Uranium Mining

There are two main methods used to mine uranium—conventional mining and the more modern alternative, in-situ recovery (ISR). In Wyoming, uranium mining is primarily done through in-situ recovery. However, there are some plans for conventional mines in the Gas Hills and Crooks Gap districts.

Mining is the removal of material from the earth's interior for the purpose of extracting a commodity of interest (uranium, gold, aluminum, etc.). After mining, uranium ore is processed into yellowcake, a type of uranium concentrate powder obtained from leach solutions. Yellowcake is then converted into a form that can be enriched to fuel grade concentration, and ultimately fabricated into fuel rod assemblies for electrical generation.

ISR mining
Completed in-situ recovery well field at Cameco’s Smith Ranch-Highland facilities in Converse County. [Credit: WSGS]

Wyoming Uranium Mines

Wyoming began commercially mining uranium in the 1950s and has since produced more than a quarter of a billion pounds of yellowcake. There are currently four active mining operations in Wyoming (three in the Powder River Basin and one in the Great Divide Basin) and several other projects in various stages of regulatory review. The operating mines are the Smith Ranch-Highland operation (Cameco) in Converse County, Nichols Ranch (Energy Fuels) in Johnson County, and the Lance Project (Strata Energy) in Crook County (U.S. Energy Information Administration). The combined production from Wyoming mines in 2018 was 635,000 pounds of U3O8.

Some mining operations have been put on hold until more favorable market conditions return. Prior to 2018, there were six in-situ recovery (ISR) mines in operation. The Smith Ranch-Highland mine was the leading uranium producer in the United States for more than two decades.

In-situ Recovery

ISR mining
Conceptual diagram of in-situ recovery-type mining of a roll-front. [Credit: WSGS]

In-situ recovery, or ISR (also referred to as ISL or in-situ leach), is more economical and is considered to have a lower environmental impact than conventional mining. It is the preferred method of uranium mining if the uranium occurs in a shallow deposit hosted in water-saturated porous and permeable sedimentary rocks. ISR dates back to the early 1960s in Wyoming’s Gas Hills and Shirley Basin uranium districts. In-situ recovery is essentially the reverse of the natural geologic processes that originally concentrated uranium in its host rock. After natural processes oxidize and leach uranium from its source rocks, surface water and ultimately groundwater transport uranium in solution to a reducing environment in a porous host rock where the uranium is deposited. In the in-situ recovery process, uranium minerals are oxidized, remobilized, and pumped to the surface for processing. One of the advantages of this method is that there is very little surface disturbance other than the necessary infrastructure.

History of In-situ Recovery

The in-situ recovery (ISR) method was developed on an industrial scale in Texas in the 1970s, and since 1993 has been the only uranium extraction method used in Wyoming. The history of ISR dates back to the early 1960s in the Gas Hills and Shirley Basin uranium districts. Miners found that leaching solutions could be pumped through permeable tailings and through the host rock underground. The ISR process leaves the host rock in place and removes uranium by pumping a mixture of water and oxidizing agents through the rock, including dissolved gases such as oxygen (O2) or carbon dioxide (CO2).

The mixture, called a lixiviant, consists of water pumped from the orebody aquifer, plus the oxidizing agents added at the surface. In order to remove uranium from its location in the orebody, the lixiviant is pumped into the aquifer through injection wells, then through the orebody, and back to the surface through extraction wells. The lixiviant frees the uranium from the orebody and into a solution so that it can be removed at the surface by an ion exchange process. In addition to injection and production/extraction wells, ISR operations utilize monitor wells, which continually sample the water at the margins of the orebody—laterally as well as above and below—to ensure that the injected water does not migrate away from the targeted ore zone and into adjacent aquifers, an occurrence called an excursion.

Conventional Mining

Conventional mining involves the physical removal of ore from the ground by surface (open pit) or underground mining. Surface mining requires removing overburden (topsoil, sand, gravel, etc.) down to the top of the orebody. Then the ore is removed by heavy equipment, loaded into haul trucks, and driven to the mill. Underground mining involves either adits (horizontal tunnels) or sinking a vertical shaft from the surface followed by driving adits at depth to reach the orebody. The main factors that determine whether to mine by open pit or underground are depth to the orebody and cost of production. Orebodies lying less than about 500 feet below the surface are typically surface mined as it is much cheaper than underground mining. After extraction, the uranium ore is transported to a processing plant where it is milled. This process involves crushing the ore, chemically extracting the uranium, and concentrating it into yellowcake.

Yellowcake (uranium oxide), the end product of uranium mining. [Credit: WSGS]
Open Pit Surface Mine
Paydirt open pit surface mine in the Crooks Gap area, southeastern Fremont County, circa 1970. [Credit: U.S. Department of Energy]


Kelsey Kehoe, kelsey.kehoe@wyo.gov