Evaluating Rare Earth Element Deposits
“The Chinese Bayan Obo deposit is the main world producer of LREE which are dominantly hosted in bastnaesite and monazite, and lesser fluoro-carbonates, within a carbonatite-related hydrothermally replaced dolomitic marble. Niobium (Nb) is a valuable by-product. Tonnages are reported to be 48Mt at 6% TREO and 2.2 million tonnes ("Mt") at 0.13% Nb (Kynicky, et al, 2012.Since the early 1970s, lateritic deposits, generally 8-10 metres (“m”) thick, in southern China have been recognised as being enriched in HREE and constitute an easily recoverable resource (Kynicky, et al, 2012; Chi and Tian, 2008). Various terms have been used to describe this style of mineralisation including “ionic clays”, “elution-deposited” ore and “ion-adsorbed” (Chi and Tian, 2008). These REE are derived from secondary processes and are loosely bound via adsorption processes within clay minerals. Although these ores are low grade (eg 0.05-0.2% REO) they are near-surface and have low extraction and processing costs.Reporting of resource tonnages of this style of REE mineralisation is somewhat ambiguous, with 10Mt suggested as a guide (Kynicky et al, 2012) though Chi and Tian (2012) suggest that “prospective reserves” in Southern China amount to 50MtAEGC 2018, Sydney Australiaparts per million (ppm) for the individual elements. REO the appropriate oxide formulae. REE typically occur in 2 with quoted grades between 0.12-0.19% REO consisting of 57-92% REO in the ionic form (Chi and Tian, 2012). This style of mineralisation has been regarded as unique (Chi and Tian, 2008, p 2) though, as the Tantalus project in Madagascar and the Serra Verde project in Brazil demonstrate, it is likely that similar deposits exist elsewhere.”
“Some corporate proponents seek to highlight their rare earth deposits by emphasising the high ratio of the generally more valuable HREO to LREO compared with LREO-enriched deposits. These apparently high ratios may, however, be largely due to yttrium being part of the HREO. Yttrium may dominate a particular mix of HREO though its value generally ranks below Pr, Nd, Eu, Tb, Dy, Tm, Yb and Lu. A further consideration is that mining and separating REO from a higher grade LREO deposit may be a more cost-effective source of HREO than low grade, HREO-enriched deposits. For example, Weng et al., (2013) quote two REE deposits with resource grades of 640 ppm and 292 ppm as possible significant resources of the future by virtue of their HREO contents. These deposits, however, will have to compete with established and emerging operations with TREO grades between 10 to 100 times higher.”
http://sydney2018.aseg.org.au/Documents/Tuesday%20Abstracts/T4.3E.pdf
Ann: Drilling Expands Mt Stirling REE Footprint, page-7
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