Metallurgical Optimisation Update
In brief · summary, not quotable
Cobra Resources plc announced favorable preliminary results from flow-sheet optimization studies at its Boland ISR project, aimed at reducing costs and maximizing the value of strategic rare earth metals. Tests with ANSTO demonstrated that the Boland mineralisation can generate sufficient acid to achieve optimal REE recovery. A large-scale ISR column yielded 66% HREO recoveries from a 55kg sample using an AMSUL 0.3M lixiviant (pH3) in just 17 days, with acid consumption at 3.88kg/t. Furthermore, a 175g sample of low-grade mineralisation, when dosed with 13g of H2O2, produced over 2 grams of 'free' sulphuric acid, achieving a pH of 2.75, highlighting the potential to reduce or eliminate the need for sulphuric acid.
Full announcement
Select text to share a quote on X · sign in to keep highlights & notes in your COBR notes
Cobra (LSE: COBR), a South Australian mineral exploration and development company, is pleased to announce highly favourable preliminary results from flow-sheet optimisation studies aimed at reducing cost and maximising the value of strategic rare earth metals, particularly Dysprosium and Terbium, from its Boland In situ recovery ("ISR") project in South Australia.
The Boland Project is unique when compared to traditional ionic clay hosted rare earth ("REE") deposits as REEs have been mobilised from underlying weathered granites (saprolite) and absorbed to fine organics within the Pidinga Formation, a highly permeable paleo-sediment bound by impermeable clays. This unique environment not only enables ISR, the lowest cost and most sustainable form of mining, but forms anoxic conditions where organic matter breaks down and forms Pyrite. Pyrite (FeS2) is a primary source of sulphur used in the generation of sulphuric acid, the largest consumable cost in the treatment of Ionic clays.
In collaboration with the Australian Nuclear Scientific Technology Organisation ("ANSTO"), preliminary tests have demonstrated that sufficient acid can be generated form the mineralisation to achieve the required acidities for optimal REE recovery.
Highlights
- Recently, a large scale ISR column yielded 66% HREO recoveries from a 55kg sample using an (NH4)2SO4 "AMSUL" 0.3M lixiviant (pH3) in just 17 days where acid consumption was just 3.88kg/t
- A 175g sample of low-grade Boland mineralisation was dosed with hydrogen peroxide, (H2O2) an effective oxidant aimed at identifying the impact of the oxidation-reduction potential ("ORP") on leaching performance.
- After 8 hours and the addition of 13g of H2O2, over 2 grams 'free' sulphuric acid were produced yielding a test condition acidity of pH 2.75, below the optimal recovery conditions of pH 3
- This highlights the potential to introduce an oxidant into the ISR process to further reduce, and in some circumstances eliminate, the need for sulphuric acid
- This process has the added benefit of being the preferred method to supress cerium from recovered ISR liquor - pending liquor assays from the test will demonstrate the potential cerium suppression and associated REE recoveries
- Further tests are underway on higher grade mineralisation, where both acid generation and REE recovery will be determined. Additional tests using low cost and readily accessible oxidants are also planned
Rupert Verco, Managing Director of Cobra, commented:
"Our Boland Dysprosium and Terbium project now has two distinct advantages over other ionic clay projects:
- Boland's unique geology enables controlled ISR - a sustainable and low-cost mining process - which allows us to reduce capital costs and operational risks associated with handling clay ores, and
- The mineralisation's unique chemistry that will enable us to minimise our sulphuric acid consumption, further reducing operational costs and project carbon emissions by utilising the orebody's chemistry to achieve optimal recovery conditions.
The Boland Project metallurgy keeps getting better and better. Not only is the geology amenable to low-cost extraction, the mineralisation is capable of doing much of the work itself. Minimising operational costs through such ingenuity will greatly strengthen the economics of the Boland Project. Whilst these results are leftfield, when coupled with recent ISR column results, the narrative becomes obviously clear: we are unlocking the potential of a unique Rare Earth discovery that can meet the needs of emerging markets."
