Mineral Deposit Evaporite cycles within the Paradox Formation exhibit a lateral extent of over 11,000 square miles in southeastern Utah and southwestern Colorado (Hite 1960). The Pennsylvanian-age Paradox Formation records multiple episodes of evaporitic deposition, predominantly consisting of massive, crystalline halite with economically attractive occurrences of potash. Deposition of the evaporite soccurred in a vast, flat basin resulting in each additional layer, or bed, being originally deposited in a horizontally planar orientation. Subsequent deposition of overlying sediments provided enough lithostatic pressure to initiate lateral and vertical migration of the more buoyant salt deposits. In many instances, salt flowed towardlinear subsurface structures, such as a fault, and then upward to form what is known as a salt wall. The rising salt typically forms an anticline in overlying strata with surficial expressions of 30 to 75 miles long and 2 to 4 miles wide (Doelling 1985). This collection of northwest-trending, elongate structures is referred to as the Paradox Basin fold and fault belt. Due to the highly deformed nature of the evaporite deposits, it is not uncommon to encounter very high-angle and even over turned strata in exploratory drill holes. The Intrepidlease area is in the southwestern portion of the fold and fault belt where broad salt anticlines are more common than high-angle salt walls. Local examples of these domal salt-cored anticlines include the Big Flat, Cane Creek, and Lisbon Valley anticlines. Because strata within the Intrepid lease boundary have experienced considerably less movement of salt bodies compared to areas to the northeast, the potash deposits of economic interest are significantly less deformed and therefore more suitable for economic extraction. Intrepid-Moab commercially produces potash from two zones, referred to as Bed 5 and Bed 9. These beds are part of a thick sequence of evaporite cycles predominantly composed of halite interspersed with sedimentary layers of black shale and anhydrite. WithinBeds 5 and 9, the sylvinite is bounded above and below by occurrences of halite. Sylvite and halite are both water-soluble by nature. Byusing water already saturated with sodium, it is possible to selectively dissolve a greater amount of the potassium chloride ore. The term ‘potash’ is used to describe a number of potassium-bearing compounds. Of these, the mineral sylvite commands the greatest economic interest. Sylvite is commonly found mixed with halite, or sodium-chloride (NaCl), to form the mineral sylvinite. Sylvinite is known to have a K2O content of up to 62% in its purest form. Significant Mineralized Zones Potash is documented to exist in 17 of the 29 evaporite cycles that comprise the Paradox Formation. Of these 17, two areprincipally targeted by Intrepid for commercial potash production: Bed 5 and Bed 9. Based on locally recovered drill core, geophysical logs, and on historical mining data, Bed 5 has an average thickness of 10.24 ft. Average depth to the top of Bed 5 is 3,113 ft and the average K2O grade is 22.98%. Likewise, Bed 9 has an average thickness of 8.1 ft, anaverage depth of 4,013 ft, and an average K2O grade of 29.75%. Although K2O, or potassium oxide, is not the preferred chemical formused in commercial consumption, potash grades are typically reported as ‘K2O equivalent’ to allow for a standard unit of comparison. Inaddition, it should be noted that K2O is approximately 83% potassium by weight, where as KCl is 52% potassium by weight. Thus, KCl provides less potassium than an equal amount of K2O.

Mining at Intrepid-Moab is by the solution mining technique referred to as “selective solution mining.” Selective solution mining dissolves only the KCl component of the sylvinite and leaves the sodium chloride component underground.

Brine saturated in NaCl and partially saturated in KCl is injected into either the old mine workings of Bed 5 or the horizontal Bed 9 caverns via injection wells. Brine that is near saturation with KCl (pregnant brine solution) is with drawn via extraction wells. The old works solution is essentially an underground lake. The horizontal caverns operate under pressure, thus requiring the injection and extraction to take place simultaneously. The pregnant brine solution is piped to shallow evaporation/solar ponds with an aerial expanse ofapproximately 400 acres.

KCl production is a function of brine grade and the well extraction rate and is limited by the solar ponds’ evaporation rate. Brine grade is a function of retention time within each bed.

Solution Mining Bed 5
Since 1971, solution mining from Bed 5 has produced approximately 5.5 Mt of KCl.

Since 2015, extracted brine from Bed 5 is a mixture of KCl from both beds and therefore, it is not possible to determine exactly how much of each bed’s KCl is being produced. For this estimation, the assumption is made that all injected KCl is extracted on an annual basis. Therefore, Bed 5 KCl production is the difference in KCl extracted from the wells and Bed 9 injection. Extraction brine is currently sourced from seven wells.

Future production plans for the Intrepid-Moab operation include continued production from Bed 5 and Bed 9. In 2021, Bed 5 contributed approximately 41% of the total KCl produced by the Intrepid-Moab operation.

Future recovery of potash from solution mining in the existing Bed 5 cavern is possible from both updip and horizontal locations from the existing mine perimeter and from new Bed 5 horizontal caverns.

Solution Mining Bed 9
Solution mining in Bed 9 began on July 30, 2002, with the drilling of two horizontal wells. An additional well was drilled into this system in 2005. This series of three wells make up Cavern 1. An additional horizontal well was drilled into Cavern 1 in 2012 to stimulate additional production from this cavern. Two new caverns, Caverns 2 and 3, were drilled in 2012–2013 and consist of four wells. Injection into Cavern 2 began in early 2013. Cavern 3 injection began in 2014. Approximately 950,000 t of KCl have been produced from Bed 9 since 2003.

The development of horizontal caverns for solution mining in Bed 9 was novel and unprecedented in 2002 in the potash industry when Intrepid-Moab drilled the first wells. The horizontal holes were drilled with the intent of maintaining contact with Bed 9 and developing caverns laterally by selective solution mining. The net KCl tons sent from Bed 9 since 2003, on average, 48,000 t of KCl have been extracted per annum. The proportion of tons extracted from Bed 9 is approximately 70% of total extracted tons since 2013. Since 2015, approximately 25% of the extraction from Bed 9 has been injected into the Bed 5 old working scavern.

Mining by solution methods ends with the delivery of the brine to the evaporation ponds. Mineral processing begins with pond sequencing to enhance crystallization of the potash. The crystals remaining in the ponds after solar evaporation are harvested and processed through the mill where the potash is separated from other salts, then concentrated by flotation. The concentrates are then dried, compacted, and screened into premium grades of white potash. Both potash and salt products are processed at the plant facility at a rate of 400 to 1,200 tons per day (tpd).

The Intrepid-Moab processing plant uses nominally 350M gallons per year of river water to produce 350M gallons per year of NaCl-saturated (21% by weight) evaporation pond feed solution at 6.5–7.5% KCl. The injection liquor typically contains 2% KCl and is near NaCl saturation (21%). The evaporation ponds concentrate and crystallize the brine to produce about 530,000 tpy of crystalat 15% K2O (22-24% KCl) with the rema ........