Oriole Resources (LSE:ORR), the AIM-listed exploration and development company focused on Central and West Africa, has reported results from metallurgical testing at its 50%-owned Bibemi gold project in north-eastern Cameroon, identifying ultra-fine grinding as a potential alternative to the pressure oxidation process included in its existing development assessment.
Testing conducted by ALS Ltd. in Perth, Australia, returned gold recoveries exceeding 90% from oxide samples after 24 hours of cyanide leaching. Additional work on sulphide material produced downstream recoveries of between 94% and 98% from flotation concentrates following ultra-fine grinding.
The results will inform an updated Preliminary Economic Assessment (PEA), which Oriole expects to complete later in the current quarter.
Oxide Samples Deliver Gold Recoveries Above 90%
The metallurgical programme examined two near-surface oxide samples and two sulphide samples collected from the Bibemi project.
Testing confirmed that the oxide material could be processed using conventional cyanidation, achieving gold recoveries above 90% after 24 hours of leaching at a grind size of 75 microns.
Oriole said these results were consistent with earlier metallurgical work conducted by SGS South Africa between 2022 and 2024.
The sulphide samples underwent flotation testing at the same 75-micron grind size, producing gold recoveries of 81% and 82%, respectively.
Further testing focused on processing the resulting flotation concentrates using ultra-fine grinding as an alternative to the pressure oxidation method previously considered for the project.
Ultra-Fine Grinding Produces 94% to 98% Downstream Recovery
ALS tested the sulphide flotation concentrates after grinding them to particle sizes of 20 microns and 10 microns, followed by cyanide leaching.
The process achieved downstream gold recoveries ranging from 94% to 98% after 72 hours.
These percentages represent recovery from the flotation concentrate rather than the original sulphide feed material, from which approximately 81% to 82% of the gold was recovered during the flotation stage.
Oriole reported that overall gold recovery using the ultra-fine grinding process was broadly comparable with the assumptions underlying the pressure oxidation flowsheet in its existing PEA.
The previous assessment assumed overall gold recovery of 85%, based on a processing sequence involving flotation, pressure oxidation of the flotation concentrate and subsequent leaching.
According to Oriole, ultra-fine grinding could offer several operational differences compared with pressure oxidation, including a simpler processing plant, the elimination of high-pressure equipment and reduced requirements for specialised autoclave construction materials.
The company also identified potential reductions in operational complexity and the level of specialist management and supervision required.
These potential benefits remain subject to further engineering and economic assessment.
Updated Economic Assessment Expected Later This Quarter
Oriole has engaged Stirling Process Engineering Ltd to undertake a detailed comparison of the alternative mineral processing options.
The study will examine the capital and operating costs associated with an ultra-fine grinding flowsheet relative to the pressure oxidation process included in the existing project assessment.
Oriole said preliminary indications suggest that capital and operating costs for the two processing routes are likely to be comparable, although the detailed study has not yet been completed.
The findings are expected to be incorporated into an updated PEA, scheduled for completion later in the current quarter.
The assessment will provide additional information to support the selection of a processing method for the proposed Bibemi mining operation.
Bibemi Gold Resource Stands at 460,000 Ounces
The Bibemi project covers approximately 177 square kilometres in Cameroon’s North region.
Exploration has identified gold mineralisation across four principal prospects: Bakassi Zone 1, Bakassi Zone 2, Lawa West and Lawa East.
These prospects occur within a mineralised hydrothermal system extending approximately 12 kilometres at surface.
Bibemi has a reported Mineral Resource Estimate of 6.96 million tonnes grading 2.06 grams per tonne gold, containing approximately 460,000 ounces.
Of the total resource, 100,000 ounces are classified as Indicated, with the remaining ounces classified as Inferred under the JORC Code.
The resource is contained entirely within the BZ1-MRE zone and was calculated using a cut-off grade of 0.40 grams per tonne gold, constrained by a pit shell based on a gold price of US$2,750 per ounce.
Oriole has also identified an Exploration Target across the wider Bibemi project of between 3.0 million and 5.0 million tonnes grading between 1.50 and 2.50 grams per tonne gold, equivalent to approximately 145,000 to 400,000 ounces of contained gold.
The Exploration Target is separate from the established Mineral Resource Estimate and represents potential mineralisation requiring further evaluation.
Proposed Open-Pit Mine Targets 89,000 Ounces of Gold
Oriole is negotiating an Exploitation Licence for a proposed small-scale open-pit mining operation at Bibemi.
The company has submitted an Exploitation Licence Application supported by a PEA examining an optimised mining scenario targeting approximately 89,000 ounces of gold, largely centred on the project’s 100,000-ounce Indicated Resource.
The existing assessment assumes a seven-year mine life and average annual gold production of approximately 10,000 ounces.
Oriole described the PEA as being at Scoping Study level, meaning further technical and economic evaluation is required before the proposed development can progress.
The updated metallurgical assessment will consider whether ultra-fine grinding can replace the pressure oxidation circuit assumed in the original processing design.
CEO Comments on Metallurgical Results
Martin Rosser, Chief Executive Officer of Oriole Resources, commented:
“We welcome the latest Bibemi mineral processing test results as there is now encouraging potential for an improved flowsheet as an alternative to the earlier one developed using pressure oxidation. As such, the provisional indication is that capital and operating costs will likely be comparable, with significant operational benefits, thus confirming ultra-fine grinding as a viable alternative. We look forward to receiving Stirling’s detailed trade-off study.
“Having the option of a processing flowsheet that uses ultra-fine grinding gives processing method flexibility compared to one using POX. Both methods will have pros and cons for the processing of other gold-telluride deposits that may occur in Cameroon, dependent upon the magnitude of plant throughput and ore mineralogy.”
More About Oriole Resources
Oriole Resources is an AIM-listed mineral exploration and development company focused on gold projects in Central and West Africa.
The company holds a 50% interest in the Bibemi gold project in Cameroon, where it is progressing technical studies and negotiations for an Exploitation Licence covering a proposed small-scale open-pit operation.
Current work includes evaluating mineral processing alternatives, refining development cost estimates and updating the project’s Preliminary Economic Assessment.
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