TIDMEST
RNS Number : 9179C
East Star Resources PLC
16 June 2023
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16 June 2023
East Star Resources Plc
("East Star" or the "Company")
Rare Earth Metallurgical Results
East Star Resources Plc (LSE:EST), which is defining mineral
resources in Kazakhstan for the energy revolution, announces the
results of the mineralogy and leaching studies of eight samples
from the Talairyk rare earths project in Kazakhstan. The test work
was the result of an academic study conducted by the School of
Applied Sciences, University of Brighton, UK, to understand the
minerology of a representative sample from the Reverse Circulation
drilling conducted at the Talairyk deposit by East Star in October
2022.
Highlights of the study:
-- The mineralogy and total rare earth elements (TREE)
concentrations of the Talairyk samples are comparable to ion
adsorption deposits globally with a kaolinite-dominated mineralogy
and 815-5,185 ppm TREE
-- Single phase leach results from ammonium sulphate have lower recovery with peak results (pH4) demonstrating 7.5% recovery of NdPr meaning the leachability of the tested samples is not representative of proven ion adsorption clay deposits
-- Peak results from sulphuric acid single phase leach
demonstrated 26%-34% NdPr, 14-18% Dy and 18-21% Tb recovery
suggesting further test work is required to assess if there is a
potential route to commercial extraction
-- Sequential leach tests resulted in an average total recovery
of 90.6% of Neodymium and Praseodymium ( NdPr), 90.7% Terbium (Tb)
and 73.8% Dysprosium (Dy) demonstrating that the majority of REEs
are liberated from leach resistant silicate materials
-- The highest percentage leached in sequential leaching
experiments in most cases was by a strong reductant followed by a
strong acid, suggesting REEs are held in oxides and reactive
phosphate minerals, with rare earth elements also held in
carbonates in some samples
-- The Company is consulting with metallurgical specialists to assess the next phase of testing
Alex Walker, East Star CEO, commented:
"Sequential leach testing clearly demonstrates that a majority
of REEs have been liberated from primary minerals during the
weathering process and are now associated with other mineral
phases. Our understanding of the minerology and potential for
economic extraction of rare earth elements from the Talairyk
deposit has grown significantly and, while not definitive, it will
allow us to plan a low-cost assessment of what additional test work
is required to identify if an economic process to leach rare earth
elements from the weathered material is possible.
"We would like to express our gratitude to Dr Martin Smith of
the University of Brighton who led this study on our behalf."
A full copy of the report is available in Annex A to this
announcement.
For further information visit the Company's website at
www.eaststarplc.com , or contact:
East Star Resources Plc
Alex Walker, Chief Executive Officer
Tel: +44 (0)20 7390 0234 (via Vigo Consulting)
Peterhouse Capital Limited (Corporate Broker)
Duncan Vasey / Lucy Williams
Tel: +44 (0) 20 7469 0930
Vigo Consulting (Investor Relations)
Ben Simons / Peter Jacob
Tel: +44 (0)20 7390 0234
About East Star Resources Plc
East Star Resources is focused on the discovery and development
of strategic minerals required for the energy revolution. With an
initial nine licenses covering 1,321.5 km(2) in three mineral rich
districts of Kazakhstan, East Star is undertaking an intensive
exploration programme, applying modern geophysics to discover
minerals in levels that were not previously explored. The Company
also intends to further expand its licence portfolio in Kazakhstan.
East Star's management are based permanently on the ground,
supported by local expertise, and joint ventures with the state
mining company.
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The person who arranged for the release of this announcement was
Alex Walker, CEO of the Company.
Competent Persons Statement
Mineral deposit characterisation within the report has been
reviewed and approved by Professor Martin Smith CGeol FGS, FMS.
Professor Smith is Professor of Geochemistry, a geologist,
geochemist and mineralogist, and is the Associate Dean for Research
and Enterprise in the School of Applied Sciences at the University
of Brighton. He has 25 years' experience in geochemistry applied to
problems in mineral deposit geology, hydrogeology and environmental
mineralogy, and has been a Chartered Geologist with the Geological
Society of London since 2012. Professor Smith has sufficient
experience with ionic adsorption rare earth deposits and mineral
deposit characterisation to make the assessment associated with
this announcement in the form and context in which it appears.
