Terrain Minerals Hits 93.7% Gold Recovery at Lightning Clearing Path to Scoping Study
Key Takeaways
- Gold recoveries of 87.0%, 92.1%, and 93.7% were achieved from Composites 1, 2, and 3 respectively using a standard gravity plus CIL flowsheet at P80 75 microns — no complex processing required.
- No refractory or preg-robbing behaviour was identified, with total carbon at or below 0.03% across all composites, confirming a free-milling feedstock.
- Under optimised conditions, Composites 2 and 3 reached 91.7% and 95.3% recovery at the 24-hour mark — within normal plant residence times and consistent with existing Australian gold plant design parameters.
- Conventional processing confirmation opens the possibility of toll-treating ore through a nearby existing facility, a low-capital development pathway that would be unavailable to a project requiring bespoke processing.
- The Lightning Gold Project hosts a maiden Inferred Mineral Resource of 677,000 tonnes at 2.5 g/t gold for 54,000 ounces, with a Scoping Study identified as the next major milestone following these metallurgical results.
Lightning Gold passes the processing test with gold recoveries up to 93.7%
Terrain Minerals (ASX: TMX) has completed its first metallurgical testwork program at the Lightning Gold Project, part of the Smokebush Project in Western Australia, with results confirming the mineralisation responds well to conventional gravity and carbon-in-leach (CIL) processing. Gold recoveries of 87.0%, 92.1%, and 93.7% were achieved from Composites 1, 2, and 3 respectively, at a standard grind of P80 75 microns. The testwork was completed by Independent Metallurgical Operations Pty Ltd (IMO) in Perth.
The metallurgical results provide a crucial technical foundation following the initial discovery of gold and silver at the target, confirming the extracted material can be processed efficiently.
Critically, no refractory or preg-robbing behaviour was identified. Total carbon was at or below 0.03% across all composites, and sulphide sulphur ranged from 0.74% to 1.35%, consistent with a free-milling feedstock. Conventional processing confirmation removes a key technical risk and broadens the development pathways available to the project.
Key points from the announcement:
- Conventional processing confirmed: Overall recoveries of 87.0%, 92.1%, and 93.7% from Composites 1, 2, and 3 using a gravity plus cyanide leach flowsheet
- Standard grind, no fine grinding required: Recoveries achieved at P80 75 microns; Composite 3 reached 93.0% at that grind under standard reagent conditions
- Recoveries within normal plant residence times: At the 24-hour mark under optimised conditions, Composites 1, 2, and 3 returned 82.1%, 91.7%, and 95.3% respectively
- Meaningful gravity recoveries: Knelson concentrator returns of 32.6%, 30.6%, and 50.8% from Composites 1, 2, and 3 ahead of leaching
- Composite 1 responded to routine adjustment: Baseline recovery of 75.4% lifted to 87.0% through increased cyanide dosage with potentiometric titration control and addition of 100 g/t lead nitrate
- No refractory or preg-robbing behaviour identified: A platform for future study-level work is now established
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What the results mean — understanding conventional gold processing
The processing route available to a gold deposit is one of the most important determinants of its economic potential. Confirming a conventional flowsheet means the project avoids the significantly higher capital and operating costs associated with more complex alternatives.
Here is how a conventional gravity plus CIL plant works in plain language: ore is crushed and ground to a target particle size (in this case P80 75 microns), free gold is captured in a gravity circuit using centrifugal concentrators before the slurry enters the leach tanks, the gravity concentrate is treated separately by intensive cyanide leach, and the remaining slurry passes through a series of agitated tanks where cyanide dissolves the gold into solution. Activated carbon adsorbs the dissolved gold, which is then stripped, electrowinned, and smelted to doré.
The alternatives that were not required at Lightning carry materially higher costs and complexity:
- Roasting burns off sulphide minerals to expose gold but requires high-temperature kilns and significant environmental controls
- Pressure oxidation achieves the same oxidation step under heat and pressure, demanding specialised autoclave equipment and substantial capital expenditure
- Bio-leaching uses bacteria to oxidise sulphide minerals, which is slower and operationally complex
- Ultra-fine grinding improves gold liberation but adds significant energy costs and specialised milling equipment
None of these appear to be required at Lightning. That absence matters because it preserves the possibility of toll-treating mineralisation through an existing nearby plant, a low-capital development pathway that would not be available to a project requiring a bespoke processing circuit.
