Phosphate rock is the primary source of phosphorus for industrial applications. Phosphorus in phosphate rock most commonly occurs within apatite (Ca5(PO4)3(F,Cl,OH). Apatite is found in sedimentary, igneous, and metamorphic rocks. There are six economic deposit types for phosphate rock: 1) marine phosphorites, 2) igneous apatite, 3) residual phosphorites, 4) river pebble phosphate deposits, 5) phosphatized rock, and 6) guano. 


The primary industrial application of phosphate rock is the production of fertilizer used to add phosphorus to soil. Phosphorus (P) is a nutrient vital for all life as a component in DNA and RNA, and also adenosine triphosphate, which facilitates energy transfer within cells. Terrestrial plants incorporate phosphorus from soil, while animals receive phosphorus through their diet. In nature, phosphorus is often a limiting factor with respect to the quantity of life an ecosystem can support. In soil, natural soluble phosphorus that can be taken up by plants typically makes up less than 10 percent of total phosphorus in the soil. In agricultural settings, natural availability of soluble phosphorus is prohibitively low, thus phosphorus must be added to the soil by means of a topical fertilizer. Similarly, phosphorus feed-additives may be required for ruminant livestock.


The United States is the third largest producer of phosphate rock globally. Currently, the bulk of domestic production occurs in Florida and North Carolina, with remaining production in Idaho and Utah. Phosphate production in Idaho and Utah is from the so-called Western Phosphate Field, an area covered by the Permian-aged Phosphoria Formation. The eastern portion of the Western Phosphate Field covers the western half of Wyoming. Though the Phosphoria Formation thins eastward from Idaho into Wyoming, notable phosphate rock deposits within the Phosphoria Formation are present in Wyoming.

At present, there are no active phosphate rock mines in Wyoming, though mining did occur intermittently through the 20th century. Phosphate rock in Wyoming was first mined in 1907, and production in the western portion of the state continued sporadically until the opening of the Leefe mine in 1947. Production of phosphate rock in Wyoming last occurred in 1977. The Leefe Mine, located approximately 30 miles west of Kemmerer, produced phosphate rock from 1947 to 1977 from the Phosphoria Formation. Although production in Wyoming has been dormant for more than 35 years, the phosphate mining industry has a robust presence in southeastern Idaho and northeastern Utah, and a phosphate processing facility is located near Rock Springs, Wyoming. Thus, phosphate rock deposits in western Wyoming are relatively close to existing phosphate processing infrastructure.

Map of Western Phosphate Field
Map showing extent of the Western Phosphate Field, outlined, and outcrops the Phosphoria Formation and related rocks in black. Modified from McKelvey and others (1959).

Wyoming Occurrences

Of the six deposit types listed above, only marine phosphorites and igneous apatite are known to occur in Wyoming. Marine phosphorites are well documented within the Permian Phosphoria Formation of western to central Wyoming; these are the only phosphate rock occurrences in Wyoming likely to be of a grade and extent to attract economic interest. No extensive high-grade igneous phosphate deposits are known in Wyoming, but the typical host rock-types are not uncommon to the state, and anomalously high concentrations of igneous apatite have been recognized in the state. In the central Laramie Range, apatite is associated with magnetite-ilmenite deposits within the Laramie Anorthosite Complex. Magnetite-ilmenite bodies at the Taylor Deposit host up to 60 percent apatite. Apatite also was identified at two other magnetite-ilmenite deposits, which were labeled deposits #1 and #6. At deposit #1, varying amounts of apatite occur within iron-rich lenses. At deposit #6, apatite is abundant within an irregular dike, though a sample of this dike yielded only slightly greater than 2 percent P2O5 .

Phosphate rock
Phosphate rock in the Meade Peak Member of the Phosphoria Formation near the Middle Fork of Pine Creek, east of Cokeville, Wyo. [Credit: Jacob Carnes, WSGS]

Thick, medium- to high-grade occurrences of phosphate rock of the Phosphoria Formation are most common in western Wyoming, but may extend into central Wyoming. The Meade Peak Member of the Phosphoria Formation in the Overthrust Belt exhibits the highest potential for economically viable phosphate rock deposits with respect to grade and thickness; however, the steep inclination and discontinuity of beds may preclude mineability at many locations. All historic phosphate mining in Wyoming targeted the Meade Peak Member in the Overthrust Belt. Southeast of Lander, the Meade Peak Member and, to a lesser degree, the Retort Member of the Phosphoria Formation host important phosphate deposits along the northeastern flank of the Wind River Range. The Lander deposits are low- to medium-grade, but the structural geology of the area is relatively simple compared to the Overthrust Belt.

Weakly indurated phosphate rock
Weakly indurated phosphate rock in the outcrop above Shafer Creek. [Credit: Jacob Carnes, WSGS]
typical texture of phosphate rock
Close-up photograph showing typical texture of phosphate rock from the Phosphoria Formation.  [Credit: Jacob Carnes, WSGS]
Outcrop of the Meade Peak Member
Outcrop of the Meade Peak Member and the overlying Rex Chert Member of the Phosphoria Formation above Shafer Creek along USFS Rd. 10166, in Lincoln County, Wyo. [Credit: Jacob Carnes, WSGS]


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Kelsey Kehoe,