ANNEX A
Report to East Star on mineralogy and leaching behaviour of
Weathering Profile samples from Kazakhstan
Prof. M. Smith, P. Lyons, M. Grove.
School of Applied Sciences, University of Brighton, U.K.
1. Introduction
This report presents the results of mineralogical and leaching
studies of weathered rock samples from Kazakhstan provide by East
Star. Bulk rock data obtained by 4 acid digestion was provided for
comparative purposes by East Star for these samples. Eight samples
were provided and subjected to three single stage leach procedures
(using ammonium sulphate, magnesium chloride and sulphuric acid at
pH2). The residues of the ammonium sulphate leach were then
subjected to a further 4 stage sequential leach procedure modified
from the BCR701 standard technique (Rauret et al., 2017)
The aims of the study where to identify the leachable
concentration of REE+Sc+Y, to assess the likely mineral hosts, and
to provide data to test if easily leachable REE+Sc+Y might be
present in the weathered soil profiles. Throughout this report we
define light REE (LREE) as the elements from La to Eu, and heavy
REE (HREE) as the elements Gd to Lu plus Y. In addition we report
uranium and thorium concentrations in the leach solutions as
potential deleterious elements.
2. Methods
The mineralogy of samples was determined by X-ray Diffraction
(XRD) at the University of Brighton using a Rigaku Miniflex
diffractometer, with an accelerating voltage of 40kV and beam
current of 35nA. Samples were irradiated on a spinning stage in
deep well powder mounts with a step size of 0.01deg and a count
time of 10secs per step, over an angular range of 5-70deg 2theta.
Data were analysed using the Rigaku SmartLab software and the
Powder Diffraction Data File 2014.
For single stage leaching tests 1 g of sample was weighed, and
then leached in 40ml of leach solution for one hour in an 'end over
end' shaker. The solutions used were magnesium chloride at pH6
(leaches adsorbed metals with minimal carbonate dissolution,
ammonium sulphate at pH4 (the first stage of the BCR701 method
leach below), and sulphuric acid at pH2 (strong acid leach) - for
each solution samples were shaken for 1 hour. The 8 samples were
sequentially leached using the solid residue from the ammonium
sulphate leach experiment, following a modified version of the
BCR701 standard technique (Rauret et al., 2017). In each case 1g of
dried, ground sample was leached with the following sequence:
-- Ammonium sulphate at pH4 for 1 hour - exchangeable cations on
clay minerals, and fine grained, reactive carbonates. It is also
the main leach used in industrial ion adsorption deposit
leaching
-- Acetic acid at pH 2.4 for 16 hours. This is a weak acid leach
which will remove reactive carbonates
-- Hydroxylammonium chloride at pH1.5 for 16 hours. - This will
reduce reactive iron oxides and leach the contained cations, so
indicates the iron oxyhydroxide bound portion
-- Hydrogen peroxide heated at 80degC, followed by ammonium
acetate at pH 2 for 16 hours to remove oxidizable material
(sulphides and organic matter)
-- Concentrated Nitric acid at pH <1 for 16 hours. This is a strong acid leacH
In each case samples were leached in an end over end shaker,
then centrifuged at 3000rpm before being decanted to a new
centrifuge tube. The resulting leach solutions were analysed by
ICP-MS using an Agilent 7900 ICP-MS, in He gas collision cell mode,
using online addition of rhodium as an internal standard.
Calibration was carried out using solution standards (Inorganic
Ventures standard solution CCS-1, containing all REE, Sc, Y, U and
Th). Standards were matrix matched to unknowns using the stock
lixiviant solutions and diluted with 2% nitric acid to give
calibration solutions at 0, 1, 10, 100 and 500ppb. Leachate
solutions where diluted to 1125x for all leach solutions, and 1250x
for hydroxylammonium chloride solution prior to analysis. There are
no certified reference materials for leaching experiments for the
REE, but procedural blanks were typically below 0.1ppb in the
analysed solution (0.1ppm equivalent in the lixiviant) and
calculated analytical standard values were typically within 5% at
500 and 100ppb and 10% at 10 and 1ppb. Yttrium is shown as a pseudo
lanthanide with atomic mass between Dy and Ho throughout.
