Gold Mountain Confirms Up to 66% Rare Earth Extraction at Brazilian IAC Prospect
Gold Mountain confirms ionic adsorption clay mineralisation at Capivara with up to 65.9% rare earth extraction
Gold Mountain has reported encouraging metallurgical test results from its Capivara Prospect, with rare earth extraction rates of up to 65.9% for TREY-Ce and 63.6% for magnet rare earths achieved using ammonium sulphate desorption at pH 4. The results provide strong evidence consistent with Ionic Adsorption Clay (IAC) style mineralisation, a deposit type favourable for low-cost extraction.
The testing, conducted by ANSTO — described by the company as a globally recognised leader in rare earth processing and metallurgy — focused on the upper saprolite zone only. Deeper sections of the weathering profile have yet to be evaluated, suggesting potential for further improvement at depth. The Capivara Prospect sits within the company’s 2,512 km² Down Under Project in northeastern Brazil.
IAC-style mineralisation is considered commercially attractive due to its lower capital and operating costs, simpler processing requirements, and reduced environmental footprint compared to hard rock rare earth deposits. This confirmation represents a significant milestone for the Down Under Project, according to management.
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What is ionic adsorption clay mineralisation and why does it matter?
Ionic Adsorption Clay deposits are characterised by rare earth elements loosely bound to clay minerals within weathered profiles. This allows extraction through simple ion-exchange leaching rather than intensive crushing and grinding, which are typically required for hard rock deposits.
The commercial appeal of IAC deposits stems from their lower capital and operating costs, simpler processing flowsheets, and reduced environmental impact. IAC deposits in southern China have historically dominated global heavy rare earth supply, establishing the deposit type as a preferred target for rare earth developers seeking cost-competitive production.
Gold Mountain’s exploration strategy is explicitly focused on identifying rare earth deposits that can be processed using low-cost extraction methods with a low environmental footprint while producing a high-quality rare earth product. The Capivara results align directly with this objective.
Deeper drilling at Capivara reveals improving extraction at depth
Metallurgical testing of hole CPAD250007 at Capivara revealed a clear vertical improvement in extraction rates. The deeper sample interval returned 65.9% TREY-Ce extraction at 10-13 metres, a substantial increase from 18.5% in the near-surface interval at 5-7 metres.
The uppermost sample returned less than 20% extractable TREY, demonstrating that modest near-surface results do not necessarily reflect metallurgical potential at depth. This vertical pattern suggests the most prospective saprolite-hosted zones may lie below current shallow drilling.
Additional auger drilling completed to the south of the tested hole has intersected more than 25 metres of weathered material, indicating substantial saprolite thickness within the prospect area. Management has stated that shallow auger holes will be re-drilled using newer, higher-capacity auger rigs to better test the prospective saprolite profile.
| Depth Interval (m) | TREY-Ce Extraction (%) | Magnet REE Extraction (%) |
|---|---|---|
| 5-7 | 18.5 | 18.4 |
| 7-10 | 42.6 | 40.9 |
| 10-13 | 65.9 | 62.6 |
The improving extraction profile at depth supports the case for follow-up deeper drilling to fully evaluate the metallurgical characteristics of the weathering profile.
Three priority target areas identified at Irajuba Prospect
In addition to Capivara, three separate clusters within the Irajuba Prospect have been identified with characteristics consistent with potential IAC mineralisation. These clusters were defined based on low concentrations of deleterious elements — specifically aluminium, iron, and calcium — in leach liquors, an important consideration for downstream processing economics.
The tested drill holes at Irajuba span up to 16 kilometres, demonstrating the broad extent of the mineralised system. Capivara is located approximately 70 kilometres from Irajuba, indicating the scale of the Down Under Project’s rare earth potential.
The identification of multiple target areas across a large project footprint increases exploration optionality and reduces reliance on a single prospect. This systematic approach to target generation is central to Gold Mountain’s exploration methodology.
Metallurgical variability highlights areas requiring deeper evaluation
Desorption responses varied considerably across the Irajuba Prospect, which the company interprets to reflect differences in rare earth mineral associations within the weathering profile. Samples returning greater than approximately 20% ammonium sulphate extractable TREY with low deleterious elements will be prioritised for follow-up drilling.
Importantly, many auger drill holes did not reach the base of the weathering profile and therefore may not have fully tested the most prospective saprolite-hosted horizons. This suggests that the shallow drilling completed to date may underestimate metallurgical potential at depth.
Chemical Index of Alteration (CIA) analysis indicates that increasing rare earth extraction associated with decreasing CIA values is considered favourable and may indicate additional areas prospective for IAC-style mineralisation.
The criteria for prioritising follow-up drilling include:
- Greater than ~20% TREY extraction at pH 4
- Low concentrations of Al, Fe, Ca in leach liquors
- Declining CIA values with depth
- Shallow holes that did not reach base of weathering profile
This systematic approach to identifying favourable zones reduces exploration risk and focuses capital on the highest-potential areas.
Acid profiling tests demonstrate extraction potential under stronger conditions
Samples returning relatively low extraction at pH 4 were subjected to additional testing at pH 2, pH 1, and 50 g/L acid concentrations to assess potential for improved performance under more acidic conditions. Magnet rare earth extraction increased significantly under stronger acid leaching.
For example, sample MT0028 increased from 1.9% at pH 4 to 50.4% at 50 g/L acid concentration. However, the company notes an important caveat: lower pH desorption increases mobilisation of aluminium and other deleterious elements, which subsequently require removal during downstream processing to produce a high-purity rare earth product.
The economic viability of these stronger acid conditions is yet to be demonstrated. While standard IAC leaching at pH 4 remains the preferred processing route, the acid profiling work demonstrates that higher-grade material may be recoverable through alternative processing routes if economics support it.
Executive commentary and next steps
David Evans, Executive Director
“The metallurgical test results received from ANSTO confirm the presence of Ionic Adsorption Clay (IAC) style rare earth mineralisation at the Capivara Prospect, representing a significant milestone for the Down Under Project…”
Evans emphasised that desorption test work from clustered samples in eastern Irajuba has identified areas with “elevated rare earth grades combined with low contaminant levels,” highlighting additional targets with considerable exploration potential.
Planned work includes:
- Detailed follow-up drilling at Capivara as additional assays arrive
- Deeper auger drilling around holes with encouraging near-surface results
- Continued regional auger drilling to systematically evaluate all significant stream sediment anomalies
- Routine submission of significant REE intersections to ANSTO for desorption testing
Management has articulated a clear path forward with systematic drilling and metallurgical testing designed to support future JORC Mineral Resource estimation where appropriate.
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Building a pipeline of rare earth targets across 2,512 km²
Metallurgical results have now been received for 58 samples collected from both diamond drilling and auger drilling programmes completed at Irajuba and Capivara. The company’s regional auger drilling programme is continuing, with additional auger teams being deployed to accelerate coverage.
The systematic exploration approach is expected to generate a growing pipeline of targets across the project area. Interpretation of outstanding stream sediment results will continue as assays are received, with follow-up drilling prioritised over significant TREO anomalies.
The scale of the project and systematic exploration methodology positions Gold Mountain to identify multiple resource targets rather than depending on a single discovery. This exploration strategy aligns with the company’s objective of building a portfolio of IAC-style rare earth prospects that can be processed using low-cost extraction methods.
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