Paradox Basin, Southeast Utah
The Paradox Basin is a northwest-trending structural foreland basin formed during the Paleozoic because of downwarping and infilling by clastic sedimentary deposits, evaporite salts, and limestone. Basin deposits are composed of more than 6,096 m of Cambrian to Quaternary sedimentary rocks. Sedimentary units consist of 4,572 m of terrigenous clastic sediments shed along the Uncompahgre uplift to the east during the Pennsylvanian to Permian Period. A 1,219- to 1,829-m section of Pennsylvanian evaporites formed in the Paradox Basin during retreat of an intercontinental seaway that had inundated most of what is Utah.

The Paradox Basin is located mostly in southeast Utah and southwest Colorado, but it extends into northeast Arizona and northwest New Mexico. A carbonate platform in the south bordering the central Paradox Basin forms a constructional deposit of carbonaceous minerals with topographic relief and is a remnant of a Paleozoic seaway. The evaporite salts that were deposited in the Middle Pennsylvanian are used to define the basin boundary. The basin is bordered on the northeast by a Precambrian-cored anticlinal uplift associated with the Uncompahgre Plateau (Nuccio and Condon, 2000). The San Juan dome, a Precambriancored uplift partly covered by Tertiary volcanic rocks, forms the eastern boundary of the basin. Cretaceous sedimentary rocks exposed along the Hogback monocline southwest of Durango, Colorado form the southeast border. The southern and southwest basin borders are not well defined structurally but are delineated mainly by the extent of Pennsylvanian evaporite deposits and by the Monument upwarp, a classic Colorado Plateau monoclinal fold (Nuccio and Condon, 2000). The San Rafael Swell, a Laramide dome that formed over uplifted Precambrian rocks, marks the northwest basin boundary. The Uinta Basin merges with the Paradox Basin along the northern margin of the Paradox Basin.

The Pennsylvanian Paradox Member of the Hermosa Formation is an economic source of potash currently mined near Moab, Utah. Potash deposition in the Paradox Basin was controlled over time by evolution of brine compositions with late-stage brines having a higher concentration of potassium. Potash in brine is highly soluble, and potassium minerals are among the last phases to precipitate. Common precipitation sequences for ocean brine are calcite-gypsum or anhydrite-halite-potash. Episodic transgressive (inundation) and regressive (retreat) seaway events are recorded in a section of core collected near the active Cane Creek Mine, 14.5 kilometers (km) west of Moab, Utah. A 283-m section of continuous core shows four black shale and two limestone depositional intervals preceded by evaporite mineralization. Some shale intervals are hydrocarbon rich and have been investigated as source rocks for oil and gas in the Paradox Basin (Nuccio and Condon, 2000)

In Utah, the miners pump water deep underground to reach the potash ore. Potash is soluble, so water dissolves it into a brine. That brine gets pumped into underground caverns, where the potash continues to dissolve. Eventually, a highly-concentrated brine is pumped all the way to the surface and into one of the evaporation ponds shown above.

Potash ore at Moab is mined from two stacked ore zones: the original mine workings in Potash 5 and the horizontal caverns in Potash 9.

Water is saturated with salt and the resulting brine is pumped through injection wells into the underground mine workings. The injected brine preferentially dissolves the potash from layers buried between 2,400 and 4,000 feet below the surface. As the brine preferentially dissolves the potassium, the double saturated potassium and salt brine becomes heavier than the salt saturated brine causing it to sink to low points in the mining caverns. Extraction wells are installed at the lowpoints to pump the potash rich brine to the surface, where it is placed into 400 acres of shallow evaporation ponds just southwest of the mine. Blue dye, similar to food coloring, is added to the evaporation pond brines, to aid in absorption of sunlight. There, the water, aided by approximately 300 days of sunshine and an average of just five percent relative humidity, evaporates, leaving potash and salt crystals in the pond. The evaporation process, requiring only solar energy, is highly environmentally fri ........