- 01Flotation recovered 83% of residue cobalt into a concentrate comprising 4% of residue mass.
- 02Emmie Bluff hosts ~23,000t of cobalt.
- 03Overall recovery and economics remain unproven.
Coda Minerals (ASX: COD) has recovered 83% of the cobalt remaining after initial leaching into a concentrate representing just 4% of the residue mass in laboratory flotation testing at its Elizabeth Creek copper-silver project in South Australia.
The result opens a possible route to extracting a metal currently excluded from the project’s copper-silver economic model, rather than sending much of it to tailings.
At Emmie Bluff, where the latest work was conducted, the mineral resource contains approximately 23,000 tonnes of cobalt, providing a material incentive to investigate the additional processing step.
However, the company must still demonstrate that cobalt can be extracted from the concentrate economically, with the flotation figures representing preliminary laboratory results rather than a proven overall recovery rate.
Remaining Metal Recovery
The proposed approach adds conventional flotation after the primary whole-ore chloride leach, which is designed principally to recover copper and silver, but before the remaining material is sent to tailings.
Previous testing of representative Emmie Bluff samples achieved average cobalt extraction of 39.7% during leaching, leaving most of the metal in the residue and prompting the investigation of a second recovery stage.
The residue in the latest flotation test was upgraded to a concentrate grading 1.48% cobalt, with an 83% recovery of the cobalt contained in that residue.
That compares with 73% recovery into a 1.28% cobalt concentrate comprising 5.5% of the residue mass in an earlier test using a different sample and process conditions.
The revised test incorporated additional cleaning and grinding steps, although the two sets of results are not directly comparable because their feed materials differed.
Assessing Commercial Value
The distinction between recovering cobalt from leach residue and recovering it from the original ore is central to assessing the potential economic benefit.
The separate leaching and flotation tests have not yet been combined in an integrated circuit, so their recovery percentages cannot be multiplied to establish an overall project recovery.
“The task now is to extract the cobalt from that concentrate and demonstrate that it makes economic sense,” chief executive officer Chris Stevens said.
Coda’s preferred option is to return the cobalt-bearing concentrate to the existing chloride leach circuit, potentially avoiding the expense of a dedicated metal-extraction plant if further testing succeeds.
If that route proves unsuitable, a separate circuit remains an alternative, although additional capital and operating costs would need to be assessed before cobalt revenue could enter the project economics.
PFS Work Progressing
Further leaching tests are examining whether regrinding can remove coatings that inhibit access to carrollite, the principal cobalt mineral, before a second 24-hour leach.
Planned recycled-material and sample-variability testing will then assess whether the preliminary flotation performance can be sustained under more representative operating conditions.
The wider pre-feasibility study is also progressing, with process modelling advanced and flood and crushing-and-grinding studies materially completed to support plant design decisions.
Groundwater drilling is nearing completion, while a greenhouse gas assessment has begun as part of environmental work supporting a future mining lease application.
Ultimately, the company will need technical and cost evidence before deciding whether residue flotation belongs in the Elizabeth Creek flowsheet, while retaining the option of flotation as the primary processing route.
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