3. Results
3.1 Mineralogy
The results of XRD determination of mineralogy are shown in
Figure 1. The dominant mineralogical components at all levels in
the samples are quartz (SiO(2) ), muscovite/illite ( KAl(2)
(AlSi(3) O(10) )(F,OH)(2) ) and Kaolinite ( Al(2) Si(2) O(5)
(OH)(4) ). Samples deeper in the profiles (18-24cm) have relict
K-feldspar. A single sample had a detectable REE-phosphate mineral
(Monazite - REE(PO(4) )), but this was very close to the detection
limit for the technique (1% by mass). Sample TLR029 4-6 potentially
contained calcium zeolite (chabazite-heulandite series). The
mineralogy is very similar to that reported for ion adsorption
deposits in Madagascar and China (Sanematsu and Watanabe, 2016;
Estrade et al., 2019; Li et al., 2019).
Quartz Muscovite/illite Kaolinite K-feldspar Monazite Zeolite Total
-------------- ------- ----------------- ---------- ----------- --------- -------- ------
TLR001 6-10 38.8 15.60 45.6 100
TLR001 14-18 41.7 27.5 30.8 100
TLR010 5-8 68.4 18.8 12.9 100
TLR010 8-10 74.7 20.1 5.2 100
TLR010 18-22 43.3 15.7 14.5 26.5 100
TLR011 24-28 12.3 76.3 7.5 2.9 1 100
TLR017 24-28 64.4 19.9 15.7 100
TLR029 4-6 27.2 16.3 31.2 6.9 18.4 100
-------------- ------- ----------------- ---------- ----------- --------- -------- ------
Table 1: Mineral compositions of samples determined from XRD
using the RIR method
Figure 1: results of XRD measurements of sample mineralogy
3.2 Bulk REE contents
Figure 2: Bulk REE+Sc+Y+U+Th contents of samples from data
provided by East Star
Bulk rock REE contents determined by 4 acid digestion and ICP-MS
were provided by East Star. The data are presented in Table 2 and
are shown as chondrite normalised REE patterns in Figure 2.
Chondrite normalisation is used as the natural concentrations of
the REE vary dramatically between elements and normalisation allows
trends to be visualised. The bulk REE contents of the samples
(815-5185mg/kg) are comparable to those from ion adsorption
deposits in weathered granitoids from China (740-3800mg/kg;
Sanematsu and Watanabe 2016; Li et al., 2017), Madagascar
(150-5400mg/kg; 85% of samples below 2000mg/kg; Estrade et al.,
2019) and Serra Verde, Brazil (resource estimate of 911Mt at
1200mg/kg; Pinto Ward, 2017). The samples are richer in LREE
(La-Eu, 387-4148mg/kg) than HREE (332-1037mg/kg) as is typical for
ion adsorption deposits except for restricted examples in China
which are HREE dominated (Li et al. 2017). The highest
concentrations are in sample TLR010 8-10 (5185mg/kg), where 50% of
the REE+Y concentration is made up of Ce. Cerium is redox sensitive
and can be concentrated in oxide rich zones of weathering profiles
effectively separating it from the other REE. This results in the
positive Ce anomaly relative to La and Pr in Figure 2. Negative Ce
anomalies typically occur deeper in profiles, where Ce is retained
in overlying oxidised layers. The overall REE patterns apart from
Ce are typical of granitic rocks.
