Wyoming has produced both precious and base metals in the past. Precious metals are relatively scarce and include gold, silver, and the platinum-group metals. Base metals are those of relatively inferior value compared to precious metals. Base metals are generally more chemically active than precious metals and include copper, lead, zinc, and molybdenum. Although significant metals production has not occurred since iron ore mining ended at South Pass in 1984, rapidly increasing metals prices during recent years have spurred considerable interest in and increased exploration for Wyoming’s gold, platinum, copper, iron, rare earth elements, titanium, and related metals.
The Atlantic City iron mine produced up to 2 million tons of iron pellets per year
between 1962 and 1984.
Precambrian rocks exposed in the cores of mountain uplifts, Tertiary volcanic and intrusive rocks, and related placer deposits are the dominant hosts for Wyoming’s metal resources (see the Wyoming State Geologic Map). However, some metals deposits also occur in Phanerozoic sedimentary rocks. The Archean craton, also known as the Wyoming Craton (or Province), is part of the ancient core of the North American continent and dominates Wyoming’s Precambrian rock exposures. The Archean rocks are more than 2.5 billion years old and are often compared to rocks in some of the world’s richest precious-metal-producing areas, such as the Archean cratons of Western Australia, South Africa, and the Superior Province of Canada.
Gold, copper, and iron have all been mined from these rocks in Wyoming. Younger Precambrian (Proterozoic) rocks accreted along the south edge of the Archean craton in the Medicine Bow Mountains and in the Sierra Madre include two large layered mafic-ultramafic complexes and a variety of intrusive and metamorphic rocks that host both base and precious metals, including platinum. Tertiary volcanic rocks in the Absaroka Volcanic Plateau in northwest Wyoming host large base and precious metal deposits. Tertiary volcanic rocks in the Rattlesnake Hills of central Wyoming carry disseminated gold, and Tertiary intrusive rocks in the Bear Lodge Mountains in northeast Wyoming host large-tonnage low-grade rare earth and thorium deposits, along with low-grade gold mineralization.
Recommended Reference Material
Further information on most of Wyoming’s metals deposits can be found in the following WSGS publications:
WSGS Bulletin 68, The geology of Wyoming’s precious metal lode and placer deposits, by W. Dan Hausel, 1989, 248 p.
WSGS Bulletin 70, Copper, lead, zinc, molybdenum, and other associated metal deposits of Wyoming, by W. Dan Hausel, 1997, 229 p.
WSGS Map Series MS-14, Metallic and industrial minerals map of Wyoming, by R.E. Harris, W.D. Hausel, and J.E. Meyer, 1985, scale 1:500,000.
A comprehensive summary of the geology of Wyoming, helpful in understanding Wyoming’s metal deposits, is found in:
WSGS Memoir 5, Geology of Wyoming, edited by Arthur W. Snoke, James R. Steidmann, and Sheila M. Roberts (1993), 937 p.
Additional overviews of Wyoming’s geology are found in:
WSGS Bulletin 67, Traveler’s guide to the geology of Wyoming, by Donald L. Blackstone, Jr., 1988, 130 p.
USGS, Geologic Map of Wyoming, by J.D. Love, and A.C. Christiansen, 1985, scale 1:500,000.
For a complete listing of WSGS materials, go to the Online Store.