Splinter Rock REE Project
The Splinter Rock project is located approximately ~150km by road northeast of Esperance. The rare earth element (REE) mineralisation at the Splinter Rock Project occurs in the weathered profile (in-situ regolith) adjacent to Booanya granitic basement rocks which are enriched in REE.
The strong enrichments in REE distinguishes Booanya granites from all other granite groups in the Esperance area. CSIRO have been engaged to use cutting edge exploration tools to assist OD6 in targeting the most likely areas of significant REE mineralisation.
Four significant prospect areas have been identified at Splinter Rock, being: Scrum, Centre, Flanker and Prop. The prospects contain amongst the thickest and highest grades of clay hosted REE’s in Australia. The thickness, area and density of the clays show the massive potential scale of REE at Splinter Rock. An updated mineral resource estimate of 682 Mt @ 1,338 TREO at 1,000 ppm cut-off grade was announced in May 2024.
Highlights include:
- High grade indicated MRE at the stand-out Inside Centre prospect of 119Mt at 1,632 ppm TREO with 23% Magnet Rare Earth Oxides (MagREO) with near surface mineralisation up to 70m thick
- Less than 10% of targeted clay basin area included in the estimate, with on-going exploration to further expand the known mineralisation
- High value MagREO represent an average of ~23% of TREO grade
- Continued exploration prioritisation of ‘best of the best’ in terms of grade, MagREO content, thickness and metallurgical recovery
Figure showing the Splinter Rock rare earth project tonnage and grade curve.
Table showing the mineral resource estimate at Splinter Rock – by prospect at 1,000 ppm TREO cutoff grade.
| Prospect | Category | Tonnes (Mt) | TREO (ppm) | Pr6O11 (ppm) | Nd2O3 (ppm) | Tb4O7 (ppm) | Dy2O3 (ppm) | MREO (ppm) | MREO/TREO (%) |
|---|---|---|---|---|---|---|---|---|---|
| Inside Centre | Indicated | 119 | 1,632 | 79 | 271 | 2 | 12 | 366 | 22.4 |
| Centre | Inferred | 276 | 1,342 | 65 | 228 | 3 | 15 | 310 | 23.1 |
| Centre NW | Inferred | 21 | 1,255 | 65 | 227 | 3 | 14 | 309 | 24.6 |
| Scrum | Inferred | 126 | 1,228 | 58 | 210 | 3 | 15 | 285 | 23.2 |
| Flanker | Inferred | 45 | 1,250 | 59 | 212 | 3 | 16 | 290 | 23.2 |
| Prop | Inferred | 94 | 1,160 | 53 | 190 | 2 | 13 | 259 | 22.3 |
| Total | Inferred | 682 | 1,338 | 64 | 226 | 3 | 14 | 307 | 22.9 |
The Prospects
Centre Prospect
The Centre Prospect target area has been defined from OD6’s digital elevation model (DEM), recent mid-time AEM preliminary imagery and CSIRO modelled AEM combined with the results of existing drilling. Drilling indicates that REEs occur in thick clays of the prospect that vary between 10 m to 70m with TREO assay intercepts up to 2,200ppm. Inside Centre is a high-grade deep clay channel at the southern end of the resource and is approximately 2km long by 1km wide. Centre North-West is a narrow channel to the north-west of the main Centre basin, that also exhibits properties similar to Inside Centre. The Centre Prospect is overlain by a shallow transported cover and leached clays of approximately 5 m to 15 m thickness above the rare earth clay host. The target area covers 136km2 and extends approximately 27km along its axis and between 5km and 10km wide. Initial Metallurgical acid leach tests achieved 42% to 90% recovery of MagREE (average 60%).
Scrum Prospect
Scrum is defined in a similar manner to Centre and the REE-bearing clays clay areas that vary between 10m to 50m with TREO assay intercepts up to 2,180ppm. The prospect is partly covered by a sand with thickness varying between approximately 15m to 35m above the clay hosted rare earth areas. Target area covers 26km2 and extend along an approximately 11km axis between 1km and 5km wide. Initial Metallurgical acid leach tests achieved 40% to 89% recovery of MagREE (average 65%).
