A growing global concern about supplies of "rare earth" elements for computers, hybrid cars and other staples of everyday life has sparked exploration in Arizona and across the Southwest.

A Tucson mining company is looking for the elements on state and federal lands near Tombstone.

An Australian firm found some in La Paz County near California, but ultimately decided the deposit wasn't rich enough to be mined at today's prices.

In New Mexico, three drilling projects are under way or done.

The periodic table includes 17 rare earth elements. They're contained in minerals and are in great demand as critical components of high-tech products and electronics.

State geologists for Arizona and New Mexico and a top University of Arizona mineral researcher say potential exists for finding economically viable deposits here - possibly with the state's extensive copper deposits. One reason for their optimism: Arizona has some rock formations similar to those where rare earth elements have been found in New Mexico.

A push to find rare-earth elements in the United States and other countries has accelerated since 2010, when China imposed limits on the amount of rare-earth elements it exports. Although it controls only 36 percent of known global rare-earth reserves, China produces about 95 percent of rare earths used worldwide due to low labor costs, abundant supply and lax environmental regulations, says the U.S. Environmental Protection Agency.

The export limits have dramatically boosted global rare-earth prices and made many countries, including the U.S., seek other sources.

not much exploration in past

Historically, Arizona hasn't had much rare-earth exploration activity. The conventional wisdom has been that the elements aren't likely to be found here in large enough quantities that it makes sense to mine them, said Lee Allison, director of the Arizona Geological Survey.

A federal rare-earth researcher in Tucson and a mining industry consultant are guarded or skeptical about Arizona's prospects. But the federal researcher, Keith Long, a U.S. Geological Survey official who has written two rare-earth studies, says a full assessment would be wise.

Arizona hasn't done surveys to find out if mining rare-earth elements would make sense in the state. New Mexico, by contrast, has financed major surveys at the rate of $50,000 to $100,000 a year since 1985.

"Looking from the global perspective, which is how USGS looks for things, Arizona is not high on the list of places to look," said Long, a geologist and mineral economist. "But from a state perspective, knowing what you have is important information."

exploration is up

Activity here is picking up.

• Tucson-based Liberty Star Uranium & Metals Corp. has reported finding four of 17 known rare-earth elements in soil and vegetation samples from a deposit just southeast of Tombstone where the company was looking for copper. It has federal mining claims and state mineral exploration permits covering about 9,000 acres.

• Australia-based AusAmerican Mining Corp. has discovered rare-earth deposits on federal land in western Arizona's La Paz County. But after finding very low grades, it decided the project wasn't worth pursuing for now.

• Allison, Arizona's top state geologist, said two large companies are evaluating rare-earth deposits to see if they're worth mining.

• The three New Mexico drilling projects are at the Texas border, and in central and south-central New Mexico. Exploration also is occurring near Taos, said Virginia McLemore, a senior economic geologist at New Mexico Tech in Socorro.

• In Southern California near Nevada in late 2010, Colorado-based Molycorp Inc. reopened the Mountain Pass Mine, which had been closed for eight years after operating for 50. It's the only mine for rare-earth minerals operating in the U.S. and one of 10 globally. It employs about 450 people and expects to be producing roughly 19,500 tons of rare-earth-oxide materials a year by mid-2013.

new mexico a source

Mineral economist Long's 2010 study identifies about a dozen states, including New Mexico, as principal sources of rare earth deposits in the U.S.

Arizona does not make his list because it lacks the type of rocks likely to contain rare earth minerals. New Mexico, however, has the Rio Grande Rift, a large fault that exposes weakness in the Earth's crust and makes it easier for molten rocks to intrude upward.

Long sees limited potential for Arizona rare-earth elements in Precambrian rock formations near Prescott. As for the Tombstone elements under investigation by Liberty Star, he said the company hasn't released enough information to assess their significance.

Liberty Star president and CEO James Briscoe declined to discuss his company's findings beyond what's in the company's news releases. They say geochemical sampling found one heavy rare earth element - considered rarer and more valuable - and three light rare-earth elements. Liberty Star says it has a rare earth "anomaly" there - a deposit it didn't expect to find - covering at least 7 to 9 square miles.

But Garrett Hatch, a partner in an Illinois-based metals research company, said rare earth deposits he is aware of in Arizona and New Mexico "are not what I would call world-class."

And even if good deposits are found, he said, "you've got to do lots of drilling, lots of analysis, and you've got to figure out can you process the mineral? A lot of this can take several years."

arizona being studied

When New Mexico Tech's McLemore spoke last November at an Arizona Geological Society meeting, she said rare-earth deposits might be found here if more was done to look for them.

She disagreed with USGS researcher Long on a key point. She said New Mexico's rare earth-bearing rocks are not related to the Rio Grande Rift but to a separate belt of alkaline-based igneous rock along the Rocky Mountains that's exposed in uplifts bordering the rift. The rare-earth deposits are 450 million years old compared with 35 million years for the Rio Grande Rift, she said.

She said she sees potential for rare earth minerals in Arizona in pegmatites, coarse-grained, igneous rock deposits containing interlocking crystals that are typically found in granite formations. Many central Arizona mountains lie in a "pegmatite belt," running from California east and south to Phoenix and Tucson, she said.

Mary Poulton, director of UA's Lowell Institute for Mineral Resources, said its researchers believe strong geologic associations could exist between some rare earth and copper deposits.

"We know there's rare earth mineralization in the state," Poulton said. "We don't know how many elements exist per deposit, but certainly the geological environment that created copper deposits also has the potential to include rare earths."

Her department and two others are conducting studies related to the processing of rare earth elements. The others are Chemistry as well as Soil, Water and Engineering, she said.

She said that for competitive reasons, the research - financed by a mix of private and public sources - will remain confidential until it's finished in about two years.