Uranium (U) is a very heavy metal usually found as an oxide, such as uraninite (UO2) or coffinite (U(SiO4)1-x ?(OH)4x). It occurs nearly everywhere on the planet, even in sea water, but may become concentrated in ore deposits under the right geological conditions and processes. In its purest form, uranium is a silvery white metal, but usually occurs as an oxidized mineral. Its density is nearly that of gold, about 19 grams per cubic centimeter (g/cm3). Although it exists as several different isotopes (atoms of the same element with different numbers of neutrons), most naturally occurring uranium is 238U (99.27%), followed by 235U (0.73%). Uranium’s atomic number is 92, meaning that there are 92 protons in its nucleus. The rest of the particles in the nucleus are neutrons: 146 in 238U and 143 in 235U. The 235U isotope is less stable – it decays more rapidly than 238U and is the form of uranium used to fuel nuclear reactors.

Uranium is usually found in porous sedimentary rocks such as sandstones or conglomerates, but some large deposits are associated with igneous and metamorphic rocks. Uranium atoms are similar in size and chemical properties to calcium atoms, so as rocks form, uranium often substitutes for calcium in minerals such as plagioclase (very common in granites). Thus, calcium-rich rocks such as granite typically contain more uranium than other rocks, and are thought to be the source of many uranium ore deposits. Particles ejected from ancient volcanoes – particles often chemically similar to granitic rocks – are another possible source of uranium ore deposits. These two possibilities are still the center of debate among scientists trying to determine the source of uranium deposits. What really matters, though, is the vast supply of energy uranium can provide.

Nuclear Fuel Cycle

Uranium Quick Facts

  • Symbol – U
  • Atomic number – 92 (number of protons in the nucleus)
  • Atomic weight – 238.02891 atomic mass units
  • Density – 19.05 grams per cubic centimeter (g/cm3)
  • Group name – actinide (belonging to the Actinium series)
  • Global abundance (estimated)
    • Crustal rocks – 1.8 ppm by weight (parts per million)
    • Sea water – 3.3 ppm
    • Human body (ave.) – 1 ppm
  • Color – metallic gray
  • Classification – metal
  • Isotopes
    • 234U – 0.0055% of naturally occurring U
    • 235U – 0.72% of naturally occurring U
    • 238U – 99.2745% of naturally occurring U
  • Other properties of U
    • Ductile
    • Malleable
    • Moh hardness ~ 6
    • Melting point: 2070º F, 1132º C, 1405º K
  • Discovered in 1789 in Germany by Martin Klaproth
  • First isolated in 1841 by Eugene-Melchoir Peligot, who used potassium to reduce anhydrous uranium chloride (UC14)
  • Radioactive properties of U discovered by Antoine Becquerel, 1896
  • Early uses
    • Coloring agent for glass and ceramic glazes
    • Source for radium (Ra) for Pierre and Marie Curie’s experiments on radioactivity
  • Common uranium-bearing minerals

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The WSGS provides geologic and mineral resource information, including locations of occurrences, reserves, ore grades, historical production, and future economic trends for uranium and various other minerals. The WSGS strives to provide as many resources as possible to the public, industry, and other government agencies via collection of historic documents and data, research, and collaboration. Visit or for additional statistics and information on the uranium industry.

A Brief History of Uranium in Wyoming

The Wyoming uranium industry dates back to 1918, when prospectors sought radium for Marie Curie’s first radioactivity experiments from tailings piles at the Silver Cliff mine near present-day Lusk. Later discoveries were made near Wamsutter at Lost Creek and in the Black Hills area of Crook County.

