Ore sample from the underground mining operation in the Intrepid Potash administration building

An unusual suite of rocks is present underneath the canyon country surrounding Moab: salt deposits along with other evaporite minerals such as potash (potassium chloride that occurs as the mineral sylvite). Evaporite minerals are deposited from hypersaline seas known to geologists as restricted basins. Approximately 310 million years ago, a restricted basin existed in what is now southeastern Utah. Rivers cascading down from the Ancestral Rocky Mountains to the northeast carried dissolved salts and other minerals into the basin, which was partially, or even sometimes completely, cut off from the open ocean. Because circulation with normal ocean water did not exist, concentrations of sodium, potassium, and other ions in the water progressively increased with evaporation, ultimately reaching concentrations where first salt (halite), and then potash precipitated to form vast layers of salts on the sea floor. (The December 2019 Geology Happenings article describes the geology of the potash deposits in more detail. See www.moabhappenings.com/Geology

The Paradox Formation consists of great thicknesses of halite, black shale and other rocks that were deposited in that restricted basin. These rocks were deposited in regular sequences (cycles) that began when fresh seawater flooded the basin and normal sedimentary rocks such as shale and limestone were deposited, followed by halite and potash as evaporation proceeded. A small percentage of the evaporite minerals in the Paradox Formation is potash, which is valuable for its use in fertilizers, in industrial applications, and as a feed additive. Because of potash’s economic importance, the deposits that were formed in this ancient sea include a potash ore body that is mined by Intrepid Potash along the crest of the Cane Creek anticline (an upwarp in the rock layers) approximately 15 miles south of Moab.

Potash was first discovered beneath southeastern Utah in the 1920s when sylvinite, which is a mixture of halite and sylvite, was encountered in exploratory oil wells. At the Cane Creek site, potash was identified in oil wells in 1956. The presence of the anticline was critical to the subsequent development of the mining operation because the fold brought the potash closer to the surface, making commercial development more feasible.

Solar evaporation pond

In the early 1960s, the Texas Gulf Sulphur Company began to develop the reserves. A 2,789-foot deep shaft was sunk to reach the uppermost sylvinite layer, and a processing mill was built. The state constructed a new road (Highway 279) to the potash plant, and the Denver and Rio Grande Railroad built a spur to connect the new mine to markets.

But traditional underground mining of the deposits proved difficult. Temperatures in the mine were high, the sylvinite layer undulated which made following the ore body challenging, and explosive gases were present. In 1963, an explosion killed 18 miners just before the mine was to go into production.

In 1970, the operation switched to solution mining, a process that takes advantage of potash’s high solubility. Water (actually a sodium brine made by mixing river water with halite) is pumped into the mine to dissolve potash, which is, in turn, pumped out, and into solar evaporation ponds. The sodium brine is advantageous because it allows the selective dissolution of potassium, leaving sodium behind. Intrepid has 23 evaporation ponds covering a total approximately 400 acres. Blue dye (similar to food coloring) is added to the evaporation ponds to increase energy absorption and evaporation rates. Each pond is harvested once a year by 25-ton scrapers. Potash is not harvested from the ponds

Potash in Intrepid’s warehouse

during the summer in order to maximize evaporation/production when the temperatures are the greatest. The harvested salt-potash mixture is sent to the mill in slurry pipes where potash is separated from salt through a process called froth flotation. During processing, compounds are added to the mixture that causes the potash to “float.” The potash is then dried, and then shipped to the warehouse. Potash produced at the Cane Creek mine is at least 95% pure, with the majority of the balance consisting of salt and moisture. Their annual potash production is between 80,000 and 120,000 tons, with wind, rain, and other weather conditions impacting production.

Intrepid Potash has operated the Cane Creek mine since 2000. Intrepid increased production by using horizontal drilling to follow the sylvinite layers and by mining a second (and deeper) sylvinite layer (Potash 9), in addition to original ore layer (Potash 5). Intrepid Potash estimates that they have reserves that should last between 70 and 100 years at the Cane Creek mine.

Potash “floats” during the separation process

Geology plays an oversized role in nearly every aspect of canyon country. The influence of geology is sometimes self-evident, such as with the scenery. But sometimes it is not as obvious. For Intrepid potash, the key factors are the combination of the 310-million year old restricted basin where sylvite was precipitated after extreme evaporation, and the slight upwarp at the Cane Creek anticline that brought this valuable commodity closer to the surface where the salts from that ancient sea are now harvested.

Special thanks to Intrepid Potash and the Moab Festival of Science for inviting the public to an excellent tour of the mine site in September 2019.

The solution mining process. Modified slightly from an Utah Geological Survey illustration. Used courtesy of the Utah Geological Survey.`