Background to sulphuric acid generation tests
- Diagnostic and acid consumption tests at benign acidities >pH4 showed that additional acid was generated during tests taking pH set points below pH targets. Refer to announcement dated 11 September 2025
- Oxidants such as hydrogen peroxide and ferric sulphate are commonly added to lixiviants in uranium ISR to promote the mobilisation of uranium to solution
- An oxidant could be introduced within a pre-conditioning phase of ISR treatment to catalyse the oxidation of pyrite, in a similar reaction as shown below;
- FeS2 + 8 H2O2 → Fe2+ + 2 SO42- + 8 H2O
- 2 SO42 + 4 H+ → 2 H2SO4
- The results of this study support that oxidation alone would reduce the starting acidity of the aquifer and ultimately reduce the required addition of sulphuric acid
- All Boland mineralisation samples submitted to ANSTO to support metallurgical flowsheet studies contained relatively high levels of sulphur. Testing was performed on a low-grade REE sample with a sulphur content of 3%
- Three tests were performed at different ORP targeted endpoints (300mV, 450mV and 525mV) that were controlled by the addition of hydrogen peroxide. The generation of sulphuric acid was measured across 8 hours
- Tests were run at ambient temperature and at a 20% solid density
Figure 1. The generation of H2SO4 (grams) at varying levels of hydrogen peroxide addition and the corresponding acid generation after 8 hours.
- Further tests will be performed to determine the amount of REEs recoverable through this process without acid addition, and to support economic assessment of the acid generation potential from standard assay chemistry
Boland Project
Follow this link to watch a short video of CEO Rupert Verco explaining the results released in this announcement: https://investors.cobraplc.com/link/eolX4r
Further information relating to Boland and these results are presented in the appendices.
- Exploration update: "Met Study Supports Even Lower-Cost Recoveries", dated 11th September 2025
- Exploration update: "Low-Cost Recoveries from Optimised Testing", dated 11th August 2025
- Exploration update: "Rare Earth ISR System beyond Boland", dated 4th August 2025
- Exploration update: "Favourable Boland Metallurgical Results", dated 21st July 2025
- Exploration update: "Boland Project Update", dated 26th June 2025
- Wudinna Project Update: "Boland Aircore Drill Results", dated 25th February 2025
- Wudinna Project Update: "2nd Bench Scale ISR Study & £1.7M Placing", dated 26 November 2024
- Wudinna Project Update: "ISR Bench Scale Study Completion", dated 4 November 2024
of heavy rare earths", dated 28 August 2024
Regional map showing Cobra's tenements in South Australia
Follow us on social media:
LinkedIn: https://www.linkedin.com/company/cobraresourcesplc
X: https://twitter.com/Cobra_Resources
Subscribe to our news alert service: https://investors.cobraplc.com/auth/signup
Appendix 1: Background information - the Boland Project and ISR
Figure A1: Comparison between the Chinese and the proposed Boland process for ISR mining of REEs
Appendix 2: JORC Code, 2012 Edition - Table 3
| Criteria | JORC Code explanation | Commentary |
| Sampling techniques | · Nature and quality of sampling (eg cut channels, random chips, or specific specialised industry standard measurement tools appropriate to the minerals under investigation, such as down hole gamma sondes, or handheld XRF instruments, etc). These examples should not be taken as limiting the broad meaning of sampling. · Include reference to measures taken to ensure sample representivity and the appropriate calibration of any measurement tools or systems used. · Aspects of the determination of mineralisation that are Material to the Public Report. · In cases where 'industry standard' work has been done this would be relatively simple (eg 'reverse circulation drilling was used to obtain 1 m samples from which 3 kg was pulverised to produce a 30 g charge for fire assay'). In other cases more explanation may be required, such as where there is coarse gold that has inherent sampling problems. Unusual commodities or mineralisation types (eg submarine nodules) may warrant disclosure of detailed information. | Pre 2023 · Historic Rotary Mud drilling targeting