Abstract
Rare earth elements (REE) are essential raw materials used in modern technology. Current production of REE is dominated by hard-rock mining, particularly in China, which typically requires high energy input. In order to expand the resource base of the REE, it is important to determine what alternative sources exist. REE placers have been known for many years, and require less energy than mining of hard rock, but the REE ore minerals are typically derived from eroded granitic rocks and are commonly radioactive. Other types of REE placers, such as those derived from volcanic activity, are rare. The Aksu Diamas heavy mineral placer in Turkey has been assessed for potential REE extraction as a by-product of magnetite production, but its genesis was not previously well understood. REE at Aksu Diamas are hosted in an array of mineral phases, including apatite, chevkinite group minerals (CGM), monazite, allanite and britholite, which are concentrated in lenses and channels in unconsolidated Quaternary sands. Fingerprinting of pyroxene, CGM, magnetite and zircon have identified the source of the placer as the nearby Gölcük alkaline volcanic complex, which has a history of eruption throughout the Plio-Quaternary. Heavy minerals were eroded from tephra and reworked into basinal sediments. This type of deposit may represent a potential resource of REE in other areas of alkaline volcanism.
Highlights
Rare earth elements (REE) are considered as critical metals, due to their widespread use in many “green” technologies
Between the years 2011 and 2015, a five-fold increase in delineated global REE resources was identified—with almost 40% of these in Europe (Greenland, Sweden, Germany and Turkey) [10]. The majority of these discoveries are in carbonatites and alkaline rocks, there is an ongoing emphasis on research into alternative sources and the genesis of other types of REE deposits [11,12]
((Ce,La,Ca,Th)4 (Fe2+,Mg)(Fe2+,Ti,Fe3+ )2 (Ti,Fe3+ )2 (Si2 O7 )2 O8 ) is found amongst titaniferous magnetite, ilmenite, haematite, rutile, zircon, monazite and pyroxene [30]. These heavy minerals are derived from volcanic tuffs, from the nearby Latium volcano, Alban Hills, that have been reworked into beach sand deposits [30,31]. This paper describes another example of a placer that we propose is derived from extrusive volcanic sources, the Aksu Diamas deposit at Çanakli in the Burdur Province of Turkey
Summary
Rare earth elements (REE) are considered as critical metals, due to their widespread use in many “green” technologies. Primary global resources of the REE [1] are dominantly hosted in carbonatite [2]. The main deposits currently producing REE are carbonatite-hosted, including Bayan Obo in China [4,5], Maoniuping in China [6,7] and Mount Weld in Australia [2]. From the 1980s, China became the world’s largest producer of REE, and by 2010 about 95% of the global supply originated from China [8]. The majority of these discoveries are in carbonatites and alkaline rocks, there is an ongoing emphasis on research into alternative sources and the genesis of other types of REE deposits [11,12]. Examples of alternative REE sources include ion adsorption clays [13], alumina production waste [14], off-shore heavy mineral sands [15], deep ocean
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