3.3 Single stage leaching
The results of single stage leaching experiments are presented
in Tables 3 to 5 and Figures 3-7. Magnesium chloride solution at
pH6 leached from 0.8 to 5.9mg/kg total REE from the samples (Table
3). Ammonium sulphate solution a pH4 leached from 21 to 87mg/kg
total REE from the samples (Table 5). Sulphuric acid at pH leached
from 43 to 209mg/kg total REE from the samples (Table 4). The
highest leached concentration by sulphuric acid was 209mg/kg from
sample TLR011 24-28, which also corresponded to the highest
percentage leached of 17.4%. Sulphuric acid was by far the most
effective single stage leach solution tested. The relative
distribution of individual REE leached is shown in Figures 3-5. The
relative REE distribution does not change dramatically with leach
solution relative to the bedrock distribution, but there is a 100
fold increase in the amount leached from the highest pH (6) to the
lowest pH (2). This suggests that the REE are not significantly
present ion adsorbed form but are at least partly present in an
acid soluble mineral. The highest concentrations leached by
ammonium sulphate and sulphuric acid are in samples TLR010 8-10
(184 mg/kg in sulphuric acid) TLR010 18-22 (165mg/kg in sulphuric
acid) and TLR011 24-28 (209mg/kg in sulphuric acid). The highest
percentages leached in sulphuric acid were from TLR010 18-22 (20.3%
TREE) and TLR011 24-28 (17.5% TREE). These are not the highest
concentration samples, and the data indicate a difference in
mineralogy in these samples.
Figure 6 shows the concentration and percentage leached by each
solution in terms of total REE, LREE and HREE. Magnesium chloride
showed overall leached concentrations below 10mg/kg, and less than
1% of the bulk REE concentration. Ammonium sulphate leached less
than 10% of the bulk REE, with a slight preference for the LREE
relative to the HREE. Sulphuric acid also leached less than 10% of
the bulk REE for most samples, but up to 20% in two samples -
TLR011 24-28 and TLR010 18-22. Overall, the data are consistent
with a low proportion of clay adsorbed REE in the samples (less
than 10%), but with some REE (20-30%) hosted in a sulphuric acid
soluble LREE-bearing mineral in TLR011 24-28 and TLR010 18-22. This
could be a carbonate or fluorcarbonate (e.g. bastnaesite) mineral
but at a concentration below detection for XRD. Monazite is soluble
in sulphur acid at high T (Kumari et al., 2015), so fine grained,
reactive monazite may also be partially dissolved at low T.
Microscopic examination would be needed to confirm this and
identify the mineral.
Figure 6: REE concentration leached by the three single stage
leach reagents (LHS) and percentage leached (RHS) showing relative
proportions of LREE and HREE
Figure 7 shows the percentage of each REE leached by each
solution. The greater proportions leached from TLR011 24-28 and
TLR010 18-22 are shown at a different scale to other samples. The
proportions of individual elements leached are relatively constant,
except for TLR010 5-8, where a higher proportion of HREE were
leached, and TLR011 24-28 and TLR010 18-22 a higher proportion of
the LREE were leached. For TLR011 24-28 and TLR010 18-22 this
potentially indicates the presence of an acid soluble LREE- bearing
mineral as noted above. For TLR010 5-8, this may relate to
breakdown of a HREE-bearing mineral, or release of HREE from an
oxide mineral as Ce is also leached at a higher proportion.
3.4 Sequential leaching
The concentrations leached as part of the sequential leach
procedure are presented in Tables 6 to 9, and Figures 8 to 12. The
ammonium sulphate leach was taken as the first stage of the
procedure, targeting clay adsorbed and reactive carbonate hosted
REE. This removed from 21-87mg/kg REE as noted above. The acetic
acid leach targeted more resistant carbonate minerals and weak acid
soluble material and removed from 15 to 179mg/kg. The hydroxyl
ammonium chloride leach targeted reducible minerals (oxides and
oxy-hydroxides) and removed from 369 to 2015mg/kg. The hydrogen
peroxide/ammonium acetate leach targeted oxidizable material
(sulphides and organic matter) and removed 30-226mg/kg. Nitric acid
targeted strong acid soluble phases and leached 47 to 1301mg/kg.
The highest proportions leached were in hydroxyl ammonium chloride
and nitric acid suggesting the majority of non-refractory REE are
in oxides or strong acid soluble minerals (fluorcarbonates or
fine-grained monazite are a possibility). The highest acetic acid
soluble contents were in TLR011 24-28 and TLR010 18-22, suggesting
the presence of carbonate soluble REE. For most leaches there is
very little selectivity between HREE and LREE, but for samples
TLR011 24-28 and TLR029 4-6 preferentially more HREE are removed in
nitric acid (Figure 11) suggesting the presence of an acid soluble
HREE-enriched mineral (a HREE fluorcarbonate or xenotime are
possibilities). Higher concentrations of Ce are always leached by
hydroxyl ammonium chloride as Ce is associated with oxides (Figure
9).
