Did you know there are salt mines in Arizona? Arizona has several large rock salt deposits (see story from AZcentral about a large salt mine in Glendale). Salt is recovered by solution mining where water is pumped into the deposit to dissolve the salt and the resulting brine is put into solar evaporation ponds. This salt is used for industrial applications. The cavity left by solution mining can be used to store liquid petroleum gas (LPG) as is done near Phoenix and Holbrook, and could be used to store natural gas. Otherwise the cavity remains filled with water. The Arizona Geological Survey (AZGS) notes “Arizona may be the only state in the west with salt bodies large enough for storage of LPG and natural gas between the main sources of supply and demand. The high deliverability of natural gas stored in salt caverns is a distinct advantage over storage in depleted oil and gas fields and aquifer reservoirs.”
AZGS Circular 30 has detailed descriptions of salt deposits in Arizona. The map below shows the location of Arizona’s salt, known deposits in green, potential deposits in orange.
Rock salt deposits result from evaporation of lakes like the Great Salt Lake of Utah and from evaporation of much smaller closed basins. There were many such lakes in Arizona. Salt may be associated with other evaporite minerals such a gypsum and anhydrite, both calcium sulfates.
Tertiary-age salt deposits in the valleys of the Basin and Range province tend to be the thickest, while the older Permian-age deposits on the Colorado Plateau are the most widespread. According to AZGS, “The Tertiary salt in Maricopa County near Luke Air Force Base west of Phoenix and in Mohave County north of Kingman is at least 6,000 ft thick and may be 8,000 to 10,000 ft thick or more. These deposits cover tens of square miles. Even though the salt deposits in the Holbrook Basin are not as thick as the salt in the Basin and Range Province, they have an aggregate thickness of 655 ft southeast of Holbrook and cover a much larger area. Permian salt underlies more than 3,500 square miles in southern Navajo and Apache Counties.”
Rock salt crops out in places along the Verde River, and precipitated salt occurs along the Salt River (that’s how it got it’s name).
The known deposits in Arizona were encountered when drilling for other things. Exploration information about known and potential salt deposits comes mainly from gravity surveys and modeling, seismic surveys, and few drill holes. Major salt deposits are associated with gravity lows (less dense than surrounding rock) and with tightly-spaced gravity contours (indicating a basin). There are four gravity lows in the Tucson Basin which AZGS says may coincide with four sub-basins that could hold salt.
I found this story by following the Arizona Geological Survey on Facebook: their page is here.