INTRODUCTION
Potash prices are skyrocketing and may soar to $1,000 or more per ton by the end of 2008 (Figure 1). Rapidly rising demand for fertilizer and limited expansion of production are leading causes of the increase (Sergeant, 2008). Good potash deposits are rare, there are few global producers, and growth in demand is great; generally bad news for consumers. The good news is that the dramatic increase in price has renewed interest in Arizona potash deposits. Yes, Arizona has potash!
This article is adapted from the recently released open-file report OFR-08-07, “Potash and related resources of the Holbrook basin, Arizona” (Rauzi, 2008).

Arizona Potash
Potash in Arizona is present near the top of extensive salt (halite - NaCl) deposits in the Permian Supai

formation (270-220 Ma) of east-central Arizona (Figures 2, 3, and 4), where bedded salt underlies Potash in Arizona is present near the top of extensive salt (halite - NaCl) deposits in the Permian Supai formation (270-220 Ma) of east-central Arizona (Figures 2, 3, and 4), where bedded salt underlies about 3,500 square miles and attains a maximum aggregate thickness of 655 ft (Rauzi, 2000). The extent of the salt defines the Holbrook salt basin. Potash underlies about 600 square miles and ranges up to about 40 ft thick. The gross volume of potash as depicted on Figure 2 is 1.36 cubic miles (5.68 cubic kilometers) or 2.5 billion tons (2.27 billion metric tons) assuming a deposit wide average of 20% K2O.

Potash is confined to the northern part of the basin where bedded salt reaches its maximum thickness (Rauzi, 2000). The salt appears to have formed by desiccation of saline mud flats and salt pans of an inner sabkha (supra-tidal environment in arid climates). The occurrence of potash near the top of the salt deposit may be due to the relative solubility of potash and salt during the evaporation of sea water across the sabkha. Repeated incursions of sea water appear to have preferentially dissolved and re-precipitated the potash thereby separating and concentrating the potassium from the halite.  In the 1960s and 1970s, Arkla Exploration Company and Duval Corporation drilled more than 100 holes to delineate the potash in the Holbrook salt basin. Only five

Figure 2. Map showing thickness of potash in the Holbrook salt basin, Apache and Navajo Counties, Arizona. Contour interval is 10 ft. Note former helium producing area near northeastern extent of potash deposits and LPG-storage facility near the northwestern extent.

holes  were drilled through the entire thickness of salt but 127 holes were drilled into the upper 100 to 300 ft of salt where potash is present. Most holes were cored through the upper 100 ft of salt to get direct information about the nature of the potash deposits. Arkla and Duval reported the presence of potassium minerals sylvite (KCl), carnallite (KMgCl3), and polyhalite (K2Ca2Mg(SO4)4·2H2O) in the main potash “pay zone.” Scattered blebs and traces of potash persist to about 30 ft below the main potash “pay zone.” Well logs, samples, and core descriptions from the potash drilling are available in the well files of the Arizona Oil and Gas Conservation Commission at the Arizona Geological Survey in Tucson.To date, there has been no commercial production of potash in Arizona by conventional or solution mining even though drilling by late 1965 indicated about 450 million tons of ore-grade K2O covering an area of 80 square miles (Cox, 1965). Cox estimated that 100 million tons of at least 60% product were economically recoverable. By early 1966, Arkla estimated a potential of more than 285 million tons of nearly 20% average grade K2O underlying its lease block (Carr, 1966). Carr reported that the amount under Arkla’s prospective area exceeded the minimum economic requirement to justify mine and process installation by 540%. Overproduction of potash in Saskatchewan during a period of government subsidies and a global glut of potash in the late 1960s may have been the biggest factors in preventing development of Arizona potash at the time.
Another factor in the lack of exploitation of Arizona potash may be that the area underlain by potash in east-central Arizona is approximately centered under Petrified Forest National Park (PFNP; Figure 2). The Petrified Forest Expansion Act of 2004 substantially increases the area of potash underlying the park. The location of the potash under the PFNP will require a creative approach to full access and future development of Arizona’s strategic potash deposits. A combination of State Trust and public and private land is available for potential development east and southwest of the PFNP.