Flanker Prospect
Flanker has been defined in a similar manner to Centre, with REEs occurring in thick clays that vary between 10m to 30m and TREO assay intercepts of up to 2,050ppm. This is covered by shallow transported cover and saprolitic clays of 3 m to 15m thickness above the REE host clay. The target covers 42km2 and extends approximately 17 km along axis, varying between 3 km and 5 km wide. This prospect is shallow, with clay hosted REE to within 3m of surface with preliminary early-time AEM imagery used to define it. This data exhibits influence from near-surface conductive salts. Initial Metallurgical acid leach tests achieved 41% to 76% recovery of MagREE (average 55%).
Prop Prospect
Prop has been defined in a similar manner to Centre with REEs occurring in thick clay areas that vary between 10 m to 80m with TREO assay intercepts up to 2,450ppm. Variable transported cover and upper saprolitic clays occur to approximately 3m to 24m thickness above the rare earth clay hosts. The target area covers 58km2 and extends approximate 11km along axis and up to 9km wide. Late-time AEM preliminary imagery has been used to define the target, which contains some of the thickest accumulations of clay identified to date. Initial Metallurgical acid leach tests achieved 40% to 96% recovery of MagREE (average 70%).
REE Processing Guide
OD6 metals is proposing the following innovative processing flowsheet to deliver rare earth products based on the test work completed to date.
- Heap Leach with Nanofiltration (NF), Ion Exchange (IX) and Impurity Removal (IR)
- ~75% Nd & Pr overall Recovery
- High-quality Mixed Rare Earth Carbonate (MREC) of ~56% TREO
- High-quality Mixed Rare Earth Hydroxide (MREH) of ~59% TREO
- Superior product quality with low levels of impurities (Al, Fe, P, Si)
- Extremely low uranium and thorium content (<0.001% U + Th)
- Optimised capital and operating cost drivers
Central to the flowsheet is the use of a site based chlor-alkali facility that utilises salt and water to produce two reagents, namely hydrochloric acid (HCl) and sodium hydroxide (NaOH). HCl is used to leach the rare earth elements, then NaOH is used to remove impurities, precipitate a mixed rare earth carbonate or hydroxide product (MREC/H) and neutralise the clays prior to in pit disposal.
Chlor-alkali Process and Vendor Information
The chlor-alkali process involves passing an electric current through high purity sodium chloride (NaCl or salt) brine to produce hydrogen, chlorine and caustic soda. The hydrogen and chlorine can then be combined into hydrochloric acid. The equations to create caustic soda (NaOH) and hydrogen chloride (HCl) are:
2H2O (l) + 2NaCl (aq) —-> H2 (g) + Cl2 (g) + 2NaOH (aq)
H2 (g) + Cl2 (g) —–> 2HCl (g)
OD6 has obtained information from and held discussions with chlor-alkali electrolyser vendors and experts to determine if owning and operating a site based facility is a viable option. To date all indications are that this is likely to provide the lowest operating cost for a long term project that will form an integrated processing facility with storage tanks for HCl and NaOH to buffer any disruptions.
Based on the publicly available information associated with a BICHLOR™ Electrolyser, plus informal discussion, the following key details are noted for a single chlor-alkali electrolyser:
- Power consumption is the major cost at 1,990 kWhr/te NaOH @ 6 kA/m2.
- Normally allow for 350 days operation and 7kA/m2.
- Normally operate at 385mbarg, 90°C and 32wt% NaOH.
- Can produce up to 62ktpa HCl and 69ktpa of NaOH.
- Indicative pricing for a chlor-alkali electrolyser is approximately £3M each (A$5.7M).
- Multiple smaller electrolysers can be utilised to provide operation flexibility.
A chlor-alkali facility would also consist of the key production steps outlined in Figure 2 along with the associated equipment. Figure 3 also provides an example of scale of two operational
electrolysers.
At an average consumption of 16 kg HCl / tonne of ore a single electrolyser based on the above information could provide sufficient reagents to treat ~4Mtpa of clay ore. The average acid consumption may potentially be lower based on the potential removal of coarse grained (>75um) material which is yet to be reported.
Given power being the main cost driver OD6 envisages that low-cost power supply would be sourced from an owned and operated hybrid power system consisting of solar, wind turbines, energy storage and gas or diesel powered generators. OD6 understands that a similar facility that is currently powering the Esperance township and surrounding areas is currently achieving a 70% renewable power penetration rate which is significant achievement that OD6 should aim to replicate.
On an owned and operated basis, utilising low cost power supply, OD6 has an aspiration target to achieve an operational reagent consumption cost that would be equivalent to about $5-6/t of processed clay ore, assuming sunk capital costs.