The first major discovery, however, resulted from Dr. John David Love’s assertion that uranium was likely to be found in and associated with the tuffaceous sediments of the Oligocene White River Formation (38-24 million years old) in the Powder River Basin. Love, working for the USGS at the time, hypothesized that uranium deposits should occur in the Pumpkin Buttes area of southwest Campbell County. Aerial surveys in 1950 revealed dozens of anomalies in the area, and in October of 1951, Love, Dick Hose, and Franklyn B. Van Houten checked the area in the field with a scintillometer and verified the occurrence. They collected samples later determined to consist of as much as 15% uranium oxide. The U.S. Atomic Energy Commission (AEC) was eager to purchase uranium ore for its nuclear weapons program and established a buying station in Edgemont, SD, for that purpose. Small mines in the Black Hill area and the Powder River Basin, operated by companies including Homestake Mining Co., Globe Mining, and Kerr-McGee, shipped the first uranium ore to Edgemont in 1953.

Also in 1953, Neil McNeice discovered what would eventually become the Lucky Mc deposit in the Gas Hills uranium district of the Wind River Basin. Other discoveries at Crook’s Gap, in the Shirley Basin, and in the Black Hills area were made over the next few years. Major uranium-producing areas of Wyoming over the years have included the Powder River Basin, Wind River Basin, Great Divide Basin, Shirley Basin, and Green Mountain and Crooks Gap areas (see map)

These discoveries not only led to outstanding production of yellowcake (the product of uranium ore processing which is then used to make fuel for power plants) but also fueled economic growth and employment in the state. More than 5,300 people worked in the uranium industry in one capacity or another in 1980. Cities and towns around Wyoming grew significantly during the boom cycles, and in the case of Jeffrey City in Fremont County, transformed from a homestead to a town of more than 4,000. However, the bust cycles took their toll, and when prices plummeted after the Three Mile Island incident in 1979, Jeffrey City was all but deserted within a few years.

Uranium production in Wyoming

Wyoming has been the nation’s leading producer of uranium ore since 1995, and also encompasses the country's largest uranium reserves. Since 1991, all Wyoming uranium has been recovered by the in-situ recovery (ISR) method, sometimes referred to as in-situ leach (ISL). Wyoming currently (2014) produces from five ISR uranium mines; the Smith Ranch-Highland (SR-H) ISR operation in west-central Converse County has been producing by ISR since the early 1980s, and is operated by Power Resources, a wholly-owned subsidiary of Cameco Corporation of Saskatoon, Saskatchewan, Canada. That company also owns and operates the North Butte ISR mine, and processes the uranium from that field at SR-H. North Butte is one of the several prominent flat-topped mesas of Pumpkin Buttes in the Powder River Basin in southwestern Campbell County, Wyoming.

There are also two other ISR mines in operation in the Pumpkin Buttes district. The Willow Creek operation is owned by Uranium One and produces yellowcake at their Irigaray plant in southeastern Johnson County. The well fields of Willow Creek are on the northwestern flank of Pumpkin Buttes. In April 2014, Uranerz Corporation began production at their Nichols Ranch ISR mine about nine miles south of Willow Creek.

Elsewhere in Wyoming, there is one other uranium mine in production and several in the permitting and development stages. The Lost Creek ISR mine in northeastern Sweetwater County began production in August, 2013. Additional mines are expected to commence yellowcake production from the western Black Hills area, Shirley Basin, the Gas Hills of the Wind River Basin, and numerous other mines in the Powder River Basin.

Uranium Mining in the United States

Currently (2013), seven uranium mines, all ISR, operate in the United States. Crow Butte in northwestern Nebraska is also owned by Cameco Corporation of Saskatoon, Saskatchewan, Canada. In 2013, Crow Butte produced about 800,000 pounds of U3O8 by the ISR method.

The other uranium-producing sites are all located in south Texas. They are the Palangana mine and Hobson plant, both owned and operated by Uranium Resources, Inc., Lewisville, TX, and Alta Mesa, owned and operated by Mestena Uranium, LLC. The combined annual production from the Texas operations is around 800,000 pounds of U3O8.

With the recent upsurge in yellowcake spot prices over the last several years, exploration and claim-staking activity has increased in Wyoming and several other Rocky Mountain states, including Arizona, Colorado, Montana, New Mexico, and Utah. Some of these states could also begin producing uranium in the near future.

Additional Uranium Information: