Arizona Geological Survey: Potash Case Study

Potash is an essential ingredient in fertilizers.

The term potash is loosely defined and refers to substances whose potassium content is expressed in terms of potassium oxide (K2O).

A study by the Arizona Geological Survey (AZGS) describes the size and distribution of a large potash deposit in the Holbrook Basin of east-central Arizona: “Potash and related resources of the Holbrook Basin, Arizona” (OFR-08-07).

Holbrook Basin Potash

The Holbrook Basin potash deposit is present in the Permian Supai Formation (270 – 220 Ma) of east-central Arizona. It was first characterized by extensive drilling in the 1960s.

Skyrocketing potash prices over the past several years have led to extensive leasing and mineral exploration in the area prompting AZGS geoscientist, Steve Rauzi, to reevaluate this resource (see figure: Thickness of potash in the Holbrook salt basin).

Extent, Volume, and Tonnage

The deposit underlies 600 square miles east of Holbrook, Arizona. The roof of the potash deposit is situated ~700 to 2000 feet below the ground surface; most of the deposit is found at about 1200 to 1300 ft deep. Maximum thickness of the potash is about 40 feet. Total volume estimates range from 5.68 to 6.45 cubic kilometers.

Reports of the average grade of potash range from 6% to 20%. Calculating tonnage for the entire deposit, assuming 6% and 20% grades, yields 682 million metric tons to 2.27 billion metric tons, respectively.

Proximity to Petrified Forest National Park

Approximately 20% of the deposit underlies Petrified Forest National Park and is closed to mining. An additional 30% underlies lands included in the Petrified Forest Expansion Act of 2004. The remaining 50% is a combination of private, State Trust, and Native American Tribal lands.

At present, the US Geological Survey estimates U.S. potash resources at six billion tons, the bulk of which is found at depths greater than 6000 feet. U.S. farmers used 5.2 million metric tons of potash in 2007; 80% of which was imported. Currently, U.S. potash production is limited to Michigan, New Mexico (largest U.S. producer), and Utah.

ADDITIONAL INFORMATION: For more information contact Arizona Geological Survey geoscientist, Michael Conway (fmconway@email.arizona.edu).

Potash Resources in Arizona


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