paleochannel hosted uranium was completed. Some residue samples were retained in the Tonsley Core Library, downhole geophysical logging was the primary data collected for these holes. · Select historic sample residues over Boland were analysed as reported in RNS 1834M (26 April 2024) 2023 Aircore · A combination of 2m and 3m samples were collected in green bags via a rig mounted cyclone. A PVC spear was used to collect a 2-4kg sub sample from each green bag. Sampling commenced from the collar point with samples submitted for analysis from the top of saprolite. · Samples were submitted to Bureau Veritas Laboratories, Adelaide and pulverized to produce a 4-acid digest sample. 2024-2025 SONIC · Drill results are outlined in RNS 0297I (25 March 2024) · Core was scanned by a SciAps X555 pXRF to determine sample intervals. Intervals through mineralized zones were taken at 10cm. Through waste, sample intervals were lengthened to 50cm. Core was halved by knife cutting. XRF scan locations were taken on an inner surface of the core to ensure readings were taken on fresh sample faces. · Samples were submitted to Bureau Veritas Laboratories, Adelaide and pulverized to produce a 4 acid digest sample. Aircore · 1m sample intervals of 2-4 kg were taken via PVC spear from green bags at the rig. Select samples were submitted to the lab for analysis. From 0-6 m in each hole samples were composited to 3m. · Samples were submitted to Bureau Veritas Laboratories, Adelaide and pulverized to produce a 4 acid digest sample. |
| Drilling techniques | · Drill type (eg core, reverse circulation, open-hole hammer, rotary air blast, auger, Bangka, sonic, etc) and details (eg core diameter, triple or standard tube, depth of diamond tails, face-sampling bit or other type, whether core is oriented and if so, by what method, etc). | Pre 2023 · Drill methods include Rotary Mud and AC 2023 · Drilling completed by McLeod Drilling Pty Ltd using 75.7mm NQ air core drilling techniques from an ALMET aircore rig mounted on a Toyota Landcruiser 6x6 and a 200psi, 400cfm Sullair compressor. 2024-2025 · Sonic Core drilling completed Star Drilling using 4" core with a SDR12 drill rig. Holes were reamed to 6" or 8" to enable casing and screens to be installed · Aircore Drilling completed by McLeod Drilling Pty Ltd using 75.7mm NQ air core drilling techniques from an ALMET aircore rig mounted on a Toyota Landcruiser 6x6 and a 200psi, 400cfm Sullair compressor. |
| Sub-sampling techniques and sample preparation | · If core, whether cut or sawn and whether quarter, half or all core taken. · If non-core, whether riffled, tube sampled, rotary split, etc and whether sampled wet or dry. · For all sample types, the nature, quality and appropriateness of the sample preparation technique. · Quality control procedures adopted for all sub-sampling stages to maximise representivity of samples. · Measures taken to ensure that the sampling is representative of the in situ material collected, including for instance results for field duplicate/second-half sampling. · Whether sample sizes are appropriate to the grain size of the material being sampled. | Pre 2023 · Historic Residue samples were generally 2m composites and were stored at the South Australian Drill Core Reference Library at Tonsley, a subsample of approximately 20g was removed for lab submission. · Select samples of geological interest were selected for lab submission · No QAQC samples were included in the submission of these samples. Sample results were intended to indicate mineralisation potential but would not be suitable for resource estimation Post 2023 · A PVC spear was used to collect 2-4kg of sub-sample from each AC sample length controlled the sample volume submitted to the lab. · Additional sub-sampling was performed through the preparation and processing of samples according to the Bureau Veritas internal protocols. · Field duplicate AC samples were collected from the green bags using a PVC spear scoop at a 1 in 25 sample frequency. · Sample sizes are considered appropriate for the material being sampled. · Assessment of duplicate results indicated this sub - sample method provided appropriate repeatability for rare earths. Sonic Drilling · Field duplicate samples were taken nominally every 1 in 25 samples where the sampled interval was quartered. · Blanks and Standards were submitted every 25 samples · Half core samples were taken where lab geochemistry sample were taken in 2024. · For 2025 drilling, quarter core was submitted to the lab for geochemical testing. · In holes where only column leach test samples have been submitted, full core samples have been submitted. In holes where geochemical samples were submitted three quarter core sanmples were submitted for column leach testing.. |
