Phosphate Rock

Phosphate rock can be any rock or sediment with sufficiently high concentrations of some form of the mineral fluorapatite (Ca5(PO4)3F) to be of commercial value. Fluorapatite composes the mineral part of vertebrate bones and teeth. Collophane is the massive fine-grained variety of apatite in phosphate rock. Commercial phosphate rock is usually sedimentary in origin and is used primarily as a plant nutrient, either by direct application to the soils as a powdered product or in the manufacture of superphosphate or triple super-phosphate fertilizer. Elemental phosphorus and phosphoric chemicals are also derived from phosphate rock and are used in detergents, insecticides, matches, fireworks, and many other products.

Phosphate rock was discovered in Arkansas in 1895. During the early 1900’s, several thousand tons were mined by underground and surface methods in Independence County and shipped to a plant in North Little Rock for processing into super-phosphate fertilizer. This operation ceased when higher grade material from Tennessee and Florida entered the market. Potential commercial deposits are present in the Cason Shale (Ordovician-Silurian) along the White River Valley and nearby areas in Independence, Stone, Izard, Searcy, and Marion Counties. A deposit in Upper Mississippian rocks along the Searcy-Van Buren County line a few miles south of Leslie was mined during the 1960’s. Other minor phosphate rock deposits are known, but have not been explored.

Since phosphate rock is a low-cost commodity, certain cost-limiting conditions must be met for a deposit to be minable. A typical phosphate mining operation uses open-pit methods, is a large volume producer, and requires large amounts of water for upgrading the raw material. Low-cost transportation to markets is also essential. Current economic conditions preclude commercial utilization of the Arkansas phosphate rock, but could become significant when supplies from other states are exhausted.

References

Branner, J. C., 1897, The phosphate deposits of Arkansas: American Institute of Mining Engineers Transactions, v. 26, p. 580-598.

Wells, C. J., 1949, Hickory Valley phosphate deposit in Independence County, Arkansas: Arkansas Resources and Development Commission, Division of Geology Bulletin 19, 37 p.