The 24-hour recovery figure is the investor-relevant metric here. Bottle roll leach tests are run over 48 hours as a laboratory convention, with more effective mixing than a full-scale plant achieves. Most Australian gold plants are designed for a total leach residence time of 24 to 36 hours, so the 24-hour result provides the more conservative, real-world reference point for plant design.
The numbers behind the result
The testwork comprised 18 leach tests across three composites, including a grind sensitivity series and a reagent optimisation series. Table 1 below summarises the headline results.
| Composite | Head Grade (g/t Au) | Gravity Recovery (%) | Baseline 48hr Recovery (%) | Optimised 48hr Recovery (%) |
|---|---|---|---|---|
| Composite 1 | 2.55 | 32.6 | 75.4 | 87.0 |
| Composite 2 | 0.93 | 30.6 | 89.5 | 92.1 |
| Composite 3 | 1.47 | 50.8 | 93.0 | 93.7 |
Table 2 shows how quickly those recoveries were delivered relative to normal plant residence times.
| Composite | 24hr Recovery, Baseline (%) | 24hr Recovery, Optimised (%) | 48hr Recovery, Optimised (%) |
|---|---|---|---|
| Composite 1 | 66.0 | 82.1 | 87.0 |
| Composite 2 | 79.8 | 91.7 | 92.1 |
| Composite 3 | 88.7 | 95.3 | 93.6 |
Under optimised conditions, Composites 2 and 3 were essentially at full recovery by the 24-hour mark. Composite 1 reached 82.1% at 24 hours under optimised conditions, compared with 66.0% under standard conditions at the same grind. That improvement was delivered inside a normal plant residence time rather than requiring an extended one.
Composite 1’s improvement path is worth noting. Baseline recovery of 75.4% was lifted to 87.0% through increased cyanide dosage with potentiometric titration control and the addition of 100 g/t lead nitrate, all of which are standard practice in operating gold plants. Gravity recoveries were also meaningful across all composites, with the Knelson concentrator returning 32.6%, 30.6%, and 50.8% from Composites 1, 2, and 3 respectively before the leach circuit was applied. Leach kinetics curves for all three composites (Diagrams 1, 2, and 3 in the source announcement) provide additional detail on recovery rates through time.
Justin Virgin, Executive Director, Terrain Minerals
“This is exactly the result we were looking for. The testwork shows that Lightning gold can be treated through a conventional gold processing plant, with recoveries in the high eighties to low nineties, a straightforward grind size and a meaningful proportion of the gold recoverable by gravity. Importantly, we have seen no indication of refractory behaviour. Taken together, these results point to a simple, conventional processing pathway for Lightning and give us increased confidence in the Project’s development potential.”
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What comes next — the path toward study-level work
These metallurgical results provide the basis for Terrain Minerals to advance Lightning toward study-level work, with the company indicating a Scoping Study as the next major milestone. Three activities are planned for the 2027 metallurgical programme:
- Diamond core confirmatory gravity and cyanide leach testwork, to establish whether the recoveries reported here, which are based on RC chip composites, are representative of diamond core material
- Reagent dosage optimisation testwork, separately assessing the contribution of potentiometric titration control, increased cyanide dosage, and lead nitrate addition, and optimising the lead nitrate dosage rate
- Integration of metallurgical results with resource and geological work at Lightning to inform the next stage of study work
The Lightning Gold Project sits within granted Mining Lease M59/796, part of the Smokebush Project approximately 350 kilometres north of Perth in the Yalgoo Mineral Field. The project hosts a maiden Inferred Mineral Resource of 677,000 tonnes at 2.5 g/t gold for 54,000 ounces of gold (announced 27 July 2026), and sits within an active gold corridor near Vault Minerals’ Rothsay Gold Mine (approximately 15 kilometres away) and Capricorn Metals’ Golden Range Project within the same mineral field. Investors should note that the project is subject to a 1% net smelter royalty on the first 100,000 ounces of gold, held by an unrelated third party.
Justin Virgin, Executive Director, Terrain Minerals
“Whilst it is still too early to make any statement on the potential economic viability of the Project, these results do provide more than sufficient confidence for the Company to continue advancing towards a future Scoping Study at the Lightning Gold Project.”
Conventional processing confirmation means future work at Lightning can concentrate on defining and extending mineralisation rather than solving a processing problem. For early-stage investors watching the path to study-level work, that is a material de-risking step.
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