| Quality of assay data and laboratory tests | · The nature, quality and appropriateness of the assaying and laboratory procedures used and whether the technique is considered partial or total. · For geophysical tools, spectrometers, handheld XRF instruments, etc, the parameters used in determining the analysis including instrument make and model, reading times, calibrations factors applied and their derivation, etc. · Nature of quality control procedures adopted (eg standards, blanks, duplicates, external laboratory checks) and whether acceptable levels of accuracy (ie lack of bias) and precision have been established. | · Samples were submitted to Bureau Veritas, Adelaide for preparation and analysis. Multi-element geochemistry were digested by four acid ICP-MS/ ICP-OES and analysed for Ag, Ce, Cu, Dy, Er, Eu, Gd, Ho, La, Lu, Mg, Na, Nd, P, Pr, Sc, Sm, Tb, Th, Tm, U, Y and Yb. · Field rare earth standards were submitted at a frequency of 1 in 25 samples. · Field duplicate samples were submitted at a frequency of 1 in 25 samples. · Reported assays pass the companies implemented QAQC database reports · Internal lab blanks, standards and repeats for rare earths indicated acceptable assay accuracy. Sample Characterisation Test Work performed by the Australian Nuclear Science and Technology Organisation (ANSTO) · Full core samples were submitted to Australian Nuclear Science and Technology Organisation (ANSTO), Sydney for preparation and analysis. The core was split in half along the vertical axis, and one half further split into 10 even fractions along the length of the half-core. Additional sub-sampling, homogenisation and drying steps were performed to generate ~260 g (dry equivalent) samples for head assay according to the laboratory internal protocols. · Multi element geochemistry of solid samples were analysed at ANSTO (Sydney) by XRF for the major gangue elements Al, Ca, Fe, K, Mg, Mn, Na, Ni, P, Si, S, and Zn. · Multi element geochemistry of solid samples were additionally analysed at ALS Geochemistry Laboratory (Brisbane) on behalf of ANSTO by lithium tetraborate digest ICP-MS and analysed for Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Tb, Th, Tm, U, Y and Yb. · Reported assays are to acceptable levels of accuracy and precision. · Internal laboratory blanks, standards and repeats for rare earths indicated acceptable assay accuracy. · Samples retained for metallurgical analysis were immediately vacuum packed, nitrogen purged and refrigerated. · These samples were refrigerated throughout transport. Metallurgical Leach Test Work performed by the Australian Nuclear Science and Technology Organisation (ANSTO) · ANSTO laboratories prepared ~80g samples for diagnostic leaches, a 443g sample for a slurry leach and a 660g sample for a column leach. Sub-samples were prepared from full cores according to the laboratory internal protocols. Diagnostic and slurry leaching were carried out in baffled leach vessels equipped with an overhead stirrer and applying a 0.5 M (NH4)2SO4 lixiviant solution, adjusted to the select pH using H2SO4. · 0.5 M H2SO4 was utilised to maintain the test pH for the duration of the test, if necessary. The acid addition was measured. · Thief liquor samples were taken periodically. · At the completion of each test, the final pH was measured, the slurry was vacuum filtered to separate the primary filtrate. · The thief samples and primary filtrate were analysed as follows: o ICP-MS for Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Mn, Nd, Pb, Pr, Sc, Sm, Tb, Th, Tm, U, Y, Yb. o ICP-OES for Al, Ca, Fe, K, Mg, Mn, Na, Si. · The water wash was stored but not analysed. · Column leaching was carried out in horizontal leaching column. The