Summary:
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.