Study identifies supervolcanoes as new source of lithium

Updated 2017-08-17 10:31:15 Xinhua

A new study identifies lake sediments preserved within some ancient supervolcanoes as a source of lithium, which is used to make the lithium-ion batteries powering mobile electronics.

Published Wednesday in Nature Communications, the study details a new method for locating lithium in supervolcanic lake deposits. Currently, most of the silvery-white metal comes from pegmatite deposits in Australia and brine deposits in high-altitude salt flats in Chile.

Supervolcanoes can produce massive eruptions of hundreds to thousands of cubic kilometers of magma. As the enormous loss of magma causes the roof of the chamber to collapse following eruption, they appear as huge holes in the ground, known as calderas, rather than the cone-like shape typically associated with volcanoes.

The hole often fills with water to form a lake. Over tens of thousands of years, rainfall and hot springs leach out lithium from the volcanic deposits. The lithium accumulates, along with sediments, in the caldera lake, where it becomes concentrated in a clay called hectorite. Such supervolcanoes pose little risk of eruption because they are ancient.

To identify which supervolcanoes offer the best sources of lithium, researchers led by Gail Mahood, a professor of geological sciences at Stanford University's School of Earth, Energy & Environmental Sciences, measured the original concentration of lithium in the magma, because it is very difficult to measure directly the volatile element that easily shifts from solid to liquid to vapor.

To reach tiny bits of magma trapped in crystals during growth within the magma chamber, the researchers sliced through the host crystals to expose preserved magma blebs, which are 10 to 100 microns in diameter, then analyzed them with the Sensitive High Resolution Ion Microprobe, or SHRIMP, in the SHRIMP-RG Laboratory at Stanford Earth, which is able to measure the isotopic and elemental abundances in minerals at a 30 micrometer-scale.

The team analyzed samples from a number of volcano sites, mostly in the United States, and determined that lithium concentrations varied widely as a function of the tectonic setting of the supervolcano.

And by analyzing other trace elements to determine their correlations with lithium concentrations, the researchers discovered that the trace elements can be used as a proxy for original lithium concentration: for example, greater abundance of easily analyzed rubidium in the bulk deposits indicates more lithium, whereas high concentrations of zirconium indicate less lithium.

"We can essentially use the zirconium content to determine the lithium content within about 100 parts per million," lead author Thomas Benson, a recent PhD graduate at Stanford Earth, who began working on the study in 2012, was quoted as saying in a news release. "Now that we have a way to easily find more of these lithium deposits, it shows that this fundamental geological work can help solve societal problems - that's really exciting."

The researchers said exploring supervolcanoes for lithium would diversify its global supply.

Since its discovery in the 1800s, lithium has largely been used in psychiatric treatments and nuclear weapons. Beginning in the 2000s, lithium became the major component of lithium-ion batteries, which today provide portable power for everything from cellphones and laptops to electric cars.

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