column was pressurised with nitrogen to 6 bar and submerged in a temperature controlled bath. · A 0.5 M (NH4)2SO4 lixiviant solution, adjusted to the select pH using H2SO4 was fed to the column at a controlled flowrate. · PLS collected from the end of the column was weighed, the SH and pH measured and the free acid concentration determined by titration. Liquor samples were taken from the collected PLS and analysed as follows: o ICP-MS for Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Mn, Nd, Pb, Pr, Sc, Sm, Tb, Th, Tm, U, Y, Yb. o ICP-OES for Al, Ca, Fe, K, Mg, Mn, Na, Si. · The column leach test has been completed. Assays of the column have adjusted head grades of the initial bench scale study. Recoveries have been adjusted accordingly. |
| Verification of sampling and assaying | · The verification of significant intersections by either independent or alternative company personnel. · The use of twinned holes. · Documentation of primary data, data entry procedures, data verification, data storage (physical and electronic) protocols. · Discuss any adjustment to assay data. | · Sampling data was recorded in field books, checked upon digitising and transferred to database. · Geological logging was undertaken digitally via the MX Deposit logging interface and synchronised to the database at least daily during the drill programme. · Compositing of assays was undertaken and reviewed by Cobra Resources staff. · Original copies of laboratory assay data are retained digitally on the Cobra Resources server for future reference. · Samples have been spatially verified through the use of Datamine and Leapfrog geological software for pre 2021 and post 2021 samples and assays. · Twinned drillholes from pre 2021 and post 2021 drill programs showed acceptable spatial and grade repeatability. · Physical copies of field sampling books are retained by Cobra Resources for future reference. · Significant intersections have been prepared by Mr Robert Blythman and reviewed by Mr Rupert Verco |
| Location of data points | · Accuracy and quality of surveys used to locate drill holes (collar and down-hole surveys), trenches, mine workings and other locations used in Mineral Resource estimation. · Specification of the grid system used. · Quality and adequacy of topographic control. | 2021-2023 · Collar locations were initially surveyed using a mobile phone utilising the Avenza Map app. Collar points recorded with a GPS horizontal accuracy within 5 m. · RC Collar locations were picked up using a Leica CS20 base and Rover with an instrument precision of 0.05 cm accuracy. · Locations are recorded in geodetic datum GDA 94 zone 53. · No downhole surveying was undertaken on AC holes. All holes were set up vertically and are assumed vertical. · RC holes have been down hole surveyed using a Reflex TN-14 true north seeking downhole survey tool or Reflex multishot · Downhole surveys were assessed for quality prior to export of data. Poor quality surveys were downgraded in the database to be excluded from export. · All surveys are corrected to MGA 94 Zone 53 within the MX Deposit database. · Cased collars of sonic drilling shall be surveyed before a mineral resource estimate 2024 Aircore · Collar locations were initially surveyed using A mobile phone GPS utilising the Avenza Map app. Collar points recorded with a horizontal accuracy within 5m. · Locations are recorded in geodetic datum GDA 94 zone 53. · No downhole surveying was undertaken on AC or Sonic holes. All holes were set up vertically and are assumed vertical. · Higher accuracy GPS will be undertaken on sonic core drilling to support future resource estimates |
| Appendix 4: Section 2 reporting of exploration results | ||
| Criteria | JORC Code explanation | Commentary |