Figure 3. Diagrammatic structure section A-A’ trending northeast-southwest showing northern edge of Supai salt, extent of potash de-posits, and former helium producing area near the northeastern limit of the salt and potash deposits. Vertical scale exaggerated 65 times.

Figure 4. Diagrammatic structure section B-B’ trending northwest-southeast showing northern edge of Supai salt, extent of potash deposits, and storage well for liquefied petroleum gas (LPG) with cavern leached near the top of the salt deposits. Vertical scale exag-gerated 65 times.

Other Geologic Resource in the Holbrook salt basin
Helium: Helium was produced near the northeastern limit of the potash deposits from 1961 to 1976 (Figures 2 and 3). Wells in the Pinta Dome and Navajo Springs fields (Conley, 1974) produced nearly 700 million cubic feet of grade-A helium from the Permian Coconino Sandstone. Helium concentrations ranged up to 10% and averaged 8%, which is some of the richest helium-bearing gas ever produced. Spencer (1983) and Rauzi (2003) reviewed the geologic setting, production, and future potential of helium in Arizona.
Helium is vital in obtaining the extremely cold temperatures essential in cryogenic and superconducting technologies. Helium is also used for pressurizing and purging, welding cover gas, controlled atmospheres, leak detection, breathing mixtures, and filling blimps, weather balloons, and party balloons.

Hydrocarbon Storage: The bedded salt (halite) associated with the potash is used to form caverns to store liquefied petroleum gas (LPG). A cavern is formed by drilling a hole into the salt and pumping fresh water through steel pipe. The fresh water dissolves the salt and the resulting brine is pumped out of the hole. Some brine is stored at the surface for later use and some is pumped back into deep underground rock formations. The shape and size of the cavern is determined by controlling the amount and direction of fresh water pumped into the hole.
Enterprise Products operates the LPG-storage facility, which is about 20 miles east of Holbrook at Adamana (Figures 2 and 4). Propane and butane are the most common types of LPG. Most propane is used as fuel to heat homes in the winter whereas butane is commonly used to blend gasoline at refineries. The Adamana facility was first constructed in the early 1970s.
There are 11 storage wells at Adamana with a total capacity of about 90 million gallons. The top of the salt is about 900 ft below the ground surface. The caverns are leached about 75 ft below the top of the salt, have an average radius of 60 ft and height of 95 ft. Individual cavern volumes range from about 7 to 11 million gallons. The Adamana facility is served by the BNSF railroad (Rauzi 2000 and 2002).

Future
The time is right for potash development in Arizona. A creative approach will be necessary for exploitation, however, because of proximity to the PFNP. There also remains good potential for additional storage of LPG along the BNSF railroad, and for future helium discovery in the region. Many of the small structures in the area have yet to be drilled.

Cox, M.W., 1965, Holbrook potash deposits: private unpublished report dated September 22, 1965.

Conley, J.N., 1974, Pinta Dome-Navajo Springs-East Navajo Springs helium gas pools, Apache County, Arizona, well location map: Arizona Geological Survey Publication OG-14, www.azogcc.az.gov.

Rauzi, S.L., 2000, Permian salt in the Holbrook Basin, Arizona: Arizona Geological Survey Open-File Report 00-03.

Rauzi, S.L., 2003, Review of Helium production and potential in Arizona: Arizona Geological Survey Open-File Report OFR 03-5.

Sergeant, Barry, 2008, Potash for the green(ing) giant: article dated May 13, 2008, www.Mineweb.com.

Spencer, J.E., 1983, Helium resources and production in Arizona: Arizona Bureau of Geology and Min-eral Technology Fieldnotes, v. 13, no. 2, www.azgs.az.gov.