Volcanic-Derived Placers as a Potential Resource of Rare Earth Elements: The Aksu Diamas Case Study, Turkey

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.

The Effect of X-ray Energy Overlaps on the Microanalysis of Chevkinite (Ce, La, Ca, Th)4(Fe2+, Mg)2(Ti, Fe3+)3Si4O22 Using SEM EDS-WDS

“…It is appreciated that the standards should ideally reflect the composition of the unknown mineral analysed, but for the chevkinite mineral, this is challenging. For this purpose, two types of standards have been used: manufactured REE glasses standards [29] and BGS in house standard, augite pyroxene, which are both frequently analysed by CAMEXA SX50 electron microprobe and SEM-EDS systems at BGS in the past [7,16,30]. Procedures used for the SEM-EDS quantitative microanalysis were in line with those recommended by the ASTM Standard [31].…”

“…The multi-technique approach is important to the thorough understanding of materials and processes at micro-and nano-scale, from which inferences on large-scale systems and processes can be made. Contextual data for the chevkinite analysed here is presented in Deady et al [7].…”

“…The chevkinite grains analysed in this study were from the Aksu Diamas iron-REE placer deposit in Turkey [7]. Samples were sieved to collect the 125-250 μm size fraction.…”

“…Here, we provide details of the microanalytical investigation of chevkinite-(Ce). Samples originated from the heavy mineral placer deposit Aksu Diamas in Turkey, which has been assessed for potential REE extraction as a by-product of magnetite production [7]. The REE content in chevkinite is dominated by the LREE [8], making chevkinite a potential future resource of the LREE [7].…”

Editorial for Special Issue “Rare Earth Deposits and Challenges of World REE Demand for High-Tech and Green-Tech at the Beginning of the 3rd Millennium”

“…Sedimentary-hosted REE accumulations offer potential for greater ease of extraction, but may be lower in concentration than bedrock hosted deposits, or face issues of radioactivity when derived from the weathering of granitic protoliths. Deady et al [19] investigated these issues in relation to volcanic derived placers at Aksu Diamas, Turkey, finding that a range of REE and REE-bearing minerals are concentrated with Quaternary sediments derived from weathering of alkaline igneous rocks. Rudmin et al [20] extend the study of sedimentary deposits to those produced by authigenesis, identifying processes for the formation of REE phosphates in ooidal ironstones and discussing the implications for potential future processing.…”