Figure 8. Chondrite normalised concentrations leached by acetic
acid
Figure 9. Chondrite normalised concentrations leached by
Hydroxyl ammonium chloride
Figure 10. Chondrite normalised concentrations leached by
Hydrogen Peroxide and Ammonium Acetate
Figure 11. Chondrite normalised concentrations leached by nitric
acid
Figure 12 shows the sum totals of % REE leached during the
sequential extraction procedure for each sample. The total exceeds
100% in some instances as a result of the summed analytical errors
through the 5-stage leach procedure. Totals significantly below
100% (-5%) indicate REE hosted in minerals not affected by the
leach solutions, likely including silicates, monazite and
zircon.
For all samples the proportion leached by ammonium sulphate is
below 10%. For ion adsorption deposits the accepted proportion
weakly bound to clay minerals (and therefore leachable by ammonium
sulphate) is 50% minimum. The samples do not therefore indicate an
ion adsorption deposit resource.
For samples TLR001 6-10, TLR001 14-18, TLR 010 5-8 and TLR010
8-10 the largest proportion of REE leached is by hydroxyl ammonium
chloride and nitric acid, and this nears 100% for Pr to Gd. This
suggests that these REE are held in oxides as trace elements or are
present as acid soluble REE accessory minerals (possibly
fluorcarbonates or fine grained, reactive monazite). The totals for
La-Ce are below 100% and suggest a proportion (15-40%) of these
elements are held in non-reactive minerals (e.g. coarse-grained
monazite, allanite, as trace metals in rock forming silicates). The
totals for Dy to Lu are also below 100% and suggest a portion
(15-55%) held in non-reactive minerals (e.g. coarse-grained
xenotime, zircon, as trace metals in rock forming silicates).
For samples TLR010 18-22 and TLR011 24-28 up to 30% of the REE
were leachable by acetic acid, alongside significant portions
leachable by hydroxyl ammonium chloride. This suggests a
significant proportion of the REE present as carbonate of
fluorcarbonate minerals, or as trace elements in major element
carbonates (e.g. calcite). Low totals for the HREE in these samples
suggest a portion (40-60%) held in non-reactive minerals (e.g.
coarse-grained xenotime, zircon, as trace metals in rock forming
silicates).
For samples TLR017 24-28 and TLR029 4-6 the majority of the REE
are leached by hydroxyl ammonium chloride and nitric acid, with a
preference for the LREE. This suggests that these REE are held in
oxides as trace elements, or are present as acid soluble REE
accessory minerals (possibly fluorcarbonates or fine grained,
reactive monazite). The low leach proportions for the HREE suggest
the presence of a non-reactive HREE bearing phase (e.g.
zircon).
The two highest bulk REE contents are in TLR010 8-10 and TLR017
24-28. These had the highest proportion leached by hydroxyl
ammonium chloride and nitric acid, with highest proportions leached
including Pr, Nd and Gd.
Figure 12. Percentage leached by sequential leach solutions
3.5 Behaviour of uranium and thorium
Figure 13: Cross plots of actinide concentration versus total
REE concentration for individual leaches (top) and sequential
leaches (bottom)
Uranium and thorium were included in all leach experiments as
radioactivity is a significant issue for some REE deposits. They
are plotted against the total REE content in Figure 13. For the
single stage leaches Th concentrations remain below 5mg/kg in most
cases, and Th is not significantly mobilised by the leaching
process. Uranium leaching shows a positive correlation with the pH
of the solutions but is not leached in concentrations above
2mg/kg.
For the sequential leach solutions both Th (up to 50mg/kg) and U
(up to 9mg/kg) are mobilised by hydroxylammonium chloride. This
leach is designed to target oxide phases and is thus likely to
leach actinides from oxides (thorianite; uraninite and secondary
uranium oxides) alongside mobilising the REE.
3.6 Scandium
Scandium was included in the analysis as it is present in the
commercially available calibration standards and may co-concentrate
with REE. Leachable Sc was below 1mg/kg in all experiments.
