Phosphate
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.
Applications
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.
Production
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.
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 .
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.
References
Allaway, W.H., 1962, Relation of soil to plant and animal nutrition, in Proceedings, Cornell Nutrition Conference: Cornell University, Ithaca, New York, p. 13–23.
Environmental Literacy Council, 2013, Phosphorus cycle, accessed April 2015, at http://www.enviroliteracy.org/article.php/480.html.
Jasinski, S.M., Lee, W.H., and Causey, J.D., 2004, The history of the Western Phosphate Field, in Hein, J.R., ed., Life cycle of the Phosphoria Formation: Handbook of Exploration and Environmental Geochemistry, v. 8: Amsterdam, Elsevier, p. 45–61.
Ozanne, P.G., 1980, Phosphate nutrition of plants – a general treatise, in Khasawneh, F.E., Sample, E.C., and Kamprath, E. J. eds., The role of phosphorus in agriculture: Madison, Wis., American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, p. 559–590.
Reid, R.L., 1980, Relationship between phosphorus nutrition of plants and the phosphorus nutrition of animals and man, in Khasawneh, F.E., Sample, E.C., and Kamprath, E.J. eds., The role of phosphorus in agriculture: Madison, Wis., American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, p. 847–886.
Underwood, E.J., and Suttle, E.J., 1999, The mineral nutrition of livestock, 3d edition: Wallingford, UK, CAB International, 614 p.
Wyoming Department of Revenue, 1973–1978 Annual report: Cheyenne, Wyoming.
Wyoming State Board of Equalization, 1926–1972 Biennial report: Cheyenne, Wyoming.
Contact:
Kelsey Kehoe, kelsey.kehoe@wyo.gov