| Mineral tenement and land tenure status | · Type, reference name/number, location and ownership including agreements or material issues with third parties such as joint ventures, partnerships, overriding royalties, native title interests, historical sites, wilderness or national park and environmental settings. · The security of the tenure held at the time of reporting along with any known impediments to obtaining a licence to operate in the area. | · Boland is located on EL5953, currently owned 100% by Peninsula Resources limited, a wholly owned subsidiary of Andromeda Metals Limited. · In 2024, Cobra through its subsidiary Lady Alice Mines purchased the remaining ownership of the Wudinna Project tenements. · An application through partial surrender is currently with the South Australian Government which will see LAM as the 100% owner of areas of the Wudinna Project. · Alcrest Royalties Australia Pty Ltd retains a 1.5% NSR royalty over future mineral production from licenses EL6001, EL5953, EL6131, EL6317 and EL6489. · A Native Title Agreement is in place with the Barngarla people. · Aboriginal heritage surveys have been completed over EL5953, with no sites located in the immediate vicinity of aircore drilling |
| Geology | · Deposit type, geological setting and style of mineralisation. | · Target mineralisation is ionic rare earth mineralisation that occurs primarily within the Pidinga Formation within the Narlaby Palaeochannel, immediately above REE enriched Hiltaba Suite Granites · Ionic REE mineralisation also occurs in and adjacent to the Garford formation clays and silty sands. · Significant chemical (pH & eH) differences exist between underlying saprolite and overlying Palaeochannel sediments. REEs are absorbed to reduced organics found within the Pidinga Formation · Benchtop metallurgy studies indicate ISR amenability of rare earths within the Pidinga Formation basal sands summarized in RNS 1285Q (16 December 2024) · Ionic REE mineralisation is confirmed through metallurgical desorption testing where high recoveries are achieved at benign acidities (pH4-3) at ambient temperature. · QEMSCAN and petrology analysis support REE ionic mineralisation, with little to no secondary phases identified. · Ionic REE mineralisation occurs in reduced clay intervals that contact both saprolite and permeable sand units. Mineralisation contains variable sand quantities that yield permeability and promote in-situ recovery potential · Mineralisation is located within a confined aquifer |
| Data aggregation methods | · In reporting Exploration Results, weighting averaging techniques, maximum and/or minimum grade truncations (eg cutting of high grades) and cut-off grades are usually Material and should be stated. · Where aggregate intercepts incorporate short lengths of high grade results and longer lengths of low grade results, the procedure used for such aggregation should be stated and some typical examples of such aggregations should be shown in detail. · The assumptions used for any reporting of metal equivalent values should be clearly stated. | · Reported summary intercepts are weighted averages based on length. · No maximum/ minimum grade cuts have been applied. · No metal equivalent values have been calculated. · Rare earth element analyses were originally reported in elemental form and have been converted to relevant oxide concentrations in line with industry standards. Conversion factors tabulated below: Element Oxide Factor Cerium CeO2 1.2284 Dysprosium Dy2O3 1.1477 Erbium Er2O3 1.1435 Europium Eu2O3 1.1579 Gadolinium Gd2O3 1.1526 Holmium Ho2O3 1.1455 Lanthanum La2O3 1.1728 Lutetium Lu2O3 1.1371 Neodymium Nd2O3 1.1664 Praseodymium Pr6O11 1.2082 Scandium Sc2O3 1.5338 Samarium Sm2O3 1.1596 Terbium Tb4O7 1.1762 Thulium Tm2O3 1.1421 Yttrium Y2O3 1.2699 Ytterbium Yb2O3 1.1387 · The reporting of REE oxides is done so in accordance with industry standards with the following calculations applied: · TREO = La2O3 + CeO2 + Pr6O11 + Nd2O3 + Sm2O3 + Eu2O3 + Gd2O3 + Tb4O7 + Dy2O3 + Ho2O3 + Er2O3 + Tm2O3 + Yb2O3 + Lu2O3 + Y2O3 · LREO = La2O3 + CeO2 + Pr6O11 + Nd2O3 · HREO = Sm2O3 + Eu2O3 + Gd2O3 + Tb4O7 + Dy2O3 + Ho2O3 + Er2O3 + Tm2O3 + Yb2O3 + Lu2O3 + Y2O3 · MREO = Nd2O3 + Pr6O11 + Tb4O7 + Dy2O3 · NdPr = Nd2O3 + Pr6O11 · TREO-Ce = TREO - CeO2 · % Nd = Nd2O3/ TREO · % Pr = Pr6O11/TREO · % Dy = Dy2O3/TREO · % HREO = HREO/TREO · % LREO = LREO/TREO · XRF results are used as an indication of potential grade only. Due to detection limits only a combined content of Ce, La, Nd, Pr & Y has been used. XRF grades have not been converted to oxide. |
Cleaned text: letterheads, contacts and legal notices removed. View the original announcement ↗ · Company filings. Not investment advice.