A team of geologists and materials scientists from the University of Erlangen-Nuremberg in Erlangen, Germany, has found a new way of finding previously untapped rare earth deposits.

Researchers behind the new study suggest that contrary to what the name "rare earth metals" might suggest, these materials are actually distributed fairly equally in all parts of the world. They noted, however, that not all deposits are economically viable and can be extracted just as easily. It led them to propose a new technique in locating these deposits.

Researchers explain their new technique for finding rare earth metals in an article titled "Cumulate olivine: A novel host for heavy rare earth element mineralization," appearing in the journal Geology.

Rare Earth Oxides
(Photo: Peggy Greb, US department of agriculture, via Wikimedia Commons)
These rare-earth oxides are used as tracers to determine which parts of a watershed are eroding. Clockwise from top center: praseodymium, cerium, lanthanum, neodymium, samarium, and gadolinium.

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Finding Rare Earth Metals in Igneous Rocks

Researchers have examined rock samples from the Vergenoeg fluorite mine located in South Africa. It was here that they discovered fayalite crystals  - an iron-rich member of the olivine mineral group - deposited in sediments of granite-like magma potentially has rich amounts of heavy rare earth elements. Fayalite is a rock reddish-brown to black in color and is mainly used as a gemstone and a material for sandblasting processes. This mineral is available worldwide, mostly in igneous rocks, from volcanic activity and abyssal rocks, igneous rocks formed deep in the crust.

They also explained that olivine, the class of minerals where fayalite belongs, and its rare earth element systematics remain poorly understood. Using atom probe tomography maps, researchers verified the highest heavy rare earth elements in the fayalite's crystal lattice form. This integration into the lattice is facilitated by traces of lithium that act as the main charge balancer in the chemical structure.

Additionally, the German team used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) - an advanced analytical method that uses micro-sampling to provide high precision elemental analysis of solid materials - to discover that cumulate fayalite in the South African site's Paleoproterozoic Vergenoeg F-Fe-REE contains the highest recorded REE contents, reading HREE enrichment at about 6000x chondritic values.

"Since heavy rare earth elements are becoming increasingly scarce on the world market, the discovery of fayalite as a new potential source for locating new deposits of rare earth is extremely important for the economy," said Dr. Reiner Klemd from the Geozentrum Nordbayern at the University of Erlangen-Nuremberg.

Rare Earth Elements

Those called rare earth elements, or rare earth metals, belong to a set of 17 similarly structured heavy metals. According to the American Geosciences Institute, this set includes the fifteen lanthanides on the periodic table, plus yttrium and scandium.

Additionally, the US Geological Survey explains that these rare earth elements are used in a wide range of applications - high-tech consumer electronics, defense, navigation and communication systems, and more. It also reported that back in 1993, 38 percent of the world's supplies of these materials come from China, 33 percent from the United States, 12 percent from Australia, and five percent each from India and Malaysia. However, by 2011, China already accounts for 97 percent of the world's supplies of rare earth elements.


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