information Circular 32, 53 p.
Hausel, W.D., 1994, Economic geology of the Cooper Hill mining district,
Medicine Bow Mountains, southeastern Wyoming: Wyoming State Geological Survey
Report of Investigations 49, 22 p., scale 1:24,000.
Hausel, W.D., 1994, Economic geology of the Seminoe Mountains mining district,
Carbon County, Wyoming: Wyoming State Geological Survey Report of Investigations
50, 31 p., scale 1:24,000.
Hausel, W.D., 1996, Geology and gold mineralization of the Rattlesnake Hills,
Granite Mountains, Wyoming: Wyoming State Geological Survey Report of
Investigations 52, 28 p., scale 1:24,000.
Hausel, W.D., 1997, Copper, lead, zinc, molybdenum, and other associated metal
deposits of Wyoming: Wyoming State Geological Survey Bulletin 70, 229 p.
Hausel, W.D., 2006, Revised geologic map of the Miners Delight Quadrangle,
Fremont County, Wyoming: Wyoming State Geological Survey Map Series 38, scale
Hausel, W.D., 2007, Revised geologic map of the South Pass City Quadrangle,
Fremont County, Wyoming: Wyoming State Geological Survey Map Series 74, scale
Hausel, W.D., Edwards, B.R., and Graff, P.J., 1992, Geology and mineralization
of the Wyoming Province: Wyoming State Geological Survey Reprint 52, 18 p.
Hausel, W.D., Graff, P.J., and Albert, K.G., 1985, Economic geology of the
Copper Mountain supracrustal belt, Owl Creek Mountains, Fremont County, Wyoming:
Wyoming State Geological Survey Report of Investigations 28, 33 p., scale
Hills, F.A., and Houston, R.S., 1979, Early Proterozoic tectonics of the central
Rocky Mountains, North America: University of Wyoming Contributions to Geology,
v. 17, no. 2, p. 89-109.
Houston, R.S., 1993, Late Archean and Early Proterozoic geology of southeastern
Wyoming in Snoke, A.W., Steidtmann, J.R., and Roberts, S.M., (eds.),
Geology of Wyoming: Wyoming State Geological Survey Memoir 5, p.78-116.
Houston, R.S., and others, 1968 (reprinted 1978), A regional study of rocks of
Precambrian Age in that part of the Medicine Bow Mountains lying in southeastern
Wyoming – with a chapter on the relationship between Precambrian and Laramide
structure: Wyoming State Geological Survey Memoir 1, 167p., 5 plates, scale
Karlstrom, K.E., and Houston, R.S., 1984, The Cheyenne Belt: Analysis of a
Proterozoic suture in southern Wyoming: Precambrian Research, v. 25, p. 415-446.
Klein, T., 1974, Geology and mineral deposits of the Silver Crown Mining District,
Laramie County, Wyoming: Wyoming State Geological Survey Preliminary Report No. 14, 27 p.,
scale 1:1,200 and ~ 1:25,344.
Love, J.D., Antweiler, J.C., and Mosier, E.L., 1978, A new look at the origin
and volume of the Dickie Springs-Oregon Gulch placer gold at the south end of
the Wind River Mountains in Boyd, R.G., Olson, G.M., and Boberg, W.W.,
(eds.), Resources of the Wind River Basin: Wyoming Geological Association
Thirtieth Annual Field Conference Guidebook, p. 379-391.
Love, J.D., and Christiansen, A.C., comps., 1985, Geologic map of Wyoming: U.S.
Geological Survey, 3 sheets, scale 1:500,000, rereleased in 2014 by the Wyoming State Geological Survey.
Marketwire – Canada, 2012, Strathmore Reports Positive Preliminary Economic Assessment for
Copper King Gold-Copper Project, accessed September 2012 at http://www.equities.com/news/headline-story?dt=2012-09-13&val=477134&cat=material.
McCallum, M.E., 1968, The Centennial Ridge gold-platinum district, Albany County,
Wyoming: Wyoming State Geological Survey Preliminary Report 7, 13 p., scale 1:20,000.
McCallum, M.E., and Orback, C.J., 1968, The New Rambler copper-gold-platinum district,
Albany and Carbon counties, Wyoming: Wyoming State Geological Survey Preliminary Report 8, 12 p.,
Snoke, A.W., Steidmann, J.R., and Roberts, S.M., 1993, Geology of Wyoming:
Wyoming State Geological Survey Memoir 5, 937 p.
Sutherland, W.M., 2007, Geologic map of the Sundance 30′ x 60′ Quadrangle, Crook and Weston counties,
Wyoming and Lawrence and Pennington counties, South Dakota: Wyoming State Geological Survey Map Series
78, 26 p., scale 1:100,000.
Sutherland, W.M., 2008, Geologic map of the Devils Tower 30' x 60' Quadrangle,
Crook County, Wyoming, Lawrence and Butte counties, South Dakota, and Carter County, Montana:
Wyoming State Geological Survey Map Series 81, 29 p., scale 1:100,000.
Sutherland, W.M., and Cola, E.C., 2015, Iron Resources of Wyoming: Wyoming State Geological Survey
Report of Investigations 67, 92 p.
Sutherland, W.M., and Cola, E.C., 2016, A comprehensive report on rare earth elements in Wyoming:
Wyoming State Geological Survey Report of Investigations 71, 137 p.
Sutherland, W.M., and Hausel, W.D., 2003, Geologic Map of the Rattlesnake Hills 30’ x 60’ quadrangle,
Fremont and Natrona Counties, Wyoming: Wyoming State Geological Survey Map Series 61, 28 p., scale 1:100,000.
Sutherland, W.M., and Hausel, W.D., 2005, Preliminary geologic map of the Saratoga 30′ x 60′ Quadrangle:
Wyoming State Geological Survey Open File Report 04-10, 34 p., scale 1:100,000.
Sutherland, W.M., and Hausel, W.D., 2005, Preliminary geologic map of the Keystone Quadrangle,
Albany and Carbon Counties, Wyoming: Wyoming State Geological Survey Open File Report 05-6, 21 p., scale 1:24,000.
Sutherland, W.M., and Hausel, W.D., 2005, Geologic map of the Barlow Gap Quadrangle, Fremont County,
Wyoming: Wyoming State Geological Survey Map Series 67, scale 1:24,000.
Sutherland, W.M., and Hausel, W.D., 2006, Geologic map of the South Pass 30′ x 60′ Quadrangle,
Fremont and Sweetwater counties, Wyoming: Wyoming State Geological Survey Map Series 70, 23 p., scale 1:100,000.
Sutherland, W.M., and Worman, B.N., 2013, Preliminary geologic map of the Blackjack Ranch quadrangle,
Natrona County, Wyoming: Wyoming State Geological Survey Open File Report 13-3, 24 p., scale 1:24,000.
Ver Ploeg, A.J., and Boyd, C.S., 2007, Geologic map of the Laramie 30′ x 60′ Quadrangle, Albany and Laramie
counties, Wyoming: Wyoming State Geological Survey Map Series 77, scale 1:100,000.
Wilson, W.H., 1964, The Kirwin mineralized area, Park County, Wyoming: Geological Survey of
Wyoming [Wyoming State Geological Survey] Preliminary Report 2, 20 p., scale 1:24,000.