4. Conclusions
-- The mineralogy and total REE concentrations of the sample set
provided are comparable to ion adsorption deposits globally with a
kaolinite-rich mineralogy and 815-5185mg/kg Total REE
-- The easily leachable fraction of the sample set provided
(i.e. that leachable by ammonium sulphate solution) is below 10%
indicating that an ion adsorption deposit comparable resource is
not present in the samples tested
-- Of the single stage leaches tested, sulphuric acid gave the
best recoveries at around 5% of the total REE content. Recoveries
were better in samples TLR011 24-28 and TLR010 18-22 at 25-29%
(165.5-209.6mg/kg) indicating a variation in mineralogy, with the
possible presence of a carbonate mineral in these samples
-- The only REE mineral tentatively identified from XRD was
monazite (REEPO(4) ). This is soluble in hot sulphuric acid so
higher recoveries may be possible with longer leach times or
heating
-- In the sequential leaching procedure sub-100% totals suggest
a significant portion of the REE (up to 50% for some elements) are
present in resistant minerals (e.g. silicates, zircon)
-- The highest percentage leached in sequential leaching
experiments was using hydroxyl ammonium chloride and nitric acid
(combined percentage leached from 30-100% depending on element)
indicating a strong oxide and strong acid soluble fraction. Highest
recoveries were for Nd to Dy. This suggests REE held in oxides or
phosphate minerals
-- In samples TLR010 18-22 and TLR011 24-28 up to 20% REE were
leachable by acetic acid indicating a carbonate component
-- Low summed percentage leached for La-Ce and Dy-Lu indicate
REE hosted in minerals insoluble in the reagents tested here -
these are likely held in resistant phase (silicate minerals,
zircon, coarse grained phosphates)
Key points and Recommendations
-- The representative samples tested are not indicative of an
ion adsorption type deposit as classified by Sanematsu, K. and
Watanabe Y
-- Recoverable portions of the REE are present using a strong
acid leach alongside a reagent targeting oxides, although the REE
contents are very low compared to a typical bedrock (carbonatite)
deposit
-- Deeper knowledge of mineralogy could identify the host REE
minerals and hence possible leaching solutions. This would require
mineral separation or light/electron microscopy as the proportions
of REE minerals are below detection limits for XRD
-- The samples TLR010 18-22 and TLR011 24-28 are distinct from
the others in terms of having a carbonate hosted REE fraction and
may merit further investigation if they constitute part of an
identifiable rock body or weathering horizon
References
Estrade, G., Marquis, E., Smith, M. P. Goodenough, K., Nason, P.
(2019) REE concentration processes in ion adsorption deposits:
Evidence from the Ambohimirahavavy alkaline complex in Madagascar.
Ore Geology Reviews 112, 103027
Kumari Panda, Kumar Jha, Kumar, Jin Young Lee (2015) Process
development to recover rare earth metals from monazite mineral: A
review. Minerals Engineering 79, 102-115.
Li, M., Zhou, M.F., Williams-Jones, A.E. (2019) The Genesis of
Regolith-Hosted Heavy Rare Earth Element Deposits: Insights from
the World-Class Zudong Deposit in Jiangxi Province, South China.
Economic Geology, v. 114, no. 3, pp. 541-568
Pinto-Ward, C. (2017) Controls on the Enrichment of the Serra
Verde Rare Earth Deposit, Brazil. Unpublished PhD thesis, Imperial
College London. 442pp.
Rauret G., Lopez-Sanchez J.F., Lück D., Yli-Halla M., Muntau H.,
Quevauviller P. (2001) EUR-19775 - The certification of the
extractable contents (mass fractions) of Cd, Cr, Cu, Ni, Pb and Zn
in freshwater sediment following sequential extraction procedure
BCR-701. BCR information series, European Commission.
Sanematsu, K. and Watanabe Y. (2016) Characteristics and genesis
of ion adsorption-type rare earth element deposits. In P.L.
Verplanck, M.W. Hitzman (Eds.), Rare Earth and Critical Elements in
Ore Deposits, Society of Economic Geologists,
https://doi.org/10.5382/Rev.18.03 .
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