Several South Australian kaolin clay mine developers have stumbled across a nice bonus in recent months – potentially commercial amounts of rare earth elements (REEs).
The relationship between REEs and kaolin-containing clays has been known about for a long time and in fact a large amount of Chinese REEs are being produced from ion-adsorption clay deposits often associated with kaolin.
This type of mineralization is rarely found outside of China and is generally considered to be some of the cheapest and most readily accessible sources of heavy rare earths. In recent years, South Australia has started to emerge as a potentially significant producer of kaolin and now it looks like the state could become a new source of highly valuable REEs.
Kaolin itself is growing in importance as a critical new element in the green energy future. The most important of the industrial clays in terms of both consumption and value, its properties of fine particle size, platy shape, inertness, non-toxicity, and high brightness and whiteness make it a most versatile mineral, with applications in a wide variety of industries.
The largest single market, taking ~40% of production, is the paper industry where kaolin is used to fill the spaces between cellulose fibres, and as a coating agent to produce high gloss paper with good printability. Other uses include clay-based ceramics and refractories, white cement, fibreglass, and fillers and extenders in rubber, paint, plastic, and adhesives. Recently it has been identified as having significant potential in the areas of solar panel construction and the manufacture of “green steel”.
Kaolin’s growing demand and the potential of much saught after REEs has certainly attracted attention to the stock of Australian junior minerals explorers iTech (STO: ITECH), ChemX Materials (ASX: CMX) and Andromeda Metals (ASX: AND).
iTech
iTech has just commenced second stage metallurgical trials at its Caralue Bluff high purity kaolin and clay hosted REE project on the Eyre Peninsula in South Australia.
In early October this year, the company received the results from the first stage of diagnostic metallurgical test work at the Caralue Bluff Project. The aim of the test work was to determine if standardized leach conditions for ionic clay hosted rare earths would readily liberate the rare earth element hosted in the high purity kaolin clays at Caralue Bluff.
Tests were undertaken at pH 4 with 0.5M ammonium sulphate and sulphuric acid to assess the ionic component and at pH 1 with just sulphuric acid to assess the colloidal component. All tests were undertaken at atmospheric pressure and temperature.
Maximum recoveries of the four magnet REEs (Nd, Pr, Dy, and Tb) range between 28-65% which suggest the potential to increase extractions with variations to the leaching conditions.
In consultation with experts at the Australian Nuclear Science Organisation (ANSTO), iTech has now commenced stage two leaching trials with the aim of increasing recoveries by testing the effects of increasing acid concentration and/or increasing leaching temperature. Another option the company will be investigating is to leach the beneficiated kaolin fraction (-45 micron) which has shown significantly increased REE grades.
“Clay hosted REE projects typically have complex metallurgy, and it normally takes several iterations of test work to ‘crack the code’ for good recoveries.
“Having a high purity kaolin as the host to REE mineralization at Caralue Bluff allows iTech to explore a range of metallurgical techniques to recover the REEs into solution while keeping impurities at low levels,” managing director, Mike Schwarz, said.
The Australian Nuclear Science Organisation (ANSTO) is undertaking a testwork programme to determine the optimum conditions for liberating the REE from the clay host materials
Andromeda Metals
Andromeda Metals has identified elevated total rare earth oxides (TREO) in assays from its Bronze Whaler prospect. The company is excited about the regional opportunity for ion-adsorption deposits (IAD) and it is assessing the potential that deposits of the Great White Kaolin Project share several similarities to Chinese IADs, which are the world’s primary source for heavy rare earth elements.
The company elected to re-test samples from Great White following the identification of elevated REEs at the Bronze Whaler prospect in handheld xrf results. All samples from a 2019 Bronze Whaler drilling programme were subsequently submitted for analysis for the full suite of REEs.
Subsequent assay results included 18m @ 1752ppm TREO and 5.0m @ 2256ppm TREO.
ChemX
ChemX Materials recently revealed that significant REE potential has been confirmed at its Kimba Kaolin-REE project on the Eyre Peninsula.
Final assays from kaolin-REE targets at the company’s Eyre Peninsula tenements identified widespread REEs across the tenements delivering high grades of TREO plus yttrium.
Managing director, David Leavy, said significant intercepts came from a total of 363 sub 45-micron TREO assay results across 80 drill holes. The concentration of TREO in parts per million (ppm) ranged from 19ppm (low) to 2468ppm (maximum) with the average and median as 505ppm and 404ppm, respectively.
“These assay results confirm a significant body of clay hosted REE within ChemX’s tenements and will assist to rapidly advance our tenement geological modelling programme,” Mr Leavy said.
“As an integral part of the REE study programme, the Australian Nuclear Science Organisation (ANSTO) is undertaking a testwork programme to determine the optimum conditions for liberating the REE from the clay host materials.
“These REE results, together with several other regional discoveries are very positive for future development options.”
Samples collected from the Kelly Tank, Bunora East and Bunora South prospects, comprised predominantly kaolin clay associated with silica as quartz sand, and mica with variable quantities of iron oxides, were screened at sub 45 micron and assayed.
“The results demonstrate the strong potential of the company’s Eyre Peninsula tenements for ionically adsorbed REE,” Mr Leavy said.
Further results interpretation is in progress and will inform future exploration activities.
“The relevance of REE being associated with kaolin clay is that; they are loosely bonded to the surface of the clay particles and can be readily displaced by simple low-cost chemical solutions which can be further processed to recover the individual rare earth oxides,” Mr Leavy said.
“ChemX has engaged ANSTO to conduct diagnostic testwork for determination of potential REE extractability, with the results of this programme expected late 2022.
“Once received, this report will inform ChemX on feasible flowsheet optionality and serve as a key input to future downstream processing studies.”
